… | |
… | |
10 | |
10 | |
11 | // a single header file is required |
11 | // a single header file is required |
12 | #include <ev.h> |
12 | #include <ev.h> |
13 | |
13 | |
14 | // every watcher type has its own typedef'd struct |
14 | // every watcher type has its own typedef'd struct |
15 | // with the name ev_<type> |
15 | // with the name ev_TYPE |
16 | ev_io stdin_watcher; |
16 | ev_io stdin_watcher; |
17 | ev_timer timeout_watcher; |
17 | ev_timer timeout_watcher; |
18 | |
18 | |
19 | // all watcher callbacks have a similar signature |
19 | // all watcher callbacks have a similar signature |
20 | // this callback is called when data is readable on stdin |
20 | // this callback is called when data is readable on stdin |
… | |
… | |
276 | |
276 | |
277 | =back |
277 | =back |
278 | |
278 | |
279 | =head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
279 | =head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
280 | |
280 | |
281 | An event loop is described by a C<ev_loop *>. The library knows two |
281 | An event loop is described by a C<struct ev_loop *> (the C<struct> |
282 | types of such loops, the I<default> loop, which supports signals and child |
282 | is I<not> optional in this case, as there is also an C<ev_loop> |
283 | events, and dynamically created loops which do not. |
283 | I<function>). |
|
|
284 | |
|
|
285 | The library knows two types of such loops, the I<default> loop, which |
|
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286 | supports signals and child events, and dynamically created loops which do |
|
|
287 | not. |
284 | |
288 | |
285 | =over 4 |
289 | =over 4 |
286 | |
290 | |
287 | =item struct ev_loop *ev_default_loop (unsigned int flags) |
291 | =item struct ev_loop *ev_default_loop (unsigned int flags) |
288 | |
292 | |
… | |
… | |
294 | 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 |
295 | function. |
299 | function. |
296 | |
300 | |
297 | 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 |
298 | 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, |
299 | as loops cannot bes hared easily between threads anyway). |
303 | as loops cannot be shared easily between threads anyway). |
300 | |
304 | |
301 | 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 |
302 | 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 |
303 | 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 |
304 | 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 |
… | |
… | |
380 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
384 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
381 | |
385 | |
382 | 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, |
383 | but it scales phenomenally better. While poll and select usually scale |
387 | but it scales phenomenally better. While poll and select usually scale |
384 | 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), |
385 | 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). |
386 | of shortcomings, such as silently dropping events in some hard-to-detect |
390 | |
387 | cases and requiring a system call per fd change, no fork support and bad |
391 | The epoll mechanism deserves honorable mention as the most misdesigned |
388 | support for dup. |
392 | of the more advanced event mechanisms: mere annoyances include silently |
|
|
393 | dropping file descriptors, requiring a system call per change per file |
|
|
394 | descriptor (and unnecessary guessing of parameters), problems with dup and |
|
|
395 | so on. The biggest issue is fork races, however - if a program forks then |
|
|
396 | I<both> parent and child process have to recreate the epoll set, which can |
|
|
397 | take considerable time (one syscall per file descriptor) and is of course |
|
|
398 | hard to detect. |
|
|
399 | |
|
|
400 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
|
|
401 | of course I<doesn't>, and epoll just loves to report events for totally |
|
|
402 | I<different> file descriptors (even already closed ones, so one cannot |
|
|
403 | even remove them from the set) than registered in the set (especially |
|
|
404 | on SMP systems). Libev tries to counter these spurious notifications by |
|
|
405 | employing an additional generation counter and comparing that against the |
|
|
406 | events to filter out spurious ones, recreating the set when required. |
389 | |
407 | |
390 | 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 |
391 | 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 |
392 | (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 |
393 | 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 |
394 | very well if you register events for both fds. |
412 | file descriptors might not work very well if you register events for both |
395 | |
413 | file descriptors. |
396 | Please note that epoll sometimes generates spurious notifications, so you |
|
|
397 | need to use non-blocking I/O or other means to avoid blocking when no data |
|
|
398 | (or space) is available. |
|
|
399 | |
414 | |
400 | Best performance from this backend is achieved by not unregistering all |
415 | Best performance from this backend is achieved by not unregistering all |
401 | 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, |
402 | 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 |
403 | 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 |
404 | extra overhead. |
419 | extra overhead. A fork can both result in spurious notifications as well |
|
|
420 | as in libev having to destroy and recreate the epoll object, which can |
|
|
421 | take considerable time and thus should be avoided. |
405 | |
422 | |
406 | While nominally embeddable in other event loops, this feature is broken in |
423 | While nominally embeddable in other event loops, this feature is broken in |
407 | all kernel versions tested so far. |
424 | all kernel versions tested so far. |
408 | |
425 | |
409 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
426 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
410 | C<EVBACKEND_POLL>. |
427 | C<EVBACKEND_POLL>. |
411 | |
428 | |
412 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
429 | =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
413 | |
430 | |
414 | Kqueue deserves special mention, as at the time of this writing, it was |
431 | Kqueue deserves special mention, as at the time of this writing, it |
415 | broken on all BSDs except NetBSD (usually it doesn't work reliably with |
432 | was broken on all BSDs except NetBSD (usually it doesn't work reliably |
416 | anything but sockets and pipes, except on Darwin, where of course it's |
433 | with anything but sockets and pipes, except on Darwin, where of course |
417 | completely useless). For this reason it's not being "auto-detected" unless |
434 | it's completely useless). Unlike epoll, however, whose brokenness |
418 | you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or |
435 | is by design, these kqueue bugs can (and eventually will) be fixed |
419 | libev was compiled on a known-to-be-good (-enough) system like NetBSD. |
436 | without API changes to existing programs. For this reason it's not being |
|
|
437 | "auto-detected" unless you explicitly specify it in the flags (i.e. using |
|
|
438 | C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) |
|
|
439 | system like NetBSD. |
420 | |
440 | |
421 | You still can embed kqueue into a normal poll or select backend and use it |
441 | You still can embed kqueue into a normal poll or select backend and use it |
422 | only for sockets (after having made sure that sockets work with kqueue on |
442 | only for sockets (after having made sure that sockets work with kqueue on |
423 | the target platform). See C<ev_embed> watchers for more info. |
443 | the target platform). See C<ev_embed> watchers for more info. |
424 | |
444 | |
425 | It scales in the same way as the epoll backend, but the interface to the |
445 | It scales in the same way as the epoll backend, but the interface to the |
426 | kernel is more efficient (which says nothing about its actual speed, of |
446 | kernel is more efficient (which says nothing about its actual speed, of |
427 | course). While stopping, setting and starting an I/O watcher does never |
447 | course). While stopping, setting and starting an I/O watcher does never |
428 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
448 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
429 | two event changes per incident. Support for C<fork ()> is very bad and it |
449 | two event changes per incident. Support for C<fork ()> is very bad (but |
430 | drops fds silently in similarly hard-to-detect cases. |
450 | sane, unlike epoll) and it drops fds silently in similarly hard-to-detect |
|
|
451 | cases |
431 | |
452 | |
432 | This backend usually performs well under most conditions. |
453 | This backend usually performs well under most conditions. |
433 | |
454 | |
434 | While nominally embeddable in other event loops, this doesn't work |
455 | While nominally embeddable in other event loops, this doesn't work |
435 | everywhere, so you might need to test for this. And since it is broken |
456 | everywhere, so you might need to test for this. And since it is broken |
… | |
… | |
464 | might perform better. |
485 | might perform better. |
465 | |
486 | |
466 | On the positive side, with the exception of the spurious readiness |
487 | On the positive side, with the exception of the spurious readiness |
467 | notifications, this backend actually performed fully to specification |
488 | notifications, this backend actually performed fully to specification |
468 | in all tests and is fully embeddable, which is a rare feat among the |
489 | in all tests and is fully embeddable, which is a rare feat among the |
469 | OS-specific backends. |
490 | OS-specific backends (I vastly prefer correctness over speed hacks). |
470 | |
491 | |
471 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
492 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
472 | C<EVBACKEND_POLL>. |
493 | C<EVBACKEND_POLL>. |
473 | |
494 | |
474 | =item C<EVBACKEND_ALL> |
495 | =item C<EVBACKEND_ALL> |
… | |
… | |
527 | responsibility to either stop all watchers cleanly yourself I<before> |
548 | responsibility to either stop all watchers cleanly yourself I<before> |
528 | calling this function, or cope with the fact afterwards (which is usually |
549 | calling this function, or cope with the fact afterwards (which is usually |
529 | the easiest thing, you can just ignore the watchers and/or C<free ()> them |
550 | the easiest thing, you can just ignore the watchers and/or C<free ()> them |
530 | for example). |
551 | for example). |
531 | |
552 | |
532 | Note that certain global state, such as signal state, will not be freed by |
553 | Note that certain global state, such as signal state (and installed signal |
533 | this function, and related watchers (such as signal and child watchers) |
554 | handlers), will not be freed by this function, and related watchers (such |
534 | would need to be stopped manually. |
555 | as signal and child watchers) would need to be stopped manually. |
535 | |
556 | |
536 | In general it is not advisable to call this function except in the |
557 | In general it is not advisable to call this function except in the |
537 | rare occasion where you really need to free e.g. the signal handling |
558 | rare occasion where you really need to free e.g. the signal handling |
538 | pipe fds. If you need dynamically allocated loops it is better to use |
559 | pipe fds. If you need dynamically allocated loops it is better to use |
539 | C<ev_loop_new> and C<ev_loop_destroy>). |
560 | C<ev_loop_new> and C<ev_loop_destroy>). |
… | |
… | |
631 | the loop. |
652 | the loop. |
632 | |
653 | |
633 | A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
654 | A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
634 | necessary) and will handle those and any already outstanding ones. It |
655 | necessary) and will handle those and any already outstanding ones. It |
635 | will block your process until at least one new event arrives (which could |
656 | will block your process until at least one new event arrives (which could |
636 | be an event internal to libev itself, so there is no guarentee that a |
657 | be an event internal to libev itself, so there is no guarantee that a |
637 | user-registered callback will be called), and will return after one |
658 | user-registered callback will be called), and will return after one |
638 | iteration of the loop. |
659 | iteration of the loop. |
639 | |
660 | |
640 | This is useful if you are waiting for some external event in conjunction |
661 | This is useful if you are waiting for some external event in conjunction |
641 | with something not expressible using other libev watchers (i.e. "roll your |
662 | with something not expressible using other libev watchers (i.e. "roll your |
… | |
… | |
768 | they fire on, say, one-second boundaries only. |
789 | they fire on, say, one-second boundaries only. |
769 | |
790 | |
770 | =item ev_loop_verify (loop) |
791 | =item ev_loop_verify (loop) |
771 | |
792 | |
772 | This function only does something when C<EV_VERIFY> support has been |
793 | This function only does something when C<EV_VERIFY> support has been |
773 | compiled in. which is the default for non-minimal builds. It tries to go |
794 | compiled in, which is the default for non-minimal builds. It tries to go |
774 | through all internal structures and checks them for validity. If anything |
795 | through all internal structures and checks them for validity. If anything |
775 | is found to be inconsistent, it will print an error message to standard |
796 | is found to be inconsistent, it will print an error message to standard |
776 | error and call C<abort ()>. |
797 | error and call C<abort ()>. |
777 | |
798 | |
778 | This can be used to catch bugs inside libev itself: under normal |
799 | This can be used to catch bugs inside libev itself: under normal |
… | |
… | |
781 | |
802 | |
782 | =back |
803 | =back |
783 | |
804 | |
784 | |
805 | |
785 | =head1 ANATOMY OF A WATCHER |
806 | =head1 ANATOMY OF A WATCHER |
|
|
807 | |
|
|
808 | In the following description, uppercase C<TYPE> in names stands for the |
|
|
809 | watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer |
|
|
810 | watchers and C<ev_io_start> for I/O watchers. |
786 | |
811 | |
787 | A watcher is a structure that you create and register to record your |
812 | A watcher is a structure that you create and register to record your |
788 | interest in some event. For instance, if you want to wait for STDIN to |
813 | interest in some event. For instance, if you want to wait for STDIN to |
789 | become readable, you would create an C<ev_io> watcher for that: |
814 | become readable, you would create an C<ev_io> watcher for that: |
790 | |
815 | |
… | |
… | |
793 | ev_io_stop (w); |
818 | ev_io_stop (w); |
794 | ev_unloop (loop, EVUNLOOP_ALL); |
819 | ev_unloop (loop, EVUNLOOP_ALL); |
795 | } |
820 | } |
796 | |
821 | |
797 | struct ev_loop *loop = ev_default_loop (0); |
822 | struct ev_loop *loop = ev_default_loop (0); |
|
|
823 | |
798 | ev_io stdin_watcher; |
824 | ev_io stdin_watcher; |
|
|
825 | |
799 | ev_init (&stdin_watcher, my_cb); |
826 | ev_init (&stdin_watcher, my_cb); |
800 | ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
827 | ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
801 | ev_io_start (loop, &stdin_watcher); |
828 | ev_io_start (loop, &stdin_watcher); |
|
|
829 | |
802 | ev_loop (loop, 0); |
830 | ev_loop (loop, 0); |
803 | |
831 | |
804 | As you can see, you are responsible for allocating the memory for your |
832 | As you can see, you are responsible for allocating the memory for your |
805 | watcher structures (and it is usually a bad idea to do this on the stack, |
833 | watcher structures (and it is I<usually> a bad idea to do this on the |
806 | although this can sometimes be quite valid). |
834 | stack). |
|
|
835 | |
|
|
836 | Each watcher has an associated watcher structure (called C<struct ev_TYPE> |
|
|
837 | or simply C<ev_TYPE>, as typedefs are provided for all watcher structs). |
807 | |
838 | |
808 | Each watcher structure must be initialised by a call to C<ev_init |
839 | Each watcher structure must be initialised by a call to C<ev_init |
809 | (watcher *, callback)>, which expects a callback to be provided. This |
840 | (watcher *, callback)>, which expects a callback to be provided. This |
810 | callback gets invoked each time the event occurs (or, in the case of I/O |
841 | callback gets invoked each time the event occurs (or, in the case of I/O |
811 | watchers, each time the event loop detects that the file descriptor given |
842 | watchers, each time the event loop detects that the file descriptor given |
812 | is readable and/or writable). |
843 | is readable and/or writable). |
813 | |
844 | |
814 | Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
845 | Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >> |
815 | with arguments specific to this watcher type. There is also a macro |
846 | macro to configure it, with arguments specific to the watcher type. There |
816 | to combine initialisation and setting in one call: C<< ev_<type>_init |
847 | is also a macro to combine initialisation and setting in one call: C<< |
817 | (watcher *, callback, ...) >>. |
848 | ev_TYPE_init (watcher *, callback, ...) >>. |
818 | |
849 | |
819 | To make the watcher actually watch out for events, you have to start it |
850 | To make the watcher actually watch out for events, you have to start it |
820 | with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
851 | with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher |
821 | *) >>), and you can stop watching for events at any time by calling the |
852 | *) >>), and you can stop watching for events at any time by calling the |
822 | corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
853 | corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>. |
823 | |
854 | |
824 | As long as your watcher is active (has been started but not stopped) you |
855 | As long as your watcher is active (has been started but not stopped) you |
825 | must not touch the values stored in it. Most specifically you must never |
856 | must not touch the values stored in it. Most specifically you must never |
826 | reinitialise it or call its C<set> macro. |
857 | reinitialise it or call its C<ev_TYPE_set> macro. |
827 | |
858 | |
828 | Each and every callback receives the event loop pointer as first, the |
859 | Each and every callback receives the event loop pointer as first, the |
829 | registered watcher structure as second, and a bitset of received events as |
860 | registered watcher structure as second, and a bitset of received events as |
830 | third argument. |
861 | third argument. |
831 | |
862 | |
… | |
… | |
912 | |
943 | |
913 | =back |
944 | =back |
914 | |
945 | |
915 | =head2 GENERIC WATCHER FUNCTIONS |
946 | =head2 GENERIC WATCHER FUNCTIONS |
916 | |
947 | |
917 | In the following description, C<TYPE> stands for the watcher type, |
|
|
918 | e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers. |
|
|
919 | |
|
|
920 | =over 4 |
948 | =over 4 |
921 | |
949 | |
922 | =item C<ev_init> (ev_TYPE *watcher, callback) |
950 | =item C<ev_init> (ev_TYPE *watcher, callback) |
923 | |
951 | |
924 | This macro initialises the generic portion of a watcher. The contents |
952 | This macro initialises the generic portion of a watcher. The contents |
… | |
… | |
1032 | The default priority used by watchers when no priority has been set is |
1060 | The default priority used by watchers when no priority has been set is |
1033 | always C<0>, which is supposed to not be too high and not be too low :). |
1061 | always C<0>, which is supposed to not be too high and not be too low :). |
1034 | |
1062 | |
1035 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1063 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1036 | fine, as long as you do not mind that the priority value you query might |
1064 | fine, as long as you do not mind that the priority value you query might |
1037 | or might not have been adjusted to be within valid range. |
1065 | or might not have been clamped to the valid range. |
1038 | |
1066 | |
1039 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1067 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1040 | |
1068 | |
1041 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1069 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1042 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1070 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
… | |
… | |
1426 | |
1454 | |
1427 | Changing the timeout is trivial as well (if it isn't hard-coded in the |
1455 | Changing the timeout is trivial as well (if it isn't hard-coded in the |
1428 | callback :) - just change the timeout and invoke the callback, which will |
1456 | callback :) - just change the timeout and invoke the callback, which will |
1429 | fix things for you. |
1457 | fix things for you. |
1430 | |
1458 | |
1431 | =item 4. Whee, use a double-linked list for your timeouts. |
1459 | =item 4. Wee, just use a double-linked list for your timeouts. |
1432 | |
1460 | |
1433 | If there is not one request, but many thousands, all employing some kind |
1461 | If there is not one request, but many thousands (millions...), all |
1434 | of timeout with the same timeout value, then one can do even better: |
1462 | employing some kind of timeout with the same timeout value, then one can |
|
|
1463 | do even better: |
1435 | |
1464 | |
1436 | When starting the timeout, calculate the timeout value and put the timeout |
1465 | When starting the timeout, calculate the timeout value and put the timeout |
1437 | at the I<end> of the list. |
1466 | at the I<end> of the list. |
1438 | |
1467 | |
1439 | Then use an C<ev_timer> to fire when the timeout at the I<beginning> of |
1468 | Then use an C<ev_timer> to fire when the timeout at the I<beginning> of |
… | |
… | |
1448 | complication, and having to use a constant timeout. The constant timeout |
1477 | complication, and having to use a constant timeout. The constant timeout |
1449 | ensures that the list stays sorted. |
1478 | ensures that the list stays sorted. |
1450 | |
1479 | |
1451 | =back |
1480 | =back |
1452 | |
1481 | |
1453 | So what method is the best? |
1482 | So which method the best? |
1454 | |
1483 | |
1455 | The method #2 is a simple no-brain-required solution that is adequate in |
1484 | Method #2 is a simple no-brain-required solution that is adequate in most |
1456 | most situations. Method #3 requires a bit more thinking, but handles many |
1485 | situations. Method #3 requires a bit more thinking, but handles many cases |
1457 | cases better, and isn't very complicated either. In most case, choosing |
1486 | better, and isn't very complicated either. In most case, choosing either |
1458 | either one is fine. |
1487 | one is fine, with #3 being better in typical situations. |
1459 | |
1488 | |
1460 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1489 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1461 | rather complicated, but extremely efficient, something that really pays |
1490 | rather complicated, but extremely efficient, something that really pays |
1462 | off after the first or so million of active timers, i.e. it's usually |
1491 | off after the first million or so of active timers, i.e. it's usually |
1463 | overkill :) |
1492 | overkill :) |
1464 | |
1493 | |
1465 | =head3 The special problem of time updates |
1494 | =head3 The special problem of time updates |
1466 | |
1495 | |
1467 | Establishing the current time is a costly operation (it usually takes at |
1496 | Establishing the current time is a costly operation (it usually takes at |
… | |
… | |
1898 | |
1927 | |
1899 | |
1928 | |
1900 | =head2 C<ev_stat> - did the file attributes just change? |
1929 | =head2 C<ev_stat> - did the file attributes just change? |
1901 | |
1930 | |
1902 | This watches a file system path for attribute changes. That is, it calls |
1931 | This watches a file system path for attribute changes. That is, it calls |
1903 | C<stat> regularly (or when the OS says it changed) and sees if it changed |
1932 | C<stat> on that path in regular intervals (or when the OS says it changed) |
1904 | compared to the last time, invoking the callback if it did. |
1933 | and sees if it changed compared to the last time, invoking the callback if |
|
|
1934 | it did. |
1905 | |
1935 | |
1906 | The path does not need to exist: changing from "path exists" to "path does |
1936 | The path does not need to exist: changing from "path exists" to "path does |
1907 | not exist" is a status change like any other. The condition "path does |
1937 | not exist" is a status change like any other. The condition "path does not |
1908 | not exist" is signified by the C<st_nlink> field being zero (which is |
1938 | exist" (or more correctly "path cannot be stat'ed") is signified by the |
1909 | otherwise always forced to be at least one) and all the other fields of |
1939 | C<st_nlink> field being zero (which is otherwise always forced to be at |
1910 | the stat buffer having unspecified contents. |
1940 | least one) and all the other fields of the stat buffer having unspecified |
|
|
1941 | contents. |
1911 | |
1942 | |
1912 | The path I<should> be absolute and I<must not> end in a slash. If it is |
1943 | The path I<must not> end in a slash or contain special components such as |
|
|
1944 | C<.> or C<..>. The path I<should> be absolute: If it is relative and |
1913 | relative and your working directory changes, the behaviour is undefined. |
1945 | your working directory changes, then the behaviour is undefined. |
1914 | |
1946 | |
1915 | Since there is no standard kernel interface to do this, the portable |
1947 | Since there is no portable change notification interface available, the |
1916 | implementation simply calls C<stat (2)> regularly on the path to see if |
1948 | portable implementation simply calls C<stat(2)> regularly on the path |
1917 | it changed somehow. You can specify a recommended polling interval for |
1949 | to see if it changed somehow. You can specify a recommended polling |
1918 | this case. If you specify a polling interval of C<0> (highly recommended!) |
1950 | interval for this case. If you specify a polling interval of C<0> (highly |
1919 | then a I<suitable, unspecified default> value will be used (which |
1951 | recommended!) then a I<suitable, unspecified default> value will be used |
1920 | you can expect to be around five seconds, although this might change |
1952 | (which you can expect to be around five seconds, although this might |
1921 | dynamically). Libev will also impose a minimum interval which is currently |
1953 | change dynamically). Libev will also impose a minimum interval which is |
1922 | around C<0.1>, but thats usually overkill. |
1954 | currently around C<0.1>, but that's usually overkill. |
1923 | |
1955 | |
1924 | This watcher type is not meant for massive numbers of stat watchers, |
1956 | This watcher type is not meant for massive numbers of stat watchers, |
1925 | as even with OS-supported change notifications, this can be |
1957 | as even with OS-supported change notifications, this can be |
1926 | resource-intensive. |
1958 | resource-intensive. |
1927 | |
1959 | |
1928 | At the time of this writing, the only OS-specific interface implemented |
1960 | At the time of this writing, the only OS-specific interface implemented |
1929 | is the Linux inotify interface (implementing kqueue support is left as |
1961 | is the Linux inotify interface (implementing kqueue support is left as an |
1930 | an exercise for the reader. Note, however, that the author sees no way |
1962 | exercise for the reader. Note, however, that the author sees no way of |
1931 | of implementing C<ev_stat> semantics with kqueue). |
1963 | implementing C<ev_stat> semantics with kqueue, except as a hint). |
1932 | |
1964 | |
1933 | =head3 ABI Issues (Largefile Support) |
1965 | =head3 ABI Issues (Largefile Support) |
1934 | |
1966 | |
1935 | Libev by default (unless the user overrides this) uses the default |
1967 | Libev by default (unless the user overrides this) uses the default |
1936 | compilation environment, which means that on systems with large file |
1968 | compilation environment, which means that on systems with large file |
1937 | support disabled by default, you get the 32 bit version of the stat |
1969 | support disabled by default, you get the 32 bit version of the stat |
1938 | structure. When using the library from programs that change the ABI to |
1970 | structure. When using the library from programs that change the ABI to |
1939 | use 64 bit file offsets the programs will fail. In that case you have to |
1971 | use 64 bit file offsets the programs will fail. In that case you have to |
1940 | compile libev with the same flags to get binary compatibility. This is |
1972 | compile libev with the same flags to get binary compatibility. This is |
1941 | obviously the case with any flags that change the ABI, but the problem is |
1973 | obviously the case with any flags that change the ABI, but the problem is |
1942 | most noticeably disabled with ev_stat and large file support. |
1974 | most noticeably displayed with ev_stat and large file support. |
1943 | |
1975 | |
1944 | The solution for this is to lobby your distribution maker to make large |
1976 | The solution for this is to lobby your distribution maker to make large |
1945 | file interfaces available by default (as e.g. FreeBSD does) and not |
1977 | file interfaces available by default (as e.g. FreeBSD does) and not |
1946 | optional. Libev cannot simply switch on large file support because it has |
1978 | optional. Libev cannot simply switch on large file support because it has |
1947 | to exchange stat structures with application programs compiled using the |
1979 | to exchange stat structures with application programs compiled using the |
1948 | default compilation environment. |
1980 | default compilation environment. |
1949 | |
1981 | |
1950 | =head3 Inotify and Kqueue |
1982 | =head3 Inotify and Kqueue |
1951 | |
1983 | |
1952 | When C<inotify (7)> support has been compiled into libev (generally |
1984 | When C<inotify (7)> support has been compiled into libev and present at |
1953 | only available with Linux 2.6.25 or above due to bugs in earlier |
1985 | runtime, it will be used to speed up change detection where possible. The |
1954 | implementations) and present at runtime, it will be used to speed up |
1986 | inotify descriptor will be created lazily when the first C<ev_stat> |
1955 | change detection where possible. The inotify descriptor will be created |
1987 | watcher is being started. |
1956 | lazily when the first C<ev_stat> watcher is being started. |
|
|
1957 | |
1988 | |
1958 | Inotify presence does not change the semantics of C<ev_stat> watchers |
1989 | Inotify presence does not change the semantics of C<ev_stat> watchers |
1959 | except that changes might be detected earlier, and in some cases, to avoid |
1990 | except that changes might be detected earlier, and in some cases, to avoid |
1960 | making regular C<stat> calls. Even in the presence of inotify support |
1991 | making regular C<stat> calls. Even in the presence of inotify support |
1961 | there are many cases where libev has to resort to regular C<stat> polling, |
1992 | there are many cases where libev has to resort to regular C<stat> polling, |
1962 | but as long as the path exists, libev usually gets away without polling. |
1993 | but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too |
|
|
1994 | many bugs), the path exists (i.e. stat succeeds), and the path resides on |
|
|
1995 | a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and |
|
|
1996 | xfs are fully working) libev usually gets away without polling. |
1963 | |
1997 | |
1964 | There is no support for kqueue, as apparently it cannot be used to |
1998 | There is no support for kqueue, as apparently it cannot be used to |
1965 | implement this functionality, due to the requirement of having a file |
1999 | implement this functionality, due to the requirement of having a file |
1966 | descriptor open on the object at all times, and detecting renames, unlinks |
2000 | descriptor open on the object at all times, and detecting renames, unlinks |
1967 | etc. is difficult. |
2001 | etc. is difficult. |
1968 | |
2002 | |
1969 | =head3 The special problem of stat time resolution |
2003 | =head3 The special problem of stat time resolution |
1970 | |
2004 | |
1971 | The C<stat ()> system call only supports full-second resolution portably, and |
2005 | The C<stat ()> system call only supports full-second resolution portably, |
1972 | even on systems where the resolution is higher, most file systems still |
2006 | and even on systems where the resolution is higher, most file systems |
1973 | only support whole seconds. |
2007 | still only support whole seconds. |
1974 | |
2008 | |
1975 | That means that, if the time is the only thing that changes, you can |
2009 | That means that, if the time is the only thing that changes, you can |
1976 | easily miss updates: on the first update, C<ev_stat> detects a change and |
2010 | easily miss updates: on the first update, C<ev_stat> detects a change and |
1977 | calls your callback, which does something. When there is another update |
2011 | calls your callback, which does something. When there is another update |
1978 | within the same second, C<ev_stat> will be unable to detect unless the |
2012 | within the same second, C<ev_stat> will be unable to detect unless the |
… | |
… | |
2617 | =over 4 |
2651 | =over 4 |
2618 | |
2652 | |
2619 | =item ev_async_init (ev_async *, callback) |
2653 | =item ev_async_init (ev_async *, callback) |
2620 | |
2654 | |
2621 | Initialises and configures the async watcher - it has no parameters of any |
2655 | Initialises and configures the async watcher - it has no parameters of any |
2622 | kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless, |
2656 | kind. There is a C<ev_async_set> macro, but using it is utterly pointless, |
2623 | trust me. |
2657 | trust me. |
2624 | |
2658 | |
2625 | =item ev_async_send (loop, ev_async *) |
2659 | =item ev_async_send (loop, ev_async *) |
2626 | |
2660 | |
2627 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
2661 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
… | |
… | |
2946 | =item D |
2980 | =item D |
2947 | |
2981 | |
2948 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2982 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2949 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2983 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2950 | |
2984 | |
|
|
2985 | =item Ocaml |
|
|
2986 | |
|
|
2987 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
|
|
2988 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
|
|
2989 | |
2951 | =back |
2990 | =back |
2952 | |
2991 | |
2953 | |
2992 | |
2954 | =head1 MACRO MAGIC |
2993 | =head1 MACRO MAGIC |
2955 | |
2994 | |
… | |
… | |
3055 | |
3094 | |
3056 | #define EV_STANDALONE 1 |
3095 | #define EV_STANDALONE 1 |
3057 | #include "ev.h" |
3096 | #include "ev.h" |
3058 | |
3097 | |
3059 | Both header files and implementation files can be compiled with a C++ |
3098 | Both header files and implementation files can be compiled with a C++ |
3060 | compiler (at least, thats a stated goal, and breakage will be treated |
3099 | compiler (at least, that's a stated goal, and breakage will be treated |
3061 | as a bug). |
3100 | as a bug). |
3062 | |
3101 | |
3063 | You need the following files in your source tree, or in a directory |
3102 | You need the following files in your source tree, or in a directory |
3064 | in your include path (e.g. in libev/ when using -Ilibev): |
3103 | in your include path (e.g. in libev/ when using -Ilibev): |
3065 | |
3104 | |
… | |
… | |
3537 | loop, as long as you don't confuse yourself). The only exception is that |
3576 | loop, as long as you don't confuse yourself). The only exception is that |
3538 | you must not do this from C<ev_periodic> reschedule callbacks. |
3577 | you must not do this from C<ev_periodic> reschedule callbacks. |
3539 | |
3578 | |
3540 | Care has been taken to ensure that libev does not keep local state inside |
3579 | Care has been taken to ensure that libev does not keep local state inside |
3541 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
3580 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
3542 | they do not clal any callbacks. |
3581 | they do not call any callbacks. |
3543 | |
3582 | |
3544 | =head2 COMPILER WARNINGS |
3583 | =head2 COMPILER WARNINGS |
3545 | |
3584 | |
3546 | Depending on your compiler and compiler settings, you might get no or a |
3585 | Depending on your compiler and compiler settings, you might get no or a |
3547 | lot of warnings when compiling libev code. Some people are apparently |
3586 | lot of warnings when compiling libev code. Some people are apparently |
… | |
… | |
3581 | ==2274== definitely lost: 0 bytes in 0 blocks. |
3620 | ==2274== definitely lost: 0 bytes in 0 blocks. |
3582 | ==2274== possibly lost: 0 bytes in 0 blocks. |
3621 | ==2274== possibly lost: 0 bytes in 0 blocks. |
3583 | ==2274== still reachable: 256 bytes in 1 blocks. |
3622 | ==2274== still reachable: 256 bytes in 1 blocks. |
3584 | |
3623 | |
3585 | Then there is no memory leak, just as memory accounted to global variables |
3624 | Then there is no memory leak, just as memory accounted to global variables |
3586 | is not a memleak - the memory is still being refernced, and didn't leak. |
3625 | is not a memleak - the memory is still being referenced, and didn't leak. |
3587 | |
3626 | |
3588 | Similarly, under some circumstances, valgrind might report kernel bugs |
3627 | Similarly, under some circumstances, valgrind might report kernel bugs |
3589 | as if it were a bug in libev (e.g. in realloc or in the poll backend, |
3628 | as if it were a bug in libev (e.g. in realloc or in the poll backend, |
3590 | although an acceptable workaround has been found here), or it might be |
3629 | although an acceptable workaround has been found here), or it might be |
3591 | confused. |
3630 | confused. |
… | |
… | |
3829 | =back |
3868 | =back |
3830 | |
3869 | |
3831 | |
3870 | |
3832 | =head1 AUTHOR |
3871 | =head1 AUTHOR |
3833 | |
3872 | |
3834 | Marc Lehmann <libev@schmorp.de>. |
3873 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
3835 | |
3874 | |