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Revision 1.19 by root, Mon Nov 12 09:02:16 2007 UTC vs.
Revision 1.23 by root, Mon Nov 12 18:40:21 2007 UTC

417in each iteration of the event loop (This behaviour is called 417in each iteration of the event loop (This behaviour is called
418level-triggering because you keep receiving events as long as the 418level-triggering because you keep receiving events as long as the
419condition persists. Remember you can stop the watcher if you don't want to 419condition persists. Remember you can stop the watcher if you don't want to
420act on the event and neither want to receive future events). 420act on the event and neither want to receive future events).
421 421
422In general you can register as many read and/or write event watchers oer 422In general you can register as many read and/or write event watchers per
423fd as you want (as long as you don't confuse yourself). Setting all file 423fd as you want (as long as you don't confuse yourself). Setting all file
424descriptors to non-blocking mode is also usually a good idea (but not 424descriptors to non-blocking mode is also usually a good idea (but not
425required if you know what you are doing). 425required if you know what you are doing).
426 426
427You have to be careful with dup'ed file descriptors, though. Some backends 427You have to be careful with dup'ed file descriptors, though. Some backends
428(the linux epoll backend is a notable example) cannot handle dup'ed file 428(the linux epoll backend is a notable example) cannot handle dup'ed file
429descriptors correctly if you register interest in two or more fds pointing 429descriptors correctly if you register interest in two or more fds pointing
430to the same file/socket etc. description. 430to the same file/socket etc. description (that is, they share the same
431underlying "file open").
431 432
432If you must do this, then force the use of a known-to-be-good backend 433If you must do this, then force the use of a known-to-be-good backend
433(at the time of this writing, this includes only EVMETHOD_SELECT and 434(at the time of this writing, this includes only EVMETHOD_SELECT and
434EVMETHOD_POLL). 435EVMETHOD_POLL).
435 436
449 450
450Timer watchers are simple relative timers that generate an event after a 451Timer watchers are simple relative timers that generate an event after a
451given time, and optionally repeating in regular intervals after that. 452given time, and optionally repeating in regular intervals after that.
452 453
453The timers are based on real time, that is, if you register an event that 454The timers are based on real time, that is, if you register an event that
454times out after an hour and youreset your system clock to last years 455times out after an hour and you reset your system clock to last years
455time, it will still time out after (roughly) and hour. "Roughly" because 456time, it will still time out after (roughly) and hour. "Roughly" because
456detecting time jumps is hard, and soem inaccuracies are unavoidable (the 457detecting time jumps is hard, and soem inaccuracies are unavoidable (the
457monotonic clock option helps a lot here). 458monotonic clock option helps a lot here).
458 459
459The relative timeouts are calculated relative to the C<ev_now ()> 460The relative timeouts are calculated relative to the C<ev_now ()>
460time. This is usually the right thing as this timestamp refers to the time 461time. This is usually the right thing as this timestamp refers to the time
461of the event triggering whatever timeout you are modifying/starting. If 462of the event triggering whatever timeout you are modifying/starting. If
462you suspect event processing to be delayed and you *need* to base the timeout 463you suspect event processing to be delayed and you *need* to base the timeout
463ion the current time, use something like this to adjust for this: 464on the current time, use something like this to adjust for this:
464 465
465 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 466 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
466 467
467=over 4 468=over 4
468 469
476later, again, and again, until stopped manually. 477later, again, and again, until stopped manually.
477 478
478The timer itself will do a best-effort at avoiding drift, that is, if you 479The timer itself will do a best-effort at avoiding drift, that is, if you
479configure a timer to trigger every 10 seconds, then it will trigger at 480configure a timer to trigger every 10 seconds, then it will trigger at
480exactly 10 second intervals. If, however, your program cannot keep up with 481exactly 10 second intervals. If, however, your program cannot keep up with
481the timer (ecause it takes longer than those 10 seconds to do stuff) the 482the timer (because it takes longer than those 10 seconds to do stuff) the
482timer will not fire more than once per event loop iteration. 483timer will not fire more than once per event loop iteration.
483 484
484=item ev_timer_again (loop) 485=item ev_timer_again (loop)
485 486
486This will act as if the timer timed out and restart it again if it is 487This will act as if the timer timed out and restart it again if it is
677=back 678=back
678 679
679=head2 C<ev_prepare> and C<ev_check> - customise your event loop 680=head2 C<ev_prepare> and C<ev_check> - customise your event loop
680 681
681Prepare and check watchers are usually (but not always) used in tandem: 682Prepare and check watchers are usually (but not always) used in tandem:
682Prepare watchers get invoked before the process blocks and check watchers 683prepare watchers get invoked before the process blocks and check watchers
683afterwards. 684afterwards.
684 685
685Their main purpose is to integrate other event mechanisms into libev. This 686Their main purpose is to integrate other event mechanisms into libev. This
686could be used, for example, to track variable changes, implement your own 687could be used, for example, to track variable changes, implement your own
687watchers, integrate net-snmp or a coroutine library and lots more. 688watchers, integrate net-snmp or a coroutine library and lots more.
690to be watched by the other library, registering C<ev_io> watchers for 691to be watched by the other library, registering C<ev_io> watchers for
691them and starting an C<ev_timer> watcher for any timeouts (many libraries 692them and starting an C<ev_timer> watcher for any timeouts (many libraries
692provide just this functionality). Then, in the check watcher you check for 693provide just this functionality). Then, in the check watcher you check for
693any events that occured (by checking the pending status of all watchers 694any events that occured (by checking the pending status of all watchers
694and stopping them) and call back into the library. The I/O and timer 695and stopping them) and call back into the library. The I/O and timer
695callbacks will never actually be called (but must be valid neverthelles, 696callbacks will never actually be called (but must be valid nevertheless,
696because you never know, you know?). 697because you never know, you know?).
697 698
698As another example, the Perl Coro module uses these hooks to integrate 699As another example, the Perl Coro module uses these hooks to integrate
699coroutines into libev programs, by yielding to other active coroutines 700coroutines into libev programs, by yielding to other active coroutines
700during each prepare and only letting the process block if no coroutines 701during each prepare and only letting the process block if no coroutines
701are ready to run (its actually more complicated, it only runs coroutines 702are ready to run (it's actually more complicated: it only runs coroutines
702with priority higher than the event loop and one lower priority once, 703with priority higher than or equal to the event loop and one coroutine
703using idle watchers to keep the event loop from blocking if lower-priority 704of lower priority, but only once, using idle watchers to keep the event
704coroutines exist, thus mapping low-priority coroutines to idle/background 705loop from blocking if lower-priority coroutines are active, thus mapping
705tasks). 706low-priority coroutines to idle/background tasks).
706 707
707=over 4 708=over 4
708 709
709=item ev_prepare_init (ev_prepare *, callback) 710=item ev_prepare_init (ev_prepare *, callback)
710 711
725=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 726=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
726 727
727This function combines a simple timer and an I/O watcher, calls your 728This function combines a simple timer and an I/O watcher, calls your
728callback on whichever event happens first and automatically stop both 729callback on whichever event happens first and automatically stop both
729watchers. This is useful if you want to wait for a single event on an fd 730watchers. This is useful if you want to wait for a single event on an fd
730or timeout without havign to allocate/configure/start/stop/free one or 731or timeout without having to allocate/configure/start/stop/free one or
731more watchers yourself. 732more watchers yourself.
732 733
733If C<fd> is less than 0, then no I/O watcher will be started and events 734If C<fd> is less than 0, then no I/O watcher will be started and events
734is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and 735is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
735C<events> set will be craeted and started. 736C<events> set will be craeted and started.
738started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and 739started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
739repeat = 0) will be started. While C<0> is a valid timeout, it is of 740repeat = 0) will be started. While C<0> is a valid timeout, it is of
740dubious value. 741dubious value.
741 742
742The callback has the type C<void (*cb)(int revents, void *arg)> and gets 743The callback has the type C<void (*cb)(int revents, void *arg)> and gets
743passed an events set like normal event callbacks (with a combination of 744passed an C<revents> set like normal event callbacks (a combination of
744C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> 745C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
745value passed to C<ev_once>: 746value passed to C<ev_once>:
746 747
747 static void stdin_ready (int revents, void *arg) 748 static void stdin_ready (int revents, void *arg)
748 { 749 {
769 770
770Feed an event as if the given signal occured (loop must be the default loop!). 771Feed an event as if the given signal occured (loop must be the default loop!).
771 772
772=back 773=back
773 774
775=head1 LIBEVENT EMULATION
776
777TBD.
778
779=head1 C++ SUPPORT
780
781TBD.
782
774=head1 AUTHOR 783=head1 AUTHOR
775 784
776Marc Lehmann <libev@schmorp.de>. 785Marc Lehmann <libev@schmorp.de>.
777 786

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