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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-27" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2012-04-19" "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"
136.Vb 1
137\& #include <ev.h>
138.Ve
139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140.IX Subsection "EXAMPLE PROGRAM"
137.Vb 2 141.Vb 2
138\& /* this is the only header you need */ 142\& // a single header file is required
139\& #include <ev.h> 143\& #include <ev.h>
140.Ve 144\&
141.PP 145\& #include <stdio.h> // for puts
142.Vb 3 146\&
143\& /* what follows is a fully working example program */ 147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
144\& ev_io stdin_watcher; 149\& ev_io stdin_watcher;
145\& ev_timer timeout_watcher; 150\& ev_timer timeout_watcher;
146.Ve 151\&
147.PP 152\& // all watcher callbacks have a similar signature
148.Vb 8
149\& /* called when data readable on stdin */ 153\& // this callback is called when data is readable on stdin
150\& static void 154\& static void
151\& stdin_cb (EV_P_ struct ev_io *w, int revents) 155\& stdin_cb (EV_P_ ev_io *w, int revents)
152\& { 156\& {
153\& /* puts ("stdin ready"); */ 157\& puts ("stdin ready");
154\& ev_io_stop (EV_A_ w); /* just a syntax example */ 158\& // for one\-shot events, one must manually stop the watcher
155\& 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);
156\& } 164\& }
157.Ve 165\&
158.PP 166\& // another callback, this time for a time\-out
159.Vb 6
160\& static void 167\& static void
161\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 168\& timeout_cb (EV_P_ ev_timer *w, int revents)
162\& { 169\& {
163\& /* puts ("timeout"); */ 170\& puts ("timeout");
164\& 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);
165\& } 173\& }
166.Ve 174\&
167.PP
168.Vb 4
169\& int 175\& int
170\& main (void) 176\& main (void)
171\& { 177\& {
172\& struct ev_loop *loop = ev_default_loop (0); 178\& // use the default event loop unless you have special needs
173.Ve 179\& struct ev_loop *loop = EV_DEFAULT;
174.PP 180\&
175.Vb 3
176\& /* 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
177\& 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);
178\& ev_io_start (loop, &stdin_watcher); 184\& ev_io_start (loop, &stdin_watcher);
179.Ve 185\&
180.PP 186\& // initialise a timer watcher, then start it
181.Vb 3
182\& /* simple non-repeating 5.5 second timeout */ 187\& // simple non\-repeating 5.5 second timeout
183\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
184\& ev_timer_start (loop, &timeout_watcher); 189\& ev_timer_start (loop, &timeout_watcher);
185.Ve 190\&
186.PP 191\& // now wait for events to arrive
187.Vb 2
188\& /* loop till timeout or data ready */
189\& ev_loop (loop, 0); 192\& ev_run (loop, 0);
190.Ve 193\&
191.PP 194\& // break was called, so exit
192.Vb 2
193\& return 0; 195\& return 0;
194\& } 196\& }
195.Ve 197.Ve
196.SH "DESCRIPTION" 198.SH "ABOUT THIS DOCUMENT"
197.IX Header "DESCRIPTION" 199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
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"
198Libev 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
199file descriptor being readable or a timeout occuring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
200these event sources and provide your program with events. 224these event sources and provide your program with events.
201.PP 225.PP
202To 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
203(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
204communicate events via a callback mechanism. 228communicate events via a callback mechanism.
205.PP 229.PP
206You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
207watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
208details 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
209watcher. 233watcher.
210.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
211.IX Header "FEATURES" 235.IX Subsection "FEATURES"
212Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
213kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
214timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
215events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
216loop mechanism itself (idle, prepare and check watchers). It also is quite 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
217fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
218it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
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
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).
247.PP
248It also is quite fast (see this
249benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
250for example).
219.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
220.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
221Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
222will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
223about various configuration options please have a look at the file 255more info about various configuration options please have a look at
224\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
225support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
226argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
227will not have this argument. 259this argument.
228.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
229.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
230Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
231(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
232the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
233called \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
234to 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
235it, you should treat it as such. 267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
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.
236.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
237.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
238These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
239library in any way. 293library in any way.
240.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
241.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
242Returns 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
243\&\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
244you 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).
245.IP "int ev_version_major ()" 4 311.IP "int ev_version_major ()" 4
246.IX Item "int ev_version_major ()" 312.IX Item "int ev_version_major ()"
247.PD 0 313.PD 0
248.IP "int ev_version_minor ()" 4 314.IP "int ev_version_minor ()" 4
249.IX Item "int ev_version_minor ()" 315.IX Item "int ev_version_minor ()"
250.PD 316.PD
251You can find out the major and minor version numbers of the library 317You can find out the major and minor \s-1ABI\s0 version numbers of the library
252you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 318you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
253\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 319\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
254symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 320symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
255version of the library your program was compiled against. 321version of the library your program was compiled against.
256.Sp 322.Sp
323These version numbers refer to the \s-1ABI\s0 version of the library, not the
324release version.
325.Sp
257Usually, it's a good idea to terminate if the major versions mismatch, 326Usually, it's a good idea to terminate if the major versions mismatch,
258as this indicates an incompatible change. Minor versions are usually 327as this indicates an incompatible change. Minor versions are usually
259compatible to older versions, so a larger minor version alone is usually 328compatible to older versions, so a larger minor version alone is usually
260not a problem. 329not a problem.
261.Sp 330.Sp
262Example: make sure we haven't accidentally been linked against the wrong 331Example: Make sure we haven't accidentally been linked against the wrong
263version: 332version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333such as \s-1LFS\s0 or reentrancy).
264.Sp 334.Sp
265.Vb 3 335.Vb 3
266\& assert (("libev version mismatch", 336\& assert (("libev version mismatch",
267\& ev_version_major () == EV_VERSION_MAJOR 337\& ev_version_major () == EV_VERSION_MAJOR
268\& && ev_version_minor () >= EV_VERSION_MINOR)); 338\& && ev_version_minor () >= EV_VERSION_MINOR));
269.Ve 339.Ve
270.IP "unsigned int ev_supported_backends ()" 4 340.IP "unsigned int ev_supported_backends ()" 4
271.IX Item "unsigned int ev_supported_backends ()" 341.IX Item "unsigned int ev_supported_backends ()"
272Return 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
273value) compiled into this binary of libev (independent of their 343value) compiled into this binary of libev (independent of their
… …
276.Sp 346.Sp
277Example: 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
278a 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
279.Sp 349.Sp
280.Vb 2 350.Vb 2
281\& assert (("sorry, no epoll, no sex", 351\& assert (("sorry, no epoll, no sex",
282\& ev_supported_backends () & EVBACKEND_EPOLL)); 352\& ev_supported_backends () & EVBACKEND_EPOLL));
283.Ve 353.Ve
284.IP "unsigned int ev_recommended_backends ()" 4 354.IP "unsigned int ev_recommended_backends ()" 4
285.IX Item "unsigned int ev_recommended_backends ()" 355.IX Item "unsigned int ev_recommended_backends ()"
286Return 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
287recommended 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
288returned 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
289most BSDs and will not be autodetected unless you explicitly request it 360and will not be auto-detected unless you explicitly request it (assuming
290(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
291libev will probe for if you specify no backends explicitly. 362probe for if you specify no backends explicitly.
292.IP "unsigned int ev_embeddable_backends ()" 4 363.IP "unsigned int ev_embeddable_backends ()" 4
293.IX Item "unsigned int ev_embeddable_backends ()" 364.IX Item "unsigned int ev_embeddable_backends ()"
294Returns 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
295is the theoretical, all\-platform, value. To find which backends 366value is platform-specific but can include backends not available on the
296might be supported on the current system, you would need to look at 367current system. To find which embeddable backends might be supported on
297\&\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 ()
298recommended ones. 369& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
299.Sp 370.Sp
300See 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.
301.IP "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 4 372.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
302.IX Item "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 373.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
303Sets the allocation function to use (the prototype and semantics are 374Sets the allocation function to use (the prototype is similar \- the
304identical to the realloc C function). It is used to allocate and free 375semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
305memory (no surprises here). If it returns zero when memory needs to be 376used to allocate and free memory (no surprises here). If it returns zero
306allocated, the library might abort or take some potentially destructive 377when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
307action. The default is your system realloc function. 378or take some potentially destructive action.
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.
308.Sp 383.Sp
309You could override this function in high-availability programs to, say, 384You could override this function in high-availability programs to, say,
310free 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,
311or 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.
312.Sp 387.Sp
313Example: 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
314retries: better than mine). 389retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
315.Sp 390.Sp
316.Vb 6 391.Vb 6
317\& static void * 392\& static void *
318\& persistent_realloc (void *ptr, size_t size) 393\& persistent_realloc (void *ptr, size_t size)
319\& { 394\& {
320\& for (;;) 395\& for (;;)
321\& { 396\& {
322\& void *newptr = realloc (ptr, size); 397\& void *newptr = realloc (ptr, size);
323.Ve 398\&
324.Sp
325.Vb 2
326\& if (newptr) 399\& if (newptr)
327\& return newptr; 400\& return newptr;
328.Ve 401\&
329.Sp
330.Vb 3
331\& sleep (60); 402\& sleep (60);
332\& } 403\& }
333\& } 404\& }
334.Ve 405\&
335.Sp
336.Vb 2
337\& ... 406\& ...
338\& ev_set_allocator (persistent_realloc); 407\& ev_set_allocator (persistent_realloc);
339.Ve 408.Ve
340.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 409.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
341.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 410.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
342Set the callback function to call on a retryable syscall error (such 411Set the callback function to call on a retryable system call error (such
343as failed select, poll, epoll_wait). The message is a printable string 412as failed select, poll, epoll_wait). The message is a printable string
344indicating the system call or subsystem causing the problem. If this 413indicating the system call or subsystem causing the problem. If this
345callback 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
346matter what, when it returns. That is, libev will generally retry the 415matter what, when it returns. That is, libev will generally retry the
347requested 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
348(such as abort). 417(such as abort).
349.Sp 418.Sp
350Example: do the same thing as libev does internally: 419Example: This is basically the same thing that libev does internally, too.
351.Sp 420.Sp
352.Vb 6 421.Vb 6
353\& static void 422\& static void
354\& fatal_error (const char *msg) 423\& fatal_error (const char *msg)
355\& { 424\& {
356\& perror (msg); 425\& perror (msg);
357\& abort (); 426\& abort ();
358\& } 427\& }
359.Ve 428\&
360.Sp
361.Vb 2
362\& ... 429\& ...
363\& ev_set_syserr_cb (fatal_error); 430\& ev_set_syserr_cb (fatal_error);
364.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.
365.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 444.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
366.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 445.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
367An 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
368types 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
369events, and dynamically created loops which do not. 448libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
370.PP 449.PP
371If 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
372in your main thread (or in a separate thread) and for each thread you 451supports child process events, and dynamically created event loops which
373create, you also create another event loop. Libev itself does no locking 452do not.
374whatsoever, so if you mix calls to the same event loop in different
375threads, make sure you lock (this is usually a bad idea, though, even if
376done correctly, because it's hideous and inefficient).
377.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 453.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
378.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 454.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
379This 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
380yet 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
381false. 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
382flags. 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".
383.Sp 465.Sp
384If 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
385function. 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.
386.Sp 501.Sp
387The flags argument can be used to specify special behaviour or specific 502The flags argument can be used to specify special behaviour or specific
388backends 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).
389.Sp 504.Sp
390The following flags are supported: 505The following flags are supported:
… …
395The 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
396thing, believe me). 511thing, believe me).
397.ie n .IP """EVFLAG_NOENV""" 4 512.ie n .IP """EVFLAG_NOENV""" 4
398.el .IP "\f(CWEVFLAG_NOENV\fR" 4 513.el .IP "\f(CWEVFLAG_NOENV\fR" 4
399.IX Item "EVFLAG_NOENV" 514.IX Item "EVFLAG_NOENV"
400If 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
401or setgid) then libev will \fInot\fR look at the environment variable 516or setgid) then libev will \fInot\fR look at the environment variable
402\&\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
403override 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
404useful 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
405around bugs. 520around bugs.
521.ie n .IP """EVFLAG_FORKCHECK""" 4
522.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
523.IX Item "EVFLAG_FORKCHECK"
524Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
525make libev check for a fork in each iteration by enabling this flag.
526.Sp
527This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
528and thus this might slow down your event loop if you do a lot of loop
529iterations and little real work, but is usually not noticeable (on my
530GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
531without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
532\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
533.Sp
534The big advantage of this flag is that you can forget about fork (and
535forget about forgetting to tell libev about forking) when you use this
536flag.
537.Sp
538This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
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.
406.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 575.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
407.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
408.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 577.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
409This 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
410libev 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,
411but 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
412using 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
413the 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).
414.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
415.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
416.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)"
417And 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
418select, but handles sparse fds better and has no artificial limit on the 598than select, but handles sparse fds better and has no artificial
419number 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
420lot 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.
421.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 606.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
422.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 607.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
423.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
424For 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
425but it scales phenomenally better. While poll and select usually scale like 613it scales phenomenally better. While poll and select usually scale like
426O(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
427either O(1) or O(active_fds). 615fd), epoll scales either O(1) or O(active_fds).
428.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
429While 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
430result in some caching, there is still a syscall per such incident 646will result in some caching, there is still a system call per such
431(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
432best 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
433well if you register events for both fds. 649file descriptors might not work very well if you register events for both
650file descriptors.
434.Sp 651.Sp
435Please note that epoll sometimes generates spurious notifications, so you 652Best performance from this backend is achieved by not unregistering all
436need 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,
437(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.
438.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
439.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
440.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 671.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
441Kqueue deserves special mention, as at the time of this writing, it 672Kqueue deserves special mention, as at the time of this writing, it
442was 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
443anything but sockets and pipes, except on Darwin, where of course its 674with anything but sockets and pipes, except on Darwin, where of course
444completely 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
445unless 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
446\&\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.
447.Sp 685.Sp
448It 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
449kernel is more efficient (which says nothing about its actual speed, of 687kernel is more efficient (which says nothing about its actual speed, of
450course). While starting and stopping an I/O watcher does not cause an 688course). While stopping, setting and starting an I/O watcher does never
451extra 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
452incident, so its best to avoid that. 690two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
691might have to leak fd's on fork, but it's more sane than epoll) and it
692drops fds silently in similarly hard-to-detect cases
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.
453.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 706.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
454.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 707.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
455.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 708.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
456This 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.
457.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 713.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
458.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 714.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
459.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 715.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
460This uses the Solaris 10 port mechanism. As with everything on Solaris, 716This uses the Solaris 10 event port mechanism. As with everything on Solaris,
461it'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)).
462.Sp 718.Sp
463Please note that solaris ports can result in a lot of spurious 719While this backend scales well, it requires one system call per active
464notifications, 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
465blocking 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.
466.ie n .IP """EVBACKEND_ALL""" 4 741.ie n .IP """EVBACKEND_ALL""" 4
467.el .IP "\f(CWEVBACKEND_ALL\fR" 4 742.el .IP "\f(CWEVBACKEND_ALL\fR" 4
468.IX Item "EVBACKEND_ALL" 743.IX Item "EVBACKEND_ALL"
469Try all backends (even potentially broken ones that wouldn't be tried 744Try all backends (even potentially broken ones that wouldn't be tried
470with \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
471\&\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).
472.RE 757.RE
473.RS 4 758.RS 4
474.Sp 759.Sp
475If 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,
476backends 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
477specified, most compiled-in backend will be tried, usually in reverse 762here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
478order of their flag values :) 763()\*(C'\fR will be tried.
479.Sp 764.Sp
480The most typical usage is like this: 765Example: Try to create a event loop that uses epoll and nothing else.
481.Sp 766.Sp
482.Vb 2 767.Vb 3
483\& if (!ev_default_loop (0)) 768\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
484\& 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");
485.Ve 771.Ve
486.Sp 772.Sp
487Restrict libev to the select and poll backends, and do not allow 773Example: Use whatever libev has to offer, but make sure that kqueue is
488environment settings to be taken into account: 774used if available.
489.Sp 775.Sp
490.Vb 1 776.Vb 1
491\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492.Ve
493.Sp
494Use whatever libev has to offer, but make sure that kqueue is used if
495available (warning, breaks stuff, best use only with your own private
496event loop and only if you know the \s-1OS\s0 supports your types of fds):
497.Sp
498.Vb 1
499\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 777\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
500.Ve 778.Ve
501.RE 779.RE
502.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
505always distinct from the default loop. Unlike the default loop, it cannot
506handle signal and child watchers, and attempts to do so will be greeted by
507undefined behaviour (or a failed assertion if assertions are enabled).
508.Sp
509Example: try to create a event loop that uses epoll and nothing else.
510.Sp
511.Vb 3
512\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
513\& if (!epoller)
514\& fatal ("no epoll found here, maybe it hides under your chair");
515.Ve
516.IP "ev_default_destroy ()" 4 780.IP "ev_loop_destroy (loop)" 4
517.IX Item "ev_default_destroy ()" 781.IX Item "ev_loop_destroy (loop)"
518Destroys the default loop again (frees all memory and kernel state 782Destroys an event loop object (frees all memory and kernel state
519etc.). 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
520sense, 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
521responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 785responsibility to either stop all watchers cleanly yourself \fIbefore\fR
522calling this function, or cope with the fact afterwards (which is usually 786calling this function, or cope with the fact afterwards (which is usually
523the easiest thing, youc na 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
524for example). 788for example).
525.IP "ev_loop_destroy (loop)" 4
526.IX Item "ev_loop_destroy (loop)"
527Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
528earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
529.IP "ev_default_fork ()" 4
530.IX Item "ev_default_fork ()"
531This function reinitialises the kernel state for backends that have
532one. Despite the name, you can call it anytime, but it makes most sense
533after forking, in either the parent or child process (or both, but that
534again makes little sense).
535.Sp 789.Sp
536You \fImust\fR call this function in the child process after forking if and 790Note that certain global state, such as signal state (and installed signal
537only if you want to use the event library in both processes. If you just 791handlers), will not be freed by this function, and related watchers (such
538fork+exec, you don't have to call it. 792as signal and child watchers) would need to be stopped manually.
539.Sp 793.Sp
540The function itself is quite fast and it's usually not a problem to call 794This function is normally used on loop objects allocated by
541it just in case after a fork. To make this easy, the function will fit in 795\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
542quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 796\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
543.Sp 797.Sp
544.Vb 1 798Note that it is not advisable to call this function on the default loop
545\& pthread_atfork (0, 0, ev_default_fork); 799except in the rare occasion where you really need to free its resources.
546.Ve 800If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
547.Sp 801and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
548At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
549without calling this function, so if you force one of those backends you
550do not need to care.
551.IP "ev_loop_fork (loop)" 4 802.IP "ev_loop_fork (loop)" 4
552.IX Item "ev_loop_fork (loop)" 803.IX Item "ev_loop_fork (loop)"
553Like \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
554\&\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
555after 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.
842.IP "unsigned int ev_iteration (loop)" 4
843.IX Item "unsigned int ev_iteration (loop)"
844Returns the current iteration count for the event loop, which is identical
845to the number of times libev did poll for new events. It starts at \f(CW0\fR
846and happily wraps around with enough iterations.
847.Sp
848This value can sometimes be useful as a generation counter of sorts (it
849\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
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.
556.IP "unsigned int ev_backend (loop)" 4 865.IP "unsigned int ev_backend (loop)" 4
557.IX Item "unsigned int ev_backend (loop)" 866.IX Item "unsigned int ev_backend (loop)"
558Returns 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
559use. 868use.
560.IP "ev_tstamp ev_now (loop)" 4 869.IP "ev_tstamp ev_now (loop)" 4
561.IX Item "ev_tstamp ev_now (loop)" 870.IX Item "ev_tstamp ev_now (loop)"
562Returns 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
563received events and started processing them. This timestamp does not 872received events and started processing them. This timestamp does not
564change 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
565time 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
566event 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).
567.IP "ev_loop (loop, int flags)" 4 914.IP "bool ev_run (loop, int flags)" 4
568.IX Item "ev_loop (loop, int flags)" 915.IX Item "bool ev_run (loop, int flags)"
569Finally, this is it, the event handler. This function usually is called 916Finally, this is it, the event handler. This function usually is called
570after you initialised all your watchers and you want to start handling 917after you have initialised all your watchers and you want to start
571events. 918handling events. It will ask the operating system for any new events, call
919the watcher callbacks, and then repeat the whole process indefinitely: This
920is why event loops are called \fIloops\fR.
572.Sp 921.Sp
573If 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
574either 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.
575.Sp 925.Sp
926The return value is false if there are no more active watchers (which
927usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
928(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
929.Sp
576Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 930Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
577relying on all watchers to be stopped when deciding when a program has 931relying on all watchers to be stopped when deciding when a program has
578finished (especially in interactive programs), but having a program that 932finished (especially in interactive programs), but having a program
579automatically loops as long as it has to and no longer by virtue of 933that automatically loops as long as it has to and no longer by virtue
580relying on its watchers stopping correctly is a thing of beauty. 934of relying on its watchers stopping correctly, that is truly a thing of
935beauty.
581.Sp 936.Sp
937This function is \fImostly\fR exception-safe \- you can break out of a
938\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
939exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
940will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
941.Sp
582A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 942A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
583those events and any outstanding ones, but will not block your process in 943those events and any already outstanding ones, but will not wait and
584case there are no events and will return after one iteration of the loop. 944block your process in case there are no events and will return after one
945iteration of the loop. This is sometimes useful to poll and handle new
946events while doing lengthy calculations, to keep the program responsive.
585.Sp 947.Sp
586A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 948A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
587neccessary) and will handle those and any outstanding ones. It will block 949necessary) and will handle those and any already outstanding ones. It
588your process until at least one new event arrives, and will return after 950will block your process until at least one new event arrives (which could
589one iteration of the loop. This is useful if you are waiting for some 951be an event internal to libev itself, so there is no guarantee that a
590external event in conjunction with something not expressible using other 952user-registered callback will be called), and will return after one
953iteration of the loop.
954.Sp
955This is useful if you are waiting for some external event in conjunction
956with something not expressible using other libev watchers (i.e. "roll your
591libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 957own \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
592usually a better approach for this kind of thing. 958usually a better approach for this kind of thing.
593.Sp 959.Sp
594Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 960Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
961understanding, not a guarantee that things will work exactly like this in
962future versions):
595.Sp 963.Sp
596.Vb 18 964.Vb 10
597\& * If there are no active watchers (reference count is zero), return. 965\& \- Increment loop depth.
598\& - Queue prepare watchers and then call all outstanding watchers. 966\& \- Reset the ev_break status.
967\& \- Before the first iteration, call any pending watchers.
968\& LOOP:
969\& \- If EVFLAG_FORKCHECK was used, check for a fork.
970\& \- If a fork was detected (by any means), queue and call all fork watchers.
971\& \- Queue and call all prepare watchers.
972\& \- If ev_break was called, goto FINISH.
599\& - If we have been forked, recreate the kernel state. 973\& \- If we have been forked, detach and recreate the kernel state
974\& as to not disturb the other process.
600\& - Update the kernel state with all outstanding changes. 975\& \- Update the kernel state with all outstanding changes.
601\& - Update the "event loop time". 976\& \- Update the "event loop time" (ev_now ()).
602\& - Calculate for how long to block. 977\& \- Calculate for how long to sleep or block, if at all
978\& (active idle watchers, EVRUN_NOWAIT or not having
979\& any active watchers at all will result in not sleeping).
980\& \- Sleep if the I/O and timer collect interval say so.
981\& \- Increment loop iteration counter.
603\& - Block the process, waiting for any events. 982\& \- Block the process, waiting for any events.
604\& - Queue all outstanding I/O (fd) events. 983\& \- Queue all outstanding I/O (fd) events.
605\& - Update the "event loop time" and do time jump handling. 984\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
606\& - Queue all outstanding timers. 985\& \- Queue all expired timers.
607\& - Queue all outstanding periodics. 986\& \- Queue all expired periodics.
608\& - If no events are pending now, queue all idle watchers. 987\& \- Queue all idle watchers with priority higher than that of pending events.
609\& - Queue all check watchers. 988\& \- Queue all check watchers.
610\& - Call all queued watchers in reverse order (i.e. check watchers first). 989\& \- Call all queued watchers in reverse order (i.e. check watchers first).
611\& Signals and child watchers are implemented as I/O watchers, and will 990\& Signals and child watchers are implemented as I/O watchers, and will
612\& be handled here by queueing them when their watcher gets executed. 991\& be handled here by queueing them when their watcher gets executed.
613\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 992\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
614\& were used, return, otherwise continue with step *. 993\& were used, or there are no active watchers, goto FINISH, otherwise
994\& continue with step LOOP.
995\& FINISH:
996\& \- Reset the ev_break status iff it was EVBREAK_ONE.
997\& \- Decrement the loop depth.
998\& \- Return.
615.Ve 999.Ve
616.Sp 1000.Sp
617Example: queue some jobs and then loop until no events are outsanding 1001Example: Queue some jobs and then loop until no events are outstanding
618anymore. 1002anymore.
619.Sp 1003.Sp
620.Vb 4 1004.Vb 4
621\& ... queue jobs here, make sure they register event watchers as long 1005\& ... queue jobs here, make sure they register event watchers as long
622\& ... as they still have work to do (even an idle watcher will do..) 1006\& ... as they still have work to do (even an idle watcher will do..)
623\& ev_loop (my_loop, 0); 1007\& ev_run (my_loop, 0);
624\& ... jobs done. yeah! 1008\& ... jobs done or somebody called break. yeah!
625.Ve 1009.Ve
626.IP "ev_unloop (loop, how)" 4 1010.IP "ev_break (loop, how)" 4
627.IX Item "ev_unloop (loop, how)" 1011.IX Item "ev_break (loop, how)"
628Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1012Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
629has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1013has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
630\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1014\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
631\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1015\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1016.Sp
1017This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1018.Sp
1019It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1020which case it will have no effect.
632.IP "ev_ref (loop)" 4 1021.IP "ev_ref (loop)" 4
633.IX Item "ev_ref (loop)" 1022.IX Item "ev_ref (loop)"
634.PD 0 1023.PD 0
635.IP "ev_unref (loop)" 4 1024.IP "ev_unref (loop)" 4
636.IX Item "ev_unref (loop)" 1025.IX Item "ev_unref (loop)"
637.PD 1026.PD
638Ref/unref can be used to add or remove a reference count on the event 1027Ref/unref can be used to add or remove a reference count on the event
639loop: Every watcher keeps one reference, and as long as the reference 1028loop: Every watcher keeps one reference, and as long as the reference
640count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1029count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
641a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1030.Sp
642returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1031This is useful when you have a watcher that you never intend to
1032unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1033returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1034before stopping it.
1035.Sp
643example, libev itself uses this for its internal signal pipe: It is not 1036As an example, libev itself uses this for its internal signal pipe: It
644visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1037is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
645no event watchers registered by it are active. It is also an excellent 1038exiting if no event watchers registered by it are active. It is also an
646way to do this for generic recurring timers or from within third-party 1039excellent way to do this for generic recurring timers or from within
647libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1040third-party libraries. Just remember to \fIunref after start\fR and \fIref
1041before stop\fR (but only if the watcher wasn't active before, or was active
1042before, respectively. Note also that libev might stop watchers itself
1043(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1044in the callback).
648.Sp 1045.Sp
649Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1046Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
650running when nothing else is active. 1047running when nothing else is active.
651.Sp 1048.Sp
652.Vb 4 1049.Vb 4
653\& struct dv_signal exitsig; 1050\& ev_signal exitsig;
654\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1051\& ev_signal_init (&exitsig, sig_cb, SIGINT);
655\& ev_signal_start (myloop, &exitsig); 1052\& ev_signal_start (loop, &exitsig);
656\& evf_unref (myloop); 1053\& ev_unref (loop);
657.Ve 1054.Ve
658.Sp 1055.Sp
659Example: for some weird reason, unregister the above signal handler again. 1056Example: For some weird reason, unregister the above signal handler again.
660.Sp 1057.Sp
661.Vb 2 1058.Vb 2
662\& ev_ref (myloop); 1059\& ev_ref (loop);
663\& ev_signal_stop (myloop, &exitsig); 1060\& ev_signal_stop (loop, &exitsig);
664.Ve 1061.Ve
1062.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1063.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1064.PD 0
1065.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1066.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1067.PD
1068These advanced functions influence the time that libev will spend waiting
1069for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1070will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1071latency.
1072.Sp
1073Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1074allows libev to delay invocation of I/O and timer/periodic callbacks
1075to increase efficiency of loop iterations (or to increase power-saving
1076opportunities).
1077.Sp
1078The idea is that sometimes your program runs just fast enough to handle
1079one (or very few) event(s) per loop iteration. While this makes the
1080program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1081events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1082overhead for the actual polling but can deliver many events at once.
1083.Sp
1084By setting a higher \fIio collect interval\fR you allow libev to spend more
1085time collecting I/O events, so you can handle more events per iteration,
1086at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1087\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1088introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1089sleep time ensures that libev will not poll for I/O events more often then
1090once per this interval, on average (as long as the host time resolution is
1091good enough).
1092.Sp
1093Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1094to spend more time collecting timeouts, at the expense of increased
1095latency/jitter/inexactness (the watcher callback will be called
1096later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1097value will not introduce any overhead in libev.
1098.Sp
1099Many (busy) programs can usually benefit by setting the I/O collect
1100interval to a value near \f(CW0.1\fR or so, which is often enough for
1101interactive servers (of course not for games), likewise for timeouts. It
1102usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1103as this approaches the timing granularity of most systems. Note that if
1104you do transactions with the outside world and you can't increase the
1105parallelity, then this setting will limit your transaction rate (if you
1106need to poll once per transaction and the I/O collect interval is 0.01,
1107then you can't do more than 100 transactions per second).
1108.Sp
1109Setting the \fItimeout collect interval\fR can improve the opportunity for
1110saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1111are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1112times the process sleeps and wakes up again. Another useful technique to
1113reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1114they fire on, say, one-second boundaries only.
1115.Sp
1116Example: we only need 0.1s timeout granularity, and we wish not to poll
1117more often than 100 times per second:
1118.Sp
1119.Vb 2
1120\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1121\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1122.Ve
1123.IP "ev_invoke_pending (loop)" 4
1124.IX Item "ev_invoke_pending (loop)"
1125This call will simply invoke all pending watchers while resetting their
1126pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1127but when overriding the invoke callback this call comes handy. This
1128function can be invoked from a watcher \- this can be useful for example
1129when you want to do some lengthy calculation and want to pass further
1130event handling to another thread (you still have to make sure only one
1131thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1132.IP "int ev_pending_count (loop)" 4
1133.IX Item "int ev_pending_count (loop)"
1134Returns the number of pending watchers \- zero indicates that no watchers
1135are pending.
1136.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1137.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1138This overrides the invoke pending functionality of the loop: Instead of
1139invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1140this callback instead. This is useful, for example, when you want to
1141invoke the actual watchers inside another context (another thread etc.).
1142.Sp
1143If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1144callback.
1145.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1146.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1147Sometimes you want to share the same loop between multiple threads. This
1148can be done relatively simply by putting mutex_lock/unlock calls around
1149each call to a libev function.
1150.Sp
1151However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1152to wait for it to return. One way around this is to wake up the event
1153loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1154\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1155.Sp
1156When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1157suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1158afterwards.
1159.Sp
1160Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1161\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1162.Sp
1163While event loop modifications are allowed between invocations of
1164\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1165modifications done will affect the event loop, i.e. adding watchers will
1166have no effect on the set of file descriptors being watched, or the time
1167waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1168to take note of any changes you made.
1169.Sp
1170In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1171invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1172.Sp
1173See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1174document.
1175.IP "ev_set_userdata (loop, void *data)" 4
1176.IX Item "ev_set_userdata (loop, void *data)"
1177.PD 0
1178.IP "void *ev_userdata (loop)" 4
1179.IX Item "void *ev_userdata (loop)"
1180.PD
1181Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1182\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1183\&\f(CW0\fR.
1184.Sp
1185These two functions can be used to associate arbitrary data with a loop,
1186and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1187\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1188any other purpose as well.
1189.IP "ev_verify (loop)" 4
1190.IX Item "ev_verify (loop)"
1191This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1192compiled in, which is the default for non-minimal builds. It tries to go
1193through all internal structures and checks them for validity. If anything
1194is found to be inconsistent, it will print an error message to standard
1195error and call \f(CW\*(C`abort ()\*(C'\fR.
1196.Sp
1197This can be used to catch bugs inside libev itself: under normal
1198circumstances, this function will never abort as of course libev keeps its
1199data structures consistent.
665.SH "ANATOMY OF A WATCHER" 1200.SH "ANATOMY OF A WATCHER"
666.IX Header "ANATOMY OF A WATCHER" 1201.IX Header "ANATOMY OF A WATCHER"
1202In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1203watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1204watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1205.PP
667A watcher is a structure that you create and register to record your 1206A watcher is an opaque structure that you allocate and register to record
668interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1207your interest in some event. To make a concrete example, imagine you want
669become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1208to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1209for that:
670.PP 1210.PP
671.Vb 5 1211.Vb 5
672\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1212\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
673\& { 1213\& {
674\& ev_io_stop (w); 1214\& ev_io_stop (w);
675\& ev_unloop (loop, EVUNLOOP_ALL); 1215\& ev_break (loop, EVBREAK_ALL);
676\& } 1216\& }
677.Ve 1217\&
678.PP
679.Vb 6
680\& struct ev_loop *loop = ev_default_loop (0); 1218\& struct ev_loop *loop = ev_default_loop (0);
1219\&
681\& struct ev_io stdin_watcher; 1220\& ev_io stdin_watcher;
1221\&
682\& ev_init (&stdin_watcher, my_cb); 1222\& ev_init (&stdin_watcher, my_cb);
683\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1223\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
684\& ev_io_start (loop, &stdin_watcher); 1224\& ev_io_start (loop, &stdin_watcher);
1225\&
685\& ev_loop (loop, 0); 1226\& ev_run (loop, 0);
686.Ve 1227.Ve
687.PP 1228.PP
688As you can see, you are responsible for allocating the memory for your 1229As you can see, you are responsible for allocating the memory for your
689watcher structures (and it is usually a bad idea to do this on the stack, 1230watcher structures (and it is \fIusually\fR a bad idea to do this on the
690although this can sometimes be quite valid). 1231stack).
691.PP 1232.PP
1233Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1234or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1235.PP
692Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1236Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
693(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1237*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
694callback gets invoked each time the event occurs (or, in the case of io 1238invoked each time the event occurs (or, in the case of I/O watchers, each
695watchers, each time the event loop detects that the file descriptor given 1239time the event loop detects that the file descriptor given is readable
696is readable and/or writable). 1240and/or writable).
697.PP 1241.PP
698Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1242Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
699with arguments specific to this watcher type. There is also a macro 1243macro to configure it, with arguments specific to the watcher type. There
700to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1244is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
701(watcher *, callback, ...)\*(C'\fR.
702.PP 1245.PP
703To make the watcher actually watch out for events, you have to start it 1246To make the watcher actually watch out for events, you have to start it
704with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1247with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
705*)\*(C'\fR), and you can stop watching for events at any time by calling the 1248*)\*(C'\fR), and you can stop watching for events at any time by calling the
706corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1249corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
707.PP 1250.PP
708As long as your watcher is active (has been started but not stopped) you 1251As long as your watcher is active (has been started but not stopped) you
709must not touch the values stored in it. Most specifically you must never 1252must not touch the values stored in it. Most specifically you must never
710reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1253reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
711.PP 1254.PP
712Each and every callback receives the event loop pointer as first, the 1255Each and every callback receives the event loop pointer as first, the
713registered watcher structure as second, and a bitset of received events as 1256registered watcher structure as second, and a bitset of received events as
714third argument. 1257third argument.
715.PP 1258.PP
… …
724.el .IP "\f(CWEV_WRITE\fR" 4 1267.el .IP "\f(CWEV_WRITE\fR" 4
725.IX Item "EV_WRITE" 1268.IX Item "EV_WRITE"
726.PD 1269.PD
727The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1270The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
728writable. 1271writable.
729.ie n .IP """EV_TIMEOUT""" 4 1272.ie n .IP """EV_TIMER""" 4
730.el .IP "\f(CWEV_TIMEOUT\fR" 4 1273.el .IP "\f(CWEV_TIMER\fR" 4
731.IX Item "EV_TIMEOUT" 1274.IX Item "EV_TIMER"
732The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1275The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
733.ie n .IP """EV_PERIODIC""" 4 1276.ie n .IP """EV_PERIODIC""" 4
734.el .IP "\f(CWEV_PERIODIC\fR" 4 1277.el .IP "\f(CWEV_PERIODIC\fR" 4
735.IX Item "EV_PERIODIC" 1278.IX Item "EV_PERIODIC"
736The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1279The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
756.PD 0 1299.PD 0
757.ie n .IP """EV_CHECK""" 4 1300.ie n .IP """EV_CHECK""" 4
758.el .IP "\f(CWEV_CHECK\fR" 4 1301.el .IP "\f(CWEV_CHECK\fR" 4
759.IX Item "EV_CHECK" 1302.IX Item "EV_CHECK"
760.PD 1303.PD
761All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1304All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
762to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1305to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
763\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1306\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
764received events. Callbacks of both watcher types can start and stop as 1307received events. Callbacks of both watcher types can start and stop as
765many watchers as they want, and all of them will be taken into account 1308many watchers as they want, and all of them will be taken into account
766(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1309(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
767\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1310\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
768.ie n .IP """EV_EMBED""" 4 1311.ie n .IP """EV_EMBED""" 4
769.el .IP "\f(CWEV_EMBED\fR" 4 1312.el .IP "\f(CWEV_EMBED\fR" 4
770.IX Item "EV_EMBED" 1313.IX Item "EV_EMBED"
771The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1314The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
772.ie n .IP """EV_FORK""" 4 1315.ie n .IP """EV_FORK""" 4
773.el .IP "\f(CWEV_FORK\fR" 4 1316.el .IP "\f(CWEV_FORK\fR" 4
774.IX Item "EV_FORK" 1317.IX Item "EV_FORK"
775The event loop has been resumed in the child process after fork (see 1318The event loop has been resumed in the child process after fork (see
776\&\f(CW\*(C`ev_fork\*(C'\fR). 1319\&\f(CW\*(C`ev_fork\*(C'\fR).
1320.ie n .IP """EV_CLEANUP""" 4
1321.el .IP "\f(CWEV_CLEANUP\fR" 4
1322.IX Item "EV_CLEANUP"
1323The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1324.ie n .IP """EV_ASYNC""" 4
1325.el .IP "\f(CWEV_ASYNC\fR" 4
1326.IX Item "EV_ASYNC"
1327The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1328.ie n .IP """EV_CUSTOM""" 4
1329.el .IP "\f(CWEV_CUSTOM\fR" 4
1330.IX Item "EV_CUSTOM"
1331Not ever sent (or otherwise used) by libev itself, but can be freely used
1332by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
777.ie n .IP """EV_ERROR""" 4 1333.ie n .IP """EV_ERROR""" 4
778.el .IP "\f(CWEV_ERROR\fR" 4 1334.el .IP "\f(CWEV_ERROR\fR" 4
779.IX Item "EV_ERROR" 1335.IX Item "EV_ERROR"
780An unspecified error has occured, the watcher has been stopped. This might 1336An unspecified error has occurred, the watcher has been stopped. This might
781happen because the watcher could not be properly started because libev 1337happen because the watcher could not be properly started because libev
782ran out of memory, a file descriptor was found to be closed or any other 1338ran out of memory, a file descriptor was found to be closed or any other
1339problem. Libev considers these application bugs.
1340.Sp
783problem. You best act on it by reporting the problem and somehow coping 1341You best act on it by reporting the problem and somehow coping with the
784with the watcher being stopped. 1342watcher being stopped. Note that well-written programs should not receive
1343an error ever, so when your watcher receives it, this usually indicates a
1344bug in your program.
785.Sp 1345.Sp
786Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1346Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
787for example it might indicate that a fd is readable or writable, and if 1347example it might indicate that a fd is readable or writable, and if your
788your callbacks is well-written it can just attempt the operation and cope 1348callbacks is well-written it can just attempt the operation and cope with
789with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1349the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
790programs, though, so beware. 1350programs, though, as the fd could already be closed and reused for another
1351thing, so beware.
791.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1352.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
792.IX Subsection "GENERIC WATCHER FUNCTIONS" 1353.IX Subsection "GENERIC WATCHER FUNCTIONS"
793In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
794e.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.
795.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1354.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
796.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1355.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
797.IX Item "ev_init (ev_TYPE *watcher, callback)" 1356.IX Item "ev_init (ev_TYPE *watcher, callback)"
798This macro initialises the generic portion of a watcher. The contents 1357This macro initialises the generic portion of a watcher. The contents
799of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1358of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
803which rolls both calls into one. 1362which rolls both calls into one.
804.Sp 1363.Sp
805You can reinitialise a watcher at any time as long as it has been stopped 1364You can reinitialise a watcher at any time as long as it has been stopped
806(or never started) and there are no pending events outstanding. 1365(or never started) and there are no pending events outstanding.
807.Sp 1366.Sp
808The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1367The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
809int revents)\*(C'\fR. 1368int revents)\*(C'\fR.
1369.Sp
1370Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1371.Sp
1372.Vb 3
1373\& ev_io w;
1374\& ev_init (&w, my_cb);
1375\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1376.Ve
810.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1377.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
811.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1378.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
812.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1379.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
813This macro initialises the type-specific parts of a watcher. You need to 1380This macro initialises the type-specific parts of a watcher. You need to
814call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1381call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
815call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1382call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
816macro on a watcher that is active (it can be pending, however, which is a 1383macro on a watcher that is active (it can be pending, however, which is a
817difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1384difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
818.Sp 1385.Sp
819Although some watcher types do not have type-specific arguments 1386Although some watcher types do not have type-specific arguments
820(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1387(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1388.Sp
1389See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
821.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1390.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
822.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1391.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
823.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1392.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
824This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1393This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
825calls into a single call. This is the most convinient method to initialise 1394calls into a single call. This is the most convenient method to initialise
826a watcher. The same limitations apply, of course. 1395a watcher. The same limitations apply, of course.
1396.Sp
1397Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1398.Sp
1399.Vb 1
1400\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1401.Ve
827.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1402.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
828.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1403.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
829.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1404.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
830Starts (activates) the given watcher. Only active watchers will receive 1405Starts (activates) the given watcher. Only active watchers will receive
831events. If the watcher is already active nothing will happen. 1406events. If the watcher is already active nothing will happen.
1407.Sp
1408Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1409whole section.
1410.Sp
1411.Vb 1
1412\& ev_io_start (EV_DEFAULT_UC, &w);
1413.Ve
832.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1414.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
833.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1415.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
834.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1416.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
835Stops the given watcher again (if active) and clears the pending 1417Stops the given watcher if active, and clears the pending status (whether
1418the watcher was active or not).
1419.Sp
836status. It is possible that stopped watchers are pending (for example, 1420It is possible that stopped watchers are pending \- for example,
837non-repeating timers are being stopped when they become pending), but 1421non-repeating timers are being stopped when they become pending \- but
838\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1422calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
839you want to free or reuse the memory used by the watcher it is therefore a 1423pending. If you want to free or reuse the memory used by the watcher it is
840good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1424therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
841.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1425.IP "bool ev_is_active (ev_TYPE *watcher)" 4
842.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1426.IX Item "bool ev_is_active (ev_TYPE *watcher)"
843Returns a true value iff the watcher is active (i.e. it has been started 1427Returns a true value iff the watcher is active (i.e. it has been started
844and not yet been stopped). As long as a watcher is active you must not modify 1428and not yet been stopped). As long as a watcher is active you must not modify
845it. 1429it.
846.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1430.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
847.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1431.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
848Returns a true value iff the watcher is pending, (i.e. it has outstanding 1432Returns a true value iff the watcher is pending, (i.e. it has outstanding
849events but its callback has not yet been invoked). As long as a watcher 1433events but its callback has not yet been invoked). As long as a watcher
850is pending (but not active) you must not call an init function on it (but 1434is pending (but not active) you must not call an init function on it (but
851\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1435\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
852libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1436make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1437it).
853.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1438.IP "callback ev_cb (ev_TYPE *watcher)" 4
854.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1439.IX Item "callback ev_cb (ev_TYPE *watcher)"
855Returns the callback currently set on the watcher. 1440Returns the callback currently set on the watcher.
856.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1441.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
857.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1442.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
858Change the callback. You can change the callback at virtually any time 1443Change the callback. You can change the callback at virtually any time
859(modulo threads). 1444(modulo threads).
860.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1445.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
861.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1446.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
862Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1447.PD 0
863and read at any time, libev will completely ignore it. This can be used 1448.IP "int ev_priority (ev_TYPE *watcher)" 4
864to associate arbitrary data with your watcher. If you need more data and 1449.IX Item "int ev_priority (ev_TYPE *watcher)"
865don't want to allocate memory and store a pointer to it in that data 1450.PD
866member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1451Set and query the priority of the watcher. The priority is a small
867data: 1452integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1453(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1454before watchers with lower priority, but priority will not keep watchers
1455from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1456.Sp
1457If you need to suppress invocation when higher priority events are pending
1458you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1459.Sp
1460You \fImust not\fR change the priority of a watcher as long as it is active or
1461pending.
1462.Sp
1463Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1464fine, as long as you do not mind that the priority value you query might
1465or might not have been clamped to the valid range.
1466.Sp
1467The default priority used by watchers when no priority has been set is
1468always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1469.Sp
1470See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1471priorities.
1472.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1473.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1474Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1475\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1476can deal with that fact, as both are simply passed through to the
1477callback.
1478.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1479.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1480If the watcher is pending, this function clears its pending status and
1481returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1482watcher isn't pending it does nothing and returns \f(CW0\fR.
1483.Sp
1484Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1485callback to be invoked, which can be accomplished with this function.
1486.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1487.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1488Feeds the given event set into the event loop, as if the specified event
1489had happened for the specified watcher (which must be a pointer to an
1490initialised but not necessarily started event watcher). Obviously you must
1491not free the watcher as long as it has pending events.
1492.Sp
1493Stopping the watcher, letting libev invoke it, or calling
1494\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1495not started in the first place.
1496.Sp
1497See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1498functions that do not need a watcher.
868.PP 1499.PP
1500See 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
1501\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1502.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1503.IX Subsection "WATCHER STATES"
1504There are various watcher states mentioned throughout this manual \-
1505active, pending and so on. In this section these states and the rules to
1506transition between them will be described in more detail \- and while these
1507rules might look complicated, they usually do \*(L"the right thing\*(R".
1508.IP "initialiased" 4
1509.IX Item "initialiased"
1510Before a watcher can be registered with the event loop it has to be
1511initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1512\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1513.Sp
1514In this state it is simply some block of memory that is suitable for
1515use in an event loop. It can be moved around, freed, reused etc. at
1516will \- as long as you either keep the memory contents intact, or call
1517\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1518.IP "started/running/active" 4
1519.IX Item "started/running/active"
1520Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1521property of the event loop, and is actively waiting for events. While in
1522this state it cannot be accessed (except in a few documented ways), moved,
1523freed or anything else \- the only legal thing is to keep a pointer to it,
1524and call libev functions on it that are documented to work on active watchers.
1525.IP "pending" 4
1526.IX Item "pending"
1527If a watcher is active and libev determines that an event it is interested
1528in has occurred (such as a timer expiring), it will become pending. It will
1529stay in this pending state until either it is stopped or its callback is
1530about to be invoked, so it is not normally pending inside the watcher
1531callback.
1532.Sp
1533The watcher might or might not be active while it is pending (for example,
1534an expired non-repeating timer can be pending but no longer active). If it
1535is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1536but it is still property of the event loop at this time, so cannot be
1537moved, freed or reused. And if it is active the rules described in the
1538previous item still apply.
1539.Sp
1540It is also possible to feed an event on a watcher that is not active (e.g.
1541via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1542active.
1543.IP "stopped" 4
1544.IX Item "stopped"
1545A watcher can be stopped implicitly by libev (in which case it might still
1546be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1547latter will clear any pending state the watcher might be in, regardless
1548of whether it was active or not, so stopping a watcher explicitly before
1549freeing it is often a good idea.
1550.Sp
1551While stopped (and not pending) the watcher is essentially in the
1552initialised state, that is, it can be reused, moved, modified in any way
1553you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1554it again).
1555.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1556.IX Subsection "WATCHER PRIORITY MODELS"
1557Many event loops support \fIwatcher priorities\fR, which are usually small
1558integers that influence the ordering of event callback invocation
1559between watchers in some way, all else being equal.
1560.PP
1561In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1562description for the more technical details such as the actual priority
1563range.
1564.PP
1565There are two common ways how these these priorities are being interpreted
1566by event loops:
1567.PP
1568In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1569of lower priority watchers, which means as long as higher priority
1570watchers receive events, lower priority watchers are not being invoked.
1571.PP
1572The less common only-for-ordering model uses priorities solely to order
1573callback invocation within a single event loop iteration: Higher priority
1574watchers are invoked before lower priority ones, but they all get invoked
1575before polling for new events.
1576.PP
1577Libev uses the second (only-for-ordering) model for all its watchers
1578except for idle watchers (which use the lock-out model).
1579.PP
1580The rationale behind this is that implementing the lock-out model for
1581watchers is not well supported by most kernel interfaces, and most event
1582libraries will just poll for the same events again and again as long as
1583their callbacks have not been executed, which is very inefficient in the
1584common case of one high-priority watcher locking out a mass of lower
1585priority ones.
1586.PP
1587Static (ordering) priorities are most useful when you have two or more
1588watchers handling the same resource: a typical usage example is having an
1589\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1590timeouts. Under load, data might be received while the program handles
1591other jobs, but since timers normally get invoked first, the timeout
1592handler will be executed before checking for data. In that case, giving
1593the timer a lower priority than the I/O watcher ensures that I/O will be
1594handled first even under adverse conditions (which is usually, but not
1595always, what you want).
1596.PP
1597Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1598will only be executed when no same or higher priority watchers have
1599received events, they can be used to implement the \*(L"lock-out\*(R" model when
1600required.
1601.PP
1602For example, to emulate how many other event libraries handle priorities,
1603you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1604the normal watcher callback, you just start the idle watcher. The real
1605processing is done in the idle watcher callback. This causes libev to
1606continuously poll and process kernel event data for the watcher, but when
1607the lock-out case is known to be rare (which in turn is rare :), this is
1608workable.
1609.PP
1610Usually, however, the lock-out model implemented that way will perform
1611miserably under the type of load it was designed to handle. In that case,
1612it might be preferable to stop the real watcher before starting the
1613idle watcher, so the kernel will not have to process the event in case
1614the actual processing will be delayed for considerable time.
1615.PP
1616Here is an example of an I/O watcher that should run at a strictly lower
1617priority than the default, and which should only process data when no
1618other events are pending:
1619.PP
869.Vb 7 1620.Vb 2
870\& struct my_io 1621\& ev_idle idle; // actual processing watcher
1622\& ev_io io; // actual event watcher
1623\&
1624\& static void
1625\& io_cb (EV_P_ ev_io *w, int revents)
871\& { 1626\& {
872\& struct ev_io io; 1627\& // stop the I/O watcher, we received the event, but
873\& int otherfd; 1628\& // are not yet ready to handle it.
874\& void *somedata; 1629\& ev_io_stop (EV_A_ w);
875\& struct whatever *mostinteresting; 1630\&
1631\& // start the idle watcher to handle the actual event.
1632\& // it will not be executed as long as other watchers
1633\& // with the default priority are receiving events.
1634\& ev_idle_start (EV_A_ &idle);
876\& } 1635\& }
877.Ve 1636\&
878.PP 1637\& static void
879And since your callback will be called with a pointer to the watcher, you 1638\& idle_cb (EV_P_ ev_idle *w, int revents)
880can cast it back to your own type:
881.PP
882.Vb 5
883\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
884\& { 1639\& {
885\& struct my_io *w = (struct my_io *)w_; 1640\& // actual processing
886\& ... 1641\& read (STDIN_FILENO, ...);
1642\&
1643\& // have to start the I/O watcher again, as
1644\& // we have handled the event
1645\& ev_io_start (EV_P_ &io);
887\& } 1646\& }
1647\&
1648\& // initialisation
1649\& ev_idle_init (&idle, idle_cb);
1650\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1651\& ev_io_start (EV_DEFAULT_ &io);
888.Ve 1652.Ve
889.PP 1653.PP
890More interesting and less C\-conformant ways of catsing your callback type 1654In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
891have been omitted.... 1655low-priority connections can not be locked out forever under load. This
1656enables your program to keep a lower latency for important connections
1657during short periods of high load, while not completely locking out less
1658important ones.
892.SH "WATCHER TYPES" 1659.SH "WATCHER TYPES"
893.IX Header "WATCHER TYPES" 1660.IX Header "WATCHER TYPES"
894This section describes each watcher in detail, but will not repeat 1661This section describes each watcher in detail, but will not repeat
895information given in the last section. Any initialisation/set macros, 1662information given in the last section. Any initialisation/set macros,
896functions and members specific to the watcher type are explained. 1663functions and members specific to the watcher type are explained.
… …
901watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1668watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
902means you can expect it to have some sensible content while the watcher 1669means you can expect it to have some sensible content while the watcher
903is active, but you can also modify it. Modifying it may not do something 1670is active, but you can also modify it. Modifying it may not do something
904sensible or take immediate effect (or do anything at all), but libev will 1671sensible or take immediate effect (or do anything at all), but libev will
905not crash or malfunction in any way. 1672not crash or malfunction in any way.
906.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1673.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
907.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1674.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
908.IX Subsection "ev_io - is this file descriptor readable or writable?" 1675.IX Subsection "ev_io - is this file descriptor readable or writable?"
909I/O watchers check whether a file descriptor is readable or writable 1676I/O watchers check whether a file descriptor is readable or writable
910in each iteration of the event loop, or, more precisely, when reading 1677in each iteration of the event loop, or, more precisely, when reading
911would not block the process and writing would at least be able to write 1678would not block the process and writing would at least be able to write
912some data. This behaviour is called level-triggering because you keep 1679some data. This behaviour is called level-triggering because you keep
… …
917In general you can register as many read and/or write event watchers per 1684In general you can register as many read and/or write event watchers per
918fd as you want (as long as you don't confuse yourself). Setting all file 1685fd as you want (as long as you don't confuse yourself). Setting all file
919descriptors to non-blocking mode is also usually a good idea (but not 1686descriptors to non-blocking mode is also usually a good idea (but not
920required if you know what you are doing). 1687required if you know what you are doing).
921.PP 1688.PP
922You have to be careful with dup'ed file descriptors, though. Some backends
923(the linux epoll backend is a notable example) cannot handle dup'ed file
924descriptors correctly if you register interest in two or more fds pointing
925to the same underlying file/socket/etc. description (that is, they share
926the same underlying \*(L"file open\*(R").
927.PP
928If you must do this, then force the use of a known-to-be-good backend
929(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
930\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
931.PP
932Another thing you have to watch out for is that it is quite easy to 1689Another thing you have to watch out for is that it is quite easy to
933receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1690receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
934be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1691be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
935because there is no data. Not only are some backends known to create a 1692because there is no data. It is very easy to get into this situation even
936lot of those (for example solaris ports), it is very easy to get into 1693with a relatively standard program structure. Thus it is best to always
937this situation even with a relatively standard program structure. Thus 1694use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
938it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
939\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1695preferable to a program hanging until some data arrives.
940.PP 1696.PP
941If you cannot run the fd in non-blocking mode (for example you should not 1697If you cannot run the fd in non-blocking mode (for example you should
942play around with an Xlib connection), then you have to seperately re-test 1698not play around with an Xlib connection), then you have to separately
943wether a file descriptor is really ready with a known-to-be good interface 1699re-test whether a file descriptor is really ready with a known-to-be good
944such as poll (fortunately in our Xlib example, Xlib already does this on 1700interface such as poll (fortunately in the case of Xlib, it already does
945its own, so its quite safe to use). 1701this on its own, so its quite safe to use). Some people additionally
1702use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1703indefinitely.
1704.PP
1705But really, best use non-blocking mode.
1706.PP
1707\fIThe special problem of disappearing file descriptors\fR
1708.IX Subsection "The special problem of disappearing file descriptors"
1709.PP
1710Some backends (e.g. kqueue, epoll) need to be told about closing a file
1711descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1712such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1713descriptor, but when it goes away, the operating system will silently drop
1714this interest. If another file descriptor with the same number then is
1715registered with libev, there is no efficient way to see that this is, in
1716fact, a different file descriptor.
1717.PP
1718To avoid having to explicitly tell libev about such cases, libev follows
1719the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1720will assume that this is potentially a new file descriptor, otherwise
1721it is assumed that the file descriptor stays the same. That means that
1722you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
1723descriptor even if the file descriptor number itself did not change.
1724.PP
1725This is how one would do it normally anyway, the important point is that
1726the libev application should not optimise around libev but should leave
1727optimisations to libev.
1728.PP
1729\fIThe special problem of dup'ed file descriptors\fR
1730.IX Subsection "The special problem of dup'ed file descriptors"
1731.PP
1732Some backends (e.g. epoll), cannot register events for file descriptors,
1733but only events for the underlying file descriptions. That means when you
1734have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1735events for them, only one file descriptor might actually receive events.
1736.PP
1737There is no workaround possible except not registering events
1738for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1739\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1740.PP
1741\fIThe special problem of files\fR
1742.IX Subsection "The special problem of files"
1743.PP
1744Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1745representing files, and expect it to become ready when their program
1746doesn't block on disk accesses (which can take a long time on their own).
1747.PP
1748However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1749notification as soon as the kernel knows whether and how much data is
1750there, and in the case of open files, that's always the case, so you
1751always get a readiness notification instantly, and your read (or possibly
1752write) will still block on the disk I/O.
1753.PP
1754Another way to view it is that in the case of sockets, pipes, character
1755devices and so on, there is another party (the sender) that delivers data
1756on its own, but in the case of files, there is no such thing: the disk
1757will not send data on its own, simply because it doesn't know what you
1758wish to read \- you would first have to request some data.
1759.PP
1760Since files are typically not-so-well supported by advanced notification
1761mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1762to files, even though you should not use it. The reason for this is
1763convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1764usually a tty, often a pipe, but also sometimes files or special devices
1765(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1766\&\fI/dev/urandom\fR), and even though the file might better be served with
1767asynchronous I/O instead of with non-blocking I/O, it is still useful when
1768it \*(L"just works\*(R" instead of freezing.
1769.PP
1770So avoid file descriptors pointing to files when you know it (e.g. use
1771libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1772when you rarely read from a file instead of from a socket, and want to
1773reuse the same code path.
1774.PP
1775\fIThe special problem of fork\fR
1776.IX Subsection "The special problem of fork"
1777.PP
1778Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1779useless behaviour. Libev fully supports fork, but needs to be told about
1780it in the child if you want to continue to use it in the child.
1781.PP
1782To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1783()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1784\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1785.PP
1786\fIThe special problem of \s-1SIGPIPE\s0\fR
1787.IX Subsection "The special problem of SIGPIPE"
1788.PP
1789While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1790when writing to a pipe whose other end has been closed, your program gets
1791sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1792this is sensible behaviour, for daemons, this is usually undesirable.
1793.PP
1794So when you encounter spurious, unexplained daemon exits, make sure you
1795ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1796somewhere, as that would have given you a big clue).
1797.PP
1798\fIThe special problem of \fIaccept()\fIing when you can't\fR
1799.IX Subsection "The special problem of accept()ing when you can't"
1800.PP
1801Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1802found in post\-2004 Linux) have the peculiar behaviour of not removing a
1803connection from the pending queue in all error cases.
1804.PP
1805For example, larger servers often run out of file descriptors (because
1806of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1807rejecting the connection, leading to libev signalling readiness on
1808the next iteration again (the connection still exists after all), and
1809typically causing the program to loop at 100% \s-1CPU\s0 usage.
1810.PP
1811Unfortunately, the set of errors that cause this issue differs between
1812operating systems, there is usually little the app can do to remedy the
1813situation, and no known thread-safe method of removing the connection to
1814cope with overload is known (to me).
1815.PP
1816One of the easiest ways to handle this situation is to just ignore it
1817\&\- when the program encounters an overload, it will just loop until the
1818situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1819event-based way to handle this situation, so it's the best one can do.
1820.PP
1821A better way to handle the situation is to log any errors other than
1822\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1823messages, and continue as usual, which at least gives the user an idea of
1824what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1825the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1826usage.
1827.PP
1828If your program is single-threaded, then you could also keep a dummy file
1829descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1830when 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,
1831close that fd, and create a new dummy fd. This will gracefully refuse
1832clients under typical overload conditions.
1833.PP
1834The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1835is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1836opportunity for a DoS attack.
1837.PP
1838\fIWatcher-Specific Functions\fR
1839.IX Subsection "Watcher-Specific Functions"
946.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1840.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
947.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1841.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
948.PD 0 1842.PD 0
949.IP "ev_io_set (ev_io *, int fd, int events)" 4 1843.IP "ev_io_set (ev_io *, int fd, int events)" 4
950.IX Item "ev_io_set (ev_io *, int fd, int events)" 1844.IX Item "ev_io_set (ev_io *, int fd, int events)"
951.PD 1845.PD
952Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1846Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
953rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1847receive 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
954\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1848\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
955.IP "int fd [read\-only]" 4 1849.IP "int fd [read\-only]" 4
956.IX Item "int fd [read-only]" 1850.IX Item "int fd [read-only]"
957The file descriptor being watched. 1851The file descriptor being watched.
958.IP "int events [read\-only]" 4 1852.IP "int events [read\-only]" 4
959.IX Item "int events [read-only]" 1853.IX Item "int events [read-only]"
960The events being watched. 1854The events being watched.
961.PP 1855.PP
1856\fIExamples\fR
1857.IX Subsection "Examples"
1858.PP
962Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1859Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
963readable, but only once. Since it is likely line\-buffered, you could 1860readable, but only once. Since it is likely line-buffered, you could
964attempt to read a whole line in the callback: 1861attempt to read a whole line in the callback.
965.PP 1862.PP
966.Vb 6 1863.Vb 6
967\& static void 1864\& static void
968\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1865\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
969\& { 1866\& {
970\& ev_io_stop (loop, w); 1867\& ev_io_stop (loop, w);
971\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1868\& .. read from stdin here (or from w\->fd) and handle any I/O errors
972\& } 1869\& }
973.Ve 1870\&
974.PP
975.Vb 6
976\& ... 1871\& ...
977\& struct ev_loop *loop = ev_default_init (0); 1872\& struct ev_loop *loop = ev_default_init (0);
978\& struct ev_io stdin_readable; 1873\& ev_io stdin_readable;
979\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1874\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
980\& ev_io_start (loop, &stdin_readable); 1875\& ev_io_start (loop, &stdin_readable);
981\& ev_loop (loop, 0); 1876\& ev_run (loop, 0);
982.Ve 1877.Ve
983.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1878.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
984.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1879.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
985.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1880.IX Subsection "ev_timer - relative and optionally repeating timeouts"
986Timer watchers are simple relative timers that generate an event after a 1881Timer watchers are simple relative timers that generate an event after a
987given time, and optionally repeating in regular intervals after that. 1882given time, and optionally repeating in regular intervals after that.
988.PP 1883.PP
989The timers are based on real time, that is, if you register an event that 1884The timers are based on real time, that is, if you register an event that
990times out after an hour and you reset your system clock to last years 1885times out after an hour and you reset your system clock to January last
991time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1886year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
992detecting time jumps is hard, and some inaccuracies are unavoidable (the 1887detecting time jumps is hard, and some inaccuracies are unavoidable (the
993monotonic clock option helps a lot here). 1888monotonic clock option helps a lot here).
1889.PP
1890The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1891passed (not \fIat\fR, so on systems with very low-resolution clocks this
1892might introduce a small delay, see \*(L"the special problem of being too
1893early\*(R", below). If multiple timers become ready during the same loop
1894iteration then the ones with earlier time-out values are invoked before
1895ones of the same priority with later time-out values (but this is no
1896longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1897.PP
1898\fIBe smart about timeouts\fR
1899.IX Subsection "Be smart about timeouts"
1900.PP
1901Many real-world problems involve some kind of timeout, usually for error
1902recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1903you want to raise some error after a while.
1904.PP
1905What follows are some ways to handle this problem, from obvious and
1906inefficient to smart and efficient.
1907.PP
1908In the following, a 60 second activity timeout is assumed \- a timeout that
1909gets reset to 60 seconds each time there is activity (e.g. each time some
1910data or other life sign was received).
1911.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1912.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1913This is the most obvious, but not the most simple way: In the beginning,
1914start the watcher:
1915.Sp
1916.Vb 2
1917\& ev_timer_init (timer, callback, 60., 0.);
1918\& ev_timer_start (loop, timer);
1919.Ve
1920.Sp
1921Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1922and start it again:
1923.Sp
1924.Vb 3
1925\& ev_timer_stop (loop, timer);
1926\& ev_timer_set (timer, 60., 0.);
1927\& ev_timer_start (loop, timer);
1928.Ve
1929.Sp
1930This is relatively simple to implement, but means that each time there is
1931some activity, libev will first have to remove the timer from its internal
1932data structure and then add it again. Libev tries to be fast, but it's
1933still not a constant-time operation.
1934.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1935.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1936.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1937This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1938\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1939.Sp
1940To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1941of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1942successfully read or write some data. If you go into an idle state where
1943you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1944the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1945.Sp
1946That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1947\&\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
1948member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1949.Sp
1950At start:
1951.Sp
1952.Vb 3
1953\& ev_init (timer, callback);
1954\& timer\->repeat = 60.;
1955\& ev_timer_again (loop, timer);
1956.Ve
1957.Sp
1958Each time there is some activity:
1959.Sp
1960.Vb 1
1961\& ev_timer_again (loop, timer);
1962.Ve
1963.Sp
1964It is even possible to change the time-out on the fly, regardless of
1965whether the watcher is active or not:
1966.Sp
1967.Vb 2
1968\& timer\->repeat = 30.;
1969\& ev_timer_again (loop, timer);
1970.Ve
1971.Sp
1972This is slightly more efficient then stopping/starting the timer each time
1973you want to modify its timeout value, as libev does not have to completely
1974remove and re-insert the timer from/into its internal data structure.
1975.Sp
1976It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1977.IP "3. Let the timer time out, but then re-arm it as required." 4
1978.IX Item "3. Let the timer time out, but then re-arm it as required."
1979This method is more tricky, but usually most efficient: Most timeouts are
1980relatively long compared to the intervals between other activity \- in
1981our example, within 60 seconds, there are usually many I/O events with
1982associated activity resets.
1983.Sp
1984In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1985but remember the time of last activity, and check for a real timeout only
1986within the callback:
1987.Sp
1988.Vb 3
1989\& ev_tstamp timeout = 60.;
1990\& ev_tstamp last_activity; // time of last activity
1991\& ev_timer timer;
1992\&
1993\& static void
1994\& callback (EV_P_ ev_timer *w, int revents)
1995\& {
1996\& // calculate when the timeout would happen
1997\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
1998\&
1999\& // if negative, it means we the timeout already occured
2000\& if (after < 0.)
2001\& {
2002\& // timeout occurred, take action
2003\& }
2004\& else
2005\& {
2006\& // callback was invoked, but there was some recent
2007\& // activity. simply restart the timer to time out
2008\& // after "after" seconds, which is the earliest time
2009\& // the timeout can occur.
2010\& ev_timer_set (w, after, 0.);
2011\& ev_timer_start (EV_A_ w);
2012\& }
2013\& }
2014.Ve
2015.Sp
2016To summarise the callback: first calculate in how many seconds the
2017timeout will occur (by calculating the absolute time when it would occur,
2018\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2019(EV_A)\*(C'\fR from that).
2020.Sp
2021If this value is negative, then we are already past the timeout, i.e. we
2022timed out, and need to do whatever is needed in this case.
2023.Sp
2024Otherwise, we now the earliest time at which the timeout would trigger,
2025and simply start the timer with this timeout value.
2026.Sp
2027In other words, each time the callback is invoked it will check whether
2028the timeout cocured. If not, it will simply reschedule itself to check
2029again at the earliest time it could time out. Rinse. Repeat.
2030.Sp
2031This scheme causes more callback invocations (about one every 60 seconds
2032minus half the average time between activity), but virtually no calls to
2033libev to change the timeout.
2034.Sp
2035To start the machinery, simply initialise the watcher and set
2036\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2037now), then call the callback, which will \*(L"do the right thing\*(R" and start
2038the timer:
2039.Sp
2040.Vb 3
2041\& last_activity = ev_now (EV_A);
2042\& ev_init (&timer, callback);
2043\& callback (EV_A_ &timer, 0);
2044.Ve
2045.Sp
2046When there is some activity, simply store the current time in
2047\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2048.Sp
2049.Vb 2
2050\& if (activity detected)
2051\& last_activity = ev_now (EV_A);
2052.Ve
2053.Sp
2054When your timeout value changes, then the timeout can be changed by simply
2055providing a new value, stopping the timer and calling the callback, which
2056will agaion do the right thing (for example, time out immediately :).
2057.Sp
2058.Vb 3
2059\& timeout = new_value;
2060\& ev_timer_stop (EV_A_ &timer);
2061\& callback (EV_A_ &timer, 0);
2062.Ve
2063.Sp
2064This technique is slightly more complex, but in most cases where the
2065time-out is unlikely to be triggered, much more efficient.
2066.IP "4. Wee, just use a double-linked list for your timeouts." 4
2067.IX Item "4. Wee, just use a double-linked list for your timeouts."
2068If there is not one request, but many thousands (millions...), all
2069employing some kind of timeout with the same timeout value, then one can
2070do even better:
2071.Sp
2072When starting the timeout, calculate the timeout value and put the timeout
2073at the \fIend\fR of the list.
2074.Sp
2075Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2076the list is expected to fire (for example, using the technique #3).
2077.Sp
2078When there is some activity, remove the timer from the list, recalculate
2079the timeout, append it to the end of the list again, and make sure to
2080update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2081.Sp
2082This way, one can manage an unlimited number of timeouts in O(1) time for
2083starting, stopping and updating the timers, at the expense of a major
2084complication, and having to use a constant timeout. The constant timeout
2085ensures that the list stays sorted.
2086.PP
2087So which method the best?
2088.PP
2089Method #2 is a simple no-brain-required solution that is adequate in most
2090situations. Method #3 requires a bit more thinking, but handles many cases
2091better, and isn't very complicated either. In most case, choosing either
2092one is fine, with #3 being better in typical situations.
2093.PP
2094Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2095rather complicated, but extremely efficient, something that really pays
2096off after the first million or so of active timers, i.e. it's usually
2097overkill :)
2098.PP
2099\fIThe special problem of being too early\fR
2100.IX Subsection "The special problem of being too early"
2101.PP
2102If you ask a timer to call your callback after three seconds, then
2103you expect it to be invoked after three seconds \- but of course, this
2104cannot be guaranteed to infinite precision. Less obviously, it cannot be
2105guaranteed to any precision by libev \- imagine somebody suspending the
2106process with a \s-1STOP\s0 signal for a few hours for example.
2107.PP
2108So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2109delay has occurred, but cannot guarantee this.
2110.PP
2111A less obvious failure mode is calling your callback too early: many event
2112loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2113this can cause your callback to be invoked much earlier than you would
2114expect.
2115.PP
2116To see why, imagine a system with a clock that only offers full second
2117resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2118yourself). If you schedule a one-second timer at the time 500.9, then the
2119event loop will schedule your timeout to elapse at a system time of 500
2120(500.9 truncated to the resolution) + 1, or 501.
2121.PP
2122If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2123501\*(R" and invoke the callback 0.1s after it was started, even though a
2124one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2125intentions.
2126.PP
2127This is the reason why libev will never invoke the callback if the elapsed
2128delay equals the requested delay, but only when the elapsed delay is
2129larger than the requested delay. In the example above, libev would only invoke
2130the callback at system time 502, or 1.1s after the timer was started.
2131.PP
2132So, while libev cannot guarantee that your callback will be invoked
2133exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2134delay has actually elapsed, or in other words, it always errs on the \*(L"too
2135late\*(R" side of things.
2136.PP
2137\fIThe special problem of time updates\fR
2138.IX Subsection "The special problem of time updates"
2139.PP
2140Establishing the current time is a costly operation (it usually takes
2141at least one system call): \s-1EV\s0 therefore updates its idea of the current
2142time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2143growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2144lots of events in one iteration.
994.PP 2145.PP
995The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2146The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
996time. This is usually the right thing as this timestamp refers to the time 2147time. This is usually the right thing as this timestamp refers to the time
997of the event triggering whatever timeout you are modifying/starting. If 2148of the event triggering whatever timeout you are modifying/starting. If
998you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2149you suspect event processing to be delayed and you \fIneed\fR to base the
999on the current time, use something like this to adjust for this: 2150timeout on the current time, use something like this to adjust for this:
1000.PP 2151.PP
1001.Vb 1 2152.Vb 1
1002\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2153\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1003.Ve 2154.Ve
1004.PP 2155.PP
1005The callback is guarenteed to be invoked only when its timeout has passed, 2156If the event loop is suspended for a long time, you can also force an
1006but if multiple timers become ready during the same loop iteration then 2157update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1007order of execution is undefined. 2158()\*(C'\fR.
2159.PP
2160\fIThe special problem of unsynchronised clocks\fR
2161.IX Subsection "The special problem of unsynchronised clocks"
2162.PP
2163Modern systems have a variety of clocks \- libev itself uses the normal
2164\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2165jumps).
2166.PP
2167Neither of these clocks is synchronised with each other or any other clock
2168on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2169than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2170a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2171than a directly following call to \f(CW\*(C`time\*(C'\fR.
2172.PP
2173The moral of this is to only compare libev-related timestamps with
2174\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2175a second or so.
2176.PP
2177One more problem arises due to this lack of synchronisation: if libev uses
2178the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2179or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2180invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2181.PP
2182This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2183libev makes sure your callback is not invoked before the delay happened,
2184\&\fImeasured according to the real time\fR, not the system clock.
2185.PP
2186If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2187connection after 100 seconds\*(R") then this shouldn't bother you as it is
2188exactly the right behaviour.
2189.PP
2190If you want to compare wall clock/system timestamps to your timers, then
2191you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2192time, where your comparisons will always generate correct results.
2193.PP
2194\fIThe special problems of suspended animation\fR
2195.IX Subsection "The special problems of suspended animation"
2196.PP
2197When you leave the server world it is quite customary to hit machines that
2198can suspend/hibernate \- what happens to the clocks during such a suspend?
2199.PP
2200Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2201all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2202to run until the system is suspended, but they will not advance while the
2203system is suspended. That means, on resume, it will be as if the program
2204was frozen for a few seconds, but the suspend time will not be counted
2205towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2206clock advanced as expected, but if it is used as sole clocksource, then a
2207long suspend would be detected as a time jump by libev, and timers would
2208be adjusted accordingly.
2209.PP
2210I would not be surprised to see different behaviour in different between
2211operating systems, \s-1OS\s0 versions or even different hardware.
2212.PP
2213The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2214time jump in the monotonic clocks and the realtime clock. If the program
2215is suspended for a very long time, and monotonic clock sources are in use,
2216then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2217will be counted towards the timers. When no monotonic clock source is in
2218use, then libev will again assume a timejump and adjust accordingly.
2219.PP
2220It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2221and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2222deterministic behaviour in this case (you can do nothing against
2223\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2224.PP
2225\fIWatcher-Specific Functions and Data Members\fR
2226.IX Subsection "Watcher-Specific Functions and Data Members"
1008.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2227.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1009.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2228.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1010.PD 0 2229.PD 0
1011.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2230.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1012.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2231.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1013.PD 2232.PD
1014Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2233Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1015\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2234is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1016timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2235reached. If it is positive, then the timer will automatically be
1017later, again, and again, until stopped manually. 2236configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2237until stopped manually.
1018.Sp 2238.Sp
1019The timer itself will do a best-effort at avoiding drift, that is, if you 2239The timer itself will do a best-effort at avoiding drift, that is, if
1020configure a timer to trigger every 10 seconds, then it will trigger at 2240you configure a timer to trigger every 10 seconds, then it will normally
1021exactly 10 second intervals. If, however, your program cannot keep up with 2241trigger at exactly 10 second intervals. If, however, your program cannot
1022the timer (because it takes longer than those 10 seconds to do stuff) the 2242keep up with the timer (because it takes longer than those 10 seconds to
1023timer will not fire more than once per event loop iteration. 2243do stuff) the timer will not fire more than once per event loop iteration.
1024.IP "ev_timer_again (loop)" 4 2244.IP "ev_timer_again (loop, ev_timer *)" 4
1025.IX Item "ev_timer_again (loop)" 2245.IX Item "ev_timer_again (loop, ev_timer *)"
1026This will act as if the timer timed out and restart it again if it is 2246This will act as if the timer timed out, and restarts it again if it is
1027repeating. The exact semantics are: 2247repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2248timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1028.Sp 2249.Sp
1029If the timer is started but nonrepeating, stop it. 2250The exact semantics are as in the following rules, all of which will be
2251applied to the watcher:
2252.RS 4
2253.IP "If the timer is pending, the pending status is always cleared." 4
2254.IX Item "If the timer is pending, the pending status is always cleared."
2255.PD 0
2256.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2257.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2258.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2259.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2260.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2261.RE
2262.RS 4
2263.PD
1030.Sp 2264.Sp
1031If the timer is repeating, either start it if necessary (with the repeat 2265This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1032value), or reset the running timer to the repeat value. 2266usage example.
2267.RE
2268.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2269.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2270Returns the remaining time until a timer fires. If the timer is active,
2271then this time is relative to the current event loop time, otherwise it's
2272the timeout value currently configured.
1033.Sp 2273.Sp
1034This sounds a bit complicated, but here is a useful and typical 2274That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1035example: Imagine you have a tcp connection and you want a so-called 2275\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1036idle timeout, that is, you want to be called when there have been, 2276will return \f(CW4\fR. When the timer expires and is restarted, it will return
1037say, 60 seconds of inactivity on the socket. The easiest way to do 2277roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1038this is to configure an \f(CW\*(C`ev_timer\*(C'\fR with \f(CW\*(C`after\*(C'\fR=\f(CW\*(C`repeat\*(C'\fR=\f(CW60\fR and calling 2278too), and so on.
1039\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1040you go into an idle state where you do not expect data to travel on the
1041socket, you can stop the timer, and again will automatically restart it if
1042need be.
1043.Sp
1044You can also ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR altogether
1045and only ever use the \f(CW\*(C`repeat\*(C'\fR value:
1046.Sp
1047.Vb 8
1048\& ev_timer_init (timer, callback, 0., 5.);
1049\& ev_timer_again (loop, timer);
1050\& ...
1051\& timer->again = 17.;
1052\& ev_timer_again (loop, timer);
1053\& ...
1054\& timer->again = 10.;
1055\& ev_timer_again (loop, timer);
1056.Ve
1057.Sp
1058This is more efficient then stopping/starting the timer eahc time you want
1059to modify its timeout value.
1060.IP "ev_tstamp repeat [read\-write]" 4 2279.IP "ev_tstamp repeat [read\-write]" 4
1061.IX Item "ev_tstamp repeat [read-write]" 2280.IX Item "ev_tstamp repeat [read-write]"
1062The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2281The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1063or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2282or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1064which is also when any modifications are taken into account. 2283which is also when any modifications are taken into account.
1065.PP 2284.PP
2285\fIExamples\fR
2286.IX Subsection "Examples"
2287.PP
1066Example: create a timer that fires after 60 seconds. 2288Example: Create a timer that fires after 60 seconds.
1067.PP 2289.PP
1068.Vb 5 2290.Vb 5
1069\& static void 2291\& static void
1070\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2292\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1071\& { 2293\& {
1072\& .. one minute over, w is actually stopped right here 2294\& .. one minute over, w is actually stopped right here
1073\& } 2295\& }
1074.Ve 2296\&
1075.PP
1076.Vb 3
1077\& struct ev_timer mytimer; 2297\& ev_timer mytimer;
1078\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2298\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1079\& ev_timer_start (loop, &mytimer); 2299\& ev_timer_start (loop, &mytimer);
1080.Ve 2300.Ve
1081.PP 2301.PP
1082Example: create a timeout timer that times out after 10 seconds of 2302Example: Create a timeout timer that times out after 10 seconds of
1083inactivity. 2303inactivity.
1084.PP 2304.PP
1085.Vb 5 2305.Vb 5
1086\& static void 2306\& static void
1087\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2307\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1088\& { 2308\& {
1089\& .. ten seconds without any activity 2309\& .. ten seconds without any activity
1090\& } 2310\& }
1091.Ve 2311\&
1092.PP
1093.Vb 4
1094\& struct ev_timer mytimer; 2312\& ev_timer mytimer;
1095\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2313\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1096\& ev_timer_again (&mytimer); /* start timer */ 2314\& ev_timer_again (&mytimer); /* start timer */
1097\& ev_loop (loop, 0); 2315\& ev_run (loop, 0);
1098.Ve 2316\&
1099.PP
1100.Vb 3
1101\& // and in some piece of code that gets executed on any "activity": 2317\& // and in some piece of code that gets executed on any "activity":
1102\& // reset the timeout to start ticking again at 10 seconds 2318\& // reset the timeout to start ticking again at 10 seconds
1103\& ev_timer_again (&mytimer); 2319\& ev_timer_again (&mytimer);
1104.Ve 2320.Ve
1105.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2321.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1106.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2322.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1107.IX Subsection "ev_periodic - to cron or not to cron?" 2323.IX Subsection "ev_periodic - to cron or not to cron?"
1108Periodic watchers are also timers of a kind, but they are very versatile 2324Periodic watchers are also timers of a kind, but they are very versatile
1109(and unfortunately a bit complex). 2325(and unfortunately a bit complex).
1110.PP 2326.PP
1111Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2327Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1112but on wallclock time (absolute time). You can tell a periodic watcher 2328relative time, the physical time that passes) but on wall clock time
1113to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2329(absolute time, the thing you can read on your calender or clock). The
1114periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2330difference is that wall clock time can run faster or slower than real
1115+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2331time, and time jumps are not uncommon (e.g. when you adjust your
1116take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2332wrist-watch).
1117roughly 10 seconds later and of course not if you reset your system time
1118again).
1119.PP 2333.PP
1120They can also be used to implement vastly more complex timers, such as 2334You can tell a periodic watcher to trigger after some specific point
1121triggering an event on eahc midnight, local time. 2335in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2336seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2337not a delay) and then reset your system clock to January of the previous
2338year, then it will take a year or more to trigger the event (unlike an
2339\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2340it, as it uses a relative timeout).
1122.PP 2341.PP
2342\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2343timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2344other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2345those cannot react to time jumps.
2346.PP
1123As with timers, the callback is guarenteed to be invoked only when the 2347As with timers, the callback is guaranteed to be invoked only when the
1124time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2348point in time where it is supposed to trigger has passed. If multiple
1125during the same loop iteration then order of execution is undefined. 2349timers become ready during the same loop iteration then the ones with
2350earlier time-out values are invoked before ones with later time-out values
2351(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2352.PP
2353\fIWatcher-Specific Functions and Data Members\fR
2354.IX Subsection "Watcher-Specific Functions and Data Members"
1126.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2355.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1127.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2356.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1128.PD 0 2357.PD 0
1129.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2358.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1130.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2359.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1131.PD 2360.PD
1132Lots of arguments, lets sort it out... There are basically three modes of 2361Lots of arguments, let's sort it out... There are basically three modes of
1133operation, and we will explain them from simplest to complex: 2362operation, and we will explain them from simplest to most complex:
1134.RS 4 2363.RS 4
1135.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2364.IP "\(bu" 4
1136.IX Item "absolute timer (interval = reschedule_cb = 0)" 2365absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2366.Sp
1137In this configuration the watcher triggers an event at the wallclock time 2367In this configuration the watcher triggers an event after the wall clock
1138\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2368time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1139that is, if it is to be run at January 1st 2011 then it will run when the 2369time jump occurs, that is, if it is to be run at January 1st 2011 then it
1140system time reaches or surpasses this time. 2370will be stopped and invoked when the system clock reaches or surpasses
1141.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2371this point in time.
1142.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2372.IP "\(bu" 4
2373repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2374.Sp
1143In this mode the watcher will always be scheduled to time out at the next 2375In this mode the watcher will always be scheduled to time out at the next
1144\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2376\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1145of any time jumps. 2377negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2378argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1146.Sp 2379.Sp
1147This can be used to create timers that do not drift with respect to system 2380This can be used to create timers that do not drift with respect to the
1148time: 2381system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2382hour, on the hour (with respect to \s-1UTC\s0):
1149.Sp 2383.Sp
1150.Vb 1 2384.Vb 1
1151\& ev_periodic_set (&periodic, 0., 3600., 0); 2385\& ev_periodic_set (&periodic, 0., 3600., 0);
1152.Ve 2386.Ve
1153.Sp 2387.Sp
1154This doesn't mean there will always be 3600 seconds in between triggers, 2388This doesn't mean there will always be 3600 seconds in between triggers,
1155but only that the the callback will be called when the system time shows a 2389but only that the callback will be called when the system time shows a
1156full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2390full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1157by 3600. 2391by 3600.
1158.Sp 2392.Sp
1159Another way to think about it (for the mathematically inclined) is that 2393Another way to think about it (for the mathematically inclined) is that
1160\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2394\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1161time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2395time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1162.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2396.Sp
1163.IX Item "manual reschedule mode (reschedule_cb = callback)" 2397The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2398interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2399microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2400at most a similar magnitude as the current time (say, within a factor of
2401ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2402\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2403.Sp
2404Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2405speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2406will of course deteriorate. Libev itself tries to be exact to be about one
2407millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2408.IP "\(bu" 4
2409manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2410.Sp
1164In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2411In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1165ignored. Instead, each time the periodic watcher gets scheduled, the 2412ignored. Instead, each time the periodic watcher gets scheduled, the
1166reschedule callback will be called with the watcher as first, and the 2413reschedule callback will be called with the watcher as first, and the
1167current time as second argument. 2414current time as second argument.
1168.Sp 2415.Sp
1169\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2416\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1170ever, or make any event loop modifications\fR. If you need to stop it, 2417or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1171return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2418allowed by documentation here\fR.
1172starting a prepare watcher).
1173.Sp 2419.Sp
2420If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2421it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2422only event loop modification you are allowed to do).
2423.Sp
1174Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2424The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1175ev_tstamp now)\*(C'\fR, e.g.: 2425*w, ev_tstamp now)\*(C'\fR, e.g.:
1176.Sp 2426.Sp
1177.Vb 4 2427.Vb 5
2428\& static ev_tstamp
1178\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2429\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1179\& { 2430\& {
1180\& return now + 60.; 2431\& return now + 60.;
1181\& } 2432\& }
1182.Ve 2433.Ve
1183.Sp 2434.Sp
1184It must return the next time to trigger, based on the passed time value 2435It must return the next time to trigger, based on the passed time value
1185(that is, the lowest time value larger than to the second argument). It 2436(that is, the lowest time value larger than to the second argument). It
1186will usually be called just before the callback will be triggered, but 2437will usually be called just before the callback will be triggered, but
1187might be called at other times, too. 2438might be called at other times, too.
1188.Sp 2439.Sp
1189\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2440\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1190passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2441equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1191.Sp 2442.Sp
1192This can be used to create very complex timers, such as a timer that 2443This can be used to create very complex timers, such as a timer that
1193triggers on each midnight, local time. To do this, you would calculate the 2444triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1194next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2445next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1195you do this is, again, up to you (but it is not trivial, which is the main 2446you do this is, again, up to you (but it is not trivial, which is the main
1196reason I omitted it as an example). 2447reason I omitted it as an example).
1197.RE 2448.RE
1198.RS 4 2449.RS 4
… …
1201.IX Item "ev_periodic_again (loop, ev_periodic *)" 2452.IX Item "ev_periodic_again (loop, ev_periodic *)"
1202Simply stops and restarts the periodic watcher again. This is only useful 2453Simply stops and restarts the periodic watcher again. This is only useful
1203when you changed some parameters or the reschedule callback would return 2454when you changed some parameters or the reschedule callback would return
1204a different time than the last time it was called (e.g. in a crond like 2455a different time than the last time it was called (e.g. in a crond like
1205program when the crontabs have changed). 2456program when the crontabs have changed).
2457.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2458.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2459When active, returns the absolute time that the watcher is supposed
2460to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2461\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2462rescheduling modes.
2463.IP "ev_tstamp offset [read\-write]" 4
2464.IX Item "ev_tstamp offset [read-write]"
2465When repeating, this contains the offset value, otherwise this is the
2466absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2467although libev might modify this value for better numerical stability).
2468.Sp
2469Can be modified any time, but changes only take effect when the periodic
2470timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1206.IP "ev_tstamp interval [read\-write]" 4 2471.IP "ev_tstamp interval [read\-write]" 4
1207.IX Item "ev_tstamp interval [read-write]" 2472.IX Item "ev_tstamp interval [read-write]"
1208The current interval value. Can be modified any time, but changes only 2473The current interval value. Can be modified any time, but changes only
1209take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2474take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1210called. 2475called.
1211.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2476.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1212.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2477.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1213The current reschedule callback, or \f(CW0\fR, if this functionality is 2478The current reschedule callback, or \f(CW0\fR, if this functionality is
1214switched off. Can be changed any time, but changes only take effect when 2479switched off. Can be changed any time, but changes only take effect when
1215the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2480the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1216.PP 2481.PP
2482\fIExamples\fR
2483.IX Subsection "Examples"
2484.PP
1217Example: call a callback every hour, or, more precisely, whenever the 2485Example: Call a callback every hour, or, more precisely, whenever the
1218system clock is divisible by 3600. The callback invocation times have 2486system time is divisible by 3600. The callback invocation times have
1219potentially a lot of jittering, but good long-term stability. 2487potentially a lot of jitter, but good long-term stability.
1220.PP 2488.PP
1221.Vb 5 2489.Vb 5
1222\& static void 2490\& static void
1223\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2491\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1224\& { 2492\& {
1225\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2493\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1226\& } 2494\& }
1227.Ve 2495\&
1228.PP
1229.Vb 3
1230\& struct ev_periodic hourly_tick; 2496\& ev_periodic hourly_tick;
1231\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2497\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1232\& ev_periodic_start (loop, &hourly_tick); 2498\& ev_periodic_start (loop, &hourly_tick);
1233.Ve 2499.Ve
1234.PP 2500.PP
1235Example: the same as above, but use a reschedule callback to do it: 2501Example: The same as above, but use a reschedule callback to do it:
1236.PP 2502.PP
1237.Vb 1 2503.Vb 1
1238\& #include <math.h> 2504\& #include <math.h>
1239.Ve 2505\&
1240.PP
1241.Vb 5
1242\& static ev_tstamp 2506\& static ev_tstamp
1243\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2507\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1244\& { 2508\& {
1245\& return fmod (now, 3600.) + 3600.; 2509\& return now + (3600. \- fmod (now, 3600.));
1246\& } 2510\& }
1247.Ve 2511\&
1248.PP
1249.Vb 1
1250\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2512\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1251.Ve 2513.Ve
1252.PP 2514.PP
1253Example: call a callback every hour, starting now: 2515Example: Call a callback every hour, starting now:
1254.PP 2516.PP
1255.Vb 4 2517.Vb 4
1256\& struct ev_periodic hourly_tick; 2518\& ev_periodic hourly_tick;
1257\& ev_periodic_init (&hourly_tick, clock_cb, 2519\& ev_periodic_init (&hourly_tick, clock_cb,
1258\& fmod (ev_now (loop), 3600.), 3600., 0); 2520\& fmod (ev_now (loop), 3600.), 3600., 0);
1259\& ev_periodic_start (loop, &hourly_tick); 2521\& ev_periodic_start (loop, &hourly_tick);
1260.Ve 2522.Ve
1261.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2523.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1262.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2524.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1263.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2525.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1264Signal watchers will trigger an event when the process receives a specific 2526Signal watchers will trigger an event when the process receives a specific
1265signal one or more times. Even though signals are very asynchronous, libev 2527signal one or more times. Even though signals are very asynchronous, libev
1266will try it's best to deliver signals synchronously, i.e. as part of the 2528will try its best to deliver signals synchronously, i.e. as part of the
1267normal event processing, like any other event. 2529normal event processing, like any other event.
1268.PP 2530.PP
2531If you want signals to be delivered truly asynchronously, just use
2532\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2533the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2534synchronously wake up an event loop.
2535.PP
1269You can configure as many watchers as you like per signal. Only when the 2536You can configure as many watchers as you like for the same signal, but
2537only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2538default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2539\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2540the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2541.PP
1270first watcher gets started will libev actually register a signal watcher 2542When the first watcher gets started will libev actually register something
1271with the kernel (thus it coexists with your own signal handlers as long 2543with the kernel (thus it coexists with your own signal handlers as long as
1272as you don't register any with libev). Similarly, when the last signal 2544you don't register any with libev for the same signal).
1273watcher for a signal is stopped libev will reset the signal handler to 2545.PP
1274\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2546If possible and supported, libev will install its handlers with
2547\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2548not be unduly interrupted. If you have a problem with system calls getting
2549interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2550and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2551.PP
2552\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2553.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2554.PP
2555Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2556(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2557stopping it again), that is, libev might or might not block the signal,
2558and might or might not set or restore the installed signal handler (but
2559see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2560.PP
2561While this does not matter for the signal disposition (libev never
2562sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2563\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2564certain signals to be blocked.
2565.PP
2566This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2567the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2568choice usually).
2569.PP
2570The simplest way to ensure that the signal mask is reset in the child is
2571to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2572catch fork calls done by libraries (such as the libc) as well.
2573.PP
2574In current versions of libev, the signal will not be blocked indefinitely
2575unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2576the window of opportunity for problems, it will not go away, as libev
2577\&\fIhas\fR to modify the signal mask, at least temporarily.
2578.PP
2579So I can't stress this enough: \fIIf you do not reset your signal mask when
2580you expect it to be empty, you have a race condition in your code\fR. This
2581is not a libev-specific thing, this is true for most event libraries.
2582.PP
2583\fIThe special problem of threads signal handling\fR
2584.IX Subsection "The special problem of threads signal handling"
2585.PP
2586\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2587a lot of functionality (sigfd, sigwait etc.) only really works if all
2588threads in a process block signals, which is hard to achieve.
2589.PP
2590When you want to use sigwait (or mix libev signal handling with your own
2591for the same signals), you can tackle this problem by globally blocking
2592all signals before creating any threads (or creating them with a fully set
2593sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2594loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2595these signals. You can pass on any signals that libev might be interested
2596in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2597.PP
2598\fIWatcher-Specific Functions and Data Members\fR
2599.IX Subsection "Watcher-Specific Functions and Data Members"
1275.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2600.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1276.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2601.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1277.PD 0 2602.PD 0
1278.IP "ev_signal_set (ev_signal *, int signum)" 4 2603.IP "ev_signal_set (ev_signal *, int signum)" 4
1279.IX Item "ev_signal_set (ev_signal *, int signum)" 2604.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1281Configures the watcher to trigger on the given signal number (usually one 2606Configures the watcher to trigger on the given signal number (usually one
1282of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2607of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1283.IP "int signum [read\-only]" 4 2608.IP "int signum [read\-only]" 4
1284.IX Item "int signum [read-only]" 2609.IX Item "int signum [read-only]"
1285The signal the watcher watches out for. 2610The signal the watcher watches out for.
2611.PP
2612\fIExamples\fR
2613.IX Subsection "Examples"
2614.PP
2615Example: Try to exit cleanly on \s-1SIGINT\s0.
2616.PP
2617.Vb 5
2618\& static void
2619\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2620\& {
2621\& ev_break (loop, EVBREAK_ALL);
2622\& }
2623\&
2624\& ev_signal signal_watcher;
2625\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2626\& ev_signal_start (loop, &signal_watcher);
2627.Ve
1286.ie n .Sh """ev_child"" \- watch out for process status changes" 2628.ie n .SS """ev_child"" \- watch out for process status changes"
1287.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2629.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1288.IX Subsection "ev_child - watch out for process status changes" 2630.IX Subsection "ev_child - watch out for process status changes"
1289Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2631Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1290some child status changes (most typically when a child of yours dies). 2632some child status changes (most typically when a child of yours dies or
2633exits). It is permissible to install a child watcher \fIafter\fR the child
2634has been forked (which implies it might have already exited), as long
2635as the event loop isn't entered (or is continued from a watcher), i.e.,
2636forking and then immediately registering a watcher for the child is fine,
2637but forking and registering a watcher a few event loop iterations later or
2638in the next callback invocation is not.
2639.PP
2640Only the default event loop is capable of handling signals, and therefore
2641you can only register child watchers in the default event loop.
2642.PP
2643Due to some design glitches inside libev, child watchers will always be
2644handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2645libev)
2646.PP
2647\fIProcess Interaction\fR
2648.IX Subsection "Process Interaction"
2649.PP
2650Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2651initialised. This is necessary to guarantee proper behaviour even if the
2652first child watcher is started after the child exits. The occurrence
2653of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2654synchronously as part of the event loop processing. Libev always reaps all
2655children, even ones not watched.
2656.PP
2657\fIOverriding the Built-In Processing\fR
2658.IX Subsection "Overriding the Built-In Processing"
2659.PP
2660Libev offers no special support for overriding the built-in child
2661processing, but if your application collides with libev's default child
2662handler, you can override it easily by installing your own handler for
2663\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2664default loop never gets destroyed. You are encouraged, however, to use an
2665event-based approach to child reaping and thus use libev's support for
2666that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2667.PP
2668\fIStopping the Child Watcher\fR
2669.IX Subsection "Stopping the Child Watcher"
2670.PP
2671Currently, the child watcher never gets stopped, even when the
2672child terminates, so normally one needs to stop the watcher in the
2673callback. Future versions of libev might stop the watcher automatically
2674when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2675problem).
2676.PP
2677\fIWatcher-Specific Functions and Data Members\fR
2678.IX Subsection "Watcher-Specific Functions and Data Members"
1291.IP "ev_child_init (ev_child *, callback, int pid)" 4 2679.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1292.IX Item "ev_child_init (ev_child *, callback, int pid)" 2680.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1293.PD 0 2681.PD 0
1294.IP "ev_child_set (ev_child *, int pid)" 4 2682.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1295.IX Item "ev_child_set (ev_child *, int pid)" 2683.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1296.PD 2684.PD
1297Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2685Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1298\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2686\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1299at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2687at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1300the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2688the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1301\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2689\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1302process causing the status change. 2690process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2691activate the watcher when the process terminates) or \f(CW1\fR (additionally
2692activate the watcher when the process is stopped or continued).
1303.IP "int pid [read\-only]" 4 2693.IP "int pid [read\-only]" 4
1304.IX Item "int pid [read-only]" 2694.IX Item "int pid [read-only]"
1305The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2695The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1306.IP "int rpid [read\-write]" 4 2696.IP "int rpid [read\-write]" 4
1307.IX Item "int rpid [read-write]" 2697.IX Item "int rpid [read-write]"
… …
1309.IP "int rstatus [read\-write]" 4 2699.IP "int rstatus [read\-write]" 4
1310.IX Item "int rstatus [read-write]" 2700.IX Item "int rstatus [read-write]"
1311The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2701The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1312\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2702\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1313.PP 2703.PP
1314Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2704\fIExamples\fR
2705.IX Subsection "Examples"
1315.PP 2706.PP
2707Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2708its completion.
2709.PP
1316.Vb 5 2710.Vb 1
2711\& ev_child cw;
2712\&
1317\& static void 2713\& static void
1318\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2714\& child_cb (EV_P_ ev_child *w, int revents)
1319\& { 2715\& {
1320\& ev_unloop (loop, EVUNLOOP_ALL); 2716\& ev_child_stop (EV_A_ w);
2717\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1321\& } 2718\& }
2719\&
2720\& pid_t pid = fork ();
2721\&
2722\& if (pid < 0)
2723\& // error
2724\& else if (pid == 0)
2725\& {
2726\& // the forked child executes here
2727\& exit (1);
2728\& }
2729\& else
2730\& {
2731\& ev_child_init (&cw, child_cb, pid, 0);
2732\& ev_child_start (EV_DEFAULT_ &cw);
2733\& }
1322.Ve 2734.Ve
1323.PP
1324.Vb 3
1325\& struct ev_signal signal_watcher;
1326\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1327\& ev_signal_start (loop, &sigint_cb);
1328.Ve
1329.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2735.ie n .SS """ev_stat"" \- did the file attributes just change?"
1330.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2736.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1331.IX Subsection "ev_stat - did the file attributes just change?" 2737.IX Subsection "ev_stat - did the file attributes just change?"
1332This watches a filesystem path for attribute changes. That is, it calls 2738This watches a file system path for attribute changes. That is, it calls
1333\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2739\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1334compared to the last time, invoking the callback if it did. 2740and sees if it changed compared to the last time, invoking the callback if
2741it did.
1335.PP 2742.PP
1336The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2743The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1337not exist\*(R" is a status change like any other. The condition \*(L"path does 2744not exist\*(R" is a status change like any other. The condition \*(L"path does not
1338not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2745exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1339otherwise always forced to be at least one) and all the other fields of 2746\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1340the stat buffer having unspecified contents. 2747least one) and all the other fields of the stat buffer having unspecified
2748contents.
1341.PP 2749.PP
1342Since there is no standard to do this, the portable implementation simply 2750The path \fImust not\fR end in a slash or contain special components such as
1343calls \f(CW\*(C`stat (2)\*(C'\fR regulalry on the path to see if it changed somehow. You 2751\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1344can specify a recommended polling interval for this case. If you specify 2752your working directory changes, then the behaviour is undefined.
1345a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2753.PP
1346unspecified default\fR value will be used (which you can expect to be around 2754Since there is no portable change notification interface available, the
1347five seconds, although this might change dynamically). Libev will also 2755portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1348impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2756to see if it changed somehow. You can specify a recommended polling
1349usually overkill. 2757interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2758recommended!) then a \fIsuitable, unspecified default\fR value will be used
2759(which you can expect to be around five seconds, although this might
2760change dynamically). Libev will also impose a minimum interval which is
2761currently around \f(CW0.1\fR, but that's usually overkill.
1350.PP 2762.PP
1351This watcher type is not meant for massive numbers of stat watchers, 2763This watcher type is not meant for massive numbers of stat watchers,
1352as even with OS-supported change notifications, this can be 2764as even with OS-supported change notifications, this can be
1353resource\-intensive. 2765resource-intensive.
1354.PP 2766.PP
1355At the time of this writing, no specific \s-1OS\s0 backends are implemented, but 2767At the time of this writing, the only OS-specific interface implemented
1356if demand increases, at least a kqueue and inotify backend will be added. 2768is the Linux inotify interface (implementing kqueue support is left as an
2769exercise for the reader. Note, however, that the author sees no way of
2770implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2771.PP
2772\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2773.IX Subsection "ABI Issues (Largefile Support)"
2774.PP
2775Libev by default (unless the user overrides this) uses the default
2776compilation environment, which means that on systems with large file
2777support disabled by default, you get the 32 bit version of the stat
2778structure. When using the library from programs that change the \s-1ABI\s0 to
2779use 64 bit file offsets the programs will fail. In that case you have to
2780compile libev with the same flags to get binary compatibility. This is
2781obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2782most noticeably displayed with ev_stat and large file support.
2783.PP
2784The solution for this is to lobby your distribution maker to make large
2785file interfaces available by default (as e.g. FreeBSD does) and not
2786optional. Libev cannot simply switch on large file support because it has
2787to exchange stat structures with application programs compiled using the
2788default compilation environment.
2789.PP
2790\fIInotify and Kqueue\fR
2791.IX Subsection "Inotify and Kqueue"
2792.PP
2793When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2794runtime, it will be used to speed up change detection where possible. The
2795inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2796watcher is being started.
2797.PP
2798Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2799except that changes might be detected earlier, and in some cases, to avoid
2800making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2801there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2802but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2803many bugs), the path exists (i.e. stat succeeds), and the path resides on
2804a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2805xfs are fully working) libev usually gets away without polling.
2806.PP
2807There is no support for kqueue, as apparently it cannot be used to
2808implement this functionality, due to the requirement of having a file
2809descriptor open on the object at all times, and detecting renames, unlinks
2810etc. is difficult.
2811.PP
2812\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2813.IX Subsection "stat () is a synchronous operation"
2814.PP
2815Libev doesn't normally do any kind of I/O itself, and so is not blocking
2816the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2817()\*(C'\fR, which is a synchronous operation.
2818.PP
2819For local paths, this usually doesn't matter: unless the system is very
2820busy or the intervals between stat's are large, a stat call will be fast,
2821as the path data is usually in memory already (except when starting the
2822watcher).
2823.PP
2824For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2825time due to network issues, and even under good conditions, a stat call
2826often takes multiple milliseconds.
2827.PP
2828Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2829paths, although this is fully supported by libev.
2830.PP
2831\fIThe special problem of stat time resolution\fR
2832.IX Subsection "The special problem of stat time resolution"
2833.PP
2834The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2835and even on systems where the resolution is higher, most file systems
2836still only support whole seconds.
2837.PP
2838That means that, if the time is the only thing that changes, you can
2839easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2840calls your callback, which does something. When there is another update
2841within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2842stat data does change in other ways (e.g. file size).
2843.PP
2844The solution to this is to delay acting on a change for slightly more
2845than a second (or till slightly after the next full second boundary), using
2846a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2847ev_timer_again (loop, w)\*(C'\fR).
2848.PP
2849The \f(CW.02\fR offset is added to work around small timing inconsistencies
2850of some operating systems (where the second counter of the current time
2851might be be delayed. One such system is the Linux kernel, where a call to
2852\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2853a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2854update file times then there will be a small window where the kernel uses
2855the previous second to update file times but libev might already execute
2856the timer callback).
2857.PP
2858\fIWatcher-Specific Functions and Data Members\fR
2859.IX Subsection "Watcher-Specific Functions and Data Members"
1357.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2860.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1358.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2861.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1359.PD 0 2862.PD 0
1360.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 2863.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1361.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 2864.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1364\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2867\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1365be detected and should normally be specified as \f(CW0\fR to let libev choose 2868be detected and should normally be specified as \f(CW0\fR to let libev choose
1366a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2869a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1367path for as long as the watcher is active. 2870path for as long as the watcher is active.
1368.Sp 2871.Sp
1369The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2872The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1370relative to the attributes at the time the watcher was started (or the 2873relative to the attributes at the time the watcher was started (or the
1371last change was detected). 2874last change was detected).
1372.IP "ev_stat_stat (ev_stat *)" 4 2875.IP "ev_stat_stat (loop, ev_stat *)" 4
1373.IX Item "ev_stat_stat (ev_stat *)" 2876.IX Item "ev_stat_stat (loop, ev_stat *)"
1374Updates the stat buffer immediately with new values. If you change the 2877Updates the stat buffer immediately with new values. If you change the
1375watched path in your callback, you could call this fucntion to avoid 2878watched path in your callback, you could call this function to avoid
1376detecting this change (while introducing a race condition). Can also be 2879detecting this change (while introducing a race condition if you are not
1377useful simply to find out the new values. 2880the only one changing the path). Can also be useful simply to find out the
2881new values.
1378.IP "ev_statdata attr [read\-only]" 4 2882.IP "ev_statdata attr [read\-only]" 4
1379.IX Item "ev_statdata attr [read-only]" 2883.IX Item "ev_statdata attr [read-only]"
1380The most-recently detected attributes of the file. Although the type is of 2884The most-recently detected attributes of the file. Although the type is
1381\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 2885\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2886suitable for your system, but you can only rely on the POSIX-standardised
1382suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 2887members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1383was some error while \f(CW\*(C`stat\*(C'\fRing the file. 2888some error while \f(CW\*(C`stat\*(C'\fRing the file.
1384.IP "ev_statdata prev [read\-only]" 4 2889.IP "ev_statdata prev [read\-only]" 4
1385.IX Item "ev_statdata prev [read-only]" 2890.IX Item "ev_statdata prev [read-only]"
1386The previous attributes of the file. The callback gets invoked whenever 2891The previous attributes of the file. The callback gets invoked whenever
1387\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 2892\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2893differ: \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,
2894\&\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.
1388.IP "ev_tstamp interval [read\-only]" 4 2895.IP "ev_tstamp interval [read\-only]" 4
1389.IX Item "ev_tstamp interval [read-only]" 2896.IX Item "ev_tstamp interval [read-only]"
1390The specified interval. 2897The specified interval.
1391.IP "const char *path [read\-only]" 4 2898.IP "const char *path [read\-only]" 4
1392.IX Item "const char *path [read-only]" 2899.IX Item "const char *path [read-only]"
1393The filesystem path that is being watched. 2900The file system path that is being watched.
2901.PP
2902\fIExamples\fR
2903.IX Subsection "Examples"
1394.PP 2904.PP
1395Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 2905Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1396.PP 2906.PP
1397.Vb 15 2907.Vb 10
1398\& static void 2908\& static void
1399\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 2909\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1400\& { 2910\& {
1401\& /* /etc/passwd changed in some way */ 2911\& /* /etc/passwd changed in some way */
1402\& if (w->attr.st_nlink) 2912\& if (w\->attr.st_nlink)
1403\& { 2913\& {
1404\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 2914\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1405\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 2915\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1406\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 2916\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1407\& } 2917\& }
1408\& else 2918\& else
1409\& /* you shalt not abuse printf for puts */ 2919\& /* you shalt not abuse printf for puts */
1410\& puts ("wow, /etc/passwd is not there, expect problems. " 2920\& puts ("wow, /etc/passwd is not there, expect problems. "
1411\& "if this is windows, they already arrived\en"); 2921\& "if this is windows, they already arrived\en");
1412\& } 2922\& }
2923\&
2924\& ...
2925\& ev_stat passwd;
2926\&
2927\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2928\& ev_stat_start (loop, &passwd);
1413.Ve 2929.Ve
2930.PP
2931Example: Like above, but additionally use a one-second delay so we do not
2932miss updates (however, frequent updates will delay processing, too, so
2933one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2934\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1414.PP 2935.PP
1415.Vb 2 2936.Vb 2
2937\& static ev_stat passwd;
2938\& static ev_timer timer;
2939\&
2940\& static void
2941\& timer_cb (EV_P_ ev_timer *w, int revents)
2942\& {
2943\& ev_timer_stop (EV_A_ w);
2944\&
2945\& /* now it\*(Aqs one second after the most recent passwd change */
2946\& }
2947\&
2948\& static void
2949\& stat_cb (EV_P_ ev_stat *w, int revents)
2950\& {
2951\& /* reset the one\-second timer */
2952\& ev_timer_again (EV_A_ &timer);
2953\& }
2954\&
1416\& ... 2955\& ...
1417\& ev_stat passwd;
1418.Ve
1419.PP
1420.Vb 2
1421\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 2956\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1422\& ev_stat_start (loop, &passwd); 2957\& ev_stat_start (loop, &passwd);
2958\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1423.Ve 2959.Ve
1424.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 2960.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1425.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 2961.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1426.IX Subsection "ev_idle - when you've got nothing better to do..." 2962.IX Subsection "ev_idle - when you've got nothing better to do..."
1427Idle watchers trigger events when there are no other events are pending 2963Idle watchers trigger events when no other events of the same or higher
1428(prepare, check and other idle watchers do not count). That is, as long 2964priority are pending (prepare, check and other idle watchers do not count
1429as your process is busy handling sockets or timeouts (or even signals, 2965as receiving \*(L"events\*(R").
1430imagine) it will not be triggered. But when your process is idle all idle 2966.PP
1431watchers are being called again and again, once per event loop iteration \- 2967That is, as long as your process is busy handling sockets or timeouts
2968(or even signals, imagine) of the same or higher priority it will not be
2969triggered. But when your process is idle (or only lower-priority watchers
2970are pending), the idle watchers are being called once per event loop
1432until stopped, that is, or your process receives more events and becomes 2971iteration \- until stopped, that is, or your process receives more events
1433busy. 2972and becomes busy again with higher priority stuff.
1434.PP 2973.PP
1435The most noteworthy effect is that as long as any idle watchers are 2974The most noteworthy effect is that as long as any idle watchers are
1436active, the process will not block when waiting for new events. 2975active, the process will not block when waiting for new events.
1437.PP 2976.PP
1438Apart from keeping your process non-blocking (which is a useful 2977Apart from keeping your process non-blocking (which is a useful
1439effect on its own sometimes), idle watchers are a good place to do 2978effect on its own sometimes), idle watchers are a good place to do
1440\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2979\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1441event loop has handled all outstanding events. 2980event loop has handled all outstanding events.
2981.PP
2982\fIWatcher-Specific Functions and Data Members\fR
2983.IX Subsection "Watcher-Specific Functions and Data Members"
1442.IP "ev_idle_init (ev_signal *, callback)" 4 2984.IP "ev_idle_init (ev_idle *, callback)" 4
1443.IX Item "ev_idle_init (ev_signal *, callback)" 2985.IX Item "ev_idle_init (ev_idle *, callback)"
1444Initialises and configures the idle watcher \- it has no parameters of any 2986Initialises and configures the idle watcher \- it has no parameters of any
1445kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2987kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1446believe me. 2988believe me.
1447.PP 2989.PP
2990\fIExamples\fR
2991.IX Subsection "Examples"
2992.PP
1448Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 2993Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1449callback, free it. Alos, use no error checking, as usual. 2994callback, free it. Also, use no error checking, as usual.
1450.PP 2995.PP
1451.Vb 7 2996.Vb 7
1452\& static void 2997\& static void
1453\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2998\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1454\& { 2999\& {
1455\& free (w); 3000\& free (w);
1456\& // now do something you wanted to do when the program has 3001\& // now do something you wanted to do when the program has
1457\& // no longer asnything immediate to do. 3002\& // no longer anything immediate to do.
1458\& } 3003\& }
1459.Ve 3004\&
1460.PP
1461.Vb 3
1462\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3005\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1463\& ev_idle_init (idle_watcher, idle_cb); 3006\& ev_idle_init (idle_watcher, idle_cb);
1464\& ev_idle_start (loop, idle_cb); 3007\& ev_idle_start (loop, idle_watcher);
1465.Ve 3008.Ve
1466.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3009.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1467.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3010.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1468.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3011.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1469Prepare and check watchers are usually (but not always) used in tandem: 3012Prepare and check watchers are usually (but not always) used in pairs:
1470prepare watchers get invoked before the process blocks and check watchers 3013prepare watchers get invoked before the process blocks and check watchers
1471afterwards. 3014afterwards.
1472.PP 3015.PP
1473You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3016You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
1474the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3017the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1475watchers. Other loops than the current one are fine, however. The 3018watchers. Other loops than the current one are fine, however. The
1476rationale behind this is that you do not need to check for recursion in 3019rationale behind this is that you do not need to check for recursion in
1477those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3020those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1478\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3021\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1479called in pairs bracketing the blocking call. 3022called in pairs bracketing the blocking call.
1480.PP 3023.PP
1481Their main purpose is to integrate other event mechanisms into libev and 3024Their main purpose is to integrate other event mechanisms into libev and
1482their use is somewhat advanced. This could be used, for example, to track 3025their use is somewhat advanced. They could be used, for example, to track
1483variable changes, implement your own watchers, integrate net-snmp or a 3026variable changes, implement your own watchers, integrate net-snmp or a
1484coroutine library and lots more. They are also occasionally useful if 3027coroutine library and lots more. They are also occasionally useful if
1485you cache some data and want to flush it before blocking (for example, 3028you cache some data and want to flush it before blocking (for example,
1486in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3029in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1487watcher). 3030watcher).
1488.PP 3031.PP
1489This is done by examining in each prepare call which file descriptors need 3032This is done by examining in each prepare call which file descriptors
1490to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3033need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1491them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3034for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1492provide just this functionality). Then, in the check watcher you check for 3035libraries provide exactly this functionality). Then, in the check watcher,
1493any events that occured (by checking the pending status of all watchers 3036you check for any events that occurred (by checking the pending status
1494and stopping them) and call back into the library. The I/O and timer 3037of all watchers and stopping them) and call back into the library. The
1495callbacks will never actually be called (but must be valid nevertheless, 3038I/O and timer callbacks will never actually be called (but must be valid
1496because you never know, you know?). 3039nevertheless, because you never know, you know?).
1497.PP 3040.PP
1498As another example, the Perl Coro module uses these hooks to integrate 3041As another example, the Perl Coro module uses these hooks to integrate
1499coroutines into libev programs, by yielding to other active coroutines 3042coroutines into libev programs, by yielding to other active coroutines
1500during each prepare and only letting the process block if no coroutines 3043during each prepare and only letting the process block if no coroutines
1501are ready to run (it's actually more complicated: it only runs coroutines 3044are ready to run (it's actually more complicated: it only runs coroutines
1502with priority higher than or equal to the event loop and one coroutine 3045with priority higher than or equal to the event loop and one coroutine
1503of lower priority, but only once, using idle watchers to keep the event 3046of lower priority, but only once, using idle watchers to keep the event
1504loop from blocking if lower-priority coroutines are active, thus mapping 3047loop from blocking if lower-priority coroutines are active, thus mapping
1505low-priority coroutines to idle/background tasks). 3048low-priority coroutines to idle/background tasks).
3049.PP
3050It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
3051priority, to ensure that they are being run before any other watchers
3052after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
3053.PP
3054Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3055activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3056might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3057\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3058loops those other event loops might be in an unusable state until their
3059\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3060others).
3061.PP
3062\fIWatcher-Specific Functions and Data Members\fR
3063.IX Subsection "Watcher-Specific Functions and Data Members"
1506.IP "ev_prepare_init (ev_prepare *, callback)" 4 3064.IP "ev_prepare_init (ev_prepare *, callback)" 4
1507.IX Item "ev_prepare_init (ev_prepare *, callback)" 3065.IX Item "ev_prepare_init (ev_prepare *, callback)"
1508.PD 0 3066.PD 0
1509.IP "ev_check_init (ev_check *, callback)" 4 3067.IP "ev_check_init (ev_check *, callback)" 4
1510.IX Item "ev_check_init (ev_check *, callback)" 3068.IX Item "ev_check_init (ev_check *, callback)"
1511.PD 3069.PD
1512Initialises and configures the prepare or check watcher \- they have no 3070Initialises and configures the prepare or check watcher \- they have no
1513parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3071parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1514macros, but using them is utterly, utterly and completely pointless. 3072macros, but using them is utterly, utterly, utterly and completely
3073pointless.
1515.PP 3074.PP
1516Example: To include a library such as adns, you would add \s-1IO\s0 watchers 3075\fIExamples\fR
1517and a timeout watcher in a prepare handler, as required by libadns, and 3076.IX Subsection "Examples"
3077.PP
3078There are a number of principal ways to embed other event loops or modules
3079into libev. Here are some ideas on how to include libadns into libev
3080(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3081use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3082Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3083Glib event loop).
3084.PP
3085Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1518in a check watcher, destroy them and call into libadns. What follows is 3086and in a check watcher, destroy them and call into libadns. What follows
1519pseudo-code only of course: 3087is pseudo-code only of course. This requires you to either use a low
3088priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3089the callbacks for the IO/timeout watchers might not have been called yet.
1520.PP 3090.PP
1521.Vb 2 3091.Vb 2
1522\& static ev_io iow [nfd]; 3092\& static ev_io iow [nfd];
1523\& static ev_timer tw; 3093\& static ev_timer tw;
1524.Ve 3094\&
1525.PP
1526.Vb 9
1527\& static void 3095\& static void
1528\& io_cb (ev_loop *loop, ev_io *w, int revents) 3096\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1529\& { 3097\& {
1530\& // set the relevant poll flags
1531\& // could also call adns_processreadable etc. here
1532\& struct pollfd *fd = (struct pollfd *)w->data;
1533\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1534\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1535\& } 3098\& }
1536.Ve 3099\&
1537.PP
1538.Vb 7
1539\& // create io watchers for each fd and a timer before blocking 3100\& // create io watchers for each fd and a timer before blocking
1540\& static void 3101\& static void
1541\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3102\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1542\& { 3103\& {
1543\& int timeout = 3600000;truct pollfd fds [nfd]; 3104\& int timeout = 3600000;
3105\& struct pollfd fds [nfd];
1544\& // actual code will need to loop here and realloc etc. 3106\& // actual code will need to loop here and realloc etc.
1545\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3107\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1546.Ve 3108\&
1547.PP
1548.Vb 3
1549\& /* the callback is illegal, but won't be called as we stop during check */ 3109\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1550\& ev_timer_init (&tw, 0, timeout * 1e-3); 3110\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1551\& ev_timer_start (loop, &tw); 3111\& ev_timer_start (loop, &tw);
1552.Ve 3112\&
1553.PP
1554.Vb 6
1555\& // create on ev_io per pollfd 3113\& // create one ev_io per pollfd
1556\& for (int i = 0; i < nfd; ++i) 3114\& for (int i = 0; i < nfd; ++i)
1557\& { 3115\& {
1558\& ev_io_init (iow + i, io_cb, fds [i].fd, 3116\& ev_io_init (iow + i, io_cb, fds [i].fd,
1559\& ((fds [i].events & POLLIN ? EV_READ : 0) 3117\& ((fds [i].events & POLLIN ? EV_READ : 0)
1560\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3118\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3119\&
3120\& fds [i].revents = 0;
3121\& ev_io_start (loop, iow + i);
3122\& }
3123\& }
3124\&
3125\& // stop all watchers after blocking
3126\& static void
3127\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3128\& {
3129\& ev_timer_stop (loop, &tw);
3130\&
3131\& for (int i = 0; i < nfd; ++i)
3132\& {
3133\& // set the relevant poll flags
3134\& // could also call adns_processreadable etc. here
3135\& struct pollfd *fd = fds + i;
3136\& int revents = ev_clear_pending (iow + i);
3137\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3138\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3139\&
3140\& // now stop the watcher
3141\& ev_io_stop (loop, iow + i);
3142\& }
3143\&
3144\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3145\& }
1561.Ve 3146.Ve
3147.PP
3148Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3149in the prepare watcher and would dispose of the check watcher.
3150.PP
3151Method 3: If the module to be embedded supports explicit event
3152notification (libadns does), you can also make use of the actual watcher
3153callbacks, and only destroy/create the watchers in the prepare watcher.
1562.PP 3154.PP
1563.Vb 5 3155.Vb 5
1564\& fds [i].revents = 0;
1565\& iow [i].data = fds + i;
1566\& ev_io_start (loop, iow + i);
1567\& }
1568\& }
1569.Ve
1570.PP
1571.Vb 5
1572\& // stop all watchers after blocking
1573\& static void 3156\& static void
1574\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3157\& timer_cb (EV_P_ ev_timer *w, int revents)
1575\& { 3158\& {
1576\& ev_timer_stop (loop, &tw); 3159\& adns_state ads = (adns_state)w\->data;
1577.Ve 3160\& update_now (EV_A);
1578.PP 3161\&
1579.Vb 2 3162\& adns_processtimeouts (ads, &tv_now);
1580\& for (int i = 0; i < nfd; ++i)
1581\& ev_io_stop (loop, iow + i);
1582.Ve
1583.PP
1584.Vb 2
1585\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1586\& } 3163\& }
3164\&
3165\& static void
3166\& io_cb (EV_P_ ev_io *w, int revents)
3167\& {
3168\& adns_state ads = (adns_state)w\->data;
3169\& update_now (EV_A);
3170\&
3171\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3172\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3173\& }
3174\&
3175\& // do not ever call adns_afterpoll
1587.Ve 3176.Ve
3177.PP
3178Method 4: Do not use a prepare or check watcher because the module you
3179want to embed is not flexible enough to support it. Instead, you can
3180override their poll function. The drawback with this solution is that the
3181main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3182this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3183libglib event loop.
3184.PP
3185.Vb 4
3186\& static gint
3187\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3188\& {
3189\& int got_events = 0;
3190\&
3191\& for (n = 0; n < nfds; ++n)
3192\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3193\&
3194\& if (timeout >= 0)
3195\& // create/start timer
3196\&
3197\& // poll
3198\& ev_run (EV_A_ 0);
3199\&
3200\& // stop timer again
3201\& if (timeout >= 0)
3202\& ev_timer_stop (EV_A_ &to);
3203\&
3204\& // stop io watchers again \- their callbacks should have set
3205\& for (n = 0; n < nfds; ++n)
3206\& ev_io_stop (EV_A_ iow [n]);
3207\&
3208\& return got_events;
3209\& }
3210.Ve
1588.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3211.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1589.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3212.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1590.IX Subsection "ev_embed - when one backend isn't enough..." 3213.IX Subsection "ev_embed - when one backend isn't enough..."
1591This is a rather advanced watcher type that lets you embed one event loop 3214This is a rather advanced watcher type that lets you embed one event loop
1592into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3215into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1593loop, other types of watchers might be handled in a delayed or incorrect 3216loop, other types of watchers might be handled in a delayed or incorrect
1594fashion and must not be used). 3217fashion and must not be used).
… …
1597prioritise I/O. 3220prioritise I/O.
1598.PP 3221.PP
1599As an example for a bug workaround, the kqueue backend might only support 3222As an example for a bug workaround, the kqueue backend might only support
1600sockets on some platform, so it is unusable as generic backend, but you 3223sockets on some platform, so it is unusable as generic backend, but you
1601still want to make use of it because you have many sockets and it scales 3224still want to make use of it because you have many sockets and it scales
1602so nicely. In this case, you would create a kqueue-based loop and embed it 3225so nicely. In this case, you would create a kqueue-based loop and embed
1603into your default loop (which might use e.g. poll). Overall operation will 3226it into your default loop (which might use e.g. poll). Overall operation
1604be a bit slower because first libev has to poll and then call kevent, but 3227will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1605at least you can use both at what they are best. 3228\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3229best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1606.PP 3230.PP
1607As for prioritising I/O: rarely you have the case where some fds have 3231As for prioritising I/O: under rare circumstances you have the case where
1608to be watched and handled very quickly (with low latency), and even 3232some fds have to be watched and handled very quickly (with low latency),
1609priorities and idle watchers might have too much overhead. In this case 3233and even priorities and idle watchers might have too much overhead. In
1610you would put all the high priority stuff in one loop and all the rest in 3234this case you would put all the high priority stuff in one loop and all
1611a second one, and embed the second one in the first. 3235the rest in a second one, and embed the second one in the first.
1612.PP 3236.PP
1613As long as the watcher is active, the callback will be invoked every time 3237As long as the watcher is active, the callback will be invoked every
1614there might be events pending in the embedded loop. The callback must then 3238time there might be events pending in the embedded loop. The callback
1615call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3239must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1616their callbacks (you could also start an idle watcher to give the embedded 3240sweep and invoke their callbacks (the callback doesn't need to invoke the
1617loop strictly lower priority for example). You can also set the callback 3241\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1618to \f(CW0\fR, in which case the embed watcher will automatically execute the 3242to give the embedded loop strictly lower priority for example).
1619embedded loop sweep.
1620.PP 3243.PP
1621As long as the watcher is started it will automatically handle events. The 3244You can also set the callback to \f(CW0\fR, in which case the embed watcher
1622callback will be invoked whenever some events have been handled. You can 3245will automatically execute the embedded loop sweep whenever necessary.
1623set the callback to \f(CW0\fR to avoid having to specify one if you are not
1624interested in that.
1625.PP 3246.PP
1626Also, there have not currently been made special provisions for forking: 3247Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1627when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3248is active, i.e., the embedded loop will automatically be forked when the
1628but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3249embedding loop forks. In other cases, the user is responsible for calling
1629yourself. 3250\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1630.PP 3251.PP
1631Unfortunately, not all backends are embeddable, only the ones returned by 3252Unfortunately, not all backends are embeddable: only the ones returned by
1632\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3253\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1633portable one. 3254portable one.
1634.PP 3255.PP
1635So when you want to use this feature you will always have to be prepared 3256So when you want to use this feature you will always have to be prepared
1636that you cannot get an embeddable loop. The recommended way to get around 3257that you cannot get an embeddable loop. The recommended way to get around
1637this is to have a separate variables for your embeddable loop, try to 3258this is to have a separate variables for your embeddable loop, try to
1638create it, and if that fails, use the normal loop for everything: 3259create it, and if that fails, use the normal loop for everything.
1639.PP 3260.PP
1640.Vb 3 3261\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1641\& struct ev_loop *loop_hi = ev_default_init (0); 3262.IX Subsection "ev_embed and fork"
1642\& struct ev_loop *loop_lo = 0;
1643\& struct ev_embed embed;
1644.Ve
1645.PP 3263.PP
1646.Vb 5 3264While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1647\& // see if there is a chance of getting one that works 3265automatically be applied to the embedded loop as well, so no special
1648\& // (remember that a flags value of 0 means autodetection) 3266fork handling is required in that case. When the watcher is not running,
1649\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3267however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1650\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3268as applicable.
1651\& : 0;
1652.Ve
1653.PP 3269.PP
1654.Vb 8 3270\fIWatcher-Specific Functions and Data Members\fR
1655\& // if we got one, then embed it, otherwise default to loop_hi 3271.IX Subsection "Watcher-Specific Functions and Data Members"
1656\& if (loop_lo)
1657\& {
1658\& ev_embed_init (&embed, 0, loop_lo);
1659\& ev_embed_start (loop_hi, &embed);
1660\& }
1661\& else
1662\& loop_lo = loop_hi;
1663.Ve
1664.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3272.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1665.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3273.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1666.PD 0 3274.PD 0
1667.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3275.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1668.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3276.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1669.PD 3277.PD
1670Configures the watcher to embed the given loop, which must be 3278Configures the watcher to embed the given loop, which must be
1671embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3279embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1672invoked automatically, otherwise it is the responsibility of the callback 3280invoked automatically, otherwise it is the responsibility of the callback
1673to invoke it (it will continue to be called until the sweep has been done, 3281to invoke it (it will continue to be called until the sweep has been done,
1674if you do not want thta, you need to temporarily stop the embed watcher). 3282if you do not want that, you need to temporarily stop the embed watcher).
1675.IP "ev_embed_sweep (loop, ev_embed *)" 4 3283.IP "ev_embed_sweep (loop, ev_embed *)" 4
1676.IX Item "ev_embed_sweep (loop, ev_embed *)" 3284.IX Item "ev_embed_sweep (loop, ev_embed *)"
1677Make a single, non-blocking sweep over the embedded loop. This works 3285Make a single, non-blocking sweep over the embedded loop. This works
1678similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3286similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1679apropriate way for embedded loops. 3287appropriate way for embedded loops.
1680.IP "struct ev_loop *loop [read\-only]" 4 3288.IP "struct ev_loop *other [read\-only]" 4
1681.IX Item "struct ev_loop *loop [read-only]" 3289.IX Item "struct ev_loop *other [read-only]"
1682The embedded event loop. 3290The embedded event loop.
3291.PP
3292\fIExamples\fR
3293.IX Subsection "Examples"
3294.PP
3295Example: Try to get an embeddable event loop and embed it into the default
3296event loop. If that is not possible, use the default loop. The default
3297loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3298\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3299used).
3300.PP
3301.Vb 3
3302\& struct ev_loop *loop_hi = ev_default_init (0);
3303\& struct ev_loop *loop_lo = 0;
3304\& ev_embed embed;
3305\&
3306\& // see if there is a chance of getting one that works
3307\& // (remember that a flags value of 0 means autodetection)
3308\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3309\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3310\& : 0;
3311\&
3312\& // if we got one, then embed it, otherwise default to loop_hi
3313\& if (loop_lo)
3314\& {
3315\& ev_embed_init (&embed, 0, loop_lo);
3316\& ev_embed_start (loop_hi, &embed);
3317\& }
3318\& else
3319\& loop_lo = loop_hi;
3320.Ve
3321.PP
3322Example: Check if kqueue is available but not recommended and create
3323a kqueue backend for use with sockets (which usually work with any
3324kqueue implementation). Store the kqueue/socket\-only event loop in
3325\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3326.PP
3327.Vb 3
3328\& struct ev_loop *loop = ev_default_init (0);
3329\& struct ev_loop *loop_socket = 0;
3330\& ev_embed embed;
3331\&
3332\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3333\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3334\& {
3335\& ev_embed_init (&embed, 0, loop_socket);
3336\& ev_embed_start (loop, &embed);
3337\& }
3338\&
3339\& if (!loop_socket)
3340\& loop_socket = loop;
3341\&
3342\& // now use loop_socket for all sockets, and loop for everything else
3343.Ve
1683.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3344.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
1684.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3345.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1685.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3346.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1686Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3347Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1687whoever is a good citizen cared to tell libev about it by calling 3348whoever is a good citizen cared to tell libev about it by calling
1688\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3349\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
1689event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3350event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
1690and only in the child after the fork. If whoever good citizen calling 3351and only in the child after the fork. If whoever good citizen calling
1691\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3352\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
1692handlers will be invoked, too, of course. 3353handlers will be invoked, too, of course.
3354.PP
3355\fIThe special problem of life after fork \- how is it possible?\fR
3356.IX Subsection "The special problem of life after fork - how is it possible?"
3357.PP
3358Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3359up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3360sequence should be handled by libev without any problems.
3361.PP
3362This changes when the application actually wants to do event handling
3363in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3364fork.
3365.PP
3366The default mode of operation (for libev, with application help to detect
3367forks) is to duplicate all the state in the child, as would be expected
3368when \fIeither\fR the parent \fIor\fR the child process continues.
3369.PP
3370When both processes want to continue using libev, then this is usually the
3371wrong result. In that case, usually one process (typically the parent) is
3372supposed to continue with all watchers in place as before, while the other
3373process typically wants to start fresh, i.e. without any active watchers.
3374.PP
3375The cleanest and most efficient way to achieve that with libev is to
3376simply create a new event loop, which of course will be \*(L"empty\*(R", and
3377use that for new watchers. This has the advantage of not touching more
3378memory than necessary, and thus avoiding the copy-on-write, and the
3379disadvantage of having to use multiple event loops (which do not support
3380signal watchers).
3381.PP
3382When this is not possible, or you want to use the default loop for
3383other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3384\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3385Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3386watchers, so you have to be careful not to execute code that modifies
3387those watchers. Note also that in that case, you have to re-register any
3388signal watchers.
3389.PP
3390\fIWatcher-Specific Functions and Data Members\fR
3391.IX Subsection "Watcher-Specific Functions and Data Members"
1693.IP "ev_fork_init (ev_signal *, callback)" 4 3392.IP "ev_fork_init (ev_fork *, callback)" 4
1694.IX Item "ev_fork_init (ev_signal *, callback)" 3393.IX Item "ev_fork_init (ev_fork *, callback)"
1695Initialises and configures the fork watcher \- it has no parameters of any 3394Initialises and configures the fork watcher \- it has no parameters of any
1696kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3395kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1697believe me. 3396really.
3397.ie n .SS """ev_cleanup"" \- even the best things end"
3398.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3399.IX Subsection "ev_cleanup - even the best things end"
3400Cleanup watchers are called just before the event loop is being destroyed
3401by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3402.PP
3403While there is no guarantee that the event loop gets destroyed, cleanup
3404watchers provide a convenient method to install cleanup hooks for your
3405program, worker threads and so on \- you just to make sure to destroy the
3406loop when you want them to be invoked.
3407.PP
3408Cleanup watchers are invoked in the same way as any other watcher. Unlike
3409all other watchers, they do not keep a reference to the event loop (which
3410makes a lot of sense if you think about it). Like all other watchers, you
3411can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3412.PP
3413\fIWatcher-Specific Functions and Data Members\fR
3414.IX Subsection "Watcher-Specific Functions and Data Members"
3415.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3416.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3417Initialises and configures the cleanup watcher \- it has no parameters of
3418any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3419pointless, I assure you.
3420.PP
3421Example: Register an atexit handler to destroy the default loop, so any
3422cleanup functions are called.
3423.PP
3424.Vb 5
3425\& static void
3426\& program_exits (void)
3427\& {
3428\& ev_loop_destroy (EV_DEFAULT_UC);
3429\& }
3430\&
3431\& ...
3432\& atexit (program_exits);
3433.Ve
3434.ie n .SS """ev_async"" \- how to wake up an event loop"
3435.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3436.IX Subsection "ev_async - how to wake up an event loop"
3437In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3438asynchronous sources such as signal handlers (as opposed to multiple event
3439loops \- those are of course safe to use in different threads).
3440.PP
3441Sometimes, however, you need to wake up an event loop you do not control,
3442for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3443watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3444it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3445.PP
3446This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3447too, are asynchronous in nature, and signals, too, will be compressed
3448(i.e. the number of callback invocations may be less than the number of
3449\&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3450of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3451signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3452even without knowing which loop owns the signal.
3453.PP
3454\fIQueueing\fR
3455.IX Subsection "Queueing"
3456.PP
3457\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3458is that the author does not know of a simple (or any) algorithm for a
3459multiple-writer-single-reader queue that works in all cases and doesn't
3460need elaborate support such as pthreads or unportable memory access
3461semantics.
3462.PP
3463That means that if you want to queue data, you have to provide your own
3464queue. But at least I can tell you how to implement locking around your
3465queue:
3466.IP "queueing from a signal handler context" 4
3467.IX Item "queueing from a signal handler context"
3468To implement race-free queueing, you simply add to the queue in the signal
3469handler but you block the signal handler in the watcher callback. Here is
3470an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3471.Sp
3472.Vb 1
3473\& static ev_async mysig;
3474\&
3475\& static void
3476\& sigusr1_handler (void)
3477\& {
3478\& sometype data;
3479\&
3480\& // no locking etc.
3481\& queue_put (data);
3482\& ev_async_send (EV_DEFAULT_ &mysig);
3483\& }
3484\&
3485\& static void
3486\& mysig_cb (EV_P_ ev_async *w, int revents)
3487\& {
3488\& sometype data;
3489\& sigset_t block, prev;
3490\&
3491\& sigemptyset (&block);
3492\& sigaddset (&block, SIGUSR1);
3493\& sigprocmask (SIG_BLOCK, &block, &prev);
3494\&
3495\& while (queue_get (&data))
3496\& process (data);
3497\&
3498\& if (sigismember (&prev, SIGUSR1)
3499\& sigprocmask (SIG_UNBLOCK, &block, 0);
3500\& }
3501.Ve
3502.Sp
3503(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3504instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3505either...).
3506.IP "queueing from a thread context" 4
3507.IX Item "queueing from a thread context"
3508The strategy for threads is different, as you cannot (easily) block
3509threads but you can easily preempt them, so to queue safely you need to
3510employ a traditional mutex lock, such as in this pthread example:
3511.Sp
3512.Vb 2
3513\& static ev_async mysig;
3514\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3515\&
3516\& static void
3517\& otherthread (void)
3518\& {
3519\& // only need to lock the actual queueing operation
3520\& pthread_mutex_lock (&mymutex);
3521\& queue_put (data);
3522\& pthread_mutex_unlock (&mymutex);
3523\&
3524\& ev_async_send (EV_DEFAULT_ &mysig);
3525\& }
3526\&
3527\& static void
3528\& mysig_cb (EV_P_ ev_async *w, int revents)
3529\& {
3530\& pthread_mutex_lock (&mymutex);
3531\&
3532\& while (queue_get (&data))
3533\& process (data);
3534\&
3535\& pthread_mutex_unlock (&mymutex);
3536\& }
3537.Ve
3538.PP
3539\fIWatcher-Specific Functions and Data Members\fR
3540.IX Subsection "Watcher-Specific Functions and Data Members"
3541.IP "ev_async_init (ev_async *, callback)" 4
3542.IX Item "ev_async_init (ev_async *, callback)"
3543Initialises and configures the async watcher \- it has no parameters of any
3544kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3545trust me.
3546.IP "ev_async_send (loop, ev_async *)" 4
3547.IX Item "ev_async_send (loop, ev_async *)"
3548Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3549an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3550returns.
3551.Sp
3552Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3553signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3554embedding section below on what exactly this means).
3555.Sp
3556Note that, as with other watchers in libev, multiple events might get
3557compressed into a single callback invocation (another way to look at
3558this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3559\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3560.Sp
3561This call incurs the overhead of at most one extra system call per event
3562loop iteration, if the event loop is blocked, and no syscall at all if
3563the event loop (or your program) is processing events. That means that
3564repeated calls are basically free (there is no need to avoid calls for
3565performance reasons) and that the overhead becomes smaller (typically
3566zero) under load.
3567.IP "bool = ev_async_pending (ev_async *)" 4
3568.IX Item "bool = ev_async_pending (ev_async *)"
3569Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3570watcher but the event has not yet been processed (or even noted) by the
3571event loop.
3572.Sp
3573\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3574the loop iterates next and checks for the watcher to have become active,
3575it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3576quickly check whether invoking the loop might be a good idea.
3577.Sp
3578Not that this does \fInot\fR check whether the watcher itself is pending,
3579only whether it has been requested to make this watcher pending: there
3580is a time window between the event loop checking and resetting the async
3581notification, and the callback being invoked.
1698.SH "OTHER FUNCTIONS" 3582.SH "OTHER FUNCTIONS"
1699.IX Header "OTHER FUNCTIONS" 3583.IX Header "OTHER FUNCTIONS"
1700There are some other functions of possible interest. Described. Here. Now. 3584There are some other functions of possible interest. Described. Here. Now.
1701.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3585.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1702.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3586.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1703This function combines a simple timer and an I/O watcher, calls your 3587This function combines a simple timer and an I/O watcher, calls your
1704callback on whichever event happens first and automatically stop both 3588callback on whichever event happens first and automatically stops both
1705watchers. This is useful if you want to wait for a single event on an fd 3589watchers. This is useful if you want to wait for a single event on an fd
1706or timeout without having to allocate/configure/start/stop/free one or 3590or timeout without having to allocate/configure/start/stop/free one or
1707more watchers yourself. 3591more watchers yourself.
1708.Sp 3592.Sp
1709If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3593If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1710is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3594\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1711\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3595the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1712.Sp 3596.Sp
1713If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3597If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1714started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3598started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1715repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3599repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1716dubious value.
1717.Sp 3600.Sp
1718The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3601The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1719passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3602passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1720\&\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 3603\&\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
1721value passed to \f(CW\*(C`ev_once\*(C'\fR: 3604value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3605a timeout and an io event at the same time \- you probably should give io
3606events precedence.
3607.Sp
3608Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
1722.Sp 3609.Sp
1723.Vb 7 3610.Vb 7
1724\& static void stdin_ready (int revents, void *arg) 3611\& static void stdin_ready (int revents, void *arg)
3612\& {
3613\& if (revents & EV_READ)
3614\& /* stdin might have data for us, joy! */;
3615\& else if (revents & EV_TIMER)
3616\& /* doh, nothing entered */;
3617\& }
3618\&
3619\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3620.Ve
3621.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3622.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3623Feed an event on the given fd, as if a file descriptor backend detected
3624the given events.
3625.IP "ev_feed_signal_event (loop, int signum)" 4
3626.IX Item "ev_feed_signal_event (loop, int signum)"
3627Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3628which is async-safe.
3629.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3630.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3631This section explains some common idioms that are not immediately
3632obvious. Note that examples are sprinkled over the whole manual, and this
3633section only contains stuff that wouldn't fit anywhere else.
3634.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3635.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3636Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3637or modify at any time: libev will completely ignore it. This can be used
3638to associate arbitrary data with your watcher. If you need more data and
3639don't want to allocate memory separately and store a pointer to it in that
3640data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3641data:
3642.PP
3643.Vb 7
3644\& struct my_io
3645\& {
3646\& ev_io io;
3647\& int otherfd;
3648\& void *somedata;
3649\& struct whatever *mostinteresting;
3650\& };
3651\&
3652\& ...
3653\& struct my_io w;
3654\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3655.Ve
3656.PP
3657And since your callback will be called with a pointer to the watcher, you
3658can cast it back to your own type:
3659.PP
3660.Vb 5
3661\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3662\& {
3663\& struct my_io *w = (struct my_io *)w_;
3664\& ...
3665\& }
3666.Ve
3667.PP
3668More interesting and less C\-conformant ways of casting your callback
3669function type instead have been omitted.
3670.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3671.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3672Another common scenario is to use some data structure with multiple
3673embedded watchers, in effect creating your own watcher that combines
3674multiple libev event sources into one \*(L"super-watcher\*(R":
3675.PP
3676.Vb 6
3677\& struct my_biggy
3678\& {
3679\& int some_data;
3680\& ev_timer t1;
3681\& ev_timer t2;
3682\& }
3683.Ve
3684.PP
3685In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3686complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3687the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3688to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3689real programmers):
3690.PP
3691.Vb 1
3692\& #include <stddef.h>
3693\&
3694\& static void
3695\& t1_cb (EV_P_ ev_timer *w, int revents)
3696\& {
3697\& struct my_biggy big = (struct my_biggy *)
3698\& (((char *)w) \- offsetof (struct my_biggy, t1));
3699\& }
3700\&
3701\& static void
3702\& t2_cb (EV_P_ ev_timer *w, int revents)
3703\& {
3704\& struct my_biggy big = (struct my_biggy *)
3705\& (((char *)w) \- offsetof (struct my_biggy, t2));
3706\& }
3707.Ve
3708.SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3709.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3710Often you have structures like this in event-based programs:
3711.PP
3712.Vb 4
3713\& callback ()
1725\& { 3714\& {
1726\& if (revents & EV_TIMEOUT) 3715\& free (request);
1727\& /* doh, nothing entered */;
1728\& else if (revents & EV_READ)
1729\& /* stdin might have data for us, joy! */;
1730\& } 3716\& }
3717\&
3718\& request = start_new_request (..., callback);
1731.Ve 3719.Ve
1732.Sp 3720.PP
3721The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3722used to cancel the operation, or do other things with it.
3723.PP
3724It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3725immediately invoke the callback, for example, to report errors. Or you add
3726some caching layer that finds that it can skip the lengthy aspects of the
3727operation and simply invoke the callback with the result.
3728.PP
3729The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3730has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3731.PP
3732Even if you pass the request by some safer means to the callback, you
3733might want to do something to the request after starting it, such as
3734canceling it, which probably isn't working so well when the callback has
3735already been invoked.
3736.PP
3737A common way around all these issues is to make sure that
3738\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3739\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3740delay invoking the callback by e.g. using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher
3741for example, or more sneakily, by reusing an existing (stopped) watcher
3742and pushing it into the pending queue:
3743.PP
1733.Vb 1 3744.Vb 2
1734\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3745\& ev_set_cb (watcher, callback);
3746\& ev_feed_event (EV_A_ watcher, 0);
1735.Ve 3747.Ve
1736.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3748.PP
1737.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3749This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1738Feeds the given event set into the event loop, as if the specified event 3750invoked, while not delaying callback invocation too much.
1739had happened for the specified watcher (which must be a pointer to an 3751.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
1740initialised but not necessarily started event watcher). 3752.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1741.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3753Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1742.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3754\&\fImodal\fR interaction, which is most easily implemented by recursively
1743Feed an event on the given fd, as if a file descriptor backend detected 3755invoking \f(CW\*(C`ev_run\*(C'\fR.
1744the given events it. 3756.PP
1745.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3757This brings the problem of exiting \- a callback might want to finish the
1746.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3758main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1747Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3759a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1748loop!). 3760and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3761other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3762.PP
3763The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3764invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3765triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3766.PP
3767.Vb 2
3768\& // main loop
3769\& int exit_main_loop = 0;
3770\&
3771\& while (!exit_main_loop)
3772\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3773\&
3774\& // in a modal watcher
3775\& int exit_nested_loop = 0;
3776\&
3777\& while (!exit_nested_loop)
3778\& ev_run (EV_A_ EVRUN_ONCE);
3779.Ve
3780.PP
3781To exit from any of these loops, just set the corresponding exit variable:
3782.PP
3783.Vb 2
3784\& // exit modal loop
3785\& exit_nested_loop = 1;
3786\&
3787\& // exit main program, after modal loop is finished
3788\& exit_main_loop = 1;
3789\&
3790\& // exit both
3791\& exit_main_loop = exit_nested_loop = 1;
3792.Ve
3793.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3794.IX Subsection "THREAD LOCKING EXAMPLE"
3795Here is a fictitious example of how to run an event loop in a different
3796thread from where callbacks are being invoked and watchers are
3797created/added/removed.
3798.PP
3799For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3800which uses exactly this technique (which is suited for many high-level
3801languages).
3802.PP
3803The example uses a pthread mutex to protect the loop data, a condition
3804variable to wait for callback invocations, an async watcher to notify the
3805event loop thread and an unspecified mechanism to wake up the main thread.
3806.PP
3807First, you need to associate some data with the event loop:
3808.PP
3809.Vb 6
3810\& typedef struct {
3811\& mutex_t lock; /* global loop lock */
3812\& ev_async async_w;
3813\& thread_t tid;
3814\& cond_t invoke_cv;
3815\& } userdata;
3816\&
3817\& void prepare_loop (EV_P)
3818\& {
3819\& // for simplicity, we use a static userdata struct.
3820\& static userdata u;
3821\&
3822\& ev_async_init (&u\->async_w, async_cb);
3823\& ev_async_start (EV_A_ &u\->async_w);
3824\&
3825\& pthread_mutex_init (&u\->lock, 0);
3826\& pthread_cond_init (&u\->invoke_cv, 0);
3827\&
3828\& // now associate this with the loop
3829\& ev_set_userdata (EV_A_ u);
3830\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3831\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3832\&
3833\& // then create the thread running ev_run
3834\& pthread_create (&u\->tid, 0, l_run, EV_A);
3835\& }
3836.Ve
3837.PP
3838The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3839solely to wake up the event loop so it takes notice of any new watchers
3840that might have been added:
3841.PP
3842.Vb 5
3843\& static void
3844\& async_cb (EV_P_ ev_async *w, int revents)
3845\& {
3846\& // just used for the side effects
3847\& }
3848.Ve
3849.PP
3850The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3851protecting the loop data, respectively.
3852.PP
3853.Vb 6
3854\& static void
3855\& l_release (EV_P)
3856\& {
3857\& userdata *u = ev_userdata (EV_A);
3858\& pthread_mutex_unlock (&u\->lock);
3859\& }
3860\&
3861\& static void
3862\& l_acquire (EV_P)
3863\& {
3864\& userdata *u = ev_userdata (EV_A);
3865\& pthread_mutex_lock (&u\->lock);
3866\& }
3867.Ve
3868.PP
3869The event loop thread first acquires the mutex, and then jumps straight
3870into \f(CW\*(C`ev_run\*(C'\fR:
3871.PP
3872.Vb 4
3873\& void *
3874\& l_run (void *thr_arg)
3875\& {
3876\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3877\&
3878\& l_acquire (EV_A);
3879\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3880\& ev_run (EV_A_ 0);
3881\& l_release (EV_A);
3882\&
3883\& return 0;
3884\& }
3885.Ve
3886.PP
3887Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3888signal the main thread via some unspecified mechanism (signals? pipe
3889writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3890have been called (in a while loop because a) spurious wakeups are possible
3891and b) skipping inter-thread-communication when there are no pending
3892watchers is very beneficial):
3893.PP
3894.Vb 4
3895\& static void
3896\& l_invoke (EV_P)
3897\& {
3898\& userdata *u = ev_userdata (EV_A);
3899\&
3900\& while (ev_pending_count (EV_A))
3901\& {
3902\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3903\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3904\& }
3905\& }
3906.Ve
3907.PP
3908Now, whenever the main thread gets told to invoke pending watchers, it
3909will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3910thread to continue:
3911.PP
3912.Vb 4
3913\& static void
3914\& real_invoke_pending (EV_P)
3915\& {
3916\& userdata *u = ev_userdata (EV_A);
3917\&
3918\& pthread_mutex_lock (&u\->lock);
3919\& ev_invoke_pending (EV_A);
3920\& pthread_cond_signal (&u\->invoke_cv);
3921\& pthread_mutex_unlock (&u\->lock);
3922\& }
3923.Ve
3924.PP
3925Whenever you want to start/stop a watcher or do other modifications to an
3926event loop, you will now have to lock:
3927.PP
3928.Vb 2
3929\& ev_timer timeout_watcher;
3930\& userdata *u = ev_userdata (EV_A);
3931\&
3932\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3933\&
3934\& pthread_mutex_lock (&u\->lock);
3935\& ev_timer_start (EV_A_ &timeout_watcher);
3936\& ev_async_send (EV_A_ &u\->async_w);
3937\& pthread_mutex_unlock (&u\->lock);
3938.Ve
3939.PP
3940Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3941an event loop currently blocking in the kernel will have no knowledge
3942about the newly added timer. By waking up the loop it will pick up any new
3943watchers in the next event loop iteration.
3944.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3945.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3946While the overhead of a callback that e.g. schedules a thread is small, it
3947is still an overhead. If you embed libev, and your main usage is with some
3948kind of threads or coroutines, you might want to customise libev so that
3949doesn't need callbacks anymore.
3950.PP
3951Imagine you have coroutines that you can switch to using a function
3952\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3953and that due to some magic, the currently active coroutine is stored in a
3954global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3955event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3956the differing \f(CW\*(C`;\*(C'\fR conventions):
3957.PP
3958.Vb 2
3959\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3960\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3961.Ve
3962.PP
3963That means instead of having a C callback function, you store the
3964coroutine to switch to in each watcher, and instead of having libev call
3965your callback, you instead have it switch to that coroutine.
3966.PP
3967A coroutine might now wait for an event with a function called
3968\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3969matter when, or whether the watcher is active or not when this function is
3970called):
3971.PP
3972.Vb 6
3973\& void
3974\& wait_for_event (ev_watcher *w)
3975\& {
3976\& ev_cb_set (w) = current_coro;
3977\& switch_to (libev_coro);
3978\& }
3979.Ve
3980.PP
3981That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3982continues the libev coroutine, which, when appropriate, switches back to
3983this or any other coroutine.
3984.PP
3985You can do similar tricks if you have, say, threads with an event queue \-
3986instead of storing a coroutine, you store the queue object and instead of
3987switching to a coroutine, you push the watcher onto the queue and notify
3988any waiters.
3989.PP
3990To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3991files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3992.PP
3993.Vb 4
3994\& // my_ev.h
3995\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3996\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3997\& #include "../libev/ev.h"
3998\&
3999\& // my_ev.c
4000\& #define EV_H "my_ev.h"
4001\& #include "../libev/ev.c"
4002.Ve
4003.PP
4004And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4005\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4006can even use \fIev.h\fR as header file name directly.
1749.SH "LIBEVENT EMULATION" 4007.SH "LIBEVENT EMULATION"
1750.IX Header "LIBEVENT EMULATION" 4008.IX Header "LIBEVENT EMULATION"
1751Libev offers a compatibility emulation layer for libevent. It cannot 4009Libev offers a compatibility emulation layer for libevent. It cannot
1752emulate the internals of libevent, so here are some usage hints: 4010emulate the internals of libevent, so here are some usage hints:
4011.IP "\(bu" 4
4012Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4013.Sp
4014This was the newest libevent version available when libev was implemented,
4015and is still mostly unchanged in 2010.
4016.IP "\(bu" 4
1753.IP "* Use it by including <event.h>, as usual." 4 4017Use it by including <event.h>, as usual.
1754.IX Item "Use it by including <event.h>, as usual." 4018.IP "\(bu" 4
1755.PD 0 4019The following members are fully supported: ev_base, ev_callback,
1756.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4020ev_arg, ev_fd, ev_res, ev_events.
1757.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4021.IP "\(bu" 4
1758.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 4022Avoid using ev_flags and the EVLIST_*\-macros, while it is
1759.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)." 4023maintained by libev, it does not work exactly the same way as in libevent (consider
1760.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 4024it a private \s-1API\s0).
1761.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." 4025.IP "\(bu" 4
4026Priorities are not currently supported. Initialising priorities
4027will fail and all watchers will have the same priority, even though there
4028is an ev_pri field.
4029.IP "\(bu" 4
4030In libevent, the last base created gets the signals, in libev, the
4031base that registered the signal gets the signals.
4032.IP "\(bu" 4
1762.IP "* Other members are not supported." 4 4033Other members are not supported.
1763.IX Item "Other members are not supported." 4034.IP "\(bu" 4
1764.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4035The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1765.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4036to use the libev header file and library.
1766.PD
1767.SH "\*(C+ SUPPORT" 4037.SH "\*(C+ SUPPORT"
1768.IX Header " SUPPORT" 4038.IX Header " SUPPORT"
4039.SS "C \s-1API\s0"
4040.IX Subsection "C API"
4041The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4042libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4043will work fine.
4044.PP
4045Proper exception specifications might have to be added to callbacks passed
4046to libev: exceptions may be thrown only from watcher callbacks, all
4047other callbacks (allocator, syserr, loop acquire/release and periodioc
4048reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4049()\*(C'\fR specification. If you have code that needs to be compiled as both C
4050and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4051.PP
4052.Vb 6
4053\& static void
4054\& fatal_error (const char *msg) EV_THROW
4055\& {
4056\& perror (msg);
4057\& abort ();
4058\& }
4059\&
4060\& ...
4061\& ev_set_syserr_cb (fatal_error);
4062.Ve
4063.PP
4064The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4065\&\f(CW\*(C`ev_inoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4066because it runs cleanup watchers).
4067.PP
4068Throwing exceptions in watcher callbacks is only supported if libev itself
4069is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4070throwing exceptions through C libraries (most do).
4071.SS "\*(C+ \s-1API\s0"
4072.IX Subsection " API"
1769Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4073Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1770you to use some convinience methods to start/stop watchers and also change 4074you to use some convenience methods to start/stop watchers and also change
1771the callback model to a model using method callbacks on objects. 4075the callback model to a model using method callbacks on objects.
1772.PP 4076.PP
1773To use it, 4077To use it,
1774.PP 4078.PP
1775.Vb 1 4079.Vb 1
1776\& #include <ev++.h> 4080\& #include <ev++.h>
1777.Ve 4081.Ve
1778.PP 4082.PP
1779(it is not installed by default). This automatically includes \fIev.h\fR 4083This automatically includes \fIev.h\fR and puts all of its definitions (many
1780and puts all of its definitions (many of them macros) into the global 4084of them macros) into the global namespace. All \*(C+ specific things are
1781namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4085put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4086options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1782.PP 4087.PP
1783It should support all the same embedding options as \fIev.h\fR, most notably 4088Care has been taken to keep the overhead low. The only data member the \*(C+
1784\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4089classes add (compared to plain C\-style watchers) is the event loop pointer
4090that the watcher is associated with (or no additional members at all if
4091you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4092.PP
4093Currently, functions, static and non-static member functions and classes
4094with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4095to add as long as they only need one additional pointer for context. If
4096you need support for other types of functors please contact the author
4097(preferably after implementing it).
4098.PP
4099For all this to work, your \*(C+ compiler either has to use the same calling
4100conventions as your C compiler (for static member functions), or you have
4101to embed libev and compile libev itself as \*(C+.
1785.PP 4102.PP
1786Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4103Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1787.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4104.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1788.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4105.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1789.IX Item "ev::READ, ev::WRITE etc." 4106.IX Item "ev::READ, ev::WRITE etc."
1790These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4107These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1791macros from \fIev.h\fR. 4108macros from \fIev.h\fR.
1792.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4109.ie n .IP """ev::tstamp"", ""ev::now""" 4
1793.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4110.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1794.IX Item "ev::tstamp, ev::now" 4111.IX Item "ev::tstamp, ev::now"
1795Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4112Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1796.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 4113.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1797.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4114.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1798.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4115.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1799For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4116For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1800the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4117the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1801which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4118which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1802defines by many implementations. 4119defined by many implementations.
1803.Sp 4120.Sp
1804All of those classes have these methods: 4121All of those classes have these methods:
1805.RS 4 4122.RS 4
1806.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4123.IP "ev::TYPE::TYPE ()" 4
1807.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4124.IX Item "ev::TYPE::TYPE ()"
1808.PD 0 4125.PD 0
1809.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4126.IP "ev::TYPE::TYPE (loop)" 4
1810.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4127.IX Item "ev::TYPE::TYPE (loop)"
1811.IP "ev::TYPE::~TYPE" 4 4128.IP "ev::TYPE::~TYPE" 4
1812.IX Item "ev::TYPE::~TYPE" 4129.IX Item "ev::TYPE::~TYPE"
1813.PD 4130.PD
1814The constructor takes a pointer to an object and a method pointer to 4131The constructor (optionally) takes an event loop to associate the watcher
1815the event handler callback to call in this class. The constructor calls 4132with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1816\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4133.Sp
1817before starting it. If you do not specify a loop then the constructor 4134The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1818automatically associates the default loop with this watcher. 4135\&\f(CW\*(C`set\*(C'\fR method before starting it.
4136.Sp
4137It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4138method to set a callback before you can start the watcher.
4139.Sp
4140(The reason why you have to use a method is a limitation in \*(C+ which does
4141not allow explicit template arguments for constructors).
1819.Sp 4142.Sp
1820The destructor automatically stops the watcher if it is active. 4143The destructor automatically stops the watcher if it is active.
4144.IP "w\->set<class, &class::method> (object *)" 4
4145.IX Item "w->set<class, &class::method> (object *)"
4146This method sets the callback method to call. The method has to have a
4147signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4148first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4149parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4150.Sp
4151This method synthesizes efficient thunking code to call your method from
4152the C callback that libev requires. If your compiler can inline your
4153callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4154your compiler is good :), then the method will be fully inlined into the
4155thunking function, making it as fast as a direct C callback.
4156.Sp
4157Example: simple class declaration and watcher initialisation
4158.Sp
4159.Vb 4
4160\& struct myclass
4161\& {
4162\& void io_cb (ev::io &w, int revents) { }
4163\& }
4164\&
4165\& myclass obj;
4166\& ev::io iow;
4167\& iow.set <myclass, &myclass::io_cb> (&obj);
4168.Ve
4169.IP "w\->set (object *)" 4
4170.IX Item "w->set (object *)"
4171This is a variation of a method callback \- leaving out the method to call
4172will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4173functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4174the time. Incidentally, you can then also leave out the template argument
4175list.
4176.Sp
4177The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4178int revents)\*(C'\fR.
4179.Sp
4180See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4181.Sp
4182Example: use a functor object as callback.
4183.Sp
4184.Vb 7
4185\& struct myfunctor
4186\& {
4187\& void operator() (ev::io &w, int revents)
4188\& {
4189\& ...
4190\& }
4191\& }
4192\&
4193\& myfunctor f;
4194\&
4195\& ev::io w;
4196\& w.set (&f);
4197.Ve
4198.IP "w\->set<function> (void *data = 0)" 4
4199.IX Item "w->set<function> (void *data = 0)"
4200Also sets a callback, but uses a static method or plain function as
4201callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4202\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4203.Sp
4204The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4205.Sp
4206See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4207.Sp
4208Example: Use a plain function as callback.
4209.Sp
4210.Vb 2
4211\& static void io_cb (ev::io &w, int revents) { }
4212\& iow.set <io_cb> ();
4213.Ve
1821.IP "w\->set (struct ev_loop *)" 4 4214.IP "w\->set (loop)" 4
1822.IX Item "w->set (struct ev_loop *)" 4215.IX Item "w->set (loop)"
1823Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4216Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1824do this when the watcher is inactive (and not pending either). 4217do this when the watcher is inactive (and not pending either).
1825.IP "w\->set ([args])" 4 4218.IP "w\->set ([arguments])" 4
1826.IX Item "w->set ([args])" 4219.IX Item "w->set ([arguments])"
1827Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4220Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
1828called at least once. Unlike the C counterpart, an active watcher gets 4221method or a suitable start method must be called at least once. Unlike the
1829automatically stopped and restarted. 4222C counterpart, an active watcher gets automatically stopped and restarted
4223when reconfiguring it with this method.
1830.IP "w\->start ()" 4 4224.IP "w\->start ()" 4
1831.IX Item "w->start ()" 4225.IX Item "w->start ()"
1832Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4226Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1833constructor already takes the loop. 4227constructor already stores the event loop.
4228.IP "w\->start ([arguments])" 4
4229.IX Item "w->start ([arguments])"
4230Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4231convenient to wrap them in one call. Uses the same type of arguments as
4232the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1834.IP "w\->stop ()" 4 4233.IP "w\->stop ()" 4
1835.IX Item "w->stop ()" 4234.IX Item "w->stop ()"
1836Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4235Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1837.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4236.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1838.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4237.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1839.IX Item "w->again () ev::timer, ev::periodic only" 4238.IX Item "w->again () (ev::timer, ev::periodic only)"
1840For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4239For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1841\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4240\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1842.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4241.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1843.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4242.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1844.IX Item "w->sweep () ev::embed only" 4243.IX Item "w->sweep () (ev::embed only)"
1845Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4244Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1846.ie n .IP "w\->update () ""ev::stat"" only" 4 4245.ie n .IP "w\->update () (""ev::stat"" only)" 4
1847.el .IP "w\->update () \f(CWev::stat\fR only" 4 4246.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
1848.IX Item "w->update () ev::stat only" 4247.IX Item "w->update () (ev::stat only)"
1849Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4248Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1850.RE 4249.RE
1851.RS 4 4250.RS 4
1852.RE 4251.RE
1853.PP 4252.PP
1854Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4253Example: Define a class with two I/O and idle watchers, start the I/O
1855the constructor. 4254watchers in the constructor.
1856.PP 4255.PP
1857.Vb 4 4256.Vb 5
1858\& class myclass 4257\& class myclass
1859\& { 4258\& {
1860\& ev_io io; void io_cb (ev::io &w, int revents); 4259\& ev::io io ; void io_cb (ev::io &w, int revents);
4260\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1861\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4261\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
1862.Ve 4262\&
1863.PP
1864.Vb 2
1865\& myclass (); 4263\& myclass (int fd)
4264\& {
4265\& io .set <myclass, &myclass::io_cb > (this);
4266\& io2 .set <myclass, &myclass::io2_cb > (this);
4267\& idle.set <myclass, &myclass::idle_cb> (this);
4268\&
4269\& io.set (fd, ev::WRITE); // configure the watcher
4270\& io.start (); // start it whenever convenient
4271\&
4272\& io2.start (fd, ev::READ); // set + start in one call
4273\& }
1866\& } 4274\& };
1867.Ve 4275.Ve
1868.PP 4276.SH "OTHER LANGUAGE BINDINGS"
1869.Vb 6 4277.IX Header "OTHER LANGUAGE BINDINGS"
1870\& myclass::myclass (int fd) 4278Libev does not offer other language bindings itself, but bindings for a
1871\& : io (this, &myclass::io_cb), 4279number of languages exist in the form of third-party packages. If you know
1872\& idle (this, &myclass::idle_cb) 4280any interesting language binding in addition to the ones listed here, drop
1873\& { 4281me a note.
1874\& io.start (fd, ev::READ); 4282.IP "Perl" 4
1875\& } 4283.IX Item "Perl"
1876.Ve 4284The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4285libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4286there are additional modules that implement libev-compatible interfaces
4287to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4288\&\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
4289and \f(CW\*(C`EV::Glib\*(C'\fR).
4290.Sp
4291It can be found and installed via \s-1CPAN\s0, its homepage is at
4292<http://software.schmorp.de/pkg/EV>.
4293.IP "Python" 4
4294.IX Item "Python"
4295Python bindings can be found at <http://code.google.com/p/pyev/>. It
4296seems to be quite complete and well-documented.
4297.IP "Ruby" 4
4298.IX Item "Ruby"
4299Tony Arcieri has written a ruby extension that offers access to a subset
4300of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4301more on top of it. It can be found via gem servers. Its homepage is at
4302<http://rev.rubyforge.org/>.
4303.Sp
4304Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4305makes rev work even on mingw.
4306.IP "Haskell" 4
4307.IX Item "Haskell"
4308A haskell binding to libev is available at
4309http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4310.IP "D" 4
4311.IX Item "D"
4312Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4313be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4314.IP "Ocaml" 4
4315.IX Item "Ocaml"
4316Erkki Seppala has written Ocaml bindings for libev, to be found at
4317http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4318.IP "Lua" 4
4319.IX Item "Lua"
4320Brian Maher has written a partial interface to libev for lua (at the
4321time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4322http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
1877.SH "MACRO MAGIC" 4323.SH "MACRO MAGIC"
1878.IX Header "MACRO MAGIC" 4324.IX Header "MACRO MAGIC"
1879Libev can be compiled with a variety of options, the most fundemantal is 4325Libev can be compiled with a variety of options, the most fundamental
1880\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and 4326of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
1881callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4327functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1882.PP 4328.PP
1883To make it easier to write programs that cope with either variant, the 4329To make it easier to write programs that cope with either variant, the
1884following macros are defined: 4330following macros are defined:
1885.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4331.ie n .IP """EV_A"", ""EV_A_""" 4
1886.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4332.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
1887.IX Item "EV_A, EV_A_" 4333.IX Item "EV_A, EV_A_"
1888This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4334This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
1889loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4335loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
1890\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4336\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
1891.Sp 4337.Sp
1892.Vb 3 4338.Vb 3
1893\& ev_unref (EV_A); 4339\& ev_unref (EV_A);
1894\& ev_timer_add (EV_A_ watcher); 4340\& ev_timer_add (EV_A_ watcher);
1895\& ev_loop (EV_A_ 0); 4341\& ev_run (EV_A_ 0);
1896.Ve 4342.Ve
1897.Sp 4343.Sp
1898It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4344It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
1899which is often provided by the following macro. 4345which is often provided by the following macro.
1900.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4346.ie n .IP """EV_P"", ""EV_P_""" 4
1901.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4347.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
1902.IX Item "EV_P, EV_P_" 4348.IX Item "EV_P, EV_P_"
1903This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4349This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
1904loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4350loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
1905\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4351\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
1906.Sp 4352.Sp
1907.Vb 2 4353.Vb 2
1908\& // this is how ev_unref is being declared 4354\& // this is how ev_unref is being declared
1909\& static void ev_unref (EV_P); 4355\& static void ev_unref (EV_P);
1910.Ve 4356\&
1911.Sp
1912.Vb 2
1913\& // this is how you can declare your typical callback 4357\& // this is how you can declare your typical callback
1914\& static void cb (EV_P_ ev_timer *w, int revents) 4358\& static void cb (EV_P_ ev_timer *w, int revents)
1915.Ve 4359.Ve
1916.Sp 4360.Sp
1917It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4361It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
1918suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4362suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
1919.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4363.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
1920.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4364.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
1921.IX Item "EV_DEFAULT, EV_DEFAULT_" 4365.IX Item "EV_DEFAULT, EV_DEFAULT_"
1922Similar to the other two macros, this gives you the value of the default 4366Similar to the other two macros, this gives you the value of the default
1923loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4367loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4368will be initialised if it isn't already initialised.
4369.Sp
4370For non-multiplicity builds, these macros do nothing, so you always have
4371to initialise the loop somewhere.
4372.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4373.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4374.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4375Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4376default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4377is undefined when the default loop has not been initialised by a previous
4378execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4379.Sp
4380It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4381watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1924.PP 4382.PP
1925Example: Declare and initialise a check watcher, working regardless of 4383Example: Declare and initialise a check watcher, utilising the above
1926wether multiple loops are supported or not. 4384macros so it will work regardless of whether multiple loops are supported
4385or not.
1927.PP 4386.PP
1928.Vb 5 4387.Vb 5
1929\& static void 4388\& static void
1930\& check_cb (EV_P_ ev_timer *w, int revents) 4389\& check_cb (EV_P_ ev_timer *w, int revents)
1931\& { 4390\& {
1932\& ev_check_stop (EV_A_ w); 4391\& ev_check_stop (EV_A_ w);
1933\& } 4392\& }
1934.Ve 4393\&
1935.PP
1936.Vb 4
1937\& ev_check check; 4394\& ev_check check;
1938\& ev_check_init (&check, check_cb); 4395\& ev_check_init (&check, check_cb);
1939\& ev_check_start (EV_DEFAULT_ &check); 4396\& ev_check_start (EV_DEFAULT_ &check);
1940\& ev_loop (EV_DEFAULT_ 0); 4397\& ev_run (EV_DEFAULT_ 0);
1941.Ve 4398.Ve
1942.SH "EMBEDDING" 4399.SH "EMBEDDING"
1943.IX Header "EMBEDDING" 4400.IX Header "EMBEDDING"
1944Libev can (and often is) directly embedded into host 4401Libev can (and often is) directly embedded into host
1945applications. Examples of applications that embed it include the Deliantra 4402applications. Examples of applications that embed it include the Deliantra
1946Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4403Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1947and rxvt\-unicode. 4404and rxvt-unicode.
1948.PP 4405.PP
1949The goal is to enable you to just copy the neecssary files into your 4406The goal is to enable you to just copy the necessary files into your
1950source directory without having to change even a single line in them, so 4407source directory without having to change even a single line in them, so
1951you can easily upgrade by simply copying (or having a checked-out copy of 4408you can easily upgrade by simply copying (or having a checked-out copy of
1952libev somewhere in your source tree). 4409libev somewhere in your source tree).
1953.Sh "\s-1FILESETS\s0" 4410.SS "\s-1FILESETS\s0"
1954.IX Subsection "FILESETS" 4411.IX Subsection "FILESETS"
1955Depending on what features you need you need to include one or more sets of files 4412Depending on what features you need you need to include one or more sets of files
1956in your app. 4413in your application.
1957.PP 4414.PP
1958\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4415\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
1959.IX Subsection "CORE EVENT LOOP" 4416.IX Subsection "CORE EVENT LOOP"
1960.PP 4417.PP
1961To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4418To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1962configuration (no autoconf): 4419configuration (no autoconf):
1963.PP 4420.PP
1964.Vb 2 4421.Vb 2
1965\& #define EV_STANDALONE 1 4422\& #define EV_STANDALONE 1
1966\& #include "ev.c" 4423\& #include "ev.c"
1967.Ve 4424.Ve
1968.PP 4425.PP
1969This will automatically include \fIev.h\fR, too, and should be done in a 4426This will automatically include \fIev.h\fR, too, and should be done in a
1970single C source file only to provide the function implementations. To use 4427single C source file only to provide the function implementations. To use
1971it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4428it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1972done by writing a wrapper around \fIev.h\fR that you can include instead and 4429done by writing a wrapper around \fIev.h\fR that you can include instead and
1973where you can put other configuration options): 4430where you can put other configuration options):
1974.PP 4431.PP
1975.Vb 2 4432.Vb 2
1976\& #define EV_STANDALONE 1 4433\& #define EV_STANDALONE 1
1977\& #include "ev.h" 4434\& #include "ev.h"
1978.Ve 4435.Ve
1979.PP 4436.PP
1980Both header files and implementation files can be compiled with a \*(C+ 4437Both header files and implementation files can be compiled with a \*(C+
1981compiler (at least, thats a stated goal, and breakage will be treated 4438compiler (at least, that's a stated goal, and breakage will be treated
1982as a bug). 4439as a bug).
1983.PP 4440.PP
1984You need the following files in your source tree, or in a directory 4441You need the following files in your source tree, or in a directory
1985in your include path (e.g. in libev/ when using \-Ilibev): 4442in your include path (e.g. in libev/ when using \-Ilibev):
1986.PP 4443.PP
1987.Vb 4 4444.Vb 4
1988\& ev.h 4445\& ev.h
1989\& ev.c 4446\& ev.c
1990\& ev_vars.h 4447\& ev_vars.h
1991\& ev_wrap.h 4448\& ev_wrap.h
1992.Ve 4449\&
1993.PP
1994.Vb 1
1995\& ev_win32.c required on win32 platforms only 4450\& ev_win32.c required on win32 platforms only
1996.Ve 4451\&
1997.PP
1998.Vb 5
1999\& ev_select.c only when select backend is enabled (which is by default) 4452\& ev_select.c only when select backend is enabled (which is enabled by default)
2000\& ev_poll.c only when poll backend is enabled (disabled by default) 4453\& ev_poll.c only when poll backend is enabled (disabled by default)
2001\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4454\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2002\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4455\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2003\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4456\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2004.Ve 4457.Ve
2005.PP 4458.PP
2006\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4459\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2007to compile this single file. 4460to compile this single file.
2008.PP 4461.PP
… …
2010.IX Subsection "LIBEVENT COMPATIBILITY API" 4463.IX Subsection "LIBEVENT COMPATIBILITY API"
2011.PP 4464.PP
2012To include the libevent compatibility \s-1API\s0, also include: 4465To include the libevent compatibility \s-1API\s0, also include:
2013.PP 4466.PP
2014.Vb 1 4467.Vb 1
2015\& #include "event.c" 4468\& #include "event.c"
2016.Ve 4469.Ve
2017.PP 4470.PP
2018in the file including \fIev.c\fR, and: 4471in the file including \fIev.c\fR, and:
2019.PP 4472.PP
2020.Vb 1 4473.Vb 1
2021\& #include "event.h" 4474\& #include "event.h"
2022.Ve 4475.Ve
2023.PP 4476.PP
2024in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4477in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2025.PP 4478.PP
2026You need the following additional files for this: 4479You need the following additional files for this:
2027.PP 4480.PP
2028.Vb 2 4481.Vb 2
2029\& event.h 4482\& event.h
2030\& event.c 4483\& event.c
2031.Ve 4484.Ve
2032.PP 4485.PP
2033\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4486\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2034.IX Subsection "AUTOCONF SUPPORT" 4487.IX Subsection "AUTOCONF SUPPORT"
2035.PP 4488.PP
2036Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4489Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2037whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4490whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2038\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4491\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2039include \fIconfig.h\fR and configure itself accordingly. 4492include \fIconfig.h\fR and configure itself accordingly.
2040.PP 4493.PP
2041For this of course you need the m4 file: 4494For this of course you need the m4 file:
2042.PP 4495.PP
2043.Vb 1 4496.Vb 1
2044\& libev.m4 4497\& libev.m4
2045.Ve 4498.Ve
2046.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4499.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2047.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4500.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2048Libev can be configured via a variety of preprocessor symbols you have to define 4501Libev can be configured via a variety of preprocessor symbols you have to
2049before including any of its files. The default is not to build for multiplicity 4502define before including (or compiling) any of its files. The default in
2050and only include the select backend. 4503the absence of autoconf is documented for every option.
4504.PP
4505Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4506values when compiling libev vs. including \fIev.h\fR, so it is permissible
4507to redefine them before including \fIev.h\fR without breaking compatibility
4508to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4509users of libev and the libev code itself must be compiled with compatible
4510settings.
4511.IP "\s-1EV_COMPAT3\s0 (h)" 4
4512.IX Item "EV_COMPAT3 (h)"
4513Backwards compatibility is a major concern for libev. This is why this
4514release of libev comes with wrappers for the functions and symbols that
4515have been renamed between libev version 3 and 4.
4516.Sp
4517You can disable these wrappers (to test compatibility with future
4518versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4519sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4520from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4521typedef in that case.
4522.Sp
4523In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4524and in some even more future version the compatibility code will be
4525removed completely.
2051.IP "\s-1EV_STANDALONE\s0" 4 4526.IP "\s-1EV_STANDALONE\s0 (h)" 4
2052.IX Item "EV_STANDALONE" 4527.IX Item "EV_STANDALONE (h)"
2053Must always be \f(CW1\fR if you do not use autoconf configuration, which 4528Must always be \f(CW1\fR if you do not use autoconf configuration, which
2054keeps libev from including \fIconfig.h\fR, and it also defines dummy 4529keeps libev from including \fIconfig.h\fR, and it also defines dummy
2055implementations for some libevent functions (such as logging, which is not 4530implementations for some libevent functions (such as logging, which is not
2056supported). It will also not define any of the structs usually found in 4531supported). It will also not define any of the structs usually found in
2057\&\fIevent.h\fR that are not directly supported by the libev core alone. 4532\&\fIevent.h\fR that are not directly supported by the libev core alone.
4533.Sp
4534In standalone mode, libev will still try to automatically deduce the
4535configuration, but has to be more conservative.
4536.IP "\s-1EV_USE_FLOOR\s0" 4
4537.IX Item "EV_USE_FLOOR"
4538If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4539periodic reschedule calculations, otherwise libev will fall back on a
4540portable (slower) implementation. If you enable this, you usually have to
4541link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4542function is not available will fail, so the safe default is to not enable
4543this.
2058.IP "\s-1EV_USE_MONOTONIC\s0" 4 4544.IP "\s-1EV_USE_MONOTONIC\s0" 4
2059.IX Item "EV_USE_MONOTONIC" 4545.IX Item "EV_USE_MONOTONIC"
2060If defined to be \f(CW1\fR, libev will try to detect the availability of the 4546If defined to be \f(CW1\fR, libev will try to detect the availability of the
2061monotonic clock option at both compiletime and runtime. Otherwise no use 4547monotonic clock option at both compile time and runtime. Otherwise no
2062of the monotonic clock option will be attempted. If you enable this, you 4548use of the monotonic clock option will be attempted. If you enable this,
2063usually have to link against librt or something similar. Enabling it when 4549you usually have to link against librt or something similar. Enabling it
2064the functionality isn't available is safe, though, althoguh you have 4550when the functionality isn't available is safe, though, although you have
2065to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4551to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2066function is hiding in (often \fI\-lrt\fR). 4552function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2067.IP "\s-1EV_USE_REALTIME\s0" 4 4553.IP "\s-1EV_USE_REALTIME\s0" 4
2068.IX Item "EV_USE_REALTIME" 4554.IX Item "EV_USE_REALTIME"
2069If defined to be \f(CW1\fR, libev will try to detect the availability of the 4555If defined to be \f(CW1\fR, libev will try to detect the availability of the
2070realtime clock option at compiletime (and assume its availability at 4556real-time clock option at compile time (and assume its availability
2071runtime if successful). Otherwise no use of the realtime clock option will 4557at runtime if successful). Otherwise no use of the real-time clock
2072be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4558option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2073(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4559by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2074in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4560correctness. See the note about libraries in the description of
4561\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4562\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4563.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4564.IX Item "EV_USE_CLOCK_SYSCALL"
4565If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4566of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4567exists 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
4568unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4569programs needlessly. Using a direct syscall is slightly slower (in
4570theory), because no optimised vdso implementation can be used, but avoids
4571the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4572higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4573.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4574.IX Item "EV_USE_NANOSLEEP"
4575If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4576and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4577.IP "\s-1EV_USE_EVENTFD\s0" 4
4578.IX Item "EV_USE_EVENTFD"
4579If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4580available and will probe for kernel support at runtime. This will improve
4581\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4582If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
45832.7 or newer, otherwise disabled.
2075.IP "\s-1EV_USE_SELECT\s0" 4 4584.IP "\s-1EV_USE_SELECT\s0" 4
2076.IX Item "EV_USE_SELECT" 4585.IX Item "EV_USE_SELECT"
2077If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4586If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2078\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4587\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2079other method takes over, select will be it. Otherwise the select backend 4588other method takes over, select will be it. Otherwise the select backend
2080will not be compiled in. 4589will not be compiled in.
2081.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4590.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2082.IX Item "EV_SELECT_USE_FD_SET" 4591.IX Item "EV_SELECT_USE_FD_SET"
2083If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4592If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2084structure. This is useful if libev doesn't compile due to a missing 4593structure. This is useful if libev doesn't compile due to a missing
2085\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4594\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2086exotic systems. This usually limits the range of file descriptors to some 4595on exotic systems. This usually limits the range of file descriptors to
2087low limit such as 1024 or might have other limitations (winsocket only 4596some low limit such as 1024 or might have other limitations (winsocket
2088allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4597only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2089influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4598configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2090.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4599.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2091.IX Item "EV_SELECT_IS_WINSOCKET" 4600.IX Item "EV_SELECT_IS_WINSOCKET"
2092When defined to \f(CW1\fR, the select backend will assume that 4601When defined to \f(CW1\fR, the select backend will assume that
2093select/socket/connect etc. don't understand file descriptors but 4602select/socket/connect etc. don't understand file descriptors but
2094wants osf handles on win32 (this is the case when the select to 4603wants osf handles on win32 (this is the case when the select to
2095be used is the winsock select). This means that it will call 4604be used is the winsock select). This means that it will call
2096\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4605\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2097it is assumed that all these functions actually work on fds, even 4606it is assumed that all these functions actually work on fds, even
2098on win32. Should not be defined on non\-win32 platforms. 4607on win32. Should not be defined on non\-win32 platforms.
4608.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4609.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4610If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4611file descriptors to socket handles. When not defining this symbol (the
4612default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4613correct. In some cases, programs use their own file descriptor management,
4614in which case they can provide this function to map fds to socket handles.
4615.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4616.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4617If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4618using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4619their own fd to handle mapping, overwriting this function makes it easier
4620to do so. This can be done by defining this macro to an appropriate value.
4621.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4622.IX Item "EV_WIN32_CLOSE_FD(fd)"
4623If programs implement their own fd to handle mapping on win32, then this
4624macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4625file descriptors again. Note that the replacement function has to close
4626the underlying \s-1OS\s0 handle.
2099.IP "\s-1EV_USE_POLL\s0" 4 4627.IP "\s-1EV_USE_POLL\s0" 4
2100.IX Item "EV_USE_POLL" 4628.IX Item "EV_USE_POLL"
2101If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4629If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2102backend. Otherwise it will be enabled on non\-win32 platforms. It 4630backend. Otherwise it will be enabled on non\-win32 platforms. It
2103takes precedence over select. 4631takes precedence over select.
2104.IP "\s-1EV_USE_EPOLL\s0" 4 4632.IP "\s-1EV_USE_EPOLL\s0" 4
2105.IX Item "EV_USE_EPOLL" 4633.IX Item "EV_USE_EPOLL"
2106If defined to be \f(CW1\fR, libev will compile in support for the Linux 4634If defined to be \f(CW1\fR, libev will compile in support for the Linux
2107\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4635\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2108otherwise another method will be used as fallback. This is the 4636otherwise another method will be used as fallback. This is the preferred
2109preferred backend for GNU/Linux systems. 4637backend for GNU/Linux systems. If undefined, it will be enabled if the
4638headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2110.IP "\s-1EV_USE_KQUEUE\s0" 4 4639.IP "\s-1EV_USE_KQUEUE\s0" 4
2111.IX Item "EV_USE_KQUEUE" 4640.IX Item "EV_USE_KQUEUE"
2112If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4641If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2113\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4642\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2114otherwise another method will be used as fallback. This is the preferred 4643otherwise another method will be used as fallback. This is the preferred
… …
212410 port style backend. Its availability will be detected at runtime, 465310 port style backend. Its availability will be detected at runtime,
2125otherwise another method will be used as fallback. This is the preferred 4654otherwise another method will be used as fallback. This is the preferred
2126backend for Solaris 10 systems. 4655backend for Solaris 10 systems.
2127.IP "\s-1EV_USE_DEVPOLL\s0" 4 4656.IP "\s-1EV_USE_DEVPOLL\s0" 4
2128.IX Item "EV_USE_DEVPOLL" 4657.IX Item "EV_USE_DEVPOLL"
2129reserved for future expansion, works like the \s-1USE\s0 symbols above. 4658Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4659.IP "\s-1EV_USE_INOTIFY\s0" 4
4660.IX Item "EV_USE_INOTIFY"
4661If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4662interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4663be detected at runtime. If undefined, it will be enabled if the headers
4664indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4665.IP "\s-1EV_NO_SMP\s0" 4
4666.IX Item "EV_NO_SMP"
4667If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4668between threads, that is, threads can be used, but threads never run on
4669different cpus (or different cpu cores). This reduces dependencies
4670and makes libev faster.
4671.IP "\s-1EV_NO_THREADS\s0" 4
4672.IX Item "EV_NO_THREADS"
4673If defined to be \f(CW1\fR, libev will assume that it will never be called
4674from different threads, which is a stronger assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR,
4675above. This reduces dependencies and makes libev faster.
4676.IP "\s-1EV_ATOMIC_T\s0" 4
4677.IX Item "EV_ATOMIC_T"
4678Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4679access is atomic and serialised with respect to other threads or signal
4680contexts. No such type is easily found in the C language, so you can
4681provide your own type that you know is safe for your purposes. It is used
4682both for signal handler \*(L"locking\*(R" as well as for signal and thread safety
4683in \f(CW\*(C`ev_async\*(C'\fR watchers.
4684.Sp
4685In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4686(from \fIsignal.h\fR), which is usually good enough on most platforms,
4687although strictly speaking using a type that also implies a memory fence
4688is required.
2130.IP "\s-1EV_H\s0" 4 4689.IP "\s-1EV_H\s0 (h)" 4
2131.IX Item "EV_H" 4690.IX Item "EV_H (h)"
2132The name of the \fIev.h\fR header file used to include it. The default if 4691The name of the \fIev.h\fR header file used to include it. The default if
2133undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4692undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2134can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4693used to virtually rename the \fIev.h\fR header file in case of conflicts.
2135.IP "\s-1EV_CONFIG_H\s0" 4 4694.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2136.IX Item "EV_CONFIG_H" 4695.IX Item "EV_CONFIG_H (h)"
2137If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4696If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2138\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4697\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2139\&\f(CW\*(C`EV_H\*(C'\fR, above. 4698\&\f(CW\*(C`EV_H\*(C'\fR, above.
2140.IP "\s-1EV_EVENT_H\s0" 4 4699.IP "\s-1EV_EVENT_H\s0 (h)" 4
2141.IX Item "EV_EVENT_H" 4700.IX Item "EV_EVENT_H (h)"
2142Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4701Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2143of how the \fIevent.h\fR header can be found. 4702of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2144.IP "\s-1EV_PROTOTYPES\s0" 4 4703.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2145.IX Item "EV_PROTOTYPES" 4704.IX Item "EV_PROTOTYPES (h)"
2146If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4705If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2147prototypes, but still define all the structs and other symbols. This is 4706prototypes, but still define all the structs and other symbols. This is
2148occasionally useful if you want to provide your own wrapper functions 4707occasionally useful if you want to provide your own wrapper functions
2149around libev functions. 4708around libev functions.
2150.IP "\s-1EV_MULTIPLICITY\s0" 4 4709.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2152If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4711If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2153will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4712will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2154additional independent event loops. Otherwise there will be no support 4713additional independent event loops. Otherwise there will be no support
2155for multiple event loops and there is no first event loop pointer 4714for multiple event loops and there is no first event loop pointer
2156argument. Instead, all functions act on the single default loop. 4715argument. Instead, all functions act on the single default loop.
2157.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4716.Sp
2158.IX Item "EV_PERIODIC_ENABLE" 4717Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
2159If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4718default loop when multiplicity is switched off \- you always have to
2160defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4719initialise the loop manually in this case.
2161code.
2162.IP "\s-1EV_EMBED_ENABLE\s0" 4
2163.IX Item "EV_EMBED_ENABLE"
2164If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2165defined to be \f(CW0\fR, then they are not.
2166.IP "\s-1EV_STAT_ENABLE\s0" 4
2167.IX Item "EV_STAT_ENABLE"
2168If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2169defined to be \f(CW0\fR, then they are not.
2170.IP "\s-1EV_FORK_ENABLE\s0" 4
2171.IX Item "EV_FORK_ENABLE"
2172If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2173defined to be \f(CW0\fR, then they are not.
2174.IP "\s-1EV_MINIMAL\s0" 4 4720.IP "\s-1EV_MINPRI\s0" 4
2175.IX Item "EV_MINIMAL" 4721.IX Item "EV_MINPRI"
4722.PD 0
4723.IP "\s-1EV_MAXPRI\s0" 4
4724.IX Item "EV_MAXPRI"
4725.PD
4726The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4727\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4728provide for more priorities by overriding those symbols (usually defined
4729to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4730.Sp
4731When doing priority-based operations, libev usually has to linearly search
4732all the priorities, so having many of them (hundreds) uses a lot of space
4733and time, so using the defaults of five priorities (\-2 .. +2) is usually
4734fine.
4735.Sp
4736If your embedding application does not need any priorities, defining these
4737both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4738.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
4739.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."
4740If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4741the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4742is not. Disabling watcher types mainly saves code size.
4743.IP "\s-1EV_FEATURES\s0" 4
4744.IX Item "EV_FEATURES"
2176If you need to shave off some kilobytes of code at the expense of some 4745If you need to shave off some kilobytes of code at the expense of some
2177speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4746speed (but with the full \s-1API\s0), you can define this symbol to request
2178some inlining decisions, saves roughly 30% codesize of amd64. 4747certain subsets of functionality. The default is to enable all features
4748that can be enabled on the platform.
4749.Sp
4750A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4751with some broad features you want) and then selectively re-enable
4752additional parts you want, for example if you want everything minimal,
4753but multiple event loop support, async and child watchers and the poll
4754backend, use this:
4755.Sp
4756.Vb 5
4757\& #define EV_FEATURES 0
4758\& #define EV_MULTIPLICITY 1
4759\& #define EV_USE_POLL 1
4760\& #define EV_CHILD_ENABLE 1
4761\& #define EV_ASYNC_ENABLE 1
4762.Ve
4763.Sp
4764The actual value is a bitset, it can be a combination of the following
4765values (by default, all of these are enabled):
4766.RS 4
4767.ie n .IP "1 \- faster/larger code" 4
4768.el .IP "\f(CW1\fR \- faster/larger code" 4
4769.IX Item "1 - faster/larger code"
4770Use larger code to speed up some operations.
4771.Sp
4772Currently this is used to override some inlining decisions (enlarging the
4773code size by roughly 30% on amd64).
4774.Sp
4775When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4776gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4777assertions.
4778.Sp
4779The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4780(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4781.ie n .IP "2 \- faster/larger data structures" 4
4782.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4783.IX Item "2 - faster/larger data structures"
4784Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4785hash table sizes and so on. This will usually further increase code size
4786and can additionally have an effect on the size of data structures at
4787runtime.
4788.Sp
4789The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4790(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4791.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4792.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4793.IX Item "4 - full API configuration"
4794This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4795enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4796.ie n .IP "8 \- full \s-1API\s0" 4
4797.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4798.IX Item "8 - full API"
4799This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4800details on which parts of the \s-1API\s0 are still available without this
4801feature, and do not complain if this subset changes over time.
4802.ie n .IP "16 \- enable all optional watcher types" 4
4803.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4804.IX Item "16 - enable all optional watcher types"
4805Enables all optional watcher types. If you want to selectively enable
4806only some watcher types other than I/O and timers (e.g. prepare,
4807embed, async, child...) you can enable them manually by defining
4808\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4809.ie n .IP "32 \- enable all backends" 4
4810.el .IP "\f(CW32\fR \- enable all backends" 4
4811.IX Item "32 - enable all backends"
4812This enables all backends \- without this feature, you need to enable at
4813least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4814.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4815.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4816.IX Item "64 - enable OS-specific helper APIs"
4817Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4818default.
4819.RE
4820.RS 4
4821.Sp
4822Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4823reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4824code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4825watchers, timers and monotonic clock support.
4826.Sp
4827With an intelligent-enough linker (gcc+binutils are intelligent enough
4828when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4829your program might be left out as well \- a binary starting a timer and an
4830I/O watcher then might come out at only 5Kb.
4831.RE
4832.IP "\s-1EV_API_STATIC\s0" 4
4833.IX Item "EV_API_STATIC"
4834If this symbol is defined (by default it is not), then all identifiers
4835will have static linkage. This means that libev will not export any
4836identifiers, and you cannot link against libev anymore. This can be useful
4837when you embed libev, only want to use libev functions in a single file,
4838and do not want its identifiers to be visible.
4839.Sp
4840To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4841wants to use libev.
4842.Sp
4843This option only works when libev is compiled with a C compiler, as \*(C+
4844doesn't support the required declaration syntax.
4845.IP "\s-1EV_AVOID_STDIO\s0" 4
4846.IX Item "EV_AVOID_STDIO"
4847If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4848functions (printf, scanf, perror etc.). This will increase the code size
4849somewhat, but if your program doesn't otherwise depend on stdio and your
4850libc allows it, this avoids linking in the stdio library which is quite
4851big.
4852.Sp
4853Note that error messages might become less precise when this option is
4854enabled.
4855.IP "\s-1EV_NSIG\s0" 4
4856.IX Item "EV_NSIG"
4857The highest supported signal number, +1 (or, the number of
4858signals): Normally, libev tries to deduce the maximum number of signals
4859automatically, but sometimes this fails, in which case it can be
4860specified. Also, using a lower number than detected (\f(CW32\fR should be
4861good for about any system in existence) can save some memory, as libev
4862statically allocates some 12\-24 bytes per signal number.
2179.IP "\s-1EV_PID_HASHSIZE\s0" 4 4863.IP "\s-1EV_PID_HASHSIZE\s0" 4
2180.IX Item "EV_PID_HASHSIZE" 4864.IX Item "EV_PID_HASHSIZE"
2181\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 4865\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2182pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 4866pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2183than enough. If you need to manage thousands of children you might want to 4867usually more than enough. If you need to manage thousands of children you
2184increase this value. 4868might want to increase this value (\fImust\fR be a power of two).
4869.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4870.IX Item "EV_INOTIFY_HASHSIZE"
4871\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4872inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4873disabled), usually more than enough. If you need to manage thousands of
4874\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4875power of two).
4876.IP "\s-1EV_USE_4HEAP\s0" 4
4877.IX Item "EV_USE_4HEAP"
4878Heaps are not very cache-efficient. To improve the cache-efficiency of the
4879timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4880to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4881faster performance with many (thousands) of watchers.
4882.Sp
4883The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4884will be \f(CW0\fR.
4885.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4886.IX Item "EV_HEAP_CACHE_AT"
4887Heaps are not very cache-efficient. To improve the cache-efficiency of the
4888timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4889the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4890which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4891but avoids random read accesses on heap changes. This improves performance
4892noticeably with many (hundreds) of watchers.
4893.Sp
4894The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4895will be \f(CW0\fR.
4896.IP "\s-1EV_VERIFY\s0" 4
4897.IX Item "EV_VERIFY"
4898Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4899be done: If set to \f(CW0\fR, no internal verification code will be compiled
4900in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4901called. If set to \f(CW2\fR, then the internal verification code will be
4902called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4903verification code will be called very frequently, which will slow down
4904libev considerably.
4905.Sp
4906The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4907will be \f(CW0\fR.
2185.IP "\s-1EV_COMMON\s0" 4 4908.IP "\s-1EV_COMMON\s0" 4
2186.IX Item "EV_COMMON" 4909.IX Item "EV_COMMON"
2187By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4910By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2188this macro to a something else you can include more and other types of 4911this macro to something else you can include more and other types of
2189members. You have to define it each time you include one of the files, 4912members. You have to define it each time you include one of the files,
2190though, and it must be identical each time. 4913though, and it must be identical each time.
2191.Sp 4914.Sp
2192For example, the perl \s-1EV\s0 module uses something like this: 4915For example, the perl \s-1EV\s0 module uses something like this:
2193.Sp 4916.Sp
2194.Vb 3 4917.Vb 3
2195\& #define EV_COMMON \e 4918\& #define EV_COMMON \e
2196\& SV *self; /* contains this struct */ \e 4919\& SV *self; /* contains this struct */ \e
2197\& SV *cb_sv, *fh /* note no trailing ";" */ 4920\& SV *cb_sv, *fh /* note no trailing ";" */
2198.Ve 4921.Ve
2199.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 4922.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2200.IX Item "EV_CB_DECLARE (type)" 4923.IX Item "EV_CB_DECLARE (type)"
2201.PD 0 4924.PD 0
2202.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 4925.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2204.IP "ev_set_cb (ev, cb)" 4 4927.IP "ev_set_cb (ev, cb)" 4
2205.IX Item "ev_set_cb (ev, cb)" 4928.IX Item "ev_set_cb (ev, cb)"
2206.PD 4929.PD
2207Can be used to change the callback member declaration in each watcher, 4930Can be used to change the callback member declaration in each watcher,
2208and the way callbacks are invoked and set. Must expand to a struct member 4931and the way callbacks are invoked and set. Must expand to a struct member
2209definition and a statement, respectively. See the \fIev.v\fR header file for 4932definition and a statement, respectively. See the \fIev.h\fR header file for
2210their default definitions. One possible use for overriding these is to 4933their default definitions. One possible use for overriding these is to
2211avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 4934avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2212method calls instead of plain function calls in \*(C+. 4935method calls instead of plain function calls in \*(C+.
4936.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4937.IX Subsection "EXPORTED API SYMBOLS"
4938If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4939exported symbols, you can use the provided \fISymbol.*\fR files which list
4940all public symbols, one per line:
4941.PP
4942.Vb 2
4943\& Symbols.ev for libev proper
4944\& Symbols.event for the libevent emulation
4945.Ve
4946.PP
4947This can also be used to rename all public symbols to avoid clashes with
4948multiple versions of libev linked together (which is obviously bad in
4949itself, but sometimes it is inconvenient to avoid this).
4950.PP
4951A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4952include before including \fIev.h\fR:
4953.PP
4954.Vb 1
4955\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4956.Ve
4957.PP
4958This would create a file \fIwrap.h\fR which essentially looks like this:
4959.PP
4960.Vb 4
4961\& #define ev_backend myprefix_ev_backend
4962\& #define ev_check_start myprefix_ev_check_start
4963\& #define ev_check_stop myprefix_ev_check_stop
4964\& ...
4965.Ve
2213.Sh "\s-1EXAMPLES\s0" 4966.SS "\s-1EXAMPLES\s0"
2214.IX Subsection "EXAMPLES" 4967.IX Subsection "EXAMPLES"
2215For a real-world example of a program the includes libev 4968For a real-world example of a program the includes libev
2216verbatim, you can have a look at the \s-1EV\s0 perl module 4969verbatim, you can have a look at the \s-1EV\s0 perl module
2217(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 4970(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2218the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 4971the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2219interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 4972interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2220will be compiled. It is pretty complex because it provides its own header 4973will be compiled. It is pretty complex because it provides its own header
2221file. 4974file.
2222.Sp 4975.PP
2223The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 4976The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2224that everybody includes and which overrides some autoconf choices: 4977that everybody includes and which overrides some configure choices:
2225.Sp 4978.PP
2226.Vb 4 4979.Vb 8
4980\& #define EV_FEATURES 8
4981\& #define EV_USE_SELECT 1
4982\& #define EV_PREPARE_ENABLE 1
4983\& #define EV_IDLE_ENABLE 1
4984\& #define EV_SIGNAL_ENABLE 1
4985\& #define EV_CHILD_ENABLE 1
2227\& #define EV_USE_POLL 0 4986\& #define EV_USE_STDEXCEPT 0
2228\& #define EV_MULTIPLICITY 0
2229\& #define EV_PERIODICS 0
2230\& #define EV_CONFIG_H <config.h> 4987\& #define EV_CONFIG_H <config.h>
2231.Ve 4988\&
2232.Sp
2233.Vb 1
2234\& #include "ev++.h" 4989\& #include "ev++.h"
2235.Ve 4990.Ve
2236.Sp 4991.PP
2237And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 4992And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2238.Sp 4993.PP
2239.Vb 2 4994.Vb 2
2240\& #include "ev_cpp.h" 4995\& #include "ev_cpp.h"
2241\& #include "ev.c" 4996\& #include "ev.c"
2242.Ve 4997.Ve
4998.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4999.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5000.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
5001.IX Subsection "THREADS AND COROUTINES"
5002\fI\s-1THREADS\s0\fR
5003.IX Subsection "THREADS"
5004.PP
5005All libev functions are reentrant and thread-safe unless explicitly
5006documented otherwise, but libev implements no locking itself. This means
5007that you can use as many loops as you want in parallel, as long as there
5008are no concurrent calls into any libev function with the same loop
5009parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5010of course): libev guarantees that different event loops share no data
5011structures that need any locking.
5012.PP
5013Or to put it differently: calls with different loop parameters can be done
5014concurrently from multiple threads, calls with the same loop parameter
5015must be done serially (but can be done from different threads, as long as
5016only one thread ever is inside a call at any point in time, e.g. by using
5017a mutex per loop).
5018.PP
5019Specifically to support threads (and signal handlers), libev implements
5020so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5021concurrency on the same event loop, namely waking it up \*(L"from the
5022outside\*(R".
5023.PP
5024If you want to know which design (one loop, locking, or multiple loops
5025without or something else still) is best for your problem, then I cannot
5026help you, but here is some generic advice:
5027.IP "\(bu" 4
5028most applications have a main thread: use the default libev loop
5029in that thread, or create a separate thread running only the default loop.
5030.Sp
5031This helps integrating other libraries or software modules that use libev
5032themselves and don't care/know about threading.
5033.IP "\(bu" 4
5034one loop per thread is usually a good model.
5035.Sp
5036Doing this is almost never wrong, sometimes a better-performance model
5037exists, but it is always a good start.
5038.IP "\(bu" 4
5039other models exist, such as the leader/follower pattern, where one
5040loop is handed through multiple threads in a kind of round-robin fashion.
5041.Sp
5042Choosing a model is hard \- look around, learn, know that usually you can do
5043better than you currently do :\-)
5044.IP "\(bu" 4
5045often you need to talk to some other thread which blocks in the
5046event loop.
5047.Sp
5048\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5049(or from signal contexts...).
5050.Sp
5051An example use would be to communicate signals or other events that only
5052work in the default loop by registering the signal watcher with the
5053default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5054watcher callback into the event loop interested in the signal.
5055.PP
5056See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
5057.PP
5058\fI\s-1COROUTINES\s0\fR
5059.IX Subsection "COROUTINES"
5060.PP
5061Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5062libev fully supports nesting calls to its functions from different
5063coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5064different coroutines, and switch freely between both coroutines running
5065the loop, as long as you don't confuse yourself). The only exception is
5066that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5067.PP
5068Care has been taken to ensure that libev does not keep local state inside
5069\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5070they do not call any callbacks.
5071.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
5072.IX Subsection "COMPILER WARNINGS"
5073Depending on your compiler and compiler settings, you might get no or a
5074lot of warnings when compiling libev code. Some people are apparently
5075scared by this.
5076.PP
5077However, these are unavoidable for many reasons. For one, each compiler
5078has different warnings, and each user has different tastes regarding
5079warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5080targeting a specific compiler and compiler-version.
5081.PP
5082Another reason is that some compiler warnings require elaborate
5083workarounds, or other changes to the code that make it less clear and less
5084maintainable.
5085.PP
5086And of course, some compiler warnings are just plain stupid, or simply
5087wrong (because they don't actually warn about the condition their message
5088seems to warn about). For example, certain older gcc versions had some
5089warnings that resulted in an extreme number of false positives. These have
5090been fixed, but some people still insist on making code warn-free with
5091such buggy versions.
5092.PP
5093While libev is written to generate as few warnings as possible,
5094\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5095with any compiler warnings enabled unless you are prepared to cope with
5096them (e.g. by ignoring them). Remember that warnings are just that:
5097warnings, not errors, or proof of bugs.
5098.SS "\s-1VALGRIND\s0"
5099.IX Subsection "VALGRIND"
5100Valgrind has a special section here because it is a popular tool that is
5101highly useful. Unfortunately, valgrind reports are very hard to interpret.
5102.PP
5103If you think you found a bug (memory leak, uninitialised data access etc.)
5104in libev, then check twice: If valgrind reports something like:
5105.PP
5106.Vb 3
5107\& ==2274== definitely lost: 0 bytes in 0 blocks.
5108\& ==2274== possibly lost: 0 bytes in 0 blocks.
5109\& ==2274== still reachable: 256 bytes in 1 blocks.
5110.Ve
5111.PP
5112Then there is no memory leak, just as memory accounted to global variables
5113is not a memleak \- the memory is still being referenced, and didn't leak.
5114.PP
5115Similarly, under some circumstances, valgrind might report kernel bugs
5116as if it were a bug in libev (e.g. in realloc or in the poll backend,
5117although an acceptable workaround has been found here), or it might be
5118confused.
5119.PP
5120Keep in mind that valgrind is a very good tool, but only a tool. Don't
5121make it into some kind of religion.
5122.PP
5123If you are unsure about something, feel free to contact the mailing list
5124with the full valgrind report and an explanation on why you think this
5125is a bug in libev (best check the archives, too :). However, don't be
5126annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5127of learning how to interpret valgrind properly.
5128.PP
5129If you need, for some reason, empty reports from valgrind for your project
5130I suggest using suppression lists.
5131.SH "PORTABILITY NOTES"
5132.IX Header "PORTABILITY NOTES"
5133.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
5134.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5135GNU/Linux is the only common platform that supports 64 bit file/large file
5136interfaces but \fIdisables\fR them by default.
5137.PP
5138That means that libev compiled in the default environment doesn't support
5139files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5140.PP
5141Unfortunately, many programs try to work around this GNU/Linux issue
5142by enabling the large file \s-1API\s0, which makes them incompatible with the
5143standard libev compiled for their system.
5144.PP
5145Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5146suddenly make it incompatible to the default compile time environment,
5147i.e. all programs not using special compile switches.
5148.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
5149.IX Subsection "OS/X AND DARWIN BUGS"
5150The whole thing is a bug if you ask me \- basically any system interface
5151you touch is broken, whether it is locales, poll, kqueue or even the
5152OpenGL drivers.
5153.PP
5154\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5155.IX Subsection "kqueue is buggy"
5156.PP
5157The kqueue syscall is broken in all known versions \- most versions support
5158only sockets, many support pipes.
5159.PP
5160Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5161rotten platform, but of course you can still ask for it when creating a
5162loop \- embedding a socket-only kqueue loop into a select-based one is
5163probably going to work well.
5164.PP
5165\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5166.IX Subsection "poll is buggy"
5167.PP
5168Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5169implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5170release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5171.PP
5172Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5173this rotten platform, but of course you can still ask for it when creating
5174a loop.
5175.PP
5176\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5177.IX Subsection "select is buggy"
5178.PP
5179All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5180one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
5181descriptors you can pass in to 1024 \- your program suddenly crashes when
5182you use more.
5183.PP
5184There is an undocumented \*(L"workaround\*(R" for this \- defining
5185\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5186work on \s-1OS/X\s0.
5187.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5188.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5189\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5190.IX Subsection "errno reentrancy"
5191.PP
5192The default compile environment on Solaris is unfortunately so
5193thread-unsafe that you can't even use components/libraries compiled
5194without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5195defined by default. A valid, if stupid, implementation choice.
5196.PP
5197If you want to use libev in threaded environments you have to make sure
5198it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5199.PP
5200\fIEvent port backend\fR
5201.IX Subsection "Event port backend"
5202.PP
5203The scalable event interface for Solaris is called \*(L"event
5204ports\*(R". Unfortunately, this mechanism is very buggy in all major
5205releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5206a large number of spurious wakeups, make sure you have all the relevant
5207and latest kernel patches applied. No, I don't know which ones, but there
5208are multiple ones to apply, and afterwards, event ports actually work
5209great.
5210.PP
5211If you can't get it to work, you can try running the program by setting
5212the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5213\&\f(CW\*(C`select\*(C'\fR backends.
5214.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
5215.IX Subsection "AIX POLL BUG"
5216\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5217this by trying to avoid the poll backend altogether (i.e. it's not even
5218compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5219with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
5220.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5221.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5222\fIGeneral issues\fR
5223.IX Subsection "General issues"
5224.PP
5225Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5226requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5227model. Libev still offers limited functionality on this platform in
5228the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5229descriptors. This only applies when using Win32 natively, not when using
5230e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5231as every compiler comes with a slightly differently broken/incompatible
5232environment.
5233.PP
5234Lifting these limitations would basically require the full
5235re-implementation of the I/O system. If you are into this kind of thing,
5236then note that glib does exactly that for you in a very portable way (note
5237also that glib is the slowest event library known to man).
5238.PP
5239There is no supported compilation method available on windows except
5240embedding it into other applications.
5241.PP
5242Sensible signal handling is officially unsupported by Microsoft \- libev
5243tries its best, but under most conditions, signals will simply not work.
5244.PP
5245Not a libev limitation but worth mentioning: windows apparently doesn't
5246accept large writes: instead of resulting in a partial write, windows will
5247either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5248so make sure you only write small amounts into your sockets (less than a
5249megabyte seems safe, but this apparently depends on the amount of memory
5250available).
5251.PP
5252Due to the many, low, and arbitrary limits on the win32 platform and
5253the abysmal performance of winsockets, using a large number of sockets
5254is not recommended (and not reasonable). If your program needs to use
5255more than a hundred or so sockets, then likely it needs to use a totally
5256different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5257notification model, which cannot be implemented efficiently on windows
5258(due to Microsoft monopoly games).
5259.PP
5260A typical way to use libev under windows is to embed it (see the embedding
5261section for details) and use the following \fIevwrap.h\fR header file instead
5262of \fIev.h\fR:
5263.PP
5264.Vb 2
5265\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5266\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5267\&
5268\& #include "ev.h"
5269.Ve
5270.PP
5271And compile the following \fIevwrap.c\fR file into your project (make sure
5272you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5273.PP
5274.Vb 2
5275\& #include "evwrap.h"
5276\& #include "ev.c"
5277.Ve
5278.PP
5279\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5280.IX Subsection "The winsocket select function"
5281.PP
5282The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5283requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5284also extremely buggy). This makes select very inefficient, and also
5285requires a mapping from file descriptors to socket handles (the Microsoft
5286C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5287discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5288\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5289.PP
5290The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5291libraries and raw winsocket select is:
5292.PP
5293.Vb 2
5294\& #define EV_USE_SELECT 1
5295\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5296.Ve
5297.PP
5298Note that winsockets handling of fd sets is O(n), so you can easily get a
5299complexity in the O(nA\*^X) range when using win32.
5300.PP
5301\fILimited number of file descriptors\fR
5302.IX Subsection "Limited number of file descriptors"
5303.PP
5304Windows has numerous arbitrary (and low) limits on things.
5305.PP
5306Early versions of winsocket's select only supported waiting for a maximum
5307of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5308can only wait for \f(CW64\fR things at the same time internally; Microsoft
5309recommends spawning a chain of threads and wait for 63 handles and the
5310previous thread in each. Sounds great!).
5311.PP
5312Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5313to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5314call (which might be in libev or elsewhere, for example, perl and many
5315other interpreters do their own select emulation on windows).
5316.PP
5317Another limit is the number of file descriptors in the Microsoft runtime
5318libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5319fetish or something like this inside Microsoft). You can increase this
5320by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5321(another arbitrary limit), but is broken in many versions of the Microsoft
5322runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5323(depending on windows version and/or the phase of the moon). To get more,
5324you need to wrap all I/O functions and provide your own fd management, but
5325the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5326.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5327.IX Subsection "PORTABILITY REQUIREMENTS"
5328In addition to a working ISO-C implementation and of course the
5329backend-specific APIs, libev relies on a few additional extensions:
5330.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5331.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5332.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5333Libev assumes not only that all watcher pointers have the same internal
5334structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5335assumes that the same (machine) code can be used to call any watcher
5336callback: The watcher callbacks have different type signatures, but libev
5337calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5338.IP "pointer accesses must be thread-atomic" 4
5339.IX Item "pointer accesses must be thread-atomic"
5340Accessing a pointer value must be atomic, it must both be readable and
5341writable in one piece \- this is the case on all current architectures.
5342.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5343.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5344.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5345The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5346\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5347threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5348believed to be sufficiently portable.
5349.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5350.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5351.IX Item "sigprocmask must work in a threaded environment"
5352Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5353allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5354pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5355thread\*(R" or will block signals process-wide, both behaviours would
5356be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5357\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5358.Sp
5359The most portable way to handle signals is to block signals in all threads
5360except the initial one, and run the default loop in the initial thread as
5361well.
5362.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5363.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5364.IX Item "long must be large enough for common memory allocation sizes"
5365To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5366instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5367systems (Microsoft...) this might be unexpectedly low, but is still at
5368least 31 bits everywhere, which is enough for hundreds of millions of
5369watchers.
5370.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5371.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5372.IX Item "double must hold a time value in seconds with enough accuracy"
5373The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5374have at least 51 bits of mantissa (and 9 bits of exponent), which is
5375good enough for at least into the year 4000 with millisecond accuracy
5376(the design goal for libev). This requirement is overfulfilled by
5377implementations using \s-1IEEE\s0 754, which is basically all existing ones.
5378.Sp
5379With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
5380year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5381is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5382something like that, just kidding).
5383.PP
5384If you know of other additional requirements drop me a note.
2243.SH "COMPLEXITIES" 5385.SH "ALGORITHMIC COMPLEXITIES"
2244.IX Header "COMPLEXITIES" 5386.IX Header "ALGORITHMIC COMPLEXITIES"
2245In this section the complexities of (many of) the algorithms used inside 5387In this section the complexities of (many of) the algorithms used inside
2246libev will be explained. For complexity discussions about backends see the 5388libev will be documented. For complexity discussions about backends see
2247documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5389the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2248.RS 4 5390.PP
5391All of the following are about amortised time: If an array needs to be
5392extended, libev needs to realloc and move the whole array, but this
5393happens asymptotically rarer with higher number of elements, so O(1) might
5394mean that libev does a lengthy realloc operation in rare cases, but on
5395average it is much faster and asymptotically approaches constant time.
2249.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5396.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2250.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5397.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5398This means that, when you have a watcher that triggers in one hour and
5399there are 100 watchers that would trigger before that, then inserting will
5400have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5401.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5402.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5403That means that changing a timer costs less than removing/adding them,
5404as only the relative motion in the event queue has to be paid for.
5405.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5406.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5407These just add the watcher into an array or at the head of a list.
5408.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5409.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2251.PD 0 5410.PD 0
2252.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2253.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2254.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2255.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2256.IP "Stopping check/prepare/idle watchers: O(1)" 4
2257.IX Item "Stopping check/prepare/idle watchers: O(1)"
2258.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 4 5411.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2259.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 5412.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5413.PD
5414These watchers are stored in lists, so they need to be walked to find the
5415correct watcher to remove. The lists are usually short (you don't usually
5416have many watchers waiting for the same fd or signal: one is typical, two
5417is rare).
2260.IP "Finding the next timer per loop iteration: O(1)" 4 5418.IP "Finding the next timer in each loop iteration: O(1)" 4
2261.IX Item "Finding the next timer per loop iteration: O(1)" 5419.IX Item "Finding the next timer in each loop iteration: O(1)"
5420By virtue of using a binary or 4\-heap, the next timer is always found at a
5421fixed position in the storage array.
2262.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5422.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2263.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5423.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2264.IP "Activating one watcher: O(1)" 4 5424A change means an I/O watcher gets started or stopped, which requires
2265.IX Item "Activating one watcher: O(1)" 5425libev to recalculate its status (and possibly tell the kernel, depending
2266.RE 5426on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2267.RS 4 5427.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5428.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5429.PD 0
5430.IP "Priority handling: O(number_of_priorities)" 4
5431.IX Item "Priority handling: O(number_of_priorities)"
2268.PD 5432.PD
5433Priorities are implemented by allocating some space for each
5434priority. When doing priority-based operations, libev usually has to
5435linearly search all the priorities, but starting/stopping and activating
5436watchers becomes O(1) with respect to priority handling.
5437.IP "Sending an ev_async: O(1)" 4
5438.IX Item "Sending an ev_async: O(1)"
5439.PD 0
5440.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5441.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5442.IP "Processing signals: O(max_signal_number)" 4
5443.IX Item "Processing signals: O(max_signal_number)"
5444.PD
5445Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5446calls in the current loop iteration and the loop is currently
5447blocked. Checking for async and signal events involves iterating over all
5448running async watchers or all signal numbers.
5449.SH "PORTING FROM LIBEV 3.X TO 4.X"
5450.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5451The major version 4 introduced some incompatible changes to the \s-1API\s0.
5452.PP
5453At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5454for all changes, so most programs should still compile. The compatibility
5455layer might be removed in later versions of libev, so better update to the
5456new \s-1API\s0 early than late.
5457.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5458.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5459.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5460The backward compatibility mechanism can be controlled by
5461\&\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
5462section.
5463.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5464.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5465.IX Item "ev_default_destroy and ev_default_fork have been removed"
5466These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5467.Sp
5468.Vb 2
5469\& ev_loop_destroy (EV_DEFAULT_UC);
5470\& ev_loop_fork (EV_DEFAULT);
5471.Ve
5472.IP "function/symbol renames" 4
5473.IX Item "function/symbol renames"
5474A number of functions and symbols have been renamed:
5475.Sp
5476.Vb 3
5477\& ev_loop => ev_run
5478\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5479\& EVLOOP_ONESHOT => EVRUN_ONCE
5480\&
5481\& ev_unloop => ev_break
5482\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5483\& EVUNLOOP_ONE => EVBREAK_ONE
5484\& EVUNLOOP_ALL => EVBREAK_ALL
5485\&
5486\& EV_TIMEOUT => EV_TIMER
5487\&
5488\& ev_loop_count => ev_iteration
5489\& ev_loop_depth => ev_depth
5490\& ev_loop_verify => ev_verify
5491.Ve
5492.Sp
5493Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5494\&\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
5495associated constants have been renamed to not collide with the \f(CW\*(C`struct
5496ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5497as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5498\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5499typedef.
5500.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5501.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5502.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5503The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5504mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5505and work, but the library code will of course be larger.
5506.SH "GLOSSARY"
5507.IX Header "GLOSSARY"
5508.IP "active" 4
5509.IX Item "active"
5510A watcher is active as long as it has been started and not yet stopped.
5511See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5512.IP "application" 4
5513.IX Item "application"
5514In this document, an application is whatever is using libev.
5515.IP "backend" 4
5516.IX Item "backend"
5517The part of the code dealing with the operating system interfaces.
5518.IP "callback" 4
5519.IX Item "callback"
5520The address of a function that is called when some event has been
5521detected. Callbacks are being passed the event loop, the watcher that
5522received the event, and the actual event bitset.
5523.IP "callback/watcher invocation" 4
5524.IX Item "callback/watcher invocation"
5525The act of calling the callback associated with a watcher.
5526.IP "event" 4
5527.IX Item "event"
5528A change of state of some external event, such as data now being available
5529for reading on a file descriptor, time having passed or simply not having
5530any other events happening anymore.
5531.Sp
5532In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5533\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5534.IP "event library" 4
5535.IX Item "event library"
5536A software package implementing an event model and loop.
5537.IP "event loop" 4
5538.IX Item "event loop"
5539An entity that handles and processes external events and converts them
5540into callback invocations.
5541.IP "event model" 4
5542.IX Item "event model"
5543The model used to describe how an event loop handles and processes
5544watchers and events.
5545.IP "pending" 4
5546.IX Item "pending"
5547A watcher is pending as soon as the corresponding event has been
5548detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5549.IP "real time" 4
5550.IX Item "real time"
5551The physical time that is observed. It is apparently strictly monotonic :)
5552.IP "wall-clock time" 4
5553.IX Item "wall-clock time"
5554The time and date as shown on clocks. Unlike real time, it can actually
5555be wrong and jump forwards and backwards, e.g. when you adjust your
5556clock.
5557.IP "watcher" 4
5558.IX Item "watcher"
5559A data structure that describes interest in certain events. Watchers need
5560to be started (attached to an event loop) before they can receive events.
2269.SH "AUTHOR" 5561.SH "AUTHOR"
2270.IX Header "AUTHOR" 5562.IX Header "AUTHOR"
2271Marc Lehmann <libev@schmorp.de>. 5563Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5564Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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