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Revision 1.428 by root, Thu May 30 18:51:57 2013 UTC vs.
Revision 1.454 by root, Tue Jun 25 05:17:50 2019 UTC

1=encoding utf-8
2
1=head1 NAME 3=head1 NAME
2 4
3libev - a high performance full-featured event loop written in C 5libev - a high performance full-featured event loop written in C
4 6
5=head1 SYNOPSIS 7=head1 SYNOPSIS
103details of the event, and then hand it over to libev by I<starting> the 105details of the event, and then hand it over to libev by I<starting> the
104watcher. 106watcher.
105 107
106=head2 FEATURES 108=head2 FEATURES
107 109
108Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the 110Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109BSD-specific C<kqueue> and the Solaris-specific event port mechanisms 111interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110for file descriptor events (C<ev_io>), the Linux C<inotify> interface 112mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner 113interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative 114inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113timers (C<ev_timer>), absolute timers with customised rescheduling 115timers (C<ev_timer>), absolute timers with customised rescheduling
114(C<ev_periodic>), synchronous signals (C<ev_signal>), process status 116(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115change events (C<ev_child>), and event watchers dealing with the event 117change events (C<ev_child>), and event watchers dealing with the event
116loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and 118loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
263 265
264You could override this function in high-availability programs to, say, 266You could override this function in high-availability programs to, say,
265free some memory if it cannot allocate memory, to use a special allocator, 267free some memory if it cannot allocate memory, to use a special allocator,
266or even to sleep a while and retry until some memory is available. 268or even to sleep a while and retry until some memory is available.
267 269
270Example: The following is the C<realloc> function that libev itself uses
271which should work with C<realloc> and C<free> functions of all kinds and
272is probably a good basis for your own implementation.
273
274 static void *
275 ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
276 {
277 if (size)
278 return realloc (ptr, size);
279
280 free (ptr);
281 return 0;
282 }
283
268Example: Replace the libev allocator with one that waits a bit and then 284Example: Replace the libev allocator with one that waits a bit and then
269retries (example requires a standards-compliant C<realloc>). 285retries.
270 286
271 static void * 287 static void *
272 persistent_realloc (void *ptr, size_t size) 288 persistent_realloc (void *ptr, size_t size)
273 { 289 {
290 if (!size)
291 {
292 free (ptr);
293 return 0;
294 }
295
274 for (;;) 296 for (;;)
275 { 297 {
276 void *newptr = realloc (ptr, size); 298 void *newptr = realloc (ptr, size);
277 299
278 if (newptr) 300 if (newptr)
409make libev check for a fork in each iteration by enabling this flag. 431make libev check for a fork in each iteration by enabling this flag.
410 432
411This works by calling C<getpid ()> on every iteration of the loop, 433This works by calling C<getpid ()> on every iteration of the loop,
412and thus this might slow down your event loop if you do a lot of loop 434and thus this might slow down your event loop if you do a lot of loop
413iterations and little real work, but is usually not noticeable (on my 435iterations and little real work, but is usually not noticeable (on my
414GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence 436GNU/Linux system for example, C<getpid> is actually a simple 5-insn
415without a system call and thus I<very> fast, but my GNU/Linux system also has 437sequence without a system call and thus I<very> fast, but my GNU/Linux
416C<pthread_atfork> which is even faster). 438system also has C<pthread_atfork> which is even faster). (Update: glibc
439versions 2.25 apparently removed the C<getpid> optimisation again).
417 440
418The big advantage of this flag is that you can forget about fork (and 441The big advantage of this flag is that you can forget about fork (and
419forget about forgetting to tell libev about forking) when you use this 442forget about forgetting to tell libev about forking, although you still
420flag. 443have to ignore C<SIGPIPE>) when you use this flag.
421 444
422This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS> 445This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
423environment variable. 446environment variable.
424 447
425=item C<EVFLAG_NOINOTIFY> 448=item C<EVFLAG_NOINOTIFY>
488This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and 511This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
489C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>. 512C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
490 513
491=item C<EVBACKEND_EPOLL> (value 4, Linux) 514=item C<EVBACKEND_EPOLL> (value 4, Linux)
492 515
493Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 516Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
494kernels). 517kernels).
495 518
496For few fds, this backend is a bit little slower than poll and select, but 519For few fds, this backend is a bit little slower than poll and select, but
497it scales phenomenally better. While poll and select usually scale like 520it scales phenomenally better. While poll and select usually scale like
498O(total_fds) where total_fds is the total number of fds (or the highest 521O(total_fds) where total_fds is the total number of fds (or the highest
544All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or 567All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
545faster than epoll for maybe up to a hundred file descriptors, depending on 568faster than epoll for maybe up to a hundred file descriptors, depending on
546the usage. So sad. 569the usage. So sad.
547 570
548While nominally embeddable in other event loops, this feature is broken in 571While nominally embeddable in other event loops, this feature is broken in
549all kernel versions tested so far. 572a lot of kernel revisions, but probably(!) works in current versions.
550 573
551This backend maps C<EV_READ> and C<EV_WRITE> in the same way as 574This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
552C<EVBACKEND_POLL>. 575C<EVBACKEND_POLL>.
553 576
577=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
578
579Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
580io_submit(2) >>) event interface available in post-4.18 kernels (but libev
581only tries to use it in 4.19+).
582
583This is another Linux train wreck of an event interface.
584
585If this backend works for you (as of this writing, it was very
586experimental), it is the best event interface available on Linux and might
587be well worth enabling it - if it isn't available in your kernel this will
588be detected and this backend will be skipped.
589
590This backend can batch oneshot requests and supports a user-space ring
591buffer to receive events. It also doesn't suffer from most of the design
592problems of epoll (such as not being able to remove event sources from
593the epoll set), and generally sounds too good to be true. Because, this
594being the Linux kernel, of course it suffers from a whole new set of
595limitations, forcing you to fall back to epoll, inheriting all its design
596issues.
597
598For one, it is not easily embeddable (but probably could be done using
599an event fd at some extra overhead). It also is subject to a system wide
600limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
601requests are left, this backend will be skipped during initialisation, and
602will switch to epoll when the loop is active.
603
604Most problematic in practice, however, is that not all file descriptors
605work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
606files, F</dev/null> and many others are supported, but ttys do not work
607properly (a known bug that the kernel developers don't care about, see
608L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
609(yet?) a generic event polling interface.
610
611Overall, it seems the Linux developers just don't want it to have a
612generic event handling mechanism other than C<select> or C<poll>.
613
614To work around all these problem, the current version of libev uses its
615epoll backend as a fallback for file descriptor types that do not work. Or
616falls back completely to epoll if the kernel acts up.
617
618This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
619C<EVBACKEND_POLL>.
620
554=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) 621=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
555 622
556Kqueue deserves special mention, as at the time of this writing, it 623Kqueue deserves special mention, as at the time this backend was
557was broken on all BSDs except NetBSD (usually it doesn't work reliably 624implemented, it was broken on all BSDs except NetBSD (usually it doesn't
558with anything but sockets and pipes, except on Darwin, where of course 625work reliably with anything but sockets and pipes, except on Darwin,
559it's completely useless). Unlike epoll, however, whose brokenness 626where of course it's completely useless). Unlike epoll, however, whose
560is by design, these kqueue bugs can (and eventually will) be fixed 627brokenness is by design, these kqueue bugs can be (and mostly have been)
561without API changes to existing programs. For this reason it's not being 628fixed without API changes to existing programs. For this reason it's not
562"auto-detected" unless you explicitly specify it in the flags (i.e. using 629being "auto-detected" on all platforms unless you explicitly specify it
563C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) 630in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
564system like NetBSD. 631known-to-be-good (-enough) system like NetBSD.
565 632
566You still can embed kqueue into a normal poll or select backend and use it 633You still can embed kqueue into a normal poll or select backend and use it
567only for sockets (after having made sure that sockets work with kqueue on 634only for sockets (after having made sure that sockets work with kqueue on
568the target platform). See C<ev_embed> watchers for more info. 635the target platform). See C<ev_embed> watchers for more info.
569 636
570It scales in the same way as the epoll backend, but the interface to the 637It scales in the same way as the epoll backend, but the interface to the
571kernel is more efficient (which says nothing about its actual speed, of 638kernel is more efficient (which says nothing about its actual speed, of
572course). While stopping, setting and starting an I/O watcher does never 639course). While stopping, setting and starting an I/O watcher does never
573cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to 640cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
574two event changes per incident. Support for C<fork ()> is very bad (you 641two event changes per incident. Support for C<fork ()> is very bad (you
575might have to leak fd's on fork, but it's more sane than epoll) and it 642might have to leak fds on fork, but it's more sane than epoll) and it
576drops fds silently in similarly hard-to-detect cases. 643drops fds silently in similarly hard-to-detect cases.
577 644
578This backend usually performs well under most conditions. 645This backend usually performs well under most conditions.
579 646
580While nominally embeddable in other event loops, this doesn't work 647While nominally embeddable in other event loops, this doesn't work
655Example: Use whatever libev has to offer, but make sure that kqueue is 722Example: Use whatever libev has to offer, but make sure that kqueue is
656used if available. 723used if available.
657 724
658 struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE); 725 struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
659 726
727Example: Similarly, on linux, you mgiht want to take advantage of the
728linux aio backend if possible, but fall back to something else if that
729isn't available.
730
731 struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
732
660=item ev_loop_destroy (loop) 733=item ev_loop_destroy (loop)
661 734
662Destroys an event loop object (frees all memory and kernel state 735Destroys an event loop object (frees all memory and kernel state
663etc.). None of the active event watchers will be stopped in the normal 736etc.). None of the active event watchers will be stopped in the normal
664sense, so e.g. C<ev_is_active> might still return true. It is your 737sense, so e.g. C<ev_is_active> might still return true. It is your
680If you need dynamically allocated loops it is better to use C<ev_loop_new> 753If you need dynamically allocated loops it is better to use C<ev_loop_new>
681and C<ev_loop_destroy>. 754and C<ev_loop_destroy>.
682 755
683=item ev_loop_fork (loop) 756=item ev_loop_fork (loop)
684 757
685This function sets a flag that causes subsequent C<ev_run> iterations to 758This function sets a flag that causes subsequent C<ev_run> iterations
686reinitialise the kernel state for backends that have one. Despite the 759to reinitialise the kernel state for backends that have one. Despite
687name, you can call it anytime, but it makes most sense after forking, in 760the name, you can call it anytime you are allowed to start or stop
688the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the 761watchers (except inside an C<ev_prepare> callback), but it makes most
762sense after forking, in the child process. You I<must> call it (or use
689child before resuming or calling C<ev_run>. 763C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
690 764
765In addition, if you want to reuse a loop (via this function or
766C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
767
691Again, you I<have> to call it on I<any> loop that you want to re-use after 768Again, you I<have> to call it on I<any> loop that you want to re-use after
692a fork, I<even if you do not plan to use the loop in the parent>. This is 769a fork, I<even if you do not plan to use the loop in the parent>. This is
693because some kernel interfaces *cough* I<kqueue> *cough* do funny things 770because some kernel interfaces *cough* I<kqueue> *cough* do funny things
694during fork. 771during fork.
695 772
696On the other hand, you only need to call this function in the child 773On the other hand, you only need to call this function in the child
1603 1680
1604But really, best use non-blocking mode. 1681But really, best use non-blocking mode.
1605 1682
1606=head3 The special problem of disappearing file descriptors 1683=head3 The special problem of disappearing file descriptors
1607 1684
1608Some backends (e.g. kqueue, epoll) need to be told about closing a file 1685Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1609descriptor (either due to calling C<close> explicitly or any other means, 1686a file descriptor (either due to calling C<close> explicitly or any other
1610such as C<dup2>). The reason is that you register interest in some file 1687means, such as C<dup2>). The reason is that you register interest in some
1611descriptor, but when it goes away, the operating system will silently drop 1688file descriptor, but when it goes away, the operating system will silently
1612this interest. If another file descriptor with the same number then is 1689drop this interest. If another file descriptor with the same number then
1613registered with libev, there is no efficient way to see that this is, in 1690is registered with libev, there is no efficient way to see that this is,
1614fact, a different file descriptor. 1691in fact, a different file descriptor.
1615 1692
1616To avoid having to explicitly tell libev about such cases, libev follows 1693To avoid having to explicitly tell libev about such cases, libev follows
1617the following policy: Each time C<ev_io_set> is being called, libev 1694the following policy: Each time C<ev_io_set> is being called, libev
1618will assume that this is potentially a new file descriptor, otherwise 1695will assume that this is potentially a new file descriptor, otherwise
1619it is assumed that the file descriptor stays the same. That means that 1696it is assumed that the file descriptor stays the same. That means that
1668when you rarely read from a file instead of from a socket, and want to 1745when you rarely read from a file instead of from a socket, and want to
1669reuse the same code path. 1746reuse the same code path.
1670 1747
1671=head3 The special problem of fork 1748=head3 The special problem of fork
1672 1749
1673Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit 1750Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1674useless behaviour. Libev fully supports fork, but needs to be told about 1751at all or exhibit useless behaviour. Libev fully supports fork, but needs
1675it in the child if you want to continue to use it in the child. 1752to be told about it in the child if you want to continue to use it in the
1753child.
1676 1754
1677To support fork in your child processes, you have to call C<ev_loop_fork 1755To support fork in your child processes, you have to call C<ev_loop_fork
1678()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to 1756()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1679C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. 1757C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1680 1758
2026 2104
2027The relative timeouts are calculated relative to the C<ev_now ()> 2105The relative timeouts are calculated relative to the C<ev_now ()>
2028time. This is usually the right thing as this timestamp refers to the time 2106time. This is usually the right thing as this timestamp refers to the time
2029of the event triggering whatever timeout you are modifying/starting. If 2107of the event triggering whatever timeout you are modifying/starting. If
2030you suspect event processing to be delayed and you I<need> to base the 2108you suspect event processing to be delayed and you I<need> to base the
2031timeout on the current time, use something like this to adjust for this: 2109timeout on the current time, use something like the following to adjust
2110for it:
2032 2111
2033 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2112 ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
2034 2113
2035If the event loop is suspended for a long time, you can also force an 2114If the event loop is suspended for a long time, you can also force an
2036update of the time returned by C<ev_now ()> by calling C<ev_now_update 2115update of the time returned by C<ev_now ()> by calling C<ev_now_update
2037()>. 2116()>, although that will push the event time of all outstanding events
2117further into the future.
2038 2118
2039=head3 The special problem of unsynchronised clocks 2119=head3 The special problem of unsynchronised clocks
2040 2120
2041Modern systems have a variety of clocks - libev itself uses the normal 2121Modern systems have a variety of clocks - libev itself uses the normal
2042"wall clock" clock and, if available, the monotonic clock (to avoid time 2122"wall clock" clock and, if available, the monotonic clock (to avoid time
2105 2185
2106=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 2186=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2107 2187
2108=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) 2188=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2109 2189
2110Configure the timer to trigger after C<after> seconds. If C<repeat> 2190Configure the timer to trigger after C<after> seconds (fractional and
2111is C<0.>, then it will automatically be stopped once the timeout is 2191negative values are supported). If C<repeat> is C<0.>, then it will
2112reached. If it is positive, then the timer will automatically be 2192automatically be stopped once the timeout is reached. If it is positive,
2113configured to trigger again C<repeat> seconds later, again, and again, 2193then the timer will automatically be configured to trigger again C<repeat>
2114until stopped manually. 2194seconds later, again, and again, until stopped manually.
2115 2195
2116The timer itself will do a best-effort at avoiding drift, that is, if 2196The timer itself will do a best-effort at avoiding drift, that is, if
2117you configure a timer to trigger every 10 seconds, then it will normally 2197you configure a timer to trigger every 10 seconds, then it will normally
2118trigger at exactly 10 second intervals. If, however, your program cannot 2198trigger at exactly 10 second intervals. If, however, your program cannot
2119keep up with the timer (because it takes longer than those 10 seconds to 2199keep up with the timer (because it takes longer than those 10 seconds to
2201Periodic watchers are also timers of a kind, but they are very versatile 2281Periodic watchers are also timers of a kind, but they are very versatile
2202(and unfortunately a bit complex). 2282(and unfortunately a bit complex).
2203 2283
2204Unlike C<ev_timer>, periodic watchers are not based on real time (or 2284Unlike C<ev_timer>, periodic watchers are not based on real time (or
2205relative time, the physical time that passes) but on wall clock time 2285relative time, the physical time that passes) but on wall clock time
2206(absolute time, the thing you can read on your calender or clock). The 2286(absolute time, the thing you can read on your calendar or clock). The
2207difference is that wall clock time can run faster or slower than real 2287difference is that wall clock time can run faster or slower than real
2208time, and time jumps are not uncommon (e.g. when you adjust your 2288time, and time jumps are not uncommon (e.g. when you adjust your
2209wrist-watch). 2289wrist-watch).
2210 2290
2211You can tell a periodic watcher to trigger after some specific point 2291You can tell a periodic watcher to trigger after some specific point
2216C<ev_timer>, which would still trigger roughly 10 seconds after starting 2296C<ev_timer>, which would still trigger roughly 10 seconds after starting
2217it, as it uses a relative timeout). 2297it, as it uses a relative timeout).
2218 2298
2219C<ev_periodic> watchers can also be used to implement vastly more complex 2299C<ev_periodic> watchers can also be used to implement vastly more complex
2220timers, such as triggering an event on each "midnight, local time", or 2300timers, such as triggering an event on each "midnight, local time", or
2221other complicated rules. This cannot be done with C<ev_timer> watchers, as 2301other complicated rules. This cannot easily be done with C<ev_timer>
2222those cannot react to time jumps. 2302watchers, as those cannot react to time jumps.
2223 2303
2224As with timers, the callback is guaranteed to be invoked only when the 2304As with timers, the callback is guaranteed to be invoked only when the
2225point in time where it is supposed to trigger has passed. If multiple 2305point in time where it is supposed to trigger has passed. If multiple
2226timers become ready during the same loop iteration then the ones with 2306timers become ready during the same loop iteration then the ones with
2227earlier time-out values are invoked before ones with later time-out values 2307earlier time-out values are invoked before ones with later time-out values
2313 2393
2314NOTE: I<< This callback must always return a time that is higher than or 2394NOTE: I<< This callback must always return a time that is higher than or
2315equal to the passed C<now> value >>. 2395equal to the passed C<now> value >>.
2316 2396
2317This can be used to create very complex timers, such as a timer that 2397This can be used to create very complex timers, such as a timer that
2318triggers on "next midnight, local time". To do this, you would calculate the 2398triggers on "next midnight, local time". To do this, you would calculate
2319next midnight after C<now> and return the timestamp value for this. How 2399the next midnight after C<now> and return the timestamp value for
2320you do this is, again, up to you (but it is not trivial, which is the main 2400this. Here is a (completely untested, no error checking) example on how to
2321reason I omitted it as an example). 2401do this:
2402
2403 #include <time.h>
2404
2405 static ev_tstamp
2406 my_rescheduler (ev_periodic *w, ev_tstamp now)
2407 {
2408 time_t tnow = (time_t)now;
2409 struct tm tm;
2410 localtime_r (&tnow, &tm);
2411
2412 tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2413 ++tm.tm_mday; // midnight next day
2414
2415 return mktime (&tm);
2416 }
2417
2418Note: this code might run into trouble on days that have more then two
2419midnights (beginning and end).
2322 2420
2323=back 2421=back
2324 2422
2325=item ev_periodic_again (loop, ev_periodic *) 2423=item ev_periodic_again (loop, ev_periodic *)
2326 2424
2391 2489
2392 ev_periodic hourly_tick; 2490 ev_periodic hourly_tick;
2393 ev_periodic_init (&hourly_tick, clock_cb, 2491 ev_periodic_init (&hourly_tick, clock_cb,
2394 fmod (ev_now (loop), 3600.), 3600., 0); 2492 fmod (ev_now (loop), 3600.), 3600., 0);
2395 ev_periodic_start (loop, &hourly_tick); 2493 ev_periodic_start (loop, &hourly_tick);
2396 2494
2397 2495
2398=head2 C<ev_signal> - signal me when a signal gets signalled! 2496=head2 C<ev_signal> - signal me when a signal gets signalled!
2399 2497
2400Signal watchers will trigger an event when the process receives a specific 2498Signal watchers will trigger an event when the process receives a specific
2401signal one or more times. Even though signals are very asynchronous, libev 2499signal one or more times. Even though signals are very asynchronous, libev
2411only within the same loop, i.e. you can watch for C<SIGINT> in your 2509only within the same loop, i.e. you can watch for C<SIGINT> in your
2412default loop and for C<SIGIO> in another loop, but you cannot watch for 2510default loop and for C<SIGIO> in another loop, but you cannot watch for
2413C<SIGINT> in both the default loop and another loop at the same time. At 2511C<SIGINT> in both the default loop and another loop at the same time. At
2414the moment, C<SIGCHLD> is permanently tied to the default loop. 2512the moment, C<SIGCHLD> is permanently tied to the default loop.
2415 2513
2416When the first watcher gets started will libev actually register something 2514Only after the first watcher for a signal is started will libev actually
2417with the kernel (thus it coexists with your own signal handlers as long as 2515register something with the kernel. It thus coexists with your own signal
2418you don't register any with libev for the same signal). 2516handlers as long as you don't register any with libev for the same signal.
2419 2517
2420If possible and supported, libev will install its handlers with 2518If possible and supported, libev will install its handlers with
2421C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should 2519C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2422not be unduly interrupted. If you have a problem with system calls getting 2520not be unduly interrupted. If you have a problem with system calls getting
2423interrupted by signals you can block all signals in an C<ev_check> watcher 2521interrupted by signals you can block all signals in an C<ev_check> watcher
2905 3003
2906Prepare and check watchers are often (but not always) used in pairs: 3004Prepare and check watchers are often (but not always) used in pairs:
2907prepare watchers get invoked before the process blocks and check watchers 3005prepare watchers get invoked before the process blocks and check watchers
2908afterwards. 3006afterwards.
2909 3007
2910You I<must not> call C<ev_run> or similar functions that enter 3008You I<must not> call C<ev_run> (or similar functions that enter the
2911the current event loop from either C<ev_prepare> or C<ev_check> 3009current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2912watchers. Other loops than the current one are fine, however. The 3010C<ev_check> watchers. Other loops than the current one are fine,
2913rationale behind this is that you do not need to check for recursion in 3011however. The rationale behind this is that you do not need to check
2914those watchers, i.e. the sequence will always be C<ev_prepare>, blocking, 3012for recursion in those watchers, i.e. the sequence will always be
2915C<ev_check> so if you have one watcher of each kind they will always be 3013C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2916called in pairs bracketing the blocking call. 3014kind they will always be called in pairs bracketing the blocking call.
2917 3015
2918Their main purpose is to integrate other event mechanisms into libev and 3016Their main purpose is to integrate other event mechanisms into libev and
2919their use is somewhat advanced. They could be used, for example, to track 3017their use is somewhat advanced. They could be used, for example, to track
2920variable changes, implement your own watchers, integrate net-snmp or a 3018variable changes, implement your own watchers, integrate net-snmp or a
2921coroutine library and lots more. They are also occasionally useful if 3019coroutine library and lots more. They are also occasionally useful if
3211used). 3309used).
3212 3310
3213 struct ev_loop *loop_hi = ev_default_init (0); 3311 struct ev_loop *loop_hi = ev_default_init (0);
3214 struct ev_loop *loop_lo = 0; 3312 struct ev_loop *loop_lo = 0;
3215 ev_embed embed; 3313 ev_embed embed;
3216 3314
3217 // see if there is a chance of getting one that works 3315 // see if there is a chance of getting one that works
3218 // (remember that a flags value of 0 means autodetection) 3316 // (remember that a flags value of 0 means autodetection)
3219 loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3317 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3220 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3318 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3221 : 0; 3319 : 0;
3235C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too). 3333C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3236 3334
3237 struct ev_loop *loop = ev_default_init (0); 3335 struct ev_loop *loop = ev_default_init (0);
3238 struct ev_loop *loop_socket = 0; 3336 struct ev_loop *loop_socket = 0;
3239 ev_embed embed; 3337 ev_embed embed;
3240 3338
3241 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) 3339 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3242 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) 3340 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3243 { 3341 {
3244 ev_embed_init (&embed, 0, loop_socket); 3342 ev_embed_init (&embed, 0, loop_socket);
3245 ev_embed_start (loop, &embed); 3343 ev_embed_start (loop, &embed);
3261and calls it in the wrong process, the fork handlers will be invoked, too, 3359and calls it in the wrong process, the fork handlers will be invoked, too,
3262of course. 3360of course.
3263 3361
3264=head3 The special problem of life after fork - how is it possible? 3362=head3 The special problem of life after fork - how is it possible?
3265 3363
3266Most uses of C<fork()> consist of forking, then some simple calls to set 3364Most uses of C<fork ()> consist of forking, then some simple calls to set
3267up/change the process environment, followed by a call to C<exec()>. This 3365up/change the process environment, followed by a call to C<exec()>. This
3268sequence should be handled by libev without any problems. 3366sequence should be handled by libev without any problems.
3269 3367
3270This changes when the application actually wants to do event handling 3368This changes when the application actually wants to do event handling
3271in the child, or both parent in child, in effect "continuing" after the 3369in the child, or both parent in child, in effect "continuing" after the
3509 3607
3510There are some other functions of possible interest. Described. Here. Now. 3608There are some other functions of possible interest. Described. Here. Now.
3511 3609
3512=over 4 3610=over 4
3513 3611
3514=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 3612=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3515 3613
3516This function combines a simple timer and an I/O watcher, calls your 3614This function combines a simple timer and an I/O watcher, calls your
3517callback on whichever event happens first and automatically stops both 3615callback on whichever event happens first and automatically stops both
3518watchers. This is useful if you want to wait for a single event on an fd 3616watchers. This is useful if you want to wait for a single event on an fd
3519or timeout without having to allocate/configure/start/stop/free one or 3617or timeout without having to allocate/configure/start/stop/free one or
3895To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two 3993To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
3896files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: 3994files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
3897 3995
3898 // my_ev.h 3996 // my_ev.h
3899 #define EV_CB_DECLARE(type) struct my_coro *cb; 3997 #define EV_CB_DECLARE(type) struct my_coro *cb;
3900 #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); 3998 #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
3901 #include "../libev/ev.h" 3999 #include "../libev/ev.h"
3902 4000
3903 // my_ev.c 4001 // my_ev.c
3904 #define EV_H "my_ev.h" 4002 #define EV_H "my_ev.h"
3905 #include "../libev/ev.c" 4003 #include "../libev/ev.c"
3951The normal C API should work fine when used from C++: both ev.h and the 4049The normal C API should work fine when used from C++: both ev.h and the
3952libev sources can be compiled as C++. Therefore, code that uses the C API 4050libev sources can be compiled as C++. Therefore, code that uses the C API
3953will work fine. 4051will work fine.
3954 4052
3955Proper exception specifications might have to be added to callbacks passed 4053Proper exception specifications might have to be added to callbacks passed
3956to libev: exceptions may be thrown only from watcher callbacks, all 4054to libev: exceptions may be thrown only from watcher callbacks, all other
3957other callbacks (allocator, syserr, loop acquire/release and periodic 4055callbacks (allocator, syserr, loop acquire/release and periodic reschedule
3958reschedule callbacks) must not throw exceptions, and might need a C<throw 4056callbacks) must not throw exceptions, and might need a C<noexcept>
3959()> specification. If you have code that needs to be compiled as both C 4057specification. If you have code that needs to be compiled as both C and
3960and C++ you can use the C<EV_THROW> macro for this: 4058C++ you can use the C<EV_NOEXCEPT> macro for this:
3961 4059
3962 static void 4060 static void
3963 fatal_error (const char *msg) EV_THROW 4061 fatal_error (const char *msg) EV_NOEXCEPT
3964 { 4062 {
3965 perror (msg); 4063 perror (msg);
3966 abort (); 4064 abort ();
3967 } 4065 }
3968 4066
4095 void operator() (ev::io &w, int revents) 4193 void operator() (ev::io &w, int revents)
4096 { 4194 {
4097 ... 4195 ...
4098 } 4196 }
4099 } 4197 }
4100 4198
4101 myfunctor f; 4199 myfunctor f;
4102 4200
4103 ev::io w; 4201 ev::io w;
4104 w.set (&f); 4202 w.set (&f);
4105 4203
4378 ev_vars.h 4476 ev_vars.h
4379 ev_wrap.h 4477 ev_wrap.h
4380 4478
4381 ev_win32.c required on win32 platforms only 4479 ev_win32.c required on win32 platforms only
4382 4480
4383 ev_select.c only when select backend is enabled (which is enabled by default) 4481 ev_select.c only when select backend is enabled
4384 ev_poll.c only when poll backend is enabled (disabled by default) 4482 ev_poll.c only when poll backend is enabled
4385 ev_epoll.c only when the epoll backend is enabled (disabled by default) 4483 ev_epoll.c only when the epoll backend is enabled
4484 ev_linuxaio.c only when the linux aio backend is enabled
4386 ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4485 ev_kqueue.c only when the kqueue backend is enabled
4387 ev_port.c only when the solaris port backend is enabled (disabled by default) 4486 ev_port.c only when the solaris port backend is enabled
4388 4487
4389F<ev.c> includes the backend files directly when enabled, so you only need 4488F<ev.c> includes the backend files directly when enabled, so you only need
4390to compile this single file. 4489to compile this single file.
4391 4490
4392=head3 LIBEVENT COMPATIBILITY API 4491=head3 LIBEVENT COMPATIBILITY API
4580If defined to be C<1>, libev will compile in support for the Linux 4679If defined to be C<1>, libev will compile in support for the Linux
4581C<epoll>(7) backend. Its availability will be detected at runtime, 4680C<epoll>(7) backend. Its availability will be detected at runtime,
4582otherwise another method will be used as fallback. This is the preferred 4681otherwise another method will be used as fallback. This is the preferred
4583backend for GNU/Linux systems. If undefined, it will be enabled if the 4682backend for GNU/Linux systems. If undefined, it will be enabled if the
4584headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. 4683headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4684
4685=item EV_USE_LINUXAIO
4686
4687If defined to be C<1>, libev will compile in support for the Linux
4688aio backend. Due to it's currenbt limitations it has to be requested
4689explicitly. If undefined, it will be enabled on linux, otherwise
4690disabled.
4585 4691
4586=item EV_USE_KQUEUE 4692=item EV_USE_KQUEUE
4587 4693
4588If defined to be C<1>, libev will compile in support for the BSD style 4694If defined to be C<1>, libev will compile in support for the BSD style
4589C<kqueue>(2) backend. Its actual availability will be detected at runtime, 4695C<kqueue>(2) backend. Its actual availability will be detected at runtime,
5292structure (guaranteed by POSIX but not by ISO C for example), but it also 5398structure (guaranteed by POSIX but not by ISO C for example), but it also
5293assumes that the same (machine) code can be used to call any watcher 5399assumes that the same (machine) code can be used to call any watcher
5294callback: The watcher callbacks have different type signatures, but libev 5400callback: The watcher callbacks have different type signatures, but libev
5295calls them using an C<ev_watcher *> internally. 5401calls them using an C<ev_watcher *> internally.
5296 5402
5403=item null pointers and integer zero are represented by 0 bytes
5404
5405Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
5406relies on this setting pointers and integers to null.
5407
5297=item pointer accesses must be thread-atomic 5408=item pointer accesses must be thread-atomic
5298 5409
5299Accessing a pointer value must be atomic, it must both be readable and 5410Accessing a pointer value must be atomic, it must both be readable and
5300writable in one piece - this is the case on all current architectures. 5411writable in one piece - this is the case on all current architectures.
5301 5412

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