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384 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
384 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
385 | |
385 | |
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). The epoll design has a number |
389 | epoll scales either O(1) or O(active_fds). |
390 | of shortcomings, such as silently dropping events in some hard-to-detect |
390 | |
391 | cases and requiring a system call per fd change, no fork support and bad |
391 | The epoll syscalls are the most misdesigned of the more advanced event |
392 | support for dup. |
392 | mechanisms: problems include silently dropping fds, requiring a system |
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393 | call per change per fd (and unnecessary guessing of parameters), problems |
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394 | with dup and so on. The biggest issue is fork races, however - if a |
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395 | program forks then I<both> parent and child process have to recreate the |
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396 | epoll set, which can take considerable time (one syscall per fd) and is of |
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397 | course hard to detect. |
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398 | |
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399 | Epoll is also notoriously buggy - embedding epoll fds should work, but |
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400 | of course doesn't, and epoll just loves to report events for totally |
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401 | I<different> file descriptors (even already closed ones, so one cannot |
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402 | even remove them from the set) than registered in the set (especially |
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403 | on SMP systems). Libev tries to counter these spurious notifications by |
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404 | employing an additional generation counter and comparing that against the |
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405 | events to filter out spurious ones. |
393 | |
406 | |
394 | While stopping, setting and starting an I/O watcher in the same iteration |
407 | While stopping, setting and starting an I/O watcher in the same iteration |
395 | will result in some caching, there is still a system call per such incident |
408 | will result in some caching, there is still a system call per such incident |
396 | (because the fd could point to a different file description now), so its |
409 | (because the fd could point to a different file description now), so its |
397 | best to avoid that. Also, C<dup ()>'ed file descriptors might not work |
410 | best to avoid that. Also, C<dup ()>'ed file descriptors might not work |
398 | very well if you register events for both fds. |
411 | very well if you register events for both fds. |
399 | |
412 | |
400 | Please note that epoll sometimes generates spurious notifications, so you |
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401 | need to use non-blocking I/O or other means to avoid blocking when no data |
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402 | (or space) is available. |
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403 | |
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404 | Best performance from this backend is achieved by not unregistering all |
413 | Best performance from this backend is achieved by not unregistering all |
405 | watchers for a file descriptor until it has been closed, if possible, |
414 | watchers for a file descriptor until it has been closed, if possible, |
406 | i.e. keep at least one watcher active per fd at all times. Stopping and |
415 | i.e. keep at least one watcher active per fd at all times. Stopping and |
407 | starting a watcher (without re-setting it) also usually doesn't cause |
416 | starting a watcher (without re-setting it) also usually doesn't cause |
408 | extra overhead. |
417 | extra overhead. A fork can both result in spurious notifications as well |
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418 | as in libev having to destroy and recreate the epoll object, which can |
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419 | take considerable time and thus should be avoided. |
409 | |
420 | |
410 | While nominally embeddable in other event loops, this feature is broken in |
421 | While nominally embeddable in other event loops, this feature is broken in |
411 | all kernel versions tested so far. |
422 | all kernel versions tested so far. |
412 | |
423 | |
413 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
424 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
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… | |
428 | |
439 | |
429 | It scales in the same way as the epoll backend, but the interface to the |
440 | It scales in the same way as the epoll backend, but the interface to the |
430 | kernel is more efficient (which says nothing about its actual speed, of |
441 | kernel is more efficient (which says nothing about its actual speed, of |
431 | course). While stopping, setting and starting an I/O watcher does never |
442 | course). While stopping, setting and starting an I/O watcher does never |
432 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
443 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
433 | two event changes per incident. Support for C<fork ()> is very bad and it |
444 | two event changes per incident. Support for C<fork ()> is very bad (but |
434 | drops fds silently in similarly hard-to-detect cases. |
445 | sane, unlike epoll) and it drops fds silently in similarly hard-to-detect |
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446 | cases |
435 | |
447 | |
436 | This backend usually performs well under most conditions. |
448 | This backend usually performs well under most conditions. |
437 | |
449 | |
438 | While nominally embeddable in other event loops, this doesn't work |
450 | While nominally embeddable in other event loops, this doesn't work |
439 | everywhere, so you might need to test for this. And since it is broken |
451 | everywhere, so you might need to test for this. And since it is broken |
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468 | might perform better. |
480 | might perform better. |
469 | |
481 | |
470 | On the positive side, with the exception of the spurious readiness |
482 | On the positive side, with the exception of the spurious readiness |
471 | notifications, this backend actually performed fully to specification |
483 | notifications, this backend actually performed fully to specification |
472 | in all tests and is fully embeddable, which is a rare feat among the |
484 | in all tests and is fully embeddable, which is a rare feat among the |
473 | OS-specific backends. |
485 | OS-specific backends (I vastly prefer correctness over speed hacks). |
474 | |
486 | |
475 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
487 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
476 | C<EVBACKEND_POLL>. |
488 | C<EVBACKEND_POLL>. |
477 | |
489 | |
478 | =item C<EVBACKEND_ALL> |
490 | =item C<EVBACKEND_ALL> |
… | |
… | |
531 | responsibility to either stop all watchers cleanly yourself I<before> |
543 | responsibility to either stop all watchers cleanly yourself I<before> |
532 | calling this function, or cope with the fact afterwards (which is usually |
544 | calling this function, or cope with the fact afterwards (which is usually |
533 | the easiest thing, you can just ignore the watchers and/or C<free ()> them |
545 | the easiest thing, you can just ignore the watchers and/or C<free ()> them |
534 | for example). |
546 | for example). |
535 | |
547 | |
536 | Note that certain global state, such as signal state, will not be freed by |
548 | Note that certain global state, such as signal state (and installed signal |
537 | this function, and related watchers (such as signal and child watchers) |
549 | handlers), will not be freed by this function, and related watchers (such |
538 | would need to be stopped manually. |
550 | as signal and child watchers) would need to be stopped manually. |
539 | |
551 | |
540 | In general it is not advisable to call this function except in the |
552 | In general it is not advisable to call this function except in the |
541 | rare occasion where you really need to free e.g. the signal handling |
553 | rare occasion where you really need to free e.g. the signal handling |
542 | pipe fds. If you need dynamically allocated loops it is better to use |
554 | pipe fds. If you need dynamically allocated loops it is better to use |
543 | C<ev_loop_new> and C<ev_loop_destroy>). |
555 | C<ev_loop_new> and C<ev_loop_destroy>). |
… | |
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1043 | The default priority used by watchers when no priority has been set is |
1055 | The default priority used by watchers when no priority has been set is |
1044 | always C<0>, which is supposed to not be too high and not be too low :). |
1056 | always C<0>, which is supposed to not be too high and not be too low :). |
1045 | |
1057 | |
1046 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1058 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1047 | fine, as long as you do not mind that the priority value you query might |
1059 | fine, as long as you do not mind that the priority value you query might |
1048 | or might not have been adjusted to be within valid range. |
1060 | or might not have been clamped to the valid range. |
1049 | |
1061 | |
1050 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1062 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1051 | |
1063 | |
1052 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1064 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1053 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1065 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
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2958 | =item D |
2970 | =item D |
2959 | |
2971 | |
2960 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2972 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2961 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2973 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2962 | |
2974 | |
|
|
2975 | =item Ocaml |
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2976 | |
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2977 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
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2978 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
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2979 | |
2963 | =back |
2980 | =back |
2964 | |
2981 | |
2965 | |
2982 | |
2966 | =head1 MACRO MAGIC |
2983 | =head1 MACRO MAGIC |
2967 | |
2984 | |