… | |
… | |
105 | details of the event, and then hand it over to libev by I<starting> the |
105 | details of the event, and then hand it over to libev by I<starting> the |
106 | watcher. |
106 | watcher. |
107 | |
107 | |
108 | =head2 FEATURES |
108 | =head2 FEATURES |
109 | |
109 | |
110 | Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the |
110 | Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll> |
111 | BSD-specific C<kqueue> and the Solaris-specific event port mechanisms |
111 | interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port |
112 | for file descriptor events (C<ev_io>), the Linux C<inotify> interface |
112 | mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify> |
113 | (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner |
113 | interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner |
114 | inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative |
114 | inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative |
115 | timers (C<ev_timer>), absolute timers with customised rescheduling |
115 | timers (C<ev_timer>), absolute timers with customised rescheduling |
116 | (C<ev_periodic>), synchronous signals (C<ev_signal>), process status |
116 | (C<ev_periodic>), synchronous signals (C<ev_signal>), process status |
117 | change events (C<ev_child>), and event watchers dealing with the event |
117 | change events (C<ev_child>), and event watchers dealing with the event |
118 | loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and |
118 | loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and |
… | |
… | |
265 | |
265 | |
266 | You could override this function in high-availability programs to, say, |
266 | You could override this function in high-availability programs to, say, |
267 | free some memory if it cannot allocate memory, to use a special allocator, |
267 | free some memory if it cannot allocate memory, to use a special allocator, |
268 | or even to sleep a while and retry until some memory is available. |
268 | or even to sleep a while and retry until some memory is available. |
269 | |
269 | |
|
|
270 | Example: The following is the C<realloc> function that libev itself uses |
|
|
271 | which should work with C<realloc> and C<free> functions of all kinds and |
|
|
272 | is 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 | |
270 | Example: Replace the libev allocator with one that waits a bit and then |
284 | Example: Replace the libev allocator with one that waits a bit and then |
271 | retries (example requires a standards-compliant C<realloc>). |
285 | retries. |
272 | |
286 | |
273 | static void * |
287 | static void * |
274 | persistent_realloc (void *ptr, size_t size) |
288 | persistent_realloc (void *ptr, size_t size) |
275 | { |
289 | { |
|
|
290 | if (!size) |
|
|
291 | { |
|
|
292 | free (ptr); |
|
|
293 | return 0; |
|
|
294 | } |
|
|
295 | |
276 | for (;;) |
296 | for (;;) |
277 | { |
297 | { |
278 | void *newptr = realloc (ptr, size); |
298 | void *newptr = realloc (ptr, size); |
279 | |
299 | |
280 | if (newptr) |
300 | if (newptr) |
… | |
… | |
491 | This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and |
511 | This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and |
492 | C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>. |
512 | C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>. |
493 | |
513 | |
494 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
514 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
495 | |
515 | |
496 | Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
516 | Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
497 | kernels). |
517 | kernels). |
498 | |
518 | |
499 | For few fds, this backend is a bit little slower than poll and select, but |
519 | For few fds, this backend is a bit little slower than poll and select, but |
500 | it scales phenomenally better. While poll and select usually scale like |
520 | it scales phenomenally better. While poll and select usually scale like |
501 | O(total_fds) where total_fds is the total number of fds (or the highest |
521 | O(total_fds) where total_fds is the total number of fds (or the highest |
… | |
… | |
547 | All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or |
567 | All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or |
548 | faster than epoll for maybe up to a hundred file descriptors, depending on |
568 | faster than epoll for maybe up to a hundred file descriptors, depending on |
549 | the usage. So sad. |
569 | the usage. So sad. |
550 | |
570 | |
551 | While nominally embeddable in other event loops, this feature is broken in |
571 | While nominally embeddable in other event loops, this feature is broken in |
552 | all kernel versions tested so far. |
572 | a lot of kernel revisions, but probably(!) works in current versions. |
553 | |
573 | |
554 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
574 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
555 | C<EVBACKEND_POLL>. |
575 | C<EVBACKEND_POLL>. |
556 | |
576 | |
|
|
577 | =item C<EVBACKEND_LINUXAIO> (value 64, Linux) |
|
|
578 | |
|
|
579 | Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<< |
|
|
580 | io_submit(2) >>) event interface available in post-4.18 kernels (but libev |
|
|
581 | only tries to use it in 4.19+). |
|
|
582 | |
|
|
583 | This is another Linux train wreck of an event interface. |
|
|
584 | |
|
|
585 | If this backend works for you (as of this writing, it was very |
|
|
586 | experimental), it is the best event interface available on Linux and might |
|
|
587 | be well worth enabling it - if it isn't available in your kernel this will |
|
|
588 | be detected and this backend will be skipped. |
|
|
589 | |
|
|
590 | This backend can batch oneshot requests and supports a user-space ring |
|
|
591 | buffer to receive events. It also doesn't suffer from most of the design |
|
|
592 | problems of epoll (such as not being able to remove event sources from |
|
|
593 | the epoll set), and generally sounds too good to be true. Because, this |
|
|
594 | being the Linux kernel, of course it suffers from a whole new set of |
|
|
595 | limitations, forcing you to fall back to epoll, inheriting all its design |
|
|
596 | issues. |
|
|
597 | |
|
|
598 | For one, it is not easily embeddable (but probably could be done using |
|
|
599 | an event fd at some extra overhead). It also is subject to a system wide |
|
|
600 | limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO |
|
|
601 | requests are left, this backend will be skipped during initialisation, and |
|
|
602 | will switch to epoll when the loop is active. |
|
|
603 | |
|
|
604 | Most problematic in practice, however, is that not all file descriptors |
|
|
605 | work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds, |
|
|
606 | files, F</dev/null> and many others are supported, but ttys do not work |
|
|
607 | properly (a known bug that the kernel developers don't care about, see |
|
|
608 | L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not |
|
|
609 | (yet?) a generic event polling interface. |
|
|
610 | |
|
|
611 | Overall, it seems the Linux developers just don't want it to have a |
|
|
612 | generic event handling mechanism other than C<select> or C<poll>. |
|
|
613 | |
|
|
614 | To work around all these problem, the current version of libev uses its |
|
|
615 | epoll backend as a fallback for file descriptor types that do not work. Or |
|
|
616 | falls back completely to epoll if the kernel acts up. |
|
|
617 | |
|
|
618 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
|
|
619 | C<EVBACKEND_POLL>. |
|
|
620 | |
557 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
621 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
558 | |
622 | |
559 | Kqueue deserves special mention, as at the time of this writing, it |
623 | Kqueue deserves special mention, as at the time this backend was |
560 | was broken on all BSDs except NetBSD (usually it doesn't work reliably |
624 | implemented, it was broken on all BSDs except NetBSD (usually it doesn't |
561 | with anything but sockets and pipes, except on Darwin, where of course |
625 | work reliably with anything but sockets and pipes, except on Darwin, |
562 | it's completely useless). Unlike epoll, however, whose brokenness |
626 | where of course it's completely useless). Unlike epoll, however, whose |
563 | is by design, these kqueue bugs can (and eventually will) be fixed |
627 | brokenness is by design, these kqueue bugs can be (and mostly have been) |
564 | without API changes to existing programs. For this reason it's not being |
628 | fixed without API changes to existing programs. For this reason it's not |
565 | "auto-detected" unless you explicitly specify it in the flags (i.e. using |
629 | being "auto-detected" on all platforms unless you explicitly specify it |
566 | C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) |
630 | in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a |
567 | system like NetBSD. |
631 | known-to-be-good (-enough) system like NetBSD. |
568 | |
632 | |
569 | You still can embed kqueue into a normal poll or select backend and use it |
633 | You still can embed kqueue into a normal poll or select backend and use it |
570 | only for sockets (after having made sure that sockets work with kqueue on |
634 | only for sockets (after having made sure that sockets work with kqueue on |
571 | the target platform). See C<ev_embed> watchers for more info. |
635 | the target platform). See C<ev_embed> watchers for more info. |
572 | |
636 | |
573 | It scales in the same way as the epoll backend, but the interface to the |
637 | It scales in the same way as the epoll backend, but the interface to the |
574 | kernel is more efficient (which says nothing about its actual speed, of |
638 | kernel is more efficient (which says nothing about its actual speed, of |
575 | course). While stopping, setting and starting an I/O watcher does never |
639 | course). While stopping, setting and starting an I/O watcher does never |
576 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
640 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
577 | two event changes per incident. Support for C<fork ()> is very bad (you |
641 | two event changes per incident. Support for C<fork ()> is very bad (you |
578 | might have to leak fd's on fork, but it's more sane than epoll) and it |
642 | might have to leak fds on fork, but it's more sane than epoll) and it |
579 | drops fds silently in similarly hard-to-detect cases. |
643 | drops fds silently in similarly hard-to-detect cases. |
580 | |
644 | |
581 | This backend usually performs well under most conditions. |
645 | This backend usually performs well under most conditions. |
582 | |
646 | |
583 | While nominally embeddable in other event loops, this doesn't work |
647 | While nominally embeddable in other event loops, this doesn't work |
… | |
… | |
657 | |
721 | |
658 | Example: Use whatever libev has to offer, but make sure that kqueue is |
722 | Example: Use whatever libev has to offer, but make sure that kqueue is |
659 | used if available. |
723 | used if available. |
660 | |
724 | |
661 | 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); |
|
|
726 | |
|
|
727 | Example: Similarly, on linux, you mgiht want to take advantage of the |
|
|
728 | linux aio backend if possible, but fall back to something else if that |
|
|
729 | isn't available. |
|
|
730 | |
|
|
731 | struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO); |
662 | |
732 | |
663 | =item ev_loop_destroy (loop) |
733 | =item ev_loop_destroy (loop) |
664 | |
734 | |
665 | Destroys an event loop object (frees all memory and kernel state |
735 | Destroys an event loop object (frees all memory and kernel state |
666 | etc.). None of the active event watchers will be stopped in the normal |
736 | etc.). None of the active event watchers will be stopped in the normal |
… | |
… | |
1610 | |
1680 | |
1611 | But really, best use non-blocking mode. |
1681 | But really, best use non-blocking mode. |
1612 | |
1682 | |
1613 | =head3 The special problem of disappearing file descriptors |
1683 | =head3 The special problem of disappearing file descriptors |
1614 | |
1684 | |
1615 | Some backends (e.g. kqueue, epoll) need to be told about closing a file |
1685 | Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing |
1616 | descriptor (either due to calling C<close> explicitly or any other means, |
1686 | a file descriptor (either due to calling C<close> explicitly or any other |
1617 | such as C<dup2>). The reason is that you register interest in some file |
1687 | means, such as C<dup2>). The reason is that you register interest in some |
1618 | descriptor, but when it goes away, the operating system will silently drop |
1688 | file descriptor, but when it goes away, the operating system will silently |
1619 | this interest. If another file descriptor with the same number then is |
1689 | drop this interest. If another file descriptor with the same number then |
1620 | registered with libev, there is no efficient way to see that this is, in |
1690 | is registered with libev, there is no efficient way to see that this is, |
1621 | fact, a different file descriptor. |
1691 | in fact, a different file descriptor. |
1622 | |
1692 | |
1623 | To avoid having to explicitly tell libev about such cases, libev follows |
1693 | To avoid having to explicitly tell libev about such cases, libev follows |
1624 | the following policy: Each time C<ev_io_set> is being called, libev |
1694 | the following policy: Each time C<ev_io_set> is being called, libev |
1625 | will assume that this is potentially a new file descriptor, otherwise |
1695 | will assume that this is potentially a new file descriptor, otherwise |
1626 | it is assumed that the file descriptor stays the same. That means that |
1696 | it is assumed that the file descriptor stays the same. That means that |
… | |
… | |
1675 | when you rarely read from a file instead of from a socket, and want to |
1745 | when you rarely read from a file instead of from a socket, and want to |
1676 | reuse the same code path. |
1746 | reuse the same code path. |
1677 | |
1747 | |
1678 | =head3 The special problem of fork |
1748 | =head3 The special problem of fork |
1679 | |
1749 | |
1680 | Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1750 | Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()> |
1681 | useless behaviour. Libev fully supports fork, but needs to be told about |
1751 | at all or exhibit useless behaviour. Libev fully supports fork, but needs |
1682 | it in the child if you want to continue to use it in the child. |
1752 | to be told about it in the child if you want to continue to use it in the |
|
|
1753 | child. |
1683 | |
1754 | |
1684 | To support fork in your child processes, you have to call C<ev_loop_fork |
1755 | To support fork in your child processes, you have to call C<ev_loop_fork |
1685 | ()> 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 |
1686 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1757 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1687 | |
1758 | |
… | |
… | |
4408 | ev_win32.c required on win32 platforms only |
4479 | ev_win32.c required on win32 platforms only |
4409 | |
4480 | |
4410 | ev_select.c only when select backend is enabled |
4481 | ev_select.c only when select backend is enabled |
4411 | ev_poll.c only when poll backend is enabled |
4482 | ev_poll.c only when poll backend is enabled |
4412 | ev_epoll.c only when the epoll backend is enabled |
4483 | ev_epoll.c only when the epoll backend is enabled |
|
|
4484 | ev_linuxaio.c only when the linux aio backend is enabled |
4413 | ev_kqueue.c only when the kqueue backend is enabled |
4485 | ev_kqueue.c only when the kqueue backend is enabled |
4414 | ev_port.c only when the solaris port backend is enabled |
4486 | ev_port.c only when the solaris port backend is enabled |
4415 | |
4487 | |
4416 | F<ev.c> includes the backend files directly when enabled, so you only need |
4488 | F<ev.c> includes the backend files directly when enabled, so you only need |
4417 | to compile this single file. |
4489 | to compile this single file. |
… | |
… | |
4607 | If defined to be C<1>, libev will compile in support for the Linux |
4679 | If defined to be C<1>, libev will compile in support for the Linux |
4608 | C<epoll>(7) backend. Its availability will be detected at runtime, |
4680 | C<epoll>(7) backend. Its availability will be detected at runtime, |
4609 | otherwise another method will be used as fallback. This is the preferred |
4681 | otherwise another method will be used as fallback. This is the preferred |
4610 | backend for GNU/Linux systems. If undefined, it will be enabled if the |
4682 | backend for GNU/Linux systems. If undefined, it will be enabled if the |
4611 | headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4683 | headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
|
|
4684 | |
|
|
4685 | =item EV_USE_LINUXAIO |
|
|
4686 | |
|
|
4687 | If defined to be C<1>, libev will compile in support for the Linux |
|
|
4688 | aio backend. Due to it's currenbt limitations it has to be requested |
|
|
4689 | explicitly. If undefined, it will be enabled on linux, otherwise |
|
|
4690 | disabled. |
4612 | |
4691 | |
4613 | =item EV_USE_KQUEUE |
4692 | =item EV_USE_KQUEUE |
4614 | |
4693 | |
4615 | If defined to be C<1>, libev will compile in support for the BSD style |
4694 | If defined to be C<1>, libev will compile in support for the BSD style |
4616 | C<kqueue>(2) backend. Its actual availability will be detected at runtime, |
4695 | C<kqueue>(2) backend. Its actual availability will be detected at runtime, |