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39F<README.embed> in the libev distribution. If libev was configured without 39F<README.embed> in the libev distribution. If libev was configured without
40support for multiple event loops, then all functions taking an initial 40support for multiple event loops, then all functions taking an initial
41argument of name C<loop> (which is always of type C<struct ev_loop *>) 41argument of name C<loop> (which is always of type C<struct ev_loop *>)
42will not have this argument. 42will not have this argument.
43 43
44=head1 TIME AND OTHER GLOBAL FUNCTIONS 44=head1 TIME REPRESENTATION
45 45
46Libev represents time as a single floating point number, representing the 46Libev represents time as a single floating point number, representing the
47(fractional) number of seconds since the (POSIX) epoch (somewhere near 47(fractional) number of seconds since the (POSIX) epoch (somewhere near
48the beginning of 1970, details are complicated, don't ask). This type is 48the beginning of 1970, details are complicated, don't ask). This type is
49called C<ev_tstamp>, which is what you should use too. It usually aliases 49called C<ev_tstamp>, which is what you should use too. It usually aliases
50to the double type in C. 50to the double type in C.
51 51
52=head1 GLOBAL FUNCTIONS
53
54These functions can be called anytime, even before initialising the
55library in any way.
56
52=over 4 57=over 4
53 58
54=item ev_tstamp ev_time () 59=item ev_tstamp ev_time ()
55 60
56Returns the current time as libev would use it. 61Returns the current time as libev would use it. Please note that the
62C<ev_now> function is usually faster and also often returns the timestamp
63you actually want to know.
57 64
58=item int ev_version_major () 65=item int ev_version_major ()
59 66
60=item int ev_version_minor () 67=item int ev_version_minor ()
61 68
99An event loop is described by a C<struct ev_loop *>. The library knows two 106An event loop is described by a C<struct ev_loop *>. The library knows two
100types of such loops, the I<default> loop, which supports signals and child 107types of such loops, the I<default> loop, which supports signals and child
101events, and dynamically created loops which do not. 108events, and dynamically created loops which do not.
102 109
103If you use threads, a common model is to run the default event loop 110If you use threads, a common model is to run the default event loop
104in your main thread (or in a separate thrad) and for each thread you 111in your main thread (or in a separate thread) and for each thread you
105create, you also create another event loop. Libev itself does no locking 112create, you also create another event loop. Libev itself does no locking
106whatsoever, so if you mix calls to the same event loop in different 113whatsoever, so if you mix calls to the same event loop in different
107threads, make sure you lock (this is usually a bad idea, though, even if 114threads, make sure you lock (this is usually a bad idea, though, even if
108done correctly, because it's hideous and inefficient). 115done correctly, because it's hideous and inefficient).
109 116
138C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will 145C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139override the flags completely if it is found in the environment. This is 146override the flags completely if it is found in the environment. This is
140useful to try out specific backends to test their performance, or to work 147useful to try out specific backends to test their performance, or to work
141around bugs. 148around bugs.
142 149
143=item C<EVMETHOD_SELECT> (portable select backend) 150=item C<EVMETHOD_SELECT> (value 1, portable select backend)
144 151
152This is your standard select(2) backend. Not I<completely> standard, as
153libev tries to roll its own fd_set with no limits on the number of fds,
154but if that fails, expect a fairly low limit on the number of fds when
155using this backend. It doesn't scale too well (O(highest_fd)), but its usually
156the fastest backend for a low number of fds.
157
145=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows) 158=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)
146 159
160And this is your standard poll(2) backend. It's more complicated than
161select, but handles sparse fds better and has no artificial limit on the
162number of fds you can use (except it will slow down considerably with a
163lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
164
147=item C<EVMETHOD_EPOLL> (linux only) 165=item C<EVMETHOD_EPOLL> (value 4, Linux)
148 166
149=item C<EVMETHOD_KQUEUE> (some bsds only) 167For few fds, this backend is a bit little slower than poll and select,
168but it scales phenomenally better. While poll and select usually scale like
169O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
170either O(1) or O(active_fds).
150 171
172While stopping and starting an I/O watcher in the same iteration will
173result in some caching, there is still a syscall per such incident
174(because the fd could point to a different file description now), so its
175best to avoid that. Also, dup()ed file descriptors might not work very
176well if you register events for both fds.
177
178=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)
179
180Kqueue deserves special mention, as at the time of this writing, it
181was broken on all BSDs except NetBSD (usually it doesn't work with
182anything but sockets and pipes, except on Darwin, where of course its
183completely useless). For this reason its not being "autodetected" unless
184you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).
185
186It scales in the same way as the epoll backend, but the interface to the
187kernel is more efficient (which says nothing about its actual speed, of
188course). While starting and stopping an I/O watcher does not cause an
189extra syscall as with epoll, it still adds up to four event changes per
190incident, so its best to avoid that.
191
151=item C<EVMETHOD_DEVPOLL> (solaris 8 only) 192=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)
152 193
194This is not implemented yet (and might never be).
195
153=item C<EVMETHOD_PORT> (solaris 10 only) 196=item C<EVMETHOD_PORT> (value 32, Solaris 10)
197
198This uses the Solaris 10 port mechanism. As with everything on Solaris,
199it's really slow, but it still scales very well (O(active_fds)).
200
201=item C<EVMETHOD_ALL>
202
203Try all backends (even potentially broken ones that wouldn't be tried
204with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.
206
207=back
154 208
155If one or more of these are ored into the flags value, then only these 209If one or more of these are ored into the flags value, then only these
156backends will be tried (in the reverse order as given here). If one are 210backends will be tried (in the reverse order as given here). If none are
157specified, any backend will do. 211specified, most compiled-in backend will be tried, usually in reverse
158 212order of their flag values :)
159=back
160 213
161=item struct ev_loop *ev_loop_new (unsigned int flags) 214=item struct ev_loop *ev_loop_new (unsigned int flags)
162 215
163Similar to C<ev_default_loop>, but always creates a new event loop that is 216Similar to C<ev_default_loop>, but always creates a new event loop that is
164always distinct from the default loop. Unlike the default loop, it cannot 217always distinct from the default loop. Unlike the default loop, it cannot
232 285
233This flags value could be used to implement alternative looping 286This flags value could be used to implement alternative looping
234constructs, but the C<prepare> and C<check> watchers provide a better and 287constructs, but the C<prepare> and C<check> watchers provide a better and
235more generic mechanism. 288more generic mechanism.
236 289
290Here are the gory details of what ev_loop does:
291
292 1. If there are no active watchers (reference count is zero), return.
293 2. Queue and immediately call all prepare watchers.
294 3. If we have been forked, recreate the kernel state.
295 4. Update the kernel state with all outstanding changes.
296 5. Update the "event loop time".
297 6. Calculate for how long to block.
298 7. Block the process, waiting for events.
299 8. Update the "event loop time" and do time jump handling.
300 9. Queue all outstanding timers.
301 10. Queue all outstanding periodics.
302 11. If no events are pending now, queue all idle watchers.
303 12. Queue all check watchers.
304 13. Call all queued watchers in reverse order (i.e. check watchers first).
305 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306 was used, return, otherwise continue with step #1.
307
237=item ev_unloop (loop, how) 308=item ev_unloop (loop, how)
238 309
239Can be used to make a call to C<ev_loop> return early (but only after it 310Can be used to make a call to C<ev_loop> return early (but only after it
240has processed all outstanding events). The C<how> argument must be either 311has processed all outstanding events). The C<how> argument must be either
241C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or 312C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. 313C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
243 314
244=item ev_ref (loop) 315=item ev_ref (loop)
245 316
246=item ev_unref (loop) 317=item ev_unref (loop)
412in each iteration of the event loop (This behaviour is called 483in each iteration of the event loop (This behaviour is called
413level-triggering because you keep receiving events as long as the 484level-triggering because you keep receiving events as long as the
414condition persists. Remember you can stop the watcher if you don't want to 485condition persists. Remember you can stop the watcher if you don't want to
415act on the event and neither want to receive future events). 486act on the event and neither want to receive future events).
416 487
417In general you can register as many read and/or write event watchers oer 488In general you can register as many read and/or write event watchers per
418fd as you want (as long as you don't confuse yourself). Setting all file 489fd as you want (as long as you don't confuse yourself). Setting all file
419descriptors to non-blocking mode is also usually a good idea (but not 490descriptors to non-blocking mode is also usually a good idea (but not
420required if you know what you are doing). 491required if you know what you are doing).
421 492
422You have to be careful with dup'ed file descriptors, though. Some backends 493You have to be careful with dup'ed file descriptors, though. Some backends
423(the linux epoll backend is a notable example) cannot handle dup'ed file 494(the linux epoll backend is a notable example) cannot handle dup'ed file
424descriptors correctly if you register interest in two or more fds pointing 495descriptors correctly if you register interest in two or more fds pointing
425to the same file/socket etc. description. 496to the same underlying file/socket etc. description (that is, they share
497the same underlying "file open").
426 498
427If you must do this, then force the use of a known-to-be-good backend 499If you must do this, then force the use of a known-to-be-good backend
428(at the time of this writing, this includes only EVMETHOD_SELECT and 500(at the time of this writing, this includes only EVMETHOD_SELECT and
429EVMETHOD_POLL). 501EVMETHOD_POLL).
430 502
444 516
445Timer watchers are simple relative timers that generate an event after a 517Timer watchers are simple relative timers that generate an event after a
446given time, and optionally repeating in regular intervals after that. 518given time, and optionally repeating in regular intervals after that.
447 519
448The timers are based on real time, that is, if you register an event that 520The timers are based on real time, that is, if you register an event that
449times out after an hour and youreset your system clock to last years 521times out after an hour and you reset your system clock to last years
450time, it will still time out after (roughly) and hour. "Roughly" because 522time, it will still time out after (roughly) and hour. "Roughly" because
451detecting time jumps is hard, and soem inaccuracies are unavoidable (the 523detecting time jumps is hard, and some inaccuracies are unavoidable (the
452monotonic clock option helps a lot here). 524monotonic clock option helps a lot here).
453 525
454The relative timeouts are calculated relative to the C<ev_now ()> 526The relative timeouts are calculated relative to the C<ev_now ()>
455time. This is usually the right thing as this timestamp refers to the time 527time. This is usually the right thing as this timestamp refers to the time
456of the event triggering whatever timeout you are modifying/starting. If 528of the event triggering whatever timeout you are modifying/starting. If
457you suspect event processing to be delayed and you *need* to base the timeout 529you suspect event processing to be delayed and you I<need> to base the timeout
458ion the current time, use something like this to adjust for this: 530on the current time, use something like this to adjust for this:
459 531
460 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 532 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533
534The callback is guarenteed to be invoked only when its timeout has passed,
535but if multiple timers become ready during the same loop iteration then
536order of execution is undefined.
461 537
462=over 4 538=over 4
463 539
464=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 540=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465 541
471later, again, and again, until stopped manually. 547later, again, and again, until stopped manually.
472 548
473The timer itself will do a best-effort at avoiding drift, that is, if you 549The timer itself will do a best-effort at avoiding drift, that is, if you
474configure a timer to trigger every 10 seconds, then it will trigger at 550configure a timer to trigger every 10 seconds, then it will trigger at
475exactly 10 second intervals. If, however, your program cannot keep up with 551exactly 10 second intervals. If, however, your program cannot keep up with
476the timer (ecause it takes longer than those 10 seconds to do stuff) the 552the timer (because it takes longer than those 10 seconds to do stuff) the
477timer will not fire more than once per event loop iteration. 553timer will not fire more than once per event loop iteration.
478 554
479=item ev_timer_again (loop) 555=item ev_timer_again (loop)
480 556
481This will act as if the timer timed out and restart it again if it is 557This will act as if the timer timed out and restart it again if it is
512again). 588again).
513 589
514They can also be used to implement vastly more complex timers, such as 590They can also be used to implement vastly more complex timers, such as
515triggering an event on eahc midnight, local time. 591triggering an event on eahc midnight, local time.
516 592
593As with timers, the callback is guarenteed to be invoked only when the
594time (C<at>) has been passed, but if multiple periodic timers become ready
595during the same loop iteration then order of execution is undefined.
596
517=over 4 597=over 4
518 598
519=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) 599=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520 600
521=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) 601=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522 602
523Lots of arguments, lets sort it out... There are basically three modes of 603Lots of arguments, lets sort it out... There are basically three modes of
524operation, and we will explain them from simplest to complex: 604operation, and we will explain them from simplest to complex:
525
526 605
527=over 4 606=over 4
528 607
529=item * absolute timer (interval = reschedule_cb = 0) 608=item * absolute timer (interval = reschedule_cb = 0)
530 609
558In this mode the values for C<interval> and C<at> are both being 637In this mode the values for C<interval> and C<at> are both being
559ignored. Instead, each time the periodic watcher gets scheduled, the 638ignored. Instead, each time the periodic watcher gets scheduled, the
560reschedule callback will be called with the watcher as first, and the 639reschedule callback will be called with the watcher as first, and the
561current time as second argument. 640current time as second argument.
562 641
563NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 642NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564periodic watcher, ever, or make any event loop modifications>. If you need 643ever, or make any event loop modifications>. If you need to stop it,
565to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards. 644return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
566 645starting a prepare watcher).
567Also, I<< this callback must always return a time that is later than the
568passed C<now> value >>. Not even C<now> itself will be ok.
569 646
570Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 647Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571ev_tstamp now)>, e.g.: 648ev_tstamp now)>, e.g.:
572 649
573 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 650 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
578It must return the next time to trigger, based on the passed time value 655It must return the next time to trigger, based on the passed time value
579(that is, the lowest time value larger than to the second argument). It 656(that is, the lowest time value larger than to the second argument). It
580will usually be called just before the callback will be triggered, but 657will usually be called just before the callback will be triggered, but
581might be called at other times, too. 658might be called at other times, too.
582 659
660NOTE: I<< This callback must always return a time that is later than the
661passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
662
583This can be used to create very complex timers, such as a timer that 663This can be used to create very complex timers, such as a timer that
584triggers on each midnight, local time. To do this, you would calculate the 664triggers on each midnight, local time. To do this, you would calculate the
585next midnight after C<now> and return the timestamp value for this. How you do this 665next midnight after C<now> and return the timestamp value for this. How
586is, again, up to you (but it is not trivial). 666you do this is, again, up to you (but it is not trivial, which is the main
667reason I omitted it as an example).
587 668
588=back 669=back
589 670
590=item ev_periodic_again (loop, ev_periodic *) 671=item ev_periodic_again (loop, ev_periodic *)
591 672
670=back 751=back
671 752
672=head2 C<ev_prepare> and C<ev_check> - customise your event loop 753=head2 C<ev_prepare> and C<ev_check> - customise your event loop
673 754
674Prepare and check watchers are usually (but not always) used in tandem: 755Prepare and check watchers are usually (but not always) used in tandem:
675Prepare watchers get invoked before the process blocks and check watchers 756prepare watchers get invoked before the process blocks and check watchers
676afterwards. 757afterwards.
677 758
678Their main purpose is to integrate other event mechanisms into libev. This 759Their main purpose is to integrate other event mechanisms into libev. This
679could be used, for example, to track variable changes, implement your own 760could be used, for example, to track variable changes, implement your own
680watchers, integrate net-snmp or a coroutine library and lots more. 761watchers, integrate net-snmp or a coroutine library and lots more.
683to be watched by the other library, registering C<ev_io> watchers for 764to be watched by the other library, registering C<ev_io> watchers for
684them and starting an C<ev_timer> watcher for any timeouts (many libraries 765them and starting an C<ev_timer> watcher for any timeouts (many libraries
685provide just this functionality). Then, in the check watcher you check for 766provide just this functionality). Then, in the check watcher you check for
686any events that occured (by checking the pending status of all watchers 767any events that occured (by checking the pending status of all watchers
687and stopping them) and call back into the library. The I/O and timer 768and stopping them) and call back into the library. The I/O and timer
688callbacks will never actually be called (but must be valid neverthelles, 769callbacks will never actually be called (but must be valid nevertheless,
689because you never know, you know?). 770because you never know, you know?).
690 771
691As another example, the Perl Coro module uses these hooks to integrate 772As another example, the Perl Coro module uses these hooks to integrate
692coroutines into libev programs, by yielding to other active coroutines 773coroutines into libev programs, by yielding to other active coroutines
693during each prepare and only letting the process block if no coroutines 774during each prepare and only letting the process block if no coroutines
694are ready to run (its actually more complicated, it only runs coroutines 775are ready to run (it's actually more complicated: it only runs coroutines
695with priority higher than the event loop and one lower priority once, 776with priority higher than or equal to the event loop and one coroutine
696using idle watchers to keep the event loop from blocking if lower-priority 777of lower priority, but only once, using idle watchers to keep the event
697coroutines exist, thus mapping low-priority coroutines to idle/background 778loop from blocking if lower-priority coroutines are active, thus mapping
698tasks). 779low-priority coroutines to idle/background tasks).
699 780
700=over 4 781=over 4
701 782
702=item ev_prepare_init (ev_prepare *, callback) 783=item ev_prepare_init (ev_prepare *, callback)
703 784
718=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 799=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719 800
720This function combines a simple timer and an I/O watcher, calls your 801This function combines a simple timer and an I/O watcher, calls your
721callback on whichever event happens first and automatically stop both 802callback on whichever event happens first and automatically stop both
722watchers. This is useful if you want to wait for a single event on an fd 803watchers. This is useful if you want to wait for a single event on an fd
723or timeout without havign to allocate/configure/start/stop/free one or 804or timeout without having to allocate/configure/start/stop/free one or
724more watchers yourself. 805more watchers yourself.
725 806
726If C<fd> is less than 0, then no I/O watcher will be started and events 807If C<fd> is less than 0, then no I/O watcher will be started and events
727is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and 808is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
728C<events> set will be craeted and started. 809C<events> set will be craeted and started.
731started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and 812started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732repeat = 0) will be started. While C<0> is a valid timeout, it is of 813repeat = 0) will be started. While C<0> is a valid timeout, it is of
733dubious value. 814dubious value.
734 815
735The callback has the type C<void (*cb)(int revents, void *arg)> and gets 816The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736passed an events set like normal event callbacks (with a combination of 817passed an C<revents> set like normal event callbacks (a combination of
737C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> 818C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738value passed to C<ev_once>: 819value passed to C<ev_once>:
739 820
740 static void stdin_ready (int revents, void *arg) 821 static void stdin_ready (int revents, void *arg)
741 { 822 {
762 843
763Feed an event as if the given signal occured (loop must be the default loop!). 844Feed an event as if the given signal occured (loop must be the default loop!).
764 845
765=back 846=back
766 847
848=head1 LIBEVENT EMULATION
849
850Libev offers a compatibility emulation layer for libevent. It cannot
851emulate the internals of libevent, so here are some usage hints:
852
853=over 4
854
855=item * Use it by including <event.h>, as usual.
856
857=item * The following members are fully supported: ev_base, ev_callback,
858ev_arg, ev_fd, ev_res, ev_events.
859
860=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
861maintained by libev, it does not work exactly the same way as in libevent (consider
862it a private API).
863
864=item * Priorities are not currently supported. Initialising priorities
865will fail and all watchers will have the same priority, even though there
866is an ev_pri field.
867
868=item * Other members are not supported.
869
870=item * The libev emulation is I<not> ABI compatible to libevent, you need
871to use the libev header file and library.
872
873=back
874
875=head1 C++ SUPPORT
876
877TBD.
878
767=head1 AUTHOR 879=head1 AUTHOR
768 880
769Marc Lehmann <libev@schmorp.de>. 881Marc Lehmann <libev@schmorp.de>.
770 882

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