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

File Contents

# User Rev Content
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126 root 1.65 .IX Title "LIBEV 3"
127 root 1.85 .TH LIBEV 3 "2011-01-11" "libev-4.03" "libev - high performance full featured event loop"
128 root 1.60 .\" 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 root 1.1 .SH "NAME"
133     libev \- a high performance full\-featured event loop written in C
134     .SH "SYNOPSIS"
135     .IX Header "SYNOPSIS"
136 root 1.28 .Vb 1
137 root 1.68 \& #include <ev.h>
138 root 1.28 .Ve
139 root 1.79 .SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140 root 1.59 .IX Subsection "EXAMPLE PROGRAM"
141 root 1.61 .Vb 2
142 root 1.68 \& // a single header file is required
143     \& #include <ev.h>
144 root 1.60 \&
145 root 1.74 \& #include <stdio.h> // for puts
146     \&
147 root 1.68 \& // every watcher type has its own typedef\*(Aqd struct
148 root 1.73 \& // with the name ev_TYPE
149 root 1.68 \& 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 root 1.73 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 root 1.68 \& {
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 root 1.82 \& // this causes all nested ev_run\*(Aqs to stop iterating
163     \& ev_break (EV_A_ EVBREAK_ALL);
164 root 1.68 \& }
165     \&
166     \& // another callback, this time for a time\-out
167     \& static void
168 root 1.73 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 root 1.68 \& {
170     \& puts ("timeout");
171 root 1.82 \& // this causes the innermost ev_run to stop iterating
172     \& ev_break (EV_A_ EVBREAK_ONE);
173 root 1.68 \& }
174     \&
175     \& int
176     \& main (void)
177     \& {
178     \& // use the default event loop unless you have special needs
179 root 1.82 \& struct ev_loop *loop = EV_DEFAULT;
180 root 1.68 \&
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 root 1.82 \& ev_run (loop, 0);
193 root 1.68 \&
194     \& // unloop was called, so exit
195     \& return 0;
196     \& }
197 root 1.27 .Ve
198 root 1.78 .SH "ABOUT THIS DOCUMENT"
199     .IX Header "ABOUT THIS DOCUMENT"
200     This document documents the libev software package.
201     .PP
202 root 1.61 The newest version of this document is also available as an html-formatted
203 root 1.39 web page you might find easier to navigate when reading it for the first
204 root 1.66 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205 root 1.39 .PP
206 root 1.78 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 root 1.82 Familiarity with event based programming techniques in general is assumed
212 root 1.78 throughout this document.
213 root 1.82 .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 root 1.78 .SH "ABOUT LIBEV"
221     .IX Header "ABOUT LIBEV"
222 root 1.1 Libev is an event loop: you register interest in certain events (such as a
223 root 1.54 file descriptor being readable or a timeout occurring), and it will manage
224 root 1.1 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 root 1.79 .SS "\s-1FEATURES\s0"
235 root 1.59 .IX Subsection "FEATURES"
236 root 1.31 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 root 1.80 (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 root 1.28 .PP
248     It also is quite fast (see this
249 root 1.79 <benchmark> comparing it to libevent
250 root 1.28 for example).
251 root 1.79 .SS "\s-1CONVENTIONS\s0"
252 root 1.59 .IX Subsection "CONVENTIONS"
253 root 1.61 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 root 1.81 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259 root 1.61 this argument.
260 root 1.79 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
261 root 1.59 .IX Subsection "TIME REPRESENTATION"
262 root 1.78 Libev represents time as a single floating point number, representing
263 root 1.82 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 root 1.67 .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 root 1.68 a system call indicating a condition libev cannot fix), it calls the callback
278 root 1.67 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 root 1.1 .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 root 1.2 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 root 1.82 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 root 1.57 .IP "ev_sleep (ev_tstamp interval)" 4
301     .IX Item "ev_sleep (ev_tstamp interval)"
302 root 1.56 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 root 1.68 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
305 root 1.1 .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 root 1.48 You can find out the major and minor \s-1ABI\s0 version numbers of the library
312 root 1.1 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 root 1.48 These version numbers refer to the \s-1ABI\s0 version of the library, not the
318     release version.
319 root 1.47 .Sp
320 root 1.1 Usually, it's a good idea to terminate if the major versions mismatch,
321 root 1.47 as this indicates an incompatible change. Minor versions are usually
322 root 1.1 compatible to older versions, so a larger minor version alone is usually
323     not a problem.
324 root 1.9 .Sp
325 root 1.28 Example: Make sure we haven't accidentally been linked against the wrong
326 root 1.82 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327     such as \s-1LFS\s0 or reentrancy).
328 root 1.9 .Sp
329     .Vb 3
330 root 1.68 \& assert (("libev version mismatch",
331     \& ev_version_major () == EV_VERSION_MAJOR
332     \& && ev_version_minor () >= EV_VERSION_MINOR));
333 root 1.9 .Ve
334 root 1.6 .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 root 1.9 .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 root 1.68 \& assert (("sorry, no epoll, no sex",
346     \& ev_supported_backends () & EVBACKEND_EPOLL));
347 root 1.9 .Ve
348 root 1.6 .IP "unsigned int ev_recommended_backends ()" 4
349     .IX Item "unsigned int ev_recommended_backends ()"
350 root 1.82 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 root 1.10 .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 root 1.82 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 root 1.10 .Sp
365     See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
366 root 1.84 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
367     .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
368 root 1.32 Sets the allocation function to use (the prototype is similar \- the
369 root 1.64 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 root 1.1 .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 root 1.9 .Sp
382 root 1.28 Example: Replace the libev allocator with one that waits a bit and then
383 root 1.64 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
384 root 1.9 .Sp
385     .Vb 6
386     \& static void *
387 root 1.26 \& persistent_realloc (void *ptr, size_t size)
388 root 1.9 \& {
389     \& for (;;)
390     \& {
391     \& void *newptr = realloc (ptr, size);
392 root 1.60 \&
393 root 1.9 \& if (newptr)
394     \& return newptr;
395 root 1.60 \&
396 root 1.9 \& sleep (60);
397     \& }
398     \& }
399 root 1.60 \&
400 root 1.9 \& ...
401     \& ev_set_allocator (persistent_realloc);
402     .Ve
403 root 1.84 .IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
404     .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
405 root 1.68 Set the callback function to call on a retryable system call error (such
406 root 1.1 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 root 1.68 callback is set, then libev will expect it to remedy the situation, no
409 root 1.1 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 root 1.9 .Sp
413 root 1.28 Example: This is basically the same thing that libev does internally, too.
414 root 1.9 .Sp
415     .Vb 6
416     \& static void
417     \& fatal_error (const char *msg)
418     \& {
419     \& perror (msg);
420     \& abort ();
421     \& }
422 root 1.60 \&
423 root 1.9 \& ...
424     \& ev_set_syserr_cb (fatal_error);
425     .Ve
426 root 1.85 .IP "ev_feed_signal (int signum)" 4
427     .IX Item "ev_feed_signal (int signum)"
428     This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
429     safe to call this function at any time, from any context, including signal
430     handlers or random threads.
431     .Sp
432     Its main use is to customise signal handling in your process, especially
433     in the presence of threads. For example, you could block signals
434     by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
435     creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
436     mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
437     \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
438 root 1.82 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
439     .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
440     An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
441     \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
442     libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
443 root 1.73 .PP
444     The library knows two types of such loops, the \fIdefault\fR loop, which
445 root 1.82 supports child process events, and dynamically created event loops which
446     do not.
447 root 1.1 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
448     .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
449 root 1.82 This returns the \*(L"default\*(R" event loop object, which is what you should
450     normally use when you just need \*(L"the event loop\*(R". Event loop objects and
451     the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
452     \&\f(CW\*(C`ev_loop_new\*(C'\fR.
453     .Sp
454     If the default loop is already initialised then this function simply
455     returns it (and ignores the flags. If that is troubling you, check
456     \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
457     flags, which should almost always be \f(CW0\fR, unless the caller is also the
458     one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
459 root 1.1 .Sp
460     If you don't know what event loop to use, use the one returned from this
461 root 1.82 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
462 root 1.1 .Sp
463 root 1.63 Note that this function is \fInot\fR thread-safe, so if you want to use it
464 root 1.82 from multiple threads, you have to employ some kind of mutex (note also
465     that this case is unlikely, as loops cannot be shared easily between
466     threads anyway).
467     .Sp
468     The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
469     and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
470     a problem for your application you can either create a dynamic loop with
471     \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
472     \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
473     .Sp
474     Example: This is the most typical usage.
475     .Sp
476     .Vb 2
477     \& if (!ev_default_loop (0))
478     \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
479     .Ve
480     .Sp
481     Example: Restrict libev to the select and poll backends, and do not allow
482     environment settings to be taken into account:
483     .Sp
484     .Vb 1
485     \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
486     .Ve
487     .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
488     .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
489     This will create and initialise a new event loop object. If the loop
490     could not be initialised, returns false.
491 root 1.63 .Sp
492 root 1.85 This function is thread-safe, and one common way to use libev with
493     threads is indeed to create one loop per thread, and using the default
494     loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
495 root 1.60 .Sp
496 root 1.1 The flags argument can be used to specify special behaviour or specific
497 root 1.8 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
498 root 1.1 .Sp
499 root 1.8 The following flags are supported:
500 root 1.1 .RS 4
501     .ie n .IP """EVFLAG_AUTO""" 4
502     .el .IP "\f(CWEVFLAG_AUTO\fR" 4
503     .IX Item "EVFLAG_AUTO"
504     The default flags value. Use this if you have no clue (it's the right
505     thing, believe me).
506     .ie n .IP """EVFLAG_NOENV""" 4
507     .el .IP "\f(CWEVFLAG_NOENV\fR" 4
508     .IX Item "EVFLAG_NOENV"
509 root 1.68 If this flag bit is or'ed into the flag value (or the program runs setuid
510 root 1.1 or setgid) then libev will \fInot\fR look at the environment variable
511     \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
512     override the flags completely if it is found in the environment. This is
513     useful to try out specific backends to test their performance, or to work
514     around bugs.
515 root 1.35 .ie n .IP """EVFLAG_FORKCHECK""" 4
516     .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
517     .IX Item "EVFLAG_FORKCHECK"
518 root 1.82 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
519     make libev check for a fork in each iteration by enabling this flag.
520 root 1.35 .Sp
521     This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
522     and thus this might slow down your event loop if you do a lot of loop
523 root 1.37 iterations and little real work, but is usually not noticeable (on my
524 root 1.61 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
525 root 1.68 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
526 root 1.35 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
527     .Sp
528     The big advantage of this flag is that you can forget about fork (and
529     forget about forgetting to tell libev about forking) when you use this
530     flag.
531     .Sp
532 root 1.68 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
533 root 1.35 environment variable.
534 root 1.80 .ie n .IP """EVFLAG_NOINOTIFY""" 4
535     .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
536     .IX Item "EVFLAG_NOINOTIFY"
537     When this flag is specified, then libev will not attempt to use the
538 root 1.84 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
539 root 1.80 testing, this flag can be useful to conserve inotify file descriptors, as
540     otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
541 root 1.81 .ie n .IP """EVFLAG_SIGNALFD""" 4
542     .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
543     .IX Item "EVFLAG_SIGNALFD"
544     When this flag is specified, then libev will attempt to use the
545 root 1.84 \&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
546 root 1.81 delivers signals synchronously, which makes it both faster and might make
547     it possible to get the queued signal data. It can also simplify signal
548     handling with threads, as long as you properly block signals in your
549     threads that are not interested in handling them.
550     .Sp
551     Signalfd will not be used by default as this changes your signal mask, and
552     there are a lot of shoddy libraries and programs (glib's threadpool for
553     example) that can't properly initialise their signal masks.
554 root 1.85 .ie n .IP """EVFLAG_NOSIGMASK""" 4
555     .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
556     .IX Item "EVFLAG_NOSIGMASK"
557     When this flag is specified, then libev will avoid to modify the signal
558     mask. Specifically, this means you ahve to make sure signals are unblocked
559     when you want to receive them.
560     .Sp
561     This behaviour is useful when you want to do your own signal handling, or
562     want to handle signals only in specific threads and want to avoid libev
563     unblocking the signals.
564     .Sp
565     This flag's behaviour will become the default in future versions of libev.
566 root 1.6 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
567     .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
568     .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
569 root 1.3 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
570     libev tries to roll its own fd_set with no limits on the number of fds,
571     but if that fails, expect a fairly low limit on the number of fds when
572 root 1.58 using this backend. It doesn't scale too well (O(highest_fd)), but its
573 root 1.60 usually the fastest backend for a low number of (low-numbered :) fds.
574 root 1.58 .Sp
575     To get good performance out of this backend you need a high amount of
576 root 1.68 parallelism (most of the file descriptors should be busy). If you are
577 root 1.58 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
578     connections as possible during one iteration. You might also want to have
579     a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
580 root 1.67 readiness notifications you get per iteration.
581 root 1.71 .Sp
582     This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
583     \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
584     \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
585 root 1.6 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
586     .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
587     .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
588 root 1.58 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
589     than select, but handles sparse fds better and has no artificial
590     limit on the number of fds you can use (except it will slow down
591     considerably with a lot of inactive fds). It scales similarly to select,
592     i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
593     performance tips.
594 root 1.71 .Sp
595     This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
596     \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
597 root 1.6 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
598     .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
599     .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
600 root 1.81 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
601     kernels).
602     .Sp
603 root 1.3 For few fds, this backend is a bit little slower than poll and select,
604 root 1.54 but it scales phenomenally better. While poll and select usually scale
605     like O(total_fds) where n is the total number of fds (or the highest fd),
606 root 1.73 epoll scales either O(1) or O(active_fds).
607     .Sp
608     The epoll mechanism deserves honorable mention as the most misdesigned
609     of the more advanced event mechanisms: mere annoyances include silently
610     dropping file descriptors, requiring a system call per change per file
611 root 1.84 descriptor (and unnecessary guessing of parameters), problems with dup,
612     returning before the timeout value, resulting in additional iterations
613     (and only giving 5ms accuracy while select on the same platform gives
614     0.1ms) and so on. The biggest issue is fork races, however \- if a program
615     forks then \fIboth\fR parent and child process have to recreate the epoll
616     set, which can take considerable time (one syscall per file descriptor)
617     and is of course hard to detect.
618 root 1.73 .Sp
619     Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
620     of course \fIdoesn't\fR, and epoll just loves to report events for totally
621     \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
622     even remove them from the set) than registered in the set (especially
623     on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
624     employing an additional generation counter and comparing that against the
625 root 1.82 events to filter out spurious ones, recreating the set when required. Last
626     not least, it also refuses to work with some file descriptors which work
627     perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
628 root 1.3 .Sp
629 root 1.85 Epoll is truly the train wreck analog among event poll mechanisms,
630     a frankenpoll, cobbled together in a hurry, no thought to design or
631     interaction with others.
632 root 1.84 .Sp
633 root 1.54 While stopping, setting and starting an I/O watcher in the same iteration
634 root 1.73 will result in some caching, there is still a system call per such
635     incident (because the same \fIfile descriptor\fR could point to a different
636     \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
637     file descriptors might not work very well if you register events for both
638     file descriptors.
639 root 1.58 .Sp
640     Best performance from this backend is achieved by not unregistering all
641 root 1.71 watchers for a file descriptor until it has been closed, if possible,
642     i.e. keep at least one watcher active per fd at all times. Stopping and
643     starting a watcher (without re-setting it) also usually doesn't cause
644 root 1.73 extra overhead. A fork can both result in spurious notifications as well
645     as in libev having to destroy and recreate the epoll object, which can
646     take considerable time and thus should be avoided.
647 root 1.58 .Sp
648 root 1.74 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
649     faster than epoll for maybe up to a hundred file descriptors, depending on
650     the usage. So sad.
651     .Sp
652 root 1.68 While nominally embeddable in other event loops, this feature is broken in
653 root 1.58 all kernel versions tested so far.
654 root 1.71 .Sp
655     This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
656     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
657 root 1.6 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
658     .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
659     .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
660 root 1.73 Kqueue deserves special mention, as at the time of this writing, it
661     was broken on all BSDs except NetBSD (usually it doesn't work reliably
662     with anything but sockets and pipes, except on Darwin, where of course
663     it's completely useless). Unlike epoll, however, whose brokenness
664     is by design, these kqueue bugs can (and eventually will) be fixed
665     without \s-1API\s0 changes to existing programs. For this reason it's not being
666     \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
667     \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
668     system like NetBSD.
669 root 1.3 .Sp
670 root 1.57 You still can embed kqueue into a normal poll or select backend and use it
671     only for sockets (after having made sure that sockets work with kqueue on
672     the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
673     .Sp
674 root 1.3 It scales in the same way as the epoll backend, but the interface to the
675 root 1.57 kernel is more efficient (which says nothing about its actual speed, of
676     course). While stopping, setting and starting an I/O watcher does never
677 root 1.68 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
678 root 1.73 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
679     sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
680     cases
681 root 1.58 .Sp
682     This backend usually performs well under most conditions.
683     .Sp
684     While nominally embeddable in other event loops, this doesn't work
685     everywhere, so you might need to test for this. And since it is broken
686     almost everywhere, you should only use it when you have a lot of sockets
687     (for which it usually works), by embedding it into another event loop
688 root 1.75 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
689     also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
690 root 1.71 .Sp
691     This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
692     \&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
693     \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
694 root 1.6 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
695     .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
696     .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
697 root 1.58 This is not implemented yet (and might never be, unless you send me an
698     implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
699     and is not embeddable, which would limit the usefulness of this backend
700     immensely.
701 root 1.6 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
702     .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
703     .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
704 root 1.54 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
705 root 1.3 it's really slow, but it still scales very well (O(active_fds)).
706 root 1.7 .Sp
707 root 1.58 While this backend scales well, it requires one system call per active
708     file descriptor per loop iteration. For small and medium numbers of file
709     descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
710     might perform better.
711 root 1.60 .Sp
712 root 1.85 On the positive side, this backend actually performed fully to
713     specification in all tests and is fully embeddable, which is a rare feat
714     among the OS-specific backends (I vastly prefer correctness over speed
715     hacks).
716     .Sp
717     On the negative side, the interface is \fIbizarre\fR \- so bizarre that
718     even sun itself gets it wrong in their code examples: The event polling
719     function sometimes returning events to the caller even though an error
720     occurred, but with no indication whether it has done so or not (yes, it's
721     even documented that way) \- deadly for edge-triggered interfaces where
722     you absolutely have to know whether an event occurred or not because you
723     have to re-arm the watcher.
724     .Sp
725     Fortunately libev seems to be able to work around these idiocies.
726 root 1.71 .Sp
727     This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
728     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
729 root 1.6 .ie n .IP """EVBACKEND_ALL""" 4
730     .el .IP "\f(CWEVBACKEND_ALL\fR" 4
731     .IX Item "EVBACKEND_ALL"
732 root 1.4 Try all backends (even potentially broken ones that wouldn't be tried
733     with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
734 root 1.6 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
735 root 1.58 .Sp
736 root 1.85 It is definitely not recommended to use this flag, use whatever
737     \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
738     at all.
739     .ie n .IP """EVBACKEND_MASK""" 4
740     .el .IP "\f(CWEVBACKEND_MASK\fR" 4
741     .IX Item "EVBACKEND_MASK"
742     Not a backend at all, but a mask to select all backend bits from a
743     \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
744     value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
745 root 1.1 .RE
746     .RS 4
747 root 1.3 .Sp
748 root 1.80 If one or more of the backend flags are or'ed into the flags value,
749     then only these backends will be tried (in the reverse order as listed
750     here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
751     ()\*(C'\fR will be tried.
752 root 1.8 .Sp
753 root 1.82 Example: Try to create a event loop that uses epoll and nothing else.
754 root 1.8 .Sp
755 root 1.82 .Vb 3
756     \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
757     \& if (!epoller)
758     \& fatal ("no epoll found here, maybe it hides under your chair");
759 root 1.8 .Ve
760     .Sp
761 root 1.71 Example: Use whatever libev has to offer, but make sure that kqueue is
762 root 1.82 used if available.
763 root 1.8 .Sp
764     .Vb 1
765 root 1.82 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
766 root 1.8 .Ve
767 root 1.1 .RE
768 root 1.82 .IP "ev_loop_destroy (loop)" 4
769     .IX Item "ev_loop_destroy (loop)"
770     Destroys an event loop object (frees all memory and kernel state
771 root 1.12 etc.). None of the active event watchers will be stopped in the normal
772     sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
773 root 1.68 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
774 root 1.12 calling this function, or cope with the fact afterwards (which is usually
775 root 1.52 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
776 root 1.12 for example).
777 root 1.52 .Sp
778 root 1.73 Note that certain global state, such as signal state (and installed signal
779     handlers), will not be freed by this function, and related watchers (such
780     as signal and child watchers) would need to be stopped manually.
781 root 1.52 .Sp
782 root 1.82 This function is normally used on loop objects allocated by
783     \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
784     \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
785     .Sp
786     Note that it is not advisable to call this function on the default loop
787 root 1.84 except in the rare occasion where you really need to free its resources.
788 root 1.82 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
789     and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
790     .IP "ev_loop_fork (loop)" 4
791     .IX Item "ev_loop_fork (loop)"
792     This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
793     reinitialise the kernel state for backends that have one. Despite the
794 root 1.60 name, you can call it anytime, but it makes most sense after forking, in
795 root 1.82 the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
796     child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
797     .Sp
798     Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
799     a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
800     because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
801     during fork.
802 root 1.60 .Sp
803     On the other hand, you only need to call this function in the child
804 root 1.82 process if and only if you want to use the event loop in the child. If
805     you just fork+exec or create a new loop in the child, you don't have to
806     call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
807     difference, but libev will usually detect this case on its own and do a
808     costly reset of the backend).
809 root 1.1 .Sp
810     The function itself is quite fast and it's usually not a problem to call
811 root 1.82 it just in case after a fork.
812     .Sp
813     Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
814     using pthreads.
815 root 1.1 .Sp
816 root 1.82 .Vb 5
817     \& static void
818     \& post_fork_child (void)
819     \& {
820     \& ev_loop_fork (EV_DEFAULT);
821     \& }
822     \&
823     \& ...
824     \& pthread_atfork (0, 0, post_fork_child);
825 root 1.1 .Ve
826 root 1.61 .IP "int ev_is_default_loop (loop)" 4
827     .IX Item "int ev_is_default_loop (loop)"
828 root 1.71 Returns true when the given loop is, in fact, the default loop, and false
829     otherwise.
830 root 1.82 .IP "unsigned int ev_iteration (loop)" 4
831     .IX Item "unsigned int ev_iteration (loop)"
832     Returns the current iteration count for the event loop, which is identical
833     to the number of times libev did poll for new events. It starts at \f(CW0\fR
834     and happily wraps around with enough iterations.
835 root 1.37 .Sp
836     This value can sometimes be useful as a generation counter of sorts (it
837     \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
838 root 1.82 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
839     prepare and check phases.
840     .IP "unsigned int ev_depth (loop)" 4
841     .IX Item "unsigned int ev_depth (loop)"
842     Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
843 root 1.85 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
844 root 1.79 .Sp
845 root 1.82 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
846     \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
847 root 1.79 in which case it is higher.
848     .Sp
849 root 1.85 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
850     throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
851     as a hint to avoid such ungentleman-like behaviour unless it's really
852     convenient, in which case it is fully supported.
853 root 1.6 .IP "unsigned int ev_backend (loop)" 4
854     .IX Item "unsigned int ev_backend (loop)"
855     Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
856 root 1.1 use.
857     .IP "ev_tstamp ev_now (loop)" 4
858     .IX Item "ev_tstamp ev_now (loop)"
859     Returns the current \*(L"event loop time\*(R", which is the time the event loop
860 root 1.9 received events and started processing them. This timestamp does not
861     change as long as callbacks are being processed, and this is also the base
862     time used for relative timers. You can treat it as the timestamp of the
863 root 1.54 event occurring (or more correctly, libev finding out about it).
864 root 1.71 .IP "ev_now_update (loop)" 4
865     .IX Item "ev_now_update (loop)"
866     Establishes the current time by querying the kernel, updating the time
867     returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
868 root 1.82 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
869 root 1.71 .Sp
870     This function is rarely useful, but when some event callback runs for a
871     very long time without entering the event loop, updating libev's idea of
872     the current time is a good idea.
873     .Sp
874     See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
875 root 1.78 .IP "ev_suspend (loop)" 4
876     .IX Item "ev_suspend (loop)"
877     .PD 0
878     .IP "ev_resume (loop)" 4
879     .IX Item "ev_resume (loop)"
880     .PD
881 root 1.82 These two functions suspend and resume an event loop, for use when the
882     loop is not used for a while and timeouts should not be processed.
883 root 1.78 .Sp
884     A typical use case would be an interactive program such as a game: When
885     the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
886     would be best to handle timeouts as if no time had actually passed while
887     the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
888     in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
889     \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
890     .Sp
891     Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
892     between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
893     will be rescheduled (that is, they will lose any events that would have
894 root 1.82 occurred while suspended).
895 root 1.78 .Sp
896     After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
897     given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
898     without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
899     .Sp
900     Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
901     event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
902 root 1.82 .IP "ev_run (loop, int flags)" 4
903     .IX Item "ev_run (loop, int flags)"
904 root 1.1 Finally, this is it, the event handler. This function usually is called
905 root 1.81 after you have initialised all your watchers and you want to start
906 root 1.82 handling events. It will ask the operating system for any new events, call
907     the watcher callbacks, an then repeat the whole process indefinitely: This
908     is why event loops are called \fIloops\fR.
909 root 1.1 .Sp
910 root 1.82 If the flags argument is specified as \f(CW0\fR, it will keep handling events
911     until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
912     called.
913 root 1.1 .Sp
914 root 1.82 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
915 root 1.9 relying on all watchers to be stopped when deciding when a program has
916 root 1.71 finished (especially in interactive programs), but having a program
917     that automatically loops as long as it has to and no longer by virtue
918     of relying on its watchers stopping correctly, that is truly a thing of
919     beauty.
920 root 1.9 .Sp
921 root 1.85 This function is also \fImostly\fR exception-safe \- you can break out of
922     a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
923     exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
924     will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
925     .Sp
926 root 1.82 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
927     those events and any already outstanding ones, but will not wait and
928     block your process in case there are no events and will return after one
929     iteration of the loop. This is sometimes useful to poll and handle new
930     events while doing lengthy calculations, to keep the program responsive.
931 root 1.1 .Sp
932 root 1.82 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
933 root 1.71 necessary) and will handle those and any already outstanding ones. It
934     will block your process until at least one new event arrives (which could
935 root 1.73 be an event internal to libev itself, so there is no guarantee that a
936 root 1.71 user-registered callback will be called), and will return after one
937     iteration of the loop.
938     .Sp
939     This is useful if you are waiting for some external event in conjunction
940     with something not expressible using other libev watchers (i.e. "roll your
941 root 1.82 own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
942 root 1.8 usually a better approach for this kind of thing.
943     .Sp
944 root 1.82 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
945 root 1.8 .Sp
946 root 1.60 .Vb 10
947 root 1.82 \& \- Increment loop depth.
948     \& \- Reset the ev_break status.
949 root 1.60 \& \- Before the first iteration, call any pending watchers.
950 root 1.82 \& LOOP:
951     \& \- If EVFLAG_FORKCHECK was used, check for a fork.
952 root 1.71 \& \- If a fork was detected (by any means), queue and call all fork watchers.
953 root 1.60 \& \- Queue and call all prepare watchers.
954 root 1.82 \& \- If ev_break was called, goto FINISH.
955 root 1.71 \& \- If we have been forked, detach and recreate the kernel state
956     \& as to not disturb the other process.
957 root 1.60 \& \- Update the kernel state with all outstanding changes.
958 root 1.71 \& \- Update the "event loop time" (ev_now ()).
959 root 1.60 \& \- Calculate for how long to sleep or block, if at all
960 root 1.82 \& (active idle watchers, EVRUN_NOWAIT or not having
961 root 1.60 \& any active watchers at all will result in not sleeping).
962     \& \- Sleep if the I/O and timer collect interval say so.
963 root 1.82 \& \- Increment loop iteration counter.
964 root 1.60 \& \- Block the process, waiting for any events.
965     \& \- Queue all outstanding I/O (fd) events.
966 root 1.71 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
967     \& \- Queue all expired timers.
968     \& \- Queue all expired periodics.
969 root 1.82 \& \- Queue all idle watchers with priority higher than that of pending events.
970 root 1.60 \& \- Queue all check watchers.
971     \& \- Call all queued watchers in reverse order (i.e. check watchers first).
972 root 1.8 \& Signals and child watchers are implemented as I/O watchers, and will
973     \& be handled here by queueing them when their watcher gets executed.
974 root 1.82 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
975     \& were used, or there are no active watchers, goto FINISH, otherwise
976     \& continue with step LOOP.
977     \& FINISH:
978     \& \- Reset the ev_break status iff it was EVBREAK_ONE.
979     \& \- Decrement the loop depth.
980     \& \- Return.
981 root 1.2 .Ve
982 root 1.9 .Sp
983 root 1.60 Example: Queue some jobs and then loop until no events are outstanding
984 root 1.9 anymore.
985     .Sp
986     .Vb 4
987     \& ... queue jobs here, make sure they register event watchers as long
988     \& ... as they still have work to do (even an idle watcher will do..)
989 root 1.82 \& ev_run (my_loop, 0);
990 root 1.71 \& ... jobs done or somebody called unloop. yeah!
991 root 1.9 .Ve
992 root 1.82 .IP "ev_break (loop, how)" 4
993     .IX Item "ev_break (loop, how)"
994     Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
995 root 1.1 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
996 root 1.82 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
997     \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
998 root 1.60 .Sp
999 root 1.85 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1000 root 1.72 .Sp
1001 root 1.85 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1002     which case it will have no effect.
1003 root 1.1 .IP "ev_ref (loop)" 4
1004     .IX Item "ev_ref (loop)"
1005     .PD 0
1006     .IP "ev_unref (loop)" 4
1007     .IX Item "ev_unref (loop)"
1008     .PD
1009     Ref/unref can be used to add or remove a reference count on the event
1010     loop: Every watcher keeps one reference, and as long as the reference
1011 root 1.82 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1012 root 1.71 .Sp
1013 root 1.81 This is useful when you have a watcher that you never intend to
1014 root 1.82 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1015 root 1.81 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1016     before stopping it.
1017 root 1.71 .Sp
1018 root 1.78 As an example, libev itself uses this for its internal signal pipe: It
1019 root 1.82 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1020 root 1.78 exiting if no event watchers registered by it are active. It is also an
1021     excellent way to do this for generic recurring timers or from within
1022     third-party libraries. Just remember to \fIunref after start\fR and \fIref
1023     before stop\fR (but only if the watcher wasn't active before, or was active
1024     before, respectively. Note also that libev might stop watchers itself
1025     (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1026     in the callback).
1027 root 1.9 .Sp
1028 root 1.82 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1029 root 1.9 running when nothing else is active.
1030     .Sp
1031     .Vb 4
1032 root 1.73 \& ev_signal exitsig;
1033 root 1.68 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1034     \& ev_signal_start (loop, &exitsig);
1035 root 1.85 \& ev_unref (loop);
1036 root 1.9 .Ve
1037     .Sp
1038 root 1.28 Example: For some weird reason, unregister the above signal handler again.
1039 root 1.9 .Sp
1040     .Vb 2
1041 root 1.68 \& ev_ref (loop);
1042     \& ev_signal_stop (loop, &exitsig);
1043 root 1.9 .Ve
1044 root 1.57 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1045     .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1046 root 1.56 .PD 0
1047 root 1.57 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1048     .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1049 root 1.56 .PD
1050     These advanced functions influence the time that libev will spend waiting
1051 root 1.71 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1052     will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1053     latency.
1054 root 1.56 .Sp
1055     Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1056 root 1.71 allows libev to delay invocation of I/O and timer/periodic callbacks
1057     to increase efficiency of loop iterations (or to increase power-saving
1058     opportunities).
1059     .Sp
1060     The idea is that sometimes your program runs just fast enough to handle
1061     one (or very few) event(s) per loop iteration. While this makes the
1062     program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1063 root 1.56 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1064     overhead for the actual polling but can deliver many events at once.
1065     .Sp
1066     By setting a higher \fIio collect interval\fR you allow libev to spend more
1067     time collecting I/O events, so you can handle more events per iteration,
1068     at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1069 root 1.58 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1070 root 1.79 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1071     sleep time ensures that libev will not poll for I/O events more often then
1072     once per this interval, on average.
1073 root 1.56 .Sp
1074     Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1075     to spend more time collecting timeouts, at the expense of increased
1076 root 1.71 latency/jitter/inexactness (the watcher callback will be called
1077     later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1078     value will not introduce any overhead in libev.
1079 root 1.56 .Sp
1080 root 1.68 Many (busy) programs can usually benefit by setting the I/O collect
1081 root 1.57 interval to a value near \f(CW0.1\fR or so, which is often enough for
1082     interactive servers (of course not for games), likewise for timeouts. It
1083     usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1084 root 1.79 as this approaches the timing granularity of most systems. Note that if
1085     you do transactions with the outside world and you can't increase the
1086     parallelity, then this setting will limit your transaction rate (if you
1087     need to poll once per transaction and the I/O collect interval is 0.01,
1088 root 1.82 then you can't do more than 100 transactions per second).
1089 root 1.71 .Sp
1090     Setting the \fItimeout collect interval\fR can improve the opportunity for
1091     saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1092     are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1093     times the process sleeps and wakes up again. Another useful technique to
1094     reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1095     they fire on, say, one-second boundaries only.
1096 root 1.79 .Sp
1097     Example: we only need 0.1s timeout granularity, and we wish not to poll
1098     more often than 100 times per second:
1099     .Sp
1100     .Vb 2
1101     \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1102     \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1103     .Ve
1104     .IP "ev_invoke_pending (loop)" 4
1105     .IX Item "ev_invoke_pending (loop)"
1106     This call will simply invoke all pending watchers while resetting their
1107 root 1.82 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1108     but when overriding the invoke callback this call comes handy. This
1109     function can be invoked from a watcher \- this can be useful for example
1110     when you want to do some lengthy calculation and want to pass further
1111     event handling to another thread (you still have to make sure only one
1112     thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1113 root 1.79 .IP "int ev_pending_count (loop)" 4
1114     .IX Item "int ev_pending_count (loop)"
1115     Returns the number of pending watchers \- zero indicates that no watchers
1116     are pending.
1117     .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1118     .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1119     This overrides the invoke pending functionality of the loop: Instead of
1120 root 1.82 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1121 root 1.79 this callback instead. This is useful, for example, when you want to
1122     invoke the actual watchers inside another context (another thread etc.).
1123     .Sp
1124     If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1125     callback.
1126     .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1127     .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1128     Sometimes you want to share the same loop between multiple threads. This
1129     can be done relatively simply by putting mutex_lock/unlock calls around
1130     each call to a libev function.
1131     .Sp
1132 root 1.82 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1133     to wait for it to return. One way around this is to wake up the event
1134     loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1135     \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1136 root 1.79 .Sp
1137     When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1138     suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1139     afterwards.
1140     .Sp
1141     Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1142     \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1143     .Sp
1144     While event loop modifications are allowed between invocations of
1145     \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1146     modifications done will affect the event loop, i.e. adding watchers will
1147     have no effect on the set of file descriptors being watched, or the time
1148 root 1.82 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1149 root 1.79 to take note of any changes you made.
1150     .Sp
1151 root 1.82 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1152 root 1.79 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1153     .Sp
1154     See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1155     document.
1156     .IP "ev_set_userdata (loop, void *data)" 4
1157     .IX Item "ev_set_userdata (loop, void *data)"
1158     .PD 0
1159 root 1.85 .IP "void *ev_userdata (loop)" 4
1160     .IX Item "void *ev_userdata (loop)"
1161 root 1.79 .PD
1162     Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1163     \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1164 root 1.85 \&\f(CW0\fR.
1165 root 1.79 .Sp
1166     These two functions can be used to associate arbitrary data with a loop,
1167     and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1168     \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1169     any other purpose as well.
1170 root 1.82 .IP "ev_verify (loop)" 4
1171     .IX Item "ev_verify (loop)"
1172 root 1.67 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1173 root 1.73 compiled in, which is the default for non-minimal builds. It tries to go
1174 root 1.71 through all internal structures and checks them for validity. If anything
1175     is found to be inconsistent, it will print an error message to standard
1176     error and call \f(CW\*(C`abort ()\*(C'\fR.
1177 root 1.67 .Sp
1178     This can be used to catch bugs inside libev itself: under normal
1179     circumstances, this function will never abort as of course libev keeps its
1180     data structures consistent.
1181 root 1.1 .SH "ANATOMY OF A WATCHER"
1182     .IX Header "ANATOMY OF A WATCHER"
1183 root 1.73 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1184     watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1185     watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1186     .PP
1187 root 1.82 A watcher is an opaque structure that you allocate and register to record
1188     your interest in some event. To make a concrete example, imagine you want
1189     to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1190     for that:
1191 root 1.1 .PP
1192     .Vb 5
1193 root 1.73 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1194 root 1.68 \& {
1195     \& ev_io_stop (w);
1196 root 1.82 \& ev_break (loop, EVBREAK_ALL);
1197 root 1.68 \& }
1198     \&
1199     \& struct ev_loop *loop = ev_default_loop (0);
1200 root 1.73 \&
1201     \& ev_io stdin_watcher;
1202     \&
1203 root 1.68 \& ev_init (&stdin_watcher, my_cb);
1204     \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1205     \& ev_io_start (loop, &stdin_watcher);
1206 root 1.73 \&
1207 root 1.82 \& ev_run (loop, 0);
1208 root 1.1 .Ve
1209     .PP
1210     As you can see, you are responsible for allocating the memory for your
1211 root 1.73 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1212     stack).
1213     .PP
1214     Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1215     or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1216 root 1.1 .PP
1217 root 1.82 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1218     *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1219     invoked each time the event occurs (or, in the case of I/O watchers, each
1220     time the event loop detects that the file descriptor given is readable
1221     and/or writable).
1222 root 1.1 .PP
1223 root 1.73 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1224     macro to configure it, with arguments specific to the watcher type. There
1225     is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1226 root 1.1 .PP
1227     To make the watcher actually watch out for events, you have to start it
1228 root 1.73 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1229 root 1.1 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1230 root 1.73 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1231 root 1.1 .PP
1232     As long as your watcher is active (has been started but not stopped) you
1233     must not touch the values stored in it. Most specifically you must never
1234 root 1.73 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1235 root 1.1 .PP
1236     Each and every callback receives the event loop pointer as first, the
1237     registered watcher structure as second, and a bitset of received events as
1238     third argument.
1239     .PP
1240     The received events usually include a single bit per event type received
1241     (you can receive multiple events at the same time). The possible bit masks
1242     are:
1243     .ie n .IP """EV_READ""" 4
1244     .el .IP "\f(CWEV_READ\fR" 4
1245     .IX Item "EV_READ"
1246     .PD 0
1247     .ie n .IP """EV_WRITE""" 4
1248     .el .IP "\f(CWEV_WRITE\fR" 4
1249     .IX Item "EV_WRITE"
1250     .PD
1251     The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1252     writable.
1253 root 1.82 .ie n .IP """EV_TIMER""" 4
1254     .el .IP "\f(CWEV_TIMER\fR" 4
1255     .IX Item "EV_TIMER"
1256 root 1.1 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1257     .ie n .IP """EV_PERIODIC""" 4
1258     .el .IP "\f(CWEV_PERIODIC\fR" 4
1259     .IX Item "EV_PERIODIC"
1260     The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1261     .ie n .IP """EV_SIGNAL""" 4
1262     .el .IP "\f(CWEV_SIGNAL\fR" 4
1263     .IX Item "EV_SIGNAL"
1264     The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1265     .ie n .IP """EV_CHILD""" 4
1266     .el .IP "\f(CWEV_CHILD\fR" 4
1267     .IX Item "EV_CHILD"
1268     The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1269 root 1.22 .ie n .IP """EV_STAT""" 4
1270     .el .IP "\f(CWEV_STAT\fR" 4
1271     .IX Item "EV_STAT"
1272     The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1273 root 1.1 .ie n .IP """EV_IDLE""" 4
1274     .el .IP "\f(CWEV_IDLE\fR" 4
1275     .IX Item "EV_IDLE"
1276     The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1277     .ie n .IP """EV_PREPARE""" 4
1278     .el .IP "\f(CWEV_PREPARE\fR" 4
1279     .IX Item "EV_PREPARE"
1280     .PD 0
1281     .ie n .IP """EV_CHECK""" 4
1282     .el .IP "\f(CWEV_CHECK\fR" 4
1283     .IX Item "EV_CHECK"
1284     .PD
1285 root 1.82 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
1286 root 1.1 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1287 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
1288 root 1.1 received events. Callbacks of both watcher types can start and stop as
1289     many watchers as they want, and all of them will be taken into account
1290     (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1291 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1292 root 1.24 .ie n .IP """EV_EMBED""" 4
1293     .el .IP "\f(CWEV_EMBED\fR" 4
1294     .IX Item "EV_EMBED"
1295     The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1296     .ie n .IP """EV_FORK""" 4
1297     .el .IP "\f(CWEV_FORK\fR" 4
1298     .IX Item "EV_FORK"
1299     The event loop has been resumed in the child process after fork (see
1300     \&\f(CW\*(C`ev_fork\*(C'\fR).
1301 root 1.82 .ie n .IP """EV_CLEANUP""" 4
1302     .el .IP "\f(CWEV_CLEANUP\fR" 4
1303     .IX Item "EV_CLEANUP"
1304     The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1305 root 1.61 .ie n .IP """EV_ASYNC""" 4
1306     .el .IP "\f(CWEV_ASYNC\fR" 4
1307     .IX Item "EV_ASYNC"
1308     The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1309 root 1.78 .ie n .IP """EV_CUSTOM""" 4
1310     .el .IP "\f(CWEV_CUSTOM\fR" 4
1311     .IX Item "EV_CUSTOM"
1312     Not ever sent (or otherwise used) by libev itself, but can be freely used
1313     by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1314 root 1.1 .ie n .IP """EV_ERROR""" 4
1315     .el .IP "\f(CWEV_ERROR\fR" 4
1316     .IX Item "EV_ERROR"
1317 root 1.68 An unspecified error has occurred, the watcher has been stopped. This might
1318 root 1.1 happen because the watcher could not be properly started because libev
1319     ran out of memory, a file descriptor was found to be closed or any other
1320 root 1.73 problem. Libev considers these application bugs.
1321     .Sp
1322     You best act on it by reporting the problem and somehow coping with the
1323     watcher being stopped. Note that well-written programs should not receive
1324     an error ever, so when your watcher receives it, this usually indicates a
1325     bug in your program.
1326 root 1.1 .Sp
1327 root 1.71 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1328     example it might indicate that a fd is readable or writable, and if your
1329     callbacks is well-written it can just attempt the operation and cope with
1330     the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1331     programs, though, as the fd could already be closed and reused for another
1332     thing, so beware.
1333 root 1.79 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1334 root 1.17 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1335 root 1.11 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1336     .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1337     .IX Item "ev_init (ev_TYPE *watcher, callback)"
1338     This macro initialises the generic portion of a watcher. The contents
1339     of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1340     the generic parts of the watcher are initialised, you \fIneed\fR to call
1341     the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1342     type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1343     which rolls both calls into one.
1344     .Sp
1345     You can reinitialise a watcher at any time as long as it has been stopped
1346     (or never started) and there are no pending events outstanding.
1347     .Sp
1348 root 1.73 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1349 root 1.11 int revents)\*(C'\fR.
1350 root 1.71 .Sp
1351     Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1352     .Sp
1353     .Vb 3
1354     \& ev_io w;
1355     \& ev_init (&w, my_cb);
1356     \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1357     .Ve
1358 root 1.81 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1359     .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1360     .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1361 root 1.11 This macro initialises the type-specific parts of a watcher. You need to
1362     call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1363     call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1364     macro on a watcher that is active (it can be pending, however, which is a
1365     difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1366     .Sp
1367     Although some watcher types do not have type-specific arguments
1368     (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1369 root 1.71 .Sp
1370     See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1371 root 1.11 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1372     .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1373     .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1374 root 1.68 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1375     calls into a single call. This is the most convenient method to initialise
1376 root 1.11 a watcher. The same limitations apply, of course.
1377 root 1.71 .Sp
1378     Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1379     .Sp
1380     .Vb 1
1381     \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1382     .Ve
1383 root 1.81 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1384     .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1385     .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1386 root 1.11 Starts (activates) the given watcher. Only active watchers will receive
1387     events. If the watcher is already active nothing will happen.
1388 root 1.71 .Sp
1389     Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1390     whole section.
1391     .Sp
1392     .Vb 1
1393     \& ev_io_start (EV_DEFAULT_UC, &w);
1394     .Ve
1395 root 1.81 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1396     .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1397     .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1398 root 1.72 Stops the given watcher if active, and clears the pending status (whether
1399     the watcher was active or not).
1400     .Sp
1401     It is possible that stopped watchers are pending \- for example,
1402     non-repeating timers are being stopped when they become pending \- but
1403     calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1404     pending. If you want to free or reuse the memory used by the watcher it is
1405     therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1406 root 1.11 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1407     .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1408     Returns a true value iff the watcher is active (i.e. it has been started
1409     and not yet been stopped). As long as a watcher is active you must not modify
1410     it.
1411     .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1412     .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1413     Returns a true value iff the watcher is pending, (i.e. it has outstanding
1414     events but its callback has not yet been invoked). As long as a watcher
1415     is pending (but not active) you must not call an init function on it (but
1416 root 1.43 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1417     make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1418     it).
1419 root 1.29 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1420     .IX Item "callback ev_cb (ev_TYPE *watcher)"
1421 root 1.11 Returns the callback currently set on the watcher.
1422     .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1423     .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1424     Change the callback. You can change the callback at virtually any time
1425     (modulo threads).
1426 root 1.81 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1427     .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1428 root 1.37 .PD 0
1429     .IP "int ev_priority (ev_TYPE *watcher)" 4
1430     .IX Item "int ev_priority (ev_TYPE *watcher)"
1431     .PD
1432     Set and query the priority of the watcher. The priority is a small
1433     integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1434     (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1435     before watchers with lower priority, but priority will not keep watchers
1436     from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1437     .Sp
1438     If you need to suppress invocation when higher priority events are pending
1439     you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1440     .Sp
1441 root 1.43 You \fImust not\fR change the priority of a watcher as long as it is active or
1442     pending.
1443     .Sp
1444 root 1.78 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1445     fine, as long as you do not mind that the priority value you query might
1446     or might not have been clamped to the valid range.
1447     .Sp
1448 root 1.37 The default priority used by watchers when no priority has been set is
1449     always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1450     .Sp
1451 root 1.78 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1452     priorities.
1453 root 1.43 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1454     .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1455     Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1456     \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1457 root 1.71 can deal with that fact, as both are simply passed through to the
1458     callback.
1459 root 1.43 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1460     .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1461 root 1.71 If the watcher is pending, this function clears its pending status and
1462     returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1463 root 1.43 watcher isn't pending it does nothing and returns \f(CW0\fR.
1464 root 1.71 .Sp
1465     Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1466     callback to be invoked, which can be accomplished with this function.
1467 root 1.81 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1468     .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1469     Feeds the given event set into the event loop, as if the specified event
1470     had happened for the specified watcher (which must be a pointer to an
1471     initialised but not necessarily started event watcher). Obviously you must
1472     not free the watcher as long as it has pending events.
1473     .Sp
1474     Stopping the watcher, letting libev invoke it, or calling
1475     \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1476     not started in the first place.
1477     .Sp
1478     See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1479     functions that do not need a watcher.
1480 root 1.1 .PP
1481 root 1.85 See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1482     \&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1483 root 1.82 .SS "\s-1WATCHER\s0 \s-1STATES\s0"
1484     .IX Subsection "WATCHER STATES"
1485     There are various watcher states mentioned throughout this manual \-
1486     active, pending and so on. In this section these states and the rules to
1487     transition between them will be described in more detail \- and while these
1488     rules might look complicated, they usually do \*(L"the right thing\*(R".
1489     .IP "initialiased" 4
1490     .IX Item "initialiased"
1491     Before a watcher can be registered with the event looop it has to be
1492     initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1493     \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1494     .Sp
1495     In this state it is simply some block of memory that is suitable for use
1496     in an event loop. It can be moved around, freed, reused etc. at will.
1497     .IP "started/running/active" 4
1498     .IX Item "started/running/active"
1499     Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1500     property of the event loop, and is actively waiting for events. While in
1501     this state it cannot be accessed (except in a few documented ways), moved,
1502     freed or anything else \- the only legal thing is to keep a pointer to it,
1503     and call libev functions on it that are documented to work on active watchers.
1504     .IP "pending" 4
1505     .IX Item "pending"
1506     If a watcher is active and libev determines that an event it is interested
1507     in has occurred (such as a timer expiring), it will become pending. It will
1508     stay in this pending state until either it is stopped or its callback is
1509     about to be invoked, so it is not normally pending inside the watcher
1510     callback.
1511     .Sp
1512     The watcher might or might not be active while it is pending (for example,
1513     an expired non-repeating timer can be pending but no longer active). If it
1514     is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1515     but it is still property of the event loop at this time, so cannot be
1516     moved, freed or reused. And if it is active the rules described in the
1517     previous item still apply.
1518     .Sp
1519     It is also possible to feed an event on a watcher that is not active (e.g.
1520     via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1521     active.
1522     .IP "stopped" 4
1523     .IX Item "stopped"
1524     A watcher can be stopped implicitly by libev (in which case it might still
1525     be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1526     latter will clear any pending state the watcher might be in, regardless
1527     of whether it was active or not, so stopping a watcher explicitly before
1528     freeing it is often a good idea.
1529     .Sp
1530     While stopped (and not pending) the watcher is essentially in the
1531     initialised state, that is it can be reused, moved, modified in any way
1532     you wish.
1533 root 1.79 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1534 root 1.78 .IX Subsection "WATCHER PRIORITY MODELS"
1535     Many event loops support \fIwatcher priorities\fR, which are usually small
1536     integers that influence the ordering of event callback invocation
1537     between watchers in some way, all else being equal.
1538     .PP
1539     In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1540     description for the more technical details such as the actual priority
1541     range.
1542     .PP
1543     There are two common ways how these these priorities are being interpreted
1544     by event loops:
1545     .PP
1546     In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1547     of lower priority watchers, which means as long as higher priority
1548     watchers receive events, lower priority watchers are not being invoked.
1549     .PP
1550     The less common only-for-ordering model uses priorities solely to order
1551     callback invocation within a single event loop iteration: Higher priority
1552     watchers are invoked before lower priority ones, but they all get invoked
1553     before polling for new events.
1554     .PP
1555     Libev uses the second (only-for-ordering) model for all its watchers
1556     except for idle watchers (which use the lock-out model).
1557     .PP
1558     The rationale behind this is that implementing the lock-out model for
1559     watchers is not well supported by most kernel interfaces, and most event
1560     libraries will just poll for the same events again and again as long as
1561     their callbacks have not been executed, which is very inefficient in the
1562     common case of one high-priority watcher locking out a mass of lower
1563     priority ones.
1564     .PP
1565     Static (ordering) priorities are most useful when you have two or more
1566     watchers handling the same resource: a typical usage example is having an
1567     \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1568     timeouts. Under load, data might be received while the program handles
1569     other jobs, but since timers normally get invoked first, the timeout
1570     handler will be executed before checking for data. In that case, giving
1571     the timer a lower priority than the I/O watcher ensures that I/O will be
1572     handled first even under adverse conditions (which is usually, but not
1573     always, what you want).
1574     .PP
1575     Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1576     will only be executed when no same or higher priority watchers have
1577     received events, they can be used to implement the \*(L"lock-out\*(R" model when
1578     required.
1579     .PP
1580     For example, to emulate how many other event libraries handle priorities,
1581     you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1582     the normal watcher callback, you just start the idle watcher. The real
1583     processing is done in the idle watcher callback. This causes libev to
1584 root 1.82 continuously poll and process kernel event data for the watcher, but when
1585 root 1.78 the lock-out case is known to be rare (which in turn is rare :), this is
1586     workable.
1587     .PP
1588     Usually, however, the lock-out model implemented that way will perform
1589     miserably under the type of load it was designed to handle. In that case,
1590     it might be preferable to stop the real watcher before starting the
1591     idle watcher, so the kernel will not have to process the event in case
1592     the actual processing will be delayed for considerable time.
1593     .PP
1594     Here is an example of an I/O watcher that should run at a strictly lower
1595     priority than the default, and which should only process data when no
1596     other events are pending:
1597     .PP
1598     .Vb 2
1599     \& ev_idle idle; // actual processing watcher
1600     \& ev_io io; // actual event watcher
1601     \&
1602     \& static void
1603     \& io_cb (EV_P_ ev_io *w, int revents)
1604     \& {
1605     \& // stop the I/O watcher, we received the event, but
1606     \& // are not yet ready to handle it.
1607     \& ev_io_stop (EV_A_ w);
1608     \&
1609 root 1.82 \& // start the idle watcher to handle the actual event.
1610 root 1.78 \& // it will not be executed as long as other watchers
1611     \& // with the default priority are receiving events.
1612     \& ev_idle_start (EV_A_ &idle);
1613     \& }
1614     \&
1615     \& static void
1616 root 1.79 \& idle_cb (EV_P_ ev_idle *w, int revents)
1617 root 1.78 \& {
1618     \& // actual processing
1619     \& read (STDIN_FILENO, ...);
1620     \&
1621     \& // have to start the I/O watcher again, as
1622     \& // we have handled the event
1623     \& ev_io_start (EV_P_ &io);
1624     \& }
1625     \&
1626     \& // initialisation
1627     \& ev_idle_init (&idle, idle_cb);
1628     \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1629     \& ev_io_start (EV_DEFAULT_ &io);
1630     .Ve
1631     .PP
1632     In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1633     low-priority connections can not be locked out forever under load. This
1634     enables your program to keep a lower latency for important connections
1635     during short periods of high load, while not completely locking out less
1636     important ones.
1637 root 1.1 .SH "WATCHER TYPES"
1638     .IX Header "WATCHER TYPES"
1639     This section describes each watcher in detail, but will not repeat
1640 root 1.22 information given in the last section. Any initialisation/set macros,
1641     functions and members specific to the watcher type are explained.
1642     .PP
1643     Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1644     while the watcher is active, you can look at the member and expect some
1645     sensible content, but you must not modify it (you can modify it while the
1646     watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1647     means you can expect it to have some sensible content while the watcher
1648     is active, but you can also modify it. Modifying it may not do something
1649     sensible or take immediate effect (or do anything at all), but libev will
1650     not crash or malfunction in any way.
1651 root 1.79 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1652     .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1653 root 1.17 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1654 root 1.1 I/O watchers check whether a file descriptor is readable or writable
1655 root 1.17 in each iteration of the event loop, or, more precisely, when reading
1656     would not block the process and writing would at least be able to write
1657     some data. This behaviour is called level-triggering because you keep
1658     receiving events as long as the condition persists. Remember you can stop
1659     the watcher if you don't want to act on the event and neither want to
1660     receive future events.
1661 root 1.1 .PP
1662     In general you can register as many read and/or write event watchers per
1663     fd as you want (as long as you don't confuse yourself). Setting all file
1664     descriptors to non-blocking mode is also usually a good idea (but not
1665     required if you know what you are doing).
1666     .PP
1667 root 1.17 Another thing you have to watch out for is that it is quite easy to
1668 root 1.85 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1669 root 1.17 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1670 root 1.85 because there is no data. It is very easy to get into this situation even
1671     with a relatively standard program structure. Thus it is best to always
1672     use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1673     preferable to a program hanging until some data arrives.
1674 root 1.17 .PP
1675 root 1.71 If you cannot run the fd in non-blocking mode (for example you should
1676     not play around with an Xlib connection), then you have to separately
1677     re-test whether a file descriptor is really ready with a known-to-be good
1678 root 1.85 interface such as poll (fortunately in the case of Xlib, it already does
1679     this on its own, so its quite safe to use). Some people additionally
1680 root 1.71 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1681     indefinitely.
1682     .PP
1683     But really, best use non-blocking mode.
1684 root 1.49 .PP
1685     \fIThe special problem of disappearing file descriptors\fR
1686     .IX Subsection "The special problem of disappearing file descriptors"
1687     .PP
1688 root 1.54 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1689 root 1.71 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1690     such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1691 root 1.49 descriptor, but when it goes away, the operating system will silently drop
1692     this interest. If another file descriptor with the same number then is
1693     registered with libev, there is no efficient way to see that this is, in
1694     fact, a different file descriptor.
1695     .PP
1696     To avoid having to explicitly tell libev about such cases, libev follows
1697     the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1698     will assume that this is potentially a new file descriptor, otherwise
1699     it is assumed that the file descriptor stays the same. That means that
1700     you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
1701     descriptor even if the file descriptor number itself did not change.
1702     .PP
1703     This is how one would do it normally anyway, the important point is that
1704     the libev application should not optimise around libev but should leave
1705     optimisations to libev.
1706 root 1.50 .PP
1707 root 1.55 \fIThe special problem of dup'ed file descriptors\fR
1708     .IX Subsection "The special problem of dup'ed file descriptors"
1709 root 1.54 .PP
1710     Some backends (e.g. epoll), cannot register events for file descriptors,
1711 root 1.59 but only events for the underlying file descriptions. That means when you
1712     have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1713     events for them, only one file descriptor might actually receive events.
1714 root 1.54 .PP
1715 root 1.59 There is no workaround possible except not registering events
1716     for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1717 root 1.54 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1718     .PP
1719 root 1.85 \fIThe special problem of files\fR
1720     .IX Subsection "The special problem of files"
1721     .PP
1722     Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1723     representing files, and expect it to become ready when their program
1724     doesn't block on disk accesses (which can take a long time on their own).
1725     .PP
1726     However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1727     notification as soon as the kernel knows whether and how much data is
1728     there, and in the case of open files, that's always the case, so you
1729     always get a readiness notification instantly, and your read (or possibly
1730     write) will still block on the disk I/O.
1731     .PP
1732     Another way to view it is that in the case of sockets, pipes, character
1733     devices and so on, there is another party (the sender) that delivers data
1734     on its own, but in the case of files, there is no such thing: the disk
1735     will not send data on its own, simply because it doesn't know what you
1736     wish to read \- you would first have to request some data.
1737     .PP
1738     Since files are typically not-so-well supported by advanced notification
1739     mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1740     to files, even though you should not use it. The reason for this is
1741     convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1742     usually a tty, often a pipe, but also sometimes files or special devices
1743     (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1744     \&\fI/dev/urandom\fR), and even though the file might better be served with
1745     asynchronous I/O instead of with non-blocking I/O, it is still useful when
1746     it \*(L"just works\*(R" instead of freezing.
1747     .PP
1748     So avoid file descriptors pointing to files when you know it (e.g. use
1749     libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1750     when you rarely read from a file instead of from a socket, and want to
1751     reuse the same code path.
1752     .PP
1753 root 1.54 \fIThe special problem of fork\fR
1754     .IX Subsection "The special problem of fork"
1755     .PP
1756     Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1757     useless behaviour. Libev fully supports fork, but needs to be told about
1758 root 1.85 it in the child if you want to continue to use it in the child.
1759 root 1.54 .PP
1760 root 1.85 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1761     ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1762     \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1763 root 1.54 .PP
1764 root 1.63 \fIThe special problem of \s-1SIGPIPE\s0\fR
1765     .IX Subsection "The special problem of SIGPIPE"
1766     .PP
1767 root 1.71 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1768     when writing to a pipe whose other end has been closed, your program gets
1769     sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1770     this is sensible behaviour, for daemons, this is usually undesirable.
1771 root 1.63 .PP
1772     So when you encounter spurious, unexplained daemon exits, make sure you
1773     ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1774     somewhere, as that would have given you a big clue).
1775     .PP
1776 root 1.82 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1777     .IX Subsection "The special problem of accept()ing when you can't"
1778     .PP
1779     Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1780     found in post\-2004 Linux) have the peculiar behaviour of not removing a
1781     connection from the pending queue in all error cases.
1782     .PP
1783     For example, larger servers often run out of file descriptors (because
1784     of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1785     rejecting the connection, leading to libev signalling readiness on
1786     the next iteration again (the connection still exists after all), and
1787     typically causing the program to loop at 100% \s-1CPU\s0 usage.
1788     .PP
1789     Unfortunately, the set of errors that cause this issue differs between
1790     operating systems, there is usually little the app can do to remedy the
1791     situation, and no known thread-safe method of removing the connection to
1792     cope with overload is known (to me).
1793     .PP
1794     One of the easiest ways to handle this situation is to just ignore it
1795     \&\- when the program encounters an overload, it will just loop until the
1796     situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1797     event-based way to handle this situation, so it's the best one can do.
1798     .PP
1799     A better way to handle the situation is to log any errors other than
1800     \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1801     messages, and continue as usual, which at least gives the user an idea of
1802     what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1803     the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1804     usage.
1805     .PP
1806     If your program is single-threaded, then you could also keep a dummy file
1807     descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1808     when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1809     close that fd, and create a new dummy fd. This will gracefully refuse
1810     clients under typical overload conditions.
1811     .PP
1812     The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1813     is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1814     opportunity for a DoS attack.
1815     .PP
1816 root 1.50 \fIWatcher-Specific Functions\fR
1817     .IX Subsection "Watcher-Specific Functions"
1818 root 1.1 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1819     .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1820     .PD 0
1821     .IP "ev_io_set (ev_io *, int fd, int events)" 4
1822     .IX Item "ev_io_set (ev_io *, int fd, int events)"
1823     .PD
1824 root 1.17 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1825 root 1.71 receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1826     \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1827 root 1.22 .IP "int fd [read\-only]" 4
1828     .IX Item "int fd [read-only]"
1829     The file descriptor being watched.
1830     .IP "int events [read\-only]" 4
1831     .IX Item "int events [read-only]"
1832     The events being watched.
1833 root 1.9 .PP
1834 root 1.60 \fIExamples\fR
1835     .IX Subsection "Examples"
1836     .PP
1837 root 1.28 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1838 root 1.60 readable, but only once. Since it is likely line-buffered, you could
1839 root 1.28 attempt to read a whole line in the callback.
1840 root 1.9 .PP
1841     .Vb 6
1842 root 1.68 \& static void
1843 root 1.73 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1844 root 1.68 \& {
1845     \& ev_io_stop (loop, w);
1846 root 1.71 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1847 root 1.68 \& }
1848     \&
1849     \& ...
1850     \& struct ev_loop *loop = ev_default_init (0);
1851 root 1.73 \& ev_io stdin_readable;
1852 root 1.68 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1853     \& ev_io_start (loop, &stdin_readable);
1854 root 1.82 \& ev_run (loop, 0);
1855 root 1.9 .Ve
1856 root 1.79 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1857     .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1858 root 1.17 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1859 root 1.1 Timer watchers are simple relative timers that generate an event after a
1860     given time, and optionally repeating in regular intervals after that.
1861     .PP
1862     The timers are based on real time, that is, if you register an event that
1863 root 1.68 times out after an hour and you reset your system clock to January last
1864 root 1.71 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1865 root 1.2 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1866 root 1.1 monotonic clock option helps a lot here).
1867     .PP
1868 root 1.71 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1869 root 1.78 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1870     might introduce a small delay). If multiple timers become ready during the
1871     same loop iteration then the ones with earlier time-out values are invoked
1872 root 1.79 before ones of the same priority with later time-out values (but this is
1873 root 1.82 no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1874 root 1.71 .PP
1875 root 1.73 \fIBe smart about timeouts\fR
1876     .IX Subsection "Be smart about timeouts"
1877     .PP
1878     Many real-world problems involve some kind of timeout, usually for error
1879     recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1880     you want to raise some error after a while.
1881     .PP
1882     What follows are some ways to handle this problem, from obvious and
1883     inefficient to smart and efficient.
1884     .PP
1885     In the following, a 60 second activity timeout is assumed \- a timeout that
1886     gets reset to 60 seconds each time there is activity (e.g. each time some
1887     data or other life sign was received).
1888     .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1889     .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1890     This is the most obvious, but not the most simple way: In the beginning,
1891     start the watcher:
1892     .Sp
1893     .Vb 2
1894     \& ev_timer_init (timer, callback, 60., 0.);
1895     \& ev_timer_start (loop, timer);
1896     .Ve
1897     .Sp
1898     Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1899     and start it again:
1900     .Sp
1901     .Vb 3
1902     \& ev_timer_stop (loop, timer);
1903     \& ev_timer_set (timer, 60., 0.);
1904     \& ev_timer_start (loop, timer);
1905     .Ve
1906     .Sp
1907     This is relatively simple to implement, but means that each time there is
1908     some activity, libev will first have to remove the timer from its internal
1909     data structure and then add it again. Libev tries to be fast, but it's
1910     still not a constant-time operation.
1911     .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1912     .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1913     .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1914     This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1915     \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1916     .Sp
1917     To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1918     of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1919     successfully read or write some data. If you go into an idle state where
1920     you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1921     the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1922     .Sp
1923     That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1924     \&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
1925     member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1926     .Sp
1927     At start:
1928     .Sp
1929     .Vb 3
1930 root 1.79 \& ev_init (timer, callback);
1931 root 1.73 \& timer\->repeat = 60.;
1932     \& ev_timer_again (loop, timer);
1933     .Ve
1934     .Sp
1935     Each time there is some activity:
1936     .Sp
1937     .Vb 1
1938     \& ev_timer_again (loop, timer);
1939     .Ve
1940     .Sp
1941     It is even possible to change the time-out on the fly, regardless of
1942     whether the watcher is active or not:
1943     .Sp
1944     .Vb 2
1945     \& timer\->repeat = 30.;
1946     \& ev_timer_again (loop, timer);
1947     .Ve
1948     .Sp
1949     This is slightly more efficient then stopping/starting the timer each time
1950     you want to modify its timeout value, as libev does not have to completely
1951     remove and re-insert the timer from/into its internal data structure.
1952     .Sp
1953     It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1954     .IP "3. Let the timer time out, but then re-arm it as required." 4
1955     .IX Item "3. Let the timer time out, but then re-arm it as required."
1956     This method is more tricky, but usually most efficient: Most timeouts are
1957     relatively long compared to the intervals between other activity \- in
1958     our example, within 60 seconds, there are usually many I/O events with
1959     associated activity resets.
1960     .Sp
1961     In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1962     but remember the time of last activity, and check for a real timeout only
1963     within the callback:
1964     .Sp
1965     .Vb 1
1966     \& ev_tstamp last_activity; // time of last activity
1967     \&
1968     \& static void
1969     \& callback (EV_P_ ev_timer *w, int revents)
1970     \& {
1971     \& ev_tstamp now = ev_now (EV_A);
1972     \& ev_tstamp timeout = last_activity + 60.;
1973     \&
1974     \& // if last_activity + 60. is older than now, we did time out
1975     \& if (timeout < now)
1976     \& {
1977 root 1.82 \& // timeout occurred, take action
1978 root 1.73 \& }
1979     \& else
1980     \& {
1981     \& // callback was invoked, but there was some activity, re\-arm
1982     \& // the watcher to fire in last_activity + 60, which is
1983     \& // guaranteed to be in the future, so "again" is positive:
1984 root 1.74 \& w\->repeat = timeout \- now;
1985 root 1.73 \& ev_timer_again (EV_A_ w);
1986     \& }
1987     \& }
1988     .Ve
1989     .Sp
1990     To summarise the callback: first calculate the real timeout (defined
1991     as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1992     been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1993     the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1994     re-schedule the timer to fire at that future time, to see if maybe we have
1995     a timeout then.
1996     .Sp
1997     Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1998     \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1999     .Sp
2000     This scheme causes more callback invocations (about one every 60 seconds
2001     minus half the average time between activity), but virtually no calls to
2002     libev to change the timeout.
2003     .Sp
2004     To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
2005     to the current time (meaning we just have some activity :), then call the
2006     callback, which will \*(L"do the right thing\*(R" and start the timer:
2007     .Sp
2008     .Vb 3
2009 root 1.79 \& ev_init (timer, callback);
2010 root 1.73 \& last_activity = ev_now (loop);
2011 root 1.82 \& callback (loop, timer, EV_TIMER);
2012 root 1.73 .Ve
2013     .Sp
2014     And when there is some activity, simply store the current time in
2015     \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2016     .Sp
2017     .Vb 1
2018 root 1.82 \& last_activity = ev_now (loop);
2019 root 1.73 .Ve
2020     .Sp
2021     This technique is slightly more complex, but in most cases where the
2022     time-out is unlikely to be triggered, much more efficient.
2023     .Sp
2024     Changing the timeout is trivial as well (if it isn't hard-coded in the
2025     callback :) \- just change the timeout and invoke the callback, which will
2026     fix things for you.
2027     .IP "4. Wee, just use a double-linked list for your timeouts." 4
2028     .IX Item "4. Wee, just use a double-linked list for your timeouts."
2029     If there is not one request, but many thousands (millions...), all
2030     employing some kind of timeout with the same timeout value, then one can
2031     do even better:
2032     .Sp
2033     When starting the timeout, calculate the timeout value and put the timeout
2034     at the \fIend\fR of the list.
2035     .Sp
2036     Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2037     the list is expected to fire (for example, using the technique #3).
2038     .Sp
2039     When there is some activity, remove the timer from the list, recalculate
2040     the timeout, append it to the end of the list again, and make sure to
2041     update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2042     .Sp
2043     This way, one can manage an unlimited number of timeouts in O(1) time for
2044     starting, stopping and updating the timers, at the expense of a major
2045     complication, and having to use a constant timeout. The constant timeout
2046     ensures that the list stays sorted.
2047     .PP
2048     So which method the best?
2049     .PP
2050     Method #2 is a simple no-brain-required solution that is adequate in most
2051     situations. Method #3 requires a bit more thinking, but handles many cases
2052     better, and isn't very complicated either. In most case, choosing either
2053     one is fine, with #3 being better in typical situations.
2054     .PP
2055     Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2056     rather complicated, but extremely efficient, something that really pays
2057     off after the first million or so of active timers, i.e. it's usually
2058     overkill :)
2059     .PP
2060 root 1.71 \fIThe special problem of time updates\fR
2061     .IX Subsection "The special problem of time updates"
2062     .PP
2063     Establishing the current time is a costly operation (it usually takes at
2064     least two system calls): \s-1EV\s0 therefore updates its idea of the current
2065 root 1.82 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2066 root 1.71 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2067     lots of events in one iteration.
2068     .PP
2069 root 1.1 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2070     time. This is usually the right thing as this timestamp refers to the time
2071 root 1.2 of the event triggering whatever timeout you are modifying/starting. If
2072 root 1.71 you suspect event processing to be delayed and you \fIneed\fR to base the
2073     timeout on the current time, use something like this to adjust for this:
2074 root 1.1 .PP
2075     .Vb 1
2076 root 1.60 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
2077 root 1.1 .Ve
2078 root 1.2 .PP
2079 root 1.71 If the event loop is suspended for a long time, you can also force an
2080     update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2081     ()\*(C'\fR.
2082 root 1.50 .PP
2083 root 1.79 \fIThe special problems of suspended animation\fR
2084     .IX Subsection "The special problems of suspended animation"
2085     .PP
2086     When you leave the server world it is quite customary to hit machines that
2087     can suspend/hibernate \- what happens to the clocks during such a suspend?
2088     .PP
2089     Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2090     all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2091     to run until the system is suspended, but they will not advance while the
2092     system is suspended. That means, on resume, it will be as if the program
2093     was frozen for a few seconds, but the suspend time will not be counted
2094     towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2095     clock advanced as expected, but if it is used as sole clocksource, then a
2096     long suspend would be detected as a time jump by libev, and timers would
2097     be adjusted accordingly.
2098     .PP
2099     I would not be surprised to see different behaviour in different between
2100     operating systems, \s-1OS\s0 versions or even different hardware.
2101     .PP
2102     The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2103     time jump in the monotonic clocks and the realtime clock. If the program
2104     is suspended for a very long time, and monotonic clock sources are in use,
2105     then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2106     will be counted towards the timers. When no monotonic clock source is in
2107     use, then libev will again assume a timejump and adjust accordingly.
2108     .PP
2109     It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2110     and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2111     deterministic behaviour in this case (you can do nothing against
2112     \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2113     .PP
2114 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2115     .IX Subsection "Watcher-Specific Functions and Data Members"
2116 root 1.1 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2117     .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2118     .PD 0
2119     .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2120     .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2121     .PD
2122 root 1.67 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2123     is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2124     reached. If it is positive, then the timer will automatically be
2125     configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2126     until stopped manually.
2127     .Sp
2128     The timer itself will do a best-effort at avoiding drift, that is, if
2129     you configure a timer to trigger every 10 seconds, then it will normally
2130     trigger at exactly 10 second intervals. If, however, your program cannot
2131     keep up with the timer (because it takes longer than those 10 seconds to
2132     do stuff) the timer will not fire more than once per event loop iteration.
2133 root 1.61 .IP "ev_timer_again (loop, ev_timer *)" 4
2134     .IX Item "ev_timer_again (loop, ev_timer *)"
2135 root 1.1 This will act as if the timer timed out and restart it again if it is
2136     repeating. The exact semantics are:
2137     .Sp
2138 root 1.34 If the timer is pending, its pending status is cleared.
2139 root 1.1 .Sp
2140 root 1.68 If the timer is started but non-repeating, stop it (as if it timed out).
2141 root 1.34 .Sp
2142     If the timer is repeating, either start it if necessary (with the
2143     \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
2144 root 1.1 .Sp
2145 root 1.73 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2146     usage example.
2147 root 1.81 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2148     .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2149 root 1.79 Returns the remaining time until a timer fires. If the timer is active,
2150     then this time is relative to the current event loop time, otherwise it's
2151     the timeout value currently configured.
2152     .Sp
2153     That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2154 root 1.82 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2155 root 1.79 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2156     roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2157     too), and so on.
2158 root 1.22 .IP "ev_tstamp repeat [read\-write]" 4
2159     .IX Item "ev_tstamp repeat [read-write]"
2160     The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2161 root 1.71 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2162 root 1.22 which is also when any modifications are taken into account.
2163 root 1.9 .PP
2164 root 1.60 \fIExamples\fR
2165     .IX Subsection "Examples"
2166     .PP
2167 root 1.28 Example: Create a timer that fires after 60 seconds.
2168 root 1.9 .PP
2169     .Vb 5
2170 root 1.68 \& static void
2171 root 1.73 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2172 root 1.68 \& {
2173     \& .. one minute over, w is actually stopped right here
2174     \& }
2175     \&
2176 root 1.73 \& ev_timer mytimer;
2177 root 1.68 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2178     \& ev_timer_start (loop, &mytimer);
2179 root 1.9 .Ve
2180     .PP
2181 root 1.28 Example: Create a timeout timer that times out after 10 seconds of
2182 root 1.9 inactivity.
2183     .PP
2184     .Vb 5
2185 root 1.68 \& static void
2186 root 1.73 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2187 root 1.68 \& {
2188     \& .. ten seconds without any activity
2189     \& }
2190     \&
2191 root 1.73 \& ev_timer mytimer;
2192 root 1.68 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2193     \& ev_timer_again (&mytimer); /* start timer */
2194 root 1.82 \& ev_run (loop, 0);
2195 root 1.68 \&
2196     \& // and in some piece of code that gets executed on any "activity":
2197     \& // reset the timeout to start ticking again at 10 seconds
2198     \& ev_timer_again (&mytimer);
2199 root 1.9 .Ve
2200 root 1.79 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2201     .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2202 root 1.17 .IX Subsection "ev_periodic - to cron or not to cron?"
2203 root 1.1 Periodic watchers are also timers of a kind, but they are very versatile
2204     (and unfortunately a bit complex).
2205     .PP
2206 root 1.78 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2207     relative time, the physical time that passes) but on wall clock time
2208     (absolute time, the thing you can read on your calender or clock). The
2209     difference is that wall clock time can run faster or slower than real
2210     time, and time jumps are not uncommon (e.g. when you adjust your
2211     wrist-watch).
2212     .PP
2213     You can tell a periodic watcher to trigger after some specific point
2214     in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2215     seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2216     not a delay) and then reset your system clock to January of the previous
2217     year, then it will take a year or more to trigger the event (unlike an
2218     \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2219     it, as it uses a relative timeout).
2220     .PP
2221     \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2222     timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2223     other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2224     those cannot react to time jumps.
2225 root 1.2 .PP
2226 root 1.68 As with timers, the callback is guaranteed to be invoked only when the
2227 root 1.78 point in time where it is supposed to trigger has passed. If multiple
2228     timers become ready during the same loop iteration then the ones with
2229     earlier time-out values are invoked before ones with later time-out values
2230 root 1.82 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2231 root 1.50 .PP
2232     \fIWatcher-Specific Functions and Data Members\fR
2233     .IX Subsection "Watcher-Specific Functions and Data Members"
2234 root 1.78 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2235     .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2236 root 1.1 .PD 0
2237 root 1.78 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2238     .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2239 root 1.1 .PD
2240 root 1.78 Lots of arguments, let's sort it out... There are basically three modes of
2241 root 1.71 operation, and we will explain them from simplest to most complex:
2242 root 1.1 .RS 4
2243 root 1.60 .IP "\(bu" 4
2244 root 1.78 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2245 root 1.60 .Sp
2246 root 1.68 In this configuration the watcher triggers an event after the wall clock
2247 root 1.78 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2248     time jump occurs, that is, if it is to be run at January 1st 2011 then it
2249     will be stopped and invoked when the system clock reaches or surpasses
2250     this point in time.
2251 root 1.60 .IP "\(bu" 4
2252 root 1.78 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2253 root 1.60 .Sp
2254 root 1.1 In this mode the watcher will always be scheduled to time out at the next
2255 root 1.78 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2256     negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2257     argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2258 root 1.1 .Sp
2259 root 1.71 This can be used to create timers that do not drift with respect to the
2260 root 1.78 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2261     hour, on the hour (with respect to \s-1UTC\s0):
2262 root 1.1 .Sp
2263     .Vb 1
2264     \& ev_periodic_set (&periodic, 0., 3600., 0);
2265     .Ve
2266     .Sp
2267     This doesn't mean there will always be 3600 seconds in between triggers,
2268 root 1.68 but only that the callback will be called when the system time shows a
2269 root 1.1 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2270     by 3600.
2271     .Sp
2272     Another way to think about it (for the mathematically inclined) is that
2273     \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2274 root 1.78 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2275 root 1.46 .Sp
2276 root 1.78 For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2277 root 1.46 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2278 root 1.67 this value, and in fact is often specified as zero.
2279     .Sp
2280 root 1.68 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2281 root 1.67 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2282 root 1.68 will of course deteriorate. Libev itself tries to be exact to be about one
2283 root 1.67 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2284 root 1.60 .IP "\(bu" 4
2285 root 1.78 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2286 root 1.60 .Sp
2287 root 1.78 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2288 root 1.1 ignored. Instead, each time the periodic watcher gets scheduled, the
2289     reschedule callback will be called with the watcher as first, and the
2290     current time as second argument.
2291     .Sp
2292 root 1.78 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2293     or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2294     allowed by documentation here\fR.
2295 root 1.67 .Sp
2296     If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2297     it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2298     only event loop modification you are allowed to do).
2299 root 1.1 .Sp
2300 root 1.73 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2301 root 1.67 *w, ev_tstamp now)\*(C'\fR, e.g.:
2302 root 1.1 .Sp
2303 root 1.73 .Vb 5
2304     \& static ev_tstamp
2305     \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2306 root 1.1 \& {
2307     \& return now + 60.;
2308     \& }
2309     .Ve
2310     .Sp
2311     It must return the next time to trigger, based on the passed time value
2312     (that is, the lowest time value larger than to the second argument). It
2313     will usually be called just before the callback will be triggered, but
2314     might be called at other times, too.
2315     .Sp
2316 root 1.67 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2317     equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2318 root 1.1 .Sp
2319     This can be used to create very complex timers, such as a timer that
2320 root 1.67 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2321 root 1.1 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2322     you do this is, again, up to you (but it is not trivial, which is the main
2323     reason I omitted it as an example).
2324     .RE
2325     .RS 4
2326     .RE
2327     .IP "ev_periodic_again (loop, ev_periodic *)" 4
2328     .IX Item "ev_periodic_again (loop, ev_periodic *)"
2329     Simply stops and restarts the periodic watcher again. This is only useful
2330     when you changed some parameters or the reschedule callback would return
2331     a different time than the last time it was called (e.g. in a crond like
2332     program when the crontabs have changed).
2333 root 1.65 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2334     .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2335 root 1.78 When active, returns the absolute time that the watcher is supposed
2336     to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2337     \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2338     rescheduling modes.
2339 root 1.46 .IP "ev_tstamp offset [read\-write]" 4
2340     .IX Item "ev_tstamp offset [read-write]"
2341     When repeating, this contains the offset value, otherwise this is the
2342 root 1.78 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2343     although libev might modify this value for better numerical stability).
2344 root 1.46 .Sp
2345     Can be modified any time, but changes only take effect when the periodic
2346     timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2347 root 1.22 .IP "ev_tstamp interval [read\-write]" 4
2348     .IX Item "ev_tstamp interval [read-write]"
2349     The current interval value. Can be modified any time, but changes only
2350     take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2351     called.
2352 root 1.73 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2353     .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2354 root 1.22 The current reschedule callback, or \f(CW0\fR, if this functionality is
2355     switched off. Can be changed any time, but changes only take effect when
2356     the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2357 root 1.9 .PP
2358 root 1.60 \fIExamples\fR
2359     .IX Subsection "Examples"
2360     .PP
2361 root 1.28 Example: Call a callback every hour, or, more precisely, whenever the
2362 root 1.71 system time is divisible by 3600. The callback invocation times have
2363 root 1.68 potentially a lot of jitter, but good long-term stability.
2364 root 1.9 .PP
2365     .Vb 5
2366 root 1.68 \& static void
2367 root 1.82 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2368 root 1.68 \& {
2369     \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2370     \& }
2371     \&
2372 root 1.73 \& ev_periodic hourly_tick;
2373 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2374     \& ev_periodic_start (loop, &hourly_tick);
2375 root 1.9 .Ve
2376     .PP
2377 root 1.28 Example: The same as above, but use a reschedule callback to do it:
2378 root 1.9 .PP
2379     .Vb 1
2380 root 1.68 \& #include <math.h>
2381 root 1.60 \&
2382 root 1.68 \& static ev_tstamp
2383 root 1.73 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2384 root 1.68 \& {
2385 root 1.71 \& return now + (3600. \- fmod (now, 3600.));
2386 root 1.68 \& }
2387 root 1.60 \&
2388 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2389 root 1.9 .Ve
2390     .PP
2391 root 1.28 Example: Call a callback every hour, starting now:
2392 root 1.9 .PP
2393     .Vb 4
2394 root 1.73 \& ev_periodic hourly_tick;
2395 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb,
2396     \& fmod (ev_now (loop), 3600.), 3600., 0);
2397     \& ev_periodic_start (loop, &hourly_tick);
2398 root 1.9 .Ve
2399 root 1.79 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2400     .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2401 root 1.17 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2402 root 1.1 Signal watchers will trigger an event when the process receives a specific
2403     signal one or more times. Even though signals are very asynchronous, libev
2404 root 1.84 will try its best to deliver signals synchronously, i.e. as part of the
2405 root 1.1 normal event processing, like any other event.
2406     .PP
2407 root 1.80 If you want signals to be delivered truly asynchronously, just use
2408     \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2409     the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2410     synchronously wake up an event loop.
2411     .PP
2412     You can configure as many watchers as you like for the same signal, but
2413     only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2414     default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2415     \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2416     the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2417 root 1.71 .PP
2418 root 1.80 When the first watcher gets started will libev actually register something
2419 root 1.71 with the kernel (thus it coexists with your own signal handlers as long as
2420 root 1.80 you don't register any with libev for the same signal).
2421     .PP
2422 root 1.61 If possible and supported, libev will install its handlers with
2423 root 1.80 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2424     not be unduly interrupted. If you have a problem with system calls getting
2425     interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2426     and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2427 root 1.61 .PP
2428 root 1.81 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2429     .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2430     .PP
2431     Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2432     (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2433     stopping it again), that is, libev might or might not block the signal,
2434     and might or might not set or restore the installed signal handler.
2435     .PP
2436     While this does not matter for the signal disposition (libev never
2437     sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2438     \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2439     certain signals to be blocked.
2440     .PP
2441     This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2442     the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2443     choice usually).
2444     .PP
2445     The simplest way to ensure that the signal mask is reset in the child is
2446     to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2447     catch fork calls done by libraries (such as the libc) as well.
2448     .PP
2449     In current versions of libev, the signal will not be blocked indefinitely
2450     unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2451     the window of opportunity for problems, it will not go away, as libev
2452     \&\fIhas\fR to modify the signal mask, at least temporarily.
2453     .PP
2454     So I can't stress this enough: \fIIf you do not reset your signal mask when
2455     you expect it to be empty, you have a race condition in your code\fR. This
2456     is not a libev-specific thing, this is true for most event libraries.
2457     .PP
2458 root 1.85 \fIThe special problem of threads signal handling\fR
2459     .IX Subsection "The special problem of threads signal handling"
2460     .PP
2461     \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2462     a lot of functionality (sigfd, sigwait etc.) only really works if all
2463     threads in a process block signals, which is hard to achieve.
2464     .PP
2465     When you want to use sigwait (or mix libev signal handling with your own
2466     for the same signals), you can tackle this problem by globally blocking
2467     all signals before creating any threads (or creating them with a fully set
2468     sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2469     loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2470     these signals. You can pass on any signals that libev might be interested
2471     in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2472     .PP
2473 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2474     .IX Subsection "Watcher-Specific Functions and Data Members"
2475 root 1.1 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2476     .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2477     .PD 0
2478     .IP "ev_signal_set (ev_signal *, int signum)" 4
2479     .IX Item "ev_signal_set (ev_signal *, int signum)"
2480     .PD
2481     Configures the watcher to trigger on the given signal number (usually one
2482     of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2483 root 1.22 .IP "int signum [read\-only]" 4
2484     .IX Item "int signum [read-only]"
2485     The signal the watcher watches out for.
2486 root 1.61 .PP
2487     \fIExamples\fR
2488     .IX Subsection "Examples"
2489     .PP
2490 root 1.72 Example: Try to exit cleanly on \s-1SIGINT\s0.
2491 root 1.61 .PP
2492     .Vb 5
2493 root 1.68 \& static void
2494 root 1.73 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2495 root 1.68 \& {
2496 root 1.82 \& ev_break (loop, EVBREAK_ALL);
2497 root 1.68 \& }
2498     \&
2499 root 1.73 \& ev_signal signal_watcher;
2500 root 1.68 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2501 root 1.72 \& ev_signal_start (loop, &signal_watcher);
2502 root 1.61 .Ve
2503 root 1.79 .ie n .SS """ev_child"" \- watch out for process status changes"
2504     .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2505 root 1.17 .IX Subsection "ev_child - watch out for process status changes"
2506 root 1.1 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2507 root 1.71 some child status changes (most typically when a child of yours dies or
2508     exits). It is permissible to install a child watcher \fIafter\fR the child
2509     has been forked (which implies it might have already exited), as long
2510     as the event loop isn't entered (or is continued from a watcher), i.e.,
2511     forking and then immediately registering a watcher for the child is fine,
2512 root 1.79 but forking and registering a watcher a few event loop iterations later or
2513     in the next callback invocation is not.
2514 root 1.61 .PP
2515     Only the default event loop is capable of handling signals, and therefore
2516 root 1.68 you can only register child watchers in the default event loop.
2517 root 1.61 .PP
2518 root 1.79 Due to some design glitches inside libev, child watchers will always be
2519     handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2520     libev)
2521     .PP
2522 root 1.61 \fIProcess Interaction\fR
2523     .IX Subsection "Process Interaction"
2524     .PP
2525     Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2526 root 1.80 initialised. This is necessary to guarantee proper behaviour even if the
2527     first child watcher is started after the child exits. The occurrence
2528 root 1.61 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2529     synchronously as part of the event loop processing. Libev always reaps all
2530     children, even ones not watched.
2531     .PP
2532     \fIOverriding the Built-In Processing\fR
2533     .IX Subsection "Overriding the Built-In Processing"
2534     .PP
2535     Libev offers no special support for overriding the built-in child
2536     processing, but if your application collides with libev's default child
2537     handler, you can override it easily by installing your own handler for
2538     \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2539     default loop never gets destroyed. You are encouraged, however, to use an
2540     event-based approach to child reaping and thus use libev's support for
2541     that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2542 root 1.50 .PP
2543 root 1.71 \fIStopping the Child Watcher\fR
2544     .IX Subsection "Stopping the Child Watcher"
2545     .PP
2546     Currently, the child watcher never gets stopped, even when the
2547     child terminates, so normally one needs to stop the watcher in the
2548     callback. Future versions of libev might stop the watcher automatically
2549 root 1.80 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2550     problem).
2551 root 1.71 .PP
2552 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2553     .IX Subsection "Watcher-Specific Functions and Data Members"
2554 root 1.60 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2555     .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2556 root 1.1 .PD 0
2557 root 1.60 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2558     .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2559 root 1.1 .PD
2560     Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2561     \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2562     at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2563     the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2564     \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2565 root 1.60 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2566     activate the watcher when the process terminates) or \f(CW1\fR (additionally
2567     activate the watcher when the process is stopped or continued).
2568 root 1.22 .IP "int pid [read\-only]" 4
2569     .IX Item "int pid [read-only]"
2570     The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2571     .IP "int rpid [read\-write]" 4
2572     .IX Item "int rpid [read-write]"
2573     The process id that detected a status change.
2574     .IP "int rstatus [read\-write]" 4
2575     .IX Item "int rstatus [read-write]"
2576     The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2577     \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2578 root 1.9 .PP
2579 root 1.60 \fIExamples\fR
2580     .IX Subsection "Examples"
2581     .PP
2582 root 1.61 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2583     its completion.
2584 root 1.9 .PP
2585 root 1.61 .Vb 1
2586 root 1.68 \& ev_child cw;
2587 root 1.61 \&
2588 root 1.68 \& static void
2589 root 1.73 \& child_cb (EV_P_ ev_child *w, int revents)
2590 root 1.68 \& {
2591     \& ev_child_stop (EV_A_ w);
2592     \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2593     \& }
2594     \&
2595     \& pid_t pid = fork ();
2596     \&
2597     \& if (pid < 0)
2598     \& // error
2599     \& else if (pid == 0)
2600     \& {
2601     \& // the forked child executes here
2602     \& exit (1);
2603     \& }
2604     \& else
2605     \& {
2606     \& ev_child_init (&cw, child_cb, pid, 0);
2607     \& ev_child_start (EV_DEFAULT_ &cw);
2608     \& }
2609 root 1.9 .Ve
2610 root 1.79 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2611     .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2612 root 1.22 .IX Subsection "ev_stat - did the file attributes just change?"
2613 root 1.68 This watches a file system path for attribute changes. That is, it calls
2614 root 1.73 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2615     and sees if it changed compared to the last time, invoking the callback if
2616     it did.
2617 root 1.22 .PP
2618     The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2619 root 1.74 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2620     exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2621     \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2622     least one) and all the other fields of the stat buffer having unspecified
2623     contents.
2624 root 1.22 .PP
2625 root 1.73 The path \fImust not\fR end in a slash or contain special components such as
2626     \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2627     your working directory changes, then the behaviour is undefined.
2628     .PP
2629     Since there is no portable change notification interface available, the
2630     portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2631     to see if it changed somehow. You can specify a recommended polling
2632     interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2633     recommended!) then a \fIsuitable, unspecified default\fR value will be used
2634     (which you can expect to be around five seconds, although this might
2635     change dynamically). Libev will also impose a minimum interval which is
2636     currently around \f(CW0.1\fR, but that's usually overkill.
2637 root 1.22 .PP
2638     This watcher type is not meant for massive numbers of stat watchers,
2639     as even with OS-supported change notifications, this can be
2640 root 1.60 resource-intensive.
2641 root 1.22 .PP
2642 root 1.71 At the time of this writing, the only OS-specific interface implemented
2643 root 1.74 is the Linux inotify interface (implementing kqueue support is left as an
2644     exercise for the reader. Note, however, that the author sees no way of
2645     implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2646 root 1.50 .PP
2647 root 1.63 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2648     .IX Subsection "ABI Issues (Largefile Support)"
2649     .PP
2650     Libev by default (unless the user overrides this) uses the default
2651 root 1.69 compilation environment, which means that on systems with large file
2652     support disabled by default, you get the 32 bit version of the stat
2653 root 1.63 structure. When using the library from programs that change the \s-1ABI\s0 to
2654     use 64 bit file offsets the programs will fail. In that case you have to
2655     compile libev with the same flags to get binary compatibility. This is
2656     obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2657 root 1.73 most noticeably displayed with ev_stat and large file support.
2658 root 1.69 .PP
2659     The solution for this is to lobby your distribution maker to make large
2660     file interfaces available by default (as e.g. FreeBSD does) and not
2661     optional. Libev cannot simply switch on large file support because it has
2662     to exchange stat structures with application programs compiled using the
2663     default compilation environment.
2664 root 1.63 .PP
2665 root 1.71 \fIInotify and Kqueue\fR
2666     .IX Subsection "Inotify and Kqueue"
2667 root 1.59 .PP
2668 root 1.74 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2669     runtime, it will be used to speed up change detection where possible. The
2670     inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2671     watcher is being started.
2672 root 1.59 .PP
2673 root 1.65 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2674 root 1.59 except that changes might be detected earlier, and in some cases, to avoid
2675 root 1.65 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2676 root 1.71 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2677 root 1.74 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2678     many bugs), the path exists (i.e. stat succeeds), and the path resides on
2679     a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2680     xfs are fully working) libev usually gets away without polling.
2681 root 1.59 .PP
2682 root 1.71 There is no support for kqueue, as apparently it cannot be used to
2683 root 1.59 implement this functionality, due to the requirement of having a file
2684 root 1.71 descriptor open on the object at all times, and detecting renames, unlinks
2685     etc. is difficult.
2686 root 1.59 .PP
2687 root 1.74 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2688     .IX Subsection "stat () is a synchronous operation"
2689     .PP
2690     Libev doesn't normally do any kind of I/O itself, and so is not blocking
2691     the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2692     ()\*(C'\fR, which is a synchronous operation.
2693     .PP
2694     For local paths, this usually doesn't matter: unless the system is very
2695     busy or the intervals between stat's are large, a stat call will be fast,
2696 root 1.75 as the path data is usually in memory already (except when starting the
2697 root 1.74 watcher).
2698     .PP
2699     For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2700     time due to network issues, and even under good conditions, a stat call
2701     often takes multiple milliseconds.
2702     .PP
2703     Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2704     paths, although this is fully supported by libev.
2705     .PP
2706 root 1.59 \fIThe special problem of stat time resolution\fR
2707     .IX Subsection "The special problem of stat time resolution"
2708     .PP
2709 root 1.73 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2710     and even on systems where the resolution is higher, most file systems
2711     still only support whole seconds.
2712 root 1.59 .PP
2713 root 1.65 That means that, if the time is the only thing that changes, you can
2714     easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2715     calls your callback, which does something. When there is another update
2716 root 1.71 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2717     stat data does change in other ways (e.g. file size).
2718 root 1.65 .PP
2719     The solution to this is to delay acting on a change for slightly more
2720 root 1.67 than a second (or till slightly after the next full second boundary), using
2721 root 1.65 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2722     ev_timer_again (loop, w)\*(C'\fR).
2723     .PP
2724     The \f(CW.02\fR offset is added to work around small timing inconsistencies
2725     of some operating systems (where the second counter of the current time
2726     might be be delayed. One such system is the Linux kernel, where a call to
2727     \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2728     a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2729     update file times then there will be a small window where the kernel uses
2730     the previous second to update file times but libev might already execute
2731     the timer callback).
2732 root 1.59 .PP
2733 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2734     .IX Subsection "Watcher-Specific Functions and Data Members"
2735 root 1.22 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2736     .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2737     .PD 0
2738     .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2739     .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2740     .PD
2741     Configures the watcher to wait for status changes of the given
2742     \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2743     be detected and should normally be specified as \f(CW0\fR to let libev choose
2744     a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2745     path for as long as the watcher is active.
2746     .Sp
2747 root 1.71 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2748     relative to the attributes at the time the watcher was started (or the
2749     last change was detected).
2750 root 1.61 .IP "ev_stat_stat (loop, ev_stat *)" 4
2751     .IX Item "ev_stat_stat (loop, ev_stat *)"
2752 root 1.22 Updates the stat buffer immediately with new values. If you change the
2753 root 1.65 watched path in your callback, you could call this function to avoid
2754     detecting this change (while introducing a race condition if you are not
2755     the only one changing the path). Can also be useful simply to find out the
2756     new values.
2757 root 1.22 .IP "ev_statdata attr [read\-only]" 4
2758     .IX Item "ev_statdata attr [read-only]"
2759 root 1.65 The most-recently detected attributes of the file. Although the type is
2760 root 1.22 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2761 root 1.65 suitable for your system, but you can only rely on the POSIX-standardised
2762     members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2763     some error while \f(CW\*(C`stat\*(C'\fRing the file.
2764 root 1.22 .IP "ev_statdata prev [read\-only]" 4
2765     .IX Item "ev_statdata prev [read-only]"
2766     The previous attributes of the file. The callback gets invoked whenever
2767 root 1.65 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2768     differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
2769     \&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
2770 root 1.22 .IP "ev_tstamp interval [read\-only]" 4
2771     .IX Item "ev_tstamp interval [read-only]"
2772     The specified interval.
2773     .IP "const char *path [read\-only]" 4
2774     .IX Item "const char *path [read-only]"
2775 root 1.68 The file system path that is being watched.
2776 root 1.22 .PP
2777 root 1.59 \fIExamples\fR
2778     .IX Subsection "Examples"
2779     .PP
2780 root 1.22 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2781     .PP
2782 root 1.60 .Vb 10
2783 root 1.68 \& static void
2784     \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2785     \& {
2786     \& /* /etc/passwd changed in some way */
2787     \& if (w\->attr.st_nlink)
2788     \& {
2789     \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2790     \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2791     \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2792     \& }
2793     \& else
2794     \& /* you shalt not abuse printf for puts */
2795     \& puts ("wow, /etc/passwd is not there, expect problems. "
2796     \& "if this is windows, they already arrived\en");
2797     \& }
2798 root 1.60 \&
2799 root 1.68 \& ...
2800     \& ev_stat passwd;
2801 root 1.60 \&
2802 root 1.68 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2803     \& ev_stat_start (loop, &passwd);
2804 root 1.22 .Ve
2805 root 1.59 .PP
2806     Example: Like above, but additionally use a one-second delay so we do not
2807     miss updates (however, frequent updates will delay processing, too, so
2808     one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2809     \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2810     .PP
2811     .Vb 2
2812 root 1.68 \& static ev_stat passwd;
2813     \& static ev_timer timer;
2814 root 1.60 \&
2815 root 1.68 \& static void
2816     \& timer_cb (EV_P_ ev_timer *w, int revents)
2817     \& {
2818     \& ev_timer_stop (EV_A_ w);
2819     \&
2820     \& /* now it\*(Aqs one second after the most recent passwd change */
2821     \& }
2822     \&
2823     \& static void
2824     \& stat_cb (EV_P_ ev_stat *w, int revents)
2825     \& {
2826     \& /* reset the one\-second timer */
2827     \& ev_timer_again (EV_A_ &timer);
2828     \& }
2829     \&
2830     \& ...
2831     \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2832     \& ev_stat_start (loop, &passwd);
2833     \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2834 root 1.59 .Ve
2835 root 1.79 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2836     .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2837 root 1.17 .IX Subsection "ev_idle - when you've got nothing better to do..."
2838 root 1.37 Idle watchers trigger events when no other events of the same or higher
2839 root 1.71 priority are pending (prepare, check and other idle watchers do not count
2840     as receiving \*(L"events\*(R").
2841 root 1.37 .PP
2842     That is, as long as your process is busy handling sockets or timeouts
2843     (or even signals, imagine) of the same or higher priority it will not be
2844     triggered. But when your process is idle (or only lower-priority watchers
2845     are pending), the idle watchers are being called once per event loop
2846     iteration \- until stopped, that is, or your process receives more events
2847     and becomes busy again with higher priority stuff.
2848 root 1.1 .PP
2849     The most noteworthy effect is that as long as any idle watchers are
2850     active, the process will not block when waiting for new events.
2851     .PP
2852     Apart from keeping your process non-blocking (which is a useful
2853     effect on its own sometimes), idle watchers are a good place to do
2854 root 1.60 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2855 root 1.1 event loop has handled all outstanding events.
2856 root 1.50 .PP
2857     \fIWatcher-Specific Functions and Data Members\fR
2858     .IX Subsection "Watcher-Specific Functions and Data Members"
2859 root 1.78 .IP "ev_idle_init (ev_idle *, callback)" 4
2860     .IX Item "ev_idle_init (ev_idle *, callback)"
2861 root 1.1 Initialises and configures the idle watcher \- it has no parameters of any
2862     kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2863     believe me.
2864 root 1.9 .PP
2865 root 1.60 \fIExamples\fR
2866     .IX Subsection "Examples"
2867     .PP
2868 root 1.28 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2869     callback, free it. Also, use no error checking, as usual.
2870 root 1.9 .PP
2871     .Vb 7
2872 root 1.68 \& static void
2873 root 1.73 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2874 root 1.68 \& {
2875     \& free (w);
2876     \& // now do something you wanted to do when the program has
2877     \& // no longer anything immediate to do.
2878     \& }
2879     \&
2880 root 1.73 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2881 root 1.68 \& ev_idle_init (idle_watcher, idle_cb);
2882 root 1.79 \& ev_idle_start (loop, idle_watcher);
2883 root 1.9 .Ve
2884 root 1.79 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
2885     .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2886 root 1.17 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2887 root 1.71 Prepare and check watchers are usually (but not always) used in pairs:
2888 root 1.1 prepare watchers get invoked before the process blocks and check watchers
2889     afterwards.
2890     .PP
2891 root 1.82 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2892 root 1.20 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2893     watchers. Other loops than the current one are fine, however. The
2894     rationale behind this is that you do not need to check for recursion in
2895     those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2896     \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2897     called in pairs bracketing the blocking call.
2898     .PP
2899 root 1.10 Their main purpose is to integrate other event mechanisms into libev and
2900 root 1.71 their use is somewhat advanced. They could be used, for example, to track
2901 root 1.10 variable changes, implement your own watchers, integrate net-snmp or a
2902 root 1.20 coroutine library and lots more. They are also occasionally useful if
2903     you cache some data and want to flush it before blocking (for example,
2904     in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2905     watcher).
2906 root 1.1 .PP
2907 root 1.71 This is done by examining in each prepare call which file descriptors
2908     need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2909     for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2910     libraries provide exactly this functionality). Then, in the check watcher,
2911     you check for any events that occurred (by checking the pending status
2912     of all watchers and stopping them) and call back into the library. The
2913     I/O and timer callbacks will never actually be called (but must be valid
2914     nevertheless, because you never know, you know?).
2915 root 1.1 .PP
2916     As another example, the Perl Coro module uses these hooks to integrate
2917     coroutines into libev programs, by yielding to other active coroutines
2918     during each prepare and only letting the process block if no coroutines
2919     are ready to run (it's actually more complicated: it only runs coroutines
2920     with priority higher than or equal to the event loop and one coroutine
2921     of lower priority, but only once, using idle watchers to keep the event
2922     loop from blocking if lower-priority coroutines are active, thus mapping
2923     low-priority coroutines to idle/background tasks).
2924 root 1.45 .PP
2925     It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2926     priority, to ensure that they are being run before any other watchers
2927 root 1.71 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2928     .PP
2929     Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2930     activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2931     might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2932     \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2933     loops those other event loops might be in an unusable state until their
2934     \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2935     others).
2936 root 1.50 .PP
2937     \fIWatcher-Specific Functions and Data Members\fR
2938     .IX Subsection "Watcher-Specific Functions and Data Members"
2939 root 1.1 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2940     .IX Item "ev_prepare_init (ev_prepare *, callback)"
2941     .PD 0
2942     .IP "ev_check_init (ev_check *, callback)" 4
2943     .IX Item "ev_check_init (ev_check *, callback)"
2944     .PD
2945     Initialises and configures the prepare or check watcher \- they have no
2946     parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2947 root 1.71 macros, but using them is utterly, utterly, utterly and completely
2948     pointless.
2949 root 1.9 .PP
2950 root 1.60 \fIExamples\fR
2951     .IX Subsection "Examples"
2952     .PP
2953 root 1.44 There are a number of principal ways to embed other event loops or modules
2954     into libev. Here are some ideas on how to include libadns into libev
2955     (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2956 root 1.65 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2957     Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2958     Glib event loop).
2959 root 1.44 .PP
2960     Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2961     and in a check watcher, destroy them and call into libadns. What follows
2962     is pseudo-code only of course. This requires you to either use a low
2963     priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2964     the callbacks for the IO/timeout watchers might not have been called yet.
2965 root 1.20 .PP
2966     .Vb 2
2967 root 1.68 \& static ev_io iow [nfd];
2968     \& static ev_timer tw;
2969     \&
2970     \& static void
2971 root 1.73 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2972 root 1.68 \& {
2973     \& }
2974     \&
2975     \& // create io watchers for each fd and a timer before blocking
2976     \& static void
2977 root 1.73 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2978 root 1.68 \& {
2979     \& int timeout = 3600000;
2980     \& struct pollfd fds [nfd];
2981     \& // actual code will need to loop here and realloc etc.
2982     \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2983     \&
2984     \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2985 root 1.79 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2986 root 1.68 \& ev_timer_start (loop, &tw);
2987 root 1.60 \&
2988 root 1.68 \& // create one ev_io per pollfd
2989     \& for (int i = 0; i < nfd; ++i)
2990     \& {
2991     \& ev_io_init (iow + i, io_cb, fds [i].fd,
2992     \& ((fds [i].events & POLLIN ? EV_READ : 0)
2993     \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2994     \&
2995     \& fds [i].revents = 0;
2996     \& ev_io_start (loop, iow + i);
2997     \& }
2998     \& }
2999     \&
3000     \& // stop all watchers after blocking
3001     \& static void
3002 root 1.73 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3003 root 1.68 \& {
3004     \& ev_timer_stop (loop, &tw);
3005     \&
3006     \& for (int i = 0; i < nfd; ++i)
3007     \& {
3008     \& // set the relevant poll flags
3009     \& // could also call adns_processreadable etc. here
3010     \& struct pollfd *fd = fds + i;
3011     \& int revents = ev_clear_pending (iow + i);
3012     \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3013     \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3014 root 1.60 \&
3015 root 1.68 \& // now stop the watcher
3016     \& ev_io_stop (loop, iow + i);
3017     \& }
3018     \&
3019     \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3020     \& }
3021 root 1.20 .Ve
3022 root 1.44 .PP
3023     Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3024     in the prepare watcher and would dispose of the check watcher.
3025     .PP
3026     Method 3: If the module to be embedded supports explicit event
3027 root 1.68 notification (libadns does), you can also make use of the actual watcher
3028 root 1.44 callbacks, and only destroy/create the watchers in the prepare watcher.
3029     .PP
3030     .Vb 5
3031 root 1.68 \& static void
3032     \& timer_cb (EV_P_ ev_timer *w, int revents)
3033     \& {
3034     \& adns_state ads = (adns_state)w\->data;
3035     \& update_now (EV_A);
3036     \&
3037     \& adns_processtimeouts (ads, &tv_now);
3038     \& }
3039     \&
3040     \& static void
3041     \& io_cb (EV_P_ ev_io *w, int revents)
3042     \& {
3043     \& adns_state ads = (adns_state)w\->data;
3044     \& update_now (EV_A);
3045 root 1.60 \&
3046 root 1.68 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3047     \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3048     \& }
3049     \&
3050     \& // do not ever call adns_afterpoll
3051 root 1.44 .Ve
3052     .PP
3053     Method 4: Do not use a prepare or check watcher because the module you
3054 root 1.71 want to embed is not flexible enough to support it. Instead, you can
3055     override their poll function. The drawback with this solution is that the
3056     main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3057     this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3058     libglib event loop.
3059 root 1.44 .PP
3060     .Vb 4
3061 root 1.68 \& static gint
3062     \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3063     \& {
3064     \& int got_events = 0;
3065     \&
3066     \& for (n = 0; n < nfds; ++n)
3067     \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3068     \&
3069     \& if (timeout >= 0)
3070     \& // create/start timer
3071     \&
3072     \& // poll
3073 root 1.82 \& ev_run (EV_A_ 0);
3074 root 1.68 \&
3075     \& // stop timer again
3076     \& if (timeout >= 0)
3077     \& ev_timer_stop (EV_A_ &to);
3078 root 1.60 \&
3079 root 1.68 \& // stop io watchers again \- their callbacks should have set
3080     \& for (n = 0; n < nfds; ++n)
3081     \& ev_io_stop (EV_A_ iow [n]);
3082     \&
3083     \& return got_events;
3084     \& }
3085 root 1.44 .Ve
3086 root 1.79 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3087     .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3088 root 1.17 .IX Subsection "ev_embed - when one backend isn't enough..."
3089 root 1.10 This is a rather advanced watcher type that lets you embed one event loop
3090 root 1.11 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3091     loop, other types of watchers might be handled in a delayed or incorrect
3092 root 1.57 fashion and must not be used).
3093 root 1.10 .PP
3094     There are primarily two reasons you would want that: work around bugs and
3095     prioritise I/O.
3096     .PP
3097     As an example for a bug workaround, the kqueue backend might only support
3098     sockets on some platform, so it is unusable as generic backend, but you
3099     still want to make use of it because you have many sockets and it scales
3100 root 1.71 so nicely. In this case, you would create a kqueue-based loop and embed
3101     it into your default loop (which might use e.g. poll). Overall operation
3102     will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3103     \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3104     best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3105     .PP
3106     As for prioritising I/O: under rare circumstances you have the case where
3107     some fds have to be watched and handled very quickly (with low latency),
3108     and even priorities and idle watchers might have too much overhead. In
3109     this case you would put all the high priority stuff in one loop and all
3110     the rest in a second one, and embed the second one in the first.
3111 root 1.10 .PP
3112 root 1.75 As long as the watcher is active, the callback will be invoked every
3113     time there might be events pending in the embedded loop. The callback
3114     must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3115     sweep and invoke their callbacks (the callback doesn't need to invoke the
3116     \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3117     to give the embedded loop strictly lower priority for example).
3118     .PP
3119     You can also set the callback to \f(CW0\fR, in which case the embed watcher
3120     will automatically execute the embedded loop sweep whenever necessary.
3121     .PP
3122     Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3123     is active, i.e., the embedded loop will automatically be forked when the
3124     embedding loop forks. In other cases, the user is responsible for calling
3125     \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3126 root 1.10 .PP
3127 root 1.71 Unfortunately, not all backends are embeddable: only the ones returned by
3128 root 1.10 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3129     portable one.
3130     .PP
3131     So when you want to use this feature you will always have to be prepared
3132     that you cannot get an embeddable loop. The recommended way to get around
3133     this is to have a separate variables for your embeddable loop, try to
3134 root 1.60 create it, and if that fails, use the normal loop for everything.
3135 root 1.50 .PP
3136 root 1.71 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3137     .IX Subsection "ev_embed and fork"
3138     .PP
3139     While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3140     automatically be applied to the embedded loop as well, so no special
3141     fork handling is required in that case. When the watcher is not running,
3142     however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3143     as applicable.
3144     .PP
3145 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
3146     .IX Subsection "Watcher-Specific Functions and Data Members"
3147 root 1.11 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3148     .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3149 root 1.10 .PD 0
3150 root 1.11 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3151     .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3152 root 1.10 .PD
3153 root 1.11 Configures the watcher to embed the given loop, which must be
3154     embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3155     invoked automatically, otherwise it is the responsibility of the callback
3156     to invoke it (it will continue to be called until the sweep has been done,
3157 root 1.68 if you do not want that, you need to temporarily stop the embed watcher).
3158 root 1.11 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3159     .IX Item "ev_embed_sweep (loop, ev_embed *)"
3160     Make a single, non-blocking sweep over the embedded loop. This works
3161 root 1.82 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3162 root 1.68 appropriate way for embedded loops.
3163 root 1.54 .IP "struct ev_loop *other [read\-only]" 4
3164     .IX Item "struct ev_loop *other [read-only]"
3165 root 1.22 The embedded event loop.
3166 root 1.60 .PP
3167     \fIExamples\fR
3168     .IX Subsection "Examples"
3169     .PP
3170     Example: Try to get an embeddable event loop and embed it into the default
3171     event loop. If that is not possible, use the default loop. The default
3172 root 1.68 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3173     \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3174 root 1.60 used).
3175     .PP
3176     .Vb 3
3177 root 1.68 \& struct ev_loop *loop_hi = ev_default_init (0);
3178     \& struct ev_loop *loop_lo = 0;
3179 root 1.73 \& ev_embed embed;
3180 root 1.68 \&
3181     \& // see if there is a chance of getting one that works
3182     \& // (remember that a flags value of 0 means autodetection)
3183     \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3184     \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3185     \& : 0;
3186     \&
3187     \& // if we got one, then embed it, otherwise default to loop_hi
3188     \& if (loop_lo)
3189     \& {
3190     \& ev_embed_init (&embed, 0, loop_lo);
3191     \& ev_embed_start (loop_hi, &embed);
3192     \& }
3193     \& else
3194     \& loop_lo = loop_hi;
3195 root 1.60 .Ve
3196     .PP
3197     Example: Check if kqueue is available but not recommended and create
3198     a kqueue backend for use with sockets (which usually work with any
3199     kqueue implementation). Store the kqueue/socket\-only event loop in
3200     \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3201     .PP
3202     .Vb 3
3203 root 1.68 \& struct ev_loop *loop = ev_default_init (0);
3204     \& struct ev_loop *loop_socket = 0;
3205 root 1.73 \& ev_embed embed;
3206 root 1.68 \&
3207     \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3208     \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3209     \& {
3210     \& ev_embed_init (&embed, 0, loop_socket);
3211     \& ev_embed_start (loop, &embed);
3212     \& }
3213 root 1.60 \&
3214 root 1.68 \& if (!loop_socket)
3215     \& loop_socket = loop;
3216 root 1.60 \&
3217 root 1.68 \& // now use loop_socket for all sockets, and loop for everything else
3218 root 1.60 .Ve
3219 root 1.79 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3220     .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3221 root 1.24 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3222     Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3223     whoever is a good citizen cared to tell libev about it by calling
3224     \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3225     event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3226     and only in the child after the fork. If whoever good citizen calling
3227     \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3228     handlers will be invoked, too, of course.
3229 root 1.51 .PP
3230 root 1.78 \fIThe special problem of life after fork \- how is it possible?\fR
3231     .IX Subsection "The special problem of life after fork - how is it possible?"
3232     .PP
3233 root 1.82 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3234 root 1.78 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3235     sequence should be handled by libev without any problems.
3236     .PP
3237     This changes when the application actually wants to do event handling
3238     in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3239     fork.
3240     .PP
3241     The default mode of operation (for libev, with application help to detect
3242     forks) is to duplicate all the state in the child, as would be expected
3243     when \fIeither\fR the parent \fIor\fR the child process continues.
3244     .PP
3245     When both processes want to continue using libev, then this is usually the
3246     wrong result. In that case, usually one process (typically the parent) is
3247     supposed to continue with all watchers in place as before, while the other
3248     process typically wants to start fresh, i.e. without any active watchers.
3249     .PP
3250     The cleanest and most efficient way to achieve that with libev is to
3251     simply create a new event loop, which of course will be \*(L"empty\*(R", and
3252     use that for new watchers. This has the advantage of not touching more
3253     memory than necessary, and thus avoiding the copy-on-write, and the
3254     disadvantage of having to use multiple event loops (which do not support
3255     signal watchers).
3256     .PP
3257     When this is not possible, or you want to use the default loop for
3258     other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3259 root 1.82 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3260     Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3261     watchers, so you have to be careful not to execute code that modifies
3262     those watchers. Note also that in that case, you have to re-register any
3263     signal watchers.
3264 root 1.78 .PP
3265 root 1.51 \fIWatcher-Specific Functions and Data Members\fR
3266     .IX Subsection "Watcher-Specific Functions and Data Members"
3267 root 1.82 .IP "ev_fork_init (ev_fork *, callback)" 4
3268     .IX Item "ev_fork_init (ev_fork *, callback)"
3269 root 1.24 Initialises and configures the fork watcher \- it has no parameters of any
3270     kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3271 root 1.82 really.
3272     .ie n .SS """ev_cleanup"" \- even the best things end"
3273     .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3274     .IX Subsection "ev_cleanup - even the best things end"
3275     Cleanup watchers are called just before the event loop is being destroyed
3276     by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3277     .PP
3278     While there is no guarantee that the event loop gets destroyed, cleanup
3279     watchers provide a convenient method to install cleanup hooks for your
3280     program, worker threads and so on \- you just to make sure to destroy the
3281     loop when you want them to be invoked.
3282     .PP
3283     Cleanup watchers are invoked in the same way as any other watcher. Unlike
3284     all other watchers, they do not keep a reference to the event loop (which
3285     makes a lot of sense if you think about it). Like all other watchers, you
3286     can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3287     .PP
3288     \fIWatcher-Specific Functions and Data Members\fR
3289     .IX Subsection "Watcher-Specific Functions and Data Members"
3290     .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3291     .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3292     Initialises and configures the cleanup watcher \- it has no parameters of
3293     any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3294     pointless, I assure you.
3295     .PP
3296     Example: Register an atexit handler to destroy the default loop, so any
3297     cleanup functions are called.
3298     .PP
3299     .Vb 5
3300     \& static void
3301     \& program_exits (void)
3302     \& {
3303     \& ev_loop_destroy (EV_DEFAULT_UC);
3304     \& }
3305     \&
3306     \& ...
3307     \& atexit (program_exits);
3308     .Ve
3309     .ie n .SS """ev_async"" \- how to wake up an event loop"
3310     .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3311     .IX Subsection "ev_async - how to wake up an event loop"
3312     In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3313 root 1.61 asynchronous sources such as signal handlers (as opposed to multiple event
3314     loops \- those are of course safe to use in different threads).
3315     .PP
3316 root 1.82 Sometimes, however, you need to wake up an event loop you do not control,
3317     for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3318     watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3319     it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3320 root 1.61 .PP
3321     This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3322     too, are asynchronous in nature, and signals, too, will be compressed
3323     (i.e. the number of callback invocations may be less than the number of
3324 root 1.85 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3325     of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3326     signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3327     even without knowing which loop owns the signal.
3328 root 1.61 .PP
3329     Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3330     just the default loop.
3331     .PP
3332     \fIQueueing\fR
3333     .IX Subsection "Queueing"
3334     .PP
3335     \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3336     is that the author does not know of a simple (or any) algorithm for a
3337     multiple-writer-single-reader queue that works in all cases and doesn't
3338 root 1.81 need elaborate support such as pthreads or unportable memory access
3339     semantics.
3340 root 1.61 .PP
3341     That means that if you want to queue data, you have to provide your own
3342 root 1.71 queue. But at least I can tell you how to implement locking around your
3343 root 1.61 queue:
3344     .IP "queueing from a signal handler context" 4
3345     .IX Item "queueing from a signal handler context"
3346     To implement race-free queueing, you simply add to the queue in the signal
3347 root 1.72 handler but you block the signal handler in the watcher callback. Here is
3348     an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3349 root 1.61 .Sp
3350     .Vb 1
3351     \& static ev_async mysig;
3352     \&
3353     \& static void
3354     \& sigusr1_handler (void)
3355     \& {
3356     \& sometype data;
3357     \&
3358     \& // no locking etc.
3359     \& queue_put (data);
3360     \& ev_async_send (EV_DEFAULT_ &mysig);
3361     \& }
3362     \&
3363     \& static void
3364     \& mysig_cb (EV_P_ ev_async *w, int revents)
3365     \& {
3366     \& sometype data;
3367     \& sigset_t block, prev;
3368     \&
3369     \& sigemptyset (&block);
3370     \& sigaddset (&block, SIGUSR1);
3371     \& sigprocmask (SIG_BLOCK, &block, &prev);
3372     \&
3373     \& while (queue_get (&data))
3374     \& process (data);
3375     \&
3376     \& if (sigismember (&prev, SIGUSR1)
3377     \& sigprocmask (SIG_UNBLOCK, &block, 0);
3378     \& }
3379     .Ve
3380     .Sp
3381     (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3382     instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3383     either...).
3384     .IP "queueing from a thread context" 4
3385     .IX Item "queueing from a thread context"
3386     The strategy for threads is different, as you cannot (easily) block
3387     threads but you can easily preempt them, so to queue safely you need to
3388     employ a traditional mutex lock, such as in this pthread example:
3389     .Sp
3390     .Vb 2
3391     \& static ev_async mysig;
3392     \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3393     \&
3394     \& static void
3395     \& otherthread (void)
3396     \& {
3397     \& // only need to lock the actual queueing operation
3398     \& pthread_mutex_lock (&mymutex);
3399     \& queue_put (data);
3400     \& pthread_mutex_unlock (&mymutex);
3401     \&
3402     \& ev_async_send (EV_DEFAULT_ &mysig);
3403     \& }
3404     \&
3405     \& static void
3406     \& mysig_cb (EV_P_ ev_async *w, int revents)
3407     \& {
3408     \& pthread_mutex_lock (&mymutex);
3409     \&
3410     \& while (queue_get (&data))
3411     \& process (data);
3412     \&
3413     \& pthread_mutex_unlock (&mymutex);
3414     \& }
3415     .Ve
3416     .PP
3417     \fIWatcher-Specific Functions and Data Members\fR
3418     .IX Subsection "Watcher-Specific Functions and Data Members"
3419     .IP "ev_async_init (ev_async *, callback)" 4
3420     .IX Item "ev_async_init (ev_async *, callback)"
3421     Initialises and configures the async watcher \- it has no parameters of any
3422 root 1.73 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3423 root 1.71 trust me.
3424 root 1.61 .IP "ev_async_send (loop, ev_async *)" 4
3425     .IX Item "ev_async_send (loop, ev_async *)"
3426     Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3427     an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3428 root 1.71 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3429 root 1.68 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3430 root 1.61 section below on what exactly this means).
3431     .Sp
3432 root 1.78 Note that, as with other watchers in libev, multiple events might get
3433     compressed into a single callback invocation (another way to look at this
3434     is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3435     reset when the event loop detects that).
3436     .Sp
3437     This call incurs the overhead of a system call only once per event loop
3438     iteration, so while the overhead might be noticeable, it doesn't apply to
3439     repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3440 root 1.63 .IP "bool = ev_async_pending (ev_async *)" 4
3441     .IX Item "bool = ev_async_pending (ev_async *)"
3442     Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3443     watcher but the event has not yet been processed (or even noted) by the
3444     event loop.
3445     .Sp
3446     \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3447     the loop iterates next and checks for the watcher to have become active,
3448     it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3449 root 1.68 quickly check whether invoking the loop might be a good idea.
3450 root 1.63 .Sp
3451 root 1.78 Not that this does \fInot\fR check whether the watcher itself is pending,
3452     only whether it has been requested to make this watcher pending: there
3453     is a time window between the event loop checking and resetting the async
3454     notification, and the callback being invoked.
3455 root 1.1 .SH "OTHER FUNCTIONS"
3456     .IX Header "OTHER FUNCTIONS"
3457     There are some other functions of possible interest. Described. Here. Now.
3458     .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3459     .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3460     This function combines a simple timer and an I/O watcher, calls your
3461 root 1.72 callback on whichever event happens first and automatically stops both
3462 root 1.1 watchers. This is useful if you want to wait for a single event on an fd
3463     or timeout without having to allocate/configure/start/stop/free one or
3464     more watchers yourself.
3465     .Sp
3466 root 1.72 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3467     \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3468     the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3469 root 1.1 .Sp
3470     If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3471     started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3472 root 1.72 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3473 root 1.1 .Sp
3474 root 1.82 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3475 root 1.1 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3476 root 1.82 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3477 root 1.72 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3478     a timeout and an io event at the same time \- you probably should give io
3479     events precedence.
3480     .Sp
3481     Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3482 root 1.1 .Sp
3483     .Vb 7
3484 root 1.68 \& static void stdin_ready (int revents, void *arg)
3485     \& {
3486 root 1.72 \& if (revents & EV_READ)
3487     \& /* stdin might have data for us, joy! */;
3488 root 1.82 \& else if (revents & EV_TIMER)
3489 root 1.68 \& /* doh, nothing entered */;
3490     \& }
3491 root 1.60 \&
3492 root 1.68 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3493 root 1.1 .Ve
3494 root 1.81 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3495     .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3496 root 1.1 Feed an event on the given fd, as if a file descriptor backend detected
3497     the given events it.
3498 root 1.81 .IP "ev_feed_signal_event (loop, int signum)" 4
3499     .IX Item "ev_feed_signal_event (loop, int signum)"
3500 root 1.85 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3501     which is async-safe.
3502     .SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3503     .IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3504     This section explains some common idioms that are not immediately
3505     obvious. Note that examples are sprinkled over the whole manual, and this
3506     section only contains stuff that wouldn't fit anywhere else.
3507     .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3508     .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3509     Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3510     or modify at any time: libev will completely ignore it. This can be used
3511     to associate arbitrary data with your watcher. If you need more data and
3512     don't want to allocate memory separately and store a pointer to it in that
3513     data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3514     data:
3515     .PP
3516     .Vb 7
3517     \& struct my_io
3518     \& {
3519     \& ev_io io;
3520     \& int otherfd;
3521     \& void *somedata;
3522     \& struct whatever *mostinteresting;
3523     \& };
3524     \&
3525     \& ...
3526     \& struct my_io w;
3527     \& ev_io_init (&w.io, my_cb, fd, EV_READ);
3528     .Ve
3529     .PP
3530     And since your callback will be called with a pointer to the watcher, you
3531     can cast it back to your own type:
3532     .PP
3533     .Vb 5
3534     \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3535     \& {
3536     \& struct my_io *w = (struct my_io *)w_;
3537     \& ...
3538     \& }
3539     .Ve
3540     .PP
3541     More interesting and less C\-conformant ways of casting your callback
3542     function type instead have been omitted.
3543     .SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3544     .IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3545     Another common scenario is to use some data structure with multiple
3546     embedded watchers, in effect creating your own watcher that combines
3547     multiple libev event sources into one \*(L"super-watcher\*(R":
3548     .PP
3549     .Vb 6
3550     \& struct my_biggy
3551     \& {
3552     \& int some_data;
3553     \& ev_timer t1;
3554     \& ev_timer t2;
3555     \& }
3556     .Ve
3557     .PP
3558     In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3559     complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3560     the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3561     to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3562     real programmers):
3563     .PP
3564     .Vb 1
3565     \& #include <stddef.h>
3566     \&
3567     \& static void
3568     \& t1_cb (EV_P_ ev_timer *w, int revents)
3569     \& {
3570     \& struct my_biggy big = (struct my_biggy *)
3571     \& (((char *)w) \- offsetof (struct my_biggy, t1));
3572     \& }
3573     \&
3574     \& static void
3575     \& t2_cb (EV_P_ ev_timer *w, int revents)
3576     \& {
3577     \& struct my_biggy big = (struct my_biggy *)
3578     \& (((char *)w) \- offsetof (struct my_biggy, t2));
3579     \& }
3580     .Ve
3581     .SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3582     .IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3583     Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3584     \&\fImodal\fR interaction, which is most easily implemented by recursively
3585     invoking \f(CW\*(C`ev_run\*(C'\fR.
3586     .PP
3587     This brings the problem of exiting \- a callback might want to finish the
3588     main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3589     a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3590     and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3591     other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3592     .PP
3593     The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3594     invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3595     triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3596     .PP
3597     .Vb 2
3598     \& // main loop
3599     \& int exit_main_loop = 0;
3600     \&
3601     \& while (!exit_main_loop)
3602     \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3603     \&
3604     \& // in a model watcher
3605     \& int exit_nested_loop = 0;
3606     \&
3607     \& while (!exit_nested_loop)
3608     \& ev_run (EV_A_ EVRUN_ONCE);
3609     .Ve
3610     .PP
3611     To exit from any of these loops, just set the corresponding exit variable:
3612     .PP
3613     .Vb 2
3614     \& // exit modal loop
3615     \& exit_nested_loop = 1;
3616     \&
3617     \& // exit main program, after modal loop is finished
3618     \& exit_main_loop = 1;
3619     \&
3620     \& // exit both
3621     \& exit_main_loop = exit_nested_loop = 1;
3622     .Ve
3623     .SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3624     .IX Subsection "THREAD LOCKING EXAMPLE"
3625     Here is a fictitious example of how to run an event loop in a different
3626     thread from where callbacks are being invoked and watchers are
3627     created/added/removed.
3628     .PP
3629     For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3630     which uses exactly this technique (which is suited for many high-level
3631     languages).
3632     .PP
3633     The example uses a pthread mutex to protect the loop data, a condition
3634     variable to wait for callback invocations, an async watcher to notify the
3635     event loop thread and an unspecified mechanism to wake up the main thread.
3636     .PP
3637     First, you need to associate some data with the event loop:
3638     .PP
3639     .Vb 6
3640     \& typedef struct {
3641     \& mutex_t lock; /* global loop lock */
3642     \& ev_async async_w;
3643     \& thread_t tid;
3644     \& cond_t invoke_cv;
3645     \& } userdata;
3646     \&
3647     \& void prepare_loop (EV_P)
3648     \& {
3649     \& // for simplicity, we use a static userdata struct.
3650     \& static userdata u;
3651     \&
3652     \& ev_async_init (&u\->async_w, async_cb);
3653     \& ev_async_start (EV_A_ &u\->async_w);
3654     \&
3655     \& pthread_mutex_init (&u\->lock, 0);
3656     \& pthread_cond_init (&u\->invoke_cv, 0);
3657     \&
3658     \& // now associate this with the loop
3659     \& ev_set_userdata (EV_A_ u);
3660     \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3661     \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3662     \&
3663     \& // then create the thread running ev_loop
3664     \& pthread_create (&u\->tid, 0, l_run, EV_A);
3665     \& }
3666     .Ve
3667     .PP
3668     The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3669     solely to wake up the event loop so it takes notice of any new watchers
3670     that might have been added:
3671     .PP
3672     .Vb 5
3673     \& static void
3674     \& async_cb (EV_P_ ev_async *w, int revents)
3675     \& {
3676     \& // just used for the side effects
3677     \& }
3678     .Ve
3679     .PP
3680     The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3681     protecting the loop data, respectively.
3682     .PP
3683     .Vb 6
3684     \& static void
3685     \& l_release (EV_P)
3686     \& {
3687     \& userdata *u = ev_userdata (EV_A);
3688     \& pthread_mutex_unlock (&u\->lock);
3689     \& }
3690     \&
3691     \& static void
3692     \& l_acquire (EV_P)
3693     \& {
3694     \& userdata *u = ev_userdata (EV_A);
3695     \& pthread_mutex_lock (&u\->lock);
3696     \& }
3697     .Ve
3698     .PP
3699     The event loop thread first acquires the mutex, and then jumps straight
3700     into \f(CW\*(C`ev_run\*(C'\fR:
3701     .PP
3702     .Vb 4
3703     \& void *
3704     \& l_run (void *thr_arg)
3705     \& {
3706     \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3707     \&
3708     \& l_acquire (EV_A);
3709     \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3710     \& ev_run (EV_A_ 0);
3711     \& l_release (EV_A);
3712     \&
3713     \& return 0;
3714     \& }
3715     .Ve
3716     .PP
3717     Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3718     signal the main thread via some unspecified mechanism (signals? pipe
3719     writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3720     have been called (in a while loop because a) spurious wakeups are possible
3721     and b) skipping inter-thread-communication when there are no pending
3722     watchers is very beneficial):
3723     .PP
3724     .Vb 4
3725     \& static void
3726     \& l_invoke (EV_P)
3727     \& {
3728     \& userdata *u = ev_userdata (EV_A);
3729     \&
3730     \& while (ev_pending_count (EV_A))
3731     \& {
3732     \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3733     \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3734     \& }
3735     \& }
3736     .Ve
3737     .PP
3738     Now, whenever the main thread gets told to invoke pending watchers, it
3739     will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3740     thread to continue:
3741     .PP
3742     .Vb 4
3743     \& static void
3744     \& real_invoke_pending (EV_P)
3745     \& {
3746     \& userdata *u = ev_userdata (EV_A);
3747     \&
3748     \& pthread_mutex_lock (&u\->lock);
3749     \& ev_invoke_pending (EV_A);
3750     \& pthread_cond_signal (&u\->invoke_cv);
3751     \& pthread_mutex_unlock (&u\->lock);
3752     \& }
3753     .Ve
3754     .PP
3755     Whenever you want to start/stop a watcher or do other modifications to an
3756     event loop, you will now have to lock:
3757     .PP
3758     .Vb 2
3759     \& ev_timer timeout_watcher;
3760     \& userdata *u = ev_userdata (EV_A);
3761     \&
3762     \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3763     \&
3764     \& pthread_mutex_lock (&u\->lock);
3765     \& ev_timer_start (EV_A_ &timeout_watcher);
3766     \& ev_async_send (EV_A_ &u\->async_w);
3767     \& pthread_mutex_unlock (&u\->lock);
3768     .Ve
3769     .PP
3770     Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3771     an event loop currently blocking in the kernel will have no knowledge
3772     about the newly added timer. By waking up the loop it will pick up any new
3773     watchers in the next event loop iteration.
3774     .SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3775     .IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3776     While the overhead of a callback that e.g. schedules a thread is small, it
3777     is still an overhead. If you embed libev, and your main usage is with some
3778     kind of threads or coroutines, you might want to customise libev so that
3779     doesn't need callbacks anymore.
3780     .PP
3781     Imagine you have coroutines that you can switch to using a function
3782     \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3783     and that due to some magic, the currently active coroutine is stored in a
3784     global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3785     event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3786     the differing \f(CW\*(C`;\*(C'\fR conventions):
3787     .PP
3788     .Vb 2
3789     \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3790     \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3791     .Ve
3792     .PP
3793     That means instead of having a C callback function, you store the
3794     coroutine to switch to in each watcher, and instead of having libev call
3795     your callback, you instead have it switch to that coroutine.
3796     .PP
3797     A coroutine might now wait for an event with a function called
3798     \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3799     matter when, or whether the watcher is active or not when this function is
3800     called):
3801     .PP
3802     .Vb 6
3803     \& void
3804     \& wait_for_event (ev_watcher *w)
3805     \& {
3806     \& ev_cb_set (w) = current_coro;
3807     \& switch_to (libev_coro);
3808     \& }
3809     .Ve
3810     .PP
3811     That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3812     continues the libev coroutine, which, when appropriate, switches back to
3813     this or any other coroutine. I am sure if you sue this your own :)
3814     .PP
3815     You can do similar tricks if you have, say, threads with an event queue \-
3816     instead of storing a coroutine, you store the queue object and instead of
3817     switching to a coroutine, you push the watcher onto the queue and notify
3818     any waiters.
3819     .PP
3820     To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3821     files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3822     .PP
3823     .Vb 4
3824     \& // my_ev.h
3825     \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3826     \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3827     \& #include "../libev/ev.h"
3828     \&
3829     \& // my_ev.c
3830     \& #define EV_H "my_ev.h"
3831     \& #include "../libev/ev.c"
3832     .Ve
3833     .PP
3834     And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
3835     \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
3836     can even use \fIev.h\fR as header file name directly.
3837 root 1.1 .SH "LIBEVENT EMULATION"
3838     .IX Header "LIBEVENT EMULATION"
3839     Libev offers a compatibility emulation layer for libevent. It cannot
3840     emulate the internals of libevent, so here are some usage hints:
3841 root 1.60 .IP "\(bu" 4
3842 root 1.85 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
3843     .Sp
3844     This was the newest libevent version available when libev was implemented,
3845     and is still mostly unchanged in 2010.
3846     .IP "\(bu" 4
3847 root 1.60 Use it by including <event.h>, as usual.
3848     .IP "\(bu" 4
3849     The following members are fully supported: ev_base, ev_callback,
3850     ev_arg, ev_fd, ev_res, ev_events.
3851     .IP "\(bu" 4
3852     Avoid using ev_flags and the EVLIST_*\-macros, while it is
3853     maintained by libev, it does not work exactly the same way as in libevent (consider
3854     it a private \s-1API\s0).
3855     .IP "\(bu" 4
3856     Priorities are not currently supported. Initialising priorities
3857     will fail and all watchers will have the same priority, even though there
3858     is an ev_pri field.
3859     .IP "\(bu" 4
3860 root 1.64 In libevent, the last base created gets the signals, in libev, the
3861 root 1.85 base that registered the signal gets the signals.
3862 root 1.64 .IP "\(bu" 4
3863 root 1.60 Other members are not supported.
3864     .IP "\(bu" 4
3865     The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
3866     to use the libev header file and library.
3867 root 1.1 .SH "\*(C+ SUPPORT"
3868     .IX Header " SUPPORT"
3869 root 1.13 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3870 root 1.68 you to use some convenience methods to start/stop watchers and also change
3871 root 1.13 the callback model to a model using method callbacks on objects.
3872     .PP
3873     To use it,
3874     .PP
3875     .Vb 1
3876 root 1.68 \& #include <ev++.h>
3877 root 1.13 .Ve
3878     .PP
3879 root 1.41 This automatically includes \fIev.h\fR and puts all of its definitions (many
3880     of them macros) into the global namespace. All \*(C+ specific things are
3881     put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3882     options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3883     .PP
3884 root 1.42 Care has been taken to keep the overhead low. The only data member the \*(C+
3885     classes add (compared to plain C\-style watchers) is the event loop pointer
3886     that the watcher is associated with (or no additional members at all if
3887     you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3888 root 1.41 .PP
3889 root 1.85 Currently, functions, static and non-static member functions and classes
3890     with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
3891     to add as long as they only need one additional pointer for context. If
3892     you need support for other types of functors please contact the author
3893     (preferably after implementing it).
3894 root 1.13 .PP
3895     Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3896 root 1.79 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3897 root 1.13 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3898     .IX Item "ev::READ, ev::WRITE etc."
3899     These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3900     macros from \fIev.h\fR.
3901 root 1.79 .ie n .IP """ev::tstamp"", ""ev::now""" 4
3902 root 1.13 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3903     .IX Item "ev::tstamp, ev::now"
3904     Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3905 root 1.79 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3906 root 1.13 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3907     .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3908     For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3909     the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3910     which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3911     defines by many implementations.
3912     .Sp
3913     All of those classes have these methods:
3914     .RS 4
3915 root 1.41 .IP "ev::TYPE::TYPE ()" 4
3916     .IX Item "ev::TYPE::TYPE ()"
3917 root 1.13 .PD 0
3918 root 1.81 .IP "ev::TYPE::TYPE (loop)" 4
3919     .IX Item "ev::TYPE::TYPE (loop)"
3920 root 1.13 .IP "ev::TYPE::~TYPE" 4
3921     .IX Item "ev::TYPE::~TYPE"
3922     .PD
3923 root 1.41 The constructor (optionally) takes an event loop to associate the watcher
3924     with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3925     .Sp
3926     The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3927     \&\f(CW\*(C`set\*(C'\fR method before starting it.
3928     .Sp
3929     It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3930     method to set a callback before you can start the watcher.
3931     .Sp
3932     (The reason why you have to use a method is a limitation in \*(C+ which does
3933     not allow explicit template arguments for constructors).
3934 root 1.13 .Sp
3935     The destructor automatically stops the watcher if it is active.
3936 root 1.41 .IP "w\->set<class, &class::method> (object *)" 4
3937     .IX Item "w->set<class, &class::method> (object *)"
3938     This method sets the callback method to call. The method has to have a
3939     signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3940     first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3941     parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3942     .Sp
3943     This method synthesizes efficient thunking code to call your method from
3944     the C callback that libev requires. If your compiler can inline your
3945     callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3946     your compiler is good :), then the method will be fully inlined into the
3947     thunking function, making it as fast as a direct C callback.
3948     .Sp
3949     Example: simple class declaration and watcher initialisation
3950     .Sp
3951     .Vb 4
3952 root 1.68 \& struct myclass
3953     \& {
3954     \& void io_cb (ev::io &w, int revents) { }
3955     \& }
3956     \&
3957     \& myclass obj;
3958     \& ev::io iow;
3959     \& iow.set <myclass, &myclass::io_cb> (&obj);
3960 root 1.41 .Ve
3961 root 1.75 .IP "w\->set (object *)" 4
3962     .IX Item "w->set (object *)"
3963     This is a variation of a method callback \- leaving out the method to call
3964     will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3965     functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3966     the time. Incidentally, you can then also leave out the template argument
3967     list.
3968     .Sp
3969     The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3970     int revents)\*(C'\fR.
3971     .Sp
3972     See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3973     .Sp
3974     Example: use a functor object as callback.
3975     .Sp
3976     .Vb 7
3977     \& struct myfunctor
3978     \& {
3979     \& void operator() (ev::io &w, int revents)
3980     \& {
3981     \& ...
3982     \& }
3983     \& }
3984     \&
3985     \& myfunctor f;
3986     \&
3987     \& ev::io w;
3988     \& w.set (&f);
3989     .Ve
3990 root 1.43 .IP "w\->set<function> (void *data = 0)" 4
3991     .IX Item "w->set<function> (void *data = 0)"
3992 root 1.41 Also sets a callback, but uses a static method or plain function as
3993     callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3994     \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3995     .Sp
3996 root 1.43 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3997     .Sp
3998 root 1.41 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3999 root 1.43 .Sp
4000 root 1.71 Example: Use a plain function as callback.
4001 root 1.43 .Sp
4002     .Vb 2
4003 root 1.68 \& static void io_cb (ev::io &w, int revents) { }
4004     \& iow.set <io_cb> ();
4005 root 1.43 .Ve
4006 root 1.81 .IP "w\->set (loop)" 4
4007     .IX Item "w->set (loop)"
4008 root 1.13 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4009     do this when the watcher is inactive (and not pending either).
4010 root 1.68 .IP "w\->set ([arguments])" 4
4011     .IX Item "w->set ([arguments])"
4012 root 1.82 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
4013     method or a suitable start method must be called at least once. Unlike the
4014     C counterpart, an active watcher gets automatically stopped and restarted
4015     when reconfiguring it with this method.
4016 root 1.13 .IP "w\->start ()" 4
4017     .IX Item "w->start ()"
4018 root 1.41 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4019     constructor already stores the event loop.
4020 root 1.82 .IP "w\->start ([arguments])" 4
4021     .IX Item "w->start ([arguments])"
4022     Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4023     convenient to wrap them in one call. Uses the same type of arguments as
4024     the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4025 root 1.13 .IP "w\->stop ()" 4
4026     .IX Item "w->stop ()"
4027     Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4028 root 1.79 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4029 root 1.52 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4030     .IX Item "w->again () (ev::timer, ev::periodic only)"
4031 root 1.13 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4032     \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4033 root 1.52 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4034     .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4035     .IX Item "w->sweep () (ev::embed only)"
4036 root 1.13 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4037 root 1.52 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4038     .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4039     .IX Item "w->update () (ev::stat only)"
4040 root 1.23 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4041 root 1.13 .RE
4042     .RS 4
4043     .RE
4044     .PP
4045 root 1.82 Example: Define a class with two I/O and idle watchers, start the I/O
4046     watchers in the constructor.
4047 root 1.13 .PP
4048 root 1.82 .Vb 5
4049 root 1.68 \& class myclass
4050     \& {
4051 root 1.71 \& ev::io io ; void io_cb (ev::io &w, int revents);
4052 root 1.82 \& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
4053 root 1.71 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4054 root 1.68 \&
4055     \& myclass (int fd)
4056     \& {
4057     \& io .set <myclass, &myclass::io_cb > (this);
4058 root 1.82 \& io2 .set <myclass, &myclass::io2_cb > (this);
4059 root 1.68 \& idle.set <myclass, &myclass::idle_cb> (this);
4060     \&
4061 root 1.82 \& io.set (fd, ev::WRITE); // configure the watcher
4062     \& io.start (); // start it whenever convenient
4063     \&
4064     \& io2.start (fd, ev::READ); // set + start in one call
4065 root 1.68 \& }
4066     \& };
4067 root 1.13 .Ve
4068 root 1.62 .SH "OTHER LANGUAGE BINDINGS"
4069     .IX Header "OTHER LANGUAGE BINDINGS"
4070     Libev does not offer other language bindings itself, but bindings for a
4071 root 1.68 number of languages exist in the form of third-party packages. If you know
4072 root 1.62 any interesting language binding in addition to the ones listed here, drop
4073     me a note.
4074     .IP "Perl" 4
4075     .IX Item "Perl"
4076     The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4077     libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4078     there are additional modules that implement libev-compatible interfaces
4079 root 1.71 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4080     \&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4081     and \f(CW\*(C`EV::Glib\*(C'\fR).
4082 root 1.62 .Sp
4083 root 1.68 It can be found and installed via \s-1CPAN\s0, its homepage is at
4084 root 1.62 <http://software.schmorp.de/pkg/EV>.
4085 root 1.68 .IP "Python" 4
4086     .IX Item "Python"
4087     Python bindings can be found at <http://code.google.com/p/pyev/>. It
4088 root 1.78 seems to be quite complete and well-documented.
4089 root 1.62 .IP "Ruby" 4
4090     .IX Item "Ruby"
4091     Tony Arcieri has written a ruby extension that offers access to a subset
4092 root 1.68 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4093 root 1.62 more on top of it. It can be found via gem servers. Its homepage is at
4094     <http://rev.rubyforge.org/>.
4095 root 1.75 .Sp
4096     Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4097     makes rev work even on mingw.
4098 root 1.78 .IP "Haskell" 4
4099     .IX Item "Haskell"
4100     A haskell binding to libev is available at
4101     <http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4102 root 1.62 .IP "D" 4
4103     .IX Item "D"
4104     Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4105 root 1.71 be found at <http://proj.llucax.com.ar/wiki/evd>.
4106 root 1.73 .IP "Ocaml" 4
4107     .IX Item "Ocaml"
4108     Erkki Seppala has written Ocaml bindings for libev, to be found at
4109     <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4110 root 1.80 .IP "Lua" 4
4111     .IX Item "Lua"
4112 root 1.82 Brian Maher has written a partial interface to libev for lua (at the
4113     time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4114 root 1.80 <http://github.com/brimworks/lua\-ev>.
4115 root 1.24 .SH "MACRO MAGIC"
4116     .IX Header "MACRO MAGIC"
4117 root 1.68 Libev can be compiled with a variety of options, the most fundamental
4118 root 1.52 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4119     functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4120 root 1.24 .PP
4121     To make it easier to write programs that cope with either variant, the
4122     following macros are defined:
4123 root 1.79 .ie n .IP """EV_A"", ""EV_A_""" 4
4124 root 1.24 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4125     .IX Item "EV_A, EV_A_"
4126     This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4127     loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4128     \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4129     .Sp
4130     .Vb 3
4131 root 1.68 \& ev_unref (EV_A);
4132     \& ev_timer_add (EV_A_ watcher);
4133 root 1.82 \& ev_run (EV_A_ 0);
4134 root 1.24 .Ve
4135     .Sp
4136     It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4137     which is often provided by the following macro.
4138 root 1.79 .ie n .IP """EV_P"", ""EV_P_""" 4
4139 root 1.24 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4140     .IX Item "EV_P, EV_P_"
4141     This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4142     loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4143     \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4144     .Sp
4145     .Vb 2
4146 root 1.68 \& // this is how ev_unref is being declared
4147     \& static void ev_unref (EV_P);
4148 root 1.60 \&
4149 root 1.68 \& // this is how you can declare your typical callback
4150     \& static void cb (EV_P_ ev_timer *w, int revents)
4151 root 1.24 .Ve
4152     .Sp
4153     It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4154     suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4155 root 1.79 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4156 root 1.24 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4157     .IX Item "EV_DEFAULT, EV_DEFAULT_"
4158     Similar to the other two macros, this gives you the value of the default
4159     loop, if multiple loops are supported (\*(L"ev loop default\*(R").
4160 root 1.79 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4161 root 1.64 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4162     .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4163     Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4164     default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4165     is undefined when the default loop has not been initialised by a previous
4166     execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4167     .Sp
4168     It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4169     watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4170 root 1.24 .PP
4171 root 1.36 Example: Declare and initialise a check watcher, utilising the above
4172 root 1.38 macros so it will work regardless of whether multiple loops are supported
4173 root 1.36 or not.
4174 root 1.24 .PP
4175     .Vb 5
4176 root 1.68 \& static void
4177     \& check_cb (EV_P_ ev_timer *w, int revents)
4178     \& {
4179     \& ev_check_stop (EV_A_ w);
4180     \& }
4181     \&
4182     \& ev_check check;
4183     \& ev_check_init (&check, check_cb);
4184     \& ev_check_start (EV_DEFAULT_ &check);
4185 root 1.82 \& ev_run (EV_DEFAULT_ 0);
4186 root 1.24 .Ve
4187 root 1.14 .SH "EMBEDDING"
4188     .IX Header "EMBEDDING"
4189     Libev can (and often is) directly embedded into host
4190     applications. Examples of applications that embed it include the Deliantra
4191     Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4192 root 1.60 and rxvt-unicode.
4193 root 1.14 .PP
4194 root 1.54 The goal is to enable you to just copy the necessary files into your
4195 root 1.14 source directory without having to change even a single line in them, so
4196     you can easily upgrade by simply copying (or having a checked-out copy of
4197     libev somewhere in your source tree).
4198 root 1.79 .SS "\s-1FILESETS\s0"
4199 root 1.14 .IX Subsection "FILESETS"
4200     Depending on what features you need you need to include one or more sets of files
4201 root 1.68 in your application.
4202 root 1.14 .PP
4203     \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4204     .IX Subsection "CORE EVENT LOOP"
4205     .PP
4206     To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4207     configuration (no autoconf):
4208     .PP
4209     .Vb 2
4210 root 1.68 \& #define EV_STANDALONE 1
4211     \& #include "ev.c"
4212 root 1.14 .Ve
4213     .PP
4214     This will automatically include \fIev.h\fR, too, and should be done in a
4215     single C source file only to provide the function implementations. To use
4216     it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4217     done by writing a wrapper around \fIev.h\fR that you can include instead and
4218     where you can put other configuration options):
4219     .PP
4220     .Vb 2
4221 root 1.68 \& #define EV_STANDALONE 1
4222     \& #include "ev.h"
4223 root 1.14 .Ve
4224     .PP
4225     Both header files and implementation files can be compiled with a \*(C+
4226 root 1.73 compiler (at least, that's a stated goal, and breakage will be treated
4227 root 1.14 as a bug).
4228     .PP
4229     You need the following files in your source tree, or in a directory
4230     in your include path (e.g. in libev/ when using \-Ilibev):
4231     .PP
4232     .Vb 4
4233 root 1.68 \& ev.h
4234     \& ev.c
4235     \& ev_vars.h
4236     \& ev_wrap.h
4237     \&
4238     \& ev_win32.c required on win32 platforms only
4239     \&
4240     \& ev_select.c only when select backend is enabled (which is enabled by default)
4241     \& ev_poll.c only when poll backend is enabled (disabled by default)
4242     \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4243     \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4244     \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4245 root 1.14 .Ve
4246     .PP
4247     \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4248 root 1.18 to compile this single file.
4249 root 1.14 .PP
4250     \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4251     .IX Subsection "LIBEVENT COMPATIBILITY API"
4252     .PP
4253     To include the libevent compatibility \s-1API\s0, also include:
4254     .PP
4255     .Vb 1
4256 root 1.68 \& #include "event.c"
4257 root 1.14 .Ve
4258     .PP
4259     in the file including \fIev.c\fR, and:
4260     .PP
4261     .Vb 1
4262 root 1.68 \& #include "event.h"
4263 root 1.14 .Ve
4264     .PP
4265     in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4266     .PP
4267     You need the following additional files for this:
4268     .PP
4269     .Vb 2
4270 root 1.68 \& event.h
4271     \& event.c
4272 root 1.14 .Ve
4273     .PP
4274     \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4275     .IX Subsection "AUTOCONF SUPPORT"
4276     .PP
4277 root 1.68 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4278 root 1.14 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4279 root 1.18 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4280     include \fIconfig.h\fR and configure itself accordingly.
4281 root 1.14 .PP
4282     For this of course you need the m4 file:
4283     .PP
4284     .Vb 1
4285 root 1.68 \& libev.m4
4286 root 1.14 .Ve
4287 root 1.79 .SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4288 root 1.14 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4289 root 1.64 Libev can be configured via a variety of preprocessor symbols you have to
4290 root 1.82 define before including (or compiling) any of its files. The default in
4291     the absence of autoconf is documented for every option.
4292     .PP
4293     Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4294     values when compiling libev vs. including \fIev.h\fR, so it is permissible
4295     to redefine them before including \fIev.h\fR without breaking compatibility
4296     to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4297     users of libev and the libev code itself must be compiled with compatible
4298     settings.
4299     .IP "\s-1EV_COMPAT3\s0 (h)" 4
4300     .IX Item "EV_COMPAT3 (h)"
4301     Backwards compatibility is a major concern for libev. This is why this
4302     release of libev comes with wrappers for the functions and symbols that
4303     have been renamed between libev version 3 and 4.
4304     .Sp
4305     You can disable these wrappers (to test compatibility with future
4306     versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4307     sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4308     from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4309     typedef in that case.
4310     .Sp
4311     In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4312     and in some even more future version the compatibility code will be
4313     removed completely.
4314     .IP "\s-1EV_STANDALONE\s0 (h)" 4
4315     .IX Item "EV_STANDALONE (h)"
4316 root 1.14 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4317     keeps libev from including \fIconfig.h\fR, and it also defines dummy
4318     implementations for some libevent functions (such as logging, which is not
4319     supported). It will also not define any of the structs usually found in
4320     \&\fIevent.h\fR that are not directly supported by the libev core alone.
4321 root 1.75 .Sp
4322 root 1.80 In standalone mode, libev will still try to automatically deduce the
4323 root 1.75 configuration, but has to be more conservative.
4324 root 1.14 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4325     .IX Item "EV_USE_MONOTONIC"
4326     If defined to be \f(CW1\fR, libev will try to detect the availability of the
4327 root 1.75 monotonic clock option at both compile time and runtime. Otherwise no
4328     use of the monotonic clock option will be attempted. If you enable this,
4329     you usually have to link against librt or something similar. Enabling it
4330     when the functionality isn't available is safe, though, although you have
4331 root 1.14 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4332 root 1.75 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4333 root 1.14 .IP "\s-1EV_USE_REALTIME\s0" 4
4334     .IX Item "EV_USE_REALTIME"
4335     If defined to be \f(CW1\fR, libev will try to detect the availability of the
4336 root 1.77 real-time clock option at compile time (and assume its availability
4337     at runtime if successful). Otherwise no use of the real-time clock
4338     option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4339     by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4340     correctness. See the note about libraries in the description of
4341     \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4342     \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4343 root 1.75 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4344     .IX Item "EV_USE_CLOCK_SYSCALL"
4345     If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4346     of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4347     exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4348     unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4349     programs needlessly. Using a direct syscall is slightly slower (in
4350     theory), because no optimised vdso implementation can be used, but avoids
4351     the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4352     higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4353 root 1.56 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4354     .IX Item "EV_USE_NANOSLEEP"
4355     If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4356     and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4357 root 1.64 .IP "\s-1EV_USE_EVENTFD\s0" 4
4358     .IX Item "EV_USE_EVENTFD"
4359     If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4360     available and will probe for kernel support at runtime. This will improve
4361     \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4362     If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4363     2.7 or newer, otherwise disabled.
4364 root 1.14 .IP "\s-1EV_USE_SELECT\s0" 4
4365     .IX Item "EV_USE_SELECT"
4366     If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4367 root 1.68 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4368 root 1.14 other method takes over, select will be it. Otherwise the select backend
4369     will not be compiled in.
4370     .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4371     .IX Item "EV_SELECT_USE_FD_SET"
4372     If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4373     structure. This is useful if libev doesn't compile due to a missing
4374 root 1.75 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4375     on exotic systems. This usually limits the range of file descriptors to
4376     some low limit such as 1024 or might have other limitations (winsocket
4377     only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4378     configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4379 root 1.14 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4380     .IX Item "EV_SELECT_IS_WINSOCKET"
4381     When defined to \f(CW1\fR, the select backend will assume that
4382     select/socket/connect etc. don't understand file descriptors but
4383     wants osf handles on win32 (this is the case when the select to
4384     be used is the winsock select). This means that it will call
4385     \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4386     it is assumed that all these functions actually work on fds, even
4387     on win32. Should not be defined on non\-win32 platforms.
4388 root 1.81 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4389     .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4390 root 1.60 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4391     file descriptors to socket handles. When not defining this symbol (the
4392     default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4393     correct. In some cases, programs use their own file descriptor management,
4394     in which case they can provide this function to map fds to socket handles.
4395 root 1.81 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4396     .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4397     If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4398     using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4399     their own fd to handle mapping, overwriting this function makes it easier
4400     to do so. This can be done by defining this macro to an appropriate value.
4401     .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4402     .IX Item "EV_WIN32_CLOSE_FD(fd)"
4403     If programs implement their own fd to handle mapping on win32, then this
4404     macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4405     file descriptors again. Note that the replacement function has to close
4406     the underlying \s-1OS\s0 handle.
4407 root 1.14 .IP "\s-1EV_USE_POLL\s0" 4
4408     .IX Item "EV_USE_POLL"
4409     If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4410     backend. Otherwise it will be enabled on non\-win32 platforms. It
4411     takes precedence over select.
4412     .IP "\s-1EV_USE_EPOLL\s0" 4
4413     .IX Item "EV_USE_EPOLL"
4414     If defined to be \f(CW1\fR, libev will compile in support for the Linux
4415     \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4416 root 1.64 otherwise another method will be used as fallback. This is the preferred
4417     backend for GNU/Linux systems. If undefined, it will be enabled if the
4418     headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4419 root 1.14 .IP "\s-1EV_USE_KQUEUE\s0" 4
4420     .IX Item "EV_USE_KQUEUE"
4421     If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4422     \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4423     otherwise another method will be used as fallback. This is the preferred
4424     backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4425     supports some types of fds correctly (the only platform we found that
4426     supports ptys for example was NetBSD), so kqueue might be compiled in, but
4427     not be used unless explicitly requested. The best way to use it is to find
4428 root 1.16 out whether kqueue supports your type of fd properly and use an embedded
4429 root 1.14 kqueue loop.
4430     .IP "\s-1EV_USE_PORT\s0" 4
4431     .IX Item "EV_USE_PORT"
4432     If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4433     10 port style backend. Its availability will be detected at runtime,
4434     otherwise another method will be used as fallback. This is the preferred
4435     backend for Solaris 10 systems.
4436     .IP "\s-1EV_USE_DEVPOLL\s0" 4
4437     .IX Item "EV_USE_DEVPOLL"
4438 root 1.68 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4439 root 1.30 .IP "\s-1EV_USE_INOTIFY\s0" 4
4440     .IX Item "EV_USE_INOTIFY"
4441     If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4442     interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4443 root 1.64 be detected at runtime. If undefined, it will be enabled if the headers
4444     indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4445 root 1.61 .IP "\s-1EV_ATOMIC_T\s0" 4
4446     .IX Item "EV_ATOMIC_T"
4447     Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4448     access is atomic with respect to other threads or signal contexts. No such
4449     type is easily found in the C language, so you can provide your own type
4450     that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4451     as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4452     .Sp
4453 root 1.68 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4454 root 1.61 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4455 root 1.82 .IP "\s-1EV_H\s0 (h)" 4
4456     .IX Item "EV_H (h)"
4457 root 1.14 The name of the \fIev.h\fR header file used to include it. The default if
4458 root 1.60 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4459     used to virtually rename the \fIev.h\fR header file in case of conflicts.
4460 root 1.82 .IP "\s-1EV_CONFIG_H\s0 (h)" 4
4461     .IX Item "EV_CONFIG_H (h)"
4462 root 1.14 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4463     \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4464     \&\f(CW\*(C`EV_H\*(C'\fR, above.
4465 root 1.82 .IP "\s-1EV_EVENT_H\s0 (h)" 4
4466     .IX Item "EV_EVENT_H (h)"
4467 root 1.14 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4468 root 1.60 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4469 root 1.82 .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4470     .IX Item "EV_PROTOTYPES (h)"
4471 root 1.14 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4472     prototypes, but still define all the structs and other symbols. This is
4473     occasionally useful if you want to provide your own wrapper functions
4474     around libev functions.
4475     .IP "\s-1EV_MULTIPLICITY\s0" 4
4476     .IX Item "EV_MULTIPLICITY"
4477     If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4478     will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4479     additional independent event loops. Otherwise there will be no support
4480     for multiple event loops and there is no first event loop pointer
4481     argument. Instead, all functions act on the single default loop.
4482 root 1.39 .IP "\s-1EV_MINPRI\s0" 4
4483     .IX Item "EV_MINPRI"
4484     .PD 0
4485     .IP "\s-1EV_MAXPRI\s0" 4
4486     .IX Item "EV_MAXPRI"
4487     .PD
4488     The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4489     \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4490     provide for more priorities by overriding those symbols (usually defined
4491     to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4492     .Sp
4493     When doing priority-based operations, libev usually has to linearly search
4494     all the priorities, so having many of them (hundreds) uses a lot of space
4495     and time, so using the defaults of five priorities (\-2 .. +2) is usually
4496     fine.
4497     .Sp
4498 root 1.71 If your embedding application does not need any priorities, defining these
4499     both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4500 root 1.82 .IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4501     .IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4502     If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4503     the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4504     is not. Disabling watcher types mainly saves code size.
4505     .IP "\s-1EV_FEATURES\s0" 4
4506     .IX Item "EV_FEATURES"
4507 root 1.22 If you need to shave off some kilobytes of code at the expense of some
4508 root 1.82 speed (but with the full \s-1API\s0), you can define this symbol to request
4509     certain subsets of functionality. The default is to enable all features
4510     that can be enabled on the platform.
4511     .Sp
4512     A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4513     with some broad features you want) and then selectively re-enable
4514     additional parts you want, for example if you want everything minimal,
4515     but multiple event loop support, async and child watchers and the poll
4516     backend, use this:
4517     .Sp
4518     .Vb 5
4519     \& #define EV_FEATURES 0
4520     \& #define EV_MULTIPLICITY 1
4521     \& #define EV_USE_POLL 1
4522     \& #define EV_CHILD_ENABLE 1
4523     \& #define EV_ASYNC_ENABLE 1
4524     .Ve
4525     .Sp
4526     The actual value is a bitset, it can be a combination of the following
4527     values:
4528     .RS 4
4529     .ie n .IP "1 \- faster/larger code" 4
4530     .el .IP "\f(CW1\fR \- faster/larger code" 4
4531     .IX Item "1 - faster/larger code"
4532     Use larger code to speed up some operations.
4533     .Sp
4534     Currently this is used to override some inlining decisions (enlarging the
4535     code size by roughly 30% on amd64).
4536     .Sp
4537     When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4538     gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4539     assertions.
4540     .ie n .IP "2 \- faster/larger data structures" 4
4541     .el .IP "\f(CW2\fR \- faster/larger data structures" 4
4542     .IX Item "2 - faster/larger data structures"
4543     Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4544     hash table sizes and so on. This will usually further increase code size
4545     and can additionally have an effect on the size of data structures at
4546     runtime.
4547     .ie n .IP "4 \- full \s-1API\s0 configuration" 4
4548     .el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4549     .IX Item "4 - full API configuration"
4550     This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4551     enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4552     .ie n .IP "8 \- full \s-1API\s0" 4
4553     .el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4554     .IX Item "8 - full API"
4555     This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4556     details on which parts of the \s-1API\s0 are still available without this
4557     feature, and do not complain if this subset changes over time.
4558     .ie n .IP "16 \- enable all optional watcher types" 4
4559     .el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4560     .IX Item "16 - enable all optional watcher types"
4561     Enables all optional watcher types. If you want to selectively enable
4562     only some watcher types other than I/O and timers (e.g. prepare,
4563     embed, async, child...) you can enable them manually by defining
4564     \&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4565     .ie n .IP "32 \- enable all backends" 4
4566     .el .IP "\f(CW32\fR \- enable all backends" 4
4567     .IX Item "32 - enable all backends"
4568     This enables all backends \- without this feature, you need to enable at
4569     least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4570     .ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4571     .el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4572     .IX Item "64 - enable OS-specific helper APIs"
4573     Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4574     default.
4575     .RE
4576     .RS 4
4577     .Sp
4578     Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4579     reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4580     code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4581     watchers, timers and monotonic clock support.
4582     .Sp
4583     With an intelligent-enough linker (gcc+binutils are intelligent enough
4584     when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4585     your program might be left out as well \- a binary starting a timer and an
4586     I/O watcher then might come out at only 5Kb.
4587     .RE
4588     .IP "\s-1EV_AVOID_STDIO\s0" 4
4589     .IX Item "EV_AVOID_STDIO"
4590     If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4591     functions (printf, scanf, perror etc.). This will increase the code size
4592     somewhat, but if your program doesn't otherwise depend on stdio and your
4593     libc allows it, this avoids linking in the stdio library which is quite
4594     big.
4595     .Sp
4596     Note that error messages might become less precise when this option is
4597     enabled.
4598 root 1.80 .IP "\s-1EV_NSIG\s0" 4
4599     .IX Item "EV_NSIG"
4600     The highest supported signal number, +1 (or, the number of
4601     signals): Normally, libev tries to deduce the maximum number of signals
4602     automatically, but sometimes this fails, in which case it can be
4603     specified. Also, using a lower number than detected (\f(CW32\fR should be
4604 root 1.82 good for about any system in existence) can save some memory, as libev
4605 root 1.80 statically allocates some 12\-24 bytes per signal number.
4606 root 1.25 .IP "\s-1EV_PID_HASHSIZE\s0" 4
4607     .IX Item "EV_PID_HASHSIZE"
4608     \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4609 root 1.82 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4610     usually more than enough. If you need to manage thousands of children you
4611     might want to increase this value (\fImust\fR be a power of two).
4612 root 1.30 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4613     .IX Item "EV_INOTIFY_HASHSIZE"
4614 root 1.59 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4615 root 1.82 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4616     disabled), usually more than enough. If you need to manage thousands of
4617     \&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4618     power of two).
4619 root 1.65 .IP "\s-1EV_USE_4HEAP\s0" 4
4620     .IX Item "EV_USE_4HEAP"
4621     Heaps are not very cache-efficient. To improve the cache-efficiency of the
4622 root 1.71 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4623     to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4624     faster performance with many (thousands) of watchers.
4625 root 1.65 .Sp
4626 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4627     will be \f(CW0\fR.
4628 root 1.65 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4629     .IX Item "EV_HEAP_CACHE_AT"
4630     Heaps are not very cache-efficient. To improve the cache-efficiency of the
4631 root 1.71 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4632 root 1.65 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4633     which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4634 root 1.67 but avoids random read accesses on heap changes. This improves performance
4635 root 1.71 noticeably with many (hundreds) of watchers.
4636 root 1.65 .Sp
4637 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4638     will be \f(CW0\fR.
4639 root 1.67 .IP "\s-1EV_VERIFY\s0" 4
4640     .IX Item "EV_VERIFY"
4641 root 1.82 Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4642 root 1.67 be done: If set to \f(CW0\fR, no internal verification code will be compiled
4643     in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4644     called. If set to \f(CW2\fR, then the internal verification code will be
4645     called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4646     verification code will be called very frequently, which will slow down
4647     libev considerably.
4648     .Sp
4649 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4650     will be \f(CW0\fR.
4651 root 1.14 .IP "\s-1EV_COMMON\s0" 4
4652     .IX Item "EV_COMMON"
4653     By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4654 root 1.82 this macro to something else you can include more and other types of
4655 root 1.14 members. You have to define it each time you include one of the files,
4656     though, and it must be identical each time.
4657     .Sp
4658     For example, the perl \s-1EV\s0 module uses something like this:
4659     .Sp
4660     .Vb 3
4661 root 1.68 \& #define EV_COMMON \e
4662     \& SV *self; /* contains this struct */ \e
4663     \& SV *cb_sv, *fh /* note no trailing ";" */
4664 root 1.14 .Ve
4665 root 1.19 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4666     .IX Item "EV_CB_DECLARE (type)"
4667 root 1.14 .PD 0
4668 root 1.19 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4669     .IX Item "EV_CB_INVOKE (watcher, revents)"
4670     .IP "ev_set_cb (ev, cb)" 4
4671     .IX Item "ev_set_cb (ev, cb)"
4672 root 1.14 .PD
4673     Can be used to change the callback member declaration in each watcher,
4674     and the way callbacks are invoked and set. Must expand to a struct member
4675 root 1.54 definition and a statement, respectively. See the \fIev.h\fR header file for
4676 root 1.14 their default definitions. One possible use for overriding these is to
4677 root 1.19 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4678     method calls instead of plain function calls in \*(C+.
4679 root 1.79 .SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4680 root 1.53 .IX Subsection "EXPORTED API SYMBOLS"
4681 root 1.68 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4682 root 1.53 exported symbols, you can use the provided \fISymbol.*\fR files which list
4683     all public symbols, one per line:
4684 root 1.60 .PP
4685 root 1.53 .Vb 2
4686 root 1.68 \& Symbols.ev for libev proper
4687     \& Symbols.event for the libevent emulation
4688 root 1.53 .Ve
4689 root 1.60 .PP
4690 root 1.53 This can also be used to rename all public symbols to avoid clashes with
4691     multiple versions of libev linked together (which is obviously bad in
4692 root 1.68 itself, but sometimes it is inconvenient to avoid this).
4693 root 1.60 .PP
4694 root 1.54 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4695 root 1.53 include before including \fIev.h\fR:
4696 root 1.60 .PP
4697 root 1.53 .Vb 1
4698 root 1.60 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4699 root 1.53 .Ve
4700 root 1.60 .PP
4701 root 1.53 This would create a file \fIwrap.h\fR which essentially looks like this:
4702 root 1.60 .PP
4703 root 1.53 .Vb 4
4704     \& #define ev_backend myprefix_ev_backend
4705     \& #define ev_check_start myprefix_ev_check_start
4706     \& #define ev_check_stop myprefix_ev_check_stop
4707     \& ...
4708     .Ve
4709 root 1.79 .SS "\s-1EXAMPLES\s0"
4710 root 1.14 .IX Subsection "EXAMPLES"
4711     For a real-world example of a program the includes libev
4712     verbatim, you can have a look at the \s-1EV\s0 perl module
4713     (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4714     the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4715     interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4716     will be compiled. It is pretty complex because it provides its own header
4717     file.
4718 root 1.60 .PP
4719 root 1.14 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4720 root 1.36 that everybody includes and which overrides some configure choices:
4721 root 1.60 .PP
4722 root 1.82 .Vb 8
4723     \& #define EV_FEATURES 8
4724     \& #define EV_USE_SELECT 1
4725     \& #define EV_PREPARE_ENABLE 1
4726     \& #define EV_IDLE_ENABLE 1
4727     \& #define EV_SIGNAL_ENABLE 1
4728     \& #define EV_CHILD_ENABLE 1
4729     \& #define EV_USE_STDEXCEPT 0
4730 root 1.68 \& #define EV_CONFIG_H <config.h>
4731 root 1.60 \&
4732 root 1.68 \& #include "ev++.h"
4733 root 1.14 .Ve
4734 root 1.60 .PP
4735 root 1.14 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4736 root 1.60 .PP
4737 root 1.14 .Vb 2
4738 root 1.68 \& #include "ev_cpp.h"
4739     \& #include "ev.c"
4740 root 1.14 .Ve
4741 root 1.85 .SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4742     .IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4743 root 1.79 .SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4744 root 1.72 .IX Subsection "THREADS AND COROUTINES"
4745     \fI\s-1THREADS\s0\fR
4746 root 1.64 .IX Subsection "THREADS"
4747 root 1.72 .PP
4748 root 1.71 All libev functions are reentrant and thread-safe unless explicitly
4749 root 1.72 documented otherwise, but libev implements no locking itself. This means
4750     that you can use as many loops as you want in parallel, as long as there
4751     are no concurrent calls into any libev function with the same loop
4752     parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4753     of course): libev guarantees that different event loops share no data
4754 root 1.71 structures that need any locking.
4755     .PP
4756     Or to put it differently: calls with different loop parameters can be done
4757     concurrently from multiple threads, calls with the same loop parameter
4758     must be done serially (but can be done from different threads, as long as
4759     only one thread ever is inside a call at any point in time, e.g. by using
4760     a mutex per loop).
4761     .PP
4762     Specifically to support threads (and signal handlers), libev implements
4763     so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4764     concurrency on the same event loop, namely waking it up \*(L"from the
4765     outside\*(R".
4766 root 1.64 .PP
4767 root 1.70 If you want to know which design (one loop, locking, or multiple loops
4768     without or something else still) is best for your problem, then I cannot
4769 root 1.71 help you, but here is some generic advice:
4770 root 1.64 .IP "\(bu" 4
4771     most applications have a main thread: use the default libev loop
4772 root 1.68 in that thread, or create a separate thread running only the default loop.
4773 root 1.64 .Sp
4774     This helps integrating other libraries or software modules that use libev
4775     themselves and don't care/know about threading.
4776     .IP "\(bu" 4
4777     one loop per thread is usually a good model.
4778     .Sp
4779     Doing this is almost never wrong, sometimes a better-performance model
4780     exists, but it is always a good start.
4781     .IP "\(bu" 4
4782     other models exist, such as the leader/follower pattern, where one
4783 root 1.68 loop is handed through multiple threads in a kind of round-robin fashion.
4784 root 1.64 .Sp
4785 root 1.68 Choosing a model is hard \- look around, learn, know that usually you can do
4786 root 1.64 better than you currently do :\-)
4787     .IP "\(bu" 4
4788     often you need to talk to some other thread which blocks in the
4789 root 1.71 event loop.
4790     .Sp
4791     \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4792     (or from signal contexts...).
4793     .Sp
4794     An example use would be to communicate signals or other events that only
4795     work in the default loop by registering the signal watcher with the
4796     default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4797     watcher callback into the event loop interested in the signal.
4798 root 1.72 .PP
4799 root 1.85 See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
4800 root 1.79 .PP
4801 root 1.72 \fI\s-1COROUTINES\s0\fR
4802 root 1.64 .IX Subsection "COROUTINES"
4803 root 1.72 .PP
4804     Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4805     libev fully supports nesting calls to its functions from different
4806 root 1.82 coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4807 root 1.79 different coroutines, and switch freely between both coroutines running
4808     the loop, as long as you don't confuse yourself). The only exception is
4809     that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4810 root 1.64 .PP
4811 root 1.71 Care has been taken to ensure that libev does not keep local state inside
4812 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4813 root 1.73 they do not call any callbacks.
4814 root 1.79 .SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4815 root 1.72 .IX Subsection "COMPILER WARNINGS"
4816     Depending on your compiler and compiler settings, you might get no or a
4817     lot of warnings when compiling libev code. Some people are apparently
4818     scared by this.
4819     .PP
4820     However, these are unavoidable for many reasons. For one, each compiler
4821     has different warnings, and each user has different tastes regarding
4822     warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4823     targeting a specific compiler and compiler-version.
4824     .PP
4825     Another reason is that some compiler warnings require elaborate
4826     workarounds, or other changes to the code that make it less clear and less
4827     maintainable.
4828     .PP
4829     And of course, some compiler warnings are just plain stupid, or simply
4830     wrong (because they don't actually warn about the condition their message
4831     seems to warn about). For example, certain older gcc versions had some
4832 root 1.82 warnings that resulted in an extreme number of false positives. These have
4833 root 1.72 been fixed, but some people still insist on making code warn-free with
4834     such buggy versions.
4835     .PP
4836     While libev is written to generate as few warnings as possible,
4837     \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4838     with any compiler warnings enabled unless you are prepared to cope with
4839     them (e.g. by ignoring them). Remember that warnings are just that:
4840     warnings, not errors, or proof of bugs.
4841 root 1.79 .SS "\s-1VALGRIND\s0"
4842 root 1.72 .IX Subsection "VALGRIND"
4843     Valgrind has a special section here because it is a popular tool that is
4844     highly useful. Unfortunately, valgrind reports are very hard to interpret.
4845     .PP
4846     If you think you found a bug (memory leak, uninitialised data access etc.)
4847     in libev, then check twice: If valgrind reports something like:
4848     .PP
4849     .Vb 3
4850     \& ==2274== definitely lost: 0 bytes in 0 blocks.
4851     \& ==2274== possibly lost: 0 bytes in 0 blocks.
4852     \& ==2274== still reachable: 256 bytes in 1 blocks.
4853     .Ve
4854     .PP
4855     Then there is no memory leak, just as memory accounted to global variables
4856 root 1.73 is not a memleak \- the memory is still being referenced, and didn't leak.
4857 root 1.72 .PP
4858     Similarly, under some circumstances, valgrind might report kernel bugs
4859     as if it were a bug in libev (e.g. in realloc or in the poll backend,
4860     although an acceptable workaround has been found here), or it might be
4861     confused.
4862     .PP
4863     Keep in mind that valgrind is a very good tool, but only a tool. Don't
4864     make it into some kind of religion.
4865     .PP
4866     If you are unsure about something, feel free to contact the mailing list
4867     with the full valgrind report and an explanation on why you think this
4868     is a bug in libev (best check the archives, too :). However, don't be
4869     annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4870     of learning how to interpret valgrind properly.
4871 root 1.60 .PP
4872 root 1.72 If you need, for some reason, empty reports from valgrind for your project
4873     I suggest using suppression lists.
4874     .SH "PORTABILITY NOTES"
4875     .IX Header "PORTABILITY NOTES"
4876 root 1.82 .SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4877     .IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4878     GNU/Linux is the only common platform that supports 64 bit file/large file
4879     interfaces but \fIdisables\fR them by default.
4880     .PP
4881     That means that libev compiled in the default environment doesn't support
4882     files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4883     .PP
4884     Unfortunately, many programs try to work around this GNU/Linux issue
4885     by enabling the large file \s-1API\s0, which makes them incompatible with the
4886     standard libev compiled for their system.
4887     .PP
4888     Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4889     suddenly make it incompatible to the default compile time environment,
4890     i.e. all programs not using special compile switches.
4891     .SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4892     .IX Subsection "OS/X AND DARWIN BUGS"
4893     The whole thing is a bug if you ask me \- basically any system interface
4894     you touch is broken, whether it is locales, poll, kqueue or even the
4895     OpenGL drivers.
4896     .PP
4897     \fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4898     .IX Subsection "kqueue is buggy"
4899     .PP
4900     The kqueue syscall is broken in all known versions \- most versions support
4901     only sockets, many support pipes.
4902     .PP
4903     Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4904     rotten platform, but of course you can still ask for it when creating a
4905     loop \- embedding a socket-only kqueue loop into a select-based one is
4906     probably going to work well.
4907     .PP
4908     \fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4909     .IX Subsection "poll is buggy"
4910     .PP
4911     Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4912     implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4913     release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4914     .PP
4915     Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4916     this rotten platform, but of course you can still ask for it when creating
4917     a loop.
4918     .PP
4919     \fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4920     .IX Subsection "select is buggy"
4921     .PP
4922     All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4923     one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4924     descriptors you can pass in to 1024 \- your program suddenly crashes when
4925     you use more.
4926     .PP
4927     There is an undocumented \*(L"workaround\*(R" for this \- defining
4928     \&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4929     work on \s-1OS/X\s0.
4930     .SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4931     .IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4932     \fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4933     .IX Subsection "errno reentrancy"
4934     .PP
4935     The default compile environment on Solaris is unfortunately so
4936     thread-unsafe that you can't even use components/libraries compiled
4937     without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4938     defined by default. A valid, if stupid, implementation choice.
4939     .PP
4940     If you want to use libev in threaded environments you have to make sure
4941     it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4942     .PP
4943     \fIEvent port backend\fR
4944     .IX Subsection "Event port backend"
4945     .PP
4946     The scalable event interface for Solaris is called \*(L"event
4947     ports\*(R". Unfortunately, this mechanism is very buggy in all major
4948     releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4949     a large number of spurious wakeups, make sure you have all the relevant
4950     and latest kernel patches applied. No, I don't know which ones, but there
4951     are multiple ones to apply, and afterwards, event ports actually work
4952     great.
4953     .PP
4954     If you can't get it to work, you can try running the program by setting
4955     the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4956     \&\f(CW\*(C`select\*(C'\fR backends.
4957     .SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4958     .IX Subsection "AIX POLL BUG"
4959     \&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4960     this by trying to avoid the poll backend altogether (i.e. it's not even
4961     compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4962     with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4963 root 1.79 .SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4964 root 1.72 .IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4965 root 1.82 \fIGeneral issues\fR
4966     .IX Subsection "General issues"
4967     .PP
4968 root 1.60 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4969     requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4970     model. Libev still offers limited functionality on this platform in
4971     the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4972     descriptors. This only applies when using Win32 natively, not when using
4973 root 1.82 e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4974     as every compielr comes with a slightly differently broken/incompatible
4975     environment.
4976 root 1.60 .PP
4977 root 1.65 Lifting these limitations would basically require the full
4978 root 1.82 re-implementation of the I/O system. If you are into this kind of thing,
4979     then note that glib does exactly that for you in a very portable way (note
4980     also that glib is the slowest event library known to man).
4981 root 1.65 .PP
4982 root 1.60 There is no supported compilation method available on windows except
4983     embedding it into other applications.
4984     .PP
4985 root 1.78 Sensible signal handling is officially unsupported by Microsoft \- libev
4986     tries its best, but under most conditions, signals will simply not work.
4987     .PP
4988 root 1.68 Not a libev limitation but worth mentioning: windows apparently doesn't
4989     accept large writes: instead of resulting in a partial write, windows will
4990     either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4991     so make sure you only write small amounts into your sockets (less than a
4992 root 1.71 megabyte seems safe, but this apparently depends on the amount of memory
4993 root 1.68 available).
4994     .PP
4995 root 1.65 Due to the many, low, and arbitrary limits on the win32 platform and
4996     the abysmal performance of winsockets, using a large number of sockets
4997     is not recommended (and not reasonable). If your program needs to use
4998     more than a hundred or so sockets, then likely it needs to use a totally
4999 root 1.67 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5000 root 1.65 notification model, which cannot be implemented efficiently on windows
5001 root 1.78 (due to Microsoft monopoly games).
5002 root 1.68 .PP
5003     A typical way to use libev under windows is to embed it (see the embedding
5004     section for details) and use the following \fIevwrap.h\fR header file instead
5005     of \fIev.h\fR:
5006     .PP
5007     .Vb 2
5008     \& #define EV_STANDALONE /* keeps ev from requiring config.h */
5009     \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5010     \&
5011     \& #include "ev.h"
5012     .Ve
5013     .PP
5014     And compile the following \fIevwrap.c\fR file into your project (make sure
5015 root 1.71 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5016 root 1.68 .PP
5017     .Vb 2
5018     \& #include "evwrap.h"
5019     \& #include "ev.c"
5020     .Ve
5021 root 1.82 .PP
5022     \fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5023     .IX Subsection "The winsocket select function"
5024     .PP
5025 root 1.67 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5026     requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5027     also extremely buggy). This makes select very inefficient, and also
5028 root 1.68 requires a mapping from file descriptors to socket handles (the Microsoft
5029     C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5030 root 1.67 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5031     \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5032 root 1.82 .PP
5033 root 1.68 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5034 root 1.60 libraries and raw winsocket select is:
5035 root 1.82 .PP
5036 root 1.60 .Vb 2
5037 root 1.68 \& #define EV_USE_SELECT 1
5038     \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5039 root 1.60 .Ve
5040 root 1.82 .PP
5041 root 1.60 Note that winsockets handling of fd sets is O(n), so you can easily get a
5042     complexity in the O(nA\*^X) range when using win32.
5043 root 1.82 .PP
5044     \fILimited number of file descriptors\fR
5045     .IX Subsection "Limited number of file descriptors"
5046     .PP
5047 root 1.65 Windows has numerous arbitrary (and low) limits on things.
5048 root 1.82 .PP
5049 root 1.65 Early versions of winsocket's select only supported waiting for a maximum
5050     of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5051 root 1.68 can only wait for \f(CW64\fR things at the same time internally; Microsoft
5052 root 1.65 recommends spawning a chain of threads and wait for 63 handles and the
5053 root 1.78 previous thread in each. Sounds great!).
5054 root 1.82 .PP
5055 root 1.60 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5056     to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5057 root 1.78 call (which might be in libev or elsewhere, for example, perl and many
5058     other interpreters do their own select emulation on windows).
5059 root 1.82 .PP
5060 root 1.68 Another limit is the number of file descriptors in the Microsoft runtime
5061 root 1.78 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5062     fetish or something like this inside Microsoft). You can increase this
5063     by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5064     (another arbitrary limit), but is broken in many versions of the Microsoft
5065     runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5066     (depending on windows version and/or the phase of the moon). To get more,
5067     you need to wrap all I/O functions and provide your own fd management, but
5068     the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5069 root 1.79 .SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5070 root 1.72 .IX Subsection "PORTABILITY REQUIREMENTS"
5071     In addition to a working ISO-C implementation and of course the
5072     backend-specific APIs, libev relies on a few additional extensions:
5073 root 1.79 .ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5074 root 1.68 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5075     .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5076     Libev assumes not only that all watcher pointers have the same internal
5077     structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5078     assumes that the same (machine) code can be used to call any watcher
5079     callback: The watcher callbacks have different type signatures, but libev
5080     calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5081 root 1.82 .IP "pointer accesses must be thread-atomic" 4
5082     .IX Item "pointer accesses must be thread-atomic"
5083     Accessing a pointer value must be atomic, it must both be readable and
5084     writable in one piece \- this is the case on all current architectures.
5085 root 1.65 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5086     .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5087     .IX Item "sig_atomic_t volatile must be thread-atomic as well"
5088     The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5089 root 1.71 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5090 root 1.65 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5091     believed to be sufficiently portable.
5092     .ie n .IP """sigprocmask"" must work in a threaded environment" 4
5093     .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5094     .IX Item "sigprocmask must work in a threaded environment"
5095     Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5096     allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5097     pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5098     thread\*(R" or will block signals process-wide, both behaviours would
5099     be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5100     \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5101     .Sp
5102     The most portable way to handle signals is to block signals in all threads
5103     except the initial one, and run the default loop in the initial thread as
5104     well.
5105     .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5106     .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5107     .IX Item "long must be large enough for common memory allocation sizes"
5108 root 1.72 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5109     instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5110     systems (Microsoft...) this might be unexpectedly low, but is still at
5111     least 31 bits everywhere, which is enough for hundreds of millions of
5112     watchers.
5113 root 1.65 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5114     .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5115     .IX Item "double must hold a time value in seconds with enough accuracy"
5116     The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5117 root 1.82 have at least 51 bits of mantissa (and 9 bits of exponent), which is
5118     good enough for at least into the year 4000 with millisecond accuracy
5119     (the design goal for libev). This requirement is overfulfilled by
5120     implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
5121     \&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
5122 root 1.65 .PP
5123     If you know of other additional requirements drop me a note.
5124 root 1.72 .SH "ALGORITHMIC COMPLEXITIES"
5125     .IX Header "ALGORITHMIC COMPLEXITIES"
5126     In this section the complexities of (many of) the algorithms used inside
5127     libev will be documented. For complexity discussions about backends see
5128     the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5129 root 1.67 .PP
5130 root 1.72 All of the following are about amortised time: If an array needs to be
5131     extended, libev needs to realloc and move the whole array, but this
5132     happens asymptotically rarer with higher number of elements, so O(1) might
5133     mean that libev does a lengthy realloc operation in rare cases, but on
5134     average it is much faster and asymptotically approaches constant time.
5135     .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5136     .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5137     This means that, when you have a watcher that triggers in one hour and
5138     there are 100 watchers that would trigger before that, then inserting will
5139     have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5140     .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5141     .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5142     That means that changing a timer costs less than removing/adding them,
5143     as only the relative motion in the event queue has to be paid for.
5144     .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5145     .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5146     These just add the watcher into an array or at the head of a list.
5147     .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5148     .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5149     .PD 0
5150     .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5151     .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5152     .PD
5153     These watchers are stored in lists, so they need to be walked to find the
5154     correct watcher to remove. The lists are usually short (you don't usually
5155     have many watchers waiting for the same fd or signal: one is typical, two
5156     is rare).
5157     .IP "Finding the next timer in each loop iteration: O(1)" 4
5158     .IX Item "Finding the next timer in each loop iteration: O(1)"
5159     By virtue of using a binary or 4\-heap, the next timer is always found at a
5160     fixed position in the storage array.
5161     .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5162     .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5163     A change means an I/O watcher gets started or stopped, which requires
5164     libev to recalculate its status (and possibly tell the kernel, depending
5165     on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5166     .IP "Activating one watcher (putting it into the pending state): O(1)" 4
5167     .IX Item "Activating one watcher (putting it into the pending state): O(1)"
5168     .PD 0
5169     .IP "Priority handling: O(number_of_priorities)" 4
5170     .IX Item "Priority handling: O(number_of_priorities)"
5171     .PD
5172     Priorities are implemented by allocating some space for each
5173     priority. When doing priority-based operations, libev usually has to
5174     linearly search all the priorities, but starting/stopping and activating
5175     watchers becomes O(1) with respect to priority handling.
5176     .IP "Sending an ev_async: O(1)" 4
5177     .IX Item "Sending an ev_async: O(1)"
5178     .PD 0
5179     .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5180     .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5181     .IP "Processing signals: O(max_signal_number)" 4
5182     .IX Item "Processing signals: O(max_signal_number)"
5183     .PD
5184     Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5185     calls in the current loop iteration. Checking for async and signal events
5186     involves iterating over all running async watchers or all signal numbers.
5187 root 1.82 .SH "PORTING FROM LIBEV 3.X TO 4.X"
5188     .IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5189     The major version 4 introduced some incompatible changes to the \s-1API\s0.
5190     .PP
5191     At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5192     for all changes, so most programs should still compile. The compatibility
5193     layer might be removed in later versions of libev, so better update to the
5194     new \s-1API\s0 early than late.
5195     .ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5196     .el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5197     .IX Item "EV_COMPAT3 backwards compatibility mechanism"
5198     The backward compatibility mechanism can be controlled by
5199     \&\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
5200     section.
5201     .ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5202     .el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5203     .IX Item "ev_default_destroy and ev_default_fork have been removed"
5204     These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5205     .Sp
5206     .Vb 2
5207     \& ev_loop_destroy (EV_DEFAULT_UC);
5208     \& ev_loop_fork (EV_DEFAULT);
5209     .Ve
5210     .IP "function/symbol renames" 4
5211     .IX Item "function/symbol renames"
5212     A number of functions and symbols have been renamed:
5213     .Sp
5214     .Vb 3
5215     \& ev_loop => ev_run
5216     \& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5217     \& EVLOOP_ONESHOT => EVRUN_ONCE
5218     \&
5219     \& ev_unloop => ev_break
5220     \& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5221     \& EVUNLOOP_ONE => EVBREAK_ONE
5222     \& EVUNLOOP_ALL => EVBREAK_ALL
5223     \&
5224     \& EV_TIMEOUT => EV_TIMER
5225     \&
5226     \& ev_loop_count => ev_iteration
5227     \& ev_loop_depth => ev_depth
5228     \& ev_loop_verify => ev_verify
5229     .Ve
5230     .Sp
5231     Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5232     \&\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
5233     associated constants have been renamed to not collide with the \f(CW\*(C`struct
5234     ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5235     as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5236     \&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5237     typedef.
5238     .ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5239     .el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5240     .IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5241     The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5242     mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5243     and work, but the library code will of course be larger.
5244 root 1.78 .SH "GLOSSARY"
5245     .IX Header "GLOSSARY"
5246     .IP "active" 4
5247     .IX Item "active"
5248 root 1.82 A watcher is active as long as it has been started and not yet stopped.
5249     See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5250 root 1.78 .IP "application" 4
5251     .IX Item "application"
5252     In this document, an application is whatever is using libev.
5253 root 1.82 .IP "backend" 4
5254     .IX Item "backend"
5255     The part of the code dealing with the operating system interfaces.
5256 root 1.78 .IP "callback" 4
5257     .IX Item "callback"
5258     The address of a function that is called when some event has been
5259     detected. Callbacks are being passed the event loop, the watcher that
5260     received the event, and the actual event bitset.
5261 root 1.82 .IP "callback/watcher invocation" 4
5262     .IX Item "callback/watcher invocation"
5263 root 1.78 The act of calling the callback associated with a watcher.
5264     .IP "event" 4
5265     .IX Item "event"
5266     A change of state of some external event, such as data now being available
5267     for reading on a file descriptor, time having passed or simply not having
5268     any other events happening anymore.
5269     .Sp
5270     In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5271 root 1.82 \&\f(CW\*(C`EV_TIMER\*(C'\fR).
5272 root 1.78 .IP "event library" 4
5273     .IX Item "event library"
5274     A software package implementing an event model and loop.
5275     .IP "event loop" 4
5276     .IX Item "event loop"
5277     An entity that handles and processes external events and converts them
5278     into callback invocations.
5279     .IP "event model" 4
5280     .IX Item "event model"
5281     The model used to describe how an event loop handles and processes
5282     watchers and events.
5283     .IP "pending" 4
5284     .IX Item "pending"
5285 root 1.82 A watcher is pending as soon as the corresponding event has been
5286     detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5287 root 1.78 .IP "real time" 4
5288     .IX Item "real time"
5289     The physical time that is observed. It is apparently strictly monotonic :)
5290     .IP "wall-clock time" 4
5291     .IX Item "wall-clock time"
5292     The time and date as shown on clocks. Unlike real time, it can actually
5293     be wrong and jump forwards and backwards, e.g. when the you adjust your
5294     clock.
5295     .IP "watcher" 4
5296     .IX Item "watcher"
5297     A data structure that describes interest in certain events. Watchers need
5298     to be started (attached to an event loop) before they can receive events.
5299 root 1.1 .SH "AUTHOR"
5300     .IX Header "AUTHOR"
5301 root 1.82 Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5302     Magnusson and Emanuele Giaquinta.