… | |
… | |
503 | |
503 | |
504 | =head2 IDLE WATCHERS |
504 | =head2 IDLE WATCHERS |
505 | |
505 | |
506 | $w = AnyEvent->idle (cb => <callback>); |
506 | $w = AnyEvent->idle (cb => <callback>); |
507 | |
507 | |
508 | Sometimes there is a need to do something, but it is not so important |
508 | Repeatedly invoke the callback after the process becomes idle, until |
509 | to do it instantly, but only when there is nothing better to do. This |
509 | either the watcher is destroyed or new events have been detected. |
510 | "nothing better to do" is usually defined to be "no other events need |
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|
511 | attention by the event loop". |
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512 | |
510 | |
513 | Idle watchers ideally get invoked when the event loop has nothing |
511 | Idle watchers are useful when there is a need to do something, but it |
514 | better to do, just before it would block the process to wait for new |
512 | is not so important (or wise) to do it instantly. The callback will be |
515 | events. Instead of blocking, the idle watcher is invoked. |
513 | invoked only when there is "nothing better to do", which is usually |
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|
514 | defined as "all outstanding events have been handled and no new events |
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|
515 | have been detected". That means that idle watchers ideally get invoked |
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516 | when the event loop has just polled for new events but none have been |
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517 | detected. Instead of blocking to wait for more events, the idle watchers |
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|
518 | will be invoked. |
516 | |
519 | |
517 | Most event loops unfortunately do not really support idle watchers (only |
520 | Unfortunately, most event loops do not really support idle watchers (only |
518 | EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent |
521 | EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent |
519 | will simply call the callback "from time to time". |
522 | will simply call the callback "from time to time". |
520 | |
523 | |
521 | Example: read lines from STDIN, but only process them when the |
524 | Example: read lines from STDIN, but only process them when the |
522 | program is otherwise idle: |
525 | program is otherwise idle: |
… | |
… | |
2534 | |
2537 | |
2535 | |
2538 | |
2536 | =head1 FORK |
2539 | =head1 FORK |
2537 | |
2540 | |
2538 | Most event libraries are not fork-safe. The ones who are usually are |
2541 | Most event libraries are not fork-safe. The ones who are usually are |
2539 | because they rely on inefficient but fork-safe C<select> or C<poll> |
2542 | because they rely on inefficient but fork-safe C<select> or C<poll> calls |
2540 | calls. Only L<EV> is fully fork-aware. |
2543 | - higher performance APIs such as BSD's kqueue or the dreaded Linux epoll |
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|
2544 | are usually badly thought-out hacks that are incompatible with fork in |
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|
2545 | one way or another. Only L<EV> is fully fork-aware and ensures that you |
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|
2546 | continue event-processing in both parent and child (or both, if you know |
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|
2547 | what you are doing). |
2541 | |
2548 | |
2542 | This means that, in general, you cannot fork and do event processing |
2549 | This means that, in general, you cannot fork and do event processing in |
2543 | in the child if a watcher was created before the fork (which in turn |
2550 | the child if the event library was initialised before the fork (which |
2544 | initialises the event library). |
2551 | usually happens when the first AnyEvent watcher is created, or the library |
|
|
2552 | is loaded). |
2545 | |
2553 | |
2546 | If you have to fork, you must either do so I<before> creating your first |
2554 | If you have to fork, you must either do so I<before> creating your first |
2547 | watcher OR you must not use AnyEvent at all in the child OR you must do |
2555 | watcher OR you must not use AnyEvent at all in the child OR you must do |
2548 | something completely out of the scope of AnyEvent. |
2556 | something completely out of the scope of AnyEvent. |
2549 | |
2557 | |
2550 | The problem of doing event processing in the parent I<and> the child |
2558 | The problem of doing event processing in the parent I<and> the child |
2551 | is much more complicated: even for backends that I<are> fork-aware or |
2559 | is much more complicated: even for backends that I<are> fork-aware or |
2552 | fork-safe, their behaviour is not usually what you want: fork clones all |
2560 | fork-safe, their behaviour is not usually what you want: fork clones all |
2553 | watchers, that means all timers, I/O watchers etc. are active in both |
2561 | watchers, that means all timers, I/O watchers etc. are active in both |
2554 | parent and child, which is almost never what you want. |
2562 | parent and child, which is almost never what you want. USing C<exec> |
|
|
2563 | to start worker children from some kind of manage rprocess is usually |
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|
2564 | preferred, because it is much easier and cleaner, at the expense of having |
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|
2565 | to have another binary. |
2555 | |
2566 | |
2556 | |
2567 | |
2557 | =head1 SECURITY CONSIDERATIONS |
2568 | =head1 SECURITY CONSIDERATIONS |
2558 | |
2569 | |
2559 | AnyEvent can be forced to load any event model via |
2570 | AnyEvent can be forced to load any event model via |