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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title "EV 1" 135.IX Title "LIBEV 3"
132.TH EV 1 "2007-12-19" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2013-12-27" "libev-4.15" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "EXAMPLE PROGRAM" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "EXAMPLE PROGRAM" 149.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1
143\& #include <ev.h>
144.Ve
145.PP
146.Vb 2 150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
147\& ev_io stdin_watcher; 158\& ev_io stdin_watcher;
148\& ev_timer timeout_watcher; 159\& ev_timer timeout_watcher;
149.Ve 160\&
150.PP 161\& // all watcher callbacks have a similar signature
151.Vb 8
152\& /* called when data readable on stdin */ 162\& // this callback is called when data is readable on stdin
153\& static void 163\& static void
154\& stdin_cb (EV_P_ struct ev_io *w, int revents) 164\& stdin_cb (EV_P_ ev_io *w, int revents)
155\& { 165\& {
156\& /* puts ("stdin ready"); */ 166\& puts ("stdin ready");
157\& ev_io_stop (EV_A_ w); /* just a syntax example */ 167\& // for one\-shot events, one must manually stop the watcher
158\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
159\& } 173\& }
160.Ve 174\&
161.PP 175\& // another callback, this time for a time\-out
162.Vb 6
163\& static void 176\& static void
164\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 177\& timeout_cb (EV_P_ ev_timer *w, int revents)
165\& { 178\& {
166\& /* puts ("timeout"); */ 179\& puts ("timeout");
167\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
168\& } 182\& }
169.Ve 183\&
170.PP
171.Vb 4
172\& int 184\& int
173\& main (void) 185\& main (void)
174\& { 186\& {
175\& struct ev_loop *loop = ev_default_loop (0); 187\& // use the default event loop unless you have special needs
176.Ve 188\& struct ev_loop *loop = EV_DEFAULT;
177.PP 189\&
178.Vb 3
179\& /* initialise an io watcher, then start it */ 190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
180\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181\& ev_io_start (loop, &stdin_watcher); 193\& ev_io_start (loop, &stdin_watcher);
182.Ve 194\&
183.PP 195\& // initialise a timer watcher, then start it
184.Vb 3
185\& /* simple non-repeating 5.5 second timeout */ 196\& // simple non\-repeating 5.5 second timeout
186\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187\& ev_timer_start (loop, &timeout_watcher); 198\& ev_timer_start (loop, &timeout_watcher);
188.Ve 199\&
189.PP 200\& // now wait for events to arrive
190.Vb 2
191\& /* loop till timeout or data ready */
192\& ev_loop (loop, 0); 201\& ev_run (loop, 0);
193.Ve 202\&
194.PP 203\& // break was called, so exit
195.Vb 2
196\& return 0; 204\& return 0;
197\& } 205\& }
198.Ve 206.Ve
199.SH "DESCRIPTION" 207.SH "ABOUT THIS DOCUMENT"
200.IX Header "DESCRIPTION" 208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
201The newest version of this document is also available as a html-formatted 211The newest version of this document is also available as an html-formatted
202web page you might find easier to navigate when reading it for the first 212web page you might find easier to navigate when reading it for the first
203time: <http://cvs.schmorp.de/libev/ev.html>. 213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
204.PP 214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
205Libev is an event loop: you register interest in certain events (such as a 231Libev is an event loop: you register interest in certain events (such as a
206file descriptor being readable or a timeout occuring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
207these event sources and provide your program with events. 233these event sources and provide your program with events.
208.PP 234.PP
209To do this, it must take more or less complete control over your process 235To do this, it must take more or less complete control over your process
210(or thread) by executing the \fIevent loop\fR handler, and will then 236(or thread) by executing the \fIevent loop\fR handler, and will then
211communicate events via a callback mechanism. 237communicate events via a callback mechanism.
212.PP 238.PP
213You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
214watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
215details of the event, and then hand it over to libev by \fIstarting\fR the 241details of the event, and then hand it over to libev by \fIstarting\fR the
216watcher. 242watcher.
217.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
218.IX Header "FEATURES" 244.IX Subsection "FEATURES"
219Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the 245Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
220BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms 246BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
221for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface 247for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
222(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers 248(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
223with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
224(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
225watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
226\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as 252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
227file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events 253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
228(\f(CW\*(C`ev_fork\*(C'\fR). 254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
229.PP 256.PP
230It also is quite fast (see this 257It also is quite fast (see this
231benchmark comparing it to libevent 258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
232for example). 259for example).
233.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
234.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
235Libev is very configurable. In this manual the default configuration will 262Libev is very configurable. In this manual the default (and most common)
236be described, which supports multiple event loops. For more info about 263configuration will be described, which supports multiple event loops. For
237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 264more info about various configuration options please have a look at
238this manual. If libev was configured without support for multiple event 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
239loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR 266for multiple event loops, then all functions taking an initial argument of
240(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument. 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
268this argument.
241.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
242.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
243Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
245the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
246called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
247to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
248it, you should treat it as some floatingpoint value. Unlike the name 276any calculations on it, you should treat it as some floating point value.
277.PP
249component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences 278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
250throughout libev. 279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
297extensive consistency checking code. These do not trigger under normal
298circumstances, as they indicate either a bug in libev or worse.
251.SH "GLOBAL FUNCTIONS" 299.SH "GLOBAL FUNCTIONS"
252.IX Header "GLOBAL FUNCTIONS" 300.IX Header "GLOBAL FUNCTIONS"
253These functions can be called anytime, even before initialising the 301These functions can be called anytime, even before initialising the
254library in any way. 302library in any way.
255.IP "ev_tstamp ev_time ()" 4 303.IP "ev_tstamp ev_time ()" 4
256.IX Item "ev_tstamp ev_time ()" 304.IX Item "ev_tstamp ev_time ()"
257Returns the current time as libev would use it. Please note that the 305Returns the current time as libev would use it. Please note that the
258\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 306\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
259you actually want to know. 307you actually want to know. Also interesting is the combination of
308\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
309.IP "ev_sleep (ev_tstamp interval)" 4
310.IX Item "ev_sleep (ev_tstamp interval)"
311Sleep for the given interval: The current thread will be blocked
312until either it is interrupted or the given time interval has
313passed (approximately \- it might return a bit earlier even if not
314interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
315.Sp
316Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
317.Sp
318The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
319with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
260.IP "int ev_version_major ()" 4 320.IP "int ev_version_major ()" 4
261.IX Item "int ev_version_major ()" 321.IX Item "int ev_version_major ()"
262.PD 0 322.PD 0
263.IP "int ev_version_minor ()" 4 323.IP "int ev_version_minor ()" 4
264.IX Item "int ev_version_minor ()" 324.IX Item "int ev_version_minor ()"
… …
276as this indicates an incompatible change. Minor versions are usually 336as this indicates an incompatible change. Minor versions are usually
277compatible to older versions, so a larger minor version alone is usually 337compatible to older versions, so a larger minor version alone is usually
278not a problem. 338not a problem.
279.Sp 339.Sp
280Example: Make sure we haven't accidentally been linked against the wrong 340Example: Make sure we haven't accidentally been linked against the wrong
281version. 341version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
342such as \s-1LFS\s0 or reentrancy).
282.Sp 343.Sp
283.Vb 3 344.Vb 3
284\& assert (("libev version mismatch", 345\& assert (("libev version mismatch",
285\& ev_version_major () == EV_VERSION_MAJOR 346\& ev_version_major () == EV_VERSION_MAJOR
286\& && ev_version_minor () >= EV_VERSION_MINOR)); 347\& && ev_version_minor () >= EV_VERSION_MINOR));
287.Ve 348.Ve
288.IP "unsigned int ev_supported_backends ()" 4 349.IP "unsigned int ev_supported_backends ()" 4
289.IX Item "unsigned int ev_supported_backends ()" 350.IX Item "unsigned int ev_supported_backends ()"
290Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 351Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
291value) compiled into this binary of libev (independent of their 352value) compiled into this binary of libev (independent of their
… …
294.Sp 355.Sp
295Example: make sure we have the epoll method, because yeah this is cool and 356Example: make sure we have the epoll method, because yeah this is cool and
296a must have and can we have a torrent of it please!!!11 357a must have and can we have a torrent of it please!!!11
297.Sp 358.Sp
298.Vb 2 359.Vb 2
299\& assert (("sorry, no epoll, no sex", 360\& assert (("sorry, no epoll, no sex",
300\& ev_supported_backends () & EVBACKEND_EPOLL)); 361\& ev_supported_backends () & EVBACKEND_EPOLL));
301.Ve 362.Ve
302.IP "unsigned int ev_recommended_backends ()" 4 363.IP "unsigned int ev_recommended_backends ()" 4
303.IX Item "unsigned int ev_recommended_backends ()" 364.IX Item "unsigned int ev_recommended_backends ()"
304Return the set of all backends compiled into this binary of libev and also 365Return the set of all backends compiled into this binary of libev and
305recommended for this platform. This set is often smaller than the one 366also recommended for this platform, meaning it will work for most file
367descriptor types. This set is often smaller than the one returned by
306returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 368\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
307most BSDs and will not be autodetected unless you explicitly request it 369and will not be auto-detected unless you explicitly request it (assuming
308(assuming you know what you are doing). This is the set of backends that 370you know what you are doing). This is the set of backends that libev will
309libev will probe for if you specify no backends explicitly. 371probe for if you specify no backends explicitly.
310.IP "unsigned int ev_embeddable_backends ()" 4 372.IP "unsigned int ev_embeddable_backends ()" 4
311.IX Item "unsigned int ev_embeddable_backends ()" 373.IX Item "unsigned int ev_embeddable_backends ()"
312Returns the set of backends that are embeddable in other event loops. This 374Returns the set of backends that are embeddable in other event loops. This
313is the theoretical, all\-platform, value. To find which backends 375value is platform-specific but can include backends not available on the
314might be supported on the current system, you would need to look at 376current system. To find which embeddable backends might be supported on
315\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 377the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
316recommended ones. 378& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
317.Sp 379.Sp
318See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 380See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
319.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 381.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
320.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 382.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
321Sets the allocation function to use (the prototype is similar \- the 383Sets the allocation function to use (the prototype is similar \- the
322semantics is identical \- to the realloc C function). It is used to 384semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
323allocate and free memory (no surprises here). If it returns zero when 385used to allocate and free memory (no surprises here). If it returns zero
324memory needs to be allocated, the library might abort or take some 386when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
325potentially destructive action. The default is your system realloc 387or take some potentially destructive action.
326function. 388.Sp
389Since some systems (at least OpenBSD and Darwin) fail to implement
390correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
391\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
327.Sp 392.Sp
328You could override this function in high-availability programs to, say, 393You could override this function in high-availability programs to, say,
329free some memory if it cannot allocate memory, to use a special allocator, 394free some memory if it cannot allocate memory, to use a special allocator,
330or even to sleep a while and retry until some memory is available. 395or even to sleep a while and retry until some memory is available.
331.Sp 396.Sp
332Example: Replace the libev allocator with one that waits a bit and then 397Example: Replace the libev allocator with one that waits a bit and then
333retries). 398retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
334.Sp 399.Sp
335.Vb 6 400.Vb 6
336\& static void * 401\& static void *
337\& persistent_realloc (void *ptr, size_t size) 402\& persistent_realloc (void *ptr, size_t size)
338\& { 403\& {
339\& for (;;) 404\& for (;;)
340\& { 405\& {
341\& void *newptr = realloc (ptr, size); 406\& void *newptr = realloc (ptr, size);
342.Ve 407\&
343.Sp
344.Vb 2
345\& if (newptr) 408\& if (newptr)
346\& return newptr; 409\& return newptr;
347.Ve 410\&
348.Sp
349.Vb 3
350\& sleep (60); 411\& sleep (60);
351\& } 412\& }
352\& } 413\& }
353.Ve 414\&
354.Sp
355.Vb 2
356\& ... 415\& ...
357\& ev_set_allocator (persistent_realloc); 416\& ev_set_allocator (persistent_realloc);
358.Ve 417.Ve
359.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 418.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
360.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 419.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
361Set the callback function to call on a retryable syscall error (such 420Set the callback function to call on a retryable system call error (such
362as failed select, poll, epoll_wait). The message is a printable string 421as failed select, poll, epoll_wait). The message is a printable string
363indicating the system call or subsystem causing the problem. If this 422indicating the system call or subsystem causing the problem. If this
364callback is set, then libev will expect it to remedy the sitution, no 423callback is set, then libev will expect it to remedy the situation, no
365matter what, when it returns. That is, libev will generally retry the 424matter what, when it returns. That is, libev will generally retry the
366requested operation, or, if the condition doesn't go away, do bad stuff 425requested operation, or, if the condition doesn't go away, do bad stuff
367(such as abort). 426(such as abort).
368.Sp 427.Sp
369Example: This is basically the same thing that libev does internally, too. 428Example: This is basically the same thing that libev does internally, too.
… …
373\& fatal_error (const char *msg) 432\& fatal_error (const char *msg)
374\& { 433\& {
375\& perror (msg); 434\& perror (msg);
376\& abort (); 435\& abort ();
377\& } 436\& }
378.Ve 437\&
379.Sp
380.Vb 2
381\& ... 438\& ...
382\& ev_set_syserr_cb (fatal_error); 439\& ev_set_syserr_cb (fatal_error);
383.Ve 440.Ve
441.IP "ev_feed_signal (int signum)" 4
442.IX Item "ev_feed_signal (int signum)"
443This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
444safe to call this function at any time, from any context, including signal
445handlers or random threads.
446.Sp
447Its main use is to customise signal handling in your process, especially
448in the presence of threads. For example, you could block signals
449by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
450creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
451mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
452\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
384.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 453.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
385.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 454.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
386An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 455An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
387types of such loops, the \fIdefault\fR loop, which supports signals and child 456\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
388events, and dynamically created loops which do not. 457libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
389.PP 458.PP
390If you use threads, a common model is to run the default event loop 459The library knows two types of such loops, the \fIdefault\fR loop, which
391in your main thread (or in a separate thread) and for each thread you 460supports child process events, and dynamically created event loops which
392create, you also create another event loop. Libev itself does no locking 461do not.
393whatsoever, so if you mix calls to the same event loop in different
394threads, make sure you lock (this is usually a bad idea, though, even if
395done correctly, because it's hideous and inefficient).
396.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 462.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
397.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 463.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
398This will initialise the default event loop if it hasn't been initialised 464This returns the \*(L"default\*(R" event loop object, which is what you should
399yet and return it. If the default loop could not be initialised, returns 465normally use when you just need \*(L"the event loop\*(R". Event loop objects and
400false. If it already was initialised it simply returns it (and ignores the 466the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
401flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 467\&\f(CW\*(C`ev_loop_new\*(C'\fR.
468.Sp
469If the default loop is already initialised then this function simply
470returns it (and ignores the flags. If that is troubling you, check
471\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
472flags, which should almost always be \f(CW0\fR, unless the caller is also the
473one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
402.Sp 474.Sp
403If you don't know what event loop to use, use the one returned from this 475If you don't know what event loop to use, use the one returned from this
404function. 476function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
477.Sp
478Note that this function is \fInot\fR thread-safe, so if you want to use it
479from multiple threads, you have to employ some kind of mutex (note also
480that this case is unlikely, as loops cannot be shared easily between
481threads anyway).
482.Sp
483The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
484and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
485a problem for your application you can either create a dynamic loop with
486\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
487\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
488.Sp
489Example: This is the most typical usage.
490.Sp
491.Vb 2
492\& if (!ev_default_loop (0))
493\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
494.Ve
495.Sp
496Example: Restrict libev to the select and poll backends, and do not allow
497environment settings to be taken into account:
498.Sp
499.Vb 1
500\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
501.Ve
502.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504This will create and initialise a new event loop object. If the loop
505could not be initialised, returns false.
506.Sp
507This function is thread-safe, and one common way to use libev with
508threads is indeed to create one loop per thread, and using the default
509loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
405.Sp 510.Sp
406The flags argument can be used to specify special behaviour or specific 511The flags argument can be used to specify special behaviour or specific
407backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 512backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
408.Sp 513.Sp
409The following flags are supported: 514The following flags are supported:
… …
414The default flags value. Use this if you have no clue (it's the right 519The default flags value. Use this if you have no clue (it's the right
415thing, believe me). 520thing, believe me).
416.ie n .IP """EVFLAG_NOENV""" 4 521.ie n .IP """EVFLAG_NOENV""" 4
417.el .IP "\f(CWEVFLAG_NOENV\fR" 4 522.el .IP "\f(CWEVFLAG_NOENV\fR" 4
418.IX Item "EVFLAG_NOENV" 523.IX Item "EVFLAG_NOENV"
419If this flag bit is ored into the flag value (or the program runs setuid 524If this flag bit is or'ed into the flag value (or the program runs setuid
420or setgid) then libev will \fInot\fR look at the environment variable 525or setgid) then libev will \fInot\fR look at the environment variable
421\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 526\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
422override the flags completely if it is found in the environment. This is 527override the flags completely if it is found in the environment. This is
423useful to try out specific backends to test their performance, or to work 528useful to try out specific backends to test their performance, to work
424around bugs. 529around bugs, or to make libev threadsafe (accessing environment variables
530cannot be done in a threadsafe way, but usually it works if no other
531thread modifies them).
425.ie n .IP """EVFLAG_FORKCHECK""" 4 532.ie n .IP """EVFLAG_FORKCHECK""" 4
426.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 533.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
427.IX Item "EVFLAG_FORKCHECK" 534.IX Item "EVFLAG_FORKCHECK"
428Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after 535Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
429a fork, you can also make libev check for a fork in each iteration by 536make libev check for a fork in each iteration by enabling this flag.
430enabling this flag.
431.Sp 537.Sp
432This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, 538This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
433and thus this might slow down your event loop if you do a lot of loop 539and thus this might slow down your event loop if you do a lot of loop
434iterations and little real work, but is usually not noticeable (on my 540iterations and little real work, but is usually not noticeable (on my
435Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence 541GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
436without a syscall and thus \fIvery\fR fast, but my Linux system also has 542without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
437\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). 543\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
438.Sp 544.Sp
439The big advantage of this flag is that you can forget about fork (and 545The big advantage of this flag is that you can forget about fork (and
440forget about forgetting to tell libev about forking) when you use this 546forget about forgetting to tell libev about forking) when you use this
441flag. 547flag.
442.Sp 548.Sp
443This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR 549This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
444environment variable. 550environment variable.
551.ie n .IP """EVFLAG_NOINOTIFY""" 4
552.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
553.IX Item "EVFLAG_NOINOTIFY"
554When this flag is specified, then libev will not attempt to use the
555\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
556testing, this flag can be useful to conserve inotify file descriptors, as
557otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
558.ie n .IP """EVFLAG_SIGNALFD""" 4
559.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
560.IX Item "EVFLAG_SIGNALFD"
561When this flag is specified, then libev will attempt to use the
562\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
563delivers signals synchronously, which makes it both faster and might make
564it possible to get the queued signal data. It can also simplify signal
565handling with threads, as long as you properly block signals in your
566threads that are not interested in handling them.
567.Sp
568Signalfd will not be used by default as this changes your signal mask, and
569there are a lot of shoddy libraries and programs (glib's threadpool for
570example) that can't properly initialise their signal masks.
571.ie n .IP """EVFLAG_NOSIGMASK""" 4
572.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
573.IX Item "EVFLAG_NOSIGMASK"
574When this flag is specified, then libev will avoid to modify the signal
575mask. Specifically, this means you have to make sure signals are unblocked
576when you want to receive them.
577.Sp
578This behaviour is useful when you want to do your own signal handling, or
579want to handle signals only in specific threads and want to avoid libev
580unblocking the signals.
581.Sp
582It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
583\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
584.Sp
585This flag's behaviour will become the default in future versions of libev.
445.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 586.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
446.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 587.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
447.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 588.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
448This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 589This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
449libev tries to roll its own fd_set with no limits on the number of fds, 590libev tries to roll its own fd_set with no limits on the number of fds,
450but if that fails, expect a fairly low limit on the number of fds when 591but if that fails, expect a fairly low limit on the number of fds when
451using this backend. It doesn't scale too well (O(highest_fd)), but its usually 592using this backend. It doesn't scale too well (O(highest_fd)), but its
452the fastest backend for a low number of fds. 593usually the fastest backend for a low number of (low-numbered :) fds.
594.Sp
595To get good performance out of this backend you need a high amount of
596parallelism (most of the file descriptors should be busy). If you are
597writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
598connections as possible during one iteration. You might also want to have
599a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
600readiness notifications you get per iteration.
601.Sp
602This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
603\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
604\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
453.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 605.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
454.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 606.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
455.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 607.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
456And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 608And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
457select, but handles sparse fds better and has no artificial limit on the 609than select, but handles sparse fds better and has no artificial
458number of fds you can use (except it will slow down considerably with a 610limit on the number of fds you can use (except it will slow down
459lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 611considerably with a lot of inactive fds). It scales similarly to select,
612i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
613performance tips.
614.Sp
615This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
616\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
460.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 617.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
461.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 618.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
462.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 619.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
620Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
621kernels).
622.Sp
463For few fds, this backend is a bit little slower than poll and select, 623For few fds, this backend is a bit little slower than poll and select, but
464but it scales phenomenally better. While poll and select usually scale like 624it scales phenomenally better. While poll and select usually scale like
465O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 625O(total_fds) where total_fds is the total number of fds (or the highest
466either O(1) or O(active_fds). 626fd), epoll scales either O(1) or O(active_fds).
467.Sp 627.Sp
628The epoll mechanism deserves honorable mention as the most misdesigned
629of the more advanced event mechanisms: mere annoyances include silently
630dropping file descriptors, requiring a system call per change per file
631descriptor (and unnecessary guessing of parameters), problems with dup,
632returning before the timeout value, resulting in additional iterations
633(and only giving 5ms accuracy while select on the same platform gives
6340.1ms) and so on. The biggest issue is fork races, however \- if a program
635forks then \fIboth\fR parent and child process have to recreate the epoll
636set, which can take considerable time (one syscall per file descriptor)
637and is of course hard to detect.
638.Sp
639Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
640but of course \fIdoesn't\fR, and epoll just loves to report events for
641totally \fIdifferent\fR file descriptors (even already closed ones, so
642one cannot even remove them from the set) than registered in the set
643(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
644notifications by employing an additional generation counter and comparing
645that against the events to filter out spurious ones, recreating the set
646when required. Epoll also erroneously rounds down timeouts, but gives you
647no way to know when and by how much, so sometimes you have to busy-wait
648because epoll returns immediately despite a nonzero timeout. And last
649not least, it also refuses to work with some file descriptors which work
650perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
651.Sp
652Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
653cobbled together in a hurry, no thought to design or interaction with
654others. Oh, the pain, will it ever stop...
655.Sp
468While stopping and starting an I/O watcher in the same iteration will 656While stopping, setting and starting an I/O watcher in the same iteration
469result in some caching, there is still a syscall per such incident 657will result in some caching, there is still a system call per such
470(because the fd could point to a different file description now), so its 658incident (because the same \fIfile descriptor\fR could point to a different
471best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 659\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
472well if you register events for both fds. 660file descriptors might not work very well if you register events for both
661file descriptors.
473.Sp 662.Sp
474Please note that epoll sometimes generates spurious notifications, so you 663Best performance from this backend is achieved by not unregistering all
475need to use non-blocking I/O or other means to avoid blocking when no data 664watchers for a file descriptor until it has been closed, if possible,
476(or space) is available. 665i.e. keep at least one watcher active per fd at all times. Stopping and
666starting a watcher (without re-setting it) also usually doesn't cause
667extra overhead. A fork can both result in spurious notifications as well
668as in libev having to destroy and recreate the epoll object, which can
669take considerable time and thus should be avoided.
670.Sp
671All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
672faster than epoll for maybe up to a hundred file descriptors, depending on
673the usage. So sad.
674.Sp
675While nominally embeddable in other event loops, this feature is broken in
676all kernel versions tested so far.
677.Sp
678This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
679\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
477.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 680.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
478.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 681.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
479.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 682.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
480Kqueue deserves special mention, as at the time of this writing, it 683Kqueue deserves special mention, as at the time of this writing, it
481was broken on all BSDs except NetBSD (usually it doesn't work with 684was broken on all BSDs except NetBSD (usually it doesn't work reliably
482anything but sockets and pipes, except on Darwin, where of course its 685with anything but sockets and pipes, except on Darwin, where of course
483completely useless). For this reason its not being \*(L"autodetected\*(R" 686it's completely useless). Unlike epoll, however, whose brokenness
687is by design, these kqueue bugs can (and eventually will) be fixed
688without \s-1API\s0 changes to existing programs. For this reason it's not being
484unless you explicitly specify it explicitly in the flags (i.e. using 689\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
485\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 690\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
691system like NetBSD.
692.Sp
693You still can embed kqueue into a normal poll or select backend and use it
694only for sockets (after having made sure that sockets work with kqueue on
695the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
486.Sp 696.Sp
487It scales in the same way as the epoll backend, but the interface to the 697It scales in the same way as the epoll backend, but the interface to the
488kernel is more efficient (which says nothing about its actual speed, of 698kernel is more efficient (which says nothing about its actual speed, of
489course). While starting and stopping an I/O watcher does not cause an 699course). While stopping, setting and starting an I/O watcher does never
490extra syscall as with epoll, it still adds up to four event changes per 700cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
491incident, so its best to avoid that. 701two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
702might have to leak fd's on fork, but it's more sane than epoll) and it
703drops fds silently in similarly hard-to-detect cases.
704.Sp
705This backend usually performs well under most conditions.
706.Sp
707While nominally embeddable in other event loops, this doesn't work
708everywhere, so you might need to test for this. And since it is broken
709almost everywhere, you should only use it when you have a lot of sockets
710(for which it usually works), by embedding it into another event loop
711(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
712also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
713.Sp
714This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
715\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
716\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
492.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 717.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
493.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 718.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
494.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 719.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
495This is not implemented yet (and might never be). 720This is not implemented yet (and might never be, unless you send me an
721implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
722and is not embeddable, which would limit the usefulness of this backend
723immensely.
496.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 724.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
497.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 725.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
498.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 726.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
499This uses the Solaris 10 port mechanism. As with everything on Solaris, 727This uses the Solaris 10 event port mechanism. As with everything on Solaris,
500it's really slow, but it still scales very well (O(active_fds)). 728it's really slow, but it still scales very well (O(active_fds)).
501.Sp 729.Sp
502Please note that solaris ports can result in a lot of spurious 730While this backend scales well, it requires one system call per active
503notifications, so you need to use non-blocking I/O or other means to avoid 731file descriptor per loop iteration. For small and medium numbers of file
504blocking when no data (or space) is available. 732descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
733might perform better.
734.Sp
735On the positive side, this backend actually performed fully to
736specification in all tests and is fully embeddable, which is a rare feat
737among the OS-specific backends (I vastly prefer correctness over speed
738hacks).
739.Sp
740On the negative side, the interface is \fIbizarre\fR \- so bizarre that
741even sun itself gets it wrong in their code examples: The event polling
742function sometimes returns events to the caller even though an error
743occurred, but with no indication whether it has done so or not (yes, it's
744even documented that way) \- deadly for edge-triggered interfaces where you
745absolutely have to know whether an event occurred or not because you have
746to re-arm the watcher.
747.Sp
748Fortunately libev seems to be able to work around these idiocies.
749.Sp
750This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
751\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
505.ie n .IP """EVBACKEND_ALL""" 4 752.ie n .IP """EVBACKEND_ALL""" 4
506.el .IP "\f(CWEVBACKEND_ALL\fR" 4 753.el .IP "\f(CWEVBACKEND_ALL\fR" 4
507.IX Item "EVBACKEND_ALL" 754.IX Item "EVBACKEND_ALL"
508Try all backends (even potentially broken ones that wouldn't be tried 755Try all backends (even potentially broken ones that wouldn't be tried
509with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 756with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
510\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 757\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
758.Sp
759It is definitely not recommended to use this flag, use whatever
760\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
761at all.
762.ie n .IP """EVBACKEND_MASK""" 4
763.el .IP "\f(CWEVBACKEND_MASK\fR" 4
764.IX Item "EVBACKEND_MASK"
765Not a backend at all, but a mask to select all backend bits from a
766\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
767value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
511.RE 768.RE
512.RS 4 769.RS 4
513.Sp 770.Sp
514If one or more of these are ored into the flags value, then only these 771If one or more of the backend flags are or'ed into the flags value,
515backends will be tried (in the reverse order as given here). If none are 772then only these backends will be tried (in the reverse order as listed
516specified, most compiled-in backend will be tried, usually in reverse 773here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
517order of their flag values :) 774()\*(C'\fR will be tried.
518.Sp 775.Sp
519The most typical usage is like this: 776Example: Try to create a event loop that uses epoll and nothing else.
520.Sp 777.Sp
521.Vb 2 778.Vb 3
522\& if (!ev_default_loop (0)) 779\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
523\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 780\& if (!epoller)
781\& fatal ("no epoll found here, maybe it hides under your chair");
524.Ve 782.Ve
525.Sp 783.Sp
526Restrict libev to the select and poll backends, and do not allow 784Example: Use whatever libev has to offer, but make sure that kqueue is
527environment settings to be taken into account: 785used if available.
528.Sp 786.Sp
529.Vb 1 787.Vb 1
530\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
531.Ve
532.Sp
533Use whatever libev has to offer, but make sure that kqueue is used if
534available (warning, breaks stuff, best use only with your own private
535event loop and only if you know the \s-1OS\s0 supports your types of fds):
536.Sp
537.Vb 1
538\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 788\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
539.Ve 789.Ve
540.RE 790.RE
541.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
542.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
543Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
544always distinct from the default loop. Unlike the default loop, it cannot
545handle signal and child watchers, and attempts to do so will be greeted by
546undefined behaviour (or a failed assertion if assertions are enabled).
547.Sp
548Example: Try to create a event loop that uses epoll and nothing else.
549.Sp
550.Vb 3
551\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
552\& if (!epoller)
553\& fatal ("no epoll found here, maybe it hides under your chair");
554.Ve
555.IP "ev_default_destroy ()" 4 791.IP "ev_loop_destroy (loop)" 4
556.IX Item "ev_default_destroy ()" 792.IX Item "ev_loop_destroy (loop)"
557Destroys the default loop again (frees all memory and kernel state 793Destroys an event loop object (frees all memory and kernel state
558etc.). None of the active event watchers will be stopped in the normal 794etc.). None of the active event watchers will be stopped in the normal
559sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 795sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
560responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 796responsibility to either stop all watchers cleanly yourself \fIbefore\fR
561calling this function, or cope with the fact afterwards (which is usually 797calling this function, or cope with the fact afterwards (which is usually
562the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 798the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
563for example). 799for example).
564.Sp 800.Sp
565Not that certain global state, such as signal state, will not be freed by 801Note that certain global state, such as signal state (and installed signal
566this function, and related watchers (such as signal and child watchers) 802handlers), will not be freed by this function, and related watchers (such
567would need to be stopped manually. 803as signal and child watchers) would need to be stopped manually.
568.Sp 804.Sp
569In general it is not advisable to call this function except in the 805This function is normally used on loop objects allocated by
570rare occasion where you really need to free e.g. the signal handling 806\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
571pipe fds. If you need dynamically allocated loops it is better to use 807\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
572\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
573.IP "ev_loop_destroy (loop)" 4
574.IX Item "ev_loop_destroy (loop)"
575Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
576earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
577.IP "ev_default_fork ()" 4
578.IX Item "ev_default_fork ()"
579This function reinitialises the kernel state for backends that have
580one. Despite the name, you can call it anytime, but it makes most sense
581after forking, in either the parent or child process (or both, but that
582again makes little sense).
583.Sp 808.Sp
584You \fImust\fR call this function in the child process after forking if and 809Note that it is not advisable to call this function on the default loop
585only if you want to use the event library in both processes. If you just 810except in the rare occasion where you really need to free its resources.
586fork+exec, you don't have to call it. 811If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
587.Sp 812and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
588The function itself is quite fast and it's usually not a problem to call
589it just in case after a fork. To make this easy, the function will fit in
590quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
591.Sp
592.Vb 1
593\& pthread_atfork (0, 0, ev_default_fork);
594.Ve
595.Sp
596At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
597without calling this function, so if you force one of those backends you
598do not need to care.
599.IP "ev_loop_fork (loop)" 4 813.IP "ev_loop_fork (loop)" 4
600.IX Item "ev_loop_fork (loop)" 814.IX Item "ev_loop_fork (loop)"
601Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 815This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
602\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 816reinitialise the kernel state for backends that have one. Despite the
603after fork, and how you do this is entirely your own problem. 817name, you can call it anytime, but it makes most sense after forking, in
818the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
819child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
820.Sp
821Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
822a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
823because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
824during fork.
825.Sp
826On the other hand, you only need to call this function in the child
827process if and only if you want to use the event loop in the child. If
828you just fork+exec or create a new loop in the child, you don't have to
829call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
830difference, but libev will usually detect this case on its own and do a
831costly reset of the backend).
832.Sp
833The function itself is quite fast and it's usually not a problem to call
834it just in case after a fork.
835.Sp
836Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
837using pthreads.
838.Sp
839.Vb 5
840\& static void
841\& post_fork_child (void)
842\& {
843\& ev_loop_fork (EV_DEFAULT);
844\& }
845\&
846\& ...
847\& pthread_atfork (0, 0, post_fork_child);
848.Ve
849.IP "int ev_is_default_loop (loop)" 4
850.IX Item "int ev_is_default_loop (loop)"
851Returns true when the given loop is, in fact, the default loop, and false
852otherwise.
604.IP "unsigned int ev_loop_count (loop)" 4 853.IP "unsigned int ev_iteration (loop)" 4
605.IX Item "unsigned int ev_loop_count (loop)" 854.IX Item "unsigned int ev_iteration (loop)"
606Returns the count of loop iterations for the loop, which is identical to 855Returns the current iteration count for the event loop, which is identical
607the number of times libev did poll for new events. It starts at \f(CW0\fR and 856to the number of times libev did poll for new events. It starts at \f(CW0\fR
608happily wraps around with enough iterations. 857and happily wraps around with enough iterations.
609.Sp 858.Sp
610This value can sometimes be useful as a generation counter of sorts (it 859This value can sometimes be useful as a generation counter of sorts (it
611\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with 860\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
612\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls. 861\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
862prepare and check phases.
863.IP "unsigned int ev_depth (loop)" 4
864.IX Item "unsigned int ev_depth (loop)"
865Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
866times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
867.Sp
868Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
869\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
870in which case it is higher.
871.Sp
872Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
873throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
874as a hint to avoid such ungentleman-like behaviour unless it's really
875convenient, in which case it is fully supported.
613.IP "unsigned int ev_backend (loop)" 4 876.IP "unsigned int ev_backend (loop)" 4
614.IX Item "unsigned int ev_backend (loop)" 877.IX Item "unsigned int ev_backend (loop)"
615Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 878Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
616use. 879use.
617.IP "ev_tstamp ev_now (loop)" 4 880.IP "ev_tstamp ev_now (loop)" 4
618.IX Item "ev_tstamp ev_now (loop)" 881.IX Item "ev_tstamp ev_now (loop)"
619Returns the current \*(L"event loop time\*(R", which is the time the event loop 882Returns the current \*(L"event loop time\*(R", which is the time the event loop
620received events and started processing them. This timestamp does not 883received events and started processing them. This timestamp does not
621change as long as callbacks are being processed, and this is also the base 884change as long as callbacks are being processed, and this is also the base
622time used for relative timers. You can treat it as the timestamp of the 885time used for relative timers. You can treat it as the timestamp of the
623event occuring (or more correctly, libev finding out about it). 886event occurring (or more correctly, libev finding out about it).
887.IP "ev_now_update (loop)" 4
888.IX Item "ev_now_update (loop)"
889Establishes the current time by querying the kernel, updating the time
890returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
891is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
892.Sp
893This function is rarely useful, but when some event callback runs for a
894very long time without entering the event loop, updating libev's idea of
895the current time is a good idea.
896.Sp
897See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
898.IP "ev_suspend (loop)" 4
899.IX Item "ev_suspend (loop)"
900.PD 0
901.IP "ev_resume (loop)" 4
902.IX Item "ev_resume (loop)"
903.PD
904These two functions suspend and resume an event loop, for use when the
905loop is not used for a while and timeouts should not be processed.
906.Sp
907A typical use case would be an interactive program such as a game: When
908the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
909would be best to handle timeouts as if no time had actually passed while
910the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
911in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
912\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
913.Sp
914Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
915between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
916will be rescheduled (that is, they will lose any events that would have
917occurred while suspended).
918.Sp
919After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
920given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
921without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
922.Sp
923Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
924event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
624.IP "ev_loop (loop, int flags)" 4 925.IP "bool ev_run (loop, int flags)" 4
625.IX Item "ev_loop (loop, int flags)" 926.IX Item "bool ev_run (loop, int flags)"
626Finally, this is it, the event handler. This function usually is called 927Finally, this is it, the event handler. This function usually is called
627after you initialised all your watchers and you want to start handling 928after you have initialised all your watchers and you want to start
628events. 929handling events. It will ask the operating system for any new events, call
930the watcher callbacks, and then repeat the whole process indefinitely: This
931is why event loops are called \fIloops\fR.
629.Sp 932.Sp
630If the flags argument is specified as \f(CW0\fR, it will not return until 933If the flags argument is specified as \f(CW0\fR, it will keep handling events
631either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 934until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
935called.
632.Sp 936.Sp
937The return value is false if there are no more active watchers (which
938usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
939(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
940.Sp
633Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 941Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
634relying on all watchers to be stopped when deciding when a program has 942relying on all watchers to be stopped when deciding when a program has
635finished (especially in interactive programs), but having a program that 943finished (especially in interactive programs), but having a program
636automatically loops as long as it has to and no longer by virtue of 944that automatically loops as long as it has to and no longer by virtue
637relying on its watchers stopping correctly is a thing of beauty. 945of relying on its watchers stopping correctly, that is truly a thing of
946beauty.
638.Sp 947.Sp
948This function is \fImostly\fR exception-safe \- you can break out of a
949\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
950exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
951will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
952.Sp
639A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 953A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
640those events and any outstanding ones, but will not block your process in 954those events and any already outstanding ones, but will not wait and
641case there are no events and will return after one iteration of the loop. 955block your process in case there are no events and will return after one
956iteration of the loop. This is sometimes useful to poll and handle new
957events while doing lengthy calculations, to keep the program responsive.
642.Sp 958.Sp
643A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 959A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
644neccessary) and will handle those and any outstanding ones. It will block 960necessary) and will handle those and any already outstanding ones. It
645your process until at least one new event arrives, and will return after 961will block your process until at least one new event arrives (which could
646one iteration of the loop. This is useful if you are waiting for some 962be an event internal to libev itself, so there is no guarantee that a
647external event in conjunction with something not expressible using other 963user-registered callback will be called), and will return after one
964iteration of the loop.
965.Sp
966This is useful if you are waiting for some external event in conjunction
967with something not expressible using other libev watchers (i.e. "roll your
648libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 968own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
649usually a better approach for this kind of thing. 969usually a better approach for this kind of thing.
650.Sp 970.Sp
651Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 971Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
972understanding, not a guarantee that things will work exactly like this in
973future versions):
652.Sp 974.Sp
653.Vb 19 975.Vb 10
976\& \- Increment loop depth.
977\& \- Reset the ev_break status.
654\& - Before the first iteration, call any pending watchers. 978\& \- Before the first iteration, call any pending watchers.
655\& * If there are no active watchers (reference count is zero), return. 979\& LOOP:
656\& - Queue all prepare watchers and then call all outstanding watchers. 980\& \- If EVFLAG_FORKCHECK was used, check for a fork.
981\& \- If a fork was detected (by any means), queue and call all fork watchers.
982\& \- Queue and call all prepare watchers.
983\& \- If ev_break was called, goto FINISH.
657\& - If we have been forked, recreate the kernel state. 984\& \- If we have been forked, detach and recreate the kernel state
985\& as to not disturb the other process.
658\& - Update the kernel state with all outstanding changes. 986\& \- Update the kernel state with all outstanding changes.
659\& - Update the "event loop time". 987\& \- Update the "event loop time" (ev_now ()).
660\& - Calculate for how long to block. 988\& \- Calculate for how long to sleep or block, if at all
989\& (active idle watchers, EVRUN_NOWAIT or not having
990\& any active watchers at all will result in not sleeping).
991\& \- Sleep if the I/O and timer collect interval say so.
992\& \- Increment loop iteration counter.
661\& - Block the process, waiting for any events. 993\& \- Block the process, waiting for any events.
662\& - Queue all outstanding I/O (fd) events. 994\& \- Queue all outstanding I/O (fd) events.
663\& - Update the "event loop time" and do time jump handling. 995\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
664\& - Queue all outstanding timers. 996\& \- Queue all expired timers.
665\& - Queue all outstanding periodics. 997\& \- Queue all expired periodics.
666\& - If no events are pending now, queue all idle watchers. 998\& \- Queue all idle watchers with priority higher than that of pending events.
667\& - Queue all check watchers. 999\& \- Queue all check watchers.
668\& - Call all queued watchers in reverse order (i.e. check watchers first). 1000\& \- Call all queued watchers in reverse order (i.e. check watchers first).
669\& Signals and child watchers are implemented as I/O watchers, and will 1001\& Signals and child watchers are implemented as I/O watchers, and will
670\& be handled here by queueing them when their watcher gets executed. 1002\& be handled here by queueing them when their watcher gets executed.
671\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1003\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
672\& were used, return, otherwise continue with step *. 1004\& were used, or there are no active watchers, goto FINISH, otherwise
1005\& continue with step LOOP.
1006\& FINISH:
1007\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1008\& \- Decrement the loop depth.
1009\& \- Return.
673.Ve 1010.Ve
674.Sp 1011.Sp
675Example: Queue some jobs and then loop until no events are outsanding 1012Example: Queue some jobs and then loop until no events are outstanding
676anymore. 1013anymore.
677.Sp 1014.Sp
678.Vb 4 1015.Vb 4
679\& ... queue jobs here, make sure they register event watchers as long 1016\& ... queue jobs here, make sure they register event watchers as long
680\& ... as they still have work to do (even an idle watcher will do..) 1017\& ... as they still have work to do (even an idle watcher will do..)
681\& ev_loop (my_loop, 0); 1018\& ev_run (my_loop, 0);
682\& ... jobs done. yeah! 1019\& ... jobs done or somebody called break. yeah!
683.Ve 1020.Ve
684.IP "ev_unloop (loop, how)" 4 1021.IP "ev_break (loop, how)" 4
685.IX Item "ev_unloop (loop, how)" 1022.IX Item "ev_break (loop, how)"
686Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1023Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
687has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1024has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
688\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1025\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
689\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1026\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1027.Sp
1028This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1029.Sp
1030It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1031which case it will have no effect.
690.IP "ev_ref (loop)" 4 1032.IP "ev_ref (loop)" 4
691.IX Item "ev_ref (loop)" 1033.IX Item "ev_ref (loop)"
692.PD 0 1034.PD 0
693.IP "ev_unref (loop)" 4 1035.IP "ev_unref (loop)" 4
694.IX Item "ev_unref (loop)" 1036.IX Item "ev_unref (loop)"
695.PD 1037.PD
696Ref/unref can be used to add or remove a reference count on the event 1038Ref/unref can be used to add or remove a reference count on the event
697loop: Every watcher keeps one reference, and as long as the reference 1039loop: Every watcher keeps one reference, and as long as the reference
698count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1040count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
699a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1041.Sp
700returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1042This is useful when you have a watcher that you never intend to
1043unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1044returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1045before stopping it.
1046.Sp
701example, libev itself uses this for its internal signal pipe: It is not 1047As an example, libev itself uses this for its internal signal pipe: It
702visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1048is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
703no event watchers registered by it are active. It is also an excellent 1049exiting if no event watchers registered by it are active. It is also an
704way to do this for generic recurring timers or from within third-party 1050excellent way to do this for generic recurring timers or from within
705libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1051third-party libraries. Just remember to \fIunref after start\fR and \fIref
1052before stop\fR (but only if the watcher wasn't active before, or was active
1053before, respectively. Note also that libev might stop watchers itself
1054(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1055in the callback).
706.Sp 1056.Sp
707Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1057Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
708running when nothing else is active. 1058running when nothing else is active.
709.Sp 1059.Sp
710.Vb 4 1060.Vb 4
711\& struct ev_signal exitsig; 1061\& ev_signal exitsig;
712\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1062\& ev_signal_init (&exitsig, sig_cb, SIGINT);
713\& ev_signal_start (loop, &exitsig); 1063\& ev_signal_start (loop, &exitsig);
714\& evf_unref (loop); 1064\& ev_unref (loop);
715.Ve 1065.Ve
716.Sp 1066.Sp
717Example: For some weird reason, unregister the above signal handler again. 1067Example: For some weird reason, unregister the above signal handler again.
718.Sp 1068.Sp
719.Vb 2 1069.Vb 2
720\& ev_ref (loop); 1070\& ev_ref (loop);
721\& ev_signal_stop (loop, &exitsig); 1071\& ev_signal_stop (loop, &exitsig);
722.Ve 1072.Ve
1073.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1074.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1075.PD 0
1076.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1077.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1078.PD
1079These advanced functions influence the time that libev will spend waiting
1080for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1081will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1082latency.
1083.Sp
1084Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1085allows libev to delay invocation of I/O and timer/periodic callbacks
1086to increase efficiency of loop iterations (or to increase power-saving
1087opportunities).
1088.Sp
1089The idea is that sometimes your program runs just fast enough to handle
1090one (or very few) event(s) per loop iteration. While this makes the
1091program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1092events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1093overhead for the actual polling but can deliver many events at once.
1094.Sp
1095By setting a higher \fIio collect interval\fR you allow libev to spend more
1096time collecting I/O events, so you can handle more events per iteration,
1097at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1098\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1099introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1100sleep time ensures that libev will not poll for I/O events more often then
1101once per this interval, on average (as long as the host time resolution is
1102good enough).
1103.Sp
1104Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1105to spend more time collecting timeouts, at the expense of increased
1106latency/jitter/inexactness (the watcher callback will be called
1107later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1108value will not introduce any overhead in libev.
1109.Sp
1110Many (busy) programs can usually benefit by setting the I/O collect
1111interval to a value near \f(CW0.1\fR or so, which is often enough for
1112interactive servers (of course not for games), likewise for timeouts. It
1113usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1114as this approaches the timing granularity of most systems. Note that if
1115you do transactions with the outside world and you can't increase the
1116parallelity, then this setting will limit your transaction rate (if you
1117need to poll once per transaction and the I/O collect interval is 0.01,
1118then you can't do more than 100 transactions per second).
1119.Sp
1120Setting the \fItimeout collect interval\fR can improve the opportunity for
1121saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1122are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1123times the process sleeps and wakes up again. Another useful technique to
1124reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1125they fire on, say, one-second boundaries only.
1126.Sp
1127Example: we only need 0.1s timeout granularity, and we wish not to poll
1128more often than 100 times per second:
1129.Sp
1130.Vb 2
1131\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1132\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1133.Ve
1134.IP "ev_invoke_pending (loop)" 4
1135.IX Item "ev_invoke_pending (loop)"
1136This call will simply invoke all pending watchers while resetting their
1137pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1138but when overriding the invoke callback this call comes handy. This
1139function can be invoked from a watcher \- this can be useful for example
1140when you want to do some lengthy calculation and want to pass further
1141event handling to another thread (you still have to make sure only one
1142thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1143.IP "int ev_pending_count (loop)" 4
1144.IX Item "int ev_pending_count (loop)"
1145Returns the number of pending watchers \- zero indicates that no watchers
1146are pending.
1147.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1148.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1149This overrides the invoke pending functionality of the loop: Instead of
1150invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1151this callback instead. This is useful, for example, when you want to
1152invoke the actual watchers inside another context (another thread etc.).
1153.Sp
1154If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1155callback.
1156.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1157.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1158Sometimes you want to share the same loop between multiple threads. This
1159can be done relatively simply by putting mutex_lock/unlock calls around
1160each call to a libev function.
1161.Sp
1162However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1163to wait for it to return. One way around this is to wake up the event
1164loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1165\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1166.Sp
1167When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1168suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1169afterwards.
1170.Sp
1171Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1172\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1173.Sp
1174While event loop modifications are allowed between invocations of
1175\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1176modifications done will affect the event loop, i.e. adding watchers will
1177have no effect on the set of file descriptors being watched, or the time
1178waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1179to take note of any changes you made.
1180.Sp
1181In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1182invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1183.Sp
1184See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1185document.
1186.IP "ev_set_userdata (loop, void *data)" 4
1187.IX Item "ev_set_userdata (loop, void *data)"
1188.PD 0
1189.IP "void *ev_userdata (loop)" 4
1190.IX Item "void *ev_userdata (loop)"
1191.PD
1192Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1193\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1194\&\f(CW0\fR.
1195.Sp
1196These two functions can be used to associate arbitrary data with a loop,
1197and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1198\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1199any other purpose as well.
1200.IP "ev_verify (loop)" 4
1201.IX Item "ev_verify (loop)"
1202This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1203compiled in, which is the default for non-minimal builds. It tries to go
1204through all internal structures and checks them for validity. If anything
1205is found to be inconsistent, it will print an error message to standard
1206error and call \f(CW\*(C`abort ()\*(C'\fR.
1207.Sp
1208This can be used to catch bugs inside libev itself: under normal
1209circumstances, this function will never abort as of course libev keeps its
1210data structures consistent.
723.SH "ANATOMY OF A WATCHER" 1211.SH "ANATOMY OF A WATCHER"
724.IX Header "ANATOMY OF A WATCHER" 1212.IX Header "ANATOMY OF A WATCHER"
1213In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1214watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1215watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1216.PP
725A watcher is a structure that you create and register to record your 1217A watcher is an opaque structure that you allocate and register to record
726interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1218your interest in some event. To make a concrete example, imagine you want
727become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1219to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1220for that:
728.PP 1221.PP
729.Vb 5 1222.Vb 5
730\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1223\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
731\& { 1224\& {
732\& ev_io_stop (w); 1225\& ev_io_stop (w);
733\& ev_unloop (loop, EVUNLOOP_ALL); 1226\& ev_break (loop, EVBREAK_ALL);
734\& } 1227\& }
735.Ve 1228\&
736.PP
737.Vb 6
738\& struct ev_loop *loop = ev_default_loop (0); 1229\& struct ev_loop *loop = ev_default_loop (0);
1230\&
739\& struct ev_io stdin_watcher; 1231\& ev_io stdin_watcher;
1232\&
740\& ev_init (&stdin_watcher, my_cb); 1233\& ev_init (&stdin_watcher, my_cb);
741\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1234\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
742\& ev_io_start (loop, &stdin_watcher); 1235\& ev_io_start (loop, &stdin_watcher);
1236\&
743\& ev_loop (loop, 0); 1237\& ev_run (loop, 0);
744.Ve 1238.Ve
745.PP 1239.PP
746As you can see, you are responsible for allocating the memory for your 1240As you can see, you are responsible for allocating the memory for your
747watcher structures (and it is usually a bad idea to do this on the stack, 1241watcher structures (and it is \fIusually\fR a bad idea to do this on the
748although this can sometimes be quite valid). 1242stack).
749.PP 1243.PP
1244Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1245or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1246.PP
750Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1247Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
751(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1248*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
752callback gets invoked each time the event occurs (or, in the case of io 1249invoked each time the event occurs (or, in the case of I/O watchers, each
753watchers, each time the event loop detects that the file descriptor given 1250time the event loop detects that the file descriptor given is readable
754is readable and/or writable). 1251and/or writable).
755.PP 1252.PP
756Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1253Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
757with arguments specific to this watcher type. There is also a macro 1254macro to configure it, with arguments specific to the watcher type. There
758to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1255is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
759(watcher *, callback, ...)\*(C'\fR.
760.PP 1256.PP
761To make the watcher actually watch out for events, you have to start it 1257To make the watcher actually watch out for events, you have to start it
762with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1258with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
763*)\*(C'\fR), and you can stop watching for events at any time by calling the 1259*)\*(C'\fR), and you can stop watching for events at any time by calling the
764corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1260corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
765.PP 1261.PP
766As long as your watcher is active (has been started but not stopped) you 1262As long as your watcher is active (has been started but not stopped) you
767must not touch the values stored in it. Most specifically you must never 1263must not touch the values stored in it. Most specifically you must never
768reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1264reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
769.PP 1265.PP
770Each and every callback receives the event loop pointer as first, the 1266Each and every callback receives the event loop pointer as first, the
771registered watcher structure as second, and a bitset of received events as 1267registered watcher structure as second, and a bitset of received events as
772third argument. 1268third argument.
773.PP 1269.PP
… …
782.el .IP "\f(CWEV_WRITE\fR" 4 1278.el .IP "\f(CWEV_WRITE\fR" 4
783.IX Item "EV_WRITE" 1279.IX Item "EV_WRITE"
784.PD 1280.PD
785The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1281The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
786writable. 1282writable.
787.ie n .IP """EV_TIMEOUT""" 4 1283.ie n .IP """EV_TIMER""" 4
788.el .IP "\f(CWEV_TIMEOUT\fR" 4 1284.el .IP "\f(CWEV_TIMER\fR" 4
789.IX Item "EV_TIMEOUT" 1285.IX Item "EV_TIMER"
790The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1286The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
791.ie n .IP """EV_PERIODIC""" 4 1287.ie n .IP """EV_PERIODIC""" 4
792.el .IP "\f(CWEV_PERIODIC\fR" 4 1288.el .IP "\f(CWEV_PERIODIC\fR" 4
793.IX Item "EV_PERIODIC" 1289.IX Item "EV_PERIODIC"
794The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1290The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
814.PD 0 1310.PD 0
815.ie n .IP """EV_CHECK""" 4 1311.ie n .IP """EV_CHECK""" 4
816.el .IP "\f(CWEV_CHECK\fR" 4 1312.el .IP "\f(CWEV_CHECK\fR" 4
817.IX Item "EV_CHECK" 1313.IX Item "EV_CHECK"
818.PD 1314.PD
819All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1315All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
820to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1316gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
821\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1317just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1318for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1319watchers invoked before the event loop sleeps or polls for new events, and
1320\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1321or lower priority within an event loop iteration.
1322.Sp
822received events. Callbacks of both watcher types can start and stop as 1323Callbacks of both watcher types can start and stop as many watchers as
823many watchers as they want, and all of them will be taken into account 1324they want, and all of them will be taken into account (for example, a
824(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1325\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
825\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1326blocking).
826.ie n .IP """EV_EMBED""" 4 1327.ie n .IP """EV_EMBED""" 4
827.el .IP "\f(CWEV_EMBED\fR" 4 1328.el .IP "\f(CWEV_EMBED\fR" 4
828.IX Item "EV_EMBED" 1329.IX Item "EV_EMBED"
829The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1330The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
830.ie n .IP """EV_FORK""" 4 1331.ie n .IP """EV_FORK""" 4
831.el .IP "\f(CWEV_FORK\fR" 4 1332.el .IP "\f(CWEV_FORK\fR" 4
832.IX Item "EV_FORK" 1333.IX Item "EV_FORK"
833The event loop has been resumed in the child process after fork (see 1334The event loop has been resumed in the child process after fork (see
834\&\f(CW\*(C`ev_fork\*(C'\fR). 1335\&\f(CW\*(C`ev_fork\*(C'\fR).
1336.ie n .IP """EV_CLEANUP""" 4
1337.el .IP "\f(CWEV_CLEANUP\fR" 4
1338.IX Item "EV_CLEANUP"
1339The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1340.ie n .IP """EV_ASYNC""" 4
1341.el .IP "\f(CWEV_ASYNC\fR" 4
1342.IX Item "EV_ASYNC"
1343The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1344.ie n .IP """EV_CUSTOM""" 4
1345.el .IP "\f(CWEV_CUSTOM\fR" 4
1346.IX Item "EV_CUSTOM"
1347Not ever sent (or otherwise used) by libev itself, but can be freely used
1348by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
835.ie n .IP """EV_ERROR""" 4 1349.ie n .IP """EV_ERROR""" 4
836.el .IP "\f(CWEV_ERROR\fR" 4 1350.el .IP "\f(CWEV_ERROR\fR" 4
837.IX Item "EV_ERROR" 1351.IX Item "EV_ERROR"
838An unspecified error has occured, the watcher has been stopped. This might 1352An unspecified error has occurred, the watcher has been stopped. This might
839happen because the watcher could not be properly started because libev 1353happen because the watcher could not be properly started because libev
840ran out of memory, a file descriptor was found to be closed or any other 1354ran out of memory, a file descriptor was found to be closed or any other
1355problem. Libev considers these application bugs.
1356.Sp
841problem. You best act on it by reporting the problem and somehow coping 1357You best act on it by reporting the problem and somehow coping with the
842with the watcher being stopped. 1358watcher being stopped. Note that well-written programs should not receive
1359an error ever, so when your watcher receives it, this usually indicates a
1360bug in your program.
843.Sp 1361.Sp
844Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1362Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
845for example it might indicate that a fd is readable or writable, and if 1363example it might indicate that a fd is readable or writable, and if your
846your callbacks is well-written it can just attempt the operation and cope 1364callbacks is well-written it can just attempt the operation and cope with
847with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1365the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
848programs, though, so beware. 1366programs, though, as the fd could already be closed and reused for another
1367thing, so beware.
849.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1368.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
850.IX Subsection "GENERIC WATCHER FUNCTIONS" 1369.IX Subsection "GENERIC WATCHER FUNCTIONS"
851In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
852e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
853.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1370.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
854.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1371.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
855.IX Item "ev_init (ev_TYPE *watcher, callback)" 1372.IX Item "ev_init (ev_TYPE *watcher, callback)"
856This macro initialises the generic portion of a watcher. The contents 1373This macro initialises the generic portion of a watcher. The contents
857of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1374of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
861which rolls both calls into one. 1378which rolls both calls into one.
862.Sp 1379.Sp
863You can reinitialise a watcher at any time as long as it has been stopped 1380You can reinitialise a watcher at any time as long as it has been stopped
864(or never started) and there are no pending events outstanding. 1381(or never started) and there are no pending events outstanding.
865.Sp 1382.Sp
866The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1383The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
867int revents)\*(C'\fR. 1384int revents)\*(C'\fR.
1385.Sp
1386Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1387.Sp
1388.Vb 3
1389\& ev_io w;
1390\& ev_init (&w, my_cb);
1391\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1392.Ve
868.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1393.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
869.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1394.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
870.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1395.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
871This macro initialises the type-specific parts of a watcher. You need to 1396This macro initialises the type-specific parts of a watcher. You need to
872call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1397call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
873call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1398call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
874macro on a watcher that is active (it can be pending, however, which is a 1399macro on a watcher that is active (it can be pending, however, which is a
875difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1400difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
876.Sp 1401.Sp
877Although some watcher types do not have type-specific arguments 1402Although some watcher types do not have type-specific arguments
878(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1403(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1404.Sp
1405See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
879.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1406.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
880.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1407.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
881.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1408.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
882This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1409This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
883calls into a single call. This is the most convinient method to initialise 1410calls into a single call. This is the most convenient method to initialise
884a watcher. The same limitations apply, of course. 1411a watcher. The same limitations apply, of course.
1412.Sp
1413Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1414.Sp
1415.Vb 1
1416\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1417.Ve
885.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1418.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
886.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1419.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
887.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1420.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
888Starts (activates) the given watcher. Only active watchers will receive 1421Starts (activates) the given watcher. Only active watchers will receive
889events. If the watcher is already active nothing will happen. 1422events. If the watcher is already active nothing will happen.
1423.Sp
1424Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1425whole section.
1426.Sp
1427.Vb 1
1428\& ev_io_start (EV_DEFAULT_UC, &w);
1429.Ve
890.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1430.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
891.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1431.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
892.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1432.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
893Stops the given watcher again (if active) and clears the pending 1433Stops the given watcher if active, and clears the pending status (whether
1434the watcher was active or not).
1435.Sp
894status. It is possible that stopped watchers are pending (for example, 1436It is possible that stopped watchers are pending \- for example,
895non-repeating timers are being stopped when they become pending), but 1437non-repeating timers are being stopped when they become pending \- but
896\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1438calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
897you want to free or reuse the memory used by the watcher it is therefore a 1439pending. If you want to free or reuse the memory used by the watcher it is
898good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1440therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
899.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1441.IP "bool ev_is_active (ev_TYPE *watcher)" 4
900.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1442.IX Item "bool ev_is_active (ev_TYPE *watcher)"
901Returns a true value iff the watcher is active (i.e. it has been started 1443Returns a true value iff the watcher is active (i.e. it has been started
902and not yet been stopped). As long as a watcher is active you must not modify 1444and not yet been stopped). As long as a watcher is active you must not modify
903it. 1445it.
… …
910make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR 1452make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
911it). 1453it).
912.IP "callback ev_cb (ev_TYPE *watcher)" 4 1454.IP "callback ev_cb (ev_TYPE *watcher)" 4
913.IX Item "callback ev_cb (ev_TYPE *watcher)" 1455.IX Item "callback ev_cb (ev_TYPE *watcher)"
914Returns the callback currently set on the watcher. 1456Returns the callback currently set on the watcher.
915.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1457.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
916.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1458.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
917Change the callback. You can change the callback at virtually any time 1459Change the callback. You can change the callback at virtually any time
918(modulo threads). 1460(modulo threads).
919.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 1461.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
920.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" 1462.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
921.PD 0 1463.PD 0
922.IP "int ev_priority (ev_TYPE *watcher)" 4 1464.IP "int ev_priority (ev_TYPE *watcher)" 4
923.IX Item "int ev_priority (ev_TYPE *watcher)" 1465.IX Item "int ev_priority (ev_TYPE *watcher)"
924.PD 1466.PD
925Set and query the priority of the watcher. The priority is a small 1467Set and query the priority of the watcher. The priority is a small
926integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR 1468integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
927(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked 1469(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
928before watchers with lower priority, but priority will not keep watchers 1470before watchers with lower priority, but priority will not keep watchers
929from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). 1471from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
930.Sp 1472.Sp
931This means that priorities are \fIonly\fR used for ordering callback
932invocation after new events have been received. This is useful, for
933example, to reduce latency after idling, or more often, to bind two
934watchers on the same event and make sure one is called first.
935.Sp
936If you need to suppress invocation when higher priority events are pending 1473If you need to suppress invocation when higher priority events are pending
937you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. 1474you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
938.Sp 1475.Sp
939You \fImust not\fR change the priority of a watcher as long as it is active or 1476You \fImust not\fR change the priority of a watcher as long as it is active or
940pending. 1477pending.
941.Sp 1478.Sp
1479Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1480fine, as long as you do not mind that the priority value you query might
1481or might not have been clamped to the valid range.
1482.Sp
942The default priority used by watchers when no priority has been set is 1483The default priority used by watchers when no priority has been set is
943always \f(CW0\fR, which is supposed to not be too high and not be too low :). 1484always \f(CW0\fR, which is supposed to not be too high and not be too low :).
944.Sp 1485.Sp
945Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is 1486See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
946fine, as long as you do not mind that the priority value you query might 1487priorities.
947or might not have been adjusted to be within valid range.
948.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 1488.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
949.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" 1489.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
950Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither 1490Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
951\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback 1491\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
952can deal with that fact. 1492can deal with that fact, as both are simply passed through to the
1493callback.
953.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 1494.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
954.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" 1495.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
955If the watcher is pending, this function returns clears its pending status 1496If the watcher is pending, this function clears its pending status and
956and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the 1497returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
957watcher isn't pending it does nothing and returns \f(CW0\fR. 1498watcher isn't pending it does nothing and returns \f(CW0\fR.
958.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1499.Sp
959.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1500Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
960Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1501callback to be invoked, which can be accomplished with this function.
961and read at any time, libev will completely ignore it. This can be used 1502.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
962to associate arbitrary data with your watcher. If you need more data and 1503.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
963don't want to allocate memory and store a pointer to it in that data 1504Feeds the given event set into the event loop, as if the specified event
964member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1505had happened for the specified watcher (which must be a pointer to an
965data: 1506initialised but not necessarily started event watcher). Obviously you must
1507not free the watcher as long as it has pending events.
1508.Sp
1509Stopping the watcher, letting libev invoke it, or calling
1510\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1511not started in the first place.
1512.Sp
1513See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1514functions that do not need a watcher.
966.PP 1515.PP
1516See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1517OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1518.SS "\s-1WATCHER STATES\s0"
1519.IX Subsection "WATCHER STATES"
1520There are various watcher states mentioned throughout this manual \-
1521active, pending and so on. In this section these states and the rules to
1522transition between them will be described in more detail \- and while these
1523rules might look complicated, they usually do \*(L"the right thing\*(R".
1524.IP "initialised" 4
1525.IX Item "initialised"
1526Before a watcher can be registered with the event loop it has to be
1527initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1528\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1529.Sp
1530In this state it is simply some block of memory that is suitable for
1531use in an event loop. It can be moved around, freed, reused etc. at
1532will \- as long as you either keep the memory contents intact, or call
1533\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1534.IP "started/running/active" 4
1535.IX Item "started/running/active"
1536Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1537property of the event loop, and is actively waiting for events. While in
1538this state it cannot be accessed (except in a few documented ways), moved,
1539freed or anything else \- the only legal thing is to keep a pointer to it,
1540and call libev functions on it that are documented to work on active watchers.
1541.IP "pending" 4
1542.IX Item "pending"
1543If a watcher is active and libev determines that an event it is interested
1544in has occurred (such as a timer expiring), it will become pending. It will
1545stay in this pending state until either it is stopped or its callback is
1546about to be invoked, so it is not normally pending inside the watcher
1547callback.
1548.Sp
1549The watcher might or might not be active while it is pending (for example,
1550an expired non-repeating timer can be pending but no longer active). If it
1551is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1552but it is still property of the event loop at this time, so cannot be
1553moved, freed or reused. And if it is active the rules described in the
1554previous item still apply.
1555.Sp
1556It is also possible to feed an event on a watcher that is not active (e.g.
1557via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1558active.
1559.IP "stopped" 4
1560.IX Item "stopped"
1561A watcher can be stopped implicitly by libev (in which case it might still
1562be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1563latter will clear any pending state the watcher might be in, regardless
1564of whether it was active or not, so stopping a watcher explicitly before
1565freeing it is often a good idea.
1566.Sp
1567While stopped (and not pending) the watcher is essentially in the
1568initialised state, that is, it can be reused, moved, modified in any way
1569you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1570it again).
1571.SS "\s-1WATCHER PRIORITY MODELS\s0"
1572.IX Subsection "WATCHER PRIORITY MODELS"
1573Many event loops support \fIwatcher priorities\fR, which are usually small
1574integers that influence the ordering of event callback invocation
1575between watchers in some way, all else being equal.
1576.PP
1577In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1578description for the more technical details such as the actual priority
1579range.
1580.PP
1581There are two common ways how these these priorities are being interpreted
1582by event loops:
1583.PP
1584In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1585of lower priority watchers, which means as long as higher priority
1586watchers receive events, lower priority watchers are not being invoked.
1587.PP
1588The less common only-for-ordering model uses priorities solely to order
1589callback invocation within a single event loop iteration: Higher priority
1590watchers are invoked before lower priority ones, but they all get invoked
1591before polling for new events.
1592.PP
1593Libev uses the second (only-for-ordering) model for all its watchers
1594except for idle watchers (which use the lock-out model).
1595.PP
1596The rationale behind this is that implementing the lock-out model for
1597watchers is not well supported by most kernel interfaces, and most event
1598libraries will just poll for the same events again and again as long as
1599their callbacks have not been executed, which is very inefficient in the
1600common case of one high-priority watcher locking out a mass of lower
1601priority ones.
1602.PP
1603Static (ordering) priorities are most useful when you have two or more
1604watchers handling the same resource: a typical usage example is having an
1605\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1606timeouts. Under load, data might be received while the program handles
1607other jobs, but since timers normally get invoked first, the timeout
1608handler will be executed before checking for data. In that case, giving
1609the timer a lower priority than the I/O watcher ensures that I/O will be
1610handled first even under adverse conditions (which is usually, but not
1611always, what you want).
1612.PP
1613Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1614will only be executed when no same or higher priority watchers have
1615received events, they can be used to implement the \*(L"lock-out\*(R" model when
1616required.
1617.PP
1618For example, to emulate how many other event libraries handle priorities,
1619you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1620the normal watcher callback, you just start the idle watcher. The real
1621processing is done in the idle watcher callback. This causes libev to
1622continuously poll and process kernel event data for the watcher, but when
1623the lock-out case is known to be rare (which in turn is rare :), this is
1624workable.
1625.PP
1626Usually, however, the lock-out model implemented that way will perform
1627miserably under the type of load it was designed to handle. In that case,
1628it might be preferable to stop the real watcher before starting the
1629idle watcher, so the kernel will not have to process the event in case
1630the actual processing will be delayed for considerable time.
1631.PP
1632Here is an example of an I/O watcher that should run at a strictly lower
1633priority than the default, and which should only process data when no
1634other events are pending:
1635.PP
967.Vb 7 1636.Vb 2
968\& struct my_io 1637\& ev_idle idle; // actual processing watcher
969\& { 1638\& ev_io io; // actual event watcher
970\& struct ev_io io; 1639\&
971\& int otherfd;
972\& void *somedata;
973\& struct whatever *mostinteresting;
974\& }
975.Ve
976.PP
977And since your callback will be called with a pointer to the watcher, you
978can cast it back to your own type:
979.PP
980.Vb 5
981\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
982\& {
983\& struct my_io *w = (struct my_io *)w_;
984\& ...
985\& }
986.Ve
987.PP
988More interesting and less C\-conformant ways of casting your callback type
989instead have been omitted.
990.PP
991Another common scenario is having some data structure with multiple
992watchers:
993.PP
994.Vb 6
995\& struct my_biggy
996\& {
997\& int some_data;
998\& ev_timer t1;
999\& ev_timer t2;
1000\& }
1001.Ve
1002.PP
1003In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1004you need to use \f(CW\*(C`offsetof\*(C'\fR:
1005.PP
1006.Vb 1
1007\& #include <stddef.h>
1008.Ve
1009.PP
1010.Vb 6
1011\& static void 1640\& static void
1012\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1641\& io_cb (EV_P_ ev_io *w, int revents)
1013\& { 1642\& {
1014\& struct my_biggy big = (struct my_biggy * 1643\& // stop the I/O watcher, we received the event, but
1015\& (((char *)w) - offsetof (struct my_biggy, t1)); 1644\& // are not yet ready to handle it.
1645\& ev_io_stop (EV_A_ w);
1646\&
1647\& // start the idle watcher to handle the actual event.
1648\& // it will not be executed as long as other watchers
1649\& // with the default priority are receiving events.
1650\& ev_idle_start (EV_A_ &idle);
1016\& } 1651\& }
1017.Ve 1652\&
1018.PP
1019.Vb 6
1020\& static void 1653\& static void
1021\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1654\& idle_cb (EV_P_ ev_idle *w, int revents)
1022\& { 1655\& {
1023\& struct my_biggy big = (struct my_biggy * 1656\& // actual processing
1024\& (((char *)w) - offsetof (struct my_biggy, t2)); 1657\& read (STDIN_FILENO, ...);
1658\&
1659\& // have to start the I/O watcher again, as
1660\& // we have handled the event
1661\& ev_io_start (EV_P_ &io);
1025\& } 1662\& }
1663\&
1664\& // initialisation
1665\& ev_idle_init (&idle, idle_cb);
1666\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1667\& ev_io_start (EV_DEFAULT_ &io);
1026.Ve 1668.Ve
1669.PP
1670In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1671low-priority connections can not be locked out forever under load. This
1672enables your program to keep a lower latency for important connections
1673during short periods of high load, while not completely locking out less
1674important ones.
1027.SH "WATCHER TYPES" 1675.SH "WATCHER TYPES"
1028.IX Header "WATCHER TYPES" 1676.IX Header "WATCHER TYPES"
1029This section describes each watcher in detail, but will not repeat 1677This section describes each watcher in detail, but will not repeat
1030information given in the last section. Any initialisation/set macros, 1678information given in the last section. Any initialisation/set macros,
1031functions and members specific to the watcher type are explained. 1679functions and members specific to the watcher type are explained.
… …
1036watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1684watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1037means you can expect it to have some sensible content while the watcher 1685means you can expect it to have some sensible content while the watcher
1038is active, but you can also modify it. Modifying it may not do something 1686is active, but you can also modify it. Modifying it may not do something
1039sensible or take immediate effect (or do anything at all), but libev will 1687sensible or take immediate effect (or do anything at all), but libev will
1040not crash or malfunction in any way. 1688not crash or malfunction in any way.
1041.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1689.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1042.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1690.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1043.IX Subsection "ev_io - is this file descriptor readable or writable?" 1691.IX Subsection "ev_io - is this file descriptor readable or writable?"
1044I/O watchers check whether a file descriptor is readable or writable 1692I/O watchers check whether a file descriptor is readable or writable
1045in each iteration of the event loop, or, more precisely, when reading 1693in each iteration of the event loop, or, more precisely, when reading
1046would not block the process and writing would at least be able to write 1694would not block the process and writing would at least be able to write
1047some data. This behaviour is called level-triggering because you keep 1695some data. This behaviour is called level-triggering because you keep
… …
1052In general you can register as many read and/or write event watchers per 1700In general you can register as many read and/or write event watchers per
1053fd as you want (as long as you don't confuse yourself). Setting all file 1701fd as you want (as long as you don't confuse yourself). Setting all file
1054descriptors to non-blocking mode is also usually a good idea (but not 1702descriptors to non-blocking mode is also usually a good idea (but not
1055required if you know what you are doing). 1703required if you know what you are doing).
1056.PP 1704.PP
1057You have to be careful with dup'ed file descriptors, though. Some backends
1058(the linux epoll backend is a notable example) cannot handle dup'ed file
1059descriptors correctly if you register interest in two or more fds pointing
1060to the same underlying file/socket/etc. description (that is, they share
1061the same underlying \*(L"file open\*(R").
1062.PP
1063If you must do this, then force the use of a known-to-be-good backend
1064(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1065\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1066.PP
1067Another thing you have to watch out for is that it is quite easy to 1705Another thing you have to watch out for is that it is quite easy to
1068receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1706receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1069be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1707be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1070because there is no data. Not only are some backends known to create a 1708because there is no data. It is very easy to get into this situation even
1071lot of those (for example solaris ports), it is very easy to get into 1709with a relatively standard program structure. Thus it is best to always
1072this situation even with a relatively standard program structure. Thus 1710use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1073it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1074\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1711preferable to a program hanging until some data arrives.
1075.PP 1712.PP
1076If you cannot run the fd in non-blocking mode (for example you should not 1713If you cannot run the fd in non-blocking mode (for example you should
1077play around with an Xlib connection), then you have to seperately re-test 1714not play around with an Xlib connection), then you have to separately
1078whether a file descriptor is really ready with a known-to-be good interface 1715re-test whether a file descriptor is really ready with a known-to-be good
1079such as poll (fortunately in our Xlib example, Xlib already does this on 1716interface such as poll (fortunately in the case of Xlib, it already does
1080its own, so its quite safe to use). 1717this on its own, so its quite safe to use). Some people additionally
1718use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1719indefinitely.
1720.PP
1721But really, best use non-blocking mode.
1081.PP 1722.PP
1082\fIThe special problem of disappearing file descriptors\fR 1723\fIThe special problem of disappearing file descriptors\fR
1083.IX Subsection "The special problem of disappearing file descriptors" 1724.IX Subsection "The special problem of disappearing file descriptors"
1084.PP 1725.PP
1085Some backends (e.g kqueue, epoll) need to be told about closing a file 1726Some backends (e.g. kqueue, epoll) need to be told about closing a file
1086descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means, 1727descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1087such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file 1728such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1088descriptor, but when it goes away, the operating system will silently drop 1729descriptor, but when it goes away, the operating system will silently drop
1089this interest. If another file descriptor with the same number then is 1730this interest. If another file descriptor with the same number then is
1090registered with libev, there is no efficient way to see that this is, in 1731registered with libev, there is no efficient way to see that this is, in
1091fact, a different file descriptor. 1732fact, a different file descriptor.
1092.PP 1733.PP
… …
1098descriptor even if the file descriptor number itself did not change. 1739descriptor even if the file descriptor number itself did not change.
1099.PP 1740.PP
1100This is how one would do it normally anyway, the important point is that 1741This is how one would do it normally anyway, the important point is that
1101the libev application should not optimise around libev but should leave 1742the libev application should not optimise around libev but should leave
1102optimisations to libev. 1743optimisations to libev.
1744.PP
1745\fIThe special problem of dup'ed file descriptors\fR
1746.IX Subsection "The special problem of dup'ed file descriptors"
1747.PP
1748Some backends (e.g. epoll), cannot register events for file descriptors,
1749but only events for the underlying file descriptions. That means when you
1750have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1751events for them, only one file descriptor might actually receive events.
1752.PP
1753There is no workaround possible except not registering events
1754for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1755\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1756.PP
1757\fIThe special problem of files\fR
1758.IX Subsection "The special problem of files"
1759.PP
1760Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1761representing files, and expect it to become ready when their program
1762doesn't block on disk accesses (which can take a long time on their own).
1763.PP
1764However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1765notification as soon as the kernel knows whether and how much data is
1766there, and in the case of open files, that's always the case, so you
1767always get a readiness notification instantly, and your read (or possibly
1768write) will still block on the disk I/O.
1769.PP
1770Another way to view it is that in the case of sockets, pipes, character
1771devices and so on, there is another party (the sender) that delivers data
1772on its own, but in the case of files, there is no such thing: the disk
1773will not send data on its own, simply because it doesn't know what you
1774wish to read \- you would first have to request some data.
1775.PP
1776Since files are typically not-so-well supported by advanced notification
1777mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1778to files, even though you should not use it. The reason for this is
1779convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1780usually a tty, often a pipe, but also sometimes files or special devices
1781(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1782\&\fI/dev/urandom\fR), and even though the file might better be served with
1783asynchronous I/O instead of with non-blocking I/O, it is still useful when
1784it \*(L"just works\*(R" instead of freezing.
1785.PP
1786So avoid file descriptors pointing to files when you know it (e.g. use
1787libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1788when you rarely read from a file instead of from a socket, and want to
1789reuse the same code path.
1790.PP
1791\fIThe special problem of fork\fR
1792.IX Subsection "The special problem of fork"
1793.PP
1794Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1795useless behaviour. Libev fully supports fork, but needs to be told about
1796it in the child if you want to continue to use it in the child.
1797.PP
1798To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1799()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1800\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1801.PP
1802\fIThe special problem of \s-1SIGPIPE\s0\fR
1803.IX Subsection "The special problem of SIGPIPE"
1804.PP
1805While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1806when writing to a pipe whose other end has been closed, your program gets
1807sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1808this is sensible behaviour, for daemons, this is usually undesirable.
1809.PP
1810So when you encounter spurious, unexplained daemon exits, make sure you
1811ignore \s-1SIGPIPE \s0(and maybe make sure you log the exit status of your daemon
1812somewhere, as that would have given you a big clue).
1813.PP
1814\fIThe special problem of \fIaccept()\fIing when you can't\fR
1815.IX Subsection "The special problem of accept()ing when you can't"
1816.PP
1817Many implementations of the \s-1POSIX \s0\f(CW\*(C`accept\*(C'\fR function (for example,
1818found in post\-2004 Linux) have the peculiar behaviour of not removing a
1819connection from the pending queue in all error cases.
1820.PP
1821For example, larger servers often run out of file descriptors (because
1822of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1823rejecting the connection, leading to libev signalling readiness on
1824the next iteration again (the connection still exists after all), and
1825typically causing the program to loop at 100% \s-1CPU\s0 usage.
1826.PP
1827Unfortunately, the set of errors that cause this issue differs between
1828operating systems, there is usually little the app can do to remedy the
1829situation, and no known thread-safe method of removing the connection to
1830cope with overload is known (to me).
1831.PP
1832One of the easiest ways to handle this situation is to just ignore it
1833\&\- when the program encounters an overload, it will just loop until the
1834situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1835event-based way to handle this situation, so it's the best one can do.
1836.PP
1837A better way to handle the situation is to log any errors other than
1838\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1839messages, and continue as usual, which at least gives the user an idea of
1840what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1841the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1842usage.
1843.PP
1844If your program is single-threaded, then you could also keep a dummy file
1845descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1846when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1847close that fd, and create a new dummy fd. This will gracefully refuse
1848clients under typical overload conditions.
1849.PP
1850The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1851is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1852opportunity for a DoS attack.
1103.PP 1853.PP
1104\fIWatcher-Specific Functions\fR 1854\fIWatcher-Specific Functions\fR
1105.IX Subsection "Watcher-Specific Functions" 1855.IX Subsection "Watcher-Specific Functions"
1106.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1856.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1107.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1857.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1108.PD 0 1858.PD 0
1109.IP "ev_io_set (ev_io *, int fd, int events)" 4 1859.IP "ev_io_set (ev_io *, int fd, int events)" 4
1110.IX Item "ev_io_set (ev_io *, int fd, int events)" 1860.IX Item "ev_io_set (ev_io *, int fd, int events)"
1111.PD 1861.PD
1112Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1862Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1113rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1863receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1114\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1864\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1115.IP "int fd [read\-only]" 4 1865.IP "int fd [read\-only]" 4
1116.IX Item "int fd [read-only]" 1866.IX Item "int fd [read-only]"
1117The file descriptor being watched. 1867The file descriptor being watched.
1118.IP "int events [read\-only]" 4 1868.IP "int events [read\-only]" 4
1119.IX Item "int events [read-only]" 1869.IX Item "int events [read-only]"
1120The events being watched. 1870The events being watched.
1121.PP 1871.PP
1872\fIExamples\fR
1873.IX Subsection "Examples"
1874.PP
1122Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1875Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1123readable, but only once. Since it is likely line\-buffered, you could 1876readable, but only once. Since it is likely line-buffered, you could
1124attempt to read a whole line in the callback. 1877attempt to read a whole line in the callback.
1125.PP 1878.PP
1126.Vb 6 1879.Vb 6
1127\& static void 1880\& static void
1128\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1881\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1129\& { 1882\& {
1130\& ev_io_stop (loop, w); 1883\& ev_io_stop (loop, w);
1131\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1884\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1132\& } 1885\& }
1133.Ve 1886\&
1134.PP
1135.Vb 6
1136\& ... 1887\& ...
1137\& struct ev_loop *loop = ev_default_init (0); 1888\& struct ev_loop *loop = ev_default_init (0);
1138\& struct ev_io stdin_readable; 1889\& ev_io stdin_readable;
1139\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1890\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1140\& ev_io_start (loop, &stdin_readable); 1891\& ev_io_start (loop, &stdin_readable);
1141\& ev_loop (loop, 0); 1892\& ev_run (loop, 0);
1142.Ve 1893.Ve
1143.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1894.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1144.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1895.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1145.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1896.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1146Timer watchers are simple relative timers that generate an event after a 1897Timer watchers are simple relative timers that generate an event after a
1147given time, and optionally repeating in regular intervals after that. 1898given time, and optionally repeating in regular intervals after that.
1148.PP 1899.PP
1149The timers are based on real time, that is, if you register an event that 1900The timers are based on real time, that is, if you register an event that
1150times out after an hour and you reset your system clock to last years 1901times out after an hour and you reset your system clock to January last
1151time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1902year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1152detecting time jumps is hard, and some inaccuracies are unavoidable (the 1903detecting time jumps is hard, and some inaccuracies are unavoidable (the
1153monotonic clock option helps a lot here). 1904monotonic clock option helps a lot here).
1905.PP
1906The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1907passed (not \fIat\fR, so on systems with very low-resolution clocks this
1908might introduce a small delay, see \*(L"the special problem of being too
1909early\*(R", below). If multiple timers become ready during the same loop
1910iteration then the ones with earlier time-out values are invoked before
1911ones of the same priority with later time-out values (but this is no
1912longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1913.PP
1914\fIBe smart about timeouts\fR
1915.IX Subsection "Be smart about timeouts"
1916.PP
1917Many real-world problems involve some kind of timeout, usually for error
1918recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1919you want to raise some error after a while.
1920.PP
1921What follows are some ways to handle this problem, from obvious and
1922inefficient to smart and efficient.
1923.PP
1924In the following, a 60 second activity timeout is assumed \- a timeout that
1925gets reset to 60 seconds each time there is activity (e.g. each time some
1926data or other life sign was received).
1927.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1928.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1929This is the most obvious, but not the most simple way: In the beginning,
1930start the watcher:
1931.Sp
1932.Vb 2
1933\& ev_timer_init (timer, callback, 60., 0.);
1934\& ev_timer_start (loop, timer);
1935.Ve
1936.Sp
1937Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1938and start it again:
1939.Sp
1940.Vb 3
1941\& ev_timer_stop (loop, timer);
1942\& ev_timer_set (timer, 60., 0.);
1943\& ev_timer_start (loop, timer);
1944.Ve
1945.Sp
1946This is relatively simple to implement, but means that each time there is
1947some activity, libev will first have to remove the timer from its internal
1948data structure and then add it again. Libev tries to be fast, but it's
1949still not a constant-time operation.
1950.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1951.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1952.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1953This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1954\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1955.Sp
1956To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1957of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1958successfully read or write some data. If you go into an idle state where
1959you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1960the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1961.Sp
1962That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1963\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
1964member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1965.Sp
1966At start:
1967.Sp
1968.Vb 3
1969\& ev_init (timer, callback);
1970\& timer\->repeat = 60.;
1971\& ev_timer_again (loop, timer);
1972.Ve
1973.Sp
1974Each time there is some activity:
1975.Sp
1976.Vb 1
1977\& ev_timer_again (loop, timer);
1978.Ve
1979.Sp
1980It is even possible to change the time-out on the fly, regardless of
1981whether the watcher is active or not:
1982.Sp
1983.Vb 2
1984\& timer\->repeat = 30.;
1985\& ev_timer_again (loop, timer);
1986.Ve
1987.Sp
1988This is slightly more efficient then stopping/starting the timer each time
1989you want to modify its timeout value, as libev does not have to completely
1990remove and re-insert the timer from/into its internal data structure.
1991.Sp
1992It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1993.IP "3. Let the timer time out, but then re-arm it as required." 4
1994.IX Item "3. Let the timer time out, but then re-arm it as required."
1995This method is more tricky, but usually most efficient: Most timeouts are
1996relatively long compared to the intervals between other activity \- in
1997our example, within 60 seconds, there are usually many I/O events with
1998associated activity resets.
1999.Sp
2000In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2001but remember the time of last activity, and check for a real timeout only
2002within the callback:
2003.Sp
2004.Vb 3
2005\& ev_tstamp timeout = 60.;
2006\& ev_tstamp last_activity; // time of last activity
2007\& ev_timer timer;
2008\&
2009\& static void
2010\& callback (EV_P_ ev_timer *w, int revents)
2011\& {
2012\& // calculate when the timeout would happen
2013\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2014\&
2015\& // if negative, it means we the timeout already occurred
2016\& if (after < 0.)
2017\& {
2018\& // timeout occurred, take action
2019\& }
2020\& else
2021\& {
2022\& // callback was invoked, but there was some recent
2023\& // activity. simply restart the timer to time out
2024\& // after "after" seconds, which is the earliest time
2025\& // the timeout can occur.
2026\& ev_timer_set (w, after, 0.);
2027\& ev_timer_start (EV_A_ w);
2028\& }
2029\& }
2030.Ve
2031.Sp
2032To summarise the callback: first calculate in how many seconds the
2033timeout will occur (by calculating the absolute time when it would occur,
2034\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2035(EV_A)\*(C'\fR from that).
2036.Sp
2037If this value is negative, then we are already past the timeout, i.e. we
2038timed out, and need to do whatever is needed in this case.
2039.Sp
2040Otherwise, we now the earliest time at which the timeout would trigger,
2041and simply start the timer with this timeout value.
2042.Sp
2043In other words, each time the callback is invoked it will check whether
2044the timeout occurred. If not, it will simply reschedule itself to check
2045again at the earliest time it could time out. Rinse. Repeat.
2046.Sp
2047This scheme causes more callback invocations (about one every 60 seconds
2048minus half the average time between activity), but virtually no calls to
2049libev to change the timeout.
2050.Sp
2051To start the machinery, simply initialise the watcher and set
2052\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2053now), then call the callback, which will \*(L"do the right thing\*(R" and start
2054the timer:
2055.Sp
2056.Vb 3
2057\& last_activity = ev_now (EV_A);
2058\& ev_init (&timer, callback);
2059\& callback (EV_A_ &timer, 0);
2060.Ve
2061.Sp
2062When there is some activity, simply store the current time in
2063\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2064.Sp
2065.Vb 2
2066\& if (activity detected)
2067\& last_activity = ev_now (EV_A);
2068.Ve
2069.Sp
2070When your timeout value changes, then the timeout can be changed by simply
2071providing a new value, stopping the timer and calling the callback, which
2072will again do the right thing (for example, time out immediately :).
2073.Sp
2074.Vb 3
2075\& timeout = new_value;
2076\& ev_timer_stop (EV_A_ &timer);
2077\& callback (EV_A_ &timer, 0);
2078.Ve
2079.Sp
2080This technique is slightly more complex, but in most cases where the
2081time-out is unlikely to be triggered, much more efficient.
2082.IP "4. Wee, just use a double-linked list for your timeouts." 4
2083.IX Item "4. Wee, just use a double-linked list for your timeouts."
2084If there is not one request, but many thousands (millions...), all
2085employing some kind of timeout with the same timeout value, then one can
2086do even better:
2087.Sp
2088When starting the timeout, calculate the timeout value and put the timeout
2089at the \fIend\fR of the list.
2090.Sp
2091Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2092the list is expected to fire (for example, using the technique #3).
2093.Sp
2094When there is some activity, remove the timer from the list, recalculate
2095the timeout, append it to the end of the list again, and make sure to
2096update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2097.Sp
2098This way, one can manage an unlimited number of timeouts in O(1) time for
2099starting, stopping and updating the timers, at the expense of a major
2100complication, and having to use a constant timeout. The constant timeout
2101ensures that the list stays sorted.
2102.PP
2103So which method the best?
2104.PP
2105Method #2 is a simple no-brain-required solution that is adequate in most
2106situations. Method #3 requires a bit more thinking, but handles many cases
2107better, and isn't very complicated either. In most case, choosing either
2108one is fine, with #3 being better in typical situations.
2109.PP
2110Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2111rather complicated, but extremely efficient, something that really pays
2112off after the first million or so of active timers, i.e. it's usually
2113overkill :)
2114.PP
2115\fIThe special problem of being too early\fR
2116.IX Subsection "The special problem of being too early"
2117.PP
2118If you ask a timer to call your callback after three seconds, then
2119you expect it to be invoked after three seconds \- but of course, this
2120cannot be guaranteed to infinite precision. Less obviously, it cannot be
2121guaranteed to any precision by libev \- imagine somebody suspending the
2122process with a \s-1STOP\s0 signal for a few hours for example.
2123.PP
2124So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2125delay has occurred, but cannot guarantee this.
2126.PP
2127A less obvious failure mode is calling your callback too early: many event
2128loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2129this can cause your callback to be invoked much earlier than you would
2130expect.
2131.PP
2132To see why, imagine a system with a clock that only offers full second
2133resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2134yourself). If you schedule a one-second timer at the time 500.9, then the
2135event loop will schedule your timeout to elapse at a system time of 500
2136(500.9 truncated to the resolution) + 1, or 501.
2137.PP
2138If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2139501\*(R" and invoke the callback 0.1s after it was started, even though a
2140one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2141intentions.
2142.PP
2143This is the reason why libev will never invoke the callback if the elapsed
2144delay equals the requested delay, but only when the elapsed delay is
2145larger than the requested delay. In the example above, libev would only invoke
2146the callback at system time 502, or 1.1s after the timer was started.
2147.PP
2148So, while libev cannot guarantee that your callback will be invoked
2149exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2150delay has actually elapsed, or in other words, it always errs on the \*(L"too
2151late\*(R" side of things.
2152.PP
2153\fIThe special problem of time updates\fR
2154.IX Subsection "The special problem of time updates"
2155.PP
2156Establishing the current time is a costly operation (it usually takes
2157at least one system call): \s-1EV\s0 therefore updates its idea of the current
2158time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2159growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2160lots of events in one iteration.
1154.PP 2161.PP
1155The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2162The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1156time. This is usually the right thing as this timestamp refers to the time 2163time. This is usually the right thing as this timestamp refers to the time
1157of the event triggering whatever timeout you are modifying/starting. If 2164of the event triggering whatever timeout you are modifying/starting. If
1158you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2165you suspect event processing to be delayed and you \fIneed\fR to base the
1159on the current time, use something like this to adjust for this: 2166timeout on the current time, use something like this to adjust for this:
1160.PP 2167.PP
1161.Vb 1 2168.Vb 1
1162\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2169\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1163.Ve 2170.Ve
1164.PP 2171.PP
1165The callback is guarenteed to be invoked only when its timeout has passed, 2172If the event loop is suspended for a long time, you can also force an
1166but if multiple timers become ready during the same loop iteration then 2173update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1167order of execution is undefined. 2174()\*(C'\fR.
2175.PP
2176\fIThe special problem of unsynchronised clocks\fR
2177.IX Subsection "The special problem of unsynchronised clocks"
2178.PP
2179Modern systems have a variety of clocks \- libev itself uses the normal
2180\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2181jumps).
2182.PP
2183Neither of these clocks is synchronised with each other or any other clock
2184on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2185than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2186a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2187than a directly following call to \f(CW\*(C`time\*(C'\fR.
2188.PP
2189The moral of this is to only compare libev-related timestamps with
2190\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2191a second or so.
2192.PP
2193One more problem arises due to this lack of synchronisation: if libev uses
2194the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2195or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2196invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2197.PP
2198This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2199libev makes sure your callback is not invoked before the delay happened,
2200\&\fImeasured according to the real time\fR, not the system clock.
2201.PP
2202If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2203connection after 100 seconds\*(R") then this shouldn't bother you as it is
2204exactly the right behaviour.
2205.PP
2206If you want to compare wall clock/system timestamps to your timers, then
2207you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2208time, where your comparisons will always generate correct results.
2209.PP
2210\fIThe special problems of suspended animation\fR
2211.IX Subsection "The special problems of suspended animation"
2212.PP
2213When you leave the server world it is quite customary to hit machines that
2214can suspend/hibernate \- what happens to the clocks during such a suspend?
2215.PP
2216Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2217all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2218to run until the system is suspended, but they will not advance while the
2219system is suspended. That means, on resume, it will be as if the program
2220was frozen for a few seconds, but the suspend time will not be counted
2221towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2222clock advanced as expected, but if it is used as sole clocksource, then a
2223long suspend would be detected as a time jump by libev, and timers would
2224be adjusted accordingly.
2225.PP
2226I would not be surprised to see different behaviour in different between
2227operating systems, \s-1OS\s0 versions or even different hardware.
2228.PP
2229The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2230time jump in the monotonic clocks and the realtime clock. If the program
2231is suspended for a very long time, and monotonic clock sources are in use,
2232then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2233will be counted towards the timers. When no monotonic clock source is in
2234use, then libev will again assume a timejump and adjust accordingly.
2235.PP
2236It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2237and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2238deterministic behaviour in this case (you can do nothing against
2239\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1168.PP 2240.PP
1169\fIWatcher-Specific Functions and Data Members\fR 2241\fIWatcher-Specific Functions and Data Members\fR
1170.IX Subsection "Watcher-Specific Functions and Data Members" 2242.IX Subsection "Watcher-Specific Functions and Data Members"
1171.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2243.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1172.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2244.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1173.PD 0 2245.PD 0
1174.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2246.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1175.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2247.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1176.PD 2248.PD
1177Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2249Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1178\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2250is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1179timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2251reached. If it is positive, then the timer will automatically be
1180later, again, and again, until stopped manually. 2252configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2253until stopped manually.
1181.Sp 2254.Sp
1182The timer itself will do a best-effort at avoiding drift, that is, if you 2255The timer itself will do a best-effort at avoiding drift, that is, if
1183configure a timer to trigger every 10 seconds, then it will trigger at 2256you configure a timer to trigger every 10 seconds, then it will normally
1184exactly 10 second intervals. If, however, your program cannot keep up with 2257trigger at exactly 10 second intervals. If, however, your program cannot
1185the timer (because it takes longer than those 10 seconds to do stuff) the 2258keep up with the timer (because it takes longer than those 10 seconds to
1186timer will not fire more than once per event loop iteration. 2259do stuff) the timer will not fire more than once per event loop iteration.
1187.IP "ev_timer_again (loop)" 4 2260.IP "ev_timer_again (loop, ev_timer *)" 4
1188.IX Item "ev_timer_again (loop)" 2261.IX Item "ev_timer_again (loop, ev_timer *)"
1189This will act as if the timer timed out and restart it again if it is 2262This will act as if the timer timed out, and restarts it again if it is
1190repeating. The exact semantics are: 2263repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2264timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1191.Sp 2265.Sp
2266The exact semantics are as in the following rules, all of which will be
2267applied to the watcher:
2268.RS 4
1192If the timer is pending, its pending status is cleared. 2269.IP "If the timer is pending, the pending status is always cleared." 4
1193.Sp 2270.IX Item "If the timer is pending, the pending status is always cleared."
2271.PD 0
1194If the timer is started but nonrepeating, stop it (as if it timed out). 2272.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2273.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2274.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2275.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2276.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2277.RE
2278.RS 4
2279.PD
1195.Sp 2280.Sp
1196If the timer is repeating, either start it if necessary (with the 2281This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1197\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. 2282usage example.
2283.RE
2284.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2285.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2286Returns the remaining time until a timer fires. If the timer is active,
2287then this time is relative to the current event loop time, otherwise it's
2288the timeout value currently configured.
1198.Sp 2289.Sp
1199This sounds a bit complicated, but here is a useful and typical 2290That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1200example: Imagine you have a tcp connection and you want a so-called idle 2291\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1201timeout, that is, you want to be called when there have been, say, 60 2292will return \f(CW4\fR. When the timer expires and is restarted, it will return
1202seconds of inactivity on the socket. The easiest way to do this is to 2293roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1203configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call 2294too), and so on.
1204\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1205you go into an idle state where you do not expect data to travel on the
1206socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1207automatically restart it if need be.
1208.Sp
1209That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1210altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1211.Sp
1212.Vb 8
1213\& ev_timer_init (timer, callback, 0., 5.);
1214\& ev_timer_again (loop, timer);
1215\& ...
1216\& timer->again = 17.;
1217\& ev_timer_again (loop, timer);
1218\& ...
1219\& timer->again = 10.;
1220\& ev_timer_again (loop, timer);
1221.Ve
1222.Sp
1223This is more slightly efficient then stopping/starting the timer each time
1224you want to modify its timeout value.
1225.IP "ev_tstamp repeat [read\-write]" 4 2295.IP "ev_tstamp repeat [read\-write]" 4
1226.IX Item "ev_tstamp repeat [read-write]" 2296.IX Item "ev_tstamp repeat [read-write]"
1227The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2297The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1228or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2298or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1229which is also when any modifications are taken into account. 2299which is also when any modifications are taken into account.
1230.PP 2300.PP
2301\fIExamples\fR
2302.IX Subsection "Examples"
2303.PP
1231Example: Create a timer that fires after 60 seconds. 2304Example: Create a timer that fires after 60 seconds.
1232.PP 2305.PP
1233.Vb 5 2306.Vb 5
1234\& static void 2307\& static void
1235\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2308\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1236\& { 2309\& {
1237\& .. one minute over, w is actually stopped right here 2310\& .. one minute over, w is actually stopped right here
1238\& } 2311\& }
1239.Ve 2312\&
1240.PP
1241.Vb 3
1242\& struct ev_timer mytimer; 2313\& ev_timer mytimer;
1243\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2314\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1244\& ev_timer_start (loop, &mytimer); 2315\& ev_timer_start (loop, &mytimer);
1245.Ve 2316.Ve
1246.PP 2317.PP
1247Example: Create a timeout timer that times out after 10 seconds of 2318Example: Create a timeout timer that times out after 10 seconds of
1248inactivity. 2319inactivity.
1249.PP 2320.PP
1250.Vb 5 2321.Vb 5
1251\& static void 2322\& static void
1252\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2323\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1253\& { 2324\& {
1254\& .. ten seconds without any activity 2325\& .. ten seconds without any activity
1255\& } 2326\& }
1256.Ve 2327\&
1257.PP
1258.Vb 4
1259\& struct ev_timer mytimer; 2328\& ev_timer mytimer;
1260\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2329\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1261\& ev_timer_again (&mytimer); /* start timer */ 2330\& ev_timer_again (&mytimer); /* start timer */
1262\& ev_loop (loop, 0); 2331\& ev_run (loop, 0);
1263.Ve 2332\&
1264.PP
1265.Vb 3
1266\& // and in some piece of code that gets executed on any "activity": 2333\& // and in some piece of code that gets executed on any "activity":
1267\& // reset the timeout to start ticking again at 10 seconds 2334\& // reset the timeout to start ticking again at 10 seconds
1268\& ev_timer_again (&mytimer); 2335\& ev_timer_again (&mytimer);
1269.Ve 2336.Ve
1270.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2337.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1271.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2338.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1272.IX Subsection "ev_periodic - to cron or not to cron?" 2339.IX Subsection "ev_periodic - to cron or not to cron?"
1273Periodic watchers are also timers of a kind, but they are very versatile 2340Periodic watchers are also timers of a kind, but they are very versatile
1274(and unfortunately a bit complex). 2341(and unfortunately a bit complex).
1275.PP 2342.PP
1276Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2343Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1277but on wallclock time (absolute time). You can tell a periodic watcher 2344relative time, the physical time that passes) but on wall clock time
1278to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2345(absolute time, the thing you can read on your calender or clock). The
1279periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2346difference is that wall clock time can run faster or slower than real
1280+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2347time, and time jumps are not uncommon (e.g. when you adjust your
1281take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2348wrist-watch).
1282roughly 10 seconds later).
1283.PP 2349.PP
1284They can also be used to implement vastly more complex timers, such as 2350You can tell a periodic watcher to trigger after some specific point
1285triggering an event on each midnight, local time or other, complicated, 2351in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1286rules. 2352seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2353not a delay) and then reset your system clock to January of the previous
2354year, then it will take a year or more to trigger the event (unlike an
2355\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2356it, as it uses a relative timeout).
1287.PP 2357.PP
2358\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2359timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2360other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2361those cannot react to time jumps.
2362.PP
1288As with timers, the callback is guarenteed to be invoked only when the 2363As with timers, the callback is guaranteed to be invoked only when the
1289time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2364point in time where it is supposed to trigger has passed. If multiple
1290during the same loop iteration then order of execution is undefined. 2365timers become ready during the same loop iteration then the ones with
2366earlier time-out values are invoked before ones with later time-out values
2367(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1291.PP 2368.PP
1292\fIWatcher-Specific Functions and Data Members\fR 2369\fIWatcher-Specific Functions and Data Members\fR
1293.IX Subsection "Watcher-Specific Functions and Data Members" 2370.IX Subsection "Watcher-Specific Functions and Data Members"
1294.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2371.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1295.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2372.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1296.PD 0 2373.PD 0
1297.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2374.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1298.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2375.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1299.PD 2376.PD
1300Lots of arguments, lets sort it out... There are basically three modes of 2377Lots of arguments, let's sort it out... There are basically three modes of
1301operation, and we will explain them from simplest to complex: 2378operation, and we will explain them from simplest to most complex:
1302.RS 4 2379.RS 4
2380.IP "\(bu" 4
1303.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 2381absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1304.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" 2382.Sp
1305In this configuration the watcher triggers an event at the wallclock time 2383In this configuration the watcher triggers an event after the wall clock
1306\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2384time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1307that is, if it is to be run at January 1st 2011 then it will run when the 2385time jump occurs, that is, if it is to be run at January 1st 2011 then it
1308system time reaches or surpasses this time. 2386will be stopped and invoked when the system clock reaches or surpasses
1309.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4 2387this point in time.
1310.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 2388.IP "\(bu" 4
2389repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2390.Sp
1311In this mode the watcher will always be scheduled to time out at the next 2391In this mode the watcher will always be scheduled to time out at the next
1312\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) 2392\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1313and then repeat, regardless of any time jumps. 2393negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2394argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1314.Sp 2395.Sp
1315This can be used to create timers that do not drift with respect to system 2396This can be used to create timers that do not drift with respect to the
1316time: 2397system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2398hour, on the hour (with respect to \s-1UTC\s0):
1317.Sp 2399.Sp
1318.Vb 1 2400.Vb 1
1319\& ev_periodic_set (&periodic, 0., 3600., 0); 2401\& ev_periodic_set (&periodic, 0., 3600., 0);
1320.Ve 2402.Ve
1321.Sp 2403.Sp
1322This doesn't mean there will always be 3600 seconds in between triggers, 2404This doesn't mean there will always be 3600 seconds in between triggers,
1323but only that the the callback will be called when the system time shows a 2405but only that the callback will be called when the system time shows a
1324full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2406full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1325by 3600. 2407by 3600.
1326.Sp 2408.Sp
1327Another way to think about it (for the mathematically inclined) is that 2409Another way to think about it (for the mathematically inclined) is that
1328\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2410\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1329time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2411time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1330.Sp 2412.Sp
1331For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near 2413The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
1332\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for 2414interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
1333this value. 2415microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2416at most a similar magnitude as the current time (say, within a factor of
2417ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2418\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2419.Sp
2420Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2421speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2422will of course deteriorate. Libev itself tries to be exact to be about one
2423millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2424.IP "\(bu" 4
1334.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 2425manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1335.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 2426.Sp
1336In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2427In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1337ignored. Instead, each time the periodic watcher gets scheduled, the 2428ignored. Instead, each time the periodic watcher gets scheduled, the
1338reschedule callback will be called with the watcher as first, and the 2429reschedule callback will be called with the watcher as first, and the
1339current time as second argument. 2430current time as second argument.
1340.Sp 2431.Sp
1341\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2432\&\s-1NOTE: \s0\fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1342ever, or make any event loop modifications\fR. If you need to stop it, 2433or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1343return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2434allowed by documentation here\fR.
2435.Sp
2436If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1344starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). 2437it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2438only event loop modification you are allowed to do).
1345.Sp 2439.Sp
1346Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2440The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1347ev_tstamp now)\*(C'\fR, e.g.: 2441*w, ev_tstamp now)\*(C'\fR, e.g.:
1348.Sp 2442.Sp
1349.Vb 4 2443.Vb 5
2444\& static ev_tstamp
1350\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2445\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1351\& { 2446\& {
1352\& return now + 60.; 2447\& return now + 60.;
1353\& } 2448\& }
1354.Ve 2449.Ve
1355.Sp 2450.Sp
1356It must return the next time to trigger, based on the passed time value 2451It must return the next time to trigger, based on the passed time value
1357(that is, the lowest time value larger than to the second argument). It 2452(that is, the lowest time value larger than to the second argument). It
1358will usually be called just before the callback will be triggered, but 2453will usually be called just before the callback will be triggered, but
1359might be called at other times, too. 2454might be called at other times, too.
1360.Sp 2455.Sp
1361\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2456\&\s-1NOTE: \s0\fIThis callback must always return a time that is higher than or
1362passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2457equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1363.Sp 2458.Sp
1364This can be used to create very complex timers, such as a timer that 2459This can be used to create very complex timers, such as a timer that
1365triggers on each midnight, local time. To do this, you would calculate the 2460triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1366next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2461next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1367you do this is, again, up to you (but it is not trivial, which is the main 2462you do this is, again, up to you (but it is not trivial, which is the main
1368reason I omitted it as an example). 2463reason I omitted it as an example).
1369.RE 2464.RE
1370.RS 4 2465.RS 4
… …
1373.IX Item "ev_periodic_again (loop, ev_periodic *)" 2468.IX Item "ev_periodic_again (loop, ev_periodic *)"
1374Simply stops and restarts the periodic watcher again. This is only useful 2469Simply stops and restarts the periodic watcher again. This is only useful
1375when you changed some parameters or the reschedule callback would return 2470when you changed some parameters or the reschedule callback would return
1376a different time than the last time it was called (e.g. in a crond like 2471a different time than the last time it was called (e.g. in a crond like
1377program when the crontabs have changed). 2472program when the crontabs have changed).
2473.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2474.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2475When active, returns the absolute time that the watcher is supposed
2476to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2477\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2478rescheduling modes.
1378.IP "ev_tstamp offset [read\-write]" 4 2479.IP "ev_tstamp offset [read\-write]" 4
1379.IX Item "ev_tstamp offset [read-write]" 2480.IX Item "ev_tstamp offset [read-write]"
1380When repeating, this contains the offset value, otherwise this is the 2481When repeating, this contains the offset value, otherwise this is the
1381absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). 2482absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2483although libev might modify this value for better numerical stability).
1382.Sp 2484.Sp
1383Can be modified any time, but changes only take effect when the periodic 2485Can be modified any time, but changes only take effect when the periodic
1384timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2486timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1385.IP "ev_tstamp interval [read\-write]" 4 2487.IP "ev_tstamp interval [read\-write]" 4
1386.IX Item "ev_tstamp interval [read-write]" 2488.IX Item "ev_tstamp interval [read-write]"
1387The current interval value. Can be modified any time, but changes only 2489The current interval value. Can be modified any time, but changes only
1388take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2490take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1389called. 2491called.
1390.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2492.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1391.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2493.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1392The current reschedule callback, or \f(CW0\fR, if this functionality is 2494The current reschedule callback, or \f(CW0\fR, if this functionality is
1393switched off. Can be changed any time, but changes only take effect when 2495switched off. Can be changed any time, but changes only take effect when
1394the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2496the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1395.IP "ev_tstamp at [read\-only]" 4 2497.PP
1396.IX Item "ev_tstamp at [read-only]" 2498\fIExamples\fR
1397When active, contains the absolute time that the watcher is supposed to 2499.IX Subsection "Examples"
1398trigger next.
1399.PP 2500.PP
1400Example: Call a callback every hour, or, more precisely, whenever the 2501Example: Call a callback every hour, or, more precisely, whenever the
1401system clock is divisible by 3600. The callback invocation times have 2502system time is divisible by 3600. The callback invocation times have
1402potentially a lot of jittering, but good long-term stability. 2503potentially a lot of jitter, but good long-term stability.
1403.PP 2504.PP
1404.Vb 5 2505.Vb 5
1405\& static void 2506\& static void
1406\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2507\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1407\& { 2508\& {
1408\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2509\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1409\& } 2510\& }
1410.Ve 2511\&
1411.PP
1412.Vb 3
1413\& struct ev_periodic hourly_tick; 2512\& ev_periodic hourly_tick;
1414\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2513\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1415\& ev_periodic_start (loop, &hourly_tick); 2514\& ev_periodic_start (loop, &hourly_tick);
1416.Ve 2515.Ve
1417.PP 2516.PP
1418Example: The same as above, but use a reschedule callback to do it: 2517Example: The same as above, but use a reschedule callback to do it:
1419.PP 2518.PP
1420.Vb 1 2519.Vb 1
1421\& #include <math.h> 2520\& #include <math.h>
1422.Ve 2521\&
1423.PP
1424.Vb 5
1425\& static ev_tstamp 2522\& static ev_tstamp
1426\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2523\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1427\& { 2524\& {
1428\& return fmod (now, 3600.) + 3600.; 2525\& return now + (3600. \- fmod (now, 3600.));
1429\& } 2526\& }
1430.Ve 2527\&
1431.PP
1432.Vb 1
1433\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2528\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1434.Ve 2529.Ve
1435.PP 2530.PP
1436Example: Call a callback every hour, starting now: 2531Example: Call a callback every hour, starting now:
1437.PP 2532.PP
1438.Vb 4 2533.Vb 4
1439\& struct ev_periodic hourly_tick; 2534\& ev_periodic hourly_tick;
1440\& ev_periodic_init (&hourly_tick, clock_cb, 2535\& ev_periodic_init (&hourly_tick, clock_cb,
1441\& fmod (ev_now (loop), 3600.), 3600., 0); 2536\& fmod (ev_now (loop), 3600.), 3600., 0);
1442\& ev_periodic_start (loop, &hourly_tick); 2537\& ev_periodic_start (loop, &hourly_tick);
1443.Ve 2538.Ve
1444.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2539.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1445.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2540.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1446.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2541.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1447Signal watchers will trigger an event when the process receives a specific 2542Signal watchers will trigger an event when the process receives a specific
1448signal one or more times. Even though signals are very asynchronous, libev 2543signal one or more times. Even though signals are very asynchronous, libev
1449will try it's best to deliver signals synchronously, i.e. as part of the 2544will try its best to deliver signals synchronously, i.e. as part of the
1450normal event processing, like any other event. 2545normal event processing, like any other event.
1451.PP 2546.PP
2547If you want signals to be delivered truly asynchronously, just use
2548\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2549the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2550synchronously wake up an event loop.
2551.PP
1452You can configure as many watchers as you like per signal. Only when the 2552You can configure as many watchers as you like for the same signal, but
1453first watcher gets started will libev actually register a signal watcher 2553only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1454with the kernel (thus it coexists with your own signal handlers as long 2554default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1455as you don't register any with libev). Similarly, when the last signal 2555\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1456watcher for a signal is stopped libev will reset the signal handler to 2556the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1457\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2557.PP
2558Only after the first watcher for a signal is started will libev actually
2559register something with the kernel. It thus coexists with your own signal
2560handlers as long as you don't register any with libev for the same signal.
2561.PP
2562If possible and supported, libev will install its handlers with
2563\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2564not be unduly interrupted. If you have a problem with system calls getting
2565interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2566and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2567.PP
2568\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2569.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2570.PP
2571Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2572(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2573stopping it again), that is, libev might or might not block the signal,
2574and might or might not set or restore the installed signal handler (but
2575see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2576.PP
2577While this does not matter for the signal disposition (libev never
2578sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2579\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2580certain signals to be blocked.
2581.PP
2582This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2583the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2584choice usually).
2585.PP
2586The simplest way to ensure that the signal mask is reset in the child is
2587to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2588catch fork calls done by libraries (such as the libc) as well.
2589.PP
2590In current versions of libev, the signal will not be blocked indefinitely
2591unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API \s0(\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2592the window of opportunity for problems, it will not go away, as libev
2593\&\fIhas\fR to modify the signal mask, at least temporarily.
2594.PP
2595So I can't stress this enough: \fIIf you do not reset your signal mask when
2596you expect it to be empty, you have a race condition in your code\fR. This
2597is not a libev-specific thing, this is true for most event libraries.
2598.PP
2599\fIThe special problem of threads signal handling\fR
2600.IX Subsection "The special problem of threads signal handling"
2601.PP
2602\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2603a lot of functionality (sigfd, sigwait etc.) only really works if all
2604threads in a process block signals, which is hard to achieve.
2605.PP
2606When you want to use sigwait (or mix libev signal handling with your own
2607for the same signals), you can tackle this problem by globally blocking
2608all signals before creating any threads (or creating them with a fully set
2609sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2610loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2611these signals. You can pass on any signals that libev might be interested
2612in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
1458.PP 2613.PP
1459\fIWatcher-Specific Functions and Data Members\fR 2614\fIWatcher-Specific Functions and Data Members\fR
1460.IX Subsection "Watcher-Specific Functions and Data Members" 2615.IX Subsection "Watcher-Specific Functions and Data Members"
1461.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2616.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1462.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2617.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
… …
1467Configures the watcher to trigger on the given signal number (usually one 2622Configures the watcher to trigger on the given signal number (usually one
1468of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2623of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1469.IP "int signum [read\-only]" 4 2624.IP "int signum [read\-only]" 4
1470.IX Item "int signum [read-only]" 2625.IX Item "int signum [read-only]"
1471The signal the watcher watches out for. 2626The signal the watcher watches out for.
2627.PP
2628\fIExamples\fR
2629.IX Subsection "Examples"
2630.PP
2631Example: Try to exit cleanly on \s-1SIGINT.\s0
2632.PP
2633.Vb 5
2634\& static void
2635\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2636\& {
2637\& ev_break (loop, EVBREAK_ALL);
2638\& }
2639\&
2640\& ev_signal signal_watcher;
2641\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2642\& ev_signal_start (loop, &signal_watcher);
2643.Ve
1472.ie n .Sh """ev_child"" \- watch out for process status changes" 2644.ie n .SS """ev_child"" \- watch out for process status changes"
1473.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2645.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1474.IX Subsection "ev_child - watch out for process status changes" 2646.IX Subsection "ev_child - watch out for process status changes"
1475Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2647Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1476some child status changes (most typically when a child of yours dies). 2648some child status changes (most typically when a child of yours dies or
2649exits). It is permissible to install a child watcher \fIafter\fR the child
2650has been forked (which implies it might have already exited), as long
2651as the event loop isn't entered (or is continued from a watcher), i.e.,
2652forking and then immediately registering a watcher for the child is fine,
2653but forking and registering a watcher a few event loop iterations later or
2654in the next callback invocation is not.
2655.PP
2656Only the default event loop is capable of handling signals, and therefore
2657you can only register child watchers in the default event loop.
2658.PP
2659Due to some design glitches inside libev, child watchers will always be
2660handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2661libev)
2662.PP
2663\fIProcess Interaction\fR
2664.IX Subsection "Process Interaction"
2665.PP
2666Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2667initialised. This is necessary to guarantee proper behaviour even if the
2668first child watcher is started after the child exits. The occurrence
2669of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2670synchronously as part of the event loop processing. Libev always reaps all
2671children, even ones not watched.
2672.PP
2673\fIOverriding the Built-In Processing\fR
2674.IX Subsection "Overriding the Built-In Processing"
2675.PP
2676Libev offers no special support for overriding the built-in child
2677processing, but if your application collides with libev's default child
2678handler, you can override it easily by installing your own handler for
2679\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2680default loop never gets destroyed. You are encouraged, however, to use an
2681event-based approach to child reaping and thus use libev's support for
2682that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2683.PP
2684\fIStopping the Child Watcher\fR
2685.IX Subsection "Stopping the Child Watcher"
2686.PP
2687Currently, the child watcher never gets stopped, even when the
2688child terminates, so normally one needs to stop the watcher in the
2689callback. Future versions of libev might stop the watcher automatically
2690when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2691problem).
1477.PP 2692.PP
1478\fIWatcher-Specific Functions and Data Members\fR 2693\fIWatcher-Specific Functions and Data Members\fR
1479.IX Subsection "Watcher-Specific Functions and Data Members" 2694.IX Subsection "Watcher-Specific Functions and Data Members"
1480.IP "ev_child_init (ev_child *, callback, int pid)" 4 2695.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1481.IX Item "ev_child_init (ev_child *, callback, int pid)" 2696.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1482.PD 0 2697.PD 0
1483.IP "ev_child_set (ev_child *, int pid)" 4 2698.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1484.IX Item "ev_child_set (ev_child *, int pid)" 2699.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1485.PD 2700.PD
1486Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2701Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1487\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2702\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1488at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2703at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1489the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2704the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1490\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2705\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1491process causing the status change. 2706process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2707activate the watcher when the process terminates) or \f(CW1\fR (additionally
2708activate the watcher when the process is stopped or continued).
1492.IP "int pid [read\-only]" 4 2709.IP "int pid [read\-only]" 4
1493.IX Item "int pid [read-only]" 2710.IX Item "int pid [read-only]"
1494The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2711The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1495.IP "int rpid [read\-write]" 4 2712.IP "int rpid [read\-write]" 4
1496.IX Item "int rpid [read-write]" 2713.IX Item "int rpid [read-write]"
… …
1498.IP "int rstatus [read\-write]" 4 2715.IP "int rstatus [read\-write]" 4
1499.IX Item "int rstatus [read-write]" 2716.IX Item "int rstatus [read-write]"
1500The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2717The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1501\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2718\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1502.PP 2719.PP
1503Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2720\fIExamples\fR
2721.IX Subsection "Examples"
1504.PP 2722.PP
2723Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2724its completion.
2725.PP
1505.Vb 5 2726.Vb 1
2727\& ev_child cw;
2728\&
1506\& static void 2729\& static void
1507\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2730\& child_cb (EV_P_ ev_child *w, int revents)
1508\& { 2731\& {
1509\& ev_unloop (loop, EVUNLOOP_ALL); 2732\& ev_child_stop (EV_A_ w);
2733\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1510\& } 2734\& }
2735\&
2736\& pid_t pid = fork ();
2737\&
2738\& if (pid < 0)
2739\& // error
2740\& else if (pid == 0)
2741\& {
2742\& // the forked child executes here
2743\& exit (1);
2744\& }
2745\& else
2746\& {
2747\& ev_child_init (&cw, child_cb, pid, 0);
2748\& ev_child_start (EV_DEFAULT_ &cw);
2749\& }
1511.Ve 2750.Ve
1512.PP
1513.Vb 3
1514\& struct ev_signal signal_watcher;
1515\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1516\& ev_signal_start (loop, &sigint_cb);
1517.Ve
1518.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2751.ie n .SS """ev_stat"" \- did the file attributes just change?"
1519.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2752.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1520.IX Subsection "ev_stat - did the file attributes just change?" 2753.IX Subsection "ev_stat - did the file attributes just change?"
1521This watches a filesystem path for attribute changes. That is, it calls 2754This watches a file system path for attribute changes. That is, it calls
1522\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2755\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1523compared to the last time, invoking the callback if it did. 2756and sees if it changed compared to the last time, invoking the callback
2757if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2758happen after the watcher has been started will be reported.
1524.PP 2759.PP
1525The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2760The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1526not exist\*(R" is a status change like any other. The condition \*(L"path does 2761not exist\*(R" is a status change like any other. The condition \*(L"path does not
1527not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2762exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1528otherwise always forced to be at least one) and all the other fields of 2763\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1529the stat buffer having unspecified contents. 2764least one) and all the other fields of the stat buffer having unspecified
2765contents.
1530.PP 2766.PP
1531The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2767The path \fImust not\fR end in a slash or contain special components such as
2768\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1532relative and your working directory changes, the behaviour is undefined. 2769your working directory changes, then the behaviour is undefined.
1533.PP 2770.PP
1534Since there is no standard to do this, the portable implementation simply 2771Since there is no portable change notification interface available, the
1535calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You 2772portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1536can specify a recommended polling interval for this case. If you specify 2773to see if it changed somehow. You can specify a recommended polling
1537a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2774interval for this case. If you specify a polling interval of \f(CW0\fR (highly
1538unspecified default\fR value will be used (which you can expect to be around 2775recommended!) then a \fIsuitable, unspecified default\fR value will be used
1539five seconds, although this might change dynamically). Libev will also 2776(which you can expect to be around five seconds, although this might
1540impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2777change dynamically). Libev will also impose a minimum interval which is
1541usually overkill. 2778currently around \f(CW0.1\fR, but that's usually overkill.
1542.PP 2779.PP
1543This watcher type is not meant for massive numbers of stat watchers, 2780This watcher type is not meant for massive numbers of stat watchers,
1544as even with OS-supported change notifications, this can be 2781as even with OS-supported change notifications, this can be
1545resource\-intensive. 2782resource-intensive.
1546.PP 2783.PP
1547At the time of this writing, only the Linux inotify interface is 2784At the time of this writing, the only OS-specific interface implemented
1548implemented (implementing kqueue support is left as an exercise for the 2785is the Linux inotify interface (implementing kqueue support is left as an
1549reader). Inotify will be used to give hints only and should not change the 2786exercise for the reader. Note, however, that the author sees no way of
1550semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 2787implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
1551to fall back to regular polling again even with inotify, but changes are 2788.PP
1552usually detected immediately, and if the file exists there will be no 2789\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1553polling. 2790.IX Subsection "ABI Issues (Largefile Support)"
2791.PP
2792Libev by default (unless the user overrides this) uses the default
2793compilation environment, which means that on systems with large file
2794support disabled by default, you get the 32 bit version of the stat
2795structure. When using the library from programs that change the \s-1ABI\s0 to
2796use 64 bit file offsets the programs will fail. In that case you have to
2797compile libev with the same flags to get binary compatibility. This is
2798obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2799most noticeably displayed with ev_stat and large file support.
2800.PP
2801The solution for this is to lobby your distribution maker to make large
2802file interfaces available by default (as e.g. FreeBSD does) and not
2803optional. Libev cannot simply switch on large file support because it has
2804to exchange stat structures with application programs compiled using the
2805default compilation environment.
2806.PP
2807\fIInotify and Kqueue\fR
2808.IX Subsection "Inotify and Kqueue"
2809.PP
2810When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2811runtime, it will be used to speed up change detection where possible. The
2812inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2813watcher is being started.
2814.PP
2815Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2816except that changes might be detected earlier, and in some cases, to avoid
2817making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2818there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2819but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2820many bugs), the path exists (i.e. stat succeeds), and the path resides on
2821a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2822xfs are fully working) libev usually gets away without polling.
2823.PP
2824There is no support for kqueue, as apparently it cannot be used to
2825implement this functionality, due to the requirement of having a file
2826descriptor open on the object at all times, and detecting renames, unlinks
2827etc. is difficult.
2828.PP
2829\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2830.IX Subsection "stat () is a synchronous operation"
2831.PP
2832Libev doesn't normally do any kind of I/O itself, and so is not blocking
2833the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2834()\*(C'\fR, which is a synchronous operation.
2835.PP
2836For local paths, this usually doesn't matter: unless the system is very
2837busy or the intervals between stat's are large, a stat call will be fast,
2838as the path data is usually in memory already (except when starting the
2839watcher).
2840.PP
2841For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2842time due to network issues, and even under good conditions, a stat call
2843often takes multiple milliseconds.
2844.PP
2845Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2846paths, although this is fully supported by libev.
2847.PP
2848\fIThe special problem of stat time resolution\fR
2849.IX Subsection "The special problem of stat time resolution"
2850.PP
2851The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2852and even on systems where the resolution is higher, most file systems
2853still only support whole seconds.
2854.PP
2855That means that, if the time is the only thing that changes, you can
2856easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2857calls your callback, which does something. When there is another update
2858within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2859stat data does change in other ways (e.g. file size).
2860.PP
2861The solution to this is to delay acting on a change for slightly more
2862than a second (or till slightly after the next full second boundary), using
2863a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2864ev_timer_again (loop, w)\*(C'\fR).
2865.PP
2866The \f(CW.02\fR offset is added to work around small timing inconsistencies
2867of some operating systems (where the second counter of the current time
2868might be be delayed. One such system is the Linux kernel, where a call to
2869\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2870a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2871update file times then there will be a small window where the kernel uses
2872the previous second to update file times but libev might already execute
2873the timer callback).
1554.PP 2874.PP
1555\fIWatcher-Specific Functions and Data Members\fR 2875\fIWatcher-Specific Functions and Data Members\fR
1556.IX Subsection "Watcher-Specific Functions and Data Members" 2876.IX Subsection "Watcher-Specific Functions and Data Members"
1557.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2877.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1558.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2878.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
… …
1564\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2884\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1565be detected and should normally be specified as \f(CW0\fR to let libev choose 2885be detected and should normally be specified as \f(CW0\fR to let libev choose
1566a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2886a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1567path for as long as the watcher is active. 2887path for as long as the watcher is active.
1568.Sp 2888.Sp
1569The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2889The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1570relative to the attributes at the time the watcher was started (or the 2890relative to the attributes at the time the watcher was started (or the
1571last change was detected). 2891last change was detected).
1572.IP "ev_stat_stat (ev_stat *)" 4 2892.IP "ev_stat_stat (loop, ev_stat *)" 4
1573.IX Item "ev_stat_stat (ev_stat *)" 2893.IX Item "ev_stat_stat (loop, ev_stat *)"
1574Updates the stat buffer immediately with new values. If you change the 2894Updates the stat buffer immediately with new values. If you change the
1575watched path in your callback, you could call this fucntion to avoid 2895watched path in your callback, you could call this function to avoid
1576detecting this change (while introducing a race condition). Can also be 2896detecting this change (while introducing a race condition if you are not
1577useful simply to find out the new values. 2897the only one changing the path). Can also be useful simply to find out the
2898new values.
1578.IP "ev_statdata attr [read\-only]" 4 2899.IP "ev_statdata attr [read\-only]" 4
1579.IX Item "ev_statdata attr [read-only]" 2900.IX Item "ev_statdata attr [read-only]"
1580The most-recently detected attributes of the file. Although the type is of 2901The most-recently detected attributes of the file. Although the type is
1581\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 2902\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2903suitable for your system, but you can only rely on the POSIX-standardised
1582suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 2904members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1583was some error while \f(CW\*(C`stat\*(C'\fRing the file. 2905some error while \f(CW\*(C`stat\*(C'\fRing the file.
1584.IP "ev_statdata prev [read\-only]" 4 2906.IP "ev_statdata prev [read\-only]" 4
1585.IX Item "ev_statdata prev [read-only]" 2907.IX Item "ev_statdata prev [read-only]"
1586The previous attributes of the file. The callback gets invoked whenever 2908The previous attributes of the file. The callback gets invoked whenever
1587\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 2909\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2910differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
2911\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
1588.IP "ev_tstamp interval [read\-only]" 4 2912.IP "ev_tstamp interval [read\-only]" 4
1589.IX Item "ev_tstamp interval [read-only]" 2913.IX Item "ev_tstamp interval [read-only]"
1590The specified interval. 2914The specified interval.
1591.IP "const char *path [read\-only]" 4 2915.IP "const char *path [read\-only]" 4
1592.IX Item "const char *path [read-only]" 2916.IX Item "const char *path [read-only]"
1593The filesystem path that is being watched. 2917The file system path that is being watched.
2918.PP
2919\fIExamples\fR
2920.IX Subsection "Examples"
1594.PP 2921.PP
1595Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 2922Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1596.PP 2923.PP
1597.Vb 15 2924.Vb 10
1598\& static void 2925\& static void
1599\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 2926\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1600\& { 2927\& {
1601\& /* /etc/passwd changed in some way */ 2928\& /* /etc/passwd changed in some way */
1602\& if (w->attr.st_nlink) 2929\& if (w\->attr.st_nlink)
1603\& { 2930\& {
1604\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 2931\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1605\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 2932\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1606\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 2933\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1607\& } 2934\& }
1608\& else 2935\& else
1609\& /* you shalt not abuse printf for puts */ 2936\& /* you shalt not abuse printf for puts */
1610\& puts ("wow, /etc/passwd is not there, expect problems. " 2937\& puts ("wow, /etc/passwd is not there, expect problems. "
1611\& "if this is windows, they already arrived\en"); 2938\& "if this is windows, they already arrived\en");
1612\& } 2939\& }
2940\&
2941\& ...
2942\& ev_stat passwd;
2943\&
2944\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2945\& ev_stat_start (loop, &passwd);
1613.Ve 2946.Ve
2947.PP
2948Example: Like above, but additionally use a one-second delay so we do not
2949miss updates (however, frequent updates will delay processing, too, so
2950one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2951\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1614.PP 2952.PP
1615.Vb 2 2953.Vb 2
2954\& static ev_stat passwd;
2955\& static ev_timer timer;
2956\&
2957\& static void
2958\& timer_cb (EV_P_ ev_timer *w, int revents)
2959\& {
2960\& ev_timer_stop (EV_A_ w);
2961\&
2962\& /* now it\*(Aqs one second after the most recent passwd change */
2963\& }
2964\&
2965\& static void
2966\& stat_cb (EV_P_ ev_stat *w, int revents)
2967\& {
2968\& /* reset the one\-second timer */
2969\& ev_timer_again (EV_A_ &timer);
2970\& }
2971\&
1616\& ... 2972\& ...
1617\& ev_stat passwd;
1618.Ve
1619.PP
1620.Vb 2
1621\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 2973\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1622\& ev_stat_start (loop, &passwd); 2974\& ev_stat_start (loop, &passwd);
2975\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1623.Ve 2976.Ve
1624.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 2977.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1625.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 2978.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1626.IX Subsection "ev_idle - when you've got nothing better to do..." 2979.IX Subsection "ev_idle - when you've got nothing better to do..."
1627Idle watchers trigger events when no other events of the same or higher 2980Idle watchers trigger events when no other events of the same or higher
1628priority are pending (prepare, check and other idle watchers do not 2981priority are pending (prepare, check and other idle watchers do not count
1629count). 2982as receiving \*(L"events\*(R").
1630.PP 2983.PP
1631That is, as long as your process is busy handling sockets or timeouts 2984That is, as long as your process is busy handling sockets or timeouts
1632(or even signals, imagine) of the same or higher priority it will not be 2985(or even signals, imagine) of the same or higher priority it will not be
1633triggered. But when your process is idle (or only lower-priority watchers 2986triggered. But when your process is idle (or only lower-priority watchers
1634are pending), the idle watchers are being called once per event loop 2987are pending), the idle watchers are being called once per event loop
… …
1638The most noteworthy effect is that as long as any idle watchers are 2991The most noteworthy effect is that as long as any idle watchers are
1639active, the process will not block when waiting for new events. 2992active, the process will not block when waiting for new events.
1640.PP 2993.PP
1641Apart from keeping your process non-blocking (which is a useful 2994Apart from keeping your process non-blocking (which is a useful
1642effect on its own sometimes), idle watchers are a good place to do 2995effect on its own sometimes), idle watchers are a good place to do
1643\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2996\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1644event loop has handled all outstanding events. 2997event loop has handled all outstanding events.
2998.PP
2999\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3000.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3001.PP
3002As long as there is at least one active idle watcher, libev will never
3003sleep unnecessarily. Or in other words, it will loop as fast as possible.
3004For this to work, the idle watcher doesn't need to be invoked at all \- the
3005lowest priority will do.
3006.PP
3007This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3008to do something on each event loop iteration \- for example to balance load
3009between different connections.
3010.PP
3011See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3012example.
1645.PP 3013.PP
1646\fIWatcher-Specific Functions and Data Members\fR 3014\fIWatcher-Specific Functions and Data Members\fR
1647.IX Subsection "Watcher-Specific Functions and Data Members" 3015.IX Subsection "Watcher-Specific Functions and Data Members"
1648.IP "ev_idle_init (ev_signal *, callback)" 4 3016.IP "ev_idle_init (ev_idle *, callback)" 4
1649.IX Item "ev_idle_init (ev_signal *, callback)" 3017.IX Item "ev_idle_init (ev_idle *, callback)"
1650Initialises and configures the idle watcher \- it has no parameters of any 3018Initialises and configures the idle watcher \- it has no parameters of any
1651kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3019kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1652believe me. 3020believe me.
1653.PP 3021.PP
3022\fIExamples\fR
3023.IX Subsection "Examples"
3024.PP
1654Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 3025Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1655callback, free it. Also, use no error checking, as usual. 3026callback, free it. Also, use no error checking, as usual.
1656.PP 3027.PP
1657.Vb 7 3028.Vb 5
1658\& static void 3029\& static void
1659\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3030\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1660\& { 3031\& {
3032\& // stop the watcher
3033\& ev_idle_stop (loop, w);
3034\&
3035\& // now we can free it
1661\& free (w); 3036\& free (w);
3037\&
1662\& // now do something you wanted to do when the program has 3038\& // now do something you wanted to do when the program has
1663\& // no longer asnything immediate to do. 3039\& // no longer anything immediate to do.
1664\& } 3040\& }
1665.Ve 3041\&
1666.PP
1667.Vb 3
1668\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3042\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1669\& ev_idle_init (idle_watcher, idle_cb); 3043\& ev_idle_init (idle_watcher, idle_cb);
1670\& ev_idle_start (loop, idle_cb); 3044\& ev_idle_start (loop, idle_watcher);
1671.Ve 3045.Ve
1672.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3046.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1673.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3047.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1674.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3048.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1675Prepare and check watchers are usually (but not always) used in tandem: 3049Prepare and check watchers are often (but not always) used in pairs:
1676prepare watchers get invoked before the process blocks and check watchers 3050prepare watchers get invoked before the process blocks and check watchers
1677afterwards. 3051afterwards.
1678.PP 3052.PP
1679You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3053You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
1680the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3054the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1681watchers. Other loops than the current one are fine, however. The 3055watchers. Other loops than the current one are fine, however. The
1682rationale behind this is that you do not need to check for recursion in 3056rationale behind this is that you do not need to check for recursion in
1683those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3057those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1684\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3058\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1685called in pairs bracketing the blocking call. 3059called in pairs bracketing the blocking call.
1686.PP 3060.PP
1687Their main purpose is to integrate other event mechanisms into libev and 3061Their main purpose is to integrate other event mechanisms into libev and
1688their use is somewhat advanced. This could be used, for example, to track 3062their use is somewhat advanced. They could be used, for example, to track
1689variable changes, implement your own watchers, integrate net-snmp or a 3063variable changes, implement your own watchers, integrate net-snmp or a
1690coroutine library and lots more. They are also occasionally useful if 3064coroutine library and lots more. They are also occasionally useful if
1691you cache some data and want to flush it before blocking (for example, 3065you cache some data and want to flush it before blocking (for example,
1692in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3066in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1693watcher). 3067watcher).
1694.PP 3068.PP
1695This is done by examining in each prepare call which file descriptors need 3069This is done by examining in each prepare call which file descriptors
1696to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3070need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1697them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3071for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1698provide just this functionality). Then, in the check watcher you check for 3072libraries provide exactly this functionality). Then, in the check watcher,
1699any events that occured (by checking the pending status of all watchers 3073you check for any events that occurred (by checking the pending status
1700and stopping them) and call back into the library. The I/O and timer 3074of all watchers and stopping them) and call back into the library. The
1701callbacks will never actually be called (but must be valid nevertheless, 3075I/O and timer callbacks will never actually be called (but must be valid
1702because you never know, you know?). 3076nevertheless, because you never know, you know?).
1703.PP 3077.PP
1704As another example, the Perl Coro module uses these hooks to integrate 3078As another example, the Perl Coro module uses these hooks to integrate
1705coroutines into libev programs, by yielding to other active coroutines 3079coroutines into libev programs, by yielding to other active coroutines
1706during each prepare and only letting the process block if no coroutines 3080during each prepare and only letting the process block if no coroutines
1707are ready to run (it's actually more complicated: it only runs coroutines 3081are ready to run (it's actually more complicated: it only runs coroutines
1708with priority higher than or equal to the event loop and one coroutine 3082with priority higher than or equal to the event loop and one coroutine
1709of lower priority, but only once, using idle watchers to keep the event 3083of lower priority, but only once, using idle watchers to keep the event
1710loop from blocking if lower-priority coroutines are active, thus mapping 3084loop from blocking if lower-priority coroutines are active, thus mapping
1711low-priority coroutines to idle/background tasks). 3085low-priority coroutines to idle/background tasks).
1712.PP 3086.PP
1713It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 3087When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
1714priority, to ensure that they are being run before any other watchers 3088highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3089any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3090watchers).
3091.PP
1715after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 3092Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
1716too) should not activate (\*(L"feed\*(R") events into libev. While libev fully 3093activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
1717supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers did 3094might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
1718their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event 3095\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
1719loops those other event loops might be in an unusable state until their 3096loops those other event loops might be in an unusable state until their
1720\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with 3097\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1721others). 3098others).
3099.PP
3100\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3101.IX Subsection "Abusing an ev_check watcher for its side-effect"
3102.PP
3103\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3104useful because they are called once per event loop iteration. For
3105example, if you want to handle a large number of connections fairly, you
3106normally only do a bit of work for each active connection, and if there
3107is more work to do, you wait for the next event loop iteration, so other
3108connections have a chance of making progress.
3109.PP
3110Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3111next event loop iteration. However, that isn't as soon as possible \-
3112without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3113.PP
3114This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3115single global idle watcher that is active as long as you have one active
3116\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3117will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3118invoked. Neither watcher alone can do that.
1722.PP 3119.PP
1723\fIWatcher-Specific Functions and Data Members\fR 3120\fIWatcher-Specific Functions and Data Members\fR
1724.IX Subsection "Watcher-Specific Functions and Data Members" 3121.IX Subsection "Watcher-Specific Functions and Data Members"
1725.IP "ev_prepare_init (ev_prepare *, callback)" 4 3122.IP "ev_prepare_init (ev_prepare *, callback)" 4
1726.IX Item "ev_prepare_init (ev_prepare *, callback)" 3123.IX Item "ev_prepare_init (ev_prepare *, callback)"
… …
1728.IP "ev_check_init (ev_check *, callback)" 4 3125.IP "ev_check_init (ev_check *, callback)" 4
1729.IX Item "ev_check_init (ev_check *, callback)" 3126.IX Item "ev_check_init (ev_check *, callback)"
1730.PD 3127.PD
1731Initialises and configures the prepare or check watcher \- they have no 3128Initialises and configures the prepare or check watcher \- they have no
1732parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3129parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1733macros, but using them is utterly, utterly and completely pointless. 3130macros, but using them is utterly, utterly, utterly and completely
3131pointless.
3132.PP
3133\fIExamples\fR
3134.IX Subsection "Examples"
1734.PP 3135.PP
1735There are a number of principal ways to embed other event loops or modules 3136There are a number of principal ways to embed other event loops or modules
1736into libev. Here are some ideas on how to include libadns into libev 3137into libev. Here are some ideas on how to include libadns into libev
1737(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could 3138(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1738use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR 3139use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
1739embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 3140Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
1740into the Glib event loop). 3141Glib event loop).
1741.PP 3142.PP
1742Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, 3143Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1743and in a check watcher, destroy them and call into libadns. What follows 3144and in a check watcher, destroy them and call into libadns. What follows
1744is pseudo-code only of course. This requires you to either use a low 3145is pseudo-code only of course. This requires you to either use a low
1745priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as 3146priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1746the callbacks for the IO/timeout watchers might not have been called yet. 3147the callbacks for the IO/timeout watchers might not have been called yet.
1747.PP 3148.PP
1748.Vb 2 3149.Vb 2
1749\& static ev_io iow [nfd]; 3150\& static ev_io iow [nfd];
1750\& static ev_timer tw; 3151\& static ev_timer tw;
1751.Ve 3152\&
1752.PP
1753.Vb 4
1754\& static void 3153\& static void
1755\& io_cb (ev_loop *loop, ev_io *w, int revents) 3154\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1756\& { 3155\& {
1757\& } 3156\& }
1758.Ve 3157\&
1759.PP
1760.Vb 8
1761\& // create io watchers for each fd and a timer before blocking 3158\& // create io watchers for each fd and a timer before blocking
1762\& static void 3159\& static void
1763\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3160\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1764\& { 3161\& {
1765\& int timeout = 3600000; 3162\& int timeout = 3600000;
1766\& struct pollfd fds [nfd]; 3163\& struct pollfd fds [nfd];
1767\& // actual code will need to loop here and realloc etc. 3164\& // actual code will need to loop here and realloc etc.
1768\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3165\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1769.Ve 3166\&
1770.PP
1771.Vb 3
1772\& /* the callback is illegal, but won't be called as we stop during check */ 3167\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1773\& ev_timer_init (&tw, 0, timeout * 1e-3); 3168\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1774\& ev_timer_start (loop, &tw); 3169\& ev_timer_start (loop, &tw);
1775.Ve 3170\&
1776.PP
1777.Vb 6
1778\& // create one ev_io per pollfd 3171\& // create one ev_io per pollfd
1779\& for (int i = 0; i < nfd; ++i) 3172\& for (int i = 0; i < nfd; ++i)
1780\& { 3173\& {
1781\& ev_io_init (iow + i, io_cb, fds [i].fd, 3174\& ev_io_init (iow + i, io_cb, fds [i].fd,
1782\& ((fds [i].events & POLLIN ? EV_READ : 0) 3175\& ((fds [i].events & POLLIN ? EV_READ : 0)
1783\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3176\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1784.Ve 3177\&
1785.PP
1786.Vb 4
1787\& fds [i].revents = 0; 3178\& fds [i].revents = 0;
1788\& ev_io_start (loop, iow + i); 3179\& ev_io_start (loop, iow + i);
1789\& } 3180\& }
1790\& } 3181\& }
1791.Ve 3182\&
1792.PP
1793.Vb 5
1794\& // stop all watchers after blocking 3183\& // stop all watchers after blocking
1795\& static void 3184\& static void
1796\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3185\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1797\& { 3186\& {
1798\& ev_timer_stop (loop, &tw); 3187\& ev_timer_stop (loop, &tw);
1799.Ve 3188\&
1800.PP
1801.Vb 8
1802\& for (int i = 0; i < nfd; ++i) 3189\& for (int i = 0; i < nfd; ++i)
1803\& { 3190\& {
1804\& // set the relevant poll flags 3191\& // set the relevant poll flags
1805\& // could also call adns_processreadable etc. here 3192\& // could also call adns_processreadable etc. here
1806\& struct pollfd *fd = fds + i; 3193\& struct pollfd *fd = fds + i;
1807\& int revents = ev_clear_pending (iow + i); 3194\& int revents = ev_clear_pending (iow + i);
1808\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; 3195\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1809\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; 3196\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1810.Ve 3197\&
1811.PP
1812.Vb 3
1813\& // now stop the watcher 3198\& // now stop the watcher
1814\& ev_io_stop (loop, iow + i); 3199\& ev_io_stop (loop, iow + i);
1815\& } 3200\& }
1816.Ve 3201\&
1817.PP
1818.Vb 2
1819\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 3202\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1820\& } 3203\& }
1821.Ve 3204.Ve
1822.PP 3205.PP
1823Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR 3206Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
1824in the prepare watcher and would dispose of the check watcher. 3207in the prepare watcher and would dispose of the check watcher.
1825.PP 3208.PP
1826Method 3: If the module to be embedded supports explicit event 3209Method 3: If the module to be embedded supports explicit event
1827notification (adns does), you can also make use of the actual watcher 3210notification (libadns does), you can also make use of the actual watcher
1828callbacks, and only destroy/create the watchers in the prepare watcher. 3211callbacks, and only destroy/create the watchers in the prepare watcher.
1829.PP 3212.PP
1830.Vb 5 3213.Vb 5
1831\& static void 3214\& static void
1832\& timer_cb (EV_P_ ev_timer *w, int revents) 3215\& timer_cb (EV_P_ ev_timer *w, int revents)
1833\& { 3216\& {
1834\& adns_state ads = (adns_state)w->data; 3217\& adns_state ads = (adns_state)w\->data;
1835\& update_now (EV_A); 3218\& update_now (EV_A);
1836.Ve 3219\&
1837.PP
1838.Vb 2
1839\& adns_processtimeouts (ads, &tv_now); 3220\& adns_processtimeouts (ads, &tv_now);
1840\& } 3221\& }
1841.Ve 3222\&
1842.PP
1843.Vb 5
1844\& static void 3223\& static void
1845\& io_cb (EV_P_ ev_io *w, int revents) 3224\& io_cb (EV_P_ ev_io *w, int revents)
1846\& { 3225\& {
1847\& adns_state ads = (adns_state)w->data; 3226\& adns_state ads = (adns_state)w\->data;
1848\& update_now (EV_A); 3227\& update_now (EV_A);
1849.Ve 3228\&
1850.PP
1851.Vb 3
1852\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); 3229\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
1853\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); 3230\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
1854\& } 3231\& }
1855.Ve 3232\&
1856.PP
1857.Vb 1
1858\& // do not ever call adns_afterpoll 3233\& // do not ever call adns_afterpoll
1859.Ve 3234.Ve
1860.PP 3235.PP
1861Method 4: Do not use a prepare or check watcher because the module you 3236Method 4: Do not use a prepare or check watcher because the module you
1862want to embed is too inflexible to support it. Instead, youc na override 3237want to embed is not flexible enough to support it. Instead, you can
1863their poll function. The drawback with this solution is that the main 3238override their poll function. The drawback with this solution is that the
1864loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does 3239main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
1865this. 3240this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3241libglib event loop.
1866.PP 3242.PP
1867.Vb 4 3243.Vb 4
1868\& static gint 3244\& static gint
1869\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) 3245\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1870\& { 3246\& {
1871\& int got_events = 0; 3247\& int got_events = 0;
1872.Ve 3248\&
1873.PP
1874.Vb 2
1875\& for (n = 0; n < nfds; ++n) 3249\& for (n = 0; n < nfds; ++n)
1876\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events 3250\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1877.Ve 3251\&
1878.PP
1879.Vb 2
1880\& if (timeout >= 0) 3252\& if (timeout >= 0)
1881\& // create/start timer 3253\& // create/start timer
1882.Ve 3254\&
1883.PP
1884.Vb 2
1885\& // poll 3255\& // poll
1886\& ev_loop (EV_A_ 0); 3256\& ev_run (EV_A_ 0);
1887.Ve 3257\&
1888.PP
1889.Vb 3
1890\& // stop timer again 3258\& // stop timer again
1891\& if (timeout >= 0) 3259\& if (timeout >= 0)
1892\& ev_timer_stop (EV_A_ &to); 3260\& ev_timer_stop (EV_A_ &to);
1893.Ve 3261\&
1894.PP
1895.Vb 3
1896\& // stop io watchers again - their callbacks should have set 3262\& // stop io watchers again \- their callbacks should have set
1897\& for (n = 0; n < nfds; ++n) 3263\& for (n = 0; n < nfds; ++n)
1898\& ev_io_stop (EV_A_ iow [n]); 3264\& ev_io_stop (EV_A_ iow [n]);
1899.Ve 3265\&
1900.PP
1901.Vb 2
1902\& return got_events; 3266\& return got_events;
1903\& } 3267\& }
1904.Ve 3268.Ve
1905.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3269.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1906.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3270.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1907.IX Subsection "ev_embed - when one backend isn't enough..." 3271.IX Subsection "ev_embed - when one backend isn't enough..."
1908This is a rather advanced watcher type that lets you embed one event loop 3272This is a rather advanced watcher type that lets you embed one event loop
1909into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3273into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1910loop, other types of watchers might be handled in a delayed or incorrect 3274loop, other types of watchers might be handled in a delayed or incorrect
1911fashion and must not be used). 3275fashion and must not be used).
… …
1914prioritise I/O. 3278prioritise I/O.
1915.PP 3279.PP
1916As an example for a bug workaround, the kqueue backend might only support 3280As an example for a bug workaround, the kqueue backend might only support
1917sockets on some platform, so it is unusable as generic backend, but you 3281sockets on some platform, so it is unusable as generic backend, but you
1918still want to make use of it because you have many sockets and it scales 3282still want to make use of it because you have many sockets and it scales
1919so nicely. In this case, you would create a kqueue-based loop and embed it 3283so nicely. In this case, you would create a kqueue-based loop and embed
1920into your default loop (which might use e.g. poll). Overall operation will 3284it into your default loop (which might use e.g. poll). Overall operation
1921be a bit slower because first libev has to poll and then call kevent, but 3285will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1922at least you can use both at what they are best. 3286\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3287best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1923.PP 3288.PP
1924As for prioritising I/O: rarely you have the case where some fds have 3289As for prioritising I/O: under rare circumstances you have the case where
1925to be watched and handled very quickly (with low latency), and even 3290some fds have to be watched and handled very quickly (with low latency),
1926priorities and idle watchers might have too much overhead. In this case 3291and even priorities and idle watchers might have too much overhead. In
1927you would put all the high priority stuff in one loop and all the rest in 3292this case you would put all the high priority stuff in one loop and all
1928a second one, and embed the second one in the first. 3293the rest in a second one, and embed the second one in the first.
1929.PP 3294.PP
1930As long as the watcher is active, the callback will be invoked every time 3295As long as the watcher is active, the callback will be invoked every
1931there might be events pending in the embedded loop. The callback must then 3296time there might be events pending in the embedded loop. The callback
1932call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3297must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1933their callbacks (you could also start an idle watcher to give the embedded 3298sweep and invoke their callbacks (the callback doesn't need to invoke the
1934loop strictly lower priority for example). You can also set the callback 3299\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1935to \f(CW0\fR, in which case the embed watcher will automatically execute the 3300to give the embedded loop strictly lower priority for example).
1936embedded loop sweep.
1937.PP 3301.PP
1938As long as the watcher is started it will automatically handle events. The 3302You can also set the callback to \f(CW0\fR, in which case the embed watcher
1939callback will be invoked whenever some events have been handled. You can 3303will automatically execute the embedded loop sweep whenever necessary.
1940set the callback to \f(CW0\fR to avoid having to specify one if you are not
1941interested in that.
1942.PP 3304.PP
1943Also, there have not currently been made special provisions for forking: 3305Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1944when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3306is active, i.e., the embedded loop will automatically be forked when the
1945but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3307embedding loop forks. In other cases, the user is responsible for calling
1946yourself. 3308\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1947.PP 3309.PP
1948Unfortunately, not all backends are embeddable, only the ones returned by 3310Unfortunately, not all backends are embeddable: only the ones returned by
1949\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3311\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1950portable one. 3312portable one.
1951.PP 3313.PP
1952So when you want to use this feature you will always have to be prepared 3314So when you want to use this feature you will always have to be prepared
1953that you cannot get an embeddable loop. The recommended way to get around 3315that you cannot get an embeddable loop. The recommended way to get around
1954this is to have a separate variables for your embeddable loop, try to 3316this is to have a separate variables for your embeddable loop, try to
1955create it, and if that fails, use the normal loop for everything: 3317create it, and if that fails, use the normal loop for everything.
1956.PP 3318.PP
1957.Vb 3 3319\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1958\& struct ev_loop *loop_hi = ev_default_init (0); 3320.IX Subsection "ev_embed and fork"
1959\& struct ev_loop *loop_lo = 0;
1960\& struct ev_embed embed;
1961.Ve
1962.PP 3321.PP
1963.Vb 5 3322While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1964\& // see if there is a chance of getting one that works 3323automatically be applied to the embedded loop as well, so no special
1965\& // (remember that a flags value of 0 means autodetection) 3324fork handling is required in that case. When the watcher is not running,
1966\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3325however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1967\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3326as applicable.
1968\& : 0;
1969.Ve
1970.PP
1971.Vb 8
1972\& // if we got one, then embed it, otherwise default to loop_hi
1973\& if (loop_lo)
1974\& {
1975\& ev_embed_init (&embed, 0, loop_lo);
1976\& ev_embed_start (loop_hi, &embed);
1977\& }
1978\& else
1979\& loop_lo = loop_hi;
1980.Ve
1981.PP 3327.PP
1982\fIWatcher-Specific Functions and Data Members\fR 3328\fIWatcher-Specific Functions and Data Members\fR
1983.IX Subsection "Watcher-Specific Functions and Data Members" 3329.IX Subsection "Watcher-Specific Functions and Data Members"
1984.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3330.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1985.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3331.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1986.PD 0 3332.PD 0
1987.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3333.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1988.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3334.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1989.PD 3335.PD
1990Configures the watcher to embed the given loop, which must be 3336Configures the watcher to embed the given loop, which must be
1991embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3337embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1992invoked automatically, otherwise it is the responsibility of the callback 3338invoked automatically, otherwise it is the responsibility of the callback
1993to invoke it (it will continue to be called until the sweep has been done, 3339to invoke it (it will continue to be called until the sweep has been done,
1994if you do not want thta, you need to temporarily stop the embed watcher). 3340if you do not want that, you need to temporarily stop the embed watcher).
1995.IP "ev_embed_sweep (loop, ev_embed *)" 4 3341.IP "ev_embed_sweep (loop, ev_embed *)" 4
1996.IX Item "ev_embed_sweep (loop, ev_embed *)" 3342.IX Item "ev_embed_sweep (loop, ev_embed *)"
1997Make a single, non-blocking sweep over the embedded loop. This works 3343Make a single, non-blocking sweep over the embedded loop. This works
1998similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3344similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1999apropriate way for embedded loops. 3345appropriate way for embedded loops.
2000.IP "struct ev_loop *loop [read\-only]" 4 3346.IP "struct ev_loop *other [read\-only]" 4
2001.IX Item "struct ev_loop *loop [read-only]" 3347.IX Item "struct ev_loop *other [read-only]"
2002The embedded event loop. 3348The embedded event loop.
3349.PP
3350\fIExamples\fR
3351.IX Subsection "Examples"
3352.PP
3353Example: Try to get an embeddable event loop and embed it into the default
3354event loop. If that is not possible, use the default loop. The default
3355loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3356\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3357used).
3358.PP
3359.Vb 3
3360\& struct ev_loop *loop_hi = ev_default_init (0);
3361\& struct ev_loop *loop_lo = 0;
3362\& ev_embed embed;
3363\&
3364\& // see if there is a chance of getting one that works
3365\& // (remember that a flags value of 0 means autodetection)
3366\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3367\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3368\& : 0;
3369\&
3370\& // if we got one, then embed it, otherwise default to loop_hi
3371\& if (loop_lo)
3372\& {
3373\& ev_embed_init (&embed, 0, loop_lo);
3374\& ev_embed_start (loop_hi, &embed);
3375\& }
3376\& else
3377\& loop_lo = loop_hi;
3378.Ve
3379.PP
3380Example: Check if kqueue is available but not recommended and create
3381a kqueue backend for use with sockets (which usually work with any
3382kqueue implementation). Store the kqueue/socket\-only event loop in
3383\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3384.PP
3385.Vb 3
3386\& struct ev_loop *loop = ev_default_init (0);
3387\& struct ev_loop *loop_socket = 0;
3388\& ev_embed embed;
3389\&
3390\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3391\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3392\& {
3393\& ev_embed_init (&embed, 0, loop_socket);
3394\& ev_embed_start (loop, &embed);
3395\& }
3396\&
3397\& if (!loop_socket)
3398\& loop_socket = loop;
3399\&
3400\& // now use loop_socket for all sockets, and loop for everything else
3401.Ve
2003.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3402.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
2004.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3403.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2005.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3404.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2006Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3405Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2007whoever is a good citizen cared to tell libev about it by calling 3406whoever is a good citizen cared to tell libev about it by calling
2008\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3407\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
2009event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3408and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
2010and only in the child after the fork. If whoever good citizen calling 3409after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
2011\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3410and calls it in the wrong process, the fork handlers will be invoked, too,
2012handlers will be invoked, too, of course. 3411of course.
3412.PP
3413\fIThe special problem of life after fork \- how is it possible?\fR
3414.IX Subsection "The special problem of life after fork - how is it possible?"
3415.PP
3416Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3417up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3418sequence should be handled by libev without any problems.
3419.PP
3420This changes when the application actually wants to do event handling
3421in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3422fork.
3423.PP
3424The default mode of operation (for libev, with application help to detect
3425forks) is to duplicate all the state in the child, as would be expected
3426when \fIeither\fR the parent \fIor\fR the child process continues.
3427.PP
3428When both processes want to continue using libev, then this is usually the
3429wrong result. In that case, usually one process (typically the parent) is
3430supposed to continue with all watchers in place as before, while the other
3431process typically wants to start fresh, i.e. without any active watchers.
3432.PP
3433The cleanest and most efficient way to achieve that with libev is to
3434simply create a new event loop, which of course will be \*(L"empty\*(R", and
3435use that for new watchers. This has the advantage of not touching more
3436memory than necessary, and thus avoiding the copy-on-write, and the
3437disadvantage of having to use multiple event loops (which do not support
3438signal watchers).
3439.PP
3440When this is not possible, or you want to use the default loop for
3441other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3442\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3443Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3444watchers, so you have to be careful not to execute code that modifies
3445those watchers. Note also that in that case, you have to re-register any
3446signal watchers.
2013.PP 3447.PP
2014\fIWatcher-Specific Functions and Data Members\fR 3448\fIWatcher-Specific Functions and Data Members\fR
2015.IX Subsection "Watcher-Specific Functions and Data Members" 3449.IX Subsection "Watcher-Specific Functions and Data Members"
2016.IP "ev_fork_init (ev_signal *, callback)" 4 3450.IP "ev_fork_init (ev_fork *, callback)" 4
2017.IX Item "ev_fork_init (ev_signal *, callback)" 3451.IX Item "ev_fork_init (ev_fork *, callback)"
2018Initialises and configures the fork watcher \- it has no parameters of any 3452Initialises and configures the fork watcher \- it has no parameters of any
2019kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3453kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2020believe me. 3454really.
3455.ie n .SS """ev_cleanup"" \- even the best things end"
3456.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3457.IX Subsection "ev_cleanup - even the best things end"
3458Cleanup watchers are called just before the event loop is being destroyed
3459by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3460.PP
3461While there is no guarantee that the event loop gets destroyed, cleanup
3462watchers provide a convenient method to install cleanup hooks for your
3463program, worker threads and so on \- you just to make sure to destroy the
3464loop when you want them to be invoked.
3465.PP
3466Cleanup watchers are invoked in the same way as any other watcher. Unlike
3467all other watchers, they do not keep a reference to the event loop (which
3468makes a lot of sense if you think about it). Like all other watchers, you
3469can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3470.PP
3471\fIWatcher-Specific Functions and Data Members\fR
3472.IX Subsection "Watcher-Specific Functions and Data Members"
3473.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3474.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3475Initialises and configures the cleanup watcher \- it has no parameters of
3476any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3477pointless, I assure you.
3478.PP
3479Example: Register an atexit handler to destroy the default loop, so any
3480cleanup functions are called.
3481.PP
3482.Vb 5
3483\& static void
3484\& program_exits (void)
3485\& {
3486\& ev_loop_destroy (EV_DEFAULT_UC);
3487\& }
3488\&
3489\& ...
3490\& atexit (program_exits);
3491.Ve
3492.ie n .SS """ev_async"" \- how to wake up an event loop"
3493.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3494.IX Subsection "ev_async - how to wake up an event loop"
3495In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3496asynchronous sources such as signal handlers (as opposed to multiple event
3497loops \- those are of course safe to use in different threads).
3498.PP
3499Sometimes, however, you need to wake up an event loop you do not control,
3500for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3501watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3502it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3503.PP
3504This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3505too, are asynchronous in nature, and signals, too, will be compressed
3506(i.e. the number of callback invocations may be less than the number of
3507\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3508of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3509signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3510even without knowing which loop owns the signal.
3511.PP
3512\fIQueueing\fR
3513.IX Subsection "Queueing"
3514.PP
3515\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3516is that the author does not know of a simple (or any) algorithm for a
3517multiple-writer-single-reader queue that works in all cases and doesn't
3518need elaborate support such as pthreads or unportable memory access
3519semantics.
3520.PP
3521That means that if you want to queue data, you have to provide your own
3522queue. But at least I can tell you how to implement locking around your
3523queue:
3524.IP "queueing from a signal handler context" 4
3525.IX Item "queueing from a signal handler context"
3526To implement race-free queueing, you simply add to the queue in the signal
3527handler but you block the signal handler in the watcher callback. Here is
3528an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3529.Sp
3530.Vb 1
3531\& static ev_async mysig;
3532\&
3533\& static void
3534\& sigusr1_handler (void)
3535\& {
3536\& sometype data;
3537\&
3538\& // no locking etc.
3539\& queue_put (data);
3540\& ev_async_send (EV_DEFAULT_ &mysig);
3541\& }
3542\&
3543\& static void
3544\& mysig_cb (EV_P_ ev_async *w, int revents)
3545\& {
3546\& sometype data;
3547\& sigset_t block, prev;
3548\&
3549\& sigemptyset (&block);
3550\& sigaddset (&block, SIGUSR1);
3551\& sigprocmask (SIG_BLOCK, &block, &prev);
3552\&
3553\& while (queue_get (&data))
3554\& process (data);
3555\&
3556\& if (sigismember (&prev, SIGUSR1)
3557\& sigprocmask (SIG_UNBLOCK, &block, 0);
3558\& }
3559.Ve
3560.Sp
3561(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3562instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3563either...).
3564.IP "queueing from a thread context" 4
3565.IX Item "queueing from a thread context"
3566The strategy for threads is different, as you cannot (easily) block
3567threads but you can easily preempt them, so to queue safely you need to
3568employ a traditional mutex lock, such as in this pthread example:
3569.Sp
3570.Vb 2
3571\& static ev_async mysig;
3572\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3573\&
3574\& static void
3575\& otherthread (void)
3576\& {
3577\& // only need to lock the actual queueing operation
3578\& pthread_mutex_lock (&mymutex);
3579\& queue_put (data);
3580\& pthread_mutex_unlock (&mymutex);
3581\&
3582\& ev_async_send (EV_DEFAULT_ &mysig);
3583\& }
3584\&
3585\& static void
3586\& mysig_cb (EV_P_ ev_async *w, int revents)
3587\& {
3588\& pthread_mutex_lock (&mymutex);
3589\&
3590\& while (queue_get (&data))
3591\& process (data);
3592\&
3593\& pthread_mutex_unlock (&mymutex);
3594\& }
3595.Ve
3596.PP
3597\fIWatcher-Specific Functions and Data Members\fR
3598.IX Subsection "Watcher-Specific Functions and Data Members"
3599.IP "ev_async_init (ev_async *, callback)" 4
3600.IX Item "ev_async_init (ev_async *, callback)"
3601Initialises and configures the async watcher \- it has no parameters of any
3602kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3603trust me.
3604.IP "ev_async_send (loop, ev_async *)" 4
3605.IX Item "ev_async_send (loop, ev_async *)"
3606Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3607an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3608returns.
3609.Sp
3610Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3611signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3612embedding section below on what exactly this means).
3613.Sp
3614Note that, as with other watchers in libev, multiple events might get
3615compressed into a single callback invocation (another way to look at
3616this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3617\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3618.Sp
3619This call incurs the overhead of at most one extra system call per event
3620loop iteration, if the event loop is blocked, and no syscall at all if
3621the event loop (or your program) is processing events. That means that
3622repeated calls are basically free (there is no need to avoid calls for
3623performance reasons) and that the overhead becomes smaller (typically
3624zero) under load.
3625.IP "bool = ev_async_pending (ev_async *)" 4
3626.IX Item "bool = ev_async_pending (ev_async *)"
3627Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3628watcher but the event has not yet been processed (or even noted) by the
3629event loop.
3630.Sp
3631\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3632the loop iterates next and checks for the watcher to have become active,
3633it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3634quickly check whether invoking the loop might be a good idea.
3635.Sp
3636Not that this does \fInot\fR check whether the watcher itself is pending,
3637only whether it has been requested to make this watcher pending: there
3638is a time window between the event loop checking and resetting the async
3639notification, and the callback being invoked.
2021.SH "OTHER FUNCTIONS" 3640.SH "OTHER FUNCTIONS"
2022.IX Header "OTHER FUNCTIONS" 3641.IX Header "OTHER FUNCTIONS"
2023There are some other functions of possible interest. Described. Here. Now. 3642There are some other functions of possible interest. Described. Here. Now.
2024.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3643.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2025.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3644.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2026This function combines a simple timer and an I/O watcher, calls your 3645This function combines a simple timer and an I/O watcher, calls your
2027callback on whichever event happens first and automatically stop both 3646callback on whichever event happens first and automatically stops both
2028watchers. This is useful if you want to wait for a single event on an fd 3647watchers. This is useful if you want to wait for a single event on an fd
2029or timeout without having to allocate/configure/start/stop/free one or 3648or timeout without having to allocate/configure/start/stop/free one or
2030more watchers yourself. 3649more watchers yourself.
2031.Sp 3650.Sp
2032If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3651If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
2033is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3652\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
2034\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3653the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
2035.Sp 3654.Sp
2036If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3655If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2037started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3656started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2038repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3657repeat = 0) will be started. \f(CW0\fR is a valid timeout.
2039dubious value.
2040.Sp 3658.Sp
2041The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3659The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
2042passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3660passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2043\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3661\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
2044value passed to \f(CW\*(C`ev_once\*(C'\fR: 3662value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3663a timeout and an io event at the same time \- you probably should give io
3664events precedence.
3665.Sp
3666Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
2045.Sp 3667.Sp
2046.Vb 7 3668.Vb 7
2047\& static void stdin_ready (int revents, void *arg) 3669\& static void stdin_ready (int revents, void *arg)
3670\& {
3671\& if (revents & EV_READ)
3672\& /* stdin might have data for us, joy! */;
3673\& else if (revents & EV_TIMER)
3674\& /* doh, nothing entered */;
3675\& }
3676\&
3677\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3678.Ve
3679.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3680.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3681Feed an event on the given fd, as if a file descriptor backend detected
3682the given events.
3683.IP "ev_feed_signal_event (loop, int signum)" 4
3684.IX Item "ev_feed_signal_event (loop, int signum)"
3685Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3686which is async-safe.
3687.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3688.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3689This section explains some common idioms that are not immediately
3690obvious. Note that examples are sprinkled over the whole manual, and this
3691section only contains stuff that wouldn't fit anywhere else.
3692.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3693.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3694Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3695or modify at any time: libev will completely ignore it. This can be used
3696to associate arbitrary data with your watcher. If you need more data and
3697don't want to allocate memory separately and store a pointer to it in that
3698data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3699data:
3700.PP
3701.Vb 7
3702\& struct my_io
3703\& {
3704\& ev_io io;
3705\& int otherfd;
3706\& void *somedata;
3707\& struct whatever *mostinteresting;
3708\& };
3709\&
3710\& ...
3711\& struct my_io w;
3712\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3713.Ve
3714.PP
3715And since your callback will be called with a pointer to the watcher, you
3716can cast it back to your own type:
3717.PP
3718.Vb 5
3719\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3720\& {
3721\& struct my_io *w = (struct my_io *)w_;
3722\& ...
3723\& }
3724.Ve
3725.PP
3726More interesting and less C\-conformant ways of casting your callback
3727function type instead have been omitted.
3728.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3729.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3730Another common scenario is to use some data structure with multiple
3731embedded watchers, in effect creating your own watcher that combines
3732multiple libev event sources into one \*(L"super-watcher\*(R":
3733.PP
3734.Vb 6
3735\& struct my_biggy
3736\& {
3737\& int some_data;
3738\& ev_timer t1;
3739\& ev_timer t2;
3740\& }
3741.Ve
3742.PP
3743In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3744complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3745the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3746to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3747real programmers):
3748.PP
3749.Vb 1
3750\& #include <stddef.h>
3751\&
3752\& static void
3753\& t1_cb (EV_P_ ev_timer *w, int revents)
3754\& {
3755\& struct my_biggy big = (struct my_biggy *)
3756\& (((char *)w) \- offsetof (struct my_biggy, t1));
3757\& }
3758\&
3759\& static void
3760\& t2_cb (EV_P_ ev_timer *w, int revents)
3761\& {
3762\& struct my_biggy big = (struct my_biggy *)
3763\& (((char *)w) \- offsetof (struct my_biggy, t2));
3764\& }
3765.Ve
3766.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3767.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3768Often you have structures like this in event-based programs:
3769.PP
3770.Vb 4
3771\& callback ()
2048\& { 3772\& {
2049\& if (revents & EV_TIMEOUT) 3773\& free (request);
2050\& /* doh, nothing entered */;
2051\& else if (revents & EV_READ)
2052\& /* stdin might have data for us, joy! */;
2053\& } 3774\& }
3775\&
3776\& request = start_new_request (..., callback);
2054.Ve 3777.Ve
2055.Sp 3778.PP
3779The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3780used to cancel the operation, or do other things with it.
3781.PP
3782It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3783immediately invoke the callback, for example, to report errors. Or you add
3784some caching layer that finds that it can skip the lengthy aspects of the
3785operation and simply invoke the callback with the result.
3786.PP
3787The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3788has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3789.PP
3790Even if you pass the request by some safer means to the callback, you
3791might want to do something to the request after starting it, such as
3792canceling it, which probably isn't working so well when the callback has
3793already been invoked.
3794.PP
3795A common way around all these issues is to make sure that
3796\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3797\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3798delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3799example, or more sneakily, by reusing an existing (stopped) watcher and
3800pushing it into the pending queue:
3801.PP
2056.Vb 1 3802.Vb 2
2057\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3803\& ev_set_cb (watcher, callback);
3804\& ev_feed_event (EV_A_ watcher, 0);
2058.Ve 3805.Ve
2059.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3806.PP
2060.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3807This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
2061Feeds the given event set into the event loop, as if the specified event 3808invoked, while not delaying callback invocation too much.
2062had happened for the specified watcher (which must be a pointer to an 3809.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
2063initialised but not necessarily started event watcher). 3810.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
2064.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3811Often (especially in \s-1GUI\s0 toolkits) there are places where you have
2065.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3812\&\fImodal\fR interaction, which is most easily implemented by recursively
2066Feed an event on the given fd, as if a file descriptor backend detected 3813invoking \f(CW\*(C`ev_run\*(C'\fR.
2067the given events it. 3814.PP
2068.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3815This brings the problem of exiting \- a callback might want to finish the
2069.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3816main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
2070Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3817a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
2071loop!). 3818and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3819other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3820.PP
3821The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3822invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3823triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3824.PP
3825.Vb 2
3826\& // main loop
3827\& int exit_main_loop = 0;
3828\&
3829\& while (!exit_main_loop)
3830\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3831\&
3832\& // in a modal watcher
3833\& int exit_nested_loop = 0;
3834\&
3835\& while (!exit_nested_loop)
3836\& ev_run (EV_A_ EVRUN_ONCE);
3837.Ve
3838.PP
3839To exit from any of these loops, just set the corresponding exit variable:
3840.PP
3841.Vb 2
3842\& // exit modal loop
3843\& exit_nested_loop = 1;
3844\&
3845\& // exit main program, after modal loop is finished
3846\& exit_main_loop = 1;
3847\&
3848\& // exit both
3849\& exit_main_loop = exit_nested_loop = 1;
3850.Ve
3851.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3852.IX Subsection "THREAD LOCKING EXAMPLE"
3853Here is a fictitious example of how to run an event loop in a different
3854thread from where callbacks are being invoked and watchers are
3855created/added/removed.
3856.PP
3857For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3858which uses exactly this technique (which is suited for many high-level
3859languages).
3860.PP
3861The example uses a pthread mutex to protect the loop data, a condition
3862variable to wait for callback invocations, an async watcher to notify the
3863event loop thread and an unspecified mechanism to wake up the main thread.
3864.PP
3865First, you need to associate some data with the event loop:
3866.PP
3867.Vb 6
3868\& typedef struct {
3869\& mutex_t lock; /* global loop lock */
3870\& ev_async async_w;
3871\& thread_t tid;
3872\& cond_t invoke_cv;
3873\& } userdata;
3874\&
3875\& void prepare_loop (EV_P)
3876\& {
3877\& // for simplicity, we use a static userdata struct.
3878\& static userdata u;
3879\&
3880\& ev_async_init (&u\->async_w, async_cb);
3881\& ev_async_start (EV_A_ &u\->async_w);
3882\&
3883\& pthread_mutex_init (&u\->lock, 0);
3884\& pthread_cond_init (&u\->invoke_cv, 0);
3885\&
3886\& // now associate this with the loop
3887\& ev_set_userdata (EV_A_ u);
3888\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3889\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3890\&
3891\& // then create the thread running ev_run
3892\& pthread_create (&u\->tid, 0, l_run, EV_A);
3893\& }
3894.Ve
3895.PP
3896The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3897solely to wake up the event loop so it takes notice of any new watchers
3898that might have been added:
3899.PP
3900.Vb 5
3901\& static void
3902\& async_cb (EV_P_ ev_async *w, int revents)
3903\& {
3904\& // just used for the side effects
3905\& }
3906.Ve
3907.PP
3908The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3909protecting the loop data, respectively.
3910.PP
3911.Vb 6
3912\& static void
3913\& l_release (EV_P)
3914\& {
3915\& userdata *u = ev_userdata (EV_A);
3916\& pthread_mutex_unlock (&u\->lock);
3917\& }
3918\&
3919\& static void
3920\& l_acquire (EV_P)
3921\& {
3922\& userdata *u = ev_userdata (EV_A);
3923\& pthread_mutex_lock (&u\->lock);
3924\& }
3925.Ve
3926.PP
3927The event loop thread first acquires the mutex, and then jumps straight
3928into \f(CW\*(C`ev_run\*(C'\fR:
3929.PP
3930.Vb 4
3931\& void *
3932\& l_run (void *thr_arg)
3933\& {
3934\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3935\&
3936\& l_acquire (EV_A);
3937\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3938\& ev_run (EV_A_ 0);
3939\& l_release (EV_A);
3940\&
3941\& return 0;
3942\& }
3943.Ve
3944.PP
3945Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3946signal the main thread via some unspecified mechanism (signals? pipe
3947writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3948have been called (in a while loop because a) spurious wakeups are possible
3949and b) skipping inter-thread-communication when there are no pending
3950watchers is very beneficial):
3951.PP
3952.Vb 4
3953\& static void
3954\& l_invoke (EV_P)
3955\& {
3956\& userdata *u = ev_userdata (EV_A);
3957\&
3958\& while (ev_pending_count (EV_A))
3959\& {
3960\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3961\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3962\& }
3963\& }
3964.Ve
3965.PP
3966Now, whenever the main thread gets told to invoke pending watchers, it
3967will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3968thread to continue:
3969.PP
3970.Vb 4
3971\& static void
3972\& real_invoke_pending (EV_P)
3973\& {
3974\& userdata *u = ev_userdata (EV_A);
3975\&
3976\& pthread_mutex_lock (&u\->lock);
3977\& ev_invoke_pending (EV_A);
3978\& pthread_cond_signal (&u\->invoke_cv);
3979\& pthread_mutex_unlock (&u\->lock);
3980\& }
3981.Ve
3982.PP
3983Whenever you want to start/stop a watcher or do other modifications to an
3984event loop, you will now have to lock:
3985.PP
3986.Vb 2
3987\& ev_timer timeout_watcher;
3988\& userdata *u = ev_userdata (EV_A);
3989\&
3990\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3991\&
3992\& pthread_mutex_lock (&u\->lock);
3993\& ev_timer_start (EV_A_ &timeout_watcher);
3994\& ev_async_send (EV_A_ &u\->async_w);
3995\& pthread_mutex_unlock (&u\->lock);
3996.Ve
3997.PP
3998Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3999an event loop currently blocking in the kernel will have no knowledge
4000about the newly added timer. By waking up the loop it will pick up any new
4001watchers in the next event loop iteration.
4002.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4003.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4004While the overhead of a callback that e.g. schedules a thread is small, it
4005is still an overhead. If you embed libev, and your main usage is with some
4006kind of threads or coroutines, you might want to customise libev so that
4007doesn't need callbacks anymore.
4008.PP
4009Imagine you have coroutines that you can switch to using a function
4010\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4011and that due to some magic, the currently active coroutine is stored in a
4012global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4013event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4014the differing \f(CW\*(C`;\*(C'\fR conventions):
4015.PP
4016.Vb 2
4017\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4018\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4019.Ve
4020.PP
4021That means instead of having a C callback function, you store the
4022coroutine to switch to in each watcher, and instead of having libev call
4023your callback, you instead have it switch to that coroutine.
4024.PP
4025A coroutine might now wait for an event with a function called
4026\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4027matter when, or whether the watcher is active or not when this function is
4028called):
4029.PP
4030.Vb 6
4031\& void
4032\& wait_for_event (ev_watcher *w)
4033\& {
4034\& ev_set_cb (w, current_coro);
4035\& switch_to (libev_coro);
4036\& }
4037.Ve
4038.PP
4039That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4040continues the libev coroutine, which, when appropriate, switches back to
4041this or any other coroutine.
4042.PP
4043You can do similar tricks if you have, say, threads with an event queue \-
4044instead of storing a coroutine, you store the queue object and instead of
4045switching to a coroutine, you push the watcher onto the queue and notify
4046any waiters.
4047.PP
4048To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4049files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4050.PP
4051.Vb 4
4052\& // my_ev.h
4053\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4054\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
4055\& #include "../libev/ev.h"
4056\&
4057\& // my_ev.c
4058\& #define EV_H "my_ev.h"
4059\& #include "../libev/ev.c"
4060.Ve
4061.PP
4062And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4063\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4064can even use \fIev.h\fR as header file name directly.
2072.SH "LIBEVENT EMULATION" 4065.SH "LIBEVENT EMULATION"
2073.IX Header "LIBEVENT EMULATION" 4066.IX Header "LIBEVENT EMULATION"
2074Libev offers a compatibility emulation layer for libevent. It cannot 4067Libev offers a compatibility emulation layer for libevent. It cannot
2075emulate the internals of libevent, so here are some usage hints: 4068emulate the internals of libevent, so here are some usage hints:
4069.IP "\(bu" 4
4070Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4071.Sp
4072This was the newest libevent version available when libev was implemented,
4073and is still mostly unchanged in 2010.
4074.IP "\(bu" 4
2076.IP "* Use it by including <event.h>, as usual." 4 4075Use it by including <event.h>, as usual.
2077.IX Item "Use it by including <event.h>, as usual." 4076.IP "\(bu" 4
2078.PD 0 4077The following members are fully supported: ev_base, ev_callback,
2079.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4078ev_arg, ev_fd, ev_res, ev_events.
2080.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4079.IP "\(bu" 4
2081.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 4080Avoid using ev_flags and the EVLIST_*\-macros, while it is
2082.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 4081maintained by libev, it does not work exactly the same way as in libevent (consider
2083.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 4082it a private \s-1API\s0).
2084.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4083.IP "\(bu" 4
4084Priorities are not currently supported. Initialising priorities
4085will fail and all watchers will have the same priority, even though there
4086is an ev_pri field.
4087.IP "\(bu" 4
4088In libevent, the last base created gets the signals, in libev, the
4089base that registered the signal gets the signals.
4090.IP "\(bu" 4
2085.IP "* Other members are not supported." 4 4091Other members are not supported.
2086.IX Item "Other members are not supported." 4092.IP "\(bu" 4
2087.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4093The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2088.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4094to use the libev header file and library.
2089.PD
2090.SH "\*(C+ SUPPORT" 4095.SH "\*(C+ SUPPORT"
2091.IX Header " SUPPORT" 4096.IX Header " SUPPORT"
4097.SS "C \s-1API\s0"
4098.IX Subsection "C API"
4099The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4100libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4101will work fine.
4102.PP
4103Proper exception specifications might have to be added to callbacks passed
4104to libev: exceptions may be thrown only from watcher callbacks, all
4105other callbacks (allocator, syserr, loop acquire/release and periodic
4106reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4107()\*(C'\fR specification. If you have code that needs to be compiled as both C
4108and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4109.PP
4110.Vb 6
4111\& static void
4112\& fatal_error (const char *msg) EV_THROW
4113\& {
4114\& perror (msg);
4115\& abort ();
4116\& }
4117\&
4118\& ...
4119\& ev_set_syserr_cb (fatal_error);
4120.Ve
4121.PP
4122The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4123\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4124because it runs cleanup watchers).
4125.PP
4126Throwing exceptions in watcher callbacks is only supported if libev itself
4127is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4128throwing exceptions through C libraries (most do).
4129.SS "\*(C+ \s-1API\s0"
4130.IX Subsection " API"
2092Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4131Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2093you to use some convinience methods to start/stop watchers and also change 4132you to use some convenience methods to start/stop watchers and also change
2094the callback model to a model using method callbacks on objects. 4133the callback model to a model using method callbacks on objects.
2095.PP 4134.PP
2096To use it, 4135To use it,
2097.PP 4136.PP
2098.Vb 1 4137.Vb 1
2099\& #include <ev++.h> 4138\& #include <ev++.h>
2100.Ve 4139.Ve
2101.PP 4140.PP
2102This automatically includes \fIev.h\fR and puts all of its definitions (many 4141This automatically includes \fIev.h\fR and puts all of its definitions (many
2103of them macros) into the global namespace. All \*(C+ specific things are 4142of them macros) into the global namespace. All \*(C+ specific things are
2104put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding 4143put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
… …
2107Care has been taken to keep the overhead low. The only data member the \*(C+ 4146Care has been taken to keep the overhead low. The only data member the \*(C+
2108classes add (compared to plain C\-style watchers) is the event loop pointer 4147classes add (compared to plain C\-style watchers) is the event loop pointer
2109that the watcher is associated with (or no additional members at all if 4148that the watcher is associated with (or no additional members at all if
2110you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). 4149you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2111.PP 4150.PP
2112Currently, functions, and static and non-static member functions can be 4151Currently, functions, static and non-static member functions and classes
2113used as callbacks. Other types should be easy to add as long as they only 4152with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
2114need one additional pointer for context. If you need support for other 4153to add as long as they only need one additional pointer for context. If
2115types of functors please contact the author (preferably after implementing 4154you need support for other types of functors please contact the author
2116it). 4155(preferably after implementing it).
4156.PP
4157For all this to work, your \*(C+ compiler either has to use the same calling
4158conventions as your C compiler (for static member functions), or you have
4159to embed libev and compile libev itself as \*(C+.
2117.PP 4160.PP
2118Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4161Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2119.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4162.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
2120.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4163.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2121.IX Item "ev::READ, ev::WRITE etc." 4164.IX Item "ev::READ, ev::WRITE etc."
2122These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4165These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2123macros from \fIev.h\fR. 4166macros from \fIev.h\fR.
2124.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4167.ie n .IP """ev::tstamp"", ""ev::now""" 4
2125.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4168.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2126.IX Item "ev::tstamp, ev::now" 4169.IX Item "ev::tstamp, ev::now"
2127Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4170Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2128.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 4171.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
2129.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4172.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2130.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4173.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2131For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4174For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2132the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4175the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2133which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4176which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2134defines by many implementations. 4177defined by many implementations.
2135.Sp 4178.Sp
2136All of those classes have these methods: 4179All of those classes have these methods:
2137.RS 4 4180.RS 4
2138.IP "ev::TYPE::TYPE ()" 4 4181.IP "ev::TYPE::TYPE ()" 4
2139.IX Item "ev::TYPE::TYPE ()" 4182.IX Item "ev::TYPE::TYPE ()"
2140.PD 0 4183.PD 0
2141.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 4184.IP "ev::TYPE::TYPE (loop)" 4
2142.IX Item "ev::TYPE::TYPE (struct ev_loop *)" 4185.IX Item "ev::TYPE::TYPE (loop)"
2143.IP "ev::TYPE::~TYPE" 4 4186.IP "ev::TYPE::~TYPE" 4
2144.IX Item "ev::TYPE::~TYPE" 4187.IX Item "ev::TYPE::~TYPE"
2145.PD 4188.PD
2146The constructor (optionally) takes an event loop to associate the watcher 4189The constructor (optionally) takes an event loop to associate the watcher
2147with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. 4190with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
… …
2170thunking function, making it as fast as a direct C callback. 4213thunking function, making it as fast as a direct C callback.
2171.Sp 4214.Sp
2172Example: simple class declaration and watcher initialisation 4215Example: simple class declaration and watcher initialisation
2173.Sp 4216.Sp
2174.Vb 4 4217.Vb 4
2175\& struct myclass 4218\& struct myclass
2176\& { 4219\& {
2177\& void io_cb (ev::io &w, int revents) { } 4220\& void io_cb (ev::io &w, int revents) { }
2178\& } 4221\& }
2179.Ve 4222\&
2180.Sp
2181.Vb 3
2182\& myclass obj; 4223\& myclass obj;
2183\& ev::io iow; 4224\& ev::io iow;
2184\& iow.set <myclass, &myclass::io_cb> (&obj); 4225\& iow.set <myclass, &myclass::io_cb> (&obj);
4226.Ve
4227.IP "w\->set (object *)" 4
4228.IX Item "w->set (object *)"
4229This is a variation of a method callback \- leaving out the method to call
4230will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4231functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4232the time. Incidentally, you can then also leave out the template argument
4233list.
4234.Sp
4235The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4236int revents)\*(C'\fR.
4237.Sp
4238See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4239.Sp
4240Example: use a functor object as callback.
4241.Sp
4242.Vb 7
4243\& struct myfunctor
4244\& {
4245\& void operator() (ev::io &w, int revents)
4246\& {
4247\& ...
4248\& }
4249\& }
4250\&
4251\& myfunctor f;
4252\&
4253\& ev::io w;
4254\& w.set (&f);
2185.Ve 4255.Ve
2186.IP "w\->set<function> (void *data = 0)" 4 4256.IP "w\->set<function> (void *data = 0)" 4
2187.IX Item "w->set<function> (void *data = 0)" 4257.IX Item "w->set<function> (void *data = 0)"
2188Also sets a callback, but uses a static method or plain function as 4258Also sets a callback, but uses a static method or plain function as
2189callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's 4259callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
… …
2191.Sp 4261.Sp
2192The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. 4262The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2193.Sp 4263.Sp
2194See the method\-\f(CW\*(C`set\*(C'\fR above for more details. 4264See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2195.Sp 4265.Sp
2196Example: 4266Example: Use a plain function as callback.
2197.Sp 4267.Sp
2198.Vb 2 4268.Vb 2
2199\& static void io_cb (ev::io &w, int revents) { } 4269\& static void io_cb (ev::io &w, int revents) { }
2200\& iow.set <io_cb> (); 4270\& iow.set <io_cb> ();
2201.Ve 4271.Ve
2202.IP "w\->set (struct ev_loop *)" 4 4272.IP "w\->set (loop)" 4
2203.IX Item "w->set (struct ev_loop *)" 4273.IX Item "w->set (loop)"
2204Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4274Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2205do this when the watcher is inactive (and not pending either). 4275do this when the watcher is inactive (and not pending either).
2206.IP "w\->set ([args])" 4 4276.IP "w\->set ([arguments])" 4
2207.IX Item "w->set ([args])" 4277.IX Item "w->set ([arguments])"
2208Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4278Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4279with the same arguments. Either this method or a suitable start method
2209called at least once. Unlike the C counterpart, an active watcher gets 4280must be called at least once. Unlike the C counterpart, an active watcher
2210automatically stopped and restarted when reconfiguring it with this 4281gets automatically stopped and restarted when reconfiguring it with this
2211method. 4282method.
4283.Sp
4284For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4285clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
2212.IP "w\->start ()" 4 4286.IP "w\->start ()" 4
2213.IX Item "w->start ()" 4287.IX Item "w->start ()"
2214Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the 4288Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2215constructor already stores the event loop. 4289constructor already stores the event loop.
4290.IP "w\->start ([arguments])" 4
4291.IX Item "w->start ([arguments])"
4292Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4293convenient to wrap them in one call. Uses the same type of arguments as
4294the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
2216.IP "w\->stop ()" 4 4295.IP "w\->stop ()" 4
2217.IX Item "w->stop ()" 4296.IX Item "w->stop ()"
2218Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4297Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2219.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4 4298.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
2220.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4 4299.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2221.IX Item "w->again () (ev::timer, ev::periodic only)" 4300.IX Item "w->again () (ev::timer, ev::periodic only)"
2222For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4301For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2223\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4302\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2224.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 4303.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
… …
2231Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4310Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2232.RE 4311.RE
2233.RS 4 4312.RS 4
2234.RE 4313.RE
2235.PP 4314.PP
2236Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4315Example: Define a class with two I/O and idle watchers, start the I/O
2237the constructor. 4316watchers in the constructor.
2238.PP 4317.PP
2239.Vb 4 4318.Vb 5
2240\& class myclass 4319\& class myclass
2241\& { 4320\& {
2242\& ev_io io; void io_cb (ev::io &w, int revents); 4321\& ev::io io ; void io_cb (ev::io &w, int revents);
4322\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
2243\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4323\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2244.Ve 4324\&
2245.PP
2246.Vb 2
2247\& myclass (); 4325\& myclass (int fd)
2248\& }
2249.Ve
2250.PP
2251.Vb 4
2252\& myclass::myclass (int fd)
2253\& { 4326\& {
2254\& io .set <myclass, &myclass::io_cb > (this); 4327\& io .set <myclass, &myclass::io_cb > (this);
4328\& io2 .set <myclass, &myclass::io2_cb > (this);
2255\& idle.set <myclass, &myclass::idle_cb> (this); 4329\& idle.set <myclass, &myclass::idle_cb> (this);
2256.Ve 4330\&
2257.PP 4331\& io.set (fd, ev::WRITE); // configure the watcher
2258.Vb 2 4332\& io.start (); // start it whenever convenient
2259\& io.start (fd, ev::READ); 4333\&
4334\& io2.start (fd, ev::READ); // set + start in one call
4335\& }
2260\& } 4336\& };
2261.Ve 4337.Ve
4338.SH "OTHER LANGUAGE BINDINGS"
4339.IX Header "OTHER LANGUAGE BINDINGS"
4340Libev does not offer other language bindings itself, but bindings for a
4341number of languages exist in the form of third-party packages. If you know
4342any interesting language binding in addition to the ones listed here, drop
4343me a note.
4344.IP "Perl" 4
4345.IX Item "Perl"
4346The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4347libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4348there are additional modules that implement libev-compatible interfaces
4349to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4350\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4351and \f(CW\*(C`EV::Glib\*(C'\fR).
4352.Sp
4353It can be found and installed via \s-1CPAN,\s0 its homepage is at
4354<http://software.schmorp.de/pkg/EV>.
4355.IP "Python" 4
4356.IX Item "Python"
4357Python bindings can be found at <http://code.google.com/p/pyev/>. It
4358seems to be quite complete and well-documented.
4359.IP "Ruby" 4
4360.IX Item "Ruby"
4361Tony Arcieri has written a ruby extension that offers access to a subset
4362of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4363more on top of it. It can be found via gem servers. Its homepage is at
4364<http://rev.rubyforge.org/>.
4365.Sp
4366Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4367makes rev work even on mingw.
4368.IP "Haskell" 4
4369.IX Item "Haskell"
4370A haskell binding to libev is available at
4371<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4372.IP "D" 4
4373.IX Item "D"
4374Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4375be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4376.IP "Ocaml" 4
4377.IX Item "Ocaml"
4378Erkki Seppala has written Ocaml bindings for libev, to be found at
4379<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4380.IP "Lua" 4
4381.IX Item "Lua"
4382Brian Maher has written a partial interface to libev for lua (at the
4383time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4384<http://github.com/brimworks/lua\-ev>.
4385.IP "Javascript" 4
4386.IX Item "Javascript"
4387Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4388.IP "Others" 4
4389.IX Item "Others"
4390There are others, and I stopped counting.
2262.SH "MACRO MAGIC" 4391.SH "MACRO MAGIC"
2263.IX Header "MACRO MAGIC" 4392.IX Header "MACRO MAGIC"
2264Libev can be compiled with a variety of options, the most fundamantal 4393Libev can be compiled with a variety of options, the most fundamental
2265of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) 4394of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2266functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4395functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2267.PP 4396.PP
2268To make it easier to write programs that cope with either variant, the 4397To make it easier to write programs that cope with either variant, the
2269following macros are defined: 4398following macros are defined:
2270.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4399.ie n .IP """EV_A"", ""EV_A_""" 4
2271.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4400.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2272.IX Item "EV_A, EV_A_" 4401.IX Item "EV_A, EV_A_"
2273This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4402This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2274loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4403loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2275\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4404\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2276.Sp 4405.Sp
2277.Vb 3 4406.Vb 3
2278\& ev_unref (EV_A); 4407\& ev_unref (EV_A);
2279\& ev_timer_add (EV_A_ watcher); 4408\& ev_timer_add (EV_A_ watcher);
2280\& ev_loop (EV_A_ 0); 4409\& ev_run (EV_A_ 0);
2281.Ve 4410.Ve
2282.Sp 4411.Sp
2283It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4412It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2284which is often provided by the following macro. 4413which is often provided by the following macro.
2285.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4414.ie n .IP """EV_P"", ""EV_P_""" 4
2286.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4415.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2287.IX Item "EV_P, EV_P_" 4416.IX Item "EV_P, EV_P_"
2288This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4417This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2289loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4418loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2290\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4419\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2291.Sp 4420.Sp
2292.Vb 2 4421.Vb 2
2293\& // this is how ev_unref is being declared 4422\& // this is how ev_unref is being declared
2294\& static void ev_unref (EV_P); 4423\& static void ev_unref (EV_P);
2295.Ve 4424\&
2296.Sp
2297.Vb 2
2298\& // this is how you can declare your typical callback 4425\& // this is how you can declare your typical callback
2299\& static void cb (EV_P_ ev_timer *w, int revents) 4426\& static void cb (EV_P_ ev_timer *w, int revents)
2300.Ve 4427.Ve
2301.Sp 4428.Sp
2302It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4429It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2303suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4430suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2304.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4431.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
2305.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4432.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2306.IX Item "EV_DEFAULT, EV_DEFAULT_" 4433.IX Item "EV_DEFAULT, EV_DEFAULT_"
2307Similar to the other two macros, this gives you the value of the default 4434Similar to the other two macros, this gives you the value of the default
2308loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4435loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4436will be initialised if it isn't already initialised.
4437.Sp
4438For non-multiplicity builds, these macros do nothing, so you always have
4439to initialise the loop somewhere.
4440.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4441.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4442.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4443Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4444default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4445is undefined when the default loop has not been initialised by a previous
4446execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4447.Sp
4448It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4449watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2309.PP 4450.PP
2310Example: Declare and initialise a check watcher, utilising the above 4451Example: Declare and initialise a check watcher, utilising the above
2311macros so it will work regardless of whether multiple loops are supported 4452macros so it will work regardless of whether multiple loops are supported
2312or not. 4453or not.
2313.PP 4454.PP
2314.Vb 5 4455.Vb 5
2315\& static void 4456\& static void
2316\& check_cb (EV_P_ ev_timer *w, int revents) 4457\& check_cb (EV_P_ ev_timer *w, int revents)
2317\& { 4458\& {
2318\& ev_check_stop (EV_A_ w); 4459\& ev_check_stop (EV_A_ w);
2319\& } 4460\& }
2320.Ve 4461\&
2321.PP
2322.Vb 4
2323\& ev_check check; 4462\& ev_check check;
2324\& ev_check_init (&check, check_cb); 4463\& ev_check_init (&check, check_cb);
2325\& ev_check_start (EV_DEFAULT_ &check); 4464\& ev_check_start (EV_DEFAULT_ &check);
2326\& ev_loop (EV_DEFAULT_ 0); 4465\& ev_run (EV_DEFAULT_ 0);
2327.Ve 4466.Ve
2328.SH "EMBEDDING" 4467.SH "EMBEDDING"
2329.IX Header "EMBEDDING" 4468.IX Header "EMBEDDING"
2330Libev can (and often is) directly embedded into host 4469Libev can (and often is) directly embedded into host
2331applications. Examples of applications that embed it include the Deliantra 4470applications. Examples of applications that embed it include the Deliantra
2332Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4471Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2333and rxvt\-unicode. 4472and rxvt-unicode.
2334.PP 4473.PP
2335The goal is to enable you to just copy the neecssary files into your 4474The goal is to enable you to just copy the necessary files into your
2336source directory without having to change even a single line in them, so 4475source directory without having to change even a single line in them, so
2337you can easily upgrade by simply copying (or having a checked-out copy of 4476you can easily upgrade by simply copying (or having a checked-out copy of
2338libev somewhere in your source tree). 4477libev somewhere in your source tree).
2339.Sh "\s-1FILESETS\s0" 4478.SS "\s-1FILESETS\s0"
2340.IX Subsection "FILESETS" 4479.IX Subsection "FILESETS"
2341Depending on what features you need you need to include one or more sets of files 4480Depending on what features you need you need to include one or more sets of files
2342in your app. 4481in your application.
2343.PP 4482.PP
2344\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4483\fI\s-1CORE EVENT LOOP\s0\fR
2345.IX Subsection "CORE EVENT LOOP" 4484.IX Subsection "CORE EVENT LOOP"
2346.PP 4485.PP
2347To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4486To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2348configuration (no autoconf): 4487configuration (no autoconf):
2349.PP 4488.PP
2350.Vb 2 4489.Vb 2
2351\& #define EV_STANDALONE 1 4490\& #define EV_STANDALONE 1
2352\& #include "ev.c" 4491\& #include "ev.c"
2353.Ve 4492.Ve
2354.PP 4493.PP
2355This will automatically include \fIev.h\fR, too, and should be done in a 4494This will automatically include \fIev.h\fR, too, and should be done in a
2356single C source file only to provide the function implementations. To use 4495single C source file only to provide the function implementations. To use
2357it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4496it, do the same for \fIev.h\fR in all files wishing to use this \s-1API \s0(best
2358done by writing a wrapper around \fIev.h\fR that you can include instead and 4497done by writing a wrapper around \fIev.h\fR that you can include instead and
2359where you can put other configuration options): 4498where you can put other configuration options):
2360.PP 4499.PP
2361.Vb 2 4500.Vb 2
2362\& #define EV_STANDALONE 1 4501\& #define EV_STANDALONE 1
2363\& #include "ev.h" 4502\& #include "ev.h"
2364.Ve 4503.Ve
2365.PP 4504.PP
2366Both header files and implementation files can be compiled with a \*(C+ 4505Both header files and implementation files can be compiled with a \*(C+
2367compiler (at least, thats a stated goal, and breakage will be treated 4506compiler (at least, that's a stated goal, and breakage will be treated
2368as a bug). 4507as a bug).
2369.PP 4508.PP
2370You need the following files in your source tree, or in a directory 4509You need the following files in your source tree, or in a directory
2371in your include path (e.g. in libev/ when using \-Ilibev): 4510in your include path (e.g. in libev/ when using \-Ilibev):
2372.PP 4511.PP
2373.Vb 4 4512.Vb 4
2374\& ev.h 4513\& ev.h
2375\& ev.c 4514\& ev.c
2376\& ev_vars.h 4515\& ev_vars.h
2377\& ev_wrap.h 4516\& ev_wrap.h
2378.Ve 4517\&
2379.PP
2380.Vb 1
2381\& ev_win32.c required on win32 platforms only 4518\& ev_win32.c required on win32 platforms only
2382.Ve 4519\&
2383.PP
2384.Vb 5
2385\& ev_select.c only when select backend is enabled (which is enabled by default) 4520\& ev_select.c only when select backend is enabled (which is enabled by default)
2386\& ev_poll.c only when poll backend is enabled (disabled by default) 4521\& ev_poll.c only when poll backend is enabled (disabled by default)
2387\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4522\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2388\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4523\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2389\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4524\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2390.Ve 4525.Ve
2391.PP 4526.PP
2392\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4527\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2393to compile this single file. 4528to compile this single file.
2394.PP 4529.PP
2395\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4530\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
2396.IX Subsection "LIBEVENT COMPATIBILITY API" 4531.IX Subsection "LIBEVENT COMPATIBILITY API"
2397.PP 4532.PP
2398To include the libevent compatibility \s-1API\s0, also include: 4533To include the libevent compatibility \s-1API,\s0 also include:
2399.PP 4534.PP
2400.Vb 1 4535.Vb 1
2401\& #include "event.c" 4536\& #include "event.c"
2402.Ve 4537.Ve
2403.PP 4538.PP
2404in the file including \fIev.c\fR, and: 4539in the file including \fIev.c\fR, and:
2405.PP 4540.PP
2406.Vb 1 4541.Vb 1
2407\& #include "event.h" 4542\& #include "event.h"
2408.Ve 4543.Ve
2409.PP 4544.PP
2410in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4545in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
2411.PP 4546.PP
2412You need the following additional files for this: 4547You need the following additional files for this:
2413.PP 4548.PP
2414.Vb 2 4549.Vb 2
2415\& event.h 4550\& event.h
2416\& event.c 4551\& event.c
2417.Ve 4552.Ve
2418.PP 4553.PP
2419\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4554\fI\s-1AUTOCONF SUPPORT\s0\fR
2420.IX Subsection "AUTOCONF SUPPORT" 4555.IX Subsection "AUTOCONF SUPPORT"
2421.PP 4556.PP
2422Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4557Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2423whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4558whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2424\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4559\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2425include \fIconfig.h\fR and configure itself accordingly. 4560include \fIconfig.h\fR and configure itself accordingly.
2426.PP 4561.PP
2427For this of course you need the m4 file: 4562For this of course you need the m4 file:
2428.PP 4563.PP
2429.Vb 1 4564.Vb 1
2430\& libev.m4 4565\& libev.m4
2431.Ve 4566.Ve
2432.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4567.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
2433.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4568.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2434Libev can be configured via a variety of preprocessor symbols you have to define 4569Libev can be configured via a variety of preprocessor symbols you have to
2435before including any of its files. The default is not to build for multiplicity 4570define before including (or compiling) any of its files. The default in
2436and only include the select backend. 4571the absence of autoconf is documented for every option.
4572.PP
4573Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4574values when compiling libev vs. including \fIev.h\fR, so it is permissible
4575to redefine them before including \fIev.h\fR without breaking compatibility
4576to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4577users of libev and the libev code itself must be compiled with compatible
4578settings.
4579.IP "\s-1EV_COMPAT3 \s0(h)" 4
4580.IX Item "EV_COMPAT3 (h)"
4581Backwards compatibility is a major concern for libev. This is why this
4582release of libev comes with wrappers for the functions and symbols that
4583have been renamed between libev version 3 and 4.
4584.Sp
4585You can disable these wrappers (to test compatibility with future
4586versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4587sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4588from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4589typedef in that case.
4590.Sp
4591In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4592and in some even more future version the compatibility code will be
4593removed completely.
2437.IP "\s-1EV_STANDALONE\s0" 4 4594.IP "\s-1EV_STANDALONE \s0(h)" 4
2438.IX Item "EV_STANDALONE" 4595.IX Item "EV_STANDALONE (h)"
2439Must always be \f(CW1\fR if you do not use autoconf configuration, which 4596Must always be \f(CW1\fR if you do not use autoconf configuration, which
2440keeps libev from including \fIconfig.h\fR, and it also defines dummy 4597keeps libev from including \fIconfig.h\fR, and it also defines dummy
2441implementations for some libevent functions (such as logging, which is not 4598implementations for some libevent functions (such as logging, which is not
2442supported). It will also not define any of the structs usually found in 4599supported). It will also not define any of the structs usually found in
2443\&\fIevent.h\fR that are not directly supported by the libev core alone. 4600\&\fIevent.h\fR that are not directly supported by the libev core alone.
4601.Sp
4602In standalone mode, libev will still try to automatically deduce the
4603configuration, but has to be more conservative.
4604.IP "\s-1EV_USE_FLOOR\s0" 4
4605.IX Item "EV_USE_FLOOR"
4606If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4607periodic reschedule calculations, otherwise libev will fall back on a
4608portable (slower) implementation. If you enable this, you usually have to
4609link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4610function is not available will fail, so the safe default is to not enable
4611this.
2444.IP "\s-1EV_USE_MONOTONIC\s0" 4 4612.IP "\s-1EV_USE_MONOTONIC\s0" 4
2445.IX Item "EV_USE_MONOTONIC" 4613.IX Item "EV_USE_MONOTONIC"
2446If defined to be \f(CW1\fR, libev will try to detect the availability of the 4614If defined to be \f(CW1\fR, libev will try to detect the availability of the
2447monotonic clock option at both compiletime and runtime. Otherwise no use 4615monotonic clock option at both compile time and runtime. Otherwise no
2448of the monotonic clock option will be attempted. If you enable this, you 4616use of the monotonic clock option will be attempted. If you enable this,
2449usually have to link against librt or something similar. Enabling it when 4617you usually have to link against librt or something similar. Enabling it
2450the functionality isn't available is safe, though, althoguh you have 4618when the functionality isn't available is safe, though, although you have
2451to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4619to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2452function is hiding in (often \fI\-lrt\fR). 4620function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2453.IP "\s-1EV_USE_REALTIME\s0" 4 4621.IP "\s-1EV_USE_REALTIME\s0" 4
2454.IX Item "EV_USE_REALTIME" 4622.IX Item "EV_USE_REALTIME"
2455If defined to be \f(CW1\fR, libev will try to detect the availability of the 4623If defined to be \f(CW1\fR, libev will try to detect the availability of the
2456realtime clock option at compiletime (and assume its availability at 4624real-time clock option at compile time (and assume its availability
2457runtime if successful). Otherwise no use of the realtime clock option will 4625at runtime if successful). Otherwise no use of the real-time clock
2458be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4626option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2459(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4627by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2460in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4628correctness. See the note about libraries in the description of
4629\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4630\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4631.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4632.IX Item "EV_USE_CLOCK_SYSCALL"
4633If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4634of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4635exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4636unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4637programs needlessly. Using a direct syscall is slightly slower (in
4638theory), because no optimised vdso implementation can be used, but avoids
4639the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4640higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4641.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4642.IX Item "EV_USE_NANOSLEEP"
4643If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4644and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4645.IP "\s-1EV_USE_EVENTFD\s0" 4
4646.IX Item "EV_USE_EVENTFD"
4647If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4648available and will probe for kernel support at runtime. This will improve
4649\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4650If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
46512.7 or newer, otherwise disabled.
2461.IP "\s-1EV_USE_SELECT\s0" 4 4652.IP "\s-1EV_USE_SELECT\s0" 4
2462.IX Item "EV_USE_SELECT" 4653.IX Item "EV_USE_SELECT"
2463If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4654If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2464\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4655\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2465other method takes over, select will be it. Otherwise the select backend 4656other method takes over, select will be it. Otherwise the select backend
2466will not be compiled in. 4657will not be compiled in.
2467.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4658.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2468.IX Item "EV_SELECT_USE_FD_SET" 4659.IX Item "EV_SELECT_USE_FD_SET"
2469If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4660If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2470structure. This is useful if libev doesn't compile due to a missing 4661structure. This is useful if libev doesn't compile due to a missing
2471\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4662\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2472exotic systems. This usually limits the range of file descriptors to some 4663on exotic systems. This usually limits the range of file descriptors to
2473low limit such as 1024 or might have other limitations (winsocket only 4664some low limit such as 1024 or might have other limitations (winsocket
2474allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4665only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2475influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4666configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2476.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4667.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2477.IX Item "EV_SELECT_IS_WINSOCKET" 4668.IX Item "EV_SELECT_IS_WINSOCKET"
2478When defined to \f(CW1\fR, the select backend will assume that 4669When defined to \f(CW1\fR, the select backend will assume that
2479select/socket/connect etc. don't understand file descriptors but 4670select/socket/connect etc. don't understand file descriptors but
2480wants osf handles on win32 (this is the case when the select to 4671wants osf handles on win32 (this is the case when the select to
2481be used is the winsock select). This means that it will call 4672be used is the winsock select). This means that it will call
2482\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4673\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2483it is assumed that all these functions actually work on fds, even 4674it is assumed that all these functions actually work on fds, even
2484on win32. Should not be defined on non\-win32 platforms. 4675on win32. Should not be defined on non\-win32 platforms.
4676.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4677.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4678If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4679file descriptors to socket handles. When not defining this symbol (the
4680default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4681correct. In some cases, programs use their own file descriptor management,
4682in which case they can provide this function to map fds to socket handles.
4683.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4684.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4685If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4686using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4687their own fd to handle mapping, overwriting this function makes it easier
4688to do so. This can be done by defining this macro to an appropriate value.
4689.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4690.IX Item "EV_WIN32_CLOSE_FD(fd)"
4691If programs implement their own fd to handle mapping on win32, then this
4692macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4693file descriptors again. Note that the replacement function has to close
4694the underlying \s-1OS\s0 handle.
4695.IP "\s-1EV_USE_WSASOCKET\s0" 4
4696.IX Item "EV_USE_WSASOCKET"
4697If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4698communication socket, which works better in some environments. Otherwise,
4699the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4700environments.
2485.IP "\s-1EV_USE_POLL\s0" 4 4701.IP "\s-1EV_USE_POLL\s0" 4
2486.IX Item "EV_USE_POLL" 4702.IX Item "EV_USE_POLL"
2487If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4703If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2488backend. Otherwise it will be enabled on non\-win32 platforms. It 4704backend. Otherwise it will be enabled on non\-win32 platforms. It
2489takes precedence over select. 4705takes precedence over select.
2490.IP "\s-1EV_USE_EPOLL\s0" 4 4706.IP "\s-1EV_USE_EPOLL\s0" 4
2491.IX Item "EV_USE_EPOLL" 4707.IX Item "EV_USE_EPOLL"
2492If defined to be \f(CW1\fR, libev will compile in support for the Linux 4708If defined to be \f(CW1\fR, libev will compile in support for the Linux
2493\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4709\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2494otherwise another method will be used as fallback. This is the 4710otherwise another method will be used as fallback. This is the preferred
2495preferred backend for GNU/Linux systems. 4711backend for GNU/Linux systems. If undefined, it will be enabled if the
4712headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2496.IP "\s-1EV_USE_KQUEUE\s0" 4 4713.IP "\s-1EV_USE_KQUEUE\s0" 4
2497.IX Item "EV_USE_KQUEUE" 4714.IX Item "EV_USE_KQUEUE"
2498If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4715If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2499\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4716\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2500otherwise another method will be used as fallback. This is the preferred 4717otherwise another method will be used as fallback. This is the preferred
… …
251010 port style backend. Its availability will be detected at runtime, 472710 port style backend. Its availability will be detected at runtime,
2511otherwise another method will be used as fallback. This is the preferred 4728otherwise another method will be used as fallback. This is the preferred
2512backend for Solaris 10 systems. 4729backend for Solaris 10 systems.
2513.IP "\s-1EV_USE_DEVPOLL\s0" 4 4730.IP "\s-1EV_USE_DEVPOLL\s0" 4
2514.IX Item "EV_USE_DEVPOLL" 4731.IX Item "EV_USE_DEVPOLL"
2515reserved for future expansion, works like the \s-1USE\s0 symbols above. 4732Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2516.IP "\s-1EV_USE_INOTIFY\s0" 4 4733.IP "\s-1EV_USE_INOTIFY\s0" 4
2517.IX Item "EV_USE_INOTIFY" 4734.IX Item "EV_USE_INOTIFY"
2518If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4735If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2519interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 4736interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2520be detected at runtime. 4737be detected at runtime. If undefined, it will be enabled if the headers
4738indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4739.IP "\s-1EV_NO_SMP\s0" 4
4740.IX Item "EV_NO_SMP"
4741If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4742between threads, that is, threads can be used, but threads never run on
4743different cpus (or different cpu cores). This reduces dependencies
4744and makes libev faster.
4745.IP "\s-1EV_NO_THREADS\s0" 4
4746.IX Item "EV_NO_THREADS"
4747If defined to be \f(CW1\fR, libev will assume that it will never be called from
4748different threads (that includes signal handlers), which is a stronger
4749assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4750libev faster.
4751.IP "\s-1EV_ATOMIC_T\s0" 4
4752.IX Item "EV_ATOMIC_T"
4753Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4754access is atomic with respect to other threads or signal contexts. No
4755such type is easily found in the C language, so you can provide your own
4756type that you know is safe for your purposes. It is used both for signal
4757handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4758watchers.
4759.Sp
4760In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4761(from \fIsignal.h\fR), which is usually good enough on most platforms.
2521.IP "\s-1EV_H\s0" 4 4762.IP "\s-1EV_H \s0(h)" 4
2522.IX Item "EV_H" 4763.IX Item "EV_H (h)"
2523The name of the \fIev.h\fR header file used to include it. The default if 4764The name of the \fIev.h\fR header file used to include it. The default if
2524undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4765undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2525can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4766used to virtually rename the \fIev.h\fR header file in case of conflicts.
2526.IP "\s-1EV_CONFIG_H\s0" 4 4767.IP "\s-1EV_CONFIG_H \s0(h)" 4
2527.IX Item "EV_CONFIG_H" 4768.IX Item "EV_CONFIG_H (h)"
2528If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4769If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2529\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4770\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2530\&\f(CW\*(C`EV_H\*(C'\fR, above. 4771\&\f(CW\*(C`EV_H\*(C'\fR, above.
2531.IP "\s-1EV_EVENT_H\s0" 4 4772.IP "\s-1EV_EVENT_H \s0(h)" 4
2532.IX Item "EV_EVENT_H" 4773.IX Item "EV_EVENT_H (h)"
2533Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4774Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2534of how the \fIevent.h\fR header can be found. 4775of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2535.IP "\s-1EV_PROTOTYPES\s0" 4 4776.IP "\s-1EV_PROTOTYPES \s0(h)" 4
2536.IX Item "EV_PROTOTYPES" 4777.IX Item "EV_PROTOTYPES (h)"
2537If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4778If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2538prototypes, but still define all the structs and other symbols. This is 4779prototypes, but still define all the structs and other symbols. This is
2539occasionally useful if you want to provide your own wrapper functions 4780occasionally useful if you want to provide your own wrapper functions
2540around libev functions. 4781around libev functions.
2541.IP "\s-1EV_MULTIPLICITY\s0" 4 4782.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2543If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4784If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2544will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4785will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2545additional independent event loops. Otherwise there will be no support 4786additional independent event loops. Otherwise there will be no support
2546for multiple event loops and there is no first event loop pointer 4787for multiple event loops and there is no first event loop pointer
2547argument. Instead, all functions act on the single default loop. 4788argument. Instead, all functions act on the single default loop.
4789.Sp
4790Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4791default loop when multiplicity is switched off \- you always have to
4792initialise the loop manually in this case.
2548.IP "\s-1EV_MINPRI\s0" 4 4793.IP "\s-1EV_MINPRI\s0" 4
2549.IX Item "EV_MINPRI" 4794.IX Item "EV_MINPRI"
2550.PD 0 4795.PD 0
2551.IP "\s-1EV_MAXPRI\s0" 4 4796.IP "\s-1EV_MAXPRI\s0" 4
2552.IX Item "EV_MAXPRI" 4797.IX Item "EV_MAXPRI"
… …
2559When doing priority-based operations, libev usually has to linearly search 4804When doing priority-based operations, libev usually has to linearly search
2560all the priorities, so having many of them (hundreds) uses a lot of space 4805all the priorities, so having many of them (hundreds) uses a lot of space
2561and time, so using the defaults of five priorities (\-2 .. +2) is usually 4806and time, so using the defaults of five priorities (\-2 .. +2) is usually
2562fine. 4807fine.
2563.Sp 4808.Sp
2564If your embedding app does not need any priorities, defining these both to 4809If your embedding application does not need any priorities, defining these
2565\&\f(CW0\fR will save some memory and cpu. 4810both to \f(CW0\fR will save some memory and \s-1CPU.\s0
2566.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4811.IP "\s-1EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE.\s0" 4
2567.IX Item "EV_PERIODIC_ENABLE" 4812.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
2568If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4813If undefined or defined to be \f(CW1\fR (and the platform supports it), then
2569defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4814the respective watcher type is supported. If defined to be \f(CW0\fR, then it
2570code. 4815is not. Disabling watcher types mainly saves code size.
2571.IP "\s-1EV_IDLE_ENABLE\s0" 4
2572.IX Item "EV_IDLE_ENABLE"
2573If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2574defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2575code.
2576.IP "\s-1EV_EMBED_ENABLE\s0" 4
2577.IX Item "EV_EMBED_ENABLE"
2578If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2579defined to be \f(CW0\fR, then they are not.
2580.IP "\s-1EV_STAT_ENABLE\s0" 4 4816.IP "\s-1EV_FEATURES\s0" 4
2581.IX Item "EV_STAT_ENABLE" 4817.IX Item "EV_FEATURES"
2582If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2583defined to be \f(CW0\fR, then they are not.
2584.IP "\s-1EV_FORK_ENABLE\s0" 4
2585.IX Item "EV_FORK_ENABLE"
2586If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2587defined to be \f(CW0\fR, then they are not.
2588.IP "\s-1EV_MINIMAL\s0" 4
2589.IX Item "EV_MINIMAL"
2590If you need to shave off some kilobytes of code at the expense of some 4818If you need to shave off some kilobytes of code at the expense of some
2591speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4819speed (but with the full \s-1API\s0), you can define this symbol to request
2592some inlining decisions, saves roughly 30% codesize of amd64. 4820certain subsets of functionality. The default is to enable all features
4821that can be enabled on the platform.
4822.Sp
4823A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4824with some broad features you want) and then selectively re-enable
4825additional parts you want, for example if you want everything minimal,
4826but multiple event loop support, async and child watchers and the poll
4827backend, use this:
4828.Sp
4829.Vb 5
4830\& #define EV_FEATURES 0
4831\& #define EV_MULTIPLICITY 1
4832\& #define EV_USE_POLL 1
4833\& #define EV_CHILD_ENABLE 1
4834\& #define EV_ASYNC_ENABLE 1
4835.Ve
4836.Sp
4837The actual value is a bitset, it can be a combination of the following
4838values (by default, all of these are enabled):
4839.RS 4
4840.ie n .IP "1 \- faster/larger code" 4
4841.el .IP "\f(CW1\fR \- faster/larger code" 4
4842.IX Item "1 - faster/larger code"
4843Use larger code to speed up some operations.
4844.Sp
4845Currently this is used to override some inlining decisions (enlarging the
4846code size by roughly 30% on amd64).
4847.Sp
4848When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4849gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4850assertions.
4851.Sp
4852The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4853(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4854.ie n .IP "2 \- faster/larger data structures" 4
4855.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4856.IX Item "2 - faster/larger data structures"
4857Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4858hash table sizes and so on. This will usually further increase code size
4859and can additionally have an effect on the size of data structures at
4860runtime.
4861.Sp
4862The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4863(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4864.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4865.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4866.IX Item "4 - full API configuration"
4867This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4868enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4869.ie n .IP "8 \- full \s-1API\s0" 4
4870.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4871.IX Item "8 - full API"
4872This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4873details on which parts of the \s-1API\s0 are still available without this
4874feature, and do not complain if this subset changes over time.
4875.ie n .IP "16 \- enable all optional watcher types" 4
4876.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4877.IX Item "16 - enable all optional watcher types"
4878Enables all optional watcher types. If you want to selectively enable
4879only some watcher types other than I/O and timers (e.g. prepare,
4880embed, async, child...) you can enable them manually by defining
4881\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4882.ie n .IP "32 \- enable all backends" 4
4883.el .IP "\f(CW32\fR \- enable all backends" 4
4884.IX Item "32 - enable all backends"
4885This enables all backends \- without this feature, you need to enable at
4886least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4887.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4888.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4889.IX Item "64 - enable OS-specific helper APIs"
4890Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4891default.
4892.RE
4893.RS 4
4894.Sp
4895Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4896reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4897code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4898watchers, timers and monotonic clock support.
4899.Sp
4900With an intelligent-enough linker (gcc+binutils are intelligent enough
4901when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4902your program might be left out as well \- a binary starting a timer and an
4903I/O watcher then might come out at only 5Kb.
4904.RE
4905.IP "\s-1EV_API_STATIC\s0" 4
4906.IX Item "EV_API_STATIC"
4907If this symbol is defined (by default it is not), then all identifiers
4908will have static linkage. This means that libev will not export any
4909identifiers, and you cannot link against libev anymore. This can be useful
4910when you embed libev, only want to use libev functions in a single file,
4911and do not want its identifiers to be visible.
4912.Sp
4913To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4914wants to use libev.
4915.Sp
4916This option only works when libev is compiled with a C compiler, as \*(C+
4917doesn't support the required declaration syntax.
4918.IP "\s-1EV_AVOID_STDIO\s0" 4
4919.IX Item "EV_AVOID_STDIO"
4920If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4921functions (printf, scanf, perror etc.). This will increase the code size
4922somewhat, but if your program doesn't otherwise depend on stdio and your
4923libc allows it, this avoids linking in the stdio library which is quite
4924big.
4925.Sp
4926Note that error messages might become less precise when this option is
4927enabled.
4928.IP "\s-1EV_NSIG\s0" 4
4929.IX Item "EV_NSIG"
4930The highest supported signal number, +1 (or, the number of
4931signals): Normally, libev tries to deduce the maximum number of signals
4932automatically, but sometimes this fails, in which case it can be
4933specified. Also, using a lower number than detected (\f(CW32\fR should be
4934good for about any system in existence) can save some memory, as libev
4935statically allocates some 12\-24 bytes per signal number.
2593.IP "\s-1EV_PID_HASHSIZE\s0" 4 4936.IP "\s-1EV_PID_HASHSIZE\s0" 4
2594.IX Item "EV_PID_HASHSIZE" 4937.IX Item "EV_PID_HASHSIZE"
2595\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 4938\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2596pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 4939pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2597than enough. If you need to manage thousands of children you might want to 4940usually more than enough. If you need to manage thousands of children you
2598increase this value (\fImust\fR be a power of two). 4941might want to increase this value (\fImust\fR be a power of two).
2599.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 4942.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2600.IX Item "EV_INOTIFY_HASHSIZE" 4943.IX Item "EV_INOTIFY_HASHSIZE"
2601\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 4944\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2602inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 4945inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
2603usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 4946disabled), usually more than enough. If you need to manage thousands of
2604watchers you might want to increase this value (\fImust\fR be a power of 4947\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2605two). 4948power of two).
4949.IP "\s-1EV_USE_4HEAP\s0" 4
4950.IX Item "EV_USE_4HEAP"
4951Heaps are not very cache-efficient. To improve the cache-efficiency of the
4952timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4953to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4954faster performance with many (thousands) of watchers.
4955.Sp
4956The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4957will be \f(CW0\fR.
4958.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4959.IX Item "EV_HEAP_CACHE_AT"
4960Heaps are not very cache-efficient. To improve the cache-efficiency of the
4961timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4962the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4963which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4964but avoids random read accesses on heap changes. This improves performance
4965noticeably with many (hundreds) of watchers.
4966.Sp
4967The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4968will be \f(CW0\fR.
4969.IP "\s-1EV_VERIFY\s0" 4
4970.IX Item "EV_VERIFY"
4971Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4972be done: If set to \f(CW0\fR, no internal verification code will be compiled
4973in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4974called. If set to \f(CW2\fR, then the internal verification code will be
4975called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4976verification code will be called very frequently, which will slow down
4977libev considerably.
4978.Sp
4979The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4980will be \f(CW0\fR.
2606.IP "\s-1EV_COMMON\s0" 4 4981.IP "\s-1EV_COMMON\s0" 4
2607.IX Item "EV_COMMON" 4982.IX Item "EV_COMMON"
2608By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4983By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2609this macro to a something else you can include more and other types of 4984this macro to something else you can include more and other types of
2610members. You have to define it each time you include one of the files, 4985members. You have to define it each time you include one of the files,
2611though, and it must be identical each time. 4986though, and it must be identical each time.
2612.Sp 4987.Sp
2613For example, the perl \s-1EV\s0 module uses something like this: 4988For example, the perl \s-1EV\s0 module uses something like this:
2614.Sp 4989.Sp
2615.Vb 3 4990.Vb 3
2616\& #define EV_COMMON \e 4991\& #define EV_COMMON \e
2617\& SV *self; /* contains this struct */ \e 4992\& SV *self; /* contains this struct */ \e
2618\& SV *cb_sv, *fh /* note no trailing ";" */ 4993\& SV *cb_sv, *fh /* note no trailing ";" */
2619.Ve 4994.Ve
2620.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 4995.IP "\s-1EV_CB_DECLARE \s0(type)" 4
2621.IX Item "EV_CB_DECLARE (type)" 4996.IX Item "EV_CB_DECLARE (type)"
2622.PD 0 4997.PD 0
2623.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 4998.IP "\s-1EV_CB_INVOKE \s0(watcher, revents)" 4
2624.IX Item "EV_CB_INVOKE (watcher, revents)" 4999.IX Item "EV_CB_INVOKE (watcher, revents)"
2625.IP "ev_set_cb (ev, cb)" 4 5000.IP "ev_set_cb (ev, cb)" 4
2626.IX Item "ev_set_cb (ev, cb)" 5001.IX Item "ev_set_cb (ev, cb)"
2627.PD 5002.PD
2628Can be used to change the callback member declaration in each watcher, 5003Can be used to change the callback member declaration in each watcher,
2629and the way callbacks are invoked and set. Must expand to a struct member 5004and the way callbacks are invoked and set. Must expand to a struct member
2630definition and a statement, respectively. See the \fIev.v\fR header file for 5005definition and a statement, respectively. See the \fIev.h\fR header file for
2631their default definitions. One possible use for overriding these is to 5006their default definitions. One possible use for overriding these is to
2632avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5007avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2633method calls instead of plain function calls in \*(C+. 5008method calls instead of plain function calls in \*(C+.
2634.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0" 5009.SS "\s-1EXPORTED API SYMBOLS\s0"
2635.IX Subsection "EXPORTED API SYMBOLS" 5010.IX Subsection "EXPORTED API SYMBOLS"
2636If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of 5011If you need to re-export the \s-1API \s0(e.g. via a \s-1DLL\s0) and you need a list of
2637exported symbols, you can use the provided \fISymbol.*\fR files which list 5012exported symbols, you can use the provided \fISymbol.*\fR files which list
2638all public symbols, one per line: 5013all public symbols, one per line:
2639.Sp 5014.PP
2640.Vb 2 5015.Vb 2
2641\& Symbols.ev for libev proper 5016\& Symbols.ev for libev proper
2642\& Symbols.event for the libevent emulation 5017\& Symbols.event for the libevent emulation
2643.Ve 5018.Ve
2644.Sp 5019.PP
2645This can also be used to rename all public symbols to avoid clashes with 5020This can also be used to rename all public symbols to avoid clashes with
2646multiple versions of libev linked together (which is obviously bad in 5021multiple versions of libev linked together (which is obviously bad in
2647itself, but sometimes it is inconvinient to avoid this). 5022itself, but sometimes it is inconvenient to avoid this).
2648.Sp 5023.PP
2649A sed comamnd like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to 5024A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
2650include before including \fIev.h\fR: 5025include before including \fIev.h\fR:
2651.Sp 5026.PP
2652.Vb 1 5027.Vb 1
2653\& <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h 5028\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
2654.Ve 5029.Ve
2655.Sp 5030.PP
2656This would create a file \fIwrap.h\fR which essentially looks like this: 5031This would create a file \fIwrap.h\fR which essentially looks like this:
2657.Sp 5032.PP
2658.Vb 4 5033.Vb 4
2659\& #define ev_backend myprefix_ev_backend 5034\& #define ev_backend myprefix_ev_backend
2660\& #define ev_check_start myprefix_ev_check_start 5035\& #define ev_check_start myprefix_ev_check_start
2661\& #define ev_check_stop myprefix_ev_check_stop 5036\& #define ev_check_stop myprefix_ev_check_stop
2662\& ... 5037\& ...
2663.Ve 5038.Ve
2664.Sh "\s-1EXAMPLES\s0" 5039.SS "\s-1EXAMPLES\s0"
2665.IX Subsection "EXAMPLES" 5040.IX Subsection "EXAMPLES"
2666For a real-world example of a program the includes libev 5041For a real-world example of a program the includes libev
2667verbatim, you can have a look at the \s-1EV\s0 perl module 5042verbatim, you can have a look at the \s-1EV\s0 perl module
2668(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5043(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2669the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5044the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2670interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5045interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2671will be compiled. It is pretty complex because it provides its own header 5046will be compiled. It is pretty complex because it provides its own header
2672file. 5047file.
2673.Sp 5048.PP
2674The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5049The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2675that everybody includes and which overrides some configure choices: 5050that everybody includes and which overrides some configure choices:
2676.Sp 5051.PP
2677.Vb 9 5052.Vb 8
2678\& #define EV_MINIMAL 1 5053\& #define EV_FEATURES 8
2679\& #define EV_USE_POLL 0 5054\& #define EV_USE_SELECT 1
2680\& #define EV_MULTIPLICITY 0
2681\& #define EV_PERIODIC_ENABLE 0 5055\& #define EV_PREPARE_ENABLE 1
5056\& #define EV_IDLE_ENABLE 1
2682\& #define EV_STAT_ENABLE 0 5057\& #define EV_SIGNAL_ENABLE 1
2683\& #define EV_FORK_ENABLE 0 5058\& #define EV_CHILD_ENABLE 1
5059\& #define EV_USE_STDEXCEPT 0
2684\& #define EV_CONFIG_H <config.h> 5060\& #define EV_CONFIG_H <config.h>
2685\& #define EV_MINPRI 0 5061\&
2686\& #define EV_MAXPRI 0
2687.Ve
2688.Sp
2689.Vb 1
2690\& #include "ev++.h" 5062\& #include "ev++.h"
2691.Ve 5063.Ve
2692.Sp 5064.PP
2693And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5065And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2694.Sp 5066.PP
2695.Vb 2 5067.Vb 2
2696\& #include "ev_cpp.h" 5068\& #include "ev_cpp.h"
2697\& #include "ev.c" 5069\& #include "ev.c"
2698.Ve 5070.Ve
5071.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5072.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5073.SS "\s-1THREADS AND COROUTINES\s0"
5074.IX Subsection "THREADS AND COROUTINES"
5075\fI\s-1THREADS\s0\fR
5076.IX Subsection "THREADS"
5077.PP
5078All libev functions are reentrant and thread-safe unless explicitly
5079documented otherwise, but libev implements no locking itself. This means
5080that you can use as many loops as you want in parallel, as long as there
5081are no concurrent calls into any libev function with the same loop
5082parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5083of course): libev guarantees that different event loops share no data
5084structures that need any locking.
5085.PP
5086Or to put it differently: calls with different loop parameters can be done
5087concurrently from multiple threads, calls with the same loop parameter
5088must be done serially (but can be done from different threads, as long as
5089only one thread ever is inside a call at any point in time, e.g. by using
5090a mutex per loop).
5091.PP
5092Specifically to support threads (and signal handlers), libev implements
5093so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5094concurrency on the same event loop, namely waking it up \*(L"from the
5095outside\*(R".
5096.PP
5097If you want to know which design (one loop, locking, or multiple loops
5098without or something else still) is best for your problem, then I cannot
5099help you, but here is some generic advice:
5100.IP "\(bu" 4
5101most applications have a main thread: use the default libev loop
5102in that thread, or create a separate thread running only the default loop.
5103.Sp
5104This helps integrating other libraries or software modules that use libev
5105themselves and don't care/know about threading.
5106.IP "\(bu" 4
5107one loop per thread is usually a good model.
5108.Sp
5109Doing this is almost never wrong, sometimes a better-performance model
5110exists, but it is always a good start.
5111.IP "\(bu" 4
5112other models exist, such as the leader/follower pattern, where one
5113loop is handed through multiple threads in a kind of round-robin fashion.
5114.Sp
5115Choosing a model is hard \- look around, learn, know that usually you can do
5116better than you currently do :\-)
5117.IP "\(bu" 4
5118often you need to talk to some other thread which blocks in the
5119event loop.
5120.Sp
5121\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5122(or from signal contexts...).
5123.Sp
5124An example use would be to communicate signals or other events that only
5125work in the default loop by registering the signal watcher with the
5126default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5127watcher callback into the event loop interested in the signal.
5128.PP
5129See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5130.PP
5131\fI\s-1COROUTINES\s0\fR
5132.IX Subsection "COROUTINES"
5133.PP
5134Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5135libev fully supports nesting calls to its functions from different
5136coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5137different coroutines, and switch freely between both coroutines running
5138the loop, as long as you don't confuse yourself). The only exception is
5139that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5140.PP
5141Care has been taken to ensure that libev does not keep local state inside
5142\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5143they do not call any callbacks.
5144.SS "\s-1COMPILER WARNINGS\s0"
5145.IX Subsection "COMPILER WARNINGS"
5146Depending on your compiler and compiler settings, you might get no or a
5147lot of warnings when compiling libev code. Some people are apparently
5148scared by this.
5149.PP
5150However, these are unavoidable for many reasons. For one, each compiler
5151has different warnings, and each user has different tastes regarding
5152warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5153targeting a specific compiler and compiler-version.
5154.PP
5155Another reason is that some compiler warnings require elaborate
5156workarounds, or other changes to the code that make it less clear and less
5157maintainable.
5158.PP
5159And of course, some compiler warnings are just plain stupid, or simply
5160wrong (because they don't actually warn about the condition their message
5161seems to warn about). For example, certain older gcc versions had some
5162warnings that resulted in an extreme number of false positives. These have
5163been fixed, but some people still insist on making code warn-free with
5164such buggy versions.
5165.PP
5166While libev is written to generate as few warnings as possible,
5167\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5168with any compiler warnings enabled unless you are prepared to cope with
5169them (e.g. by ignoring them). Remember that warnings are just that:
5170warnings, not errors, or proof of bugs.
5171.SS "\s-1VALGRIND\s0"
5172.IX Subsection "VALGRIND"
5173Valgrind has a special section here because it is a popular tool that is
5174highly useful. Unfortunately, valgrind reports are very hard to interpret.
5175.PP
5176If you think you found a bug (memory leak, uninitialised data access etc.)
5177in libev, then check twice: If valgrind reports something like:
5178.PP
5179.Vb 3
5180\& ==2274== definitely lost: 0 bytes in 0 blocks.
5181\& ==2274== possibly lost: 0 bytes in 0 blocks.
5182\& ==2274== still reachable: 256 bytes in 1 blocks.
5183.Ve
5184.PP
5185Then there is no memory leak, just as memory accounted to global variables
5186is not a memleak \- the memory is still being referenced, and didn't leak.
5187.PP
5188Similarly, under some circumstances, valgrind might report kernel bugs
5189as if it were a bug in libev (e.g. in realloc or in the poll backend,
5190although an acceptable workaround has been found here), or it might be
5191confused.
5192.PP
5193Keep in mind that valgrind is a very good tool, but only a tool. Don't
5194make it into some kind of religion.
5195.PP
5196If you are unsure about something, feel free to contact the mailing list
5197with the full valgrind report and an explanation on why you think this
5198is a bug in libev (best check the archives, too :). However, don't be
5199annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5200of learning how to interpret valgrind properly.
5201.PP
5202If you need, for some reason, empty reports from valgrind for your project
5203I suggest using suppression lists.
5204.SH "PORTABILITY NOTES"
5205.IX Header "PORTABILITY NOTES"
5206.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5207.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5208GNU/Linux is the only common platform that supports 64 bit file/large file
5209interfaces but \fIdisables\fR them by default.
5210.PP
5211That means that libev compiled in the default environment doesn't support
5212files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5213.PP
5214Unfortunately, many programs try to work around this GNU/Linux issue
5215by enabling the large file \s-1API,\s0 which makes them incompatible with the
5216standard libev compiled for their system.
5217.PP
5218Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5219suddenly make it incompatible to the default compile time environment,
5220i.e. all programs not using special compile switches.
5221.SS "\s-1OS/X AND DARWIN BUGS\s0"
5222.IX Subsection "OS/X AND DARWIN BUGS"
5223The whole thing is a bug if you ask me \- basically any system interface
5224you touch is broken, whether it is locales, poll, kqueue or even the
5225OpenGL drivers.
5226.PP
5227\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5228.IX Subsection "kqueue is buggy"
5229.PP
5230The kqueue syscall is broken in all known versions \- most versions support
5231only sockets, many support pipes.
5232.PP
5233Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5234rotten platform, but of course you can still ask for it when creating a
5235loop \- embedding a socket-only kqueue loop into a select-based one is
5236probably going to work well.
5237.PP
5238\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5239.IX Subsection "poll is buggy"
5240.PP
5241Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5242implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5243release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5244.PP
5245Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5246this rotten platform, but of course you can still ask for it when creating
5247a loop.
5248.PP
5249\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5250.IX Subsection "select is buggy"
5251.PP
5252All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5253one up as well: On \s-1OS/X, \s0\f(CW\*(C`select\*(C'\fR actively limits the number of file
5254descriptors you can pass in to 1024 \- your program suddenly crashes when
5255you use more.
5256.PP
5257There is an undocumented \*(L"workaround\*(R" for this \- defining
5258\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5259work on \s-1OS/X.\s0
5260.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5261.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5262\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5263.IX Subsection "errno reentrancy"
5264.PP
5265The default compile environment on Solaris is unfortunately so
5266thread-unsafe that you can't even use components/libraries compiled
5267without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5268defined by default. A valid, if stupid, implementation choice.
5269.PP
5270If you want to use libev in threaded environments you have to make sure
5271it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5272.PP
5273\fIEvent port backend\fR
5274.IX Subsection "Event port backend"
5275.PP
5276The scalable event interface for Solaris is called \*(L"event
5277ports\*(R". Unfortunately, this mechanism is very buggy in all major
5278releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5279a large number of spurious wakeups, make sure you have all the relevant
5280and latest kernel patches applied. No, I don't know which ones, but there
5281are multiple ones to apply, and afterwards, event ports actually work
5282great.
5283.PP
5284If you can't get it to work, you can try running the program by setting
5285the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5286\&\f(CW\*(C`select\*(C'\fR backends.
5287.SS "\s-1AIX POLL BUG\s0"
5288.IX Subsection "AIX POLL BUG"
5289\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5290this by trying to avoid the poll backend altogether (i.e. it's not even
5291compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5292with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5293.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5294.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5295\fIGeneral issues\fR
5296.IX Subsection "General issues"
5297.PP
5298Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5299requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5300model. Libev still offers limited functionality on this platform in
5301the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5302descriptors. This only applies when using Win32 natively, not when using
5303e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5304as every compiler comes with a slightly differently broken/incompatible
5305environment.
5306.PP
5307Lifting these limitations would basically require the full
5308re-implementation of the I/O system. If you are into this kind of thing,
5309then note that glib does exactly that for you in a very portable way (note
5310also that glib is the slowest event library known to man).
5311.PP
5312There is no supported compilation method available on windows except
5313embedding it into other applications.
5314.PP
5315Sensible signal handling is officially unsupported by Microsoft \- libev
5316tries its best, but under most conditions, signals will simply not work.
5317.PP
5318Not a libev limitation but worth mentioning: windows apparently doesn't
5319accept large writes: instead of resulting in a partial write, windows will
5320either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5321so make sure you only write small amounts into your sockets (less than a
5322megabyte seems safe, but this apparently depends on the amount of memory
5323available).
5324.PP
5325Due to the many, low, and arbitrary limits on the win32 platform and
5326the abysmal performance of winsockets, using a large number of sockets
5327is not recommended (and not reasonable). If your program needs to use
5328more than a hundred or so sockets, then likely it needs to use a totally
5329different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5330notification model, which cannot be implemented efficiently on windows
5331(due to Microsoft monopoly games).
5332.PP
5333A typical way to use libev under windows is to embed it (see the embedding
5334section for details) and use the following \fIevwrap.h\fR header file instead
5335of \fIev.h\fR:
5336.PP
5337.Vb 2
5338\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5339\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5340\&
5341\& #include "ev.h"
5342.Ve
5343.PP
5344And compile the following \fIevwrap.c\fR file into your project (make sure
5345you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5346.PP
5347.Vb 2
5348\& #include "evwrap.h"
5349\& #include "ev.c"
5350.Ve
5351.PP
5352\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5353.IX Subsection "The winsocket select function"
5354.PP
5355The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5356requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5357also extremely buggy). This makes select very inefficient, and also
5358requires a mapping from file descriptors to socket handles (the Microsoft
5359C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5360discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5361\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5362.PP
5363The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5364libraries and raw winsocket select is:
5365.PP
5366.Vb 2
5367\& #define EV_USE_SELECT 1
5368\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5369.Ve
5370.PP
5371Note that winsockets handling of fd sets is O(n), so you can easily get a
5372complexity in the O(nX) range when using win32.
5373.PP
5374\fILimited number of file descriptors\fR
5375.IX Subsection "Limited number of file descriptors"
5376.PP
5377Windows has numerous arbitrary (and low) limits on things.
5378.PP
5379Early versions of winsocket's select only supported waiting for a maximum
5380of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5381can only wait for \f(CW64\fR things at the same time internally; Microsoft
5382recommends spawning a chain of threads and wait for 63 handles and the
5383previous thread in each. Sounds great!).
5384.PP
5385Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5386to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5387call (which might be in libev or elsewhere, for example, perl and many
5388other interpreters do their own select emulation on windows).
5389.PP
5390Another limit is the number of file descriptors in the Microsoft runtime
5391libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5392fetish or something like this inside Microsoft). You can increase this
5393by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5394(another arbitrary limit), but is broken in many versions of the Microsoft
5395runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5396(depending on windows version and/or the phase of the moon). To get more,
5397you need to wrap all I/O functions and provide your own fd management, but
5398the cost of calling select (O(nX)) will likely make this unworkable.
5399.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5400.IX Subsection "PORTABILITY REQUIREMENTS"
5401In addition to a working ISO-C implementation and of course the
5402backend-specific APIs, libev relies on a few additional extensions:
5403.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5404.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5405.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5406Libev assumes not only that all watcher pointers have the same internal
5407structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5408assumes that the same (machine) code can be used to call any watcher
5409callback: The watcher callbacks have different type signatures, but libev
5410calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5411.IP "pointer accesses must be thread-atomic" 4
5412.IX Item "pointer accesses must be thread-atomic"
5413Accessing a pointer value must be atomic, it must both be readable and
5414writable in one piece \- this is the case on all current architectures.
5415.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5416.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5417.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5418The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5419\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5420threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5421believed to be sufficiently portable.
5422.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5423.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5424.IX Item "sigprocmask must work in a threaded environment"
5425Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5426allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5427pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5428thread\*(R" or will block signals process-wide, both behaviours would
5429be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5430\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5431.Sp
5432The most portable way to handle signals is to block signals in all threads
5433except the initial one, and run the signal handling loop in the initial
5434thread as well.
5435.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5436.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5437.IX Item "long must be large enough for common memory allocation sizes"
5438To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5439instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5440systems (Microsoft...) this might be unexpectedly low, but is still at
5441least 31 bits everywhere, which is enough for hundreds of millions of
5442watchers.
5443.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5444.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5445.IX Item "double must hold a time value in seconds with enough accuracy"
5446The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5447have at least 51 bits of mantissa (and 9 bits of exponent), which is
5448good enough for at least into the year 4000 with millisecond accuracy
5449(the design goal for libev). This requirement is overfulfilled by
5450implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5451.Sp
5452With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5453year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5454is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5455something like that, just kidding).
5456.PP
5457If you know of other additional requirements drop me a note.
2699.SH "COMPLEXITIES" 5458.SH "ALGORITHMIC COMPLEXITIES"
2700.IX Header "COMPLEXITIES" 5459.IX Header "ALGORITHMIC COMPLEXITIES"
2701In this section the complexities of (many of) the algorithms used inside 5460In this section the complexities of (many of) the algorithms used inside
2702libev will be explained. For complexity discussions about backends see the 5461libev will be documented. For complexity discussions about backends see
2703documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5462the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2704.Sp 5463.PP
2705All of the following are about amortised time: If an array needs to be 5464All of the following are about amortised time: If an array needs to be
2706extended, libev needs to realloc and move the whole array, but this 5465extended, libev needs to realloc and move the whole array, but this
2707happens asymptotically never with higher number of elements, so O(1) might 5466happens asymptotically rarer with higher number of elements, so O(1) might
2708mean it might do a lengthy realloc operation in rare cases, but on average 5467mean that libev does a lengthy realloc operation in rare cases, but on
2709it is much faster and asymptotically approaches constant time. 5468average it is much faster and asymptotically approaches constant time.
2710.RS 4
2711.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5469.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2712.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5470.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2713This means that, when you have a watcher that triggers in one hour and 5471This means that, when you have a watcher that triggers in one hour and
2714there are 100 watchers that would trigger before that then inserting will 5472there are 100 watchers that would trigger before that, then inserting will
2715have to skip those 100 watchers. 5473have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2716.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4 5474.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2717.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 5475.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2718That means that for changing a timer costs less than removing/adding them 5476That means that changing a timer costs less than removing/adding them,
2719as only the relative motion in the event queue has to be paid for. 5477as only the relative motion in the event queue has to be paid for.
2720.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 5478.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
2721.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 5479.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
2722These just add the watcher into an array or at the head of a list. 5480These just add the watcher into an array or at the head of a list.
5481.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
2723=item Stopping check/prepare/idle watchers: O(1) 5482.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5483.PD 0
2724.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5484.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2725.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5485.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5486.PD
2726These watchers are stored in lists then need to be walked to find the 5487These watchers are stored in lists, so they need to be walked to find the
2727correct watcher to remove. The lists are usually short (you don't usually 5488correct watcher to remove. The lists are usually short (you don't usually
2728have many watchers waiting for the same fd or signal). 5489have many watchers waiting for the same fd or signal: one is typical, two
5490is rare).
2729.IP "Finding the next timer per loop iteration: O(1)" 4 5491.IP "Finding the next timer in each loop iteration: O(1)" 4
2730.IX Item "Finding the next timer per loop iteration: O(1)" 5492.IX Item "Finding the next timer in each loop iteration: O(1)"
2731.PD 0 5493By virtue of using a binary or 4\-heap, the next timer is always found at a
5494fixed position in the storage array.
2732.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5495.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2733.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5496.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2734.PD
2735A change means an I/O watcher gets started or stopped, which requires 5497A change means an I/O watcher gets started or stopped, which requires
2736libev to recalculate its status (and possibly tell the kernel). 5498libev to recalculate its status (and possibly tell the kernel, depending
2737.IP "Activating one watcher: O(1)" 4 5499on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2738.IX Item "Activating one watcher: O(1)" 5500.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5501.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2739.PD 0 5502.PD 0
2740.IP "Priority handling: O(number_of_priorities)" 4 5503.IP "Priority handling: O(number_of_priorities)" 4
2741.IX Item "Priority handling: O(number_of_priorities)" 5504.IX Item "Priority handling: O(number_of_priorities)"
2742.PD 5505.PD
2743Priorities are implemented by allocating some space for each 5506Priorities are implemented by allocating some space for each
2744priority. When doing priority-based operations, libev usually has to 5507priority. When doing priority-based operations, libev usually has to
2745linearly search all the priorities. 5508linearly search all the priorities, but starting/stopping and activating
2746.RE 5509watchers becomes O(1) with respect to priority handling.
2747.RS 4 5510.IP "Sending an ev_async: O(1)" 4
5511.IX Item "Sending an ev_async: O(1)"
5512.PD 0
5513.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5514.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5515.IP "Processing signals: O(max_signal_number)" 4
5516.IX Item "Processing signals: O(max_signal_number)"
5517.PD
5518Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5519calls in the current loop iteration and the loop is currently
5520blocked. Checking for async and signal events involves iterating over all
5521running async watchers or all signal numbers.
5522.SH "PORTING FROM LIBEV 3.X TO 4.X"
5523.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5524The major version 4 introduced some incompatible changes to the \s-1API.\s0
5525.PP
5526At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5527for all changes, so most programs should still compile. The compatibility
5528layer might be removed in later versions of libev, so better update to the
5529new \s-1API\s0 early than late.
5530.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5531.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5532.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5533The backward compatibility mechanism can be controlled by
5534\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5535section.
5536.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5537.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5538.IX Item "ev_default_destroy and ev_default_fork have been removed"
5539These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5540.Sp
5541.Vb 2
5542\& ev_loop_destroy (EV_DEFAULT_UC);
5543\& ev_loop_fork (EV_DEFAULT);
5544.Ve
5545.IP "function/symbol renames" 4
5546.IX Item "function/symbol renames"
5547A number of functions and symbols have been renamed:
5548.Sp
5549.Vb 3
5550\& ev_loop => ev_run
5551\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5552\& EVLOOP_ONESHOT => EVRUN_ONCE
5553\&
5554\& ev_unloop => ev_break
5555\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5556\& EVUNLOOP_ONE => EVBREAK_ONE
5557\& EVUNLOOP_ALL => EVBREAK_ALL
5558\&
5559\& EV_TIMEOUT => EV_TIMER
5560\&
5561\& ev_loop_count => ev_iteration
5562\& ev_loop_depth => ev_depth
5563\& ev_loop_verify => ev_verify
5564.Ve
5565.Sp
5566Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5567\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5568associated constants have been renamed to not collide with the \f(CW\*(C`struct
5569ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5570as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5571\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5572typedef.
5573.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5574.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5575.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5576The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5577mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5578and work, but the library code will of course be larger.
5579.SH "GLOSSARY"
5580.IX Header "GLOSSARY"
5581.IP "active" 4
5582.IX Item "active"
5583A watcher is active as long as it has been started and not yet stopped.
5584See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5585.IP "application" 4
5586.IX Item "application"
5587In this document, an application is whatever is using libev.
5588.IP "backend" 4
5589.IX Item "backend"
5590The part of the code dealing with the operating system interfaces.
5591.IP "callback" 4
5592.IX Item "callback"
5593The address of a function that is called when some event has been
5594detected. Callbacks are being passed the event loop, the watcher that
5595received the event, and the actual event bitset.
5596.IP "callback/watcher invocation" 4
5597.IX Item "callback/watcher invocation"
5598The act of calling the callback associated with a watcher.
5599.IP "event" 4
5600.IX Item "event"
5601A change of state of some external event, such as data now being available
5602for reading on a file descriptor, time having passed or simply not having
5603any other events happening anymore.
5604.Sp
5605In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5606\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5607.IP "event library" 4
5608.IX Item "event library"
5609A software package implementing an event model and loop.
5610.IP "event loop" 4
5611.IX Item "event loop"
5612An entity that handles and processes external events and converts them
5613into callback invocations.
5614.IP "event model" 4
5615.IX Item "event model"
5616The model used to describe how an event loop handles and processes
5617watchers and events.
5618.IP "pending" 4
5619.IX Item "pending"
5620A watcher is pending as soon as the corresponding event has been
5621detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5622.IP "real time" 4
5623.IX Item "real time"
5624The physical time that is observed. It is apparently strictly monotonic :)
5625.IP "wall-clock time" 4
5626.IX Item "wall-clock time"
5627The time and date as shown on clocks. Unlike real time, it can actually
5628be wrong and jump forwards and backwards, e.g. when you adjust your
5629clock.
5630.IP "watcher" 4
5631.IX Item "watcher"
5632A data structure that describes interest in certain events. Watchers need
5633to be started (attached to an event loop) before they can receive events.
2748.SH "AUTHOR" 5634.SH "AUTHOR"
2749.IX Header "AUTHOR" 5635.IX Header "AUTHOR"
2750Marc Lehmann <libev@schmorp.de>. 5636Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5637Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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