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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 #include <ev.h> 11 #include <ev.h>
12 12
13 ev_io stdin_watcher; 13 ev_io stdin_watcher;
14 ev_timer timeout_watcher; 14 ev_timer timeout_watcher;
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53The newest version of this document is also available as a html-formatted 53The newest version of this document is also available as a html-formatted
54web page you might find easier to navigate when reading it for the first 54web page you might find easier to navigate when reading it for the first
55time: L<http://cvs.schmorp.de/libev/ev.html>. 55time: L<http://cvs.schmorp.de/libev/ev.html>.
56 56
57Libev is an event loop: you register interest in certain events (such as a 57Libev is an event loop: you register interest in certain events (such as a
58file descriptor being readable or a timeout occuring), and it will manage 58file descriptor being readable or a timeout occurring), and it will manage
59these event sources and provide your program with events. 59these event sources and provide your program with events.
60 60
61To do this, it must take more or less complete control over your process 61To do this, it must take more or less complete control over your process
62(or thread) by executing the I<event loop> handler, and will then 62(or thread) by executing the I<event loop> handler, and will then
63communicate events via a callback mechanism. 63communicate events via a callback mechanism.
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65You register interest in certain events by registering so-called I<event 65You register interest in certain events by registering so-called I<event
66watchers>, which are relatively small C structures you initialise with the 66watchers>, 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 67details of the event, and then hand it over to libev by I<starting> the
68watcher. 68watcher.
69 69
70=head1 FEATURES 70=head2 FEATURES
71 71
72Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the 72Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73BSD-specific C<kqueue> and the Solaris-specific event port mechanisms 73BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74for file descriptor events (C<ev_io>), the Linux C<inotify> interface 74for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers 75(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
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82 82
83It also is quite fast (see this 83It also is quite fast (see this
84L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent 84L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85for example). 85for example).
86 86
87=head1 CONVENTIONS 87=head2 CONVENTIONS
88 88
89Libev is very configurable. In this manual the default configuration will 89Libev is very configurable. In this manual the default configuration will
90be described, which supports multiple event loops. For more info about 90be described, which supports multiple event loops. For more info about
91various configuration options please have a look at B<EMBED> section in 91various configuration options please have a look at B<EMBED> section in
92this manual. If libev was configured without support for multiple event 92this manual. If libev was configured without support for multiple event
93loops, then all functions taking an initial argument of name C<loop> 93loops, then all functions taking an initial argument of name C<loop>
94(which is always of type C<struct ev_loop *>) will not have this argument. 94(which is always of type C<struct ev_loop *>) will not have this argument.
95 95
96=head1 TIME REPRESENTATION 96=head2 TIME REPRESENTATION
97 97
98Libev represents time as a single floating point number, representing the 98Libev represents time as a single floating point number, representing the
99(fractional) number of seconds since the (POSIX) epoch (somewhere near 99(fractional) number of seconds since the (POSIX) epoch (somewhere near
100the beginning of 1970, details are complicated, don't ask). This type is 100the 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 101called C<ev_tstamp>, which is what you should use too. It usually aliases
102to the C<double> type in C, and when you need to do any calculations on 102to the C<double> type in C, and when you need to do any calculations on
103it, you should treat it as such. 103it, you should treat it as some floatingpoint value. Unlike the name
104component C<stamp> might indicate, it is also used for time differences
105throughout libev.
104 106
105=head1 GLOBAL FUNCTIONS 107=head1 GLOBAL FUNCTIONS
106 108
107These functions can be called anytime, even before initialising the 109These functions can be called anytime, even before initialising the
108library in any way. 110library in any way.
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113 115
114Returns the current time as libev would use it. Please note that the 116Returns the current time as libev would use it. Please note that the
115C<ev_now> function is usually faster and also often returns the timestamp 117C<ev_now> function is usually faster and also often returns the timestamp
116you actually want to know. 118you actually want to know.
117 119
120=item ev_sleep (ev_tstamp interval)
121
122Sleep for the given interval: The current thread will be blocked until
123either it is interrupted or the given time interval has passed. Basically
124this is a subsecond-resolution C<sleep ()>.
125
118=item int ev_version_major () 126=item int ev_version_major ()
119 127
120=item int ev_version_minor () 128=item int ev_version_minor ()
121 129
122You can find out the major and minor API/ABI version numbers of the library 130You can find out the major and minor ABI version numbers of the library
123you linked against by calling the functions C<ev_version_major> and 131you linked against by calling the functions C<ev_version_major> and
124C<ev_version_minor>. If you want, you can compare against the global 132C<ev_version_minor>. If you want, you can compare against the global
125symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the 133symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126version of the library your program was compiled against. 134version of the library your program was compiled against.
127 135
128These version numbers refer to the API and ABI version of the library, not 136These version numbers refer to the ABI version of the library, not the
129the release version. 137release version.
130 138
131Usually, it's a good idea to terminate if the major versions mismatch, 139Usually, it's a good idea to terminate if the major versions mismatch,
132as this indicates an incompatible change. Minor versions are usually 140as this indicates an incompatible change. Minor versions are usually
133compatible to older versions, so a larger minor version alone is usually 141compatible to older versions, so a larger minor version alone is usually
134not a problem. 142not a problem.
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298=item C<EVBACKEND_SELECT> (value 1, portable select backend) 306=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299 307
300This is your standard select(2) backend. Not I<completely> standard, as 308This is your standard select(2) backend. Not I<completely> standard, as
301libev tries to roll its own fd_set with no limits on the number of fds, 309libev tries to roll its own fd_set with no limits on the number of fds,
302but if that fails, expect a fairly low limit on the number of fds when 310but if that fails, expect a fairly low limit on the number of fds when
303using this backend. It doesn't scale too well (O(highest_fd)), but its usually 311using this backend. It doesn't scale too well (O(highest_fd)), but its
304the fastest backend for a low number of fds. 312usually the fastest backend for a low number of (low-numbered :) fds.
313
314To get good performance out of this backend you need a high amount of
315parallelity (most of the file descriptors should be busy). If you are
316writing a server, you should C<accept ()> in a loop to accept as many
317connections as possible during one iteration. You might also want to have
318a look at C<ev_set_io_collect_interval ()> to increase the amount of
319readyness notifications you get per iteration.
305 320
306=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows) 321=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
307 322
308And this is your standard poll(2) backend. It's more complicated than 323And this is your standard poll(2) backend. It's more complicated
309select, but handles sparse fds better and has no artificial limit on the 324than select, but handles sparse fds better and has no artificial
310number of fds you can use (except it will slow down considerably with a 325limit on the number of fds you can use (except it will slow down
311lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 326considerably with a lot of inactive fds). It scales similarly to select,
327i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328performance tips.
312 329
313=item C<EVBACKEND_EPOLL> (value 4, Linux) 330=item C<EVBACKEND_EPOLL> (value 4, Linux)
314 331
315For few fds, this backend is a bit little slower than poll and select, 332For few fds, this backend is a bit little slower than poll and select,
316but it scales phenomenally better. While poll and select usually scale like 333but it scales phenomenally better. While poll and select usually scale
317O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 334like O(total_fds) where n is the total number of fds (or the highest fd),
318either O(1) or O(active_fds). 335epoll scales either O(1) or O(active_fds). The epoll design has a number
336of shortcomings, such as silently dropping events in some hard-to-detect
337cases and rewiring a syscall per fd change, no fork support and bad
338support for dup.
319 339
320While stopping and starting an I/O watcher in the same iteration will 340While stopping, setting and starting an I/O watcher in the same iteration
321result in some caching, there is still a syscall per such incident 341will result in some caching, there is still a syscall per such incident
322(because the fd could point to a different file description now), so its 342(because the fd could point to a different file description now), so its
323best to avoid that. Also, dup()ed file descriptors might not work very 343best to avoid that. Also, C<dup ()>'ed file descriptors might not work
324well if you register events for both fds. 344very well if you register events for both fds.
325 345
326Please note that epoll sometimes generates spurious notifications, so you 346Please note that epoll sometimes generates spurious notifications, so you
327need to use non-blocking I/O or other means to avoid blocking when no data 347need to use non-blocking I/O or other means to avoid blocking when no data
328(or space) is available. 348(or space) is available.
329 349
350Best performance from this backend is achieved by not unregistering all
351watchers for a file descriptor until it has been closed, if possible, i.e.
352keep at least one watcher active per fd at all times.
353
354While nominally embeddeble in other event loops, this feature is broken in
355all kernel versions tested so far.
356
330=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) 357=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331 358
332Kqueue deserves special mention, as at the time of this writing, it 359Kqueue deserves special mention, as at the time of this writing, it
333was broken on all BSDs except NetBSD (usually it doesn't work with 360was broken on all BSDs except NetBSD (usually it doesn't work reliably
334anything but sockets and pipes, except on Darwin, where of course its 361with anything but sockets and pipes, except on Darwin, where of course
335completely useless). For this reason its not being "autodetected" 362it's completely useless). For this reason it's not being "autodetected"
336unless you explicitly specify it explicitly in the flags (i.e. using 363unless you explicitly specify it explicitly in the flags (i.e. using
337C<EVBACKEND_KQUEUE>). 364C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365system like NetBSD.
366
367You still can embed kqueue into a normal poll or select backend and use it
368only for sockets (after having made sure that sockets work with kqueue on
369the target platform). See C<ev_embed> watchers for more info.
338 370
339It scales in the same way as the epoll backend, but the interface to the 371It scales in the same way as the epoll backend, but the interface to the
340kernel is more efficient (which says nothing about its actual speed, of 372kernel is more efficient (which says nothing about its actual speed, of
341course). While starting and stopping an I/O watcher does not cause an 373course). While stopping, setting and starting an I/O watcher does never
342extra syscall as with epoll, it still adds up to four event changes per 374cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
343incident, so its best to avoid that. 375two event changes per incident, support for C<fork ()> is very bad and it
376drops fds silently in similarly hard-to-detect cases.
377
378This backend usually performs well under most conditions.
379
380While nominally embeddable in other event loops, this doesn't work
381everywhere, so you might need to test for this. And since it is broken
382almost everywhere, you should only use it when you have a lot of sockets
383(for which it usually works), by embedding it into another event loop
384(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
385sockets.
344 386
345=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8) 387=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346 388
347This is not implemented yet (and might never be). 389This is not implemented yet (and might never be, unless you send me an
390implementation). According to reports, C</dev/poll> only supports sockets
391and is not embeddable, which would limit the usefulness of this backend
392immensely.
348 393
349=item C<EVBACKEND_PORT> (value 32, Solaris 10) 394=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350 395
351This uses the Solaris 10 port mechanism. As with everything on Solaris, 396This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352it's really slow, but it still scales very well (O(active_fds)). 397it's really slow, but it still scales very well (O(active_fds)).
353 398
354Please note that solaris ports can result in a lot of spurious 399Please note that solaris event ports can deliver a lot of spurious
355notifications, so you need to use non-blocking I/O or other means to avoid 400notifications, so you need to use non-blocking I/O or other means to avoid
356blocking when no data (or space) is available. 401blocking when no data (or space) is available.
402
403While this backend scales well, it requires one system call per active
404file descriptor per loop iteration. For small and medium numbers of file
405descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406might perform better.
357 407
358=item C<EVBACKEND_ALL> 408=item C<EVBACKEND_ALL>
359 409
360Try all backends (even potentially broken ones that wouldn't be tried 410Try all backends (even potentially broken ones that wouldn't be tried
361with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as 411with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
362C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. 412C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413
414It is definitely not recommended to use this flag.
363 415
364=back 416=back
365 417
366If one or more of these are ored into the flags value, then only these 418If one or more of these are ored into the flags value, then only these
367backends will be tried (in the reverse order as given here). If none are 419backends will be tried (in the reverse order as given here). If none are
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402Destroys the default loop again (frees all memory and kernel state 454Destroys the default loop again (frees all memory and kernel state
403etc.). None of the active event watchers will be stopped in the normal 455etc.). None of the active event watchers will be stopped in the normal
404sense, so e.g. C<ev_is_active> might still return true. It is your 456sense, so e.g. C<ev_is_active> might still return true. It is your
405responsibility to either stop all watchers cleanly yoursef I<before> 457responsibility to either stop all watchers cleanly yoursef I<before>
406calling this function, or cope with the fact afterwards (which is usually 458calling this function, or cope with the fact afterwards (which is usually
407the easiest thing, youc na just ignore the watchers and/or C<free ()> them 459the easiest thing, you can just ignore the watchers and/or C<free ()> them
408for example). 460for example).
461
462Note that certain global state, such as signal state, will not be freed by
463this function, and related watchers (such as signal and child watchers)
464would need to be stopped manually.
465
466In general it is not advisable to call this function except in the
467rare occasion where you really need to free e.g. the signal handling
468pipe fds. If you need dynamically allocated loops it is better to use
469C<ev_loop_new> and C<ev_loop_destroy>).
409 470
410=item ev_loop_destroy (loop) 471=item ev_loop_destroy (loop)
411 472
412Like C<ev_default_destroy>, but destroys an event loop created by an 473Like C<ev_default_destroy>, but destroys an event loop created by an
413earlier call to C<ev_loop_new>. 474earlier call to C<ev_loop_new>.
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458 519
459Returns the current "event loop time", which is the time the event loop 520Returns the current "event loop time", which is the time the event loop
460received events and started processing them. This timestamp does not 521received events and started processing them. This timestamp does not
461change as long as callbacks are being processed, and this is also the base 522change as long as callbacks are being processed, and this is also the base
462time used for relative timers. You can treat it as the timestamp of the 523time used for relative timers. You can treat it as the timestamp of the
463event occuring (or more correctly, libev finding out about it). 524event occurring (or more correctly, libev finding out about it).
464 525
465=item ev_loop (loop, int flags) 526=item ev_loop (loop, int flags)
466 527
467Finally, this is it, the event handler. This function usually is called 528Finally, this is it, the event handler. This function usually is called
468after you initialised all your watchers and you want to start handling 529after you initialised all your watchers and you want to start handling
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490usually a better approach for this kind of thing. 551usually a better approach for this kind of thing.
491 552
492Here are the gory details of what C<ev_loop> does: 553Here are the gory details of what C<ev_loop> does:
493 554
494 - Before the first iteration, call any pending watchers. 555 - Before the first iteration, call any pending watchers.
495 * If there are no active watchers (reference count is zero), return. 556 * If EVFLAG_FORKCHECK was used, check for a fork.
496 - Queue all prepare watchers and then call all outstanding watchers. 557 - If a fork was detected, queue and call all fork watchers.
558 - Queue and call all prepare watchers.
497 - If we have been forked, recreate the kernel state. 559 - If we have been forked, recreate the kernel state.
498 - Update the kernel state with all outstanding changes. 560 - Update the kernel state with all outstanding changes.
499 - Update the "event loop time". 561 - Update the "event loop time".
500 - Calculate for how long to block. 562 - Calculate for how long to sleep or block, if at all
563 (active idle watchers, EVLOOP_NONBLOCK or not having
564 any active watchers at all will result in not sleeping).
565 - Sleep if the I/O and timer collect interval say so.
501 - Block the process, waiting for any events. 566 - Block the process, waiting for any events.
502 - Queue all outstanding I/O (fd) events. 567 - Queue all outstanding I/O (fd) events.
503 - Update the "event loop time" and do time jump handling. 568 - Update the "event loop time" and do time jump handling.
504 - Queue all outstanding timers. 569 - Queue all outstanding timers.
505 - Queue all outstanding periodics. 570 - Queue all outstanding periodics.
506 - If no events are pending now, queue all idle watchers. 571 - If no events are pending now, queue all idle watchers.
507 - Queue all check watchers. 572 - Queue all check watchers.
508 - Call all queued watchers in reverse order (i.e. check watchers first). 573 - Call all queued watchers in reverse order (i.e. check watchers first).
509 Signals and child watchers are implemented as I/O watchers, and will 574 Signals and child watchers are implemented as I/O watchers, and will
510 be handled here by queueing them when their watcher gets executed. 575 be handled here by queueing them when their watcher gets executed.
511 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 576 - If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
512 were used, return, otherwise continue with step *. 577 were used, or there are no active watchers, return, otherwise
578 continue with step *.
513 579
514Example: Queue some jobs and then loop until no events are outsanding 580Example: Queue some jobs and then loop until no events are outstanding
515anymore. 581anymore.
516 582
517 ... queue jobs here, make sure they register event watchers as long 583 ... queue jobs here, make sure they register event watchers as long
518 ... as they still have work to do (even an idle watcher will do..) 584 ... as they still have work to do (even an idle watcher will do..)
519 ev_loop (my_loop, 0); 585 ev_loop (my_loop, 0);
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523 589
524Can be used to make a call to C<ev_loop> return early (but only after it 590Can be used to make a call to C<ev_loop> return early (but only after it
525has processed all outstanding events). The C<how> argument must be either 591has processed all outstanding events). The C<how> argument must be either
526C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or 592C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
527C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. 593C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
594
595This "unloop state" will be cleared when entering C<ev_loop> again.
528 596
529=item ev_ref (loop) 597=item ev_ref (loop)
530 598
531=item ev_unref (loop) 599=item ev_unref (loop)
532 600
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552Example: For some weird reason, unregister the above signal handler again. 620Example: For some weird reason, unregister the above signal handler again.
553 621
554 ev_ref (loop); 622 ev_ref (loop);
555 ev_signal_stop (loop, &exitsig); 623 ev_signal_stop (loop, &exitsig);
556 624
625=item ev_set_io_collect_interval (loop, ev_tstamp interval)
626
627=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
628
629These advanced functions influence the time that libev will spend waiting
630for events. Both are by default C<0>, meaning that libev will try to
631invoke timer/periodic callbacks and I/O callbacks with minimum latency.
632
633Setting these to a higher value (the C<interval> I<must> be >= C<0>)
634allows libev to delay invocation of I/O and timer/periodic callbacks to
635increase efficiency of loop iterations.
636
637The background is that sometimes your program runs just fast enough to
638handle one (or very few) event(s) per loop iteration. While this makes
639the program responsive, it also wastes a lot of CPU time to poll for new
640events, especially with backends like C<select ()> which have a high
641overhead for the actual polling but can deliver many events at once.
642
643By setting a higher I<io collect interval> you allow libev to spend more
644time collecting I/O events, so you can handle more events per iteration,
645at the cost of increasing latency. Timeouts (both C<ev_periodic> and
646C<ev_timer>) will be not affected. Setting this to a non-null value will
647introduce an additional C<ev_sleep ()> call into most loop iterations.
648
649Likewise, by setting a higher I<timeout collect interval> you allow libev
650to spend more time collecting timeouts, at the expense of increased
651latency (the watcher callback will be called later). C<ev_io> watchers
652will not be affected. Setting this to a non-null value will not introduce
653any overhead in libev.
654
655Many (busy) programs can usually benefit by setting the io collect
656interval to a value near C<0.1> or so, which is often enough for
657interactive servers (of course not for games), likewise for timeouts. It
658usually doesn't make much sense to set it to a lower value than C<0.01>,
659as this approsaches the timing granularity of most systems.
660
557=back 661=back
558 662
559 663
560=head1 ANATOMY OF A WATCHER 664=head1 ANATOMY OF A WATCHER
561 665
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886In general you can register as many read and/or write event watchers per 990In general you can register as many read and/or write event watchers per
887fd as you want (as long as you don't confuse yourself). Setting all file 991fd as you want (as long as you don't confuse yourself). Setting all file
888descriptors to non-blocking mode is also usually a good idea (but not 992descriptors to non-blocking mode is also usually a good idea (but not
889required if you know what you are doing). 993required if you know what you are doing).
890 994
891You have to be careful with dup'ed file descriptors, though. Some backends
892(the linux epoll backend is a notable example) cannot handle dup'ed file
893descriptors correctly if you register interest in two or more fds pointing
894to the same underlying file/socket/etc. description (that is, they share
895the same underlying "file open").
896
897If you must do this, then force the use of a known-to-be-good backend 995If you must do this, then force the use of a known-to-be-good backend
898(at the time of this writing, this includes only C<EVBACKEND_SELECT> and 996(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899C<EVBACKEND_POLL>). 997C<EVBACKEND_POLL>).
900 998
901Another thing you have to watch out for is that it is quite easy to 999Another thing you have to watch out for is that it is quite easy to
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911play around with an Xlib connection), then you have to seperately re-test 1009play around with an Xlib connection), then you have to seperately re-test
912whether a file descriptor is really ready with a known-to-be good interface 1010whether a file descriptor is really ready with a known-to-be good interface
913such as poll (fortunately in our Xlib example, Xlib already does this on 1011such as poll (fortunately in our Xlib example, Xlib already does this on
914its own, so its quite safe to use). 1012its own, so its quite safe to use).
915 1013
1014=head3 The special problem of disappearing file descriptors
1015
1016Some backends (e.g. kqueue, epoll) need to be told about closing a file
1017descriptor (either by calling C<close> explicitly or by any other means,
1018such as C<dup>). The reason is that you register interest in some file
1019descriptor, but when it goes away, the operating system will silently drop
1020this interest. If another file descriptor with the same number then is
1021registered with libev, there is no efficient way to see that this is, in
1022fact, a different file descriptor.
1023
1024To avoid having to explicitly tell libev about such cases, libev follows
1025the following policy: Each time C<ev_io_set> is being called, libev
1026will assume that this is potentially a new file descriptor, otherwise
1027it is assumed that the file descriptor stays the same. That means that
1028you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
1029descriptor even if the file descriptor number itself did not change.
1030
1031This is how one would do it normally anyway, the important point is that
1032the libev application should not optimise around libev but should leave
1033optimisations to libev.
1034
1035=head3 The special problem of dup'ed file descriptors
1036
1037Some backends (e.g. epoll), cannot register events for file descriptors,
1038but only events for the underlying file descriptions. That means when you
1039have C<dup ()>'ed file descriptors or weirder constellations, and register
1040events for them, only one file descriptor might actually receive events.
1041
1042There is no workaround possible except not registering events
1043for potentially C<dup ()>'ed file descriptors, or to resort to
1044C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1045
1046=head3 The special problem of fork
1047
1048Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1049useless behaviour. Libev fully supports fork, but needs to be told about
1050it in the child.
1051
1052To support fork in your programs, you either have to call
1053C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1054enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1055C<EVBACKEND_POLL>.
1056
1057
1058=head3 Watcher-Specific Functions
1059
916=over 4 1060=over 4
917 1061
918=item ev_io_init (ev_io *, callback, int fd, int events) 1062=item ev_io_init (ev_io *, callback, int fd, int events)
919 1063
920=item ev_io_set (ev_io *, int fd, int events) 1064=item ev_io_set (ev_io *, int fd, int events)
… …
930=item int events [read-only] 1074=item int events [read-only]
931 1075
932The events being watched. 1076The events being watched.
933 1077
934=back 1078=back
1079
1080=head3 Examples
935 1081
936Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well 1082Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
937readable, but only once. Since it is likely line-buffered, you could 1083readable, but only once. Since it is likely line-buffered, you could
938attempt to read a whole line in the callback. 1084attempt to read a whole line in the callback.
939 1085
… …
972 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1118 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
973 1119
974The callback is guarenteed to be invoked only when its timeout has passed, 1120The callback is guarenteed to be invoked only when its timeout has passed,
975but if multiple timers become ready during the same loop iteration then 1121but if multiple timers become ready during the same loop iteration then
976order of execution is undefined. 1122order of execution is undefined.
1123
1124=head3 Watcher-Specific Functions and Data Members
977 1125
978=over 4 1126=over 4
979 1127
980=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 1128=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
981 1129
… …
1035or C<ev_timer_again> is called and determines the next timeout (if any), 1183or C<ev_timer_again> is called and determines the next timeout (if any),
1036which is also when any modifications are taken into account. 1184which is also when any modifications are taken into account.
1037 1185
1038=back 1186=back
1039 1187
1188=head3 Examples
1189
1040Example: Create a timer that fires after 60 seconds. 1190Example: Create a timer that fires after 60 seconds.
1041 1191
1042 static void 1192 static void
1043 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1193 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1044 { 1194 {
… …
1087 1237
1088As with timers, the callback is guarenteed to be invoked only when the 1238As with timers, the callback is guarenteed to be invoked only when the
1089time (C<at>) has been passed, but if multiple periodic timers become ready 1239time (C<at>) has been passed, but if multiple periodic timers become ready
1090during the same loop iteration then order of execution is undefined. 1240during the same loop iteration then order of execution is undefined.
1091 1241
1242=head3 Watcher-Specific Functions and Data Members
1243
1092=over 4 1244=over 4
1093 1245
1094=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) 1246=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1095 1247
1096=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) 1248=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
… …
1192 1344
1193The current reschedule callback, or C<0>, if this functionality is 1345The current reschedule callback, or C<0>, if this functionality is
1194switched off. Can be changed any time, but changes only take effect when 1346switched off. Can be changed any time, but changes only take effect when
1195the periodic timer fires or C<ev_periodic_again> is being called. 1347the periodic timer fires or C<ev_periodic_again> is being called.
1196 1348
1349=item ev_tstamp at [read-only]
1350
1351When active, contains the absolute time that the watcher is supposed to
1352trigger next.
1353
1197=back 1354=back
1355
1356=head3 Examples
1198 1357
1199Example: Call a callback every hour, or, more precisely, whenever the 1358Example: Call a callback every hour, or, more precisely, whenever the
1200system clock is divisible by 3600. The callback invocation times have 1359system clock is divisible by 3600. The callback invocation times have
1201potentially a lot of jittering, but good long-term stability. 1360potentially a lot of jittering, but good long-term stability.
1202 1361
… …
1242with the kernel (thus it coexists with your own signal handlers as long 1401with the kernel (thus it coexists with your own signal handlers as long
1243as you don't register any with libev). Similarly, when the last signal 1402as you don't register any with libev). Similarly, when the last signal
1244watcher for a signal is stopped libev will reset the signal handler to 1403watcher for a signal is stopped libev will reset the signal handler to
1245SIG_DFL (regardless of what it was set to before). 1404SIG_DFL (regardless of what it was set to before).
1246 1405
1406=head3 Watcher-Specific Functions and Data Members
1407
1247=over 4 1408=over 4
1248 1409
1249=item ev_signal_init (ev_signal *, callback, int signum) 1410=item ev_signal_init (ev_signal *, callback, int signum)
1250 1411
1251=item ev_signal_set (ev_signal *, int signum) 1412=item ev_signal_set (ev_signal *, int signum)
… …
1262 1423
1263=head2 C<ev_child> - watch out for process status changes 1424=head2 C<ev_child> - watch out for process status changes
1264 1425
1265Child watchers trigger when your process receives a SIGCHLD in response to 1426Child watchers trigger when your process receives a SIGCHLD in response to
1266some child status changes (most typically when a child of yours dies). 1427some child status changes (most typically when a child of yours dies).
1428
1429=head3 Watcher-Specific Functions and Data Members
1267 1430
1268=over 4 1431=over 4
1269 1432
1270=item ev_child_init (ev_child *, callback, int pid) 1433=item ev_child_init (ev_child *, callback, int pid)
1271 1434
… …
1290 1453
1291The process exit/trace status caused by C<rpid> (see your systems 1454The process exit/trace status caused by C<rpid> (see your systems
1292C<waitpid> and C<sys/wait.h> documentation for details). 1455C<waitpid> and C<sys/wait.h> documentation for details).
1293 1456
1294=back 1457=back
1458
1459=head3 Examples
1295 1460
1296Example: Try to exit cleanly on SIGINT and SIGTERM. 1461Example: Try to exit cleanly on SIGINT and SIGTERM.
1297 1462
1298 static void 1463 static void
1299 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 1464 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
… …
1340semantics of C<ev_stat> watchers, which means that libev sometimes needs 1505semantics of C<ev_stat> watchers, which means that libev sometimes needs
1341to fall back to regular polling again even with inotify, but changes are 1506to fall back to regular polling again even with inotify, but changes are
1342usually detected immediately, and if the file exists there will be no 1507usually detected immediately, and if the file exists there will be no
1343polling. 1508polling.
1344 1509
1510=head3 Inotify
1511
1512When C<inotify (7)> support has been compiled into libev (generally only
1513available on Linux) and present at runtime, it will be used to speed up
1514change detection where possible. The inotify descriptor will be created lazily
1515when the first C<ev_stat> watcher is being started.
1516
1517Inotify presense does not change the semantics of C<ev_stat> watchers
1518except that changes might be detected earlier, and in some cases, to avoid
1519making regular C<stat> calls. Even in the presense of inotify support
1520there are many cases where libev has to resort to regular C<stat> polling.
1521
1522(There is no support for kqueue, as apparently it cannot be used to
1523implement this functionality, due to the requirement of having a file
1524descriptor open on the object at all times).
1525
1526=head3 The special problem of stat time resolution
1527
1528The C<stat ()> syscall only supports full-second resolution portably, and
1529even on systems where the resolution is higher, many filesystems still
1530only support whole seconds.
1531
1532That means that, if the time is the only thing that changes, you might
1533miss updates: on the first update, C<ev_stat> detects a change and calls
1534your callback, which does something. When there is another update within
1535the same second, C<ev_stat> will be unable to detect it.
1536
1537The solution to this is to delay acting on a change for a second (or till
1538the next second boundary), using a roughly one-second delay C<ev_timer>
1539(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
1540is added to work around small timing inconsistencies of some operating
1541systems.
1542
1543=head3 Watcher-Specific Functions and Data Members
1544
1345=over 4 1545=over 4
1346 1546
1347=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval) 1547=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1348 1548
1349=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval) 1549=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
… …
1384=item const char *path [read-only] 1584=item const char *path [read-only]
1385 1585
1386The filesystem path that is being watched. 1586The filesystem path that is being watched.
1387 1587
1388=back 1588=back
1589
1590=head3 Examples
1389 1591
1390Example: Watch C</etc/passwd> for attribute changes. 1592Example: Watch C</etc/passwd> for attribute changes.
1391 1593
1392 static void 1594 static void
1393 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 1595 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
… …
1406 } 1608 }
1407 1609
1408 ... 1610 ...
1409 ev_stat passwd; 1611 ev_stat passwd;
1410 1612
1411 ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 1613 ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1412 ev_stat_start (loop, &passwd); 1614 ev_stat_start (loop, &passwd);
1615
1616Example: Like above, but additionally use a one-second delay so we do not
1617miss updates (however, frequent updates will delay processing, too, so
1618one might do the work both on C<ev_stat> callback invocation I<and> on
1619C<ev_timer> callback invocation).
1620
1621 static ev_stat passwd;
1622 static ev_timer timer;
1623
1624 static void
1625 timer_cb (EV_P_ ev_timer *w, int revents)
1626 {
1627 ev_timer_stop (EV_A_ w);
1628
1629 /* now it's one second after the most recent passwd change */
1630 }
1631
1632 static void
1633 stat_cb (EV_P_ ev_stat *w, int revents)
1634 {
1635 /* reset the one-second timer */
1636 ev_timer_again (EV_A_ &timer);
1637 }
1638
1639 ...
1640 ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1641 ev_stat_start (loop, &passwd);
1642 ev_timer_init (&timer, timer_cb, 0., 1.01);
1413 1643
1414 1644
1415=head2 C<ev_idle> - when you've got nothing better to do... 1645=head2 C<ev_idle> - when you've got nothing better to do...
1416 1646
1417Idle watchers trigger events when no other events of the same or higher 1647Idle watchers trigger events when no other events of the same or higher
… …
1431Apart from keeping your process non-blocking (which is a useful 1661Apart from keeping your process non-blocking (which is a useful
1432effect on its own sometimes), idle watchers are a good place to do 1662effect on its own sometimes), idle watchers are a good place to do
1433"pseudo-background processing", or delay processing stuff to after the 1663"pseudo-background processing", or delay processing stuff to after the
1434event loop has handled all outstanding events. 1664event loop has handled all outstanding events.
1435 1665
1666=head3 Watcher-Specific Functions and Data Members
1667
1436=over 4 1668=over 4
1437 1669
1438=item ev_idle_init (ev_signal *, callback) 1670=item ev_idle_init (ev_signal *, callback)
1439 1671
1440Initialises and configures the idle watcher - it has no parameters of any 1672Initialises and configures the idle watcher - it has no parameters of any
1441kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 1673kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1442believe me. 1674believe me.
1443 1675
1444=back 1676=back
1677
1678=head3 Examples
1445 1679
1446Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the 1680Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1447callback, free it. Also, use no error checking, as usual. 1681callback, free it. Also, use no error checking, as usual.
1448 1682
1449 static void 1683 static void
… …
1501 1735
1502It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>) 1736It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1503priority, to ensure that they are being run before any other watchers 1737priority, to ensure that they are being run before any other watchers
1504after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers, 1738after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1505too) should not activate ("feed") events into libev. While libev fully 1739too) should not activate ("feed") events into libev. While libev fully
1506supports this, they will be called before other C<ev_check> watchers did 1740supports this, they will be called before other C<ev_check> watchers
1507their job. As C<ev_check> watchers are often used to embed other event 1741did their job. As C<ev_check> watchers are often used to embed other
1508loops those other event loops might be in an unusable state until their 1742(non-libev) event loops those other event loops might be in an unusable
1509C<ev_check> watcher ran (always remind yourself to coexist peacefully with 1743state until their C<ev_check> watcher ran (always remind yourself to
1510others). 1744coexist peacefully with others).
1745
1746=head3 Watcher-Specific Functions and Data Members
1511 1747
1512=over 4 1748=over 4
1513 1749
1514=item ev_prepare_init (ev_prepare *, callback) 1750=item ev_prepare_init (ev_prepare *, callback)
1515 1751
… …
1518Initialises and configures the prepare or check watcher - they have no 1754Initialises and configures the prepare or check watcher - they have no
1519parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 1755parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1520macros, but using them is utterly, utterly and completely pointless. 1756macros, but using them is utterly, utterly and completely pointless.
1521 1757
1522=back 1758=back
1759
1760=head3 Examples
1523 1761
1524There are a number of principal ways to embed other event loops or modules 1762There are a number of principal ways to embed other event loops or modules
1525into libev. Here are some ideas on how to include libadns into libev 1763into libev. Here are some ideas on how to include libadns into libev
1526(there is a Perl module named C<EV::ADNS> that does this, which you could 1764(there is a Perl module named C<EV::ADNS> that does this, which you could
1527use for an actually working example. Another Perl module named C<EV::Glib> 1765use for an actually working example. Another Perl module named C<EV::Glib>
… …
1696portable one. 1934portable one.
1697 1935
1698So when you want to use this feature you will always have to be prepared 1936So when you want to use this feature you will always have to be prepared
1699that you cannot get an embeddable loop. The recommended way to get around 1937that you cannot get an embeddable loop. The recommended way to get around
1700this is to have a separate variables for your embeddable loop, try to 1938this is to have a separate variables for your embeddable loop, try to
1701create it, and if that fails, use the normal loop for everything: 1939create it, and if that fails, use the normal loop for everything.
1940
1941=head3 Watcher-Specific Functions and Data Members
1942
1943=over 4
1944
1945=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1946
1947=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1948
1949Configures the watcher to embed the given loop, which must be
1950embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1951invoked automatically, otherwise it is the responsibility of the callback
1952to invoke it (it will continue to be called until the sweep has been done,
1953if you do not want thta, you need to temporarily stop the embed watcher).
1954
1955=item ev_embed_sweep (loop, ev_embed *)
1956
1957Make a single, non-blocking sweep over the embedded loop. This works
1958similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1959apropriate way for embedded loops.
1960
1961=item struct ev_loop *other [read-only]
1962
1963The embedded event loop.
1964
1965=back
1966
1967=head3 Examples
1968
1969Example: Try to get an embeddable event loop and embed it into the default
1970event loop. If that is not possible, use the default loop. The default
1971loop is stored in C<loop_hi>, while the mebeddable loop is stored in
1972C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
1973used).
1702 1974
1703 struct ev_loop *loop_hi = ev_default_init (0); 1975 struct ev_loop *loop_hi = ev_default_init (0);
1704 struct ev_loop *loop_lo = 0; 1976 struct ev_loop *loop_lo = 0;
1705 struct ev_embed embed; 1977 struct ev_embed embed;
1706 1978
… …
1717 ev_embed_start (loop_hi, &embed); 1989 ev_embed_start (loop_hi, &embed);
1718 } 1990 }
1719 else 1991 else
1720 loop_lo = loop_hi; 1992 loop_lo = loop_hi;
1721 1993
1722=over 4 1994Example: Check if kqueue is available but not recommended and create
1995a kqueue backend for use with sockets (which usually work with any
1996kqueue implementation). Store the kqueue/socket-only event loop in
1997C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1723 1998
1724=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop) 1999 struct ev_loop *loop = ev_default_init (0);
2000 struct ev_loop *loop_socket = 0;
2001 struct ev_embed embed;
2002
2003 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2004 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2005 {
2006 ev_embed_init (&embed, 0, loop_socket);
2007 ev_embed_start (loop, &embed);
2008 }
1725 2009
1726=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop) 2010 if (!loop_socket)
2011 loop_socket = loop;
1727 2012
1728Configures the watcher to embed the given loop, which must be 2013 // now use loop_socket for all sockets, and loop for everything else
1729embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1730invoked automatically, otherwise it is the responsibility of the callback
1731to invoke it (it will continue to be called until the sweep has been done,
1732if you do not want thta, you need to temporarily stop the embed watcher).
1733
1734=item ev_embed_sweep (loop, ev_embed *)
1735
1736Make a single, non-blocking sweep over the embedded loop. This works
1737similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1738apropriate way for embedded loops.
1739
1740=item struct ev_loop *loop [read-only]
1741
1742The embedded event loop.
1743
1744=back
1745 2014
1746 2015
1747=head2 C<ev_fork> - the audacity to resume the event loop after a fork 2016=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1748 2017
1749Fork watchers are called when a C<fork ()> was detected (usually because 2018Fork watchers are called when a C<fork ()> was detected (usually because
… …
1752event loop blocks next and before C<ev_check> watchers are being called, 2021event loop blocks next and before C<ev_check> watchers are being called,
1753and only in the child after the fork. If whoever good citizen calling 2022and only in the child after the fork. If whoever good citizen calling
1754C<ev_default_fork> cheats and calls it in the wrong process, the fork 2023C<ev_default_fork> cheats and calls it in the wrong process, the fork
1755handlers will be invoked, too, of course. 2024handlers will be invoked, too, of course.
1756 2025
2026=head3 Watcher-Specific Functions and Data Members
2027
1757=over 4 2028=over 4
1758 2029
1759=item ev_fork_init (ev_signal *, callback) 2030=item ev_fork_init (ev_signal *, callback)
1760 2031
1761Initialises and configures the fork watcher - it has no parameters of any 2032Initialises and configures the fork watcher - it has no parameters of any
… …
1977 2248
1978=item w->stop () 2249=item w->stop ()
1979 2250
1980Stops the watcher if it is active. Again, no C<loop> argument. 2251Stops the watcher if it is active. Again, no C<loop> argument.
1981 2252
1982=item w->again () C<ev::timer>, C<ev::periodic> only 2253=item w->again () (C<ev::timer>, C<ev::periodic> only)
1983 2254
1984For C<ev::timer> and C<ev::periodic>, this invokes the corresponding 2255For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1985C<ev_TYPE_again> function. 2256C<ev_TYPE_again> function.
1986 2257
1987=item w->sweep () C<ev::embed> only 2258=item w->sweep () (C<ev::embed> only)
1988 2259
1989Invokes C<ev_embed_sweep>. 2260Invokes C<ev_embed_sweep>.
1990 2261
1991=item w->update () C<ev::stat> only 2262=item w->update () (C<ev::stat> only)
1992 2263
1993Invokes C<ev_stat_stat>. 2264Invokes C<ev_stat_stat>.
1994 2265
1995=back 2266=back
1996 2267
… …
2016 } 2287 }
2017 2288
2018 2289
2019=head1 MACRO MAGIC 2290=head1 MACRO MAGIC
2020 2291
2021Libev can be compiled with a variety of options, the most fundemantal is 2292Libev can be compiled with a variety of options, the most fundamantal
2022C<EV_MULTIPLICITY>. This option determines whether (most) functions and 2293of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2023callbacks have an initial C<struct ev_loop *> argument. 2294functions and callbacks have an initial C<struct ev_loop *> argument.
2024 2295
2025To make it easier to write programs that cope with either variant, the 2296To make it easier to write programs that cope with either variant, the
2026following macros are defined: 2297following macros are defined:
2027 2298
2028=over 4 2299=over 4
… …
2082Libev can (and often is) directly embedded into host 2353Libev can (and often is) directly embedded into host
2083applications. Examples of applications that embed it include the Deliantra 2354applications. Examples of applications that embed it include the Deliantra
2084Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe) 2355Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2085and rxvt-unicode. 2356and rxvt-unicode.
2086 2357
2087The goal is to enable you to just copy the neecssary files into your 2358The goal is to enable you to just copy the necessary files into your
2088source directory without having to change even a single line in them, so 2359source directory without having to change even a single line in them, so
2089you can easily upgrade by simply copying (or having a checked-out copy of 2360you can easily upgrade by simply copying (or having a checked-out copy of
2090libev somewhere in your source tree). 2361libev somewhere in your source tree).
2091 2362
2092=head2 FILESETS 2363=head2 FILESETS
… …
2182 2453
2183If defined to be C<1>, libev will try to detect the availability of the 2454If defined to be C<1>, libev will try to detect the availability of the
2184monotonic clock option at both compiletime and runtime. Otherwise no use 2455monotonic clock option at both compiletime and runtime. Otherwise no use
2185of the monotonic clock option will be attempted. If you enable this, you 2456of the monotonic clock option will be attempted. If you enable this, you
2186usually have to link against librt or something similar. Enabling it when 2457usually have to link against librt or something similar. Enabling it when
2187the functionality isn't available is safe, though, althoguh you have 2458the functionality isn't available is safe, though, although you have
2188to make sure you link against any libraries where the C<clock_gettime> 2459to make sure you link against any libraries where the C<clock_gettime>
2189function is hiding in (often F<-lrt>). 2460function is hiding in (often F<-lrt>).
2190 2461
2191=item EV_USE_REALTIME 2462=item EV_USE_REALTIME
2192 2463
2193If defined to be C<1>, libev will try to detect the availability of the 2464If defined to be C<1>, libev will try to detect the availability of the
2194realtime clock option at compiletime (and assume its availability at 2465realtime clock option at compiletime (and assume its availability at
2195runtime if successful). Otherwise no use of the realtime clock option will 2466runtime if successful). Otherwise no use of the realtime clock option will
2196be attempted. This effectively replaces C<gettimeofday> by C<clock_get 2467be attempted. This effectively replaces C<gettimeofday> by C<clock_get
2197(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries 2468(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
2198in the description of C<EV_USE_MONOTONIC>, though. 2469note about libraries in the description of C<EV_USE_MONOTONIC>, though.
2470
2471=item EV_USE_NANOSLEEP
2472
2473If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2474and will use it for delays. Otherwise it will use C<select ()>.
2199 2475
2200=item EV_USE_SELECT 2476=item EV_USE_SELECT
2201 2477
2202If undefined or defined to be C<1>, libev will compile in support for the 2478If undefined or defined to be C<1>, libev will compile in support for the
2203C<select>(2) backend. No attempt at autodetection will be done: if no 2479C<select>(2) backend. No attempt at autodetection will be done: if no
… …
2221wants osf handles on win32 (this is the case when the select to 2497wants osf handles on win32 (this is the case when the select to
2222be used is the winsock select). This means that it will call 2498be used is the winsock select). This means that it will call
2223C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise, 2499C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2224it is assumed that all these functions actually work on fds, even 2500it is assumed that all these functions actually work on fds, even
2225on win32. Should not be defined on non-win32 platforms. 2501on win32. Should not be defined on non-win32 platforms.
2502
2503=item EV_FD_TO_WIN32_HANDLE
2504
2505If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2506file descriptors to socket handles. When not defining this symbol (the
2507default), then libev will call C<_get_osfhandle>, which is usually
2508correct. In some cases, programs use their own file descriptor management,
2509in which case they can provide this function to map fds to socket handles.
2226 2510
2227=item EV_USE_POLL 2511=item EV_USE_POLL
2228 2512
2229If defined to be C<1>, libev will compile in support for the C<poll>(2) 2513If defined to be C<1>, libev will compile in support for the C<poll>(2)
2230backend. Otherwise it will be enabled on non-win32 platforms. It 2514backend. Otherwise it will be enabled on non-win32 platforms. It
… …
2267be detected at runtime. 2551be detected at runtime.
2268 2552
2269=item EV_H 2553=item EV_H
2270 2554
2271The name of the F<ev.h> header file used to include it. The default if 2555The name of the F<ev.h> header file used to include it. The default if
2272undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This 2556undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to
2273can be used to virtually rename the F<ev.h> header file in case of conflicts. 2557virtually rename the F<ev.h> header file in case of conflicts.
2274 2558
2275=item EV_CONFIG_H 2559=item EV_CONFIG_H
2276 2560
2277If C<EV_STANDALONE> isn't C<1>, this variable can be used to override 2561If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2278F<ev.c>'s idea of where to find the F<config.h> file, similarly to 2562F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2279C<EV_H>, above. 2563C<EV_H>, above.
2280 2564
2281=item EV_EVENT_H 2565=item EV_EVENT_H
2282 2566
2283Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea 2567Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2284of how the F<event.h> header can be found. 2568of how the F<event.h> header can be found, the dfeault is C<"event.h">.
2285 2569
2286=item EV_PROTOTYPES 2570=item EV_PROTOTYPES
2287 2571
2288If defined to be C<0>, then F<ev.h> will not define any function 2572If defined to be C<0>, then F<ev.h> will not define any function
2289prototypes, but still define all the structs and other symbols. This is 2573prototypes, but still define all the structs and other symbols. This is
… …
2355than enough. If you need to manage thousands of children you might want to 2639than enough. If you need to manage thousands of children you might want to
2356increase this value (I<must> be a power of two). 2640increase this value (I<must> be a power of two).
2357 2641
2358=item EV_INOTIFY_HASHSIZE 2642=item EV_INOTIFY_HASHSIZE
2359 2643
2360C<ev_staz> watchers use a small hash table to distribute workload by 2644C<ev_stat> watchers use a small hash table to distribute workload by
2361inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>), 2645inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2362usually more than enough. If you need to manage thousands of C<ev_stat> 2646usually more than enough. If you need to manage thousands of C<ev_stat>
2363watchers you might want to increase this value (I<must> be a power of 2647watchers you might want to increase this value (I<must> be a power of
2364two). 2648two).
2365 2649
… …
2382 2666
2383=item ev_set_cb (ev, cb) 2667=item ev_set_cb (ev, cb)
2384 2668
2385Can be used to change the callback member declaration in each watcher, 2669Can be used to change the callback member declaration in each watcher,
2386and the way callbacks are invoked and set. Must expand to a struct member 2670and the way callbacks are invoked and set. Must expand to a struct member
2387definition and a statement, respectively. See the F<ev.v> header file for 2671definition and a statement, respectively. See the F<ev.h> header file for
2388their default definitions. One possible use for overriding these is to 2672their default definitions. One possible use for overriding these is to
2389avoid the C<struct ev_loop *> as first argument in all cases, or to use 2673avoid the C<struct ev_loop *> as first argument in all cases, or to use
2390method calls instead of plain function calls in C++. 2674method calls instead of plain function calls in C++.
2675
2676=head2 EXPORTED API SYMBOLS
2677
2678If you need to re-export the API (e.g. via a dll) and you need a list of
2679exported symbols, you can use the provided F<Symbol.*> files which list
2680all public symbols, one per line:
2681
2682 Symbols.ev for libev proper
2683 Symbols.event for the libevent emulation
2684
2685This can also be used to rename all public symbols to avoid clashes with
2686multiple versions of libev linked together (which is obviously bad in
2687itself, but sometimes it is inconvinient to avoid this).
2688
2689A sed command like this will create wrapper C<#define>'s that you need to
2690include before including F<ev.h>:
2691
2692 <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
2693
2694This would create a file F<wrap.h> which essentially looks like this:
2695
2696 #define ev_backend myprefix_ev_backend
2697 #define ev_check_start myprefix_ev_check_start
2698 #define ev_check_stop myprefix_ev_check_stop
2699 ...
2391 2700
2392=head2 EXAMPLES 2701=head2 EXAMPLES
2393 2702
2394For a real-world example of a program the includes libev 2703For a real-world example of a program the includes libev
2395verbatim, you can have a look at the EV perl module 2704verbatim, you can have a look at the EV perl module
… …
2436 2745
2437=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers) 2746=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2438 2747
2439This means that, when you have a watcher that triggers in one hour and 2748This means that, when you have a watcher that triggers in one hour and
2440there are 100 watchers that would trigger before that then inserting will 2749there are 100 watchers that would trigger before that then inserting will
2441have to skip those 100 watchers. 2750have to skip roughly seven (C<ld 100>) of these watchers.
2442 2751
2443=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers) 2752=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2444 2753
2445That means that for changing a timer costs less than removing/adding them 2754That means that changing a timer costs less than removing/adding them
2446as only the relative motion in the event queue has to be paid for. 2755as only the relative motion in the event queue has to be paid for.
2447 2756
2448=item Starting io/check/prepare/idle/signal/child watchers: O(1) 2757=item Starting io/check/prepare/idle/signal/child watchers: O(1)
2449 2758
2450These just add the watcher into an array or at the head of a list. 2759These just add the watcher into an array or at the head of a list.
2760
2451=item Stopping check/prepare/idle watchers: O(1) 2761=item Stopping check/prepare/idle watchers: O(1)
2452 2762
2453=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) 2763=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2454 2764
2455These watchers are stored in lists then need to be walked to find the 2765These watchers are stored in lists then need to be walked to find the
2456correct watcher to remove. The lists are usually short (you don't usually 2766correct watcher to remove. The lists are usually short (you don't usually
2457have many watchers waiting for the same fd or signal). 2767have many watchers waiting for the same fd or signal).
2458 2768
2459=item Finding the next timer per loop iteration: O(1) 2769=item Finding the next timer in each loop iteration: O(1)
2770
2771By virtue of using a binary heap, the next timer is always found at the
2772beginning of the storage array.
2460 2773
2461=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd) 2774=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2462 2775
2463A change means an I/O watcher gets started or stopped, which requires 2776A change means an I/O watcher gets started or stopped, which requires
2464libev to recalculate its status (and possibly tell the kernel). 2777libev to recalculate its status (and possibly tell the kernel, depending
2778on backend and wether C<ev_io_set> was used).
2465 2779
2466=item Activating one watcher: O(1) 2780=item Activating one watcher (putting it into the pending state): O(1)
2467 2781
2468=item Priority handling: O(number_of_priorities) 2782=item Priority handling: O(number_of_priorities)
2469 2783
2470Priorities are implemented by allocating some space for each 2784Priorities are implemented by allocating some space for each
2471priority. When doing priority-based operations, libev usually has to 2785priority. When doing priority-based operations, libev usually has to
2472linearly search all the priorities. 2786linearly search all the priorities, but starting/stopping and activating
2787watchers becomes O(1) w.r.t. prioritiy handling.
2473 2788
2474=back 2789=back
2475 2790
2476 2791
2792=head1 Win32 platform limitations and workarounds
2793
2794Win32 doesn't support any of the standards (e.g. POSIX) that libev
2795requires, and its I/O model is fundamentally incompatible with the POSIX
2796model. Libev still offers limited functionality on this platform in
2797the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2798descriptors. This only applies when using Win32 natively, not when using
2799e.g. cygwin.
2800
2801There is no supported compilation method available on windows except
2802embedding it into other applications.
2803
2804Due to the many, low, and arbitrary limits on the win32 platform and the
2805abysmal performance of winsockets, using a large number of sockets is not
2806recommended (and not reasonable). If your program needs to use more than
2807a hundred or so sockets, then likely it needs to use a totally different
2808implementation for windows, as libev offers the POSIX model, which cannot
2809be implemented efficiently on windows (microsoft monopoly games).
2810
2811=over 4
2812
2813=item The winsocket select function
2814
2815The winsocket C<select> function doesn't follow POSIX in that it requires
2816socket I<handles> and not socket I<file descriptors>. This makes select
2817very inefficient, and also requires a mapping from file descriptors
2818to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
2819C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
2820symbols for more info.
2821
2822The configuration for a "naked" win32 using the microsoft runtime
2823libraries and raw winsocket select is:
2824
2825 #define EV_USE_SELECT 1
2826 #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2827
2828Note that winsockets handling of fd sets is O(n), so you can easily get a
2829complexity in the O(n²) range when using win32.
2830
2831=item Limited number of file descriptors
2832
2833Windows has numerous arbitrary (and low) limits on things. Early versions
2834of winsocket's select only supported waiting for a max. of C<64> handles
2835(probably owning to the fact that all windows kernels can only wait for
2836C<64> things at the same time internally; microsoft recommends spawning a
2837chain of threads and wait for 63 handles and the previous thread in each).
2838
2839Newer versions support more handles, but you need to define C<FD_SETSIZE>
2840to some high number (e.g. C<2048>) before compiling the winsocket select
2841call (which might be in libev or elsewhere, for example, perl does its own
2842select emulation on windows).
2843
2844Another limit is the number of file descriptors in the microsoft runtime
2845libraries, which by default is C<64> (there must be a hidden I<64> fetish
2846or something like this inside microsoft). You can increase this by calling
2847C<_setmaxstdio>, which can increase this limit to C<2048> (another
2848arbitrary limit), but is broken in many versions of the microsoft runtime
2849libraries.
2850
2851This might get you to about C<512> or C<2048> sockets (depending on
2852windows version and/or the phase of the moon). To get more, you need to
2853wrap all I/O functions and provide your own fd management, but the cost of
2854calling select (O(n²)) will likely make this unworkable.
2855
2856=back
2857
2858
2477=head1 AUTHOR 2859=head1 AUTHOR
2478 2860
2479Marc Lehmann <libev@schmorp.de>. 2861Marc Lehmann <libev@schmorp.de>.
2480 2862

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