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Revision: 1.85
Committed: Tue Jan 11 13:45:28 2011 UTC (13 years, 6 months ago) by root
Branch: MAIN
CVS Tags: rel-4_03
Changes since 1.84: +488 -277 lines
Log Message:
4.03

File Contents

# Content
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123 .rm #[ #] #H #V #F C
124 .\" ========================================================================
125 .\"
126 .IX Title "LIBEV 3"
127 .TH LIBEV 3 "2011-01-11" "libev-4.03" "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
132 .SH "NAME"
133 libev \- a high performance full\-featured event loop written in C
134 .SH "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"
141 .Vb 2
142 \& // a single header file is required
143 \& #include <ev.h>
144 \&
145 \& #include <stdio.h> // for puts
146 \&
147 \& // every watcher type has its own typedef\*(Aqd struct
148 \& // with the name ev_TYPE
149 \& ev_io stdin_watcher;
150 \& ev_timer timeout_watcher;
151 \&
152 \& // all watcher callbacks have a similar signature
153 \& // this callback is called when data is readable on stdin
154 \& static void
155 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 \& {
157 \& puts ("stdin ready");
158 \& // for one\-shot events, one must manually stop the watcher
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);
164 \& }
165 \&
166 \& // another callback, this time for a time\-out
167 \& static void
168 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 \& {
170 \& puts ("timeout");
171 \& // this causes the innermost ev_run to stop iterating
172 \& ev_break (EV_A_ EVBREAK_ONE);
173 \& }
174 \&
175 \& int
176 \& main (void)
177 \& {
178 \& // use the default event loop unless you have special needs
179 \& struct ev_loop *loop = EV_DEFAULT;
180 \&
181 \& // initialise an io watcher, then start it
182 \& // this one will watch for stdin to become readable
183 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184 \& ev_io_start (loop, &stdin_watcher);
185 \&
186 \& // initialise a timer watcher, then start it
187 \& // simple non\-repeating 5.5 second timeout
188 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189 \& ev_timer_start (loop, &timeout_watcher);
190 \&
191 \& // now wait for events to arrive
192 \& ev_run (loop, 0);
193 \&
194 \& // unloop was called, so exit
195 \& return 0;
196 \& }
197 .Ve
198 .SH "ABOUT THIS DOCUMENT"
199 .IX Header "ABOUT THIS DOCUMENT"
200 This document documents the libev software package.
201 .PP
202 The newest version of this document is also available as an html-formatted
203 web page you might find easier to navigate when reading it for the first
204 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205 .PP
206 While this document tries to be as complete as possible in documenting
207 libev, its usage and the rationale behind its design, it is not a tutorial
208 on event-based programming, nor will it introduce event-based programming
209 with libev.
210 .PP
211 Familiarity with event based programming techniques in general is assumed
212 throughout this document.
213 .SH "WHAT TO READ WHEN IN A HURRY"
214 .IX Header "WHAT TO READ WHEN IN A HURRY"
215 This manual tries to be very detailed, but unfortunately, this also makes
216 it very long. If you just want to know the basics of libev, I suggest
217 reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218 look 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"
222 Libev is an event loop: you register interest in certain events (such as a
223 file descriptor being readable or a timeout occurring), and it will manage
224 these event sources and provide your program with events.
225 .PP
226 To do this, it must take more or less complete control over your process
227 (or thread) by executing the \fIevent loop\fR handler, and will then
228 communicate events via a callback mechanism.
229 .PP
230 You register interest in certain events by registering so-called \fIevent
231 watchers\fR, which are relatively small C structures you initialise with the
232 details of the event, and then hand it over to libev by \fIstarting\fR the
233 watcher.
234 .SS "\s-1FEATURES\s0"
235 .IX Subsection "FEATURES"
236 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
237 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
238 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
239 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
240 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
241 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
242 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244 loop 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
246 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247 .PP
248 It also is quite fast (see this
249 <benchmark> comparing it to libevent
250 for example).
251 .SS "\s-1CONVENTIONS\s0"
252 .IX Subsection "CONVENTIONS"
253 Libev is very configurable. In this manual the default (and most common)
254 configuration will be described, which supports multiple event loops. For
255 more info about various configuration options please have a look at
256 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
257 for multiple event loops, then all functions taking an initial argument of
258 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259 this argument.
260 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
261 .IX Subsection "TIME REPRESENTATION"
262 Libev represents time as a single floating point number, representing
263 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
264 somewhere near the beginning of 1970, details are complicated, don't
265 ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
266 too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267 any calculations on it, you should treat it as some floating point value.
268 .PP
269 Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270 time differences (e.g. delays) throughout libev.
271 .SH "ERROR HANDLING"
272 .IX Header "ERROR HANDLING"
273 Libev knows three classes of errors: operating system errors, usage errors
274 and internal errors (bugs).
275 .PP
276 When libev catches an operating system error it cannot handle (for example
277 a system call indicating a condition libev cannot fix), it calls the callback
278 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280 ()\*(C'\fR.
281 .PP
282 When libev detects a usage error such as a negative timer interval, then
283 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285 the libev caller and need to be fixed there.
286 .PP
287 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288 extensive consistency checking code. These do not trigger under normal
289 circumstances, as they indicate either a bug in libev or worse.
290 .SH "GLOBAL FUNCTIONS"
291 .IX Header "GLOBAL FUNCTIONS"
292 These functions can be called anytime, even before initialising the
293 library in any way.
294 .IP "ev_tstamp ev_time ()" 4
295 .IX Item "ev_tstamp ev_time ()"
296 Returns the current time as libev would use it. Please note that the
297 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
298 you actually want to know. Also interesting is the combination of
299 \&\f(CW\*(C`ev_update_now\*(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)"
302 Sleep for the given interval: The current thread will be blocked until
303 either it is interrupted or the given time interval has passed. Basically
304 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
305 .IP "int ev_version_major ()" 4
306 .IX Item "int ev_version_major ()"
307 .PD 0
308 .IP "int ev_version_minor ()" 4
309 .IX Item "int ev_version_minor ()"
310 .PD
311 You can find out the major and minor \s-1ABI\s0 version numbers of the library
312 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
313 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
314 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
315 version of the library your program was compiled against.
316 .Sp
317 These version numbers refer to the \s-1ABI\s0 version of the library, not the
318 release version.
319 .Sp
320 Usually, it's a good idea to terminate if the major versions mismatch,
321 as this indicates an incompatible change. Minor versions are usually
322 compatible to older versions, so a larger minor version alone is usually
323 not a problem.
324 .Sp
325 Example: Make sure we haven't accidentally been linked against the wrong
326 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327 such as \s-1LFS\s0 or reentrancy).
328 .Sp
329 .Vb 3
330 \& assert (("libev version mismatch",
331 \& ev_version_major () == EV_VERSION_MAJOR
332 \& && ev_version_minor () >= EV_VERSION_MINOR));
333 .Ve
334 .IP "unsigned int ev_supported_backends ()" 4
335 .IX Item "unsigned int ev_supported_backends ()"
336 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
337 value) compiled into this binary of libev (independent of their
338 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
339 a description of the set values.
340 .Sp
341 Example: make sure we have the epoll method, because yeah this is cool and
342 a must have and can we have a torrent of it please!!!11
343 .Sp
344 .Vb 2
345 \& assert (("sorry, no epoll, no sex",
346 \& ev_supported_backends () & EVBACKEND_EPOLL));
347 .Ve
348 .IP "unsigned int ev_recommended_backends ()" 4
349 .IX Item "unsigned int ev_recommended_backends ()"
350 Return the set of all backends compiled into this binary of libev and
351 also recommended for this platform, meaning it will work for most file
352 descriptor types. This set is often smaller than the one returned by
353 \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
354 and will not be auto-detected unless you explicitly request it (assuming
355 you know what you are doing). This is the set of backends that libev will
356 probe for if you specify no backends explicitly.
357 .IP "unsigned int ev_embeddable_backends ()" 4
358 .IX Item "unsigned int ev_embeddable_backends ()"
359 Returns the set of backends that are embeddable in other event loops. This
360 value is platform-specific but can include backends not available on the
361 current system. To find which embeddable backends might be supported on
362 the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
363 & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
364 .Sp
365 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
366 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
367 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
368 Sets the allocation function to use (the prototype is similar \- the
369 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
370 used to allocate and free memory (no surprises here). If it returns zero
371 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
372 or take some potentially destructive action.
373 .Sp
374 Since some systems (at least OpenBSD and Darwin) fail to implement
375 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
377 .Sp
378 You could override this function in high-availability programs to, say,
379 free some memory if it cannot allocate memory, to use a special allocator,
380 or even to sleep a while and retry until some memory is available.
381 .Sp
382 Example: Replace the libev allocator with one that waits a bit and then
383 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
384 .Sp
385 .Vb 6
386 \& static void *
387 \& persistent_realloc (void *ptr, size_t size)
388 \& {
389 \& for (;;)
390 \& {
391 \& void *newptr = realloc (ptr, size);
392 \&
393 \& if (newptr)
394 \& return newptr;
395 \&
396 \& sleep (60);
397 \& }
398 \& }
399 \&
400 \& ...
401 \& ev_set_allocator (persistent_realloc);
402 .Ve
403 .IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
404 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
405 Set the callback function to call on a retryable system call error (such
406 as failed select, poll, epoll_wait). The message is a printable string
407 indicating the system call or subsystem causing the problem. If this
408 callback is set, then libev will expect it to remedy the situation, no
409 matter what, when it returns. That is, libev will generally retry the
410 requested operation, or, if the condition doesn't go away, do bad stuff
411 (such as abort).
412 .Sp
413 Example: This is basically the same thing that libev does internally, too.
414 .Sp
415 .Vb 6
416 \& static void
417 \& fatal_error (const char *msg)
418 \& {
419 \& perror (msg);
420 \& abort ();
421 \& }
422 \&
423 \& ...
424 \& ev_set_syserr_cb (fatal_error);
425 .Ve
426 .IP "ev_feed_signal (int signum)" 4
427 .IX Item "ev_feed_signal (int signum)"
428 This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
429 safe to call this function at any time, from any context, including signal
430 handlers or random threads.
431 .Sp
432 Its main use is to customise signal handling in your process, especially
433 in the presence of threads. For example, you could block signals
434 by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
435 creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
436 mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
437 \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
438 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
439 .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
440 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
441 \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
442 libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
443 .PP
444 The library knows two types of such loops, the \fIdefault\fR loop, which
445 supports child process events, and dynamically created event loops which
446 do not.
447 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
448 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
449 This returns the \*(L"default\*(R" event loop object, which is what you should
450 normally use when you just need \*(L"the event loop\*(R". Event loop objects and
451 the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
452 \&\f(CW\*(C`ev_loop_new\*(C'\fR.
453 .Sp
454 If the default loop is already initialised then this function simply
455 returns it (and ignores the flags. If that is troubling you, check
456 \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
457 flags, which should almost always be \f(CW0\fR, unless the caller is also the
458 one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
459 .Sp
460 If you don't know what event loop to use, use the one returned from this
461 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
462 .Sp
463 Note that this function is \fInot\fR thread-safe, so if you want to use it
464 from multiple threads, you have to employ some kind of mutex (note also
465 that this case is unlikely, as loops cannot be shared easily between
466 threads anyway).
467 .Sp
468 The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
469 and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
470 a problem for your application you can either create a dynamic loop with
471 \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
472 \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
473 .Sp
474 Example: This is the most typical usage.
475 .Sp
476 .Vb 2
477 \& if (!ev_default_loop (0))
478 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
479 .Ve
480 .Sp
481 Example: Restrict libev to the select and poll backends, and do not allow
482 environment settings to be taken into account:
483 .Sp
484 .Vb 1
485 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
486 .Ve
487 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
488 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
489 This will create and initialise a new event loop object. If the loop
490 could not be initialised, returns false.
491 .Sp
492 This function is thread-safe, and one common way to use libev with
493 threads is indeed to create one loop per thread, and using the default
494 loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
495 .Sp
496 The flags argument can be used to specify special behaviour or specific
497 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
498 .Sp
499 The following flags are supported:
500 .RS 4
501 .ie n .IP """EVFLAG_AUTO""" 4
502 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
503 .IX Item "EVFLAG_AUTO"
504 The default flags value. Use this if you have no clue (it's the right
505 thing, believe me).
506 .ie n .IP """EVFLAG_NOENV""" 4
507 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
508 .IX Item "EVFLAG_NOENV"
509 If this flag bit is or'ed into the flag value (or the program runs setuid
510 or setgid) then libev will \fInot\fR look at the environment variable
511 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
512 override the flags completely if it is found in the environment. This is
513 useful to try out specific backends to test their performance, or to work
514 around bugs.
515 .ie n .IP """EVFLAG_FORKCHECK""" 4
516 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
517 .IX Item "EVFLAG_FORKCHECK"
518 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
519 make libev check for a fork in each iteration by enabling this flag.
520 .Sp
521 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
522 and thus this might slow down your event loop if you do a lot of loop
523 iterations and little real work, but is usually not noticeable (on my
524 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
525 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
526 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
527 .Sp
528 The big advantage of this flag is that you can forget about fork (and
529 forget about forgetting to tell libev about forking) when you use this
530 flag.
531 .Sp
532 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
533 environment variable.
534 .ie n .IP """EVFLAG_NOINOTIFY""" 4
535 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
536 .IX Item "EVFLAG_NOINOTIFY"
537 When this flag is specified, then libev will not attempt to use the
538 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
539 testing, this flag can be useful to conserve inotify file descriptors, as
540 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
541 .ie n .IP """EVFLAG_SIGNALFD""" 4
542 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
543 .IX Item "EVFLAG_SIGNALFD"
544 When this flag is specified, then libev will attempt to use the
545 \&\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
546 delivers signals synchronously, which makes it both faster and might make
547 it possible to get the queued signal data. It can also simplify signal
548 handling with threads, as long as you properly block signals in your
549 threads that are not interested in handling them.
550 .Sp
551 Signalfd will not be used by default as this changes your signal mask, and
552 there are a lot of shoddy libraries and programs (glib's threadpool for
553 example) that can't properly initialise their signal masks.
554 .ie n .IP """EVFLAG_NOSIGMASK""" 4
555 .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
556 .IX Item "EVFLAG_NOSIGMASK"
557 When this flag is specified, then libev will avoid to modify the signal
558 mask. Specifically, this means you ahve to make sure signals are unblocked
559 when you want to receive them.
560 .Sp
561 This behaviour is useful when you want to do your own signal handling, or
562 want to handle signals only in specific threads and want to avoid libev
563 unblocking the signals.
564 .Sp
565 This flag's behaviour will become the default in future versions of libev.
566 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
567 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
568 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
569 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
570 libev tries to roll its own fd_set with no limits on the number of fds,
571 but if that fails, expect a fairly low limit on the number of fds when
572 using this backend. It doesn't scale too well (O(highest_fd)), but its
573 usually the fastest backend for a low number of (low-numbered :) fds.
574 .Sp
575 To get good performance out of this backend you need a high amount of
576 parallelism (most of the file descriptors should be busy). If you are
577 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
578 connections as possible during one iteration. You might also want to have
579 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
580 readiness notifications you get per iteration.
581 .Sp
582 This 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
583 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
584 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
585 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
586 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
587 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
588 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
589 than select, but handles sparse fds better and has no artificial
590 limit on the number of fds you can use (except it will slow down
591 considerably with a lot of inactive fds). It scales similarly to select,
592 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
593 performance tips.
594 .Sp
595 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
596 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
597 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
598 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
599 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
600 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
601 kernels).
602 .Sp
603 For few fds, this backend is a bit little slower than poll and select,
604 but it scales phenomenally better. While poll and select usually scale
605 like O(total_fds) where n is the total number of fds (or the highest fd),
606 epoll scales either O(1) or O(active_fds).
607 .Sp
608 The epoll mechanism deserves honorable mention as the most misdesigned
609 of the more advanced event mechanisms: mere annoyances include silently
610 dropping file descriptors, requiring a system call per change per file
611 descriptor (and unnecessary guessing of parameters), problems with dup,
612 returning before the timeout value, resulting in additional iterations
613 (and only giving 5ms accuracy while select on the same platform gives
614 0.1ms) and so on. The biggest issue is fork races, however \- if a program
615 forks then \fIboth\fR parent and child process have to recreate the epoll
616 set, which can take considerable time (one syscall per file descriptor)
617 and is of course hard to detect.
618 .Sp
619 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
620 of course \fIdoesn't\fR, and epoll just loves to report events for totally
621 \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
622 even remove them from the set) than registered in the set (especially
623 on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
624 employing an additional generation counter and comparing that against the
625 events to filter out spurious ones, recreating the set when required. Last
626 not least, it also refuses to work with some file descriptors which work
627 perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
628 .Sp
629 Epoll is truly the train wreck analog among event poll mechanisms,
630 a frankenpoll, cobbled together in a hurry, no thought to design or
631 interaction with others.
632 .Sp
633 While stopping, setting and starting an I/O watcher in the same iteration
634 will result in some caching, there is still a system call per such
635 incident (because the same \fIfile descriptor\fR could point to a different
636 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
637 file descriptors might not work very well if you register events for both
638 file descriptors.
639 .Sp
640 Best performance from this backend is achieved by not unregistering all
641 watchers for a file descriptor until it has been closed, if possible,
642 i.e. keep at least one watcher active per fd at all times. Stopping and
643 starting a watcher (without re-setting it) also usually doesn't cause
644 extra overhead. A fork can both result in spurious notifications as well
645 as in libev having to destroy and recreate the epoll object, which can
646 take considerable time and thus should be avoided.
647 .Sp
648 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
649 faster than epoll for maybe up to a hundred file descriptors, depending on
650 the usage. So sad.
651 .Sp
652 While nominally embeddable in other event loops, this feature is broken in
653 all kernel versions tested so far.
654 .Sp
655 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
656 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
657 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
658 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
659 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
660 Kqueue deserves special mention, as at the time of this writing, it
661 was broken on all BSDs except NetBSD (usually it doesn't work reliably
662 with anything but sockets and pipes, except on Darwin, where of course
663 it's completely useless). Unlike epoll, however, whose brokenness
664 is by design, these kqueue bugs can (and eventually will) be fixed
665 without \s-1API\s0 changes to existing programs. For this reason it's not being
666 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
667 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
668 system like NetBSD.
669 .Sp
670 You still can embed kqueue into a normal poll or select backend and use it
671 only for sockets (after having made sure that sockets work with kqueue on
672 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
673 .Sp
674 It scales in the same way as the epoll backend, but the interface to the
675 kernel is more efficient (which says nothing about its actual speed, of
676 course). While stopping, setting and starting an I/O watcher does never
677 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
678 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
679 sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
680 cases
681 .Sp
682 This backend usually performs well under most conditions.
683 .Sp
684 While nominally embeddable in other event loops, this doesn't work
685 everywhere, so you might need to test for this. And since it is broken
686 almost everywhere, you should only use it when you have a lot of sockets
687 (for which it usually works), by embedding it into another event loop
688 (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
689 also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
690 .Sp
691 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
692 \&\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
693 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
694 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
695 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
696 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
697 This is not implemented yet (and might never be, unless you send me an
698 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
699 and is not embeddable, which would limit the usefulness of this backend
700 immensely.
701 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
702 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
703 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
704 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
705 it's really slow, but it still scales very well (O(active_fds)).
706 .Sp
707 While this backend scales well, it requires one system call per active
708 file descriptor per loop iteration. For small and medium numbers of file
709 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
710 might perform better.
711 .Sp
712 On the positive side, this backend actually performed fully to
713 specification in all tests and is fully embeddable, which is a rare feat
714 among the OS-specific backends (I vastly prefer correctness over speed
715 hacks).
716 .Sp
717 On the negative side, the interface is \fIbizarre\fR \- so bizarre that
718 even sun itself gets it wrong in their code examples: The event polling
719 function sometimes returning events to the caller even though an error
720 occurred, but with no indication whether it has done so or not (yes, it's
721 even documented that way) \- deadly for edge-triggered interfaces where
722 you absolutely have to know whether an event occurred or not because you
723 have to re-arm the watcher.
724 .Sp
725 Fortunately libev seems to be able to work around these idiocies.
726 .Sp
727 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
728 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
729 .ie n .IP """EVBACKEND_ALL""" 4
730 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
731 .IX Item "EVBACKEND_ALL"
732 Try all backends (even potentially broken ones that wouldn't be tried
733 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
734 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
735 .Sp
736 It is definitely not recommended to use this flag, use whatever
737 \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
738 at all.
739 .ie n .IP """EVBACKEND_MASK""" 4
740 .el .IP "\f(CWEVBACKEND_MASK\fR" 4
741 .IX Item "EVBACKEND_MASK"
742 Not a backend at all, but a mask to select all backend bits from a
743 \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
744 value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
745 .RE
746 .RS 4
747 .Sp
748 If one or more of the backend flags are or'ed into the flags value,
749 then only these backends will be tried (in the reverse order as listed
750 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
751 ()\*(C'\fR will be tried.
752 .Sp
753 Example: Try to create a event loop that uses epoll and nothing else.
754 .Sp
755 .Vb 3
756 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
757 \& if (!epoller)
758 \& fatal ("no epoll found here, maybe it hides under your chair");
759 .Ve
760 .Sp
761 Example: Use whatever libev has to offer, but make sure that kqueue is
762 used if available.
763 .Sp
764 .Vb 1
765 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
766 .Ve
767 .RE
768 .IP "ev_loop_destroy (loop)" 4
769 .IX Item "ev_loop_destroy (loop)"
770 Destroys an event loop object (frees all memory and kernel state
771 etc.). None of the active event watchers will be stopped in the normal
772 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
773 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
774 calling this function, or cope with the fact afterwards (which is usually
775 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
776 for example).
777 .Sp
778 Note that certain global state, such as signal state (and installed signal
779 handlers), will not be freed by this function, and related watchers (such
780 as signal and child watchers) would need to be stopped manually.
781 .Sp
782 This function is normally used on loop objects allocated by
783 \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
784 \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
785 .Sp
786 Note that it is not advisable to call this function on the default loop
787 except in the rare occasion where you really need to free its resources.
788 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
789 and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
790 .IP "ev_loop_fork (loop)" 4
791 .IX Item "ev_loop_fork (loop)"
792 This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
793 reinitialise the kernel state for backends that have one. Despite the
794 name, you can call it anytime, but it makes most sense after forking, in
795 the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
796 child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
797 .Sp
798 Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
799 a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
800 because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
801 during fork.
802 .Sp
803 On the other hand, you only need to call this function in the child
804 process if and only if you want to use the event loop in the child. If
805 you just fork+exec or create a new loop in the child, you don't have to
806 call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
807 difference, but libev will usually detect this case on its own and do a
808 costly reset of the backend).
809 .Sp
810 The function itself is quite fast and it's usually not a problem to call
811 it just in case after a fork.
812 .Sp
813 Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
814 using pthreads.
815 .Sp
816 .Vb 5
817 \& static void
818 \& post_fork_child (void)
819 \& {
820 \& ev_loop_fork (EV_DEFAULT);
821 \& }
822 \&
823 \& ...
824 \& pthread_atfork (0, 0, post_fork_child);
825 .Ve
826 .IP "int ev_is_default_loop (loop)" 4
827 .IX Item "int ev_is_default_loop (loop)"
828 Returns true when the given loop is, in fact, the default loop, and false
829 otherwise.
830 .IP "unsigned int ev_iteration (loop)" 4
831 .IX Item "unsigned int ev_iteration (loop)"
832 Returns the current iteration count for the event loop, which is identical
833 to the number of times libev did poll for new events. It starts at \f(CW0\fR
834 and happily wraps around with enough iterations.
835 .Sp
836 This value can sometimes be useful as a generation counter of sorts (it
837 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
838 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
839 prepare and check phases.
840 .IP "unsigned int ev_depth (loop)" 4
841 .IX Item "unsigned int ev_depth (loop)"
842 Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
843 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
844 .Sp
845 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
846 \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
847 in which case it is higher.
848 .Sp
849 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
850 throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
851 as a hint to avoid such ungentleman-like behaviour unless it's really
852 convenient, in which case it is fully supported.
853 .IP "unsigned int ev_backend (loop)" 4
854 .IX Item "unsigned int ev_backend (loop)"
855 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
856 use.
857 .IP "ev_tstamp ev_now (loop)" 4
858 .IX Item "ev_tstamp ev_now (loop)"
859 Returns the current \*(L"event loop time\*(R", which is the time the event loop
860 received events and started processing them. This timestamp does not
861 change as long as callbacks are being processed, and this is also the base
862 time used for relative timers. You can treat it as the timestamp of the
863 event occurring (or more correctly, libev finding out about it).
864 .IP "ev_now_update (loop)" 4
865 .IX Item "ev_now_update (loop)"
866 Establishes the current time by querying the kernel, updating the time
867 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
868 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
869 .Sp
870 This function is rarely useful, but when some event callback runs for a
871 very long time without entering the event loop, updating libev's idea of
872 the current time is a good idea.
873 .Sp
874 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
875 .IP "ev_suspend (loop)" 4
876 .IX Item "ev_suspend (loop)"
877 .PD 0
878 .IP "ev_resume (loop)" 4
879 .IX Item "ev_resume (loop)"
880 .PD
881 These two functions suspend and resume an event loop, for use when the
882 loop is not used for a while and timeouts should not be processed.
883 .Sp
884 A typical use case would be an interactive program such as a game: When
885 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
886 would be best to handle timeouts as if no time had actually passed while
887 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
888 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
889 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
890 .Sp
891 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
892 between \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
893 will be rescheduled (that is, they will lose any events that would have
894 occurred while suspended).
895 .Sp
896 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
897 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
898 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
899 .Sp
900 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
901 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
902 .IP "ev_run (loop, int flags)" 4
903 .IX Item "ev_run (loop, int flags)"
904 Finally, this is it, the event handler. This function usually is called
905 after you have initialised all your watchers and you want to start
906 handling events. It will ask the operating system for any new events, call
907 the watcher callbacks, an then repeat the whole process indefinitely: This
908 is why event loops are called \fIloops\fR.
909 .Sp
910 If the flags argument is specified as \f(CW0\fR, it will keep handling events
911 until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
912 called.
913 .Sp
914 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
915 relying on all watchers to be stopped when deciding when a program has
916 finished (especially in interactive programs), but having a program
917 that automatically loops as long as it has to and no longer by virtue
918 of relying on its watchers stopping correctly, that is truly a thing of
919 beauty.
920 .Sp
921 This function is also \fImostly\fR exception-safe \- you can break out of
922 a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
923 exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
924 will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
925 .Sp
926 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
927 those events and any already outstanding ones, but will not wait and
928 block your process in case there are no events and will return after one
929 iteration of the loop. This is sometimes useful to poll and handle new
930 events while doing lengthy calculations, to keep the program responsive.
931 .Sp
932 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
933 necessary) and will handle those and any already outstanding ones. It
934 will block your process until at least one new event arrives (which could
935 be an event internal to libev itself, so there is no guarantee that a
936 user-registered callback will be called), and will return after one
937 iteration of the loop.
938 .Sp
939 This is useful if you are waiting for some external event in conjunction
940 with something not expressible using other libev watchers (i.e. "roll your
941 own \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
942 usually a better approach for this kind of thing.
943 .Sp
944 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
945 .Sp
946 .Vb 10
947 \& \- Increment loop depth.
948 \& \- Reset the ev_break status.
949 \& \- Before the first iteration, call any pending watchers.
950 \& LOOP:
951 \& \- If EVFLAG_FORKCHECK was used, check for a fork.
952 \& \- If a fork was detected (by any means), queue and call all fork watchers.
953 \& \- Queue and call all prepare watchers.
954 \& \- If ev_break was called, goto FINISH.
955 \& \- If we have been forked, detach and recreate the kernel state
956 \& as to not disturb the other process.
957 \& \- Update the kernel state with all outstanding changes.
958 \& \- Update the "event loop time" (ev_now ()).
959 \& \- Calculate for how long to sleep or block, if at all
960 \& (active idle watchers, EVRUN_NOWAIT or not having
961 \& any active watchers at all will result in not sleeping).
962 \& \- Sleep if the I/O and timer collect interval say so.
963 \& \- Increment loop iteration counter.
964 \& \- Block the process, waiting for any events.
965 \& \- Queue all outstanding I/O (fd) events.
966 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
967 \& \- Queue all expired timers.
968 \& \- Queue all expired periodics.
969 \& \- Queue all idle watchers with priority higher than that of pending events.
970 \& \- Queue all check watchers.
971 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
972 \& Signals and child watchers are implemented as I/O watchers, and will
973 \& be handled here by queueing them when their watcher gets executed.
974 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
975 \& were used, or there are no active watchers, goto FINISH, otherwise
976 \& continue with step LOOP.
977 \& FINISH:
978 \& \- Reset the ev_break status iff it was EVBREAK_ONE.
979 \& \- Decrement the loop depth.
980 \& \- Return.
981 .Ve
982 .Sp
983 Example: Queue some jobs and then loop until no events are outstanding
984 anymore.
985 .Sp
986 .Vb 4
987 \& ... queue jobs here, make sure they register event watchers as long
988 \& ... as they still have work to do (even an idle watcher will do..)
989 \& ev_run (my_loop, 0);
990 \& ... jobs done or somebody called unloop. yeah!
991 .Ve
992 .IP "ev_break (loop, how)" 4
993 .IX Item "ev_break (loop, how)"
994 Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
995 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
996 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
997 \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
998 .Sp
999 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1000 .Sp
1001 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1002 which case it will have no effect.
1003 .IP "ev_ref (loop)" 4
1004 .IX Item "ev_ref (loop)"
1005 .PD 0
1006 .IP "ev_unref (loop)" 4
1007 .IX Item "ev_unref (loop)"
1008 .PD
1009 Ref/unref can be used to add or remove a reference count on the event
1010 loop: Every watcher keeps one reference, and as long as the reference
1011 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1012 .Sp
1013 This is useful when you have a watcher that you never intend to
1014 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1015 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1016 before stopping it.
1017 .Sp
1018 As an example, libev itself uses this for its internal signal pipe: It
1019 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1020 exiting if no event watchers registered by it are active. It is also an
1021 excellent way to do this for generic recurring timers or from within
1022 third-party libraries. Just remember to \fIunref after start\fR and \fIref
1023 before stop\fR (but only if the watcher wasn't active before, or was active
1024 before, respectively. Note also that libev might stop watchers itself
1025 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1026 in the callback).
1027 .Sp
1028 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1029 running when nothing else is active.
1030 .Sp
1031 .Vb 4
1032 \& ev_signal exitsig;
1033 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1034 \& ev_signal_start (loop, &exitsig);
1035 \& ev_unref (loop);
1036 .Ve
1037 .Sp
1038 Example: For some weird reason, unregister the above signal handler again.
1039 .Sp
1040 .Vb 2
1041 \& ev_ref (loop);
1042 \& ev_signal_stop (loop, &exitsig);
1043 .Ve
1044 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1045 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1046 .PD 0
1047 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1048 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1049 .PD
1050 These advanced functions influence the time that libev will spend waiting
1051 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1052 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1053 latency.
1054 .Sp
1055 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1056 allows libev to delay invocation of I/O and timer/periodic callbacks
1057 to increase efficiency of loop iterations (or to increase power-saving
1058 opportunities).
1059 .Sp
1060 The idea is that sometimes your program runs just fast enough to handle
1061 one (or very few) event(s) per loop iteration. While this makes the
1062 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1063 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1064 overhead for the actual polling but can deliver many events at once.
1065 .Sp
1066 By setting a higher \fIio collect interval\fR you allow libev to spend more
1067 time collecting I/O events, so you can handle more events per iteration,
1068 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1069 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1070 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1071 sleep time ensures that libev will not poll for I/O events more often then
1072 once per this interval, on average.
1073 .Sp
1074 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1075 to spend more time collecting timeouts, at the expense of increased
1076 latency/jitter/inexactness (the watcher callback will be called
1077 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1078 value will not introduce any overhead in libev.
1079 .Sp
1080 Many (busy) programs can usually benefit by setting the I/O collect
1081 interval to a value near \f(CW0.1\fR or so, which is often enough for
1082 interactive servers (of course not for games), likewise for timeouts. It
1083 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1084 as this approaches the timing granularity of most systems. Note that if
1085 you do transactions with the outside world and you can't increase the
1086 parallelity, then this setting will limit your transaction rate (if you
1087 need to poll once per transaction and the I/O collect interval is 0.01,
1088 then you can't do more than 100 transactions per second).
1089 .Sp
1090 Setting the \fItimeout collect interval\fR can improve the opportunity for
1091 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1092 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1093 times the process sleeps and wakes up again. Another useful technique to
1094 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1095 they fire on, say, one-second boundaries only.
1096 .Sp
1097 Example: we only need 0.1s timeout granularity, and we wish not to poll
1098 more often than 100 times per second:
1099 .Sp
1100 .Vb 2
1101 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1102 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1103 .Ve
1104 .IP "ev_invoke_pending (loop)" 4
1105 .IX Item "ev_invoke_pending (loop)"
1106 This call will simply invoke all pending watchers while resetting their
1107 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1108 but when overriding the invoke callback this call comes handy. This
1109 function can be invoked from a watcher \- this can be useful for example
1110 when you want to do some lengthy calculation and want to pass further
1111 event handling to another thread (you still have to make sure only one
1112 thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1113 .IP "int ev_pending_count (loop)" 4
1114 .IX Item "int ev_pending_count (loop)"
1115 Returns the number of pending watchers \- zero indicates that no watchers
1116 are pending.
1117 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1118 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1119 This overrides the invoke pending functionality of the loop: Instead of
1120 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1121 this callback instead. This is useful, for example, when you want to
1122 invoke the actual watchers inside another context (another thread etc.).
1123 .Sp
1124 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1125 callback.
1126 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1127 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1128 Sometimes you want to share the same loop between multiple threads. This
1129 can be done relatively simply by putting mutex_lock/unlock calls around
1130 each call to a libev function.
1131 .Sp
1132 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1133 to wait for it to return. One way around this is to wake up the event
1134 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1135 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1136 .Sp
1137 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1138 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1139 afterwards.
1140 .Sp
1141 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1142 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1143 .Sp
1144 While event loop modifications are allowed between invocations of
1145 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1146 modifications done will affect the event loop, i.e. adding watchers will
1147 have no effect on the set of file descriptors being watched, or the time
1148 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1149 to take note of any changes you made.
1150 .Sp
1151 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1152 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1153 .Sp
1154 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1155 document.
1156 .IP "ev_set_userdata (loop, void *data)" 4
1157 .IX Item "ev_set_userdata (loop, void *data)"
1158 .PD 0
1159 .IP "void *ev_userdata (loop)" 4
1160 .IX Item "void *ev_userdata (loop)"
1161 .PD
1162 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1163 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1164 \&\f(CW0\fR.
1165 .Sp
1166 These two functions can be used to associate arbitrary data with a loop,
1167 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1168 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1169 any other purpose as well.
1170 .IP "ev_verify (loop)" 4
1171 .IX Item "ev_verify (loop)"
1172 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1173 compiled in, which is the default for non-minimal builds. It tries to go
1174 through all internal structures and checks them for validity. If anything
1175 is found to be inconsistent, it will print an error message to standard
1176 error and call \f(CW\*(C`abort ()\*(C'\fR.
1177 .Sp
1178 This can be used to catch bugs inside libev itself: under normal
1179 circumstances, this function will never abort as of course libev keeps its
1180 data structures consistent.
1181 .SH "ANATOMY OF A WATCHER"
1182 .IX Header "ANATOMY OF A WATCHER"
1183 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1184 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1185 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1186 .PP
1187 A watcher is an opaque structure that you allocate and register to record
1188 your interest in some event. To make a concrete example, imagine you want
1189 to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1190 for that:
1191 .PP
1192 .Vb 5
1193 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1194 \& {
1195 \& ev_io_stop (w);
1196 \& ev_break (loop, EVBREAK_ALL);
1197 \& }
1198 \&
1199 \& struct ev_loop *loop = ev_default_loop (0);
1200 \&
1201 \& ev_io stdin_watcher;
1202 \&
1203 \& ev_init (&stdin_watcher, my_cb);
1204 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1205 \& ev_io_start (loop, &stdin_watcher);
1206 \&
1207 \& ev_run (loop, 0);
1208 .Ve
1209 .PP
1210 As you can see, you are responsible for allocating the memory for your
1211 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1212 stack).
1213 .PP
1214 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1215 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1216 .PP
1217 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1218 *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1219 invoked each time the event occurs (or, in the case of I/O watchers, each
1220 time the event loop detects that the file descriptor given is readable
1221 and/or writable).
1222 .PP
1223 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1224 macro to configure it, with arguments specific to the watcher type. There
1225 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1226 .PP
1227 To make the watcher actually watch out for events, you have to start it
1228 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1229 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1230 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1231 .PP
1232 As long as your watcher is active (has been started but not stopped) you
1233 must not touch the values stored in it. Most specifically you must never
1234 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1235 .PP
1236 Each and every callback receives the event loop pointer as first, the
1237 registered watcher structure as second, and a bitset of received events as
1238 third argument.
1239 .PP
1240 The received events usually include a single bit per event type received
1241 (you can receive multiple events at the same time). The possible bit masks
1242 are:
1243 .ie n .IP """EV_READ""" 4
1244 .el .IP "\f(CWEV_READ\fR" 4
1245 .IX Item "EV_READ"
1246 .PD 0
1247 .ie n .IP """EV_WRITE""" 4
1248 .el .IP "\f(CWEV_WRITE\fR" 4
1249 .IX Item "EV_WRITE"
1250 .PD
1251 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1252 writable.
1253 .ie n .IP """EV_TIMER""" 4
1254 .el .IP "\f(CWEV_TIMER\fR" 4
1255 .IX Item "EV_TIMER"
1256 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1257 .ie n .IP """EV_PERIODIC""" 4
1258 .el .IP "\f(CWEV_PERIODIC\fR" 4
1259 .IX Item "EV_PERIODIC"
1260 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1261 .ie n .IP """EV_SIGNAL""" 4
1262 .el .IP "\f(CWEV_SIGNAL\fR" 4
1263 .IX Item "EV_SIGNAL"
1264 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1265 .ie n .IP """EV_CHILD""" 4
1266 .el .IP "\f(CWEV_CHILD\fR" 4
1267 .IX Item "EV_CHILD"
1268 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1269 .ie n .IP """EV_STAT""" 4
1270 .el .IP "\f(CWEV_STAT\fR" 4
1271 .IX Item "EV_STAT"
1272 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1273 .ie n .IP """EV_IDLE""" 4
1274 .el .IP "\f(CWEV_IDLE\fR" 4
1275 .IX Item "EV_IDLE"
1276 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1277 .ie n .IP """EV_PREPARE""" 4
1278 .el .IP "\f(CWEV_PREPARE\fR" 4
1279 .IX Item "EV_PREPARE"
1280 .PD 0
1281 .ie n .IP """EV_CHECK""" 4
1282 .el .IP "\f(CWEV_CHECK\fR" 4
1283 .IX Item "EV_CHECK"
1284 .PD
1285 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
1286 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1287 \&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
1288 received events. Callbacks of both watcher types can start and stop as
1289 many watchers as they want, and all of them will be taken into account
1290 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1291 \&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1292 .ie n .IP """EV_EMBED""" 4
1293 .el .IP "\f(CWEV_EMBED\fR" 4
1294 .IX Item "EV_EMBED"
1295 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1296 .ie n .IP """EV_FORK""" 4
1297 .el .IP "\f(CWEV_FORK\fR" 4
1298 .IX Item "EV_FORK"
1299 The event loop has been resumed in the child process after fork (see
1300 \&\f(CW\*(C`ev_fork\*(C'\fR).
1301 .ie n .IP """EV_CLEANUP""" 4
1302 .el .IP "\f(CWEV_CLEANUP\fR" 4
1303 .IX Item "EV_CLEANUP"
1304 The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1305 .ie n .IP """EV_ASYNC""" 4
1306 .el .IP "\f(CWEV_ASYNC\fR" 4
1307 .IX Item "EV_ASYNC"
1308 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1309 .ie n .IP """EV_CUSTOM""" 4
1310 .el .IP "\f(CWEV_CUSTOM\fR" 4
1311 .IX Item "EV_CUSTOM"
1312 Not ever sent (or otherwise used) by libev itself, but can be freely used
1313 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1314 .ie n .IP """EV_ERROR""" 4
1315 .el .IP "\f(CWEV_ERROR\fR" 4
1316 .IX Item "EV_ERROR"
1317 An unspecified error has occurred, the watcher has been stopped. This might
1318 happen because the watcher could not be properly started because libev
1319 ran out of memory, a file descriptor was found to be closed or any other
1320 problem. Libev considers these application bugs.
1321 .Sp
1322 You best act on it by reporting the problem and somehow coping with the
1323 watcher being stopped. Note that well-written programs should not receive
1324 an error ever, so when your watcher receives it, this usually indicates a
1325 bug in your program.
1326 .Sp
1327 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1328 example it might indicate that a fd is readable or writable, and if your
1329 callbacks is well-written it can just attempt the operation and cope with
1330 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1331 programs, though, as the fd could already be closed and reused for another
1332 thing, so beware.
1333 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1334 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1335 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1336 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1337 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1338 This macro initialises the generic portion of a watcher. The contents
1339 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1340 the generic parts of the watcher are initialised, you \fIneed\fR to call
1341 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1342 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1343 which rolls both calls into one.
1344 .Sp
1345 You can reinitialise a watcher at any time as long as it has been stopped
1346 (or never started) and there are no pending events outstanding.
1347 .Sp
1348 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1349 int revents)\*(C'\fR.
1350 .Sp
1351 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1352 .Sp
1353 .Vb 3
1354 \& ev_io w;
1355 \& ev_init (&w, my_cb);
1356 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1357 .Ve
1358 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1359 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1360 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1361 This macro initialises the type-specific parts of a watcher. You need to
1362 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1363 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1364 macro on a watcher that is active (it can be pending, however, which is a
1365 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1366 .Sp
1367 Although some watcher types do not have type-specific arguments
1368 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1369 .Sp
1370 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1371 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1372 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1373 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1374 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1375 calls into a single call. This is the most convenient method to initialise
1376 a watcher. The same limitations apply, of course.
1377 .Sp
1378 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1379 .Sp
1380 .Vb 1
1381 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1382 .Ve
1383 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1384 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1385 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1386 Starts (activates) the given watcher. Only active watchers will receive
1387 events. If the watcher is already active nothing will happen.
1388 .Sp
1389 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1390 whole section.
1391 .Sp
1392 .Vb 1
1393 \& ev_io_start (EV_DEFAULT_UC, &w);
1394 .Ve
1395 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1396 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1397 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1398 Stops the given watcher if active, and clears the pending status (whether
1399 the watcher was active or not).
1400 .Sp
1401 It is possible that stopped watchers are pending \- for example,
1402 non-repeating timers are being stopped when they become pending \- but
1403 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1404 pending. If you want to free or reuse the memory used by the watcher it is
1405 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1406 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1407 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1408 Returns a true value iff the watcher is active (i.e. it has been started
1409 and not yet been stopped). As long as a watcher is active you must not modify
1410 it.
1411 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1412 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1413 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1414 events but its callback has not yet been invoked). As long as a watcher
1415 is pending (but not active) you must not call an init function on it (but
1416 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1417 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1418 it).
1419 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1420 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1421 Returns the callback currently set on the watcher.
1422 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1423 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1424 Change the callback. You can change the callback at virtually any time
1425 (modulo threads).
1426 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1427 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1428 .PD 0
1429 .IP "int ev_priority (ev_TYPE *watcher)" 4
1430 .IX Item "int ev_priority (ev_TYPE *watcher)"
1431 .PD
1432 Set and query the priority of the watcher. The priority is a small
1433 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1434 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1435 before watchers with lower priority, but priority will not keep watchers
1436 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1437 .Sp
1438 If you need to suppress invocation when higher priority events are pending
1439 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1440 .Sp
1441 You \fImust not\fR change the priority of a watcher as long as it is active or
1442 pending.
1443 .Sp
1444 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1445 fine, as long as you do not mind that the priority value you query might
1446 or might not have been clamped to the valid range.
1447 .Sp
1448 The default priority used by watchers when no priority has been set is
1449 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1450 .Sp
1451 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1452 priorities.
1453 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1454 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1455 Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1456 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1457 can deal with that fact, as both are simply passed through to the
1458 callback.
1459 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1460 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1461 If the watcher is pending, this function clears its pending status and
1462 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1463 watcher isn't pending it does nothing and returns \f(CW0\fR.
1464 .Sp
1465 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1466 callback to be invoked, which can be accomplished with this function.
1467 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1468 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1469 Feeds the given event set into the event loop, as if the specified event
1470 had happened for the specified watcher (which must be a pointer to an
1471 initialised but not necessarily started event watcher). Obviously you must
1472 not free the watcher as long as it has pending events.
1473 .Sp
1474 Stopping the watcher, letting libev invoke it, or calling
1475 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1476 not started in the first place.
1477 .Sp
1478 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1479 functions that do not need a watcher.
1480 .PP
1481 See 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
1482 \&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1483 .SS "\s-1WATCHER\s0 \s-1STATES\s0"
1484 .IX Subsection "WATCHER STATES"
1485 There are various watcher states mentioned throughout this manual \-
1486 active, pending and so on. In this section these states and the rules to
1487 transition between them will be described in more detail \- and while these
1488 rules might look complicated, they usually do \*(L"the right thing\*(R".
1489 .IP "initialiased" 4
1490 .IX Item "initialiased"
1491 Before a watcher can be registered with the event looop it has to be
1492 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1493 \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1494 .Sp
1495 In this state it is simply some block of memory that is suitable for use
1496 in an event loop. It can be moved around, freed, reused etc. at will.
1497 .IP "started/running/active" 4
1498 .IX Item "started/running/active"
1499 Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1500 property of the event loop, and is actively waiting for events. While in
1501 this state it cannot be accessed (except in a few documented ways), moved,
1502 freed or anything else \- the only legal thing is to keep a pointer to it,
1503 and call libev functions on it that are documented to work on active watchers.
1504 .IP "pending" 4
1505 .IX Item "pending"
1506 If a watcher is active and libev determines that an event it is interested
1507 in has occurred (such as a timer expiring), it will become pending. It will
1508 stay in this pending state until either it is stopped or its callback is
1509 about to be invoked, so it is not normally pending inside the watcher
1510 callback.
1511 .Sp
1512 The watcher might or might not be active while it is pending (for example,
1513 an expired non-repeating timer can be pending but no longer active). If it
1514 is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1515 but it is still property of the event loop at this time, so cannot be
1516 moved, freed or reused. And if it is active the rules described in the
1517 previous item still apply.
1518 .Sp
1519 It is also possible to feed an event on a watcher that is not active (e.g.
1520 via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1521 active.
1522 .IP "stopped" 4
1523 .IX Item "stopped"
1524 A watcher can be stopped implicitly by libev (in which case it might still
1525 be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1526 latter will clear any pending state the watcher might be in, regardless
1527 of whether it was active or not, so stopping a watcher explicitly before
1528 freeing it is often a good idea.
1529 .Sp
1530 While stopped (and not pending) the watcher is essentially in the
1531 initialised state, that is it can be reused, moved, modified in any way
1532 you wish.
1533 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1534 .IX Subsection "WATCHER PRIORITY MODELS"
1535 Many event loops support \fIwatcher priorities\fR, which are usually small
1536 integers that influence the ordering of event callback invocation
1537 between watchers in some way, all else being equal.
1538 .PP
1539 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1540 description for the more technical details such as the actual priority
1541 range.
1542 .PP
1543 There are two common ways how these these priorities are being interpreted
1544 by event loops:
1545 .PP
1546 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1547 of lower priority watchers, which means as long as higher priority
1548 watchers receive events, lower priority watchers are not being invoked.
1549 .PP
1550 The less common only-for-ordering model uses priorities solely to order
1551 callback invocation within a single event loop iteration: Higher priority
1552 watchers are invoked before lower priority ones, but they all get invoked
1553 before polling for new events.
1554 .PP
1555 Libev uses the second (only-for-ordering) model for all its watchers
1556 except for idle watchers (which use the lock-out model).
1557 .PP
1558 The rationale behind this is that implementing the lock-out model for
1559 watchers is not well supported by most kernel interfaces, and most event
1560 libraries will just poll for the same events again and again as long as
1561 their callbacks have not been executed, which is very inefficient in the
1562 common case of one high-priority watcher locking out a mass of lower
1563 priority ones.
1564 .PP
1565 Static (ordering) priorities are most useful when you have two or more
1566 watchers handling the same resource: a typical usage example is having an
1567 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1568 timeouts. Under load, data might be received while the program handles
1569 other jobs, but since timers normally get invoked first, the timeout
1570 handler will be executed before checking for data. In that case, giving
1571 the timer a lower priority than the I/O watcher ensures that I/O will be
1572 handled first even under adverse conditions (which is usually, but not
1573 always, what you want).
1574 .PP
1575 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1576 will only be executed when no same or higher priority watchers have
1577 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1578 required.
1579 .PP
1580 For example, to emulate how many other event libraries handle priorities,
1581 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1582 the normal watcher callback, you just start the idle watcher. The real
1583 processing is done in the idle watcher callback. This causes libev to
1584 continuously poll and process kernel event data for the watcher, but when
1585 the lock-out case is known to be rare (which in turn is rare :), this is
1586 workable.
1587 .PP
1588 Usually, however, the lock-out model implemented that way will perform
1589 miserably under the type of load it was designed to handle. In that case,
1590 it might be preferable to stop the real watcher before starting the
1591 idle watcher, so the kernel will not have to process the event in case
1592 the actual processing will be delayed for considerable time.
1593 .PP
1594 Here is an example of an I/O watcher that should run at a strictly lower
1595 priority than the default, and which should only process data when no
1596 other events are pending:
1597 .PP
1598 .Vb 2
1599 \& ev_idle idle; // actual processing watcher
1600 \& ev_io io; // actual event watcher
1601 \&
1602 \& static void
1603 \& io_cb (EV_P_ ev_io *w, int revents)
1604 \& {
1605 \& // stop the I/O watcher, we received the event, but
1606 \& // are not yet ready to handle it.
1607 \& ev_io_stop (EV_A_ w);
1608 \&
1609 \& // start the idle watcher to handle the actual event.
1610 \& // it will not be executed as long as other watchers
1611 \& // with the default priority are receiving events.
1612 \& ev_idle_start (EV_A_ &idle);
1613 \& }
1614 \&
1615 \& static void
1616 \& idle_cb (EV_P_ ev_idle *w, int revents)
1617 \& {
1618 \& // actual processing
1619 \& read (STDIN_FILENO, ...);
1620 \&
1621 \& // have to start the I/O watcher again, as
1622 \& // we have handled the event
1623 \& ev_io_start (EV_P_ &io);
1624 \& }
1625 \&
1626 \& // initialisation
1627 \& ev_idle_init (&idle, idle_cb);
1628 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1629 \& ev_io_start (EV_DEFAULT_ &io);
1630 .Ve
1631 .PP
1632 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1633 low-priority connections can not be locked out forever under load. This
1634 enables your program to keep a lower latency for important connections
1635 during short periods of high load, while not completely locking out less
1636 important ones.
1637 .SH "WATCHER TYPES"
1638 .IX Header "WATCHER TYPES"
1639 This section describes each watcher in detail, but will not repeat
1640 information given in the last section. Any initialisation/set macros,
1641 functions and members specific to the watcher type are explained.
1642 .PP
1643 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1644 while the watcher is active, you can look at the member and expect some
1645 sensible content, but you must not modify it (you can modify it while the
1646 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1647 means you can expect it to have some sensible content while the watcher
1648 is active, but you can also modify it. Modifying it may not do something
1649 sensible or take immediate effect (or do anything at all), but libev will
1650 not crash or malfunction in any way.
1651 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1652 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1653 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1654 I/O watchers check whether a file descriptor is readable or writable
1655 in each iteration of the event loop, or, more precisely, when reading
1656 would not block the process and writing would at least be able to write
1657 some data. This behaviour is called level-triggering because you keep
1658 receiving events as long as the condition persists. Remember you can stop
1659 the watcher if you don't want to act on the event and neither want to
1660 receive future events.
1661 .PP
1662 In general you can register as many read and/or write event watchers per
1663 fd as you want (as long as you don't confuse yourself). Setting all file
1664 descriptors to non-blocking mode is also usually a good idea (but not
1665 required if you know what you are doing).
1666 .PP
1667 Another thing you have to watch out for is that it is quite easy to
1668 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1669 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1670 because there is no data. It is very easy to get into this situation even
1671 with a relatively standard program structure. Thus it is best to always
1672 use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1673 preferable to a program hanging until some data arrives.
1674 .PP
1675 If you cannot run the fd in non-blocking mode (for example you should
1676 not play around with an Xlib connection), then you have to separately
1677 re-test whether a file descriptor is really ready with a known-to-be good
1678 interface such as poll (fortunately in the case of Xlib, it already does
1679 this on its own, so its quite safe to use). Some people additionally
1680 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1681 indefinitely.
1682 .PP
1683 But really, best use non-blocking mode.
1684 .PP
1685 \fIThe special problem of disappearing file descriptors\fR
1686 .IX Subsection "The special problem of disappearing file descriptors"
1687 .PP
1688 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1689 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1690 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1691 descriptor, but when it goes away, the operating system will silently drop
1692 this interest. If another file descriptor with the same number then is
1693 registered with libev, there is no efficient way to see that this is, in
1694 fact, a different file descriptor.
1695 .PP
1696 To avoid having to explicitly tell libev about such cases, libev follows
1697 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1698 will assume that this is potentially a new file descriptor, otherwise
1699 it is assumed that the file descriptor stays the same. That means that
1700 you \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
1701 descriptor even if the file descriptor number itself did not change.
1702 .PP
1703 This is how one would do it normally anyway, the important point is that
1704 the libev application should not optimise around libev but should leave
1705 optimisations to libev.
1706 .PP
1707 \fIThe special problem of dup'ed file descriptors\fR
1708 .IX Subsection "The special problem of dup'ed file descriptors"
1709 .PP
1710 Some backends (e.g. epoll), cannot register events for file descriptors,
1711 but only events for the underlying file descriptions. That means when you
1712 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1713 events for them, only one file descriptor might actually receive events.
1714 .PP
1715 There is no workaround possible except not registering events
1716 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1717 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1718 .PP
1719 \fIThe special problem of files\fR
1720 .IX Subsection "The special problem of files"
1721 .PP
1722 Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1723 representing files, and expect it to become ready when their program
1724 doesn't block on disk accesses (which can take a long time on their own).
1725 .PP
1726 However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1727 notification as soon as the kernel knows whether and how much data is
1728 there, and in the case of open files, that's always the case, so you
1729 always get a readiness notification instantly, and your read (or possibly
1730 write) will still block on the disk I/O.
1731 .PP
1732 Another way to view it is that in the case of sockets, pipes, character
1733 devices and so on, there is another party (the sender) that delivers data
1734 on its own, but in the case of files, there is no such thing: the disk
1735 will not send data on its own, simply because it doesn't know what you
1736 wish to read \- you would first have to request some data.
1737 .PP
1738 Since files are typically not-so-well supported by advanced notification
1739 mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1740 to files, even though you should not use it. The reason for this is
1741 convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1742 usually a tty, often a pipe, but also sometimes files or special devices
1743 (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1744 \&\fI/dev/urandom\fR), and even though the file might better be served with
1745 asynchronous I/O instead of with non-blocking I/O, it is still useful when
1746 it \*(L"just works\*(R" instead of freezing.
1747 .PP
1748 So avoid file descriptors pointing to files when you know it (e.g. use
1749 libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1750 when you rarely read from a file instead of from a socket, and want to
1751 reuse the same code path.
1752 .PP
1753 \fIThe special problem of fork\fR
1754 .IX Subsection "The special problem of fork"
1755 .PP
1756 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1757 useless behaviour. Libev fully supports fork, but needs to be told about
1758 it in the child if you want to continue to use it in the child.
1759 .PP
1760 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1761 ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1762 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1763 .PP
1764 \fIThe special problem of \s-1SIGPIPE\s0\fR
1765 .IX Subsection "The special problem of SIGPIPE"
1766 .PP
1767 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1768 when writing to a pipe whose other end has been closed, your program gets
1769 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1770 this is sensible behaviour, for daemons, this is usually undesirable.
1771 .PP
1772 So when you encounter spurious, unexplained daemon exits, make sure you
1773 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1774 somewhere, as that would have given you a big clue).
1775 .PP
1776 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1777 .IX Subsection "The special problem of accept()ing when you can't"
1778 .PP
1779 Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1780 found in post\-2004 Linux) have the peculiar behaviour of not removing a
1781 connection from the pending queue in all error cases.
1782 .PP
1783 For example, larger servers often run out of file descriptors (because
1784 of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1785 rejecting the connection, leading to libev signalling readiness on
1786 the next iteration again (the connection still exists after all), and
1787 typically causing the program to loop at 100% \s-1CPU\s0 usage.
1788 .PP
1789 Unfortunately, the set of errors that cause this issue differs between
1790 operating systems, there is usually little the app can do to remedy the
1791 situation, and no known thread-safe method of removing the connection to
1792 cope with overload is known (to me).
1793 .PP
1794 One of the easiest ways to handle this situation is to just ignore it
1795 \&\- when the program encounters an overload, it will just loop until the
1796 situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1797 event-based way to handle this situation, so it's the best one can do.
1798 .PP
1799 A better way to handle the situation is to log any errors other than
1800 \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1801 messages, and continue as usual, which at least gives the user an idea of
1802 what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1803 the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1804 usage.
1805 .PP
1806 If your program is single-threaded, then you could also keep a dummy file
1807 descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1808 when 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,
1809 close that fd, and create a new dummy fd. This will gracefully refuse
1810 clients under typical overload conditions.
1811 .PP
1812 The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1813 is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1814 opportunity for a DoS attack.
1815 .PP
1816 \fIWatcher-Specific Functions\fR
1817 .IX Subsection "Watcher-Specific Functions"
1818 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1819 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1820 .PD 0
1821 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1822 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1823 .PD
1824 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1825 receive 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
1826 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1827 .IP "int fd [read\-only]" 4
1828 .IX Item "int fd [read-only]"
1829 The file descriptor being watched.
1830 .IP "int events [read\-only]" 4
1831 .IX Item "int events [read-only]"
1832 The events being watched.
1833 .PP
1834 \fIExamples\fR
1835 .IX Subsection "Examples"
1836 .PP
1837 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1838 readable, but only once. Since it is likely line-buffered, you could
1839 attempt to read a whole line in the callback.
1840 .PP
1841 .Vb 6
1842 \& static void
1843 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1844 \& {
1845 \& ev_io_stop (loop, w);
1846 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1847 \& }
1848 \&
1849 \& ...
1850 \& struct ev_loop *loop = ev_default_init (0);
1851 \& ev_io stdin_readable;
1852 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1853 \& ev_io_start (loop, &stdin_readable);
1854 \& ev_run (loop, 0);
1855 .Ve
1856 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1857 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1858 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1859 Timer watchers are simple relative timers that generate an event after a
1860 given time, and optionally repeating in regular intervals after that.
1861 .PP
1862 The timers are based on real time, that is, if you register an event that
1863 times out after an hour and you reset your system clock to January last
1864 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1865 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1866 monotonic clock option helps a lot here).
1867 .PP
1868 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1869 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1870 might introduce a small delay). If multiple timers become ready during the
1871 same loop iteration then the ones with earlier time-out values are invoked
1872 before ones of the same priority with later time-out values (but this is
1873 no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1874 .PP
1875 \fIBe smart about timeouts\fR
1876 .IX Subsection "Be smart about timeouts"
1877 .PP
1878 Many real-world problems involve some kind of timeout, usually for error
1879 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1880 you want to raise some error after a while.
1881 .PP
1882 What follows are some ways to handle this problem, from obvious and
1883 inefficient to smart and efficient.
1884 .PP
1885 In the following, a 60 second activity timeout is assumed \- a timeout that
1886 gets reset to 60 seconds each time there is activity (e.g. each time some
1887 data or other life sign was received).
1888 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1889 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1890 This is the most obvious, but not the most simple way: In the beginning,
1891 start the watcher:
1892 .Sp
1893 .Vb 2
1894 \& ev_timer_init (timer, callback, 60., 0.);
1895 \& ev_timer_start (loop, timer);
1896 .Ve
1897 .Sp
1898 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1899 and start it again:
1900 .Sp
1901 .Vb 3
1902 \& ev_timer_stop (loop, timer);
1903 \& ev_timer_set (timer, 60., 0.);
1904 \& ev_timer_start (loop, timer);
1905 .Ve
1906 .Sp
1907 This is relatively simple to implement, but means that each time there is
1908 some activity, libev will first have to remove the timer from its internal
1909 data structure and then add it again. Libev tries to be fast, but it's
1910 still not a constant-time operation.
1911 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1912 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1913 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1914 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1915 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1916 .Sp
1917 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1918 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1919 successfully read or write some data. If you go into an idle state where
1920 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1921 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1922 .Sp
1923 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1924 \&\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
1925 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1926 .Sp
1927 At start:
1928 .Sp
1929 .Vb 3
1930 \& ev_init (timer, callback);
1931 \& timer\->repeat = 60.;
1932 \& ev_timer_again (loop, timer);
1933 .Ve
1934 .Sp
1935 Each time there is some activity:
1936 .Sp
1937 .Vb 1
1938 \& ev_timer_again (loop, timer);
1939 .Ve
1940 .Sp
1941 It is even possible to change the time-out on the fly, regardless of
1942 whether the watcher is active or not:
1943 .Sp
1944 .Vb 2
1945 \& timer\->repeat = 30.;
1946 \& ev_timer_again (loop, timer);
1947 .Ve
1948 .Sp
1949 This is slightly more efficient then stopping/starting the timer each time
1950 you want to modify its timeout value, as libev does not have to completely
1951 remove and re-insert the timer from/into its internal data structure.
1952 .Sp
1953 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1954 .IP "3. Let the timer time out, but then re-arm it as required." 4
1955 .IX Item "3. Let the timer time out, but then re-arm it as required."
1956 This method is more tricky, but usually most efficient: Most timeouts are
1957 relatively long compared to the intervals between other activity \- in
1958 our example, within 60 seconds, there are usually many I/O events with
1959 associated activity resets.
1960 .Sp
1961 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1962 but remember the time of last activity, and check for a real timeout only
1963 within the callback:
1964 .Sp
1965 .Vb 1
1966 \& ev_tstamp last_activity; // time of last activity
1967 \&
1968 \& static void
1969 \& callback (EV_P_ ev_timer *w, int revents)
1970 \& {
1971 \& ev_tstamp now = ev_now (EV_A);
1972 \& ev_tstamp timeout = last_activity + 60.;
1973 \&
1974 \& // if last_activity + 60. is older than now, we did time out
1975 \& if (timeout < now)
1976 \& {
1977 \& // timeout occurred, take action
1978 \& }
1979 \& else
1980 \& {
1981 \& // callback was invoked, but there was some activity, re\-arm
1982 \& // the watcher to fire in last_activity + 60, which is
1983 \& // guaranteed to be in the future, so "again" is positive:
1984 \& w\->repeat = timeout \- now;
1985 \& ev_timer_again (EV_A_ w);
1986 \& }
1987 \& }
1988 .Ve
1989 .Sp
1990 To summarise the callback: first calculate the real timeout (defined
1991 as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1992 been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1993 the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1994 re-schedule the timer to fire at that future time, to see if maybe we have
1995 a timeout then.
1996 .Sp
1997 Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1998 \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1999 .Sp
2000 This scheme causes more callback invocations (about one every 60 seconds
2001 minus half the average time between activity), but virtually no calls to
2002 libev to change the timeout.
2003 .Sp
2004 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
2005 to the current time (meaning we just have some activity :), then call the
2006 callback, which will \*(L"do the right thing\*(R" and start the timer:
2007 .Sp
2008 .Vb 3
2009 \& ev_init (timer, callback);
2010 \& last_activity = ev_now (loop);
2011 \& callback (loop, timer, EV_TIMER);
2012 .Ve
2013 .Sp
2014 And when there is some activity, simply store the current time in
2015 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2016 .Sp
2017 .Vb 1
2018 \& last_activity = ev_now (loop);
2019 .Ve
2020 .Sp
2021 This technique is slightly more complex, but in most cases where the
2022 time-out is unlikely to be triggered, much more efficient.
2023 .Sp
2024 Changing the timeout is trivial as well (if it isn't hard-coded in the
2025 callback :) \- just change the timeout and invoke the callback, which will
2026 fix things for you.
2027 .IP "4. Wee, just use a double-linked list for your timeouts." 4
2028 .IX Item "4. Wee, just use a double-linked list for your timeouts."
2029 If there is not one request, but many thousands (millions...), all
2030 employing some kind of timeout with the same timeout value, then one can
2031 do even better:
2032 .Sp
2033 When starting the timeout, calculate the timeout value and put the timeout
2034 at the \fIend\fR of the list.
2035 .Sp
2036 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2037 the list is expected to fire (for example, using the technique #3).
2038 .Sp
2039 When there is some activity, remove the timer from the list, recalculate
2040 the timeout, append it to the end of the list again, and make sure to
2041 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2042 .Sp
2043 This way, one can manage an unlimited number of timeouts in O(1) time for
2044 starting, stopping and updating the timers, at the expense of a major
2045 complication, and having to use a constant timeout. The constant timeout
2046 ensures that the list stays sorted.
2047 .PP
2048 So which method the best?
2049 .PP
2050 Method #2 is a simple no-brain-required solution that is adequate in most
2051 situations. Method #3 requires a bit more thinking, but handles many cases
2052 better, and isn't very complicated either. In most case, choosing either
2053 one is fine, with #3 being better in typical situations.
2054 .PP
2055 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2056 rather complicated, but extremely efficient, something that really pays
2057 off after the first million or so of active timers, i.e. it's usually
2058 overkill :)
2059 .PP
2060 \fIThe special problem of time updates\fR
2061 .IX Subsection "The special problem of time updates"
2062 .PP
2063 Establishing the current time is a costly operation (it usually takes at
2064 least two system calls): \s-1EV\s0 therefore updates its idea of the current
2065 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2066 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2067 lots of events in one iteration.
2068 .PP
2069 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2070 time. This is usually the right thing as this timestamp refers to the time
2071 of the event triggering whatever timeout you are modifying/starting. If
2072 you suspect event processing to be delayed and you \fIneed\fR to base the
2073 timeout on the current time, use something like this to adjust for this:
2074 .PP
2075 .Vb 1
2076 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
2077 .Ve
2078 .PP
2079 If the event loop is suspended for a long time, you can also force an
2080 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2081 ()\*(C'\fR.
2082 .PP
2083 \fIThe special problems of suspended animation\fR
2084 .IX Subsection "The special problems of suspended animation"
2085 .PP
2086 When you leave the server world it is quite customary to hit machines that
2087 can suspend/hibernate \- what happens to the clocks during such a suspend?
2088 .PP
2089 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2090 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2091 to run until the system is suspended, but they will not advance while the
2092 system is suspended. That means, on resume, it will be as if the program
2093 was frozen for a few seconds, but the suspend time will not be counted
2094 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2095 clock advanced as expected, but if it is used as sole clocksource, then a
2096 long suspend would be detected as a time jump by libev, and timers would
2097 be adjusted accordingly.
2098 .PP
2099 I would not be surprised to see different behaviour in different between
2100 operating systems, \s-1OS\s0 versions or even different hardware.
2101 .PP
2102 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2103 time jump in the monotonic clocks and the realtime clock. If the program
2104 is suspended for a very long time, and monotonic clock sources are in use,
2105 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2106 will be counted towards the timers. When no monotonic clock source is in
2107 use, then libev will again assume a timejump and adjust accordingly.
2108 .PP
2109 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2110 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2111 deterministic behaviour in this case (you can do nothing against
2112 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2113 .PP
2114 \fIWatcher-Specific Functions and Data Members\fR
2115 .IX Subsection "Watcher-Specific Functions and Data Members"
2116 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2117 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2118 .PD 0
2119 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2120 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2121 .PD
2122 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2123 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2124 reached. If it is positive, then the timer will automatically be
2125 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2126 until stopped manually.
2127 .Sp
2128 The timer itself will do a best-effort at avoiding drift, that is, if
2129 you configure a timer to trigger every 10 seconds, then it will normally
2130 trigger at exactly 10 second intervals. If, however, your program cannot
2131 keep up with the timer (because it takes longer than those 10 seconds to
2132 do stuff) the timer will not fire more than once per event loop iteration.
2133 .IP "ev_timer_again (loop, ev_timer *)" 4
2134 .IX Item "ev_timer_again (loop, ev_timer *)"
2135 This will act as if the timer timed out and restart it again if it is
2136 repeating. The exact semantics are:
2137 .Sp
2138 If the timer is pending, its pending status is cleared.
2139 .Sp
2140 If the timer is started but non-repeating, stop it (as if it timed out).
2141 .Sp
2142 If the timer is repeating, either start it if necessary (with the
2143 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
2144 .Sp
2145 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2146 usage example.
2147 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2148 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2149 Returns the remaining time until a timer fires. If the timer is active,
2150 then this time is relative to the current event loop time, otherwise it's
2151 the timeout value currently configured.
2152 .Sp
2153 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2154 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2155 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2156 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2157 too), and so on.
2158 .IP "ev_tstamp repeat [read\-write]" 4
2159 .IX Item "ev_tstamp repeat [read-write]"
2160 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2161 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2162 which is also when any modifications are taken into account.
2163 .PP
2164 \fIExamples\fR
2165 .IX Subsection "Examples"
2166 .PP
2167 Example: Create a timer that fires after 60 seconds.
2168 .PP
2169 .Vb 5
2170 \& static void
2171 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2172 \& {
2173 \& .. one minute over, w is actually stopped right here
2174 \& }
2175 \&
2176 \& ev_timer mytimer;
2177 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2178 \& ev_timer_start (loop, &mytimer);
2179 .Ve
2180 .PP
2181 Example: Create a timeout timer that times out after 10 seconds of
2182 inactivity.
2183 .PP
2184 .Vb 5
2185 \& static void
2186 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2187 \& {
2188 \& .. ten seconds without any activity
2189 \& }
2190 \&
2191 \& ev_timer mytimer;
2192 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2193 \& ev_timer_again (&mytimer); /* start timer */
2194 \& ev_run (loop, 0);
2195 \&
2196 \& // and in some piece of code that gets executed on any "activity":
2197 \& // reset the timeout to start ticking again at 10 seconds
2198 \& ev_timer_again (&mytimer);
2199 .Ve
2200 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2201 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2202 .IX Subsection "ev_periodic - to cron or not to cron?"
2203 Periodic watchers are also timers of a kind, but they are very versatile
2204 (and unfortunately a bit complex).
2205 .PP
2206 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2207 relative time, the physical time that passes) but on wall clock time
2208 (absolute time, the thing you can read on your calender or clock). The
2209 difference is that wall clock time can run faster or slower than real
2210 time, and time jumps are not uncommon (e.g. when you adjust your
2211 wrist-watch).
2212 .PP
2213 You can tell a periodic watcher to trigger after some specific point
2214 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2215 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2216 not a delay) and then reset your system clock to January of the previous
2217 year, then it will take a year or more to trigger the event (unlike an
2218 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2219 it, as it uses a relative timeout).
2220 .PP
2221 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2222 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2223 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2224 those cannot react to time jumps.
2225 .PP
2226 As with timers, the callback is guaranteed to be invoked only when the
2227 point in time where it is supposed to trigger has passed. If multiple
2228 timers become ready during the same loop iteration then the ones with
2229 earlier time-out values are invoked before ones with later time-out values
2230 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2231 .PP
2232 \fIWatcher-Specific Functions and Data Members\fR
2233 .IX Subsection "Watcher-Specific Functions and Data Members"
2234 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2235 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2236 .PD 0
2237 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2238 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2239 .PD
2240 Lots of arguments, let's sort it out... There are basically three modes of
2241 operation, and we will explain them from simplest to most complex:
2242 .RS 4
2243 .IP "\(bu" 4
2244 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2245 .Sp
2246 In this configuration the watcher triggers an event after the wall clock
2247 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2248 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2249 will be stopped and invoked when the system clock reaches or surpasses
2250 this point in time.
2251 .IP "\(bu" 4
2252 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2253 .Sp
2254 In this mode the watcher will always be scheduled to time out at the next
2255 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2256 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2257 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2258 .Sp
2259 This can be used to create timers that do not drift with respect to the
2260 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2261 hour, on the hour (with respect to \s-1UTC\s0):
2262 .Sp
2263 .Vb 1
2264 \& ev_periodic_set (&periodic, 0., 3600., 0);
2265 .Ve
2266 .Sp
2267 This doesn't mean there will always be 3600 seconds in between triggers,
2268 but only that the callback will be called when the system time shows a
2269 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2270 by 3600.
2271 .Sp
2272 Another way to think about it (for the mathematically inclined) is that
2273 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2274 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2275 .Sp
2276 For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2277 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2278 this value, and in fact is often specified as zero.
2279 .Sp
2280 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2281 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2282 will of course deteriorate. Libev itself tries to be exact to be about one
2283 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2284 .IP "\(bu" 4
2285 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2286 .Sp
2287 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2288 ignored. Instead, each time the periodic watcher gets scheduled, the
2289 reschedule callback will be called with the watcher as first, and the
2290 current time as second argument.
2291 .Sp
2292 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2293 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2294 allowed by documentation here\fR.
2295 .Sp
2296 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2297 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2298 only event loop modification you are allowed to do).
2299 .Sp
2300 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2301 *w, ev_tstamp now)\*(C'\fR, e.g.:
2302 .Sp
2303 .Vb 5
2304 \& static ev_tstamp
2305 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2306 \& {
2307 \& return now + 60.;
2308 \& }
2309 .Ve
2310 .Sp
2311 It must return the next time to trigger, based on the passed time value
2312 (that is, the lowest time value larger than to the second argument). It
2313 will usually be called just before the callback will be triggered, but
2314 might be called at other times, too.
2315 .Sp
2316 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2317 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2318 .Sp
2319 This can be used to create very complex timers, such as a timer that
2320 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2321 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2322 you do this is, again, up to you (but it is not trivial, which is the main
2323 reason I omitted it as an example).
2324 .RE
2325 .RS 4
2326 .RE
2327 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2328 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2329 Simply stops and restarts the periodic watcher again. This is only useful
2330 when you changed some parameters or the reschedule callback would return
2331 a different time than the last time it was called (e.g. in a crond like
2332 program when the crontabs have changed).
2333 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2334 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2335 When active, returns the absolute time that the watcher is supposed
2336 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2337 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2338 rescheduling modes.
2339 .IP "ev_tstamp offset [read\-write]" 4
2340 .IX Item "ev_tstamp offset [read-write]"
2341 When repeating, this contains the offset value, otherwise this is the
2342 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2343 although libev might modify this value for better numerical stability).
2344 .Sp
2345 Can be modified any time, but changes only take effect when the periodic
2346 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2347 .IP "ev_tstamp interval [read\-write]" 4
2348 .IX Item "ev_tstamp interval [read-write]"
2349 The current interval value. Can be modified any time, but changes only
2350 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2351 called.
2352 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2353 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2354 The current reschedule callback, or \f(CW0\fR, if this functionality is
2355 switched off. Can be changed any time, but changes only take effect when
2356 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2357 .PP
2358 \fIExamples\fR
2359 .IX Subsection "Examples"
2360 .PP
2361 Example: Call a callback every hour, or, more precisely, whenever the
2362 system time is divisible by 3600. The callback invocation times have
2363 potentially a lot of jitter, but good long-term stability.
2364 .PP
2365 .Vb 5
2366 \& static void
2367 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2368 \& {
2369 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2370 \& }
2371 \&
2372 \& ev_periodic hourly_tick;
2373 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2374 \& ev_periodic_start (loop, &hourly_tick);
2375 .Ve
2376 .PP
2377 Example: The same as above, but use a reschedule callback to do it:
2378 .PP
2379 .Vb 1
2380 \& #include <math.h>
2381 \&
2382 \& static ev_tstamp
2383 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2384 \& {
2385 \& return now + (3600. \- fmod (now, 3600.));
2386 \& }
2387 \&
2388 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2389 .Ve
2390 .PP
2391 Example: Call a callback every hour, starting now:
2392 .PP
2393 .Vb 4
2394 \& ev_periodic hourly_tick;
2395 \& ev_periodic_init (&hourly_tick, clock_cb,
2396 \& fmod (ev_now (loop), 3600.), 3600., 0);
2397 \& ev_periodic_start (loop, &hourly_tick);
2398 .Ve
2399 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2400 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2401 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2402 Signal watchers will trigger an event when the process receives a specific
2403 signal one or more times. Even though signals are very asynchronous, libev
2404 will try its best to deliver signals synchronously, i.e. as part of the
2405 normal event processing, like any other event.
2406 .PP
2407 If you want signals to be delivered truly asynchronously, just use
2408 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2409 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2410 synchronously wake up an event loop.
2411 .PP
2412 You can configure as many watchers as you like for the same signal, but
2413 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2414 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2415 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2416 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2417 .PP
2418 When the first watcher gets started will libev actually register something
2419 with the kernel (thus it coexists with your own signal handlers as long as
2420 you don't register any with libev for the same signal).
2421 .PP
2422 If possible and supported, libev will install its handlers with
2423 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2424 not be unduly interrupted. If you have a problem with system calls getting
2425 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2426 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2427 .PP
2428 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2429 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2430 .PP
2431 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2432 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2433 stopping it again), that is, libev might or might not block the signal,
2434 and might or might not set or restore the installed signal handler.
2435 .PP
2436 While this does not matter for the signal disposition (libev never
2437 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2438 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2439 certain signals to be blocked.
2440 .PP
2441 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2442 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2443 choice usually).
2444 .PP
2445 The simplest way to ensure that the signal mask is reset in the child is
2446 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2447 catch fork calls done by libraries (such as the libc) as well.
2448 .PP
2449 In current versions of libev, the signal will not be blocked indefinitely
2450 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2451 the window of opportunity for problems, it will not go away, as libev
2452 \&\fIhas\fR to modify the signal mask, at least temporarily.
2453 .PP
2454 So I can't stress this enough: \fIIf you do not reset your signal mask when
2455 you expect it to be empty, you have a race condition in your code\fR. This
2456 is not a libev-specific thing, this is true for most event libraries.
2457 .PP
2458 \fIThe special problem of threads signal handling\fR
2459 .IX Subsection "The special problem of threads signal handling"
2460 .PP
2461 \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2462 a lot of functionality (sigfd, sigwait etc.) only really works if all
2463 threads in a process block signals, which is hard to achieve.
2464 .PP
2465 When you want to use sigwait (or mix libev signal handling with your own
2466 for the same signals), you can tackle this problem by globally blocking
2467 all signals before creating any threads (or creating them with a fully set
2468 sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2469 loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2470 these signals. You can pass on any signals that libev might be interested
2471 in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2472 .PP
2473 \fIWatcher-Specific Functions and Data Members\fR
2474 .IX Subsection "Watcher-Specific Functions and Data Members"
2475 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2476 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2477 .PD 0
2478 .IP "ev_signal_set (ev_signal *, int signum)" 4
2479 .IX Item "ev_signal_set (ev_signal *, int signum)"
2480 .PD
2481 Configures the watcher to trigger on the given signal number (usually one
2482 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2483 .IP "int signum [read\-only]" 4
2484 .IX Item "int signum [read-only]"
2485 The signal the watcher watches out for.
2486 .PP
2487 \fIExamples\fR
2488 .IX Subsection "Examples"
2489 .PP
2490 Example: Try to exit cleanly on \s-1SIGINT\s0.
2491 .PP
2492 .Vb 5
2493 \& static void
2494 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2495 \& {
2496 \& ev_break (loop, EVBREAK_ALL);
2497 \& }
2498 \&
2499 \& ev_signal signal_watcher;
2500 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2501 \& ev_signal_start (loop, &signal_watcher);
2502 .Ve
2503 .ie n .SS """ev_child"" \- watch out for process status changes"
2504 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2505 .IX Subsection "ev_child - watch out for process status changes"
2506 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2507 some child status changes (most typically when a child of yours dies or
2508 exits). It is permissible to install a child watcher \fIafter\fR the child
2509 has been forked (which implies it might have already exited), as long
2510 as the event loop isn't entered (or is continued from a watcher), i.e.,
2511 forking and then immediately registering a watcher for the child is fine,
2512 but forking and registering a watcher a few event loop iterations later or
2513 in the next callback invocation is not.
2514 .PP
2515 Only the default event loop is capable of handling signals, and therefore
2516 you can only register child watchers in the default event loop.
2517 .PP
2518 Due to some design glitches inside libev, child watchers will always be
2519 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2520 libev)
2521 .PP
2522 \fIProcess Interaction\fR
2523 .IX Subsection "Process Interaction"
2524 .PP
2525 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2526 initialised. This is necessary to guarantee proper behaviour even if the
2527 first child watcher is started after the child exits. The occurrence
2528 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2529 synchronously as part of the event loop processing. Libev always reaps all
2530 children, even ones not watched.
2531 .PP
2532 \fIOverriding the Built-In Processing\fR
2533 .IX Subsection "Overriding the Built-In Processing"
2534 .PP
2535 Libev offers no special support for overriding the built-in child
2536 processing, but if your application collides with libev's default child
2537 handler, you can override it easily by installing your own handler for
2538 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2539 default loop never gets destroyed. You are encouraged, however, to use an
2540 event-based approach to child reaping and thus use libev's support for
2541 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2542 .PP
2543 \fIStopping the Child Watcher\fR
2544 .IX Subsection "Stopping the Child Watcher"
2545 .PP
2546 Currently, the child watcher never gets stopped, even when the
2547 child terminates, so normally one needs to stop the watcher in the
2548 callback. Future versions of libev might stop the watcher automatically
2549 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2550 problem).
2551 .PP
2552 \fIWatcher-Specific Functions and Data Members\fR
2553 .IX Subsection "Watcher-Specific Functions and Data Members"
2554 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2555 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2556 .PD 0
2557 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2558 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2559 .PD
2560 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2561 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2562 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2563 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2564 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2565 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2566 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2567 activate the watcher when the process is stopped or continued).
2568 .IP "int pid [read\-only]" 4
2569 .IX Item "int pid [read-only]"
2570 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2571 .IP "int rpid [read\-write]" 4
2572 .IX Item "int rpid [read-write]"
2573 The process id that detected a status change.
2574 .IP "int rstatus [read\-write]" 4
2575 .IX Item "int rstatus [read-write]"
2576 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2577 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2578 .PP
2579 \fIExamples\fR
2580 .IX Subsection "Examples"
2581 .PP
2582 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2583 its completion.
2584 .PP
2585 .Vb 1
2586 \& ev_child cw;
2587 \&
2588 \& static void
2589 \& child_cb (EV_P_ ev_child *w, int revents)
2590 \& {
2591 \& ev_child_stop (EV_A_ w);
2592 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2593 \& }
2594 \&
2595 \& pid_t pid = fork ();
2596 \&
2597 \& if (pid < 0)
2598 \& // error
2599 \& else if (pid == 0)
2600 \& {
2601 \& // the forked child executes here
2602 \& exit (1);
2603 \& }
2604 \& else
2605 \& {
2606 \& ev_child_init (&cw, child_cb, pid, 0);
2607 \& ev_child_start (EV_DEFAULT_ &cw);
2608 \& }
2609 .Ve
2610 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2611 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2612 .IX Subsection "ev_stat - did the file attributes just change?"
2613 This watches a file system path for attribute changes. That is, it calls
2614 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2615 and sees if it changed compared to the last time, invoking the callback if
2616 it did.
2617 .PP
2618 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2619 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2620 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2621 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2622 least one) and all the other fields of the stat buffer having unspecified
2623 contents.
2624 .PP
2625 The path \fImust not\fR end in a slash or contain special components such as
2626 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2627 your working directory changes, then the behaviour is undefined.
2628 .PP
2629 Since there is no portable change notification interface available, the
2630 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2631 to see if it changed somehow. You can specify a recommended polling
2632 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2633 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2634 (which you can expect to be around five seconds, although this might
2635 change dynamically). Libev will also impose a minimum interval which is
2636 currently around \f(CW0.1\fR, but that's usually overkill.
2637 .PP
2638 This watcher type is not meant for massive numbers of stat watchers,
2639 as even with OS-supported change notifications, this can be
2640 resource-intensive.
2641 .PP
2642 At the time of this writing, the only OS-specific interface implemented
2643 is the Linux inotify interface (implementing kqueue support is left as an
2644 exercise for the reader. Note, however, that the author sees no way of
2645 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2646 .PP
2647 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2648 .IX Subsection "ABI Issues (Largefile Support)"
2649 .PP
2650 Libev by default (unless the user overrides this) uses the default
2651 compilation environment, which means that on systems with large file
2652 support disabled by default, you get the 32 bit version of the stat
2653 structure. When using the library from programs that change the \s-1ABI\s0 to
2654 use 64 bit file offsets the programs will fail. In that case you have to
2655 compile libev with the same flags to get binary compatibility. This is
2656 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2657 most noticeably displayed with ev_stat and large file support.
2658 .PP
2659 The solution for this is to lobby your distribution maker to make large
2660 file interfaces available by default (as e.g. FreeBSD does) and not
2661 optional. Libev cannot simply switch on large file support because it has
2662 to exchange stat structures with application programs compiled using the
2663 default compilation environment.
2664 .PP
2665 \fIInotify and Kqueue\fR
2666 .IX Subsection "Inotify and Kqueue"
2667 .PP
2668 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2669 runtime, it will be used to speed up change detection where possible. The
2670 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2671 watcher is being started.
2672 .PP
2673 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2674 except that changes might be detected earlier, and in some cases, to avoid
2675 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2676 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2677 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2678 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2679 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2680 xfs are fully working) libev usually gets away without polling.
2681 .PP
2682 There is no support for kqueue, as apparently it cannot be used to
2683 implement this functionality, due to the requirement of having a file
2684 descriptor open on the object at all times, and detecting renames, unlinks
2685 etc. is difficult.
2686 .PP
2687 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2688 .IX Subsection "stat () is a synchronous operation"
2689 .PP
2690 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2691 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2692 ()\*(C'\fR, which is a synchronous operation.
2693 .PP
2694 For local paths, this usually doesn't matter: unless the system is very
2695 busy or the intervals between stat's are large, a stat call will be fast,
2696 as the path data is usually in memory already (except when starting the
2697 watcher).
2698 .PP
2699 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2700 time due to network issues, and even under good conditions, a stat call
2701 often takes multiple milliseconds.
2702 .PP
2703 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2704 paths, although this is fully supported by libev.
2705 .PP
2706 \fIThe special problem of stat time resolution\fR
2707 .IX Subsection "The special problem of stat time resolution"
2708 .PP
2709 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2710 and even on systems where the resolution is higher, most file systems
2711 still only support whole seconds.
2712 .PP
2713 That means that, if the time is the only thing that changes, you can
2714 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2715 calls your callback, which does something. When there is another update
2716 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2717 stat data does change in other ways (e.g. file size).
2718 .PP
2719 The solution to this is to delay acting on a change for slightly more
2720 than a second (or till slightly after the next full second boundary), using
2721 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2722 ev_timer_again (loop, w)\*(C'\fR).
2723 .PP
2724 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2725 of some operating systems (where the second counter of the current time
2726 might be be delayed. One such system is the Linux kernel, where a call to
2727 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2728 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2729 update file times then there will be a small window where the kernel uses
2730 the previous second to update file times but libev might already execute
2731 the timer callback).
2732 .PP
2733 \fIWatcher-Specific Functions and Data Members\fR
2734 .IX Subsection "Watcher-Specific Functions and Data Members"
2735 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2736 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2737 .PD 0
2738 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2739 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2740 .PD
2741 Configures the watcher to wait for status changes of the given
2742 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2743 be detected and should normally be specified as \f(CW0\fR to let libev choose
2744 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2745 path for as long as the watcher is active.
2746 .Sp
2747 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2748 relative to the attributes at the time the watcher was started (or the
2749 last change was detected).
2750 .IP "ev_stat_stat (loop, ev_stat *)" 4
2751 .IX Item "ev_stat_stat (loop, ev_stat *)"
2752 Updates the stat buffer immediately with new values. If you change the
2753 watched path in your callback, you could call this function to avoid
2754 detecting this change (while introducing a race condition if you are not
2755 the only one changing the path). Can also be useful simply to find out the
2756 new values.
2757 .IP "ev_statdata attr [read\-only]" 4
2758 .IX Item "ev_statdata attr [read-only]"
2759 The most-recently detected attributes of the file. Although the type is
2760 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2761 suitable for your system, but you can only rely on the POSIX-standardised
2762 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2763 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2764 .IP "ev_statdata prev [read\-only]" 4
2765 .IX Item "ev_statdata prev [read-only]"
2766 The previous attributes of the file. The callback gets invoked whenever
2767 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2768 differ: \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,
2769 \&\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.
2770 .IP "ev_tstamp interval [read\-only]" 4
2771 .IX Item "ev_tstamp interval [read-only]"
2772 The specified interval.
2773 .IP "const char *path [read\-only]" 4
2774 .IX Item "const char *path [read-only]"
2775 The file system path that is being watched.
2776 .PP
2777 \fIExamples\fR
2778 .IX Subsection "Examples"
2779 .PP
2780 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2781 .PP
2782 .Vb 10
2783 \& static void
2784 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2785 \& {
2786 \& /* /etc/passwd changed in some way */
2787 \& if (w\->attr.st_nlink)
2788 \& {
2789 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2790 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2791 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2792 \& }
2793 \& else
2794 \& /* you shalt not abuse printf for puts */
2795 \& puts ("wow, /etc/passwd is not there, expect problems. "
2796 \& "if this is windows, they already arrived\en");
2797 \& }
2798 \&
2799 \& ...
2800 \& ev_stat passwd;
2801 \&
2802 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2803 \& ev_stat_start (loop, &passwd);
2804 .Ve
2805 .PP
2806 Example: Like above, but additionally use a one-second delay so we do not
2807 miss updates (however, frequent updates will delay processing, too, so
2808 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2809 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2810 .PP
2811 .Vb 2
2812 \& static ev_stat passwd;
2813 \& static ev_timer timer;
2814 \&
2815 \& static void
2816 \& timer_cb (EV_P_ ev_timer *w, int revents)
2817 \& {
2818 \& ev_timer_stop (EV_A_ w);
2819 \&
2820 \& /* now it\*(Aqs one second after the most recent passwd change */
2821 \& }
2822 \&
2823 \& static void
2824 \& stat_cb (EV_P_ ev_stat *w, int revents)
2825 \& {
2826 \& /* reset the one\-second timer */
2827 \& ev_timer_again (EV_A_ &timer);
2828 \& }
2829 \&
2830 \& ...
2831 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2832 \& ev_stat_start (loop, &passwd);
2833 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2834 .Ve
2835 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2836 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2837 .IX Subsection "ev_idle - when you've got nothing better to do..."
2838 Idle watchers trigger events when no other events of the same or higher
2839 priority are pending (prepare, check and other idle watchers do not count
2840 as receiving \*(L"events\*(R").
2841 .PP
2842 That is, as long as your process is busy handling sockets or timeouts
2843 (or even signals, imagine) of the same or higher priority it will not be
2844 triggered. But when your process is idle (or only lower-priority watchers
2845 are pending), the idle watchers are being called once per event loop
2846 iteration \- until stopped, that is, or your process receives more events
2847 and becomes busy again with higher priority stuff.
2848 .PP
2849 The most noteworthy effect is that as long as any idle watchers are
2850 active, the process will not block when waiting for new events.
2851 .PP
2852 Apart from keeping your process non-blocking (which is a useful
2853 effect on its own sometimes), idle watchers are a good place to do
2854 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2855 event loop has handled all outstanding events.
2856 .PP
2857 \fIWatcher-Specific Functions and Data Members\fR
2858 .IX Subsection "Watcher-Specific Functions and Data Members"
2859 .IP "ev_idle_init (ev_idle *, callback)" 4
2860 .IX Item "ev_idle_init (ev_idle *, callback)"
2861 Initialises and configures the idle watcher \- it has no parameters of any
2862 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2863 believe me.
2864 .PP
2865 \fIExamples\fR
2866 .IX Subsection "Examples"
2867 .PP
2868 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2869 callback, free it. Also, use no error checking, as usual.
2870 .PP
2871 .Vb 7
2872 \& static void
2873 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2874 \& {
2875 \& free (w);
2876 \& // now do something you wanted to do when the program has
2877 \& // no longer anything immediate to do.
2878 \& }
2879 \&
2880 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2881 \& ev_idle_init (idle_watcher, idle_cb);
2882 \& ev_idle_start (loop, idle_watcher);
2883 .Ve
2884 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
2885 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2886 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2887 Prepare and check watchers are usually (but not always) used in pairs:
2888 prepare watchers get invoked before the process blocks and check watchers
2889 afterwards.
2890 .PP
2891 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2892 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2893 watchers. Other loops than the current one are fine, however. The
2894 rationale behind this is that you do not need to check for recursion in
2895 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2896 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2897 called in pairs bracketing the blocking call.
2898 .PP
2899 Their main purpose is to integrate other event mechanisms into libev and
2900 their use is somewhat advanced. They could be used, for example, to track
2901 variable changes, implement your own watchers, integrate net-snmp or a
2902 coroutine library and lots more. They are also occasionally useful if
2903 you cache some data and want to flush it before blocking (for example,
2904 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2905 watcher).
2906 .PP
2907 This is done by examining in each prepare call which file descriptors
2908 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2909 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2910 libraries provide exactly this functionality). Then, in the check watcher,
2911 you check for any events that occurred (by checking the pending status
2912 of all watchers and stopping them) and call back into the library. The
2913 I/O and timer callbacks will never actually be called (but must be valid
2914 nevertheless, because you never know, you know?).
2915 .PP
2916 As another example, the Perl Coro module uses these hooks to integrate
2917 coroutines into libev programs, by yielding to other active coroutines
2918 during each prepare and only letting the process block if no coroutines
2919 are ready to run (it's actually more complicated: it only runs coroutines
2920 with priority higher than or equal to the event loop and one coroutine
2921 of lower priority, but only once, using idle watchers to keep the event
2922 loop from blocking if lower-priority coroutines are active, thus mapping
2923 low-priority coroutines to idle/background tasks).
2924 .PP
2925 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2926 priority, to ensure that they are being run before any other watchers
2927 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2928 .PP
2929 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2930 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2931 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2932 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2933 loops those other event loops might be in an unusable state until their
2934 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2935 others).
2936 .PP
2937 \fIWatcher-Specific Functions and Data Members\fR
2938 .IX Subsection "Watcher-Specific Functions and Data Members"
2939 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2940 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2941 .PD 0
2942 .IP "ev_check_init (ev_check *, callback)" 4
2943 .IX Item "ev_check_init (ev_check *, callback)"
2944 .PD
2945 Initialises and configures the prepare or check watcher \- they have no
2946 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2947 macros, but using them is utterly, utterly, utterly and completely
2948 pointless.
2949 .PP
2950 \fIExamples\fR
2951 .IX Subsection "Examples"
2952 .PP
2953 There are a number of principal ways to embed other event loops or modules
2954 into libev. Here are some ideas on how to include libadns into libev
2955 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2956 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2957 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2958 Glib event loop).
2959 .PP
2960 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2961 and in a check watcher, destroy them and call into libadns. What follows
2962 is pseudo-code only of course. This requires you to either use a low
2963 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2964 the callbacks for the IO/timeout watchers might not have been called yet.
2965 .PP
2966 .Vb 2
2967 \& static ev_io iow [nfd];
2968 \& static ev_timer tw;
2969 \&
2970 \& static void
2971 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2972 \& {
2973 \& }
2974 \&
2975 \& // create io watchers for each fd and a timer before blocking
2976 \& static void
2977 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2978 \& {
2979 \& int timeout = 3600000;
2980 \& struct pollfd fds [nfd];
2981 \& // actual code will need to loop here and realloc etc.
2982 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2983 \&
2984 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2985 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2986 \& ev_timer_start (loop, &tw);
2987 \&
2988 \& // create one ev_io per pollfd
2989 \& for (int i = 0; i < nfd; ++i)
2990 \& {
2991 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2992 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2993 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2994 \&
2995 \& fds [i].revents = 0;
2996 \& ev_io_start (loop, iow + i);
2997 \& }
2998 \& }
2999 \&
3000 \& // stop all watchers after blocking
3001 \& static void
3002 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3003 \& {
3004 \& ev_timer_stop (loop, &tw);
3005 \&
3006 \& for (int i = 0; i < nfd; ++i)
3007 \& {
3008 \& // set the relevant poll flags
3009 \& // could also call adns_processreadable etc. here
3010 \& struct pollfd *fd = fds + i;
3011 \& int revents = ev_clear_pending (iow + i);
3012 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3013 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3014 \&
3015 \& // now stop the watcher
3016 \& ev_io_stop (loop, iow + i);
3017 \& }
3018 \&
3019 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3020 \& }
3021 .Ve
3022 .PP
3023 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3024 in the prepare watcher and would dispose of the check watcher.
3025 .PP
3026 Method 3: If the module to be embedded supports explicit event
3027 notification (libadns does), you can also make use of the actual watcher
3028 callbacks, and only destroy/create the watchers in the prepare watcher.
3029 .PP
3030 .Vb 5
3031 \& static void
3032 \& timer_cb (EV_P_ ev_timer *w, int revents)
3033 \& {
3034 \& adns_state ads = (adns_state)w\->data;
3035 \& update_now (EV_A);
3036 \&
3037 \& adns_processtimeouts (ads, &tv_now);
3038 \& }
3039 \&
3040 \& static void
3041 \& io_cb (EV_P_ ev_io *w, int revents)
3042 \& {
3043 \& adns_state ads = (adns_state)w\->data;
3044 \& update_now (EV_A);
3045 \&
3046 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3047 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3048 \& }
3049 \&
3050 \& // do not ever call adns_afterpoll
3051 .Ve
3052 .PP
3053 Method 4: Do not use a prepare or check watcher because the module you
3054 want to embed is not flexible enough to support it. Instead, you can
3055 override their poll function. The drawback with this solution is that the
3056 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3057 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3058 libglib event loop.
3059 .PP
3060 .Vb 4
3061 \& static gint
3062 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3063 \& {
3064 \& int got_events = 0;
3065 \&
3066 \& for (n = 0; n < nfds; ++n)
3067 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3068 \&
3069 \& if (timeout >= 0)
3070 \& // create/start timer
3071 \&
3072 \& // poll
3073 \& ev_run (EV_A_ 0);
3074 \&
3075 \& // stop timer again
3076 \& if (timeout >= 0)
3077 \& ev_timer_stop (EV_A_ &to);
3078 \&
3079 \& // stop io watchers again \- their callbacks should have set
3080 \& for (n = 0; n < nfds; ++n)
3081 \& ev_io_stop (EV_A_ iow [n]);
3082 \&
3083 \& return got_events;
3084 \& }
3085 .Ve
3086 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3087 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3088 .IX Subsection "ev_embed - when one backend isn't enough..."
3089 This is a rather advanced watcher type that lets you embed one event loop
3090 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3091 loop, other types of watchers might be handled in a delayed or incorrect
3092 fashion and must not be used).
3093 .PP
3094 There are primarily two reasons you would want that: work around bugs and
3095 prioritise I/O.
3096 .PP
3097 As an example for a bug workaround, the kqueue backend might only support
3098 sockets on some platform, so it is unusable as generic backend, but you
3099 still want to make use of it because you have many sockets and it scales
3100 so nicely. In this case, you would create a kqueue-based loop and embed
3101 it into your default loop (which might use e.g. poll). Overall operation
3102 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3103 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3104 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3105 .PP
3106 As for prioritising I/O: under rare circumstances you have the case where
3107 some fds have to be watched and handled very quickly (with low latency),
3108 and even priorities and idle watchers might have too much overhead. In
3109 this case you would put all the high priority stuff in one loop and all
3110 the rest in a second one, and embed the second one in the first.
3111 .PP
3112 As long as the watcher is active, the callback will be invoked every
3113 time there might be events pending in the embedded loop. The callback
3114 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3115 sweep and invoke their callbacks (the callback doesn't need to invoke the
3116 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3117 to give the embedded loop strictly lower priority for example).
3118 .PP
3119 You can also set the callback to \f(CW0\fR, in which case the embed watcher
3120 will automatically execute the embedded loop sweep whenever necessary.
3121 .PP
3122 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3123 is active, i.e., the embedded loop will automatically be forked when the
3124 embedding loop forks. In other cases, the user is responsible for calling
3125 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3126 .PP
3127 Unfortunately, not all backends are embeddable: only the ones returned by
3128 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3129 portable one.
3130 .PP
3131 So when you want to use this feature you will always have to be prepared
3132 that you cannot get an embeddable loop. The recommended way to get around
3133 this is to have a separate variables for your embeddable loop, try to
3134 create it, and if that fails, use the normal loop for everything.
3135 .PP
3136 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3137 .IX Subsection "ev_embed and fork"
3138 .PP
3139 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3140 automatically be applied to the embedded loop as well, so no special
3141 fork handling is required in that case. When the watcher is not running,
3142 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3143 as applicable.
3144 .PP
3145 \fIWatcher-Specific Functions and Data Members\fR
3146 .IX Subsection "Watcher-Specific Functions and Data Members"
3147 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3148 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3149 .PD 0
3150 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3151 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3152 .PD
3153 Configures the watcher to embed the given loop, which must be
3154 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3155 invoked automatically, otherwise it is the responsibility of the callback
3156 to invoke it (it will continue to be called until the sweep has been done,
3157 if you do not want that, you need to temporarily stop the embed watcher).
3158 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3159 .IX Item "ev_embed_sweep (loop, ev_embed *)"
3160 Make a single, non-blocking sweep over the embedded loop. This works
3161 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3162 appropriate way for embedded loops.
3163 .IP "struct ev_loop *other [read\-only]" 4
3164 .IX Item "struct ev_loop *other [read-only]"
3165 The embedded event loop.
3166 .PP
3167 \fIExamples\fR
3168 .IX Subsection "Examples"
3169 .PP
3170 Example: Try to get an embeddable event loop and embed it into the default
3171 event loop. If that is not possible, use the default loop. The default
3172 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3173 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3174 used).
3175 .PP
3176 .Vb 3
3177 \& struct ev_loop *loop_hi = ev_default_init (0);
3178 \& struct ev_loop *loop_lo = 0;
3179 \& ev_embed embed;
3180 \&
3181 \& // see if there is a chance of getting one that works
3182 \& // (remember that a flags value of 0 means autodetection)
3183 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3184 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3185 \& : 0;
3186 \&
3187 \& // if we got one, then embed it, otherwise default to loop_hi
3188 \& if (loop_lo)
3189 \& {
3190 \& ev_embed_init (&embed, 0, loop_lo);
3191 \& ev_embed_start (loop_hi, &embed);
3192 \& }
3193 \& else
3194 \& loop_lo = loop_hi;
3195 .Ve
3196 .PP
3197 Example: Check if kqueue is available but not recommended and create
3198 a kqueue backend for use with sockets (which usually work with any
3199 kqueue implementation). Store the kqueue/socket\-only event loop in
3200 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3201 .PP
3202 .Vb 3
3203 \& struct ev_loop *loop = ev_default_init (0);
3204 \& struct ev_loop *loop_socket = 0;
3205 \& ev_embed embed;
3206 \&
3207 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3208 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3209 \& {
3210 \& ev_embed_init (&embed, 0, loop_socket);
3211 \& ev_embed_start (loop, &embed);
3212 \& }
3213 \&
3214 \& if (!loop_socket)
3215 \& loop_socket = loop;
3216 \&
3217 \& // now use loop_socket for all sockets, and loop for everything else
3218 .Ve
3219 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3220 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3221 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3222 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3223 whoever is a good citizen cared to tell libev about it by calling
3224 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3225 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3226 and only in the child after the fork. If whoever good citizen calling
3227 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3228 handlers will be invoked, too, of course.
3229 .PP
3230 \fIThe special problem of life after fork \- how is it possible?\fR
3231 .IX Subsection "The special problem of life after fork - how is it possible?"
3232 .PP
3233 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3234 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3235 sequence should be handled by libev without any problems.
3236 .PP
3237 This changes when the application actually wants to do event handling
3238 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3239 fork.
3240 .PP
3241 The default mode of operation (for libev, with application help to detect
3242 forks) is to duplicate all the state in the child, as would be expected
3243 when \fIeither\fR the parent \fIor\fR the child process continues.
3244 .PP
3245 When both processes want to continue using libev, then this is usually the
3246 wrong result. In that case, usually one process (typically the parent) is
3247 supposed to continue with all watchers in place as before, while the other
3248 process typically wants to start fresh, i.e. without any active watchers.
3249 .PP
3250 The cleanest and most efficient way to achieve that with libev is to
3251 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3252 use that for new watchers. This has the advantage of not touching more
3253 memory than necessary, and thus avoiding the copy-on-write, and the
3254 disadvantage of having to use multiple event loops (which do not support
3255 signal watchers).
3256 .PP
3257 When this is not possible, or you want to use the default loop for
3258 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3259 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3260 Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3261 watchers, so you have to be careful not to execute code that modifies
3262 those watchers. Note also that in that case, you have to re-register any
3263 signal watchers.
3264 .PP
3265 \fIWatcher-Specific Functions and Data Members\fR
3266 .IX Subsection "Watcher-Specific Functions and Data Members"
3267 .IP "ev_fork_init (ev_fork *, callback)" 4
3268 .IX Item "ev_fork_init (ev_fork *, callback)"
3269 Initialises and configures the fork watcher \- it has no parameters of any
3270 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3271 really.
3272 .ie n .SS """ev_cleanup"" \- even the best things end"
3273 .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3274 .IX Subsection "ev_cleanup - even the best things end"
3275 Cleanup watchers are called just before the event loop is being destroyed
3276 by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3277 .PP
3278 While there is no guarantee that the event loop gets destroyed, cleanup
3279 watchers provide a convenient method to install cleanup hooks for your
3280 program, worker threads and so on \- you just to make sure to destroy the
3281 loop when you want them to be invoked.
3282 .PP
3283 Cleanup watchers are invoked in the same way as any other watcher. Unlike
3284 all other watchers, they do not keep a reference to the event loop (which
3285 makes a lot of sense if you think about it). Like all other watchers, you
3286 can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3287 .PP
3288 \fIWatcher-Specific Functions and Data Members\fR
3289 .IX Subsection "Watcher-Specific Functions and Data Members"
3290 .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3291 .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3292 Initialises and configures the cleanup watcher \- it has no parameters of
3293 any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3294 pointless, I assure you.
3295 .PP
3296 Example: Register an atexit handler to destroy the default loop, so any
3297 cleanup functions are called.
3298 .PP
3299 .Vb 5
3300 \& static void
3301 \& program_exits (void)
3302 \& {
3303 \& ev_loop_destroy (EV_DEFAULT_UC);
3304 \& }
3305 \&
3306 \& ...
3307 \& atexit (program_exits);
3308 .Ve
3309 .ie n .SS """ev_async"" \- how to wake up an event loop"
3310 .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3311 .IX Subsection "ev_async - how to wake up an event loop"
3312 In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3313 asynchronous sources such as signal handlers (as opposed to multiple event
3314 loops \- those are of course safe to use in different threads).
3315 .PP
3316 Sometimes, however, you need to wake up an event loop you do not control,
3317 for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3318 watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3319 it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3320 .PP
3321 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3322 too, are asynchronous in nature, and signals, too, will be compressed
3323 (i.e. the number of callback invocations may be less than the number of
3324 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3325 of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3326 signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3327 even without knowing which loop owns the signal.
3328 .PP
3329 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3330 just the default loop.
3331 .PP
3332 \fIQueueing\fR
3333 .IX Subsection "Queueing"
3334 .PP
3335 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3336 is that the author does not know of a simple (or any) algorithm for a
3337 multiple-writer-single-reader queue that works in all cases and doesn't
3338 need elaborate support such as pthreads or unportable memory access
3339 semantics.
3340 .PP
3341 That means that if you want to queue data, you have to provide your own
3342 queue. But at least I can tell you how to implement locking around your
3343 queue:
3344 .IP "queueing from a signal handler context" 4
3345 .IX Item "queueing from a signal handler context"
3346 To implement race-free queueing, you simply add to the queue in the signal
3347 handler but you block the signal handler in the watcher callback. Here is
3348 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3349 .Sp
3350 .Vb 1
3351 \& static ev_async mysig;
3352 \&
3353 \& static void
3354 \& sigusr1_handler (void)
3355 \& {
3356 \& sometype data;
3357 \&
3358 \& // no locking etc.
3359 \& queue_put (data);
3360 \& ev_async_send (EV_DEFAULT_ &mysig);
3361 \& }
3362 \&
3363 \& static void
3364 \& mysig_cb (EV_P_ ev_async *w, int revents)
3365 \& {
3366 \& sometype data;
3367 \& sigset_t block, prev;
3368 \&
3369 \& sigemptyset (&block);
3370 \& sigaddset (&block, SIGUSR1);
3371 \& sigprocmask (SIG_BLOCK, &block, &prev);
3372 \&
3373 \& while (queue_get (&data))
3374 \& process (data);
3375 \&
3376 \& if (sigismember (&prev, SIGUSR1)
3377 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3378 \& }
3379 .Ve
3380 .Sp
3381 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3382 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3383 either...).
3384 .IP "queueing from a thread context" 4
3385 .IX Item "queueing from a thread context"
3386 The strategy for threads is different, as you cannot (easily) block
3387 threads but you can easily preempt them, so to queue safely you need to
3388 employ a traditional mutex lock, such as in this pthread example:
3389 .Sp
3390 .Vb 2
3391 \& static ev_async mysig;
3392 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3393 \&
3394 \& static void
3395 \& otherthread (void)
3396 \& {
3397 \& // only need to lock the actual queueing operation
3398 \& pthread_mutex_lock (&mymutex);
3399 \& queue_put (data);
3400 \& pthread_mutex_unlock (&mymutex);
3401 \&
3402 \& ev_async_send (EV_DEFAULT_ &mysig);
3403 \& }
3404 \&
3405 \& static void
3406 \& mysig_cb (EV_P_ ev_async *w, int revents)
3407 \& {
3408 \& pthread_mutex_lock (&mymutex);
3409 \&
3410 \& while (queue_get (&data))
3411 \& process (data);
3412 \&
3413 \& pthread_mutex_unlock (&mymutex);
3414 \& }
3415 .Ve
3416 .PP
3417 \fIWatcher-Specific Functions and Data Members\fR
3418 .IX Subsection "Watcher-Specific Functions and Data Members"
3419 .IP "ev_async_init (ev_async *, callback)" 4
3420 .IX Item "ev_async_init (ev_async *, callback)"
3421 Initialises and configures the async watcher \- it has no parameters of any
3422 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3423 trust me.
3424 .IP "ev_async_send (loop, ev_async *)" 4
3425 .IX Item "ev_async_send (loop, ev_async *)"
3426 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3427 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3428 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3429 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3430 section below on what exactly this means).
3431 .Sp
3432 Note that, as with other watchers in libev, multiple events might get
3433 compressed into a single callback invocation (another way to look at this
3434 is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3435 reset when the event loop detects that).
3436 .Sp
3437 This call incurs the overhead of a system call only once per event loop
3438 iteration, so while the overhead might be noticeable, it doesn't apply to
3439 repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3440 .IP "bool = ev_async_pending (ev_async *)" 4
3441 .IX Item "bool = ev_async_pending (ev_async *)"
3442 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3443 watcher but the event has not yet been processed (or even noted) by the
3444 event loop.
3445 .Sp
3446 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3447 the loop iterates next and checks for the watcher to have become active,
3448 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3449 quickly check whether invoking the loop might be a good idea.
3450 .Sp
3451 Not that this does \fInot\fR check whether the watcher itself is pending,
3452 only whether it has been requested to make this watcher pending: there
3453 is a time window between the event loop checking and resetting the async
3454 notification, and the callback being invoked.
3455 .SH "OTHER FUNCTIONS"
3456 .IX Header "OTHER FUNCTIONS"
3457 There are some other functions of possible interest. Described. Here. Now.
3458 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3459 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3460 This function combines a simple timer and an I/O watcher, calls your
3461 callback on whichever event happens first and automatically stops both
3462 watchers. This is useful if you want to wait for a single event on an fd
3463 or timeout without having to allocate/configure/start/stop/free one or
3464 more watchers yourself.
3465 .Sp
3466 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3467 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3468 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3469 .Sp
3470 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3471 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3472 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3473 .Sp
3474 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3475 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3476 \&\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
3477 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3478 a timeout and an io event at the same time \- you probably should give io
3479 events precedence.
3480 .Sp
3481 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3482 .Sp
3483 .Vb 7
3484 \& static void stdin_ready (int revents, void *arg)
3485 \& {
3486 \& if (revents & EV_READ)
3487 \& /* stdin might have data for us, joy! */;
3488 \& else if (revents & EV_TIMER)
3489 \& /* doh, nothing entered */;
3490 \& }
3491 \&
3492 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3493 .Ve
3494 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3495 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3496 Feed an event on the given fd, as if a file descriptor backend detected
3497 the given events it.
3498 .IP "ev_feed_signal_event (loop, int signum)" 4
3499 .IX Item "ev_feed_signal_event (loop, int signum)"
3500 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3501 which is async-safe.
3502 .SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3503 .IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3504 This section explains some common idioms that are not immediately
3505 obvious. Note that examples are sprinkled over the whole manual, and this
3506 section only contains stuff that wouldn't fit anywhere else.
3507 .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3508 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3509 Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3510 or modify at any time: libev will completely ignore it. This can be used
3511 to associate arbitrary data with your watcher. If you need more data and
3512 don't want to allocate memory separately and store a pointer to it in that
3513 data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3514 data:
3515 .PP
3516 .Vb 7
3517 \& struct my_io
3518 \& {
3519 \& ev_io io;
3520 \& int otherfd;
3521 \& void *somedata;
3522 \& struct whatever *mostinteresting;
3523 \& };
3524 \&
3525 \& ...
3526 \& struct my_io w;
3527 \& ev_io_init (&w.io, my_cb, fd, EV_READ);
3528 .Ve
3529 .PP
3530 And since your callback will be called with a pointer to the watcher, you
3531 can cast it back to your own type:
3532 .PP
3533 .Vb 5
3534 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3535 \& {
3536 \& struct my_io *w = (struct my_io *)w_;
3537 \& ...
3538 \& }
3539 .Ve
3540 .PP
3541 More interesting and less C\-conformant ways of casting your callback
3542 function type instead have been omitted.
3543 .SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3544 .IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3545 Another common scenario is to use some data structure with multiple
3546 embedded watchers, in effect creating your own watcher that combines
3547 multiple libev event sources into one \*(L"super-watcher\*(R":
3548 .PP
3549 .Vb 6
3550 \& struct my_biggy
3551 \& {
3552 \& int some_data;
3553 \& ev_timer t1;
3554 \& ev_timer t2;
3555 \& }
3556 .Ve
3557 .PP
3558 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3559 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3560 the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3561 to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3562 real programmers):
3563 .PP
3564 .Vb 1
3565 \& #include <stddef.h>
3566 \&
3567 \& static void
3568 \& t1_cb (EV_P_ ev_timer *w, int revents)
3569 \& {
3570 \& struct my_biggy big = (struct my_biggy *)
3571 \& (((char *)w) \- offsetof (struct my_biggy, t1));
3572 \& }
3573 \&
3574 \& static void
3575 \& t2_cb (EV_P_ ev_timer *w, int revents)
3576 \& {
3577 \& struct my_biggy big = (struct my_biggy *)
3578 \& (((char *)w) \- offsetof (struct my_biggy, t2));
3579 \& }
3580 .Ve
3581 .SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3582 .IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3583 Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3584 \&\fImodal\fR interaction, which is most easily implemented by recursively
3585 invoking \f(CW\*(C`ev_run\*(C'\fR.
3586 .PP
3587 This brings the problem of exiting \- a callback might want to finish the
3588 main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3589 a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3590 and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3591 other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3592 .PP
3593 The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3594 invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3595 triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3596 .PP
3597 .Vb 2
3598 \& // main loop
3599 \& int exit_main_loop = 0;
3600 \&
3601 \& while (!exit_main_loop)
3602 \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3603 \&
3604 \& // in a model watcher
3605 \& int exit_nested_loop = 0;
3606 \&
3607 \& while (!exit_nested_loop)
3608 \& ev_run (EV_A_ EVRUN_ONCE);
3609 .Ve
3610 .PP
3611 To exit from any of these loops, just set the corresponding exit variable:
3612 .PP
3613 .Vb 2
3614 \& // exit modal loop
3615 \& exit_nested_loop = 1;
3616 \&
3617 \& // exit main program, after modal loop is finished
3618 \& exit_main_loop = 1;
3619 \&
3620 \& // exit both
3621 \& exit_main_loop = exit_nested_loop = 1;
3622 .Ve
3623 .SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3624 .IX Subsection "THREAD LOCKING EXAMPLE"
3625 Here is a fictitious example of how to run an event loop in a different
3626 thread from where callbacks are being invoked and watchers are
3627 created/added/removed.
3628 .PP
3629 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3630 which uses exactly this technique (which is suited for many high-level
3631 languages).
3632 .PP
3633 The example uses a pthread mutex to protect the loop data, a condition
3634 variable to wait for callback invocations, an async watcher to notify the
3635 event loop thread and an unspecified mechanism to wake up the main thread.
3636 .PP
3637 First, you need to associate some data with the event loop:
3638 .PP
3639 .Vb 6
3640 \& typedef struct {
3641 \& mutex_t lock; /* global loop lock */
3642 \& ev_async async_w;
3643 \& thread_t tid;
3644 \& cond_t invoke_cv;
3645 \& } userdata;
3646 \&
3647 \& void prepare_loop (EV_P)
3648 \& {
3649 \& // for simplicity, we use a static userdata struct.
3650 \& static userdata u;
3651 \&
3652 \& ev_async_init (&u\->async_w, async_cb);
3653 \& ev_async_start (EV_A_ &u\->async_w);
3654 \&
3655 \& pthread_mutex_init (&u\->lock, 0);
3656 \& pthread_cond_init (&u\->invoke_cv, 0);
3657 \&
3658 \& // now associate this with the loop
3659 \& ev_set_userdata (EV_A_ u);
3660 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3661 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3662 \&
3663 \& // then create the thread running ev_loop
3664 \& pthread_create (&u\->tid, 0, l_run, EV_A);
3665 \& }
3666 .Ve
3667 .PP
3668 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3669 solely to wake up the event loop so it takes notice of any new watchers
3670 that might have been added:
3671 .PP
3672 .Vb 5
3673 \& static void
3674 \& async_cb (EV_P_ ev_async *w, int revents)
3675 \& {
3676 \& // just used for the side effects
3677 \& }
3678 .Ve
3679 .PP
3680 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3681 protecting the loop data, respectively.
3682 .PP
3683 .Vb 6
3684 \& static void
3685 \& l_release (EV_P)
3686 \& {
3687 \& userdata *u = ev_userdata (EV_A);
3688 \& pthread_mutex_unlock (&u\->lock);
3689 \& }
3690 \&
3691 \& static void
3692 \& l_acquire (EV_P)
3693 \& {
3694 \& userdata *u = ev_userdata (EV_A);
3695 \& pthread_mutex_lock (&u\->lock);
3696 \& }
3697 .Ve
3698 .PP
3699 The event loop thread first acquires the mutex, and then jumps straight
3700 into \f(CW\*(C`ev_run\*(C'\fR:
3701 .PP
3702 .Vb 4
3703 \& void *
3704 \& l_run (void *thr_arg)
3705 \& {
3706 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3707 \&
3708 \& l_acquire (EV_A);
3709 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3710 \& ev_run (EV_A_ 0);
3711 \& l_release (EV_A);
3712 \&
3713 \& return 0;
3714 \& }
3715 .Ve
3716 .PP
3717 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3718 signal the main thread via some unspecified mechanism (signals? pipe
3719 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3720 have been called (in a while loop because a) spurious wakeups are possible
3721 and b) skipping inter-thread-communication when there are no pending
3722 watchers is very beneficial):
3723 .PP
3724 .Vb 4
3725 \& static void
3726 \& l_invoke (EV_P)
3727 \& {
3728 \& userdata *u = ev_userdata (EV_A);
3729 \&
3730 \& while (ev_pending_count (EV_A))
3731 \& {
3732 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3733 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3734 \& }
3735 \& }
3736 .Ve
3737 .PP
3738 Now, whenever the main thread gets told to invoke pending watchers, it
3739 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3740 thread to continue:
3741 .PP
3742 .Vb 4
3743 \& static void
3744 \& real_invoke_pending (EV_P)
3745 \& {
3746 \& userdata *u = ev_userdata (EV_A);
3747 \&
3748 \& pthread_mutex_lock (&u\->lock);
3749 \& ev_invoke_pending (EV_A);
3750 \& pthread_cond_signal (&u\->invoke_cv);
3751 \& pthread_mutex_unlock (&u\->lock);
3752 \& }
3753 .Ve
3754 .PP
3755 Whenever you want to start/stop a watcher or do other modifications to an
3756 event loop, you will now have to lock:
3757 .PP
3758 .Vb 2
3759 \& ev_timer timeout_watcher;
3760 \& userdata *u = ev_userdata (EV_A);
3761 \&
3762 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3763 \&
3764 \& pthread_mutex_lock (&u\->lock);
3765 \& ev_timer_start (EV_A_ &timeout_watcher);
3766 \& ev_async_send (EV_A_ &u\->async_w);
3767 \& pthread_mutex_unlock (&u\->lock);
3768 .Ve
3769 .PP
3770 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3771 an event loop currently blocking in the kernel will have no knowledge
3772 about the newly added timer. By waking up the loop it will pick up any new
3773 watchers in the next event loop iteration.
3774 .SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3775 .IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3776 While the overhead of a callback that e.g. schedules a thread is small, it
3777 is still an overhead. If you embed libev, and your main usage is with some
3778 kind of threads or coroutines, you might want to customise libev so that
3779 doesn't need callbacks anymore.
3780 .PP
3781 Imagine you have coroutines that you can switch to using a function
3782 \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3783 and that due to some magic, the currently active coroutine is stored in a
3784 global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3785 event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3786 the differing \f(CW\*(C`;\*(C'\fR conventions):
3787 .PP
3788 .Vb 2
3789 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3790 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3791 .Ve
3792 .PP
3793 That means instead of having a C callback function, you store the
3794 coroutine to switch to in each watcher, and instead of having libev call
3795 your callback, you instead have it switch to that coroutine.
3796 .PP
3797 A coroutine might now wait for an event with a function called
3798 \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3799 matter when, or whether the watcher is active or not when this function is
3800 called):
3801 .PP
3802 .Vb 6
3803 \& void
3804 \& wait_for_event (ev_watcher *w)
3805 \& {
3806 \& ev_cb_set (w) = current_coro;
3807 \& switch_to (libev_coro);
3808 \& }
3809 .Ve
3810 .PP
3811 That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3812 continues the libev coroutine, which, when appropriate, switches back to
3813 this or any other coroutine. I am sure if you sue this your own :)
3814 .PP
3815 You can do similar tricks if you have, say, threads with an event queue \-
3816 instead of storing a coroutine, you store the queue object and instead of
3817 switching to a coroutine, you push the watcher onto the queue and notify
3818 any waiters.
3819 .PP
3820 To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3821 files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3822 .PP
3823 .Vb 4
3824 \& // my_ev.h
3825 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3826 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3827 \& #include "../libev/ev.h"
3828 \&
3829 \& // my_ev.c
3830 \& #define EV_H "my_ev.h"
3831 \& #include "../libev/ev.c"
3832 .Ve
3833 .PP
3834 And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
3835 \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
3836 can even use \fIev.h\fR as header file name directly.
3837 .SH "LIBEVENT EMULATION"
3838 .IX Header "LIBEVENT EMULATION"
3839 Libev offers a compatibility emulation layer for libevent. It cannot
3840 emulate the internals of libevent, so here are some usage hints:
3841 .IP "\(bu" 4
3842 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
3843 .Sp
3844 This was the newest libevent version available when libev was implemented,
3845 and is still mostly unchanged in 2010.
3846 .IP "\(bu" 4
3847 Use it by including <event.h>, as usual.
3848 .IP "\(bu" 4
3849 The following members are fully supported: ev_base, ev_callback,
3850 ev_arg, ev_fd, ev_res, ev_events.
3851 .IP "\(bu" 4
3852 Avoid using ev_flags and the EVLIST_*\-macros, while it is
3853 maintained by libev, it does not work exactly the same way as in libevent (consider
3854 it a private \s-1API\s0).
3855 .IP "\(bu" 4
3856 Priorities are not currently supported. Initialising priorities
3857 will fail and all watchers will have the same priority, even though there
3858 is an ev_pri field.
3859 .IP "\(bu" 4
3860 In libevent, the last base created gets the signals, in libev, the
3861 base that registered the signal gets the signals.
3862 .IP "\(bu" 4
3863 Other members are not supported.
3864 .IP "\(bu" 4
3865 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
3866 to use the libev header file and library.
3867 .SH "\*(C+ SUPPORT"
3868 .IX Header " SUPPORT"
3869 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3870 you to use some convenience methods to start/stop watchers and also change
3871 the callback model to a model using method callbacks on objects.
3872 .PP
3873 To use it,
3874 .PP
3875 .Vb 1
3876 \& #include <ev++.h>
3877 .Ve
3878 .PP
3879 This automatically includes \fIev.h\fR and puts all of its definitions (many
3880 of them macros) into the global namespace. All \*(C+ specific things are
3881 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3882 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3883 .PP
3884 Care has been taken to keep the overhead low. The only data member the \*(C+
3885 classes add (compared to plain C\-style watchers) is the event loop pointer
3886 that the watcher is associated with (or no additional members at all if
3887 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3888 .PP
3889 Currently, functions, static and non-static member functions and classes
3890 with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
3891 to add as long as they only need one additional pointer for context. If
3892 you need support for other types of functors please contact the author
3893 (preferably after implementing it).
3894 .PP
3895 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3896 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3897 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3898 .IX Item "ev::READ, ev::WRITE etc."
3899 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3900 macros from \fIev.h\fR.
3901 .ie n .IP """ev::tstamp"", ""ev::now""" 4
3902 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3903 .IX Item "ev::tstamp, ev::now"
3904 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3905 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3906 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3907 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3908 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3909 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3910 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3911 defines by many implementations.
3912 .Sp
3913 All of those classes have these methods:
3914 .RS 4
3915 .IP "ev::TYPE::TYPE ()" 4
3916 .IX Item "ev::TYPE::TYPE ()"
3917 .PD 0
3918 .IP "ev::TYPE::TYPE (loop)" 4
3919 .IX Item "ev::TYPE::TYPE (loop)"
3920 .IP "ev::TYPE::~TYPE" 4
3921 .IX Item "ev::TYPE::~TYPE"
3922 .PD
3923 The constructor (optionally) takes an event loop to associate the watcher
3924 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3925 .Sp
3926 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3927 \&\f(CW\*(C`set\*(C'\fR method before starting it.
3928 .Sp
3929 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3930 method to set a callback before you can start the watcher.
3931 .Sp
3932 (The reason why you have to use a method is a limitation in \*(C+ which does
3933 not allow explicit template arguments for constructors).
3934 .Sp
3935 The destructor automatically stops the watcher if it is active.
3936 .IP "w\->set<class, &class::method> (object *)" 4
3937 .IX Item "w->set<class, &class::method> (object *)"
3938 This method sets the callback method to call. The method has to have a
3939 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3940 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3941 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3942 .Sp
3943 This method synthesizes efficient thunking code to call your method from
3944 the C callback that libev requires. If your compiler can inline your
3945 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3946 your compiler is good :), then the method will be fully inlined into the
3947 thunking function, making it as fast as a direct C callback.
3948 .Sp
3949 Example: simple class declaration and watcher initialisation
3950 .Sp
3951 .Vb 4
3952 \& struct myclass
3953 \& {
3954 \& void io_cb (ev::io &w, int revents) { }
3955 \& }
3956 \&
3957 \& myclass obj;
3958 \& ev::io iow;
3959 \& iow.set <myclass, &myclass::io_cb> (&obj);
3960 .Ve
3961 .IP "w\->set (object *)" 4
3962 .IX Item "w->set (object *)"
3963 This is a variation of a method callback \- leaving out the method to call
3964 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3965 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3966 the time. Incidentally, you can then also leave out the template argument
3967 list.
3968 .Sp
3969 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3970 int revents)\*(C'\fR.
3971 .Sp
3972 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3973 .Sp
3974 Example: use a functor object as callback.
3975 .Sp
3976 .Vb 7
3977 \& struct myfunctor
3978 \& {
3979 \& void operator() (ev::io &w, int revents)
3980 \& {
3981 \& ...
3982 \& }
3983 \& }
3984 \&
3985 \& myfunctor f;
3986 \&
3987 \& ev::io w;
3988 \& w.set (&f);
3989 .Ve
3990 .IP "w\->set<function> (void *data = 0)" 4
3991 .IX Item "w->set<function> (void *data = 0)"
3992 Also sets a callback, but uses a static method or plain function as
3993 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3994 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3995 .Sp
3996 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3997 .Sp
3998 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3999 .Sp
4000 Example: Use a plain function as callback.
4001 .Sp
4002 .Vb 2
4003 \& static void io_cb (ev::io &w, int revents) { }
4004 \& iow.set <io_cb> ();
4005 .Ve
4006 .IP "w\->set (loop)" 4
4007 .IX Item "w->set (loop)"
4008 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4009 do this when the watcher is inactive (and not pending either).
4010 .IP "w\->set ([arguments])" 4
4011 .IX Item "w->set ([arguments])"
4012 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
4013 method or a suitable start method must be called at least once. Unlike the
4014 C counterpart, an active watcher gets automatically stopped and restarted
4015 when reconfiguring it with this method.
4016 .IP "w\->start ()" 4
4017 .IX Item "w->start ()"
4018 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4019 constructor already stores the event loop.
4020 .IP "w\->start ([arguments])" 4
4021 .IX Item "w->start ([arguments])"
4022 Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4023 convenient to wrap them in one call. Uses the same type of arguments as
4024 the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4025 .IP "w\->stop ()" 4
4026 .IX Item "w->stop ()"
4027 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4028 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4029 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4030 .IX Item "w->again () (ev::timer, ev::periodic only)"
4031 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4032 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4033 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4034 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4035 .IX Item "w->sweep () (ev::embed only)"
4036 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4037 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4038 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4039 .IX Item "w->update () (ev::stat only)"
4040 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4041 .RE
4042 .RS 4
4043 .RE
4044 .PP
4045 Example: Define a class with two I/O and idle watchers, start the I/O
4046 watchers in the constructor.
4047 .PP
4048 .Vb 5
4049 \& class myclass
4050 \& {
4051 \& ev::io io ; void io_cb (ev::io &w, int revents);
4052 \& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
4053 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4054 \&
4055 \& myclass (int fd)
4056 \& {
4057 \& io .set <myclass, &myclass::io_cb > (this);
4058 \& io2 .set <myclass, &myclass::io2_cb > (this);
4059 \& idle.set <myclass, &myclass::idle_cb> (this);
4060 \&
4061 \& io.set (fd, ev::WRITE); // configure the watcher
4062 \& io.start (); // start it whenever convenient
4063 \&
4064 \& io2.start (fd, ev::READ); // set + start in one call
4065 \& }
4066 \& };
4067 .Ve
4068 .SH "OTHER LANGUAGE BINDINGS"
4069 .IX Header "OTHER LANGUAGE BINDINGS"
4070 Libev does not offer other language bindings itself, but bindings for a
4071 number of languages exist in the form of third-party packages. If you know
4072 any interesting language binding in addition to the ones listed here, drop
4073 me a note.
4074 .IP "Perl" 4
4075 .IX Item "Perl"
4076 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4077 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4078 there are additional modules that implement libev-compatible interfaces
4079 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4080 \&\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
4081 and \f(CW\*(C`EV::Glib\*(C'\fR).
4082 .Sp
4083 It can be found and installed via \s-1CPAN\s0, its homepage is at
4084 <http://software.schmorp.de/pkg/EV>.
4085 .IP "Python" 4
4086 .IX Item "Python"
4087 Python bindings can be found at <http://code.google.com/p/pyev/>. It
4088 seems to be quite complete and well-documented.
4089 .IP "Ruby" 4
4090 .IX Item "Ruby"
4091 Tony Arcieri has written a ruby extension that offers access to a subset
4092 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4093 more on top of it. It can be found via gem servers. Its homepage is at
4094 <http://rev.rubyforge.org/>.
4095 .Sp
4096 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4097 makes rev work even on mingw.
4098 .IP "Haskell" 4
4099 .IX Item "Haskell"
4100 A haskell binding to libev is available at
4101 <http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4102 .IP "D" 4
4103 .IX Item "D"
4104 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4105 be found at <http://proj.llucax.com.ar/wiki/evd>.
4106 .IP "Ocaml" 4
4107 .IX Item "Ocaml"
4108 Erkki Seppala has written Ocaml bindings for libev, to be found at
4109 <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4110 .IP "Lua" 4
4111 .IX Item "Lua"
4112 Brian Maher has written a partial interface to libev for lua (at the
4113 time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4114 <http://github.com/brimworks/lua\-ev>.
4115 .SH "MACRO MAGIC"
4116 .IX Header "MACRO MAGIC"
4117 Libev can be compiled with a variety of options, the most fundamental
4118 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4119 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4120 .PP
4121 To make it easier to write programs that cope with either variant, the
4122 following macros are defined:
4123 .ie n .IP """EV_A"", ""EV_A_""" 4
4124 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4125 .IX Item "EV_A, EV_A_"
4126 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4127 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4128 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4129 .Sp
4130 .Vb 3
4131 \& ev_unref (EV_A);
4132 \& ev_timer_add (EV_A_ watcher);
4133 \& ev_run (EV_A_ 0);
4134 .Ve
4135 .Sp
4136 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4137 which is often provided by the following macro.
4138 .ie n .IP """EV_P"", ""EV_P_""" 4
4139 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4140 .IX Item "EV_P, EV_P_"
4141 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4142 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4143 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4144 .Sp
4145 .Vb 2
4146 \& // this is how ev_unref is being declared
4147 \& static void ev_unref (EV_P);
4148 \&
4149 \& // this is how you can declare your typical callback
4150 \& static void cb (EV_P_ ev_timer *w, int revents)
4151 .Ve
4152 .Sp
4153 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4154 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4155 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4156 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4157 .IX Item "EV_DEFAULT, EV_DEFAULT_"
4158 Similar to the other two macros, this gives you the value of the default
4159 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
4160 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4161 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4162 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4163 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4164 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4165 is undefined when the default loop has not been initialised by a previous
4166 execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4167 .Sp
4168 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4169 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4170 .PP
4171 Example: Declare and initialise a check watcher, utilising the above
4172 macros so it will work regardless of whether multiple loops are supported
4173 or not.
4174 .PP
4175 .Vb 5
4176 \& static void
4177 \& check_cb (EV_P_ ev_timer *w, int revents)
4178 \& {
4179 \& ev_check_stop (EV_A_ w);
4180 \& }
4181 \&
4182 \& ev_check check;
4183 \& ev_check_init (&check, check_cb);
4184 \& ev_check_start (EV_DEFAULT_ &check);
4185 \& ev_run (EV_DEFAULT_ 0);
4186 .Ve
4187 .SH "EMBEDDING"
4188 .IX Header "EMBEDDING"
4189 Libev can (and often is) directly embedded into host
4190 applications. Examples of applications that embed it include the Deliantra
4191 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4192 and rxvt-unicode.
4193 .PP
4194 The goal is to enable you to just copy the necessary files into your
4195 source directory without having to change even a single line in them, so
4196 you can easily upgrade by simply copying (or having a checked-out copy of
4197 libev somewhere in your source tree).
4198 .SS "\s-1FILESETS\s0"
4199 .IX Subsection "FILESETS"
4200 Depending on what features you need you need to include one or more sets of files
4201 in your application.
4202 .PP
4203 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4204 .IX Subsection "CORE EVENT LOOP"
4205 .PP
4206 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4207 configuration (no autoconf):
4208 .PP
4209 .Vb 2
4210 \& #define EV_STANDALONE 1
4211 \& #include "ev.c"
4212 .Ve
4213 .PP
4214 This will automatically include \fIev.h\fR, too, and should be done in a
4215 single C source file only to provide the function implementations. To use
4216 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4217 done by writing a wrapper around \fIev.h\fR that you can include instead and
4218 where you can put other configuration options):
4219 .PP
4220 .Vb 2
4221 \& #define EV_STANDALONE 1
4222 \& #include "ev.h"
4223 .Ve
4224 .PP
4225 Both header files and implementation files can be compiled with a \*(C+
4226 compiler (at least, that's a stated goal, and breakage will be treated
4227 as a bug).
4228 .PP
4229 You need the following files in your source tree, or in a directory
4230 in your include path (e.g. in libev/ when using \-Ilibev):
4231 .PP
4232 .Vb 4
4233 \& ev.h
4234 \& ev.c
4235 \& ev_vars.h
4236 \& ev_wrap.h
4237 \&
4238 \& ev_win32.c required on win32 platforms only
4239 \&
4240 \& ev_select.c only when select backend is enabled (which is enabled by default)
4241 \& ev_poll.c only when poll backend is enabled (disabled by default)
4242 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4243 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4244 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4245 .Ve
4246 .PP
4247 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4248 to compile this single file.
4249 .PP
4250 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4251 .IX Subsection "LIBEVENT COMPATIBILITY API"
4252 .PP
4253 To include the libevent compatibility \s-1API\s0, also include:
4254 .PP
4255 .Vb 1
4256 \& #include "event.c"
4257 .Ve
4258 .PP
4259 in the file including \fIev.c\fR, and:
4260 .PP
4261 .Vb 1
4262 \& #include "event.h"
4263 .Ve
4264 .PP
4265 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4266 .PP
4267 You need the following additional files for this:
4268 .PP
4269 .Vb 2
4270 \& event.h
4271 \& event.c
4272 .Ve
4273 .PP
4274 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4275 .IX Subsection "AUTOCONF SUPPORT"
4276 .PP
4277 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4278 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4279 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4280 include \fIconfig.h\fR and configure itself accordingly.
4281 .PP
4282 For this of course you need the m4 file:
4283 .PP
4284 .Vb 1
4285 \& libev.m4
4286 .Ve
4287 .SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4288 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4289 Libev can be configured via a variety of preprocessor symbols you have to
4290 define before including (or compiling) any of its files. The default in
4291 the absence of autoconf is documented for every option.
4292 .PP
4293 Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4294 values when compiling libev vs. including \fIev.h\fR, so it is permissible
4295 to redefine them before including \fIev.h\fR without breaking compatibility
4296 to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4297 users of libev and the libev code itself must be compiled with compatible
4298 settings.
4299 .IP "\s-1EV_COMPAT3\s0 (h)" 4
4300 .IX Item "EV_COMPAT3 (h)"
4301 Backwards compatibility is a major concern for libev. This is why this
4302 release of libev comes with wrappers for the functions and symbols that
4303 have been renamed between libev version 3 and 4.
4304 .Sp
4305 You can disable these wrappers (to test compatibility with future
4306 versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4307 sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4308 from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4309 typedef in that case.
4310 .Sp
4311 In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4312 and in some even more future version the compatibility code will be
4313 removed completely.
4314 .IP "\s-1EV_STANDALONE\s0 (h)" 4
4315 .IX Item "EV_STANDALONE (h)"
4316 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4317 keeps libev from including \fIconfig.h\fR, and it also defines dummy
4318 implementations for some libevent functions (such as logging, which is not
4319 supported). It will also not define any of the structs usually found in
4320 \&\fIevent.h\fR that are not directly supported by the libev core alone.
4321 .Sp
4322 In standalone mode, libev will still try to automatically deduce the
4323 configuration, but has to be more conservative.
4324 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4325 .IX Item "EV_USE_MONOTONIC"
4326 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4327 monotonic clock option at both compile time and runtime. Otherwise no
4328 use of the monotonic clock option will be attempted. If you enable this,
4329 you usually have to link against librt or something similar. Enabling it
4330 when the functionality isn't available is safe, though, although you have
4331 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4332 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4333 .IP "\s-1EV_USE_REALTIME\s0" 4
4334 .IX Item "EV_USE_REALTIME"
4335 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4336 real-time clock option at compile time (and assume its availability
4337 at runtime if successful). Otherwise no use of the real-time clock
4338 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4339 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4340 correctness. See the note about libraries in the description of
4341 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4342 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4343 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4344 .IX Item "EV_USE_CLOCK_SYSCALL"
4345 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4346 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4347 exists 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
4348 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4349 programs needlessly. Using a direct syscall is slightly slower (in
4350 theory), because no optimised vdso implementation can be used, but avoids
4351 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4352 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4353 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4354 .IX Item "EV_USE_NANOSLEEP"
4355 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4356 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4357 .IP "\s-1EV_USE_EVENTFD\s0" 4
4358 .IX Item "EV_USE_EVENTFD"
4359 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4360 available and will probe for kernel support at runtime. This will improve
4361 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4362 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4363 2.7 or newer, otherwise disabled.
4364 .IP "\s-1EV_USE_SELECT\s0" 4
4365 .IX Item "EV_USE_SELECT"
4366 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4367 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4368 other method takes over, select will be it. Otherwise the select backend
4369 will not be compiled in.
4370 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4371 .IX Item "EV_SELECT_USE_FD_SET"
4372 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4373 structure. This is useful if libev doesn't compile due to a missing
4374 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4375 on exotic systems. This usually limits the range of file descriptors to
4376 some low limit such as 1024 or might have other limitations (winsocket
4377 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4378 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4379 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4380 .IX Item "EV_SELECT_IS_WINSOCKET"
4381 When defined to \f(CW1\fR, the select backend will assume that
4382 select/socket/connect etc. don't understand file descriptors but
4383 wants osf handles on win32 (this is the case when the select to
4384 be used is the winsock select). This means that it will call
4385 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4386 it is assumed that all these functions actually work on fds, even
4387 on win32. Should not be defined on non\-win32 platforms.
4388 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4389 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4390 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4391 file descriptors to socket handles. When not defining this symbol (the
4392 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4393 correct. In some cases, programs use their own file descriptor management,
4394 in which case they can provide this function to map fds to socket handles.
4395 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4396 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4397 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4398 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4399 their own fd to handle mapping, overwriting this function makes it easier
4400 to do so. This can be done by defining this macro to an appropriate value.
4401 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4402 .IX Item "EV_WIN32_CLOSE_FD(fd)"
4403 If programs implement their own fd to handle mapping on win32, then this
4404 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4405 file descriptors again. Note that the replacement function has to close
4406 the underlying \s-1OS\s0 handle.
4407 .IP "\s-1EV_USE_POLL\s0" 4
4408 .IX Item "EV_USE_POLL"
4409 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4410 backend. Otherwise it will be enabled on non\-win32 platforms. It
4411 takes precedence over select.
4412 .IP "\s-1EV_USE_EPOLL\s0" 4
4413 .IX Item "EV_USE_EPOLL"
4414 If defined to be \f(CW1\fR, libev will compile in support for the Linux
4415 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4416 otherwise another method will be used as fallback. This is the preferred
4417 backend for GNU/Linux systems. If undefined, it will be enabled if the
4418 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4419 .IP "\s-1EV_USE_KQUEUE\s0" 4
4420 .IX Item "EV_USE_KQUEUE"
4421 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4422 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4423 otherwise another method will be used as fallback. This is the preferred
4424 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4425 supports some types of fds correctly (the only platform we found that
4426 supports ptys for example was NetBSD), so kqueue might be compiled in, but
4427 not be used unless explicitly requested. The best way to use it is to find
4428 out whether kqueue supports your type of fd properly and use an embedded
4429 kqueue loop.
4430 .IP "\s-1EV_USE_PORT\s0" 4
4431 .IX Item "EV_USE_PORT"
4432 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4433 10 port style backend. Its availability will be detected at runtime,
4434 otherwise another method will be used as fallback. This is the preferred
4435 backend for Solaris 10 systems.
4436 .IP "\s-1EV_USE_DEVPOLL\s0" 4
4437 .IX Item "EV_USE_DEVPOLL"
4438 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4439 .IP "\s-1EV_USE_INOTIFY\s0" 4
4440 .IX Item "EV_USE_INOTIFY"
4441 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4442 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4443 be detected at runtime. If undefined, it will be enabled if the headers
4444 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4445 .IP "\s-1EV_ATOMIC_T\s0" 4
4446 .IX Item "EV_ATOMIC_T"
4447 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4448 access is atomic with respect to other threads or signal contexts. No such
4449 type is easily found in the C language, so you can provide your own type
4450 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4451 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4452 .Sp
4453 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4454 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4455 .IP "\s-1EV_H\s0 (h)" 4
4456 .IX Item "EV_H (h)"
4457 The name of the \fIev.h\fR header file used to include it. The default if
4458 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4459 used to virtually rename the \fIev.h\fR header file in case of conflicts.
4460 .IP "\s-1EV_CONFIG_H\s0 (h)" 4
4461 .IX Item "EV_CONFIG_H (h)"
4462 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4463 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4464 \&\f(CW\*(C`EV_H\*(C'\fR, above.
4465 .IP "\s-1EV_EVENT_H\s0 (h)" 4
4466 .IX Item "EV_EVENT_H (h)"
4467 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4468 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4469 .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4470 .IX Item "EV_PROTOTYPES (h)"
4471 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4472 prototypes, but still define all the structs and other symbols. This is
4473 occasionally useful if you want to provide your own wrapper functions
4474 around libev functions.
4475 .IP "\s-1EV_MULTIPLICITY\s0" 4
4476 .IX Item "EV_MULTIPLICITY"
4477 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4478 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4479 additional independent event loops. Otherwise there will be no support
4480 for multiple event loops and there is no first event loop pointer
4481 argument. Instead, all functions act on the single default loop.
4482 .IP "\s-1EV_MINPRI\s0" 4
4483 .IX Item "EV_MINPRI"
4484 .PD 0
4485 .IP "\s-1EV_MAXPRI\s0" 4
4486 .IX Item "EV_MAXPRI"
4487 .PD
4488 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4489 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4490 provide for more priorities by overriding those symbols (usually defined
4491 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4492 .Sp
4493 When doing priority-based operations, libev usually has to linearly search
4494 all the priorities, so having many of them (hundreds) uses a lot of space
4495 and time, so using the defaults of five priorities (\-2 .. +2) is usually
4496 fine.
4497 .Sp
4498 If your embedding application does not need any priorities, defining these
4499 both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4500 .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
4501 .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."
4502 If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4503 the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4504 is not. Disabling watcher types mainly saves code size.
4505 .IP "\s-1EV_FEATURES\s0" 4
4506 .IX Item "EV_FEATURES"
4507 If you need to shave off some kilobytes of code at the expense of some
4508 speed (but with the full \s-1API\s0), you can define this symbol to request
4509 certain subsets of functionality. The default is to enable all features
4510 that can be enabled on the platform.
4511 .Sp
4512 A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4513 with some broad features you want) and then selectively re-enable
4514 additional parts you want, for example if you want everything minimal,
4515 but multiple event loop support, async and child watchers and the poll
4516 backend, use this:
4517 .Sp
4518 .Vb 5
4519 \& #define EV_FEATURES 0
4520 \& #define EV_MULTIPLICITY 1
4521 \& #define EV_USE_POLL 1
4522 \& #define EV_CHILD_ENABLE 1
4523 \& #define EV_ASYNC_ENABLE 1
4524 .Ve
4525 .Sp
4526 The actual value is a bitset, it can be a combination of the following
4527 values:
4528 .RS 4
4529 .ie n .IP "1 \- faster/larger code" 4
4530 .el .IP "\f(CW1\fR \- faster/larger code" 4
4531 .IX Item "1 - faster/larger code"
4532 Use larger code to speed up some operations.
4533 .Sp
4534 Currently this is used to override some inlining decisions (enlarging the
4535 code size by roughly 30% on amd64).
4536 .Sp
4537 When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4538 gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4539 assertions.
4540 .ie n .IP "2 \- faster/larger data structures" 4
4541 .el .IP "\f(CW2\fR \- faster/larger data structures" 4
4542 .IX Item "2 - faster/larger data structures"
4543 Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4544 hash table sizes and so on. This will usually further increase code size
4545 and can additionally have an effect on the size of data structures at
4546 runtime.
4547 .ie n .IP "4 \- full \s-1API\s0 configuration" 4
4548 .el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4549 .IX Item "4 - full API configuration"
4550 This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4551 enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4552 .ie n .IP "8 \- full \s-1API\s0" 4
4553 .el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4554 .IX Item "8 - full API"
4555 This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4556 details on which parts of the \s-1API\s0 are still available without this
4557 feature, and do not complain if this subset changes over time.
4558 .ie n .IP "16 \- enable all optional watcher types" 4
4559 .el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4560 .IX Item "16 - enable all optional watcher types"
4561 Enables all optional watcher types. If you want to selectively enable
4562 only some watcher types other than I/O and timers (e.g. prepare,
4563 embed, async, child...) you can enable them manually by defining
4564 \&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4565 .ie n .IP "32 \- enable all backends" 4
4566 .el .IP "\f(CW32\fR \- enable all backends" 4
4567 .IX Item "32 - enable all backends"
4568 This enables all backends \- without this feature, you need to enable at
4569 least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4570 .ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4571 .el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4572 .IX Item "64 - enable OS-specific helper APIs"
4573 Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4574 default.
4575 .RE
4576 .RS 4
4577 .Sp
4578 Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4579 reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4580 code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4581 watchers, timers and monotonic clock support.
4582 .Sp
4583 With an intelligent-enough linker (gcc+binutils are intelligent enough
4584 when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4585 your program might be left out as well \- a binary starting a timer and an
4586 I/O watcher then might come out at only 5Kb.
4587 .RE
4588 .IP "\s-1EV_AVOID_STDIO\s0" 4
4589 .IX Item "EV_AVOID_STDIO"
4590 If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4591 functions (printf, scanf, perror etc.). This will increase the code size
4592 somewhat, but if your program doesn't otherwise depend on stdio and your
4593 libc allows it, this avoids linking in the stdio library which is quite
4594 big.
4595 .Sp
4596 Note that error messages might become less precise when this option is
4597 enabled.
4598 .IP "\s-1EV_NSIG\s0" 4
4599 .IX Item "EV_NSIG"
4600 The highest supported signal number, +1 (or, the number of
4601 signals): Normally, libev tries to deduce the maximum number of signals
4602 automatically, but sometimes this fails, in which case it can be
4603 specified. Also, using a lower number than detected (\f(CW32\fR should be
4604 good for about any system in existence) can save some memory, as libev
4605 statically allocates some 12\-24 bytes per signal number.
4606 .IP "\s-1EV_PID_HASHSIZE\s0" 4
4607 .IX Item "EV_PID_HASHSIZE"
4608 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4609 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4610 usually more than enough. If you need to manage thousands of children you
4611 might want to increase this value (\fImust\fR be a power of two).
4612 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4613 .IX Item "EV_INOTIFY_HASHSIZE"
4614 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4615 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4616 disabled), usually more than enough. If you need to manage thousands of
4617 \&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4618 power of two).
4619 .IP "\s-1EV_USE_4HEAP\s0" 4
4620 .IX Item "EV_USE_4HEAP"
4621 Heaps are not very cache-efficient. To improve the cache-efficiency of the
4622 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4623 to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4624 faster performance with many (thousands) of watchers.
4625 .Sp
4626 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4627 will be \f(CW0\fR.
4628 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4629 .IX Item "EV_HEAP_CACHE_AT"
4630 Heaps are not very cache-efficient. To improve the cache-efficiency of the
4631 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4632 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4633 which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4634 but avoids random read accesses on heap changes. This improves performance
4635 noticeably with many (hundreds) of watchers.
4636 .Sp
4637 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4638 will be \f(CW0\fR.
4639 .IP "\s-1EV_VERIFY\s0" 4
4640 .IX Item "EV_VERIFY"
4641 Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4642 be done: If set to \f(CW0\fR, no internal verification code will be compiled
4643 in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4644 called. If set to \f(CW2\fR, then the internal verification code will be
4645 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4646 verification code will be called very frequently, which will slow down
4647 libev considerably.
4648 .Sp
4649 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4650 will be \f(CW0\fR.
4651 .IP "\s-1EV_COMMON\s0" 4
4652 .IX Item "EV_COMMON"
4653 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4654 this macro to something else you can include more and other types of
4655 members. You have to define it each time you include one of the files,
4656 though, and it must be identical each time.
4657 .Sp
4658 For example, the perl \s-1EV\s0 module uses something like this:
4659 .Sp
4660 .Vb 3
4661 \& #define EV_COMMON \e
4662 \& SV *self; /* contains this struct */ \e
4663 \& SV *cb_sv, *fh /* note no trailing ";" */
4664 .Ve
4665 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4666 .IX Item "EV_CB_DECLARE (type)"
4667 .PD 0
4668 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4669 .IX Item "EV_CB_INVOKE (watcher, revents)"
4670 .IP "ev_set_cb (ev, cb)" 4
4671 .IX Item "ev_set_cb (ev, cb)"
4672 .PD
4673 Can be used to change the callback member declaration in each watcher,
4674 and the way callbacks are invoked and set. Must expand to a struct member
4675 definition and a statement, respectively. See the \fIev.h\fR header file for
4676 their default definitions. One possible use for overriding these is to
4677 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4678 method calls instead of plain function calls in \*(C+.
4679 .SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4680 .IX Subsection "EXPORTED API SYMBOLS"
4681 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4682 exported symbols, you can use the provided \fISymbol.*\fR files which list
4683 all public symbols, one per line:
4684 .PP
4685 .Vb 2
4686 \& Symbols.ev for libev proper
4687 \& Symbols.event for the libevent emulation
4688 .Ve
4689 .PP
4690 This can also be used to rename all public symbols to avoid clashes with
4691 multiple versions of libev linked together (which is obviously bad in
4692 itself, but sometimes it is inconvenient to avoid this).
4693 .PP
4694 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4695 include before including \fIev.h\fR:
4696 .PP
4697 .Vb 1
4698 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4699 .Ve
4700 .PP
4701 This would create a file \fIwrap.h\fR which essentially looks like this:
4702 .PP
4703 .Vb 4
4704 \& #define ev_backend myprefix_ev_backend
4705 \& #define ev_check_start myprefix_ev_check_start
4706 \& #define ev_check_stop myprefix_ev_check_stop
4707 \& ...
4708 .Ve
4709 .SS "\s-1EXAMPLES\s0"
4710 .IX Subsection "EXAMPLES"
4711 For a real-world example of a program the includes libev
4712 verbatim, you can have a look at the \s-1EV\s0 perl module
4713 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4714 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4715 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4716 will be compiled. It is pretty complex because it provides its own header
4717 file.
4718 .PP
4719 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4720 that everybody includes and which overrides some configure choices:
4721 .PP
4722 .Vb 8
4723 \& #define EV_FEATURES 8
4724 \& #define EV_USE_SELECT 1
4725 \& #define EV_PREPARE_ENABLE 1
4726 \& #define EV_IDLE_ENABLE 1
4727 \& #define EV_SIGNAL_ENABLE 1
4728 \& #define EV_CHILD_ENABLE 1
4729 \& #define EV_USE_STDEXCEPT 0
4730 \& #define EV_CONFIG_H <config.h>
4731 \&
4732 \& #include "ev++.h"
4733 .Ve
4734 .PP
4735 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4736 .PP
4737 .Vb 2
4738 \& #include "ev_cpp.h"
4739 \& #include "ev.c"
4740 .Ve
4741 .SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4742 .IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4743 .SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4744 .IX Subsection "THREADS AND COROUTINES"
4745 \fI\s-1THREADS\s0\fR
4746 .IX Subsection "THREADS"
4747 .PP
4748 All libev functions are reentrant and thread-safe unless explicitly
4749 documented otherwise, but libev implements no locking itself. This means
4750 that you can use as many loops as you want in parallel, as long as there
4751 are no concurrent calls into any libev function with the same loop
4752 parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4753 of course): libev guarantees that different event loops share no data
4754 structures that need any locking.
4755 .PP
4756 Or to put it differently: calls with different loop parameters can be done
4757 concurrently from multiple threads, calls with the same loop parameter
4758 must be done serially (but can be done from different threads, as long as
4759 only one thread ever is inside a call at any point in time, e.g. by using
4760 a mutex per loop).
4761 .PP
4762 Specifically to support threads (and signal handlers), libev implements
4763 so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4764 concurrency on the same event loop, namely waking it up \*(L"from the
4765 outside\*(R".
4766 .PP
4767 If you want to know which design (one loop, locking, or multiple loops
4768 without or something else still) is best for your problem, then I cannot
4769 help you, but here is some generic advice:
4770 .IP "\(bu" 4
4771 most applications have a main thread: use the default libev loop
4772 in that thread, or create a separate thread running only the default loop