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Revision 1.101 by ayin, Sat Dec 22 14:11:25 2007 UTC vs.
Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC

4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 #include <ev.h> 7 #include <ev.h>
8 8
9=head1 EXAMPLE PROGRAM 9=head2 EXAMPLE PROGRAM
10 10
11 // a single header file is required
11 #include <ev.h> 12 #include <ev.h>
12 13
14 // every watcher type has its own typedef'd struct
15 // with the name ev_<type>
13 ev_io stdin_watcher; 16 ev_io stdin_watcher;
14 ev_timer timeout_watcher; 17 ev_timer timeout_watcher;
15 18
19 // all watcher callbacks have a similar signature
16 /* called when data readable on stdin */ 20 // this callback is called when data is readable on stdin
17 static void 21 static void
18 stdin_cb (EV_P_ struct ev_io *w, int revents) 22 stdin_cb (EV_P_ struct ev_io *w, int revents)
19 { 23 {
20 /* puts ("stdin ready"); */ 24 puts ("stdin ready");
21 ev_io_stop (EV_A_ w); /* just a syntax example */ 25 // for one-shot events, one must manually stop the watcher
22 ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 26 // with its corresponding stop function.
27 ev_io_stop (EV_A_ w);
28
29 // this causes all nested ev_loop's to stop iterating
30 ev_unloop (EV_A_ EVUNLOOP_ALL);
23 } 31 }
24 32
33 // another callback, this time for a time-out
25 static void 34 static void
26 timeout_cb (EV_P_ struct ev_timer *w, int revents) 35 timeout_cb (EV_P_ struct ev_timer *w, int revents)
27 { 36 {
28 /* puts ("timeout"); */ 37 puts ("timeout");
29 ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 38 // this causes the innermost ev_loop to stop iterating
39 ev_unloop (EV_A_ EVUNLOOP_ONE);
30 } 40 }
31 41
32 int 42 int
33 main (void) 43 main (void)
34 { 44 {
45 // use the default event loop unless you have special needs
35 struct ev_loop *loop = ev_default_loop (0); 46 struct ev_loop *loop = ev_default_loop (0);
36 47
37 /* initialise an io watcher, then start it */ 48 // initialise an io watcher, then start it
49 // this one will watch for stdin to become readable
38 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 50 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39 ev_io_start (loop, &stdin_watcher); 51 ev_io_start (loop, &stdin_watcher);
40 52
53 // initialise a timer watcher, then start it
41 /* simple non-repeating 5.5 second timeout */ 54 // simple non-repeating 5.5 second timeout
42 ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 55 ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43 ev_timer_start (loop, &timeout_watcher); 56 ev_timer_start (loop, &timeout_watcher);
44 57
45 /* loop till timeout or data ready */ 58 // now wait for events to arrive
46 ev_loop (loop, 0); 59 ev_loop (loop, 0);
47 60
61 // unloop was called, so exit
48 return 0; 62 return 0;
49 } 63 }
50 64
51=head1 DESCRIPTION 65=head1 DESCRIPTION
52 66
53The newest version of this document is also available as a html-formatted 67The newest version of this document is also available as an html-formatted
54web page you might find easier to navigate when reading it for the first 68web page you might find easier to navigate when reading it for the first
55time: L<http://cvs.schmorp.de/libev/ev.html>. 69time: L<http://cvs.schmorp.de/libev/ev.html>.
56 70
57Libev is an event loop: you register interest in certain events (such as a 71Libev is an event loop: you register interest in certain events (such as a
58file descriptor being readable or a timeout occurring), and it will manage 72file descriptor being readable or a timeout occurring), and it will manage
65You register interest in certain events by registering so-called I<event 79You register interest in certain events by registering so-called I<event
66watchers>, which are relatively small C structures you initialise with the 80watchers>, which are relatively small C structures you initialise with the
67details of the event, and then hand it over to libev by I<starting> the 81details of the event, and then hand it over to libev by I<starting> the
68watcher. 82watcher.
69 83
70=head1 FEATURES 84=head2 FEATURES
71 85
72Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the 86Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73BSD-specific C<kqueue> and the Solaris-specific event port mechanisms 87BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74for file descriptor events (C<ev_io>), the Linux C<inotify> interface 88for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers 89(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
82 96
83It also is quite fast (see this 97It also is quite fast (see this
84L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent 98L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85for example). 99for example).
86 100
87=head1 CONVENTIONS 101=head2 CONVENTIONS
88 102
89Libev is very configurable. In this manual the default configuration will 103Libev is very configurable. In this manual the default (and most common)
90be described, which supports multiple event loops. For more info about 104configuration will be described, which supports multiple event loops. For
91various configuration options please have a look at B<EMBED> section in 105more info about various configuration options please have a look at
92this manual. If libev was configured without support for multiple event 106B<EMBED> section in this manual. If libev was configured without support
93loops, then all functions taking an initial argument of name C<loop> 107for multiple event loops, then all functions taking an initial argument of
94(which is always of type C<struct ev_loop *>) will not have this argument. 108name C<loop> (which is always of type C<struct ev_loop *>) will not have
109this argument.
95 110
96=head1 TIME REPRESENTATION 111=head2 TIME REPRESENTATION
97 112
98Libev represents time as a single floating point number, representing the 113Libev represents time as a single floating point number, representing the
99(fractional) number of seconds since the (POSIX) epoch (somewhere near 114(fractional) number of seconds since the (POSIX) epoch (somewhere near
100the beginning of 1970, details are complicated, don't ask). This type is 115the beginning of 1970, details are complicated, don't ask). This type is
101called C<ev_tstamp>, which is what you should use too. It usually aliases 116called C<ev_tstamp>, which is what you should use too. It usually aliases
260flags. If that is troubling you, check C<ev_backend ()> afterwards). 275flags. If that is troubling you, check C<ev_backend ()> afterwards).
261 276
262If you don't know what event loop to use, use the one returned from this 277If you don't know what event loop to use, use the one returned from this
263function. 278function.
264 279
280The default loop is the only loop that can handle C<ev_signal> and
281C<ev_child> watchers, and to do this, it always registers a handler
282for C<SIGCHLD>. If this is a problem for your app you can either
283create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
284can simply overwrite the C<SIGCHLD> signal handler I<after> calling
285C<ev_default_init>.
286
265The flags argument can be used to specify special behaviour or specific 287The flags argument can be used to specify special behaviour or specific
266backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>). 288backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267 289
268The following flags are supported: 290The following flags are supported:
269 291
290enabling this flag. 312enabling this flag.
291 313
292This works by calling C<getpid ()> on every iteration of the loop, 314This works by calling C<getpid ()> on every iteration of the loop,
293and thus this might slow down your event loop if you do a lot of loop 315and thus this might slow down your event loop if you do a lot of loop
294iterations and little real work, but is usually not noticeable (on my 316iterations and little real work, but is usually not noticeable (on my
295Linux system for example, C<getpid> is actually a simple 5-insn sequence 317GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296without a syscall and thus I<very> fast, but my Linux system also has 318without a syscall and thus I<very> fast, but my GNU/Linux system also has
297C<pthread_atfork> which is even faster). 319C<pthread_atfork> which is even faster).
298 320
299The big advantage of this flag is that you can forget about fork (and 321The big advantage of this flag is that you can forget about fork (and
300forget about forgetting to tell libev about forking) when you use this 322forget about forgetting to tell libev about forking) when you use this
301flag. 323flag.
306=item C<EVBACKEND_SELECT> (value 1, portable select backend) 328=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307 329
308This is your standard select(2) backend. Not I<completely> standard, as 330This is your standard select(2) backend. Not I<completely> standard, as
309libev tries to roll its own fd_set with no limits on the number of fds, 331libev tries to roll its own fd_set with no limits on the number of fds,
310but if that fails, expect a fairly low limit on the number of fds when 332but if that fails, expect a fairly low limit on the number of fds when
311using this backend. It doesn't scale too well (O(highest_fd)), but its usually 333using this backend. It doesn't scale too well (O(highest_fd)), but its
312the fastest backend for a low number of fds. 334usually the fastest backend for a low number of (low-numbered :) fds.
335
336To get good performance out of this backend you need a high amount of
337parallelity (most of the file descriptors should be busy). If you are
338writing a server, you should C<accept ()> in a loop to accept as many
339connections as possible during one iteration. You might also want to have
340a look at C<ev_set_io_collect_interval ()> to increase the amount of
341readyness notifications you get per iteration.
313 342
314=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows) 343=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315 344
316And this is your standard poll(2) backend. It's more complicated than 345And this is your standard poll(2) backend. It's more complicated
317select, but handles sparse fds better and has no artificial limit on the 346than select, but handles sparse fds better and has no artificial
318number of fds you can use (except it will slow down considerably with a 347limit on the number of fds you can use (except it will slow down
319lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 348considerably with a lot of inactive fds). It scales similarly to select,
349i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350performance tips.
320 351
321=item C<EVBACKEND_EPOLL> (value 4, Linux) 352=item C<EVBACKEND_EPOLL> (value 4, Linux)
322 353
323For few fds, this backend is a bit little slower than poll and select, 354For few fds, this backend is a bit little slower than poll and select,
324but it scales phenomenally better. While poll and select usually scale 355but it scales phenomenally better. While poll and select usually scale
325like O(total_fds) where n is the total number of fds (or the highest fd), 356like O(total_fds) where n is the total number of fds (or the highest fd),
326epoll scales either O(1) or O(active_fds). The epoll design has a number 357epoll scales either O(1) or O(active_fds). The epoll design has a number
327of shortcomings, such as silently dropping events in some hard-to-detect 358of shortcomings, such as silently dropping events in some hard-to-detect
328cases and rewiring a syscall per fd change, no fork support and bad 359cases and rewiring a syscall per fd change, no fork support and bad
329support for dup: 360support for dup.
330 361
331While stopping, setting and starting an I/O watcher in the same iteration 362While stopping, setting and starting an I/O watcher in the same iteration
332will result in some caching, there is still a syscall per such incident 363will result in some caching, there is still a syscall per such incident
333(because the fd could point to a different file description now), so its 364(because the fd could point to a different file description now), so its
334best to avoid that. Also, C<dup ()>'ed file descriptors might not work 365best to avoid that. Also, C<dup ()>'ed file descriptors might not work
335very well if you register events for both fds. 366very well if you register events for both fds.
336 367
337Please note that epoll sometimes generates spurious notifications, so you 368Please note that epoll sometimes generates spurious notifications, so you
338need to use non-blocking I/O or other means to avoid blocking when no data 369need to use non-blocking I/O or other means to avoid blocking when no data
339(or space) is available. 370(or space) is available.
371
372Best performance from this backend is achieved by not unregistering all
373watchers for a file descriptor until it has been closed, if possible, i.e.
374keep at least one watcher active per fd at all times.
375
376While nominally embeddeble in other event loops, this feature is broken in
377all kernel versions tested so far.
340 378
341=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) 379=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342 380
343Kqueue deserves special mention, as at the time of this writing, it 381Kqueue deserves special mention, as at the time of this writing, it
344was broken on all BSDs except NetBSD (usually it doesn't work reliably 382was broken on all BSDs except NetBSD (usually it doesn't work reliably
357course). While stopping, setting and starting an I/O watcher does never 395course). While stopping, setting and starting an I/O watcher does never
358cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to 396cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
359two event changes per incident, support for C<fork ()> is very bad and it 397two event changes per incident, support for C<fork ()> is very bad and it
360drops fds silently in similarly hard-to-detect cases. 398drops fds silently in similarly hard-to-detect cases.
361 399
400This backend usually performs well under most conditions.
401
402While nominally embeddable in other event loops, this doesn't work
403everywhere, so you might need to test for this. And since it is broken
404almost everywhere, you should only use it when you have a lot of sockets
405(for which it usually works), by embedding it into another event loop
406(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
407sockets.
408
362=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8) 409=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
363 410
364This is not implemented yet (and might never be). 411This is not implemented yet (and might never be, unless you send me an
412implementation). According to reports, C</dev/poll> only supports sockets
413and is not embeddable, which would limit the usefulness of this backend
414immensely.
365 415
366=item C<EVBACKEND_PORT> (value 32, Solaris 10) 416=item C<EVBACKEND_PORT> (value 32, Solaris 10)
367 417
368This uses the Solaris 10 event port mechanism. As with everything on Solaris, 418This uses the Solaris 10 event port mechanism. As with everything on Solaris,
369it's really slow, but it still scales very well (O(active_fds)). 419it's really slow, but it still scales very well (O(active_fds)).
370 420
371Please note that solaris event ports can deliver a lot of spurious 421Please note that solaris event ports can deliver a lot of spurious
372notifications, so you need to use non-blocking I/O or other means to avoid 422notifications, so you need to use non-blocking I/O or other means to avoid
373blocking when no data (or space) is available. 423blocking when no data (or space) is available.
374 424
425While this backend scales well, it requires one system call per active
426file descriptor per loop iteration. For small and medium numbers of file
427descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428might perform better.
429
430On the positive side, ignoring the spurious readyness notifications, this
431backend actually performed to specification in all tests and is fully
432embeddable, which is a rare feat among the OS-specific backends.
433
375=item C<EVBACKEND_ALL> 434=item C<EVBACKEND_ALL>
376 435
377Try all backends (even potentially broken ones that wouldn't be tried 436Try all backends (even potentially broken ones that wouldn't be tried
378with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as 437with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
379C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. 438C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
380 439
440It is definitely not recommended to use this flag.
441
381=back 442=back
382 443
383If one or more of these are ored into the flags value, then only these 444If one or more of these are ored into the flags value, then only these
384backends will be tried (in the reverse order as given here). If none are 445backends will be tried (in the reverse order as listed here). If none are
385specified, most compiled-in backend will be tried, usually in reverse 446specified, all backends in C<ev_recommended_backends ()> will be tried.
386order of their flag values :)
387 447
388The most typical usage is like this: 448The most typical usage is like this:
389 449
390 if (!ev_default_loop (0)) 450 if (!ev_default_loop (0))
391 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 451 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
438Like C<ev_default_destroy>, but destroys an event loop created by an 498Like C<ev_default_destroy>, but destroys an event loop created by an
439earlier call to C<ev_loop_new>. 499earlier call to C<ev_loop_new>.
440 500
441=item ev_default_fork () 501=item ev_default_fork ()
442 502
503This function sets a flag that causes subsequent C<ev_loop> iterations
443This function reinitialises the kernel state for backends that have 504to reinitialise the kernel state for backends that have one. Despite the
444one. Despite the name, you can call it anytime, but it makes most sense 505name, you can call it anytime, but it makes most sense after forking, in
445after forking, in either the parent or child process (or both, but that 506the child process (or both child and parent, but that again makes little
446again makes little sense). 507sense). You I<must> call it in the child before using any of the libev
508functions, and it will only take effect at the next C<ev_loop> iteration.
447 509
448You I<must> call this function in the child process after forking if and 510On the other hand, you only need to call this function in the child
449only if you want to use the event library in both processes. If you just 511process if and only if you want to use the event library in the child. If
450fork+exec, you don't have to call it. 512you just fork+exec, you don't have to call it at all.
451 513
452The function itself is quite fast and it's usually not a problem to call 514The function itself is quite fast and it's usually not a problem to call
453it just in case after a fork. To make this easy, the function will fit in 515it just in case after a fork. To make this easy, the function will fit in
454quite nicely into a call to C<pthread_atfork>: 516quite nicely into a call to C<pthread_atfork>:
455 517
456 pthread_atfork (0, 0, ev_default_fork); 518 pthread_atfork (0, 0, ev_default_fork);
457 519
458At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
459without calling this function, so if you force one of those backends you
460do not need to care.
461
462=item ev_loop_fork (loop) 520=item ev_loop_fork (loop)
463 521
464Like C<ev_default_fork>, but acts on an event loop created by 522Like C<ev_default_fork>, but acts on an event loop created by
465C<ev_loop_new>. Yes, you have to call this on every allocated event loop 523C<ev_loop_new>. Yes, you have to call this on every allocated event loop
466after fork, and how you do this is entirely your own problem. 524after fork, and how you do this is entirely your own problem.
525
526=item int ev_is_default_loop (loop)
527
528Returns true when the given loop actually is the default loop, false otherwise.
467 529
468=item unsigned int ev_loop_count (loop) 530=item unsigned int ev_loop_count (loop)
469 531
470Returns the count of loop iterations for the loop, which is identical to 532Returns the count of loop iterations for the loop, which is identical to
471the number of times libev did poll for new events. It starts at C<0> and 533the number of times libev did poll for new events. It starts at C<0> and
516usually a better approach for this kind of thing. 578usually a better approach for this kind of thing.
517 579
518Here are the gory details of what C<ev_loop> does: 580Here are the gory details of what C<ev_loop> does:
519 581
520 - Before the first iteration, call any pending watchers. 582 - Before the first iteration, call any pending watchers.
521 * If there are no active watchers (reference count is zero), return. 583 * If EVFLAG_FORKCHECK was used, check for a fork.
522 - Queue all prepare watchers and then call all outstanding watchers. 584 - If a fork was detected, queue and call all fork watchers.
585 - Queue and call all prepare watchers.
523 - If we have been forked, recreate the kernel state. 586 - If we have been forked, recreate the kernel state.
524 - Update the kernel state with all outstanding changes. 587 - Update the kernel state with all outstanding changes.
525 - Update the "event loop time". 588 - Update the "event loop time".
526 - Calculate for how long to block. 589 - Calculate for how long to sleep or block, if at all
590 (active idle watchers, EVLOOP_NONBLOCK or not having
591 any active watchers at all will result in not sleeping).
592 - Sleep if the I/O and timer collect interval say so.
527 - Block the process, waiting for any events. 593 - Block the process, waiting for any events.
528 - Queue all outstanding I/O (fd) events. 594 - Queue all outstanding I/O (fd) events.
529 - Update the "event loop time" and do time jump handling. 595 - Update the "event loop time" and do time jump handling.
530 - Queue all outstanding timers. 596 - Queue all outstanding timers.
531 - Queue all outstanding periodics. 597 - Queue all outstanding periodics.
532 - If no events are pending now, queue all idle watchers. 598 - If no events are pending now, queue all idle watchers.
533 - Queue all check watchers. 599 - Queue all check watchers.
534 - Call all queued watchers in reverse order (i.e. check watchers first). 600 - Call all queued watchers in reverse order (i.e. check watchers first).
535 Signals and child watchers are implemented as I/O watchers, and will 601 Signals and child watchers are implemented as I/O watchers, and will
536 be handled here by queueing them when their watcher gets executed. 602 be handled here by queueing them when their watcher gets executed.
537 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 603 - If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
538 were used, return, otherwise continue with step *. 604 were used, or there are no active watchers, return, otherwise
605 continue with step *.
539 606
540Example: Queue some jobs and then loop until no events are outsanding 607Example: Queue some jobs and then loop until no events are outstanding
541anymore. 608anymore.
542 609
543 ... queue jobs here, make sure they register event watchers as long 610 ... queue jobs here, make sure they register event watchers as long
544 ... as they still have work to do (even an idle watcher will do..) 611 ... as they still have work to do (even an idle watcher will do..)
545 ev_loop (my_loop, 0); 612 ev_loop (my_loop, 0);
549 616
550Can be used to make a call to C<ev_loop> return early (but only after it 617Can be used to make a call to C<ev_loop> return early (but only after it
551has processed all outstanding events). The C<how> argument must be either 618has processed all outstanding events). The C<how> argument must be either
552C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or 619C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
553C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. 620C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
621
622This "unloop state" will be cleared when entering C<ev_loop> again.
554 623
555=item ev_ref (loop) 624=item ev_ref (loop)
556 625
557=item ev_unref (loop) 626=item ev_unref (loop)
558 627
563returning, ev_unref() after starting, and ev_ref() before stopping it. For 632returning, ev_unref() after starting, and ev_ref() before stopping it. For
564example, libev itself uses this for its internal signal pipe: It is not 633example, libev itself uses this for its internal signal pipe: It is not
565visible to the libev user and should not keep C<ev_loop> from exiting if 634visible to the libev user and should not keep C<ev_loop> from exiting if
566no event watchers registered by it are active. It is also an excellent 635no event watchers registered by it are active. It is also an excellent
567way to do this for generic recurring timers or from within third-party 636way to do this for generic recurring timers or from within third-party
568libraries. Just remember to I<unref after start> and I<ref before stop>. 637libraries. Just remember to I<unref after start> and I<ref before stop>
638(but only if the watcher wasn't active before, or was active before,
639respectively).
569 640
570Example: Create a signal watcher, but keep it from keeping C<ev_loop> 641Example: Create a signal watcher, but keep it from keeping C<ev_loop>
571running when nothing else is active. 642running when nothing else is active.
572 643
573 struct ev_signal exitsig; 644 struct ev_signal exitsig;
721 792
722=item C<EV_FORK> 793=item C<EV_FORK>
723 794
724The event loop has been resumed in the child process after fork (see 795The event loop has been resumed in the child process after fork (see
725C<ev_fork>). 796C<ev_fork>).
797
798=item C<EV_ASYNC>
799
800The given async watcher has been asynchronously notified (see C<ev_async>).
726 801
727=item C<EV_ERROR> 802=item C<EV_ERROR>
728 803
729An unspecified error has occured, the watcher has been stopped. This might 804An unspecified error has occured, the watcher has been stopped. This might
730happen because the watcher could not be properly started because libev 805happen because the watcher could not be properly started because libev
948In general you can register as many read and/or write event watchers per 1023In general you can register as many read and/or write event watchers per
949fd as you want (as long as you don't confuse yourself). Setting all file 1024fd as you want (as long as you don't confuse yourself). Setting all file
950descriptors to non-blocking mode is also usually a good idea (but not 1025descriptors to non-blocking mode is also usually a good idea (but not
951required if you know what you are doing). 1026required if you know what you are doing).
952 1027
953You have to be careful with dup'ed file descriptors, though. Some backends
954(the linux epoll backend is a notable example) cannot handle dup'ed file
955descriptors correctly if you register interest in two or more fds pointing
956to the same underlying file/socket/etc. description (that is, they share
957the same underlying "file open").
958
959If you must do this, then force the use of a known-to-be-good backend 1028If you must do this, then force the use of a known-to-be-good backend
960(at the time of this writing, this includes only C<EVBACKEND_SELECT> and 1029(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
961C<EVBACKEND_POLL>). 1030C<EVBACKEND_POLL>).
962 1031
963Another thing you have to watch out for is that it is quite easy to 1032Another thing you have to watch out for is that it is quite easy to
997optimisations to libev. 1066optimisations to libev.
998 1067
999=head3 The special problem of dup'ed file descriptors 1068=head3 The special problem of dup'ed file descriptors
1000 1069
1001Some backends (e.g. epoll), cannot register events for file descriptors, 1070Some backends (e.g. epoll), cannot register events for file descriptors,
1002but only events for the underlying file descriptions. That menas when you 1071but only events for the underlying file descriptions. That means when you
1003have C<dup ()>'ed file descriptors and register events for them, only one 1072have C<dup ()>'ed file descriptors or weirder constellations, and register
1004file descriptor might actually receive events. 1073events for them, only one file descriptor might actually receive events.
1005 1074
1006There is no workaorund possible except not registering events 1075There is no workaround possible except not registering events
1007for potentially C<dup ()>'ed file descriptors or to resort to 1076for potentially C<dup ()>'ed file descriptors, or to resort to
1008C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. 1077C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1009 1078
1010=head3 The special problem of fork 1079=head3 The special problem of fork
1011 1080
1012Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit 1081Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1038=item int events [read-only] 1107=item int events [read-only]
1039 1108
1040The events being watched. 1109The events being watched.
1041 1110
1042=back 1111=back
1112
1113=head3 Examples
1043 1114
1044Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well 1115Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1045readable, but only once. Since it is likely line-buffered, you could 1116readable, but only once. Since it is likely line-buffered, you could
1046attempt to read a whole line in the callback. 1117attempt to read a whole line in the callback.
1047 1118
1100configure a timer to trigger every 10 seconds, then it will trigger at 1171configure a timer to trigger every 10 seconds, then it will trigger at
1101exactly 10 second intervals. If, however, your program cannot keep up with 1172exactly 10 second intervals. If, however, your program cannot keep up with
1102the timer (because it takes longer than those 10 seconds to do stuff) the 1173the timer (because it takes longer than those 10 seconds to do stuff) the
1103timer will not fire more than once per event loop iteration. 1174timer will not fire more than once per event loop iteration.
1104 1175
1105=item ev_timer_again (loop) 1176=item ev_timer_again (loop, ev_timer *)
1106 1177
1107This will act as if the timer timed out and restart it again if it is 1178This will act as if the timer timed out and restart it again if it is
1108repeating. The exact semantics are: 1179repeating. The exact semantics are:
1109 1180
1110If the timer is pending, its pending status is cleared. 1181If the timer is pending, its pending status is cleared.
1145or C<ev_timer_again> is called and determines the next timeout (if any), 1216or C<ev_timer_again> is called and determines the next timeout (if any),
1146which is also when any modifications are taken into account. 1217which is also when any modifications are taken into account.
1147 1218
1148=back 1219=back
1149 1220
1221=head3 Examples
1222
1150Example: Create a timer that fires after 60 seconds. 1223Example: Create a timer that fires after 60 seconds.
1151 1224
1152 static void 1225 static void
1153 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1226 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1154 { 1227 {
1217In this configuration the watcher triggers an event at the wallclock time 1290In this configuration the watcher triggers an event at the wallclock time
1218C<at> and doesn't repeat. It will not adjust when a time jump occurs, 1291C<at> and doesn't repeat. It will not adjust when a time jump occurs,
1219that is, if it is to be run at January 1st 2011 then it will run when the 1292that is, if it is to be run at January 1st 2011 then it will run when the
1220system time reaches or surpasses this time. 1293system time reaches or surpasses this time.
1221 1294
1222=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) 1295=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1223 1296
1224In this mode the watcher will always be scheduled to time out at the next 1297In this mode the watcher will always be scheduled to time out at the next
1225C<at + N * interval> time (for some integer N, which can also be negative) 1298C<at + N * interval> time (for some integer N, which can also be negative)
1226and then repeat, regardless of any time jumps. 1299and then repeat, regardless of any time jumps.
1227 1300
1310 1383
1311When active, contains the absolute time that the watcher is supposed to 1384When active, contains the absolute time that the watcher is supposed to
1312trigger next. 1385trigger next.
1313 1386
1314=back 1387=back
1388
1389=head3 Examples
1315 1390
1316Example: Call a callback every hour, or, more precisely, whenever the 1391Example: Call a callback every hour, or, more precisely, whenever the
1317system clock is divisible by 3600. The callback invocation times have 1392system clock is divisible by 3600. The callback invocation times have
1318potentially a lot of jittering, but good long-term stability. 1393potentially a lot of jittering, but good long-term stability.
1319 1394
1359with the kernel (thus it coexists with your own signal handlers as long 1434with the kernel (thus it coexists with your own signal handlers as long
1360as you don't register any with libev). Similarly, when the last signal 1435as you don't register any with libev). Similarly, when the last signal
1361watcher for a signal is stopped libev will reset the signal handler to 1436watcher for a signal is stopped libev will reset the signal handler to
1362SIG_DFL (regardless of what it was set to before). 1437SIG_DFL (regardless of what it was set to before).
1363 1438
1439If possible and supported, libev will install its handlers with
1440C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
1441interrupted. If you have a problem with syscalls getting interrupted by
1442signals you can block all signals in an C<ev_check> watcher and unblock
1443them in an C<ev_prepare> watcher.
1444
1364=head3 Watcher-Specific Functions and Data Members 1445=head3 Watcher-Specific Functions and Data Members
1365 1446
1366=over 4 1447=over 4
1367 1448
1368=item ev_signal_init (ev_signal *, callback, int signum) 1449=item ev_signal_init (ev_signal *, callback, int signum)
1376 1457
1377The signal the watcher watches out for. 1458The signal the watcher watches out for.
1378 1459
1379=back 1460=back
1380 1461
1462=head3 Examples
1463
1464Example: Try to exit cleanly on SIGINT and SIGTERM.
1465
1466 static void
1467 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1468 {
1469 ev_unloop (loop, EVUNLOOP_ALL);
1470 }
1471
1472 struct ev_signal signal_watcher;
1473 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1474 ev_signal_start (loop, &sigint_cb);
1475
1381 1476
1382=head2 C<ev_child> - watch out for process status changes 1477=head2 C<ev_child> - watch out for process status changes
1383 1478
1384Child watchers trigger when your process receives a SIGCHLD in response to 1479Child watchers trigger when your process receives a SIGCHLD in response to
1385some child status changes (most typically when a child of yours dies). 1480some child status changes (most typically when a child of yours dies). It
1481is permissible to install a child watcher I<after> the child has been
1482forked (which implies it might have already exited), as long as the event
1483loop isn't entered (or is continued from a watcher).
1484
1485Only the default event loop is capable of handling signals, and therefore
1486you can only rgeister child watchers in the default event loop.
1487
1488=head3 Process Interaction
1489
1490Libev grabs C<SIGCHLD> as soon as the default event loop is
1491initialised. This is necessary to guarantee proper behaviour even if
1492the first child watcher is started after the child exits. The occurance
1493of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1494synchronously as part of the event loop processing. Libev always reaps all
1495children, even ones not watched.
1496
1497=head3 Overriding the Built-In Processing
1498
1499Libev offers no special support for overriding the built-in child
1500processing, but if your application collides with libev's default child
1501handler, you can override it easily by installing your own handler for
1502C<SIGCHLD> after initialising the default loop, and making sure the
1503default loop never gets destroyed. You are encouraged, however, to use an
1504event-based approach to child reaping and thus use libev's support for
1505that, so other libev users can use C<ev_child> watchers freely.
1386 1506
1387=head3 Watcher-Specific Functions and Data Members 1507=head3 Watcher-Specific Functions and Data Members
1388 1508
1389=over 4 1509=over 4
1390 1510
1391=item ev_child_init (ev_child *, callback, int pid) 1511=item ev_child_init (ev_child *, callback, int pid, int trace)
1392 1512
1393=item ev_child_set (ev_child *, int pid) 1513=item ev_child_set (ev_child *, int pid, int trace)
1394 1514
1395Configures the watcher to wait for status changes of process C<pid> (or 1515Configures the watcher to wait for status changes of process C<pid> (or
1396I<any> process if C<pid> is specified as C<0>). The callback can look 1516I<any> process if C<pid> is specified as C<0>). The callback can look
1397at the C<rstatus> member of the C<ev_child> watcher structure to see 1517at the C<rstatus> member of the C<ev_child> watcher structure to see
1398the status word (use the macros from C<sys/wait.h> and see your systems 1518the status word (use the macros from C<sys/wait.h> and see your systems
1399C<waitpid> documentation). The C<rpid> member contains the pid of the 1519C<waitpid> documentation). The C<rpid> member contains the pid of the
1400process causing the status change. 1520process causing the status change. C<trace> must be either C<0> (only
1521activate the watcher when the process terminates) or C<1> (additionally
1522activate the watcher when the process is stopped or continued).
1401 1523
1402=item int pid [read-only] 1524=item int pid [read-only]
1403 1525
1404The process id this watcher watches out for, or C<0>, meaning any process id. 1526The process id this watcher watches out for, or C<0>, meaning any process id.
1405 1527
1412The process exit/trace status caused by C<rpid> (see your systems 1534The process exit/trace status caused by C<rpid> (see your systems
1413C<waitpid> and C<sys/wait.h> documentation for details). 1535C<waitpid> and C<sys/wait.h> documentation for details).
1414 1536
1415=back 1537=back
1416 1538
1417Example: Try to exit cleanly on SIGINT and SIGTERM. 1539=head3 Examples
1540
1541Example: C<fork()> a new process and install a child handler to wait for
1542its completion.
1543
1544 ev_child cw;
1418 1545
1419 static void 1546 static void
1420 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 1547 child_cb (EV_P_ struct ev_child *w, int revents)
1421 { 1548 {
1422 ev_unloop (loop, EVUNLOOP_ALL); 1549 ev_child_stop (EV_A_ w);
1550 printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1423 } 1551 }
1424 1552
1425 struct ev_signal signal_watcher; 1553 pid_t pid = fork ();
1426 ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 1554
1427 ev_signal_start (loop, &sigint_cb); 1555 if (pid < 0)
1556 // error
1557 else if (pid == 0)
1558 {
1559 // the forked child executes here
1560 exit (1);
1561 }
1562 else
1563 {
1564 ev_child_init (&cw, child_cb, pid, 0);
1565 ev_child_start (EV_DEFAULT_ &cw);
1566 }
1428 1567
1429 1568
1430=head2 C<ev_stat> - did the file attributes just change? 1569=head2 C<ev_stat> - did the file attributes just change?
1431 1570
1432This watches a filesystem path for attribute changes. That is, it calls 1571This watches a filesystem path for attribute changes. That is, it calls
1461semantics of C<ev_stat> watchers, which means that libev sometimes needs 1600semantics of C<ev_stat> watchers, which means that libev sometimes needs
1462to fall back to regular polling again even with inotify, but changes are 1601to fall back to regular polling again even with inotify, but changes are
1463usually detected immediately, and if the file exists there will be no 1602usually detected immediately, and if the file exists there will be no
1464polling. 1603polling.
1465 1604
1605=head3 Inotify
1606
1607When C<inotify (7)> support has been compiled into libev (generally only
1608available on Linux) and present at runtime, it will be used to speed up
1609change detection where possible. The inotify descriptor will be created lazily
1610when the first C<ev_stat> watcher is being started.
1611
1612Inotify presense does not change the semantics of C<ev_stat> watchers
1613except that changes might be detected earlier, and in some cases, to avoid
1614making regular C<stat> calls. Even in the presense of inotify support
1615there are many cases where libev has to resort to regular C<stat> polling.
1616
1617(There is no support for kqueue, as apparently it cannot be used to
1618implement this functionality, due to the requirement of having a file
1619descriptor open on the object at all times).
1620
1621=head3 The special problem of stat time resolution
1622
1623The C<stat ()> syscall only supports full-second resolution portably, and
1624even on systems where the resolution is higher, many filesystems still
1625only support whole seconds.
1626
1627That means that, if the time is the only thing that changes, you might
1628miss updates: on the first update, C<ev_stat> detects a change and calls
1629your callback, which does something. When there is another update within
1630the same second, C<ev_stat> will be unable to detect it.
1631
1632The solution to this is to delay acting on a change for a second (or till
1633the next second boundary), using a roughly one-second delay C<ev_timer>
1634(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
1635is added to work around small timing inconsistencies of some operating
1636systems.
1637
1466=head3 Watcher-Specific Functions and Data Members 1638=head3 Watcher-Specific Functions and Data Members
1467 1639
1468=over 4 1640=over 4
1469 1641
1470=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval) 1642=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1479 1651
1480The callback will be receive C<EV_STAT> when a change was detected, 1652The callback will be receive C<EV_STAT> when a change was detected,
1481relative to the attributes at the time the watcher was started (or the 1653relative to the attributes at the time the watcher was started (or the
1482last change was detected). 1654last change was detected).
1483 1655
1484=item ev_stat_stat (ev_stat *) 1656=item ev_stat_stat (loop, ev_stat *)
1485 1657
1486Updates the stat buffer immediately with new values. If you change the 1658Updates the stat buffer immediately with new values. If you change the
1487watched path in your callback, you could call this fucntion to avoid 1659watched path in your callback, you could call this fucntion to avoid
1488detecting this change (while introducing a race condition). Can also be 1660detecting this change (while introducing a race condition). Can also be
1489useful simply to find out the new values. 1661useful simply to find out the new values.
1507=item const char *path [read-only] 1679=item const char *path [read-only]
1508 1680
1509The filesystem path that is being watched. 1681The filesystem path that is being watched.
1510 1682
1511=back 1683=back
1684
1685=head3 Examples
1512 1686
1513Example: Watch C</etc/passwd> for attribute changes. 1687Example: Watch C</etc/passwd> for attribute changes.
1514 1688
1515 static void 1689 static void
1516 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 1690 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1529 } 1703 }
1530 1704
1531 ... 1705 ...
1532 ev_stat passwd; 1706 ev_stat passwd;
1533 1707
1534 ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 1708 ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1535 ev_stat_start (loop, &passwd); 1709 ev_stat_start (loop, &passwd);
1710
1711Example: Like above, but additionally use a one-second delay so we do not
1712miss updates (however, frequent updates will delay processing, too, so
1713one might do the work both on C<ev_stat> callback invocation I<and> on
1714C<ev_timer> callback invocation).
1715
1716 static ev_stat passwd;
1717 static ev_timer timer;
1718
1719 static void
1720 timer_cb (EV_P_ ev_timer *w, int revents)
1721 {
1722 ev_timer_stop (EV_A_ w);
1723
1724 /* now it's one second after the most recent passwd change */
1725 }
1726
1727 static void
1728 stat_cb (EV_P_ ev_stat *w, int revents)
1729 {
1730 /* reset the one-second timer */
1731 ev_timer_again (EV_A_ &timer);
1732 }
1733
1734 ...
1735 ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1736 ev_stat_start (loop, &passwd);
1737 ev_timer_init (&timer, timer_cb, 0., 1.01);
1536 1738
1537 1739
1538=head2 C<ev_idle> - when you've got nothing better to do... 1740=head2 C<ev_idle> - when you've got nothing better to do...
1539 1741
1540Idle watchers trigger events when no other events of the same or higher 1742Idle watchers trigger events when no other events of the same or higher
1566kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 1768kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1567believe me. 1769believe me.
1568 1770
1569=back 1771=back
1570 1772
1773=head3 Examples
1774
1571Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the 1775Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1572callback, free it. Also, use no error checking, as usual. 1776callback, free it. Also, use no error checking, as usual.
1573 1777
1574 static void 1778 static void
1575 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 1779 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1576 { 1780 {
1577 free (w); 1781 free (w);
1578 // now do something you wanted to do when the program has 1782 // now do something you wanted to do when the program has
1579 // no longer asnything immediate to do. 1783 // no longer anything immediate to do.
1580 } 1784 }
1581 1785
1582 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 1786 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1583 ev_idle_init (idle_watcher, idle_cb); 1787 ev_idle_init (idle_watcher, idle_cb);
1584 ev_idle_start (loop, idle_cb); 1788 ev_idle_start (loop, idle_cb);
1646parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 1850parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1647macros, but using them is utterly, utterly and completely pointless. 1851macros, but using them is utterly, utterly and completely pointless.
1648 1852
1649=back 1853=back
1650 1854
1855=head3 Examples
1856
1651There are a number of principal ways to embed other event loops or modules 1857There are a number of principal ways to embed other event loops or modules
1652into libev. Here are some ideas on how to include libadns into libev 1858into libev. Here are some ideas on how to include libadns into libev
1653(there is a Perl module named C<EV::ADNS> that does this, which you could 1859(there is a Perl module named C<EV::ADNS> that does this, which you could
1654use for an actually working example. Another Perl module named C<EV::Glib> 1860use for an actually working example. Another Perl module named C<EV::Glib>
1655embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV 1861embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
1823portable one. 2029portable one.
1824 2030
1825So when you want to use this feature you will always have to be prepared 2031So when you want to use this feature you will always have to be prepared
1826that you cannot get an embeddable loop. The recommended way to get around 2032that you cannot get an embeddable loop. The recommended way to get around
1827this is to have a separate variables for your embeddable loop, try to 2033this is to have a separate variables for your embeddable loop, try to
1828create it, and if that fails, use the normal loop for everything: 2034create it, and if that fails, use the normal loop for everything.
2035
2036=head3 Watcher-Specific Functions and Data Members
2037
2038=over 4
2039
2040=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2041
2042=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
2043
2044Configures the watcher to embed the given loop, which must be
2045embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2046invoked automatically, otherwise it is the responsibility of the callback
2047to invoke it (it will continue to be called until the sweep has been done,
2048if you do not want thta, you need to temporarily stop the embed watcher).
2049
2050=item ev_embed_sweep (loop, ev_embed *)
2051
2052Make a single, non-blocking sweep over the embedded loop. This works
2053similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
2054apropriate way for embedded loops.
2055
2056=item struct ev_loop *other [read-only]
2057
2058The embedded event loop.
2059
2060=back
2061
2062=head3 Examples
2063
2064Example: Try to get an embeddable event loop and embed it into the default
2065event loop. If that is not possible, use the default loop. The default
2066loop is stored in C<loop_hi>, while the mebeddable loop is stored in
2067C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
2068used).
1829 2069
1830 struct ev_loop *loop_hi = ev_default_init (0); 2070 struct ev_loop *loop_hi = ev_default_init (0);
1831 struct ev_loop *loop_lo = 0; 2071 struct ev_loop *loop_lo = 0;
1832 struct ev_embed embed; 2072 struct ev_embed embed;
1833 2073
1844 ev_embed_start (loop_hi, &embed); 2084 ev_embed_start (loop_hi, &embed);
1845 } 2085 }
1846 else 2086 else
1847 loop_lo = loop_hi; 2087 loop_lo = loop_hi;
1848 2088
1849=head3 Watcher-Specific Functions and Data Members 2089Example: Check if kqueue is available but not recommended and create
2090a kqueue backend for use with sockets (which usually work with any
2091kqueue implementation). Store the kqueue/socket-only event loop in
2092C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1850 2093
1851=over 4 2094 struct ev_loop *loop = ev_default_init (0);
2095 struct ev_loop *loop_socket = 0;
2096 struct ev_embed embed;
2097
2098 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2099 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2100 {
2101 ev_embed_init (&embed, 0, loop_socket);
2102 ev_embed_start (loop, &embed);
2103 }
1852 2104
1853=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop) 2105 if (!loop_socket)
2106 loop_socket = loop;
1854 2107
1855=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop) 2108 // now use loop_socket for all sockets, and loop for everything else
1856
1857Configures the watcher to embed the given loop, which must be
1858embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1859invoked automatically, otherwise it is the responsibility of the callback
1860to invoke it (it will continue to be called until the sweep has been done,
1861if you do not want thta, you need to temporarily stop the embed watcher).
1862
1863=item ev_embed_sweep (loop, ev_embed *)
1864
1865Make a single, non-blocking sweep over the embedded loop. This works
1866similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1867apropriate way for embedded loops.
1868
1869=item struct ev_loop *other [read-only]
1870
1871The embedded event loop.
1872
1873=back
1874 2109
1875 2110
1876=head2 C<ev_fork> - the audacity to resume the event loop after a fork 2111=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1877 2112
1878Fork watchers are called when a C<fork ()> was detected (usually because 2113Fork watchers are called when a C<fork ()> was detected (usually because
1894believe me. 2129believe me.
1895 2130
1896=back 2131=back
1897 2132
1898 2133
2134=head2 C<ev_async> - how to wake up another event loop
2135
2136In general, you cannot use an C<ev_loop> from multiple threads or other
2137asynchronous sources such as signal handlers (as opposed to multiple event
2138loops - those are of course safe to use in different threads).
2139
2140Sometimes, however, you need to wake up another event loop you do not
2141control, for example because it belongs to another thread. This is what
2142C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
2143can signal it by calling C<ev_async_send>, which is thread- and signal
2144safe.
2145
2146This functionality is very similar to C<ev_signal> watchers, as signals,
2147too, are asynchronous in nature, and signals, too, will be compressed
2148(i.e. the number of callback invocations may be less than the number of
2149C<ev_async_sent> calls).
2150
2151Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
2152just the default loop.
2153
2154=head3 Queueing
2155
2156C<ev_async> does not support queueing of data in any way. The reason
2157is that the author does not know of a simple (or any) algorithm for a
2158multiple-writer-single-reader queue that works in all cases and doesn't
2159need elaborate support such as pthreads.
2160
2161That means that if you want to queue data, you have to provide your own
2162queue. But at least I can tell you would implement locking around your
2163queue:
2164
2165=over 4
2166
2167=item queueing from a signal handler context
2168
2169To implement race-free queueing, you simply add to the queue in the signal
2170handler but you block the signal handler in the watcher callback. Here is an example that does that for
2171some fictitiuous SIGUSR1 handler:
2172
2173 static ev_async mysig;
2174
2175 static void
2176 sigusr1_handler (void)
2177 {
2178 sometype data;
2179
2180 // no locking etc.
2181 queue_put (data);
2182 ev_async_send (EV_DEFAULT_ &mysig);
2183 }
2184
2185 static void
2186 mysig_cb (EV_P_ ev_async *w, int revents)
2187 {
2188 sometype data;
2189 sigset_t block, prev;
2190
2191 sigemptyset (&block);
2192 sigaddset (&block, SIGUSR1);
2193 sigprocmask (SIG_BLOCK, &block, &prev);
2194
2195 while (queue_get (&data))
2196 process (data);
2197
2198 if (sigismember (&prev, SIGUSR1)
2199 sigprocmask (SIG_UNBLOCK, &block, 0);
2200 }
2201
2202(Note: pthreads in theory requires you to use C<pthread_setmask>
2203instead of C<sigprocmask> when you use threads, but libev doesn't do it
2204either...).
2205
2206=item queueing from a thread context
2207
2208The strategy for threads is different, as you cannot (easily) block
2209threads but you can easily preempt them, so to queue safely you need to
2210employ a traditional mutex lock, such as in this pthread example:
2211
2212 static ev_async mysig;
2213 static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2214
2215 static void
2216 otherthread (void)
2217 {
2218 // only need to lock the actual queueing operation
2219 pthread_mutex_lock (&mymutex);
2220 queue_put (data);
2221 pthread_mutex_unlock (&mymutex);
2222
2223 ev_async_send (EV_DEFAULT_ &mysig);
2224 }
2225
2226 static void
2227 mysig_cb (EV_P_ ev_async *w, int revents)
2228 {
2229 pthread_mutex_lock (&mymutex);
2230
2231 while (queue_get (&data))
2232 process (data);
2233
2234 pthread_mutex_unlock (&mymutex);
2235 }
2236
2237=back
2238
2239
2240=head3 Watcher-Specific Functions and Data Members
2241
2242=over 4
2243
2244=item ev_async_init (ev_async *, callback)
2245
2246Initialises and configures the async watcher - it has no parameters of any
2247kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
2248believe me.
2249
2250=item ev_async_send (loop, ev_async *)
2251
2252Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2253an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2254C<ev_feed_event>, this call is safe to do in other threads, signal or
2255similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
2256section below on what exactly this means).
2257
2258This call incurs the overhead of a syscall only once per loop iteration,
2259so while the overhead might be noticable, it doesn't apply to repeated
2260calls to C<ev_async_send>.
2261
2262=back
2263
2264
1899=head1 OTHER FUNCTIONS 2265=head1 OTHER FUNCTIONS
1900 2266
1901There are some other functions of possible interest. Described. Here. Now. 2267There are some other functions of possible interest. Described. Here. Now.
1902 2268
1903=over 4 2269=over 4
2130Example: Define a class with an IO and idle watcher, start one of them in 2496Example: Define a class with an IO and idle watcher, start one of them in
2131the constructor. 2497the constructor.
2132 2498
2133 class myclass 2499 class myclass
2134 { 2500 {
2135 ev_io io; void io_cb (ev::io &w, int revents); 2501 ev::io io; void io_cb (ev::io &w, int revents);
2136 ev_idle idle void idle_cb (ev::idle &w, int revents); 2502 ev:idle idle void idle_cb (ev::idle &w, int revents);
2137 2503
2138 myclass (); 2504 myclass (int fd)
2139 }
2140
2141 myclass::myclass (int fd)
2142 { 2505 {
2143 io .set <myclass, &myclass::io_cb > (this); 2506 io .set <myclass, &myclass::io_cb > (this);
2144 idle.set <myclass, &myclass::idle_cb> (this); 2507 idle.set <myclass, &myclass::idle_cb> (this);
2145 2508
2146 io.start (fd, ev::READ); 2509 io.start (fd, ev::READ);
2510 }
2147 } 2511 };
2512
2513
2514=head1 OTHER LANGUAGE BINDINGS
2515
2516Libev does not offer other language bindings itself, but bindings for a
2517numbe rof languages exist in the form of third-party packages. If you know
2518any interesting language binding in addition to the ones listed here, drop
2519me a note.
2520
2521=over 4
2522
2523=item Perl
2524
2525The EV module implements the full libev API and is actually used to test
2526libev. EV is developed together with libev. Apart from the EV core module,
2527there are additional modules that implement libev-compatible interfaces
2528to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
2529C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
2530
2531It can be found and installed via CPAN, its homepage is found at
2532L<http://software.schmorp.de/pkg/EV>.
2533
2534=item Ruby
2535
2536Tony Arcieri has written a ruby extension that offers access to a subset
2537of the libev API and adds filehandle abstractions, asynchronous DNS and
2538more on top of it. It can be found via gem servers. Its homepage is at
2539L<http://rev.rubyforge.org/>.
2540
2541=item D
2542
2543Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2544be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
2545
2546=back
2148 2547
2149 2548
2150=head1 MACRO MAGIC 2549=head1 MACRO MAGIC
2151 2550
2152Libev can be compiled with a variety of options, the most fundamantal 2551Libev can be compiled with a variety of options, the most fundamantal
2357wants osf handles on win32 (this is the case when the select to 2756wants osf handles on win32 (this is the case when the select to
2358be used is the winsock select). This means that it will call 2757be used is the winsock select). This means that it will call
2359C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise, 2758C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2360it is assumed that all these functions actually work on fds, even 2759it is assumed that all these functions actually work on fds, even
2361on win32. Should not be defined on non-win32 platforms. 2760on win32. Should not be defined on non-win32 platforms.
2761
2762=item EV_FD_TO_WIN32_HANDLE
2763
2764If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2765file descriptors to socket handles. When not defining this symbol (the
2766default), then libev will call C<_get_osfhandle>, which is usually
2767correct. In some cases, programs use their own file descriptor management,
2768in which case they can provide this function to map fds to socket handles.
2362 2769
2363=item EV_USE_POLL 2770=item EV_USE_POLL
2364 2771
2365If defined to be C<1>, libev will compile in support for the C<poll>(2) 2772If defined to be C<1>, libev will compile in support for the C<poll>(2)
2366backend. Otherwise it will be enabled on non-win32 platforms. It 2773backend. Otherwise it will be enabled on non-win32 platforms. It
2400 2807
2401If defined to be C<1>, libev will compile in support for the Linux inotify 2808If defined to be C<1>, libev will compile in support for the Linux inotify
2402interface to speed up C<ev_stat> watchers. Its actual availability will 2809interface to speed up C<ev_stat> watchers. Its actual availability will
2403be detected at runtime. 2810be detected at runtime.
2404 2811
2812=item EV_ATOMIC_T
2813
2814Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2815access is atomic with respect to other threads or signal contexts. No such
2816type is easily found in the C language, so you can provide your own type
2817that you know is safe for your purposes. It is used both for signal handler "locking"
2818as well as for signal and thread safety in C<ev_async> watchers.
2819
2820In the absense of this define, libev will use C<sig_atomic_t volatile>
2821(from F<signal.h>), which is usually good enough on most platforms.
2822
2405=item EV_H 2823=item EV_H
2406 2824
2407The name of the F<ev.h> header file used to include it. The default if 2825The name of the F<ev.h> header file used to include it. The default if
2408undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This 2826undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2409can be used to virtually rename the F<ev.h> header file in case of conflicts. 2827used to virtually rename the F<ev.h> header file in case of conflicts.
2410 2828
2411=item EV_CONFIG_H 2829=item EV_CONFIG_H
2412 2830
2413If C<EV_STANDALONE> isn't C<1>, this variable can be used to override 2831If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2414F<ev.c>'s idea of where to find the F<config.h> file, similarly to 2832F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2415C<EV_H>, above. 2833C<EV_H>, above.
2416 2834
2417=item EV_EVENT_H 2835=item EV_EVENT_H
2418 2836
2419Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea 2837Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2420of how the F<event.h> header can be found. 2838of how the F<event.h> header can be found, the default is C<"event.h">.
2421 2839
2422=item EV_PROTOTYPES 2840=item EV_PROTOTYPES
2423 2841
2424If defined to be C<0>, then F<ev.h> will not define any function 2842If defined to be C<0>, then F<ev.h> will not define any function
2425prototypes, but still define all the structs and other symbols. This is 2843prototypes, but still define all the structs and other symbols. This is
2476=item EV_FORK_ENABLE 2894=item EV_FORK_ENABLE
2477 2895
2478If undefined or defined to be C<1>, then fork watchers are supported. If 2896If undefined or defined to be C<1>, then fork watchers are supported. If
2479defined to be C<0>, then they are not. 2897defined to be C<0>, then they are not.
2480 2898
2899=item EV_ASYNC_ENABLE
2900
2901If undefined or defined to be C<1>, then async watchers are supported. If
2902defined to be C<0>, then they are not.
2903
2481=item EV_MINIMAL 2904=item EV_MINIMAL
2482 2905
2483If you need to shave off some kilobytes of code at the expense of some 2906If you need to shave off some kilobytes of code at the expense of some
2484speed, define this symbol to C<1>. Currently only used for gcc to override 2907speed, define this symbol to C<1>. Currently only used for gcc to override
2485some inlining decisions, saves roughly 30% codesize of amd64. 2908some inlining decisions, saves roughly 30% codesize of amd64.
2491than enough. If you need to manage thousands of children you might want to 2914than enough. If you need to manage thousands of children you might want to
2492increase this value (I<must> be a power of two). 2915increase this value (I<must> be a power of two).
2493 2916
2494=item EV_INOTIFY_HASHSIZE 2917=item EV_INOTIFY_HASHSIZE
2495 2918
2496C<ev_staz> watchers use a small hash table to distribute workload by 2919C<ev_stat> watchers use a small hash table to distribute workload by
2497inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>), 2920inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2498usually more than enough. If you need to manage thousands of C<ev_stat> 2921usually more than enough. If you need to manage thousands of C<ev_stat>
2499watchers you might want to increase this value (I<must> be a power of 2922watchers you might want to increase this value (I<must> be a power of
2500two). 2923two).
2501 2924
2597 3020
2598=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers) 3021=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2599 3022
2600This means that, when you have a watcher that triggers in one hour and 3023This means that, when you have a watcher that triggers in one hour and
2601there are 100 watchers that would trigger before that then inserting will 3024there are 100 watchers that would trigger before that then inserting will
2602have to skip those 100 watchers. 3025have to skip roughly seven (C<ld 100>) of these watchers.
2603 3026
2604=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers) 3027=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2605 3028
2606That means that for changing a timer costs less than removing/adding them 3029That means that changing a timer costs less than removing/adding them
2607as only the relative motion in the event queue has to be paid for. 3030as only the relative motion in the event queue has to be paid for.
2608 3031
2609=item Starting io/check/prepare/idle/signal/child watchers: O(1) 3032=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2610 3033
2611These just add the watcher into an array or at the head of a list. 3034These just add the watcher into an array or at the head of a list.
3035
2612=item Stopping check/prepare/idle watchers: O(1) 3036=item Stopping check/prepare/idle/fork/async watchers: O(1)
2613 3037
2614=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) 3038=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2615 3039
2616These watchers are stored in lists then need to be walked to find the 3040These watchers are stored in lists then need to be walked to find the
2617correct watcher to remove. The lists are usually short (you don't usually 3041correct watcher to remove. The lists are usually short (you don't usually
2618have many watchers waiting for the same fd or signal). 3042have many watchers waiting for the same fd or signal).
2619 3043
2620=item Finding the next timer per loop iteration: O(1) 3044=item Finding the next timer in each loop iteration: O(1)
3045
3046By virtue of using a binary heap, the next timer is always found at the
3047beginning of the storage array.
2621 3048
2622=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd) 3049=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2623 3050
2624A change means an I/O watcher gets started or stopped, which requires 3051A change means an I/O watcher gets started or stopped, which requires
2625libev to recalculate its status (and possibly tell the kernel). 3052libev to recalculate its status (and possibly tell the kernel, depending
3053on backend and wether C<ev_io_set> was used).
2626 3054
2627=item Activating one watcher: O(1) 3055=item Activating one watcher (putting it into the pending state): O(1)
2628 3056
2629=item Priority handling: O(number_of_priorities) 3057=item Priority handling: O(number_of_priorities)
2630 3058
2631Priorities are implemented by allocating some space for each 3059Priorities are implemented by allocating some space for each
2632priority. When doing priority-based operations, libev usually has to 3060priority. When doing priority-based operations, libev usually has to
2633linearly search all the priorities. 3061linearly search all the priorities, but starting/stopping and activating
3062watchers becomes O(1) w.r.t. priority handling.
3063
3064=item Sending an ev_async: O(1)
3065
3066=item Processing ev_async_send: O(number_of_async_watchers)
3067
3068=item Processing signals: O(max_signal_number)
3069
3070Sending involves a syscall I<iff> there were no other C<ev_async_send>
3071calls in the current loop iteration. Checking for async and signal events
3072involves iterating over all running async watchers or all signal numbers.
2634 3073
2635=back 3074=back
2636 3075
2637 3076
3077=head1 Win32 platform limitations and workarounds
3078
3079Win32 doesn't support any of the standards (e.g. POSIX) that libev
3080requires, and its I/O model is fundamentally incompatible with the POSIX
3081model. Libev still offers limited functionality on this platform in
3082the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3083descriptors. This only applies when using Win32 natively, not when using
3084e.g. cygwin.
3085
3086There is no supported compilation method available on windows except
3087embedding it into other applications.
3088
3089Due to the many, low, and arbitrary limits on the win32 platform and the
3090abysmal performance of winsockets, using a large number of sockets is not
3091recommended (and not reasonable). If your program needs to use more than
3092a hundred or so sockets, then likely it needs to use a totally different
3093implementation for windows, as libev offers the POSIX model, which cannot
3094be implemented efficiently on windows (microsoft monopoly games).
3095
3096=over 4
3097
3098=item The winsocket select function
3099
3100The winsocket C<select> function doesn't follow POSIX in that it requires
3101socket I<handles> and not socket I<file descriptors>. This makes select
3102very inefficient, and also requires a mapping from file descriptors
3103to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
3104C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
3105symbols for more info.
3106
3107The configuration for a "naked" win32 using the microsoft runtime
3108libraries and raw winsocket select is:
3109
3110 #define EV_USE_SELECT 1
3111 #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3112
3113Note that winsockets handling of fd sets is O(n), so you can easily get a
3114complexity in the O(n²) range when using win32.
3115
3116=item Limited number of file descriptors
3117
3118Windows has numerous arbitrary (and low) limits on things. Early versions
3119of winsocket's select only supported waiting for a max. of C<64> handles
3120(probably owning to the fact that all windows kernels can only wait for
3121C<64> things at the same time internally; microsoft recommends spawning a
3122chain of threads and wait for 63 handles and the previous thread in each).
3123
3124Newer versions support more handles, but you need to define C<FD_SETSIZE>
3125to some high number (e.g. C<2048>) before compiling the winsocket select
3126call (which might be in libev or elsewhere, for example, perl does its own
3127select emulation on windows).
3128
3129Another limit is the number of file descriptors in the microsoft runtime
3130libraries, which by default is C<64> (there must be a hidden I<64> fetish
3131or something like this inside microsoft). You can increase this by calling
3132C<_setmaxstdio>, which can increase this limit to C<2048> (another
3133arbitrary limit), but is broken in many versions of the microsoft runtime
3134libraries.
3135
3136This might get you to about C<512> or C<2048> sockets (depending on
3137windows version and/or the phase of the moon). To get more, you need to
3138wrap all I/O functions and provide your own fd management, but the cost of
3139calling select (O(n²)) will likely make this unworkable.
3140
3141=back
3142
3143
2638=head1 AUTHOR 3144=head1 AUTHOR
2639 3145
2640Marc Lehmann <libev@schmorp.de>. 3146Marc Lehmann <libev@schmorp.de>.
2641 3147

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