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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title "EV 1" 126.IX Title "LIBEV 3"
132.TH EV 1 "2007-12-18" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2012-03-23" "libev-4.11" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "EXAMPLE PROGRAM" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "EXAMPLE PROGRAM" 140.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1
143\& #include <ev.h>
144.Ve
145.PP
146.Vb 2 141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
147\& ev_io stdin_watcher; 149\& ev_io stdin_watcher;
148\& ev_timer timeout_watcher; 150\& ev_timer timeout_watcher;
149.Ve 151\&
150.PP 152\& // all watcher callbacks have a similar signature
151.Vb 8
152\& /* called when data readable on stdin */ 153\& // this callback is called when data is readable on stdin
153\& static void 154\& static void
154\& stdin_cb (EV_P_ struct ev_io *w, int revents) 155\& stdin_cb (EV_P_ ev_io *w, int revents)
155\& { 156\& {
156\& /* puts ("stdin ready"); */ 157\& puts ("stdin ready");
157\& ev_io_stop (EV_A_ w); /* just a syntax example */ 158\& // for one\-shot events, one must manually stop the watcher
158\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
159\& } 164\& }
160.Ve 165\&
161.PP 166\& // another callback, this time for a time\-out
162.Vb 6
163\& static void 167\& static void
164\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 168\& timeout_cb (EV_P_ ev_timer *w, int revents)
165\& { 169\& {
166\& /* puts ("timeout"); */ 170\& puts ("timeout");
167\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
168\& } 173\& }
169.Ve 174\&
170.PP
171.Vb 4
172\& int 175\& int
173\& main (void) 176\& main (void)
174\& { 177\& {
175\& struct ev_loop *loop = ev_default_loop (0); 178\& // use the default event loop unless you have special needs
176.Ve 179\& struct ev_loop *loop = EV_DEFAULT;
177.PP 180\&
178.Vb 3
179\& /* initialise an io watcher, then start it */ 181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
180\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181\& ev_io_start (loop, &stdin_watcher); 184\& ev_io_start (loop, &stdin_watcher);
182.Ve 185\&
183.PP 186\& // initialise a timer watcher, then start it
184.Vb 3
185\& /* simple non-repeating 5.5 second timeout */ 187\& // simple non\-repeating 5.5 second timeout
186\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187\& ev_timer_start (loop, &timeout_watcher); 189\& ev_timer_start (loop, &timeout_watcher);
188.Ve 190\&
189.PP 191\& // now wait for events to arrive
190.Vb 2
191\& /* loop till timeout or data ready */
192\& ev_loop (loop, 0); 192\& ev_run (loop, 0);
193.Ve 193\&
194.PP 194\& // break was called, so exit
195.Vb 2
196\& return 0; 195\& return 0;
197\& } 196\& }
198.Ve 197.Ve
199.SH "DESCRIPTION" 198.SH "ABOUT THIS DOCUMENT"
200.IX Header "DESCRIPTION" 199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
201The newest version of this document is also available as a html-formatted 202The 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 203web page you might find easier to navigate when reading it for the first
203time: <http://cvs.schmorp.de/libev/ev.html>. 204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
204.PP 205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
205Libev is an event loop: you register interest in certain events (such as a 222Libev 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 223file descriptor being readable or a timeout occurring), and it will manage
207these event sources and provide your program with events. 224these event sources and provide your program with events.
208.PP 225.PP
209To do this, it must take more or less complete control over your process 226To 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 227(or thread) by executing the \fIevent loop\fR handler, and will then
211communicate events via a callback mechanism. 228communicate events via a callback mechanism.
212.PP 229.PP
213You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
214watchers\fR, which are relatively small C structures you initialise with the 231watchers\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 232details of the event, and then hand it over to libev by \fIstarting\fR the
216watcher. 233watcher.
217.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
218.IX Header "FEATURES" 235.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 236Libev 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 237BSD-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 238for 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 239(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 240inter-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 241timers (\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, 242(\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 243change 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 244loop 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). 245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
229.PP 247.PP
230It also is quite fast (see this 248It also is quite fast (see this
231benchmark comparing it to libevent 249benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
232for example). 250for example).
233.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
234.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
235Libev is very configurable. In this manual the default configuration will 253Libev is very configurable. In this manual the default (and most common)
236be described, which supports multiple event loops. For more info about 254configuration will be described, which supports multiple event loops. For
237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 255more info about various configuration options please have a look at
238this manual. If libev was configured without support for multiple event 256\&\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 257for 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. 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
241.SH "TIME REPRESENTATION" 259this argument.
260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
242.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
243Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (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 264somewhere 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 265ask). 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 266too. 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 267any calculations on it, you should treat it as some floating point value.
268.PP
249component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences 269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
250throughout libev. 270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
251.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
252.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
253These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
254library in any way. 293library in any way.
255.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
256.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
257Returns the current time as libev would use it. Please note that the 296Returns 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 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
259you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked
303until either it is interrupted or the given time interval has
304passed (approximately \- it might return a bit earlier even if not
305interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
306.Sp
307Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
308.Sp
309The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
310with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
260.IP "int ev_version_major ()" 4 311.IP "int ev_version_major ()" 4
261.IX Item "int ev_version_major ()" 312.IX Item "int ev_version_major ()"
262.PD 0 313.PD 0
263.IP "int ev_version_minor ()" 4 314.IP "int ev_version_minor ()" 4
264.IX Item "int ev_version_minor ()" 315.IX Item "int ev_version_minor ()"
… …
276as this indicates an incompatible change. Minor versions are usually 327as this indicates an incompatible change. Minor versions are usually
277compatible to older versions, so a larger minor version alone is usually 328compatible to older versions, so a larger minor version alone is usually
278not a problem. 329not a problem.
279.Sp 330.Sp
280Example: Make sure we haven't accidentally been linked against the wrong 331Example: Make sure we haven't accidentally been linked against the wrong
281version. 332version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333such as \s-1LFS\s0 or reentrancy).
282.Sp 334.Sp
283.Vb 3 335.Vb 3
284\& assert (("libev version mismatch", 336\& assert (("libev version mismatch",
285\& ev_version_major () == EV_VERSION_MAJOR 337\& ev_version_major () == EV_VERSION_MAJOR
286\& && ev_version_minor () >= EV_VERSION_MINOR)); 338\& && ev_version_minor () >= EV_VERSION_MINOR));
287.Ve 339.Ve
288.IP "unsigned int ev_supported_backends ()" 4 340.IP "unsigned int ev_supported_backends ()" 4
289.IX Item "unsigned int ev_supported_backends ()" 341.IX Item "unsigned int ev_supported_backends ()"
290Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 342Return 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 343value) compiled into this binary of libev (independent of their
… …
294.Sp 346.Sp
295Example: make sure we have the epoll method, because yeah this is cool and 347Example: 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 348a must have and can we have a torrent of it please!!!11
297.Sp 349.Sp
298.Vb 2 350.Vb 2
299\& assert (("sorry, no epoll, no sex", 351\& assert (("sorry, no epoll, no sex",
300\& ev_supported_backends () & EVBACKEND_EPOLL)); 352\& ev_supported_backends () & EVBACKEND_EPOLL));
301.Ve 353.Ve
302.IP "unsigned int ev_recommended_backends ()" 4 354.IP "unsigned int ev_recommended_backends ()" 4
303.IX Item "unsigned int ev_recommended_backends ()" 355.IX Item "unsigned int ev_recommended_backends ()"
304Return the set of all backends compiled into this binary of libev and also 356Return the set of all backends compiled into this binary of libev and
305recommended for this platform. This set is often smaller than the one 357also recommended for this platform, meaning it will work for most file
358descriptor 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 359\&\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 360and 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 361you know what you are doing). This is the set of backends that libev will
309libev will probe for if you specify no backends explicitly. 362probe for if you specify no backends explicitly.
310.IP "unsigned int ev_embeddable_backends ()" 4 363.IP "unsigned int ev_embeddable_backends ()" 4
311.IX Item "unsigned int ev_embeddable_backends ()" 364.IX Item "unsigned int ev_embeddable_backends ()"
312Returns the set of backends that are embeddable in other event loops. This 365Returns the set of backends that are embeddable in other event loops. This
313is the theoretical, all\-platform, value. To find which backends 366value is platform-specific but can include backends not available on the
314might be supported on the current system, you would need to look at 367current system. To find which embeddable backends might be supported on
315\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 368the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
316recommended ones. 369& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
317.Sp 370.Sp
318See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 371See 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))" 4 372.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
320.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 373.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
321Sets the allocation function to use (the prototype is similar \- the 374Sets the allocation function to use (the prototype is similar \- the
322semantics is identical \- to the realloc C function). It is used to 375semantics 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 376used to allocate and free memory (no surprises here). If it returns zero
324memory needs to be allocated, the library might abort or take some 377when 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 378or take some potentially destructive action.
326function. 379.Sp
380Since some systems (at least OpenBSD and Darwin) fail to implement
381correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
382\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
327.Sp 383.Sp
328You could override this function in high-availability programs to, say, 384You could override this function in high-availability programs to, say,
329free some memory if it cannot allocate memory, to use a special allocator, 385free 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. 386or even to sleep a while and retry until some memory is available.
331.Sp 387.Sp
332Example: Replace the libev allocator with one that waits a bit and then 388Example: Replace the libev allocator with one that waits a bit and then
333retries). 389retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
334.Sp 390.Sp
335.Vb 6 391.Vb 6
336\& static void * 392\& static void *
337\& persistent_realloc (void *ptr, size_t size) 393\& persistent_realloc (void *ptr, size_t size)
338\& { 394\& {
339\& for (;;) 395\& for (;;)
340\& { 396\& {
341\& void *newptr = realloc (ptr, size); 397\& void *newptr = realloc (ptr, size);
342.Ve 398\&
343.Sp
344.Vb 2
345\& if (newptr) 399\& if (newptr)
346\& return newptr; 400\& return newptr;
347.Ve 401\&
348.Sp
349.Vb 3
350\& sleep (60); 402\& sleep (60);
351\& } 403\& }
352\& } 404\& }
353.Ve 405\&
354.Sp
355.Vb 2
356\& ... 406\& ...
357\& ev_set_allocator (persistent_realloc); 407\& ev_set_allocator (persistent_realloc);
358.Ve 408.Ve
359.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 409.IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
360.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 410.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
361Set the callback function to call on a retryable syscall error (such 411Set the callback function to call on a retryable system call error (such
362as failed select, poll, epoll_wait). The message is a printable string 412as failed select, poll, epoll_wait). The message is a printable string
363indicating the system call or subsystem causing the problem. If this 413indicating the system call or subsystem causing the problem. If this
364callback is set, then libev will expect it to remedy the sitution, no 414callback is set, then libev will expect it to remedy the situation, no
365matter what, when it returns. That is, libev will generally retry the 415matter what, when it returns. That is, libev will generally retry the
366requested operation, or, if the condition doesn't go away, do bad stuff 416requested operation, or, if the condition doesn't go away, do bad stuff
367(such as abort). 417(such as abort).
368.Sp 418.Sp
369Example: This is basically the same thing that libev does internally, too. 419Example: This is basically the same thing that libev does internally, too.
… …
373\& fatal_error (const char *msg) 423\& fatal_error (const char *msg)
374\& { 424\& {
375\& perror (msg); 425\& perror (msg);
376\& abort (); 426\& abort ();
377\& } 427\& }
378.Ve 428\&
379.Sp
380.Vb 2
381\& ... 429\& ...
382\& ev_set_syserr_cb (fatal_error); 430\& ev_set_syserr_cb (fatal_error);
383.Ve 431.Ve
432.IP "ev_feed_signal (int signum)" 4
433.IX Item "ev_feed_signal (int signum)"
434This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
435safe to call this function at any time, from any context, including signal
436handlers or random threads.
437.Sp
438Its main use is to customise signal handling in your process, especially
439in the presence of threads. For example, you could block signals
440by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
441creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
442mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
443\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
384.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 444.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
385.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 445.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 446An 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 447\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
388events, and dynamically created loops which do not. 448libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
389.PP 449.PP
390If you use threads, a common model is to run the default event loop 450The 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 451supports child process events, and dynamically created event loops which
392create, you also create another event loop. Libev itself does no locking 452do 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)" 4 453.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
397.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 454.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
398This will initialise the default event loop if it hasn't been initialised 455This 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 456normally 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 457the \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). 458\&\f(CW\*(C`ev_loop_new\*(C'\fR.
459.Sp
460If the default loop is already initialised then this function simply
461returns it (and ignores the flags. If that is troubling you, check
462\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
463flags, which should almost always be \f(CW0\fR, unless the caller is also the
464one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
402.Sp 465.Sp
403If you don't know what event loop to use, use the one returned from this 466If you don't know what event loop to use, use the one returned from this
404function. 467function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
468.Sp
469Note that this function is \fInot\fR thread-safe, so if you want to use it
470from multiple threads, you have to employ some kind of mutex (note also
471that this case is unlikely, as loops cannot be shared easily between
472threads anyway).
473.Sp
474The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
475and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
476a problem for your application you can either create a dynamic loop with
477\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
478\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
479.Sp
480Example: This is the most typical usage.
481.Sp
482.Vb 2
483\& if (!ev_default_loop (0))
484\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
485.Ve
486.Sp
487Example: Restrict libev to the select and poll backends, and do not allow
488environment settings to be taken into account:
489.Sp
490.Vb 1
491\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492.Ve
493.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
494.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
495This will create and initialise a new event loop object. If the loop
496could not be initialised, returns false.
497.Sp
498This function is thread-safe, and one common way to use libev with
499threads is indeed to create one loop per thread, and using the default
500loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
405.Sp 501.Sp
406The flags argument can be used to specify special behaviour or specific 502The 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). 503backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
408.Sp 504.Sp
409The following flags are supported: 505The following flags are supported:
… …
414The default flags value. Use this if you have no clue (it's the right 510The default flags value. Use this if you have no clue (it's the right
415thing, believe me). 511thing, believe me).
416.ie n .IP """EVFLAG_NOENV""" 4 512.ie n .IP """EVFLAG_NOENV""" 4
417.el .IP "\f(CWEVFLAG_NOENV\fR" 4 513.el .IP "\f(CWEVFLAG_NOENV\fR" 4
418.IX Item "EVFLAG_NOENV" 514.IX Item "EVFLAG_NOENV"
419If this flag bit is ored into the flag value (or the program runs setuid 515If 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 516or 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 517\&\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 518override 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 519useful to try out specific backends to test their performance, or to work
424around bugs. 520around bugs.
425.ie n .IP """EVFLAG_FORKCHECK""" 4 521.ie n .IP """EVFLAG_FORKCHECK""" 4
426.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 522.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
427.IX Item "EVFLAG_FORKCHECK" 523.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 524Instead 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 525make libev check for a fork in each iteration by enabling this flag.
430enabling this flag.
431.Sp 526.Sp
432This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, 527This 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 528and 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 529iterations 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 530GNU/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 531without 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). 532\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
438.Sp 533.Sp
439The big advantage of this flag is that you can forget about fork (and 534The 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 535forget about forgetting to tell libev about forking) when you use this
441flag. 536flag.
442.Sp 537.Sp
443This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR 538This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
444environment variable. 539environment variable.
540.ie n .IP """EVFLAG_NOINOTIFY""" 4
541.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
542.IX Item "EVFLAG_NOINOTIFY"
543When this flag is specified, then libev will not attempt to use the
544\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
545testing, this flag can be useful to conserve inotify file descriptors, as
546otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
547.ie n .IP """EVFLAG_SIGNALFD""" 4
548.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
549.IX Item "EVFLAG_SIGNALFD"
550When this flag is specified, then libev will attempt to use the
551\&\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
552delivers signals synchronously, which makes it both faster and might make
553it possible to get the queued signal data. It can also simplify signal
554handling with threads, as long as you properly block signals in your
555threads that are not interested in handling them.
556.Sp
557Signalfd will not be used by default as this changes your signal mask, and
558there are a lot of shoddy libraries and programs (glib's threadpool for
559example) that can't properly initialise their signal masks.
560.ie n .IP """EVFLAG_NOSIGMASK""" 4
561.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
562.IX Item "EVFLAG_NOSIGMASK"
563When this flag is specified, then libev will avoid to modify the signal
564mask. Specifically, this means you have to make sure signals are unblocked
565when you want to receive them.
566.Sp
567This behaviour is useful when you want to do your own signal handling, or
568want to handle signals only in specific threads and want to avoid libev
569unblocking the signals.
570.Sp
571It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
572\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
573.Sp
574This flag's behaviour will become the default in future versions of libev.
445.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 575.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
446.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 576.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
447.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 577.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
448This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 578This 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, 579libev 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 580but 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 581using this backend. It doesn't scale too well (O(highest_fd)), but its
452the fastest backend for a low number of fds. 582usually the fastest backend for a low number of (low-numbered :) fds.
583.Sp
584To get good performance out of this backend you need a high amount of
585parallelism (most of the file descriptors should be busy). If you are
586writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
587connections as possible during one iteration. You might also want to have
588a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
589readiness notifications you get per iteration.
590.Sp
591This 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
592\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
593\&\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)" 4 594.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)" 4 595.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)" 596.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 597And 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 598than select, but handles sparse fds better and has no artificial
458number of fds you can use (except it will slow down considerably with a 599limit 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). 600considerably with a lot of inactive fds). It scales similarly to select,
601i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
602performance tips.
603.Sp
604This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
605\&\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)" 4 606.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
461.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 607.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
462.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 608.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
609Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
610kernels).
611.Sp
463For few fds, this backend is a bit little slower than poll and select, 612For 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 613it 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 614O(total_fds) where total_fds is the total number of fds (or the highest
466either O(1) or O(active_fds). 615fd), epoll scales either O(1) or O(active_fds).
467.Sp 616.Sp
617The epoll mechanism deserves honorable mention as the most misdesigned
618of the more advanced event mechanisms: mere annoyances include silently
619dropping file descriptors, requiring a system call per change per file
620descriptor (and unnecessary guessing of parameters), problems with dup,
621returning before the timeout value, resulting in additional iterations
622(and only giving 5ms accuracy while select on the same platform gives
6230.1ms) and so on. The biggest issue is fork races, however \- if a program
624forks then \fIboth\fR parent and child process have to recreate the epoll
625set, which can take considerable time (one syscall per file descriptor)
626and is of course hard to detect.
627.Sp
628Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
629but of course \fIdoesn't\fR, and epoll just loves to report events for
630totally \fIdifferent\fR file descriptors (even already closed ones, so
631one cannot even remove them from the set) than registered in the set
632(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
633notifications by employing an additional generation counter and comparing
634that against the events to filter out spurious ones, recreating the set
635when required. Epoll also erroneously rounds down timeouts, but gives you
636no way to know when and by how much, so sometimes you have to busy-wait
637because epoll returns immediately despite a nonzero timeout. And last
638not least, it also refuses to work with some file descriptors which work
639perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
640.Sp
641Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
642cobbled together in a hurry, no thought to design or interaction with
643others. Oh, the pain, will it ever stop...
644.Sp
468While stopping and starting an I/O watcher in the same iteration will 645While stopping, setting and starting an I/O watcher in the same iteration
469result in some caching, there is still a syscall per such incident 646will 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 647incident (because the same \fIfile descriptor\fR could point to a different
471best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 648\&\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. 649file descriptors might not work very well if you register events for both
650file descriptors.
473.Sp 651.Sp
474Please note that epoll sometimes generates spurious notifications, so you 652Best 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 653watchers for a file descriptor until it has been closed, if possible,
476(or space) is available. 654i.e. keep at least one watcher active per fd at all times. Stopping and
655starting a watcher (without re-setting it) also usually doesn't cause
656extra overhead. A fork can both result in spurious notifications as well
657as in libev having to destroy and recreate the epoll object, which can
658take considerable time and thus should be avoided.
659.Sp
660All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
661faster than epoll for maybe up to a hundred file descriptors, depending on
662the usage. So sad.
663.Sp
664While nominally embeddable in other event loops, this feature is broken in
665all kernel versions tested so far.
666.Sp
667This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
668\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
477.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 669.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)" 4 670.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
479.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 671.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
480Kqueue deserves special mention, as at the time of this writing, it 672Kqueue deserves special mention, as at the time of this writing, it
481was broken on all BSDs except NetBSD (usually it doesn't work with 673was broken on all BSDs except NetBSD (usually it doesn't work reliably
482anything but sockets and pipes, except on Darwin, where of course its 674with anything but sockets and pipes, except on Darwin, where of course
483completely useless). For this reason its not being \*(L"autodetected\*(R" 675it's completely useless). Unlike epoll, however, whose brokenness
676is by design, these kqueue bugs can (and eventually will) be fixed
677without \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 678\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
485\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 679\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
680system like NetBSD.
681.Sp
682You still can embed kqueue into a normal poll or select backend and use it
683only for sockets (after having made sure that sockets work with kqueue on
684the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
486.Sp 685.Sp
487It scales in the same way as the epoll backend, but the interface to the 686It 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 687kernel is more efficient (which says nothing about its actual speed, of
489course). While starting and stopping an I/O watcher does not cause an 688course). 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 689cause 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. 690two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
691sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
692cases
693.Sp
694This backend usually performs well under most conditions.
695.Sp
696While nominally embeddable in other event loops, this doesn't work
697everywhere, so you might need to test for this. And since it is broken
698almost everywhere, you should only use it when you have a lot of sockets
699(for which it usually works), by embedding it into another event loop
700(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
701also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
702.Sp
703This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
704\&\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
705\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
492.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 706.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
493.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 707.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
494.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 708.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
495This is not implemented yet (and might never be). 709This is not implemented yet (and might never be, unless you send me an
710implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
711and is not embeddable, which would limit the usefulness of this backend
712immensely.
496.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 713.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
497.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 714.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
498.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 715.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
499This uses the Solaris 10 port mechanism. As with everything on Solaris, 716This 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)). 717it's really slow, but it still scales very well (O(active_fds)).
501.Sp 718.Sp
502Please note that solaris ports can result in a lot of spurious 719While 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 720file descriptor per loop iteration. For small and medium numbers of file
504blocking when no data (or space) is available. 721descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
722might perform better.
723.Sp
724On the positive side, this backend actually performed fully to
725specification in all tests and is fully embeddable, which is a rare feat
726among the OS-specific backends (I vastly prefer correctness over speed
727hacks).
728.Sp
729On the negative side, the interface is \fIbizarre\fR \- so bizarre that
730even sun itself gets it wrong in their code examples: The event polling
731function sometimes returns events to the caller even though an error
732occurred, but with no indication whether it has done so or not (yes, it's
733even documented that way) \- deadly for edge-triggered interfaces where you
734absolutely have to know whether an event occurred or not because you have
735to re-arm the watcher.
736.Sp
737Fortunately libev seems to be able to work around these idiocies.
738.Sp
739This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
740\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
505.ie n .IP """EVBACKEND_ALL""" 4 741.ie n .IP """EVBACKEND_ALL""" 4
506.el .IP "\f(CWEVBACKEND_ALL\fR" 4 742.el .IP "\f(CWEVBACKEND_ALL\fR" 4
507.IX Item "EVBACKEND_ALL" 743.IX Item "EVBACKEND_ALL"
508Try all backends (even potentially broken ones that wouldn't be tried 744Try 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 745with \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. 746\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
747.Sp
748It is definitely not recommended to use this flag, use whatever
749\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
750at all.
751.ie n .IP """EVBACKEND_MASK""" 4
752.el .IP "\f(CWEVBACKEND_MASK\fR" 4
753.IX Item "EVBACKEND_MASK"
754Not a backend at all, but a mask to select all backend bits from a
755\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
756value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
511.RE 757.RE
512.RS 4 758.RS 4
513.Sp 759.Sp
514If one or more of these are ored into the flags value, then only these 760If 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 761then only these backends will be tried (in the reverse order as listed
516specified, most compiled-in backend will be tried, usually in reverse 762here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
517order of their flag values :) 763()\*(C'\fR will be tried.
518.Sp 764.Sp
519The most typical usage is like this: 765Example: Try to create a event loop that uses epoll and nothing else.
520.Sp 766.Sp
521.Vb 2 767.Vb 3
522\& if (!ev_default_loop (0)) 768\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
523\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 769\& if (!epoller)
770\& fatal ("no epoll found here, maybe it hides under your chair");
524.Ve 771.Ve
525.Sp 772.Sp
526Restrict libev to the select and poll backends, and do not allow 773Example: Use whatever libev has to offer, but make sure that kqueue is
527environment settings to be taken into account: 774used if available.
528.Sp 775.Sp
529.Vb 1 776.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); 777\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
539.Ve 778.Ve
540.RE 779.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 ()" 4 780.IP "ev_loop_destroy (loop)" 4
556.IX Item "ev_default_destroy ()" 781.IX Item "ev_loop_destroy (loop)"
557Destroys the default loop again (frees all memory and kernel state 782Destroys an event loop object (frees all memory and kernel state
558etc.). None of the active event watchers will be stopped in the normal 783etc.). 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 784sense, 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 785responsibility to either stop all watchers cleanly yourself \fIbefore\fR
561calling this function, or cope with the fact afterwards (which is usually 786calling 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 787the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
563for example). 788for example).
564.Sp 789.Sp
565Not that certain global state, such as signal state, will not be freed by 790Note that certain global state, such as signal state (and installed signal
566this function, and related watchers (such as signal and child watchers) 791handlers), will not be freed by this function, and related watchers (such
567would need to be stopped manually. 792as signal and child watchers) would need to be stopped manually.
568.Sp 793.Sp
569In general it is not advisable to call this function except in the 794This function is normally used on loop objects allocated by
570rare occasion where you really need to free e.g. the signal handling 795\&\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 796\&\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 797.Sp
584You \fImust\fR call this function in the child process after forking if and 798Note 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 799except in the rare occasion where you really need to free its resources.
586fork+exec, you don't have to call it. 800If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
587.Sp 801and \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)" 4 802.IP "ev_loop_fork (loop)" 4
600.IX Item "ev_loop_fork (loop)" 803.IX Item "ev_loop_fork (loop)"
601Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 804This 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 805reinitialise the kernel state for backends that have one. Despite the
603after fork, and how you do this is entirely your own problem. 806name, you can call it anytime, but it makes most sense after forking, in
807the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
808child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
809.Sp
810Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
811a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
812because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
813during fork.
814.Sp
815On the other hand, you only need to call this function in the child
816process if and only if you want to use the event loop in the child. If
817you just fork+exec or create a new loop in the child, you don't have to
818call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
819difference, but libev will usually detect this case on its own and do a
820costly reset of the backend).
821.Sp
822The function itself is quite fast and it's usually not a problem to call
823it just in case after a fork.
824.Sp
825Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
826using pthreads.
827.Sp
828.Vb 5
829\& static void
830\& post_fork_child (void)
831\& {
832\& ev_loop_fork (EV_DEFAULT);
833\& }
834\&
835\& ...
836\& pthread_atfork (0, 0, post_fork_child);
837.Ve
838.IP "int ev_is_default_loop (loop)" 4
839.IX Item "int ev_is_default_loop (loop)"
840Returns true when the given loop is, in fact, the default loop, and false
841otherwise.
604.IP "unsigned int ev_loop_count (loop)" 4 842.IP "unsigned int ev_iteration (loop)" 4
605.IX Item "unsigned int ev_loop_count (loop)" 843.IX Item "unsigned int ev_iteration (loop)"
606Returns the count of loop iterations for the loop, which is identical to 844Returns 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 845to the number of times libev did poll for new events. It starts at \f(CW0\fR
608happily wraps around with enough iterations. 846and happily wraps around with enough iterations.
609.Sp 847.Sp
610This value can sometimes be useful as a generation counter of sorts (it 848This 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 849\&\*(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. 850\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
851prepare and check phases.
852.IP "unsigned int ev_depth (loop)" 4
853.IX Item "unsigned int ev_depth (loop)"
854Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
855times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
856.Sp
857Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
858\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
859in which case it is higher.
860.Sp
861Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
862throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
863as a hint to avoid such ungentleman-like behaviour unless it's really
864convenient, in which case it is fully supported.
613.IP "unsigned int ev_backend (loop)" 4 865.IP "unsigned int ev_backend (loop)" 4
614.IX Item "unsigned int ev_backend (loop)" 866.IX Item "unsigned int ev_backend (loop)"
615Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 867Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
616use. 868use.
617.IP "ev_tstamp ev_now (loop)" 4 869.IP "ev_tstamp ev_now (loop)" 4
618.IX Item "ev_tstamp ev_now (loop)" 870.IX Item "ev_tstamp ev_now (loop)"
619Returns the current \*(L"event loop time\*(R", which is the time the event loop 871Returns the current \*(L"event loop time\*(R", which is the time the event loop
620received events and started processing them. This timestamp does not 872received events and started processing them. This timestamp does not
621change as long as callbacks are being processed, and this is also the base 873change 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 874time used for relative timers. You can treat it as the timestamp of the
623event occuring (or more correctly, libev finding out about it). 875event occurring (or more correctly, libev finding out about it).
876.IP "ev_now_update (loop)" 4
877.IX Item "ev_now_update (loop)"
878Establishes the current time by querying the kernel, updating the time
879returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
880is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
881.Sp
882This function is rarely useful, but when some event callback runs for a
883very long time without entering the event loop, updating libev's idea of
884the current time is a good idea.
885.Sp
886See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
887.IP "ev_suspend (loop)" 4
888.IX Item "ev_suspend (loop)"
889.PD 0
890.IP "ev_resume (loop)" 4
891.IX Item "ev_resume (loop)"
892.PD
893These two functions suspend and resume an event loop, for use when the
894loop is not used for a while and timeouts should not be processed.
895.Sp
896A typical use case would be an interactive program such as a game: When
897the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
898would be best to handle timeouts as if no time had actually passed while
899the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
900in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
901\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
902.Sp
903Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
904between \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
905will be rescheduled (that is, they will lose any events that would have
906occurred while suspended).
907.Sp
908After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
909given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
910without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
911.Sp
912Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
913event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
624.IP "ev_loop (loop, int flags)" 4 914.IP "ev_run (loop, int flags)" 4
625.IX Item "ev_loop (loop, int flags)" 915.IX Item "ev_run (loop, int flags)"
626Finally, this is it, the event handler. This function usually is called 916Finally, this is it, the event handler. This function usually is called
627after you initialised all your watchers and you want to start handling 917after you have initialised all your watchers and you want to start
628events. 918handling events. It will ask the operating system for any new events, call
919the watcher callbacks, an then repeat the whole process indefinitely: This
920is why event loops are called \fIloops\fR.
629.Sp 921.Sp
630If the flags argument is specified as \f(CW0\fR, it will not return until 922If 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. 923until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
924called.
632.Sp 925.Sp
633Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 926Please 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 927relying on all watchers to be stopped when deciding when a program has
635finished (especially in interactive programs), but having a program that 928finished (especially in interactive programs), but having a program
636automatically loops as long as it has to and no longer by virtue of 929that automatically loops as long as it has to and no longer by virtue
637relying on its watchers stopping correctly is a thing of beauty. 930of relying on its watchers stopping correctly, that is truly a thing of
931beauty.
638.Sp 932.Sp
933This function is also \fImostly\fR exception-safe \- you can break out of
934a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
935exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
936will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
937.Sp
639A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 938A 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 939those 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. 940block your process in case there are no events and will return after one
941iteration of the loop. This is sometimes useful to poll and handle new
942events while doing lengthy calculations, to keep the program responsive.
642.Sp 943.Sp
643A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 944A 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 945necessary) and will handle those and any already outstanding ones. It
645your process until at least one new event arrives, and will return after 946will 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 947be an event internal to libev itself, so there is no guarantee that a
647external event in conjunction with something not expressible using other 948user-registered callback will be called), and will return after one
949iteration of the loop.
950.Sp
951This is useful if you are waiting for some external event in conjunction
952with 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 953own \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. 954usually a better approach for this kind of thing.
650.Sp 955.Sp
651Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 956Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
957understanding, not a guarantee that things will work exactly like this in
958future versions):
652.Sp 959.Sp
653.Vb 19 960.Vb 10
961\& \- Increment loop depth.
962\& \- Reset the ev_break status.
654\& - Before the first iteration, call any pending watchers. 963\& \- Before the first iteration, call any pending watchers.
655\& * If there are no active watchers (reference count is zero), return. 964\& LOOP:
656\& - Queue all prepare watchers and then call all outstanding watchers. 965\& \- If EVFLAG_FORKCHECK was used, check for a fork.
966\& \- If a fork was detected (by any means), queue and call all fork watchers.
967\& \- Queue and call all prepare watchers.
968\& \- If ev_break was called, goto FINISH.
657\& - If we have been forked, recreate the kernel state. 969\& \- If we have been forked, detach and recreate the kernel state
970\& as to not disturb the other process.
658\& - Update the kernel state with all outstanding changes. 971\& \- Update the kernel state with all outstanding changes.
659\& - Update the "event loop time". 972\& \- Update the "event loop time" (ev_now ()).
660\& - Calculate for how long to block. 973\& \- Calculate for how long to sleep or block, if at all
974\& (active idle watchers, EVRUN_NOWAIT or not having
975\& any active watchers at all will result in not sleeping).
976\& \- Sleep if the I/O and timer collect interval say so.
977\& \- Increment loop iteration counter.
661\& - Block the process, waiting for any events. 978\& \- Block the process, waiting for any events.
662\& - Queue all outstanding I/O (fd) events. 979\& \- Queue all outstanding I/O (fd) events.
663\& - Update the "event loop time" and do time jump handling. 980\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
664\& - Queue all outstanding timers. 981\& \- Queue all expired timers.
665\& - Queue all outstanding periodics. 982\& \- Queue all expired periodics.
666\& - If no events are pending now, queue all idle watchers. 983\& \- Queue all idle watchers with priority higher than that of pending events.
667\& - Queue all check watchers. 984\& \- Queue all check watchers.
668\& - Call all queued watchers in reverse order (i.e. check watchers first). 985\& \- 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 986\& Signals and child watchers are implemented as I/O watchers, and will
670\& be handled here by queueing them when their watcher gets executed. 987\& be handled here by queueing them when their watcher gets executed.
671\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 988\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
672\& were used, return, otherwise continue with step *. 989\& were used, or there are no active watchers, goto FINISH, otherwise
990\& continue with step LOOP.
991\& FINISH:
992\& \- Reset the ev_break status iff it was EVBREAK_ONE.
993\& \- Decrement the loop depth.
994\& \- Return.
673.Ve 995.Ve
674.Sp 996.Sp
675Example: Queue some jobs and then loop until no events are outsanding 997Example: Queue some jobs and then loop until no events are outstanding
676anymore. 998anymore.
677.Sp 999.Sp
678.Vb 4 1000.Vb 4
679\& ... queue jobs here, make sure they register event watchers as long 1001\& ... 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..) 1002\& ... as they still have work to do (even an idle watcher will do..)
681\& ev_loop (my_loop, 0); 1003\& ev_run (my_loop, 0);
682\& ... jobs done. yeah! 1004\& ... jobs done or somebody called break. yeah!
683.Ve 1005.Ve
684.IP "ev_unloop (loop, how)" 4 1006.IP "ev_break (loop, how)" 4
685.IX Item "ev_unloop (loop, how)" 1007.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 1008Can 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 1009has 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 1010\&\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. 1011\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1012.Sp
1013This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1014.Sp
1015It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1016which case it will have no effect.
690.IP "ev_ref (loop)" 4 1017.IP "ev_ref (loop)" 4
691.IX Item "ev_ref (loop)" 1018.IX Item "ev_ref (loop)"
692.PD 0 1019.PD 0
693.IP "ev_unref (loop)" 4 1020.IP "ev_unref (loop)" 4
694.IX Item "ev_unref (loop)" 1021.IX Item "ev_unref (loop)"
695.PD 1022.PD
696Ref/unref can be used to add or remove a reference count on the event 1023Ref/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 1024loop: 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 1025count 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 1026.Sp
700returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1027This is useful when you have a watcher that you never intend to
1028unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1029returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1030before stopping it.
1031.Sp
701example, libev itself uses this for its internal signal pipe: It is not 1032As 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 1033is 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 1034exiting 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 1035excellent way to do this for generic recurring timers or from within
705libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1036third-party libraries. Just remember to \fIunref after start\fR and \fIref
1037before stop\fR (but only if the watcher wasn't active before, or was active
1038before, respectively. Note also that libev might stop watchers itself
1039(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1040in the callback).
706.Sp 1041.Sp
707Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1042Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
708running when nothing else is active. 1043running when nothing else is active.
709.Sp 1044.Sp
710.Vb 4 1045.Vb 4
711\& struct ev_signal exitsig; 1046\& ev_signal exitsig;
712\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1047\& ev_signal_init (&exitsig, sig_cb, SIGINT);
713\& ev_signal_start (loop, &exitsig); 1048\& ev_signal_start (loop, &exitsig);
714\& evf_unref (loop); 1049\& ev_unref (loop);
715.Ve 1050.Ve
716.Sp 1051.Sp
717Example: For some weird reason, unregister the above signal handler again. 1052Example: For some weird reason, unregister the above signal handler again.
718.Sp 1053.Sp
719.Vb 2 1054.Vb 2
720\& ev_ref (loop); 1055\& ev_ref (loop);
721\& ev_signal_stop (loop, &exitsig); 1056\& ev_signal_stop (loop, &exitsig);
722.Ve 1057.Ve
1058.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1059.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1060.PD 0
1061.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1062.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1063.PD
1064These advanced functions influence the time that libev will spend waiting
1065for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1066will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1067latency.
1068.Sp
1069Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1070allows libev to delay invocation of I/O and timer/periodic callbacks
1071to increase efficiency of loop iterations (or to increase power-saving
1072opportunities).
1073.Sp
1074The idea is that sometimes your program runs just fast enough to handle
1075one (or very few) event(s) per loop iteration. While this makes the
1076program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1077events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1078overhead for the actual polling but can deliver many events at once.
1079.Sp
1080By setting a higher \fIio collect interval\fR you allow libev to spend more
1081time collecting I/O events, so you can handle more events per iteration,
1082at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1083\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1084introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1085sleep time ensures that libev will not poll for I/O events more often then
1086once per this interval, on average (as long as the host time resolution is
1087good enough).
1088.Sp
1089Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1090to spend more time collecting timeouts, at the expense of increased
1091latency/jitter/inexactness (the watcher callback will be called
1092later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1093value will not introduce any overhead in libev.
1094.Sp
1095Many (busy) programs can usually benefit by setting the I/O collect
1096interval to a value near \f(CW0.1\fR or so, which is often enough for
1097interactive servers (of course not for games), likewise for timeouts. It
1098usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1099as this approaches the timing granularity of most systems. Note that if
1100you do transactions with the outside world and you can't increase the
1101parallelity, then this setting will limit your transaction rate (if you
1102need to poll once per transaction and the I/O collect interval is 0.01,
1103then you can't do more than 100 transactions per second).
1104.Sp
1105Setting the \fItimeout collect interval\fR can improve the opportunity for
1106saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1107are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1108times the process sleeps and wakes up again. Another useful technique to
1109reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1110they fire on, say, one-second boundaries only.
1111.Sp
1112Example: we only need 0.1s timeout granularity, and we wish not to poll
1113more often than 100 times per second:
1114.Sp
1115.Vb 2
1116\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1117\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1118.Ve
1119.IP "ev_invoke_pending (loop)" 4
1120.IX Item "ev_invoke_pending (loop)"
1121This call will simply invoke all pending watchers while resetting their
1122pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1123but when overriding the invoke callback this call comes handy. This
1124function can be invoked from a watcher \- this can be useful for example
1125when you want to do some lengthy calculation and want to pass further
1126event handling to another thread (you still have to make sure only one
1127thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1128.IP "int ev_pending_count (loop)" 4
1129.IX Item "int ev_pending_count (loop)"
1130Returns the number of pending watchers \- zero indicates that no watchers
1131are pending.
1132.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1133.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1134This overrides the invoke pending functionality of the loop: Instead of
1135invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1136this callback instead. This is useful, for example, when you want to
1137invoke the actual watchers inside another context (another thread etc.).
1138.Sp
1139If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1140callback.
1141.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1142.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1143Sometimes you want to share the same loop between multiple threads. This
1144can be done relatively simply by putting mutex_lock/unlock calls around
1145each call to a libev function.
1146.Sp
1147However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1148to wait for it to return. One way around this is to wake up the event
1149loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1150\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1151.Sp
1152When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1153suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1154afterwards.
1155.Sp
1156Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1157\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1158.Sp
1159While event loop modifications are allowed between invocations of
1160\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1161modifications done will affect the event loop, i.e. adding watchers will
1162have no effect on the set of file descriptors being watched, or the time
1163waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1164to take note of any changes you made.
1165.Sp
1166In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1167invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1168.Sp
1169See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1170document.
1171.IP "ev_set_userdata (loop, void *data)" 4
1172.IX Item "ev_set_userdata (loop, void *data)"
1173.PD 0
1174.IP "void *ev_userdata (loop)" 4
1175.IX Item "void *ev_userdata (loop)"
1176.PD
1177Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1178\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1179\&\f(CW0\fR.
1180.Sp
1181These two functions can be used to associate arbitrary data with a loop,
1182and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1183\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1184any other purpose as well.
1185.IP "ev_verify (loop)" 4
1186.IX Item "ev_verify (loop)"
1187This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1188compiled in, which is the default for non-minimal builds. It tries to go
1189through all internal structures and checks them for validity. If anything
1190is found to be inconsistent, it will print an error message to standard
1191error and call \f(CW\*(C`abort ()\*(C'\fR.
1192.Sp
1193This can be used to catch bugs inside libev itself: under normal
1194circumstances, this function will never abort as of course libev keeps its
1195data structures consistent.
723.SH "ANATOMY OF A WATCHER" 1196.SH "ANATOMY OF A WATCHER"
724.IX Header "ANATOMY OF A WATCHER" 1197.IX Header "ANATOMY OF A WATCHER"
1198In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1199watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1200watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1201.PP
725A watcher is a structure that you create and register to record your 1202A 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 1203your 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: 1204to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1205for that:
728.PP 1206.PP
729.Vb 5 1207.Vb 5
730\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1208\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
731\& { 1209\& {
732\& ev_io_stop (w); 1210\& ev_io_stop (w);
733\& ev_unloop (loop, EVUNLOOP_ALL); 1211\& ev_break (loop, EVBREAK_ALL);
734\& } 1212\& }
735.Ve 1213\&
736.PP
737.Vb 6
738\& struct ev_loop *loop = ev_default_loop (0); 1214\& struct ev_loop *loop = ev_default_loop (0);
1215\&
739\& struct ev_io stdin_watcher; 1216\& ev_io stdin_watcher;
1217\&
740\& ev_init (&stdin_watcher, my_cb); 1218\& ev_init (&stdin_watcher, my_cb);
741\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1219\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
742\& ev_io_start (loop, &stdin_watcher); 1220\& ev_io_start (loop, &stdin_watcher);
1221\&
743\& ev_loop (loop, 0); 1222\& ev_run (loop, 0);
744.Ve 1223.Ve
745.PP 1224.PP
746As you can see, you are responsible for allocating the memory for your 1225As 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, 1226watcher structures (and it is \fIusually\fR a bad idea to do this on the
748although this can sometimes be quite valid). 1227stack).
749.PP 1228.PP
1229Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1230or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1231.PP
750Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1232Each 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 1233*, 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 1234invoked 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 1235time the event loop detects that the file descriptor given is readable
754is readable and/or writable). 1236and/or writable).
755.PP 1237.PP
756Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1238Each 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 1239macro 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 1240is 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 1241.PP
761To make the watcher actually watch out for events, you have to start it 1242To 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 1243with 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 1244*)\*(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. 1245corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
765.PP 1246.PP
766As long as your watcher is active (has been started but not stopped) you 1247As 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 1248must not touch the values stored in it. Most specifically you must never
768reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1249reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
769.PP 1250.PP
770Each and every callback receives the event loop pointer as first, the 1251Each and every callback receives the event loop pointer as first, the
771registered watcher structure as second, and a bitset of received events as 1252registered watcher structure as second, and a bitset of received events as
772third argument. 1253third argument.
773.PP 1254.PP
… …
782.el .IP "\f(CWEV_WRITE\fR" 4 1263.el .IP "\f(CWEV_WRITE\fR" 4
783.IX Item "EV_WRITE" 1264.IX Item "EV_WRITE"
784.PD 1265.PD
785The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1266The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
786writable. 1267writable.
787.ie n .IP """EV_TIMEOUT""" 4 1268.ie n .IP """EV_TIMER""" 4
788.el .IP "\f(CWEV_TIMEOUT\fR" 4 1269.el .IP "\f(CWEV_TIMER\fR" 4
789.IX Item "EV_TIMEOUT" 1270.IX Item "EV_TIMER"
790The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1271The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
791.ie n .IP """EV_PERIODIC""" 4 1272.ie n .IP """EV_PERIODIC""" 4
792.el .IP "\f(CWEV_PERIODIC\fR" 4 1273.el .IP "\f(CWEV_PERIODIC\fR" 4
793.IX Item "EV_PERIODIC" 1274.IX Item "EV_PERIODIC"
794The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1275The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
814.PD 0 1295.PD 0
815.ie n .IP """EV_CHECK""" 4 1296.ie n .IP """EV_CHECK""" 4
816.el .IP "\f(CWEV_CHECK\fR" 4 1297.el .IP "\f(CWEV_CHECK\fR" 4
817.IX Item "EV_CHECK" 1298.IX Item "EV_CHECK"
818.PD 1299.PD
819All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1300All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
820to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1301to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
821\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1302\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
822received events. Callbacks of both watcher types can start and stop as 1303received events. Callbacks of both watcher types can start and stop as
823many watchers as they want, and all of them will be taken into account 1304many watchers as they want, and all of them will be taken into account
824(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1305(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
825\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1306\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
826.ie n .IP """EV_EMBED""" 4 1307.ie n .IP """EV_EMBED""" 4
827.el .IP "\f(CWEV_EMBED\fR" 4 1308.el .IP "\f(CWEV_EMBED\fR" 4
828.IX Item "EV_EMBED" 1309.IX Item "EV_EMBED"
829The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1310The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
830.ie n .IP """EV_FORK""" 4 1311.ie n .IP """EV_FORK""" 4
831.el .IP "\f(CWEV_FORK\fR" 4 1312.el .IP "\f(CWEV_FORK\fR" 4
832.IX Item "EV_FORK" 1313.IX Item "EV_FORK"
833The event loop has been resumed in the child process after fork (see 1314The event loop has been resumed in the child process after fork (see
834\&\f(CW\*(C`ev_fork\*(C'\fR). 1315\&\f(CW\*(C`ev_fork\*(C'\fR).
1316.ie n .IP """EV_CLEANUP""" 4
1317.el .IP "\f(CWEV_CLEANUP\fR" 4
1318.IX Item "EV_CLEANUP"
1319The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1320.ie n .IP """EV_ASYNC""" 4
1321.el .IP "\f(CWEV_ASYNC\fR" 4
1322.IX Item "EV_ASYNC"
1323The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1324.ie n .IP """EV_CUSTOM""" 4
1325.el .IP "\f(CWEV_CUSTOM\fR" 4
1326.IX Item "EV_CUSTOM"
1327Not ever sent (or otherwise used) by libev itself, but can be freely used
1328by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
835.ie n .IP """EV_ERROR""" 4 1329.ie n .IP """EV_ERROR""" 4
836.el .IP "\f(CWEV_ERROR\fR" 4 1330.el .IP "\f(CWEV_ERROR\fR" 4
837.IX Item "EV_ERROR" 1331.IX Item "EV_ERROR"
838An unspecified error has occured, the watcher has been stopped. This might 1332An unspecified error has occurred, the watcher has been stopped. This might
839happen because the watcher could not be properly started because libev 1333happen 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 1334ran out of memory, a file descriptor was found to be closed or any other
1335problem. Libev considers these application bugs.
1336.Sp
841problem. You best act on it by reporting the problem and somehow coping 1337You best act on it by reporting the problem and somehow coping with the
842with the watcher being stopped. 1338watcher being stopped. Note that well-written programs should not receive
1339an error ever, so when your watcher receives it, this usually indicates a
1340bug in your program.
843.Sp 1341.Sp
844Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1342Libev 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 1343example 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 1344callbacks 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 1345the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
848programs, though, so beware. 1346programs, though, as the fd could already be closed and reused for another
1347thing, so beware.
849.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1348.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
850.IX Subsection "GENERIC WATCHER FUNCTIONS" 1349.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 1350.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
854.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1351.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
855.IX Item "ev_init (ev_TYPE *watcher, callback)" 1352.IX Item "ev_init (ev_TYPE *watcher, callback)"
856This macro initialises the generic portion of a watcher. The contents 1353This 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 1354of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
861which rolls both calls into one. 1358which rolls both calls into one.
862.Sp 1359.Sp
863You can reinitialise a watcher at any time as long as it has been stopped 1360You 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. 1361(or never started) and there are no pending events outstanding.
865.Sp 1362.Sp
866The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1363The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
867int revents)\*(C'\fR. 1364int revents)\*(C'\fR.
1365.Sp
1366Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1367.Sp
1368.Vb 3
1369\& ev_io w;
1370\& ev_init (&w, my_cb);
1371\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1372.Ve
868.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1373.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
869.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1374.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
870.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1375.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
871This macro initialises the type-specific parts of a watcher. You need to 1376This 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 1377call \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 1378call \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 1379macro 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). 1380difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
876.Sp 1381.Sp
877Although some watcher types do not have type-specific arguments 1382Although 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. 1383(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1384.Sp
1385See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
879.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1386.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 1387.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
881.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1388.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 1389This 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 1390calls into a single call. This is the most convenient method to initialise
884a watcher. The same limitations apply, of course. 1391a watcher. The same limitations apply, of course.
1392.Sp
1393Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1394.Sp
1395.Vb 1
1396\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1397.Ve
885.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1398.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
886.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1399.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
887.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1400.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
888Starts (activates) the given watcher. Only active watchers will receive 1401Starts (activates) the given watcher. Only active watchers will receive
889events. If the watcher is already active nothing will happen. 1402events. If the watcher is already active nothing will happen.
1403.Sp
1404Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1405whole section.
1406.Sp
1407.Vb 1
1408\& ev_io_start (EV_DEFAULT_UC, &w);
1409.Ve
890.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1410.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
891.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1411.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
892.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1412.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
893Stops the given watcher again (if active) and clears the pending 1413Stops the given watcher if active, and clears the pending status (whether
1414the watcher was active or not).
1415.Sp
894status. It is possible that stopped watchers are pending (for example, 1416It is possible that stopped watchers are pending \- for example,
895non-repeating timers are being stopped when they become pending), but 1417non-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 1418calling \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 1419pending. 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. 1420therefore 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 1421.IP "bool ev_is_active (ev_TYPE *watcher)" 4
900.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1422.IX Item "bool ev_is_active (ev_TYPE *watcher)"
901Returns a true value iff the watcher is active (i.e. it has been started 1423Returns 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 1424and not yet been stopped). As long as a watcher is active you must not modify
903it. 1425it.
… …
914Returns the callback currently set on the watcher. 1436Returns the callback currently set on the watcher.
915.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1437.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
916.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1438.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
917Change the callback. You can change the callback at virtually any time 1439Change the callback. You can change the callback at virtually any time
918(modulo threads). 1440(modulo threads).
919.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 1441.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
920.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" 1442.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
921.PD 0 1443.PD 0
922.IP "int ev_priority (ev_TYPE *watcher)" 4 1444.IP "int ev_priority (ev_TYPE *watcher)" 4
923.IX Item "int ev_priority (ev_TYPE *watcher)" 1445.IX Item "int ev_priority (ev_TYPE *watcher)"
924.PD 1446.PD
925Set and query the priority of the watcher. The priority is a small 1447Set 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 1448integer 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 1449(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 1450before watchers with lower priority, but priority will not keep watchers
929from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). 1451from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
930.Sp 1452.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 1453If 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. 1454you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
938.Sp 1455.Sp
939You \fImust not\fR change the priority of a watcher as long as it is active or 1456You \fImust not\fR change the priority of a watcher as long as it is active or
940pending. 1457pending.
941.Sp 1458.Sp
1459Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1460fine, as long as you do not mind that the priority value you query might
1461or might not have been clamped to the valid range.
1462.Sp
942The default priority used by watchers when no priority has been set is 1463The 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 :). 1464always \f(CW0\fR, which is supposed to not be too high and not be too low :).
944.Sp 1465.Sp
945Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is 1466See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
946fine, as long as you do not mind that the priority value you query might 1467priorities.
947or might not have been adjusted to be within valid range.
948.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 1468.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
949.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" 1469.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 1470Invoke 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 1471\&\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. 1472can deal with that fact, as both are simply passed through to the
1473callback.
953.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 1474.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
954.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" 1475.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
955If the watcher is pending, this function returns clears its pending status 1476If 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 1477returns 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. 1478watcher 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" 1479.Sp
959.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1480Sometimes 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 1481callback to be invoked, which can be accomplished with this function.
961and read at any time, libev will completely ignore it. This can be used 1482.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
962to associate arbitrary data with your watcher. If you need more data and 1483.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 1484Feeds 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 1485had happened for the specified watcher (which must be a pointer to an
965data: 1486initialised but not necessarily started event watcher). Obviously you must
1487not free the watcher as long as it has pending events.
1488.Sp
1489Stopping the watcher, letting libev invoke it, or calling
1490\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1491not started in the first place.
1492.Sp
1493See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1494functions that do not need a watcher.
966.PP 1495.PP
1496See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1497\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1498.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1499.IX Subsection "WATCHER STATES"
1500There are various watcher states mentioned throughout this manual \-
1501active, pending and so on. In this section these states and the rules to
1502transition between them will be described in more detail \- and while these
1503rules might look complicated, they usually do \*(L"the right thing\*(R".
1504.IP "initialiased" 4
1505.IX Item "initialiased"
1506Before a watcher can be registered with the event loop it has to be
1507initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1508\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1509.Sp
1510In this state it is simply some block of memory that is suitable for
1511use in an event loop. It can be moved around, freed, reused etc. at
1512will \- as long as you either keep the memory contents intact, or call
1513\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1514.IP "started/running/active" 4
1515.IX Item "started/running/active"
1516Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1517property of the event loop, and is actively waiting for events. While in
1518this state it cannot be accessed (except in a few documented ways), moved,
1519freed or anything else \- the only legal thing is to keep a pointer to it,
1520and call libev functions on it that are documented to work on active watchers.
1521.IP "pending" 4
1522.IX Item "pending"
1523If a watcher is active and libev determines that an event it is interested
1524in has occurred (such as a timer expiring), it will become pending. It will
1525stay in this pending state until either it is stopped or its callback is
1526about to be invoked, so it is not normally pending inside the watcher
1527callback.
1528.Sp
1529The watcher might or might not be active while it is pending (for example,
1530an expired non-repeating timer can be pending but no longer active). If it
1531is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1532but it is still property of the event loop at this time, so cannot be
1533moved, freed or reused. And if it is active the rules described in the
1534previous item still apply.
1535.Sp
1536It is also possible to feed an event on a watcher that is not active (e.g.
1537via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1538active.
1539.IP "stopped" 4
1540.IX Item "stopped"
1541A watcher can be stopped implicitly by libev (in which case it might still
1542be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1543latter will clear any pending state the watcher might be in, regardless
1544of whether it was active or not, so stopping a watcher explicitly before
1545freeing it is often a good idea.
1546.Sp
1547While stopped (and not pending) the watcher is essentially in the
1548initialised state, that is, it can be reused, moved, modified in any way
1549you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1550it again).
1551.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1552.IX Subsection "WATCHER PRIORITY MODELS"
1553Many event loops support \fIwatcher priorities\fR, which are usually small
1554integers that influence the ordering of event callback invocation
1555between watchers in some way, all else being equal.
1556.PP
1557In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1558description for the more technical details such as the actual priority
1559range.
1560.PP
1561There are two common ways how these these priorities are being interpreted
1562by event loops:
1563.PP
1564In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1565of lower priority watchers, which means as long as higher priority
1566watchers receive events, lower priority watchers are not being invoked.
1567.PP
1568The less common only-for-ordering model uses priorities solely to order
1569callback invocation within a single event loop iteration: Higher priority
1570watchers are invoked before lower priority ones, but they all get invoked
1571before polling for new events.
1572.PP
1573Libev uses the second (only-for-ordering) model for all its watchers
1574except for idle watchers (which use the lock-out model).
1575.PP
1576The rationale behind this is that implementing the lock-out model for
1577watchers is not well supported by most kernel interfaces, and most event
1578libraries will just poll for the same events again and again as long as
1579their callbacks have not been executed, which is very inefficient in the
1580common case of one high-priority watcher locking out a mass of lower
1581priority ones.
1582.PP
1583Static (ordering) priorities are most useful when you have two or more
1584watchers handling the same resource: a typical usage example is having an
1585\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1586timeouts. Under load, data might be received while the program handles
1587other jobs, but since timers normally get invoked first, the timeout
1588handler will be executed before checking for data. In that case, giving
1589the timer a lower priority than the I/O watcher ensures that I/O will be
1590handled first even under adverse conditions (which is usually, but not
1591always, what you want).
1592.PP
1593Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1594will only be executed when no same or higher priority watchers have
1595received events, they can be used to implement the \*(L"lock-out\*(R" model when
1596required.
1597.PP
1598For example, to emulate how many other event libraries handle priorities,
1599you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1600the normal watcher callback, you just start the idle watcher. The real
1601processing is done in the idle watcher callback. This causes libev to
1602continuously poll and process kernel event data for the watcher, but when
1603the lock-out case is known to be rare (which in turn is rare :), this is
1604workable.
1605.PP
1606Usually, however, the lock-out model implemented that way will perform
1607miserably under the type of load it was designed to handle. In that case,
1608it might be preferable to stop the real watcher before starting the
1609idle watcher, so the kernel will not have to process the event in case
1610the actual processing will be delayed for considerable time.
1611.PP
1612Here is an example of an I/O watcher that should run at a strictly lower
1613priority than the default, and which should only process data when no
1614other events are pending:
1615.PP
967.Vb 7 1616.Vb 2
968\& struct my_io 1617\& ev_idle idle; // actual processing watcher
969\& { 1618\& ev_io io; // actual event watcher
970\& struct ev_io io; 1619\&
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 1620\& static void
1012\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1621\& io_cb (EV_P_ ev_io *w, int revents)
1013\& { 1622\& {
1014\& struct my_biggy big = (struct my_biggy * 1623\& // stop the I/O watcher, we received the event, but
1015\& (((char *)w) - offsetof (struct my_biggy, t1)); 1624\& // are not yet ready to handle it.
1625\& ev_io_stop (EV_A_ w);
1626\&
1627\& // start the idle watcher to handle the actual event.
1628\& // it will not be executed as long as other watchers
1629\& // with the default priority are receiving events.
1630\& ev_idle_start (EV_A_ &idle);
1016\& } 1631\& }
1017.Ve 1632\&
1018.PP
1019.Vb 6
1020\& static void 1633\& static void
1021\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1634\& idle_cb (EV_P_ ev_idle *w, int revents)
1022\& { 1635\& {
1023\& struct my_biggy big = (struct my_biggy * 1636\& // actual processing
1024\& (((char *)w) - offsetof (struct my_biggy, t2)); 1637\& read (STDIN_FILENO, ...);
1638\&
1639\& // have to start the I/O watcher again, as
1640\& // we have handled the event
1641\& ev_io_start (EV_P_ &io);
1025\& } 1642\& }
1643\&
1644\& // initialisation
1645\& ev_idle_init (&idle, idle_cb);
1646\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1647\& ev_io_start (EV_DEFAULT_ &io);
1026.Ve 1648.Ve
1649.PP
1650In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1651low-priority connections can not be locked out forever under load. This
1652enables your program to keep a lower latency for important connections
1653during short periods of high load, while not completely locking out less
1654important ones.
1027.SH "WATCHER TYPES" 1655.SH "WATCHER TYPES"
1028.IX Header "WATCHER TYPES" 1656.IX Header "WATCHER TYPES"
1029This section describes each watcher in detail, but will not repeat 1657This section describes each watcher in detail, but will not repeat
1030information given in the last section. Any initialisation/set macros, 1658information given in the last section. Any initialisation/set macros,
1031functions and members specific to the watcher type are explained. 1659functions and members specific to the watcher type are explained.
… …
1036watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1664watcher 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 1665means 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 1666is 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 1667sensible or take immediate effect (or do anything at all), but libev will
1040not crash or malfunction in any way. 1668not crash or malfunction in any way.
1041.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1669.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?" 1670.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?" 1671.IX Subsection "ev_io - is this file descriptor readable or writable?"
1044I/O watchers check whether a file descriptor is readable or writable 1672I/O watchers check whether a file descriptor is readable or writable
1045in each iteration of the event loop, or, more precisely, when reading 1673in 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 1674would not block the process and writing would at least be able to write
1047some data. This behaviour is called level-triggering because you keep 1675some data. This behaviour is called level-triggering because you keep
… …
1052In general you can register as many read and/or write event watchers per 1680In 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 1681fd 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 1682descriptors to non-blocking mode is also usually a good idea (but not
1055required if you know what you are doing). 1683required if you know what you are doing).
1056.PP 1684.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 1685Another 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 1686receive \*(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 1687be 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 1688because 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 1689with a relatively standard program structure. Thus it is best to always
1072this situation even with a relatively standard program structure. Thus 1690use 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. 1691preferable to a program hanging until some data arrives.
1075.PP 1692.PP
1076If you cannot run the fd in non-blocking mode (for example you should not 1693If 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 1694not 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 1695re-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 1696interface such as poll (fortunately in the case of Xlib, it already does
1080its own, so its quite safe to use). 1697this on its own, so its quite safe to use). Some people additionally
1698use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1699indefinitely.
1700.PP
1701But really, best use non-blocking mode.
1081.PP 1702.PP
1082\fIThe special problem of disappearing file descriptors\fR 1703\fIThe special problem of disappearing file descriptors\fR
1083.IX Subsection "The special problem of disappearing file descriptors" 1704.IX Subsection "The special problem of disappearing file descriptors"
1084.PP 1705.PP
1085Some backends (e.g kqueue, epoll) need to be told about closing a file 1706Some 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, 1707descriptor (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 1708such 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 1709descriptor, but when it goes away, the operating system will silently drop
1089this interest. If another file descriptor with the same number then is 1710this 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 1711registered with libev, there is no efficient way to see that this is, in
1091fact, a different file descriptor. 1712fact, a different file descriptor.
1092.PP 1713.PP
… …
1098descriptor even if the file descriptor number itself did not change. 1719descriptor even if the file descriptor number itself did not change.
1099.PP 1720.PP
1100This is how one would do it normally anyway, the important point is that 1721This is how one would do it normally anyway, the important point is that
1101the libev application should not optimise around libev but should leave 1722the libev application should not optimise around libev but should leave
1102optimisations to libev. 1723optimisations to libev.
1724.PP
1725\fIThe special problem of dup'ed file descriptors\fR
1726.IX Subsection "The special problem of dup'ed file descriptors"
1727.PP
1728Some backends (e.g. epoll), cannot register events for file descriptors,
1729but only events for the underlying file descriptions. That means when you
1730have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1731events for them, only one file descriptor might actually receive events.
1732.PP
1733There is no workaround possible except not registering events
1734for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1735\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1736.PP
1737\fIThe special problem of files\fR
1738.IX Subsection "The special problem of files"
1739.PP
1740Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1741representing files, and expect it to become ready when their program
1742doesn't block on disk accesses (which can take a long time on their own).
1743.PP
1744However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1745notification as soon as the kernel knows whether and how much data is
1746there, and in the case of open files, that's always the case, so you
1747always get a readiness notification instantly, and your read (or possibly
1748write) will still block on the disk I/O.
1749.PP
1750Another way to view it is that in the case of sockets, pipes, character
1751devices and so on, there is another party (the sender) that delivers data
1752on its own, but in the case of files, there is no such thing: the disk
1753will not send data on its own, simply because it doesn't know what you
1754wish to read \- you would first have to request some data.
1755.PP
1756Since files are typically not-so-well supported by advanced notification
1757mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1758to files, even though you should not use it. The reason for this is
1759convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1760usually a tty, often a pipe, but also sometimes files or special devices
1761(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1762\&\fI/dev/urandom\fR), and even though the file might better be served with
1763asynchronous I/O instead of with non-blocking I/O, it is still useful when
1764it \*(L"just works\*(R" instead of freezing.
1765.PP
1766So avoid file descriptors pointing to files when you know it (e.g. use
1767libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1768when you rarely read from a file instead of from a socket, and want to
1769reuse the same code path.
1770.PP
1771\fIThe special problem of fork\fR
1772.IX Subsection "The special problem of fork"
1773.PP
1774Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1775useless behaviour. Libev fully supports fork, but needs to be told about
1776it in the child if you want to continue to use it in the child.
1777.PP
1778To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1779()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1780\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1781.PP
1782\fIThe special problem of \s-1SIGPIPE\s0\fR
1783.IX Subsection "The special problem of SIGPIPE"
1784.PP
1785While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1786when writing to a pipe whose other end has been closed, your program gets
1787sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1788this is sensible behaviour, for daemons, this is usually undesirable.
1789.PP
1790So when you encounter spurious, unexplained daemon exits, make sure you
1791ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1792somewhere, as that would have given you a big clue).
1793.PP
1794\fIThe special problem of \fIaccept()\fIing when you can't\fR
1795.IX Subsection "The special problem of accept()ing when you can't"
1796.PP
1797Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1798found in post\-2004 Linux) have the peculiar behaviour of not removing a
1799connection from the pending queue in all error cases.
1800.PP
1801For example, larger servers often run out of file descriptors (because
1802of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1803rejecting the connection, leading to libev signalling readiness on
1804the next iteration again (the connection still exists after all), and
1805typically causing the program to loop at 100% \s-1CPU\s0 usage.
1806.PP
1807Unfortunately, the set of errors that cause this issue differs between
1808operating systems, there is usually little the app can do to remedy the
1809situation, and no known thread-safe method of removing the connection to
1810cope with overload is known (to me).
1811.PP
1812One of the easiest ways to handle this situation is to just ignore it
1813\&\- when the program encounters an overload, it will just loop until the
1814situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1815event-based way to handle this situation, so it's the best one can do.
1816.PP
1817A better way to handle the situation is to log any errors other than
1818\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1819messages, and continue as usual, which at least gives the user an idea of
1820what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1821the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1822usage.
1823.PP
1824If your program is single-threaded, then you could also keep a dummy file
1825descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1826when 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,
1827close that fd, and create a new dummy fd. This will gracefully refuse
1828clients under typical overload conditions.
1829.PP
1830The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1831is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1832opportunity for a DoS attack.
1103.PP 1833.PP
1104\fIWatcher-Specific Functions\fR 1834\fIWatcher-Specific Functions\fR
1105.IX Subsection "Watcher-Specific Functions" 1835.IX Subsection "Watcher-Specific Functions"
1106.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1836.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)" 1837.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1108.PD 0 1838.PD 0
1109.IP "ev_io_set (ev_io *, int fd, int events)" 4 1839.IP "ev_io_set (ev_io *, int fd, int events)" 4
1110.IX Item "ev_io_set (ev_io *, int fd, int events)" 1840.IX Item "ev_io_set (ev_io *, int fd, int events)"
1111.PD 1841.PD
1112Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1842Configures 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 1843receive 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. 1844\&\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 1845.IP "int fd [read\-only]" 4
1116.IX Item "int fd [read-only]" 1846.IX Item "int fd [read-only]"
1117The file descriptor being watched. 1847The file descriptor being watched.
1118.IP "int events [read\-only]" 4 1848.IP "int events [read\-only]" 4
1119.IX Item "int events [read-only]" 1849.IX Item "int events [read-only]"
1120The events being watched. 1850The events being watched.
1121.PP 1851.PP
1852\fIExamples\fR
1853.IX Subsection "Examples"
1854.PP
1122Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1855Example: 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 1856readable, but only once. Since it is likely line-buffered, you could
1124attempt to read a whole line in the callback. 1857attempt to read a whole line in the callback.
1125.PP 1858.PP
1126.Vb 6 1859.Vb 6
1127\& static void 1860\& static void
1128\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1861\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1129\& { 1862\& {
1130\& ev_io_stop (loop, w); 1863\& ev_io_stop (loop, w);
1131\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1864\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1132\& } 1865\& }
1133.Ve 1866\&
1134.PP
1135.Vb 6
1136\& ... 1867\& ...
1137\& struct ev_loop *loop = ev_default_init (0); 1868\& struct ev_loop *loop = ev_default_init (0);
1138\& struct ev_io stdin_readable; 1869\& ev_io stdin_readable;
1139\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1870\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1140\& ev_io_start (loop, &stdin_readable); 1871\& ev_io_start (loop, &stdin_readable);
1141\& ev_loop (loop, 0); 1872\& ev_run (loop, 0);
1142.Ve 1873.Ve
1143.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1874.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1144.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1875.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1145.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1876.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1146Timer watchers are simple relative timers that generate an event after a 1877Timer watchers are simple relative timers that generate an event after a
1147given time, and optionally repeating in regular intervals after that. 1878given time, and optionally repeating in regular intervals after that.
1148.PP 1879.PP
1149The timers are based on real time, that is, if you register an event that 1880The 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 1881times 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 1882year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1152detecting time jumps is hard, and some inaccuracies are unavoidable (the 1883detecting time jumps is hard, and some inaccuracies are unavoidable (the
1153monotonic clock option helps a lot here). 1884monotonic clock option helps a lot here).
1885.PP
1886The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1887passed (not \fIat\fR, so on systems with very low-resolution clocks this
1888might introduce a small delay, see \*(L"the special problem of being too
1889early\*(R", below). If multiple timers become ready during the same loop
1890iteration then the ones with earlier time-out values are invoked before
1891ones of the same priority with later time-out values (but this is no
1892longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1893.PP
1894\fIBe smart about timeouts\fR
1895.IX Subsection "Be smart about timeouts"
1896.PP
1897Many real-world problems involve some kind of timeout, usually for error
1898recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1899you want to raise some error after a while.
1900.PP
1901What follows are some ways to handle this problem, from obvious and
1902inefficient to smart and efficient.
1903.PP
1904In the following, a 60 second activity timeout is assumed \- a timeout that
1905gets reset to 60 seconds each time there is activity (e.g. each time some
1906data or other life sign was received).
1907.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1908.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1909This is the most obvious, but not the most simple way: In the beginning,
1910start the watcher:
1911.Sp
1912.Vb 2
1913\& ev_timer_init (timer, callback, 60., 0.);
1914\& ev_timer_start (loop, timer);
1915.Ve
1916.Sp
1917Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1918and start it again:
1919.Sp
1920.Vb 3
1921\& ev_timer_stop (loop, timer);
1922\& ev_timer_set (timer, 60., 0.);
1923\& ev_timer_start (loop, timer);
1924.Ve
1925.Sp
1926This is relatively simple to implement, but means that each time there is
1927some activity, libev will first have to remove the timer from its internal
1928data structure and then add it again. Libev tries to be fast, but it's
1929still not a constant-time operation.
1930.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1931.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1932.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1933This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1934\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1935.Sp
1936To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1937of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1938successfully read or write some data. If you go into an idle state where
1939you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1940the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1941.Sp
1942That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1943\&\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
1944member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1945.Sp
1946At start:
1947.Sp
1948.Vb 3
1949\& ev_init (timer, callback);
1950\& timer\->repeat = 60.;
1951\& ev_timer_again (loop, timer);
1952.Ve
1953.Sp
1954Each time there is some activity:
1955.Sp
1956.Vb 1
1957\& ev_timer_again (loop, timer);
1958.Ve
1959.Sp
1960It is even possible to change the time-out on the fly, regardless of
1961whether the watcher is active or not:
1962.Sp
1963.Vb 2
1964\& timer\->repeat = 30.;
1965\& ev_timer_again (loop, timer);
1966.Ve
1967.Sp
1968This is slightly more efficient then stopping/starting the timer each time
1969you want to modify its timeout value, as libev does not have to completely
1970remove and re-insert the timer from/into its internal data structure.
1971.Sp
1972It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1973.IP "3. Let the timer time out, but then re-arm it as required." 4
1974.IX Item "3. Let the timer time out, but then re-arm it as required."
1975This method is more tricky, but usually most efficient: Most timeouts are
1976relatively long compared to the intervals between other activity \- in
1977our example, within 60 seconds, there are usually many I/O events with
1978associated activity resets.
1979.Sp
1980In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1981but remember the time of last activity, and check for a real timeout only
1982within the callback:
1983.Sp
1984.Vb 3
1985\& ev_tstamp timeout = 60.;
1986\& ev_tstamp last_activity; // time of last activity
1987\& ev_timer timer;
1988\&
1989\& static void
1990\& callback (EV_P_ ev_timer *w, int revents)
1991\& {
1992\& // calculate when the timeout would happen
1993\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
1994\&
1995\& // if negative, it means we the timeout already occured
1996\& if (after < 0.)
1997\& {
1998\& // timeout occurred, take action
1999\& }
2000\& else
2001\& {
2002\& // callback was invoked, but there was some recent
2003\& // activity. simply restart the timer to time out
2004\& // after "after" seconds, which is the earliest time
2005\& // the timeout can occur.
2006\& ev_timer_set (w, after, 0.);
2007\& ev_timer_start (EV_A_ w);
2008\& }
2009\& }
2010.Ve
2011.Sp
2012To summarise the callback: first calculate in how many seconds the
2013timeout will occur (by calculating the absolute time when it would occur,
2014\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2015(EV_A)\*(C'\fR from that).
2016.Sp
2017If this value is negative, then we are already past the timeout, i.e. we
2018timed out, and need to do whatever is needed in this case.
2019.Sp
2020Otherwise, we now the earliest time at which the timeout would trigger,
2021and simply start the timer with this timeout value.
2022.Sp
2023In other words, each time the callback is invoked it will check whether
2024the timeout cocured. If not, it will simply reschedule itself to check
2025again at the earliest time it could time out. Rinse. Repeat.
2026.Sp
2027This scheme causes more callback invocations (about one every 60 seconds
2028minus half the average time between activity), but virtually no calls to
2029libev to change the timeout.
2030.Sp
2031To start the machinery, simply initialise the watcher and set
2032\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2033now), then call the callback, which will \*(L"do the right thing\*(R" and start
2034the timer:
2035.Sp
2036.Vb 3
2037\& last_activity = ev_now (EV_A);
2038\& ev_init (&timer, callback);
2039\& callback (EV_A_ &timer, 0);
2040.Ve
2041.Sp
2042When there is some activity, simply store the current time in
2043\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2044.Sp
2045.Vb 2
2046\& if (activity detected)
2047\& last_activity = ev_now (EV_A);
2048.Ve
2049.Sp
2050When your timeout value changes, then the timeout can be changed by simply
2051providing a new value, stopping the timer and calling the callback, which
2052will agaion do the right thing (for example, time out immediately :).
2053.Sp
2054.Vb 3
2055\& timeout = new_value;
2056\& ev_timer_stop (EV_A_ &timer);
2057\& callback (EV_A_ &timer, 0);
2058.Ve
2059.Sp
2060This technique is slightly more complex, but in most cases where the
2061time-out is unlikely to be triggered, much more efficient.
2062.IP "4. Wee, just use a double-linked list for your timeouts." 4
2063.IX Item "4. Wee, just use a double-linked list for your timeouts."
2064If there is not one request, but many thousands (millions...), all
2065employing some kind of timeout with the same timeout value, then one can
2066do even better:
2067.Sp
2068When starting the timeout, calculate the timeout value and put the timeout
2069at the \fIend\fR of the list.
2070.Sp
2071Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2072the list is expected to fire (for example, using the technique #3).
2073.Sp
2074When there is some activity, remove the timer from the list, recalculate
2075the timeout, append it to the end of the list again, and make sure to
2076update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2077.Sp
2078This way, one can manage an unlimited number of timeouts in O(1) time for
2079starting, stopping and updating the timers, at the expense of a major
2080complication, and having to use a constant timeout. The constant timeout
2081ensures that the list stays sorted.
2082.PP
2083So which method the best?
2084.PP
2085Method #2 is a simple no-brain-required solution that is adequate in most
2086situations. Method #3 requires a bit more thinking, but handles many cases
2087better, and isn't very complicated either. In most case, choosing either
2088one is fine, with #3 being better in typical situations.
2089.PP
2090Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2091rather complicated, but extremely efficient, something that really pays
2092off after the first million or so of active timers, i.e. it's usually
2093overkill :)
2094.PP
2095\fIThe special problem of being too early\fR
2096.IX Subsection "The special problem of being too early"
2097.PP
2098If you ask a timer to call your callback after three seconds, then
2099you expect it to be invoked after three seconds \- but of course, this
2100cannot be guaranteed to infinite precision. Less obviously, it cannot be
2101guaranteed to any precision by libev \- imagine somebody suspending the
2102process with a \s-1STOP\s0 signal for a few hours for example.
2103.PP
2104So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2105delay has occurred, but cannot guarantee this.
2106.PP
2107A less obvious failure mode is calling your callback too early: many event
2108loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2109this can cause your callback to be invoked much earlier than you would
2110expect.
2111.PP
2112To see why, imagine a system with a clock that only offers full second
2113resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2114yourself). If you schedule a one-second timer at the time 500.9, then the
2115event loop will schedule your timeout to elapse at a system time of 500
2116(500.9 truncated to the resolution) + 1, or 501.
2117.PP
2118If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2119501\*(R" and invoke the callback 0.1s after it was started, even though a
2120one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2121intentions.
2122.PP
2123This is the reason why libev will never invoke the callback if the elapsed
2124delay equals the requested delay, but only when the elapsed delay is
2125larger than the requested delay. In the example above, libev would only invoke
2126the callback at system time 502, or 1.1s after the timer was started.
2127.PP
2128So, while libev cannot guarantee that your callback will be invoked
2129exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2130delay has actually elapsed, or in other words, it always errs on the \*(L"too
2131late\*(R" side of things.
2132.PP
2133\fIThe special problem of time updates\fR
2134.IX Subsection "The special problem of time updates"
2135.PP
2136Establishing the current time is a costly operation (it usually takes
2137at least one system call): \s-1EV\s0 therefore updates its idea of the current
2138time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2139growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2140lots of events in one iteration.
1154.PP 2141.PP
1155The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2142The 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 2143time. This is usually the right thing as this timestamp refers to the time
1157of the event triggering whatever timeout you are modifying/starting. If 2144of 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 2145you 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: 2146timeout on the current time, use something like this to adjust for this:
1160.PP 2147.PP
1161.Vb 1 2148.Vb 1
1162\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2149\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1163.Ve 2150.Ve
1164.PP 2151.PP
1165The callback is guarenteed to be invoked only when its timeout has passed, 2152If 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 2153update 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. 2154()\*(C'\fR.
2155.PP
2156\fIThe special problem of unsynchronised clocks\fR
2157.IX Subsection "The special problem of unsynchronised clocks"
2158.PP
2159Modern systems have a variety of clocks \- libev itself uses the normal
2160\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2161jumps).
2162.PP
2163Neither of these clocks is synchronised with each other or any other clock
2164on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2165than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2166a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2167than a directly following call to \f(CW\*(C`time\*(C'\fR.
2168.PP
2169The moral of this is to only compare libev-related timestamps with
2170\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2171a second or so.
2172.PP
2173One more problem arises due to this lack of synchronisation: if libev uses
2174the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2175or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2176invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2177.PP
2178This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2179libev makes sure your callback is not invoked before the delay happened,
2180\&\fImeasured according to the real time\fR, not the system clock.
2181.PP
2182If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2183connection after 100 seconds\*(R") then this shouldn't bother you as it is
2184exactly the right behaviour.
2185.PP
2186If you want to compare wall clock/system timestamps to your timers, then
2187you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2188time, where your comparisons will always generate correct results.
2189.PP
2190\fIThe special problems of suspended animation\fR
2191.IX Subsection "The special problems of suspended animation"
2192.PP
2193When you leave the server world it is quite customary to hit machines that
2194can suspend/hibernate \- what happens to the clocks during such a suspend?
2195.PP
2196Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2197all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2198to run until the system is suspended, but they will not advance while the
2199system is suspended. That means, on resume, it will be as if the program
2200was frozen for a few seconds, but the suspend time will not be counted
2201towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2202clock advanced as expected, but if it is used as sole clocksource, then a
2203long suspend would be detected as a time jump by libev, and timers would
2204be adjusted accordingly.
2205.PP
2206I would not be surprised to see different behaviour in different between
2207operating systems, \s-1OS\s0 versions or even different hardware.
2208.PP
2209The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2210time jump in the monotonic clocks and the realtime clock. If the program
2211is suspended for a very long time, and monotonic clock sources are in use,
2212then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2213will be counted towards the timers. When no monotonic clock source is in
2214use, then libev will again assume a timejump and adjust accordingly.
2215.PP
2216It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2217and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2218deterministic behaviour in this case (you can do nothing against
2219\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1168.PP 2220.PP
1169\fIWatcher-Specific Functions and Data Members\fR 2221\fIWatcher-Specific Functions and Data Members\fR
1170.IX Subsection "Watcher-Specific Functions and Data Members" 2222.IX Subsection "Watcher-Specific Functions and Data Members"
1171.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2223.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)" 2224.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1173.PD 0 2225.PD 0
1174.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2226.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)" 2227.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1176.PD 2228.PD
1177Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2229Configure 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 2230is \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 2231reached. If it is positive, then the timer will automatically be
1180later, again, and again, until stopped manually. 2232configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2233until stopped manually.
1181.Sp 2234.Sp
1182The timer itself will do a best-effort at avoiding drift, that is, if you 2235The 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 2236you configure a timer to trigger every 10 seconds, then it will normally
1184exactly 10 second intervals. If, however, your program cannot keep up with 2237trigger at exactly 10 second intervals. If, however, your program cannot
1185the timer (because it takes longer than those 10 seconds to do stuff) the 2238keep up with the timer (because it takes longer than those 10 seconds to
1186timer will not fire more than once per event loop iteration. 2239do stuff) the timer will not fire more than once per event loop iteration.
1187.IP "ev_timer_again (loop)" 4 2240.IP "ev_timer_again (loop, ev_timer *)" 4
1188.IX Item "ev_timer_again (loop)" 2241.IX Item "ev_timer_again (loop, ev_timer *)"
1189This will act as if the timer timed out and restart it again if it is 2242This will act as if the timer timed out, and restarts it again if it is
1190repeating. The exact semantics are: 2243repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2244timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1191.Sp 2245.Sp
2246The exact semantics are as in the following rules, all of which will be
2247applied to the watcher:
2248.RS 4
1192If the timer is pending, its pending status is cleared. 2249.IP "If the timer is pending, the pending status is always cleared." 4
1193.Sp 2250.IX Item "If the timer is pending, the pending status is always cleared."
2251.PD 0
1194If the timer is started but nonrepeating, stop it (as if it timed out). 2252.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2253.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2254.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2255.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2256.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2257.RE
2258.RS 4
2259.PD
1195.Sp 2260.Sp
1196If the timer is repeating, either start it if necessary (with the 2261This 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. 2262usage example.
2263.RE
2264.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2265.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2266Returns the remaining time until a timer fires. If the timer is active,
2267then this time is relative to the current event loop time, otherwise it's
2268the timeout value currently configured.
1198.Sp 2269.Sp
1199This sounds a bit complicated, but here is a useful and typical 2270That 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 2271\&\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 2272will 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 2273roughly \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 2274too), 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 2275.IP "ev_tstamp repeat [read\-write]" 4
1226.IX Item "ev_tstamp repeat [read-write]" 2276.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 2277The 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), 2278or \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. 2279which is also when any modifications are taken into account.
1230.PP 2280.PP
2281\fIExamples\fR
2282.IX Subsection "Examples"
2283.PP
1231Example: Create a timer that fires after 60 seconds. 2284Example: Create a timer that fires after 60 seconds.
1232.PP 2285.PP
1233.Vb 5 2286.Vb 5
1234\& static void 2287\& static void
1235\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2288\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1236\& { 2289\& {
1237\& .. one minute over, w is actually stopped right here 2290\& .. one minute over, w is actually stopped right here
1238\& } 2291\& }
1239.Ve 2292\&
1240.PP
1241.Vb 3
1242\& struct ev_timer mytimer; 2293\& ev_timer mytimer;
1243\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2294\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1244\& ev_timer_start (loop, &mytimer); 2295\& ev_timer_start (loop, &mytimer);
1245.Ve 2296.Ve
1246.PP 2297.PP
1247Example: Create a timeout timer that times out after 10 seconds of 2298Example: Create a timeout timer that times out after 10 seconds of
1248inactivity. 2299inactivity.
1249.PP 2300.PP
1250.Vb 5 2301.Vb 5
1251\& static void 2302\& static void
1252\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2303\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1253\& { 2304\& {
1254\& .. ten seconds without any activity 2305\& .. ten seconds without any activity
1255\& } 2306\& }
1256.Ve 2307\&
1257.PP
1258.Vb 4
1259\& struct ev_timer mytimer; 2308\& ev_timer mytimer;
1260\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2309\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1261\& ev_timer_again (&mytimer); /* start timer */ 2310\& ev_timer_again (&mytimer); /* start timer */
1262\& ev_loop (loop, 0); 2311\& ev_run (loop, 0);
1263.Ve 2312\&
1264.PP
1265.Vb 3
1266\& // and in some piece of code that gets executed on any "activity": 2313\& // and in some piece of code that gets executed on any "activity":
1267\& // reset the timeout to start ticking again at 10 seconds 2314\& // reset the timeout to start ticking again at 10 seconds
1268\& ev_timer_again (&mytimer); 2315\& ev_timer_again (&mytimer);
1269.Ve 2316.Ve
1270.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2317.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1271.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2318.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1272.IX Subsection "ev_periodic - to cron or not to cron?" 2319.IX Subsection "ev_periodic - to cron or not to cron?"
1273Periodic watchers are also timers of a kind, but they are very versatile 2320Periodic watchers are also timers of a kind, but they are very versatile
1274(and unfortunately a bit complex). 2321(and unfortunately a bit complex).
1275.PP 2322.PP
1276Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2323Unlike \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 2324relative 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 2325(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 () 2326difference 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 2327time, 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 2328wrist-watch).
1282roughly 10 seconds later).
1283.PP 2329.PP
1284They can also be used to implement vastly more complex timers, such as 2330You can tell a periodic watcher to trigger after some specific point
1285triggering an event on each midnight, local time or other, complicated, 2331in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1286rules. 2332seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2333not a delay) and then reset your system clock to January of the previous
2334year, then it will take a year or more to trigger the event (unlike an
2335\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2336it, as it uses a relative timeout).
1287.PP 2337.PP
2338\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2339timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2340other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2341those cannot react to time jumps.
2342.PP
1288As with timers, the callback is guarenteed to be invoked only when the 2343As 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 2344point in time where it is supposed to trigger has passed. If multiple
1290during the same loop iteration then order of execution is undefined. 2345timers become ready during the same loop iteration then the ones with
2346earlier time-out values are invoked before ones with later time-out values
2347(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1291.PP 2348.PP
1292\fIWatcher-Specific Functions and Data Members\fR 2349\fIWatcher-Specific Functions and Data Members\fR
1293.IX Subsection "Watcher-Specific Functions and Data Members" 2350.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 2351.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)" 2352.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1296.PD 0 2353.PD 0
1297.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2354.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)" 2355.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1299.PD 2356.PD
1300Lots of arguments, lets sort it out... There are basically three modes of 2357Lots of arguments, let's sort it out... There are basically three modes of
1301operation, and we will explain them from simplest to complex: 2358operation, and we will explain them from simplest to most complex:
1302.RS 4 2359.RS 4
2360.IP "\(bu" 4
1303.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 2361absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1304.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" 2362.Sp
1305In this configuration the watcher triggers an event at the wallclock time 2363In 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, 2364time \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 2365time jump occurs, that is, if it is to be run at January 1st 2011 then it
1308system time reaches or surpasses this time. 2366will 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 2367this point in time.
1310.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 2368.IP "\(bu" 4
2369repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2370.Sp
1311In this mode the watcher will always be scheduled to time out at the next 2371In 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) 2372\&\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. 2373negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2374argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1314.Sp 2375.Sp
1315This can be used to create timers that do not drift with respect to system 2376This can be used to create timers that do not drift with respect to the
1316time: 2377system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2378hour, on the hour (with respect to \s-1UTC\s0):
1317.Sp 2379.Sp
1318.Vb 1 2380.Vb 1
1319\& ev_periodic_set (&periodic, 0., 3600., 0); 2381\& ev_periodic_set (&periodic, 0., 3600., 0);
1320.Ve 2382.Ve
1321.Sp 2383.Sp
1322This doesn't mean there will always be 3600 seconds in between triggers, 2384This 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 2385but 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 2386full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1325by 3600. 2387by 3600.
1326.Sp 2388.Sp
1327Another way to think about it (for the mathematically inclined) is that 2389Another 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 2390\&\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. 2391time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1330.Sp 2392.Sp
1331For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near 2393The \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 2394interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
1333this value. 2395microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2396at most a similar magnitude as the current time (say, within a factor of
2397ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2398\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2399.Sp
2400Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2401speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2402will of course deteriorate. Libev itself tries to be exact to be about one
2403millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2404.IP "\(bu" 4
1334.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 2405manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1335.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 2406.Sp
1336In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2407In 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 2408ignored. Instead, each time the periodic watcher gets scheduled, the
1338reschedule callback will be called with the watcher as first, and the 2409reschedule callback will be called with the watcher as first, and the
1339current time as second argument. 2410current time as second argument.
1340.Sp 2411.Sp
1341\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2412\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1342ever, or make any event loop modifications\fR. If you need to stop it, 2413or 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 2414allowed by documentation here\fR.
2415.Sp
2416If 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). 2417it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2418only event loop modification you are allowed to do).
1345.Sp 2419.Sp
1346Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2420The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1347ev_tstamp now)\*(C'\fR, e.g.: 2421*w, ev_tstamp now)\*(C'\fR, e.g.:
1348.Sp 2422.Sp
1349.Vb 4 2423.Vb 5
2424\& static ev_tstamp
1350\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2425\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1351\& { 2426\& {
1352\& return now + 60.; 2427\& return now + 60.;
1353\& } 2428\& }
1354.Ve 2429.Ve
1355.Sp 2430.Sp
1356It must return the next time to trigger, based on the passed time value 2431It 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 2432(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 2433will usually be called just before the callback will be triggered, but
1359might be called at other times, too. 2434might be called at other times, too.
1360.Sp 2435.Sp
1361\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2436\&\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. 2437equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1363.Sp 2438.Sp
1364This can be used to create very complex timers, such as a timer that 2439This 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 2440triggers 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 2441next 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 2442you do this is, again, up to you (but it is not trivial, which is the main
1368reason I omitted it as an example). 2443reason I omitted it as an example).
1369.RE 2444.RE
1370.RS 4 2445.RS 4
… …
1373.IX Item "ev_periodic_again (loop, ev_periodic *)" 2448.IX Item "ev_periodic_again (loop, ev_periodic *)"
1374Simply stops and restarts the periodic watcher again. This is only useful 2449Simply stops and restarts the periodic watcher again. This is only useful
1375when you changed some parameters or the reschedule callback would return 2450when 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 2451a different time than the last time it was called (e.g. in a crond like
1377program when the crontabs have changed). 2452program when the crontabs have changed).
2453.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2454.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2455When active, returns the absolute time that the watcher is supposed
2456to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2457\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2458rescheduling modes.
1378.IP "ev_tstamp offset [read\-write]" 4 2459.IP "ev_tstamp offset [read\-write]" 4
1379.IX Item "ev_tstamp offset [read-write]" 2460.IX Item "ev_tstamp offset [read-write]"
1380When repeating, this contains the offset value, otherwise this is the 2461When 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). 2462absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2463although libev might modify this value for better numerical stability).
1382.Sp 2464.Sp
1383Can be modified any time, but changes only take effect when the periodic 2465Can 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. 2466timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1385.IP "ev_tstamp interval [read\-write]" 4 2467.IP "ev_tstamp interval [read\-write]" 4
1386.IX Item "ev_tstamp interval [read-write]" 2468.IX Item "ev_tstamp interval [read-write]"
1387The current interval value. Can be modified any time, but changes only 2469The 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 2470take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1389called. 2471called.
1390.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2472.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]" 2473.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 2474The current reschedule callback, or \f(CW0\fR, if this functionality is
1393switched off. Can be changed any time, but changes only take effect when 2475switched 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. 2476the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1395.IP "ev_tstamp at [read\-only]" 4 2477.PP
1396.IX Item "ev_tstamp at [read-only]" 2478\fIExamples\fR
1397When active, contains the absolute time that the watcher is supposed to 2479.IX Subsection "Examples"
1398trigger next.
1399.PP 2480.PP
1400Example: Call a callback every hour, or, more precisely, whenever the 2481Example: Call a callback every hour, or, more precisely, whenever the
1401system clock is divisible by 3600. The callback invocation times have 2482system time is divisible by 3600. The callback invocation times have
1402potentially a lot of jittering, but good long-term stability. 2483potentially a lot of jitter, but good long-term stability.
1403.PP 2484.PP
1404.Vb 5 2485.Vb 5
1405\& static void 2486\& static void
1406\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2487\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1407\& { 2488\& {
1408\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2489\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1409\& } 2490\& }
1410.Ve 2491\&
1411.PP
1412.Vb 3
1413\& struct ev_periodic hourly_tick; 2492\& ev_periodic hourly_tick;
1414\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2493\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1415\& ev_periodic_start (loop, &hourly_tick); 2494\& ev_periodic_start (loop, &hourly_tick);
1416.Ve 2495.Ve
1417.PP 2496.PP
1418Example: The same as above, but use a reschedule callback to do it: 2497Example: The same as above, but use a reschedule callback to do it:
1419.PP 2498.PP
1420.Vb 1 2499.Vb 1
1421\& #include <math.h> 2500\& #include <math.h>
1422.Ve 2501\&
1423.PP
1424.Vb 5
1425\& static ev_tstamp 2502\& static ev_tstamp
1426\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2503\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1427\& { 2504\& {
1428\& return fmod (now, 3600.) + 3600.; 2505\& return now + (3600. \- fmod (now, 3600.));
1429\& } 2506\& }
1430.Ve 2507\&
1431.PP
1432.Vb 1
1433\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2508\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1434.Ve 2509.Ve
1435.PP 2510.PP
1436Example: Call a callback every hour, starting now: 2511Example: Call a callback every hour, starting now:
1437.PP 2512.PP
1438.Vb 4 2513.Vb 4
1439\& struct ev_periodic hourly_tick; 2514\& ev_periodic hourly_tick;
1440\& ev_periodic_init (&hourly_tick, clock_cb, 2515\& ev_periodic_init (&hourly_tick, clock_cb,
1441\& fmod (ev_now (loop), 3600.), 3600., 0); 2516\& fmod (ev_now (loop), 3600.), 3600., 0);
1442\& ev_periodic_start (loop, &hourly_tick); 2517\& ev_periodic_start (loop, &hourly_tick);
1443.Ve 2518.Ve
1444.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2519.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!" 2520.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!" 2521.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1447Signal watchers will trigger an event when the process receives a specific 2522Signal watchers will trigger an event when the process receives a specific
1448signal one or more times. Even though signals are very asynchronous, libev 2523signal 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 2524will try its best to deliver signals synchronously, i.e. as part of the
1450normal event processing, like any other event. 2525normal event processing, like any other event.
1451.PP 2526.PP
2527If you want signals to be delivered truly asynchronously, just use
2528\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2529the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2530synchronously wake up an event loop.
2531.PP
1452You can configure as many watchers as you like per signal. Only when the 2532You can configure as many watchers as you like for the same signal, but
2533only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2534default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2535\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2536the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2537.PP
1453first watcher gets started will libev actually register a signal watcher 2538When the first watcher gets started will libev actually register something
1454with the kernel (thus it coexists with your own signal handlers as long 2539with the kernel (thus it coexists with your own signal handlers as long as
1455as you don't register any with libev). Similarly, when the last signal 2540you don't register any with libev for the same signal).
1456watcher for a signal is stopped libev will reset the signal handler to 2541.PP
1457\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2542If possible and supported, libev will install its handlers with
2543\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2544not be unduly interrupted. If you have a problem with system calls getting
2545interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2546and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2547.PP
2548\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2549.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2550.PP
2551Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2552(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2553stopping it again), that is, libev might or might not block the signal,
2554and might or might not set or restore the installed signal handler (but
2555see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2556.PP
2557While this does not matter for the signal disposition (libev never
2558sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2559\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2560certain signals to be blocked.
2561.PP
2562This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2563the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2564choice usually).
2565.PP
2566The simplest way to ensure that the signal mask is reset in the child is
2567to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2568catch fork calls done by libraries (such as the libc) as well.
2569.PP
2570In current versions of libev, the signal will not be blocked indefinitely
2571unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2572the window of opportunity for problems, it will not go away, as libev
2573\&\fIhas\fR to modify the signal mask, at least temporarily.
2574.PP
2575So I can't stress this enough: \fIIf you do not reset your signal mask when
2576you expect it to be empty, you have a race condition in your code\fR. This
2577is not a libev-specific thing, this is true for most event libraries.
2578.PP
2579\fIThe special problem of threads signal handling\fR
2580.IX Subsection "The special problem of threads signal handling"
2581.PP
2582\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2583a lot of functionality (sigfd, sigwait etc.) only really works if all
2584threads in a process block signals, which is hard to achieve.
2585.PP
2586When you want to use sigwait (or mix libev signal handling with your own
2587for the same signals), you can tackle this problem by globally blocking
2588all signals before creating any threads (or creating them with a fully set
2589sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2590loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2591these signals. You can pass on any signals that libev might be interested
2592in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
1458.PP 2593.PP
1459\fIWatcher-Specific Functions and Data Members\fR 2594\fIWatcher-Specific Functions and Data Members\fR
1460.IX Subsection "Watcher-Specific Functions and Data Members" 2595.IX Subsection "Watcher-Specific Functions and Data Members"
1461.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2596.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1462.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2597.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
… …
1467Configures the watcher to trigger on the given signal number (usually one 2602Configures the watcher to trigger on the given signal number (usually one
1468of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2603of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1469.IP "int signum [read\-only]" 4 2604.IP "int signum [read\-only]" 4
1470.IX Item "int signum [read-only]" 2605.IX Item "int signum [read-only]"
1471The signal the watcher watches out for. 2606The signal the watcher watches out for.
2607.PP
2608\fIExamples\fR
2609.IX Subsection "Examples"
2610.PP
2611Example: Try to exit cleanly on \s-1SIGINT\s0.
2612.PP
2613.Vb 5
2614\& static void
2615\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2616\& {
2617\& ev_break (loop, EVBREAK_ALL);
2618\& }
2619\&
2620\& ev_signal signal_watcher;
2621\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2622\& ev_signal_start (loop, &signal_watcher);
2623.Ve
1472.ie n .Sh """ev_child"" \- watch out for process status changes" 2624.ie n .SS """ev_child"" \- watch out for process status changes"
1473.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2625.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1474.IX Subsection "ev_child - watch out for process status changes" 2626.IX Subsection "ev_child - watch out for process status changes"
1475Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2627Child 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). 2628some child status changes (most typically when a child of yours dies or
2629exits). It is permissible to install a child watcher \fIafter\fR the child
2630has been forked (which implies it might have already exited), as long
2631as the event loop isn't entered (or is continued from a watcher), i.e.,
2632forking and then immediately registering a watcher for the child is fine,
2633but forking and registering a watcher a few event loop iterations later or
2634in the next callback invocation is not.
2635.PP
2636Only the default event loop is capable of handling signals, and therefore
2637you can only register child watchers in the default event loop.
2638.PP
2639Due to some design glitches inside libev, child watchers will always be
2640handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2641libev)
2642.PP
2643\fIProcess Interaction\fR
2644.IX Subsection "Process Interaction"
2645.PP
2646Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2647initialised. This is necessary to guarantee proper behaviour even if the
2648first child watcher is started after the child exits. The occurrence
2649of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2650synchronously as part of the event loop processing. Libev always reaps all
2651children, even ones not watched.
2652.PP
2653\fIOverriding the Built-In Processing\fR
2654.IX Subsection "Overriding the Built-In Processing"
2655.PP
2656Libev offers no special support for overriding the built-in child
2657processing, but if your application collides with libev's default child
2658handler, you can override it easily by installing your own handler for
2659\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2660default loop never gets destroyed. You are encouraged, however, to use an
2661event-based approach to child reaping and thus use libev's support for
2662that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2663.PP
2664\fIStopping the Child Watcher\fR
2665.IX Subsection "Stopping the Child Watcher"
2666.PP
2667Currently, the child watcher never gets stopped, even when the
2668child terminates, so normally one needs to stop the watcher in the
2669callback. Future versions of libev might stop the watcher automatically
2670when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2671problem).
1477.PP 2672.PP
1478\fIWatcher-Specific Functions and Data Members\fR 2673\fIWatcher-Specific Functions and Data Members\fR
1479.IX Subsection "Watcher-Specific Functions and Data Members" 2674.IX Subsection "Watcher-Specific Functions and Data Members"
1480.IP "ev_child_init (ev_child *, callback, int pid)" 4 2675.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1481.IX Item "ev_child_init (ev_child *, callback, int pid)" 2676.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1482.PD 0 2677.PD 0
1483.IP "ev_child_set (ev_child *, int pid)" 4 2678.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1484.IX Item "ev_child_set (ev_child *, int pid)" 2679.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1485.PD 2680.PD
1486Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2681Configures 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 2682\&\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 2683at 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 2684the 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 2685\&\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. 2686process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2687activate the watcher when the process terminates) or \f(CW1\fR (additionally
2688activate the watcher when the process is stopped or continued).
1492.IP "int pid [read\-only]" 4 2689.IP "int pid [read\-only]" 4
1493.IX Item "int pid [read-only]" 2690.IX Item "int pid [read-only]"
1494The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2691The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1495.IP "int rpid [read\-write]" 4 2692.IP "int rpid [read\-write]" 4
1496.IX Item "int rpid [read-write]" 2693.IX Item "int rpid [read-write]"
… …
1498.IP "int rstatus [read\-write]" 4 2695.IP "int rstatus [read\-write]" 4
1499.IX Item "int rstatus [read-write]" 2696.IX Item "int rstatus [read-write]"
1500The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2697The 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). 2698\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1502.PP 2699.PP
1503Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2700\fIExamples\fR
2701.IX Subsection "Examples"
1504.PP 2702.PP
2703Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2704its completion.
2705.PP
1505.Vb 5 2706.Vb 1
2707\& ev_child cw;
2708\&
1506\& static void 2709\& static void
1507\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2710\& child_cb (EV_P_ ev_child *w, int revents)
1508\& { 2711\& {
1509\& ev_unloop (loop, EVUNLOOP_ALL); 2712\& ev_child_stop (EV_A_ w);
2713\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1510\& } 2714\& }
2715\&
2716\& pid_t pid = fork ();
2717\&
2718\& if (pid < 0)
2719\& // error
2720\& else if (pid == 0)
2721\& {
2722\& // the forked child executes here
2723\& exit (1);
2724\& }
2725\& else
2726\& {
2727\& ev_child_init (&cw, child_cb, pid, 0);
2728\& ev_child_start (EV_DEFAULT_ &cw);
2729\& }
1511.Ve 2730.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?" 2731.ie n .SS """ev_stat"" \- did the file attributes just change?"
1519.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2732.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1520.IX Subsection "ev_stat - did the file attributes just change?" 2733.IX Subsection "ev_stat - did the file attributes just change?"
1521This watches a filesystem path for attribute changes. That is, it calls 2734This 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 2735\&\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. 2736and sees if it changed compared to the last time, invoking the callback if
2737it did.
1524.PP 2738.PP
1525The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2739The 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 2740not 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 2741exist\*(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 2742\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1529the stat buffer having unspecified contents. 2743least one) and all the other fields of the stat buffer having unspecified
2744contents.
1530.PP 2745.PP
1531The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2746The path \fImust not\fR end in a slash or contain special components such as
2747\&\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. 2748your working directory changes, then the behaviour is undefined.
1533.PP 2749.PP
1534Since there is no standard to do this, the portable implementation simply 2750Since 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 2751portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1536can specify a recommended polling interval for this case. If you specify 2752to see if it changed somehow. You can specify a recommended polling
1537a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2753interval 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 2754recommended!) then a \fIsuitable, unspecified default\fR value will be used
1539five seconds, although this might change dynamically). Libev will also 2755(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 2756change dynamically). Libev will also impose a minimum interval which is
1541usually overkill. 2757currently around \f(CW0.1\fR, but that's usually overkill.
1542.PP 2758.PP
1543This watcher type is not meant for massive numbers of stat watchers, 2759This watcher type is not meant for massive numbers of stat watchers,
1544as even with OS-supported change notifications, this can be 2760as even with OS-supported change notifications, this can be
1545resource\-intensive. 2761resource-intensive.
1546.PP 2762.PP
1547At the time of this writing, only the Linux inotify interface is 2763At the time of this writing, the only OS-specific interface implemented
1548implemented (implementing kqueue support is left as an exercise for the 2764is 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 2765exercise 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 2766implementing \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 2767.PP
1552usually detected immediately, and if the file exists there will be no 2768\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1553polling. 2769.IX Subsection "ABI Issues (Largefile Support)"
2770.PP
2771Libev by default (unless the user overrides this) uses the default
2772compilation environment, which means that on systems with large file
2773support disabled by default, you get the 32 bit version of the stat
2774structure. When using the library from programs that change the \s-1ABI\s0 to
2775use 64 bit file offsets the programs will fail. In that case you have to
2776compile libev with the same flags to get binary compatibility. This is
2777obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2778most noticeably displayed with ev_stat and large file support.
2779.PP
2780The solution for this is to lobby your distribution maker to make large
2781file interfaces available by default (as e.g. FreeBSD does) and not
2782optional. Libev cannot simply switch on large file support because it has
2783to exchange stat structures with application programs compiled using the
2784default compilation environment.
2785.PP
2786\fIInotify and Kqueue\fR
2787.IX Subsection "Inotify and Kqueue"
2788.PP
2789When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2790runtime, it will be used to speed up change detection where possible. The
2791inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2792watcher is being started.
2793.PP
2794Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2795except that changes might be detected earlier, and in some cases, to avoid
2796making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2797there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2798but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2799many bugs), the path exists (i.e. stat succeeds), and the path resides on
2800a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2801xfs are fully working) libev usually gets away without polling.
2802.PP
2803There is no support for kqueue, as apparently it cannot be used to
2804implement this functionality, due to the requirement of having a file
2805descriptor open on the object at all times, and detecting renames, unlinks
2806etc. is difficult.
2807.PP
2808\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2809.IX Subsection "stat () is a synchronous operation"
2810.PP
2811Libev doesn't normally do any kind of I/O itself, and so is not blocking
2812the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2813()\*(C'\fR, which is a synchronous operation.
2814.PP
2815For local paths, this usually doesn't matter: unless the system is very
2816busy or the intervals between stat's are large, a stat call will be fast,
2817as the path data is usually in memory already (except when starting the
2818watcher).
2819.PP
2820For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2821time due to network issues, and even under good conditions, a stat call
2822often takes multiple milliseconds.
2823.PP
2824Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2825paths, although this is fully supported by libev.
2826.PP
2827\fIThe special problem of stat time resolution\fR
2828.IX Subsection "The special problem of stat time resolution"
2829.PP
2830The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2831and even on systems where the resolution is higher, most file systems
2832still only support whole seconds.
2833.PP
2834That means that, if the time is the only thing that changes, you can
2835easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2836calls your callback, which does something. When there is another update
2837within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2838stat data does change in other ways (e.g. file size).
2839.PP
2840The solution to this is to delay acting on a change for slightly more
2841than a second (or till slightly after the next full second boundary), using
2842a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2843ev_timer_again (loop, w)\*(C'\fR).
2844.PP
2845The \f(CW.02\fR offset is added to work around small timing inconsistencies
2846of some operating systems (where the second counter of the current time
2847might be be delayed. One such system is the Linux kernel, where a call to
2848\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2849a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2850update file times then there will be a small window where the kernel uses
2851the previous second to update file times but libev might already execute
2852the timer callback).
1554.PP 2853.PP
1555\fIWatcher-Specific Functions and Data Members\fR 2854\fIWatcher-Specific Functions and Data Members\fR
1556.IX Subsection "Watcher-Specific Functions and Data Members" 2855.IX Subsection "Watcher-Specific Functions and Data Members"
1557.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2856.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)" 2857.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 2863\&\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 2864be 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 2865a 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. 2866path for as long as the watcher is active.
1568.Sp 2867.Sp
1569The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2868The 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 2869relative to the attributes at the time the watcher was started (or the
1571last change was detected). 2870last change was detected).
1572.IP "ev_stat_stat (ev_stat *)" 4 2871.IP "ev_stat_stat (loop, ev_stat *)" 4
1573.IX Item "ev_stat_stat (ev_stat *)" 2872.IX Item "ev_stat_stat (loop, ev_stat *)"
1574Updates the stat buffer immediately with new values. If you change the 2873Updates the stat buffer immediately with new values. If you change the
1575watched path in your callback, you could call this fucntion to avoid 2874watched path in your callback, you could call this function to avoid
1576detecting this change (while introducing a race condition). Can also be 2875detecting this change (while introducing a race condition if you are not
1577useful simply to find out the new values. 2876the only one changing the path). Can also be useful simply to find out the
2877new values.
1578.IP "ev_statdata attr [read\-only]" 4 2878.IP "ev_statdata attr [read\-only]" 4
1579.IX Item "ev_statdata attr [read-only]" 2879.IX Item "ev_statdata attr [read-only]"
1580The most-recently detected attributes of the file. Although the type is of 2880The 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 2881\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2882suitable 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 2883members 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. 2884some error while \f(CW\*(C`stat\*(C'\fRing the file.
1584.IP "ev_statdata prev [read\-only]" 4 2885.IP "ev_statdata prev [read\-only]" 4
1585.IX Item "ev_statdata prev [read-only]" 2886.IX Item "ev_statdata prev [read-only]"
1586The previous attributes of the file. The callback gets invoked whenever 2887The previous attributes of the file. The callback gets invoked whenever
1587\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 2888\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2889differ: \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,
2890\&\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 2891.IP "ev_tstamp interval [read\-only]" 4
1589.IX Item "ev_tstamp interval [read-only]" 2892.IX Item "ev_tstamp interval [read-only]"
1590The specified interval. 2893The specified interval.
1591.IP "const char *path [read\-only]" 4 2894.IP "const char *path [read\-only]" 4
1592.IX Item "const char *path [read-only]" 2895.IX Item "const char *path [read-only]"
1593The filesystem path that is being watched. 2896The file system path that is being watched.
2897.PP
2898\fIExamples\fR
2899.IX Subsection "Examples"
1594.PP 2900.PP
1595Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 2901Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1596.PP 2902.PP
1597.Vb 15 2903.Vb 10
1598\& static void 2904\& static void
1599\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 2905\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1600\& { 2906\& {
1601\& /* /etc/passwd changed in some way */ 2907\& /* /etc/passwd changed in some way */
1602\& if (w->attr.st_nlink) 2908\& if (w\->attr.st_nlink)
1603\& { 2909\& {
1604\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 2910\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1605\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 2911\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1606\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 2912\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1607\& } 2913\& }
1608\& else 2914\& else
1609\& /* you shalt not abuse printf for puts */ 2915\& /* you shalt not abuse printf for puts */
1610\& puts ("wow, /etc/passwd is not there, expect problems. " 2916\& puts ("wow, /etc/passwd is not there, expect problems. "
1611\& "if this is windows, they already arrived\en"); 2917\& "if this is windows, they already arrived\en");
1612\& } 2918\& }
2919\&
2920\& ...
2921\& ev_stat passwd;
2922\&
2923\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2924\& ev_stat_start (loop, &passwd);
1613.Ve 2925.Ve
2926.PP
2927Example: Like above, but additionally use a one-second delay so we do not
2928miss updates (however, frequent updates will delay processing, too, so
2929one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2930\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1614.PP 2931.PP
1615.Vb 2 2932.Vb 2
2933\& static ev_stat passwd;
2934\& static ev_timer timer;
2935\&
2936\& static void
2937\& timer_cb (EV_P_ ev_timer *w, int revents)
2938\& {
2939\& ev_timer_stop (EV_A_ w);
2940\&
2941\& /* now it\*(Aqs one second after the most recent passwd change */
2942\& }
2943\&
2944\& static void
2945\& stat_cb (EV_P_ ev_stat *w, int revents)
2946\& {
2947\& /* reset the one\-second timer */
2948\& ev_timer_again (EV_A_ &timer);
2949\& }
2950\&
1616\& ... 2951\& ...
1617\& ev_stat passwd;
1618.Ve
1619.PP
1620.Vb 2
1621\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 2952\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1622\& ev_stat_start (loop, &passwd); 2953\& ev_stat_start (loop, &passwd);
2954\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1623.Ve 2955.Ve
1624.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 2956.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..." 2957.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..." 2958.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 2959Idle watchers trigger events when no other events of the same or higher
1628priority are pending (prepare, check and other idle watchers do not 2960priority are pending (prepare, check and other idle watchers do not count
1629count). 2961as receiving \*(L"events\*(R").
1630.PP 2962.PP
1631That is, as long as your process is busy handling sockets or timeouts 2963That 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 2964(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 2965triggered. But when your process is idle (or only lower-priority watchers
1634are pending), the idle watchers are being called once per event loop 2966are pending), the idle watchers are being called once per event loop
… …
1638The most noteworthy effect is that as long as any idle watchers are 2970The most noteworthy effect is that as long as any idle watchers are
1639active, the process will not block when waiting for new events. 2971active, the process will not block when waiting for new events.
1640.PP 2972.PP
1641Apart from keeping your process non-blocking (which is a useful 2973Apart from keeping your process non-blocking (which is a useful
1642effect on its own sometimes), idle watchers are a good place to do 2974effect 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 2975\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1644event loop has handled all outstanding events. 2976event loop has handled all outstanding events.
1645.PP 2977.PP
1646\fIWatcher-Specific Functions and Data Members\fR 2978\fIWatcher-Specific Functions and Data Members\fR
1647.IX Subsection "Watcher-Specific Functions and Data Members" 2979.IX Subsection "Watcher-Specific Functions and Data Members"
1648.IP "ev_idle_init (ev_signal *, callback)" 4 2980.IP "ev_idle_init (ev_idle *, callback)" 4
1649.IX Item "ev_idle_init (ev_signal *, callback)" 2981.IX Item "ev_idle_init (ev_idle *, callback)"
1650Initialises and configures the idle watcher \- it has no parameters of any 2982Initialises 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, 2983kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1652believe me. 2984believe me.
1653.PP 2985.PP
2986\fIExamples\fR
2987.IX Subsection "Examples"
2988.PP
1654Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 2989Example: 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. 2990callback, free it. Also, use no error checking, as usual.
1656.PP 2991.PP
1657.Vb 7 2992.Vb 7
1658\& static void 2993\& static void
1659\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2994\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1660\& { 2995\& {
1661\& free (w); 2996\& free (w);
1662\& // now do something you wanted to do when the program has 2997\& // now do something you wanted to do when the program has
1663\& // no longer asnything immediate to do. 2998\& // no longer anything immediate to do.
1664\& } 2999\& }
1665.Ve 3000\&
1666.PP
1667.Vb 3
1668\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3001\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1669\& ev_idle_init (idle_watcher, idle_cb); 3002\& ev_idle_init (idle_watcher, idle_cb);
1670\& ev_idle_start (loop, idle_cb); 3003\& ev_idle_start (loop, idle_watcher);
1671.Ve 3004.Ve
1672.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3005.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!" 3006.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!" 3007.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1675Prepare and check watchers are usually (but not always) used in tandem: 3008Prepare and check watchers are usually (but not always) used in pairs:
1676prepare watchers get invoked before the process blocks and check watchers 3009prepare watchers get invoked before the process blocks and check watchers
1677afterwards. 3010afterwards.
1678.PP 3011.PP
1679You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3012You \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 3013the 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 3014watchers. Other loops than the current one are fine, however. The
1682rationale behind this is that you do not need to check for recursion in 3015rationale 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, 3016those 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 3017\&\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. 3018called in pairs bracketing the blocking call.
1686.PP 3019.PP
1687Their main purpose is to integrate other event mechanisms into libev and 3020Their main purpose is to integrate other event mechanisms into libev and
1688their use is somewhat advanced. This could be used, for example, to track 3021their use is somewhat advanced. They could be used, for example, to track
1689variable changes, implement your own watchers, integrate net-snmp or a 3022variable changes, implement your own watchers, integrate net-snmp or a
1690coroutine library and lots more. They are also occasionally useful if 3023coroutine library and lots more. They are also occasionally useful if
1691you cache some data and want to flush it before blocking (for example, 3024you 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 3025in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1693watcher). 3026watcher).
1694.PP 3027.PP
1695This is done by examining in each prepare call which file descriptors need 3028This 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 3029need 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 3030for 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 3031libraries provide exactly this functionality). Then, in the check watcher,
1699any events that occured (by checking the pending status of all watchers 3032you 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 3033of all watchers and stopping them) and call back into the library. The
1701callbacks will never actually be called (but must be valid nevertheless, 3034I/O and timer callbacks will never actually be called (but must be valid
1702because you never know, you know?). 3035nevertheless, because you never know, you know?).
1703.PP 3036.PP
1704As another example, the Perl Coro module uses these hooks to integrate 3037As another example, the Perl Coro module uses these hooks to integrate
1705coroutines into libev programs, by yielding to other active coroutines 3038coroutines into libev programs, by yielding to other active coroutines
1706during each prepare and only letting the process block if no coroutines 3039during each prepare and only letting the process block if no coroutines
1707are ready to run (it's actually more complicated: it only runs coroutines 3040are ready to run (it's actually more complicated: it only runs coroutines
… …
1710loop from blocking if lower-priority coroutines are active, thus mapping 3043loop from blocking if lower-priority coroutines are active, thus mapping
1711low-priority coroutines to idle/background tasks). 3044low-priority coroutines to idle/background tasks).
1712.PP 3045.PP
1713It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 3046It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
1714priority, to ensure that they are being run before any other watchers 3047priority, to ensure that they are being run before any other watchers
3048after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
3049.PP
1715after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 3050Also, \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 3051activate (\*(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 3052might 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 3053\&\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 3054loops 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 3055\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1721others). 3056others).
1722.PP 3057.PP
1723\fIWatcher-Specific Functions and Data Members\fR 3058\fIWatcher-Specific Functions and Data Members\fR
… …
1728.IP "ev_check_init (ev_check *, callback)" 4 3063.IP "ev_check_init (ev_check *, callback)" 4
1729.IX Item "ev_check_init (ev_check *, callback)" 3064.IX Item "ev_check_init (ev_check *, callback)"
1730.PD 3065.PD
1731Initialises and configures the prepare or check watcher \- they have no 3066Initialises 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 3067parameters 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. 3068macros, but using them is utterly, utterly, utterly and completely
3069pointless.
3070.PP
3071\fIExamples\fR
3072.IX Subsection "Examples"
1734.PP 3073.PP
1735There are a number of principal ways to embed other event loops or modules 3074There 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 3075into 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 3076(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 3077use 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 3078Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
1740into the Glib event loop). 3079Glib event loop).
1741.PP 3080.PP
1742Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, 3081Method 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 3082and 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 3083is 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 3084priority 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. 3085the callbacks for the IO/timeout watchers might not have been called yet.
1747.PP 3086.PP
1748.Vb 2 3087.Vb 2
1749\& static ev_io iow [nfd]; 3088\& static ev_io iow [nfd];
1750\& static ev_timer tw; 3089\& static ev_timer tw;
1751.Ve 3090\&
1752.PP
1753.Vb 4
1754\& static void 3091\& static void
1755\& io_cb (ev_loop *loop, ev_io *w, int revents) 3092\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1756\& { 3093\& {
1757\& } 3094\& }
1758.Ve 3095\&
1759.PP
1760.Vb 8
1761\& // create io watchers for each fd and a timer before blocking 3096\& // create io watchers for each fd and a timer before blocking
1762\& static void 3097\& static void
1763\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3098\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1764\& { 3099\& {
1765\& int timeout = 3600000; 3100\& int timeout = 3600000;
1766\& struct pollfd fds [nfd]; 3101\& struct pollfd fds [nfd];
1767\& // actual code will need to loop here and realloc etc. 3102\& // actual code will need to loop here and realloc etc.
1768\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3103\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1769.Ve 3104\&
1770.PP
1771.Vb 3
1772\& /* the callback is illegal, but won't be called as we stop during check */ 3105\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1773\& ev_timer_init (&tw, 0, timeout * 1e-3); 3106\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1774\& ev_timer_start (loop, &tw); 3107\& ev_timer_start (loop, &tw);
1775.Ve 3108\&
1776.PP
1777.Vb 6
1778\& // create one ev_io per pollfd 3109\& // create one ev_io per pollfd
1779\& for (int i = 0; i < nfd; ++i) 3110\& for (int i = 0; i < nfd; ++i)
1780\& { 3111\& {
1781\& ev_io_init (iow + i, io_cb, fds [i].fd, 3112\& ev_io_init (iow + i, io_cb, fds [i].fd,
1782\& ((fds [i].events & POLLIN ? EV_READ : 0) 3113\& ((fds [i].events & POLLIN ? EV_READ : 0)
1783\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3114\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1784.Ve 3115\&
1785.PP
1786.Vb 4
1787\& fds [i].revents = 0; 3116\& fds [i].revents = 0;
1788\& ev_io_start (loop, iow + i); 3117\& ev_io_start (loop, iow + i);
1789\& } 3118\& }
1790\& } 3119\& }
1791.Ve 3120\&
1792.PP
1793.Vb 5
1794\& // stop all watchers after blocking 3121\& // stop all watchers after blocking
1795\& static void 3122\& static void
1796\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3123\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1797\& { 3124\& {
1798\& ev_timer_stop (loop, &tw); 3125\& ev_timer_stop (loop, &tw);
1799.Ve 3126\&
1800.PP
1801.Vb 8
1802\& for (int i = 0; i < nfd; ++i) 3127\& for (int i = 0; i < nfd; ++i)
1803\& { 3128\& {
1804\& // set the relevant poll flags 3129\& // set the relevant poll flags
1805\& // could also call adns_processreadable etc. here 3130\& // could also call adns_processreadable etc. here
1806\& struct pollfd *fd = fds + i; 3131\& struct pollfd *fd = fds + i;
1807\& int revents = ev_clear_pending (iow + i); 3132\& int revents = ev_clear_pending (iow + i);
1808\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; 3133\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1809\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; 3134\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1810.Ve 3135\&
1811.PP
1812.Vb 3
1813\& // now stop the watcher 3136\& // now stop the watcher
1814\& ev_io_stop (loop, iow + i); 3137\& ev_io_stop (loop, iow + i);
1815\& } 3138\& }
1816.Ve 3139\&
1817.PP
1818.Vb 2
1819\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 3140\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1820\& } 3141\& }
1821.Ve 3142.Ve
1822.PP 3143.PP
1823Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR 3144Method 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. 3145in the prepare watcher and would dispose of the check watcher.
1825.PP 3146.PP
1826Method 3: If the module to be embedded supports explicit event 3147Method 3: If the module to be embedded supports explicit event
1827notification (adns does), you can also make use of the actual watcher 3148notification (libadns does), you can also make use of the actual watcher
1828callbacks, and only destroy/create the watchers in the prepare watcher. 3149callbacks, and only destroy/create the watchers in the prepare watcher.
1829.PP 3150.PP
1830.Vb 5 3151.Vb 5
1831\& static void 3152\& static void
1832\& timer_cb (EV_P_ ev_timer *w, int revents) 3153\& timer_cb (EV_P_ ev_timer *w, int revents)
1833\& { 3154\& {
1834\& adns_state ads = (adns_state)w->data; 3155\& adns_state ads = (adns_state)w\->data;
1835\& update_now (EV_A); 3156\& update_now (EV_A);
1836.Ve 3157\&
1837.PP
1838.Vb 2
1839\& adns_processtimeouts (ads, &tv_now); 3158\& adns_processtimeouts (ads, &tv_now);
1840\& } 3159\& }
1841.Ve 3160\&
1842.PP
1843.Vb 5
1844\& static void 3161\& static void
1845\& io_cb (EV_P_ ev_io *w, int revents) 3162\& io_cb (EV_P_ ev_io *w, int revents)
1846\& { 3163\& {
1847\& adns_state ads = (adns_state)w->data; 3164\& adns_state ads = (adns_state)w\->data;
1848\& update_now (EV_A); 3165\& update_now (EV_A);
1849.Ve 3166\&
1850.PP
1851.Vb 3
1852\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); 3167\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
1853\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); 3168\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
1854\& } 3169\& }
1855.Ve 3170\&
1856.PP
1857.Vb 1
1858\& // do not ever call adns_afterpoll 3171\& // do not ever call adns_afterpoll
1859.Ve 3172.Ve
1860.PP 3173.PP
1861Method 4: Do not use a prepare or check watcher because the module you 3174Method 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 3175want to embed is not flexible enough to support it. Instead, you can
1863their poll function. The drawback with this solution is that the main 3176override 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 3177main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
1865this. 3178this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3179libglib event loop.
1866.PP 3180.PP
1867.Vb 4 3181.Vb 4
1868\& static gint 3182\& static gint
1869\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) 3183\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1870\& { 3184\& {
1871\& int got_events = 0; 3185\& int got_events = 0;
1872.Ve 3186\&
1873.PP
1874.Vb 2
1875\& for (n = 0; n < nfds; ++n) 3187\& for (n = 0; n < nfds; ++n)
1876\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events 3188\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1877.Ve 3189\&
1878.PP
1879.Vb 2
1880\& if (timeout >= 0) 3190\& if (timeout >= 0)
1881\& // create/start timer 3191\& // create/start timer
1882.Ve 3192\&
1883.PP
1884.Vb 2
1885\& // poll 3193\& // poll
1886\& ev_loop (EV_A_ 0); 3194\& ev_run (EV_A_ 0);
1887.Ve 3195\&
1888.PP
1889.Vb 3
1890\& // stop timer again 3196\& // stop timer again
1891\& if (timeout >= 0) 3197\& if (timeout >= 0)
1892\& ev_timer_stop (EV_A_ &to); 3198\& ev_timer_stop (EV_A_ &to);
1893.Ve 3199\&
1894.PP
1895.Vb 3
1896\& // stop io watchers again - their callbacks should have set 3200\& // stop io watchers again \- their callbacks should have set
1897\& for (n = 0; n < nfds; ++n) 3201\& for (n = 0; n < nfds; ++n)
1898\& ev_io_stop (EV_A_ iow [n]); 3202\& ev_io_stop (EV_A_ iow [n]);
1899.Ve 3203\&
1900.PP
1901.Vb 2
1902\& return got_events; 3204\& return got_events;
1903\& } 3205\& }
1904.Ve 3206.Ve
1905.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3207.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1906.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3208.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1907.IX Subsection "ev_embed - when one backend isn't enough..." 3209.IX Subsection "ev_embed - when one backend isn't enough..."
1908This is a rather advanced watcher type that lets you embed one event loop 3210This 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 3211into 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 3212loop, other types of watchers might be handled in a delayed or incorrect
1911fashion and must not be used). 3213fashion and must not be used).
… …
1914prioritise I/O. 3216prioritise I/O.
1915.PP 3217.PP
1916As an example for a bug workaround, the kqueue backend might only support 3218As 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 3219sockets 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 3220still 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 3221so 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 3222it 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 3223will 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. 3224\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3225best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1923.PP 3226.PP
1924As for prioritising I/O: rarely you have the case where some fds have 3227As for prioritising I/O: under rare circumstances you have the case where
1925to be watched and handled very quickly (with low latency), and even 3228some fds have to be watched and handled very quickly (with low latency),
1926priorities and idle watchers might have too much overhead. In this case 3229and 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 3230this 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. 3231the rest in a second one, and embed the second one in the first.
1929.PP 3232.PP
1930As long as the watcher is active, the callback will be invoked every time 3233As 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 3234time 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 3235must 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 3236sweep and invoke their callbacks (the callback doesn't need to invoke the
1934loop strictly lower priority for example). You can also set the callback 3237\&\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 3238to give the embedded loop strictly lower priority for example).
1936embedded loop sweep.
1937.PP 3239.PP
1938As long as the watcher is started it will automatically handle events. The 3240You 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 3241will 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 3242.PP
1943Also, there have not currently been made special provisions for forking: 3243Fork 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, 3244is 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 3245embedding loop forks. In other cases, the user is responsible for calling
1946yourself. 3246\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1947.PP 3247.PP
1948Unfortunately, not all backends are embeddable, only the ones returned by 3248Unfortunately, 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 3249\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1950portable one. 3250portable one.
1951.PP 3251.PP
1952So when you want to use this feature you will always have to be prepared 3252So 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 3253that 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 3254this is to have a separate variables for your embeddable loop, try to
1955create it, and if that fails, use the normal loop for everything: 3255create it, and if that fails, use the normal loop for everything.
1956.PP 3256.PP
1957.Vb 3 3257\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1958\& struct ev_loop *loop_hi = ev_default_init (0); 3258.IX Subsection "ev_embed and fork"
1959\& struct ev_loop *loop_lo = 0;
1960\& struct ev_embed embed;
1961.Ve
1962.PP 3259.PP
1963.Vb 5 3260While 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 3261automatically be applied to the embedded loop as well, so no special
1965\& // (remember that a flags value of 0 means autodetection) 3262fork handling is required in that case. When the watcher is not running,
1966\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3263however, 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 ()) 3264as 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 3265.PP
1982\fIWatcher-Specific Functions and Data Members\fR 3266\fIWatcher-Specific Functions and Data Members\fR
1983.IX Subsection "Watcher-Specific Functions and Data Members" 3267.IX Subsection "Watcher-Specific Functions and Data Members"
1984.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3268.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)" 3269.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
… …
1989.PD 3273.PD
1990Configures the watcher to embed the given loop, which must be 3274Configures 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 3275embeddable. 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 3276invoked automatically, otherwise it is the responsibility of the callback
1993to invoke it (it will continue to be called until the sweep has been done, 3277to 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). 3278if you do not want that, you need to temporarily stop the embed watcher).
1995.IP "ev_embed_sweep (loop, ev_embed *)" 4 3279.IP "ev_embed_sweep (loop, ev_embed *)" 4
1996.IX Item "ev_embed_sweep (loop, ev_embed *)" 3280.IX Item "ev_embed_sweep (loop, ev_embed *)"
1997Make a single, non-blocking sweep over the embedded loop. This works 3281Make 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 3282similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1999apropriate way for embedded loops. 3283appropriate way for embedded loops.
2000.IP "struct ev_loop *loop [read\-only]" 4 3284.IP "struct ev_loop *other [read\-only]" 4
2001.IX Item "struct ev_loop *loop [read-only]" 3285.IX Item "struct ev_loop *other [read-only]"
2002The embedded event loop. 3286The embedded event loop.
3287.PP
3288\fIExamples\fR
3289.IX Subsection "Examples"
3290.PP
3291Example: Try to get an embeddable event loop and embed it into the default
3292event loop. If that is not possible, use the default loop. The default
3293loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3294\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3295used).
3296.PP
3297.Vb 3
3298\& struct ev_loop *loop_hi = ev_default_init (0);
3299\& struct ev_loop *loop_lo = 0;
3300\& ev_embed embed;
3301\&
3302\& // see if there is a chance of getting one that works
3303\& // (remember that a flags value of 0 means autodetection)
3304\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3305\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3306\& : 0;
3307\&
3308\& // if we got one, then embed it, otherwise default to loop_hi
3309\& if (loop_lo)
3310\& {
3311\& ev_embed_init (&embed, 0, loop_lo);
3312\& ev_embed_start (loop_hi, &embed);
3313\& }
3314\& else
3315\& loop_lo = loop_hi;
3316.Ve
3317.PP
3318Example: Check if kqueue is available but not recommended and create
3319a kqueue backend for use with sockets (which usually work with any
3320kqueue implementation). Store the kqueue/socket\-only event loop in
3321\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3322.PP
3323.Vb 3
3324\& struct ev_loop *loop = ev_default_init (0);
3325\& struct ev_loop *loop_socket = 0;
3326\& ev_embed embed;
3327\&
3328\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3329\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3330\& {
3331\& ev_embed_init (&embed, 0, loop_socket);
3332\& ev_embed_start (loop, &embed);
3333\& }
3334\&
3335\& if (!loop_socket)
3336\& loop_socket = loop;
3337\&
3338\& // now use loop_socket for all sockets, and loop for everything else
3339.Ve
2003.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3340.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" 3341.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" 3342.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 3343Fork 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 3344whoever 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 3345\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2009event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3346event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2010and only in the child after the fork. If whoever good citizen calling 3347and only in the child after the fork. If whoever good citizen calling
2011\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3348\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2012handlers will be invoked, too, of course. 3349handlers will be invoked, too, of course.
2013.PP 3350.PP
3351\fIThe special problem of life after fork \- how is it possible?\fR
3352.IX Subsection "The special problem of life after fork - how is it possible?"
3353.PP
3354Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3355up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3356sequence should be handled by libev without any problems.
3357.PP
3358This changes when the application actually wants to do event handling
3359in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3360fork.
3361.PP
3362The default mode of operation (for libev, with application help to detect
3363forks) is to duplicate all the state in the child, as would be expected
3364when \fIeither\fR the parent \fIor\fR the child process continues.
3365.PP
3366When both processes want to continue using libev, then this is usually the
3367wrong result. In that case, usually one process (typically the parent) is
3368supposed to continue with all watchers in place as before, while the other
3369process typically wants to start fresh, i.e. without any active watchers.
3370.PP
3371The cleanest and most efficient way to achieve that with libev is to
3372simply create a new event loop, which of course will be \*(L"empty\*(R", and
3373use that for new watchers. This has the advantage of not touching more
3374memory than necessary, and thus avoiding the copy-on-write, and the
3375disadvantage of having to use multiple event loops (which do not support
3376signal watchers).
3377.PP
3378When this is not possible, or you want to use the default loop for
3379other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3380\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3381Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3382watchers, so you have to be careful not to execute code that modifies
3383those watchers. Note also that in that case, you have to re-register any
3384signal watchers.
3385.PP
2014\fIWatcher-Specific Functions and Data Members\fR 3386\fIWatcher-Specific Functions and Data Members\fR
2015.IX Subsection "Watcher-Specific Functions and Data Members" 3387.IX Subsection "Watcher-Specific Functions and Data Members"
2016.IP "ev_fork_init (ev_signal *, callback)" 4 3388.IP "ev_fork_init (ev_fork *, callback)" 4
2017.IX Item "ev_fork_init (ev_signal *, callback)" 3389.IX Item "ev_fork_init (ev_fork *, callback)"
2018Initialises and configures the fork watcher \- it has no parameters of any 3390Initialises 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, 3391kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2020believe me. 3392really.
3393.ie n .SS """ev_cleanup"" \- even the best things end"
3394.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3395.IX Subsection "ev_cleanup - even the best things end"
3396Cleanup watchers are called just before the event loop is being destroyed
3397by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3398.PP
3399While there is no guarantee that the event loop gets destroyed, cleanup
3400watchers provide a convenient method to install cleanup hooks for your
3401program, worker threads and so on \- you just to make sure to destroy the
3402loop when you want them to be invoked.
3403.PP
3404Cleanup watchers are invoked in the same way as any other watcher. Unlike
3405all other watchers, they do not keep a reference to the event loop (which
3406makes a lot of sense if you think about it). Like all other watchers, you
3407can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3408.PP
3409\fIWatcher-Specific Functions and Data Members\fR
3410.IX Subsection "Watcher-Specific Functions and Data Members"
3411.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3412.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3413Initialises and configures the cleanup watcher \- it has no parameters of
3414any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3415pointless, I assure you.
3416.PP
3417Example: Register an atexit handler to destroy the default loop, so any
3418cleanup functions are called.
3419.PP
3420.Vb 5
3421\& static void
3422\& program_exits (void)
3423\& {
3424\& ev_loop_destroy (EV_DEFAULT_UC);
3425\& }
3426\&
3427\& ...
3428\& atexit (program_exits);
3429.Ve
3430.ie n .SS """ev_async"" \- how to wake up an event loop"
3431.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3432.IX Subsection "ev_async - how to wake up an event loop"
3433In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3434asynchronous sources such as signal handlers (as opposed to multiple event
3435loops \- those are of course safe to use in different threads).
3436.PP
3437Sometimes, however, you need to wake up an event loop you do not control,
3438for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3439watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3440it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3441.PP
3442This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3443too, are asynchronous in nature, and signals, too, will be compressed
3444(i.e. the number of callback invocations may be less than the number of
3445\&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3446of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3447signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3448even without knowing which loop owns the signal.
3449.PP
3450\fIQueueing\fR
3451.IX Subsection "Queueing"
3452.PP
3453\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3454is that the author does not know of a simple (or any) algorithm for a
3455multiple-writer-single-reader queue that works in all cases and doesn't
3456need elaborate support such as pthreads or unportable memory access
3457semantics.
3458.PP
3459That means that if you want to queue data, you have to provide your own
3460queue. But at least I can tell you how to implement locking around your
3461queue:
3462.IP "queueing from a signal handler context" 4
3463.IX Item "queueing from a signal handler context"
3464To implement race-free queueing, you simply add to the queue in the signal
3465handler but you block the signal handler in the watcher callback. Here is
3466an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3467.Sp
3468.Vb 1
3469\& static ev_async mysig;
3470\&
3471\& static void
3472\& sigusr1_handler (void)
3473\& {
3474\& sometype data;
3475\&
3476\& // no locking etc.
3477\& queue_put (data);
3478\& ev_async_send (EV_DEFAULT_ &mysig);
3479\& }
3480\&
3481\& static void
3482\& mysig_cb (EV_P_ ev_async *w, int revents)
3483\& {
3484\& sometype data;
3485\& sigset_t block, prev;
3486\&
3487\& sigemptyset (&block);
3488\& sigaddset (&block, SIGUSR1);
3489\& sigprocmask (SIG_BLOCK, &block, &prev);
3490\&
3491\& while (queue_get (&data))
3492\& process (data);
3493\&
3494\& if (sigismember (&prev, SIGUSR1)
3495\& sigprocmask (SIG_UNBLOCK, &block, 0);
3496\& }
3497.Ve
3498.Sp
3499(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3500instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3501either...).
3502.IP "queueing from a thread context" 4
3503.IX Item "queueing from a thread context"
3504The strategy for threads is different, as you cannot (easily) block
3505threads but you can easily preempt them, so to queue safely you need to
3506employ a traditional mutex lock, such as in this pthread example:
3507.Sp
3508.Vb 2
3509\& static ev_async mysig;
3510\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3511\&
3512\& static void
3513\& otherthread (void)
3514\& {
3515\& // only need to lock the actual queueing operation
3516\& pthread_mutex_lock (&mymutex);
3517\& queue_put (data);
3518\& pthread_mutex_unlock (&mymutex);
3519\&
3520\& ev_async_send (EV_DEFAULT_ &mysig);
3521\& }
3522\&
3523\& static void
3524\& mysig_cb (EV_P_ ev_async *w, int revents)
3525\& {
3526\& pthread_mutex_lock (&mymutex);
3527\&
3528\& while (queue_get (&data))
3529\& process (data);
3530\&
3531\& pthread_mutex_unlock (&mymutex);
3532\& }
3533.Ve
3534.PP
3535\fIWatcher-Specific Functions and Data Members\fR
3536.IX Subsection "Watcher-Specific Functions and Data Members"
3537.IP "ev_async_init (ev_async *, callback)" 4
3538.IX Item "ev_async_init (ev_async *, callback)"
3539Initialises and configures the async watcher \- it has no parameters of any
3540kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3541trust me.
3542.IP "ev_async_send (loop, ev_async *)" 4
3543.IX Item "ev_async_send (loop, ev_async *)"
3544Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3545an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3546returns.
3547.Sp
3548Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3549signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3550embedding section below on what exactly this means).
3551.Sp
3552Note that, as with other watchers in libev, multiple events might get
3553compressed into a single callback invocation (another way to look at
3554this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3555\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3556.Sp
3557This call incurs the overhead of at most one extra system call per event
3558loop iteration, if the event loop is blocked, and no syscall at all if
3559the event loop (or your program) is processing events. That means that
3560repeated calls are basically free (there is no need to avoid calls for
3561performance reasons) and that the overhead becomes smaller (typically
3562zero) under load.
3563.IP "bool = ev_async_pending (ev_async *)" 4
3564.IX Item "bool = ev_async_pending (ev_async *)"
3565Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3566watcher but the event has not yet been processed (or even noted) by the
3567event loop.
3568.Sp
3569\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3570the loop iterates next and checks for the watcher to have become active,
3571it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3572quickly check whether invoking the loop might be a good idea.
3573.Sp
3574Not that this does \fInot\fR check whether the watcher itself is pending,
3575only whether it has been requested to make this watcher pending: there
3576is a time window between the event loop checking and resetting the async
3577notification, and the callback being invoked.
2021.SH "OTHER FUNCTIONS" 3578.SH "OTHER FUNCTIONS"
2022.IX Header "OTHER FUNCTIONS" 3579.IX Header "OTHER FUNCTIONS"
2023There are some other functions of possible interest. Described. Here. Now. 3580There are some other functions of possible interest. Described. Here. Now.
2024.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3581.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)" 3582.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 3583This function combines a simple timer and an I/O watcher, calls your
2027callback on whichever event happens first and automatically stop both 3584callback 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 3585watchers. 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 3586or timeout without having to allocate/configure/start/stop/free one or
2030more watchers yourself. 3587more watchers yourself.
2031.Sp 3588.Sp
2032If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3589If \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 3590\&\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. 3591the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
2035.Sp 3592.Sp
2036If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3593If \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 3594started. 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 3595repeat = 0) will be started. \f(CW0\fR is a valid timeout.
2039dubious value.
2040.Sp 3596.Sp
2041The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3597The 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 3598passed 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 3599\&\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: 3600value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3601a timeout and an io event at the same time \- you probably should give io
3602events precedence.
3603.Sp
3604Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
2045.Sp 3605.Sp
2046.Vb 7 3606.Vb 7
2047\& static void stdin_ready (int revents, void *arg) 3607\& static void stdin_ready (int revents, void *arg)
3608\& {
3609\& if (revents & EV_READ)
3610\& /* stdin might have data for us, joy! */;
3611\& else if (revents & EV_TIMER)
3612\& /* doh, nothing entered */;
3613\& }
3614\&
3615\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3616.Ve
3617.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3618.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3619Feed an event on the given fd, as if a file descriptor backend detected
3620the given events.
3621.IP "ev_feed_signal_event (loop, int signum)" 4
3622.IX Item "ev_feed_signal_event (loop, int signum)"
3623Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3624which is async-safe.
3625.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3626.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3627This section explains some common idioms that are not immediately
3628obvious. Note that examples are sprinkled over the whole manual, and this
3629section only contains stuff that wouldn't fit anywhere else.
3630.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3631.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3632Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3633or modify at any time: libev will completely ignore it. This can be used
3634to associate arbitrary data with your watcher. If you need more data and
3635don't want to allocate memory separately and store a pointer to it in that
3636data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3637data:
3638.PP
3639.Vb 7
3640\& struct my_io
3641\& {
3642\& ev_io io;
3643\& int otherfd;
3644\& void *somedata;
3645\& struct whatever *mostinteresting;
3646\& };
3647\&
3648\& ...
3649\& struct my_io w;
3650\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3651.Ve
3652.PP
3653And since your callback will be called with a pointer to the watcher, you
3654can cast it back to your own type:
3655.PP
3656.Vb 5
3657\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3658\& {
3659\& struct my_io *w = (struct my_io *)w_;
3660\& ...
3661\& }
3662.Ve
3663.PP
3664More interesting and less C\-conformant ways of casting your callback
3665function type instead have been omitted.
3666.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3667.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3668Another common scenario is to use some data structure with multiple
3669embedded watchers, in effect creating your own watcher that combines
3670multiple libev event sources into one \*(L"super-watcher\*(R":
3671.PP
3672.Vb 6
3673\& struct my_biggy
3674\& {
3675\& int some_data;
3676\& ev_timer t1;
3677\& ev_timer t2;
3678\& }
3679.Ve
3680.PP
3681In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3682complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3683the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3684to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3685real programmers):
3686.PP
3687.Vb 1
3688\& #include <stddef.h>
3689\&
3690\& static void
3691\& t1_cb (EV_P_ ev_timer *w, int revents)
3692\& {
3693\& struct my_biggy big = (struct my_biggy *)
3694\& (((char *)w) \- offsetof (struct my_biggy, t1));
3695\& }
3696\&
3697\& static void
3698\& t2_cb (EV_P_ ev_timer *w, int revents)
3699\& {
3700\& struct my_biggy big = (struct my_biggy *)
3701\& (((char *)w) \- offsetof (struct my_biggy, t2));
3702\& }
3703.Ve
3704.SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3705.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3706Often you have structures like this in event-based programs:
3707.PP
3708.Vb 4
3709\& callback ()
2048\& { 3710\& {
2049\& if (revents & EV_TIMEOUT) 3711\& free (request);
2050\& /* doh, nothing entered */;
2051\& else if (revents & EV_READ)
2052\& /* stdin might have data for us, joy! */;
2053\& } 3712\& }
3713\&
3714\& request = start_new_request (..., callback);
2054.Ve 3715.Ve
2055.Sp 3716.PP
3717The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3718used to cancel the operation, or do other things with it.
3719.PP
3720It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3721immediately invoke the callback, for example, to report errors. Or you add
3722some caching layer that finds that it can skip the lengthy aspects of the
3723operation and simply invoke the callback with the result.
3724.PP
3725The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3726has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3727.PP
3728Even if you pass the request by some safer means to the callback, you
3729might want to do something to the request after starting it, such as
3730canceling it, which probably isn't working so well when the callback has
3731already been invoked.
3732.PP
3733A common way around all these issues is to make sure that
3734\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3735\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3736delay invoking the callback by e.g. using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher
3737for example, or more sneakily, by reusing an existing (stopped) watcher
3738and pushing it into the pending queue:
3739.PP
2056.Vb 1 3740.Vb 2
2057\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3741\& ev_set_cb (watcher, callback);
3742\& ev_feed_event (EV_A_ watcher, 0);
2058.Ve 3743.Ve
2059.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3744.PP
2060.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3745This 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 3746invoked, while not delaying callback invocation too much.
2062had happened for the specified watcher (which must be a pointer to an 3747.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
2063initialised but not necessarily started event watcher). 3748.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
2064.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3749Often (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)" 3750\&\fImodal\fR interaction, which is most easily implemented by recursively
2066Feed an event on the given fd, as if a file descriptor backend detected 3751invoking \f(CW\*(C`ev_run\*(C'\fR.
2067the given events it. 3752.PP
2068.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3753This brings the problem of exiting \- a callback might want to finish the
2069.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3754main \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 3755a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
2071loop!). 3756and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3757other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3758.PP
3759The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3760invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3761triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3762.PP
3763.Vb 2
3764\& // main loop
3765\& int exit_main_loop = 0;
3766\&
3767\& while (!exit_main_loop)
3768\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3769\&
3770\& // in a modal watcher
3771\& int exit_nested_loop = 0;
3772\&
3773\& while (!exit_nested_loop)
3774\& ev_run (EV_A_ EVRUN_ONCE);
3775.Ve
3776.PP
3777To exit from any of these loops, just set the corresponding exit variable:
3778.PP
3779.Vb 2
3780\& // exit modal loop
3781\& exit_nested_loop = 1;
3782\&
3783\& // exit main program, after modal loop is finished
3784\& exit_main_loop = 1;
3785\&
3786\& // exit both
3787\& exit_main_loop = exit_nested_loop = 1;
3788.Ve
3789.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3790.IX Subsection "THREAD LOCKING EXAMPLE"
3791Here is a fictitious example of how to run an event loop in a different
3792thread from where callbacks are being invoked and watchers are
3793created/added/removed.
3794.PP
3795For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3796which uses exactly this technique (which is suited for many high-level
3797languages).
3798.PP
3799The example uses a pthread mutex to protect the loop data, a condition
3800variable to wait for callback invocations, an async watcher to notify the
3801event loop thread and an unspecified mechanism to wake up the main thread.
3802.PP
3803First, you need to associate some data with the event loop:
3804.PP
3805.Vb 6
3806\& typedef struct {
3807\& mutex_t lock; /* global loop lock */
3808\& ev_async async_w;
3809\& thread_t tid;
3810\& cond_t invoke_cv;
3811\& } userdata;
3812\&
3813\& void prepare_loop (EV_P)
3814\& {
3815\& // for simplicity, we use a static userdata struct.
3816\& static userdata u;
3817\&
3818\& ev_async_init (&u\->async_w, async_cb);
3819\& ev_async_start (EV_A_ &u\->async_w);
3820\&
3821\& pthread_mutex_init (&u\->lock, 0);
3822\& pthread_cond_init (&u\->invoke_cv, 0);
3823\&
3824\& // now associate this with the loop
3825\& ev_set_userdata (EV_A_ u);
3826\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3827\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3828\&
3829\& // then create the thread running ev_run
3830\& pthread_create (&u\->tid, 0, l_run, EV_A);
3831\& }
3832.Ve
3833.PP
3834The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3835solely to wake up the event loop so it takes notice of any new watchers
3836that might have been added:
3837.PP
3838.Vb 5
3839\& static void
3840\& async_cb (EV_P_ ev_async *w, int revents)
3841\& {
3842\& // just used for the side effects
3843\& }
3844.Ve
3845.PP
3846The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3847protecting the loop data, respectively.
3848.PP
3849.Vb 6
3850\& static void
3851\& l_release (EV_P)
3852\& {
3853\& userdata *u = ev_userdata (EV_A);
3854\& pthread_mutex_unlock (&u\->lock);
3855\& }
3856\&
3857\& static void
3858\& l_acquire (EV_P)
3859\& {
3860\& userdata *u = ev_userdata (EV_A);
3861\& pthread_mutex_lock (&u\->lock);
3862\& }
3863.Ve
3864.PP
3865The event loop thread first acquires the mutex, and then jumps straight
3866into \f(CW\*(C`ev_run\*(C'\fR:
3867.PP
3868.Vb 4
3869\& void *
3870\& l_run (void *thr_arg)
3871\& {
3872\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3873\&
3874\& l_acquire (EV_A);
3875\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3876\& ev_run (EV_A_ 0);
3877\& l_release (EV_A);
3878\&
3879\& return 0;
3880\& }
3881.Ve
3882.PP
3883Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3884signal the main thread via some unspecified mechanism (signals? pipe
3885writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3886have been called (in a while loop because a) spurious wakeups are possible
3887and b) skipping inter-thread-communication when there are no pending
3888watchers is very beneficial):
3889.PP
3890.Vb 4
3891\& static void
3892\& l_invoke (EV_P)
3893\& {
3894\& userdata *u = ev_userdata (EV_A);
3895\&
3896\& while (ev_pending_count (EV_A))
3897\& {
3898\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3899\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3900\& }
3901\& }
3902.Ve
3903.PP
3904Now, whenever the main thread gets told to invoke pending watchers, it
3905will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3906thread to continue:
3907.PP
3908.Vb 4
3909\& static void
3910\& real_invoke_pending (EV_P)
3911\& {
3912\& userdata *u = ev_userdata (EV_A);
3913\&
3914\& pthread_mutex_lock (&u\->lock);
3915\& ev_invoke_pending (EV_A);
3916\& pthread_cond_signal (&u\->invoke_cv);
3917\& pthread_mutex_unlock (&u\->lock);
3918\& }
3919.Ve
3920.PP
3921Whenever you want to start/stop a watcher or do other modifications to an
3922event loop, you will now have to lock:
3923.PP
3924.Vb 2
3925\& ev_timer timeout_watcher;
3926\& userdata *u = ev_userdata (EV_A);
3927\&
3928\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3929\&
3930\& pthread_mutex_lock (&u\->lock);
3931\& ev_timer_start (EV_A_ &timeout_watcher);
3932\& ev_async_send (EV_A_ &u\->async_w);
3933\& pthread_mutex_unlock (&u\->lock);
3934.Ve
3935.PP
3936Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3937an event loop currently blocking in the kernel will have no knowledge
3938about the newly added timer. By waking up the loop it will pick up any new
3939watchers in the next event loop iteration.
3940.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3941.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3942While the overhead of a callback that e.g. schedules a thread is small, it
3943is still an overhead. If you embed libev, and your main usage is with some
3944kind of threads or coroutines, you might want to customise libev so that
3945doesn't need callbacks anymore.
3946.PP
3947Imagine you have coroutines that you can switch to using a function
3948\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3949and that due to some magic, the currently active coroutine is stored in a
3950global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3951event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3952the differing \f(CW\*(C`;\*(C'\fR conventions):
3953.PP
3954.Vb 2
3955\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3956\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3957.Ve
3958.PP
3959That means instead of having a C callback function, you store the
3960coroutine to switch to in each watcher, and instead of having libev call
3961your callback, you instead have it switch to that coroutine.
3962.PP
3963A coroutine might now wait for an event with a function called
3964\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3965matter when, or whether the watcher is active or not when this function is
3966called):
3967.PP
3968.Vb 6
3969\& void
3970\& wait_for_event (ev_watcher *w)
3971\& {
3972\& ev_cb_set (w) = current_coro;
3973\& switch_to (libev_coro);
3974\& }
3975.Ve
3976.PP
3977That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3978continues the libev coroutine, which, when appropriate, switches back to
3979this or any other coroutine.
3980.PP
3981You can do similar tricks if you have, say, threads with an event queue \-
3982instead of storing a coroutine, you store the queue object and instead of
3983switching to a coroutine, you push the watcher onto the queue and notify
3984any waiters.
3985.PP
3986To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3987files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3988.PP
3989.Vb 4
3990\& // my_ev.h
3991\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3992\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3993\& #include "../libev/ev.h"
3994\&
3995\& // my_ev.c
3996\& #define EV_H "my_ev.h"
3997\& #include "../libev/ev.c"
3998.Ve
3999.PP
4000And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4001\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4002can even use \fIev.h\fR as header file name directly.
2072.SH "LIBEVENT EMULATION" 4003.SH "LIBEVENT EMULATION"
2073.IX Header "LIBEVENT EMULATION" 4004.IX Header "LIBEVENT EMULATION"
2074Libev offers a compatibility emulation layer for libevent. It cannot 4005Libev offers a compatibility emulation layer for libevent. It cannot
2075emulate the internals of libevent, so here are some usage hints: 4006emulate the internals of libevent, so here are some usage hints:
4007.IP "\(bu" 4
4008Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4009.Sp
4010This was the newest libevent version available when libev was implemented,
4011and is still mostly unchanged in 2010.
4012.IP "\(bu" 4
2076.IP "* Use it by including <event.h>, as usual." 4 4013Use it by including <event.h>, as usual.
2077.IX Item "Use it by including <event.h>, as usual." 4014.IP "\(bu" 4
2078.PD 0 4015The 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 4016ev_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." 4017.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 4018Avoid 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)." 4019maintained 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 4020it 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." 4021.IP "\(bu" 4
4022Priorities are not currently supported. Initialising priorities
4023will fail and all watchers will have the same priority, even though there
4024is an ev_pri field.
4025.IP "\(bu" 4
4026In libevent, the last base created gets the signals, in libev, the
4027base that registered the signal gets the signals.
4028.IP "\(bu" 4
2085.IP "* Other members are not supported." 4 4029Other members are not supported.
2086.IX Item "Other members are not supported." 4030.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 4031The 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." 4032to use the libev header file and library.
2089.PD
2090.SH "\*(C+ SUPPORT" 4033.SH "\*(C+ SUPPORT"
2091.IX Header " SUPPORT" 4034.IX Header " SUPPORT"
2092Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4035Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2093you to use some convinience methods to start/stop watchers and also change 4036you to use some convenience methods to start/stop watchers and also change
2094the callback model to a model using method callbacks on objects. 4037the callback model to a model using method callbacks on objects.
2095.PP 4038.PP
2096To use it, 4039To use it,
2097.PP 4040.PP
2098.Vb 1 4041.Vb 1
2099\& #include <ev++.h> 4042\& #include <ev++.h>
2100.Ve 4043.Ve
2101.PP 4044.PP
2102This automatically includes \fIev.h\fR and puts all of its definitions (many 4045This automatically includes \fIev.h\fR and puts all of its definitions (many
2103of them macros) into the global namespace. All \*(C+ specific things are 4046of 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 4047put 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+ 4050Care 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 4051classes 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 4052that the watcher is associated with (or no additional members at all if
2110you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). 4053you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2111.PP 4054.PP
2112Currently, functions, and static and non-static member functions can be 4055Currently, functions, static and non-static member functions and classes
2113used as callbacks. Other types should be easy to add as long as they only 4056with \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 4057to add as long as they only need one additional pointer for context. If
2115types of functors please contact the author (preferably after implementing 4058you need support for other types of functors please contact the author
2116it). 4059(preferably after implementing it).
4060.PP
4061For all this to work, your \*(C+ compiler either has to use the same calling
4062conventions as your C compiler (for static member functions), or you have
4063to embed libev and compile libev itself as \*(C+.
2117.PP 4064.PP
2118Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4065Here 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 4066.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
2120.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4067.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2121.IX Item "ev::READ, ev::WRITE etc." 4068.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. 4069These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2123macros from \fIev.h\fR. 4070macros from \fIev.h\fR.
2124.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4071.ie n .IP """ev::tstamp"", ""ev::now""" 4
2125.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4072.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2126.IX Item "ev::tstamp, ev::now" 4073.IX Item "ev::tstamp, ev::now"
2127Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4074Aliases 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 4075.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 4076.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." 4077.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 4078For 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 4079the 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 4080which 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. 4081defined by many implementations.
2135.Sp 4082.Sp
2136All of those classes have these methods: 4083All of those classes have these methods:
2137.RS 4 4084.RS 4
2138.IP "ev::TYPE::TYPE ()" 4 4085.IP "ev::TYPE::TYPE ()" 4
2139.IX Item "ev::TYPE::TYPE ()" 4086.IX Item "ev::TYPE::TYPE ()"
2140.PD 0 4087.PD 0
2141.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 4088.IP "ev::TYPE::TYPE (loop)" 4
2142.IX Item "ev::TYPE::TYPE (struct ev_loop *)" 4089.IX Item "ev::TYPE::TYPE (loop)"
2143.IP "ev::TYPE::~TYPE" 4 4090.IP "ev::TYPE::~TYPE" 4
2144.IX Item "ev::TYPE::~TYPE" 4091.IX Item "ev::TYPE::~TYPE"
2145.PD 4092.PD
2146The constructor (optionally) takes an event loop to associate the watcher 4093The 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. 4094with. 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. 4117thunking function, making it as fast as a direct C callback.
2171.Sp 4118.Sp
2172Example: simple class declaration and watcher initialisation 4119Example: simple class declaration and watcher initialisation
2173.Sp 4120.Sp
2174.Vb 4 4121.Vb 4
2175\& struct myclass 4122\& struct myclass
2176\& { 4123\& {
2177\& void io_cb (ev::io &w, int revents) { } 4124\& void io_cb (ev::io &w, int revents) { }
2178\& } 4125\& }
2179.Ve 4126\&
2180.Sp
2181.Vb 3
2182\& myclass obj; 4127\& myclass obj;
2183\& ev::io iow; 4128\& ev::io iow;
2184\& iow.set <myclass, &myclass::io_cb> (&obj); 4129\& iow.set <myclass, &myclass::io_cb> (&obj);
4130.Ve
4131.IP "w\->set (object *)" 4
4132.IX Item "w->set (object *)"
4133This is a variation of a method callback \- leaving out the method to call
4134will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4135functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4136the time. Incidentally, you can then also leave out the template argument
4137list.
4138.Sp
4139The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4140int revents)\*(C'\fR.
4141.Sp
4142See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4143.Sp
4144Example: use a functor object as callback.
4145.Sp
4146.Vb 7
4147\& struct myfunctor
4148\& {
4149\& void operator() (ev::io &w, int revents)
4150\& {
4151\& ...
4152\& }
4153\& }
4154\&
4155\& myfunctor f;
4156\&
4157\& ev::io w;
4158\& w.set (&f);
2185.Ve 4159.Ve
2186.IP "w\->set<function> (void *data = 0)" 4 4160.IP "w\->set<function> (void *data = 0)" 4
2187.IX Item "w->set<function> (void *data = 0)" 4161.IX Item "w->set<function> (void *data = 0)"
2188Also sets a callback, but uses a static method or plain function as 4162Also 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 4163callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
… …
2191.Sp 4165.Sp
2192The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. 4166The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2193.Sp 4167.Sp
2194See the method\-\f(CW\*(C`set\*(C'\fR above for more details. 4168See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2195.Sp 4169.Sp
2196Example: 4170Example: Use a plain function as callback.
2197.Sp 4171.Sp
2198.Vb 2 4172.Vb 2
2199\& static void io_cb (ev::io &w, int revents) { } 4173\& static void io_cb (ev::io &w, int revents) { }
2200\& iow.set <io_cb> (); 4174\& iow.set <io_cb> ();
2201.Ve 4175.Ve
2202.IP "w\->set (struct ev_loop *)" 4 4176.IP "w\->set (loop)" 4
2203.IX Item "w->set (struct ev_loop *)" 4177.IX Item "w->set (loop)"
2204Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4178Associates 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). 4179do this when the watcher is inactive (and not pending either).
2206.IP "w\->set ([args])" 4 4180.IP "w\->set ([arguments])" 4
2207.IX Item "w->set ([args])" 4181.IX Item "w->set ([arguments])"
2208Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4182Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
2209called at least once. Unlike the C counterpart, an active watcher gets 4183method or a suitable start method must be called at least once. Unlike the
2210automatically stopped and restarted when reconfiguring it with this 4184C counterpart, an active watcher gets automatically stopped and restarted
2211method. 4185when reconfiguring it with this method.
2212.IP "w\->start ()" 4 4186.IP "w\->start ()" 4
2213.IX Item "w->start ()" 4187.IX Item "w->start ()"
2214Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the 4188Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2215constructor already stores the event loop. 4189constructor already stores the event loop.
4190.IP "w\->start ([arguments])" 4
4191.IX Item "w->start ([arguments])"
4192Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4193convenient to wrap them in one call. Uses the same type of arguments as
4194the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
2216.IP "w\->stop ()" 4 4195.IP "w\->stop ()" 4
2217.IX Item "w->stop ()" 4196.IX Item "w->stop ()"
2218Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4197Stops 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 4198.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 4199.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2221.IX Item "w->again () (ev::timer, ev::periodic only)" 4200.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 4201For \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. 4202\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2224.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 4203.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
… …
2231Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4210Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2232.RE 4211.RE
2233.RS 4 4212.RS 4
2234.RE 4213.RE
2235.PP 4214.PP
2236Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4215Example: Define a class with two I/O and idle watchers, start the I/O
2237the constructor. 4216watchers in the constructor.
2238.PP 4217.PP
2239.Vb 4 4218.Vb 5
2240\& class myclass 4219\& class myclass
2241\& { 4220\& {
2242\& ev_io io; void io_cb (ev::io &w, int revents); 4221\& ev::io io ; void io_cb (ev::io &w, int revents);
4222\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
2243\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4223\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2244.Ve 4224\&
2245.PP
2246.Vb 2
2247\& myclass (); 4225\& myclass (int fd)
2248\& }
2249.Ve
2250.PP
2251.Vb 4
2252\& myclass::myclass (int fd)
2253\& { 4226\& {
2254\& io .set <myclass, &myclass::io_cb > (this); 4227\& io .set <myclass, &myclass::io_cb > (this);
4228\& io2 .set <myclass, &myclass::io2_cb > (this);
2255\& idle.set <myclass, &myclass::idle_cb> (this); 4229\& idle.set <myclass, &myclass::idle_cb> (this);
2256.Ve 4230\&
2257.PP 4231\& io.set (fd, ev::WRITE); // configure the watcher
2258.Vb 2 4232\& io.start (); // start it whenever convenient
2259\& io.start (fd, ev::READ); 4233\&
4234\& io2.start (fd, ev::READ); // set + start in one call
4235\& }
2260\& } 4236\& };
2261.Ve 4237.Ve
4238.SH "OTHER LANGUAGE BINDINGS"
4239.IX Header "OTHER LANGUAGE BINDINGS"
4240Libev does not offer other language bindings itself, but bindings for a
4241number of languages exist in the form of third-party packages. If you know
4242any interesting language binding in addition to the ones listed here, drop
4243me a note.
4244.IP "Perl" 4
4245.IX Item "Perl"
4246The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4247libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4248there are additional modules that implement libev-compatible interfaces
4249to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4250\&\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
4251and \f(CW\*(C`EV::Glib\*(C'\fR).
4252.Sp
4253It can be found and installed via \s-1CPAN\s0, its homepage is at
4254<http://software.schmorp.de/pkg/EV>.
4255.IP "Python" 4
4256.IX Item "Python"
4257Python bindings can be found at <http://code.google.com/p/pyev/>. It
4258seems to be quite complete and well-documented.
4259.IP "Ruby" 4
4260.IX Item "Ruby"
4261Tony Arcieri has written a ruby extension that offers access to a subset
4262of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4263more on top of it. It can be found via gem servers. Its homepage is at
4264<http://rev.rubyforge.org/>.
4265.Sp
4266Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4267makes rev work even on mingw.
4268.IP "Haskell" 4
4269.IX Item "Haskell"
4270A haskell binding to libev is available at
4271http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4272.IP "D" 4
4273.IX Item "D"
4274Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4275be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4276.IP "Ocaml" 4
4277.IX Item "Ocaml"
4278Erkki Seppala has written Ocaml bindings for libev, to be found at
4279http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4280.IP "Lua" 4
4281.IX Item "Lua"
4282Brian Maher has written a partial interface to libev for lua (at the
4283time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4284http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
2262.SH "MACRO MAGIC" 4285.SH "MACRO MAGIC"
2263.IX Header "MACRO MAGIC" 4286.IX Header "MACRO MAGIC"
2264Libev can be compiled with a variety of options, the most fundamantal 4287Libev 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) 4288of 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. 4289functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2267.PP 4290.PP
2268To make it easier to write programs that cope with either variant, the 4291To make it easier to write programs that cope with either variant, the
2269following macros are defined: 4292following macros are defined:
2270.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4293.ie n .IP """EV_A"", ""EV_A_""" 4
2271.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4294.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2272.IX Item "EV_A, EV_A_" 4295.IX Item "EV_A, EV_A_"
2273This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4296This 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, 4297loop 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: 4298\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2276.Sp 4299.Sp
2277.Vb 3 4300.Vb 3
2278\& ev_unref (EV_A); 4301\& ev_unref (EV_A);
2279\& ev_timer_add (EV_A_ watcher); 4302\& ev_timer_add (EV_A_ watcher);
2280\& ev_loop (EV_A_ 0); 4303\& ev_run (EV_A_ 0);
2281.Ve 4304.Ve
2282.Sp 4305.Sp
2283It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4306It 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. 4307which is often provided by the following macro.
2285.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4308.ie n .IP """EV_P"", ""EV_P_""" 4
2286.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4309.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2287.IX Item "EV_P, EV_P_" 4310.IX Item "EV_P, EV_P_"
2288This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4311This 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, 4312loop 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: 4313\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2291.Sp 4314.Sp
2292.Vb 2 4315.Vb 2
2293\& // this is how ev_unref is being declared 4316\& // this is how ev_unref is being declared
2294\& static void ev_unref (EV_P); 4317\& static void ev_unref (EV_P);
2295.Ve 4318\&
2296.Sp
2297.Vb 2
2298\& // this is how you can declare your typical callback 4319\& // this is how you can declare your typical callback
2299\& static void cb (EV_P_ ev_timer *w, int revents) 4320\& static void cb (EV_P_ ev_timer *w, int revents)
2300.Ve 4321.Ve
2301.Sp 4322.Sp
2302It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4323It 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. 4324suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2304.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4325.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
2305.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4326.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2306.IX Item "EV_DEFAULT, EV_DEFAULT_" 4327.IX Item "EV_DEFAULT, EV_DEFAULT_"
2307Similar to the other two macros, this gives you the value of the default 4328Similar to the other two macros, this gives you the value of the default
2308loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4329loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4330will be initialised if it isn't already initialised.
4331.Sp
4332For non-multiplicity builds, these macros do nothing, so you always have
4333to initialise the loop somewhere.
4334.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4335.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4336.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4337Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4338default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4339is undefined when the default loop has not been initialised by a previous
4340execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4341.Sp
4342It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4343watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2309.PP 4344.PP
2310Example: Declare and initialise a check watcher, utilising the above 4345Example: Declare and initialise a check watcher, utilising the above
2311macros so it will work regardless of whether multiple loops are supported 4346macros so it will work regardless of whether multiple loops are supported
2312or not. 4347or not.
2313.PP 4348.PP
2314.Vb 5 4349.Vb 5
2315\& static void 4350\& static void
2316\& check_cb (EV_P_ ev_timer *w, int revents) 4351\& check_cb (EV_P_ ev_timer *w, int revents)
2317\& { 4352\& {
2318\& ev_check_stop (EV_A_ w); 4353\& ev_check_stop (EV_A_ w);
2319\& } 4354\& }
2320.Ve 4355\&
2321.PP
2322.Vb 4
2323\& ev_check check; 4356\& ev_check check;
2324\& ev_check_init (&check, check_cb); 4357\& ev_check_init (&check, check_cb);
2325\& ev_check_start (EV_DEFAULT_ &check); 4358\& ev_check_start (EV_DEFAULT_ &check);
2326\& ev_loop (EV_DEFAULT_ 0); 4359\& ev_run (EV_DEFAULT_ 0);
2327.Ve 4360.Ve
2328.SH "EMBEDDING" 4361.SH "EMBEDDING"
2329.IX Header "EMBEDDING" 4362.IX Header "EMBEDDING"
2330Libev can (and often is) directly embedded into host 4363Libev can (and often is) directly embedded into host
2331applications. Examples of applications that embed it include the Deliantra 4364applications. 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) 4365Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2333and rxvt\-unicode. 4366and rxvt-unicode.
2334.PP 4367.PP
2335The goal is to enable you to just copy the neecssary files into your 4368The 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 4369source 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 4370you can easily upgrade by simply copying (or having a checked-out copy of
2338libev somewhere in your source tree). 4371libev somewhere in your source tree).
2339.Sh "\s-1FILESETS\s0" 4372.SS "\s-1FILESETS\s0"
2340.IX Subsection "FILESETS" 4373.IX Subsection "FILESETS"
2341Depending on what features you need you need to include one or more sets of files 4374Depending on what features you need you need to include one or more sets of files
2342in your app. 4375in your application.
2343.PP 4376.PP
2344\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4377\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2345.IX Subsection "CORE EVENT LOOP" 4378.IX Subsection "CORE EVENT LOOP"
2346.PP 4379.PP
2347To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4380To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2348configuration (no autoconf): 4381configuration (no autoconf):
2349.PP 4382.PP
2350.Vb 2 4383.Vb 2
2351\& #define EV_STANDALONE 1 4384\& #define EV_STANDALONE 1
2352\& #include "ev.c" 4385\& #include "ev.c"
2353.Ve 4386.Ve
2354.PP 4387.PP
2355This will automatically include \fIev.h\fR, too, and should be done in a 4388This 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 4389single 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 4390it, 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 4391done by writing a wrapper around \fIev.h\fR that you can include instead and
2359where you can put other configuration options): 4392where you can put other configuration options):
2360.PP 4393.PP
2361.Vb 2 4394.Vb 2
2362\& #define EV_STANDALONE 1 4395\& #define EV_STANDALONE 1
2363\& #include "ev.h" 4396\& #include "ev.h"
2364.Ve 4397.Ve
2365.PP 4398.PP
2366Both header files and implementation files can be compiled with a \*(C+ 4399Both header files and implementation files can be compiled with a \*(C+
2367compiler (at least, thats a stated goal, and breakage will be treated 4400compiler (at least, that's a stated goal, and breakage will be treated
2368as a bug). 4401as a bug).
2369.PP 4402.PP
2370You need the following files in your source tree, or in a directory 4403You need the following files in your source tree, or in a directory
2371in your include path (e.g. in libev/ when using \-Ilibev): 4404in your include path (e.g. in libev/ when using \-Ilibev):
2372.PP 4405.PP
2373.Vb 4 4406.Vb 4
2374\& ev.h 4407\& ev.h
2375\& ev.c 4408\& ev.c
2376\& ev_vars.h 4409\& ev_vars.h
2377\& ev_wrap.h 4410\& ev_wrap.h
2378.Ve 4411\&
2379.PP
2380.Vb 1
2381\& ev_win32.c required on win32 platforms only 4412\& ev_win32.c required on win32 platforms only
2382.Ve 4413\&
2383.PP
2384.Vb 5
2385\& ev_select.c only when select backend is enabled (which is enabled by default) 4414\& 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) 4415\& 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) 4416\& 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) 4417\& 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) 4418\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2390.Ve 4419.Ve
2391.PP 4420.PP
2392\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4421\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2393to compile this single file. 4422to compile this single file.
2394.PP 4423.PP
… …
2396.IX Subsection "LIBEVENT COMPATIBILITY API" 4425.IX Subsection "LIBEVENT COMPATIBILITY API"
2397.PP 4426.PP
2398To include the libevent compatibility \s-1API\s0, also include: 4427To include the libevent compatibility \s-1API\s0, also include:
2399.PP 4428.PP
2400.Vb 1 4429.Vb 1
2401\& #include "event.c" 4430\& #include "event.c"
2402.Ve 4431.Ve
2403.PP 4432.PP
2404in the file including \fIev.c\fR, and: 4433in the file including \fIev.c\fR, and:
2405.PP 4434.PP
2406.Vb 1 4435.Vb 1
2407\& #include "event.h" 4436\& #include "event.h"
2408.Ve 4437.Ve
2409.PP 4438.PP
2410in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4439in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2411.PP 4440.PP
2412You need the following additional files for this: 4441You need the following additional files for this:
2413.PP 4442.PP
2414.Vb 2 4443.Vb 2
2415\& event.h 4444\& event.h
2416\& event.c 4445\& event.c
2417.Ve 4446.Ve
2418.PP 4447.PP
2419\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4448\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2420.IX Subsection "AUTOCONF SUPPORT" 4449.IX Subsection "AUTOCONF SUPPORT"
2421.PP 4450.PP
2422Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4451Instead 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 4452whatever 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 4453\&\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. 4454include \fIconfig.h\fR and configure itself accordingly.
2426.PP 4455.PP
2427For this of course you need the m4 file: 4456For this of course you need the m4 file:
2428.PP 4457.PP
2429.Vb 1 4458.Vb 1
2430\& libev.m4 4459\& libev.m4
2431.Ve 4460.Ve
2432.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4461.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2433.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4462.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2434Libev can be configured via a variety of preprocessor symbols you have to define 4463Libev 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 4464define before including (or compiling) any of its files. The default in
2436and only include the select backend. 4465the absence of autoconf is documented for every option.
4466.PP
4467Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4468values when compiling libev vs. including \fIev.h\fR, so it is permissible
4469to redefine them before including \fIev.h\fR without breaking compatibility
4470to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4471users of libev and the libev code itself must be compiled with compatible
4472settings.
4473.IP "\s-1EV_COMPAT3\s0 (h)" 4
4474.IX Item "EV_COMPAT3 (h)"
4475Backwards compatibility is a major concern for libev. This is why this
4476release of libev comes with wrappers for the functions and symbols that
4477have been renamed between libev version 3 and 4.
4478.Sp
4479You can disable these wrappers (to test compatibility with future
4480versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4481sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4482from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4483typedef in that case.
4484.Sp
4485In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4486and in some even more future version the compatibility code will be
4487removed completely.
2437.IP "\s-1EV_STANDALONE\s0" 4 4488.IP "\s-1EV_STANDALONE\s0 (h)" 4
2438.IX Item "EV_STANDALONE" 4489.IX Item "EV_STANDALONE (h)"
2439Must always be \f(CW1\fR if you do not use autoconf configuration, which 4490Must 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 4491keeps libev from including \fIconfig.h\fR, and it also defines dummy
2441implementations for some libevent functions (such as logging, which is not 4492implementations for some libevent functions (such as logging, which is not
2442supported). It will also not define any of the structs usually found in 4493supported). 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. 4494\&\fIevent.h\fR that are not directly supported by the libev core alone.
4495.Sp
4496In standalone mode, libev will still try to automatically deduce the
4497configuration, but has to be more conservative.
4498.IP "\s-1EV_USE_FLOOR\s0" 4
4499.IX Item "EV_USE_FLOOR"
4500If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4501periodic reschedule calculations, otherwise libev will fall back on a
4502portable (slower) implementation. If you enable this, you usually have to
4503link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4504function is not available will fail, so the safe default is to not enable
4505this.
2444.IP "\s-1EV_USE_MONOTONIC\s0" 4 4506.IP "\s-1EV_USE_MONOTONIC\s0" 4
2445.IX Item "EV_USE_MONOTONIC" 4507.IX Item "EV_USE_MONOTONIC"
2446If defined to be \f(CW1\fR, libev will try to detect the availability of the 4508If 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 4509monotonic clock option at both compile time and runtime. Otherwise no
2448of the monotonic clock option will be attempted. If you enable this, you 4510use of the monotonic clock option will be attempted. If you enable this,
2449usually have to link against librt or something similar. Enabling it when 4511you usually have to link against librt or something similar. Enabling it
2450the functionality isn't available is safe, though, althoguh you have 4512when 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 4513to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2452function is hiding in (often \fI\-lrt\fR). 4514function 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 4515.IP "\s-1EV_USE_REALTIME\s0" 4
2454.IX Item "EV_USE_REALTIME" 4516.IX Item "EV_USE_REALTIME"
2455If defined to be \f(CW1\fR, libev will try to detect the availability of the 4517If 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 4518real-time clock option at compile time (and assume its availability
2457runtime if successful). Otherwise no use of the realtime clock option will 4519at 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 4520option 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 4521by \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. 4522correctness. See the note about libraries in the description of
4523\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4524\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4525.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4526.IX Item "EV_USE_CLOCK_SYSCALL"
4527If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4528of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4529exists 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
4530unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4531programs needlessly. Using a direct syscall is slightly slower (in
4532theory), because no optimised vdso implementation can be used, but avoids
4533the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4534higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4535.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4536.IX Item "EV_USE_NANOSLEEP"
4537If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4538and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4539.IP "\s-1EV_USE_EVENTFD\s0" 4
4540.IX Item "EV_USE_EVENTFD"
4541If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4542available and will probe for kernel support at runtime. This will improve
4543\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4544If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
45452.7 or newer, otherwise disabled.
2461.IP "\s-1EV_USE_SELECT\s0" 4 4546.IP "\s-1EV_USE_SELECT\s0" 4
2462.IX Item "EV_USE_SELECT" 4547.IX Item "EV_USE_SELECT"
2463If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4548If 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 4549\&\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 4550other method takes over, select will be it. Otherwise the select backend
2466will not be compiled in. 4551will not be compiled in.
2467.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4552.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2468.IX Item "EV_SELECT_USE_FD_SET" 4553.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 4554If 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 4555structure. 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 4556\&\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 4557on exotic systems. This usually limits the range of file descriptors to
2473low limit such as 1024 or might have other limitations (winsocket only 4558some 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 4559only 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. 4560configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2476.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4561.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2477.IX Item "EV_SELECT_IS_WINSOCKET" 4562.IX Item "EV_SELECT_IS_WINSOCKET"
2478When defined to \f(CW1\fR, the select backend will assume that 4563When defined to \f(CW1\fR, the select backend will assume that
2479select/socket/connect etc. don't understand file descriptors but 4564select/socket/connect etc. don't understand file descriptors but
2480wants osf handles on win32 (this is the case when the select to 4565wants osf handles on win32 (this is the case when the select to
2481be used is the winsock select). This means that it will call 4566be 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, 4567\&\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 4568it is assumed that all these functions actually work on fds, even
2484on win32. Should not be defined on non\-win32 platforms. 4569on win32. Should not be defined on non\-win32 platforms.
4570.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4571.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4572If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4573file descriptors to socket handles. When not defining this symbol (the
4574default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4575correct. In some cases, programs use their own file descriptor management,
4576in which case they can provide this function to map fds to socket handles.
4577.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4578.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4579If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4580using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4581their own fd to handle mapping, overwriting this function makes it easier
4582to do so. This can be done by defining this macro to an appropriate value.
4583.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4584.IX Item "EV_WIN32_CLOSE_FD(fd)"
4585If programs implement their own fd to handle mapping on win32, then this
4586macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4587file descriptors again. Note that the replacement function has to close
4588the underlying \s-1OS\s0 handle.
2485.IP "\s-1EV_USE_POLL\s0" 4 4589.IP "\s-1EV_USE_POLL\s0" 4
2486.IX Item "EV_USE_POLL" 4590.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) 4591If 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 4592backend. Otherwise it will be enabled on non\-win32 platforms. It
2489takes precedence over select. 4593takes precedence over select.
2490.IP "\s-1EV_USE_EPOLL\s0" 4 4594.IP "\s-1EV_USE_EPOLL\s0" 4
2491.IX Item "EV_USE_EPOLL" 4595.IX Item "EV_USE_EPOLL"
2492If defined to be \f(CW1\fR, libev will compile in support for the Linux 4596If 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, 4597\&\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 4598otherwise another method will be used as fallback. This is the preferred
2495preferred backend for GNU/Linux systems. 4599backend for GNU/Linux systems. If undefined, it will be enabled if the
4600headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2496.IP "\s-1EV_USE_KQUEUE\s0" 4 4601.IP "\s-1EV_USE_KQUEUE\s0" 4
2497.IX Item "EV_USE_KQUEUE" 4602.IX Item "EV_USE_KQUEUE"
2498If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4603If 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, 4604\&\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 4605otherwise another method will be used as fallback. This is the preferred
… …
251010 port style backend. Its availability will be detected at runtime, 461510 port style backend. Its availability will be detected at runtime,
2511otherwise another method will be used as fallback. This is the preferred 4616otherwise another method will be used as fallback. This is the preferred
2512backend for Solaris 10 systems. 4617backend for Solaris 10 systems.
2513.IP "\s-1EV_USE_DEVPOLL\s0" 4 4618.IP "\s-1EV_USE_DEVPOLL\s0" 4
2514.IX Item "EV_USE_DEVPOLL" 4619.IX Item "EV_USE_DEVPOLL"
2515reserved for future expansion, works like the \s-1USE\s0 symbols above. 4620Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2516.IP "\s-1EV_USE_INOTIFY\s0" 4 4621.IP "\s-1EV_USE_INOTIFY\s0" 4
2517.IX Item "EV_USE_INOTIFY" 4622.IX Item "EV_USE_INOTIFY"
2518If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4623If 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 4624interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2520be detected at runtime. 4625be detected at runtime. If undefined, it will be enabled if the headers
4626indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4627.IP "\s-1EV_NO_SMP\s0" 4
4628.IX Item "EV_NO_SMP"
4629If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4630between threads, that is, threads can be used, but threads never run on
4631different cpus (or different cpu cores). This reduces dependencies
4632and makes libev faster.
4633.IP "\s-1EV_NO_THREADS\s0" 4
4634.IX Item "EV_NO_THREADS"
4635If defined to be \f(CW1\fR, libev will assume that it will never be called
4636from different threads, which is a stronger assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR,
4637above. This reduces dependencies and makes libev faster.
4638.IP "\s-1EV_ATOMIC_T\s0" 4
4639.IX Item "EV_ATOMIC_T"
4640Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4641access is atomic and serialised with respect to other threads or signal
4642contexts. No such type is easily found in the C language, so you can
4643provide your own type that you know is safe for your purposes. It is used
4644both for signal handler \*(L"locking\*(R" as well as for signal and thread safety
4645in \f(CW\*(C`ev_async\*(C'\fR watchers.
4646.Sp
4647In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4648(from \fIsignal.h\fR), which is usually good enough on most platforms,
4649although strictly speaking using a type that also implies a memory fence
4650is required.
2521.IP "\s-1EV_H\s0" 4 4651.IP "\s-1EV_H\s0 (h)" 4
2522.IX Item "EV_H" 4652.IX Item "EV_H (h)"
2523The name of the \fIev.h\fR header file used to include it. The default if 4653The 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 4654undefined 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. 4655used to virtually rename the \fIev.h\fR header file in case of conflicts.
2526.IP "\s-1EV_CONFIG_H\s0" 4 4656.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2527.IX Item "EV_CONFIG_H" 4657.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 4658If \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 4659\&\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. 4660\&\f(CW\*(C`EV_H\*(C'\fR, above.
2531.IP "\s-1EV_EVENT_H\s0" 4 4661.IP "\s-1EV_EVENT_H\s0 (h)" 4
2532.IX Item "EV_EVENT_H" 4662.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 4663Similarly 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. 4664of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2535.IP "\s-1EV_PROTOTYPES\s0" 4 4665.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2536.IX Item "EV_PROTOTYPES" 4666.IX Item "EV_PROTOTYPES (h)"
2537If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4667If 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 4668prototypes, but still define all the structs and other symbols. This is
2539occasionally useful if you want to provide your own wrapper functions 4669occasionally useful if you want to provide your own wrapper functions
2540around libev functions. 4670around libev functions.
2541.IP "\s-1EV_MULTIPLICITY\s0" 4 4671.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2543If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4673If 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 4674will 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 4675additional independent event loops. Otherwise there will be no support
2546for multiple event loops and there is no first event loop pointer 4676for multiple event loops and there is no first event loop pointer
2547argument. Instead, all functions act on the single default loop. 4677argument. Instead, all functions act on the single default loop.
4678.Sp
4679Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4680default loop when multiplicity is switched off \- you always have to
4681initialise the loop manually in this case.
2548.IP "\s-1EV_MINPRI\s0" 4 4682.IP "\s-1EV_MINPRI\s0" 4
2549.IX Item "EV_MINPRI" 4683.IX Item "EV_MINPRI"
2550.PD 0 4684.PD 0
2551.IP "\s-1EV_MAXPRI\s0" 4 4685.IP "\s-1EV_MAXPRI\s0" 4
2552.IX Item "EV_MAXPRI" 4686.IX Item "EV_MAXPRI"
… …
2559When doing priority-based operations, libev usually has to linearly search 4693When doing priority-based operations, libev usually has to linearly search
2560all the priorities, so having many of them (hundreds) uses a lot of space 4694all 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 4695and time, so using the defaults of five priorities (\-2 .. +2) is usually
2562fine. 4696fine.
2563.Sp 4697.Sp
2564If your embedding app does not need any priorities, defining these both to 4698If your embedding application does not need any priorities, defining these
2565\&\f(CW0\fR will save some memory and cpu. 4699both to \f(CW0\fR will save some memory and \s-1CPU\s0.
2566.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4700.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
2567.IX Item "EV_PERIODIC_ENABLE" 4701.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 4702If 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 4703the respective watcher type is supported. If defined to be \f(CW0\fR, then it
2570code. 4704is 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 4705.IP "\s-1EV_FEATURES\s0" 4
2581.IX Item "EV_STAT_ENABLE" 4706.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 4707If 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 4708speed (but with the full \s-1API\s0), you can define this symbol to request
2592some inlining decisions, saves roughly 30% codesize of amd64. 4709certain subsets of functionality. The default is to enable all features
4710that can be enabled on the platform.
4711.Sp
4712A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4713with some broad features you want) and then selectively re-enable
4714additional parts you want, for example if you want everything minimal,
4715but multiple event loop support, async and child watchers and the poll
4716backend, use this:
4717.Sp
4718.Vb 5
4719\& #define EV_FEATURES 0
4720\& #define EV_MULTIPLICITY 1
4721\& #define EV_USE_POLL 1
4722\& #define EV_CHILD_ENABLE 1
4723\& #define EV_ASYNC_ENABLE 1
4724.Ve
4725.Sp
4726The actual value is a bitset, it can be a combination of the following
4727values:
4728.RS 4
4729.ie n .IP "1 \- faster/larger code" 4
4730.el .IP "\f(CW1\fR \- faster/larger code" 4
4731.IX Item "1 - faster/larger code"
4732Use larger code to speed up some operations.
4733.Sp
4734Currently this is used to override some inlining decisions (enlarging the
4735code size by roughly 30% on amd64).
4736.Sp
4737When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4738gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4739assertions.
4740.ie n .IP "2 \- faster/larger data structures" 4
4741.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4742.IX Item "2 - faster/larger data structures"
4743Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4744hash table sizes and so on. This will usually further increase code size
4745and can additionally have an effect on the size of data structures at
4746runtime.
4747.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4748.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4749.IX Item "4 - full API configuration"
4750This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4751enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4752.ie n .IP "8 \- full \s-1API\s0" 4
4753.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4754.IX Item "8 - full API"
4755This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4756details on which parts of the \s-1API\s0 are still available without this
4757feature, and do not complain if this subset changes over time.
4758.ie n .IP "16 \- enable all optional watcher types" 4
4759.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4760.IX Item "16 - enable all optional watcher types"
4761Enables all optional watcher types. If you want to selectively enable
4762only some watcher types other than I/O and timers (e.g. prepare,
4763embed, async, child...) you can enable them manually by defining
4764\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4765.ie n .IP "32 \- enable all backends" 4
4766.el .IP "\f(CW32\fR \- enable all backends" 4
4767.IX Item "32 - enable all backends"
4768This enables all backends \- without this feature, you need to enable at
4769least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4770.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4771.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4772.IX Item "64 - enable OS-specific helper APIs"
4773Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4774default.
4775.RE
4776.RS 4
4777.Sp
4778Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4779reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4780code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4781watchers, timers and monotonic clock support.
4782.Sp
4783With an intelligent-enough linker (gcc+binutils are intelligent enough
4784when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4785your program might be left out as well \- a binary starting a timer and an
4786I/O watcher then might come out at only 5Kb.
4787.RE
4788.IP "\s-1EV_API_STATIC\s0" 4
4789.IX Item "EV_API_STATIC"
4790If this symbol is defined (by default it is not), then all identifiers
4791will have static linkage. This means that libev will not export any
4792identifiers, and you cannot link against libev anymore. This can be useful
4793when you embed libev, only want to use libev functions in a single file,
4794and do not want its identifiers to be visible.
4795.Sp
4796To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4797wants to use libev.
4798.Sp
4799This option only works when libev is compiled with a C compiler, as \*(C+
4800doesn't support the required declaration syntax.
4801.IP "\s-1EV_AVOID_STDIO\s0" 4
4802.IX Item "EV_AVOID_STDIO"
4803If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4804functions (printf, scanf, perror etc.). This will increase the code size
4805somewhat, but if your program doesn't otherwise depend on stdio and your
4806libc allows it, this avoids linking in the stdio library which is quite
4807big.
4808.Sp
4809Note that error messages might become less precise when this option is
4810enabled.
4811.IP "\s-1EV_NSIG\s0" 4
4812.IX Item "EV_NSIG"
4813The highest supported signal number, +1 (or, the number of
4814signals): Normally, libev tries to deduce the maximum number of signals
4815automatically, but sometimes this fails, in which case it can be
4816specified. Also, using a lower number than detected (\f(CW32\fR should be
4817good for about any system in existence) can save some memory, as libev
4818statically allocates some 12\-24 bytes per signal number.
2593.IP "\s-1EV_PID_HASHSIZE\s0" 4 4819.IP "\s-1EV_PID_HASHSIZE\s0" 4
2594.IX Item "EV_PID_HASHSIZE" 4820.IX Item "EV_PID_HASHSIZE"
2595\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 4821\&\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 4822pid. 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 4823usually more than enough. If you need to manage thousands of children you
2598increase this value (\fImust\fR be a power of two). 4824might want to increase this value (\fImust\fR be a power of two).
2599.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 4825.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2600.IX Item "EV_INOTIFY_HASHSIZE" 4826.IX Item "EV_INOTIFY_HASHSIZE"
2601\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 4827\&\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), 4828inotify 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 4829disabled), 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 4830\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2605two). 4831power of two).
4832.IP "\s-1EV_USE_4HEAP\s0" 4
4833.IX Item "EV_USE_4HEAP"
4834Heaps are not very cache-efficient. To improve the cache-efficiency of the
4835timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4836to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4837faster performance with many (thousands) of watchers.
4838.Sp
4839The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4840will be \f(CW0\fR.
4841.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4842.IX Item "EV_HEAP_CACHE_AT"
4843Heaps are not very cache-efficient. To improve the cache-efficiency of the
4844timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4845the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4846which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4847but avoids random read accesses on heap changes. This improves performance
4848noticeably with many (hundreds) of watchers.
4849.Sp
4850The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4851will be \f(CW0\fR.
4852.IP "\s-1EV_VERIFY\s0" 4
4853.IX Item "EV_VERIFY"
4854Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4855be done: If set to \f(CW0\fR, no internal verification code will be compiled
4856in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4857called. If set to \f(CW2\fR, then the internal verification code will be
4858called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4859verification code will be called very frequently, which will slow down
4860libev considerably.
4861.Sp
4862The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4863will be \f(CW0\fR.
2606.IP "\s-1EV_COMMON\s0" 4 4864.IP "\s-1EV_COMMON\s0" 4
2607.IX Item "EV_COMMON" 4865.IX Item "EV_COMMON"
2608By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4866By 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 4867this 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, 4868members. You have to define it each time you include one of the files,
2611though, and it must be identical each time. 4869though, and it must be identical each time.
2612.Sp 4870.Sp
2613For example, the perl \s-1EV\s0 module uses something like this: 4871For example, the perl \s-1EV\s0 module uses something like this:
2614.Sp 4872.Sp
2615.Vb 3 4873.Vb 3
2616\& #define EV_COMMON \e 4874\& #define EV_COMMON \e
2617\& SV *self; /* contains this struct */ \e 4875\& SV *self; /* contains this struct */ \e
2618\& SV *cb_sv, *fh /* note no trailing ";" */ 4876\& SV *cb_sv, *fh /* note no trailing ";" */
2619.Ve 4877.Ve
2620.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 4878.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2621.IX Item "EV_CB_DECLARE (type)" 4879.IX Item "EV_CB_DECLARE (type)"
2622.PD 0 4880.PD 0
2623.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 4881.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2625.IP "ev_set_cb (ev, cb)" 4 4883.IP "ev_set_cb (ev, cb)" 4
2626.IX Item "ev_set_cb (ev, cb)" 4884.IX Item "ev_set_cb (ev, cb)"
2627.PD 4885.PD
2628Can be used to change the callback member declaration in each watcher, 4886Can 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 4887and 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 4888definition and a statement, respectively. See the \fIev.h\fR header file for
2631their default definitions. One possible use for overriding these is to 4889their 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 4890avoid 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+. 4891method calls instead of plain function calls in \*(C+.
4892.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4893.IX Subsection "EXPORTED API SYMBOLS"
4894If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4895exported symbols, you can use the provided \fISymbol.*\fR files which list
4896all public symbols, one per line:
4897.PP
4898.Vb 2
4899\& Symbols.ev for libev proper
4900\& Symbols.event for the libevent emulation
4901.Ve
4902.PP
4903This can also be used to rename all public symbols to avoid clashes with
4904multiple versions of libev linked together (which is obviously bad in
4905itself, but sometimes it is inconvenient to avoid this).
4906.PP
4907A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4908include before including \fIev.h\fR:
4909.PP
4910.Vb 1
4911\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4912.Ve
4913.PP
4914This would create a file \fIwrap.h\fR which essentially looks like this:
4915.PP
4916.Vb 4
4917\& #define ev_backend myprefix_ev_backend
4918\& #define ev_check_start myprefix_ev_check_start
4919\& #define ev_check_stop myprefix_ev_check_stop
4920\& ...
4921.Ve
2634.Sh "\s-1EXAMPLES\s0" 4922.SS "\s-1EXAMPLES\s0"
2635.IX Subsection "EXAMPLES" 4923.IX Subsection "EXAMPLES"
2636For a real-world example of a program the includes libev 4924For a real-world example of a program the includes libev
2637verbatim, you can have a look at the \s-1EV\s0 perl module 4925verbatim, you can have a look at the \s-1EV\s0 perl module
2638(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 4926(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2639the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 4927the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2640interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 4928interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2641will be compiled. It is pretty complex because it provides its own header 4929will be compiled. It is pretty complex because it provides its own header
2642file. 4930file.
2643.Sp 4931.PP
2644The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 4932The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2645that everybody includes and which overrides some configure choices: 4933that everybody includes and which overrides some configure choices:
2646.Sp 4934.PP
2647.Vb 9 4935.Vb 8
2648\& #define EV_MINIMAL 1 4936\& #define EV_FEATURES 8
2649\& #define EV_USE_POLL 0 4937\& #define EV_USE_SELECT 1
2650\& #define EV_MULTIPLICITY 0
2651\& #define EV_PERIODIC_ENABLE 0 4938\& #define EV_PREPARE_ENABLE 1
4939\& #define EV_IDLE_ENABLE 1
2652\& #define EV_STAT_ENABLE 0 4940\& #define EV_SIGNAL_ENABLE 1
2653\& #define EV_FORK_ENABLE 0 4941\& #define EV_CHILD_ENABLE 1
4942\& #define EV_USE_STDEXCEPT 0
2654\& #define EV_CONFIG_H <config.h> 4943\& #define EV_CONFIG_H <config.h>
2655\& #define EV_MINPRI 0 4944\&
2656\& #define EV_MAXPRI 0
2657.Ve
2658.Sp
2659.Vb 1
2660\& #include "ev++.h" 4945\& #include "ev++.h"
2661.Ve 4946.Ve
2662.Sp 4947.PP
2663And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 4948And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2664.Sp 4949.PP
2665.Vb 2 4950.Vb 2
2666\& #include "ev_cpp.h" 4951\& #include "ev_cpp.h"
2667\& #include "ev.c" 4952\& #include "ev.c"
2668.Ve 4953.Ve
4954.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4955.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4956.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4957.IX Subsection "THREADS AND COROUTINES"
4958\fI\s-1THREADS\s0\fR
4959.IX Subsection "THREADS"
4960.PP
4961All libev functions are reentrant and thread-safe unless explicitly
4962documented otherwise, but libev implements no locking itself. This means
4963that you can use as many loops as you want in parallel, as long as there
4964are no concurrent calls into any libev function with the same loop
4965parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4966of course): libev guarantees that different event loops share no data
4967structures that need any locking.
4968.PP
4969Or to put it differently: calls with different loop parameters can be done
4970concurrently from multiple threads, calls with the same loop parameter
4971must be done serially (but can be done from different threads, as long as
4972only one thread ever is inside a call at any point in time, e.g. by using
4973a mutex per loop).
4974.PP
4975Specifically to support threads (and signal handlers), libev implements
4976so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4977concurrency on the same event loop, namely waking it up \*(L"from the
4978outside\*(R".
4979.PP
4980If you want to know which design (one loop, locking, or multiple loops
4981without or something else still) is best for your problem, then I cannot
4982help you, but here is some generic advice:
4983.IP "\(bu" 4
4984most applications have a main thread: use the default libev loop
4985in that thread, or create a separate thread running only the default loop.
4986.Sp
4987This helps integrating other libraries or software modules that use libev
4988themselves and don't care/know about threading.
4989.IP "\(bu" 4
4990one loop per thread is usually a good model.
4991.Sp
4992Doing this is almost never wrong, sometimes a better-performance model
4993exists, but it is always a good start.
4994.IP "\(bu" 4
4995other models exist, such as the leader/follower pattern, where one
4996loop is handed through multiple threads in a kind of round-robin fashion.
4997.Sp
4998Choosing a model is hard \- look around, learn, know that usually you can do
4999better than you currently do :\-)
5000.IP "\(bu" 4
5001often you need to talk to some other thread which blocks in the
5002event loop.
5003.Sp
5004\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5005(or from signal contexts...).
5006.Sp
5007An example use would be to communicate signals or other events that only
5008work in the default loop by registering the signal watcher with the
5009default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5010watcher callback into the event loop interested in the signal.
5011.PP
5012See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
5013.PP
5014\fI\s-1COROUTINES\s0\fR
5015.IX Subsection "COROUTINES"
5016.PP
5017Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5018libev fully supports nesting calls to its functions from different
5019coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5020different coroutines, and switch freely between both coroutines running
5021the loop, as long as you don't confuse yourself). The only exception is
5022that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5023.PP
5024Care has been taken to ensure that libev does not keep local state inside
5025\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5026they do not call any callbacks.
5027.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
5028.IX Subsection "COMPILER WARNINGS"
5029Depending on your compiler and compiler settings, you might get no or a
5030lot of warnings when compiling libev code. Some people are apparently
5031scared by this.
5032.PP
5033However, these are unavoidable for many reasons. For one, each compiler
5034has different warnings, and each user has different tastes regarding
5035warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5036targeting a specific compiler and compiler-version.
5037.PP
5038Another reason is that some compiler warnings require elaborate
5039workarounds, or other changes to the code that make it less clear and less
5040maintainable.
5041.PP
5042And of course, some compiler warnings are just plain stupid, or simply
5043wrong (because they don't actually warn about the condition their message
5044seems to warn about). For example, certain older gcc versions had some
5045warnings that resulted in an extreme number of false positives. These have
5046been fixed, but some people still insist on making code warn-free with
5047such buggy versions.
5048.PP
5049While libev is written to generate as few warnings as possible,
5050\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5051with any compiler warnings enabled unless you are prepared to cope with
5052them (e.g. by ignoring them). Remember that warnings are just that:
5053warnings, not errors, or proof of bugs.
5054.SS "\s-1VALGRIND\s0"
5055.IX Subsection "VALGRIND"
5056Valgrind has a special section here because it is a popular tool that is
5057highly useful. Unfortunately, valgrind reports are very hard to interpret.
5058.PP
5059If you think you found a bug (memory leak, uninitialised data access etc.)
5060in libev, then check twice: If valgrind reports something like:
5061.PP
5062.Vb 3
5063\& ==2274== definitely lost: 0 bytes in 0 blocks.
5064\& ==2274== possibly lost: 0 bytes in 0 blocks.
5065\& ==2274== still reachable: 256 bytes in 1 blocks.
5066.Ve
5067.PP
5068Then there is no memory leak, just as memory accounted to global variables
5069is not a memleak \- the memory is still being referenced, and didn't leak.
5070.PP
5071Similarly, under some circumstances, valgrind might report kernel bugs
5072as if it were a bug in libev (e.g. in realloc or in the poll backend,
5073although an acceptable workaround has been found here), or it might be
5074confused.
5075.PP
5076Keep in mind that valgrind is a very good tool, but only a tool. Don't
5077make it into some kind of religion.
5078.PP
5079If you are unsure about something, feel free to contact the mailing list
5080with the full valgrind report and an explanation on why you think this
5081is a bug in libev (best check the archives, too :). However, don't be
5082annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5083of learning how to interpret valgrind properly.
5084.PP
5085If you need, for some reason, empty reports from valgrind for your project
5086I suggest using suppression lists.
5087.SH "PORTABILITY NOTES"
5088.IX Header "PORTABILITY NOTES"
5089.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
5090.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5091GNU/Linux is the only common platform that supports 64 bit file/large file
5092interfaces but \fIdisables\fR them by default.
5093.PP
5094That means that libev compiled in the default environment doesn't support
5095files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5096.PP
5097Unfortunately, many programs try to work around this GNU/Linux issue
5098by enabling the large file \s-1API\s0, which makes them incompatible with the
5099standard libev compiled for their system.
5100.PP
5101Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5102suddenly make it incompatible to the default compile time environment,
5103i.e. all programs not using special compile switches.
5104.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
5105.IX Subsection "OS/X AND DARWIN BUGS"
5106The whole thing is a bug if you ask me \- basically any system interface
5107you touch is broken, whether it is locales, poll, kqueue or even the
5108OpenGL drivers.
5109.PP
5110\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5111.IX Subsection "kqueue is buggy"
5112.PP
5113The kqueue syscall is broken in all known versions \- most versions support
5114only sockets, many support pipes.
5115.PP
5116Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5117rotten platform, but of course you can still ask for it when creating a
5118loop \- embedding a socket-only kqueue loop into a select-based one is
5119probably going to work well.
5120.PP
5121\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5122.IX Subsection "poll is buggy"
5123.PP
5124Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5125implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5126release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5127.PP
5128Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5129this rotten platform, but of course you can still ask for it when creating
5130a loop.
5131.PP
5132\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5133.IX Subsection "select is buggy"
5134.PP
5135All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5136one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
5137descriptors you can pass in to 1024 \- your program suddenly crashes when
5138you use more.
5139.PP
5140There is an undocumented \*(L"workaround\*(R" for this \- defining
5141\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5142work on \s-1OS/X\s0.
5143.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5144.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5145\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5146.IX Subsection "errno reentrancy"
5147.PP
5148The default compile environment on Solaris is unfortunately so
5149thread-unsafe that you can't even use components/libraries compiled
5150without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5151defined by default. A valid, if stupid, implementation choice.
5152.PP
5153If you want to use libev in threaded environments you have to make sure
5154it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5155.PP
5156\fIEvent port backend\fR
5157.IX Subsection "Event port backend"
5158.PP
5159The scalable event interface for Solaris is called \*(L"event
5160ports\*(R". Unfortunately, this mechanism is very buggy in all major
5161releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5162a large number of spurious wakeups, make sure you have all the relevant
5163and latest kernel patches applied. No, I don't know which ones, but there
5164are multiple ones to apply, and afterwards, event ports actually work
5165great.
5166.PP
5167If you can't get it to work, you can try running the program by setting
5168the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5169\&\f(CW\*(C`select\*(C'\fR backends.
5170.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
5171.IX Subsection "AIX POLL BUG"
5172\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5173this by trying to avoid the poll backend altogether (i.e. it's not even
5174compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5175with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
5176.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5177.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5178\fIGeneral issues\fR
5179.IX Subsection "General issues"
5180.PP
5181Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5182requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5183model. Libev still offers limited functionality on this platform in
5184the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5185descriptors. This only applies when using Win32 natively, not when using
5186e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5187as every compiler comes with a slightly differently broken/incompatible
5188environment.
5189.PP
5190Lifting these limitations would basically require the full
5191re-implementation of the I/O system. If you are into this kind of thing,
5192then note that glib does exactly that for you in a very portable way (note
5193also that glib is the slowest event library known to man).
5194.PP
5195There is no supported compilation method available on windows except
5196embedding it into other applications.
5197.PP
5198Sensible signal handling is officially unsupported by Microsoft \- libev
5199tries its best, but under most conditions, signals will simply not work.
5200.PP
5201Not a libev limitation but worth mentioning: windows apparently doesn't
5202accept large writes: instead of resulting in a partial write, windows will
5203either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5204so make sure you only write small amounts into your sockets (less than a
5205megabyte seems safe, but this apparently depends on the amount of memory
5206available).
5207.PP
5208Due to the many, low, and arbitrary limits on the win32 platform and
5209the abysmal performance of winsockets, using a large number of sockets
5210is not recommended (and not reasonable). If your program needs to use
5211more than a hundred or so sockets, then likely it needs to use a totally
5212different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5213notification model, which cannot be implemented efficiently on windows
5214(due to Microsoft monopoly games).
5215.PP
5216A typical way to use libev under windows is to embed it (see the embedding
5217section for details) and use the following \fIevwrap.h\fR header file instead
5218of \fIev.h\fR:
5219.PP
5220.Vb 2
5221\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5222\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5223\&
5224\& #include "ev.h"
5225.Ve
5226.PP
5227And compile the following \fIevwrap.c\fR file into your project (make sure
5228you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5229.PP
5230.Vb 2
5231\& #include "evwrap.h"
5232\& #include "ev.c"
5233.Ve
5234.PP
5235\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5236.IX Subsection "The winsocket select function"
5237.PP
5238The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5239requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5240also extremely buggy). This makes select very inefficient, and also
5241requires a mapping from file descriptors to socket handles (the Microsoft
5242C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5243discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5244\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5245.PP
5246The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5247libraries and raw winsocket select is:
5248.PP
5249.Vb 2
5250\& #define EV_USE_SELECT 1
5251\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5252.Ve
5253.PP
5254Note that winsockets handling of fd sets is O(n), so you can easily get a
5255complexity in the O(nA\*^X) range when using win32.
5256.PP
5257\fILimited number of file descriptors\fR
5258.IX Subsection "Limited number of file descriptors"
5259.PP
5260Windows has numerous arbitrary (and low) limits on things.
5261.PP
5262Early versions of winsocket's select only supported waiting for a maximum
5263of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5264can only wait for \f(CW64\fR things at the same time internally; Microsoft
5265recommends spawning a chain of threads and wait for 63 handles and the
5266previous thread in each. Sounds great!).
5267.PP
5268Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5269to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5270call (which might be in libev or elsewhere, for example, perl and many
5271other interpreters do their own select emulation on windows).
5272.PP
5273Another limit is the number of file descriptors in the Microsoft runtime
5274libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5275fetish or something like this inside Microsoft). You can increase this
5276by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5277(another arbitrary limit), but is broken in many versions of the Microsoft
5278runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5279(depending on windows version and/or the phase of the moon). To get more,
5280you need to wrap all I/O functions and provide your own fd management, but
5281the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5282.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5283.IX Subsection "PORTABILITY REQUIREMENTS"
5284In addition to a working ISO-C implementation and of course the
5285backend-specific APIs, libev relies on a few additional extensions:
5286.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5287.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5288.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5289Libev assumes not only that all watcher pointers have the same internal
5290structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5291assumes that the same (machine) code can be used to call any watcher
5292callback: The watcher callbacks have different type signatures, but libev
5293calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5294.IP "pointer accesses must be thread-atomic" 4
5295.IX Item "pointer accesses must be thread-atomic"
5296Accessing a pointer value must be atomic, it must both be readable and
5297writable in one piece \- this is the case on all current architectures.
5298.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5299.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5300.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5301The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5302\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5303threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5304believed to be sufficiently portable.
5305.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5306.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5307.IX Item "sigprocmask must work in a threaded environment"
5308Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5309allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5310pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5311thread\*(R" or will block signals process-wide, both behaviours would
5312be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5313\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5314.Sp
5315The most portable way to handle signals is to block signals in all threads
5316except the initial one, and run the default loop in the initial thread as
5317well.
5318.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5319.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5320.IX Item "long must be large enough for common memory allocation sizes"
5321To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5322instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5323systems (Microsoft...) this might be unexpectedly low, but is still at
5324least 31 bits everywhere, which is enough for hundreds of millions of
5325watchers.
5326.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5327.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5328.IX Item "double must hold a time value in seconds with enough accuracy"
5329The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5330have at least 51 bits of mantissa (and 9 bits of exponent), which is
5331good enough for at least into the year 4000 with millisecond accuracy
5332(the design goal for libev). This requirement is overfulfilled by
5333implementations using \s-1IEEE\s0 754, which is basically all existing ones.
5334.Sp
5335With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
5336year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5337is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5338something like that, just kidding).
5339.PP
5340If you know of other additional requirements drop me a note.
2669.SH "COMPLEXITIES" 5341.SH "ALGORITHMIC COMPLEXITIES"
2670.IX Header "COMPLEXITIES" 5342.IX Header "ALGORITHMIC COMPLEXITIES"
2671In this section the complexities of (many of) the algorithms used inside 5343In this section the complexities of (many of) the algorithms used inside
2672libev will be explained. For complexity discussions about backends see the 5344libev will be documented. For complexity discussions about backends see
2673documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5345the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2674.Sp 5346.PP
2675All of the following are about amortised time: If an array needs to be 5347All of the following are about amortised time: If an array needs to be
2676extended, libev needs to realloc and move the whole array, but this 5348extended, libev needs to realloc and move the whole array, but this
2677happens asymptotically never with higher number of elements, so O(1) might 5349happens asymptotically rarer with higher number of elements, so O(1) might
2678mean it might do a lengthy realloc operation in rare cases, but on average 5350mean that libev does a lengthy realloc operation in rare cases, but on
2679it is much faster and asymptotically approaches constant time. 5351average it is much faster and asymptotically approaches constant time.
2680.RS 4
2681.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5352.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2682.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5353.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2683This means that, when you have a watcher that triggers in one hour and 5354This means that, when you have a watcher that triggers in one hour and
2684there are 100 watchers that would trigger before that then inserting will 5355there are 100 watchers that would trigger before that, then inserting will
2685have to skip those 100 watchers. 5356have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2686.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4 5357.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2687.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 5358.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2688That means that for changing a timer costs less than removing/adding them 5359That means that changing a timer costs less than removing/adding them,
2689as only the relative motion in the event queue has to be paid for. 5360as only the relative motion in the event queue has to be paid for.
2690.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 5361.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
2691.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 5362.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
2692These just add the watcher into an array or at the head of a list. 5363These just add the watcher into an array or at the head of a list.
5364.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
2693=item Stopping check/prepare/idle watchers: O(1) 5365.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5366.PD 0
2694.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5367.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2695.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5368.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5369.PD
2696These watchers are stored in lists then need to be walked to find the 5370These watchers are stored in lists, so they need to be walked to find the
2697correct watcher to remove. The lists are usually short (you don't usually 5371correct watcher to remove. The lists are usually short (you don't usually
2698have many watchers waiting for the same fd or signal). 5372have many watchers waiting for the same fd or signal: one is typical, two
5373is rare).
2699.IP "Finding the next timer per loop iteration: O(1)" 4 5374.IP "Finding the next timer in each loop iteration: O(1)" 4
2700.IX Item "Finding the next timer per loop iteration: O(1)" 5375.IX Item "Finding the next timer in each loop iteration: O(1)"
2701.PD 0 5376By virtue of using a binary or 4\-heap, the next timer is always found at a
5377fixed position in the storage array.
2702.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5378.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2703.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5379.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2704.PD
2705A change means an I/O watcher gets started or stopped, which requires 5380A change means an I/O watcher gets started or stopped, which requires
2706libev to recalculate its status (and possibly tell the kernel). 5381libev to recalculate its status (and possibly tell the kernel, depending
2707.IP "Activating one watcher: O(1)" 4 5382on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2708.IX Item "Activating one watcher: O(1)" 5383.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5384.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2709.PD 0 5385.PD 0
2710.IP "Priority handling: O(number_of_priorities)" 4 5386.IP "Priority handling: O(number_of_priorities)" 4
2711.IX Item "Priority handling: O(number_of_priorities)" 5387.IX Item "Priority handling: O(number_of_priorities)"
2712.PD 5388.PD
2713Priorities are implemented by allocating some space for each 5389Priorities are implemented by allocating some space for each
2714priority. When doing priority-based operations, libev usually has to 5390priority. When doing priority-based operations, libev usually has to
2715linearly search all the priorities. 5391linearly search all the priorities, but starting/stopping and activating
2716.RE 5392watchers becomes O(1) with respect to priority handling.
2717.RS 4 5393.IP "Sending an ev_async: O(1)" 4
5394.IX Item "Sending an ev_async: O(1)"
5395.PD 0
5396.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5397.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5398.IP "Processing signals: O(max_signal_number)" 4
5399.IX Item "Processing signals: O(max_signal_number)"
5400.PD
5401Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5402calls in the current loop iteration and the loop is currently
5403blocked. Checking for async and signal events involves iterating over all
5404running async watchers or all signal numbers.
5405.SH "PORTING FROM LIBEV 3.X TO 4.X"
5406.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5407The major version 4 introduced some incompatible changes to the \s-1API\s0.
5408.PP
5409At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5410for all changes, so most programs should still compile. The compatibility
5411layer might be removed in later versions of libev, so better update to the
5412new \s-1API\s0 early than late.
5413.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5414.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5415.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5416The backward compatibility mechanism can be controlled by
5417\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
5418section.
5419.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5420.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5421.IX Item "ev_default_destroy and ev_default_fork have been removed"
5422These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5423.Sp
5424.Vb 2
5425\& ev_loop_destroy (EV_DEFAULT_UC);
5426\& ev_loop_fork (EV_DEFAULT);
5427.Ve
5428.IP "function/symbol renames" 4
5429.IX Item "function/symbol renames"
5430A number of functions and symbols have been renamed:
5431.Sp
5432.Vb 3
5433\& ev_loop => ev_run
5434\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5435\& EVLOOP_ONESHOT => EVRUN_ONCE
5436\&
5437\& ev_unloop => ev_break
5438\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5439\& EVUNLOOP_ONE => EVBREAK_ONE
5440\& EVUNLOOP_ALL => EVBREAK_ALL
5441\&
5442\& EV_TIMEOUT => EV_TIMER
5443\&
5444\& ev_loop_count => ev_iteration
5445\& ev_loop_depth => ev_depth
5446\& ev_loop_verify => ev_verify
5447.Ve
5448.Sp
5449Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5450\&\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
5451associated constants have been renamed to not collide with the \f(CW\*(C`struct
5452ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5453as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5454\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5455typedef.
5456.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5457.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5458.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5459The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5460mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5461and work, but the library code will of course be larger.
5462.SH "GLOSSARY"
5463.IX Header "GLOSSARY"
5464.IP "active" 4
5465.IX Item "active"
5466A watcher is active as long as it has been started and not yet stopped.
5467See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5468.IP "application" 4
5469.IX Item "application"
5470In this document, an application is whatever is using libev.
5471.IP "backend" 4
5472.IX Item "backend"
5473The part of the code dealing with the operating system interfaces.
5474.IP "callback" 4
5475.IX Item "callback"
5476The address of a function that is called when some event has been
5477detected. Callbacks are being passed the event loop, the watcher that
5478received the event, and the actual event bitset.
5479.IP "callback/watcher invocation" 4
5480.IX Item "callback/watcher invocation"
5481The act of calling the callback associated with a watcher.
5482.IP "event" 4
5483.IX Item "event"
5484A change of state of some external event, such as data now being available
5485for reading on a file descriptor, time having passed or simply not having
5486any other events happening anymore.
5487.Sp
5488In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5489\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5490.IP "event library" 4
5491.IX Item "event library"
5492A software package implementing an event model and loop.
5493.IP "event loop" 4
5494.IX Item "event loop"
5495An entity that handles and processes external events and converts them
5496into callback invocations.
5497.IP "event model" 4
5498.IX Item "event model"
5499The model used to describe how an event loop handles and processes
5500watchers and events.
5501.IP "pending" 4
5502.IX Item "pending"
5503A watcher is pending as soon as the corresponding event has been
5504detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5505.IP "real time" 4
5506.IX Item "real time"
5507The physical time that is observed. It is apparently strictly monotonic :)
5508.IP "wall-clock time" 4
5509.IX Item "wall-clock time"
5510The time and date as shown on clocks. Unlike real time, it can actually
5511be wrong and jump forwards and backwards, e.g. when you adjust your
5512clock.
5513.IP "watcher" 4
5514.IX Item "watcher"
5515A data structure that describes interest in certain events. Watchers need
5516to be started (attached to an event loop) before they can receive events.
2718.SH "AUTHOR" 5517.SH "AUTHOR"
2719.IX Header "AUTHOR" 5518.IX Header "AUTHOR"
2720Marc Lehmann <libev@schmorp.de>. 5519Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5520Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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