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77on event-based programming, nor will it introduce event-based programming 77on event-based programming, nor will it introduce event-based programming
78with libev. 78with libev.
79 79
80Familiarity with event based programming techniques in general is assumed 80Familiarity with event based programming techniques in general is assumed
81throughout this document. 81throughout this document.
82
83=head1 WHAT TO READ WHEN IN A HURRY
84
85This manual tries to be very detailed, but unfortunately, this also makes
86it very long. If you just want to know the basics of libev, I suggest
87reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
88look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
89C<ev_timer> sections in L<WATCHER TYPES>.
82 90
83=head1 ABOUT LIBEV 91=head1 ABOUT LIBEV
84 92
85Libev is an event loop: you register interest in certain events (such as a 93Libev is an event loop: you register interest in certain events (such as a
86file descriptor being readable or a timeout occurring), and it will manage 94file descriptor being readable or a timeout occurring), and it will manage
233the current system, you would need to look at C<ev_embeddable_backends () 241the current system, you would need to look at C<ev_embeddable_backends ()
234& ev_supported_backends ()>, likewise for recommended ones. 242& ev_supported_backends ()>, likewise for recommended ones.
235 243
236See the description of C<ev_embed> watchers for more info. 244See the description of C<ev_embed> watchers for more info.
237 245
238=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT] 246=item ev_set_allocator (void *(*cb)(void *ptr, long size))
239 247
240Sets the allocation function to use (the prototype is similar - the 248Sets the allocation function to use (the prototype is similar - the
241semantics are identical to the C<realloc> C89/SuS/POSIX function). It is 249semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242used to allocate and free memory (no surprises here). If it returns zero 250used to allocate and free memory (no surprises here). If it returns zero
243when memory needs to be allocated (C<size != 0>), the library might abort 251when memory needs to be allocated (C<size != 0>), the library might abort
269 } 277 }
270 278
271 ... 279 ...
272 ev_set_allocator (persistent_realloc); 280 ev_set_allocator (persistent_realloc);
273 281
274=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT] 282=item ev_set_syserr_cb (void (*cb)(const char *msg))
275 283
276Set the callback function to call on a retryable system call error (such 284Set the callback function to call on a retryable system call error (such
277as failed select, poll, epoll_wait). The message is a printable string 285as failed select, poll, epoll_wait). The message is a printable string
278indicating the system call or subsystem causing the problem. If this 286indicating the system call or subsystem causing the problem. If this
279callback is set, then libev will expect it to remedy the situation, no 287callback is set, then libev will expect it to remedy the situation, no
291 } 299 }
292 300
293 ... 301 ...
294 ev_set_syserr_cb (fatal_error); 302 ev_set_syserr_cb (fatal_error);
295 303
304=item ev_feed_signal (int signum)
305
306This function can be used to "simulate" a signal receive. It is completely
307safe to call this function at any time, from any context, including signal
308handlers or random threads.
309
310It's main use is to customise signal handling in your process, especially
311in the presence of threads. For example, you could block signals
312by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
313creating any loops), and in one thread, use C<sigwait> or any other
314mechanism to wait for signals, then "deliver" them to libev by calling
315C<ev_feed_signal>.
316
296=back 317=back
297 318
298=head1 FUNCTIONS CONTROLLING EVENT LOOPS 319=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299 320
300An event loop is described by a C<struct ev_loop *> (the C<struct> is 321An event loop is described by a C<struct ev_loop *> (the C<struct> is
301I<not> optional in this case unless libev 3 compatibility is disabled, as 322I<not> optional in this case unless libev 3 compatibility is disabled, as
302libev 3 had an C<ev_loop> function colliding with the struct name). 323libev 3 had an C<ev_loop> function colliding with the struct name).
303 324
304The library knows two types of such loops, the I<default> loop, which 325The library knows two types of such loops, the I<default> loop, which
305supports signals and child events, and dynamically created event loops 326supports child process events, and dynamically created event loops which
306which do not. 327do not.
307 328
308=over 4 329=over 4
309 330
310=item struct ev_loop *ev_default_loop (unsigned int flags) 331=item struct ev_loop *ev_default_loop (unsigned int flags)
311 332
347=item struct ev_loop *ev_loop_new (unsigned int flags) 368=item struct ev_loop *ev_loop_new (unsigned int flags)
348 369
349This will create and initialise a new event loop object. If the loop 370This will create and initialise a new event loop object. If the loop
350could not be initialised, returns false. 371could not be initialised, returns false.
351 372
352Note that this function I<is> thread-safe, and one common way to use 373This function is thread-safe, and one common way to use libev with
353libev with threads is indeed to create one loop per thread, and using the 374threads is indeed to create one loop per thread, and using the default
354default loop in the "main" or "initial" thread. 375loop in the "main" or "initial" thread.
355 376
356The flags argument can be used to specify special behaviour or specific 377The flags argument can be used to specify special behaviour or specific
357backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>). 378backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
358 379
359The following flags are supported: 380The following flags are supported:
394environment variable. 415environment variable.
395 416
396=item C<EVFLAG_NOINOTIFY> 417=item C<EVFLAG_NOINOTIFY>
397 418
398When this flag is specified, then libev will not attempt to use the 419When this flag is specified, then libev will not attempt to use the
399I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and 420I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
400testing, this flag can be useful to conserve inotify file descriptors, as 421testing, this flag can be useful to conserve inotify file descriptors, as
401otherwise each loop using C<ev_stat> watchers consumes one inotify handle. 422otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
402 423
403=item C<EVFLAG_SIGNALFD> 424=item C<EVFLAG_SIGNALFD>
404 425
405When this flag is specified, then libev will attempt to use the 426When this flag is specified, then libev will attempt to use the
406I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API 427I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
407delivers signals synchronously, which makes it both faster and might make 428delivers signals synchronously, which makes it both faster and might make
408it possible to get the queued signal data. It can also simplify signal 429it possible to get the queued signal data. It can also simplify signal
409handling with threads, as long as you properly block signals in your 430handling with threads, as long as you properly block signals in your
410threads that are not interested in handling them. 431threads that are not interested in handling them.
411 432
412Signalfd will not be used by default as this changes your signal mask, and 433Signalfd will not be used by default as this changes your signal mask, and
413there are a lot of shoddy libraries and programs (glib's threadpool for 434there are a lot of shoddy libraries and programs (glib's threadpool for
414example) that can't properly initialise their signal masks. 435example) that can't properly initialise their signal masks.
436
437=item C<EVFLAG_NOSIGMASK>
438
439When this flag is specified, then libev will avoid to modify the signal
440mask. Specifically, this means you ahve to make sure signals are unblocked
441when you want to receive them.
442
443This behaviour is useful when you want to do your own signal handling, or
444want to handle signals only in specific threads and want to avoid libev
445unblocking the signals.
446
447This flag's behaviour will become the default in future versions of libev.
415 448
416=item C<EVBACKEND_SELECT> (value 1, portable select backend) 449=item C<EVBACKEND_SELECT> (value 1, portable select backend)
417 450
418This is your standard select(2) backend. Not I<completely> standard, as 451This is your standard select(2) backend. Not I<completely> standard, as
419libev tries to roll its own fd_set with no limits on the number of fds, 452libev tries to roll its own fd_set with no limits on the number of fds,
455epoll scales either O(1) or O(active_fds). 488epoll scales either O(1) or O(active_fds).
456 489
457The epoll mechanism deserves honorable mention as the most misdesigned 490The epoll mechanism deserves honorable mention as the most misdesigned
458of the more advanced event mechanisms: mere annoyances include silently 491of the more advanced event mechanisms: mere annoyances include silently
459dropping file descriptors, requiring a system call per change per file 492dropping file descriptors, requiring a system call per change per file
460descriptor (and unnecessary guessing of parameters), problems with dup and 493descriptor (and unnecessary guessing of parameters), problems with dup,
494returning before the timeout value, resulting in additional iterations
495(and only giving 5ms accuracy while select on the same platform gives
461so on. The biggest issue is fork races, however - if a program forks then 4960.1ms) and so on. The biggest issue is fork races, however - if a program
462I<both> parent and child process have to recreate the epoll set, which can 497forks then I<both> parent and child process have to recreate the epoll
463take considerable time (one syscall per file descriptor) and is of course 498set, which can take considerable time (one syscall per file descriptor)
464hard to detect. 499and is of course hard to detect.
465 500
466Epoll is also notoriously buggy - embedding epoll fds I<should> work, but 501Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
467of course I<doesn't>, and epoll just loves to report events for totally 502of course I<doesn't>, and epoll just loves to report events for totally
468I<different> file descriptors (even already closed ones, so one cannot 503I<different> file descriptors (even already closed ones, so one cannot
469even remove them from the set) than registered in the set (especially 504even remove them from the set) than registered in the set (especially
471employing an additional generation counter and comparing that against the 506employing an additional generation counter and comparing that against the
472events to filter out spurious ones, recreating the set when required. Last 507events to filter out spurious ones, recreating the set when required. Last
473not least, it also refuses to work with some file descriptors which work 508not least, it also refuses to work with some file descriptors which work
474perfectly fine with C<select> (files, many character devices...). 509perfectly fine with C<select> (files, many character devices...).
475 510
511Epoll is truly the train wreck analog among event poll mechanisms.
512
476While stopping, setting and starting an I/O watcher in the same iteration 513While stopping, setting and starting an I/O watcher in the same iteration
477will result in some caching, there is still a system call per such 514will result in some caching, there is still a system call per such
478incident (because the same I<file descriptor> could point to a different 515incident (because the same I<file descriptor> could point to a different
479I<file description> now), so its best to avoid that. Also, C<dup ()>'ed 516I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
480file descriptors might not work very well if you register events for both 517file descriptors might not work very well if you register events for both
568 605
569Try all backends (even potentially broken ones that wouldn't be tried 606Try all backends (even potentially broken ones that wouldn't be tried
570with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as 607with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
571C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. 608C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
572 609
573It is definitely not recommended to use this flag. 610It is definitely not recommended to use this flag, use whatever
611C<ev_recommended_backends ()> returns, or simply do not specify a backend
612at all.
613
614=item C<EVBACKEND_MASK>
615
616Not a backend at all, but a mask to select all backend bits from a
617C<flags> value, in case you want to mask out any backends from a flags
618value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
574 619
575=back 620=back
576 621
577If one or more of the backend flags are or'ed into the flags value, 622If one or more of the backend flags are or'ed into the flags value,
578then only these backends will be tried (in the reverse order as listed 623then only these backends will be tried (in the reverse order as listed
607This function is normally used on loop objects allocated by 652This function is normally used on loop objects allocated by
608C<ev_loop_new>, but it can also be used on the default loop returned by 653C<ev_loop_new>, but it can also be used on the default loop returned by
609C<ev_default_loop>, in which case it is not thread-safe. 654C<ev_default_loop>, in which case it is not thread-safe.
610 655
611Note that it is not advisable to call this function on the default loop 656Note that it is not advisable to call this function on the default loop
612except in the rare occasion where you really need to free it's resources. 657except in the rare occasion where you really need to free its resources.
613If you need dynamically allocated loops it is better to use C<ev_loop_new> 658If you need dynamically allocated loops it is better to use C<ev_loop_new>
614and C<ev_loop_destroy>. 659and C<ev_loop_destroy>.
615 660
616=item ev_loop_fork (loop) 661=item ev_loop_fork (loop)
617 662
665prepare and check phases. 710prepare and check phases.
666 711
667=item unsigned int ev_depth (loop) 712=item unsigned int ev_depth (loop)
668 713
669Returns the number of times C<ev_run> was entered minus the number of 714Returns the number of times C<ev_run> was entered minus the number of
670times C<ev_run> was exited, in other words, the recursion depth. 715times C<ev_run> was exited normally, in other words, the recursion depth.
671 716
672Outside C<ev_run>, this number is zero. In a callback, this number is 717Outside C<ev_run>, this number is zero. In a callback, this number is
673C<1>, unless C<ev_run> was invoked recursively (or from another thread), 718C<1>, unless C<ev_run> was invoked recursively (or from another thread),
674in which case it is higher. 719in which case it is higher.
675 720
676Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread 721Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
677etc.), doesn't count as "exit" - consider this as a hint to avoid such 722throwing an exception etc.), doesn't count as "exit" - consider this
678ungentleman-like behaviour unless it's really convenient. 723as a hint to avoid such ungentleman-like behaviour unless it's really
724convenient, in which case it is fully supported.
679 725
680=item unsigned int ev_backend (loop) 726=item unsigned int ev_backend (loop)
681 727
682Returns one of the C<EVBACKEND_*> flags indicating the event backend in 728Returns one of the C<EVBACKEND_*> flags indicating the event backend in
683use. 729use.
744relying on all watchers to be stopped when deciding when a program has 790relying on all watchers to be stopped when deciding when a program has
745finished (especially in interactive programs), but having a program 791finished (especially in interactive programs), but having a program
746that automatically loops as long as it has to and no longer by virtue 792that automatically loops as long as it has to and no longer by virtue
747of relying on its watchers stopping correctly, that is truly a thing of 793of relying on its watchers stopping correctly, that is truly a thing of
748beauty. 794beauty.
795
796This function is also I<mostly> exception-safe - you can break out of
797a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
798exception and so on. This does not decrement the C<ev_depth> value, nor
799will it clear any outstanding C<EVBREAK_ONE> breaks.
749 800
750A flags value of C<EVRUN_NOWAIT> will look for new events, will handle 801A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
751those events and any already outstanding ones, but will not wait and 802those events and any already outstanding ones, but will not wait and
752block your process in case there are no events and will return after one 803block your process in case there are no events and will return after one
753iteration of the loop. This is sometimes useful to poll and handle new 804iteration of the loop. This is sometimes useful to poll and handle new
815Can be used to make a call to C<ev_run> return early (but only after it 866Can be used to make a call to C<ev_run> return early (but only after it
816has processed all outstanding events). The C<how> argument must be either 867has processed all outstanding events). The C<how> argument must be either
817C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or 868C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
818C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return. 869C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
819 870
820This "unloop state" will be cleared when entering C<ev_run> again. 871This "break state" will be cleared on the next call to C<ev_run>.
821 872
822It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO## 873It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
874which case it will have no effect.
823 875
824=item ev_ref (loop) 876=item ev_ref (loop)
825 877
826=item ev_unref (loop) 878=item ev_unref (loop)
827 879
848running when nothing else is active. 900running when nothing else is active.
849 901
850 ev_signal exitsig; 902 ev_signal exitsig;
851 ev_signal_init (&exitsig, sig_cb, SIGINT); 903 ev_signal_init (&exitsig, sig_cb, SIGINT);
852 ev_signal_start (loop, &exitsig); 904 ev_signal_start (loop, &exitsig);
853 evf_unref (loop); 905 ev_unref (loop);
854 906
855Example: For some weird reason, unregister the above signal handler again. 907Example: For some weird reason, unregister the above signal handler again.
856 908
857 ev_ref (loop); 909 ev_ref (loop);
858 ev_signal_stop (loop, &exitsig); 910 ev_signal_stop (loop, &exitsig);
970See also the locking example in the C<THREADS> section later in this 1022See also the locking example in the C<THREADS> section later in this
971document. 1023document.
972 1024
973=item ev_set_userdata (loop, void *data) 1025=item ev_set_userdata (loop, void *data)
974 1026
975=item ev_userdata (loop) 1027=item void *ev_userdata (loop)
976 1028
977Set and retrieve a single C<void *> associated with a loop. When 1029Set and retrieve a single C<void *> associated with a loop. When
978C<ev_set_userdata> has never been called, then C<ev_userdata> returns 1030C<ev_set_userdata> has never been called, then C<ev_userdata> returns
979C<0.> 1031C<0>.
980 1032
981These two functions can be used to associate arbitrary data with a loop, 1033These two functions can be used to associate arbitrary data with a loop,
982and are intended solely for the C<invoke_pending_cb>, C<release> and 1034and are intended solely for the C<invoke_pending_cb>, C<release> and
983C<acquire> callbacks described above, but of course can be (ab-)used for 1035C<acquire> callbacks described above, but of course can be (ab-)used for
984any other purpose as well. 1036any other purpose as well.
1114The event loop has been resumed in the child process after fork (see 1166The event loop has been resumed in the child process after fork (see
1115C<ev_fork>). 1167C<ev_fork>).
1116 1168
1117=item C<EV_CLEANUP> 1169=item C<EV_CLEANUP>
1118 1170
1119The event loop is abotu to be destroyed (see C<ev_cleanup>). 1171The event loop is about to be destroyed (see C<ev_cleanup>).
1120 1172
1121=item C<EV_ASYNC> 1173=item C<EV_ASYNC>
1122 1174
1123The given async watcher has been asynchronously notified (see C<ev_async>). 1175The given async watcher has been asynchronously notified (see C<ev_async>).
1124 1176
1146programs, though, as the fd could already be closed and reused for another 1198programs, though, as the fd could already be closed and reused for another
1147thing, so beware. 1199thing, so beware.
1148 1200
1149=back 1201=back
1150 1202
1151=head2 WATCHER STATES
1152
1153There are various watcher states mentioned throughout this manual -
1154active, pending and so on. In this section these states and the rules to
1155transition between them will be described in more detail - and while these
1156rules might look complicated, they usually do "the right thing".
1157
1158=over 4
1159
1160=item initialiased
1161
1162Before a watcher can be registered with the event looop it has to be
1163initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1164C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1165
1166In this state it is simply some block of memory that is suitable for use
1167in an event loop. It can be moved around, freed, reused etc. at will.
1168
1169=item started/running/active
1170
1171Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1172property of the event loop, and is actively waiting for events. While in
1173this state it cannot be accessed (except in a few documented ways), moved,
1174freed or anything else - the only legal thing is to keep a pointer to it,
1175and call libev functions on it that are documented to work on active watchers.
1176
1177=item pending
1178
1179If a watcher is active and libev determines that an event it is interested
1180in has occurred (such as a timer expiring), it will become pending. It will
1181stay in this pending state until either it is stopped or its callback is
1182about to be invoked, so it is not normally pending inside the watcher
1183callback.
1184
1185The watcher might or might not be active while it is pending (for example,
1186an expired non-repeating timer can be pending but no longer active). If it
1187is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
1188but it is still property of the event loop at this time, so cannot be
1189moved, freed or reused. And if it is active the rules described in the
1190previous item still apply.
1191
1192It is also possible to feed an event on a watcher that is not active (e.g.
1193via C<ev_feed_event>), in which case it becomes pending without being
1194active.
1195
1196=item stopped
1197
1198A watcher can be stopped implicitly by libev (in which case it might still
1199be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1200latter will clear any pending state the watcher might be in, regardless
1201of whether it was active or not, so stopping a watcher explicitly before
1202freeing it is often a good idea.
1203
1204While stopped (and not pending) the watcher is essentially in the
1205initialised state, that is it can be reused, moved, modified in any way
1206you wish.
1207
1208=back
1209
1210=head2 GENERIC WATCHER FUNCTIONS 1203=head2 GENERIC WATCHER FUNCTIONS
1211 1204
1212=over 4 1205=over 4
1213 1206
1214=item C<ev_init> (ev_TYPE *watcher, callback) 1207=item C<ev_init> (ev_TYPE *watcher, callback)
1355 1348
1356See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related 1349See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1357functions that do not need a watcher. 1350functions that do not need a watcher.
1358 1351
1359=back 1352=back
1360
1361 1353
1362=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 1354=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1363 1355
1364Each watcher has, by default, a member C<void *data> that you can change 1356Each watcher has, by default, a member C<void *data> that you can change
1365and read at any time: libev will completely ignore it. This can be used 1357and read at any time: libev will completely ignore it. This can be used
1421 t2_cb (EV_P_ ev_timer *w, int revents) 1413 t2_cb (EV_P_ ev_timer *w, int revents)
1422 { 1414 {
1423 struct my_biggy big = (struct my_biggy *) 1415 struct my_biggy big = (struct my_biggy *)
1424 (((char *)w) - offsetof (struct my_biggy, t2)); 1416 (((char *)w) - offsetof (struct my_biggy, t2));
1425 } 1417 }
1418
1419=head2 WATCHER STATES
1420
1421There are various watcher states mentioned throughout this manual -
1422active, pending and so on. In this section these states and the rules to
1423transition between them will be described in more detail - and while these
1424rules might look complicated, they usually do "the right thing".
1425
1426=over 4
1427
1428=item initialiased
1429
1430Before a watcher can be registered with the event looop it has to be
1431initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1432C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1433
1434In this state it is simply some block of memory that is suitable for use
1435in an event loop. It can be moved around, freed, reused etc. at will.
1436
1437=item started/running/active
1438
1439Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1440property of the event loop, and is actively waiting for events. While in
1441this state it cannot be accessed (except in a few documented ways), moved,
1442freed or anything else - the only legal thing is to keep a pointer to it,
1443and call libev functions on it that are documented to work on active watchers.
1444
1445=item pending
1446
1447If a watcher is active and libev determines that an event it is interested
1448in has occurred (such as a timer expiring), it will become pending. It will
1449stay in this pending state until either it is stopped or its callback is
1450about to be invoked, so it is not normally pending inside the watcher
1451callback.
1452
1453The watcher might or might not be active while it is pending (for example,
1454an expired non-repeating timer can be pending but no longer active). If it
1455is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
1456but it is still property of the event loop at this time, so cannot be
1457moved, freed or reused. And if it is active the rules described in the
1458previous item still apply.
1459
1460It is also possible to feed an event on a watcher that is not active (e.g.
1461via C<ev_feed_event>), in which case it becomes pending without being
1462active.
1463
1464=item stopped
1465
1466A watcher can be stopped implicitly by libev (in which case it might still
1467be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1468latter will clear any pending state the watcher might be in, regardless
1469of whether it was active or not, so stopping a watcher explicitly before
1470freeing it is often a good idea.
1471
1472While stopped (and not pending) the watcher is essentially in the
1473initialised state, that is it can be reused, moved, modified in any way
1474you wish.
1475
1476=back
1426 1477
1427=head2 WATCHER PRIORITY MODELS 1478=head2 WATCHER PRIORITY MODELS
1428 1479
1429Many event loops support I<watcher priorities>, which are usually small 1480Many event loops support I<watcher priorities>, which are usually small
1430integers that influence the ordering of event callback invocation 1481integers that influence the ordering of event callback invocation
2249 2300
2250=head2 C<ev_signal> - signal me when a signal gets signalled! 2301=head2 C<ev_signal> - signal me when a signal gets signalled!
2251 2302
2252Signal watchers will trigger an event when the process receives a specific 2303Signal watchers will trigger an event when the process receives a specific
2253signal one or more times. Even though signals are very asynchronous, libev 2304signal one or more times. Even though signals are very asynchronous, libev
2254will try it's best to deliver signals synchronously, i.e. as part of the 2305will try its best to deliver signals synchronously, i.e. as part of the
2255normal event processing, like any other event. 2306normal event processing, like any other event.
2256 2307
2257If you want signals to be delivered truly asynchronously, just use 2308If you want signals to be delivered truly asynchronously, just use
2258C<sigaction> as you would do without libev and forget about sharing 2309C<sigaction> as you would do without libev and forget about sharing
2259the signal. You can even use C<ev_async> from a signal handler to 2310the signal. You can even use C<ev_async> from a signal handler to
2301I<has> to modify the signal mask, at least temporarily. 2352I<has> to modify the signal mask, at least temporarily.
2302 2353
2303So I can't stress this enough: I<If you do not reset your signal mask when 2354So I can't stress this enough: I<If you do not reset your signal mask when
2304you expect it to be empty, you have a race condition in your code>. This 2355you expect it to be empty, you have a race condition in your code>. This
2305is not a libev-specific thing, this is true for most event libraries. 2356is not a libev-specific thing, this is true for most event libraries.
2357
2358=head3 The special problem of threads signal handling
2359
2360POSIX threads has problematic signal handling semantics, specifically,
2361a lot of functionality (sigfd, sigwait etc.) only really works if all
2362threads in a process block signals, which is hard to achieve.
2363
2364When you want to use sigwait (or mix libev signal handling with your own
2365for the same signals), you can tackle this problem by globally blocking
2366all signals before creating any threads (or creating them with a fully set
2367sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
2368loops. Then designate one thread as "signal receiver thread" which handles
2369these signals. You can pass on any signals that libev might be interested
2370in by calling C<ev_feed_signal>.
2306 2371
2307=head3 Watcher-Specific Functions and Data Members 2372=head3 Watcher-Specific Functions and Data Members
2308 2373
2309=over 4 2374=over 4
2310 2375
3098 3163
3099=item ev_fork_init (ev_fork *, callback) 3164=item ev_fork_init (ev_fork *, callback)
3100 3165
3101Initialises and configures the fork watcher - it has no parameters of any 3166Initialises and configures the fork watcher - it has no parameters of any
3102kind. There is a C<ev_fork_set> macro, but using it is utterly pointless, 3167kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3103believe me. 3168really.
3104 3169
3105=back 3170=back
3106 3171
3107 3172
3108=head2 C<ev_cleanup> - even the best things end 3173=head2 C<ev_cleanup> - even the best things end
3109 3174
3110Cleanup watchers are called just before the event loop they are registered 3175Cleanup watchers are called just before the event loop is being destroyed
3111with is being destroyed. 3176by a call to C<ev_loop_destroy>.
3112 3177
3113While there is no guarantee that the event loop gets destroyed, cleanup 3178While there is no guarantee that the event loop gets destroyed, cleanup
3114watchers provide a convenient method to install cleanup hooks for your 3179watchers provide a convenient method to install cleanup hooks for your
3115program, worker threads and so on - you just to make sure to destroy the 3180program, worker threads and so on - you just to make sure to destroy the
3116loop when you want them to be invoked. 3181loop when you want them to be invoked.
3126 3191
3127=item ev_cleanup_init (ev_cleanup *, callback) 3192=item ev_cleanup_init (ev_cleanup *, callback)
3128 3193
3129Initialises and configures the cleanup watcher - it has no parameters of 3194Initialises and configures the cleanup watcher - it has no parameters of
3130any kind. There is a C<ev_cleanup_set> macro, but using it is utterly 3195any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
3131pointless, believe me. 3196pointless, I assure you.
3132 3197
3133=back 3198=back
3134 3199
3135Example: Register an atexit handler to destroy the default loop, so any 3200Example: Register an atexit handler to destroy the default loop, so any
3136cleanup functions are called. 3201cleanup functions are called.
3157it by calling C<ev_async_send>, which is thread- and signal safe. 3222it by calling C<ev_async_send>, which is thread- and signal safe.
3158 3223
3159This functionality is very similar to C<ev_signal> watchers, as signals, 3224This functionality is very similar to C<ev_signal> watchers, as signals,
3160too, are asynchronous in nature, and signals, too, will be compressed 3225too, are asynchronous in nature, and signals, too, will be compressed
3161(i.e. the number of callback invocations may be less than the number of 3226(i.e. the number of callback invocations may be less than the number of
3162C<ev_async_sent> calls). 3227C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3228of "global async watchers" by using a watcher on an otherwise unused
3229signal, and C<ev_feed_signal> to signal this watcher from another thread,
3230even without knowing which loop owns the signal.
3163 3231
3164Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not 3232Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3165just the default loop. 3233just the default loop.
3166 3234
3167=head3 Queueing 3235=head3 Queueing
3343Feed an event on the given fd, as if a file descriptor backend detected 3411Feed an event on the given fd, as if a file descriptor backend detected
3344the given events it. 3412the given events it.
3345 3413
3346=item ev_feed_signal_event (loop, int signum) 3414=item ev_feed_signal_event (loop, int signum)
3347 3415
3348Feed an event as if the given signal occurred (C<loop> must be the default 3416Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3349loop!). 3417which is async-safe.
3418
3419=back
3420
3421
3422=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3423
3424This section explains some common idioms that are not immediately
3425obvious. Note that examples are sprinkled over the whole manual, and this
3426section only contains stuff that wouldn't fit anywhere else.
3427
3428=over 4
3429
3430=item Model/nested event loop invocations and exit conditions.
3431
3432Often (especially in GUI toolkits) there are places where you have
3433I<modal> interaction, which is most easily implemented by recursively
3434invoking C<ev_run>.
3435
3436This brings the problem of exiting - a callback might want to finish the
3437main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3438a modal "Are you sure?" dialog is still waiting), or just the nested one
3439and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3440other combination: In these cases, C<ev_break> will not work alone.
3441
3442The solution is to maintain "break this loop" variable for each C<ev_run>
3443invocation, and use a loop around C<ev_run> until the condition is
3444triggered, using C<EVRUN_ONCE>:
3445
3446 // main loop
3447 int exit_main_loop = 0;
3448
3449 while (!exit_main_loop)
3450 ev_run (EV_DEFAULT_ EVRUN_ONCE);
3451
3452 // in a model watcher
3453 int exit_nested_loop = 0;
3454
3455 while (!exit_nested_loop)
3456 ev_run (EV_A_ EVRUN_ONCE);
3457
3458To exit from any of these loops, just set the corresponding exit variable:
3459
3460 // exit modal loop
3461 exit_nested_loop = 1;
3462
3463 // exit main program, after modal loop is finished
3464 exit_main_loop = 1;
3465
3466 // exit both
3467 exit_main_loop = exit_nested_loop = 1;
3350 3468
3351=back 3469=back
3352 3470
3353 3471
3354=head1 LIBEVENT EMULATION 3472=head1 LIBEVENT EMULATION
3355 3473
3356Libev offers a compatibility emulation layer for libevent. It cannot 3474Libev offers a compatibility emulation layer for libevent. It cannot
3357emulate the internals of libevent, so here are some usage hints: 3475emulate the internals of libevent, so here are some usage hints:
3358 3476
3359=over 4 3477=over 4
3478
3479=item * Only the libevent-1.4.1-beta API is being emulated.
3480
3481This was the newest libevent version available when libev was implemented,
3482and is still mostly unchanged in 2010.
3360 3483
3361=item * Use it by including <event.h>, as usual. 3484=item * Use it by including <event.h>, as usual.
3362 3485
3363=item * The following members are fully supported: ev_base, ev_callback, 3486=item * The following members are fully supported: ev_base, ev_callback,
3364ev_arg, ev_fd, ev_res, ev_events. 3487ev_arg, ev_fd, ev_res, ev_events.
3370=item * Priorities are not currently supported. Initialising priorities 3493=item * Priorities are not currently supported. Initialising priorities
3371will fail and all watchers will have the same priority, even though there 3494will fail and all watchers will have the same priority, even though there
3372is an ev_pri field. 3495is an ev_pri field.
3373 3496
3374=item * In libevent, the last base created gets the signals, in libev, the 3497=item * In libevent, the last base created gets the signals, in libev, the
3375first base created (== the default loop) gets the signals. 3498base that registered the signal gets the signals.
3376 3499
3377=item * Other members are not supported. 3500=item * Other members are not supported.
3378 3501
3379=item * The libev emulation is I<not> ABI compatible to libevent, you need 3502=item * The libev emulation is I<not> ABI compatible to libevent, you need
3380to use the libev header file and library. 3503to use the libev header file and library.
3399Care has been taken to keep the overhead low. The only data member the C++ 3522Care has been taken to keep the overhead low. The only data member the C++
3400classes add (compared to plain C-style watchers) is the event loop pointer 3523classes add (compared to plain C-style watchers) is the event loop pointer
3401that the watcher is associated with (or no additional members at all if 3524that the watcher is associated with (or no additional members at all if
3402you disable C<EV_MULTIPLICITY> when embedding libev). 3525you disable C<EV_MULTIPLICITY> when embedding libev).
3403 3526
3404Currently, functions, and static and non-static member functions can be 3527Currently, functions, static and non-static member functions and classes
3405used as callbacks. Other types should be easy to add as long as they only 3528with C<operator ()> can be used as callbacks. Other types should be easy
3406need one additional pointer for context. If you need support for other 3529to add as long as they only need one additional pointer for context. If
3407types of functors please contact the author (preferably after implementing 3530you need support for other types of functors please contact the author
3408it). 3531(preferably after implementing it).
3409 3532
3410Here is a list of things available in the C<ev> namespace: 3533Here is a list of things available in the C<ev> namespace:
3411 3534
3412=over 4 3535=over 4
3413 3536
4757structure (guaranteed by POSIX but not by ISO C for example), but it also 4880structure (guaranteed by POSIX but not by ISO C for example), but it also
4758assumes that the same (machine) code can be used to call any watcher 4881assumes that the same (machine) code can be used to call any watcher
4759callback: The watcher callbacks have different type signatures, but libev 4882callback: The watcher callbacks have different type signatures, but libev
4760calls them using an C<ev_watcher *> internally. 4883calls them using an C<ev_watcher *> internally.
4761 4884
4885=item pointer accesses must be thread-atomic
4886
4887Accessing a pointer value must be atomic, it must both be readable and
4888writable in one piece - this is the case on all current architectures.
4889
4762=item C<sig_atomic_t volatile> must be thread-atomic as well 4890=item C<sig_atomic_t volatile> must be thread-atomic as well
4763 4891
4764The type C<sig_atomic_t volatile> (or whatever is defined as 4892The type C<sig_atomic_t volatile> (or whatever is defined as
4765C<EV_ATOMIC_T>) must be atomic with respect to accesses from different 4893C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4766threads. This is not part of the specification for C<sig_atomic_t>, but is 4894threads. This is not part of the specification for C<sig_atomic_t>, but is
4872=back 5000=back
4873 5001
4874 5002
4875=head1 PORTING FROM LIBEV 3.X TO 4.X 5003=head1 PORTING FROM LIBEV 3.X TO 4.X
4876 5004
4877The major version 4 introduced some minor incompatible changes to the API. 5005The major version 4 introduced some incompatible changes to the API.
4878 5006
4879At the moment, the C<ev.h> header file tries to implement superficial 5007At the moment, the C<ev.h> header file provides compatibility definitions
4880compatibility, so most programs should still compile. Those might be 5008for all changes, so most programs should still compile. The compatibility
4881removed in later versions of libev, so better update early than late. 5009layer might be removed in later versions of libev, so better update to the
5010new API early than late.
4882 5011
4883=over 4 5012=over 4
5013
5014=item C<EV_COMPAT3> backwards compatibility mechanism
5015
5016The backward compatibility mechanism can be controlled by
5017C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
5018section.
4884 5019
4885=item C<ev_default_destroy> and C<ev_default_fork> have been removed 5020=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4886 5021
4887These calls can be replaced easily by their C<ev_loop_xxx> counterparts: 5022These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4888 5023
4914ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme 5049ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4915as all other watcher types. Note that C<ev_loop_fork> is still called 5050as all other watcher types. Note that C<ev_loop_fork> is still called
4916C<ev_loop_fork> because it would otherwise clash with the C<ev_fork> 5051C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4917typedef. 5052typedef.
4918 5053
4919=item C<EV_COMPAT3> backwards compatibility mechanism
4920
4921The backward compatibility mechanism can be controlled by
4922C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4923section.
4924
4925=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES> 5054=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4926 5055
4927The preprocessor symbol C<EV_MINIMAL> has been replaced by a different 5056The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4928mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile 5057mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4929and work, but the library code will of course be larger. 5058and work, but the library code will of course be larger.
5003 5132
5004=back 5133=back
5005 5134
5006=head1 AUTHOR 5135=head1 AUTHOR
5007 5136
5008Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. 5137Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5138Magnusson and Emanuele Giaquinta.
5009 5139

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