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Revision: 1.82
Committed: Mon Oct 25 10:50:13 2010 UTC (13 years, 6 months ago) by root
Branch: MAIN
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# Content
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124 .\" ========================================================================
125 .\"
126 .IX Title "LIBEV 3"
127 .TH LIBEV 3 "2010-10-25" "libev-4.00" "libev - high performance full featured event loop"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
129 .\" way too many mistakes in technical documents.
130 .if n .ad l
131 .nh
132 .SH "NAME"
133 libev \- a high performance full\-featured event loop written in C
134 .SH "SYNOPSIS"
135 .IX Header "SYNOPSIS"
136 .Vb 1
137 \& #include <ev.h>
138 .Ve
139 .SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140 .IX Subsection "EXAMPLE PROGRAM"
141 .Vb 2
142 \& // a single header file is required
143 \& #include <ev.h>
144 \&
145 \& #include <stdio.h> // for puts
146 \&
147 \& // every watcher type has its own typedef\*(Aqd struct
148 \& // with the name ev_TYPE
149 \& ev_io stdin_watcher;
150 \& ev_timer timeout_watcher;
151 \&
152 \& // all watcher callbacks have a similar signature
153 \& // this callback is called when data is readable on stdin
154 \& static void
155 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 \& {
157 \& puts ("stdin ready");
158 \& // for one\-shot events, one must manually stop the watcher
159 \& // with its corresponding stop function.
160 \& ev_io_stop (EV_A_ w);
161 \&
162 \& // this causes all nested ev_run\*(Aqs to stop iterating
163 \& ev_break (EV_A_ EVBREAK_ALL);
164 \& }
165 \&
166 \& // another callback, this time for a time\-out
167 \& static void
168 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 \& {
170 \& puts ("timeout");
171 \& // this causes the innermost ev_run to stop iterating
172 \& ev_break (EV_A_ EVBREAK_ONE);
173 \& }
174 \&
175 \& int
176 \& main (void)
177 \& {
178 \& // use the default event loop unless you have special needs
179 \& struct ev_loop *loop = EV_DEFAULT;
180 \&
181 \& // initialise an io watcher, then start it
182 \& // this one will watch for stdin to become readable
183 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184 \& ev_io_start (loop, &stdin_watcher);
185 \&
186 \& // initialise a timer watcher, then start it
187 \& // simple non\-repeating 5.5 second timeout
188 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189 \& ev_timer_start (loop, &timeout_watcher);
190 \&
191 \& // now wait for events to arrive
192 \& ev_run (loop, 0);
193 \&
194 \& // unloop was called, so exit
195 \& return 0;
196 \& }
197 .Ve
198 .SH "ABOUT THIS DOCUMENT"
199 .IX Header "ABOUT THIS DOCUMENT"
200 This document documents the libev software package.
201 .PP
202 The newest version of this document is also available as an html-formatted
203 web page you might find easier to navigate when reading it for the first
204 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205 .PP
206 While this document tries to be as complete as possible in documenting
207 libev, its usage and the rationale behind its design, it is not a tutorial
208 on event-based programming, nor will it introduce event-based programming
209 with libev.
210 .PP
211 Familiarity with event based programming techniques in general is assumed
212 throughout this document.
213 .SH "WHAT TO READ WHEN IN A HURRY"
214 .IX Header "WHAT TO READ WHEN IN A HURRY"
215 This manual tries to be very detailed, but unfortunately, this also makes
216 it very long. If you just want to know the basics of libev, I suggest
217 reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218 look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219 \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220 .SH "ABOUT LIBEV"
221 .IX Header "ABOUT LIBEV"
222 Libev is an event loop: you register interest in certain events (such as a
223 file descriptor being readable or a timeout occurring), and it will manage
224 these event sources and provide your program with events.
225 .PP
226 To do this, it must take more or less complete control over your process
227 (or thread) by executing the \fIevent loop\fR handler, and will then
228 communicate events via a callback mechanism.
229 .PP
230 You register interest in certain events by registering so-called \fIevent
231 watchers\fR, which are relatively small C structures you initialise with the
232 details of the event, and then hand it over to libev by \fIstarting\fR the
233 watcher.
234 .SS "\s-1FEATURES\s0"
235 .IX Subsection "FEATURES"
236 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
237 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
238 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
239 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
240 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
241 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
242 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244 loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245 \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247 .PP
248 It also is quite fast (see this
249 <benchmark> comparing it to libevent
250 for example).
251 .SS "\s-1CONVENTIONS\s0"
252 .IX Subsection "CONVENTIONS"
253 Libev is very configurable. In this manual the default (and most common)
254 configuration will be described, which supports multiple event loops. For
255 more info about various configuration options please have a look at
256 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
257 for multiple event loops, then all functions taking an initial argument of
258 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259 this argument.
260 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
261 .IX Subsection "TIME REPRESENTATION"
262 Libev represents time as a single floating point number, representing
263 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
264 somewhere near the beginning of 1970, details are complicated, don't
265 ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
266 too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267 any calculations on it, you should treat it as some floating point value.
268 .PP
269 Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270 time differences (e.g. delays) throughout libev.
271 .SH "ERROR HANDLING"
272 .IX Header "ERROR HANDLING"
273 Libev knows three classes of errors: operating system errors, usage errors
274 and internal errors (bugs).
275 .PP
276 When libev catches an operating system error it cannot handle (for example
277 a system call indicating a condition libev cannot fix), it calls the callback
278 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280 ()\*(C'\fR.
281 .PP
282 When libev detects a usage error such as a negative timer interval, then
283 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285 the libev caller and need to be fixed there.
286 .PP
287 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288 extensive consistency checking code. These do not trigger under normal
289 circumstances, as they indicate either a bug in libev or worse.
290 .SH "GLOBAL FUNCTIONS"
291 .IX Header "GLOBAL FUNCTIONS"
292 These functions can be called anytime, even before initialising the
293 library in any way.
294 .IP "ev_tstamp ev_time ()" 4
295 .IX Item "ev_tstamp ev_time ()"
296 Returns the current time as libev would use it. Please note that the
297 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
298 you actually want to know. Also interesting is the combination of
299 \&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300 .IP "ev_sleep (ev_tstamp interval)" 4
301 .IX Item "ev_sleep (ev_tstamp interval)"
302 Sleep for the given interval: The current thread will be blocked until
303 either it is interrupted or the given time interval has passed. Basically
304 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
305 .IP "int ev_version_major ()" 4
306 .IX Item "int ev_version_major ()"
307 .PD 0
308 .IP "int ev_version_minor ()" 4
309 .IX Item "int ev_version_minor ()"
310 .PD
311 You can find out the major and minor \s-1ABI\s0 version numbers of the library
312 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
313 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
314 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
315 version of the library your program was compiled against.
316 .Sp
317 These version numbers refer to the \s-1ABI\s0 version of the library, not the
318 release version.
319 .Sp
320 Usually, it's a good idea to terminate if the major versions mismatch,
321 as this indicates an incompatible change. Minor versions are usually
322 compatible to older versions, so a larger minor version alone is usually
323 not a problem.
324 .Sp
325 Example: Make sure we haven't accidentally been linked against the wrong
326 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327 such as \s-1LFS\s0 or reentrancy).
328 .Sp
329 .Vb 3
330 \& assert (("libev version mismatch",
331 \& ev_version_major () == EV_VERSION_MAJOR
332 \& && ev_version_minor () >= EV_VERSION_MINOR));
333 .Ve
334 .IP "unsigned int ev_supported_backends ()" 4
335 .IX Item "unsigned int ev_supported_backends ()"
336 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
337 value) compiled into this binary of libev (independent of their
338 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
339 a description of the set values.
340 .Sp
341 Example: make sure we have the epoll method, because yeah this is cool and
342 a must have and can we have a torrent of it please!!!11
343 .Sp
344 .Vb 2
345 \& assert (("sorry, no epoll, no sex",
346 \& ev_supported_backends () & EVBACKEND_EPOLL));
347 .Ve
348 .IP "unsigned int ev_recommended_backends ()" 4
349 .IX Item "unsigned int ev_recommended_backends ()"
350 Return the set of all backends compiled into this binary of libev and
351 also recommended for this platform, meaning it will work for most file
352 descriptor types. This set is often smaller than the one returned by
353 \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
354 and will not be auto-detected unless you explicitly request it (assuming
355 you know what you are doing). This is the set of backends that libev will
356 probe for if you specify no backends explicitly.
357 .IP "unsigned int ev_embeddable_backends ()" 4
358 .IX Item "unsigned int ev_embeddable_backends ()"
359 Returns the set of backends that are embeddable in other event loops. This
360 value is platform-specific but can include backends not available on the
361 current system. To find which embeddable backends might be supported on
362 the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
363 & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
364 .Sp
365 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
366 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
367 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
368 Sets the allocation function to use (the prototype is similar \- the
369 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
370 used to allocate and free memory (no surprises here). If it returns zero
371 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
372 or take some potentially destructive action.
373 .Sp
374 Since some systems (at least OpenBSD and Darwin) fail to implement
375 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
377 .Sp
378 You could override this function in high-availability programs to, say,
379 free some memory if it cannot allocate memory, to use a special allocator,
380 or even to sleep a while and retry until some memory is available.
381 .Sp
382 Example: Replace the libev allocator with one that waits a bit and then
383 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
384 .Sp
385 .Vb 6
386 \& static void *
387 \& persistent_realloc (void *ptr, size_t size)
388 \& {
389 \& for (;;)
390 \& {
391 \& void *newptr = realloc (ptr, size);
392 \&
393 \& if (newptr)
394 \& return newptr;
395 \&
396 \& sleep (60);
397 \& }
398 \& }
399 \&
400 \& ...
401 \& ev_set_allocator (persistent_realloc);
402 .Ve
403 .IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
404 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
405 Set the callback function to call on a retryable system call error (such
406 as failed select, poll, epoll_wait). The message is a printable string
407 indicating the system call or subsystem causing the problem. If this
408 callback is set, then libev will expect it to remedy the situation, no
409 matter what, when it returns. That is, libev will generally retry the
410 requested operation, or, if the condition doesn't go away, do bad stuff
411 (such as abort).
412 .Sp
413 Example: This is basically the same thing that libev does internally, too.
414 .Sp
415 .Vb 6
416 \& static void
417 \& fatal_error (const char *msg)
418 \& {
419 \& perror (msg);
420 \& abort ();
421 \& }
422 \&
423 \& ...
424 \& ev_set_syserr_cb (fatal_error);
425 .Ve
426 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
427 .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
428 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
429 \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
430 libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
431 .PP
432 The library knows two types of such loops, the \fIdefault\fR loop, which
433 supports child process events, and dynamically created event loops which
434 do not.
435 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
436 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
437 This returns the \*(L"default\*(R" event loop object, which is what you should
438 normally use when you just need \*(L"the event loop\*(R". Event loop objects and
439 the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
440 \&\f(CW\*(C`ev_loop_new\*(C'\fR.
441 .Sp
442 If the default loop is already initialised then this function simply
443 returns it (and ignores the flags. If that is troubling you, check
444 \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
445 flags, which should almost always be \f(CW0\fR, unless the caller is also the
446 one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
447 .Sp
448 If you don't know what event loop to use, use the one returned from this
449 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
450 .Sp
451 Note that this function is \fInot\fR thread-safe, so if you want to use it
452 from multiple threads, you have to employ some kind of mutex (note also
453 that this case is unlikely, as loops cannot be shared easily between
454 threads anyway).
455 .Sp
456 The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
457 and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
458 a problem for your application you can either create a dynamic loop with
459 \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
460 \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
461 .Sp
462 Example: This is the most typical usage.
463 .Sp
464 .Vb 2
465 \& if (!ev_default_loop (0))
466 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
467 .Ve
468 .Sp
469 Example: Restrict libev to the select and poll backends, and do not allow
470 environment settings to be taken into account:
471 .Sp
472 .Vb 1
473 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
474 .Ve
475 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
476 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
477 This will create and initialise a new event loop object. If the loop
478 could not be initialised, returns false.
479 .Sp
480 Note that this function \fIis\fR thread-safe, and one common way to use
481 libev with threads is indeed to create one loop per thread, and using the
482 default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
483 .Sp
484 The flags argument can be used to specify special behaviour or specific
485 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
486 .Sp
487 The following flags are supported:
488 .RS 4
489 .ie n .IP """EVFLAG_AUTO""" 4
490 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
491 .IX Item "EVFLAG_AUTO"
492 The default flags value. Use this if you have no clue (it's the right
493 thing, believe me).
494 .ie n .IP """EVFLAG_NOENV""" 4
495 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
496 .IX Item "EVFLAG_NOENV"
497 If this flag bit is or'ed into the flag value (or the program runs setuid
498 or setgid) then libev will \fInot\fR look at the environment variable
499 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
500 override the flags completely if it is found in the environment. This is
501 useful to try out specific backends to test their performance, or to work
502 around bugs.
503 .ie n .IP """EVFLAG_FORKCHECK""" 4
504 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
505 .IX Item "EVFLAG_FORKCHECK"
506 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
507 make libev check for a fork in each iteration by enabling this flag.
508 .Sp
509 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
510 and thus this might slow down your event loop if you do a lot of loop
511 iterations and little real work, but is usually not noticeable (on my
512 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
513 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
514 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
515 .Sp
516 The big advantage of this flag is that you can forget about fork (and
517 forget about forgetting to tell libev about forking) when you use this
518 flag.
519 .Sp
520 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
521 environment variable.
522 .ie n .IP """EVFLAG_NOINOTIFY""" 4
523 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
524 .IX Item "EVFLAG_NOINOTIFY"
525 When this flag is specified, then libev will not attempt to use the
526 \&\fIinotify\fR \s-1API\s0 for it's \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
527 testing, this flag can be useful to conserve inotify file descriptors, as
528 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
529 .ie n .IP """EVFLAG_SIGNALFD""" 4
530 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
531 .IX Item "EVFLAG_SIGNALFD"
532 When this flag is specified, then libev will attempt to use the
533 \&\fIsignalfd\fR \s-1API\s0 for it's \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
534 delivers signals synchronously, which makes it both faster and might make
535 it possible to get the queued signal data. It can also simplify signal
536 handling with threads, as long as you properly block signals in your
537 threads that are not interested in handling them.
538 .Sp
539 Signalfd will not be used by default as this changes your signal mask, and
540 there are a lot of shoddy libraries and programs (glib's threadpool for
541 example) that can't properly initialise their signal masks.
542 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
543 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
544 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
545 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
546 libev tries to roll its own fd_set with no limits on the number of fds,
547 but if that fails, expect a fairly low limit on the number of fds when
548 using this backend. It doesn't scale too well (O(highest_fd)), but its
549 usually the fastest backend for a low number of (low-numbered :) fds.
550 .Sp
551 To get good performance out of this backend you need a high amount of
552 parallelism (most of the file descriptors should be busy). If you are
553 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
554 connections as possible during one iteration. You might also want to have
555 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
556 readiness notifications you get per iteration.
557 .Sp
558 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
559 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
560 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
561 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
562 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
563 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
564 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
565 than select, but handles sparse fds better and has no artificial
566 limit on the number of fds you can use (except it will slow down
567 considerably with a lot of inactive fds). It scales similarly to select,
568 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
569 performance tips.
570 .Sp
571 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
572 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
573 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
574 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
575 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
576 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
577 kernels).
578 .Sp
579 For few fds, this backend is a bit little slower than poll and select,
580 but it scales phenomenally better. While poll and select usually scale
581 like O(total_fds) where n is the total number of fds (or the highest fd),
582 epoll scales either O(1) or O(active_fds).
583 .Sp
584 The epoll mechanism deserves honorable mention as the most misdesigned
585 of the more advanced event mechanisms: mere annoyances include silently
586 dropping file descriptors, requiring a system call per change per file
587 descriptor (and unnecessary guessing of parameters), problems with dup and
588 so on. The biggest issue is fork races, however \- if a program forks then
589 \&\fIboth\fR parent and child process have to recreate the epoll set, which can
590 take considerable time (one syscall per file descriptor) and is of course
591 hard to detect.
592 .Sp
593 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
594 of course \fIdoesn't\fR, and epoll just loves to report events for totally
595 \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
596 even remove them from the set) than registered in the set (especially
597 on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
598 employing an additional generation counter and comparing that against the
599 events to filter out spurious ones, recreating the set when required. Last
600 not least, it also refuses to work with some file descriptors which work
601 perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
602 .Sp
603 While stopping, setting and starting an I/O watcher in the same iteration
604 will result in some caching, there is still a system call per such
605 incident (because the same \fIfile descriptor\fR could point to a different
606 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
607 file descriptors might not work very well if you register events for both
608 file descriptors.
609 .Sp
610 Best performance from this backend is achieved by not unregistering all
611 watchers for a file descriptor until it has been closed, if possible,
612 i.e. keep at least one watcher active per fd at all times. Stopping and
613 starting a watcher (without re-setting it) also usually doesn't cause
614 extra overhead. A fork can both result in spurious notifications as well
615 as in libev having to destroy and recreate the epoll object, which can
616 take considerable time and thus should be avoided.
617 .Sp
618 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
619 faster than epoll for maybe up to a hundred file descriptors, depending on
620 the usage. So sad.
621 .Sp
622 While nominally embeddable in other event loops, this feature is broken in
623 all kernel versions tested so far.
624 .Sp
625 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
626 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
627 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
628 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
629 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
630 Kqueue deserves special mention, as at the time of this writing, it
631 was broken on all BSDs except NetBSD (usually it doesn't work reliably
632 with anything but sockets and pipes, except on Darwin, where of course
633 it's completely useless). Unlike epoll, however, whose brokenness
634 is by design, these kqueue bugs can (and eventually will) be fixed
635 without \s-1API\s0 changes to existing programs. For this reason it's not being
636 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
637 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
638 system like NetBSD.
639 .Sp
640 You still can embed kqueue into a normal poll or select backend and use it
641 only for sockets (after having made sure that sockets work with kqueue on
642 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
643 .Sp
644 It scales in the same way as the epoll backend, but the interface to the
645 kernel is more efficient (which says nothing about its actual speed, of
646 course). While stopping, setting and starting an I/O watcher does never
647 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
648 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
649 sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
650 cases
651 .Sp
652 This backend usually performs well under most conditions.
653 .Sp
654 While nominally embeddable in other event loops, this doesn't work
655 everywhere, so you might need to test for this. And since it is broken
656 almost everywhere, you should only use it when you have a lot of sockets
657 (for which it usually works), by embedding it into another event loop
658 (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
659 also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
660 .Sp
661 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
662 \&\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
663 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
664 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
665 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
666 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
667 This is not implemented yet (and might never be, unless you send me an
668 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
669 and is not embeddable, which would limit the usefulness of this backend
670 immensely.
671 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
672 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
673 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
674 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
675 it's really slow, but it still scales very well (O(active_fds)).
676 .Sp
677 Please note that Solaris event ports can deliver a lot of spurious
678 notifications, so you need to use non-blocking I/O or other means to avoid
679 blocking when no data (or space) is available.
680 .Sp
681 While this backend scales well, it requires one system call per active
682 file descriptor per loop iteration. For small and medium numbers of file
683 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
684 might perform better.
685 .Sp
686 On the positive side, with the exception of the spurious readiness
687 notifications, this backend actually performed fully to specification
688 in all tests and is fully embeddable, which is a rare feat among the
689 OS-specific backends (I vastly prefer correctness over speed hacks).
690 .Sp
691 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
692 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
693 .ie n .IP """EVBACKEND_ALL""" 4
694 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
695 .IX Item "EVBACKEND_ALL"
696 Try all backends (even potentially broken ones that wouldn't be tried
697 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
698 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
699 .Sp
700 It is definitely not recommended to use this flag.
701 .RE
702 .RS 4
703 .Sp
704 If one or more of the backend flags are or'ed into the flags value,
705 then only these backends will be tried (in the reverse order as listed
706 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
707 ()\*(C'\fR will be tried.
708 .Sp
709 Example: Try to create a event loop that uses epoll and nothing else.
710 .Sp
711 .Vb 3
712 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
713 \& if (!epoller)
714 \& fatal ("no epoll found here, maybe it hides under your chair");
715 .Ve
716 .Sp
717 Example: Use whatever libev has to offer, but make sure that kqueue is
718 used if available.
719 .Sp
720 .Vb 1
721 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
722 .Ve
723 .RE
724 .IP "ev_loop_destroy (loop)" 4
725 .IX Item "ev_loop_destroy (loop)"
726 Destroys an event loop object (frees all memory and kernel state
727 etc.). None of the active event watchers will be stopped in the normal
728 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
729 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
730 calling this function, or cope with the fact afterwards (which is usually
731 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
732 for example).
733 .Sp
734 Note that certain global state, such as signal state (and installed signal
735 handlers), will not be freed by this function, and related watchers (such
736 as signal and child watchers) would need to be stopped manually.
737 .Sp
738 This function is normally used on loop objects allocated by
739 \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
740 \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
741 .Sp
742 Note that it is not advisable to call this function on the default loop
743 except in the rare occasion where you really need to free it's resources.
744 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
745 and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
746 .IP "ev_loop_fork (loop)" 4
747 .IX Item "ev_loop_fork (loop)"
748 This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
749 reinitialise the kernel state for backends that have one. Despite the
750 name, you can call it anytime, but it makes most sense after forking, in
751 the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
752 child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
753 .Sp
754 Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
755 a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
756 because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
757 during fork.
758 .Sp
759 On the other hand, you only need to call this function in the child
760 process if and only if you want to use the event loop in the child. If
761 you just fork+exec or create a new loop in the child, you don't have to
762 call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
763 difference, but libev will usually detect this case on its own and do a
764 costly reset of the backend).
765 .Sp
766 The function itself is quite fast and it's usually not a problem to call
767 it just in case after a fork.
768 .Sp
769 Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
770 using pthreads.
771 .Sp
772 .Vb 5
773 \& static void
774 \& post_fork_child (void)
775 \& {
776 \& ev_loop_fork (EV_DEFAULT);
777 \& }
778 \&
779 \& ...
780 \& pthread_atfork (0, 0, post_fork_child);
781 .Ve
782 .IP "int ev_is_default_loop (loop)" 4
783 .IX Item "int ev_is_default_loop (loop)"
784 Returns true when the given loop is, in fact, the default loop, and false
785 otherwise.
786 .IP "unsigned int ev_iteration (loop)" 4
787 .IX Item "unsigned int ev_iteration (loop)"
788 Returns the current iteration count for the event loop, which is identical
789 to the number of times libev did poll for new events. It starts at \f(CW0\fR
790 and happily wraps around with enough iterations.
791 .Sp
792 This value can sometimes be useful as a generation counter of sorts (it
793 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
794 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
795 prepare and check phases.
796 .IP "unsigned int ev_depth (loop)" 4
797 .IX Item "unsigned int ev_depth (loop)"
798 Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
799 times \f(CW\*(C`ev_run\*(C'\fR was exited, in other words, the recursion depth.
800 .Sp
801 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
802 \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
803 in which case it is higher.
804 .Sp
805 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
806 etc.), doesn't count as \*(L"exit\*(R" \- consider this as a hint to avoid such
807 ungentleman-like behaviour unless it's really convenient.
808 .IP "unsigned int ev_backend (loop)" 4
809 .IX Item "unsigned int ev_backend (loop)"
810 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
811 use.
812 .IP "ev_tstamp ev_now (loop)" 4
813 .IX Item "ev_tstamp ev_now (loop)"
814 Returns the current \*(L"event loop time\*(R", which is the time the event loop
815 received events and started processing them. This timestamp does not
816 change as long as callbacks are being processed, and this is also the base
817 time used for relative timers. You can treat it as the timestamp of the
818 event occurring (or more correctly, libev finding out about it).
819 .IP "ev_now_update (loop)" 4
820 .IX Item "ev_now_update (loop)"
821 Establishes the current time by querying the kernel, updating the time
822 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
823 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
824 .Sp
825 This function is rarely useful, but when some event callback runs for a
826 very long time without entering the event loop, updating libev's idea of
827 the current time is a good idea.
828 .Sp
829 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
830 .IP "ev_suspend (loop)" 4
831 .IX Item "ev_suspend (loop)"
832 .PD 0
833 .IP "ev_resume (loop)" 4
834 .IX Item "ev_resume (loop)"
835 .PD
836 These two functions suspend and resume an event loop, for use when the
837 loop is not used for a while and timeouts should not be processed.
838 .Sp
839 A typical use case would be an interactive program such as a game: When
840 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
841 would be best to handle timeouts as if no time had actually passed while
842 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
843 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
844 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
845 .Sp
846 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
847 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
848 will be rescheduled (that is, they will lose any events that would have
849 occurred while suspended).
850 .Sp
851 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
852 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
853 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
854 .Sp
855 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
856 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
857 .IP "ev_run (loop, int flags)" 4
858 .IX Item "ev_run (loop, int flags)"
859 Finally, this is it, the event handler. This function usually is called
860 after you have initialised all your watchers and you want to start
861 handling events. It will ask the operating system for any new events, call
862 the watcher callbacks, an then repeat the whole process indefinitely: This
863 is why event loops are called \fIloops\fR.
864 .Sp
865 If the flags argument is specified as \f(CW0\fR, it will keep handling events
866 until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
867 called.
868 .Sp
869 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
870 relying on all watchers to be stopped when deciding when a program has
871 finished (especially in interactive programs), but having a program
872 that automatically loops as long as it has to and no longer by virtue
873 of relying on its watchers stopping correctly, that is truly a thing of
874 beauty.
875 .Sp
876 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
877 those events and any already outstanding ones, but will not wait and
878 block your process in case there are no events and will return after one
879 iteration of the loop. This is sometimes useful to poll and handle new
880 events while doing lengthy calculations, to keep the program responsive.
881 .Sp
882 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
883 necessary) and will handle those and any already outstanding ones. It
884 will block your process until at least one new event arrives (which could
885 be an event internal to libev itself, so there is no guarantee that a
886 user-registered callback will be called), and will return after one
887 iteration of the loop.
888 .Sp
889 This is useful if you are waiting for some external event in conjunction
890 with something not expressible using other libev watchers (i.e. "roll your
891 own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
892 usually a better approach for this kind of thing.
893 .Sp
894 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
895 .Sp
896 .Vb 10
897 \& \- Increment loop depth.
898 \& \- Reset the ev_break status.
899 \& \- Before the first iteration, call any pending watchers.
900 \& LOOP:
901 \& \- If EVFLAG_FORKCHECK was used, check for a fork.
902 \& \- If a fork was detected (by any means), queue and call all fork watchers.
903 \& \- Queue and call all prepare watchers.
904 \& \- If ev_break was called, goto FINISH.
905 \& \- If we have been forked, detach and recreate the kernel state
906 \& as to not disturb the other process.
907 \& \- Update the kernel state with all outstanding changes.
908 \& \- Update the "event loop time" (ev_now ()).
909 \& \- Calculate for how long to sleep or block, if at all
910 \& (active idle watchers, EVRUN_NOWAIT or not having
911 \& any active watchers at all will result in not sleeping).
912 \& \- Sleep if the I/O and timer collect interval say so.
913 \& \- Increment loop iteration counter.
914 \& \- Block the process, waiting for any events.
915 \& \- Queue all outstanding I/O (fd) events.
916 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
917 \& \- Queue all expired timers.
918 \& \- Queue all expired periodics.
919 \& \- Queue all idle watchers with priority higher than that of pending events.
920 \& \- Queue all check watchers.
921 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
922 \& Signals and child watchers are implemented as I/O watchers, and will
923 \& be handled here by queueing them when their watcher gets executed.
924 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
925 \& were used, or there are no active watchers, goto FINISH, otherwise
926 \& continue with step LOOP.
927 \& FINISH:
928 \& \- Reset the ev_break status iff it was EVBREAK_ONE.
929 \& \- Decrement the loop depth.
930 \& \- Return.
931 .Ve
932 .Sp
933 Example: Queue some jobs and then loop until no events are outstanding
934 anymore.
935 .Sp
936 .Vb 4
937 \& ... queue jobs here, make sure they register event watchers as long
938 \& ... as they still have work to do (even an idle watcher will do..)
939 \& ev_run (my_loop, 0);
940 \& ... jobs done or somebody called unloop. yeah!
941 .Ve
942 .IP "ev_break (loop, how)" 4
943 .IX Item "ev_break (loop, how)"
944 Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
945 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
946 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
947 \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
948 .Sp
949 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_run\*(C'\fR again.
950 .Sp
951 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls. ##TODO##
952 .IP "ev_ref (loop)" 4
953 .IX Item "ev_ref (loop)"
954 .PD 0
955 .IP "ev_unref (loop)" 4
956 .IX Item "ev_unref (loop)"
957 .PD
958 Ref/unref can be used to add or remove a reference count on the event
959 loop: Every watcher keeps one reference, and as long as the reference
960 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
961 .Sp
962 This is useful when you have a watcher that you never intend to
963 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
964 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
965 before stopping it.
966 .Sp
967 As an example, libev itself uses this for its internal signal pipe: It
968 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
969 exiting if no event watchers registered by it are active. It is also an
970 excellent way to do this for generic recurring timers or from within
971 third-party libraries. Just remember to \fIunref after start\fR and \fIref
972 before stop\fR (but only if the watcher wasn't active before, or was active
973 before, respectively. Note also that libev might stop watchers itself
974 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
975 in the callback).
976 .Sp
977 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
978 running when nothing else is active.
979 .Sp
980 .Vb 4
981 \& ev_signal exitsig;
982 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
983 \& ev_signal_start (loop, &exitsig);
984 \& evf_unref (loop);
985 .Ve
986 .Sp
987 Example: For some weird reason, unregister the above signal handler again.
988 .Sp
989 .Vb 2
990 \& ev_ref (loop);
991 \& ev_signal_stop (loop, &exitsig);
992 .Ve
993 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
994 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
995 .PD 0
996 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
997 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
998 .PD
999 These advanced functions influence the time that libev will spend waiting
1000 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1001 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1002 latency.
1003 .Sp
1004 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1005 allows libev to delay invocation of I/O and timer/periodic callbacks
1006 to increase efficiency of loop iterations (or to increase power-saving
1007 opportunities).
1008 .Sp
1009 The idea is that sometimes your program runs just fast enough to handle
1010 one (or very few) event(s) per loop iteration. While this makes the
1011 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1012 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1013 overhead for the actual polling but can deliver many events at once.
1014 .Sp
1015 By setting a higher \fIio collect interval\fR you allow libev to spend more
1016 time collecting I/O events, so you can handle more events per iteration,
1017 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1018 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1019 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1020 sleep time ensures that libev will not poll for I/O events more often then
1021 once per this interval, on average.
1022 .Sp
1023 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1024 to spend more time collecting timeouts, at the expense of increased
1025 latency/jitter/inexactness (the watcher callback will be called
1026 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1027 value will not introduce any overhead in libev.
1028 .Sp
1029 Many (busy) programs can usually benefit by setting the I/O collect
1030 interval to a value near \f(CW0.1\fR or so, which is often enough for
1031 interactive servers (of course not for games), likewise for timeouts. It
1032 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1033 as this approaches the timing granularity of most systems. Note that if
1034 you do transactions with the outside world and you can't increase the
1035 parallelity, then this setting will limit your transaction rate (if you
1036 need to poll once per transaction and the I/O collect interval is 0.01,
1037 then you can't do more than 100 transactions per second).
1038 .Sp
1039 Setting the \fItimeout collect interval\fR can improve the opportunity for
1040 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1041 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1042 times the process sleeps and wakes up again. Another useful technique to
1043 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1044 they fire on, say, one-second boundaries only.
1045 .Sp
1046 Example: we only need 0.1s timeout granularity, and we wish not to poll
1047 more often than 100 times per second:
1048 .Sp
1049 .Vb 2
1050 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1051 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1052 .Ve
1053 .IP "ev_invoke_pending (loop)" 4
1054 .IX Item "ev_invoke_pending (loop)"
1055 This call will simply invoke all pending watchers while resetting their
1056 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1057 but when overriding the invoke callback this call comes handy. This
1058 function can be invoked from a watcher \- this can be useful for example
1059 when you want to do some lengthy calculation and want to pass further
1060 event handling to another thread (you still have to make sure only one
1061 thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1062 .IP "int ev_pending_count (loop)" 4
1063 .IX Item "int ev_pending_count (loop)"
1064 Returns the number of pending watchers \- zero indicates that no watchers
1065 are pending.
1066 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1067 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1068 This overrides the invoke pending functionality of the loop: Instead of
1069 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1070 this callback instead. This is useful, for example, when you want to
1071 invoke the actual watchers inside another context (another thread etc.).
1072 .Sp
1073 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1074 callback.
1075 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1076 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1077 Sometimes you want to share the same loop between multiple threads. This
1078 can be done relatively simply by putting mutex_lock/unlock calls around
1079 each call to a libev function.
1080 .Sp
1081 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1082 to wait for it to return. One way around this is to wake up the event
1083 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1084 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1085 .Sp
1086 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1087 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1088 afterwards.
1089 .Sp
1090 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1091 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1092 .Sp
1093 While event loop modifications are allowed between invocations of
1094 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1095 modifications done will affect the event loop, i.e. adding watchers will
1096 have no effect on the set of file descriptors being watched, or the time
1097 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1098 to take note of any changes you made.
1099 .Sp
1100 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1101 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1102 .Sp
1103 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1104 document.
1105 .IP "ev_set_userdata (loop, void *data)" 4
1106 .IX Item "ev_set_userdata (loop, void *data)"
1107 .PD 0
1108 .IP "ev_userdata (loop)" 4
1109 .IX Item "ev_userdata (loop)"
1110 .PD
1111 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1112 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1113 \&\f(CW0.\fR
1114 .Sp
1115 These two functions can be used to associate arbitrary data with a loop,
1116 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1117 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1118 any other purpose as well.
1119 .IP "ev_verify (loop)" 4
1120 .IX Item "ev_verify (loop)"
1121 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1122 compiled in, which is the default for non-minimal builds. It tries to go
1123 through all internal structures and checks them for validity. If anything
1124 is found to be inconsistent, it will print an error message to standard
1125 error and call \f(CW\*(C`abort ()\*(C'\fR.
1126 .Sp
1127 This can be used to catch bugs inside libev itself: under normal
1128 circumstances, this function will never abort as of course libev keeps its
1129 data structures consistent.
1130 .SH "ANATOMY OF A WATCHER"
1131 .IX Header "ANATOMY OF A WATCHER"
1132 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1133 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1134 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1135 .PP
1136 A watcher is an opaque structure that you allocate and register to record
1137 your interest in some event. To make a concrete example, imagine you want
1138 to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1139 for that:
1140 .PP
1141 .Vb 5
1142 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1143 \& {
1144 \& ev_io_stop (w);
1145 \& ev_break (loop, EVBREAK_ALL);
1146 \& }
1147 \&
1148 \& struct ev_loop *loop = ev_default_loop (0);
1149 \&
1150 \& ev_io stdin_watcher;
1151 \&
1152 \& ev_init (&stdin_watcher, my_cb);
1153 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1154 \& ev_io_start (loop, &stdin_watcher);
1155 \&
1156 \& ev_run (loop, 0);
1157 .Ve
1158 .PP
1159 As you can see, you are responsible for allocating the memory for your
1160 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1161 stack).
1162 .PP
1163 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1164 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1165 .PP
1166 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1167 *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1168 invoked each time the event occurs (or, in the case of I/O watchers, each
1169 time the event loop detects that the file descriptor given is readable
1170 and/or writable).
1171 .PP
1172 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1173 macro to configure it, with arguments specific to the watcher type. There
1174 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1175 .PP
1176 To make the watcher actually watch out for events, you have to start it
1177 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1178 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1179 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1180 .PP
1181 As long as your watcher is active (has been started but not stopped) you
1182 must not touch the values stored in it. Most specifically you must never
1183 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1184 .PP
1185 Each and every callback receives the event loop pointer as first, the
1186 registered watcher structure as second, and a bitset of received events as
1187 third argument.
1188 .PP
1189 The received events usually include a single bit per event type received
1190 (you can receive multiple events at the same time). The possible bit masks
1191 are:
1192 .ie n .IP """EV_READ""" 4
1193 .el .IP "\f(CWEV_READ\fR" 4
1194 .IX Item "EV_READ"
1195 .PD 0
1196 .ie n .IP """EV_WRITE""" 4
1197 .el .IP "\f(CWEV_WRITE\fR" 4
1198 .IX Item "EV_WRITE"
1199 .PD
1200 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1201 writable.
1202 .ie n .IP """EV_TIMER""" 4
1203 .el .IP "\f(CWEV_TIMER\fR" 4
1204 .IX Item "EV_TIMER"
1205 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1206 .ie n .IP """EV_PERIODIC""" 4
1207 .el .IP "\f(CWEV_PERIODIC\fR" 4
1208 .IX Item "EV_PERIODIC"
1209 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1210 .ie n .IP """EV_SIGNAL""" 4
1211 .el .IP "\f(CWEV_SIGNAL\fR" 4
1212 .IX Item "EV_SIGNAL"
1213 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1214 .ie n .IP """EV_CHILD""" 4
1215 .el .IP "\f(CWEV_CHILD\fR" 4
1216 .IX Item "EV_CHILD"
1217 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1218 .ie n .IP """EV_STAT""" 4
1219 .el .IP "\f(CWEV_STAT\fR" 4
1220 .IX Item "EV_STAT"
1221 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1222 .ie n .IP """EV_IDLE""" 4
1223 .el .IP "\f(CWEV_IDLE\fR" 4
1224 .IX Item "EV_IDLE"
1225 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1226 .ie n .IP """EV_PREPARE""" 4
1227 .el .IP "\f(CWEV_PREPARE\fR" 4
1228 .IX Item "EV_PREPARE"
1229 .PD 0
1230 .ie n .IP """EV_CHECK""" 4
1231 .el .IP "\f(CWEV_CHECK\fR" 4
1232 .IX Item "EV_CHECK"
1233 .PD
1234 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
1235 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1236 \&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
1237 received events. Callbacks of both watcher types can start and stop as
1238 many watchers as they want, and all of them will be taken into account
1239 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1240 \&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1241 .ie n .IP """EV_EMBED""" 4
1242 .el .IP "\f(CWEV_EMBED\fR" 4
1243 .IX Item "EV_EMBED"
1244 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1245 .ie n .IP """EV_FORK""" 4
1246 .el .IP "\f(CWEV_FORK\fR" 4
1247 .IX Item "EV_FORK"
1248 The event loop has been resumed in the child process after fork (see
1249 \&\f(CW\*(C`ev_fork\*(C'\fR).
1250 .ie n .IP """EV_CLEANUP""" 4
1251 .el .IP "\f(CWEV_CLEANUP\fR" 4
1252 .IX Item "EV_CLEANUP"
1253 The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1254 .ie n .IP """EV_ASYNC""" 4
1255 .el .IP "\f(CWEV_ASYNC\fR" 4
1256 .IX Item "EV_ASYNC"
1257 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1258 .ie n .IP """EV_CUSTOM""" 4
1259 .el .IP "\f(CWEV_CUSTOM\fR" 4
1260 .IX Item "EV_CUSTOM"
1261 Not ever sent (or otherwise used) by libev itself, but can be freely used
1262 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1263 .ie n .IP """EV_ERROR""" 4
1264 .el .IP "\f(CWEV_ERROR\fR" 4
1265 .IX Item "EV_ERROR"
1266 An unspecified error has occurred, the watcher has been stopped. This might
1267 happen because the watcher could not be properly started because libev
1268 ran out of memory, a file descriptor was found to be closed or any other
1269 problem. Libev considers these application bugs.
1270 .Sp
1271 You best act on it by reporting the problem and somehow coping with the
1272 watcher being stopped. Note that well-written programs should not receive
1273 an error ever, so when your watcher receives it, this usually indicates a
1274 bug in your program.
1275 .Sp
1276 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1277 example it might indicate that a fd is readable or writable, and if your
1278 callbacks is well-written it can just attempt the operation and cope with
1279 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1280 programs, though, as the fd could already be closed and reused for another
1281 thing, so beware.
1282 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1283 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1284 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1285 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1286 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1287 This macro initialises the generic portion of a watcher. The contents
1288 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1289 the generic parts of the watcher are initialised, you \fIneed\fR to call
1290 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1291 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1292 which rolls both calls into one.
1293 .Sp
1294 You can reinitialise a watcher at any time as long as it has been stopped
1295 (or never started) and there are no pending events outstanding.
1296 .Sp
1297 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1298 int revents)\*(C'\fR.
1299 .Sp
1300 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1301 .Sp
1302 .Vb 3
1303 \& ev_io w;
1304 \& ev_init (&w, my_cb);
1305 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1306 .Ve
1307 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1308 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1309 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1310 This macro initialises the type-specific parts of a watcher. You need to
1311 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1312 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1313 macro on a watcher that is active (it can be pending, however, which is a
1314 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1315 .Sp
1316 Although some watcher types do not have type-specific arguments
1317 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1318 .Sp
1319 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1320 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1321 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1322 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1323 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1324 calls into a single call. This is the most convenient method to initialise
1325 a watcher. The same limitations apply, of course.
1326 .Sp
1327 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1328 .Sp
1329 .Vb 1
1330 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1331 .Ve
1332 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1333 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1334 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1335 Starts (activates) the given watcher. Only active watchers will receive
1336 events. If the watcher is already active nothing will happen.
1337 .Sp
1338 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1339 whole section.
1340 .Sp
1341 .Vb 1
1342 \& ev_io_start (EV_DEFAULT_UC, &w);
1343 .Ve
1344 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1345 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1346 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1347 Stops the given watcher if active, and clears the pending status (whether
1348 the watcher was active or not).
1349 .Sp
1350 It is possible that stopped watchers are pending \- for example,
1351 non-repeating timers are being stopped when they become pending \- but
1352 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1353 pending. If you want to free or reuse the memory used by the watcher it is
1354 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1355 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1356 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1357 Returns a true value iff the watcher is active (i.e. it has been started
1358 and not yet been stopped). As long as a watcher is active you must not modify
1359 it.
1360 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1361 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1362 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1363 events but its callback has not yet been invoked). As long as a watcher
1364 is pending (but not active) you must not call an init function on it (but
1365 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1366 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1367 it).
1368 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1369 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1370 Returns the callback currently set on the watcher.
1371 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1372 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1373 Change the callback. You can change the callback at virtually any time
1374 (modulo threads).
1375 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1376 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1377 .PD 0
1378 .IP "int ev_priority (ev_TYPE *watcher)" 4
1379 .IX Item "int ev_priority (ev_TYPE *watcher)"
1380 .PD
1381 Set and query the priority of the watcher. The priority is a small
1382 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1383 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1384 before watchers with lower priority, but priority will not keep watchers
1385 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1386 .Sp
1387 If you need to suppress invocation when higher priority events are pending
1388 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1389 .Sp
1390 You \fImust not\fR change the priority of a watcher as long as it is active or
1391 pending.
1392 .Sp
1393 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1394 fine, as long as you do not mind that the priority value you query might
1395 or might not have been clamped to the valid range.
1396 .Sp
1397 The default priority used by watchers when no priority has been set is
1398 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1399 .Sp
1400 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1401 priorities.
1402 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1403 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1404 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
1405 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1406 can deal with that fact, as both are simply passed through to the
1407 callback.
1408 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1409 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1410 If the watcher is pending, this function clears its pending status and
1411 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1412 watcher isn't pending it does nothing and returns \f(CW0\fR.
1413 .Sp
1414 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1415 callback to be invoked, which can be accomplished with this function.
1416 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1417 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1418 Feeds the given event set into the event loop, as if the specified event
1419 had happened for the specified watcher (which must be a pointer to an
1420 initialised but not necessarily started event watcher). Obviously you must
1421 not free the watcher as long as it has pending events.
1422 .Sp
1423 Stopping the watcher, letting libev invoke it, or calling
1424 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1425 not started in the first place.
1426 .Sp
1427 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1428 functions that do not need a watcher.
1429 .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1430 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
1431 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1432 and read at any time: libev will completely ignore it. This can be used
1433 to associate arbitrary data with your watcher. If you need more data and
1434 don't want to allocate memory and store a pointer to it in that data
1435 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1436 data:
1437 .PP
1438 .Vb 7
1439 \& struct my_io
1440 \& {
1441 \& ev_io io;
1442 \& int otherfd;
1443 \& void *somedata;
1444 \& struct whatever *mostinteresting;
1445 \& };
1446 \&
1447 \& ...
1448 \& struct my_io w;
1449 \& ev_io_init (&w.io, my_cb, fd, EV_READ);
1450 .Ve
1451 .PP
1452 And since your callback will be called with a pointer to the watcher, you
1453 can cast it back to your own type:
1454 .PP
1455 .Vb 5
1456 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1457 \& {
1458 \& struct my_io *w = (struct my_io *)w_;
1459 \& ...
1460 \& }
1461 .Ve
1462 .PP
1463 More interesting and less C\-conformant ways of casting your callback type
1464 instead have been omitted.
1465 .PP
1466 Another common scenario is to use some data structure with multiple
1467 embedded watchers:
1468 .PP
1469 .Vb 6
1470 \& struct my_biggy
1471 \& {
1472 \& int some_data;
1473 \& ev_timer t1;
1474 \& ev_timer t2;
1475 \& }
1476 .Ve
1477 .PP
1478 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1479 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1480 in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1481 some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1482 programmers):
1483 .PP
1484 .Vb 1
1485 \& #include <stddef.h>
1486 \&
1487 \& static void
1488 \& t1_cb (EV_P_ ev_timer *w, int revents)
1489 \& {
1490 \& struct my_biggy big = (struct my_biggy *)
1491 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1492 \& }
1493 \&
1494 \& static void
1495 \& t2_cb (EV_P_ ev_timer *w, int revents)
1496 \& {
1497 \& struct my_biggy big = (struct my_biggy *)
1498 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1499 \& }
1500 .Ve
1501 .SS "\s-1WATCHER\s0 \s-1STATES\s0"
1502 .IX Subsection "WATCHER STATES"
1503 There are various watcher states mentioned throughout this manual \-
1504 active, pending and so on. In this section these states and the rules to
1505 transition between them will be described in more detail \- and while these
1506 rules might look complicated, they usually do \*(L"the right thing\*(R".
1507 .IP "initialiased" 4
1508 .IX Item "initialiased"
1509 Before a watcher can be registered with the event looop it has to be
1510 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1511 \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1512 .Sp
1513 In this state it is simply some block of memory that is suitable for use
1514 in an event loop. It can be moved around, freed, reused etc. at will.
1515 .IP "started/running/active" 4
1516 .IX Item "started/running/active"
1517 Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1518 property of the event loop, and is actively waiting for events. While in
1519 this state it cannot be accessed (except in a few documented ways), moved,
1520 freed or anything else \- the only legal thing is to keep a pointer to it,
1521 and call libev functions on it that are documented to work on active watchers.
1522 .IP "pending" 4
1523 .IX Item "pending"
1524 If a watcher is active and libev determines that an event it is interested
1525 in has occurred (such as a timer expiring), it will become pending. It will
1526 stay in this pending state until either it is stopped or its callback is
1527 about to be invoked, so it is not normally pending inside the watcher
1528 callback.
1529 .Sp
1530 The watcher might or might not be active while it is pending (for example,
1531 an expired non-repeating timer can be pending but no longer active). If it
1532 is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1533 but it is still property of the event loop at this time, so cannot be
1534 moved, freed or reused. And if it is active the rules described in the
1535 previous item still apply.
1536 .Sp
1537 It is also possible to feed an event on a watcher that is not active (e.g.
1538 via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1539 active.
1540 .IP "stopped" 4
1541 .IX Item "stopped"
1542 A watcher can be stopped implicitly by libev (in which case it might still
1543 be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1544 latter will clear any pending state the watcher might be in, regardless
1545 of whether it was active or not, so stopping a watcher explicitly before
1546 freeing it is often a good idea.
1547 .Sp
1548 While stopped (and not pending) the watcher is essentially in the
1549 initialised state, that is it can be reused, moved, modified in any way
1550 you wish.
1551 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1552 .IX Subsection "WATCHER PRIORITY MODELS"
1553 Many event loops support \fIwatcher priorities\fR, which are usually small
1554 integers that influence the ordering of event callback invocation
1555 between watchers in some way, all else being equal.
1556 .PP
1557 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1558 description for the more technical details such as the actual priority
1559 range.
1560 .PP
1561 There are two common ways how these these priorities are being interpreted
1562 by event loops:
1563 .PP
1564 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1565 of lower priority watchers, which means as long as higher priority
1566 watchers receive events, lower priority watchers are not being invoked.
1567 .PP
1568 The less common only-for-ordering model uses priorities solely to order
1569 callback invocation within a single event loop iteration: Higher priority
1570 watchers are invoked before lower priority ones, but they all get invoked
1571 before polling for new events.
1572 .PP
1573 Libev uses the second (only-for-ordering) model for all its watchers
1574 except for idle watchers (which use the lock-out model).
1575 .PP
1576 The rationale behind this is that implementing the lock-out model for
1577 watchers is not well supported by most kernel interfaces, and most event
1578 libraries will just poll for the same events again and again as long as
1579 their callbacks have not been executed, which is very inefficient in the
1580 common case of one high-priority watcher locking out a mass of lower
1581 priority ones.
1582 .PP
1583 Static (ordering) priorities are most useful when you have two or more
1584 watchers handling the same resource: a typical usage example is having an
1585 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1586 timeouts. Under load, data might be received while the program handles
1587 other jobs, but since timers normally get invoked first, the timeout
1588 handler will be executed before checking for data. In that case, giving
1589 the timer a lower priority than the I/O watcher ensures that I/O will be
1590 handled first even under adverse conditions (which is usually, but not
1591 always, what you want).
1592 .PP
1593 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1594 will only be executed when no same or higher priority watchers have
1595 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1596 required.
1597 .PP
1598 For example, to emulate how many other event libraries handle priorities,
1599 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1600 the normal watcher callback, you just start the idle watcher. The real
1601 processing is done in the idle watcher callback. This causes libev to
1602 continuously poll and process kernel event data for the watcher, but when
1603 the lock-out case is known to be rare (which in turn is rare :), this is
1604 workable.
1605 .PP
1606 Usually, however, the lock-out model implemented that way will perform
1607 miserably under the type of load it was designed to handle. In that case,
1608 it might be preferable to stop the real watcher before starting the
1609 idle watcher, so the kernel will not have to process the event in case
1610 the actual processing will be delayed for considerable time.
1611 .PP
1612 Here is an example of an I/O watcher that should run at a strictly lower
1613 priority than the default, and which should only process data when no
1614 other events are pending:
1615 .PP
1616 .Vb 2
1617 \& ev_idle idle; // actual processing watcher
1618 \& ev_io io; // actual event watcher
1619 \&
1620 \& static void
1621 \& io_cb (EV_P_ ev_io *w, int revents)
1622 \& {
1623 \& // stop the I/O watcher, we received the event, but
1624 \& // are not yet ready to handle it.
1625 \& ev_io_stop (EV_A_ w);
1626 \&
1627 \& // start the idle watcher to handle the actual event.
1628 \& // it will not be executed as long as other watchers
1629 \& // with the default priority are receiving events.
1630 \& ev_idle_start (EV_A_ &idle);
1631 \& }
1632 \&
1633 \& static void
1634 \& idle_cb (EV_P_ ev_idle *w, int revents)
1635 \& {
1636 \& // actual processing
1637 \& read (STDIN_FILENO, ...);
1638 \&
1639 \& // have to start the I/O watcher again, as
1640 \& // we have handled the event
1641 \& ev_io_start (EV_P_ &io);
1642 \& }
1643 \&
1644 \& // initialisation
1645 \& ev_idle_init (&idle, idle_cb);
1646 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1647 \& ev_io_start (EV_DEFAULT_ &io);
1648 .Ve
1649 .PP
1650 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1651 low-priority connections can not be locked out forever under load. This
1652 enables your program to keep a lower latency for important connections
1653 during short periods of high load, while not completely locking out less
1654 important ones.
1655 .SH "WATCHER TYPES"
1656 .IX Header "WATCHER TYPES"
1657 This section describes each watcher in detail, but will not repeat
1658 information given in the last section. Any initialisation/set macros,
1659 functions and members specific to the watcher type are explained.
1660 .PP
1661 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1662 while the watcher is active, you can look at the member and expect some
1663 sensible content, but you must not modify it (you can modify it while the
1664 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1665 means you can expect it to have some sensible content while the watcher
1666 is active, but you can also modify it. Modifying it may not do something
1667 sensible or take immediate effect (or do anything at all), but libev will
1668 not crash or malfunction in any way.
1669 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1670 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1671 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1672 I/O watchers check whether a file descriptor is readable or writable
1673 in each iteration of the event loop, or, more precisely, when reading
1674 would not block the process and writing would at least be able to write
1675 some data. This behaviour is called level-triggering because you keep
1676 receiving events as long as the condition persists. Remember you can stop
1677 the watcher if you don't want to act on the event and neither want to
1678 receive future events.
1679 .PP
1680 In general you can register as many read and/or write event watchers per
1681 fd as you want (as long as you don't confuse yourself). Setting all file
1682 descriptors to non-blocking mode is also usually a good idea (but not
1683 required if you know what you are doing).
1684 .PP
1685 If you cannot use non-blocking mode, then force the use of a
1686 known-to-be-good backend (at the time of this writing, this includes only
1687 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
1688 descriptors for which non-blocking operation makes no sense (such as
1689 files) \- libev doesn't guarantee any specific behaviour in that case.
1690 .PP
1691 Another thing you have to watch out for is that it is quite easy to
1692 receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1693 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1694 because there is no data. Not only are some backends known to create a
1695 lot of those (for example Solaris ports), it is very easy to get into
1696 this situation even with a relatively standard program structure. Thus
1697 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1698 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1699 .PP
1700 If you cannot run the fd in non-blocking mode (for example you should
1701 not play around with an Xlib connection), then you have to separately
1702 re-test whether a file descriptor is really ready with a known-to-be good
1703 interface such as poll (fortunately in our Xlib example, Xlib already
1704 does this on its own, so its quite safe to use). Some people additionally
1705 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1706 indefinitely.
1707 .PP
1708 But really, best use non-blocking mode.
1709 .PP
1710 \fIThe special problem of disappearing file descriptors\fR
1711 .IX Subsection "The special problem of disappearing file descriptors"
1712 .PP
1713 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1714 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1715 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1716 descriptor, but when it goes away, the operating system will silently drop
1717 this interest. If another file descriptor with the same number then is
1718 registered with libev, there is no efficient way to see that this is, in
1719 fact, a different file descriptor.
1720 .PP
1721 To avoid having to explicitly tell libev about such cases, libev follows
1722 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1723 will assume that this is potentially a new file descriptor, otherwise
1724 it is assumed that the file descriptor stays the same. That means that
1725 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
1726 descriptor even if the file descriptor number itself did not change.
1727 .PP
1728 This is how one would do it normally anyway, the important point is that
1729 the libev application should not optimise around libev but should leave
1730 optimisations to libev.
1731 .PP
1732 \fIThe special problem of dup'ed file descriptors\fR
1733 .IX Subsection "The special problem of dup'ed file descriptors"
1734 .PP
1735 Some backends (e.g. epoll), cannot register events for file descriptors,
1736 but only events for the underlying file descriptions. That means when you
1737 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1738 events for them, only one file descriptor might actually receive events.
1739 .PP
1740 There is no workaround possible except not registering events
1741 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1742 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1743 .PP
1744 \fIThe special problem of fork\fR
1745 .IX Subsection "The special problem of fork"
1746 .PP
1747 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1748 useless behaviour. Libev fully supports fork, but needs to be told about
1749 it in the child.
1750 .PP
1751 To support fork in your programs, you either have to call
1752 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1753 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1754 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1755 .PP
1756 \fIThe special problem of \s-1SIGPIPE\s0\fR
1757 .IX Subsection "The special problem of SIGPIPE"
1758 .PP
1759 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1760 when writing to a pipe whose other end has been closed, your program gets
1761 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1762 this is sensible behaviour, for daemons, this is usually undesirable.
1763 .PP
1764 So when you encounter spurious, unexplained daemon exits, make sure you
1765 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1766 somewhere, as that would have given you a big clue).
1767 .PP
1768 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1769 .IX Subsection "The special problem of accept()ing when you can't"
1770 .PP
1771 Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1772 found in post\-2004 Linux) have the peculiar behaviour of not removing a
1773 connection from the pending queue in all error cases.
1774 .PP
1775 For example, larger servers often run out of file descriptors (because
1776 of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1777 rejecting the connection, leading to libev signalling readiness on
1778 the next iteration again (the connection still exists after all), and
1779 typically causing the program to loop at 100% \s-1CPU\s0 usage.
1780 .PP
1781 Unfortunately, the set of errors that cause this issue differs between
1782 operating systems, there is usually little the app can do to remedy the
1783 situation, and no known thread-safe method of removing the connection to
1784 cope with overload is known (to me).
1785 .PP
1786 One of the easiest ways to handle this situation is to just ignore it
1787 \&\- when the program encounters an overload, it will just loop until the
1788 situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1789 event-based way to handle this situation, so it's the best one can do.
1790 .PP
1791 A better way to handle the situation is to log any errors other than
1792 \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1793 messages, and continue as usual, which at least gives the user an idea of
1794 what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1795 the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1796 usage.
1797 .PP
1798 If your program is single-threaded, then you could also keep a dummy file
1799 descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1800 when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1801 close that fd, and create a new dummy fd. This will gracefully refuse
1802 clients under typical overload conditions.
1803 .PP
1804 The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1805 is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1806 opportunity for a DoS attack.
1807 .PP
1808 \fIWatcher-Specific Functions\fR
1809 .IX Subsection "Watcher-Specific Functions"
1810 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1811 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1812 .PD 0
1813 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1814 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1815 .PD
1816 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1817 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
1818 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1819 .IP "int fd [read\-only]" 4
1820 .IX Item "int fd [read-only]"
1821 The file descriptor being watched.
1822 .IP "int events [read\-only]" 4
1823 .IX Item "int events [read-only]"
1824 The events being watched.
1825 .PP
1826 \fIExamples\fR
1827 .IX Subsection "Examples"
1828 .PP
1829 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1830 readable, but only once. Since it is likely line-buffered, you could
1831 attempt to read a whole line in the callback.
1832 .PP
1833 .Vb 6
1834 \& static void
1835 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1836 \& {
1837 \& ev_io_stop (loop, w);
1838 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1839 \& }
1840 \&
1841 \& ...
1842 \& struct ev_loop *loop = ev_default_init (0);
1843 \& ev_io stdin_readable;
1844 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1845 \& ev_io_start (loop, &stdin_readable);
1846 \& ev_run (loop, 0);
1847 .Ve
1848 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1849 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1850 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1851 Timer watchers are simple relative timers that generate an event after a
1852 given time, and optionally repeating in regular intervals after that.
1853 .PP
1854 The timers are based on real time, that is, if you register an event that
1855 times out after an hour and you reset your system clock to January last
1856 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1857 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1858 monotonic clock option helps a lot here).
1859 .PP
1860 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1861 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1862 might introduce a small delay). If multiple timers become ready during the
1863 same loop iteration then the ones with earlier time-out values are invoked
1864 before ones of the same priority with later time-out values (but this is
1865 no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1866 .PP
1867 \fIBe smart about timeouts\fR
1868 .IX Subsection "Be smart about timeouts"
1869 .PP
1870 Many real-world problems involve some kind of timeout, usually for error
1871 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1872 you want to raise some error after a while.
1873 .PP
1874 What follows are some ways to handle this problem, from obvious and
1875 inefficient to smart and efficient.
1876 .PP
1877 In the following, a 60 second activity timeout is assumed \- a timeout that
1878 gets reset to 60 seconds each time there is activity (e.g. each time some
1879 data or other life sign was received).
1880 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1881 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1882 This is the most obvious, but not the most simple way: In the beginning,
1883 start the watcher:
1884 .Sp
1885 .Vb 2
1886 \& ev_timer_init (timer, callback, 60., 0.);
1887 \& ev_timer_start (loop, timer);
1888 .Ve
1889 .Sp
1890 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1891 and start it again:
1892 .Sp
1893 .Vb 3
1894 \& ev_timer_stop (loop, timer);
1895 \& ev_timer_set (timer, 60., 0.);
1896 \& ev_timer_start (loop, timer);
1897 .Ve
1898 .Sp
1899 This is relatively simple to implement, but means that each time there is
1900 some activity, libev will first have to remove the timer from its internal
1901 data structure and then add it again. Libev tries to be fast, but it's
1902 still not a constant-time operation.
1903 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1904 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1905 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1906 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1907 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1908 .Sp
1909 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1910 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1911 successfully read or write some data. If you go into an idle state where
1912 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1913 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1914 .Sp
1915 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1916 \&\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
1917 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1918 .Sp
1919 At start:
1920 .Sp
1921 .Vb 3
1922 \& ev_init (timer, callback);
1923 \& timer\->repeat = 60.;
1924 \& ev_timer_again (loop, timer);
1925 .Ve
1926 .Sp
1927 Each time there is some activity:
1928 .Sp
1929 .Vb 1
1930 \& ev_timer_again (loop, timer);
1931 .Ve
1932 .Sp
1933 It is even possible to change the time-out on the fly, regardless of
1934 whether the watcher is active or not:
1935 .Sp
1936 .Vb 2
1937 \& timer\->repeat = 30.;
1938 \& ev_timer_again (loop, timer);
1939 .Ve
1940 .Sp
1941 This is slightly more efficient then stopping/starting the timer each time
1942 you want to modify its timeout value, as libev does not have to completely
1943 remove and re-insert the timer from/into its internal data structure.
1944 .Sp
1945 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1946 .IP "3. Let the timer time out, but then re-arm it as required." 4
1947 .IX Item "3. Let the timer time out, but then re-arm it as required."
1948 This method is more tricky, but usually most efficient: Most timeouts are
1949 relatively long compared to the intervals between other activity \- in
1950 our example, within 60 seconds, there are usually many I/O events with
1951 associated activity resets.
1952 .Sp
1953 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1954 but remember the time of last activity, and check for a real timeout only
1955 within the callback:
1956 .Sp
1957 .Vb 1
1958 \& ev_tstamp last_activity; // time of last activity
1959 \&
1960 \& static void
1961 \& callback (EV_P_ ev_timer *w, int revents)
1962 \& {
1963 \& ev_tstamp now = ev_now (EV_A);
1964 \& ev_tstamp timeout = last_activity + 60.;
1965 \&
1966 \& // if last_activity + 60. is older than now, we did time out
1967 \& if (timeout < now)
1968 \& {
1969 \& // timeout occurred, take action
1970 \& }
1971 \& else
1972 \& {
1973 \& // callback was invoked, but there was some activity, re\-arm
1974 \& // the watcher to fire in last_activity + 60, which is
1975 \& // guaranteed to be in the future, so "again" is positive:
1976 \& w\->repeat = timeout \- now;
1977 \& ev_timer_again (EV_A_ w);
1978 \& }
1979 \& }
1980 .Ve
1981 .Sp
1982 To summarise the callback: first calculate the real timeout (defined
1983 as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1984 been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1985 the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1986 re-schedule the timer to fire at that future time, to see if maybe we have
1987 a timeout then.
1988 .Sp
1989 Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1990 \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1991 .Sp
1992 This scheme causes more callback invocations (about one every 60 seconds
1993 minus half the average time between activity), but virtually no calls to
1994 libev to change the timeout.
1995 .Sp
1996 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1997 to the current time (meaning we just have some activity :), then call the
1998 callback, which will \*(L"do the right thing\*(R" and start the timer:
1999 .Sp
2000 .Vb 3
2001 \& ev_init (timer, callback);
2002 \& last_activity = ev_now (loop);
2003 \& callback (loop, timer, EV_TIMER);
2004 .Ve
2005 .Sp
2006 And when there is some activity, simply store the current time in
2007 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2008 .Sp
2009 .Vb 1
2010 \& last_activity = ev_now (loop);
2011 .Ve
2012 .Sp
2013 This technique is slightly more complex, but in most cases where the
2014 time-out is unlikely to be triggered, much more efficient.
2015 .Sp
2016 Changing the timeout is trivial as well (if it isn't hard-coded in the
2017 callback :) \- just change the timeout and invoke the callback, which will
2018 fix things for you.
2019 .IP "4. Wee, just use a double-linked list for your timeouts." 4
2020 .IX Item "4. Wee, just use a double-linked list for your timeouts."
2021 If there is not one request, but many thousands (millions...), all
2022 employing some kind of timeout with the same timeout value, then one can
2023 do even better:
2024 .Sp
2025 When starting the timeout, calculate the timeout value and put the timeout
2026 at the \fIend\fR of the list.
2027 .Sp
2028 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2029 the list is expected to fire (for example, using the technique #3).
2030 .Sp
2031 When there is some activity, remove the timer from the list, recalculate
2032 the timeout, append it to the end of the list again, and make sure to
2033 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2034 .Sp
2035 This way, one can manage an unlimited number of timeouts in O(1) time for
2036 starting, stopping and updating the timers, at the expense of a major
2037 complication, and having to use a constant timeout. The constant timeout
2038 ensures that the list stays sorted.
2039 .PP
2040 So which method the best?
2041 .PP
2042 Method #2 is a simple no-brain-required solution that is adequate in most
2043 situations. Method #3 requires a bit more thinking, but handles many cases
2044 better, and isn't very complicated either. In most case, choosing either
2045 one is fine, with #3 being better in typical situations.
2046 .PP
2047 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2048 rather complicated, but extremely efficient, something that really pays
2049 off after the first million or so of active timers, i.e. it's usually
2050 overkill :)
2051 .PP
2052 \fIThe special problem of time updates\fR
2053 .IX Subsection "The special problem of time updates"
2054 .PP
2055 Establishing the current time is a costly operation (it usually takes at
2056 least two system calls): \s-1EV\s0 therefore updates its idea of the current
2057 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2058 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2059 lots of events in one iteration.
2060 .PP
2061 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2062 time. This is usually the right thing as this timestamp refers to the time
2063 of the event triggering whatever timeout you are modifying/starting. If
2064 you suspect event processing to be delayed and you \fIneed\fR to base the
2065 timeout on the current time, use something like this to adjust for this:
2066 .PP
2067 .Vb 1
2068 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
2069 .Ve
2070 .PP
2071 If the event loop is suspended for a long time, you can also force an
2072 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2073 ()\*(C'\fR.
2074 .PP
2075 \fIThe special problems of suspended animation\fR
2076 .IX Subsection "The special problems of suspended animation"
2077 .PP
2078 When you leave the server world it is quite customary to hit machines that
2079 can suspend/hibernate \- what happens to the clocks during such a suspend?
2080 .PP
2081 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2082 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2083 to run until the system is suspended, but they will not advance while the
2084 system is suspended. That means, on resume, it will be as if the program
2085 was frozen for a few seconds, but the suspend time will not be counted
2086 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2087 clock advanced as expected, but if it is used as sole clocksource, then a
2088 long suspend would be detected as a time jump by libev, and timers would
2089 be adjusted accordingly.
2090 .PP
2091 I would not be surprised to see different behaviour in different between
2092 operating systems, \s-1OS\s0 versions or even different hardware.
2093 .PP
2094 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2095 time jump in the monotonic clocks and the realtime clock. If the program
2096 is suspended for a very long time, and monotonic clock sources are in use,
2097 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2098 will be counted towards the timers. When no monotonic clock source is in
2099 use, then libev will again assume a timejump and adjust accordingly.
2100 .PP
2101 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2102 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2103 deterministic behaviour in this case (you can do nothing against
2104 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2105 .PP
2106 \fIWatcher-Specific Functions and Data Members\fR
2107 .IX Subsection "Watcher-Specific Functions and Data Members"
2108 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2109 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2110 .PD 0
2111 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2112 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2113 .PD
2114 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2115 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2116 reached. If it is positive, then the timer will automatically be
2117 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2118 until stopped manually.
2119 .Sp
2120 The timer itself will do a best-effort at avoiding drift, that is, if
2121 you configure a timer to trigger every 10 seconds, then it will normally
2122 trigger at exactly 10 second intervals. If, however, your program cannot
2123 keep up with the timer (because it takes longer than those 10 seconds to
2124 do stuff) the timer will not fire more than once per event loop iteration.
2125 .IP "ev_timer_again (loop, ev_timer *)" 4
2126 .IX Item "ev_timer_again (loop, ev_timer *)"
2127 This will act as if the timer timed out and restart it again if it is
2128 repeating. The exact semantics are:
2129 .Sp
2130 If the timer is pending, its pending status is cleared.
2131 .Sp
2132 If the timer is started but non-repeating, stop it (as if it timed out).
2133 .Sp
2134 If the timer is repeating, either start it if necessary (with the
2135 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
2136 .Sp
2137 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2138 usage example.
2139 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2140 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2141 Returns the remaining time until a timer fires. If the timer is active,
2142 then this time is relative to the current event loop time, otherwise it's
2143 the timeout value currently configured.
2144 .Sp
2145 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2146 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2147 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2148 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2149 too), and so on.
2150 .IP "ev_tstamp repeat [read\-write]" 4
2151 .IX Item "ev_tstamp repeat [read-write]"
2152 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2153 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2154 which is also when any modifications are taken into account.
2155 .PP
2156 \fIExamples\fR
2157 .IX Subsection "Examples"
2158 .PP
2159 Example: Create a timer that fires after 60 seconds.
2160 .PP
2161 .Vb 5
2162 \& static void
2163 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2164 \& {
2165 \& .. one minute over, w is actually stopped right here
2166 \& }
2167 \&
2168 \& ev_timer mytimer;
2169 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2170 \& ev_timer_start (loop, &mytimer);
2171 .Ve
2172 .PP
2173 Example: Create a timeout timer that times out after 10 seconds of
2174 inactivity.
2175 .PP
2176 .Vb 5
2177 \& static void
2178 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2179 \& {
2180 \& .. ten seconds without any activity
2181 \& }
2182 \&
2183 \& ev_timer mytimer;
2184 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2185 \& ev_timer_again (&mytimer); /* start timer */
2186 \& ev_run (loop, 0);
2187 \&
2188 \& // and in some piece of code that gets executed on any "activity":
2189 \& // reset the timeout to start ticking again at 10 seconds
2190 \& ev_timer_again (&mytimer);
2191 .Ve
2192 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2193 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2194 .IX Subsection "ev_periodic - to cron or not to cron?"
2195 Periodic watchers are also timers of a kind, but they are very versatile
2196 (and unfortunately a bit complex).
2197 .PP
2198 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2199 relative time, the physical time that passes) but on wall clock time
2200 (absolute time, the thing you can read on your calender or clock). The
2201 difference is that wall clock time can run faster or slower than real
2202 time, and time jumps are not uncommon (e.g. when you adjust your
2203 wrist-watch).
2204 .PP
2205 You can tell a periodic watcher to trigger after some specific point
2206 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2207 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2208 not a delay) and then reset your system clock to January of the previous
2209 year, then it will take a year or more to trigger the event (unlike an
2210 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2211 it, as it uses a relative timeout).
2212 .PP
2213 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2214 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2215 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2216 those cannot react to time jumps.
2217 .PP
2218 As with timers, the callback is guaranteed to be invoked only when the
2219 point in time where it is supposed to trigger has passed. If multiple
2220 timers become ready during the same loop iteration then the ones with
2221 earlier time-out values are invoked before ones with later time-out values
2222 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2223 .PP
2224 \fIWatcher-Specific Functions and Data Members\fR
2225 .IX Subsection "Watcher-Specific Functions and Data Members"
2226 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2227 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2228 .PD 0
2229 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2230 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2231 .PD
2232 Lots of arguments, let's sort it out... There are basically three modes of
2233 operation, and we will explain them from simplest to most complex:
2234 .RS 4
2235 .IP "\(bu" 4
2236 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2237 .Sp
2238 In this configuration the watcher triggers an event after the wall clock
2239 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2240 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2241 will be stopped and invoked when the system clock reaches or surpasses
2242 this point in time.
2243 .IP "\(bu" 4
2244 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2245 .Sp
2246 In this mode the watcher will always be scheduled to time out at the next
2247 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2248 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2249 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2250 .Sp
2251 This can be used to create timers that do not drift with respect to the
2252 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2253 hour, on the hour (with respect to \s-1UTC\s0):
2254 .Sp
2255 .Vb 1
2256 \& ev_periodic_set (&periodic, 0., 3600., 0);
2257 .Ve
2258 .Sp
2259 This doesn't mean there will always be 3600 seconds in between triggers,
2260 but only that the callback will be called when the system time shows a
2261 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2262 by 3600.
2263 .Sp
2264 Another way to think about it (for the mathematically inclined) is that
2265 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2266 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2267 .Sp
2268 For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2269 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2270 this value, and in fact is often specified as zero.
2271 .Sp
2272 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2273 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2274 will of course deteriorate. Libev itself tries to be exact to be about one
2275 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2276 .IP "\(bu" 4
2277 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2278 .Sp
2279 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2280 ignored. Instead, each time the periodic watcher gets scheduled, the
2281 reschedule callback will be called with the watcher as first, and the
2282 current time as second argument.
2283 .Sp
2284 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2285 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2286 allowed by documentation here\fR.
2287 .Sp
2288 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2289 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2290 only event loop modification you are allowed to do).
2291 .Sp
2292 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2293 *w, ev_tstamp now)\*(C'\fR, e.g.:
2294 .Sp
2295 .Vb 5
2296 \& static ev_tstamp
2297 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2298 \& {
2299 \& return now + 60.;
2300 \& }
2301 .Ve
2302 .Sp
2303 It must return the next time to trigger, based on the passed time value
2304 (that is, the lowest time value larger than to the second argument). It
2305 will usually be called just before the callback will be triggered, but
2306 might be called at other times, too.
2307 .Sp
2308 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2309 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2310 .Sp
2311 This can be used to create very complex timers, such as a timer that
2312 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2313 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2314 you do this is, again, up to you (but it is not trivial, which is the main
2315 reason I omitted it as an example).
2316 .RE
2317 .RS 4
2318 .RE
2319 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2320 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2321 Simply stops and restarts the periodic watcher again. This is only useful
2322 when you changed some parameters or the reschedule callback would return
2323 a different time than the last time it was called (e.g. in a crond like
2324 program when the crontabs have changed).
2325 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2326 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2327 When active, returns the absolute time that the watcher is supposed
2328 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2329 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2330 rescheduling modes.
2331 .IP "ev_tstamp offset [read\-write]" 4
2332 .IX Item "ev_tstamp offset [read-write]"
2333 When repeating, this contains the offset value, otherwise this is the
2334 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2335 although libev might modify this value for better numerical stability).
2336 .Sp
2337 Can be modified any time, but changes only take effect when the periodic
2338 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2339 .IP "ev_tstamp interval [read\-write]" 4
2340 .IX Item "ev_tstamp interval [read-write]"
2341 The current interval value. Can be modified any time, but changes only
2342 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2343 called.
2344 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2345 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2346 The current reschedule callback, or \f(CW0\fR, if this functionality is
2347 switched off. Can be changed any time, but changes only take effect when
2348 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2349 .PP
2350 \fIExamples\fR
2351 .IX Subsection "Examples"
2352 .PP
2353 Example: Call a callback every hour, or, more precisely, whenever the
2354 system time is divisible by 3600. The callback invocation times have
2355 potentially a lot of jitter, but good long-term stability.
2356 .PP
2357 .Vb 5
2358 \& static void
2359 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2360 \& {
2361 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2362 \& }
2363 \&
2364 \& ev_periodic hourly_tick;
2365 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2366 \& ev_periodic_start (loop, &hourly_tick);
2367 .Ve
2368 .PP
2369 Example: The same as above, but use a reschedule callback to do it:
2370 .PP
2371 .Vb 1
2372 \& #include <math.h>
2373 \&
2374 \& static ev_tstamp
2375 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2376 \& {
2377 \& return now + (3600. \- fmod (now, 3600.));
2378 \& }
2379 \&
2380 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2381 .Ve
2382 .PP
2383 Example: Call a callback every hour, starting now:
2384 .PP
2385 .Vb 4
2386 \& ev_periodic hourly_tick;
2387 \& ev_periodic_init (&hourly_tick, clock_cb,
2388 \& fmod (ev_now (loop), 3600.), 3600., 0);
2389 \& ev_periodic_start (loop, &hourly_tick);
2390 .Ve
2391 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2392 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2393 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2394 Signal watchers will trigger an event when the process receives a specific
2395 signal one or more times. Even though signals are very asynchronous, libev
2396 will try it's best to deliver signals synchronously, i.e. as part of the
2397 normal event processing, like any other event.
2398 .PP
2399 If you want signals to be delivered truly asynchronously, just use
2400 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2401 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2402 synchronously wake up an event loop.
2403 .PP
2404 You can configure as many watchers as you like for the same signal, but
2405 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2406 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2407 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2408 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2409 .PP
2410 When the first watcher gets started will libev actually register something
2411 with the kernel (thus it coexists with your own signal handlers as long as
2412 you don't register any with libev for the same signal).
2413 .PP
2414 If possible and supported, libev will install its handlers with
2415 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2416 not be unduly interrupted. If you have a problem with system calls getting
2417 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2418 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2419 .PP
2420 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2421 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2422 .PP
2423 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2424 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2425 stopping it again), that is, libev might or might not block the signal,
2426 and might or might not set or restore the installed signal handler.
2427 .PP
2428 While this does not matter for the signal disposition (libev never
2429 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2430 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2431 certain signals to be blocked.
2432 .PP
2433 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2434 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2435 choice usually).
2436 .PP
2437 The simplest way to ensure that the signal mask is reset in the child is
2438 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2439 catch fork calls done by libraries (such as the libc) as well.
2440 .PP
2441 In current versions of libev, the signal will not be blocked indefinitely
2442 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2443 the window of opportunity for problems, it will not go away, as libev
2444 \&\fIhas\fR to modify the signal mask, at least temporarily.
2445 .PP
2446 So I can't stress this enough: \fIIf you do not reset your signal mask when
2447 you expect it to be empty, you have a race condition in your code\fR. This
2448 is not a libev-specific thing, this is true for most event libraries.
2449 .PP
2450 \fIWatcher-Specific Functions and Data Members\fR
2451 .IX Subsection "Watcher-Specific Functions and Data Members"
2452 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2453 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2454 .PD 0
2455 .IP "ev_signal_set (ev_signal *, int signum)" 4
2456 .IX Item "ev_signal_set (ev_signal *, int signum)"
2457 .PD
2458 Configures the watcher to trigger on the given signal number (usually one
2459 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2460 .IP "int signum [read\-only]" 4
2461 .IX Item "int signum [read-only]"
2462 The signal the watcher watches out for.
2463 .PP
2464 \fIExamples\fR
2465 .IX Subsection "Examples"
2466 .PP
2467 Example: Try to exit cleanly on \s-1SIGINT\s0.
2468 .PP
2469 .Vb 5
2470 \& static void
2471 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2472 \& {
2473 \& ev_break (loop, EVBREAK_ALL);
2474 \& }
2475 \&
2476 \& ev_signal signal_watcher;
2477 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2478 \& ev_signal_start (loop, &signal_watcher);
2479 .Ve
2480 .ie n .SS """ev_child"" \- watch out for process status changes"
2481 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2482 .IX Subsection "ev_child - watch out for process status changes"
2483 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2484 some child status changes (most typically when a child of yours dies or
2485 exits). It is permissible to install a child watcher \fIafter\fR the child
2486 has been forked (which implies it might have already exited), as long
2487 as the event loop isn't entered (or is continued from a watcher), i.e.,
2488 forking and then immediately registering a watcher for the child is fine,
2489 but forking and registering a watcher a few event loop iterations later or
2490 in the next callback invocation is not.
2491 .PP
2492 Only the default event loop is capable of handling signals, and therefore
2493 you can only register child watchers in the default event loop.
2494 .PP
2495 Due to some design glitches inside libev, child watchers will always be
2496 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2497 libev)
2498 .PP
2499 \fIProcess Interaction\fR
2500 .IX Subsection "Process Interaction"
2501 .PP
2502 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2503 initialised. This is necessary to guarantee proper behaviour even if the
2504 first child watcher is started after the child exits. The occurrence
2505 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2506 synchronously as part of the event loop processing. Libev always reaps all
2507 children, even ones not watched.
2508 .PP
2509 \fIOverriding the Built-In Processing\fR
2510 .IX Subsection "Overriding the Built-In Processing"
2511 .PP
2512 Libev offers no special support for overriding the built-in child
2513 processing, but if your application collides with libev's default child
2514 handler, you can override it easily by installing your own handler for
2515 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2516 default loop never gets destroyed. You are encouraged, however, to use an
2517 event-based approach to child reaping and thus use libev's support for
2518 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2519 .PP
2520 \fIStopping the Child Watcher\fR
2521 .IX Subsection "Stopping the Child Watcher"
2522 .PP
2523 Currently, the child watcher never gets stopped, even when the
2524 child terminates, so normally one needs to stop the watcher in the
2525 callback. Future versions of libev might stop the watcher automatically
2526 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2527 problem).
2528 .PP
2529 \fIWatcher-Specific Functions and Data Members\fR
2530 .IX Subsection "Watcher-Specific Functions and Data Members"
2531 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2532 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2533 .PD 0
2534 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2535 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2536 .PD
2537 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2538 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2539 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2540 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2541 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2542 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2543 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2544 activate the watcher when the process is stopped or continued).
2545 .IP "int pid [read\-only]" 4
2546 .IX Item "int pid [read-only]"
2547 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2548 .IP "int rpid [read\-write]" 4
2549 .IX Item "int rpid [read-write]"
2550 The process id that detected a status change.
2551 .IP "int rstatus [read\-write]" 4
2552 .IX Item "int rstatus [read-write]"
2553 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2554 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2555 .PP
2556 \fIExamples\fR
2557 .IX Subsection "Examples"
2558 .PP
2559 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2560 its completion.
2561 .PP
2562 .Vb 1
2563 \& ev_child cw;
2564 \&
2565 \& static void
2566 \& child_cb (EV_P_ ev_child *w, int revents)
2567 \& {
2568 \& ev_child_stop (EV_A_ w);
2569 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2570 \& }
2571 \&
2572 \& pid_t pid = fork ();
2573 \&
2574 \& if (pid < 0)
2575 \& // error
2576 \& else if (pid == 0)
2577 \& {
2578 \& // the forked child executes here
2579 \& exit (1);
2580 \& }
2581 \& else
2582 \& {
2583 \& ev_child_init (&cw, child_cb, pid, 0);
2584 \& ev_child_start (EV_DEFAULT_ &cw);
2585 \& }
2586 .Ve
2587 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2588 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2589 .IX Subsection "ev_stat - did the file attributes just change?"
2590 This watches a file system path for attribute changes. That is, it calls
2591 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2592 and sees if it changed compared to the last time, invoking the callback if
2593 it did.
2594 .PP
2595 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2596 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2597 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2598 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2599 least one) and all the other fields of the stat buffer having unspecified
2600 contents.
2601 .PP
2602 The path \fImust not\fR end in a slash or contain special components such as
2603 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2604 your working directory changes, then the behaviour is undefined.
2605 .PP
2606 Since there is no portable change notification interface available, the
2607 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2608 to see if it changed somehow. You can specify a recommended polling
2609 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2610 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2611 (which you can expect to be around five seconds, although this might
2612 change dynamically). Libev will also impose a minimum interval which is
2613 currently around \f(CW0.1\fR, but that's usually overkill.
2614 .PP
2615 This watcher type is not meant for massive numbers of stat watchers,
2616 as even with OS-supported change notifications, this can be
2617 resource-intensive.
2618 .PP
2619 At the time of this writing, the only OS-specific interface implemented
2620 is the Linux inotify interface (implementing kqueue support is left as an
2621 exercise for the reader. Note, however, that the author sees no way of
2622 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2623 .PP
2624 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2625 .IX Subsection "ABI Issues (Largefile Support)"
2626 .PP
2627 Libev by default (unless the user overrides this) uses the default
2628 compilation environment, which means that on systems with large file
2629 support disabled by default, you get the 32 bit version of the stat
2630 structure. When using the library from programs that change the \s-1ABI\s0 to
2631 use 64 bit file offsets the programs will fail. In that case you have to
2632 compile libev with the same flags to get binary compatibility. This is
2633 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2634 most noticeably displayed with ev_stat and large file support.
2635 .PP
2636 The solution for this is to lobby your distribution maker to make large
2637 file interfaces available by default (as e.g. FreeBSD does) and not
2638 optional. Libev cannot simply switch on large file support because it has
2639 to exchange stat structures with application programs compiled using the
2640 default compilation environment.
2641 .PP
2642 \fIInotify and Kqueue\fR
2643 .IX Subsection "Inotify and Kqueue"
2644 .PP
2645 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2646 runtime, it will be used to speed up change detection where possible. The
2647 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2648 watcher is being started.
2649 .PP
2650 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2651 except that changes might be detected earlier, and in some cases, to avoid
2652 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2653 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2654 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2655 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2656 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2657 xfs are fully working) libev usually gets away without polling.
2658 .PP
2659 There is no support for kqueue, as apparently it cannot be used to
2660 implement this functionality, due to the requirement of having a file
2661 descriptor open on the object at all times, and detecting renames, unlinks
2662 etc. is difficult.
2663 .PP
2664 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2665 .IX Subsection "stat () is a synchronous operation"
2666 .PP
2667 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2668 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2669 ()\*(C'\fR, which is a synchronous operation.
2670 .PP
2671 For local paths, this usually doesn't matter: unless the system is very
2672 busy or the intervals between stat's are large, a stat call will be fast,
2673 as the path data is usually in memory already (except when starting the
2674 watcher).
2675 .PP
2676 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2677 time due to network issues, and even under good conditions, a stat call
2678 often takes multiple milliseconds.
2679 .PP
2680 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2681 paths, although this is fully supported by libev.
2682 .PP
2683 \fIThe special problem of stat time resolution\fR
2684 .IX Subsection "The special problem of stat time resolution"
2685 .PP
2686 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2687 and even on systems where the resolution is higher, most file systems
2688 still only support whole seconds.
2689 .PP
2690 That means that, if the time is the only thing that changes, you can
2691 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2692 calls your callback, which does something. When there is another update
2693 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2694 stat data does change in other ways (e.g. file size).
2695 .PP
2696 The solution to this is to delay acting on a change for slightly more
2697 than a second (or till slightly after the next full second boundary), using
2698 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2699 ev_timer_again (loop, w)\*(C'\fR).
2700 .PP
2701 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2702 of some operating systems (where the second counter of the current time
2703 might be be delayed. One such system is the Linux kernel, where a call to
2704 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2705 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2706 update file times then there will be a small window where the kernel uses
2707 the previous second to update file times but libev might already execute
2708 the timer callback).
2709 .PP
2710 \fIWatcher-Specific Functions and Data Members\fR
2711 .IX Subsection "Watcher-Specific Functions and Data Members"
2712 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2713 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2714 .PD 0
2715 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2716 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2717 .PD
2718 Configures the watcher to wait for status changes of the given
2719 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2720 be detected and should normally be specified as \f(CW0\fR to let libev choose
2721 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2722 path for as long as the watcher is active.
2723 .Sp
2724 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2725 relative to the attributes at the time the watcher was started (or the
2726 last change was detected).
2727 .IP "ev_stat_stat (loop, ev_stat *)" 4
2728 .IX Item "ev_stat_stat (loop, ev_stat *)"
2729 Updates the stat buffer immediately with new values. If you change the
2730 watched path in your callback, you could call this function to avoid
2731 detecting this change (while introducing a race condition if you are not
2732 the only one changing the path). Can also be useful simply to find out the
2733 new values.
2734 .IP "ev_statdata attr [read\-only]" 4
2735 .IX Item "ev_statdata attr [read-only]"
2736 The most-recently detected attributes of the file. Although the type is
2737 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2738 suitable for your system, but you can only rely on the POSIX-standardised
2739 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2740 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2741 .IP "ev_statdata prev [read\-only]" 4
2742 .IX Item "ev_statdata prev [read-only]"
2743 The previous attributes of the file. The callback gets invoked whenever
2744 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2745 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,
2746 \&\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.
2747 .IP "ev_tstamp interval [read\-only]" 4
2748 .IX Item "ev_tstamp interval [read-only]"
2749 The specified interval.
2750 .IP "const char *path [read\-only]" 4
2751 .IX Item "const char *path [read-only]"
2752 The file system path that is being watched.
2753 .PP
2754 \fIExamples\fR
2755 .IX Subsection "Examples"
2756 .PP
2757 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2758 .PP
2759 .Vb 10
2760 \& static void
2761 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2762 \& {
2763 \& /* /etc/passwd changed in some way */
2764 \& if (w\->attr.st_nlink)
2765 \& {
2766 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2767 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2768 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2769 \& }
2770 \& else
2771 \& /* you shalt not abuse printf for puts */
2772 \& puts ("wow, /etc/passwd is not there, expect problems. "
2773 \& "if this is windows, they already arrived\en");
2774 \& }
2775 \&
2776 \& ...
2777 \& ev_stat passwd;
2778 \&
2779 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2780 \& ev_stat_start (loop, &passwd);
2781 .Ve
2782 .PP
2783 Example: Like above, but additionally use a one-second delay so we do not
2784 miss updates (however, frequent updates will delay processing, too, so
2785 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2786 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2787 .PP
2788 .Vb 2
2789 \& static ev_stat passwd;
2790 \& static ev_timer timer;
2791 \&
2792 \& static void
2793 \& timer_cb (EV_P_ ev_timer *w, int revents)
2794 \& {
2795 \& ev_timer_stop (EV_A_ w);
2796 \&
2797 \& /* now it\*(Aqs one second after the most recent passwd change */
2798 \& }
2799 \&
2800 \& static void
2801 \& stat_cb (EV_P_ ev_stat *w, int revents)
2802 \& {
2803 \& /* reset the one\-second timer */
2804 \& ev_timer_again (EV_A_ &timer);
2805 \& }
2806 \&
2807 \& ...
2808 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2809 \& ev_stat_start (loop, &passwd);
2810 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2811 .Ve
2812 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2813 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2814 .IX Subsection "ev_idle - when you've got nothing better to do..."
2815 Idle watchers trigger events when no other events of the same or higher
2816 priority are pending (prepare, check and other idle watchers do not count
2817 as receiving \*(L"events\*(R").
2818 .PP
2819 That is, as long as your process is busy handling sockets or timeouts
2820 (or even signals, imagine) of the same or higher priority it will not be
2821 triggered. But when your process is idle (or only lower-priority watchers
2822 are pending), the idle watchers are being called once per event loop
2823 iteration \- until stopped, that is, or your process receives more events
2824 and becomes busy again with higher priority stuff.
2825 .PP
2826 The most noteworthy effect is that as long as any idle watchers are
2827 active, the process will not block when waiting for new events.
2828 .PP
2829 Apart from keeping your process non-blocking (which is a useful
2830 effect on its own sometimes), idle watchers are a good place to do
2831 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2832 event loop has handled all outstanding events.
2833 .PP
2834 \fIWatcher-Specific Functions and Data Members\fR
2835 .IX Subsection "Watcher-Specific Functions and Data Members"
2836 .IP "ev_idle_init (ev_idle *, callback)" 4
2837 .IX Item "ev_idle_init (ev_idle *, callback)"
2838 Initialises and configures the idle watcher \- it has no parameters of any
2839 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2840 believe me.
2841 .PP
2842 \fIExamples\fR
2843 .IX Subsection "Examples"
2844 .PP
2845 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2846 callback, free it. Also, use no error checking, as usual.
2847 .PP
2848 .Vb 7
2849 \& static void
2850 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2851 \& {
2852 \& free (w);
2853 \& // now do something you wanted to do when the program has
2854 \& // no longer anything immediate to do.
2855 \& }
2856 \&
2857 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2858 \& ev_idle_init (idle_watcher, idle_cb);
2859 \& ev_idle_start (loop, idle_watcher);
2860 .Ve
2861 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
2862 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2863 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2864 Prepare and check watchers are usually (but not always) used in pairs:
2865 prepare watchers get invoked before the process blocks and check watchers
2866 afterwards.
2867 .PP
2868 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2869 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2870 watchers. Other loops than the current one are fine, however. The
2871 rationale behind this is that you do not need to check for recursion in
2872 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2873 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2874 called in pairs bracketing the blocking call.
2875 .PP
2876 Their main purpose is to integrate other event mechanisms into libev and
2877 their use is somewhat advanced. They could be used, for example, to track
2878 variable changes, implement your own watchers, integrate net-snmp or a
2879 coroutine library and lots more. They are also occasionally useful if
2880 you cache some data and want to flush it before blocking (for example,
2881 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2882 watcher).
2883 .PP
2884 This is done by examining in each prepare call which file descriptors
2885 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2886 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2887 libraries provide exactly this functionality). Then, in the check watcher,
2888 you check for any events that occurred (by checking the pending status
2889 of all watchers and stopping them) and call back into the library. The
2890 I/O and timer callbacks will never actually be called (but must be valid
2891 nevertheless, because you never know, you know?).
2892 .PP
2893 As another example, the Perl Coro module uses these hooks to integrate
2894 coroutines into libev programs, by yielding to other active coroutines
2895 during each prepare and only letting the process block if no coroutines
2896 are ready to run (it's actually more complicated: it only runs coroutines
2897 with priority higher than or equal to the event loop and one coroutine
2898 of lower priority, but only once, using idle watchers to keep the event
2899 loop from blocking if lower-priority coroutines are active, thus mapping
2900 low-priority coroutines to idle/background tasks).
2901 .PP
2902 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2903 priority, to ensure that they are being run before any other watchers
2904 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2905 .PP
2906 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2907 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2908 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2909 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2910 loops those other event loops might be in an unusable state until their
2911 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2912 others).
2913 .PP
2914 \fIWatcher-Specific Functions and Data Members\fR
2915 .IX Subsection "Watcher-Specific Functions and Data Members"
2916 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2917 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2918 .PD 0
2919 .IP "ev_check_init (ev_check *, callback)" 4
2920 .IX Item "ev_check_init (ev_check *, callback)"
2921 .PD
2922 Initialises and configures the prepare or check watcher \- they have no
2923 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2924 macros, but using them is utterly, utterly, utterly and completely
2925 pointless.
2926 .PP
2927 \fIExamples\fR
2928 .IX Subsection "Examples"
2929 .PP
2930 There are a number of principal ways to embed other event loops or modules
2931 into libev. Here are some ideas on how to include libadns into libev
2932 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2933 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2934 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2935 Glib event loop).
2936 .PP
2937 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2938 and in a check watcher, destroy them and call into libadns. What follows
2939 is pseudo-code only of course. This requires you to either use a low
2940 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2941 the callbacks for the IO/timeout watchers might not have been called yet.
2942 .PP
2943 .Vb 2
2944 \& static ev_io iow [nfd];
2945 \& static ev_timer tw;
2946 \&
2947 \& static void
2948 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2949 \& {
2950 \& }
2951 \&
2952 \& // create io watchers for each fd and a timer before blocking
2953 \& static void
2954 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2955 \& {
2956 \& int timeout = 3600000;
2957 \& struct pollfd fds [nfd];
2958 \& // actual code will need to loop here and realloc etc.
2959 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2960 \&
2961 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2962 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2963 \& ev_timer_start (loop, &tw);
2964 \&
2965 \& // create one ev_io per pollfd
2966 \& for (int i = 0; i < nfd; ++i)
2967 \& {
2968 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2969 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2970 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2971 \&
2972 \& fds [i].revents = 0;
2973 \& ev_io_start (loop, iow + i);
2974 \& }
2975 \& }
2976 \&
2977 \& // stop all watchers after blocking
2978 \& static void
2979 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2980 \& {
2981 \& ev_timer_stop (loop, &tw);
2982 \&
2983 \& for (int i = 0; i < nfd; ++i)
2984 \& {
2985 \& // set the relevant poll flags
2986 \& // could also call adns_processreadable etc. here
2987 \& struct pollfd *fd = fds + i;
2988 \& int revents = ev_clear_pending (iow + i);
2989 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2990 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2991 \&
2992 \& // now stop the watcher
2993 \& ev_io_stop (loop, iow + i);
2994 \& }
2995 \&
2996 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2997 \& }
2998 .Ve
2999 .PP
3000 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3001 in the prepare watcher and would dispose of the check watcher.
3002 .PP
3003 Method 3: If the module to be embedded supports explicit event
3004 notification (libadns does), you can also make use of the actual watcher
3005 callbacks, and only destroy/create the watchers in the prepare watcher.
3006 .PP
3007 .Vb 5
3008 \& static void
3009 \& timer_cb (EV_P_ ev_timer *w, int revents)
3010 \& {
3011 \& adns_state ads = (adns_state)w\->data;
3012 \& update_now (EV_A);
3013 \&
3014 \& adns_processtimeouts (ads, &tv_now);
3015 \& }
3016 \&
3017 \& static void
3018 \& io_cb (EV_P_ ev_io *w, int revents)
3019 \& {
3020 \& adns_state ads = (adns_state)w\->data;
3021 \& update_now (EV_A);
3022 \&
3023 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3024 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3025 \& }
3026 \&
3027 \& // do not ever call adns_afterpoll
3028 .Ve
3029 .PP
3030 Method 4: Do not use a prepare or check watcher because the module you
3031 want to embed is not flexible enough to support it. Instead, you can
3032 override their poll function. The drawback with this solution is that the
3033 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3034 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3035 libglib event loop.
3036 .PP
3037 .Vb 4
3038 \& static gint
3039 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3040 \& {
3041 \& int got_events = 0;
3042 \&
3043 \& for (n = 0; n < nfds; ++n)
3044 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3045 \&
3046 \& if (timeout >= 0)
3047 \& // create/start timer
3048 \&
3049 \& // poll
3050 \& ev_run (EV_A_ 0);
3051 \&
3052 \& // stop timer again
3053 \& if (timeout >= 0)
3054 \& ev_timer_stop (EV_A_ &to);
3055 \&
3056 \& // stop io watchers again \- their callbacks should have set
3057 \& for (n = 0; n < nfds; ++n)
3058 \& ev_io_stop (EV_A_ iow [n]);
3059 \&
3060 \& return got_events;
3061 \& }
3062 .Ve
3063 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3064 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3065 .IX Subsection "ev_embed - when one backend isn't enough..."
3066 This is a rather advanced watcher type that lets you embed one event loop
3067 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3068 loop, other types of watchers might be handled in a delayed or incorrect
3069 fashion and must not be used).
3070 .PP
3071 There are primarily two reasons you would want that: work around bugs and
3072 prioritise I/O.
3073 .PP
3074 As an example for a bug workaround, the kqueue backend might only support
3075 sockets on some platform, so it is unusable as generic backend, but you
3076 still want to make use of it because you have many sockets and it scales
3077 so nicely. In this case, you would create a kqueue-based loop and embed
3078 it into your default loop (which might use e.g. poll). Overall operation
3079 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3080 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3081 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3082 .PP
3083 As for prioritising I/O: under rare circumstances you have the case where
3084 some fds have to be watched and handled very quickly (with low latency),
3085 and even priorities and idle watchers might have too much overhead. In
3086 this case you would put all the high priority stuff in one loop and all
3087 the rest in a second one, and embed the second one in the first.
3088 .PP
3089 As long as the watcher is active, the callback will be invoked every
3090 time there might be events pending in the embedded loop. The callback
3091 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3092 sweep and invoke their callbacks (the callback doesn't need to invoke the
3093 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3094 to give the embedded loop strictly lower priority for example).
3095 .PP
3096 You can also set the callback to \f(CW0\fR, in which case the embed watcher
3097 will automatically execute the embedded loop sweep whenever necessary.
3098 .PP
3099 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3100 is active, i.e., the embedded loop will automatically be forked when the
3101 embedding loop forks. In other cases, the user is responsible for calling
3102 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3103 .PP
3104 Unfortunately, not all backends are embeddable: only the ones returned by
3105 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3106 portable one.
3107 .PP
3108 So when you want to use this feature you will always have to be prepared
3109 that you cannot get an embeddable loop. The recommended way to get around
3110 this is to have a separate variables for your embeddable loop, try to
3111 create it, and if that fails, use the normal loop for everything.
3112 .PP
3113 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3114 .IX Subsection "ev_embed and fork"
3115 .PP
3116 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3117 automatically be applied to the embedded loop as well, so no special
3118 fork handling is required in that case. When the watcher is not running,
3119 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3120 as applicable.
3121 .PP
3122 \fIWatcher-Specific Functions and Data Members\fR
3123 .IX Subsection "Watcher-Specific Functions and Data Members"
3124 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3125 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3126 .PD 0
3127 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3128 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3129 .PD
3130 Configures the watcher to embed the given loop, which must be
3131 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3132 invoked automatically, otherwise it is the responsibility of the callback
3133 to invoke it (it will continue to be called until the sweep has been done,
3134 if you do not want that, you need to temporarily stop the embed watcher).
3135 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3136 .IX Item "ev_embed_sweep (loop, ev_embed *)"
3137 Make a single, non-blocking sweep over the embedded loop. This works
3138 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3139 appropriate way for embedded loops.
3140 .IP "struct ev_loop *other [read\-only]" 4
3141 .IX Item "struct ev_loop *other [read-only]"
3142 The embedded event loop.
3143 .PP
3144 \fIExamples\fR
3145 .IX Subsection "Examples"
3146 .PP
3147 Example: Try to get an embeddable event loop and embed it into the default
3148 event loop. If that is not possible, use the default loop. The default
3149 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3150 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3151 used).
3152 .PP
3153 .Vb 3
3154 \& struct ev_loop *loop_hi = ev_default_init (0);
3155 \& struct ev_loop *loop_lo = 0;
3156 \& ev_embed embed;
3157 \&
3158 \& // see if there is a chance of getting one that works
3159 \& // (remember that a flags value of 0 means autodetection)
3160 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3161 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3162 \& : 0;
3163 \&
3164 \& // if we got one, then embed it, otherwise default to loop_hi
3165 \& if (loop_lo)
3166 \& {
3167 \& ev_embed_init (&embed, 0, loop_lo);
3168 \& ev_embed_start (loop_hi, &embed);
3169 \& }
3170 \& else
3171 \& loop_lo = loop_hi;
3172 .Ve
3173 .PP
3174 Example: Check if kqueue is available but not recommended and create
3175 a kqueue backend for use with sockets (which usually work with any
3176 kqueue implementation). Store the kqueue/socket\-only event loop in
3177 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3178 .PP
3179 .Vb 3
3180 \& struct ev_loop *loop = ev_default_init (0);
3181 \& struct ev_loop *loop_socket = 0;
3182 \& ev_embed embed;
3183 \&
3184 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3185 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3186 \& {
3187 \& ev_embed_init (&embed, 0, loop_socket);
3188 \& ev_embed_start (loop, &embed);
3189 \& }
3190 \&
3191 \& if (!loop_socket)
3192 \& loop_socket = loop;
3193 \&
3194 \& // now use loop_socket for all sockets, and loop for everything else
3195 .Ve
3196 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3197 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3198 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3199 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3200 whoever is a good citizen cared to tell libev about it by calling
3201 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3202 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3203 and only in the child after the fork. If whoever good citizen calling
3204 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3205 handlers will be invoked, too, of course.
3206 .PP
3207 \fIThe special problem of life after fork \- how is it possible?\fR
3208 .IX Subsection "The special problem of life after fork - how is it possible?"
3209 .PP
3210 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3211 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3212 sequence should be handled by libev without any problems.
3213 .PP
3214 This changes when the application actually wants to do event handling
3215 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3216 fork.
3217 .PP
3218 The default mode of operation (for libev, with application help to detect
3219 forks) is to duplicate all the state in the child, as would be expected
3220 when \fIeither\fR the parent \fIor\fR the child process continues.
3221 .PP
3222 When both processes want to continue using libev, then this is usually the
3223 wrong result. In that case, usually one process (typically the parent) is
3224 supposed to continue with all watchers in place as before, while the other
3225 process typically wants to start fresh, i.e. without any active watchers.
3226 .PP
3227 The cleanest and most efficient way to achieve that with libev is to
3228 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3229 use that for new watchers. This has the advantage of not touching more
3230 memory than necessary, and thus avoiding the copy-on-write, and the
3231 disadvantage of having to use multiple event loops (which do not support
3232 signal watchers).
3233 .PP
3234 When this is not possible, or you want to use the default loop for
3235 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3236 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3237 Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3238 watchers, so you have to be careful not to execute code that modifies
3239 those watchers. Note also that in that case, you have to re-register any
3240 signal watchers.
3241 .PP
3242 \fIWatcher-Specific Functions and Data Members\fR
3243 .IX Subsection "Watcher-Specific Functions and Data Members"
3244 .IP "ev_fork_init (ev_fork *, callback)" 4
3245 .IX Item "ev_fork_init (ev_fork *, callback)"
3246 Initialises and configures the fork watcher \- it has no parameters of any
3247 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3248 really.
3249 .ie n .SS """ev_cleanup"" \- even the best things end"
3250 .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3251 .IX Subsection "ev_cleanup - even the best things end"
3252 Cleanup watchers are called just before the event loop is being destroyed
3253 by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3254 .PP
3255 While there is no guarantee that the event loop gets destroyed, cleanup
3256 watchers provide a convenient method to install cleanup hooks for your
3257 program, worker threads and so on \- you just to make sure to destroy the
3258 loop when you want them to be invoked.
3259 .PP
3260 Cleanup watchers are invoked in the same way as any other watcher. Unlike
3261 all other watchers, they do not keep a reference to the event loop (which
3262 makes a lot of sense if you think about it). Like all other watchers, you
3263 can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3264 .PP
3265 \fIWatcher-Specific Functions and Data Members\fR
3266 .IX Subsection "Watcher-Specific Functions and Data Members"
3267 .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3268 .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3269 Initialises and configures the cleanup watcher \- it has no parameters of
3270 any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3271 pointless, I assure you.
3272 .PP
3273 Example: Register an atexit handler to destroy the default loop, so any
3274 cleanup functions are called.
3275 .PP
3276 .Vb 5
3277 \& static void
3278 \& program_exits (void)
3279 \& {
3280 \& ev_loop_destroy (EV_DEFAULT_UC);
3281 \& }
3282 \&
3283 \& ...
3284 \& atexit (program_exits);
3285 .Ve
3286 .ie n .SS """ev_async"" \- how to wake up an event loop"
3287 .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3288 .IX Subsection "ev_async - how to wake up an event loop"
3289 In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3290 asynchronous sources such as signal handlers (as opposed to multiple event
3291 loops \- those are of course safe to use in different threads).
3292 .PP
3293 Sometimes, however, you need to wake up an event loop you do not control,
3294 for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3295 watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3296 it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3297 .PP
3298 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3299 too, are asynchronous in nature, and signals, too, will be compressed
3300 (i.e. the number of callback invocations may be less than the number of
3301 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3302 .PP
3303 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3304 just the default loop.
3305 .PP
3306 \fIQueueing\fR
3307 .IX Subsection "Queueing"
3308 .PP
3309 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3310 is that the author does not know of a simple (or any) algorithm for a
3311 multiple-writer-single-reader queue that works in all cases and doesn't
3312 need elaborate support such as pthreads or unportable memory access
3313 semantics.
3314 .PP
3315 That means that if you want to queue data, you have to provide your own
3316 queue. But at least I can tell you how to implement locking around your
3317 queue:
3318 .IP "queueing from a signal handler context" 4
3319 .IX Item "queueing from a signal handler context"
3320 To implement race-free queueing, you simply add to the queue in the signal
3321 handler but you block the signal handler in the watcher callback. Here is
3322 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3323 .Sp
3324 .Vb 1
3325 \& static ev_async mysig;
3326 \&
3327 \& static void
3328 \& sigusr1_handler (void)
3329 \& {
3330 \& sometype data;
3331 \&
3332 \& // no locking etc.
3333 \& queue_put (data);
3334 \& ev_async_send (EV_DEFAULT_ &mysig);
3335 \& }
3336 \&
3337 \& static void
3338 \& mysig_cb (EV_P_ ev_async *w, int revents)
3339 \& {
3340 \& sometype data;
3341 \& sigset_t block, prev;
3342 \&
3343 \& sigemptyset (&block);
3344 \& sigaddset (&block, SIGUSR1);
3345 \& sigprocmask (SIG_BLOCK, &block, &prev);
3346 \&
3347 \& while (queue_get (&data))
3348 \& process (data);
3349 \&
3350 \& if (sigismember (&prev, SIGUSR1)
3351 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3352 \& }
3353 .Ve
3354 .Sp
3355 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3356 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3357 either...).
3358 .IP "queueing from a thread context" 4
3359 .IX Item "queueing from a thread context"
3360 The strategy for threads is different, as you cannot (easily) block
3361 threads but you can easily preempt them, so to queue safely you need to
3362 employ a traditional mutex lock, such as in this pthread example:
3363 .Sp
3364 .Vb 2
3365 \& static ev_async mysig;
3366 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3367 \&
3368 \& static void
3369 \& otherthread (void)
3370 \& {
3371 \& // only need to lock the actual queueing operation
3372 \& pthread_mutex_lock (&mymutex);
3373 \& queue_put (data);
3374 \& pthread_mutex_unlock (&mymutex);
3375 \&
3376 \& ev_async_send (EV_DEFAULT_ &mysig);
3377 \& }
3378 \&
3379 \& static void
3380 \& mysig_cb (EV_P_ ev_async *w, int revents)
3381 \& {
3382 \& pthread_mutex_lock (&mymutex);
3383 \&
3384 \& while (queue_get (&data))
3385 \& process (data);
3386 \&
3387 \& pthread_mutex_unlock (&mymutex);
3388 \& }
3389 .Ve
3390 .PP
3391 \fIWatcher-Specific Functions and Data Members\fR
3392 .IX Subsection "Watcher-Specific Functions and Data Members"
3393 .IP "ev_async_init (ev_async *, callback)" 4
3394 .IX Item "ev_async_init (ev_async *, callback)"
3395 Initialises and configures the async watcher \- it has no parameters of any
3396 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3397 trust me.
3398 .IP "ev_async_send (loop, ev_async *)" 4
3399 .IX Item "ev_async_send (loop, ev_async *)"
3400 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3401 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3402 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3403 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3404 section below on what exactly this means).
3405 .Sp
3406 Note that, as with other watchers in libev, multiple events might get
3407 compressed into a single callback invocation (another way to look at this
3408 is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3409 reset when the event loop detects that).
3410 .Sp
3411 This call incurs the overhead of a system call only once per event loop
3412 iteration, so while the overhead might be noticeable, it doesn't apply to
3413 repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3414 .IP "bool = ev_async_pending (ev_async *)" 4
3415 .IX Item "bool = ev_async_pending (ev_async *)"
3416 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3417 watcher but the event has not yet been processed (or even noted) by the
3418 event loop.
3419 .Sp
3420 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3421 the loop iterates next and checks for the watcher to have become active,
3422 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3423 quickly check whether invoking the loop might be a good idea.
3424 .Sp
3425 Not that this does \fInot\fR check whether the watcher itself is pending,
3426 only whether it has been requested to make this watcher pending: there
3427 is a time window between the event loop checking and resetting the async
3428 notification, and the callback being invoked.
3429 .SH "OTHER FUNCTIONS"
3430 .IX Header "OTHER FUNCTIONS"
3431 There are some other functions of possible interest. Described. Here. Now.
3432 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3433 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3434 This function combines a simple timer and an I/O watcher, calls your
3435 callback on whichever event happens first and automatically stops both
3436 watchers. This is useful if you want to wait for a single event on an fd
3437 or timeout without having to allocate/configure/start/stop/free one or
3438 more watchers yourself.
3439 .Sp
3440 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3441 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3442 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3443 .Sp
3444 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3445 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3446 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3447 .Sp
3448 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3449 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3450 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3451 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3452 a timeout and an io event at the same time \- you probably should give io
3453 events precedence.
3454 .Sp
3455 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3456 .Sp
3457 .Vb 7
3458 \& static void stdin_ready (int revents, void *arg)
3459 \& {
3460 \& if (revents & EV_READ)
3461 \& /* stdin might have data for us, joy! */;
3462 \& else if (revents & EV_TIMER)
3463 \& /* doh, nothing entered */;
3464 \& }
3465 \&
3466 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3467 .Ve
3468 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3469 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3470 Feed an event on the given fd, as if a file descriptor backend detected
3471 the given events it.
3472 .IP "ev_feed_signal_event (loop, int signum)" 4
3473 .IX Item "ev_feed_signal_event (loop, int signum)"
3474 Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3475 loop!).
3476 .SH "LIBEVENT EMULATION"
3477 .IX Header "LIBEVENT EMULATION"
3478 Libev offers a compatibility emulation layer for libevent. It cannot
3479 emulate the internals of libevent, so here are some usage hints:
3480 .IP "\(bu" 4
3481 Use it by including <event.h>, as usual.
3482 .IP "\(bu" 4
3483 The following members are fully supported: ev_base, ev_callback,
3484 ev_arg, ev_fd, ev_res, ev_events.
3485 .IP "\(bu" 4
3486 Avoid using ev_flags and the EVLIST_*\-macros, while it is
3487 maintained by libev, it does not work exactly the same way as in libevent (consider
3488 it a private \s-1API\s0).
3489 .IP "\(bu" 4
3490 Priorities are not currently supported. Initialising priorities
3491 will fail and all watchers will have the same priority, even though there
3492 is an ev_pri field.
3493 .IP "\(bu" 4
3494 In libevent, the last base created gets the signals, in libev, the
3495 first base created (== the default loop) gets the signals.
3496 .IP "\(bu" 4
3497 Other members are not supported.
3498 .IP "\(bu" 4
3499 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
3500 to use the libev header file and library.
3501 .SH "\*(C+ SUPPORT"
3502 .IX Header " SUPPORT"
3503 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3504 you to use some convenience methods to start/stop watchers and also change
3505 the callback model to a model using method callbacks on objects.
3506 .PP
3507 To use it,
3508 .PP
3509 .Vb 1
3510 \& #include <ev++.h>
3511 .Ve
3512 .PP
3513 This automatically includes \fIev.h\fR and puts all of its definitions (many
3514 of them macros) into the global namespace. All \*(C+ specific things are
3515 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3516 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3517 .PP
3518 Care has been taken to keep the overhead low. The only data member the \*(C+
3519 classes add (compared to plain C\-style watchers) is the event loop pointer
3520 that the watcher is associated with (or no additional members at all if
3521 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3522 .PP
3523 Currently, functions, and static and non-static member functions can be
3524 used as callbacks. Other types should be easy to add as long as they only
3525 need one additional pointer for context. If you need support for other
3526 types of functors please contact the author (preferably after implementing
3527 it).
3528 .PP
3529 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3530 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3531 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3532 .IX Item "ev::READ, ev::WRITE etc."
3533 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3534 macros from \fIev.h\fR.
3535 .ie n .IP """ev::tstamp"", ""ev::now""" 4
3536 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3537 .IX Item "ev::tstamp, ev::now"
3538 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3539 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3540 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3541 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3542 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3543 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3544 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3545 defines by many implementations.
3546 .Sp
3547 All of those classes have these methods:
3548 .RS 4
3549 .IP "ev::TYPE::TYPE ()" 4
3550 .IX Item "ev::TYPE::TYPE ()"
3551 .PD 0
3552 .IP "ev::TYPE::TYPE (loop)" 4
3553 .IX Item "ev::TYPE::TYPE (loop)"
3554 .IP "ev::TYPE::~TYPE" 4
3555 .IX Item "ev::TYPE::~TYPE"
3556 .PD
3557 The constructor (optionally) takes an event loop to associate the watcher
3558 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3559 .Sp
3560 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3561 \&\f(CW\*(C`set\*(C'\fR method before starting it.
3562 .Sp
3563 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3564 method to set a callback before you can start the watcher.
3565 .Sp
3566 (The reason why you have to use a method is a limitation in \*(C+ which does
3567 not allow explicit template arguments for constructors).
3568 .Sp
3569 The destructor automatically stops the watcher if it is active.
3570 .IP "w\->set<class, &class::method> (object *)" 4
3571 .IX Item "w->set<class, &class::method> (object *)"
3572 This method sets the callback method to call. The method has to have a
3573 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3574 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3575 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3576 .Sp
3577 This method synthesizes efficient thunking code to call your method from
3578 the C callback that libev requires. If your compiler can inline your
3579 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3580 your compiler is good :), then the method will be fully inlined into the
3581 thunking function, making it as fast as a direct C callback.
3582 .Sp
3583 Example: simple class declaration and watcher initialisation
3584 .Sp
3585 .Vb 4
3586 \& struct myclass
3587 \& {
3588 \& void io_cb (ev::io &w, int revents) { }
3589 \& }
3590 \&
3591 \& myclass obj;
3592 \& ev::io iow;
3593 \& iow.set <myclass, &myclass::io_cb> (&obj);
3594 .Ve
3595 .IP "w\->set (object *)" 4
3596 .IX Item "w->set (object *)"
3597 This is a variation of a method callback \- leaving out the method to call
3598 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3599 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3600 the time. Incidentally, you can then also leave out the template argument
3601 list.
3602 .Sp
3603 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3604 int revents)\*(C'\fR.
3605 .Sp
3606 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3607 .Sp
3608 Example: use a functor object as callback.
3609 .Sp
3610 .Vb 7
3611 \& struct myfunctor
3612 \& {
3613 \& void operator() (ev::io &w, int revents)
3614 \& {
3615 \& ...
3616 \& }
3617 \& }
3618 \&
3619 \& myfunctor f;
3620 \&
3621 \& ev::io w;
3622 \& w.set (&f);
3623 .Ve
3624 .IP "w\->set<function> (void *data = 0)" 4
3625 .IX Item "w->set<function> (void *data = 0)"
3626 Also sets a callback, but uses a static method or plain function as
3627 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3628 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3629 .Sp
3630 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3631 .Sp
3632 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3633 .Sp
3634 Example: Use a plain function as callback.
3635 .Sp
3636 .Vb 2
3637 \& static void io_cb (ev::io &w, int revents) { }
3638 \& iow.set <io_cb> ();
3639 .Ve
3640 .IP "w\->set (loop)" 4
3641 .IX Item "w->set (loop)"
3642 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3643 do this when the watcher is inactive (and not pending either).
3644 .IP "w\->set ([arguments])" 4
3645 .IX Item "w->set ([arguments])"
3646 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
3647 method or a suitable start method must be called at least once. Unlike the
3648 C counterpart, an active watcher gets automatically stopped and restarted
3649 when reconfiguring it with this method.
3650 .IP "w\->start ()" 4
3651 .IX Item "w->start ()"
3652 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3653 constructor already stores the event loop.
3654 .IP "w\->start ([arguments])" 4
3655 .IX Item "w->start ([arguments])"
3656 Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
3657 convenient to wrap them in one call. Uses the same type of arguments as
3658 the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
3659 .IP "w\->stop ()" 4
3660 .IX Item "w->stop ()"
3661 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3662 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
3663 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3664 .IX Item "w->again () (ev::timer, ev::periodic only)"
3665 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3666 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3667 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3668 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3669 .IX Item "w->sweep () (ev::embed only)"
3670 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3671 .ie n .IP "w\->update () (""ev::stat"" only)" 4
3672 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3673 .IX Item "w->update () (ev::stat only)"
3674 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3675 .RE
3676 .RS 4
3677 .RE
3678 .PP
3679 Example: Define a class with two I/O and idle watchers, start the I/O
3680 watchers in the constructor.
3681 .PP
3682 .Vb 5
3683 \& class myclass
3684 \& {
3685 \& ev::io io ; void io_cb (ev::io &w, int revents);
3686 \& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
3687 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3688 \&
3689 \& myclass (int fd)
3690 \& {
3691 \& io .set <myclass, &myclass::io_cb > (this);
3692 \& io2 .set <myclass, &myclass::io2_cb > (this);
3693 \& idle.set <myclass, &myclass::idle_cb> (this);
3694 \&
3695 \& io.set (fd, ev::WRITE); // configure the watcher
3696 \& io.start (); // start it whenever convenient
3697 \&
3698 \& io2.start (fd, ev::READ); // set + start in one call
3699 \& }
3700 \& };
3701 .Ve
3702 .SH "OTHER LANGUAGE BINDINGS"
3703 .IX Header "OTHER LANGUAGE BINDINGS"
3704 Libev does not offer other language bindings itself, but bindings for a
3705 number of languages exist in the form of third-party packages. If you know
3706 any interesting language binding in addition to the ones listed here, drop
3707 me a note.
3708 .IP "Perl" 4
3709 .IX Item "Perl"
3710 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3711 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3712 there are additional modules that implement libev-compatible interfaces
3713 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),
3714 \&\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
3715 and \f(CW\*(C`EV::Glib\*(C'\fR).
3716 .Sp
3717 It can be found and installed via \s-1CPAN\s0, its homepage is at
3718 <http://software.schmorp.de/pkg/EV>.
3719 .IP "Python" 4
3720 .IX Item "Python"
3721 Python bindings can be found at <http://code.google.com/p/pyev/>. It
3722 seems to be quite complete and well-documented.
3723 .IP "Ruby" 4
3724 .IX Item "Ruby"
3725 Tony Arcieri has written a ruby extension that offers access to a subset
3726 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3727 more on top of it. It can be found via gem servers. Its homepage is at
3728 <http://rev.rubyforge.org/>.
3729 .Sp
3730 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3731 makes rev work even on mingw.
3732 .IP "Haskell" 4
3733 .IX Item "Haskell"
3734 A haskell binding to libev is available at
3735 <http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3736 .IP "D" 4
3737 .IX Item "D"
3738 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3739 be found at <http://proj.llucax.com.ar/wiki/evd>.
3740 .IP "Ocaml" 4
3741 .IX Item "Ocaml"
3742 Erkki Seppala has written Ocaml bindings for libev, to be found at
3743 <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3744 .IP "Lua" 4
3745 .IX Item "Lua"
3746 Brian Maher has written a partial interface to libev for lua (at the
3747 time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
3748 <http://github.com/brimworks/lua\-ev>.
3749 .SH "MACRO MAGIC"
3750 .IX Header "MACRO MAGIC"
3751 Libev can be compiled with a variety of options, the most fundamental
3752 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3753 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3754 .PP
3755 To make it easier to write programs that cope with either variant, the
3756 following macros are defined:
3757 .ie n .IP """EV_A"", ""EV_A_""" 4
3758 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3759 .IX Item "EV_A, EV_A_"
3760 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3761 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3762 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3763 .Sp
3764 .Vb 3
3765 \& ev_unref (EV_A);
3766 \& ev_timer_add (EV_A_ watcher);
3767 \& ev_run (EV_A_ 0);
3768 .Ve
3769 .Sp
3770 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3771 which is often provided by the following macro.
3772 .ie n .IP """EV_P"", ""EV_P_""" 4
3773 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3774 .IX Item "EV_P, EV_P_"
3775 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3776 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3777 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3778 .Sp
3779 .Vb 2
3780 \& // this is how ev_unref is being declared
3781 \& static void ev_unref (EV_P);
3782 \&
3783 \& // this is how you can declare your typical callback
3784 \& static void cb (EV_P_ ev_timer *w, int revents)
3785 .Ve
3786 .Sp
3787 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3788 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3789 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3790 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3791 .IX Item "EV_DEFAULT, EV_DEFAULT_"
3792 Similar to the other two macros, this gives you the value of the default
3793 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3794 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3795 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3796 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3797 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3798 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3799 is undefined when the default loop has not been initialised by a previous
3800 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.
3801 .Sp
3802 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3803 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3804 .PP
3805 Example: Declare and initialise a check watcher, utilising the above
3806 macros so it will work regardless of whether multiple loops are supported
3807 or not.
3808 .PP
3809 .Vb 5
3810 \& static void
3811 \& check_cb (EV_P_ ev_timer *w, int revents)
3812 \& {
3813 \& ev_check_stop (EV_A_ w);
3814 \& }
3815 \&
3816 \& ev_check check;
3817 \& ev_check_init (&check, check_cb);
3818 \& ev_check_start (EV_DEFAULT_ &check);
3819 \& ev_run (EV_DEFAULT_ 0);
3820 .Ve
3821 .SH "EMBEDDING"
3822 .IX Header "EMBEDDING"
3823 Libev can (and often is) directly embedded into host
3824 applications. Examples of applications that embed it include the Deliantra
3825 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3826 and rxvt-unicode.
3827 .PP
3828 The goal is to enable you to just copy the necessary files into your
3829 source directory without having to change even a single line in them, so
3830 you can easily upgrade by simply copying (or having a checked-out copy of
3831 libev somewhere in your source tree).
3832 .SS "\s-1FILESETS\s0"
3833 .IX Subsection "FILESETS"
3834 Depending on what features you need you need to include one or more sets of files
3835 in your application.
3836 .PP
3837 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3838 .IX Subsection "CORE EVENT LOOP"
3839 .PP
3840 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3841 configuration (no autoconf):
3842 .PP
3843 .Vb 2
3844 \& #define EV_STANDALONE 1
3845 \& #include "ev.c"
3846 .Ve
3847 .PP
3848 This will automatically include \fIev.h\fR, too, and should be done in a
3849 single C source file only to provide the function implementations. To use
3850 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3851 done by writing a wrapper around \fIev.h\fR that you can include instead and
3852 where you can put other configuration options):
3853 .PP
3854 .Vb 2
3855 \& #define EV_STANDALONE 1
3856 \& #include "ev.h"
3857 .Ve
3858 .PP
3859 Both header files and implementation files can be compiled with a \*(C+
3860 compiler (at least, that's a stated goal, and breakage will be treated
3861 as a bug).
3862 .PP
3863 You need the following files in your source tree, or in a directory
3864 in your include path (e.g. in libev/ when using \-Ilibev):
3865 .PP
3866 .Vb 4
3867 \& ev.h
3868 \& ev.c
3869 \& ev_vars.h
3870 \& ev_wrap.h
3871 \&
3872 \& ev_win32.c required on win32 platforms only
3873 \&
3874 \& ev_select.c only when select backend is enabled (which is enabled by default)
3875 \& ev_poll.c only when poll backend is enabled (disabled by default)
3876 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3877 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3878 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
3879 .Ve
3880 .PP
3881 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
3882 to compile this single file.
3883 .PP
3884 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3885 .IX Subsection "LIBEVENT COMPATIBILITY API"
3886 .PP
3887 To include the libevent compatibility \s-1API\s0, also include:
3888 .PP
3889 .Vb 1
3890 \& #include "event.c"
3891 .Ve
3892 .PP
3893 in the file including \fIev.c\fR, and:
3894 .PP
3895 .Vb 1
3896 \& #include "event.h"
3897 .Ve
3898 .PP
3899 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3900 .PP
3901 You need the following additional files for this:
3902 .PP
3903 .Vb 2
3904 \& event.h
3905 \& event.c
3906 .Ve
3907 .PP
3908 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3909 .IX Subsection "AUTOCONF SUPPORT"
3910 .PP
3911 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3912 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3913 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3914 include \fIconfig.h\fR and configure itself accordingly.
3915 .PP
3916 For this of course you need the m4 file:
3917 .PP
3918 .Vb 1
3919 \& libev.m4
3920 .Ve
3921 .SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3922 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3923 Libev can be configured via a variety of preprocessor symbols you have to
3924 define before including (or compiling) any of its files. The default in
3925 the absence of autoconf is documented for every option.
3926 .PP
3927 Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
3928 values when compiling libev vs. including \fIev.h\fR, so it is permissible
3929 to redefine them before including \fIev.h\fR without breaking compatibility
3930 to a compiled library. All other symbols change the \s-1ABI\s0, which means all
3931 users of libev and the libev code itself must be compiled with compatible
3932 settings.
3933 .IP "\s-1EV_COMPAT3\s0 (h)" 4
3934 .IX Item "EV_COMPAT3 (h)"
3935 Backwards compatibility is a major concern for libev. This is why this
3936 release of libev comes with wrappers for the functions and symbols that
3937 have been renamed between libev version 3 and 4.
3938 .Sp
3939 You can disable these wrappers (to test compatibility with future
3940 versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
3941 sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
3942 from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
3943 typedef in that case.
3944 .Sp
3945 In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
3946 and in some even more future version the compatibility code will be
3947 removed completely.
3948 .IP "\s-1EV_STANDALONE\s0 (h)" 4
3949 .IX Item "EV_STANDALONE (h)"
3950 Must always be \f(CW1\fR if you do not use autoconf configuration, which
3951 keeps libev from including \fIconfig.h\fR, and it also defines dummy
3952 implementations for some libevent functions (such as logging, which is not
3953 supported). It will also not define any of the structs usually found in
3954 \&\fIevent.h\fR that are not directly supported by the libev core alone.
3955 .Sp
3956 In standalone mode, libev will still try to automatically deduce the
3957 configuration, but has to be more conservative.
3958 .IP "\s-1EV_USE_MONOTONIC\s0" 4
3959 .IX Item "EV_USE_MONOTONIC"
3960 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3961 monotonic clock option at both compile time and runtime. Otherwise no
3962 use of the monotonic clock option will be attempted. If you enable this,
3963 you usually have to link against librt or something similar. Enabling it
3964 when the functionality isn't available is safe, though, although you have
3965 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3966 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3967 .IP "\s-1EV_USE_REALTIME\s0" 4
3968 .IX Item "EV_USE_REALTIME"
3969 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3970 real-time clock option at compile time (and assume its availability
3971 at runtime if successful). Otherwise no use of the real-time clock
3972 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3973 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3974 correctness. See the note about libraries in the description of
3975 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3976 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3977 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3978 .IX Item "EV_USE_CLOCK_SYSCALL"
3979 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3980 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3981 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
3982 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3983 programs needlessly. Using a direct syscall is slightly slower (in
3984 theory), because no optimised vdso implementation can be used, but avoids
3985 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3986 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3987 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
3988 .IX Item "EV_USE_NANOSLEEP"
3989 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3990 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3991 .IP "\s-1EV_USE_EVENTFD\s0" 4
3992 .IX Item "EV_USE_EVENTFD"
3993 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3994 available and will probe for kernel support at runtime. This will improve
3995 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3996 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3997 2.7 or newer, otherwise disabled.
3998 .IP "\s-1EV_USE_SELECT\s0" 4
3999 .IX Item "EV_USE_SELECT"
4000 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4001 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4002 other method takes over, select will be it. Otherwise the select backend
4003 will not be compiled in.
4004 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4005 .IX Item "EV_SELECT_USE_FD_SET"
4006 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4007 structure. This is useful if libev doesn't compile due to a missing
4008 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4009 on exotic systems. This usually limits the range of file descriptors to
4010 some low limit such as 1024 or might have other limitations (winsocket
4011 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4012 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4013 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4014 .IX Item "EV_SELECT_IS_WINSOCKET"
4015 When defined to \f(CW1\fR, the select backend will assume that
4016 select/socket/connect etc. don't understand file descriptors but
4017 wants osf handles on win32 (this is the case when the select to
4018 be used is the winsock select). This means that it will call
4019 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4020 it is assumed that all these functions actually work on fds, even
4021 on win32. Should not be defined on non\-win32 platforms.
4022 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4023 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4024 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4025 file descriptors to socket handles. When not defining this symbol (the
4026 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4027 correct. In some cases, programs use their own file descriptor management,
4028 in which case they can provide this function to map fds to socket handles.
4029 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4030 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4031 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4032 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4033 their own fd to handle mapping, overwriting this function makes it easier
4034 to do so. This can be done by defining this macro to an appropriate value.
4035 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4036 .IX Item "EV_WIN32_CLOSE_FD(fd)"
4037 If programs implement their own fd to handle mapping on win32, then this
4038 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4039 file descriptors again. Note that the replacement function has to close
4040 the underlying \s-1OS\s0 handle.
4041 .IP "\s-1EV_USE_POLL\s0" 4
4042 .IX Item "EV_USE_POLL"
4043 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4044 backend. Otherwise it will be enabled on non\-win32 platforms. It
4045 takes precedence over select.
4046 .IP "\s-1EV_USE_EPOLL\s0" 4
4047 .IX Item "EV_USE_EPOLL"
4048 If defined to be \f(CW1\fR, libev will compile in support for the Linux
4049 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4050 otherwise another method will be used as fallback. This is the preferred
4051 backend for GNU/Linux systems. If undefined, it will be enabled if the
4052 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4053 .IP "\s-1EV_USE_KQUEUE\s0" 4
4054 .IX Item "EV_USE_KQUEUE"
4055 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4056 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4057 otherwise another method will be used as fallback. This is the preferred
4058 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4059 supports some types of fds correctly (the only platform we found that
4060 supports ptys for example was NetBSD), so kqueue might be compiled in, but
4061 not be used unless explicitly requested. The best way to use it is to find
4062 out whether kqueue supports your type of fd properly and use an embedded
4063 kqueue loop.
4064 .IP "\s-1EV_USE_PORT\s0" 4
4065 .IX Item "EV_USE_PORT"
4066 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4067 10 port style backend. Its availability will be detected at runtime,
4068 otherwise another method will be used as fallback. This is the preferred
4069 backend for Solaris 10 systems.
4070 .IP "\s-1EV_USE_DEVPOLL\s0" 4
4071 .IX Item "EV_USE_DEVPOLL"
4072 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4073 .IP "\s-1EV_USE_INOTIFY\s0" 4
4074 .IX Item "EV_USE_INOTIFY"
4075 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4076 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4077 be detected at runtime. If undefined, it will be enabled if the headers
4078 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4079 .IP "\s-1EV_ATOMIC_T\s0" 4
4080 .IX Item "EV_ATOMIC_T"
4081 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4082 access is atomic with respect to other threads or signal contexts. No such
4083 type is easily found in the C language, so you can provide your own type
4084 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4085 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4086 .Sp
4087 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4088 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4089 .IP "\s-1EV_H\s0 (h)" 4
4090 .IX Item "EV_H (h)"
4091 The name of the \fIev.h\fR header file used to include it. The default if
4092 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4093 used to virtually rename the \fIev.h\fR header file in case of conflicts.
4094 .IP "\s-1EV_CONFIG_H\s0 (h)" 4
4095 .IX Item "EV_CONFIG_H (h)"
4096 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4097 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4098 \&\f(CW\*(C`EV_H\*(C'\fR, above.
4099 .IP "\s-1EV_EVENT_H\s0 (h)" 4
4100 .IX Item "EV_EVENT_H (h)"
4101 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4102 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4103 .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4104 .IX Item "EV_PROTOTYPES (h)"
4105 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4106 prototypes, but still define all the structs and other symbols. This is
4107 occasionally useful if you want to provide your own wrapper functions
4108 around libev functions.
4109 .IP "\s-1EV_MULTIPLICITY\s0" 4
4110 .IX Item "EV_MULTIPLICITY"
4111 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4112 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4113 additional independent event loops. Otherwise there will be no support
4114 for multiple event loops and there is no first event loop pointer
4115 argument. Instead, all functions act on the single default loop.
4116 .IP "\s-1EV_MINPRI\s0" 4
4117 .IX Item "EV_MINPRI"
4118 .PD 0
4119 .IP "\s-1EV_MAXPRI\s0" 4
4120 .IX Item "EV_MAXPRI"
4121 .PD
4122 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4123 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4124 provide for more priorities by overriding those symbols (usually defined
4125 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4126 .Sp
4127 When doing priority-based operations, libev usually has to linearly search
4128 all the priorities, so having many of them (hundreds) uses a lot of space
4129 and time, so using the defaults of five priorities (\-2 .. +2) is usually
4130 fine.
4131 .Sp
4132 If your embedding application does not need any priorities, defining these
4133 both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4134 .IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4135 .IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4136 If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4137 the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4138 is not. Disabling watcher types mainly saves code size.
4139 .IP "\s-1EV_FEATURES\s0" 4
4140 .IX Item "EV_FEATURES"
4141 If you need to shave off some kilobytes of code at the expense of some
4142 speed (but with the full \s-1API\s0), you can define this symbol to request
4143 certain subsets of functionality. The default is to enable all features
4144 that can be enabled on the platform.
4145 .Sp
4146 A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4147 with some broad features you want) and then selectively re-enable
4148 additional parts you want, for example if you want everything minimal,
4149 but multiple event loop support, async and child watchers and the poll
4150 backend, use this:
4151 .Sp
4152 .Vb 5
4153 \& #define EV_FEATURES 0
4154 \& #define EV_MULTIPLICITY 1
4155 \& #define EV_USE_POLL 1
4156 \& #define EV_CHILD_ENABLE 1
4157 \& #define EV_ASYNC_ENABLE 1
4158 .Ve
4159 .Sp
4160 The actual value is a bitset, it can be a combination of the following
4161 values:
4162 .RS 4
4163 .ie n .IP "1 \- faster/larger code" 4
4164 .el .IP "\f(CW1\fR \- faster/larger code" 4
4165 .IX Item "1 - faster/larger code"
4166 Use larger code to speed up some operations.
4167 .Sp
4168 Currently this is used to override some inlining decisions (enlarging the
4169 code size by roughly 30% on amd64).
4170 .Sp
4171 When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4172 gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4173 assertions.
4174 .ie n .IP "2 \- faster/larger data structures" 4
4175 .el .IP "\f(CW2\fR \- faster/larger data structures" 4
4176 .IX Item "2 - faster/larger data structures"
4177 Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4178 hash table sizes and so on. This will usually further increase code size
4179 and can additionally have an effect on the size of data structures at
4180 runtime.
4181 .ie n .IP "4 \- full \s-1API\s0 configuration" 4
4182 .el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4183 .IX Item "4 - full API configuration"
4184 This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4185 enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4186 .ie n .IP "8 \- full \s-1API\s0" 4
4187 .el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4188 .IX Item "8 - full API"
4189 This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4190 details on which parts of the \s-1API\s0 are still available without this
4191 feature, and do not complain if this subset changes over time.
4192 .ie n .IP "16 \- enable all optional watcher types" 4
4193 .el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4194 .IX Item "16 - enable all optional watcher types"
4195 Enables all optional watcher types. If you want to selectively enable
4196 only some watcher types other than I/O and timers (e.g. prepare,
4197 embed, async, child...) you can enable them manually by defining
4198 \&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4199 .ie n .IP "32 \- enable all backends" 4
4200 .el .IP "\f(CW32\fR \- enable all backends" 4
4201 .IX Item "32 - enable all backends"
4202 This enables all backends \- without this feature, you need to enable at
4203 least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4204 .ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4205 .el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4206 .IX Item "64 - enable OS-specific helper APIs"
4207 Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4208 default.
4209 .RE
4210 .RS 4
4211 .Sp
4212 Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4213 reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4214 code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4215 watchers, timers and monotonic clock support.
4216 .Sp
4217 With an intelligent-enough linker (gcc+binutils are intelligent enough
4218 when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4219 your program might be left out as well \- a binary starting a timer and an
4220 I/O watcher then might come out at only 5Kb.
4221 .RE
4222 .IP "\s-1EV_AVOID_STDIO\s0" 4
4223 .IX Item "EV_AVOID_STDIO"
4224 If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4225 functions (printf, scanf, perror etc.). This will increase the code size
4226 somewhat, but if your program doesn't otherwise depend on stdio and your
4227 libc allows it, this avoids linking in the stdio library which is quite
4228 big.
4229 .Sp
4230 Note that error messages might become less precise when this option is
4231 enabled.
4232 .IP "\s-1EV_NSIG\s0" 4
4233 .IX Item "EV_NSIG"
4234 The highest supported signal number, +1 (or, the number of
4235 signals): Normally, libev tries to deduce the maximum number of signals
4236 automatically, but sometimes this fails, in which case it can be
4237 specified. Also, using a lower number than detected (\f(CW32\fR should be
4238 good for about any system in existence) can save some memory, as libev
4239 statically allocates some 12\-24 bytes per signal number.
4240 .IP "\s-1EV_PID_HASHSIZE\s0" 4
4241 .IX Item "EV_PID_HASHSIZE"
4242 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4243 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4244 usually more than enough. If you need to manage thousands of children you
4245 might want to increase this value (\fImust\fR be a power of two).
4246 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4247 .IX Item "EV_INOTIFY_HASHSIZE"
4248 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4249 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4250 disabled), usually more than enough. If you need to manage thousands of
4251 \&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4252 power of two).
4253 .IP "\s-1EV_USE_4HEAP\s0" 4
4254 .IX Item "EV_USE_4HEAP"
4255 Heaps are not very cache-efficient. To improve the cache-efficiency of the
4256 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4257 to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4258 faster performance with many (thousands) of watchers.
4259 .Sp
4260 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4261 will be \f(CW0\fR.
4262 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4263 .IX Item "EV_HEAP_CACHE_AT"
4264 Heaps are not very cache-efficient. To improve the cache-efficiency of the
4265 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4266 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4267 which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4268 but avoids random read accesses on heap changes. This improves performance
4269 noticeably with many (hundreds) of watchers.
4270 .Sp
4271 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4272 will be \f(CW0\fR.
4273 .IP "\s-1EV_VERIFY\s0" 4
4274 .IX Item "EV_VERIFY"
4275 Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4276 be done: If set to \f(CW0\fR, no internal verification code will be compiled
4277 in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4278 called. If set to \f(CW2\fR, then the internal verification code will be
4279 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4280 verification code will be called very frequently, which will slow down
4281 libev considerably.
4282 .Sp
4283 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4284 will be \f(CW0\fR.
4285 .IP "\s-1EV_COMMON\s0" 4
4286 .IX Item "EV_COMMON"
4287 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4288 this macro to something else you can include more and other types of
4289 members. You have to define it each time you include one of the files,
4290 though, and it must be identical each time.
4291 .Sp
4292 For example, the perl \s-1EV\s0 module uses something like this:
4293 .Sp
4294 .Vb 3
4295 \& #define EV_COMMON \e
4296 \& SV *self; /* contains this struct */ \e
4297 \& SV *cb_sv, *fh /* note no trailing ";" */
4298 .Ve
4299 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4300 .IX Item "EV_CB_DECLARE (type)"
4301 .PD 0
4302 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4303 .IX Item "EV_CB_INVOKE (watcher, revents)"
4304 .IP "ev_set_cb (ev, cb)" 4
4305 .IX Item "ev_set_cb (ev, cb)"
4306 .PD
4307 Can be used to change the callback member declaration in each watcher,
4308 and the way callbacks are invoked and set. Must expand to a struct member
4309 definition and a statement, respectively. See the \fIev.h\fR header file for
4310 their default definitions. One possible use for overriding these is to
4311 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4312 method calls instead of plain function calls in \*(C+.
4313 .SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4314 .IX Subsection "EXPORTED API SYMBOLS"
4315 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4316 exported symbols, you can use the provided \fISymbol.*\fR files which list
4317 all public symbols, one per line:
4318 .PP
4319 .Vb 2
4320 \& Symbols.ev for libev proper
4321 \& Symbols.event for the libevent emulation
4322 .Ve
4323 .PP
4324 This can also be used to rename all public symbols to avoid clashes with
4325 multiple versions of libev linked together (which is obviously bad in
4326 itself, but sometimes it is inconvenient to avoid this).
4327 .PP
4328 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4329 include before including \fIev.h\fR:
4330 .PP
4331 .Vb 1
4332 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4333 .Ve
4334 .PP
4335 This would create a file \fIwrap.h\fR which essentially looks like this:
4336 .PP
4337 .Vb 4
4338 \& #define ev_backend myprefix_ev_backend
4339 \& #define ev_check_start myprefix_ev_check_start
4340 \& #define ev_check_stop myprefix_ev_check_stop
4341 \& ...
4342 .Ve
4343 .SS "\s-1EXAMPLES\s0"
4344 .IX Subsection "EXAMPLES"
4345 For a real-world example of a program the includes libev
4346 verbatim, you can have a look at the \s-1EV\s0 perl module
4347 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4348 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4349 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4350 will be compiled. It is pretty complex because it provides its own header
4351 file.
4352 .PP
4353 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4354 that everybody includes and which overrides some configure choices:
4355 .PP
4356 .Vb 8
4357 \& #define EV_FEATURES 8
4358 \& #define EV_USE_SELECT 1
4359 \& #define EV_PREPARE_ENABLE 1
4360 \& #define EV_IDLE_ENABLE 1
4361 \& #define EV_SIGNAL_ENABLE 1
4362 \& #define EV_CHILD_ENABLE 1
4363 \& #define EV_USE_STDEXCEPT 0
4364 \& #define EV_CONFIG_H <config.h>
4365 \&
4366 \& #include "ev++.h"
4367 .Ve
4368 .PP
4369 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4370 .PP
4371 .Vb 2
4372 \& #include "ev_cpp.h"
4373 \& #include "ev.c"
4374 .Ve
4375 .SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4376 .IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4377 .SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4378 .IX Subsection "THREADS AND COROUTINES"
4379 \fI\s-1THREADS\s0\fR
4380 .IX Subsection "THREADS"
4381 .PP
4382 All libev functions are reentrant and thread-safe unless explicitly
4383 documented otherwise, but libev implements no locking itself. This means
4384 that you can use as many loops as you want in parallel, as long as there
4385 are no concurrent calls into any libev function with the same loop
4386 parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4387 of course): libev guarantees that different event loops share no data
4388 structures that need any locking.
4389 .PP
4390 Or to put it differently: calls with different loop parameters can be done
4391 concurrently from multiple threads, calls with the same loop parameter
4392 must be done serially (but can be done from different threads, as long as
4393 only one thread ever is inside a call at any point in time, e.g. by using
4394 a mutex per loop).
4395 .PP
4396 Specifically to support threads (and signal handlers), libev implements
4397 so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4398 concurrency on the same event loop, namely waking it up \*(L"from the
4399 outside\*(R".
4400 .PP
4401 If you want to know which design (one loop, locking, or multiple loops
4402 without or something else still) is best for your problem, then I cannot
4403 help you, but here is some generic advice:
4404 .IP "\(bu" 4
4405 most applications have a main thread: use the default libev loop
4406 in that thread, or create a separate thread running only the default loop.
4407 .Sp
4408 This helps integrating other libraries or software modules that use libev
4409 themselves and don't care/know about threading.
4410 .IP "\(bu" 4
4411 one loop per thread is usually a good model.
4412 .Sp
4413 Doing this is almost never wrong, sometimes a better-performance model
4414 exists, but it is always a good start.
4415 .IP "\(bu" 4
4416 other models exist, such as the leader/follower pattern, where one
4417 loop is handed through multiple threads in a kind of round-robin fashion.
4418 .Sp
4419 Choosing a model is hard \- look around, learn, know that usually you can do
4420 better than you currently do :\-)
4421 .IP "\(bu" 4
4422 often you need to talk to some other thread which blocks in the
4423 event loop.
4424 .Sp
4425 \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4426 (or from signal contexts...).
4427 .Sp
4428 An example use would be to communicate signals or other events that only
4429 work in the default loop by registering the signal watcher with the
4430 default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4431 watcher callback into the event loop interested in the signal.
4432 .PP
4433 \s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4434 .IX Subsection "THREAD LOCKING EXAMPLE"
4435 .PP
4436 Here is a fictitious example of how to run an event loop in a different
4437 thread than where callbacks are being invoked and watchers are
4438 created/added/removed.
4439 .PP
4440 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4441 which uses exactly this technique (which is suited for many high-level
4442 languages).
4443 .PP
4444 The example uses a pthread mutex to protect the loop data, a condition
4445 variable to wait for callback invocations, an async watcher to notify the
4446 event loop thread and an unspecified mechanism to wake up the main thread.
4447 .PP
4448 First, you need to associate some data with the event loop:
4449 .PP
4450 .Vb 6
4451 \& typedef struct {
4452 \& mutex_t lock; /* global loop lock */
4453 \& ev_async async_w;
4454 \& thread_t tid;
4455 \& cond_t invoke_cv;
4456 \& } userdata;
4457 \&
4458 \& void prepare_loop (EV_P)
4459 \& {
4460 \& // for simplicity, we use a static userdata struct.
4461 \& static userdata u;
4462 \&
4463 \& ev_async_init (&u\->async_w, async_cb);
4464 \& ev_async_start (EV_A_ &u\->async_w);
4465 \&
4466 \& pthread_mutex_init (&u\->lock, 0);
4467 \& pthread_cond_init (&u\->invoke_cv, 0);
4468 \&
4469 \& // now associate this with the loop
4470 \& ev_set_userdata (EV_A_ u);
4471 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4472 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4473 \&
4474 \& // then create the thread running ev_loop
4475 \& pthread_create (&u\->tid, 0, l_run, EV_A);
4476 \& }
4477 .Ve
4478 .PP
4479 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4480 solely to wake up the event loop so it takes notice of any new watchers
4481 that might have been added:
4482 .PP
4483 .Vb 5
4484 \& static void
4485 \& async_cb (EV_P_ ev_async *w, int revents)
4486 \& {
4487 \& // just used for the side effects
4488 \& }
4489 .Ve
4490 .PP
4491 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4492 protecting the loop data, respectively.
4493 .PP
4494 .Vb 6
4495 \& static void
4496 \& l_release (EV_P)
4497 \& {
4498 \& userdata *u = ev_userdata (EV_A);
4499 \& pthread_mutex_unlock (&u\->lock);
4500 \& }
4501 \&
4502 \& static void
4503 \& l_acquire (EV_P)
4504 \& {
4505 \& userdata *u = ev_userdata (EV_A);
4506 \& pthread_mutex_lock (&u\->lock);
4507 \& }
4508 .Ve
4509 .PP
4510 The event loop thread first acquires the mutex, and then jumps straight
4511 into \f(CW\*(C`ev_run\*(C'\fR:
4512 .PP
4513 .Vb 4
4514 \& void *
4515 \& l_run (void *thr_arg)
4516 \& {
4517 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4518 \&
4519 \& l_acquire (EV_A);
4520 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4521 \& ev_run (EV_A_ 0);
4522 \& l_release (EV_A);
4523 \&
4524 \& return 0;
4525 \& }
4526 .Ve
4527 .PP
4528 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4529 signal the main thread via some unspecified mechanism (signals? pipe
4530 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4531 have been called (in a while loop because a) spurious wakeups are possible
4532 and b) skipping inter-thread-communication when there are no pending
4533 watchers is very beneficial):
4534 .PP
4535 .Vb 4
4536 \& static void
4537 \& l_invoke (EV_P)
4538 \& {
4539 \& userdata *u = ev_userdata (EV_A);
4540 \&
4541 \& while (ev_pending_count (EV_A))
4542 \& {
4543 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4544 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4545 \& }
4546 \& }
4547 .Ve
4548 .PP
4549 Now, whenever the main thread gets told to invoke pending watchers, it
4550 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4551 thread to continue:
4552 .PP
4553 .Vb 4
4554 \& static void
4555 \& real_invoke_pending (EV_P)
4556 \& {
4557 \& userdata *u = ev_userdata (EV_A);
4558 \&
4559 \& pthread_mutex_lock (&u\->lock);
4560 \& ev_invoke_pending (EV_A);
4561 \& pthread_cond_signal (&u\->invoke_cv);
4562 \& pthread_mutex_unlock (&u\->lock);
4563 \& }
4564 .Ve
4565 .PP
4566 Whenever you want to start/stop a watcher or do other modifications to an
4567 event loop, you will now have to lock:
4568 .PP
4569 .Vb 2
4570 \& ev_timer timeout_watcher;
4571 \& userdata *u = ev_userdata (EV_A);
4572 \&
4573 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4574 \&
4575 \& pthread_mutex_lock (&u\->lock);
4576 \& ev_timer_start (EV_A_ &timeout_watcher);
4577 \& ev_async_send (EV_A_ &u\->async_w);
4578 \& pthread_mutex_unlock (&u\->lock);
4579 .Ve
4580 .PP
4581 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4582 an event loop currently blocking in the kernel will have no knowledge
4583 about the newly added timer. By waking up the loop it will pick up any new
4584 watchers in the next event loop iteration.
4585 .PP
4586 \fI\s-1COROUTINES\s0\fR
4587 .IX Subsection "COROUTINES"
4588 .PP
4589 Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4590 libev fully supports nesting calls to its functions from different
4591 coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4592 different coroutines, and switch freely between both coroutines running
4593 the loop, as long as you don't confuse yourself). The only exception is
4594 that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4595 .PP
4596 Care has been taken to ensure that libev does not keep local state inside
4597 \&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4598 they do not call any callbacks.
4599 .SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4600 .IX Subsection "COMPILER WARNINGS"
4601 Depending on your compiler and compiler settings, you might get no or a
4602 lot of warnings when compiling libev code. Some people are apparently
4603 scared by this.
4604 .PP
4605 However, these are unavoidable for many reasons. For one, each compiler
4606 has different warnings, and each user has different tastes regarding
4607 warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4608 targeting a specific compiler and compiler-version.
4609 .PP
4610 Another reason is that some compiler warnings require elaborate
4611 workarounds, or other changes to the code that make it less clear and less
4612 maintainable.
4613 .PP
4614 And of course, some compiler warnings are just plain stupid, or simply
4615 wrong (because they don't actually warn about the condition their message
4616 seems to warn about). For example, certain older gcc versions had some
4617 warnings that resulted in an extreme number of false positives. These have
4618 been fixed, but some people still insist on making code warn-free with
4619 such buggy versions.
4620 .PP
4621 While libev is written to generate as few warnings as possible,
4622 \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4623 with any compiler warnings enabled unless you are prepared to cope with
4624 them (e.g. by ignoring them). Remember that warnings are just that:
4625 warnings, not errors, or proof of bugs.
4626 .SS "\s-1VALGRIND\s0"
4627 .IX Subsection "VALGRIND"
4628 Valgrind has a special section here because it is a popular tool that is
4629 highly useful. Unfortunately, valgrind reports are very hard to interpret.
4630 .PP
4631 If you think you found a bug (memory leak, uninitialised data access etc.)
4632 in libev, then check twice: If valgrind reports something like:
4633 .PP
4634 .Vb 3
4635 \& ==2274== definitely lost: 0 bytes in 0 blocks.
4636 \& ==2274== possibly lost: 0 bytes in 0 blocks.
4637 \& ==2274== still reachable: 256 bytes in 1 blocks.
4638 .Ve
4639 .PP
4640 Then there is no memory leak, just as memory accounted to global variables
4641 is not a memleak \- the memory is still being referenced, and didn't leak.
4642 .PP
4643 Similarly, under some circumstances, valgrind might report kernel bugs
4644 as if it were a bug in libev (e.g. in realloc or in the poll backend,
4645 although an acceptable workaround has been found here), or it might be
4646 confused.
4647 .PP
4648 Keep in mind that valgrind is a very good tool, but only a tool. Don't
4649 make it into some kind of religion.
4650 .PP
4651 If you are unsure about something, feel free to contact the mailing list
4652 with the full valgrind report and an explanation on why you think this
4653 is a bug in libev (best check the archives, too :). However, don't be
4654 annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4655 of learning how to interpret valgrind properly.
4656 .PP
4657 If you need, for some reason, empty reports from valgrind for your project
4658 I suggest using suppression lists.
4659 .SH "PORTABILITY NOTES"
4660 .IX Header "PORTABILITY NOTES"
4661 .SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4662 .IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4663 GNU/Linux is the only common platform that supports 64 bit file/large file
4664 interfaces but \fIdisables\fR them by default.
4665 .PP
4666 That means that libev compiled in the default environment doesn't support
4667 files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4668 .PP
4669 Unfortunately, many programs try to work around this GNU/Linux issue
4670 by enabling the large file \s-1API\s0, which makes them incompatible with the
4671 standard libev compiled for their system.
4672 .PP
4673 Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4674 suddenly make it incompatible to the default compile time environment,
4675 i.e. all programs not using special compile switches.
4676 .SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4677 .IX Subsection "OS/X AND DARWIN BUGS"
4678 The whole thing is a bug if you ask me \- basically any system interface
4679 you touch is broken, whether it is locales, poll, kqueue or even the
4680 OpenGL drivers.
4681 .PP
4682 \fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4683 .IX Subsection "kqueue is buggy"
4684 .PP
4685 The kqueue syscall is broken in all known versions \- most versions support
4686 only sockets, many support pipes.
4687 .PP
4688 Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4689 rotten platform, but of course you can still ask for it when creating a
4690 loop \- embedding a socket-only kqueue loop into a select-based one is
4691 probably going to work well.
4692 .PP
4693 \fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4694 .IX Subsection "poll is buggy"
4695 .PP
4696 Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4697 implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4698 release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4699 .PP
4700 Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4701 this rotten platform, but of course you can still ask for it when creating
4702 a loop.
4703 .PP
4704 \fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4705 .IX Subsection "select is buggy"
4706 .PP
4707 All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4708 one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4709 descriptors you can pass in to 1024 \- your program suddenly crashes when
4710 you use more.
4711 .PP
4712 There is an undocumented \*(L"workaround\*(R" for this \- defining
4713 \&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4714 work on \s-1OS/X\s0.
4715 .SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4716 .IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4717 \fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4718 .IX Subsection "errno reentrancy"
4719 .PP
4720 The default compile environment on Solaris is unfortunately so
4721 thread-unsafe that you can't even use components/libraries compiled
4722 without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4723 defined by default. A valid, if stupid, implementation choice.
4724 .PP
4725 If you want to use libev in threaded environments you have to make sure
4726 it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4727 .PP
4728 \fIEvent port backend\fR
4729 .IX Subsection "Event port backend"
4730 .PP
4731 The scalable event interface for Solaris is called \*(L"event
4732 ports\*(R". Unfortunately, this mechanism is very buggy in all major
4733 releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4734 a large number of spurious wakeups, make sure you have all the relevant
4735 and latest kernel patches applied. No, I don't know which ones, but there
4736 are multiple ones to apply, and afterwards, event ports actually work
4737 great.
4738 .PP
4739 If you can't get it to work, you can try running the program by setting
4740 the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4741 \&\f(CW\*(C`select\*(C'\fR backends.
4742 .SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4743 .IX Subsection "AIX POLL BUG"
4744 \&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4745 this by trying to avoid the poll backend altogether (i.e. it's not even
4746 compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4747 with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4748 .SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4749 .IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4750 \fIGeneral issues\fR
4751 .IX Subsection "General issues"
4752 .PP
4753 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4754 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4755 model. Libev still offers limited functionality on this platform in
4756 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4757 descriptors. This only applies when using Win32 natively, not when using
4758 e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4759 as every compielr comes with a slightly differently broken/incompatible
4760 environment.
4761 .PP
4762 Lifting these limitations would basically require the full
4763 re-implementation of the I/O system. If you are into this kind of thing,
4764 then note that glib does exactly that for you in a very portable way (note
4765 also that glib is the slowest event library known to man).
4766 .PP
4767 There is no supported compilation method available on windows except
4768 embedding it into other applications.
4769 .PP
4770 Sensible signal handling is officially unsupported by Microsoft \- libev
4771 tries its best, but under most conditions, signals will simply not work.
4772 .PP
4773 Not a libev limitation but worth mentioning: windows apparently doesn't
4774 accept large writes: instead of resulting in a partial write, windows will
4775 either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4776 so make sure you only write small amounts into your sockets (less than a
4777 megabyte seems safe, but this apparently depends on the amount of memory
4778 available).
4779 .PP
4780 Due to the many, low, and arbitrary limits on the win32 platform and
4781 the abysmal performance of winsockets, using a large number of sockets
4782 is not recommended (and not reasonable). If your program needs to use
4783 more than a hundred or so sockets, then likely it needs to use a totally
4784 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4785 notification model, which cannot be implemented efficiently on windows
4786 (due to Microsoft monopoly games).
4787 .PP
4788 A typical way to use libev under windows is to embed it (see the embedding
4789 section for details) and use the following \fIevwrap.h\fR header file instead
4790 of \fIev.h\fR:
4791 .PP
4792 .Vb 2
4793 \& #define EV_STANDALONE /* keeps ev from requiring config.h */
4794 \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4795 \&
4796 \& #include "ev.h"
4797 .Ve
4798 .PP
4799 And compile the following \fIevwrap.c\fR file into your project (make sure
4800 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4801 .PP
4802 .Vb 2
4803 \& #include "evwrap.h"
4804 \& #include "ev.c"
4805 .Ve
4806 .PP
4807 \fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
4808 .IX Subsection "The winsocket select function"
4809 .PP
4810 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4811 requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4812 also extremely buggy). This makes select very inefficient, and also
4813 requires a mapping from file descriptors to socket handles (the Microsoft
4814 C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4815 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4816 \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4817 .PP
4818 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4819 libraries and raw winsocket select is:
4820 .PP
4821 .Vb 2
4822 \& #define EV_USE_SELECT 1
4823 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4824 .Ve
4825 .PP
4826 Note that winsockets handling of fd sets is O(n), so you can easily get a
4827 complexity in the O(nA\*^X) range when using win32.
4828 .PP
4829 \fILimited number of file descriptors\fR
4830 .IX Subsection "Limited number of file descriptors"
4831 .PP
4832 Windows has numerous arbitrary (and low) limits on things.
4833 .PP
4834 Early versions of winsocket's select only supported waiting for a maximum
4835 of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4836 can only wait for \f(CW64\fR things at the same time internally; Microsoft
4837 recommends spawning a chain of threads and wait for 63 handles and the
4838 previous thread in each. Sounds great!).
4839 .PP
4840 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4841 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4842 call (which might be in libev or elsewhere, for example, perl and many
4843 other interpreters do their own select emulation on windows).
4844 .PP
4845 Another limit is the number of file descriptors in the Microsoft runtime
4846 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4847 fetish or something like this inside Microsoft). You can increase this
4848 by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4849 (another arbitrary limit), but is broken in many versions of the Microsoft
4850 runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4851 (depending on windows version and/or the phase of the moon). To get more,
4852 you need to wrap all I/O functions and provide your own fd management, but
4853 the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4854 .SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4855 .IX Subsection "PORTABILITY REQUIREMENTS"
4856 In addition to a working ISO-C implementation and of course the
4857 backend-specific APIs, libev relies on a few additional extensions:
4858 .ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4859 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4860 .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4861 Libev assumes not only that all watcher pointers have the same internal
4862 structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4863 assumes that the same (machine) code can be used to call any watcher
4864 callback: The watcher callbacks have different type signatures, but libev
4865 calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4866 .IP "pointer accesses must be thread-atomic" 4
4867 .IX Item "pointer accesses must be thread-atomic"
4868 Accessing a pointer value must be atomic, it must both be readable and
4869 writable in one piece \- this is the case on all current architectures.
4870 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4871 .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4872 .IX Item "sig_atomic_t volatile must be thread-atomic as well"
4873 The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4874 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4875 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4876 believed to be sufficiently portable.
4877 .ie n .IP """sigprocmask"" must work in a threaded environment" 4
4878 .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4879 .IX Item "sigprocmask must work in a threaded environment"
4880 Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4881 allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4882 pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4883 thread\*(R" or will block signals process-wide, both behaviours would
4884 be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4885 \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4886 .Sp
4887 The most portable way to handle signals is to block signals in all threads
4888 except the initial one, and run the default loop in the initial thread as
4889 well.
4890 .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4891 .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4892 .IX Item "long must be large enough for common memory allocation sizes"
4893 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4894 instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4895 systems (Microsoft...) this might be unexpectedly low, but is still at
4896 least 31 bits everywhere, which is enough for hundreds of millions of
4897 watchers.
4898 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4899 .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4900 .IX Item "double must hold a time value in seconds with enough accuracy"
4901 The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4902 have at least 51 bits of mantissa (and 9 bits of exponent), which is
4903 good enough for at least into the year 4000 with millisecond accuracy
4904 (the design goal for libev). This requirement is overfulfilled by
4905 implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
4906 \&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
4907 .PP
4908 If you know of other additional requirements drop me a note.
4909 .SH "ALGORITHMIC COMPLEXITIES"
4910 .IX Header "ALGORITHMIC COMPLEXITIES"
4911 In this section the complexities of (many of) the algorithms used inside
4912 libev will be documented. For complexity discussions about backends see
4913 the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4914 .PP
4915 All of the following are about amortised time: If an array needs to be
4916 extended, libev needs to realloc and move the whole array, but this
4917 happens asymptotically rarer with higher number of elements, so O(1) might
4918 mean that libev does a lengthy realloc operation in rare cases, but on
4919 average it is much faster and asymptotically approaches constant time.
4920 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4921 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4922 This means that, when you have a watcher that triggers in one hour and
4923 there are 100 watchers that would trigger before that, then inserting will
4924 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4925 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4926 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4927 That means that changing a timer costs less than removing/adding them,
4928 as only the relative motion in the event queue has to be paid for.
4929 .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4930 .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4931 These just add the watcher into an array or at the head of a list.
4932 .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4933 .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4934 .PD 0
4935 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4936 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4937 .PD
4938 These watchers are stored in lists, so they need to be walked to find the
4939 correct watcher to remove. The lists are usually short (you don't usually
4940 have many watchers waiting for the same fd or signal: one is typical, two
4941 is rare).
4942 .IP "Finding the next timer in each loop iteration: O(1)" 4
4943 .IX Item "Finding the next timer in each loop iteration: O(1)"
4944 By virtue of using a binary or 4\-heap, the next timer is always found at a
4945 fixed position in the storage array.
4946 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4947 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4948 A change means an I/O watcher gets started or stopped, which requires
4949 libev to recalculate its status (and possibly tell the kernel, depending
4950 on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4951 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
4952 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
4953 .PD 0
4954 .IP "Priority handling: O(number_of_priorities)" 4
4955 .IX Item "Priority handling: O(number_of_priorities)"
4956 .PD
4957 Priorities are implemented by allocating some space for each
4958 priority. When doing priority-based operations, libev usually has to
4959 linearly search all the priorities, but starting/stopping and activating
4960 watchers becomes O(1) with respect to priority handling.
4961 .IP "Sending an ev_async: O(1)" 4
4962 .IX Item "Sending an ev_async: O(1)"
4963 .PD 0
4964 .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4965 .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4966 .IP "Processing signals: O(max_signal_number)" 4
4967 .IX Item "Processing signals: O(max_signal_number)"
4968 .PD
4969 Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4970 calls in the current loop iteration. Checking for async and signal events
4971 involves iterating over all running async watchers or all signal numbers.
4972 .SH "PORTING FROM LIBEV 3.X TO 4.X"
4973 .IX Header "PORTING FROM LIBEV 3.X TO 4.X"
4974 The major version 4 introduced some incompatible changes to the \s-1API\s0.
4975 .PP
4976 At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
4977 for all changes, so most programs should still compile. The compatibility
4978 layer might be removed in later versions of libev, so better update to the
4979 new \s-1API\s0 early than late.
4980 .ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
4981 .el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
4982 .IX Item "EV_COMPAT3 backwards compatibility mechanism"
4983 The backward compatibility mechanism can be controlled by
4984 \&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
4985 section.
4986 .ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
4987 .el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
4988 .IX Item "ev_default_destroy and ev_default_fork have been removed"
4989 These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
4990 .Sp
4991 .Vb 2
4992 \& ev_loop_destroy (EV_DEFAULT_UC);
4993 \& ev_loop_fork (EV_DEFAULT);
4994 .Ve
4995 .IP "function/symbol renames" 4
4996 .IX Item "function/symbol renames"
4997 A number of functions and symbols have been renamed:
4998 .Sp
4999 .Vb 3
5000 \& ev_loop => ev_run
5001 \& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5002 \& EVLOOP_ONESHOT => EVRUN_ONCE
5003 \&
5004 \& ev_unloop => ev_break
5005 \& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5006 \& EVUNLOOP_ONE => EVBREAK_ONE
5007 \& EVUNLOOP_ALL => EVBREAK_ALL
5008 \&
5009 \& EV_TIMEOUT => EV_TIMER
5010 \&
5011 \& ev_loop_count => ev_iteration
5012 \& ev_loop_depth => ev_depth
5013 \& ev_loop_verify => ev_verify
5014 .Ve
5015 .Sp
5016 Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5017 \&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5018 associated constants have been renamed to not collide with the \f(CW\*(C`struct
5019 ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5020 as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5021 \&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5022 typedef.
5023 .ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5024 .el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5025 .IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5026 The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5027 mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5028 and work, but the library code will of course be larger.
5029 .SH "GLOSSARY"
5030 .IX Header "GLOSSARY"
5031 .IP "active" 4
5032 .IX Item "active"
5033 A watcher is active as long as it has been started and not yet stopped.
5034 See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5035 .IP "application" 4
5036 .IX Item "application"
5037 In this document, an application is whatever is using libev.
5038 .IP "backend" 4
5039 .IX Item "backend"
5040 The part of the code dealing with the operating system interfaces.
5041 .IP "callback" 4
5042 .IX Item "callback"
5043 The address of a function that is called when some event has been
5044 detected. Callbacks are being passed the event loop, the watcher that
5045 received the event, and the actual event bitset.
5046 .IP "callback/watcher invocation" 4
5047 .IX Item "callback/watcher invocation"
5048 The act of calling the callback associated with a watcher.
5049 .IP "event" 4
5050 .IX Item "event"
5051 A change of state of some external event, such as data now being available
5052 for reading on a file descriptor, time having passed or simply not having
5053 any other events happening anymore.
5054 .Sp
5055 In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5056 \&\f(CW\*(C`EV_TIMER\*(C'\fR).
5057 .IP "event library" 4
5058 .IX Item "event library"
5059 A software package implementing an event model and loop.
5060 .IP "event loop" 4
5061 .IX Item "event loop"
5062 An entity that handles and processes external events and converts them
5063 into callback invocations.
5064 .IP "event model" 4
5065 .IX Item "event model"
5066 The model used to describe how an event loop handles and processes
5067 watchers and events.
5068 .IP "pending" 4
5069 .IX Item "pending"
5070 A watcher is pending as soon as the corresponding event has been
5071 detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5072 .IP "real time" 4
5073 .IX Item "real time"
5074 The physical time that is observed. It is apparently strictly monotonic :)
5075 .IP "wall-clock time" 4
5076 .IX Item "wall-clock time"
5077 The time and date as shown on clocks. Unlike real time, it can actually
5078 be wrong and jump forwards and backwards, e.g. when the you adjust your
5079 clock.
5080 .IP "watcher" 4
5081 .IX Item "watcher"
5082 A data structure that describes interest in certain events. Watchers need
5083 to be started (attached to an event loop) before they can receive events.
5084 .SH "AUTHOR"
5085 .IX Header "AUTHOR"
5086 Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5087 Magnusson and Emanuele Giaquinta.