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Revision: 1.78
Committed: Tue Apr 28 00:50:19 2009 UTC (15 years, 2 months ago) by root
Branch: MAIN
CVS Tags: rel-3_6
Changes since 1.77: +358 -90 lines
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# Content
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131 .rm #[ #] #H #V #F C
132 .\" ========================================================================
133 .\"
134 .IX Title "LIBEV 3"
135 .TH LIBEV 3 "2009-04-25" "libev-3.6" "libev - high performance full featured event loop"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137 .\" way too many mistakes in technical documents.
138 .if n .ad l
139 .nh
140 .SH "NAME"
141 libev \- a high performance full\-featured event loop written in C
143 .IX Header "SYNOPSIS"
144 .Vb 1
145 \& #include <ev.h>
146 .Ve
147 .Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
148 .IX Subsection "EXAMPLE PROGRAM"
149 .Vb 2
150 \& // a single header file is required
151 \& #include <ev.h>
152 \&
153 \& #include <stdio.h> // for puts
154 \&
155 \& // every watcher type has its own typedef\*(Aqd struct
156 \& // with the name ev_TYPE
157 \& ev_io stdin_watcher;
158 \& ev_timer timeout_watcher;
159 \&
160 \& // all watcher callbacks have a similar signature
161 \& // this callback is called when data is readable on stdin
162 \& static void
163 \& stdin_cb (EV_P_ ev_io *w, int revents)
164 \& {
165 \& puts ("stdin ready");
166 \& // for one\-shot events, one must manually stop the watcher
167 \& // with its corresponding stop function.
168 \& ev_io_stop (EV_A_ w);
169 \&
170 \& // this causes all nested ev_loop\*(Aqs to stop iterating
171 \& ev_unloop (EV_A_ EVUNLOOP_ALL);
172 \& }
173 \&
174 \& // another callback, this time for a time\-out
175 \& static void
176 \& timeout_cb (EV_P_ ev_timer *w, int revents)
177 \& {
178 \& puts ("timeout");
179 \& // this causes the innermost ev_loop to stop iterating
180 \& ev_unloop (EV_A_ EVUNLOOP_ONE);
181 \& }
182 \&
183 \& int
184 \& main (void)
185 \& {
186 \& // use the default event loop unless you have special needs
187 \& struct ev_loop *loop = ev_default_loop (0);
188 \&
189 \& // initialise an io watcher, then start it
190 \& // this one will watch for stdin to become readable
191 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
192 \& ev_io_start (loop, &stdin_watcher);
193 \&
194 \& // initialise a timer watcher, then start it
195 \& // simple non\-repeating 5.5 second timeout
196 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
197 \& ev_timer_start (loop, &timeout_watcher);
198 \&
199 \& // now wait for events to arrive
200 \& ev_loop (loop, 0);
201 \&
202 \& // unloop was called, so exit
203 \& return 0;
204 \& }
205 .Ve
208 This document documents the libev software package.
209 .PP
210 The newest version of this document is also available as an html-formatted
211 web page you might find easier to navigate when reading it for the first
212 time: <>.
213 .PP
214 While this document tries to be as complete as possible in documenting
215 libev, its usage and the rationale behind its design, it is not a tutorial
216 on event-based programming, nor will it introduce event-based programming
217 with libev.
218 .PP
219 Familarity with event based programming techniques in general is assumed
220 throughout this document.
222 .IX Header "ABOUT LIBEV"
223 Libev is an event loop: you register interest in certain events (such as a
224 file descriptor being readable or a timeout occurring), and it will manage
225 these event sources and provide your program with events.
226 .PP
227 To do this, it must take more or less complete control over your process
228 (or thread) by executing the \fIevent loop\fR handler, and will then
229 communicate events via a callback mechanism.
230 .PP
231 You register interest in certain events by registering so-called \fIevent
232 watchers\fR, which are relatively small C structures you initialise with the
233 details of the event, and then hand it over to libev by \fIstarting\fR the
234 watcher.
235 .Sh "\s-1FEATURES\s0"
236 .IX Subsection "FEATURES"
237 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
238 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
239 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
240 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
241 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
242 (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
243 watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
244 \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
245 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
246 (\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 .Sh "\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`ev_loop *\*(C'\fR) will not have
259 this argument.
260 .Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
262 Libev represents time as a single floating point number, representing
263 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
264 near the beginning of 1970, details are complicated, don't ask). This
265 type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually
266 aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do any calculations
267 on it, you should treat it as some floating point value. Unlike the name
268 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
269 throughout libev.
272 Libev knows three classes of errors: operating system errors, usage errors
273 and internal errors (bugs).
274 .PP
275 When libev catches an operating system error it cannot handle (for example
276 a system call indicating a condition libev cannot fix), it calls the callback
277 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
278 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
279 ()\*(C'\fR.
280 .PP
281 When libev detects a usage error such as a negative timer interval, then
282 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
283 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
284 the libev caller and need to be fixed there.
285 .PP
286 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
287 extensive consistency checking code. These do not trigger under normal
288 circumstances, as they indicate either a bug in libev or worse.
291 These functions can be called anytime, even before initialising the
292 library in any way.
293 .IP "ev_tstamp ev_time ()" 4
294 .IX Item "ev_tstamp ev_time ()"
295 Returns the current time as libev would use it. Please note that the
296 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
297 you actually want to know.
298 .IP "ev_sleep (ev_tstamp interval)" 4
299 .IX Item "ev_sleep (ev_tstamp interval)"
300 Sleep for the given interval: The current thread will be blocked until
301 either it is interrupted or the given time interval has passed. Basically
302 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
303 .IP "int ev_version_major ()" 4
304 .IX Item "int ev_version_major ()"
305 .PD 0
306 .IP "int ev_version_minor ()" 4
307 .IX Item "int ev_version_minor ()"
308 .PD
309 You can find out the major and minor \s-1ABI\s0 version numbers of the library
310 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
311 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
312 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
313 version of the library your program was compiled against.
314 .Sp
315 These version numbers refer to the \s-1ABI\s0 version of the library, not the
316 release version.
317 .Sp
318 Usually, it's a good idea to terminate if the major versions mismatch,
319 as this indicates an incompatible change. Minor versions are usually
320 compatible to older versions, so a larger minor version alone is usually
321 not a problem.
322 .Sp
323 Example: Make sure we haven't accidentally been linked against the wrong
324 version.
325 .Sp
326 .Vb 3
327 \& assert (("libev version mismatch",
328 \& ev_version_major () == EV_VERSION_MAJOR
329 \& && ev_version_minor () >= EV_VERSION_MINOR));
330 .Ve
331 .IP "unsigned int ev_supported_backends ()" 4
332 .IX Item "unsigned int ev_supported_backends ()"
333 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
334 value) compiled into this binary of libev (independent of their
335 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
336 a description of the set values.
337 .Sp
338 Example: make sure we have the epoll method, because yeah this is cool and
339 a must have and can we have a torrent of it please!!!11
340 .Sp
341 .Vb 2
342 \& assert (("sorry, no epoll, no sex",
343 \& ev_supported_backends () & EVBACKEND_EPOLL));
344 .Ve
345 .IP "unsigned int ev_recommended_backends ()" 4
346 .IX Item "unsigned int ev_recommended_backends ()"
347 Return the set of all backends compiled into this binary of libev and also
348 recommended for this platform. This set is often smaller than the one
349 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
350 most BSDs and will not be auto-detected unless you explicitly request it
351 (assuming you know what you are doing). This is the set of backends that
352 libev will probe for if you specify no backends explicitly.
353 .IP "unsigned int ev_embeddable_backends ()" 4
354 .IX Item "unsigned int ev_embeddable_backends ()"
355 Returns the set of backends that are embeddable in other event loops. This
356 is the theoretical, all-platform, value. To find which backends
357 might be supported on the current system, you would need to look at
358 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
359 recommended ones.
360 .Sp
361 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
362 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
363 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
364 Sets the allocation function to use (the prototype is similar \- the
365 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
366 used to allocate and free memory (no surprises here). If it returns zero
367 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
368 or take some potentially destructive action.
369 .Sp
370 Since some systems (at least OpenBSD and Darwin) fail to implement
371 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
372 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
373 .Sp
374 You could override this function in high-availability programs to, say,
375 free some memory if it cannot allocate memory, to use a special allocator,
376 or even to sleep a while and retry until some memory is available.
377 .Sp
378 Example: Replace the libev allocator with one that waits a bit and then
379 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
380 .Sp
381 .Vb 6
382 \& static void *
383 \& persistent_realloc (void *ptr, size_t size)
384 \& {
385 \& for (;;)
386 \& {
387 \& void *newptr = realloc (ptr, size);
388 \&
389 \& if (newptr)
390 \& return newptr;
391 \&
392 \& sleep (60);
393 \& }
394 \& }
395 \&
396 \& ...
397 \& ev_set_allocator (persistent_realloc);
398 .Ve
399 .IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
400 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
401 Set the callback function to call on a retryable system call error (such
402 as failed select, poll, epoll_wait). The message is a printable string
403 indicating the system call or subsystem causing the problem. If this
404 callback is set, then libev will expect it to remedy the situation, no
405 matter what, when it returns. That is, libev will generally retry the
406 requested operation, or, if the condition doesn't go away, do bad stuff
407 (such as abort).
408 .Sp
409 Example: This is basically the same thing that libev does internally, too.
410 .Sp
411 .Vb 6
412 \& static void
413 \& fatal_error (const char *msg)
414 \& {
415 \& perror (msg);
416 \& abort ();
417 \& }
418 \&
419 \& ...
420 \& ev_set_syserr_cb (fatal_error);
421 .Ve
424 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
425 is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
426 \&\fIfunction\fR).
427 .PP
428 The library knows two types of such loops, the \fIdefault\fR loop, which
429 supports signals and child events, and dynamically created loops which do
430 not.
431 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
432 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
433 This will initialise the default event loop if it hasn't been initialised
434 yet and return it. If the default loop could not be initialised, returns
435 false. If it already was initialised it simply returns it (and ignores the
436 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
437 .Sp
438 If you don't know what event loop to use, use the one returned from this
439 function.
440 .Sp
441 Note that this function is \fInot\fR thread-safe, so if you want to use it
442 from multiple threads, you have to lock (note also that this is unlikely,
443 as loops cannot be shared easily between threads anyway).
444 .Sp
445 The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
446 \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
447 for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
448 create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
449 can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
450 \&\f(CW\*(C`ev_default_init\*(C'\fR.
451 .Sp
452 The flags argument can be used to specify special behaviour or specific
453 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
454 .Sp
455 The following flags are supported:
456 .RS 4
457 .ie n .IP """EVFLAG_AUTO""" 4
458 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
459 .IX Item "EVFLAG_AUTO"
460 The default flags value. Use this if you have no clue (it's the right
461 thing, believe me).
462 .ie n .IP """EVFLAG_NOENV""" 4
463 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
465 If this flag bit is or'ed into the flag value (or the program runs setuid
466 or setgid) then libev will \fInot\fR look at the environment variable
467 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
468 override the flags completely if it is found in the environment. This is
469 useful to try out specific backends to test their performance, or to work
470 around bugs.
471 .ie n .IP """EVFLAG_FORKCHECK""" 4
472 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
474 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
475 a fork, you can also make libev check for a fork in each iteration by
476 enabling this flag.
477 .Sp
478 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
479 and thus this might slow down your event loop if you do a lot of loop
480 iterations and little real work, but is usually not noticeable (on my
481 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
482 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
483 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
484 .Sp
485 The big advantage of this flag is that you can forget about fork (and
486 forget about forgetting to tell libev about forking) when you use this
487 flag.
488 .Sp
489 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
490 environment variable.
491 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
492 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
493 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
494 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
495 libev tries to roll its own fd_set with no limits on the number of fds,
496 but if that fails, expect a fairly low limit on the number of fds when
497 using this backend. It doesn't scale too well (O(highest_fd)), but its
498 usually the fastest backend for a low number of (low-numbered :) fds.
499 .Sp
500 To get good performance out of this backend you need a high amount of
501 parallelism (most of the file descriptors should be busy). If you are
502 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
503 connections as possible during one iteration. You might also want to have
504 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
505 readiness notifications you get per iteration.
506 .Sp
507 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
508 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
509 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
510 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
511 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
512 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
513 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
514 than select, but handles sparse fds better and has no artificial
515 limit on the number of fds you can use (except it will slow down
516 considerably with a lot of inactive fds). It scales similarly to select,
517 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
518 performance tips.
519 .Sp
520 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
521 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
522 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
523 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
524 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
525 For few fds, this backend is a bit little slower than poll and select,
526 but it scales phenomenally better. While poll and select usually scale
527 like O(total_fds) where n is the total number of fds (or the highest fd),
528 epoll scales either O(1) or O(active_fds).
529 .Sp
530 The epoll mechanism deserves honorable mention as the most misdesigned
531 of the more advanced event mechanisms: mere annoyances include silently
532 dropping file descriptors, requiring a system call per change per file
533 descriptor (and unnecessary guessing of parameters), problems with dup and
534 so on. The biggest issue is fork races, however \- if a program forks then
535 \&\fIboth\fR parent and child process have to recreate the epoll set, which can
536 take considerable time (one syscall per file descriptor) and is of course
537 hard to detect.
538 .Sp
539 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
540 of course \fIdoesn't\fR, and epoll just loves to report events for totally
541 \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
542 even remove them from the set) than registered in the set (especially
543 on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
544 employing an additional generation counter and comparing that against the
545 events to filter out spurious ones, recreating the set when required.
546 .Sp
547 While stopping, setting and starting an I/O watcher in the same iteration
548 will result in some caching, there is still a system call per such
549 incident (because the same \fIfile descriptor\fR could point to a different
550 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
551 file descriptors might not work very well if you register events for both
552 file descriptors.
553 .Sp
554 Best performance from this backend is achieved by not unregistering all
555 watchers for a file descriptor until it has been closed, if possible,
556 i.e. keep at least one watcher active per fd at all times. Stopping and
557 starting a watcher (without re-setting it) also usually doesn't cause
558 extra overhead. A fork can both result in spurious notifications as well
559 as in libev having to destroy and recreate the epoll object, which can
560 take considerable time and thus should be avoided.
561 .Sp
562 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
563 faster than epoll for maybe up to a hundred file descriptors, depending on
564 the usage. So sad.
565 .Sp
566 While nominally embeddable in other event loops, this feature is broken in
567 all kernel versions tested so far.
568 .Sp
569 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
570 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
571 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
572 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
573 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
574 Kqueue deserves special mention, as at the time of this writing, it
575 was broken on all BSDs except NetBSD (usually it doesn't work reliably
576 with anything but sockets and pipes, except on Darwin, where of course
577 it's completely useless). Unlike epoll, however, whose brokenness
578 is by design, these kqueue bugs can (and eventually will) be fixed
579 without \s-1API\s0 changes to existing programs. For this reason it's not being
580 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
581 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
582 system like NetBSD.
583 .Sp
584 You still can embed kqueue into a normal poll or select backend and use it
585 only for sockets (after having made sure that sockets work with kqueue on
586 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
587 .Sp
588 It scales in the same way as the epoll backend, but the interface to the
589 kernel is more efficient (which says nothing about its actual speed, of
590 course). While stopping, setting and starting an I/O watcher does never
591 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
592 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
593 sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
594 cases
595 .Sp
596 This backend usually performs well under most conditions.
597 .Sp
598 While nominally embeddable in other event loops, this doesn't work
599 everywhere, so you might need to test for this. And since it is broken
600 almost everywhere, you should only use it when you have a lot of sockets
601 (for which it usually works), by embedding it into another event loop
602 (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
603 also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
604 .Sp
605 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
606 \&\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
607 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
608 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
609 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
610 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
611 This is not implemented yet (and might never be, unless you send me an
612 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
613 and is not embeddable, which would limit the usefulness of this backend
614 immensely.
615 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
616 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
617 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
618 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
619 it's really slow, but it still scales very well (O(active_fds)).
620 .Sp
621 Please note that Solaris event ports can deliver a lot of spurious
622 notifications, so you need to use non-blocking I/O or other means to avoid
623 blocking when no data (or space) is available.
624 .Sp
625 While this backend scales well, it requires one system call per active
626 file descriptor per loop iteration. For small and medium numbers of file
627 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
628 might perform better.
629 .Sp
630 On the positive side, with the exception of the spurious readiness
631 notifications, this backend actually performed fully to specification
632 in all tests and is fully embeddable, which is a rare feat among the
633 OS-specific backends (I vastly prefer correctness over speed hacks).
634 .Sp
635 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
636 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
637 .ie n .IP """EVBACKEND_ALL""" 4
638 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
640 Try all backends (even potentially broken ones that wouldn't be tried
641 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
643 .Sp
644 It is definitely not recommended to use this flag.
645 .RE
646 .RS 4
647 .Sp
648 If one or more of these are or'ed into the flags value, then only these
649 backends will be tried (in the reverse order as listed here). If none are
650 specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
651 .Sp
652 Example: This is the most typical usage.
653 .Sp
654 .Vb 2
655 \& if (!ev_default_loop (0))
656 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
657 .Ve
658 .Sp
659 Example: Restrict libev to the select and poll backends, and do not allow
660 environment settings to be taken into account:
661 .Sp
662 .Vb 1
664 .Ve
665 .Sp
666 Example: Use whatever libev has to offer, but make sure that kqueue is
667 used if available (warning, breaks stuff, best use only with your own
668 private event loop and only if you know the \s-1OS\s0 supports your types of
669 fds):
670 .Sp
671 .Vb 1
672 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
673 .Ve
674 .RE
675 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
676 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
677 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
678 always distinct from the default loop. Unlike the default loop, it cannot
679 handle signal and child watchers, and attempts to do so will be greeted by
680 undefined behaviour (or a failed assertion if assertions are enabled).
681 .Sp
682 Note that this function \fIis\fR thread-safe, and the recommended way to use
683 libev with threads is indeed to create one loop per thread, and using the
684 default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
685 .Sp
686 Example: Try to create a event loop that uses epoll and nothing else.
687 .Sp
688 .Vb 3
689 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
690 \& if (!epoller)
691 \& fatal ("no epoll found here, maybe it hides under your chair");
692 .Ve
693 .IP "ev_default_destroy ()" 4
694 .IX Item "ev_default_destroy ()"
695 Destroys the default loop again (frees all memory and kernel state
696 etc.). None of the active event watchers will be stopped in the normal
697 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
698 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
699 calling this function, or cope with the fact afterwards (which is usually
700 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
701 for example).
702 .Sp
703 Note that certain global state, such as signal state (and installed signal
704 handlers), will not be freed by this function, and related watchers (such
705 as signal and child watchers) would need to be stopped manually.
706 .Sp
707 In general it is not advisable to call this function except in the
708 rare occasion where you really need to free e.g. the signal handling
709 pipe fds. If you need dynamically allocated loops it is better to use
710 \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
711 .IP "ev_loop_destroy (loop)" 4
712 .IX Item "ev_loop_destroy (loop)"
713 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
714 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
715 .IP "ev_default_fork ()" 4
716 .IX Item "ev_default_fork ()"
717 This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
718 to reinitialise the kernel state for backends that have one. Despite the
719 name, you can call it anytime, but it makes most sense after forking, in
720 the child process (or both child and parent, but that again makes little
721 sense). You \fImust\fR call it in the child before using any of the libev
722 functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
723 .Sp
724 On the other hand, you only need to call this function in the child
725 process if and only if you want to use the event library in the child. If
726 you just fork+exec, you don't have to call it at all.
727 .Sp
728 The function itself is quite fast and it's usually not a problem to call
729 it just in case after a fork. To make this easy, the function will fit in
730 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
731 .Sp
732 .Vb 1
733 \& pthread_atfork (0, 0, ev_default_fork);
734 .Ve
735 .IP "ev_loop_fork (loop)" 4
736 .IX Item "ev_loop_fork (loop)"
737 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
738 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
739 after fork that you want to re-use in the child, and how you do this is
740 entirely your own problem.
741 .IP "int ev_is_default_loop (loop)" 4
742 .IX Item "int ev_is_default_loop (loop)"
743 Returns true when the given loop is, in fact, the default loop, and false
744 otherwise.
745 .IP "unsigned int ev_loop_count (loop)" 4
746 .IX Item "unsigned int ev_loop_count (loop)"
747 Returns the count of loop iterations for the loop, which is identical to
748 the number of times libev did poll for new events. It starts at \f(CW0\fR and
749 happily wraps around with enough iterations.
750 .Sp
751 This value can sometimes be useful as a generation counter of sorts (it
752 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
753 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
754 .IP "unsigned int ev_backend (loop)" 4
755 .IX Item "unsigned int ev_backend (loop)"
756 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
757 use.
758 .IP "ev_tstamp ev_now (loop)" 4
759 .IX Item "ev_tstamp ev_now (loop)"
760 Returns the current \*(L"event loop time\*(R", which is the time the event loop
761 received events and started processing them. This timestamp does not
762 change as long as callbacks are being processed, and this is also the base
763 time used for relative timers. You can treat it as the timestamp of the
764 event occurring (or more correctly, libev finding out about it).
765 .IP "ev_now_update (loop)" 4
766 .IX Item "ev_now_update (loop)"
767 Establishes the current time by querying the kernel, updating the time
768 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
769 is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
770 .Sp
771 This function is rarely useful, but when some event callback runs for a
772 very long time without entering the event loop, updating libev's idea of
773 the current time is a good idea.
774 .Sp
775 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
776 .IP "ev_suspend (loop)" 4
777 .IX Item "ev_suspend (loop)"
778 .PD 0
779 .IP "ev_resume (loop)" 4
780 .IX Item "ev_resume (loop)"
781 .PD
782 These two functions suspend and resume a loop, for use when the loop is
783 not used for a while and timeouts should not be processed.
784 .Sp
785 A typical use case would be an interactive program such as a game: When
786 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
787 would be best to handle timeouts as if no time had actually passed while
788 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
789 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
790 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
791 .Sp
792 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
793 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
794 will be rescheduled (that is, they will lose any events that would have
795 occured while suspended).
796 .Sp
797 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
798 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
799 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
800 .Sp
801 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
802 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
803 .IP "ev_loop (loop, int flags)" 4
804 .IX Item "ev_loop (loop, int flags)"
805 Finally, this is it, the event handler. This function usually is called
806 after you initialised all your watchers and you want to start handling
807 events.
808 .Sp
809 If the flags argument is specified as \f(CW0\fR, it will not return until
810 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
811 .Sp
812 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
813 relying on all watchers to be stopped when deciding when a program has
814 finished (especially in interactive programs), but having a program
815 that automatically loops as long as it has to and no longer by virtue
816 of relying on its watchers stopping correctly, that is truly a thing of
817 beauty.
818 .Sp
819 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
820 those events and any already outstanding ones, but will not block your
821 process in case there are no events and will return after one iteration of
822 the loop.
823 .Sp
824 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
825 necessary) and will handle those and any already outstanding ones. It
826 will block your process until at least one new event arrives (which could
827 be an event internal to libev itself, so there is no guarantee that a
828 user-registered callback will be called), and will return after one
829 iteration of the loop.
830 .Sp
831 This is useful if you are waiting for some external event in conjunction
832 with something not expressible using other libev watchers (i.e. "roll your
833 own \f(CW\*(C`ev_loop\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
834 usually a better approach for this kind of thing.
835 .Sp
836 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
837 .Sp
838 .Vb 10
839 \& \- Before the first iteration, call any pending watchers.
840 \& * If EVFLAG_FORKCHECK was used, check for a fork.
841 \& \- If a fork was detected (by any means), queue and call all fork watchers.
842 \& \- Queue and call all prepare watchers.
843 \& \- If we have been forked, detach and recreate the kernel state
844 \& as to not disturb the other process.
845 \& \- Update the kernel state with all outstanding changes.
846 \& \- Update the "event loop time" (ev_now ()).
847 \& \- Calculate for how long to sleep or block, if at all
848 \& (active idle watchers, EVLOOP_NONBLOCK or not having
849 \& any active watchers at all will result in not sleeping).
850 \& \- Sleep if the I/O and timer collect interval say so.
851 \& \- Block the process, waiting for any events.
852 \& \- Queue all outstanding I/O (fd) events.
853 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
854 \& \- Queue all expired timers.
855 \& \- Queue all expired periodics.
856 \& \- Unless any events are pending now, queue all idle watchers.
857 \& \- Queue all check watchers.
858 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
859 \& Signals and child watchers are implemented as I/O watchers, and will
860 \& be handled here by queueing them when their watcher gets executed.
861 \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
862 \& were used, or there are no active watchers, return, otherwise
863 \& continue with step *.
864 .Ve
865 .Sp
866 Example: Queue some jobs and then loop until no events are outstanding
867 anymore.
868 .Sp
869 .Vb 4
870 \& ... queue jobs here, make sure they register event watchers as long
871 \& ... as they still have work to do (even an idle watcher will do..)
872 \& ev_loop (my_loop, 0);
873 \& ... jobs done or somebody called unloop. yeah!
874 .Ve
875 .IP "ev_unloop (loop, how)" 4
876 .IX Item "ev_unloop (loop, how)"
877 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
878 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
879 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
880 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
881 .Sp
882 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
883 .Sp
884 It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
885 .IP "ev_ref (loop)" 4
886 .IX Item "ev_ref (loop)"
887 .PD 0
888 .IP "ev_unref (loop)" 4
889 .IX Item "ev_unref (loop)"
890 .PD
891 Ref/unref can be used to add or remove a reference count on the event
892 loop: Every watcher keeps one reference, and as long as the reference
893 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
894 .Sp
895 If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
896 from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
897 stopping it.
898 .Sp
899 As an example, libev itself uses this for its internal signal pipe: It
900 is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
901 exiting if no event watchers registered by it are active. It is also an
902 excellent way to do this for generic recurring timers or from within
903 third-party libraries. Just remember to \fIunref after start\fR and \fIref
904 before stop\fR (but only if the watcher wasn't active before, or was active
905 before, respectively. Note also that libev might stop watchers itself
906 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
907 in the callback).
908 .Sp
909 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
910 running when nothing else is active.
911 .Sp
912 .Vb 4
913 \& ev_signal exitsig;
914 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
915 \& ev_signal_start (loop, &exitsig);
916 \& evf_unref (loop);
917 .Ve
918 .Sp
919 Example: For some weird reason, unregister the above signal handler again.
920 .Sp
921 .Vb 2
922 \& ev_ref (loop);
923 \& ev_signal_stop (loop, &exitsig);
924 .Ve
925 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
926 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
927 .PD 0
928 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
929 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
930 .PD
931 These advanced functions influence the time that libev will spend waiting
932 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
933 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
934 latency.
935 .Sp
936 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
937 allows libev to delay invocation of I/O and timer/periodic callbacks
938 to increase efficiency of loop iterations (or to increase power-saving
939 opportunities).
940 .Sp
941 The idea is that sometimes your program runs just fast enough to handle
942 one (or very few) event(s) per loop iteration. While this makes the
943 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
944 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
945 overhead for the actual polling but can deliver many events at once.
946 .Sp
947 By setting a higher \fIio collect interval\fR you allow libev to spend more
948 time collecting I/O events, so you can handle more events per iteration,
949 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
950 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
951 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
952 .Sp
953 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
954 to spend more time collecting timeouts, at the expense of increased
955 latency/jitter/inexactness (the watcher callback will be called
956 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
957 value will not introduce any overhead in libev.
958 .Sp
959 Many (busy) programs can usually benefit by setting the I/O collect
960 interval to a value near \f(CW0.1\fR or so, which is often enough for
961 interactive servers (of course not for games), likewise for timeouts. It
962 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
963 as this approaches the timing granularity of most systems.
964 .Sp
965 Setting the \fItimeout collect interval\fR can improve the opportunity for
966 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
967 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
968 times the process sleeps and wakes up again. Another useful technique to
969 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
970 they fire on, say, one-second boundaries only.
971 .IP "ev_loop_verify (loop)" 4
972 .IX Item "ev_loop_verify (loop)"
973 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
974 compiled in, which is the default for non-minimal builds. It tries to go
975 through all internal structures and checks them for validity. If anything
976 is found to be inconsistent, it will print an error message to standard
977 error and call \f(CW\*(C`abort ()\*(C'\fR.
978 .Sp
979 This can be used to catch bugs inside libev itself: under normal
980 circumstances, this function will never abort as of course libev keeps its
981 data structures consistent.
984 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
985 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
986 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
987 .PP
988 A watcher is a structure that you create and register to record your
989 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
990 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
991 .PP
992 .Vb 5
993 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
994 \& {
995 \& ev_io_stop (w);
996 \& ev_unloop (loop, EVUNLOOP_ALL);
997 \& }
998 \&
999 \& struct ev_loop *loop = ev_default_loop (0);
1000 \&
1001 \& ev_io stdin_watcher;
1002 \&
1003 \& ev_init (&stdin_watcher, my_cb);
1004 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1005 \& ev_io_start (loop, &stdin_watcher);
1006 \&
1007 \& ev_loop (loop, 0);
1008 .Ve
1009 .PP
1010 As you can see, you are responsible for allocating the memory for your
1011 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1012 stack).
1013 .PP
1014 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1015 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1016 .PP
1017 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
1018 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
1019 callback gets invoked each time the event occurs (or, in the case of I/O
1020 watchers, each time the event loop detects that the file descriptor given
1021 is readable and/or writable).
1022 .PP
1023 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1024 macro to configure it, with arguments specific to the watcher type. There
1025 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1026 .PP
1027 To make the watcher actually watch out for events, you have to start it
1028 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1029 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1030 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1031 .PP
1032 As long as your watcher is active (has been started but not stopped) you
1033 must not touch the values stored in it. Most specifically you must never
1034 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1035 .PP
1036 Each and every callback receives the event loop pointer as first, the
1037 registered watcher structure as second, and a bitset of received events as
1038 third argument.
1039 .PP
1040 The received events usually include a single bit per event type received
1041 (you can receive multiple events at the same time). The possible bit masks
1042 are:
1043 .ie n .IP """EV_READ""" 4
1044 .el .IP "\f(CWEV_READ\fR" 4
1045 .IX Item "EV_READ"
1046 .PD 0
1047 .ie n .IP """EV_WRITE""" 4
1048 .el .IP "\f(CWEV_WRITE\fR" 4
1049 .IX Item "EV_WRITE"
1050 .PD
1051 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1052 writable.
1053 .ie n .IP """EV_TIMEOUT""" 4
1054 .el .IP "\f(CWEV_TIMEOUT\fR" 4
1055 .IX Item "EV_TIMEOUT"
1056 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1057 .ie n .IP """EV_PERIODIC""" 4
1058 .el .IP "\f(CWEV_PERIODIC\fR" 4
1059 .IX Item "EV_PERIODIC"
1060 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1061 .ie n .IP """EV_SIGNAL""" 4
1062 .el .IP "\f(CWEV_SIGNAL\fR" 4
1063 .IX Item "EV_SIGNAL"
1064 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1065 .ie n .IP """EV_CHILD""" 4
1066 .el .IP "\f(CWEV_CHILD\fR" 4
1067 .IX Item "EV_CHILD"
1068 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1069 .ie n .IP """EV_STAT""" 4
1070 .el .IP "\f(CWEV_STAT\fR" 4
1071 .IX Item "EV_STAT"
1072 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1073 .ie n .IP """EV_IDLE""" 4
1074 .el .IP "\f(CWEV_IDLE\fR" 4
1075 .IX Item "EV_IDLE"
1076 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1077 .ie n .IP """EV_PREPARE""" 4
1078 .el .IP "\f(CWEV_PREPARE\fR" 4
1079 .IX Item "EV_PREPARE"
1080 .PD 0
1081 .ie n .IP """EV_CHECK""" 4
1082 .el .IP "\f(CWEV_CHECK\fR" 4
1083 .IX Item "EV_CHECK"
1084 .PD
1085 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
1086 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1087 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
1088 received events. Callbacks of both watcher types can start and stop as
1089 many watchers as they want, and all of them will be taken into account
1090 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1091 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1092 .ie n .IP """EV_EMBED""" 4
1093 .el .IP "\f(CWEV_EMBED\fR" 4
1094 .IX Item "EV_EMBED"
1095 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1096 .ie n .IP """EV_FORK""" 4
1097 .el .IP "\f(CWEV_FORK\fR" 4
1098 .IX Item "EV_FORK"
1099 The event loop has been resumed in the child process after fork (see
1100 \&\f(CW\*(C`ev_fork\*(C'\fR).
1101 .ie n .IP """EV_ASYNC""" 4
1102 .el .IP "\f(CWEV_ASYNC\fR" 4
1103 .IX Item "EV_ASYNC"
1104 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1105 .ie n .IP """EV_CUSTOM""" 4
1106 .el .IP "\f(CWEV_CUSTOM\fR" 4
1107 .IX Item "EV_CUSTOM"
1108 Not ever sent (or otherwise used) by libev itself, but can be freely used
1109 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1110 .ie n .IP """EV_ERROR""" 4
1111 .el .IP "\f(CWEV_ERROR\fR" 4
1112 .IX Item "EV_ERROR"
1113 An unspecified error has occurred, the watcher has been stopped. This might
1114 happen because the watcher could not be properly started because libev
1115 ran out of memory, a file descriptor was found to be closed or any other
1116 problem. Libev considers these application bugs.
1117 .Sp
1118 You best act on it by reporting the problem and somehow coping with the
1119 watcher being stopped. Note that well-written programs should not receive
1120 an error ever, so when your watcher receives it, this usually indicates a
1121 bug in your program.
1122 .Sp
1123 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1124 example it might indicate that a fd is readable or writable, and if your
1125 callbacks is well-written it can just attempt the operation and cope with
1126 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1127 programs, though, as the fd could already be closed and reused for another
1128 thing, so beware.
1129 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1131 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1132 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1133 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1134 This macro initialises the generic portion of a watcher. The contents
1135 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1136 the generic parts of the watcher are initialised, you \fIneed\fR to call
1137 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1138 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1139 which rolls both calls into one.
1140 .Sp
1141 You can reinitialise a watcher at any time as long as it has been stopped
1142 (or never started) and there are no pending events outstanding.
1143 .Sp
1144 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1145 int revents)\*(C'\fR.
1146 .Sp
1147 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1148 .Sp
1149 .Vb 3
1150 \& ev_io w;
1151 \& ev_init (&w, my_cb);
1152 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1153 .Ve
1154 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1155 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1156 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1157 This macro initialises the type-specific parts of a watcher. You need to
1158 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1159 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1160 macro on a watcher that is active (it can be pending, however, which is a
1161 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1162 .Sp
1163 Although some watcher types do not have type-specific arguments
1164 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1165 .Sp
1166 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1167 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1168 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1169 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1170 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1171 calls into a single call. This is the most convenient method to initialise
1172 a watcher. The same limitations apply, of course.
1173 .Sp
1174 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1175 .Sp
1176 .Vb 1
1177 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1178 .Ve
1179 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1180 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1181 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1182 Starts (activates) the given watcher. Only active watchers will receive
1183 events. If the watcher is already active nothing will happen.
1184 .Sp
1185 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1186 whole section.
1187 .Sp
1188 .Vb 1
1189 \& ev_io_start (EV_DEFAULT_UC, &w);
1190 .Ve
1191 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1192 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1193 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1194 Stops the given watcher if active, and clears the pending status (whether
1195 the watcher was active or not).
1196 .Sp
1197 It is possible that stopped watchers are pending \- for example,
1198 non-repeating timers are being stopped when they become pending \- but
1199 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1200 pending. If you want to free or reuse the memory used by the watcher it is
1201 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1202 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1203 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1204 Returns a true value iff the watcher is active (i.e. it has been started
1205 and not yet been stopped). As long as a watcher is active you must not modify
1206 it.
1207 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1208 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1209 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1210 events but its callback has not yet been invoked). As long as a watcher
1211 is pending (but not active) you must not call an init function on it (but
1212 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1213 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1214 it).
1215 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1216 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1217 Returns the callback currently set on the watcher.
1218 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1219 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1220 Change the callback. You can change the callback at virtually any time
1221 (modulo threads).
1222 .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1223 .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1224 .PD 0
1225 .IP "int ev_priority (ev_TYPE *watcher)" 4
1226 .IX Item "int ev_priority (ev_TYPE *watcher)"
1227 .PD
1228 Set and query the priority of the watcher. The priority is a small
1229 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1230 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1231 before watchers with lower priority, but priority will not keep watchers
1232 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1233 .Sp
1234 If you need to suppress invocation when higher priority events are pending
1235 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1236 .Sp
1237 You \fImust not\fR change the priority of a watcher as long as it is active or
1238 pending.
1239 .Sp
1240 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1241 fine, as long as you do not mind that the priority value you query might
1242 or might not have been clamped to the valid range.
1243 .Sp
1244 The default priority used by watchers when no priority has been set is
1245 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1246 .Sp
1247 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1248 priorities.
1249 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1250 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1251 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
1252 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1253 can deal with that fact, as both are simply passed through to the
1254 callback.
1255 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1256 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1257 If the watcher is pending, this function clears its pending status and
1258 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1259 watcher isn't pending it does nothing and returns \f(CW0\fR.
1260 .Sp
1261 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1262 callback to be invoked, which can be accomplished with this function.
1263 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1265 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1266 and read at any time: libev will completely ignore it. This can be used
1267 to associate arbitrary data with your watcher. If you need more data and
1268 don't want to allocate memory and store a pointer to it in that data
1269 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1270 data:
1271 .PP
1272 .Vb 7
1273 \& struct my_io
1274 \& {
1275 \& ev_io io;
1276 \& int otherfd;
1277 \& void *somedata;
1278 \& struct whatever *mostinteresting;
1279 \& };
1280 \&
1281 \& ...
1282 \& struct my_io w;
1283 \& ev_io_init (&, my_cb, fd, EV_READ);
1284 .Ve
1285 .PP
1286 And since your callback will be called with a pointer to the watcher, you
1287 can cast it back to your own type:
1288 .PP
1289 .Vb 5
1290 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1291 \& {
1292 \& struct my_io *w = (struct my_io *)w_;
1293 \& ...
1294 \& }
1295 .Ve
1296 .PP
1297 More interesting and less C\-conformant ways of casting your callback type
1298 instead have been omitted.
1299 .PP
1300 Another common scenario is to use some data structure with multiple
1301 embedded watchers:
1302 .PP
1303 .Vb 6
1304 \& struct my_biggy
1305 \& {
1306 \& int some_data;
1307 \& ev_timer t1;
1308 \& ev_timer t2;
1309 \& }
1310 .Ve
1311 .PP
1312 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1313 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1314 in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1315 some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1316 programmers):
1317 .PP
1318 .Vb 1
1319 \& #include <stddef.h>
1320 \&
1321 \& static void
1322 \& t1_cb (EV_P_ ev_timer *w, int revents)
1323 \& {
1324 \& struct my_biggy big = (struct my_biggy *
1325 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1326 \& }
1327 \&
1328 \& static void
1329 \& t2_cb (EV_P_ ev_timer *w, int revents)
1330 \& {
1331 \& struct my_biggy big = (struct my_biggy *
1332 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1333 \& }
1334 .Ve
1335 .Sh "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1337 Many event loops support \fIwatcher priorities\fR, which are usually small
1338 integers that influence the ordering of event callback invocation
1339 between watchers in some way, all else being equal.
1340 .PP
1341 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1342 description for the more technical details such as the actual priority
1343 range.
1344 .PP
1345 There are two common ways how these these priorities are being interpreted
1346 by event loops:
1347 .PP
1348 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1349 of lower priority watchers, which means as long as higher priority
1350 watchers receive events, lower priority watchers are not being invoked.
1351 .PP
1352 The less common only-for-ordering model uses priorities solely to order
1353 callback invocation within a single event loop iteration: Higher priority
1354 watchers are invoked before lower priority ones, but they all get invoked
1355 before polling for new events.
1356 .PP
1357 Libev uses the second (only-for-ordering) model for all its watchers
1358 except for idle watchers (which use the lock-out model).
1359 .PP
1360 The rationale behind this is that implementing the lock-out model for
1361 watchers is not well supported by most kernel interfaces, and most event
1362 libraries will just poll for the same events again and again as long as
1363 their callbacks have not been executed, which is very inefficient in the
1364 common case of one high-priority watcher locking out a mass of lower
1365 priority ones.
1366 .PP
1367 Static (ordering) priorities are most useful when you have two or more
1368 watchers handling the same resource: a typical usage example is having an
1369 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1370 timeouts. Under load, data might be received while the program handles
1371 other jobs, but since timers normally get invoked first, the timeout
1372 handler will be executed before checking for data. In that case, giving
1373 the timer a lower priority than the I/O watcher ensures that I/O will be
1374 handled first even under adverse conditions (which is usually, but not
1375 always, what you want).
1376 .PP
1377 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1378 will only be executed when no same or higher priority watchers have
1379 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1380 required.
1381 .PP
1382 For example, to emulate how many other event libraries handle priorities,
1383 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1384 the normal watcher callback, you just start the idle watcher. The real
1385 processing is done in the idle watcher callback. This causes libev to
1386 continously poll and process kernel event data for the watcher, but when
1387 the lock-out case is known to be rare (which in turn is rare :), this is
1388 workable.
1389 .PP
1390 Usually, however, the lock-out model implemented that way will perform
1391 miserably under the type of load it was designed to handle. In that case,
1392 it might be preferable to stop the real watcher before starting the
1393 idle watcher, so the kernel will not have to process the event in case
1394 the actual processing will be delayed for considerable time.
1395 .PP
1396 Here is an example of an I/O watcher that should run at a strictly lower
1397 priority than the default, and which should only process data when no
1398 other events are pending:
1399 .PP
1400 .Vb 2
1401 \& ev_idle idle; // actual processing watcher
1402 \& ev_io io; // actual event watcher
1403 \&
1404 \& static void
1405 \& io_cb (EV_P_ ev_io *w, int revents)
1406 \& {
1407 \& // stop the I/O watcher, we received the event, but
1408 \& // are not yet ready to handle it.
1409 \& ev_io_stop (EV_A_ w);
1410 \&
1411 \& // start the idle watcher to ahndle the actual event.
1412 \& // it will not be executed as long as other watchers
1413 \& // with the default priority are receiving events.
1414 \& ev_idle_start (EV_A_ &idle);
1415 \& }
1416 \&
1417 \& static void
1418 \& idle\-cb (EV_P_ ev_idle *w, int revents)
1419 \& {
1420 \& // actual processing
1421 \& read (STDIN_FILENO, ...);
1422 \&
1423 \& // have to start the I/O watcher again, as
1424 \& // we have handled the event
1425 \& ev_io_start (EV_P_ &io);
1426 \& }
1427 \&
1428 \& // initialisation
1429 \& ev_idle_init (&idle, idle_cb);
1430 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1431 \& ev_io_start (EV_DEFAULT_ &io);
1432 .Ve
1433 .PP
1434 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1435 low-priority connections can not be locked out forever under load. This
1436 enables your program to keep a lower latency for important connections
1437 during short periods of high load, while not completely locking out less
1438 important ones.
1440 .IX Header "WATCHER TYPES"
1441 This section describes each watcher in detail, but will not repeat
1442 information given in the last section. Any initialisation/set macros,
1443 functions and members specific to the watcher type are explained.
1444 .PP
1445 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1446 while the watcher is active, you can look at the member and expect some
1447 sensible content, but you must not modify it (you can modify it while the
1448 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1449 means you can expect it to have some sensible content while the watcher
1450 is active, but you can also modify it. Modifying it may not do something
1451 sensible or take immediate effect (or do anything at all), but libev will
1452 not crash or malfunction in any way.
1453 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1454 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1455 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1456 I/O watchers check whether a file descriptor is readable or writable
1457 in each iteration of the event loop, or, more precisely, when reading
1458 would not block the process and writing would at least be able to write
1459 some data. This behaviour is called level-triggering because you keep
1460 receiving events as long as the condition persists. Remember you can stop
1461 the watcher if you don't want to act on the event and neither want to
1462 receive future events.
1463 .PP
1464 In general you can register as many read and/or write event watchers per
1465 fd as you want (as long as you don't confuse yourself). Setting all file
1466 descriptors to non-blocking mode is also usually a good idea (but not
1467 required if you know what you are doing).
1468 .PP
1469 If you cannot use non-blocking mode, then force the use of a
1470 known-to-be-good backend (at the time of this writing, this includes only
1471 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
1472 descriptors for which non-blocking operation makes no sense (such as
1473 files) \- libev doesn't guarentee any specific behaviour in that case.
1474 .PP
1475 Another thing you have to watch out for is that it is quite easy to
1476 receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1477 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1478 because there is no data. Not only are some backends known to create a
1479 lot of those (for example Solaris ports), it is very easy to get into
1480 this situation even with a relatively standard program structure. Thus
1481 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1482 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1483 .PP
1484 If you cannot run the fd in non-blocking mode (for example you should
1485 not play around with an Xlib connection), then you have to separately
1486 re-test whether a file descriptor is really ready with a known-to-be good
1487 interface such as poll (fortunately in our Xlib example, Xlib already
1488 does this on its own, so its quite safe to use). Some people additionally
1489 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1490 indefinitely.
1491 .PP
1492 But really, best use non-blocking mode.
1493 .PP
1494 \fIThe special problem of disappearing file descriptors\fR
1495 .IX Subsection "The special problem of disappearing file descriptors"
1496 .PP
1497 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1498 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1499 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1500 descriptor, but when it goes away, the operating system will silently drop
1501 this interest. If another file descriptor with the same number then is
1502 registered with libev, there is no efficient way to see that this is, in
1503 fact, a different file descriptor.
1504 .PP
1505 To avoid having to explicitly tell libev about such cases, libev follows
1506 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1507 will assume that this is potentially a new file descriptor, otherwise
1508 it is assumed that the file descriptor stays the same. That means that
1509 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
1510 descriptor even if the file descriptor number itself did not change.
1511 .PP
1512 This is how one would do it normally anyway, the important point is that
1513 the libev application should not optimise around libev but should leave
1514 optimisations to libev.
1515 .PP
1516 \fIThe special problem of dup'ed file descriptors\fR
1517 .IX Subsection "The special problem of dup'ed file descriptors"
1518 .PP
1519 Some backends (e.g. epoll), cannot register events for file descriptors,
1520 but only events for the underlying file descriptions. That means when you
1521 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1522 events for them, only one file descriptor might actually receive events.
1523 .PP
1524 There is no workaround possible except not registering events
1525 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1526 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1527 .PP
1528 \fIThe special problem of fork\fR
1529 .IX Subsection "The special problem of fork"
1530 .PP
1531 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1532 useless behaviour. Libev fully supports fork, but needs to be told about
1533 it in the child.
1534 .PP
1535 To support fork in your programs, you either have to call
1536 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1537 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1538 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1539 .PP
1540 \fIThe special problem of \s-1SIGPIPE\s0\fR
1541 .IX Subsection "The special problem of SIGPIPE"
1542 .PP
1543 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1544 when writing to a pipe whose other end has been closed, your program gets
1545 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1546 this is sensible behaviour, for daemons, this is usually undesirable.
1547 .PP
1548 So when you encounter spurious, unexplained daemon exits, make sure you
1549 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1550 somewhere, as that would have given you a big clue).
1551 .PP
1552 \fIWatcher-Specific Functions\fR
1553 .IX Subsection "Watcher-Specific Functions"
1554 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1555 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1556 .PD 0
1557 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1558 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1559 .PD
1560 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1561 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
1562 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1563 .IP "int fd [read\-only]" 4
1564 .IX Item "int fd [read-only]"
1565 The file descriptor being watched.
1566 .IP "int events [read\-only]" 4
1567 .IX Item "int events [read-only]"
1568 The events being watched.
1569 .PP
1570 \fIExamples\fR
1571 .IX Subsection "Examples"
1572 .PP
1573 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1574 readable, but only once. Since it is likely line-buffered, you could
1575 attempt to read a whole line in the callback.
1576 .PP
1577 .Vb 6
1578 \& static void
1579 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1580 \& {
1581 \& ev_io_stop (loop, w);
1582 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1583 \& }
1584 \&
1585 \& ...
1586 \& struct ev_loop *loop = ev_default_init (0);
1587 \& ev_io stdin_readable;
1588 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1589 \& ev_io_start (loop, &stdin_readable);
1590 \& ev_loop (loop, 0);
1591 .Ve
1592 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1593 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1594 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1595 Timer watchers are simple relative timers that generate an event after a
1596 given time, and optionally repeating in regular intervals after that.
1597 .PP
1598 The timers are based on real time, that is, if you register an event that
1599 times out after an hour and you reset your system clock to January last
1600 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1601 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1602 monotonic clock option helps a lot here).
1603 .PP
1604 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1605 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1606 might introduce a small delay). If multiple timers become ready during the
1607 same loop iteration then the ones with earlier time-out values are invoked
1608 before ones with later time-out values (but this is no longer true when a
1609 callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1610 .PP
1611 \fIBe smart about timeouts\fR
1612 .IX Subsection "Be smart about timeouts"
1613 .PP
1614 Many real-world problems involve some kind of timeout, usually for error
1615 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1616 you want to raise some error after a while.
1617 .PP
1618 What follows are some ways to handle this problem, from obvious and
1619 inefficient to smart and efficient.
1620 .PP
1621 In the following, a 60 second activity timeout is assumed \- a timeout that
1622 gets reset to 60 seconds each time there is activity (e.g. each time some
1623 data or other life sign was received).
1624 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1625 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1626 This is the most obvious, but not the most simple way: In the beginning,
1627 start the watcher:
1628 .Sp
1629 .Vb 2
1630 \& ev_timer_init (timer, callback, 60., 0.);
1631 \& ev_timer_start (loop, timer);
1632 .Ve
1633 .Sp
1634 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1635 and start it again:
1636 .Sp
1637 .Vb 3
1638 \& ev_timer_stop (loop, timer);
1639 \& ev_timer_set (timer, 60., 0.);
1640 \& ev_timer_start (loop, timer);
1641 .Ve
1642 .Sp
1643 This is relatively simple to implement, but means that each time there is
1644 some activity, libev will first have to remove the timer from its internal
1645 data structure and then add it again. Libev tries to be fast, but it's
1646 still not a constant-time operation.
1647 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1648 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1649 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1650 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1651 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1652 .Sp
1653 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1654 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1655 successfully read or write some data. If you go into an idle state where
1656 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1657 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1658 .Sp
1659 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1660 \&\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
1661 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1662 .Sp
1663 At start:
1664 .Sp
1665 .Vb 3
1666 \& ev_timer_init (timer, callback);
1667 \& timer\->repeat = 60.;
1668 \& ev_timer_again (loop, timer);
1669 .Ve
1670 .Sp
1671 Each time there is some activity:
1672 .Sp
1673 .Vb 1
1674 \& ev_timer_again (loop, timer);
1675 .Ve
1676 .Sp
1677 It is even possible to change the time-out on the fly, regardless of
1678 whether the watcher is active or not:
1679 .Sp
1680 .Vb 2
1681 \& timer\->repeat = 30.;
1682 \& ev_timer_again (loop, timer);
1683 .Ve
1684 .Sp
1685 This is slightly more efficient then stopping/starting the timer each time
1686 you want to modify its timeout value, as libev does not have to completely
1687 remove and re-insert the timer from/into its internal data structure.
1688 .Sp
1689 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1690 .IP "3. Let the timer time out, but then re-arm it as required." 4
1691 .IX Item "3. Let the timer time out, but then re-arm it as required."
1692 This method is more tricky, but usually most efficient: Most timeouts are
1693 relatively long compared to the intervals between other activity \- in
1694 our example, within 60 seconds, there are usually many I/O events with
1695 associated activity resets.
1696 .Sp
1697 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1698 but remember the time of last activity, and check for a real timeout only
1699 within the callback:
1700 .Sp
1701 .Vb 1
1702 \& ev_tstamp last_activity; // time of last activity
1703 \&
1704 \& static void
1705 \& callback (EV_P_ ev_timer *w, int revents)
1706 \& {
1707 \& ev_tstamp now = ev_now (EV_A);
1708 \& ev_tstamp timeout = last_activity + 60.;
1709 \&
1710 \& // if last_activity + 60. is older than now, we did time out
1711 \& if (timeout < now)
1712 \& {
1713 \& // timeout occured, take action
1714 \& }
1715 \& else
1716 \& {
1717 \& // callback was invoked, but there was some activity, re\-arm
1718 \& // the watcher to fire in last_activity + 60, which is
1719 \& // guaranteed to be in the future, so "again" is positive:
1720 \& w\->repeat = timeout \- now;
1721 \& ev_timer_again (EV_A_ w);
1722 \& }
1723 \& }
1724 .Ve
1725 .Sp
1726 To summarise the callback: first calculate the real timeout (defined
1727 as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1728 been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1729 the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1730 re-schedule the timer to fire at that future time, to see if maybe we have
1731 a timeout then.
1732 .Sp
1733 Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1734 \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1735 .Sp
1736 This scheme causes more callback invocations (about one every 60 seconds
1737 minus half the average time between activity), but virtually no calls to
1738 libev to change the timeout.
1739 .Sp
1740 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1741 to the current time (meaning we just have some activity :), then call the
1742 callback, which will \*(L"do the right thing\*(R" and start the timer:
1743 .Sp
1744 .Vb 3
1745 \& ev_timer_init (timer, callback);
1746 \& last_activity = ev_now (loop);
1747 \& callback (loop, timer, EV_TIMEOUT);
1748 .Ve
1749 .Sp
1750 And when there is some activity, simply store the current time in
1751 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1752 .Sp
1753 .Vb 1
1754 \& last_actiivty = ev_now (loop);
1755 .Ve
1756 .Sp
1757 This technique is slightly more complex, but in most cases where the
1758 time-out is unlikely to be triggered, much more efficient.
1759 .Sp
1760 Changing the timeout is trivial as well (if it isn't hard-coded in the
1761 callback :) \- just change the timeout and invoke the callback, which will
1762 fix things for you.
1763 .IP "4. Wee, just use a double-linked list for your timeouts." 4
1764 .IX Item "4. Wee, just use a double-linked list for your timeouts."
1765 If there is not one request, but many thousands (millions...), all
1766 employing some kind of timeout with the same timeout value, then one can
1767 do even better:
1768 .Sp
1769 When starting the timeout, calculate the timeout value and put the timeout
1770 at the \fIend\fR of the list.
1771 .Sp
1772 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1773 the list is expected to fire (for example, using the technique #3).
1774 .Sp
1775 When there is some activity, remove the timer from the list, recalculate
1776 the timeout, append it to the end of the list again, and make sure to
1777 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1778 .Sp
1779 This way, one can manage an unlimited number of timeouts in O(1) time for
1780 starting, stopping and updating the timers, at the expense of a major
1781 complication, and having to use a constant timeout. The constant timeout
1782 ensures that the list stays sorted.
1783 .PP
1784 So which method the best?
1785 .PP
1786 Method #2 is a simple no-brain-required solution that is adequate in most
1787 situations. Method #3 requires a bit more thinking, but handles many cases
1788 better, and isn't very complicated either. In most case, choosing either
1789 one is fine, with #3 being better in typical situations.
1790 .PP
1791 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1792 rather complicated, but extremely efficient, something that really pays
1793 off after the first million or so of active timers, i.e. it's usually
1794 overkill :)
1795 .PP
1796 \fIThe special problem of time updates\fR
1797 .IX Subsection "The special problem of time updates"
1798 .PP
1799 Establishing the current time is a costly operation (it usually takes at
1800 least two system calls): \s-1EV\s0 therefore updates its idea of the current
1801 time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1802 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1803 lots of events in one iteration.
1804 .PP
1805 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1806 time. This is usually the right thing as this timestamp refers to the time
1807 of the event triggering whatever timeout you are modifying/starting. If
1808 you suspect event processing to be delayed and you \fIneed\fR to base the
1809 timeout on the current time, use something like this to adjust for this:
1810 .PP
1811 .Vb 1
1812 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1813 .Ve
1814 .PP
1815 If the event loop is suspended for a long time, you can also force an
1816 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1817 ()\*(C'\fR.
1818 .PP
1819 \fIWatcher-Specific Functions and Data Members\fR
1820 .IX Subsection "Watcher-Specific Functions and Data Members"
1821 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1822 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1823 .PD 0
1824 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1825 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1826 .PD
1827 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1828 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1829 reached. If it is positive, then the timer will automatically be
1830 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1831 until stopped manually.
1832 .Sp
1833 The timer itself will do a best-effort at avoiding drift, that is, if
1834 you configure a timer to trigger every 10 seconds, then it will normally
1835 trigger at exactly 10 second intervals. If, however, your program cannot
1836 keep up with the timer (because it takes longer than those 10 seconds to
1837 do stuff) the timer will not fire more than once per event loop iteration.
1838 .IP "ev_timer_again (loop, ev_timer *)" 4
1839 .IX Item "ev_timer_again (loop, ev_timer *)"
1840 This will act as if the timer timed out and restart it again if it is
1841 repeating. The exact semantics are:
1842 .Sp
1843 If the timer is pending, its pending status is cleared.
1844 .Sp
1845 If the timer is started but non-repeating, stop it (as if it timed out).
1846 .Sp
1847 If the timer is repeating, either start it if necessary (with the
1848 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1849 .Sp
1850 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1851 usage example.
1852 .IP "ev_tstamp repeat [read\-write]" 4
1853 .IX Item "ev_tstamp repeat [read-write]"
1854 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1855 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1856 which is also when any modifications are taken into account.
1857 .PP
1858 \fIExamples\fR
1859 .IX Subsection "Examples"
1860 .PP
1861 Example: Create a timer that fires after 60 seconds.
1862 .PP
1863 .Vb 5
1864 \& static void
1865 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1866 \& {
1867 \& .. one minute over, w is actually stopped right here
1868 \& }
1869 \&
1870 \& ev_timer mytimer;
1871 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1872 \& ev_timer_start (loop, &mytimer);
1873 .Ve
1874 .PP
1875 Example: Create a timeout timer that times out after 10 seconds of
1876 inactivity.
1877 .PP
1878 .Vb 5
1879 \& static void
1880 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1881 \& {
1882 \& .. ten seconds without any activity
1883 \& }
1884 \&
1885 \& ev_timer mytimer;
1886 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1887 \& ev_timer_again (&mytimer); /* start timer */
1888 \& ev_loop (loop, 0);
1889 \&
1890 \& // and in some piece of code that gets executed on any "activity":
1891 \& // reset the timeout to start ticking again at 10 seconds
1892 \& ev_timer_again (&mytimer);
1893 .Ve
1894 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1895 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1896 .IX Subsection "ev_periodic - to cron or not to cron?"
1897 Periodic watchers are also timers of a kind, but they are very versatile
1898 (and unfortunately a bit complex).
1899 .PP
1900 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1901 relative time, the physical time that passes) but on wall clock time
1902 (absolute time, the thing you can read on your calender or clock). The
1903 difference is that wall clock time can run faster or slower than real
1904 time, and time jumps are not uncommon (e.g. when you adjust your
1905 wrist-watch).
1906 .PP
1907 You can tell a periodic watcher to trigger after some specific point
1908 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1909 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
1910 not a delay) and then reset your system clock to January of the previous
1911 year, then it will take a year or more to trigger the event (unlike an
1912 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
1913 it, as it uses a relative timeout).
1914 .PP
1915 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
1916 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
1917 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
1918 those cannot react to time jumps.
1919 .PP
1920 As with timers, the callback is guaranteed to be invoked only when the
1921 point in time where it is supposed to trigger has passed. If multiple
1922 timers become ready during the same loop iteration then the ones with
1923 earlier time-out values are invoked before ones with later time-out values
1924 (but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1925 .PP
1926 \fIWatcher-Specific Functions and Data Members\fR
1927 .IX Subsection "Watcher-Specific Functions and Data Members"
1928 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1929 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1930 .PD 0
1931 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1932 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1933 .PD
1934 Lots of arguments, let's sort it out... There are basically three modes of
1935 operation, and we will explain them from simplest to most complex:
1936 .RS 4
1937 .IP "\(bu" 4
1938 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1939 .Sp
1940 In this configuration the watcher triggers an event after the wall clock
1941 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1942 time jump occurs, that is, if it is to be run at January 1st 2011 then it
1943 will be stopped and invoked when the system clock reaches or surpasses
1944 this point in time.
1945 .IP "\(bu" 4
1946 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1947 .Sp
1948 In this mode the watcher will always be scheduled to time out at the next
1949 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1950 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
1951 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1952 .Sp
1953 This can be used to create timers that do not drift with respect to the
1954 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
1955 hour, on the hour (with respect to \s-1UTC\s0):
1956 .Sp
1957 .Vb 1
1958 \& ev_periodic_set (&periodic, 0., 3600., 0);
1959 .Ve
1960 .Sp
1961 This doesn't mean there will always be 3600 seconds in between triggers,
1962 but only that the callback will be called when the system time shows a
1963 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1964 by 3600.
1965 .Sp
1966 Another way to think about it (for the mathematically inclined) is that
1967 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1968 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1969 .Sp
1970 For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
1971 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1972 this value, and in fact is often specified as zero.
1973 .Sp
1974 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
1975 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
1976 will of course deteriorate. Libev itself tries to be exact to be about one
1977 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
1978 .IP "\(bu" 4
1979 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1980 .Sp
1981 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1982 ignored. Instead, each time the periodic watcher gets scheduled, the
1983 reschedule callback will be called with the watcher as first, and the
1984 current time as second argument.
1985 .Sp
1986 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1987 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1988 allowed by documentation here\fR.
1989 .Sp
1990 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1991 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
1992 only event loop modification you are allowed to do).
1993 .Sp
1994 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1995 *w, ev_tstamp now)\*(C'\fR, e.g.:
1996 .Sp
1997 .Vb 5
1998 \& static ev_tstamp
1999 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2000 \& {
2001 \& return now + 60.;
2002 \& }
2003 .Ve
2004 .Sp
2005 It must return the next time to trigger, based on the passed time value
2006 (that is, the lowest time value larger than to the second argument). It
2007 will usually be called just before the callback will be triggered, but
2008 might be called at other times, too.
2009 .Sp
2010 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2011 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2012 .Sp
2013 This can be used to create very complex timers, such as a timer that
2014 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2015 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2016 you do this is, again, up to you (but it is not trivial, which is the main
2017 reason I omitted it as an example).
2018 .RE
2019 .RS 4
2020 .RE
2021 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2022 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2023 Simply stops and restarts the periodic watcher again. This is only useful
2024 when you changed some parameters or the reschedule callback would return
2025 a different time than the last time it was called (e.g. in a crond like
2026 program when the crontabs have changed).
2027 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2028 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2029 When active, returns the absolute time that the watcher is supposed
2030 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2031 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2032 rescheduling modes.
2033 .IP "ev_tstamp offset [read\-write]" 4
2034 .IX Item "ev_tstamp offset [read-write]"
2035 When repeating, this contains the offset value, otherwise this is the
2036 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2037 although libev might modify this value for better numerical stability).
2038 .Sp
2039 Can be modified any time, but changes only take effect when the periodic
2040 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2041 .IP "ev_tstamp interval [read\-write]" 4
2042 .IX Item "ev_tstamp interval [read-write]"
2043 The current interval value. Can be modified any time, but changes only
2044 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2045 called.
2046 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2047 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2048 The current reschedule callback, or \f(CW0\fR, if this functionality is
2049 switched off. Can be changed any time, but changes only take effect when
2050 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2051 .PP
2052 \fIExamples\fR
2053 .IX Subsection "Examples"
2054 .PP
2055 Example: Call a callback every hour, or, more precisely, whenever the
2056 system time is divisible by 3600. The callback invocation times have
2057 potentially a lot of jitter, but good long-term stability.
2058 .PP
2059 .Vb 5
2060 \& static void
2061 \& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
2062 \& {
2063 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2064 \& }
2065 \&
2066 \& ev_periodic hourly_tick;
2067 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2068 \& ev_periodic_start (loop, &hourly_tick);
2069 .Ve
2070 .PP
2071 Example: The same as above, but use a reschedule callback to do it:
2072 .PP
2073 .Vb 1
2074 \& #include <math.h>
2075 \&
2076 \& static ev_tstamp
2077 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2078 \& {
2079 \& return now + (3600. \- fmod (now, 3600.));
2080 \& }
2081 \&
2082 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2083 .Ve
2084 .PP
2085 Example: Call a callback every hour, starting now:
2086 .PP
2087 .Vb 4
2088 \& ev_periodic hourly_tick;
2089 \& ev_periodic_init (&hourly_tick, clock_cb,
2090 \& fmod (ev_now (loop), 3600.), 3600., 0);
2091 \& ev_periodic_start (loop, &hourly_tick);
2092 .Ve
2093 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
2094 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2095 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2096 Signal watchers will trigger an event when the process receives a specific
2097 signal one or more times. Even though signals are very asynchronous, libev
2098 will try it's best to deliver signals synchronously, i.e. as part of the
2099 normal event processing, like any other event.
2100 .PP
2101 If you want signals asynchronously, just use \f(CW\*(C`sigaction\*(C'\fR as you would
2102 do without libev and forget about sharing the signal. You can even use
2103 \&\f(CW\*(C`ev_async\*(C'\fR from a signal handler to synchronously wake up an event loop.
2104 .PP
2105 You can configure as many watchers as you like per signal. Only when the
2106 first watcher gets started will libev actually register a signal handler
2107 with the kernel (thus it coexists with your own signal handlers as long as
2108 you don't register any with libev for the same signal). Similarly, when
2109 the last signal watcher for a signal is stopped, libev will reset the
2110 signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
2111 .PP
2112 If possible and supported, libev will install its handlers with
2113 \&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so system calls should not be unduly
2114 interrupted. If you have a problem with system calls getting interrupted by
2115 signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
2116 them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2117 .PP
2118 \fIWatcher-Specific Functions and Data Members\fR
2119 .IX Subsection "Watcher-Specific Functions and Data Members"
2120 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2121 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2122 .PD 0
2123 .IP "ev_signal_set (ev_signal *, int signum)" 4
2124 .IX Item "ev_signal_set (ev_signal *, int signum)"
2125 .PD
2126 Configures the watcher to trigger on the given signal number (usually one
2127 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2128 .IP "int signum [read\-only]" 4
2129 .IX Item "int signum [read-only]"
2130 The signal the watcher watches out for.
2131 .PP
2132 \fIExamples\fR
2133 .IX Subsection "Examples"
2134 .PP
2135 Example: Try to exit cleanly on \s-1SIGINT\s0.
2136 .PP
2137 .Vb 5
2138 \& static void
2139 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2140 \& {
2141 \& ev_unloop (loop, EVUNLOOP_ALL);
2142 \& }
2143 \&
2144 \& ev_signal signal_watcher;
2145 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2146 \& ev_signal_start (loop, &signal_watcher);
2147 .Ve
2148 .ie n .Sh """ev_child"" \- watch out for process status changes"
2149 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
2150 .IX Subsection "ev_child - watch out for process status changes"
2151 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2152 some child status changes (most typically when a child of yours dies or
2153 exits). It is permissible to install a child watcher \fIafter\fR the child
2154 has been forked (which implies it might have already exited), as long
2155 as the event loop isn't entered (or is continued from a watcher), i.e.,
2156 forking and then immediately registering a watcher for the child is fine,
2157 but forking and registering a watcher a few event loop iterations later is
2158 not.
2159 .PP
2160 Only the default event loop is capable of handling signals, and therefore
2161 you can only register child watchers in the default event loop.
2162 .PP
2163 \fIProcess Interaction\fR
2164 .IX Subsection "Process Interaction"
2165 .PP
2166 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2167 initialised. This is necessary to guarantee proper behaviour even if
2168 the first child watcher is started after the child exits. The occurrence
2169 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2170 synchronously as part of the event loop processing. Libev always reaps all
2171 children, even ones not watched.
2172 .PP
2173 \fIOverriding the Built-In Processing\fR
2174 .IX Subsection "Overriding the Built-In Processing"
2175 .PP
2176 Libev offers no special support for overriding the built-in child
2177 processing, but if your application collides with libev's default child
2178 handler, you can override it easily by installing your own handler for
2179 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2180 default loop never gets destroyed. You are encouraged, however, to use an
2181 event-based approach to child reaping and thus use libev's support for
2182 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2183 .PP
2184 \fIStopping the Child Watcher\fR
2185 .IX Subsection "Stopping the Child Watcher"
2186 .PP
2187 Currently, the child watcher never gets stopped, even when the
2188 child terminates, so normally one needs to stop the watcher in the
2189 callback. Future versions of libev might stop the watcher automatically
2190 when a child exit is detected.
2191 .PP
2192 \fIWatcher-Specific Functions and Data Members\fR
2193 .IX Subsection "Watcher-Specific Functions and Data Members"
2194 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2195 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2196 .PD 0
2197 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2198 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2199 .PD
2200 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2201 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2202 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2203 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2204 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2205 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2206 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2207 activate the watcher when the process is stopped or continued).
2208 .IP "int pid [read\-only]" 4
2209 .IX Item "int pid [read-only]"
2210 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2211 .IP "int rpid [read\-write]" 4
2212 .IX Item "int rpid [read-write]"
2213 The process id that detected a status change.
2214 .IP "int rstatus [read\-write]" 4
2215 .IX Item "int rstatus [read-write]"
2216 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2217 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2218 .PP
2219 \fIExamples\fR
2220 .IX Subsection "Examples"
2221 .PP
2222 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2223 its completion.
2224 .PP
2225 .Vb 1
2226 \& ev_child cw;
2227 \&
2228 \& static void
2229 \& child_cb (EV_P_ ev_child *w, int revents)
2230 \& {
2231 \& ev_child_stop (EV_A_ w);
2232 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2233 \& }
2234 \&
2235 \& pid_t pid = fork ();
2236 \&
2237 \& if (pid < 0)
2238 \& // error
2239 \& else if (pid == 0)
2240 \& {
2241 \& // the forked child executes here
2242 \& exit (1);
2243 \& }
2244 \& else
2245 \& {
2246 \& ev_child_init (&cw, child_cb, pid, 0);
2247 \& ev_child_start (EV_DEFAULT_ &cw);
2248 \& }
2249 .Ve
2250 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
2251 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
2252 .IX Subsection "ev_stat - did the file attributes just change?"
2253 This watches a file system path for attribute changes. That is, it calls
2254 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2255 and sees if it changed compared to the last time, invoking the callback if
2256 it did.
2257 .PP
2258 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2259 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2260 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2261 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2262 least one) and all the other fields of the stat buffer having unspecified
2263 contents.
2264 .PP
2265 The path \fImust not\fR end in a slash or contain special components such as
2266 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2267 your working directory changes, then the behaviour is undefined.
2268 .PP
2269 Since there is no portable change notification interface available, the
2270 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2271 to see if it changed somehow. You can specify a recommended polling
2272 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2273 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2274 (which you can expect to be around five seconds, although this might
2275 change dynamically). Libev will also impose a minimum interval which is
2276 currently around \f(CW0.1\fR, but that's usually overkill.
2277 .PP
2278 This watcher type is not meant for massive numbers of stat watchers,
2279 as even with OS-supported change notifications, this can be
2280 resource-intensive.
2281 .PP
2282 At the time of this writing, the only OS-specific interface implemented
2283 is the Linux inotify interface (implementing kqueue support is left as an
2284 exercise for the reader. Note, however, that the author sees no way of
2285 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2286 .PP
2287 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2288 .IX Subsection "ABI Issues (Largefile Support)"
2289 .PP
2290 Libev by default (unless the user overrides this) uses the default
2291 compilation environment, which means that on systems with large file
2292 support disabled by default, you get the 32 bit version of the stat
2293 structure. When using the library from programs that change the \s-1ABI\s0 to
2294 use 64 bit file offsets the programs will fail. In that case you have to
2295 compile libev with the same flags to get binary compatibility. This is
2296 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2297 most noticeably displayed with ev_stat and large file support.
2298 .PP
2299 The solution for this is to lobby your distribution maker to make large
2300 file interfaces available by default (as e.g. FreeBSD does) and not
2301 optional. Libev cannot simply switch on large file support because it has
2302 to exchange stat structures with application programs compiled using the
2303 default compilation environment.
2304 .PP
2305 \fIInotify and Kqueue\fR
2306 .IX Subsection "Inotify and Kqueue"
2307 .PP
2308 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2309 runtime, it will be used to speed up change detection where possible. The
2310 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2311 watcher is being started.
2312 .PP
2313 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2314 except that changes might be detected earlier, and in some cases, to avoid
2315 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2316 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2317 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2318 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2319 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2320 xfs are fully working) libev usually gets away without polling.
2321 .PP
2322 There is no support for kqueue, as apparently it cannot be used to
2323 implement this functionality, due to the requirement of having a file
2324 descriptor open on the object at all times, and detecting renames, unlinks
2325 etc. is difficult.
2326 .PP
2327 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2328 .IX Subsection "stat () is a synchronous operation"
2329 .PP
2330 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2331 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2332 ()\*(C'\fR, which is a synchronous operation.
2333 .PP
2334 For local paths, this usually doesn't matter: unless the system is very
2335 busy or the intervals between stat's are large, a stat call will be fast,
2336 as the path data is usually in memory already (except when starting the
2337 watcher).
2338 .PP
2339 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2340 time due to network issues, and even under good conditions, a stat call
2341 often takes multiple milliseconds.
2342 .PP
2343 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2344 paths, although this is fully supported by libev.
2345 .PP
2346 \fIThe special problem of stat time resolution\fR
2347 .IX Subsection "The special problem of stat time resolution"
2348 .PP
2349 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2350 and even on systems where the resolution is higher, most file systems
2351 still only support whole seconds.
2352 .PP
2353 That means that, if the time is the only thing that changes, you can
2354 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2355 calls your callback, which does something. When there is another update
2356 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2357 stat data does change in other ways (e.g. file size).
2358 .PP
2359 The solution to this is to delay acting on a change for slightly more
2360 than a second (or till slightly after the next full second boundary), using
2361 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2362 ev_timer_again (loop, w)\*(C'\fR).
2363 .PP
2364 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2365 of some operating systems (where the second counter of the current time
2366 might be be delayed. One such system is the Linux kernel, where a call to
2367 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2368 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2369 update file times then there will be a small window where the kernel uses
2370 the previous second to update file times but libev might already execute
2371 the timer callback).
2372 .PP
2373 \fIWatcher-Specific Functions and Data Members\fR
2374 .IX Subsection "Watcher-Specific Functions and Data Members"
2375 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2376 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2377 .PD 0
2378 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2379 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2380 .PD
2381 Configures the watcher to wait for status changes of the given
2382 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2383 be detected and should normally be specified as \f(CW0\fR to let libev choose
2384 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2385 path for as long as the watcher is active.
2386 .Sp
2387 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2388 relative to the attributes at the time the watcher was started (or the
2389 last change was detected).
2390 .IP "ev_stat_stat (loop, ev_stat *)" 4
2391 .IX Item "ev_stat_stat (loop, ev_stat *)"
2392 Updates the stat buffer immediately with new values. If you change the
2393 watched path in your callback, you could call this function to avoid
2394 detecting this change (while introducing a race condition if you are not
2395 the only one changing the path). Can also be useful simply to find out the
2396 new values.
2397 .IP "ev_statdata attr [read\-only]" 4
2398 .IX Item "ev_statdata attr [read-only]"
2399 The most-recently detected attributes of the file. Although the type is
2400 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2401 suitable for your system, but you can only rely on the POSIX-standardised
2402 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2403 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2404 .IP "ev_statdata prev [read\-only]" 4
2405 .IX Item "ev_statdata prev [read-only]"
2406 The previous attributes of the file. The callback gets invoked whenever
2407 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2408 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,
2409 \&\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.
2410 .IP "ev_tstamp interval [read\-only]" 4
2411 .IX Item "ev_tstamp interval [read-only]"
2412 The specified interval.
2413 .IP "const char *path [read\-only]" 4
2414 .IX Item "const char *path [read-only]"
2415 The file system path that is being watched.
2416 .PP
2417 \fIExamples\fR
2418 .IX Subsection "Examples"
2419 .PP
2420 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2421 .PP
2422 .Vb 10
2423 \& static void
2424 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2425 \& {
2426 \& /* /etc/passwd changed in some way */
2427 \& if (w\->attr.st_nlink)
2428 \& {
2429 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2430 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2431 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2432 \& }
2433 \& else
2434 \& /* you shalt not abuse printf for puts */
2435 \& puts ("wow, /etc/passwd is not there, expect problems. "
2436 \& "if this is windows, they already arrived\en");
2437 \& }
2438 \&
2439 \& ...
2440 \& ev_stat passwd;
2441 \&
2442 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2443 \& ev_stat_start (loop, &passwd);
2444 .Ve
2445 .PP
2446 Example: Like above, but additionally use a one-second delay so we do not
2447 miss updates (however, frequent updates will delay processing, too, so
2448 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2449 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2450 .PP
2451 .Vb 2
2452 \& static ev_stat passwd;
2453 \& static ev_timer timer;
2454 \&
2455 \& static void
2456 \& timer_cb (EV_P_ ev_timer *w, int revents)
2457 \& {
2458 \& ev_timer_stop (EV_A_ w);
2459 \&
2460 \& /* now it\*(Aqs one second after the most recent passwd change */
2461 \& }
2462 \&
2463 \& static void
2464 \& stat_cb (EV_P_ ev_stat *w, int revents)
2465 \& {
2466 \& /* reset the one\-second timer */
2467 \& ev_timer_again (EV_A_ &timer);
2468 \& }
2469 \&
2470 \& ...
2471 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2472 \& ev_stat_start (loop, &passwd);
2473 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2474 .Ve
2475 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
2476 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
2477 .IX Subsection "ev_idle - when you've got nothing better to do..."
2478 Idle watchers trigger events when no other events of the same or higher
2479 priority are pending (prepare, check and other idle watchers do not count
2480 as receiving \*(L"events\*(R").
2481 .PP
2482 That is, as long as your process is busy handling sockets or timeouts
2483 (or even signals, imagine) of the same or higher priority it will not be
2484 triggered. But when your process is idle (or only lower-priority watchers
2485 are pending), the idle watchers are being called once per event loop
2486 iteration \- until stopped, that is, or your process receives more events
2487 and becomes busy again with higher priority stuff.
2488 .PP
2489 The most noteworthy effect is that as long as any idle watchers are
2490 active, the process will not block when waiting for new events.
2491 .PP
2492 Apart from keeping your process non-blocking (which is a useful
2493 effect on its own sometimes), idle watchers are a good place to do
2494 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2495 event loop has handled all outstanding events.
2496 .PP
2497 \fIWatcher-Specific Functions and Data Members\fR
2498 .IX Subsection "Watcher-Specific Functions and Data Members"
2499 .IP "ev_idle_init (ev_idle *, callback)" 4
2500 .IX Item "ev_idle_init (ev_idle *, callback)"
2501 Initialises and configures the idle watcher \- it has no parameters of any
2502 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2503 believe me.
2504 .PP
2505 \fIExamples\fR
2506 .IX Subsection "Examples"
2507 .PP
2508 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2509 callback, free it. Also, use no error checking, as usual.
2510 .PP
2511 .Vb 7
2512 \& static void
2513 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2514 \& {
2515 \& free (w);
2516 \& // now do something you wanted to do when the program has
2517 \& // no longer anything immediate to do.
2518 \& }
2519 \&
2520 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2521 \& ev_idle_init (idle_watcher, idle_cb);
2522 \& ev_idle_start (loop, idle_cb);
2523 .Ve
2524 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
2525 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2526 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2527 Prepare and check watchers are usually (but not always) used in pairs:
2528 prepare watchers get invoked before the process blocks and check watchers
2529 afterwards.
2530 .PP
2531 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2532 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2533 watchers. Other loops than the current one are fine, however. The
2534 rationale behind this is that you do not need to check for recursion in
2535 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2536 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2537 called in pairs bracketing the blocking call.
2538 .PP
2539 Their main purpose is to integrate other event mechanisms into libev and
2540 their use is somewhat advanced. They could be used, for example, to track
2541 variable changes, implement your own watchers, integrate net-snmp or a
2542 coroutine library and lots more. They are also occasionally useful if
2543 you cache some data and want to flush it before blocking (for example,
2544 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2545 watcher).
2546 .PP
2547 This is done by examining in each prepare call which file descriptors
2548 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2549 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2550 libraries provide exactly this functionality). Then, in the check watcher,
2551 you check for any events that occurred (by checking the pending status
2552 of all watchers and stopping them) and call back into the library. The
2553 I/O and timer callbacks will never actually be called (but must be valid
2554 nevertheless, because you never know, you know?).
2555 .PP
2556 As another example, the Perl Coro module uses these hooks to integrate
2557 coroutines into libev programs, by yielding to other active coroutines
2558 during each prepare and only letting the process block if no coroutines
2559 are ready to run (it's actually more complicated: it only runs coroutines
2560 with priority higher than or equal to the event loop and one coroutine
2561 of lower priority, but only once, using idle watchers to keep the event
2562 loop from blocking if lower-priority coroutines are active, thus mapping
2563 low-priority coroutines to idle/background tasks).
2564 .PP
2565 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2566 priority, to ensure that they are being run before any other watchers
2567 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2568 .PP
2569 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2570 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2571 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2572 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2573 loops those other event loops might be in an unusable state until their
2574 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2575 others).
2576 .PP
2577 \fIWatcher-Specific Functions and Data Members\fR
2578 .IX Subsection "Watcher-Specific Functions and Data Members"
2579 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2580 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2581 .PD 0
2582 .IP "ev_check_init (ev_check *, callback)" 4
2583 .IX Item "ev_check_init (ev_check *, callback)"
2584 .PD
2585 Initialises and configures the prepare or check watcher \- they have no
2586 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2587 macros, but using them is utterly, utterly, utterly and completely
2588 pointless.
2589 .PP
2590 \fIExamples\fR
2591 .IX Subsection "Examples"
2592 .PP
2593 There are a number of principal ways to embed other event loops or modules
2594 into libev. Here are some ideas on how to include libadns into libev
2595 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2596 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2597 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2598 Glib event loop).
2599 .PP
2600 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2601 and in a check watcher, destroy them and call into libadns. What follows
2602 is pseudo-code only of course. This requires you to either use a low
2603 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2604 the callbacks for the IO/timeout watchers might not have been called yet.
2605 .PP
2606 .Vb 2
2607 \& static ev_io iow [nfd];
2608 \& static ev_timer tw;
2609 \&
2610 \& static void
2611 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2612 \& {
2613 \& }
2614 \&
2615 \& // create io watchers for each fd and a timer before blocking
2616 \& static void
2617 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2618 \& {
2619 \& int timeout = 3600000;
2620 \& struct pollfd fds [nfd];
2621 \& // actual code will need to loop here and realloc etc.
2622 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2623 \&
2624 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2625 \& ev_timer_init (&tw, 0, timeout * 1e\-3);
2626 \& ev_timer_start (loop, &tw);
2627 \&
2628 \& // create one ev_io per pollfd
2629 \& for (int i = 0; i < nfd; ++i)
2630 \& {
2631 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2632 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2633 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2634 \&
2635 \& fds [i].revents = 0;
2636 \& ev_io_start (loop, iow + i);
2637 \& }
2638 \& }
2639 \&
2640 \& // stop all watchers after blocking
2641 \& static void
2642 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2643 \& {
2644 \& ev_timer_stop (loop, &tw);
2645 \&
2646 \& for (int i = 0; i < nfd; ++i)
2647 \& {
2648 \& // set the relevant poll flags
2649 \& // could also call adns_processreadable etc. here
2650 \& struct pollfd *fd = fds + i;
2651 \& int revents = ev_clear_pending (iow + i);
2652 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2653 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2654 \&
2655 \& // now stop the watcher
2656 \& ev_io_stop (loop, iow + i);
2657 \& }
2658 \&
2659 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2660 \& }
2661 .Ve
2662 .PP
2663 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2664 in the prepare watcher and would dispose of the check watcher.
2665 .PP
2666 Method 3: If the module to be embedded supports explicit event
2667 notification (libadns does), you can also make use of the actual watcher
2668 callbacks, and only destroy/create the watchers in the prepare watcher.
2669 .PP
2670 .Vb 5
2671 \& static void
2672 \& timer_cb (EV_P_ ev_timer *w, int revents)
2673 \& {
2674 \& adns_state ads = (adns_state)w\->data;
2675 \& update_now (EV_A);
2676 \&
2677 \& adns_processtimeouts (ads, &tv_now);
2678 \& }
2679 \&
2680 \& static void
2681 \& io_cb (EV_P_ ev_io *w, int revents)
2682 \& {
2683 \& adns_state ads = (adns_state)w\->data;
2684 \& update_now (EV_A);
2685 \&
2686 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2687 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2688 \& }
2689 \&
2690 \& // do not ever call adns_afterpoll
2691 .Ve
2692 .PP
2693 Method 4: Do not use a prepare or check watcher because the module you
2694 want to embed is not flexible enough to support it. Instead, you can
2695 override their poll function. The drawback with this solution is that the
2696 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2697 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2698 libglib event loop.
2699 .PP
2700 .Vb 4
2701 \& static gint
2702 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2703 \& {
2704 \& int got_events = 0;
2705 \&
2706 \& for (n = 0; n < nfds; ++n)
2707 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2708 \&
2709 \& if (timeout >= 0)
2710 \& // create/start timer
2711 \&
2712 \& // poll
2713 \& ev_loop (EV_A_ 0);
2714 \&
2715 \& // stop timer again
2716 \& if (timeout >= 0)
2717 \& ev_timer_stop (EV_A_ &to);
2718 \&
2719 \& // stop io watchers again \- their callbacks should have set
2720 \& for (n = 0; n < nfds; ++n)
2721 \& ev_io_stop (EV_A_ iow [n]);
2722 \&
2723 \& return got_events;
2724 \& }
2725 .Ve
2726 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2727 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2728 .IX Subsection "ev_embed - when one backend isn't enough..."
2729 This is a rather advanced watcher type that lets you embed one event loop
2730 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2731 loop, other types of watchers might be handled in a delayed or incorrect
2732 fashion and must not be used).
2733 .PP
2734 There are primarily two reasons you would want that: work around bugs and
2735 prioritise I/O.
2736 .PP
2737 As an example for a bug workaround, the kqueue backend might only support
2738 sockets on some platform, so it is unusable as generic backend, but you
2739 still want to make use of it because you have many sockets and it scales
2740 so nicely. In this case, you would create a kqueue-based loop and embed
2741 it into your default loop (which might use e.g. poll). Overall operation
2742 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2743 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2744 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2745 .PP
2746 As for prioritising I/O: under rare circumstances you have the case where
2747 some fds have to be watched and handled very quickly (with low latency),
2748 and even priorities and idle watchers might have too much overhead. In
2749 this case you would put all the high priority stuff in one loop and all
2750 the rest in a second one, and embed the second one in the first.
2751 .PP
2752 As long as the watcher is active, the callback will be invoked every
2753 time there might be events pending in the embedded loop. The callback
2754 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2755 sweep and invoke their callbacks (the callback doesn't need to invoke the
2756 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2757 to give the embedded loop strictly lower priority for example).
2758 .PP
2759 You can also set the callback to \f(CW0\fR, in which case the embed watcher
2760 will automatically execute the embedded loop sweep whenever necessary.
2761 .PP
2762 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2763 is active, i.e., the embedded loop will automatically be forked when the
2764 embedding loop forks. In other cases, the user is responsible for calling
2765 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2766 .PP
2767 Unfortunately, not all backends are embeddable: only the ones returned by
2768 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2769 portable one.
2770 .PP
2771 So when you want to use this feature you will always have to be prepared
2772 that you cannot get an embeddable loop. The recommended way to get around
2773 this is to have a separate variables for your embeddable loop, try to
2774 create it, and if that fails, use the normal loop for everything.
2775 .PP
2776 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2777 .IX Subsection "ev_embed and fork"
2778 .PP
2779 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2780 automatically be applied to the embedded loop as well, so no special
2781 fork handling is required in that case. When the watcher is not running,
2782 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2783 as applicable.
2784 .PP
2785 \fIWatcher-Specific Functions and Data Members\fR
2786 .IX Subsection "Watcher-Specific Functions and Data Members"
2787 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2788 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2789 .PD 0
2790 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2791 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2792 .PD
2793 Configures the watcher to embed the given loop, which must be
2794 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2795 invoked automatically, otherwise it is the responsibility of the callback
2796 to invoke it (it will continue to be called until the sweep has been done,
2797 if you do not want that, you need to temporarily stop the embed watcher).
2798 .IP "ev_embed_sweep (loop, ev_embed *)" 4
2799 .IX Item "ev_embed_sweep (loop, ev_embed *)"
2800 Make a single, non-blocking sweep over the embedded loop. This works
2801 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2802 appropriate way for embedded loops.
2803 .IP "struct ev_loop *other [read\-only]" 4
2804 .IX Item "struct ev_loop *other [read-only]"
2805 The embedded event loop.
2806 .PP
2807 \fIExamples\fR
2808 .IX Subsection "Examples"
2809 .PP
2810 Example: Try to get an embeddable event loop and embed it into the default
2811 event loop. If that is not possible, use the default loop. The default
2812 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
2813 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
2814 used).
2815 .PP
2816 .Vb 3
2817 \& struct ev_loop *loop_hi = ev_default_init (0);
2818 \& struct ev_loop *loop_lo = 0;
2819 \& ev_embed embed;
2820 \&
2821 \& // see if there is a chance of getting one that works
2822 \& // (remember that a flags value of 0 means autodetection)
2823 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2824 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2825 \& : 0;
2826 \&
2827 \& // if we got one, then embed it, otherwise default to loop_hi
2828 \& if (loop_lo)
2829 \& {
2830 \& ev_embed_init (&embed, 0, loop_lo);
2831 \& ev_embed_start (loop_hi, &embed);
2832 \& }
2833 \& else
2834 \& loop_lo = loop_hi;
2835 .Ve
2836 .PP
2837 Example: Check if kqueue is available but not recommended and create
2838 a kqueue backend for use with sockets (which usually work with any
2839 kqueue implementation). Store the kqueue/socket\-only event loop in
2840 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2841 .PP
2842 .Vb 3
2843 \& struct ev_loop *loop = ev_default_init (0);
2844 \& struct ev_loop *loop_socket = 0;
2845 \& ev_embed embed;
2846 \&
2847 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2848 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2849 \& {
2850 \& ev_embed_init (&embed, 0, loop_socket);
2851 \& ev_embed_start (loop, &embed);
2852 \& }
2853 \&
2854 \& if (!loop_socket)
2855 \& loop_socket = loop;
2856 \&
2857 \& // now use loop_socket for all sockets, and loop for everything else
2858 .Ve
2859 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2860 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2861 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2862 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2863 whoever is a good citizen cared to tell libev about it by calling
2864 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2865 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2866 and only in the child after the fork. If whoever good citizen calling
2867 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2868 handlers will be invoked, too, of course.
2869 .PP
2870 \fIThe special problem of life after fork \- how is it possible?\fR
2871 .IX Subsection "The special problem of life after fork - how is it possible?"
2872 .PP
2873 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
2874 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
2875 sequence should be handled by libev without any problems.
2876 .PP
2877 This changes when the application actually wants to do event handling
2878 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
2879 fork.
2880 .PP
2881 The default mode of operation (for libev, with application help to detect
2882 forks) is to duplicate all the state in the child, as would be expected
2883 when \fIeither\fR the parent \fIor\fR the child process continues.
2884 .PP
2885 When both processes want to continue using libev, then this is usually the
2886 wrong result. In that case, usually one process (typically the parent) is
2887 supposed to continue with all watchers in place as before, while the other
2888 process typically wants to start fresh, i.e. without any active watchers.
2889 .PP
2890 The cleanest and most efficient way to achieve that with libev is to
2891 simply create a new event loop, which of course will be \*(L"empty\*(R", and
2892 use that for new watchers. This has the advantage of not touching more
2893 memory than necessary, and thus avoiding the copy-on-write, and the
2894 disadvantage of having to use multiple event loops (which do not support
2895 signal watchers).
2896 .PP
2897 When this is not possible, or you want to use the default loop for
2898 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
2899 \&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
2900 the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
2901 have to be careful not to execute code that modifies those watchers. Note
2902 also that in that case, you have to re-register any signal watchers.
2903 .PP
2904 \fIWatcher-Specific Functions and Data Members\fR
2905 .IX Subsection "Watcher-Specific Functions and Data Members"
2906 .IP "ev_fork_init (ev_signal *, callback)" 4
2907 .IX Item "ev_fork_init (ev_signal *, callback)"
2908 Initialises and configures the fork watcher \- it has no parameters of any
2909 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2910 believe me.
2911 .ie n .Sh """ev_async"" \- how to wake up another event loop"
2912 .el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2913 .IX Subsection "ev_async - how to wake up another event loop"
2914 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2915 asynchronous sources such as signal handlers (as opposed to multiple event
2916 loops \- those are of course safe to use in different threads).
2917 .PP
2918 Sometimes, however, you need to wake up another event loop you do not
2919 control, for example because it belongs to another thread. This is what
2920 \&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2921 can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2922 safe.
2923 .PP
2924 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2925 too, are asynchronous in nature, and signals, too, will be compressed
2926 (i.e. the number of callback invocations may be less than the number of
2927 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2928 .PP
2929 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2930 just the default loop.
2931 .PP
2932 \fIQueueing\fR
2933 .IX Subsection "Queueing"
2934 .PP
2935 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2936 is that the author does not know of a simple (or any) algorithm for a
2937 multiple-writer-single-reader queue that works in all cases and doesn't
2938 need elaborate support such as pthreads.
2939 .PP
2940 That means that if you want to queue data, you have to provide your own
2941 queue. But at least I can tell you how to implement locking around your
2942 queue:
2943 .IP "queueing from a signal handler context" 4
2944 .IX Item "queueing from a signal handler context"
2945 To implement race-free queueing, you simply add to the queue in the signal
2946 handler but you block the signal handler in the watcher callback. Here is
2947 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
2948 .Sp
2949 .Vb 1
2950 \& static ev_async mysig;
2951 \&
2952 \& static void
2953 \& sigusr1_handler (void)
2954 \& {
2955 \& sometype data;
2956 \&
2957 \& // no locking etc.
2958 \& queue_put (data);
2959 \& ev_async_send (EV_DEFAULT_ &mysig);
2960 \& }
2961 \&
2962 \& static void
2963 \& mysig_cb (EV_P_ ev_async *w, int revents)
2964 \& {
2965 \& sometype data;
2966 \& sigset_t block, prev;
2967 \&
2968 \& sigemptyset (&block);
2969 \& sigaddset (&block, SIGUSR1);
2970 \& sigprocmask (SIG_BLOCK, &block, &prev);
2971 \&
2972 \& while (queue_get (&data))
2973 \& process (data);
2974 \&
2975 \& if (sigismember (&prev, SIGUSR1)
2976 \& sigprocmask (SIG_UNBLOCK, &block, 0);
2977 \& }
2978 .Ve
2979 .Sp
2980 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2981 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2982 either...).
2983 .IP "queueing from a thread context" 4
2984 .IX Item "queueing from a thread context"
2985 The strategy for threads is different, as you cannot (easily) block
2986 threads but you can easily preempt them, so to queue safely you need to
2987 employ a traditional mutex lock, such as in this pthread example:
2988 .Sp
2989 .Vb 2
2990 \& static ev_async mysig;
2991 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2992 \&
2993 \& static void
2994 \& otherthread (void)
2995 \& {
2996 \& // only need to lock the actual queueing operation
2997 \& pthread_mutex_lock (&mymutex);
2998 \& queue_put (data);
2999 \& pthread_mutex_unlock (&mymutex);
3000 \&
3001 \& ev_async_send (EV_DEFAULT_ &mysig);
3002 \& }
3003 \&
3004 \& static void
3005 \& mysig_cb (EV_P_ ev_async *w, int revents)
3006 \& {
3007 \& pthread_mutex_lock (&mymutex);
3008 \&
3009 \& while (queue_get (&data))
3010 \& process (data);
3011 \&
3012 \& pthread_mutex_unlock (&mymutex);
3013 \& }
3014 .Ve
3015 .PP
3016 \fIWatcher-Specific Functions and Data Members\fR
3017 .IX Subsection "Watcher-Specific Functions and Data Members"
3018 .IP "ev_async_init (ev_async *, callback)" 4
3019 .IX Item "ev_async_init (ev_async *, callback)"
3020 Initialises and configures the async watcher \- it has no parameters of any
3021 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3022 trust me.
3023 .IP "ev_async_send (loop, ev_async *)" 4
3024 .IX Item "ev_async_send (loop, ev_async *)"
3025 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3026 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3027 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3028 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3029 section below on what exactly this means).
3030 .Sp
3031 Note that, as with other watchers in libev, multiple events might get
3032 compressed into a single callback invocation (another way to look at this
3033 is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3034 reset when the event loop detects that).
3035 .Sp
3036 This call incurs the overhead of a system call only once per event loop
3037 iteration, so while the overhead might be noticeable, it doesn't apply to
3038 repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3039 .IP "bool = ev_async_pending (ev_async *)" 4
3040 .IX Item "bool = ev_async_pending (ev_async *)"
3041 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3042 watcher but the event has not yet been processed (or even noted) by the
3043 event loop.
3044 .Sp
3045 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3046 the loop iterates next and checks for the watcher to have become active,
3047 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3048 quickly check whether invoking the loop might be a good idea.
3049 .Sp
3050 Not that this does \fInot\fR check whether the watcher itself is pending,
3051 only whether it has been requested to make this watcher pending: there
3052 is a time window between the event loop checking and resetting the async
3053 notification, and the callback being invoked.
3056 There are some other functions of possible interest. Described. Here. Now.
3057 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3058 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3059 This function combines a simple timer and an I/O watcher, calls your
3060 callback on whichever event happens first and automatically stops both
3061 watchers. This is useful if you want to wait for a single event on an fd
3062 or timeout without having to allocate/configure/start/stop/free one or
3063 more watchers yourself.
3064 .Sp
3065 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3066 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3067 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3068 .Sp
3069 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3070 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3071 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3072 .Sp
3073 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
3074 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3075 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3076 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3077 a timeout and an io event at the same time \- you probably should give io
3078 events precedence.
3079 .Sp
3080 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3081 .Sp
3082 .Vb 7
3083 \& static void stdin_ready (int revents, void *arg)
3084 \& {
3085 \& if (revents & EV_READ)
3086 \& /* stdin might have data for us, joy! */;
3087 \& else if (revents & EV_TIMEOUT)
3088 \& /* doh, nothing entered */;
3089 \& }
3090 \&
3091 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3092 .Ve
3093 .IP "ev_feed_event (struct ev_loop *, watcher *, int revents)" 4
3094 .IX Item "ev_feed_event (struct ev_loop *, watcher *, int revents)"
3095 Feeds the given event set into the event loop, as if the specified event
3096 had happened for the specified watcher (which must be a pointer to an
3097 initialised but not necessarily started event watcher).
3098 .IP "ev_feed_fd_event (struct ev_loop *, int fd, int revents)" 4
3099 .IX Item "ev_feed_fd_event (struct ev_loop *, int fd, int revents)"
3100 Feed an event on the given fd, as if a file descriptor backend detected
3101 the given events it.
3102 .IP "ev_feed_signal_event (struct ev_loop *loop, int signum)" 4
3103 .IX Item "ev_feed_signal_event (struct ev_loop *loop, int signum)"
3104 Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3105 loop!).
3108 Libev offers a compatibility emulation layer for libevent. It cannot
3109 emulate the internals of libevent, so here are some usage hints:
3110 .IP "\(bu" 4
3111 Use it by including <event.h>, as usual.
3112 .IP "\(bu" 4
3113 The following members are fully supported: ev_base, ev_callback,
3114 ev_arg, ev_fd, ev_res, ev_events.
3115 .IP "\(bu" 4
3116 Avoid using ev_flags and the EVLIST_*\-macros, while it is
3117 maintained by libev, it does not work exactly the same way as in libevent (consider
3118 it a private \s-1API\s0).
3119 .IP "\(bu" 4
3120 Priorities are not currently supported. Initialising priorities
3121 will fail and all watchers will have the same priority, even though there
3122 is an ev_pri field.
3123 .IP "\(bu" 4
3124 In libevent, the last base created gets the signals, in libev, the
3125 first base created (== the default loop) gets the signals.
3126 .IP "\(bu" 4
3127 Other members are not supported.
3128 .IP "\(bu" 4
3129 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
3130 to use the libev header file and library.
3131 .SH "\*(C+ SUPPORT"
3132 .IX Header " SUPPORT"
3133 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3134 you to use some convenience methods to start/stop watchers and also change
3135 the callback model to a model using method callbacks on objects.
3136 .PP
3137 To use it,
3138 .PP
3139 .Vb 1
3140 \& #include <ev++.h>
3141 .Ve
3142 .PP
3143 This automatically includes \fIev.h\fR and puts all of its definitions (many
3144 of them macros) into the global namespace. All \*(C+ specific things are
3145 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3146 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3147 .PP
3148 Care has been taken to keep the overhead low. The only data member the \*(C+
3149 classes add (compared to plain C\-style watchers) is the event loop pointer
3150 that the watcher is associated with (or no additional members at all if
3151 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3152 .PP
3153 Currently, functions, and static and non-static member functions can be
3154 used as callbacks. Other types should be easy to add as long as they only
3155 need one additional pointer for context. If you need support for other
3156 types of functors please contact the author (preferably after implementing
3157 it).
3158 .PP
3159 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3160 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
3161 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3162 .IX Item "ev::READ, ev::WRITE etc."
3163 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3164 macros from \fIev.h\fR.
3165 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
3166 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3167 .IX Item "ev::tstamp, ev::now"
3168 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3169 .ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
3170 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3171 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3172 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3173 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3174 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3175 defines by many implementations.
3176 .Sp
3177 All of those classes have these methods:
3178 .RS 4
3179 .IP "ev::TYPE::TYPE ()" 4
3180 .IX Item "ev::TYPE::TYPE ()"
3181 .PD 0
3182 .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
3183 .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
3184 .IP "ev::TYPE::~TYPE" 4
3185 .IX Item "ev::TYPE::~TYPE"
3186 .PD
3187 The constructor (optionally) takes an event loop to associate the watcher
3188 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3189 .Sp
3190 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3191 \&\f(CW\*(C`set\*(C'\fR method before starting it.
3192 .Sp
3193 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3194 method to set a callback before you can start the watcher.
3195 .Sp
3196 (The reason why you have to use a method is a limitation in \*(C+ which does
3197 not allow explicit template arguments for constructors).
3198 .Sp
3199 The destructor automatically stops the watcher if it is active.
3200 .IP "w\->set<class, &class::method> (object *)" 4
3201 .IX Item "w->set<class, &class::method> (object *)"
3202 This method sets the callback method to call. The method has to have a
3203 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3204 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3205 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3206 .Sp
3207 This method synthesizes efficient thunking code to call your method from
3208 the C callback that libev requires. If your compiler can inline your
3209 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3210 your compiler is good :), then the method will be fully inlined into the
3211 thunking function, making it as fast as a direct C callback.
3212 .Sp
3213 Example: simple class declaration and watcher initialisation
3214 .Sp
3215 .Vb 4
3216 \& struct myclass
3217 \& {
3218 \& void io_cb (ev::io &w, int revents) { }
3219 \& }
3220 \&
3221 \& myclass obj;
3222 \& ev::io iow;
3223 \& iow.set <myclass, &myclass::io_cb> (&obj);
3224 .Ve
3225 .IP "w\->set (object *)" 4
3226 .IX Item "w->set (object *)"
3227 This is an \fBexperimental\fR feature that might go away in a future version.
3228 .Sp
3229 This is a variation of a method callback \- leaving out the method to call
3230 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3231 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3232 the time. Incidentally, you can then also leave out the template argument
3233 list.
3234 .Sp
3235 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3236 int revents)\*(C'\fR.
3237 .Sp
3238 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3239 .Sp
3240 Example: use a functor object as callback.
3241 .Sp
3242 .Vb 7
3243 \& struct myfunctor
3244 \& {
3245 \& void operator() (ev::io &w, int revents)
3246 \& {
3247 \& ...
3248 \& }
3249 \& }
3250 \&
3251 \& myfunctor f;
3252 \&
3253 \& ev::io w;
3254 \& w.set (&f);
3255 .Ve
3256 .IP "w\->set<function> (void *data = 0)" 4
3257 .IX Item "w->set<function> (void *data = 0)"
3258 Also sets a callback, but uses a static method or plain function as
3259 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3260 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3261 .Sp
3262 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3263 .Sp
3264 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3265 .Sp
3266 Example: Use a plain function as callback.
3267 .Sp
3268 .Vb 2
3269 \& static void io_cb (ev::io &w, int revents) { }
3270 \& iow.set <io_cb> ();
3271 .Ve
3272 .IP "w\->set (struct ev_loop *)" 4
3273 .IX Item "w->set (struct ev_loop *)"
3274 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3275 do this when the watcher is inactive (and not pending either).
3276 .IP "w\->set ([arguments])" 4
3277 .IX Item "w->set ([arguments])"
3278 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3279 called at least once. Unlike the C counterpart, an active watcher gets
3280 automatically stopped and restarted when reconfiguring it with this
3281 method.
3282 .IP "w\->start ()" 4
3283 .IX Item "w->start ()"
3284 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3285 constructor already stores the event loop.
3286 .IP "w\->stop ()" 4
3287 .IX Item "w->stop ()"
3288 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3289 .ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
3290 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3291 .IX Item "w->again () (ev::timer, ev::periodic only)"
3292 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3293 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3294 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3295 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3296 .IX Item "w->sweep () (ev::embed only)"
3297 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3298 .ie n .IP "w\->update () (""ev::stat"" only)" 4
3299 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3300 .IX Item "w->update () (ev::stat only)"
3301 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3302 .RE
3303 .RS 4
3304 .RE
3305 .PP
3306 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3307 the constructor.
3308 .PP
3309 .Vb 4
3310 \& class myclass
3311 \& {
3312 \& ev::io io ; void io_cb (ev::io &w, int revents);
3313 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3314 \&
3315 \& myclass (int fd)
3316 \& {
3317 \& io .set <myclass, &myclass::io_cb > (this);
3318 \& idle.set <myclass, &myclass::idle_cb> (this);
3319 \&
3320 \& io.start (fd, ev::READ);
3321 \& }
3322 \& };
3323 .Ve
3326 Libev does not offer other language bindings itself, but bindings for a
3327 number of languages exist in the form of third-party packages. If you know
3328 any interesting language binding in addition to the ones listed here, drop
3329 me a note.
3330 .IP "Perl" 4
3331 .IX Item "Perl"
3332 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3333 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3334 there are additional modules that implement libev-compatible interfaces
3335 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),
3336 \&\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
3337 and \f(CW\*(C`EV::Glib\*(C'\fR).
3338 .Sp
3339 It can be found and installed via \s-1CPAN\s0, its homepage is at
3340 <>.
3341 .IP "Python" 4
3342 .IX Item "Python"
3343 Python bindings can be found at <>. It
3344 seems to be quite complete and well-documented.
3345 .IP "Ruby" 4
3346 .IX Item "Ruby"
3347 Tony Arcieri has written a ruby extension that offers access to a subset
3348 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3349 more on top of it. It can be found via gem servers. Its homepage is at
3350 <>.
3351 .Sp
3352 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3353 makes rev work even on mingw.
3354 .IP "Haskell" 4
3355 .IX Item "Haskell"
3356 A haskell binding to libev is available at
3357 <\-bin/hackage\-scripts/package/hlibev>.
3358 .IP "D" 4
3359 .IX Item "D"
3360 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3361 be found at <>.
3362 .IP "Ocaml" 4
3363 .IX Item "Ocaml"
3364 Erkki Seppala has written Ocaml bindings for libev, to be found at
3365 <\-ev/>.
3367 .IX Header "MACRO MAGIC"
3368 Libev can be compiled with a variety of options, the most fundamental
3369 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3370 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3371 .PP
3372 To make it easier to write programs that cope with either variant, the
3373 following macros are defined:
3374 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
3375 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3376 .IX Item "EV_A, EV_A_"
3377 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3378 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3379 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3380 .Sp
3381 .Vb 3
3382 \& ev_unref (EV_A);
3383 \& ev_timer_add (EV_A_ watcher);
3384 \& ev_loop (EV_A_ 0);
3385 .Ve
3386 .Sp
3387 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3388 which is often provided by the following macro.
3389 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
3390 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3391 .IX Item "EV_P, EV_P_"
3392 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3393 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3394 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3395 .Sp
3396 .Vb 2
3397 \& // this is how ev_unref is being declared
3398 \& static void ev_unref (EV_P);
3399 \&
3400 \& // this is how you can declare your typical callback
3401 \& static void cb (EV_P_ ev_timer *w, int revents)
3402 .Ve
3403 .Sp
3404 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3405 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3406 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
3407 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3409 Similar to the other two macros, this gives you the value of the default
3410 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3411 .ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
3412 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3414 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3415 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3416 is undefined when the default loop has not been initialised by a previous
3417 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.
3418 .Sp
3419 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3420 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3421 .PP
3422 Example: Declare and initialise a check watcher, utilising the above
3423 macros so it will work regardless of whether multiple loops are supported
3424 or not.
3425 .PP
3426 .Vb 5
3427 \& static void
3428 \& check_cb (EV_P_ ev_timer *w, int revents)
3429 \& {
3430 \& ev_check_stop (EV_A_ w);
3431 \& }
3432 \&
3433 \& ev_check check;
3434 \& ev_check_init (&check, check_cb);
3435 \& ev_check_start (EV_DEFAULT_ &check);
3436 \& ev_loop (EV_DEFAULT_ 0);
3437 .Ve
3439 .IX Header "EMBEDDING"
3440 Libev can (and often is) directly embedded into host
3441 applications. Examples of applications that embed it include the Deliantra
3442 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3443 and rxvt-unicode.
3444 .PP
3445 The goal is to enable you to just copy the necessary files into your
3446 source directory without having to change even a single line in them, so
3447 you can easily upgrade by simply copying (or having a checked-out copy of
3448 libev somewhere in your source tree).
3449 .Sh "\s-1FILESETS\s0"
3450 .IX Subsection "FILESETS"
3451 Depending on what features you need you need to include one or more sets of files
3452 in your application.
3453 .PP
3454 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3455 .IX Subsection "CORE EVENT LOOP"
3456 .PP
3457 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3458 configuration (no autoconf):
3459 .PP
3460 .Vb 2
3461 \& #define EV_STANDALONE 1
3462 \& #include "ev.c"
3463 .Ve
3464 .PP
3465 This will automatically include \fIev.h\fR, too, and should be done in a
3466 single C source file only to provide the function implementations. To use
3467 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3468 done by writing a wrapper around \fIev.h\fR that you can include instead and
3469 where you can put other configuration options):
3470 .PP
3471 .Vb 2
3472 \& #define EV_STANDALONE 1
3473 \& #include "ev.h"
3474 .Ve
3475 .PP
3476 Both header files and implementation files can be compiled with a \*(C+
3477 compiler (at least, that's a stated goal, and breakage will be treated
3478 as a bug).
3479 .PP
3480 You need the following files in your source tree, or in a directory
3481 in your include path (e.g. in libev/ when using \-Ilibev):
3482 .PP
3483 .Vb 4
3484 \& ev.h
3485 \& ev.c
3486 \& ev_vars.h
3487 \& ev_wrap.h
3488 \&
3489 \& ev_win32.c required on win32 platforms only
3490 \&
3491 \& ev_select.c only when select backend is enabled (which is enabled by default)
3492 \& ev_poll.c only when poll backend is enabled (disabled by default)
3493 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3494 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3495 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
3496 .Ve
3497 .PP
3498 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
3499 to compile this single file.
3500 .PP
3501 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3503 .PP
3504 To include the libevent compatibility \s-1API\s0, also include:
3505 .PP
3506 .Vb 1
3507 \& #include "event.c"
3508 .Ve
3509 .PP
3510 in the file including \fIev.c\fR, and:
3511 .PP
3512 .Vb 1
3513 \& #include "event.h"
3514 .Ve
3515 .PP
3516 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3517 .PP
3518 You need the following additional files for this:
3519 .PP
3520 .Vb 2
3521 \& event.h
3522 \& event.c
3523 .Ve
3524 .PP
3525 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3526 .IX Subsection "AUTOCONF SUPPORT"
3527 .PP
3528 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3529 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3530 \&\\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3531 include \fIconfig.h\fR and configure itself accordingly.
3532 .PP
3533 For this of course you need the m4 file:
3534 .PP
3535 .Vb 1
3536 \& libev.m4
3537 .Ve
3538 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3540 Libev can be configured via a variety of preprocessor symbols you have to
3541 define before including any of its files. The default in the absence of
3542 autoconf is documented for every option.
3543 .IP "\s-1EV_STANDALONE\s0" 4
3545 Must always be \f(CW1\fR if you do not use autoconf configuration, which
3546 keeps libev from including \fIconfig.h\fR, and it also defines dummy
3547 implementations for some libevent functions (such as logging, which is not
3548 supported). It will also not define any of the structs usually found in
3549 \&\fIevent.h\fR that are not directly supported by the libev core alone.
3550 .Sp
3551 In stanbdalone mode, libev will still try to automatically deduce the
3552 configuration, but has to be more conservative.
3553 .IP "\s-1EV_USE_MONOTONIC\s0" 4
3555 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3556 monotonic clock option at both compile time and runtime. Otherwise no
3557 use of the monotonic clock option will be attempted. If you enable this,
3558 you usually have to link against librt or something similar. Enabling it
3559 when the functionality isn't available is safe, though, although you have
3560 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3561 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3562 .IP "\s-1EV_USE_REALTIME\s0" 4
3564 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3565 real-time clock option at compile time (and assume its availability
3566 at runtime if successful). Otherwise no use of the real-time clock
3567 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3568 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3569 correctness. See the note about libraries in the description of
3570 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3571 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3572 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3574 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3575 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3576 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
3577 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3578 programs needlessly. Using a direct syscall is slightly slower (in
3579 theory), because no optimised vdso implementation can be used, but avoids
3580 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3581 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3582 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
3584 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3585 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3586 .IP "\s-1EV_USE_EVENTFD\s0" 4
3587 .IX Item "EV_USE_EVENTFD"
3588 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3589 available and will probe for kernel support at runtime. This will improve
3590 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3591 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3592 2.7 or newer, otherwise disabled.
3593 .IP "\s-1EV_USE_SELECT\s0" 4
3594 .IX Item "EV_USE_SELECT"
3595 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3596 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3597 other method takes over, select will be it. Otherwise the select backend
3598 will not be compiled in.
3599 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3601 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3602 structure. This is useful if libev doesn't compile due to a missing
3603 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
3604 on exotic systems. This usually limits the range of file descriptors to
3605 some low limit such as 1024 or might have other limitations (winsocket
3606 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
3607 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
3608 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3610 When defined to \f(CW1\fR, the select backend will assume that
3611 select/socket/connect etc. don't understand file descriptors but
3612 wants osf handles on win32 (this is the case when the select to
3613 be used is the winsock select). This means that it will call
3614 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3615 it is assumed that all these functions actually work on fds, even
3616 on win32. Should not be defined on non\-win32 platforms.
3617 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
3618 .IX Item "EV_FD_TO_WIN32_HANDLE"
3619 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3620 file descriptors to socket handles. When not defining this symbol (the
3621 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3622 correct. In some cases, programs use their own file descriptor management,
3623 in which case they can provide this function to map fds to socket handles.
3624 .IP "\s-1EV_USE_POLL\s0" 4
3625 .IX Item "EV_USE_POLL"
3626 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3627 backend. Otherwise it will be enabled on non\-win32 platforms. It
3628 takes precedence over select.
3629 .IP "\s-1EV_USE_EPOLL\s0" 4
3630 .IX Item "EV_USE_EPOLL"
3631 If defined to be \f(CW1\fR, libev will compile in support for the Linux
3632 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3633 otherwise another method will be used as fallback. This is the preferred
3634 backend for GNU/Linux systems. If undefined, it will be enabled if the
3635 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3636 .IP "\s-1EV_USE_KQUEUE\s0" 4
3637 .IX Item "EV_USE_KQUEUE"
3638 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3639 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3640 otherwise another method will be used as fallback. This is the preferred
3641 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3642 supports some types of fds correctly (the only platform we found that
3643 supports ptys for example was NetBSD), so kqueue might be compiled in, but
3644 not be used unless explicitly requested. The best way to use it is to find
3645 out whether kqueue supports your type of fd properly and use an embedded
3646 kqueue loop.
3647 .IP "\s-1EV_USE_PORT\s0" 4
3648 .IX Item "EV_USE_PORT"
3649 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
3650 10 port style backend. Its availability will be detected at runtime,
3651 otherwise another method will be used as fallback. This is the preferred
3652 backend for Solaris 10 systems.
3653 .IP "\s-1EV_USE_DEVPOLL\s0" 4
3654 .IX Item "EV_USE_DEVPOLL"
3655 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3656 .IP "\s-1EV_USE_INOTIFY\s0" 4
3657 .IX Item "EV_USE_INOTIFY"
3658 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3659 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3660 be detected at runtime. If undefined, it will be enabled if the headers
3661 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3662 .IP "\s-1EV_ATOMIC_T\s0" 4
3663 .IX Item "EV_ATOMIC_T"
3664 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3665 access is atomic with respect to other threads or signal contexts. No such
3666 type is easily found in the C language, so you can provide your own type
3667 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3668 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3669 .Sp
3670 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3671 (from \fIsignal.h\fR), which is usually good enough on most platforms.
3672 .IP "\s-1EV_H\s0" 4
3673 .IX Item "EV_H"
3674 The name of the \fIev.h\fR header file used to include it. The default if
3675 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3676 used to virtually rename the \fIev.h\fR header file in case of conflicts.
3677 .IP "\s-1EV_CONFIG_H\s0" 4
3678 .IX Item "EV_CONFIG_H"
3679 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3680 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3681 \&\f(CW\*(C`EV_H\*(C'\fR, above.
3682 .IP "\s-1EV_EVENT_H\s0" 4
3683 .IX Item "EV_EVENT_H"
3684 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3685 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3686 .IP "\s-1EV_PROTOTYPES\s0" 4
3688 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3689 prototypes, but still define all the structs and other symbols. This is
3690 occasionally useful if you want to provide your own wrapper functions
3691 around libev functions.
3692 .IP "\s-1EV_MULTIPLICITY\s0" 4
3694 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3695 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3696 additional independent event loops. Otherwise there will be no support
3697 for multiple event loops and there is no first event loop pointer
3698 argument. Instead, all functions act on the single default loop.
3699 .IP "\s-1EV_MINPRI\s0" 4
3700 .IX Item "EV_MINPRI"
3701 .PD 0
3702 .IP "\s-1EV_MAXPRI\s0" 4
3703 .IX Item "EV_MAXPRI"
3704 .PD
3705 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3706 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3707 provide for more priorities by overriding those symbols (usually defined
3708 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3709 .Sp
3710 When doing priority-based operations, libev usually has to linearly search
3711 all the priorities, so having many of them (hundreds) uses a lot of space
3712 and time, so using the defaults of five priorities (\-2 .. +2) is usually
3713 fine.
3714 .Sp
3715 If your embedding application does not need any priorities, defining these
3716 both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3717 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3719 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3720 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3721 code.
3722 .IP "\s-1EV_IDLE_ENABLE\s0" 4
3723 .IX Item "EV_IDLE_ENABLE"
3724 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3725 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3726 code.
3727 .IP "\s-1EV_EMBED_ENABLE\s0" 4
3729 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3730 defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3731 watcher types, which therefore must not be disabled.
3732 .IP "\s-1EV_STAT_ENABLE\s0" 4
3733 .IX Item "EV_STAT_ENABLE"
3734 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3735 defined to be \f(CW0\fR, then they are not.
3736 .IP "\s-1EV_FORK_ENABLE\s0" 4
3737 .IX Item "EV_FORK_ENABLE"
3738 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3739 defined to be \f(CW0\fR, then they are not.
3740 .IP "\s-1EV_ASYNC_ENABLE\s0" 4
3742 If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3743 defined to be \f(CW0\fR, then they are not.
3744 .IP "\s-1EV_MINIMAL\s0" 4
3745 .IX Item "EV_MINIMAL"
3746 If you need to shave off some kilobytes of code at the expense of some
3747 speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3748 inlining decisions, saves roughly 30% code size on amd64. It also selects a
3749 much smaller 2\-heap for timer management over the default 4\-heap.
3750 .IP "\s-1EV_PID_HASHSIZE\s0" 4
3752 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3753 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3754 than enough. If you need to manage thousands of children you might want to
3755 increase this value (\fImust\fR be a power of two).
3756 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3758 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3759 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3760 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3761 watchers you might want to increase this value (\fImust\fR be a power of
3762 two).
3763 .IP "\s-1EV_USE_4HEAP\s0" 4
3764 .IX Item "EV_USE_4HEAP"
3765 Heaps are not very cache-efficient. To improve the cache-efficiency of the
3766 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3767 to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3768 faster performance with many (thousands) of watchers.
3769 .Sp
3770 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3771 (disabled).
3772 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3773 .IX Item "EV_HEAP_CACHE_AT"
3774 Heaps are not very cache-efficient. To improve the cache-efficiency of the
3775 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
3776 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3777 which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3778 but avoids random read accesses on heap changes. This improves performance
3779 noticeably with many (hundreds) of watchers.
3780 .Sp
3781 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3782 (disabled).
3783 .IP "\s-1EV_VERIFY\s0" 4
3784 .IX Item "EV_VERIFY"
3785 Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3786 be done: If set to \f(CW0\fR, no internal verification code will be compiled
3787 in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3788 called. If set to \f(CW2\fR, then the internal verification code will be
3789 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3790 verification code will be called very frequently, which will slow down
3791 libev considerably.
3792 .Sp
3793 The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3794 \&\f(CW0\fR.
3795 .IP "\s-1EV_COMMON\s0" 4
3796 .IX Item "EV_COMMON"
3797 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3798 this macro to a something else you can include more and other types of
3799 members. You have to define it each time you include one of the files,
3800 though, and it must be identical each time.
3801 .Sp
3802 For example, the perl \s-1EV\s0 module uses something like this:
3803 .Sp
3804 .Vb 3
3805 \& #define EV_COMMON \e
3806 \& SV *self; /* contains this struct */ \e
3807 \& SV *cb_sv, *fh /* note no trailing ";" */
3808 .Ve
3809 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3810 .IX Item "EV_CB_DECLARE (type)"
3811 .PD 0
3812 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3813 .IX Item "EV_CB_INVOKE (watcher, revents)"
3814 .IP "ev_set_cb (ev, cb)" 4
3815 .IX Item "ev_set_cb (ev, cb)"
3816 .PD
3817 Can be used to change the callback member declaration in each watcher,
3818 and the way callbacks are invoked and set. Must expand to a struct member
3819 definition and a statement, respectively. See the \fIev.h\fR header file for
3820 their default definitions. One possible use for overriding these is to
3821 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3822 method calls instead of plain function calls in \*(C+.
3823 .Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3824 .IX Subsection "EXPORTED API SYMBOLS"
3825 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
3826 exported symbols, you can use the provided \fISymbol.*\fR files which list
3827 all public symbols, one per line:
3828 .PP
3829 .Vb 2
3830 \& Symbols.ev for libev proper
3831 \& Symbols.event for the libevent emulation
3832 .Ve
3833 .PP
3834 This can also be used to rename all public symbols to avoid clashes with
3835 multiple versions of libev linked together (which is obviously bad in
3836 itself, but sometimes it is inconvenient to avoid this).
3837 .PP
3838 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3839 include before including \fIev.h\fR:
3840 .PP
3841 .Vb 1
3842 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3843 .Ve
3844 .PP
3845 This would create a file \fIwrap.h\fR which essentially looks like this:
3846 .PP
3847 .Vb 4
3848 \& #define ev_backend myprefix_ev_backend
3849 \& #define ev_check_start myprefix_ev_check_start
3850 \& #define ev_check_stop myprefix_ev_check_stop
3851 \& ...
3852 .Ve
3853 .Sh "\s-1EXAMPLES\s0"
3854 .IX Subsection "EXAMPLES"
3855 For a real-world example of a program the includes libev
3856 verbatim, you can have a look at the \s-1EV\s0 perl module
3857 (<>). It has the libev files in
3858 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3859 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3860 will be compiled. It is pretty complex because it provides its own header
3861 file.
3862 .PP
3863 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3864 that everybody includes and which overrides some configure choices:
3865 .PP
3866 .Vb 9
3867 \& #define EV_MINIMAL 1
3868 \& #define EV_USE_POLL 0
3869 \& #define EV_MULTIPLICITY 0
3870 \& #define EV_PERIODIC_ENABLE 0
3871 \& #define EV_STAT_ENABLE 0
3872 \& #define EV_FORK_ENABLE 0
3873 \& #define EV_CONFIG_H <config.h>
3874 \& #define EV_MINPRI 0
3875 \& #define EV_MAXPRI 0
3876 \&
3877 \& #include "ev++.h"
3878 .Ve
3879 .PP
3880 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3881 .PP
3882 .Vb 2
3883 \& #include "ev_cpp.h"
3884 \& #include "ev.c"
3885 .Ve
3888 .Sh "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
3890 \fI\s-1THREADS\s0\fR
3891 .IX Subsection "THREADS"
3892 .PP
3893 All libev functions are reentrant and thread-safe unless explicitly
3894 documented otherwise, but libev implements no locking itself. This means
3895 that you can use as many loops as you want in parallel, as long as there
3896 are no concurrent calls into any libev function with the same loop
3897 parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
3898 of course): libev guarantees that different event loops share no data
3899 structures that need any locking.
3900 .PP
3901 Or to put it differently: calls with different loop parameters can be done
3902 concurrently from multiple threads, calls with the same loop parameter
3903 must be done serially (but can be done from different threads, as long as
3904 only one thread ever is inside a call at any point in time, e.g. by using
3905 a mutex per loop).
3906 .PP
3907 Specifically to support threads (and signal handlers), libev implements
3908 so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
3909 concurrency on the same event loop, namely waking it up \*(L"from the
3910 outside\*(R".
3911 .PP
3912 If you want to know which design (one loop, locking, or multiple loops
3913 without or something else still) is best for your problem, then I cannot
3914 help you, but here is some generic advice:
3915 .IP "\(bu" 4
3916 most applications have a main thread: use the default libev loop
3917 in that thread, or create a separate thread running only the default loop.
3918 .Sp
3919 This helps integrating other libraries or software modules that use libev
3920 themselves and don't care/know about threading.
3921 .IP "\(bu" 4
3922 one loop per thread is usually a good model.
3923 .Sp
3924 Doing this is almost never wrong, sometimes a better-performance model
3925 exists, but it is always a good start.
3926 .IP "\(bu" 4
3927 other models exist, such as the leader/follower pattern, where one
3928 loop is handed through multiple threads in a kind of round-robin fashion.
3929 .Sp
3930 Choosing a model is hard \- look around, learn, know that usually you can do
3931 better than you currently do :\-)
3932 .IP "\(bu" 4
3933 often you need to talk to some other thread which blocks in the
3934 event loop.
3935 .Sp
3936 \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
3937 (or from signal contexts...).
3938 .Sp
3939 An example use would be to communicate signals or other events that only
3940 work in the default loop by registering the signal watcher with the
3941 default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
3942 watcher callback into the event loop interested in the signal.
3943 .PP
3944 \fI\s-1COROUTINES\s0\fR
3945 .IX Subsection "COROUTINES"
3946 .PP
3947 Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
3948 libev fully supports nesting calls to its functions from different
3949 coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3950 different coroutines, and switch freely between both coroutines running the
3951 loop, as long as you don't confuse yourself). The only exception is that
3952 you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3953 .PP
3954 Care has been taken to ensure that libev does not keep local state inside
3955 \&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
3956 they do not call any callbacks.
3957 .Sh "\s-1COMPILER\s0 \s-1WARNINGS\s0"
3958 .IX Subsection "COMPILER WARNINGS"
3959 Depending on your compiler and compiler settings, you might get no or a
3960 lot of warnings when compiling libev code. Some people are apparently
3961 scared by this.
3962 .PP
3963 However, these are unavoidable for many reasons. For one, each compiler
3964 has different warnings, and each user has different tastes regarding
3965 warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
3966 targeting a specific compiler and compiler-version.
3967 .PP
3968 Another reason is that some compiler warnings require elaborate
3969 workarounds, or other changes to the code that make it less clear and less
3970 maintainable.
3971 .PP
3972 And of course, some compiler warnings are just plain stupid, or simply
3973 wrong (because they don't actually warn about the condition their message
3974 seems to warn about). For example, certain older gcc versions had some
3975 warnings that resulted an extreme number of false positives. These have
3976 been fixed, but some people still insist on making code warn-free with
3977 such buggy versions.
3978 .PP
3979 While libev is written to generate as few warnings as possible,
3980 \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
3981 with any compiler warnings enabled unless you are prepared to cope with
3982 them (e.g. by ignoring them). Remember that warnings are just that:
3983 warnings, not errors, or proof of bugs.
3984 .Sh "\s-1VALGRIND\s0"
3985 .IX Subsection "VALGRIND"
3986 Valgrind has a special section here because it is a popular tool that is
3987 highly useful. Unfortunately, valgrind reports are very hard to interpret.
3988 .PP
3989 If you think you found a bug (memory leak, uninitialised data access etc.)
3990 in libev, then check twice: If valgrind reports something like:
3991 .PP
3992 .Vb 3
3993 \& ==2274== definitely lost: 0 bytes in 0 blocks.
3994 \& ==2274== possibly lost: 0 bytes in 0 blocks.
3995 \& ==2274== still reachable: 256 bytes in 1 blocks.
3996 .Ve
3997 .PP
3998 Then there is no memory leak, just as memory accounted to global variables
3999 is not a memleak \- the memory is still being referenced, and didn't leak.
4000 .PP
4001 Similarly, under some circumstances, valgrind might report kernel bugs
4002 as if it were a bug in libev (e.g. in realloc or in the poll backend,
4003 although an acceptable workaround has been found here), or it might be
4004 confused.
4005 .PP
4006 Keep in mind that valgrind is a very good tool, but only a tool. Don't
4007 make it into some kind of religion.
4008 .PP
4009 If you are unsure about something, feel free to contact the mailing list
4010 with the full valgrind report and an explanation on why you think this
4011 is a bug in libev (best check the archives, too :). However, don't be
4012 annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4013 of learning how to interpret valgrind properly.
4014 .PP
4015 If you need, for some reason, empty reports from valgrind for your project
4016 I suggest using suppression lists.
4019 .Sh "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4021 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4022 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4023 model. Libev still offers limited functionality on this platform in
4024 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4025 descriptors. This only applies when using Win32 natively, not when using
4026 e.g. cygwin.
4027 .PP
4028 Lifting these limitations would basically require the full
4029 re-implementation of the I/O system. If you are into these kinds of
4030 things, then note that glib does exactly that for you in a very portable
4031 way (note also that glib is the slowest event library known to man).
4032 .PP
4033 There is no supported compilation method available on windows except
4034 embedding it into other applications.
4035 .PP
4036 Sensible signal handling is officially unsupported by Microsoft \- libev
4037 tries its best, but under most conditions, signals will simply not work.
4038 .PP
4039 Not a libev limitation but worth mentioning: windows apparently doesn't
4040 accept large writes: instead of resulting in a partial write, windows will
4041 either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4042 so make sure you only write small amounts into your sockets (less than a
4043 megabyte seems safe, but this apparently depends on the amount of memory
4044 available).
4045 .PP
4046 Due to the many, low, and arbitrary limits on the win32 platform and
4047 the abysmal performance of winsockets, using a large number of sockets
4048 is not recommended (and not reasonable). If your program needs to use
4049 more than a hundred or so sockets, then likely it needs to use a totally
4050 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4051 notification model, which cannot be implemented efficiently on windows
4052 (due to Microsoft monopoly games).
4053 .PP
4054 A typical way to use libev under windows is to embed it (see the embedding
4055 section for details) and use the following \fIevwrap.h\fR header file instead
4056 of \fIev.h\fR:
4057 .PP
4058 .Vb 2
4059 \& #define EV_STANDALONE /* keeps ev from requiring config.h */
4060 \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4061 \&
4062 \& #include "ev.h"
4063 .Ve
4064 .PP
4065 And compile the following \fIevwrap.c\fR file into your project (make sure
4066 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4067 .PP
4068 .Vb 2
4069 \& #include "evwrap.h"
4070 \& #include "ev.c"
4071 .Ve
4072 .IP "The winsocket select function" 4
4073 .IX Item "The winsocket select function"
4074 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4075 requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4076 also extremely buggy). This makes select very inefficient, and also
4077 requires a mapping from file descriptors to socket handles (the Microsoft
4078 C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4079 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4080 \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4081 .Sp
4082 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4083 libraries and raw winsocket select is:
4084 .Sp
4085 .Vb 2
4086 \& #define EV_USE_SELECT 1
4087 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4088 .Ve
4089 .Sp
4090 Note that winsockets handling of fd sets is O(n), so you can easily get a
4091 complexity in the O(nA\*^X) range when using win32.
4092 .IP "Limited number of file descriptors" 4
4093 .IX Item "Limited number of file descriptors"
4094 Windows has numerous arbitrary (and low) limits on things.
4095 .Sp
4096 Early versions of winsocket's select only supported waiting for a maximum
4097 of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4098 can only wait for \f(CW64\fR things at the same time internally; Microsoft
4099 recommends spawning a chain of threads and wait for 63 handles and the
4100 previous thread in each. Sounds great!).
4101 .Sp
4102 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4103 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4104 call (which might be in libev or elsewhere, for example, perl and many
4105 other interpreters do their own select emulation on windows).
4106 .Sp
4107 Another limit is the number of file descriptors in the Microsoft runtime
4108 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4109 fetish or something like this inside Microsoft). You can increase this
4110 by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4111 (another arbitrary limit), but is broken in many versions of the Microsoft
4112 runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4113 (depending on windows version and/or the phase of the moon). To get more,
4114 you need to wrap all I/O functions and provide your own fd management, but
4115 the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4116 .Sh "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4118 In addition to a working ISO-C implementation and of course the
4119 backend-specific APIs, libev relies on a few additional extensions:
4120 .ie n .IP """void (*)(ev_watcher_type *, int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
4121 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4122 .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4123 Libev assumes not only that all watcher pointers have the same internal
4124 structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4125 assumes that the same (machine) code can be used to call any watcher
4126 callback: The watcher callbacks have different type signatures, but libev
4127 calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4128 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4129 .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4130 .IX Item "sig_atomic_t volatile must be thread-atomic as well"
4131 The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4132 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4133 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4134 believed to be sufficiently portable.
4135 .ie n .IP """sigprocmask"" must work in a threaded environment" 4
4136 .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4137 .IX Item "sigprocmask must work in a threaded environment"
4138 Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4139 allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4140 pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4141 thread\*(R" or will block signals process-wide, both behaviours would
4142 be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4143 \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4144 .Sp
4145 The most portable way to handle signals is to block signals in all threads
4146 except the initial one, and run the default loop in the initial thread as
4147 well.
4148 .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4149 .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4150 .IX Item "long must be large enough for common memory allocation sizes"
4151 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4152 instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4153 systems (Microsoft...) this might be unexpectedly low, but is still at
4154 least 31 bits everywhere, which is enough for hundreds of millions of
4155 watchers.
4156 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4157 .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4158 .IX Item "double must hold a time value in seconds with enough accuracy"
4159 The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4160 have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4161 enough for at least into the year 4000. This requirement is fulfilled by
4162 implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
4163 .PP
4164 If you know of other additional requirements drop me a note.
4167 In this section the complexities of (many of) the algorithms used inside
4168 libev will be documented. For complexity discussions about backends see
4169 the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4170 .PP
4171 All of the following are about amortised time: If an array needs to be
4172 extended, libev needs to realloc and move the whole array, but this
4173 happens asymptotically rarer with higher number of elements, so O(1) might
4174 mean that libev does a lengthy realloc operation in rare cases, but on
4175 average it is much faster and asymptotically approaches constant time.
4176 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4177 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4178 This means that, when you have a watcher that triggers in one hour and
4179 there are 100 watchers that would trigger before that, then inserting will
4180 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4181 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4182 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4183 That means that changing a timer costs less than removing/adding them,
4184 as only the relative motion in the event queue has to be paid for.
4185 .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4186 .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4187 These just add the watcher into an array or at the head of a list.
4188 .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4189 .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4190 .PD 0
4191 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4192 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4193 .PD
4194 These watchers are stored in lists, so they need to be walked to find the
4195 correct watcher to remove. The lists are usually short (you don't usually
4196 have many watchers waiting for the same fd or signal: one is typical, two
4197 is rare).
4198 .IP "Finding the next timer in each loop iteration: O(1)" 4
4199 .IX Item "Finding the next timer in each loop iteration: O(1)"
4200 By virtue of using a binary or 4\-heap, the next timer is always found at a
4201 fixed position in the storage array.
4202 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4203 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4204 A change means an I/O watcher gets started or stopped, which requires
4205 libev to recalculate its status (and possibly tell the kernel, depending
4206 on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4207 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
4208 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
4209 .PD 0
4210 .IP "Priority handling: O(number_of_priorities)" 4
4211 .IX Item "Priority handling: O(number_of_priorities)"
4212 .PD
4213 Priorities are implemented by allocating some space for each
4214 priority. When doing priority-based operations, libev usually has to
4215 linearly search all the priorities, but starting/stopping and activating
4216 watchers becomes O(1) with respect to priority handling.
4217 .IP "Sending an ev_async: O(1)" 4
4218 .IX Item "Sending an ev_async: O(1)"
4219 .PD 0
4220 .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4221 .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4222 .IP "Processing signals: O(max_signal_number)" 4
4223 .IX Item "Processing signals: O(max_signal_number)"
4224 .PD
4225 Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4226 calls in the current loop iteration. Checking for async and signal events
4227 involves iterating over all running async watchers or all signal numbers.
4229 .IX Header "GLOSSARY"
4230 .IP "active" 4
4231 .IX Item "active"
4232 A watcher is active as long as it has been started (has been attached to
4233 an event loop) but not yet stopped (disassociated from the event loop).
4234 .IP "application" 4
4235 .IX Item "application"
4236 In this document, an application is whatever is using libev.
4237 .IP "callback" 4
4238 .IX Item "callback"
4239 The address of a function that is called when some event has been
4240 detected. Callbacks are being passed the event loop, the watcher that
4241 received the event, and the actual event bitset.
4242 .IP "callback invocation" 4
4243 .IX Item "callback invocation"
4244 The act of calling the callback associated with a watcher.
4245 .IP "event" 4
4246 .IX Item "event"
4247 A change of state of some external event, such as data now being available
4248 for reading on a file descriptor, time having passed or simply not having
4249 any other events happening anymore.
4250 .Sp
4251 In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
4252 \&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
4253 .IP "event library" 4
4254 .IX Item "event library"
4255 A software package implementing an event model and loop.
4256 .IP "event loop" 4
4257 .IX Item "event loop"
4258 An entity that handles and processes external events and converts them
4259 into callback invocations.
4260 .IP "event model" 4
4261 .IX Item "event model"
4262 The model used to describe how an event loop handles and processes
4263 watchers and events.
4264 .IP "pending" 4
4265 .IX Item "pending"
4266 A watcher is pending as soon as the corresponding event has been detected,
4267 and stops being pending as soon as the watcher will be invoked or its
4268 pending status is explicitly cleared by the application.
4269 .Sp
4270 A watcher can be pending, but not active. Stopping a watcher also clears
4271 its pending status.
4272 .IP "real time" 4
4273 .IX Item "real time"
4274 The physical time that is observed. It is apparently strictly monotonic :)
4275 .IP "wall-clock time" 4
4276 .IX Item "wall-clock time"
4277 The time and date as shown on clocks. Unlike real time, it can actually
4278 be wrong and jump forwards and backwards, e.g. when the you adjust your
4279 clock.
4280 .IP "watcher" 4
4281 .IX Item "watcher"
4282 A data structure that describes interest in certain events. Watchers need
4283 to be started (attached to an event loop) before they can receive events.
4284 .IP "watcher invocation" 4
4285 .IX Item "watcher invocation"
4286 The act of calling the callback associated with a watcher.
4287 .SH "AUTHOR"
4288 .IX Header "AUTHOR"
4289 Marc Lehmann <>, with repeated corrections by Mikael Magnusson.