… | |
… | |
298 | If you don't know what event loop to use, use the one returned from this |
298 | If you don't know what event loop to use, use the one returned from this |
299 | function. |
299 | function. |
300 | |
300 | |
301 | Note that this function is I<not> thread-safe, so if you want to use it |
301 | Note that this function is I<not> thread-safe, so if you want to use it |
302 | from multiple threads, you have to lock (note also that this is unlikely, |
302 | from multiple threads, you have to lock (note also that this is unlikely, |
303 | as loops cannot bes hared easily between threads anyway). |
303 | as loops cannot be shared easily between threads anyway). |
304 | |
304 | |
305 | The default loop is the only loop that can handle C<ev_signal> and |
305 | The default loop is the only loop that can handle C<ev_signal> and |
306 | C<ev_child> watchers, and to do this, it always registers a handler |
306 | C<ev_child> watchers, and to do this, it always registers a handler |
307 | for C<SIGCHLD>. If this is a problem for your application you can either |
307 | for C<SIGCHLD>. If this is a problem for your application you can either |
308 | create a dynamic loop with C<ev_loop_new> that doesn't do that, or you |
308 | create a dynamic loop with C<ev_loop_new> that doesn't do that, or you |
… | |
… | |
386 | For few fds, this backend is a bit little slower than poll and select, |
386 | For few fds, this backend is a bit little slower than poll and select, |
387 | but it scales phenomenally better. While poll and select usually scale |
387 | but it scales phenomenally better. While poll and select usually scale |
388 | like O(total_fds) where n is the total number of fds (or the highest fd), |
388 | like O(total_fds) where n is the total number of fds (or the highest fd), |
389 | epoll scales either O(1) or O(active_fds). |
389 | epoll scales either O(1) or O(active_fds). |
390 | |
390 | |
391 | The epoll syscalls are the most misdesigned of the more advanced event |
391 | The epoll mechanism deserves honorable mention as the most misdesigned |
392 | mechanisms: problems include silently dropping fds, requiring a system |
392 | of the more advanced event mechanisms: mere annoyances include silently |
393 | call per change per fd (and unnecessary guessing of parameters), problems |
393 | dropping file descriptors, requiring a system call per change per file |
|
|
394 | descriptor (and unnecessary guessing of parameters), problems with dup and |
394 | with dup and so on. The biggest issue is fork races, however - if a |
395 | so on. The biggest issue is fork races, however - if a program forks then |
395 | program forks then I<both> parent and child process have to recreate the |
396 | I<both> parent and child process have to recreate the epoll set, which can |
396 | epoll set, which can take considerable time (one syscall per fd) and is of |
397 | take considerable time (one syscall per file descriptor) and is of course |
397 | course hard to detect. |
398 | hard to detect. |
398 | |
399 | |
399 | Epoll is also notoriously buggy - embedding epoll fds should work, but |
400 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
400 | of course doesn't, and epoll just loves to report events for totally |
401 | of course I<doesn't>, and epoll just loves to report events for totally |
401 | I<different> file descriptors (even already closed ones, so one cannot |
402 | I<different> file descriptors (even already closed ones, so one cannot |
402 | even remove them from the set) than registered in the set (especially |
403 | even remove them from the set) than registered in the set (especially |
403 | on SMP systems). Libev tries to counter these spurious notifications by |
404 | on SMP systems). Libev tries to counter these spurious notifications by |
404 | employing an additional generation counter and comparing that against the |
405 | employing an additional generation counter and comparing that against the |
405 | events to filter out spurious ones. |
406 | events to filter out spurious ones, recreating the set when required. |
406 | |
407 | |
407 | While stopping, setting and starting an I/O watcher in the same iteration |
408 | While stopping, setting and starting an I/O watcher in the same iteration |
408 | will result in some caching, there is still a system call per such incident |
409 | will result in some caching, there is still a system call per such |
409 | (because the fd could point to a different file description now), so its |
410 | incident (because the same I<file descriptor> could point to a different |
410 | best to avoid that. Also, C<dup ()>'ed file descriptors might not work |
411 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
411 | very well if you register events for both fds. |
412 | file descriptors might not work very well if you register events for both |
|
|
413 | file descriptors. |
412 | |
414 | |
413 | Best performance from this backend is achieved by not unregistering all |
415 | Best performance from this backend is achieved by not unregistering all |
414 | watchers for a file descriptor until it has been closed, if possible, |
416 | watchers for a file descriptor until it has been closed, if possible, |
415 | i.e. keep at least one watcher active per fd at all times. Stopping and |
417 | i.e. keep at least one watcher active per fd at all times. Stopping and |
416 | starting a watcher (without re-setting it) also usually doesn't cause |
418 | starting a watcher (without re-setting it) also usually doesn't cause |
417 | extra overhead. A fork can both result in spurious notifications as well |
419 | extra overhead. A fork can both result in spurious notifications as well |
418 | as in libev having to destroy and recreate the epoll object, which can |
420 | as in libev having to destroy and recreate the epoll object, which can |
419 | take considerable time and thus should be avoided. |
421 | take considerable time and thus should be avoided. |
420 | |
422 | |
|
|
423 | All this means that, in practise, C<EVBACKEND_SELECT> is as fast or faster |
|
|
424 | then epoll for maybe up to a hundred file descriptors. So sad. |
|
|
425 | |
421 | While nominally embeddable in other event loops, this feature is broken in |
426 | While nominally embeddable in other event loops, this feature is broken in |
422 | all kernel versions tested so far. |
427 | all kernel versions tested so far. |
423 | |
428 | |
424 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
429 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
425 | C<EVBACKEND_POLL>. |
430 | C<EVBACKEND_POLL>. |
426 | |
431 | |
427 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
432 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
428 | |
433 | |
429 | Kqueue deserves special mention, as at the time of this writing, it was |
434 | Kqueue deserves special mention, as at the time of this writing, it |
430 | broken on all BSDs except NetBSD (usually it doesn't work reliably with |
435 | was broken on all BSDs except NetBSD (usually it doesn't work reliably |
431 | anything but sockets and pipes, except on Darwin, where of course it's |
436 | with anything but sockets and pipes, except on Darwin, where of course |
432 | completely useless). For this reason it's not being "auto-detected" unless |
437 | it's completely useless). Unlike epoll, however, whose brokenness |
433 | you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or |
438 | is by design, these kqueue bugs can (and eventually will) be fixed |
434 | libev was compiled on a known-to-be-good (-enough) system like NetBSD. |
439 | without API changes to existing programs. For this reason it's not being |
|
|
440 | "auto-detected" unless you explicitly specify it in the flags (i.e. using |
|
|
441 | C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) |
|
|
442 | system like NetBSD. |
435 | |
443 | |
436 | You still can embed kqueue into a normal poll or select backend and use it |
444 | You still can embed kqueue into a normal poll or select backend and use it |
437 | only for sockets (after having made sure that sockets work with kqueue on |
445 | only for sockets (after having made sure that sockets work with kqueue on |
438 | the target platform). See C<ev_embed> watchers for more info. |
446 | the target platform). See C<ev_embed> watchers for more info. |
439 | |
447 | |
… | |
… | |
647 | the loop. |
655 | the loop. |
648 | |
656 | |
649 | A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
657 | A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
650 | necessary) and will handle those and any already outstanding ones. It |
658 | necessary) and will handle those and any already outstanding ones. It |
651 | will block your process until at least one new event arrives (which could |
659 | will block your process until at least one new event arrives (which could |
652 | be an event internal to libev itself, so there is no guarentee that a |
660 | be an event internal to libev itself, so there is no guarantee that a |
653 | user-registered callback will be called), and will return after one |
661 | user-registered callback will be called), and will return after one |
654 | iteration of the loop. |
662 | iteration of the loop. |
655 | |
663 | |
656 | This is useful if you are waiting for some external event in conjunction |
664 | This is useful if you are waiting for some external event in conjunction |
657 | with something not expressible using other libev watchers (i.e. "roll your |
665 | with something not expressible using other libev watchers (i.e. "roll your |
… | |
… | |
1927 | C<stat> on that path in regular intervals (or when the OS says it changed) |
1935 | C<stat> on that path in regular intervals (or when the OS says it changed) |
1928 | and sees if it changed compared to the last time, invoking the callback if |
1936 | and sees if it changed compared to the last time, invoking the callback if |
1929 | it did. |
1937 | it did. |
1930 | |
1938 | |
1931 | The path does not need to exist: changing from "path exists" to "path does |
1939 | The path does not need to exist: changing from "path exists" to "path does |
1932 | not exist" is a status change like any other. The condition "path does |
1940 | not exist" is a status change like any other. The condition "path does not |
1933 | not exist" is signified by the C<st_nlink> field being zero (which is |
1941 | exist" (or more correctly "path cannot be stat'ed") is signified by the |
1934 | otherwise always forced to be at least one) and all the other fields of |
1942 | C<st_nlink> field being zero (which is otherwise always forced to be at |
1935 | the stat buffer having unspecified contents. |
1943 | least one) and all the other fields of the stat buffer having unspecified |
|
|
1944 | contents. |
1936 | |
1945 | |
1937 | The path I<must not> end in a slash or contain special components such as |
1946 | The path I<must not> end in a slash or contain special components such as |
1938 | C<.> or C<..>. The path I<should> be absolute: If it is relative and |
1947 | C<.> or C<..>. The path I<should> be absolute: If it is relative and |
1939 | your working directory changes, then the behaviour is undefined. |
1948 | your working directory changes, then the behaviour is undefined. |
1940 | |
1949 | |
… | |
… | |
1943 | to see if it changed somehow. You can specify a recommended polling |
1952 | to see if it changed somehow. You can specify a recommended polling |
1944 | interval for this case. If you specify a polling interval of C<0> (highly |
1953 | interval for this case. If you specify a polling interval of C<0> (highly |
1945 | recommended!) then a I<suitable, unspecified default> value will be used |
1954 | recommended!) then a I<suitable, unspecified default> value will be used |
1946 | (which you can expect to be around five seconds, although this might |
1955 | (which you can expect to be around five seconds, although this might |
1947 | change dynamically). Libev will also impose a minimum interval which is |
1956 | change dynamically). Libev will also impose a minimum interval which is |
1948 | currently around C<0.1>, but thats usually overkill. |
1957 | currently around C<0.1>, but that's usually overkill. |
1949 | |
1958 | |
1950 | This watcher type is not meant for massive numbers of stat watchers, |
1959 | This watcher type is not meant for massive numbers of stat watchers, |
1951 | as even with OS-supported change notifications, this can be |
1960 | as even with OS-supported change notifications, this can be |
1952 | resource-intensive. |
1961 | resource-intensive. |
1953 | |
1962 | |
1954 | At the time of this writing, the only OS-specific interface implemented |
1963 | At the time of this writing, the only OS-specific interface implemented |
1955 | is the Linux inotify interface (implementing kqueue support is left as |
1964 | is the Linux inotify interface (implementing kqueue support is left as an |
1956 | an exercise for the reader. Note, however, that the author sees no way |
1965 | exercise for the reader. Note, however, that the author sees no way of |
1957 | of implementing C<ev_stat> semantics with kqueue). |
1966 | implementing C<ev_stat> semantics with kqueue, except as a hint). |
1958 | |
1967 | |
1959 | =head3 ABI Issues (Largefile Support) |
1968 | =head3 ABI Issues (Largefile Support) |
1960 | |
1969 | |
1961 | Libev by default (unless the user overrides this) uses the default |
1970 | Libev by default (unless the user overrides this) uses the default |
1962 | compilation environment, which means that on systems with large file |
1971 | compilation environment, which means that on systems with large file |
… | |
… | |
1973 | to exchange stat structures with application programs compiled using the |
1982 | to exchange stat structures with application programs compiled using the |
1974 | default compilation environment. |
1983 | default compilation environment. |
1975 | |
1984 | |
1976 | =head3 Inotify and Kqueue |
1985 | =head3 Inotify and Kqueue |
1977 | |
1986 | |
1978 | When C<inotify (7)> support has been compiled into libev (generally |
1987 | When C<inotify (7)> support has been compiled into libev and present at |
1979 | only available with Linux 2.6.25 or above due to bugs in earlier |
1988 | runtime, it will be used to speed up change detection where possible. The |
1980 | implementations) and present at runtime, it will be used to speed up |
1989 | inotify descriptor will be created lazily when the first C<ev_stat> |
1981 | change detection where possible. The inotify descriptor will be created |
1990 | watcher is being started. |
1982 | lazily when the first C<ev_stat> watcher is being started. |
|
|
1983 | |
1991 | |
1984 | Inotify presence does not change the semantics of C<ev_stat> watchers |
1992 | Inotify presence does not change the semantics of C<ev_stat> watchers |
1985 | except that changes might be detected earlier, and in some cases, to avoid |
1993 | except that changes might be detected earlier, and in some cases, to avoid |
1986 | making regular C<stat> calls. Even in the presence of inotify support |
1994 | making regular C<stat> calls. Even in the presence of inotify support |
1987 | there are many cases where libev has to resort to regular C<stat> polling, |
1995 | there are many cases where libev has to resort to regular C<stat> polling, |
1988 | but as long as the path exists, libev usually gets away without polling. |
1996 | but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too |
|
|
1997 | many bugs), the path exists (i.e. stat succeeds), and the path resides on |
|
|
1998 | a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and |
|
|
1999 | xfs are fully working) libev usually gets away without polling. |
1989 | |
2000 | |
1990 | There is no support for kqueue, as apparently it cannot be used to |
2001 | There is no support for kqueue, as apparently it cannot be used to |
1991 | implement this functionality, due to the requirement of having a file |
2002 | implement this functionality, due to the requirement of having a file |
1992 | descriptor open on the object at all times, and detecting renames, unlinks |
2003 | descriptor open on the object at all times, and detecting renames, unlinks |
1993 | etc. is difficult. |
2004 | etc. is difficult. |
|
|
2005 | |
|
|
2006 | =head3 C<stat ()> is a synchronous operation |
|
|
2007 | |
|
|
2008 | Libev doesn't normally do any kind of I/O itself, and so is not blocking |
|
|
2009 | the process. The exception are C<ev_stat> watchers - those call C<stat |
|
|
2010 | ()>, which is a synchronous operation. |
|
|
2011 | |
|
|
2012 | For local paths, this usually doesn't matter: unless the system is very |
|
|
2013 | busy or the intervals between stat's are large, a stat call will be fast, |
|
|
2014 | as the path data is suually in memory already (except when starting the |
|
|
2015 | watcher). |
|
|
2016 | |
|
|
2017 | For networked file systems, calling C<stat ()> can block an indefinite |
|
|
2018 | time due to network issues, and even under good conditions, a stat call |
|
|
2019 | often takes multiple milliseconds. |
|
|
2020 | |
|
|
2021 | Therefore, it is best to avoid using C<ev_stat> watchers on networked |
|
|
2022 | paths, although this is fully supported by libev. |
1994 | |
2023 | |
1995 | =head3 The special problem of stat time resolution |
2024 | =head3 The special problem of stat time resolution |
1996 | |
2025 | |
1997 | The C<stat ()> system call only supports full-second resolution portably, |
2026 | The C<stat ()> system call only supports full-second resolution portably, |
1998 | and even on systems where the resolution is higher, most file systems |
2027 | and even on systems where the resolution is higher, most file systems |
… | |
… | |
2643 | =over 4 |
2672 | =over 4 |
2644 | |
2673 | |
2645 | =item ev_async_init (ev_async *, callback) |
2674 | =item ev_async_init (ev_async *, callback) |
2646 | |
2675 | |
2647 | Initialises and configures the async watcher - it has no parameters of any |
2676 | Initialises and configures the async watcher - it has no parameters of any |
2648 | kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless, |
2677 | kind. There is a C<ev_async_set> macro, but using it is utterly pointless, |
2649 | trust me. |
2678 | trust me. |
2650 | |
2679 | |
2651 | =item ev_async_send (loop, ev_async *) |
2680 | =item ev_async_send (loop, ev_async *) |
2652 | |
2681 | |
2653 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
2682 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
… | |
… | |
3086 | |
3115 | |
3087 | #define EV_STANDALONE 1 |
3116 | #define EV_STANDALONE 1 |
3088 | #include "ev.h" |
3117 | #include "ev.h" |
3089 | |
3118 | |
3090 | Both header files and implementation files can be compiled with a C++ |
3119 | Both header files and implementation files can be compiled with a C++ |
3091 | compiler (at least, thats a stated goal, and breakage will be treated |
3120 | compiler (at least, that's a stated goal, and breakage will be treated |
3092 | as a bug). |
3121 | as a bug). |
3093 | |
3122 | |
3094 | You need the following files in your source tree, or in a directory |
3123 | You need the following files in your source tree, or in a directory |
3095 | in your include path (e.g. in libev/ when using -Ilibev): |
3124 | in your include path (e.g. in libev/ when using -Ilibev): |
3096 | |
3125 | |
… | |
… | |
3568 | loop, as long as you don't confuse yourself). The only exception is that |
3597 | loop, as long as you don't confuse yourself). The only exception is that |
3569 | you must not do this from C<ev_periodic> reschedule callbacks. |
3598 | you must not do this from C<ev_periodic> reschedule callbacks. |
3570 | |
3599 | |
3571 | Care has been taken to ensure that libev does not keep local state inside |
3600 | Care has been taken to ensure that libev does not keep local state inside |
3572 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
3601 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
3573 | they do not clal any callbacks. |
3602 | they do not call any callbacks. |
3574 | |
3603 | |
3575 | =head2 COMPILER WARNINGS |
3604 | =head2 COMPILER WARNINGS |
3576 | |
3605 | |
3577 | Depending on your compiler and compiler settings, you might get no or a |
3606 | Depending on your compiler and compiler settings, you might get no or a |
3578 | lot of warnings when compiling libev code. Some people are apparently |
3607 | lot of warnings when compiling libev code. Some people are apparently |
… | |
… | |
3612 | ==2274== definitely lost: 0 bytes in 0 blocks. |
3641 | ==2274== definitely lost: 0 bytes in 0 blocks. |
3613 | ==2274== possibly lost: 0 bytes in 0 blocks. |
3642 | ==2274== possibly lost: 0 bytes in 0 blocks. |
3614 | ==2274== still reachable: 256 bytes in 1 blocks. |
3643 | ==2274== still reachable: 256 bytes in 1 blocks. |
3615 | |
3644 | |
3616 | Then there is no memory leak, just as memory accounted to global variables |
3645 | Then there is no memory leak, just as memory accounted to global variables |
3617 | is not a memleak - the memory is still being refernced, and didn't leak. |
3646 | is not a memleak - the memory is still being referenced, and didn't leak. |
3618 | |
3647 | |
3619 | Similarly, under some circumstances, valgrind might report kernel bugs |
3648 | Similarly, under some circumstances, valgrind might report kernel bugs |
3620 | as if it were a bug in libev (e.g. in realloc or in the poll backend, |
3649 | as if it were a bug in libev (e.g. in realloc or in the poll backend, |
3621 | although an acceptable workaround has been found here), or it might be |
3650 | although an acceptable workaround has been found here), or it might be |
3622 | confused. |
3651 | confused. |
… | |
… | |
3860 | =back |
3889 | =back |
3861 | |
3890 | |
3862 | |
3891 | |
3863 | =head1 AUTHOR |
3892 | =head1 AUTHOR |
3864 | |
3893 | |
3865 | Marc Lehmann <libev@schmorp.de>. |
3894 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
3866 | |
3895 | |