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Revision: 1.1
Committed: Sun May 11 13:05:10 2008 UTC (16 years, 7 months ago) by root
Branch: MAIN
CVS Tags: rel-3_93, rel-3_92, rel-3_91, rel-3_16, rel-3_71, rel-3_31, rel-3_19, rel-3_18, rel-4_4, rel-4_5, rel-4_6, rel-4_7, rel-4_0, rel-4_1, rel-4_2, rel-4_3, rel-3_7, rel-3_6, rel-3_5, rel-3_4, rel-3_3, rel-3_2, rel-3_1, rel-4_17, rel-3_17, rel-4_14, rel-3_9, rel-3_8, rel-4_15, rel-3_15, rel-4_12, rel-3_03, rel-3_07, rel-4_81, rel-4_80, rel-3_261, rel-3_65, rel-3_04, rel-3_26, rel-3_02, rel-3_25, rel-3_22, rel-3_23, rel-3_06, rel-3_21, rel-4_52, rel-4_53, rel-4_51, rel-4_78, rel-4_79, rel-4_54, rel-4_74, rel-4_75, rel-4_76, rel-4_77, rel-4_71, rel-4_72, rel-4_73, rel-4_31, rel-4_32, rel-4_33, rel-4_34, rel-3_05, rel-4_11, rel-4_18, rel-4_19, HEAD
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File Contents

# User Rev Content
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131     .rm #[ #] #H #V #F C
132     .\" ========================================================================
133     .\"
134     .IX Title "LIBEIO 3"
135     .TH LIBEIO 3 "2008-05-11" "libeio-1.0" "libeio - truly asynchronous POSIX I/O"
136     .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137     .\" way too many mistakes in technical documents.
138     .if n .ad l
139     .nh
140     .SH "NAME"
141     libev \- a high performance full\-featured event loop written in C
142     .SH "SYNOPSIS"
143     .IX Header "SYNOPSIS"
144     .Vb 1
145     \& #include <ev.h>
146     .Ve
147     .Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
148     .IX Subsection "EXAMPLE PROGRAM"
149     .Vb 2
150     \& // a single header file is required
151     \& #include <ev.h>
152     \&
153     \& // every watcher type has its own typedef\*(Aqd struct
154     \& // with the name ev_<type>
155     \& ev_io stdin_watcher;
156     \& ev_timer timeout_watcher;
157     \&
158     \& // all watcher callbacks have a similar signature
159     \& // this callback is called when data is readable on stdin
160     \& static void
161     \& stdin_cb (EV_P_ struct ev_io *w, int revents)
162     \& {
163     \& puts ("stdin ready");
164     \& // for one\-shot events, one must manually stop the watcher
165     \& // with its corresponding stop function.
166     \& ev_io_stop (EV_A_ w);
167     \&
168     \& // this causes all nested ev_loop\*(Aqs to stop iterating
169     \& ev_unloop (EV_A_ EVUNLOOP_ALL);
170     \& }
171     \&
172     \& // another callback, this time for a time\-out
173     \& static void
174     \& timeout_cb (EV_P_ struct ev_timer *w, int revents)
175     \& {
176     \& puts ("timeout");
177     \& // this causes the innermost ev_loop to stop iterating
178     \& ev_unloop (EV_A_ EVUNLOOP_ONE);
179     \& }
180     \&
181     \& int
182     \& main (void)
183     \& {
184     \& // use the default event loop unless you have special needs
185     \& struct ev_loop *loop = ev_default_loop (0);
186     \&
187     \& // initialise an io watcher, then start it
188     \& // this one will watch for stdin to become readable
189     \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
190     \& ev_io_start (loop, &stdin_watcher);
191     \&
192     \& // initialise a timer watcher, then start it
193     \& // simple non\-repeating 5.5 second timeout
194     \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
195     \& ev_timer_start (loop, &timeout_watcher);
196     \&
197     \& // now wait for events to arrive
198     \& ev_loop (loop, 0);
199     \&
200     \& // unloop was called, so exit
201     \& return 0;
202     \& }
203     .Ve
204     .SH "DESCRIPTION"
205     .IX Header "DESCRIPTION"
206     The newest version of this document is also available as an html-formatted
207     web page you might find easier to navigate when reading it for the first
208     time: <http://cvs.schmorp.de/libev/ev.html>.
209     .PP
210     Libev is an event loop: you register interest in certain events (such as a
211     file descriptor being readable or a timeout occurring), and it will manage
212     these event sources and provide your program with events.
213     .PP
214     To do this, it must take more or less complete control over your process
215     (or thread) by executing the \fIevent loop\fR handler, and will then
216     communicate events via a callback mechanism.
217     .PP
218     You register interest in certain events by registering so-called \fIevent
219     watchers\fR, which are relatively small C structures you initialise with the
220     details of the event, and then hand it over to libev by \fIstarting\fR the
221     watcher.
222     .Sh "\s-1FEATURES\s0"
223     .IX Subsection "FEATURES"
224     Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
225     BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
226     for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
227     (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
228     with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
229     (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
230     watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
231     \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
232     file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
233     (\f(CW\*(C`ev_fork\*(C'\fR).
234     .PP
235     It also is quite fast (see this
236     benchmark comparing it to libevent
237     for example).
238     .Sh "\s-1CONVENTIONS\s0"
239     .IX Subsection "CONVENTIONS"
240     Libev is very configurable. In this manual the default (and most common)
241     configuration will be described, which supports multiple event loops. For
242     more info about various configuration options please have a look at
243     \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
244     for multiple event loops, then all functions taking an initial argument of
245     name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
246     this argument.
247     .Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
248     .IX Subsection "TIME REPRESENTATION"
249     Libev represents time as a single floating point number, representing the
250     (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
251     the beginning of 1970, details are complicated, don't ask). This type is
252     called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
253     to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
254     it, you should treat it as some floatingpoint value. Unlike the name
255     component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
256     throughout libev.
257     .SH "GLOBAL FUNCTIONS"
258     .IX Header "GLOBAL FUNCTIONS"
259     These functions can be called anytime, even before initialising the
260     library in any way.
261     .IP "ev_tstamp ev_time ()" 4
262     .IX Item "ev_tstamp ev_time ()"
263     Returns the current time as libev would use it. Please note that the
264     \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
265     you actually want to know.
266     .IP "ev_sleep (ev_tstamp interval)" 4
267     .IX Item "ev_sleep (ev_tstamp interval)"
268     Sleep for the given interval: The current thread will be blocked until
269     either it is interrupted or the given time interval has passed. Basically
270     this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
271     .IP "int ev_version_major ()" 4
272     .IX Item "int ev_version_major ()"
273     .PD 0
274     .IP "int ev_version_minor ()" 4
275     .IX Item "int ev_version_minor ()"
276     .PD
277     You can find out the major and minor \s-1ABI\s0 version numbers of the library
278     you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
279     \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
280     symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
281     version of the library your program was compiled against.
282     .Sp
283     These version numbers refer to the \s-1ABI\s0 version of the library, not the
284     release version.
285     .Sp
286     Usually, it's a good idea to terminate if the major versions mismatch,
287     as this indicates an incompatible change. Minor versions are usually
288     compatible to older versions, so a larger minor version alone is usually
289     not a problem.
290     .Sp
291     Example: Make sure we haven't accidentally been linked against the wrong
292     version.
293     .Sp
294     .Vb 3
295     \& assert (("libev version mismatch",
296     \& ev_version_major () == EV_VERSION_MAJOR
297     \& && ev_version_minor () >= EV_VERSION_MINOR));
298     .Ve
299     .IP "unsigned int ev_supported_backends ()" 4
300     .IX Item "unsigned int ev_supported_backends ()"
301     Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
302     value) compiled into this binary of libev (independent of their
303     availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
304     a description of the set values.
305     .Sp
306     Example: make sure we have the epoll method, because yeah this is cool and
307     a must have and can we have a torrent of it please!!!11
308     .Sp
309     .Vb 2
310     \& assert (("sorry, no epoll, no sex",
311     \& ev_supported_backends () & EVBACKEND_EPOLL));
312     .Ve
313     .IP "unsigned int ev_recommended_backends ()" 4
314     .IX Item "unsigned int ev_recommended_backends ()"
315     Return the set of all backends compiled into this binary of libev and also
316     recommended for this platform. This set is often smaller than the one
317     returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
318     most BSDs and will not be autodetected unless you explicitly request it
319     (assuming you know what you are doing). This is the set of backends that
320     libev will probe for if you specify no backends explicitly.
321     .IP "unsigned int ev_embeddable_backends ()" 4
322     .IX Item "unsigned int ev_embeddable_backends ()"
323     Returns the set of backends that are embeddable in other event loops. This
324     is the theoretical, all-platform, value. To find which backends
325     might be supported on the current system, you would need to look at
326     \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
327     recommended ones.
328     .Sp
329     See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
330     .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
331     .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
332     Sets the allocation function to use (the prototype is similar \- the
333     semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
334     used to allocate and free memory (no surprises here). If it returns zero
335     when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
336     or take some potentially destructive action.
337     .Sp
338     Since some systems (at least OpenBSD and Darwin) fail to implement
339     correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
340     \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
341     .Sp
342     You could override this function in high-availability programs to, say,
343     free some memory if it cannot allocate memory, to use a special allocator,
344     or even to sleep a while and retry until some memory is available.
345     .Sp
346     Example: Replace the libev allocator with one that waits a bit and then
347     retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
348     .Sp
349     .Vb 6
350     \& static void *
351     \& persistent_realloc (void *ptr, size_t size)
352     \& {
353     \& for (;;)
354     \& {
355     \& void *newptr = realloc (ptr, size);
356     \&
357     \& if (newptr)
358     \& return newptr;
359     \&
360     \& sleep (60);
361     \& }
362     \& }
363     \&
364     \& ...
365     \& ev_set_allocator (persistent_realloc);
366     .Ve
367     .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
368     .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
369     Set the callback function to call on a retryable syscall error (such
370     as failed select, poll, epoll_wait). The message is a printable string
371     indicating the system call or subsystem causing the problem. If this
372     callback is set, then libev will expect it to remedy the sitution, no
373     matter what, when it returns. That is, libev will generally retry the
374     requested operation, or, if the condition doesn't go away, do bad stuff
375     (such as abort).
376     .Sp
377     Example: This is basically the same thing that libev does internally, too.
378     .Sp
379     .Vb 6
380     \& static void
381     \& fatal_error (const char *msg)
382     \& {
383     \& perror (msg);
384     \& abort ();
385     \& }
386     \&
387     \& ...
388     \& ev_set_syserr_cb (fatal_error);
389     .Ve
390     .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
391     .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
392     An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
393     types of such loops, the \fIdefault\fR loop, which supports signals and child
394     events, and dynamically created loops which do not.
395     .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
396     .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
397     This will initialise the default event loop if it hasn't been initialised
398     yet and return it. If the default loop could not be initialised, returns
399     false. If it already was initialised it simply returns it (and ignores the
400     flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
401     .Sp
402     If you don't know what event loop to use, use the one returned from this
403     function.
404     .Sp
405     Note that this function is \fInot\fR thread-safe, so if you want to use it
406     from multiple threads, you have to lock (note also that this is unlikely,
407     as loops cannot bes hared easily between threads anyway).
408     .Sp
409     The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
410     \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
411     for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either
412     create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
413     can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
414     \&\f(CW\*(C`ev_default_init\*(C'\fR.
415     .Sp
416     The flags argument can be used to specify special behaviour or specific
417     backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
418     .Sp
419     The following flags are supported:
420     .RS 4
421     .ie n .IP """EVFLAG_AUTO""" 4
422     .el .IP "\f(CWEVFLAG_AUTO\fR" 4
423     .IX Item "EVFLAG_AUTO"
424     The default flags value. Use this if you have no clue (it's the right
425     thing, believe me).
426     .ie n .IP """EVFLAG_NOENV""" 4
427     .el .IP "\f(CWEVFLAG_NOENV\fR" 4
428     .IX Item "EVFLAG_NOENV"
429     If this flag bit is ored into the flag value (or the program runs setuid
430     or setgid) then libev will \fInot\fR look at the environment variable
431     \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
432     override the flags completely if it is found in the environment. This is
433     useful to try out specific backends to test their performance, or to work
434     around bugs.
435     .ie n .IP """EVFLAG_FORKCHECK""" 4
436     .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
437     .IX Item "EVFLAG_FORKCHECK"
438     Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
439     a fork, you can also make libev check for a fork in each iteration by
440     enabling this flag.
441     .Sp
442     This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
443     and thus this might slow down your event loop if you do a lot of loop
444     iterations and little real work, but is usually not noticeable (on my
445     GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
446     without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has
447     \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
448     .Sp
449     The big advantage of this flag is that you can forget about fork (and
450     forget about forgetting to tell libev about forking) when you use this
451     flag.
452     .Sp
453     This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
454     environment variable.
455     .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
456     .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
457     .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
458     This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
459     libev tries to roll its own fd_set with no limits on the number of fds,
460     but if that fails, expect a fairly low limit on the number of fds when
461     using this backend. It doesn't scale too well (O(highest_fd)), but its
462     usually the fastest backend for a low number of (low-numbered :) fds.
463     .Sp
464     To get good performance out of this backend you need a high amount of
465     parallelity (most of the file descriptors should be busy). If you are
466     writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
467     connections as possible during one iteration. You might also want to have
468     a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
469     readyness notifications you get per iteration.
470     .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
471     .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
472     .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
473     And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
474     than select, but handles sparse fds better and has no artificial
475     limit on the number of fds you can use (except it will slow down
476     considerably with a lot of inactive fds). It scales similarly to select,
477     i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
478     performance tips.
479     .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
480     .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
481     .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
482     For few fds, this backend is a bit little slower than poll and select,
483     but it scales phenomenally better. While poll and select usually scale
484     like O(total_fds) where n is the total number of fds (or the highest fd),
485     epoll scales either O(1) or O(active_fds). The epoll design has a number
486     of shortcomings, such as silently dropping events in some hard-to-detect
487     cases and requiring a syscall per fd change, no fork support and bad
488     support for dup.
489     .Sp
490     While stopping, setting and starting an I/O watcher in the same iteration
491     will result in some caching, there is still a syscall per such incident
492     (because the fd could point to a different file description now), so its
493     best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
494     very well if you register events for both fds.
495     .Sp
496     Please note that epoll sometimes generates spurious notifications, so you
497     need to use non-blocking I/O or other means to avoid blocking when no data
498     (or space) is available.
499     .Sp
500     Best performance from this backend is achieved by not unregistering all
501     watchers for a file descriptor until it has been closed, if possible, i.e.
502     keep at least one watcher active per fd at all times.
503     .Sp
504     While nominally embeddeble in other event loops, this feature is broken in
505     all kernel versions tested so far.
506     .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
507     .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
508     .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
509     Kqueue deserves special mention, as at the time of this writing, it
510     was broken on all BSDs except NetBSD (usually it doesn't work reliably
511     with anything but sockets and pipes, except on Darwin, where of course
512     it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
513     unless you explicitly specify it explicitly in the flags (i.e. using
514     \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
515     system like NetBSD.
516     .Sp
517     You still can embed kqueue into a normal poll or select backend and use it
518     only for sockets (after having made sure that sockets work with kqueue on
519     the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
520     .Sp
521     It scales in the same way as the epoll backend, but the interface to the
522     kernel is more efficient (which says nothing about its actual speed, of
523     course). While stopping, setting and starting an I/O watcher does never
524     cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
525     two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
526     drops fds silently in similarly hard-to-detect cases.
527     .Sp
528     This backend usually performs well under most conditions.
529     .Sp
530     While nominally embeddable in other event loops, this doesn't work
531     everywhere, so you might need to test for this. And since it is broken
532     almost everywhere, you should only use it when you have a lot of sockets
533     (for which it usually works), by embedding it into another event loop
534     (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
535     sockets.
536     .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
537     .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
538     .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
539     This is not implemented yet (and might never be, unless you send me an
540     implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
541     and is not embeddable, which would limit the usefulness of this backend
542     immensely.
543     .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
544     .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
545     .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
546     This uses the Solaris 10 event port mechanism. As with everything on Solaris,
547     it's really slow, but it still scales very well (O(active_fds)).
548     .Sp
549     Please note that solaris event ports can deliver a lot of spurious
550     notifications, so you need to use non-blocking I/O or other means to avoid
551     blocking when no data (or space) is available.
552     .Sp
553     While this backend scales well, it requires one system call per active
554     file descriptor per loop iteration. For small and medium numbers of file
555     descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
556     might perform better.
557     .Sp
558     On the positive side, ignoring the spurious readyness notifications, this
559     backend actually performed to specification in all tests and is fully
560     embeddable, which is a rare feat among the OS-specific backends.
561     .ie n .IP """EVBACKEND_ALL""" 4
562     .el .IP "\f(CWEVBACKEND_ALL\fR" 4
563     .IX Item "EVBACKEND_ALL"
564     Try all backends (even potentially broken ones that wouldn't be tried
565     with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
566     \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
567     .Sp
568     It is definitely not recommended to use this flag.
569     .RE
570     .RS 4
571     .Sp
572     If one or more of these are ored into the flags value, then only these
573     backends will be tried (in the reverse order as listed here). If none are
574     specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
575     .Sp
576     The most typical usage is like this:
577     .Sp
578     .Vb 2
579     \& if (!ev_default_loop (0))
580     \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
581     .Ve
582     .Sp
583     Restrict libev to the select and poll backends, and do not allow
584     environment settings to be taken into account:
585     .Sp
586     .Vb 1
587     \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
588     .Ve
589     .Sp
590     Use whatever libev has to offer, but make sure that kqueue is used if
591     available (warning, breaks stuff, best use only with your own private
592     event loop and only if you know the \s-1OS\s0 supports your types of fds):
593     .Sp
594     .Vb 1
595     \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
596     .Ve
597     .RE
598     .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
599     .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
600     Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
601     always distinct from the default loop. Unlike the default loop, it cannot
602     handle signal and child watchers, and attempts to do so will be greeted by
603     undefined behaviour (or a failed assertion if assertions are enabled).
604     .Sp
605     Note that this function \fIis\fR thread-safe, and the recommended way to use
606     libev with threads is indeed to create one loop per thread, and using the
607     default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
608     .Sp
609     Example: Try to create a event loop that uses epoll and nothing else.
610     .Sp
611     .Vb 3
612     \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
613     \& if (!epoller)
614     \& fatal ("no epoll found here, maybe it hides under your chair");
615     .Ve
616     .IP "ev_default_destroy ()" 4
617     .IX Item "ev_default_destroy ()"
618     Destroys the default loop again (frees all memory and kernel state
619     etc.). None of the active event watchers will be stopped in the normal
620     sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
621     responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
622     calling this function, or cope with the fact afterwards (which is usually
623     the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
624     for example).
625     .Sp
626     Note that certain global state, such as signal state, will not be freed by
627     this function, and related watchers (such as signal and child watchers)
628     would need to be stopped manually.
629     .Sp
630     In general it is not advisable to call this function except in the
631     rare occasion where you really need to free e.g. the signal handling
632     pipe fds. If you need dynamically allocated loops it is better to use
633     \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
634     .IP "ev_loop_destroy (loop)" 4
635     .IX Item "ev_loop_destroy (loop)"
636     Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
637     earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
638     .IP "ev_default_fork ()" 4
639     .IX Item "ev_default_fork ()"
640     This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
641     to reinitialise the kernel state for backends that have one. Despite the
642     name, you can call it anytime, but it makes most sense after forking, in
643     the child process (or both child and parent, but that again makes little
644     sense). You \fImust\fR call it in the child before using any of the libev
645     functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
646     .Sp
647     On the other hand, you only need to call this function in the child
648     process if and only if you want to use the event library in the child. If
649     you just fork+exec, you don't have to call it at all.
650     .Sp
651     The function itself is quite fast and it's usually not a problem to call
652     it just in case after a fork. To make this easy, the function will fit in
653     quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
654     .Sp
655     .Vb 1
656     \& pthread_atfork (0, 0, ev_default_fork);
657     .Ve
658     .IP "ev_loop_fork (loop)" 4
659     .IX Item "ev_loop_fork (loop)"
660     Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
661     \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
662     after fork, and how you do this is entirely your own problem.
663     .IP "int ev_is_default_loop (loop)" 4
664     .IX Item "int ev_is_default_loop (loop)"
665     Returns true when the given loop actually is the default loop, false otherwise.
666     .IP "unsigned int ev_loop_count (loop)" 4
667     .IX Item "unsigned int ev_loop_count (loop)"
668     Returns the count of loop iterations for the loop, which is identical to
669     the number of times libev did poll for new events. It starts at \f(CW0\fR and
670     happily wraps around with enough iterations.
671     .Sp
672     This value can sometimes be useful as a generation counter of sorts (it
673     \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
674     \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
675     .IP "unsigned int ev_backend (loop)" 4
676     .IX Item "unsigned int ev_backend (loop)"
677     Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
678     use.
679     .IP "ev_tstamp ev_now (loop)" 4
680     .IX Item "ev_tstamp ev_now (loop)"
681     Returns the current \*(L"event loop time\*(R", which is the time the event loop
682     received events and started processing them. This timestamp does not
683     change as long as callbacks are being processed, and this is also the base
684     time used for relative timers. You can treat it as the timestamp of the
685     event occurring (or more correctly, libev finding out about it).
686     .IP "ev_loop (loop, int flags)" 4
687     .IX Item "ev_loop (loop, int flags)"
688     Finally, this is it, the event handler. This function usually is called
689     after you initialised all your watchers and you want to start handling
690     events.
691     .Sp
692     If the flags argument is specified as \f(CW0\fR, it will not return until
693     either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
694     .Sp
695     Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
696     relying on all watchers to be stopped when deciding when a program has
697     finished (especially in interactive programs), but having a program that
698     automatically loops as long as it has to and no longer by virtue of
699     relying on its watchers stopping correctly is a thing of beauty.
700     .Sp
701     A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
702     those events and any outstanding ones, but will not block your process in
703     case there are no events and will return after one iteration of the loop.
704     .Sp
705     A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
706     neccessary) and will handle those and any outstanding ones. It will block
707     your process until at least one new event arrives, and will return after
708     one iteration of the loop. This is useful if you are waiting for some
709     external event in conjunction with something not expressible using other
710     libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
711     usually a better approach for this kind of thing.
712     .Sp
713     Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
714     .Sp
715     .Vb 10
716     \& \- Before the first iteration, call any pending watchers.
717     \& * If EVFLAG_FORKCHECK was used, check for a fork.
718     \& \- If a fork was detected, queue and call all fork watchers.
719     \& \- Queue and call all prepare watchers.
720     \& \- If we have been forked, recreate the kernel state.
721     \& \- Update the kernel state with all outstanding changes.
722     \& \- Update the "event loop time".
723     \& \- Calculate for how long to sleep or block, if at all
724     \& (active idle watchers, EVLOOP_NONBLOCK or not having
725     \& any active watchers at all will result in not sleeping).
726     \& \- Sleep if the I/O and timer collect interval say so.
727     \& \- Block the process, waiting for any events.
728     \& \- Queue all outstanding I/O (fd) events.
729     \& \- Update the "event loop time" and do time jump handling.
730     \& \- Queue all outstanding timers.
731     \& \- Queue all outstanding periodics.
732     \& \- If no events are pending now, queue all idle watchers.
733     \& \- Queue all check watchers.
734     \& \- Call all queued watchers in reverse order (i.e. check watchers first).
735     \& Signals and child watchers are implemented as I/O watchers, and will
736     \& be handled here by queueing them when their watcher gets executed.
737     \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
738     \& were used, or there are no active watchers, return, otherwise
739     \& continue with step *.
740     .Ve
741     .Sp
742     Example: Queue some jobs and then loop until no events are outstanding
743     anymore.
744     .Sp
745     .Vb 4
746     \& ... queue jobs here, make sure they register event watchers as long
747     \& ... as they still have work to do (even an idle watcher will do..)
748     \& ev_loop (my_loop, 0);
749     \& ... jobs done. yeah!
750     .Ve
751     .IP "ev_unloop (loop, how)" 4
752     .IX Item "ev_unloop (loop, how)"
753     Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
754     has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
755     \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
756     \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
757     .Sp
758     This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
759     .IP "ev_ref (loop)" 4
760     .IX Item "ev_ref (loop)"
761     .PD 0
762     .IP "ev_unref (loop)" 4
763     .IX Item "ev_unref (loop)"
764     .PD
765     Ref/unref can be used to add or remove a reference count on the event
766     loop: Every watcher keeps one reference, and as long as the reference
767     count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
768     a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
769     returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
770     example, libev itself uses this for its internal signal pipe: It is not
771     visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
772     no event watchers registered by it are active. It is also an excellent
773     way to do this for generic recurring timers or from within third-party
774     libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
775     (but only if the watcher wasn't active before, or was active before,
776     respectively).
777     .Sp
778     Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
779     running when nothing else is active.
780     .Sp
781     .Vb 4
782     \& struct ev_signal exitsig;
783     \& ev_signal_init (&exitsig, sig_cb, SIGINT);
784     \& ev_signal_start (loop, &exitsig);
785     \& evf_unref (loop);
786     .Ve
787     .Sp
788     Example: For some weird reason, unregister the above signal handler again.
789     .Sp
790     .Vb 2
791     \& ev_ref (loop);
792     \& ev_signal_stop (loop, &exitsig);
793     .Ve
794     .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
795     .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
796     .PD 0
797     .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
798     .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
799     .PD
800     These advanced functions influence the time that libev will spend waiting
801     for events. Both are by default \f(CW0\fR, meaning that libev will try to
802     invoke timer/periodic callbacks and I/O callbacks with minimum latency.
803     .Sp
804     Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
805     allows libev to delay invocation of I/O and timer/periodic callbacks to
806     increase efficiency of loop iterations.
807     .Sp
808     The background is that sometimes your program runs just fast enough to
809     handle one (or very few) event(s) per loop iteration. While this makes
810     the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
811     events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
812     overhead for the actual polling but can deliver many events at once.
813     .Sp
814     By setting a higher \fIio collect interval\fR you allow libev to spend more
815     time collecting I/O events, so you can handle more events per iteration,
816     at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
817     \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
818     introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
819     .Sp
820     Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
821     to spend more time collecting timeouts, at the expense of increased
822     latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
823     will not be affected. Setting this to a non-null value will not introduce
824     any overhead in libev.
825     .Sp
826     Many (busy) programs can usually benefit by setting the io collect
827     interval to a value near \f(CW0.1\fR or so, which is often enough for
828     interactive servers (of course not for games), likewise for timeouts. It
829     usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
830     as this approsaches the timing granularity of most systems.
831     .SH "ANATOMY OF A WATCHER"
832     .IX Header "ANATOMY OF A WATCHER"
833     A watcher is a structure that you create and register to record your
834     interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
835     become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
836     .PP
837     .Vb 5
838     \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
839     \& {
840     \& ev_io_stop (w);
841     \& ev_unloop (loop, EVUNLOOP_ALL);
842     \& }
843     \&
844     \& struct ev_loop *loop = ev_default_loop (0);
845     \& struct ev_io stdin_watcher;
846     \& ev_init (&stdin_watcher, my_cb);
847     \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
848     \& ev_io_start (loop, &stdin_watcher);
849     \& ev_loop (loop, 0);
850     .Ve
851     .PP
852     As you can see, you are responsible for allocating the memory for your
853     watcher structures (and it is usually a bad idea to do this on the stack,
854     although this can sometimes be quite valid).
855     .PP
856     Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
857     (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
858     callback gets invoked each time the event occurs (or, in the case of io
859     watchers, each time the event loop detects that the file descriptor given
860     is readable and/or writable).
861     .PP
862     Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
863     with arguments specific to this watcher type. There is also a macro
864     to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
865     (watcher *, callback, ...)\*(C'\fR.
866     .PP
867     To make the watcher actually watch out for events, you have to start it
868     with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
869     *)\*(C'\fR), and you can stop watching for events at any time by calling the
870     corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
871     .PP
872     As long as your watcher is active (has been started but not stopped) you
873     must not touch the values stored in it. Most specifically you must never
874     reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
875     .PP
876     Each and every callback receives the event loop pointer as first, the
877     registered watcher structure as second, and a bitset of received events as
878     third argument.
879     .PP
880     The received events usually include a single bit per event type received
881     (you can receive multiple events at the same time). The possible bit masks
882     are:
883     .ie n .IP """EV_READ""" 4
884     .el .IP "\f(CWEV_READ\fR" 4
885     .IX Item "EV_READ"
886     .PD 0
887     .ie n .IP """EV_WRITE""" 4
888     .el .IP "\f(CWEV_WRITE\fR" 4
889     .IX Item "EV_WRITE"
890     .PD
891     The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
892     writable.
893     .ie n .IP """EV_TIMEOUT""" 4
894     .el .IP "\f(CWEV_TIMEOUT\fR" 4
895     .IX Item "EV_TIMEOUT"
896     The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
897     .ie n .IP """EV_PERIODIC""" 4
898     .el .IP "\f(CWEV_PERIODIC\fR" 4
899     .IX Item "EV_PERIODIC"
900     The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
901     .ie n .IP """EV_SIGNAL""" 4
902     .el .IP "\f(CWEV_SIGNAL\fR" 4
903     .IX Item "EV_SIGNAL"
904     The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
905     .ie n .IP """EV_CHILD""" 4
906     .el .IP "\f(CWEV_CHILD\fR" 4
907     .IX Item "EV_CHILD"
908     The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
909     .ie n .IP """EV_STAT""" 4
910     .el .IP "\f(CWEV_STAT\fR" 4
911     .IX Item "EV_STAT"
912     The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
913     .ie n .IP """EV_IDLE""" 4
914     .el .IP "\f(CWEV_IDLE\fR" 4
915     .IX Item "EV_IDLE"
916     The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
917     .ie n .IP """EV_PREPARE""" 4
918     .el .IP "\f(CWEV_PREPARE\fR" 4
919     .IX Item "EV_PREPARE"
920     .PD 0
921     .ie n .IP """EV_CHECK""" 4
922     .el .IP "\f(CWEV_CHECK\fR" 4
923     .IX Item "EV_CHECK"
924     .PD
925     All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
926     to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
927     \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
928     received events. Callbacks of both watcher types can start and stop as
929     many watchers as they want, and all of them will be taken into account
930     (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
931     \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
932     .ie n .IP """EV_EMBED""" 4
933     .el .IP "\f(CWEV_EMBED\fR" 4
934     .IX Item "EV_EMBED"
935     The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
936     .ie n .IP """EV_FORK""" 4
937     .el .IP "\f(CWEV_FORK\fR" 4
938     .IX Item "EV_FORK"
939     The event loop has been resumed in the child process after fork (see
940     \&\f(CW\*(C`ev_fork\*(C'\fR).
941     .ie n .IP """EV_ASYNC""" 4
942     .el .IP "\f(CWEV_ASYNC\fR" 4
943     .IX Item "EV_ASYNC"
944     The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
945     .ie n .IP """EV_ERROR""" 4
946     .el .IP "\f(CWEV_ERROR\fR" 4
947     .IX Item "EV_ERROR"
948     An unspecified error has occured, the watcher has been stopped. This might
949     happen because the watcher could not be properly started because libev
950     ran out of memory, a file descriptor was found to be closed or any other
951     problem. You best act on it by reporting the problem and somehow coping
952     with the watcher being stopped.
953     .Sp
954     Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
955     for example it might indicate that a fd is readable or writable, and if
956     your callbacks is well-written it can just attempt the operation and cope
957     with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
958     programs, though, so beware.
959     .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
960     .IX Subsection "GENERIC WATCHER FUNCTIONS"
961     In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
962     e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
963     .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
964     .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
965     .IX Item "ev_init (ev_TYPE *watcher, callback)"
966     This macro initialises the generic portion of a watcher. The contents
967     of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
968     the generic parts of the watcher are initialised, you \fIneed\fR to call
969     the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
970     type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
971     which rolls both calls into one.
972     .Sp
973     You can reinitialise a watcher at any time as long as it has been stopped
974     (or never started) and there are no pending events outstanding.
975     .Sp
976     The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
977     int revents)\*(C'\fR.
978     .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
979     .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
980     .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
981     This macro initialises the type-specific parts of a watcher. You need to
982     call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
983     call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
984     macro on a watcher that is active (it can be pending, however, which is a
985     difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
986     .Sp
987     Although some watcher types do not have type-specific arguments
988     (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
989     .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
990     .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
991     .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
992     This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
993     calls into a single call. This is the most convinient method to initialise
994     a watcher. The same limitations apply, of course.
995     .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
996     .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
997     .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
998     Starts (activates) the given watcher. Only active watchers will receive
999     events. If the watcher is already active nothing will happen.
1000     .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1001     .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1002     .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1003     Stops the given watcher again (if active) and clears the pending
1004     status. It is possible that stopped watchers are pending (for example,
1005     non-repeating timers are being stopped when they become pending), but
1006     \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
1007     you want to free or reuse the memory used by the watcher it is therefore a
1008     good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1009     .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1010     .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1011     Returns a true value iff the watcher is active (i.e. it has been started
1012     and not yet been stopped). As long as a watcher is active you must not modify
1013     it.
1014     .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1015     .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1016     Returns a true value iff the watcher is pending, (i.e. it has outstanding
1017     events but its callback has not yet been invoked). As long as a watcher
1018     is pending (but not active) you must not call an init function on it (but
1019     \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1020     make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1021     it).
1022     .IP "callback ev_cb (ev_TYPE *watcher)" 4
1023     .IX Item "callback ev_cb (ev_TYPE *watcher)"
1024     Returns the callback currently set on the watcher.
1025     .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1026     .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1027     Change the callback. You can change the callback at virtually any time
1028     (modulo threads).
1029     .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1030     .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1031     .PD 0
1032     .IP "int ev_priority (ev_TYPE *watcher)" 4
1033     .IX Item "int ev_priority (ev_TYPE *watcher)"
1034     .PD
1035     Set and query the priority of the watcher. The priority is a small
1036     integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1037     (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1038     before watchers with lower priority, but priority will not keep watchers
1039     from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1040     .Sp
1041     This means that priorities are \fIonly\fR used for ordering callback
1042     invocation after new events have been received. This is useful, for
1043     example, to reduce latency after idling, or more often, to bind two
1044     watchers on the same event and make sure one is called first.
1045     .Sp
1046     If you need to suppress invocation when higher priority events are pending
1047     you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1048     .Sp
1049     You \fImust not\fR change the priority of a watcher as long as it is active or
1050     pending.
1051     .Sp
1052     The default priority used by watchers when no priority has been set is
1053     always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1054     .Sp
1055     Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1056     fine, as long as you do not mind that the priority value you query might
1057     or might not have been adjusted to be within valid range.
1058     .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1059     .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1060     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
1061     \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1062     can deal with that fact.
1063     .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1064     .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1065     If the watcher is pending, this function returns clears its pending status
1066     and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1067     watcher isn't pending it does nothing and returns \f(CW0\fR.
1068     .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1069     .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
1070     Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1071     and read at any time, libev will completely ignore it. This can be used
1072     to associate arbitrary data with your watcher. If you need more data and
1073     don't want to allocate memory and store a pointer to it in that data
1074     member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1075     data:
1076     .PP
1077     .Vb 7
1078     \& struct my_io
1079     \& {
1080     \& struct ev_io io;
1081     \& int otherfd;
1082     \& void *somedata;
1083     \& struct whatever *mostinteresting;
1084     \& }
1085     .Ve
1086     .PP
1087     And since your callback will be called with a pointer to the watcher, you
1088     can cast it back to your own type:
1089     .PP
1090     .Vb 5
1091     \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1092     \& {
1093     \& struct my_io *w = (struct my_io *)w_;
1094     \& ...
1095     \& }
1096     .Ve
1097     .PP
1098     More interesting and less C\-conformant ways of casting your callback type
1099     instead have been omitted.
1100     .PP
1101     Another common scenario is having some data structure with multiple
1102     watchers:
1103     .PP
1104     .Vb 6
1105     \& struct my_biggy
1106     \& {
1107     \& int some_data;
1108     \& ev_timer t1;
1109     \& ev_timer t2;
1110     \& }
1111     .Ve
1112     .PP
1113     In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1114     you need to use \f(CW\*(C`offsetof\*(C'\fR:
1115     .PP
1116     .Vb 1
1117     \& #include <stddef.h>
1118     \&
1119     \& static void
1120     \& t1_cb (EV_P_ struct ev_timer *w, int revents)
1121     \& {
1122     \& struct my_biggy big = (struct my_biggy *
1123     \& (((char *)w) \- offsetof (struct my_biggy, t1));
1124     \& }
1125     \&
1126     \& static void
1127     \& t2_cb (EV_P_ struct ev_timer *w, int revents)
1128     \& {
1129     \& struct my_biggy big = (struct my_biggy *
1130     \& (((char *)w) \- offsetof (struct my_biggy, t2));
1131     \& }
1132     .Ve
1133     .SH "WATCHER TYPES"
1134     .IX Header "WATCHER TYPES"
1135     This section describes each watcher in detail, but will not repeat
1136     information given in the last section. Any initialisation/set macros,
1137     functions and members specific to the watcher type are explained.
1138     .PP
1139     Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1140     while the watcher is active, you can look at the member and expect some
1141     sensible content, but you must not modify it (you can modify it while the
1142     watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1143     means you can expect it to have some sensible content while the watcher
1144     is active, but you can also modify it. Modifying it may not do something
1145     sensible or take immediate effect (or do anything at all), but libev will
1146     not crash or malfunction in any way.
1147     .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1148     .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1149     .IX Subsection "ev_io - is this file descriptor readable or writable?"
1150     I/O watchers check whether a file descriptor is readable or writable
1151     in each iteration of the event loop, or, more precisely, when reading
1152     would not block the process and writing would at least be able to write
1153     some data. This behaviour is called level-triggering because you keep
1154     receiving events as long as the condition persists. Remember you can stop
1155     the watcher if you don't want to act on the event and neither want to
1156     receive future events.
1157     .PP
1158     In general you can register as many read and/or write event watchers per
1159     fd as you want (as long as you don't confuse yourself). Setting all file
1160     descriptors to non-blocking mode is also usually a good idea (but not
1161     required if you know what you are doing).
1162     .PP
1163     If you must do this, then force the use of a known-to-be-good backend
1164     (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1165     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1166     .PP
1167     Another thing you have to watch out for is that it is quite easy to
1168     receive \*(L"spurious\*(R" readyness notifications, that is your callback might
1169     be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1170     because there is no data. Not only are some backends known to create a
1171     lot of those (for example solaris ports), it is very easy to get into
1172     this situation even with a relatively standard program structure. Thus
1173     it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1174     \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1175     .PP
1176     If you cannot run the fd in non-blocking mode (for example you should not
1177     play around with an Xlib connection), then you have to seperately re-test
1178     whether a file descriptor is really ready with a known-to-be good interface
1179     such as poll (fortunately in our Xlib example, Xlib already does this on
1180     its own, so its quite safe to use).
1181     .PP
1182     \fIThe special problem of disappearing file descriptors\fR
1183     .IX Subsection "The special problem of disappearing file descriptors"
1184     .PP
1185     Some backends (e.g. kqueue, epoll) need to be told about closing a file
1186     descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
1187     such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file
1188     descriptor, but when it goes away, the operating system will silently drop
1189     this interest. If another file descriptor with the same number then is
1190     registered with libev, there is no efficient way to see that this is, in
1191     fact, a different file descriptor.
1192     .PP
1193     To avoid having to explicitly tell libev about such cases, libev follows
1194     the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1195     will assume that this is potentially a new file descriptor, otherwise
1196     it is assumed that the file descriptor stays the same. That means that
1197     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
1198     descriptor even if the file descriptor number itself did not change.
1199     .PP
1200     This is how one would do it normally anyway, the important point is that
1201     the libev application should not optimise around libev but should leave
1202     optimisations to libev.
1203     .PP
1204     \fIThe special problem of dup'ed file descriptors\fR
1205     .IX Subsection "The special problem of dup'ed file descriptors"
1206     .PP
1207     Some backends (e.g. epoll), cannot register events for file descriptors,
1208     but only events for the underlying file descriptions. That means when you
1209     have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1210     events for them, only one file descriptor might actually receive events.
1211     .PP
1212     There is no workaround possible except not registering events
1213     for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1214     \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1215     .PP
1216     \fIThe special problem of fork\fR
1217     .IX Subsection "The special problem of fork"
1218     .PP
1219     Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1220     useless behaviour. Libev fully supports fork, but needs to be told about
1221     it in the child.
1222     .PP
1223     To support fork in your programs, you either have to call
1224     \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1225     enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1226     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1227     .PP
1228     \fIThe special problem of \s-1SIGPIPE\s0\fR
1229     .IX Subsection "The special problem of SIGPIPE"
1230     .PP
1231     While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0
1232     when reading from a pipe whose other end has been closed, your program
1233     gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most
1234     programs this is sensible behaviour, for daemons, this is usually
1235     undesirable.
1236     .PP
1237     So when you encounter spurious, unexplained daemon exits, make sure you
1238     ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1239     somewhere, as that would have given you a big clue).
1240     .PP
1241     \fIWatcher-Specific Functions\fR
1242     .IX Subsection "Watcher-Specific Functions"
1243     .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1244     .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1245     .PD 0
1246     .IP "ev_io_set (ev_io *, int fd, int events)" 4
1247     .IX Item "ev_io_set (ev_io *, int fd, int events)"
1248     .PD
1249     Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1250     rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1251     \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1252     .IP "int fd [read\-only]" 4
1253     .IX Item "int fd [read-only]"
1254     The file descriptor being watched.
1255     .IP "int events [read\-only]" 4
1256     .IX Item "int events [read-only]"
1257     The events being watched.
1258     .PP
1259     \fIExamples\fR
1260     .IX Subsection "Examples"
1261     .PP
1262     Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1263     readable, but only once. Since it is likely line-buffered, you could
1264     attempt to read a whole line in the callback.
1265     .PP
1266     .Vb 6
1267     \& static void
1268     \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1269     \& {
1270     \& ev_io_stop (loop, w);
1271     \& .. read from stdin here (or from w\->fd) and haqndle any I/O errors
1272     \& }
1273     \&
1274     \& ...
1275     \& struct ev_loop *loop = ev_default_init (0);
1276     \& struct ev_io stdin_readable;
1277     \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1278     \& ev_io_start (loop, &stdin_readable);
1279     \& ev_loop (loop, 0);
1280     .Ve
1281     .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1282     .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1283     .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1284     Timer watchers are simple relative timers that generate an event after a
1285     given time, and optionally repeating in regular intervals after that.
1286     .PP
1287     The timers are based on real time, that is, if you register an event that
1288     times out after an hour and you reset your system clock to last years
1289     time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
1290     detecting time jumps is hard, and some inaccuracies are unavoidable (the
1291     monotonic clock option helps a lot here).
1292     .PP
1293     The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1294     time. This is usually the right thing as this timestamp refers to the time
1295     of the event triggering whatever timeout you are modifying/starting. If
1296     you suspect event processing to be delayed and you \fIneed\fR to base the timeout
1297     on the current time, use something like this to adjust for this:
1298     .PP
1299     .Vb 1
1300     \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1301     .Ve
1302     .PP
1303     The callback is guarenteed to be invoked only when its timeout has passed,
1304     but if multiple timers become ready during the same loop iteration then
1305     order of execution is undefined.
1306     .PP
1307     \fIWatcher-Specific Functions and Data Members\fR
1308     .IX Subsection "Watcher-Specific Functions and Data Members"
1309     .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1310     .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1311     .PD 0
1312     .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1313     .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1314     .PD
1315     Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
1316     \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
1317     timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
1318     later, again, and again, until stopped manually.
1319     .Sp
1320     The timer itself will do a best-effort at avoiding drift, that is, if you
1321     configure a timer to trigger every 10 seconds, then it will trigger at
1322     exactly 10 second intervals. If, however, your program cannot keep up with
1323     the timer (because it takes longer than those 10 seconds to do stuff) the
1324     timer will not fire more than once per event loop iteration.
1325     .IP "ev_timer_again (loop, ev_timer *)" 4
1326     .IX Item "ev_timer_again (loop, ev_timer *)"
1327     This will act as if the timer timed out and restart it again if it is
1328     repeating. The exact semantics are:
1329     .Sp
1330     If the timer is pending, its pending status is cleared.
1331     .Sp
1332     If the timer is started but nonrepeating, stop it (as if it timed out).
1333     .Sp
1334     If the timer is repeating, either start it if necessary (with the
1335     \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1336     .Sp
1337     This sounds a bit complicated, but here is a useful and typical
1338     example: Imagine you have a tcp connection and you want a so-called idle
1339     timeout, that is, you want to be called when there have been, say, 60
1340     seconds of inactivity on the socket. The easiest way to do this is to
1341     configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
1342     \&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1343     you go into an idle state where you do not expect data to travel on the
1344     socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1345     automatically restart it if need be.
1346     .Sp
1347     That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1348     altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1349     .Sp
1350     .Vb 8
1351     \& ev_timer_init (timer, callback, 0., 5.);
1352     \& ev_timer_again (loop, timer);
1353     \& ...
1354     \& timer\->again = 17.;
1355     \& ev_timer_again (loop, timer);
1356     \& ...
1357     \& timer\->again = 10.;
1358     \& ev_timer_again (loop, timer);
1359     .Ve
1360     .Sp
1361     This is more slightly efficient then stopping/starting the timer each time
1362     you want to modify its timeout value.
1363     .IP "ev_tstamp repeat [read\-write]" 4
1364     .IX Item "ev_tstamp repeat [read-write]"
1365     The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1366     or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1367     which is also when any modifications are taken into account.
1368     .PP
1369     \fIExamples\fR
1370     .IX Subsection "Examples"
1371     .PP
1372     Example: Create a timer that fires after 60 seconds.
1373     .PP
1374     .Vb 5
1375     \& static void
1376     \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1377     \& {
1378     \& .. one minute over, w is actually stopped right here
1379     \& }
1380     \&
1381     \& struct ev_timer mytimer;
1382     \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1383     \& ev_timer_start (loop, &mytimer);
1384     .Ve
1385     .PP
1386     Example: Create a timeout timer that times out after 10 seconds of
1387     inactivity.
1388     .PP
1389     .Vb 5
1390     \& static void
1391     \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1392     \& {
1393     \& .. ten seconds without any activity
1394     \& }
1395     \&
1396     \& struct ev_timer mytimer;
1397     \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1398     \& ev_timer_again (&mytimer); /* start timer */
1399     \& ev_loop (loop, 0);
1400     \&
1401     \& // and in some piece of code that gets executed on any "activity":
1402     \& // reset the timeout to start ticking again at 10 seconds
1403     \& ev_timer_again (&mytimer);
1404     .Ve
1405     .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1406     .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1407     .IX Subsection "ev_periodic - to cron or not to cron?"
1408     Periodic watchers are also timers of a kind, but they are very versatile
1409     (and unfortunately a bit complex).
1410     .PP
1411     Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1412     but on wallclock time (absolute time). You can tell a periodic watcher
1413     to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1414     periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1415     + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1416     take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1417     roughly 10 seconds later).
1418     .PP
1419     They can also be used to implement vastly more complex timers, such as
1420     triggering an event on each midnight, local time or other, complicated,
1421     rules.
1422     .PP
1423     As with timers, the callback is guarenteed to be invoked only when the
1424     time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1425     during the same loop iteration then order of execution is undefined.
1426     .PP
1427     \fIWatcher-Specific Functions and Data Members\fR
1428     .IX Subsection "Watcher-Specific Functions and Data Members"
1429     .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1430     .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1431     .PD 0
1432     .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1433     .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1434     .PD
1435     Lots of arguments, lets sort it out... There are basically three modes of
1436     operation, and we will explain them from simplest to complex:
1437     .RS 4
1438     .IP "\(bu" 4
1439     absolute timer (at = time, interval = reschedule_cb = 0)
1440     .Sp
1441     In this configuration the watcher triggers an event at the wallclock time
1442     \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1443     that is, if it is to be run at January 1st 2011 then it will run when the
1444     system time reaches or surpasses this time.
1445     .IP "\(bu" 4
1446     repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1447     .Sp
1448     In this mode the watcher will always be scheduled to time out at the next
1449     \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
1450     and then repeat, regardless of any time jumps.
1451     .Sp
1452     This can be used to create timers that do not drift with respect to system
1453     time:
1454     .Sp
1455     .Vb 1
1456     \& ev_periodic_set (&periodic, 0., 3600., 0);
1457     .Ve
1458     .Sp
1459     This doesn't mean there will always be 3600 seconds in between triggers,
1460     but only that the the callback will be called when the system time shows a
1461     full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1462     by 3600.
1463     .Sp
1464     Another way to think about it (for the mathematically inclined) is that
1465     \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1466     time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1467     .Sp
1468     For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1469     \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1470     this value.
1471     .IP "\(bu" 4
1472     manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1473     .Sp
1474     In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1475     ignored. Instead, each time the periodic watcher gets scheduled, the
1476     reschedule callback will be called with the watcher as first, and the
1477     current time as second argument.
1478     .Sp
1479     \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1480     ever, or make any event loop modifications\fR. If you need to stop it,
1481     return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1482     starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).
1483     .Sp
1484     Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1485     ev_tstamp now)\*(C'\fR, e.g.:
1486     .Sp
1487     .Vb 4
1488     \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1489     \& {
1490     \& return now + 60.;
1491     \& }
1492     .Ve
1493     .Sp
1494     It must return the next time to trigger, based on the passed time value
1495     (that is, the lowest time value larger than to the second argument). It
1496     will usually be called just before the callback will be triggered, but
1497     might be called at other times, too.
1498     .Sp
1499     \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1500     passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
1501     .Sp
1502     This can be used to create very complex timers, such as a timer that
1503     triggers on each midnight, local time. To do this, you would calculate the
1504     next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1505     you do this is, again, up to you (but it is not trivial, which is the main
1506     reason I omitted it as an example).
1507     .RE
1508     .RS 4
1509     .RE
1510     .IP "ev_periodic_again (loop, ev_periodic *)" 4
1511     .IX Item "ev_periodic_again (loop, ev_periodic *)"
1512     Simply stops and restarts the periodic watcher again. This is only useful
1513     when you changed some parameters or the reschedule callback would return
1514     a different time than the last time it was called (e.g. in a crond like
1515     program when the crontabs have changed).
1516     .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
1517     .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
1518     When active, returns the absolute time that the watcher is supposed to
1519     trigger next.
1520     .IP "ev_tstamp offset [read\-write]" 4
1521     .IX Item "ev_tstamp offset [read-write]"
1522     When repeating, this contains the offset value, otherwise this is the
1523     absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1524     .Sp
1525     Can be modified any time, but changes only take effect when the periodic
1526     timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1527     .IP "ev_tstamp interval [read\-write]" 4
1528     .IX Item "ev_tstamp interval [read-write]"
1529     The current interval value. Can be modified any time, but changes only
1530     take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1531     called.
1532     .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1533     .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1534     The current reschedule callback, or \f(CW0\fR, if this functionality is
1535     switched off. Can be changed any time, but changes only take effect when
1536     the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1537     .PP
1538     \fIExamples\fR
1539     .IX Subsection "Examples"
1540     .PP
1541     Example: Call a callback every hour, or, more precisely, whenever the
1542     system clock is divisible by 3600. The callback invocation times have
1543     potentially a lot of jittering, but good long-term stability.
1544     .PP
1545     .Vb 5
1546     \& static void
1547     \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1548     \& {
1549     \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1550     \& }
1551     \&
1552     \& struct ev_periodic hourly_tick;
1553     \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1554     \& ev_periodic_start (loop, &hourly_tick);
1555     .Ve
1556     .PP
1557     Example: The same as above, but use a reschedule callback to do it:
1558     .PP
1559     .Vb 1
1560     \& #include <math.h>
1561     \&
1562     \& static ev_tstamp
1563     \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1564     \& {
1565     \& return fmod (now, 3600.) + 3600.;
1566     \& }
1567     \&
1568     \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1569     .Ve
1570     .PP
1571     Example: Call a callback every hour, starting now:
1572     .PP
1573     .Vb 4
1574     \& struct ev_periodic hourly_tick;
1575     \& ev_periodic_init (&hourly_tick, clock_cb,
1576     \& fmod (ev_now (loop), 3600.), 3600., 0);
1577     \& ev_periodic_start (loop, &hourly_tick);
1578     .Ve
1579     .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1580     .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1581     .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1582     Signal watchers will trigger an event when the process receives a specific
1583     signal one or more times. Even though signals are very asynchronous, libev
1584     will try it's best to deliver signals synchronously, i.e. as part of the
1585     normal event processing, like any other event.
1586     .PP
1587     You can configure as many watchers as you like per signal. Only when the
1588     first watcher gets started will libev actually register a signal watcher
1589     with the kernel (thus it coexists with your own signal handlers as long
1590     as you don't register any with libev). Similarly, when the last signal
1591     watcher for a signal is stopped libev will reset the signal handler to
1592     \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1593     .PP
1594     If possible and supported, libev will install its handlers with
1595     \&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly
1596     interrupted. If you have a problem with syscalls getting interrupted by
1597     signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1598     them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1599     .PP
1600     \fIWatcher-Specific Functions and Data Members\fR
1601     .IX Subsection "Watcher-Specific Functions and Data Members"
1602     .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1603     .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1604     .PD 0
1605     .IP "ev_signal_set (ev_signal *, int signum)" 4
1606     .IX Item "ev_signal_set (ev_signal *, int signum)"
1607     .PD
1608     Configures the watcher to trigger on the given signal number (usually one
1609     of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1610     .IP "int signum [read\-only]" 4
1611     .IX Item "int signum [read-only]"
1612     The signal the watcher watches out for.
1613     .PP
1614     \fIExamples\fR
1615     .IX Subsection "Examples"
1616     .PP
1617     Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1618     .PP
1619     .Vb 5
1620     \& static void
1621     \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1622     \& {
1623     \& ev_unloop (loop, EVUNLOOP_ALL);
1624     \& }
1625     \&
1626     \& struct ev_signal signal_watcher;
1627     \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1628     \& ev_signal_start (loop, &sigint_cb);
1629     .Ve
1630     .ie n .Sh """ev_child"" \- watch out for process status changes"
1631     .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1632     .IX Subsection "ev_child - watch out for process status changes"
1633     Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1634     some child status changes (most typically when a child of yours dies). It
1635     is permissible to install a child watcher \fIafter\fR the child has been
1636     forked (which implies it might have already exited), as long as the event
1637     loop isn't entered (or is continued from a watcher).
1638     .PP
1639     Only the default event loop is capable of handling signals, and therefore
1640     you can only rgeister child watchers in the default event loop.
1641     .PP
1642     \fIProcess Interaction\fR
1643     .IX Subsection "Process Interaction"
1644     .PP
1645     Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
1646     initialised. This is necessary to guarantee proper behaviour even if
1647     the first child watcher is started after the child exits. The occurance
1648     of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
1649     synchronously as part of the event loop processing. Libev always reaps all
1650     children, even ones not watched.
1651     .PP
1652     \fIOverriding the Built-In Processing\fR
1653     .IX Subsection "Overriding the Built-In Processing"
1654     .PP
1655     Libev offers no special support for overriding the built-in child
1656     processing, but if your application collides with libev's default child
1657     handler, you can override it easily by installing your own handler for
1658     \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
1659     default loop never gets destroyed. You are encouraged, however, to use an
1660     event-based approach to child reaping and thus use libev's support for
1661     that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
1662     .PP
1663     \fIWatcher-Specific Functions and Data Members\fR
1664     .IX Subsection "Watcher-Specific Functions and Data Members"
1665     .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1666     .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1667     .PD 0
1668     .IP "ev_child_set (ev_child *, int pid, int trace)" 4
1669     .IX Item "ev_child_set (ev_child *, int pid, int trace)"
1670     .PD
1671     Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1672     \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1673     at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1674     the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1675     \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1676     process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1677     activate the watcher when the process terminates) or \f(CW1\fR (additionally
1678     activate the watcher when the process is stopped or continued).
1679     .IP "int pid [read\-only]" 4
1680     .IX Item "int pid [read-only]"
1681     The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1682     .IP "int rpid [read\-write]" 4
1683     .IX Item "int rpid [read-write]"
1684     The process id that detected a status change.
1685     .IP "int rstatus [read\-write]" 4
1686     .IX Item "int rstatus [read-write]"
1687     The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1688     \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1689     .PP
1690     \fIExamples\fR
1691     .IX Subsection "Examples"
1692     .PP
1693     Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
1694     its completion.
1695     .PP
1696     .Vb 1
1697     \& ev_child cw;
1698     \&
1699     \& static void
1700     \& child_cb (EV_P_ struct ev_child *w, int revents)
1701     \& {
1702     \& ev_child_stop (EV_A_ w);
1703     \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1704     \& }
1705     \&
1706     \& pid_t pid = fork ();
1707     \&
1708     \& if (pid < 0)
1709     \& // error
1710     \& else if (pid == 0)
1711     \& {
1712     \& // the forked child executes here
1713     \& exit (1);
1714     \& }
1715     \& else
1716     \& {
1717     \& ev_child_init (&cw, child_cb, pid, 0);
1718     \& ev_child_start (EV_DEFAULT_ &cw);
1719     \& }
1720     .Ve
1721     .ie n .Sh """ev_stat"" \- did the file attributes just change?"
1722     .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1723     .IX Subsection "ev_stat - did the file attributes just change?"
1724     This watches a filesystem path for attribute changes. That is, it calls
1725     \&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1726     compared to the last time, invoking the callback if it did.
1727     .PP
1728     The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1729     not exist\*(R" is a status change like any other. The condition \*(L"path does
1730     not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1731     otherwise always forced to be at least one) and all the other fields of
1732     the stat buffer having unspecified contents.
1733     .PP
1734     The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1735     relative and your working directory changes, the behaviour is undefined.
1736     .PP
1737     Since there is no standard to do this, the portable implementation simply
1738     calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1739     can specify a recommended polling interval for this case. If you specify
1740     a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1741     unspecified default\fR value will be used (which you can expect to be around
1742     five seconds, although this might change dynamically). Libev will also
1743     impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1744     usually overkill.
1745     .PP
1746     This watcher type is not meant for massive numbers of stat watchers,
1747     as even with OS-supported change notifications, this can be
1748     resource-intensive.
1749     .PP
1750     At the time of this writing, only the Linux inotify interface is
1751     implemented (implementing kqueue support is left as an exercise for the
1752     reader, note, however, that the author sees no way of implementing ev_stat
1753     semantics with kqueue). Inotify will be used to give hints only and should
1754     not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev
1755     sometimes needs to fall back to regular polling again even with inotify,
1756     but changes are usually detected immediately, and if the file exists there
1757     will be no polling.
1758     .PP
1759     \fI\s-1ABI\s0 Issues (Largefile Support)\fR
1760     .IX Subsection "ABI Issues (Largefile Support)"
1761     .PP
1762     Libev by default (unless the user overrides this) uses the default
1763     compilation environment, which means that on systems with optionally
1764     disabled large file support, you get the 32 bit version of the stat
1765     structure. When using the library from programs that change the \s-1ABI\s0 to
1766     use 64 bit file offsets the programs will fail. In that case you have to
1767     compile libev with the same flags to get binary compatibility. This is
1768     obviously the case with any flags that change the \s-1ABI\s0, but the problem is
1769     most noticably with ev_stat and largefile support.
1770     .PP
1771     \fIInotify\fR
1772     .IX Subsection "Inotify"
1773     .PP
1774     When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1775     available on Linux) and present at runtime, it will be used to speed up
1776     change detection where possible. The inotify descriptor will be created lazily
1777     when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1778     .PP
1779     Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1780     except that changes might be detected earlier, and in some cases, to avoid
1781     making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
1782     there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1783     .PP
1784     (There is no support for kqueue, as apparently it cannot be used to
1785     implement this functionality, due to the requirement of having a file
1786     descriptor open on the object at all times).
1787     .PP
1788     \fIThe special problem of stat time resolution\fR
1789     .IX Subsection "The special problem of stat time resolution"
1790     .PP
1791     The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1792     even on systems where the resolution is higher, many filesystems still
1793     only support whole seconds.
1794     .PP
1795     That means that, if the time is the only thing that changes, you can
1796     easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
1797     calls your callback, which does something. When there is another update
1798     within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it as the stat
1799     data does not change.
1800     .PP
1801     The solution to this is to delay acting on a change for slightly more
1802     than second (or till slightly after the next full second boundary), using
1803     a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
1804     ev_timer_again (loop, w)\*(C'\fR).
1805     .PP
1806     The \f(CW.02\fR offset is added to work around small timing inconsistencies
1807     of some operating systems (where the second counter of the current time
1808     might be be delayed. One such system is the Linux kernel, where a call to
1809     \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
1810     a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
1811     update file times then there will be a small window where the kernel uses
1812     the previous second to update file times but libev might already execute
1813     the timer callback).
1814     .PP
1815     \fIWatcher-Specific Functions and Data Members\fR
1816     .IX Subsection "Watcher-Specific Functions and Data Members"
1817     .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1818     .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1819     .PD 0
1820     .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1821     .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1822     .PD
1823     Configures the watcher to wait for status changes of the given
1824     \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1825     be detected and should normally be specified as \f(CW0\fR to let libev choose
1826     a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1827     path for as long as the watcher is active.
1828     .Sp
1829     The callback will receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, relative
1830     to the attributes at the time the watcher was started (or the last change
1831     was detected).
1832     .IP "ev_stat_stat (loop, ev_stat *)" 4
1833     .IX Item "ev_stat_stat (loop, ev_stat *)"
1834     Updates the stat buffer immediately with new values. If you change the
1835     watched path in your callback, you could call this function to avoid
1836     detecting this change (while introducing a race condition if you are not
1837     the only one changing the path). Can also be useful simply to find out the
1838     new values.
1839     .IP "ev_statdata attr [read\-only]" 4
1840     .IX Item "ev_statdata attr [read-only]"
1841     The most-recently detected attributes of the file. Although the type is
1842     \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1843     suitable for your system, but you can only rely on the POSIX-standardised
1844     members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1845     some error while \f(CW\*(C`stat\*(C'\fRing the file.
1846     .IP "ev_statdata prev [read\-only]" 4
1847     .IX Item "ev_statdata prev [read-only]"
1848     The previous attributes of the file. The callback gets invoked whenever
1849     \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
1850     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,
1851     \&\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.
1852     .IP "ev_tstamp interval [read\-only]" 4
1853     .IX Item "ev_tstamp interval [read-only]"
1854     The specified interval.
1855     .IP "const char *path [read\-only]" 4
1856     .IX Item "const char *path [read-only]"
1857     The filesystem path that is being watched.
1858     .PP
1859     \fIExamples\fR
1860     .IX Subsection "Examples"
1861     .PP
1862     Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1863     .PP
1864     .Vb 10
1865     \& static void
1866     \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1867     \& {
1868     \& /* /etc/passwd changed in some way */
1869     \& if (w\->attr.st_nlink)
1870     \& {
1871     \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1872     \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1873     \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1874     \& }
1875     \& else
1876     \& /* you shalt not abuse printf for puts */
1877     \& puts ("wow, /etc/passwd is not there, expect problems. "
1878     \& "if this is windows, they already arrived\en");
1879     \& }
1880     \&
1881     \& ...
1882     \& ev_stat passwd;
1883     \&
1884     \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1885     \& ev_stat_start (loop, &passwd);
1886     .Ve
1887     .PP
1888     Example: Like above, but additionally use a one-second delay so we do not
1889     miss updates (however, frequent updates will delay processing, too, so
1890     one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1891     \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1892     .PP
1893     .Vb 2
1894     \& static ev_stat passwd;
1895     \& static ev_timer timer;
1896     \&
1897     \& static void
1898     \& timer_cb (EV_P_ ev_timer *w, int revents)
1899     \& {
1900     \& ev_timer_stop (EV_A_ w);
1901     \&
1902     \& /* now it\*(Aqs one second after the most recent passwd change */
1903     \& }
1904     \&
1905     \& static void
1906     \& stat_cb (EV_P_ ev_stat *w, int revents)
1907     \& {
1908     \& /* reset the one\-second timer */
1909     \& ev_timer_again (EV_A_ &timer);
1910     \& }
1911     \&
1912     \& ...
1913     \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1914     \& ev_stat_start (loop, &passwd);
1915     \& ev_timer_init (&timer, timer_cb, 0., 1.02);
1916     .Ve
1917     .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1918     .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1919     .IX Subsection "ev_idle - when you've got nothing better to do..."
1920     Idle watchers trigger events when no other events of the same or higher
1921     priority are pending (prepare, check and other idle watchers do not
1922     count).
1923     .PP
1924     That is, as long as your process is busy handling sockets or timeouts
1925     (or even signals, imagine) of the same or higher priority it will not be
1926     triggered. But when your process is idle (or only lower-priority watchers
1927     are pending), the idle watchers are being called once per event loop
1928     iteration \- until stopped, that is, or your process receives more events
1929     and becomes busy again with higher priority stuff.
1930     .PP
1931     The most noteworthy effect is that as long as any idle watchers are
1932     active, the process will not block when waiting for new events.
1933     .PP
1934     Apart from keeping your process non-blocking (which is a useful
1935     effect on its own sometimes), idle watchers are a good place to do
1936     \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1937     event loop has handled all outstanding events.
1938     .PP
1939     \fIWatcher-Specific Functions and Data Members\fR
1940     .IX Subsection "Watcher-Specific Functions and Data Members"
1941     .IP "ev_idle_init (ev_signal *, callback)" 4
1942     .IX Item "ev_idle_init (ev_signal *, callback)"
1943     Initialises and configures the idle watcher \- it has no parameters of any
1944     kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1945     believe me.
1946     .PP
1947     \fIExamples\fR
1948     .IX Subsection "Examples"
1949     .PP
1950     Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1951     callback, free it. Also, use no error checking, as usual.
1952     .PP
1953     .Vb 7
1954     \& static void
1955     \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1956     \& {
1957     \& free (w);
1958     \& // now do something you wanted to do when the program has
1959     \& // no longer anything immediate to do.
1960     \& }
1961     \&
1962     \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1963     \& ev_idle_init (idle_watcher, idle_cb);
1964     \& ev_idle_start (loop, idle_cb);
1965     .Ve
1966     .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1967     .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1968     .IX Subsection "ev_prepare and ev_check - customise your event loop!"
1969     Prepare and check watchers are usually (but not always) used in tandem:
1970     prepare watchers get invoked before the process blocks and check watchers
1971     afterwards.
1972     .PP
1973     You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1974     the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1975     watchers. Other loops than the current one are fine, however. The
1976     rationale behind this is that you do not need to check for recursion in
1977     those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1978     \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1979     called in pairs bracketing the blocking call.
1980     .PP
1981     Their main purpose is to integrate other event mechanisms into libev and
1982     their use is somewhat advanced. This could be used, for example, to track
1983     variable changes, implement your own watchers, integrate net-snmp or a
1984     coroutine library and lots more. They are also occasionally useful if
1985     you cache some data and want to flush it before blocking (for example,
1986     in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1987     watcher).
1988     .PP
1989     This is done by examining in each prepare call which file descriptors need
1990     to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1991     them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1992     provide just this functionality). Then, in the check watcher you check for
1993     any events that occured (by checking the pending status of all watchers
1994     and stopping them) and call back into the library. The I/O and timer
1995     callbacks will never actually be called (but must be valid nevertheless,
1996     because you never know, you know?).
1997     .PP
1998     As another example, the Perl Coro module uses these hooks to integrate
1999     coroutines into libev programs, by yielding to other active coroutines
2000     during each prepare and only letting the process block if no coroutines
2001     are ready to run (it's actually more complicated: it only runs coroutines
2002     with priority higher than or equal to the event loop and one coroutine
2003     of lower priority, but only once, using idle watchers to keep the event
2004     loop from blocking if lower-priority coroutines are active, thus mapping
2005     low-priority coroutines to idle/background tasks).
2006     .PP
2007     It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2008     priority, to ensure that they are being run before any other watchers
2009     after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
2010     too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
2011     supports this, they might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers
2012     did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
2013     (non-libev) event loops those other event loops might be in an unusable
2014     state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
2015     coexist peacefully with others).
2016     .PP
2017     \fIWatcher-Specific Functions and Data Members\fR
2018     .IX Subsection "Watcher-Specific Functions and Data Members"
2019     .IP "ev_prepare_init (ev_prepare *, callback)" 4
2020     .IX Item "ev_prepare_init (ev_prepare *, callback)"
2021     .PD 0
2022     .IP "ev_check_init (ev_check *, callback)" 4
2023     .IX Item "ev_check_init (ev_check *, callback)"
2024     .PD
2025     Initialises and configures the prepare or check watcher \- they have no
2026     parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2027     macros, but using them is utterly, utterly and completely pointless.
2028     .PP
2029     \fIExamples\fR
2030     .IX Subsection "Examples"
2031     .PP
2032     There are a number of principal ways to embed other event loops or modules
2033     into libev. Here are some ideas on how to include libadns into libev
2034     (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2035     use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2036     Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2037     Glib event loop).
2038     .PP
2039     Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2040     and in a check watcher, destroy them and call into libadns. What follows
2041     is pseudo-code only of course. This requires you to either use a low
2042     priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2043     the callbacks for the IO/timeout watchers might not have been called yet.
2044     .PP
2045     .Vb 2
2046     \& static ev_io iow [nfd];
2047     \& static ev_timer tw;
2048     \&
2049     \& static void
2050     \& io_cb (ev_loop *loop, ev_io *w, int revents)
2051     \& {
2052     \& }
2053     \&
2054     \& // create io watchers for each fd and a timer before blocking
2055     \& static void
2056     \& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
2057     \& {
2058     \& int timeout = 3600000;
2059     \& struct pollfd fds [nfd];
2060     \& // actual code will need to loop here and realloc etc.
2061     \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2062     \&
2063     \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2064     \& ev_timer_init (&tw, 0, timeout * 1e\-3);
2065     \& ev_timer_start (loop, &tw);
2066     \&
2067     \& // create one ev_io per pollfd
2068     \& for (int i = 0; i < nfd; ++i)
2069     \& {
2070     \& ev_io_init (iow + i, io_cb, fds [i].fd,
2071     \& ((fds [i].events & POLLIN ? EV_READ : 0)
2072     \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2073     \&
2074     \& fds [i].revents = 0;
2075     \& ev_io_start (loop, iow + i);
2076     \& }
2077     \& }
2078     \&
2079     \& // stop all watchers after blocking
2080     \& static void
2081     \& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
2082     \& {
2083     \& ev_timer_stop (loop, &tw);
2084     \&
2085     \& for (int i = 0; i < nfd; ++i)
2086     \& {
2087     \& // set the relevant poll flags
2088     \& // could also call adns_processreadable etc. here
2089     \& struct pollfd *fd = fds + i;
2090     \& int revents = ev_clear_pending (iow + i);
2091     \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2092     \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2093     \&
2094     \& // now stop the watcher
2095     \& ev_io_stop (loop, iow + i);
2096     \& }
2097     \&
2098     \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2099     \& }
2100     .Ve
2101     .PP
2102     Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2103     in the prepare watcher and would dispose of the check watcher.
2104     .PP
2105     Method 3: If the module to be embedded supports explicit event
2106     notification (adns does), you can also make use of the actual watcher
2107     callbacks, and only destroy/create the watchers in the prepare watcher.
2108     .PP
2109     .Vb 5
2110     \& static void
2111     \& timer_cb (EV_P_ ev_timer *w, int revents)
2112     \& {
2113     \& adns_state ads = (adns_state)w\->data;
2114     \& update_now (EV_A);
2115     \&
2116     \& adns_processtimeouts (ads, &tv_now);
2117     \& }
2118     \&
2119     \& static void
2120     \& io_cb (EV_P_ ev_io *w, int revents)
2121     \& {
2122     \& adns_state ads = (adns_state)w\->data;
2123     \& update_now (EV_A);
2124     \&
2125     \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2126     \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2127     \& }
2128     \&
2129     \& // do not ever call adns_afterpoll
2130     .Ve
2131     .PP
2132     Method 4: Do not use a prepare or check watcher because the module you
2133     want to embed is too inflexible to support it. Instead, youc na override
2134     their poll function. The drawback with this solution is that the main
2135     loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
2136     this.
2137     .PP
2138     .Vb 4
2139     \& static gint
2140     \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2141     \& {
2142     \& int got_events = 0;
2143     \&
2144     \& for (n = 0; n < nfds; ++n)
2145     \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2146     \&
2147     \& if (timeout >= 0)
2148     \& // create/start timer
2149     \&
2150     \& // poll
2151     \& ev_loop (EV_A_ 0);
2152     \&
2153     \& // stop timer again
2154     \& if (timeout >= 0)
2155     \& ev_timer_stop (EV_A_ &to);
2156     \&
2157     \& // stop io watchers again \- their callbacks should have set
2158     \& for (n = 0; n < nfds; ++n)
2159     \& ev_io_stop (EV_A_ iow [n]);
2160     \&
2161     \& return got_events;
2162     \& }
2163     .Ve
2164     .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2165     .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2166     .IX Subsection "ev_embed - when one backend isn't enough..."
2167     This is a rather advanced watcher type that lets you embed one event loop
2168     into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2169     loop, other types of watchers might be handled in a delayed or incorrect
2170     fashion and must not be used).
2171     .PP
2172     There are primarily two reasons you would want that: work around bugs and
2173     prioritise I/O.
2174     .PP
2175     As an example for a bug workaround, the kqueue backend might only support
2176     sockets on some platform, so it is unusable as generic backend, but you
2177     still want to make use of it because you have many sockets and it scales
2178     so nicely. In this case, you would create a kqueue-based loop and embed it
2179     into your default loop (which might use e.g. poll). Overall operation will
2180     be a bit slower because first libev has to poll and then call kevent, but
2181     at least you can use both at what they are best.
2182     .PP
2183     As for prioritising I/O: rarely you have the case where some fds have
2184     to be watched and handled very quickly (with low latency), and even
2185     priorities and idle watchers might have too much overhead. In this case
2186     you would put all the high priority stuff in one loop and all the rest in
2187     a second one, and embed the second one in the first.
2188     .PP
2189     As long as the watcher is active, the callback will be invoked every time
2190     there might be events pending in the embedded loop. The callback must then
2191     call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2192     their callbacks (you could also start an idle watcher to give the embedded
2193     loop strictly lower priority for example). You can also set the callback
2194     to \f(CW0\fR, in which case the embed watcher will automatically execute the
2195     embedded loop sweep.
2196     .PP
2197     As long as the watcher is started it will automatically handle events. The
2198     callback will be invoked whenever some events have been handled. You can
2199     set the callback to \f(CW0\fR to avoid having to specify one if you are not
2200     interested in that.
2201     .PP
2202     Also, there have not currently been made special provisions for forking:
2203     when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2204     but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2205     yourself.
2206     .PP
2207     Unfortunately, not all backends are embeddable, only the ones returned by
2208     \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2209     portable one.
2210     .PP
2211     So when you want to use this feature you will always have to be prepared
2212     that you cannot get an embeddable loop. The recommended way to get around
2213     this is to have a separate variables for your embeddable loop, try to
2214     create it, and if that fails, use the normal loop for everything.
2215     .PP
2216     \fIWatcher-Specific Functions and Data Members\fR
2217     .IX Subsection "Watcher-Specific Functions and Data Members"
2218     .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2219     .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2220     .PD 0
2221     .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2222     .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2223     .PD
2224     Configures the watcher to embed the given loop, which must be
2225     embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2226     invoked automatically, otherwise it is the responsibility of the callback
2227     to invoke it (it will continue to be called until the sweep has been done,
2228     if you do not want thta, you need to temporarily stop the embed watcher).
2229     .IP "ev_embed_sweep (loop, ev_embed *)" 4
2230     .IX Item "ev_embed_sweep (loop, ev_embed *)"
2231     Make a single, non-blocking sweep over the embedded loop. This works
2232     similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2233     apropriate way for embedded loops.
2234     .IP "struct ev_loop *other [read\-only]" 4
2235     .IX Item "struct ev_loop *other [read-only]"
2236     The embedded event loop.
2237     .PP
2238     \fIExamples\fR
2239     .IX Subsection "Examples"
2240     .PP
2241     Example: Try to get an embeddable event loop and embed it into the default
2242     event loop. If that is not possible, use the default loop. The default
2243     loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in
2244     \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be
2245     used).
2246     .PP
2247     .Vb 3
2248     \& struct ev_loop *loop_hi = ev_default_init (0);
2249     \& struct ev_loop *loop_lo = 0;
2250     \& struct ev_embed embed;
2251     \&
2252     \& // see if there is a chance of getting one that works
2253     \& // (remember that a flags value of 0 means autodetection)
2254     \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2255     \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2256     \& : 0;
2257     \&
2258     \& // if we got one, then embed it, otherwise default to loop_hi
2259     \& if (loop_lo)
2260     \& {
2261     \& ev_embed_init (&embed, 0, loop_lo);
2262     \& ev_embed_start (loop_hi, &embed);
2263     \& }
2264     \& else
2265     \& loop_lo = loop_hi;
2266     .Ve
2267     .PP
2268     Example: Check if kqueue is available but not recommended and create
2269     a kqueue backend for use with sockets (which usually work with any
2270     kqueue implementation). Store the kqueue/socket\-only event loop in
2271     \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2272     .PP
2273     .Vb 3
2274     \& struct ev_loop *loop = ev_default_init (0);
2275     \& struct ev_loop *loop_socket = 0;
2276     \& struct ev_embed embed;
2277     \&
2278     \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2279     \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2280     \& {
2281     \& ev_embed_init (&embed, 0, loop_socket);
2282     \& ev_embed_start (loop, &embed);
2283     \& }
2284     \&
2285     \& if (!loop_socket)
2286     \& loop_socket = loop;
2287     \&
2288     \& // now use loop_socket for all sockets, and loop for everything else
2289     .Ve
2290     .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2291     .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2292     .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2293     Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2294     whoever is a good citizen cared to tell libev about it by calling
2295     \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2296     event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2297     and only in the child after the fork. If whoever good citizen calling
2298     \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2299     handlers will be invoked, too, of course.
2300     .PP
2301     \fIWatcher-Specific Functions and Data Members\fR
2302     .IX Subsection "Watcher-Specific Functions and Data Members"
2303     .IP "ev_fork_init (ev_signal *, callback)" 4
2304     .IX Item "ev_fork_init (ev_signal *, callback)"
2305     Initialises and configures the fork watcher \- it has no parameters of any
2306     kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2307     believe me.
2308     .ie n .Sh """ev_async"" \- how to wake up another event loop"
2309     .el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2310     .IX Subsection "ev_async - how to wake up another event loop"
2311     In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2312     asynchronous sources such as signal handlers (as opposed to multiple event
2313     loops \- those are of course safe to use in different threads).
2314     .PP
2315     Sometimes, however, you need to wake up another event loop you do not
2316     control, for example because it belongs to another thread. This is what
2317     \&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2318     can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2319     safe.
2320     .PP
2321     This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2322     too, are asynchronous in nature, and signals, too, will be compressed
2323     (i.e. the number of callback invocations may be less than the number of
2324     \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2325     .PP
2326     Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2327     just the default loop.
2328     .PP
2329     \fIQueueing\fR
2330     .IX Subsection "Queueing"
2331     .PP
2332     \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2333     is that the author does not know of a simple (or any) algorithm for a
2334     multiple-writer-single-reader queue that works in all cases and doesn't
2335     need elaborate support such as pthreads.
2336     .PP
2337     That means that if you want to queue data, you have to provide your own
2338     queue. But at least I can tell you would implement locking around your
2339     queue:
2340     .IP "queueing from a signal handler context" 4
2341     .IX Item "queueing from a signal handler context"
2342     To implement race-free queueing, you simply add to the queue in the signal
2343     handler but you block the signal handler in the watcher callback. Here is an example that does that for
2344     some fictitiuous \s-1SIGUSR1\s0 handler:
2345     .Sp
2346     .Vb 1
2347     \& static ev_async mysig;
2348     \&
2349     \& static void
2350     \& sigusr1_handler (void)
2351     \& {
2352     \& sometype data;
2353     \&
2354     \& // no locking etc.
2355     \& queue_put (data);
2356     \& ev_async_send (EV_DEFAULT_ &mysig);
2357     \& }
2358     \&
2359     \& static void
2360     \& mysig_cb (EV_P_ ev_async *w, int revents)
2361     \& {
2362     \& sometype data;
2363     \& sigset_t block, prev;
2364     \&
2365     \& sigemptyset (&block);
2366     \& sigaddset (&block, SIGUSR1);
2367     \& sigprocmask (SIG_BLOCK, &block, &prev);
2368     \&
2369     \& while (queue_get (&data))
2370     \& process (data);
2371     \&
2372     \& if (sigismember (&prev, SIGUSR1)
2373     \& sigprocmask (SIG_UNBLOCK, &block, 0);
2374     \& }
2375     .Ve
2376     .Sp
2377     (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2378     instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2379     either...).
2380     .IP "queueing from a thread context" 4
2381     .IX Item "queueing from a thread context"
2382     The strategy for threads is different, as you cannot (easily) block
2383     threads but you can easily preempt them, so to queue safely you need to
2384     employ a traditional mutex lock, such as in this pthread example:
2385     .Sp
2386     .Vb 2
2387     \& static ev_async mysig;
2388     \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2389     \&
2390     \& static void
2391     \& otherthread (void)
2392     \& {
2393     \& // only need to lock the actual queueing operation
2394     \& pthread_mutex_lock (&mymutex);
2395     \& queue_put (data);
2396     \& pthread_mutex_unlock (&mymutex);
2397     \&
2398     \& ev_async_send (EV_DEFAULT_ &mysig);
2399     \& }
2400     \&
2401     \& static void
2402     \& mysig_cb (EV_P_ ev_async *w, int revents)
2403     \& {
2404     \& pthread_mutex_lock (&mymutex);
2405     \&
2406     \& while (queue_get (&data))
2407     \& process (data);
2408     \&
2409     \& pthread_mutex_unlock (&mymutex);
2410     \& }
2411     .Ve
2412     .PP
2413     \fIWatcher-Specific Functions and Data Members\fR
2414     .IX Subsection "Watcher-Specific Functions and Data Members"
2415     .IP "ev_async_init (ev_async *, callback)" 4
2416     .IX Item "ev_async_init (ev_async *, callback)"
2417     Initialises and configures the async watcher \- it has no parameters of any
2418     kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
2419     believe me.
2420     .IP "ev_async_send (loop, ev_async *)" 4
2421     .IX Item "ev_async_send (loop, ev_async *)"
2422     Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2423     an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2424     \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or
2425     similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2426     section below on what exactly this means).
2427     .Sp
2428     This call incurs the overhead of a syscall only once per loop iteration,
2429     so while the overhead might be noticable, it doesn't apply to repeated
2430     calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2431     .IP "bool = ev_async_pending (ev_async *)" 4
2432     .IX Item "bool = ev_async_pending (ev_async *)"
2433     Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2434     watcher but the event has not yet been processed (or even noted) by the
2435     event loop.
2436     .Sp
2437     \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2438     the loop iterates next and checks for the watcher to have become active,
2439     it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2440     quickly check wether invoking the loop might be a good idea.
2441     .Sp
2442     Not that this does \fInot\fR check wether the watcher itself is pending, only
2443     wether it has been requested to make this watcher pending.
2444     .SH "OTHER FUNCTIONS"
2445     .IX Header "OTHER FUNCTIONS"
2446     There are some other functions of possible interest. Described. Here. Now.
2447     .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2448     .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2449     This function combines a simple timer and an I/O watcher, calls your
2450     callback on whichever event happens first and automatically stop both
2451     watchers. This is useful if you want to wait for a single event on an fd
2452     or timeout without having to allocate/configure/start/stop/free one or
2453     more watchers yourself.
2454     .Sp
2455     If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
2456     is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
2457     \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
2458     .Sp
2459     If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2460     started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2461     repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
2462     dubious value.
2463     .Sp
2464     The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
2465     passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2466     \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
2467     value passed to \f(CW\*(C`ev_once\*(C'\fR:
2468     .Sp
2469     .Vb 7
2470     \& static void stdin_ready (int revents, void *arg)
2471     \& {
2472     \& if (revents & EV_TIMEOUT)
2473     \& /* doh, nothing entered */;
2474     \& else if (revents & EV_READ)
2475     \& /* stdin might have data for us, joy! */;
2476     \& }
2477     \&
2478     \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2479     .Ve
2480     .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
2481     .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
2482     Feeds the given event set into the event loop, as if the specified event
2483     had happened for the specified watcher (which must be a pointer to an
2484     initialised but not necessarily started event watcher).
2485     .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
2486     .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
2487     Feed an event on the given fd, as if a file descriptor backend detected
2488     the given events it.
2489     .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
2490     .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
2491     Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
2492     loop!).
2493     .SH "LIBEVENT EMULATION"
2494     .IX Header "LIBEVENT EMULATION"
2495     Libev offers a compatibility emulation layer for libevent. It cannot
2496     emulate the internals of libevent, so here are some usage hints:
2497     .IP "\(bu" 4
2498     Use it by including <event.h>, as usual.
2499     .IP "\(bu" 4
2500     The following members are fully supported: ev_base, ev_callback,
2501     ev_arg, ev_fd, ev_res, ev_events.
2502     .IP "\(bu" 4
2503     Avoid using ev_flags and the EVLIST_*\-macros, while it is
2504     maintained by libev, it does not work exactly the same way as in libevent (consider
2505     it a private \s-1API\s0).
2506     .IP "\(bu" 4
2507     Priorities are not currently supported. Initialising priorities
2508     will fail and all watchers will have the same priority, even though there
2509     is an ev_pri field.
2510     .IP "\(bu" 4
2511     In libevent, the last base created gets the signals, in libev, the
2512     first base created (== the default loop) gets the signals.
2513     .IP "\(bu" 4
2514     Other members are not supported.
2515     .IP "\(bu" 4
2516     The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2517     to use the libev header file and library.
2518     .SH "\*(C+ SUPPORT"
2519     .IX Header " SUPPORT"
2520     Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2521     you to use some convinience methods to start/stop watchers and also change
2522     the callback model to a model using method callbacks on objects.
2523     .PP
2524     To use it,
2525     .PP
2526     .Vb 1
2527     \& #include <ev++.h>
2528     .Ve
2529     .PP
2530     This automatically includes \fIev.h\fR and puts all of its definitions (many
2531     of them macros) into the global namespace. All \*(C+ specific things are
2532     put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2533     options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2534     .PP
2535     Care has been taken to keep the overhead low. The only data member the \*(C+
2536     classes add (compared to plain C\-style watchers) is the event loop pointer
2537     that the watcher is associated with (or no additional members at all if
2538     you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2539     .PP
2540     Currently, functions, and static and non-static member functions can be
2541     used as callbacks. Other types should be easy to add as long as they only
2542     need one additional pointer for context. If you need support for other
2543     types of functors please contact the author (preferably after implementing
2544     it).
2545     .PP
2546     Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2547     .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2548     .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2549     .IX Item "ev::READ, ev::WRITE etc."
2550     These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2551     macros from \fIev.h\fR.
2552     .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2553     .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2554     .IX Item "ev::tstamp, ev::now"
2555     Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2556     .ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
2557     .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2558     .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2559     For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2560     the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2561     which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2562     defines by many implementations.
2563     .Sp
2564     All of those classes have these methods:
2565     .RS 4
2566     .IP "ev::TYPE::TYPE ()" 4
2567     .IX Item "ev::TYPE::TYPE ()"
2568     .PD 0
2569     .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2570     .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2571     .IP "ev::TYPE::~TYPE" 4
2572     .IX Item "ev::TYPE::~TYPE"
2573     .PD
2574     The constructor (optionally) takes an event loop to associate the watcher
2575     with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2576     .Sp
2577     The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2578     \&\f(CW\*(C`set\*(C'\fR method before starting it.
2579     .Sp
2580     It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2581     method to set a callback before you can start the watcher.
2582     .Sp
2583     (The reason why you have to use a method is a limitation in \*(C+ which does
2584     not allow explicit template arguments for constructors).
2585     .Sp
2586     The destructor automatically stops the watcher if it is active.
2587     .IP "w\->set<class, &class::method> (object *)" 4
2588     .IX Item "w->set<class, &class::method> (object *)"
2589     This method sets the callback method to call. The method has to have a
2590     signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2591     first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2592     parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2593     .Sp
2594     This method synthesizes efficient thunking code to call your method from
2595     the C callback that libev requires. If your compiler can inline your
2596     callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2597     your compiler is good :), then the method will be fully inlined into the
2598     thunking function, making it as fast as a direct C callback.
2599     .Sp
2600     Example: simple class declaration and watcher initialisation
2601     .Sp
2602     .Vb 4
2603     \& struct myclass
2604     \& {
2605     \& void io_cb (ev::io &w, int revents) { }
2606     \& }
2607     \&
2608     \& myclass obj;
2609     \& ev::io iow;
2610     \& iow.set <myclass, &myclass::io_cb> (&obj);
2611     .Ve
2612     .IP "w\->set<function> (void *data = 0)" 4
2613     .IX Item "w->set<function> (void *data = 0)"
2614     Also sets a callback, but uses a static method or plain function as
2615     callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2616     \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2617     .Sp
2618     The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2619     .Sp
2620     See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2621     .Sp
2622     Example:
2623     .Sp
2624     .Vb 2
2625     \& static void io_cb (ev::io &w, int revents) { }
2626     \& iow.set <io_cb> ();
2627     .Ve
2628     .IP "w\->set (struct ev_loop *)" 4
2629     .IX Item "w->set (struct ev_loop *)"
2630     Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2631     do this when the watcher is inactive (and not pending either).
2632     .IP "w\->set ([args])" 4
2633     .IX Item "w->set ([args])"
2634     Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2635     called at least once. Unlike the C counterpart, an active watcher gets
2636     automatically stopped and restarted when reconfiguring it with this
2637     method.
2638     .IP "w\->start ()" 4
2639     .IX Item "w->start ()"
2640     Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2641     constructor already stores the event loop.
2642     .IP "w\->stop ()" 4
2643     .IX Item "w->stop ()"
2644     Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2645     .ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2646     .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2647     .IX Item "w->again () (ev::timer, ev::periodic only)"
2648     For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2649     \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2650     .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2651     .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2652     .IX Item "w->sweep () (ev::embed only)"
2653     Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2654     .ie n .IP "w\->update () (""ev::stat"" only)" 4
2655     .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2656     .IX Item "w->update () (ev::stat only)"
2657     Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2658     .RE
2659     .RS 4
2660     .RE
2661     .PP
2662     Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2663     the constructor.
2664     .PP
2665     .Vb 4
2666     \& class myclass
2667     \& {
2668     \& ev::io io; void io_cb (ev::io &w, int revents);
2669     \& ev:idle idle void idle_cb (ev::idle &w, int revents);
2670     \&
2671     \& myclass (int fd)
2672     \& {
2673     \& io .set <myclass, &myclass::io_cb > (this);
2674     \& idle.set <myclass, &myclass::idle_cb> (this);
2675     \&
2676     \& io.start (fd, ev::READ);
2677     \& }
2678     \& };
2679     .Ve
2680     .SH "OTHER LANGUAGE BINDINGS"
2681     .IX Header "OTHER LANGUAGE BINDINGS"
2682     Libev does not offer other language bindings itself, but bindings for a
2683     numbe rof languages exist in the form of third-party packages. If you know
2684     any interesting language binding in addition to the ones listed here, drop
2685     me a note.
2686     .IP "Perl" 4
2687     .IX Item "Perl"
2688     The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
2689     libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
2690     there are additional modules that implement libev-compatible interfaces
2691     to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR), \f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the
2692     \&\f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR and \f(CW\*(C`EV::Glib\*(C'\fR).
2693     .Sp
2694     It can be found and installed via \s-1CPAN\s0, its homepage is found at
2695     <http://software.schmorp.de/pkg/EV>.
2696     .IP "Ruby" 4
2697     .IX Item "Ruby"
2698     Tony Arcieri has written a ruby extension that offers access to a subset
2699     of the libev \s-1API\s0 and adds filehandle abstractions, asynchronous \s-1DNS\s0 and
2700     more on top of it. It can be found via gem servers. Its homepage is at
2701     <http://rev.rubyforge.org/>.
2702     .IP "D" 4
2703     .IX Item "D"
2704     Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
2705     be found at <http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
2706     .SH "MACRO MAGIC"
2707     .IX Header "MACRO MAGIC"
2708     Libev can be compiled with a variety of options, the most fundamantal
2709     of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2710     functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2711     .PP
2712     To make it easier to write programs that cope with either variant, the
2713     following macros are defined:
2714     .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2715     .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2716     .IX Item "EV_A, EV_A_"
2717     This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2718     loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2719     \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2720     .Sp
2721     .Vb 3
2722     \& ev_unref (EV_A);
2723     \& ev_timer_add (EV_A_ watcher);
2724     \& ev_loop (EV_A_ 0);
2725     .Ve
2726     .Sp
2727     It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2728     which is often provided by the following macro.
2729     .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2730     .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2731     .IX Item "EV_P, EV_P_"
2732     This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2733     loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2734     \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2735     .Sp
2736     .Vb 2
2737     \& // this is how ev_unref is being declared
2738     \& static void ev_unref (EV_P);
2739     \&
2740     \& // this is how you can declare your typical callback
2741     \& static void cb (EV_P_ ev_timer *w, int revents)
2742     .Ve
2743     .Sp
2744     It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2745     suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2746     .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2747     .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2748     .IX Item "EV_DEFAULT, EV_DEFAULT_"
2749     Similar to the other two macros, this gives you the value of the default
2750     loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2751     .ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
2752     .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
2753     .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
2754     Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
2755     default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
2756     is undefined when the default loop has not been initialised by a previous
2757     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.
2758     .Sp
2759     It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
2760     watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2761     .PP
2762     Example: Declare and initialise a check watcher, utilising the above
2763     macros so it will work regardless of whether multiple loops are supported
2764     or not.
2765     .PP
2766     .Vb 5
2767     \& static void
2768     \& check_cb (EV_P_ ev_timer *w, int revents)
2769     \& {
2770     \& ev_check_stop (EV_A_ w);
2771     \& }
2772     \&
2773     \& ev_check check;
2774     \& ev_check_init (&check, check_cb);
2775     \& ev_check_start (EV_DEFAULT_ &check);
2776     \& ev_loop (EV_DEFAULT_ 0);
2777     .Ve
2778     .SH "EMBEDDING"
2779     .IX Header "EMBEDDING"
2780     Libev can (and often is) directly embedded into host
2781     applications. Examples of applications that embed it include the Deliantra
2782     Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2783     and rxvt-unicode.
2784     .PP
2785     The goal is to enable you to just copy the necessary files into your
2786     source directory without having to change even a single line in them, so
2787     you can easily upgrade by simply copying (or having a checked-out copy of
2788     libev somewhere in your source tree).
2789     .Sh "\s-1FILESETS\s0"
2790     .IX Subsection "FILESETS"
2791     Depending on what features you need you need to include one or more sets of files
2792     in your app.
2793     .PP
2794     \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2795     .IX Subsection "CORE EVENT LOOP"
2796     .PP
2797     To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2798     configuration (no autoconf):
2799     .PP
2800     .Vb 2
2801     \& #define EV_STANDALONE 1
2802     \& #include "ev.c"
2803     .Ve
2804     .PP
2805     This will automatically include \fIev.h\fR, too, and should be done in a
2806     single C source file only to provide the function implementations. To use
2807     it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2808     done by writing a wrapper around \fIev.h\fR that you can include instead and
2809     where you can put other configuration options):
2810     .PP
2811     .Vb 2
2812     \& #define EV_STANDALONE 1
2813     \& #include "ev.h"
2814     .Ve
2815     .PP
2816     Both header files and implementation files can be compiled with a \*(C+
2817     compiler (at least, thats a stated goal, and breakage will be treated
2818     as a bug).
2819     .PP
2820     You need the following files in your source tree, or in a directory
2821     in your include path (e.g. in libev/ when using \-Ilibev):
2822     .PP
2823     .Vb 4
2824     \& ev.h
2825     \& ev.c
2826     \& ev_vars.h
2827     \& ev_wrap.h
2828     \&
2829     \& ev_win32.c required on win32 platforms only
2830     \&
2831     \& ev_select.c only when select backend is enabled (which is enabled by default)
2832     \& ev_poll.c only when poll backend is enabled (disabled by default)
2833     \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2834     \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2835     \& ev_port.c only when the solaris port backend is enabled (disabled by default)
2836     .Ve
2837     .PP
2838     \&\fIev.c\fR includes the backend files directly when enabled, so you only need
2839     to compile this single file.
2840     .PP
2841     \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2842     .IX Subsection "LIBEVENT COMPATIBILITY API"
2843     .PP
2844     To include the libevent compatibility \s-1API\s0, also include:
2845     .PP
2846     .Vb 1
2847     \& #include "event.c"
2848     .Ve
2849     .PP
2850     in the file including \fIev.c\fR, and:
2851     .PP
2852     .Vb 1
2853     \& #include "event.h"
2854     .Ve
2855     .PP
2856     in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2857     .PP
2858     You need the following additional files for this:
2859     .PP
2860     .Vb 2
2861     \& event.h
2862     \& event.c
2863     .Ve
2864     .PP
2865     \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2866     .IX Subsection "AUTOCONF SUPPORT"
2867     .PP
2868     Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2869     whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2870     \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2871     include \fIconfig.h\fR and configure itself accordingly.
2872     .PP
2873     For this of course you need the m4 file:
2874     .PP
2875     .Vb 1
2876     \& libev.m4
2877     .Ve
2878     .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2879     .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2880     Libev can be configured via a variety of preprocessor symbols you have to
2881     define before including any of its files. The default in the absense of
2882     autoconf is noted for every option.
2883     .IP "\s-1EV_STANDALONE\s0" 4
2884     .IX Item "EV_STANDALONE"
2885     Must always be \f(CW1\fR if you do not use autoconf configuration, which
2886     keeps libev from including \fIconfig.h\fR, and it also defines dummy
2887     implementations for some libevent functions (such as logging, which is not
2888     supported). It will also not define any of the structs usually found in
2889     \&\fIevent.h\fR that are not directly supported by the libev core alone.
2890     .IP "\s-1EV_USE_MONOTONIC\s0" 4
2891     .IX Item "EV_USE_MONOTONIC"
2892     If defined to be \f(CW1\fR, libev will try to detect the availability of the
2893     monotonic clock option at both compiletime and runtime. Otherwise no use
2894     of the monotonic clock option will be attempted. If you enable this, you
2895     usually have to link against librt or something similar. Enabling it when
2896     the functionality isn't available is safe, though, although you have
2897     to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2898     function is hiding in (often \fI\-lrt\fR).
2899     .IP "\s-1EV_USE_REALTIME\s0" 4
2900     .IX Item "EV_USE_REALTIME"
2901     If defined to be \f(CW1\fR, libev will try to detect the availability of the
2902     realtime clock option at compiletime (and assume its availability at
2903     runtime if successful). Otherwise no use of the realtime clock option will
2904     be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2905     (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
2906     note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2907     .IP "\s-1EV_USE_NANOSLEEP\s0" 4
2908     .IX Item "EV_USE_NANOSLEEP"
2909     If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2910     and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
2911     .IP "\s-1EV_USE_EVENTFD\s0" 4
2912     .IX Item "EV_USE_EVENTFD"
2913     If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
2914     available and will probe for kernel support at runtime. This will improve
2915     \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
2916     If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
2917     2.7 or newer, otherwise disabled.
2918     .IP "\s-1EV_USE_SELECT\s0" 4
2919     .IX Item "EV_USE_SELECT"
2920     If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2921     \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2922     other method takes over, select will be it. Otherwise the select backend
2923     will not be compiled in.
2924     .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2925     .IX Item "EV_SELECT_USE_FD_SET"
2926     If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2927     structure. This is useful if libev doesn't compile due to a missing
2928     \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2929     exotic systems. This usually limits the range of file descriptors to some
2930     low limit such as 1024 or might have other limitations (winsocket only
2931     allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2932     influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2933     .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2934     .IX Item "EV_SELECT_IS_WINSOCKET"
2935     When defined to \f(CW1\fR, the select backend will assume that
2936     select/socket/connect etc. don't understand file descriptors but
2937     wants osf handles on win32 (this is the case when the select to
2938     be used is the winsock select). This means that it will call
2939     \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2940     it is assumed that all these functions actually work on fds, even
2941     on win32. Should not be defined on non\-win32 platforms.
2942     .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
2943     .IX Item "EV_FD_TO_WIN32_HANDLE"
2944     If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
2945     file descriptors to socket handles. When not defining this symbol (the
2946     default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
2947     correct. In some cases, programs use their own file descriptor management,
2948     in which case they can provide this function to map fds to socket handles.
2949     .IP "\s-1EV_USE_POLL\s0" 4
2950     .IX Item "EV_USE_POLL"
2951     If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2952     backend. Otherwise it will be enabled on non\-win32 platforms. It
2953     takes precedence over select.
2954     .IP "\s-1EV_USE_EPOLL\s0" 4
2955     .IX Item "EV_USE_EPOLL"
2956     If defined to be \f(CW1\fR, libev will compile in support for the Linux
2957     \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2958     otherwise another method will be used as fallback. This is the preferred
2959     backend for GNU/Linux systems. If undefined, it will be enabled if the
2960     headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2961     .IP "\s-1EV_USE_KQUEUE\s0" 4
2962     .IX Item "EV_USE_KQUEUE"
2963     If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2964     \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2965     otherwise another method will be used as fallback. This is the preferred
2966     backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2967     supports some types of fds correctly (the only platform we found that
2968     supports ptys for example was NetBSD), so kqueue might be compiled in, but
2969     not be used unless explicitly requested. The best way to use it is to find
2970     out whether kqueue supports your type of fd properly and use an embedded
2971     kqueue loop.
2972     .IP "\s-1EV_USE_PORT\s0" 4
2973     .IX Item "EV_USE_PORT"
2974     If defined to be \f(CW1\fR, libev will compile in support for the Solaris
2975     10 port style backend. Its availability will be detected at runtime,
2976     otherwise another method will be used as fallback. This is the preferred
2977     backend for Solaris 10 systems.
2978     .IP "\s-1EV_USE_DEVPOLL\s0" 4
2979     .IX Item "EV_USE_DEVPOLL"
2980     reserved for future expansion, works like the \s-1USE\s0 symbols above.
2981     .IP "\s-1EV_USE_INOTIFY\s0" 4
2982     .IX Item "EV_USE_INOTIFY"
2983     If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2984     interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2985     be detected at runtime. If undefined, it will be enabled if the headers
2986     indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2987     .IP "\s-1EV_ATOMIC_T\s0" 4
2988     .IX Item "EV_ATOMIC_T"
2989     Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
2990     access is atomic with respect to other threads or signal contexts. No such
2991     type is easily found in the C language, so you can provide your own type
2992     that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
2993     as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
2994     .Sp
2995     In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
2996     (from \fIsignal.h\fR), which is usually good enough on most platforms.
2997     .IP "\s-1EV_H\s0" 4
2998     .IX Item "EV_H"
2999     The name of the \fIev.h\fR header file used to include it. The default if
3000     undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3001     used to virtually rename the \fIev.h\fR header file in case of conflicts.
3002     .IP "\s-1EV_CONFIG_H\s0" 4
3003     .IX Item "EV_CONFIG_H"
3004     If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3005     \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3006     \&\f(CW\*(C`EV_H\*(C'\fR, above.
3007     .IP "\s-1EV_EVENT_H\s0" 4
3008     .IX Item "EV_EVENT_H"
3009     Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3010     of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3011     .IP "\s-1EV_PROTOTYPES\s0" 4
3012     .IX Item "EV_PROTOTYPES"
3013     If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3014     prototypes, but still define all the structs and other symbols. This is
3015     occasionally useful if you want to provide your own wrapper functions
3016     around libev functions.
3017     .IP "\s-1EV_MULTIPLICITY\s0" 4
3018     .IX Item "EV_MULTIPLICITY"
3019     If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3020     will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3021     additional independent event loops. Otherwise there will be no support
3022     for multiple event loops and there is no first event loop pointer
3023     argument. Instead, all functions act on the single default loop.
3024     .IP "\s-1EV_MINPRI\s0" 4
3025     .IX Item "EV_MINPRI"
3026     .PD 0
3027     .IP "\s-1EV_MAXPRI\s0" 4
3028     .IX Item "EV_MAXPRI"
3029     .PD
3030     The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3031     \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3032     provide for more priorities by overriding those symbols (usually defined
3033     to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3034     .Sp
3035     When doing priority-based operations, libev usually has to linearly search
3036     all the priorities, so having many of them (hundreds) uses a lot of space
3037     and time, so using the defaults of five priorities (\-2 .. +2) is usually
3038     fine.
3039     .Sp
3040     If your embedding app does not need any priorities, defining these both to
3041     \&\f(CW0\fR will save some memory and cpu.
3042     .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3043     .IX Item "EV_PERIODIC_ENABLE"
3044     If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3045     defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3046     code.
3047     .IP "\s-1EV_IDLE_ENABLE\s0" 4
3048     .IX Item "EV_IDLE_ENABLE"
3049     If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3050     defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3051     code.
3052     .IP "\s-1EV_EMBED_ENABLE\s0" 4
3053     .IX Item "EV_EMBED_ENABLE"
3054     If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3055     defined to be \f(CW0\fR, then they are not.
3056     .IP "\s-1EV_STAT_ENABLE\s0" 4
3057     .IX Item "EV_STAT_ENABLE"
3058     If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3059     defined to be \f(CW0\fR, then they are not.
3060     .IP "\s-1EV_FORK_ENABLE\s0" 4
3061     .IX Item "EV_FORK_ENABLE"
3062     If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3063     defined to be \f(CW0\fR, then they are not.
3064     .IP "\s-1EV_ASYNC_ENABLE\s0" 4
3065     .IX Item "EV_ASYNC_ENABLE"
3066     If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3067     defined to be \f(CW0\fR, then they are not.
3068     .IP "\s-1EV_MINIMAL\s0" 4
3069     .IX Item "EV_MINIMAL"
3070     If you need to shave off some kilobytes of code at the expense of some
3071     speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3072     inlining decisions, saves roughly 30% codesize of amd64. It also selects a
3073     much smaller 2\-heap for timer management over the default 4\-heap.
3074     .IP "\s-1EV_PID_HASHSIZE\s0" 4
3075     .IX Item "EV_PID_HASHSIZE"
3076     \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3077     pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3078     than enough. If you need to manage thousands of children you might want to
3079     increase this value (\fImust\fR be a power of two).
3080     .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3081     .IX Item "EV_INOTIFY_HASHSIZE"
3082     \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3083     inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3084     usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3085     watchers you might want to increase this value (\fImust\fR be a power of
3086     two).
3087     .IP "\s-1EV_USE_4HEAP\s0" 4
3088     .IX Item "EV_USE_4HEAP"
3089     Heaps are not very cache-efficient. To improve the cache-efficiency of the
3090     timer and periodics heap, libev uses a 4\-heap when this symbol is defined
3091     to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has a
3092     noticable after performance with many (thousands) of watchers.
3093     .Sp
3094     The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3095     (disabled).
3096     .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3097     .IX Item "EV_HEAP_CACHE_AT"
3098     Heaps are not very cache-efficient. To improve the cache-efficiency of the
3099     timer and periodics heap, libev can cache the timestamp (\fIat\fR) within
3100     the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3101     which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3102     but avoids random read accesses on heap changes. This noticably improves
3103     performance noticably with with many (hundreds) of watchers.
3104     .Sp
3105     The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3106     (disabled).
3107     .IP "\s-1EV_COMMON\s0" 4
3108     .IX Item "EV_COMMON"
3109     By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3110     this macro to a something else you can include more and other types of
3111     members. You have to define it each time you include one of the files,
3112     though, and it must be identical each time.
3113     .Sp
3114     For example, the perl \s-1EV\s0 module uses something like this:
3115     .Sp
3116     .Vb 3
3117     \& #define EV_COMMON \e
3118     \& SV *self; /* contains this struct */ \e
3119     \& SV *cb_sv, *fh /* note no trailing ";" */
3120     .Ve
3121     .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3122     .IX Item "EV_CB_DECLARE (type)"
3123     .PD 0
3124     .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3125     .IX Item "EV_CB_INVOKE (watcher, revents)"
3126     .IP "ev_set_cb (ev, cb)" 4
3127     .IX Item "ev_set_cb (ev, cb)"
3128     .PD
3129     Can be used to change the callback member declaration in each watcher,
3130     and the way callbacks are invoked and set. Must expand to a struct member
3131     definition and a statement, respectively. See the \fIev.h\fR header file for
3132     their default definitions. One possible use for overriding these is to
3133     avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3134     method calls instead of plain function calls in \*(C+.
3135     .Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3136     .IX Subsection "EXPORTED API SYMBOLS"
3137     If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
3138     exported symbols, you can use the provided \fISymbol.*\fR files which list
3139     all public symbols, one per line:
3140     .PP
3141     .Vb 2
3142     \& Symbols.ev for libev proper
3143     \& Symbols.event for the libevent emulation
3144     .Ve
3145     .PP
3146     This can also be used to rename all public symbols to avoid clashes with
3147     multiple versions of libev linked together (which is obviously bad in
3148     itself, but sometimes it is inconvinient to avoid this).
3149     .PP
3150     A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3151     include before including \fIev.h\fR:
3152     .PP
3153     .Vb 1
3154     \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3155     .Ve