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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). The epoll design has a number |
390 | of shortcomings, such as silently dropping events in some hard-to-detect |
390 | of shortcomings, such as silently dropping events in some hard-to-detect |
391 | cases and requiring a system call per fd change, no fork support and bad |
391 | cases and requiring a system call per fd change, no fork support and bad |
392 | support for dup. |
392 | support for dup. |
393 | |
393 | |
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394 | Epoll is also notoriously buggy - embedding epoll fds should work, but |
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395 | of course doesn't, and epoll just loves to report events for totally |
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396 | I<different> file descriptors (even already closed ones) than registered |
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397 | in the set (especially on SMP systems). Libev tries to counter these |
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398 | spurious notifications by employing an additional generation counter and |
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399 | comparing that against the events to filter out spurious ones. |
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400 | |
394 | While stopping, setting and starting an I/O watcher in the same iteration |
401 | 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 |
402 | 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 |
403 | (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 |
404 | best to avoid that. Also, C<dup ()>'ed file descriptors might not work |
398 | very well if you register events for both fds. |
405 | very well if you register events for both fds. |
399 | |
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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 | |
406 | |
404 | Best performance from this backend is achieved by not unregistering all |
407 | Best performance from this backend is achieved by not unregistering all |
405 | watchers for a file descriptor until it has been closed, if possible, |
408 | 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 |
409 | 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 |
410 | starting a watcher (without re-setting it) also usually doesn't cause |
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531 | responsibility to either stop all watchers cleanly yourself I<before> |
534 | responsibility to either stop all watchers cleanly yourself I<before> |
532 | calling this function, or cope with the fact afterwards (which is usually |
535 | 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 |
536 | the easiest thing, you can just ignore the watchers and/or C<free ()> them |
534 | for example). |
537 | for example). |
535 | |
538 | |
536 | Note that certain global state, such as signal state, will not be freed by |
539 | Note that certain global state, such as signal state (and installed signal |
537 | this function, and related watchers (such as signal and child watchers) |
540 | handlers), will not be freed by this function, and related watchers (such |
538 | would need to be stopped manually. |
541 | as signal and child watchers) would need to be stopped manually. |
539 | |
542 | |
540 | In general it is not advisable to call this function except in the |
543 | 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 |
544 | 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 |
545 | pipe fds. If you need dynamically allocated loops it is better to use |
543 | C<ev_loop_new> and C<ev_loop_destroy>). |
546 | C<ev_loop_new> and C<ev_loop_destroy>). |