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Revision 1.348 by sf-exg, Sat Jan 8 17:52:39 2011 UTC

43 43
44 int 44 int
45 main (void) 45 main (void)
46 { 46 {
47 // use the default event loop unless you have special needs 47 // use the default event loop unless you have special needs
48 struct ev_loop *loop = ev_default_loop (0); 48 struct ev_loop *loop = EV_DEFAULT;
49 49
50 // initialise an io watcher, then start it 50 // initialise an io watcher, then start it
51 // this one will watch for stdin to become readable 51 // this one will watch for stdin to become readable
52 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 52 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53 ev_io_start (loop, &stdin_watcher); 53 ev_io_start (loop, &stdin_watcher);
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
124this argument. 132this argument.
125 133
126=head2 TIME REPRESENTATION 134=head2 TIME REPRESENTATION
127 135
128Libev represents time as a single floating point number, representing 136Libev represents time as a single floating point number, representing
129the (fractional) number of seconds since the (POSIX) epoch (in practise 137the (fractional) number of seconds since the (POSIX) epoch (in practice
130somewhere near the beginning of 1970, details are complicated, don't 138somewhere near the beginning of 1970, details are complicated, don't
131ask). This type is called C<ev_tstamp>, which is what you should use 139ask). This type is called C<ev_tstamp>, which is what you should use
132too. It usually aliases to the C<double> type in C. When you need to do 140too. It usually aliases to the C<double> type in C. When you need to do
133any calculations on it, you should treat it as some floating point value. 141any calculations on it, you should treat it as some floating point value.
134 142
165 173
166=item ev_tstamp ev_time () 174=item ev_tstamp ev_time ()
167 175
168Returns the current time as libev would use it. Please note that the 176Returns the current time as libev would use it. Please note that the
169C<ev_now> function is usually faster and also often returns the timestamp 177C<ev_now> function is usually faster and also often returns the timestamp
170you actually want to know. 178you actually want to know. Also interesting is the combination of
179C<ev_update_now> and C<ev_now>.
171 180
172=item ev_sleep (ev_tstamp interval) 181=item ev_sleep (ev_tstamp interval)
173 182
174Sleep for the given interval: The current thread will be blocked until 183Sleep for the given interval: The current thread will be blocked until
175either it is interrupted or the given time interval has passed. Basically 184either it is interrupted or the given time interval has passed. Basically
192as this indicates an incompatible change. Minor versions are usually 201as this indicates an incompatible change. Minor versions are usually
193compatible to older versions, so a larger minor version alone is usually 202compatible to older versions, so a larger minor version alone is usually
194not a problem. 203not a problem.
195 204
196Example: Make sure we haven't accidentally been linked against the wrong 205Example: Make sure we haven't accidentally been linked against the wrong
197version (note, however, that this will not detect ABI mismatches :). 206version (note, however, that this will not detect other ABI mismatches,
207such as LFS or reentrancy).
198 208
199 assert (("libev version mismatch", 209 assert (("libev version mismatch",
200 ev_version_major () == EV_VERSION_MAJOR 210 ev_version_major () == EV_VERSION_MAJOR
201 && ev_version_minor () >= EV_VERSION_MINOR)); 211 && ev_version_minor () >= EV_VERSION_MINOR));
202 212
213 assert (("sorry, no epoll, no sex", 223 assert (("sorry, no epoll, no sex",
214 ev_supported_backends () & EVBACKEND_EPOLL)); 224 ev_supported_backends () & EVBACKEND_EPOLL));
215 225
216=item unsigned int ev_recommended_backends () 226=item unsigned int ev_recommended_backends ()
217 227
218Return the set of all backends compiled into this binary of libev and also 228Return the set of all backends compiled into this binary of libev and
219recommended for this platform. This set is often smaller than the one 229also recommended for this platform, meaning it will work for most file
230descriptor types. This set is often smaller than the one returned by
220returned by C<ev_supported_backends>, as for example kqueue is broken on 231C<ev_supported_backends>, as for example kqueue is broken on most BSDs
221most BSDs and will not be auto-detected unless you explicitly request it 232and will not be auto-detected unless you explicitly request it (assuming
222(assuming you know what you are doing). This is the set of backends that 233you know what you are doing). This is the set of backends that libev will
223libev will probe for if you specify no backends explicitly. 234probe for if you specify no backends explicitly.
224 235
225=item unsigned int ev_embeddable_backends () 236=item unsigned int ev_embeddable_backends ()
226 237
227Returns the set of backends that are embeddable in other event loops. This 238Returns the set of backends that are embeddable in other event loops. This
228is the theoretical, all-platform, value. To find which backends 239value is platform-specific but can include backends not available on the
229might be supported on the current system, you would need to look at 240current system. To find which embeddable backends might be supported on
230C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for 241the current system, you would need to look at C<ev_embeddable_backends ()
231recommended ones. 242& ev_supported_backends ()>, likewise for recommended ones.
232 243
233See the description of C<ev_embed> watchers for more info. 244See the description of C<ev_embed> watchers for more info.
234 245
235=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT] 246=item ev_set_allocator (void *(*cb)(void *ptr, long size))
236 247
237Sets the allocation function to use (the prototype is similar - the 248Sets the allocation function to use (the prototype is similar - the
238semantics 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
239used 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
240when 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
266 } 277 }
267 278
268 ... 279 ...
269 ev_set_allocator (persistent_realloc); 280 ev_set_allocator (persistent_realloc);
270 281
271=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT] 282=item ev_set_syserr_cb (void (*cb)(const char *msg))
272 283
273Set 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
274as failed select, poll, epoll_wait). The message is a printable string 285as failed select, poll, epoll_wait). The message is a printable string
275indicating the system call or subsystem causing the problem. If this 286indicating the system call or subsystem causing the problem. If this
276callback 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
290 ... 301 ...
291 ev_set_syserr_cb (fatal_error); 302 ev_set_syserr_cb (fatal_error);
292 303
293=back 304=back
294 305
295=head1 FUNCTIONS CONTROLLING THE EVENT LOOP 306=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296 307
297An event loop is described by a C<struct ev_loop *> (the C<struct> is 308An event loop is described by a C<struct ev_loop *> (the C<struct> is
298I<not> optional in this case unless libev 3 compatibility is disabled, as 309I<not> optional in this case unless libev 3 compatibility is disabled, as
299libev 3 had an C<ev_loop> function colliding with the struct name). 310libev 3 had an C<ev_loop> function colliding with the struct name).
300 311
301The library knows two types of such loops, the I<default> loop, which 312The library knows two types of such loops, the I<default> loop, which
302supports signals and child events, and dynamically created event loops 313supports child process events, and dynamically created event loops which
303which do not. 314do not.
304 315
305=over 4 316=over 4
306 317
307=item struct ev_loop *ev_default_loop (unsigned int flags) 318=item struct ev_loop *ev_default_loop (unsigned int flags)
308 319
309This will initialise the default event loop if it hasn't been initialised 320This returns the "default" event loop object, which is what you should
310yet and return it. If the default loop could not be initialised, returns 321normally use when you just need "the event loop". Event loop objects and
311false. If it already was initialised it simply returns it (and ignores the 322the C<flags> parameter are described in more detail in the entry for
312flags. If that is troubling you, check C<ev_backend ()> afterwards). 323C<ev_loop_new>.
324
325If the default loop is already initialised then this function simply
326returns it (and ignores the flags. If that is troubling you, check
327C<ev_backend ()> afterwards). Otherwise it will create it with the given
328flags, which should almost always be C<0>, unless the caller is also the
329one calling C<ev_run> or otherwise qualifies as "the main program".
313 330
314If you don't know what event loop to use, use the one returned from this 331If you don't know what event loop to use, use the one returned from this
315function. 332function (or via the C<EV_DEFAULT> macro).
316 333
317Note that this function is I<not> thread-safe, so if you want to use it 334Note that this function is I<not> thread-safe, so if you want to use it
318from multiple threads, you have to lock (note also that this is unlikely, 335from multiple threads, you have to employ some kind of mutex (note also
319as loops cannot be shared easily between threads anyway). 336that this case is unlikely, as loops cannot be shared easily between
337threads anyway).
320 338
321The default loop is the only loop that can handle C<ev_signal> and 339The default loop is the only loop that can handle C<ev_child> watchers,
322C<ev_child> watchers, and to do this, it always registers a handler 340and to do this, it always registers a handler for C<SIGCHLD>. If this is
323for C<SIGCHLD>. If this is a problem for your application you can either 341a problem for your application you can either create a dynamic loop with
324create a dynamic loop with C<ev_loop_new> that doesn't do that, or you 342C<ev_loop_new> which doesn't do that, or you can simply overwrite the
325can simply overwrite the C<SIGCHLD> signal handler I<after> calling 343C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326C<ev_default_init>. 344
345Example: This is the most typical usage.
346
347 if (!ev_default_loop (0))
348 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
349
350Example: Restrict libev to the select and poll backends, and do not allow
351environment settings to be taken into account:
352
353 ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
354
355=item struct ev_loop *ev_loop_new (unsigned int flags)
356
357This will create and initialise a new event loop object. If the loop
358could not be initialised, returns false.
359
360This function is thread-safe, and one common way to use libev with
361threads is indeed to create one loop per thread, and using the default
362loop in the "main" or "initial" thread.
327 363
328The flags argument can be used to specify special behaviour or specific 364The flags argument can be used to specify special behaviour or specific
329backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>). 365backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330 366
331The following flags are supported: 367The following flags are supported:
366environment variable. 402environment variable.
367 403
368=item C<EVFLAG_NOINOTIFY> 404=item C<EVFLAG_NOINOTIFY>
369 405
370When this flag is specified, then libev will not attempt to use the 406When this flag is specified, then libev will not attempt to use the
371I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and 407I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
372testing, this flag can be useful to conserve inotify file descriptors, as 408testing, this flag can be useful to conserve inotify file descriptors, as
373otherwise each loop using C<ev_stat> watchers consumes one inotify handle. 409otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374 410
375=item C<EVFLAG_SIGNALFD> 411=item C<EVFLAG_SIGNALFD>
376 412
377When this flag is specified, then libev will attempt to use the 413When this flag is specified, then libev will attempt to use the
378I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API 414I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
379delivers signals synchronously, which makes it both faster and might make 415delivers signals synchronously, which makes it both faster and might make
380it possible to get the queued signal data. It can also simplify signal 416it possible to get the queued signal data. It can also simplify signal
381handling with threads, as long as you properly block signals in your 417handling with threads, as long as you properly block signals in your
382threads that are not interested in handling them. 418threads that are not interested in handling them.
383 419
427epoll scales either O(1) or O(active_fds). 463epoll scales either O(1) or O(active_fds).
428 464
429The epoll mechanism deserves honorable mention as the most misdesigned 465The epoll mechanism deserves honorable mention as the most misdesigned
430of the more advanced event mechanisms: mere annoyances include silently 466of the more advanced event mechanisms: mere annoyances include silently
431dropping file descriptors, requiring a system call per change per file 467dropping file descriptors, requiring a system call per change per file
432descriptor (and unnecessary guessing of parameters), problems with dup and 468descriptor (and unnecessary guessing of parameters), problems with dup,
469returning before the timeout value, resulting in additional iterations
470(and only giving 5ms accuracy while select on the same platform gives
433so on. The biggest issue is fork races, however - if a program forks then 4710.1ms) and so on. The biggest issue is fork races, however - if a program
434I<both> parent and child process have to recreate the epoll set, which can 472forks then I<both> parent and child process have to recreate the epoll
435take considerable time (one syscall per file descriptor) and is of course 473set, which can take considerable time (one syscall per file descriptor)
436hard to detect. 474and is of course hard to detect.
437 475
438Epoll is also notoriously buggy - embedding epoll fds I<should> work, but 476Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
439of course I<doesn't>, and epoll just loves to report events for totally 477of course I<doesn't>, and epoll just loves to report events for totally
440I<different> file descriptors (even already closed ones, so one cannot 478I<different> file descriptors (even already closed ones, so one cannot
441even remove them from the set) than registered in the set (especially 479even remove them from the set) than registered in the set (especially
443employing an additional generation counter and comparing that against the 481employing an additional generation counter and comparing that against the
444events to filter out spurious ones, recreating the set when required. Last 482events to filter out spurious ones, recreating the set when required. Last
445not least, it also refuses to work with some file descriptors which work 483not least, it also refuses to work with some file descriptors which work
446perfectly fine with C<select> (files, many character devices...). 484perfectly fine with C<select> (files, many character devices...).
447 485
486Epoll is truly the train wreck analog among event poll mechanisms.
487
448While stopping, setting and starting an I/O watcher in the same iteration 488While stopping, setting and starting an I/O watcher in the same iteration
449will result in some caching, there is still a system call per such 489will result in some caching, there is still a system call per such
450incident (because the same I<file descriptor> could point to a different 490incident (because the same I<file descriptor> could point to a different
451I<file description> now), so its best to avoid that. Also, C<dup ()>'ed 491I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
452file descriptors might not work very well if you register events for both 492file descriptors might not work very well if you register events for both
549If one or more of the backend flags are or'ed into the flags value, 589If one or more of the backend flags are or'ed into the flags value,
550then only these backends will be tried (in the reverse order as listed 590then only these backends will be tried (in the reverse order as listed
551here). If none are specified, all backends in C<ev_recommended_backends 591here). If none are specified, all backends in C<ev_recommended_backends
552()> will be tried. 592()> will be tried.
553 593
554Example: This is the most typical usage.
555
556 if (!ev_default_loop (0))
557 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
558
559Example: Restrict libev to the select and poll backends, and do not allow
560environment settings to be taken into account:
561
562 ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
563
564Example: Use whatever libev has to offer, but make sure that kqueue is
565used if available (warning, breaks stuff, best use only with your own
566private event loop and only if you know the OS supports your types of
567fds):
568
569 ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
570
571=item struct ev_loop *ev_loop_new (unsigned int flags)
572
573Similar to C<ev_default_loop>, but always creates a new event loop that is
574always distinct from the default loop.
575
576Note that this function I<is> thread-safe, and one common way to use
577libev with threads is indeed to create one loop per thread, and using the
578default loop in the "main" or "initial" thread.
579
580Example: Try to create a event loop that uses epoll and nothing else. 594Example: Try to create a event loop that uses epoll and nothing else.
581 595
582 struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); 596 struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583 if (!epoller) 597 if (!epoller)
584 fatal ("no epoll found here, maybe it hides under your chair"); 598 fatal ("no epoll found here, maybe it hides under your chair");
585 599
600Example: Use whatever libev has to offer, but make sure that kqueue is
601used if available.
602
603 struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
604
586=item ev_default_destroy () 605=item ev_loop_destroy (loop)
587 606
588Destroys the default loop (frees all memory and kernel state etc.). None 607Destroys an event loop object (frees all memory and kernel state
589of the active event watchers will be stopped in the normal sense, so 608etc.). None of the active event watchers will be stopped in the normal
590e.g. C<ev_is_active> might still return true. It is your responsibility to 609sense, so e.g. C<ev_is_active> might still return true. It is your
591either stop all watchers cleanly yourself I<before> calling this function, 610responsibility to either stop all watchers cleanly yourself I<before>
592or cope with the fact afterwards (which is usually the easiest thing, you 611calling this function, or cope with the fact afterwards (which is usually
593can just ignore the watchers and/or C<free ()> them for example). 612the easiest thing, you can just ignore the watchers and/or C<free ()> them
613for example).
594 614
595Note that certain global state, such as signal state (and installed signal 615Note that certain global state, such as signal state (and installed signal
596handlers), will not be freed by this function, and related watchers (such 616handlers), will not be freed by this function, and related watchers (such
597as signal and child watchers) would need to be stopped manually. 617as signal and child watchers) would need to be stopped manually.
598 618
599In general it is not advisable to call this function except in the 619This function is normally used on loop objects allocated by
600rare occasion where you really need to free e.g. the signal handling 620C<ev_loop_new>, but it can also be used on the default loop returned by
621C<ev_default_loop>, in which case it is not thread-safe.
622
623Note that it is not advisable to call this function on the default loop
624except in the rare occasion where you really need to free its resources.
601pipe fds. If you need dynamically allocated loops it is better to use 625If you need dynamically allocated loops it is better to use C<ev_loop_new>
602C<ev_loop_new> and C<ev_loop_destroy>. 626and C<ev_loop_destroy>.
603 627
604=item ev_loop_destroy (loop) 628=item ev_loop_fork (loop)
605 629
606Like C<ev_default_destroy>, but destroys an event loop created by an
607earlier call to C<ev_loop_new>.
608
609=item ev_default_fork ()
610
611This function sets a flag that causes subsequent C<ev_run> iterations 630This function sets a flag that causes subsequent C<ev_run> iterations to
612to reinitialise the kernel state for backends that have one. Despite the 631reinitialise the kernel state for backends that have one. Despite the
613name, you can call it anytime, but it makes most sense after forking, in 632name, you can call it anytime, but it makes most sense after forking, in
614the child process (or both child and parent, but that again makes little 633the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
615sense). You I<must> call it in the child before using any of the libev 634child before resuming or calling C<ev_run>.
616functions, and it will only take effect at the next C<ev_run> iteration.
617 635
618Again, you I<have> to call it on I<any> loop that you want to re-use after 636Again, you I<have> to call it on I<any> loop that you want to re-use after
619a fork, I<even if you do not plan to use the loop in the parent>. This is 637a fork, I<even if you do not plan to use the loop in the parent>. This is
620because some kernel interfaces *cough* I<kqueue> *cough* do funny things 638because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621during fork. 639during fork.
626call it at all (in fact, C<epoll> is so badly broken that it makes a 644call it at all (in fact, C<epoll> is so badly broken that it makes a
627difference, but libev will usually detect this case on its own and do a 645difference, but libev will usually detect this case on its own and do a
628costly reset of the backend). 646costly reset of the backend).
629 647
630The function itself is quite fast and it's usually not a problem to call 648The function itself is quite fast and it's usually not a problem to call
631it just in case after a fork. To make this easy, the function will fit in 649it just in case after a fork.
632quite nicely into a call to C<pthread_atfork>:
633 650
651Example: Automate calling C<ev_loop_fork> on the default loop when
652using pthreads.
653
654 static void
655 post_fork_child (void)
656 {
657 ev_loop_fork (EV_DEFAULT);
658 }
659
660 ...
634 pthread_atfork (0, 0, ev_default_fork); 661 pthread_atfork (0, 0, post_fork_child);
635
636=item ev_loop_fork (loop)
637
638Like C<ev_default_fork>, but acts on an event loop created by
639C<ev_loop_new>. Yes, you have to call this on every allocated event loop
640after fork that you want to re-use in the child, and how you keep track of
641them is entirely your own problem.
642 662
643=item int ev_is_default_loop (loop) 663=item int ev_is_default_loop (loop)
644 664
645Returns true when the given loop is, in fact, the default loop, and false 665Returns true when the given loop is, in fact, the default loop, and false
646otherwise. 666otherwise.
657prepare and check phases. 677prepare and check phases.
658 678
659=item unsigned int ev_depth (loop) 679=item unsigned int ev_depth (loop)
660 680
661Returns the number of times C<ev_run> was entered minus the number of 681Returns the number of times C<ev_run> was entered minus the number of
662times C<ev_run> was exited, in other words, the recursion depth. 682times C<ev_run> was exited normally, in other words, the recursion depth.
663 683
664Outside C<ev_run>, this number is zero. In a callback, this number is 684Outside C<ev_run>, this number is zero. In a callback, this number is
665C<1>, unless C<ev_run> was invoked recursively (or from another thread), 685C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666in which case it is higher. 686in which case it is higher.
667 687
668Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread 688Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
669etc.), doesn't count as "exit" - consider this as a hint to avoid such 689throwing an exception etc.), doesn't count as "exit" - consider this
670ungentleman-like behaviour unless it's really convenient. 690as a hint to avoid such ungentleman-like behaviour unless it's really
691convenient, in which case it is fully supported.
671 692
672=item unsigned int ev_backend (loop) 693=item unsigned int ev_backend (loop)
673 694
674Returns one of the C<EVBACKEND_*> flags indicating the event backend in 695Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675use. 696use.
736relying on all watchers to be stopped when deciding when a program has 757relying on all watchers to be stopped when deciding when a program has
737finished (especially in interactive programs), but having a program 758finished (especially in interactive programs), but having a program
738that automatically loops as long as it has to and no longer by virtue 759that automatically loops as long as it has to and no longer by virtue
739of relying on its watchers stopping correctly, that is truly a thing of 760of relying on its watchers stopping correctly, that is truly a thing of
740beauty. 761beauty.
762
763This function is also I<mostly> exception-safe - you can break out of
764a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
765exception and so on. This does not decrement the C<ev_depth> value, nor
766will it clear any outstanding C<EVBREAK_ONE> breaks.
741 767
742A flags value of C<EVRUN_NOWAIT> will look for new events, will handle 768A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
743those events and any already outstanding ones, but will not wait and 769those events and any already outstanding ones, but will not wait and
744block your process in case there are no events and will return after one 770block your process in case there are no events and will return after one
745iteration of the loop. This is sometimes useful to poll and handle new 771iteration of the loop. This is sometimes useful to poll and handle new
807Can be used to make a call to C<ev_run> return early (but only after it 833Can be used to make a call to C<ev_run> return early (but only after it
808has processed all outstanding events). The C<how> argument must be either 834has processed all outstanding events). The C<how> argument must be either
809C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or 835C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
810C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return. 836C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811 837
812This "unloop state" will be cleared when entering C<ev_run> again. 838This "break state" will be cleared on the next call to C<ev_run>.
813 839
814It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO## 840It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
841which case it will have no effect.
815 842
816=item ev_ref (loop) 843=item ev_ref (loop)
817 844
818=item ev_unref (loop) 845=item ev_unref (loop)
819 846
840running when nothing else is active. 867running when nothing else is active.
841 868
842 ev_signal exitsig; 869 ev_signal exitsig;
843 ev_signal_init (&exitsig, sig_cb, SIGINT); 870 ev_signal_init (&exitsig, sig_cb, SIGINT);
844 ev_signal_start (loop, &exitsig); 871 ev_signal_start (loop, &exitsig);
845 evf_unref (loop); 872 ev_unref (loop);
846 873
847Example: For some weird reason, unregister the above signal handler again. 874Example: For some weird reason, unregister the above signal handler again.
848 875
849 ev_ref (loop); 876 ev_ref (loop);
850 ev_signal_stop (loop, &exitsig); 877 ev_signal_stop (loop, &exitsig);
962See also the locking example in the C<THREADS> section later in this 989See also the locking example in the C<THREADS> section later in this
963document. 990document.
964 991
965=item ev_set_userdata (loop, void *data) 992=item ev_set_userdata (loop, void *data)
966 993
967=item ev_userdata (loop) 994=item void *ev_userdata (loop)
968 995
969Set and retrieve a single C<void *> associated with a loop. When 996Set and retrieve a single C<void *> associated with a loop. When
970C<ev_set_userdata> has never been called, then C<ev_userdata> returns 997C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971C<0.> 998C<0>.
972 999
973These two functions can be used to associate arbitrary data with a loop, 1000These two functions can be used to associate arbitrary data with a loop,
974and are intended solely for the C<invoke_pending_cb>, C<release> and 1001and are intended solely for the C<invoke_pending_cb>, C<release> and
975C<acquire> callbacks described above, but of course can be (ab-)used for 1002C<acquire> callbacks described above, but of course can be (ab-)used for
976any other purpose as well. 1003any other purpose as well.
1104=item C<EV_FORK> 1131=item C<EV_FORK>
1105 1132
1106The event loop has been resumed in the child process after fork (see 1133The event loop has been resumed in the child process after fork (see
1107C<ev_fork>). 1134C<ev_fork>).
1108 1135
1136=item C<EV_CLEANUP>
1137
1138The event loop is about to be destroyed (see C<ev_cleanup>).
1139
1109=item C<EV_ASYNC> 1140=item C<EV_ASYNC>
1110 1141
1111The given async watcher has been asynchronously notified (see C<ev_async>). 1142The given async watcher has been asynchronously notified (see C<ev_async>).
1112 1143
1113=item C<EV_CUSTOM> 1144=item C<EV_CUSTOM>
1134programs, though, as the fd could already be closed and reused for another 1165programs, though, as the fd could already be closed and reused for another
1135thing, so beware. 1166thing, so beware.
1136 1167
1137=back 1168=back
1138 1169
1139=head2 WATCHER STATES
1140
1141There are various watcher states mentioned throughout this manual -
1142active, pending and so on. In this section these states and the rules to
1143transition between them will be described in more detail - and while these
1144rules might look complicated, they usually do "the right thing".
1145
1146=over 4
1147
1148=item initialiased
1149
1150Before a watcher can be registered with the event looop it has to be
1151initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1152C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1153
1154In this state it is simply some block of memory that is suitable for use
1155in an event loop. It can be moved around, freed, reused etc. at will.
1156
1157=item started/running/active
1158
1159Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1160property of the event loop, and is actively waiting for events. While in
1161this state it cannot be accessed (except in a few documented ways), moved,
1162freed or anything else - the only legal thing is to keep a pointer to it,
1163and call libev functions on it that are documented to work on active watchers.
1164
1165=item pending
1166
1167If a watcher is active and libev determines that an event it is interested
1168in has occurred (such as a timer expiring), it will become pending. It will
1169stay in this pending state until either it is stopped or its callback is
1170about to be invoked, so it is not normally pending inside the watcher
1171callback.
1172
1173The watcher might or might not be active while it is pending (for example,
1174an expired non-repeating timer can be pending but no longer active). If it
1175is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
1176but it is still property of the event loop at this time, so cannot be
1177moved, freed or reused. And if it is active the rules described in the
1178previous item still apply.
1179
1180It is also possible to feed an event on a watcher that is not active (e.g.
1181via C<ev_feed_event>), in which case it becomes pending without being
1182active.
1183
1184=item stopped
1185
1186A watcher can be stopped implicitly by libev (in which case it might still
1187be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1188latter will clear any pending state the watcher might be in, regardless
1189of whether it was active or not, so stopping a watcher explicitly before
1190freeing it is often a good idea.
1191
1192While stopped (and not pending) the watcher is essentially in the
1193initialised state, that is it can be reused, moved, modified in any way
1194you wish.
1195
1196=back
1197
1198=head2 GENERIC WATCHER FUNCTIONS 1170=head2 GENERIC WATCHER FUNCTIONS
1199 1171
1200=over 4 1172=over 4
1201 1173
1202=item C<ev_init> (ev_TYPE *watcher, callback) 1174=item C<ev_init> (ev_TYPE *watcher, callback)
1343 1315
1344See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related 1316See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1345functions that do not need a watcher. 1317functions that do not need a watcher.
1346 1318
1347=back 1319=back
1348
1349 1320
1350=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 1321=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1351 1322
1352Each watcher has, by default, a member C<void *data> that you can change 1323Each watcher has, by default, a member C<void *data> that you can change
1353and read at any time: libev will completely ignore it. This can be used 1324and read at any time: libev will completely ignore it. This can be used
1409 t2_cb (EV_P_ ev_timer *w, int revents) 1380 t2_cb (EV_P_ ev_timer *w, int revents)
1410 { 1381 {
1411 struct my_biggy big = (struct my_biggy *) 1382 struct my_biggy big = (struct my_biggy *)
1412 (((char *)w) - offsetof (struct my_biggy, t2)); 1383 (((char *)w) - offsetof (struct my_biggy, t2));
1413 } 1384 }
1385
1386=head2 WATCHER STATES
1387
1388There are various watcher states mentioned throughout this manual -
1389active, pending and so on. In this section these states and the rules to
1390transition between them will be described in more detail - and while these
1391rules might look complicated, they usually do "the right thing".
1392
1393=over 4
1394
1395=item initialiased
1396
1397Before a watcher can be registered with the event looop it has to be
1398initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1399C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400
1401In this state it is simply some block of memory that is suitable for use
1402in an event loop. It can be moved around, freed, reused etc. at will.
1403
1404=item started/running/active
1405
1406Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1407property of the event loop, and is actively waiting for events. While in
1408this state it cannot be accessed (except in a few documented ways), moved,
1409freed or anything else - the only legal thing is to keep a pointer to it,
1410and call libev functions on it that are documented to work on active watchers.
1411
1412=item pending
1413
1414If a watcher is active and libev determines that an event it is interested
1415in has occurred (such as a timer expiring), it will become pending. It will
1416stay in this pending state until either it is stopped or its callback is
1417about to be invoked, so it is not normally pending inside the watcher
1418callback.
1419
1420The watcher might or might not be active while it is pending (for example,
1421an expired non-repeating timer can be pending but no longer active). If it
1422is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
1423but it is still property of the event loop at this time, so cannot be
1424moved, freed or reused. And if it is active the rules described in the
1425previous item still apply.
1426
1427It is also possible to feed an event on a watcher that is not active (e.g.
1428via C<ev_feed_event>), in which case it becomes pending without being
1429active.
1430
1431=item stopped
1432
1433A watcher can be stopped implicitly by libev (in which case it might still
1434be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1435latter will clear any pending state the watcher might be in, regardless
1436of whether it was active or not, so stopping a watcher explicitly before
1437freeing it is often a good idea.
1438
1439While stopped (and not pending) the watcher is essentially in the
1440initialised state, that is it can be reused, moved, modified in any way
1441you wish.
1442
1443=back
1414 1444
1415=head2 WATCHER PRIORITY MODELS 1445=head2 WATCHER PRIORITY MODELS
1416 1446
1417Many event loops support I<watcher priorities>, which are usually small 1447Many event loops support I<watcher priorities>, which are usually small
1418integers that influence the ordering of event callback invocation 1448integers that influence the ordering of event callback invocation
2237 2267
2238=head2 C<ev_signal> - signal me when a signal gets signalled! 2268=head2 C<ev_signal> - signal me when a signal gets signalled!
2239 2269
2240Signal watchers will trigger an event when the process receives a specific 2270Signal watchers will trigger an event when the process receives a specific
2241signal one or more times. Even though signals are very asynchronous, libev 2271signal one or more times. Even though signals are very asynchronous, libev
2242will try it's best to deliver signals synchronously, i.e. as part of the 2272will try its best to deliver signals synchronously, i.e. as part of the
2243normal event processing, like any other event. 2273normal event processing, like any other event.
2244 2274
2245If you want signals to be delivered truly asynchronously, just use 2275If you want signals to be delivered truly asynchronously, just use
2246C<sigaction> as you would do without libev and forget about sharing 2276C<sigaction> as you would do without libev and forget about sharing
2247the signal. You can even use C<ev_async> from a signal handler to 2277the signal. You can even use C<ev_async> from a signal handler to
3072disadvantage of having to use multiple event loops (which do not support 3102disadvantage of having to use multiple event loops (which do not support
3073signal watchers). 3103signal watchers).
3074 3104
3075When this is not possible, or you want to use the default loop for 3105When this is not possible, or you want to use the default loop for
3076other reasons, then in the process that wants to start "fresh", call 3106other reasons, then in the process that wants to start "fresh", call
3077C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying 3107C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3078the default loop will "orphan" (not stop) all registered watchers, so you 3108Destroying the default loop will "orphan" (not stop) all registered
3079have to be careful not to execute code that modifies those watchers. Note 3109watchers, so you have to be careful not to execute code that modifies
3080also that in that case, you have to re-register any signal watchers. 3110those watchers. Note also that in that case, you have to re-register any
3111signal watchers.
3081 3112
3082=head3 Watcher-Specific Functions and Data Members 3113=head3 Watcher-Specific Functions and Data Members
3083 3114
3084=over 4 3115=over 4
3085 3116
3086=item ev_fork_init (ev_signal *, callback) 3117=item ev_fork_init (ev_fork *, callback)
3087 3118
3088Initialises and configures the fork watcher - it has no parameters of any 3119Initialises and configures the fork watcher - it has no parameters of any
3089kind. There is a C<ev_fork_set> macro, but using it is utterly pointless, 3120kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090believe me. 3121really.
3091 3122
3092=back 3123=back
3124
3125
3126=head2 C<ev_cleanup> - even the best things end
3127
3128Cleanup watchers are called just before the event loop is being destroyed
3129by a call to C<ev_loop_destroy>.
3130
3131While there is no guarantee that the event loop gets destroyed, cleanup
3132watchers provide a convenient method to install cleanup hooks for your
3133program, worker threads and so on - you just to make sure to destroy the
3134loop when you want them to be invoked.
3135
3136Cleanup watchers are invoked in the same way as any other watcher. Unlike
3137all other watchers, they do not keep a reference to the event loop (which
3138makes a lot of sense if you think about it). Like all other watchers, you
3139can call libev functions in the callback, except C<ev_cleanup_start>.
3140
3141=head3 Watcher-Specific Functions and Data Members
3142
3143=over 4
3144
3145=item ev_cleanup_init (ev_cleanup *, callback)
3146
3147Initialises and configures the cleanup watcher - it has no parameters of
3148any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
3149pointless, I assure you.
3150
3151=back
3152
3153Example: Register an atexit handler to destroy the default loop, so any
3154cleanup functions are called.
3155
3156 static void
3157 program_exits (void)
3158 {
3159 ev_loop_destroy (EV_DEFAULT_UC);
3160 }
3161
3162 ...
3163 atexit (program_exits);
3093 3164
3094 3165
3095=head2 C<ev_async> - how to wake up an event loop 3166=head2 C<ev_async> - how to wake up an event loop
3096 3167
3097In general, you cannot use an C<ev_run> from multiple threads or other 3168In general, you cannot use an C<ev_run> from multiple threads or other
3296loop!). 3367loop!).
3297 3368
3298=back 3369=back
3299 3370
3300 3371
3372=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3373
3374This section explains some common idioms that are not immediately
3375obvious. Note that examples are sprinkled over the whole manual, and this
3376section only contains stuff that wouldn't fit anywhere else.
3377
3378=over 4
3379
3380=item Model/nested event loop invocations and exit conditions.
3381
3382Often (especially in GUI toolkits) there are places where you have
3383I<modal> interaction, which is most easily implemented by recursively
3384invoking C<ev_run>.
3385
3386This brings the problem of exiting - a callback might want to finish the
3387main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3388a modal "Are you sure?" dialog is still waiting), or just the nested one
3389and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3390other combination: In these cases, C<ev_break> will not work alone.
3391
3392The solution is to maintain "break this loop" variable for each C<ev_run>
3393invocation, and use a loop around C<ev_run> until the condition is
3394triggered, using C<EVRUN_ONCE>:
3395
3396 // main loop
3397 int exit_main_loop = 0;
3398
3399 while (!exit_main_loop)
3400 ev_run (EV_DEFAULT_ EVRUN_ONCE);
3401
3402 // in a model watcher
3403 int exit_nested_loop = 0;
3404
3405 while (!exit_nested_loop)
3406 ev_run (EV_A_ EVRUN_ONCE);
3407
3408To exit from any of these loops, just set the corresponding exit variable:
3409
3410 // exit modal loop
3411 exit_nested_loop = 1;
3412
3413 // exit main program, after modal loop is finished
3414 exit_main_loop = 1;
3415
3416 // exit both
3417 exit_main_loop = exit_nested_loop = 1;
3418
3419=back
3420
3421
3301=head1 LIBEVENT EMULATION 3422=head1 LIBEVENT EMULATION
3302 3423
3303Libev offers a compatibility emulation layer for libevent. It cannot 3424Libev offers a compatibility emulation layer for libevent. It cannot
3304emulate the internals of libevent, so here are some usage hints: 3425emulate the internals of libevent, so here are some usage hints:
3305 3426
3306=over 4 3427=over 4
3428
3429=item * Only the libevent-1.4.1-beta API is being emulated.
3430
3431This was the newest libevent version available when libev was implemented,
3432and is still mostly unchanged in 2010.
3307 3433
3308=item * Use it by including <event.h>, as usual. 3434=item * Use it by including <event.h>, as usual.
3309 3435
3310=item * The following members are fully supported: ev_base, ev_callback, 3436=item * The following members are fully supported: ev_base, ev_callback,
3311ev_arg, ev_fd, ev_res, ev_events. 3437ev_arg, ev_fd, ev_res, ev_events.
3317=item * Priorities are not currently supported. Initialising priorities 3443=item * Priorities are not currently supported. Initialising priorities
3318will fail and all watchers will have the same priority, even though there 3444will fail and all watchers will have the same priority, even though there
3319is an ev_pri field. 3445is an ev_pri field.
3320 3446
3321=item * In libevent, the last base created gets the signals, in libev, the 3447=item * In libevent, the last base created gets the signals, in libev, the
3322first base created (== the default loop) gets the signals. 3448base that registered the signal gets the signals.
3323 3449
3324=item * Other members are not supported. 3450=item * Other members are not supported.
3325 3451
3326=item * The libev emulation is I<not> ABI compatible to libevent, you need 3452=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327to use the libev header file and library. 3453to use the libev header file and library.
3346Care has been taken to keep the overhead low. The only data member the C++ 3472Care has been taken to keep the overhead low. The only data member the C++
3347classes add (compared to plain C-style watchers) is the event loop pointer 3473classes add (compared to plain C-style watchers) is the event loop pointer
3348that the watcher is associated with (or no additional members at all if 3474that the watcher is associated with (or no additional members at all if
3349you disable C<EV_MULTIPLICITY> when embedding libev). 3475you disable C<EV_MULTIPLICITY> when embedding libev).
3350 3476
3351Currently, functions, and static and non-static member functions can be 3477Currently, functions, static and non-static member functions and classes
3352used as callbacks. Other types should be easy to add as long as they only 3478with C<operator ()> can be used as callbacks. Other types should be easy
3353need one additional pointer for context. If you need support for other 3479to add as long as they only need one additional pointer for context. If
3354types of functors please contact the author (preferably after implementing 3480you need support for other types of functors please contact the author
3355it). 3481(preferably after implementing it).
3356 3482
3357Here is a list of things available in the C<ev> namespace: 3483Here is a list of things available in the C<ev> namespace:
3358 3484
3359=over 4 3485=over 4
3360 3486
4704structure (guaranteed by POSIX but not by ISO C for example), but it also 4830structure (guaranteed by POSIX but not by ISO C for example), but it also
4705assumes that the same (machine) code can be used to call any watcher 4831assumes that the same (machine) code can be used to call any watcher
4706callback: The watcher callbacks have different type signatures, but libev 4832callback: The watcher callbacks have different type signatures, but libev
4707calls them using an C<ev_watcher *> internally. 4833calls them using an C<ev_watcher *> internally.
4708 4834
4835=item pointer accesses must be thread-atomic
4836
4837Accessing a pointer value must be atomic, it must both be readable and
4838writable in one piece - this is the case on all current architectures.
4839
4709=item C<sig_atomic_t volatile> must be thread-atomic as well 4840=item C<sig_atomic_t volatile> must be thread-atomic as well
4710 4841
4711The type C<sig_atomic_t volatile> (or whatever is defined as 4842The type C<sig_atomic_t volatile> (or whatever is defined as
4712C<EV_ATOMIC_T>) must be atomic with respect to accesses from different 4843C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4713threads. This is not part of the specification for C<sig_atomic_t>, but is 4844threads. This is not part of the specification for C<sig_atomic_t>, but is
4819=back 4950=back
4820 4951
4821 4952
4822=head1 PORTING FROM LIBEV 3.X TO 4.X 4953=head1 PORTING FROM LIBEV 3.X TO 4.X
4823 4954
4824The major version 4 introduced some minor incompatible changes to the API. 4955The major version 4 introduced some incompatible changes to the API.
4825 4956
4826At the moment, the C<ev.h> header file tries to implement superficial 4957At the moment, the C<ev.h> header file provides compatibility definitions
4827compatibility, so most programs should still compile. Those might be 4958for all changes, so most programs should still compile. The compatibility
4828removed in later versions of libev, so better update early than late. 4959layer might be removed in later versions of libev, so better update to the
4960new API early than late.
4829 4961
4830=over 4 4962=over 4
4963
4964=item C<EV_COMPAT3> backwards compatibility mechanism
4965
4966The backward compatibility mechanism can be controlled by
4967C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4968section.
4969
4970=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4971
4972These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4973
4974 ev_loop_destroy (EV_DEFAULT_UC);
4975 ev_loop_fork (EV_DEFAULT);
4831 4976
4832=item function/symbol renames 4977=item function/symbol renames
4833 4978
4834A number of functions and symbols have been renamed: 4979A number of functions and symbols have been renamed:
4835 4980
4854ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme 4999ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4855as all other watcher types. Note that C<ev_loop_fork> is still called 5000as all other watcher types. Note that C<ev_loop_fork> is still called
4856C<ev_loop_fork> because it would otherwise clash with the C<ev_fork> 5001C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4857typedef. 5002typedef.
4858 5003
4859=item C<EV_COMPAT3> backwards compatibility mechanism
4860
4861The backward compatibility mechanism can be controlled by
4862C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4863section.
4864
4865=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES> 5004=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4866 5005
4867The preprocessor symbol C<EV_MINIMAL> has been replaced by a different 5006The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4868mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile 5007mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4869and work, but the library code will of course be larger. 5008and work, but the library code will of course be larger.
4943 5082
4944=back 5083=back
4945 5084
4946=head1 AUTHOR 5085=head1 AUTHOR
4947 5086
4948Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. 5087Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5088Magnusson and Emanuele Giaquinta.
4949 5089

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