… | |
… | |
58 | ev_timer_start (loop, &timeout_watcher); |
58 | ev_timer_start (loop, &timeout_watcher); |
59 | |
59 | |
60 | // now wait for events to arrive |
60 | // now wait for events to arrive |
61 | ev_run (loop, 0); |
61 | ev_run (loop, 0); |
62 | |
62 | |
63 | // unloop was called, so exit |
63 | // break was called, so exit |
64 | return 0; |
64 | return 0; |
65 | } |
65 | } |
66 | |
66 | |
67 | =head1 ABOUT THIS DOCUMENT |
67 | =head1 ABOUT THIS DOCUMENT |
68 | |
68 | |
… | |
… | |
178 | you actually want to know. Also interesting is the combination of |
178 | you actually want to know. Also interesting is the combination of |
179 | C<ev_update_now> and C<ev_now>. |
179 | C<ev_update_now> and C<ev_now>. |
180 | |
180 | |
181 | =item ev_sleep (ev_tstamp interval) |
181 | =item ev_sleep (ev_tstamp interval) |
182 | |
182 | |
183 | Sleep for the given interval: The current thread will be blocked until |
183 | Sleep for the given interval: The current thread will be blocked |
184 | either it is interrupted or the given time interval has passed. Basically |
184 | until either it is interrupted or the given time interval has |
|
|
185 | passed (approximately - it might return a bit earlier even if not |
|
|
186 | interrupted). Returns immediately if C<< interval <= 0 >>. |
|
|
187 | |
185 | this is a sub-second-resolution C<sleep ()>. |
188 | Basically this is a sub-second-resolution C<sleep ()>. |
|
|
189 | |
|
|
190 | The range of the C<interval> is limited - libev only guarantees to work |
|
|
191 | with sleep times of up to one day (C<< interval <= 86400 >>). |
186 | |
192 | |
187 | =item int ev_version_major () |
193 | =item int ev_version_major () |
188 | |
194 | |
189 | =item int ev_version_minor () |
195 | =item int ev_version_minor () |
190 | |
196 | |
… | |
… | |
299 | } |
305 | } |
300 | |
306 | |
301 | ... |
307 | ... |
302 | ev_set_syserr_cb (fatal_error); |
308 | ev_set_syserr_cb (fatal_error); |
303 | |
309 | |
|
|
310 | =item ev_feed_signal (int signum) |
|
|
311 | |
|
|
312 | This function can be used to "simulate" a signal receive. It is completely |
|
|
313 | safe to call this function at any time, from any context, including signal |
|
|
314 | handlers or random threads. |
|
|
315 | |
|
|
316 | Its main use is to customise signal handling in your process, especially |
|
|
317 | in the presence of threads. For example, you could block signals |
|
|
318 | by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when |
|
|
319 | creating any loops), and in one thread, use C<sigwait> or any other |
|
|
320 | mechanism to wait for signals, then "deliver" them to libev by calling |
|
|
321 | C<ev_feed_signal>. |
|
|
322 | |
304 | =back |
323 | =back |
305 | |
324 | |
306 | =head1 FUNCTIONS CONTROLLING EVENT LOOPS |
325 | =head1 FUNCTIONS CONTROLLING EVENT LOOPS |
307 | |
326 | |
308 | An event loop is described by a C<struct ev_loop *> (the C<struct> is |
327 | An event loop is described by a C<struct ev_loop *> (the C<struct> is |
… | |
… | |
419 | |
438 | |
420 | Signalfd will not be used by default as this changes your signal mask, and |
439 | Signalfd will not be used by default as this changes your signal mask, and |
421 | there are a lot of shoddy libraries and programs (glib's threadpool for |
440 | there are a lot of shoddy libraries and programs (glib's threadpool for |
422 | example) that can't properly initialise their signal masks. |
441 | example) that can't properly initialise their signal masks. |
423 | |
442 | |
|
|
443 | =item C<EVFLAG_NOSIGMASK> |
|
|
444 | |
|
|
445 | When this flag is specified, then libev will avoid to modify the signal |
|
|
446 | mask. Specifically, this means you have to make sure signals are unblocked |
|
|
447 | when you want to receive them. |
|
|
448 | |
|
|
449 | This behaviour is useful when you want to do your own signal handling, or |
|
|
450 | want to handle signals only in specific threads and want to avoid libev |
|
|
451 | unblocking the signals. |
|
|
452 | |
|
|
453 | It's also required by POSIX in a threaded program, as libev calls |
|
|
454 | C<sigprocmask>, whose behaviour is officially unspecified. |
|
|
455 | |
|
|
456 | This flag's behaviour will become the default in future versions of libev. |
|
|
457 | |
424 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
458 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
425 | |
459 | |
426 | This is your standard select(2) backend. Not I<completely> standard, as |
460 | This is your standard select(2) backend. Not I<completely> standard, as |
427 | libev tries to roll its own fd_set with no limits on the number of fds, |
461 | libev tries to roll its own fd_set with no limits on the number of fds, |
428 | but if that fails, expect a fairly low limit on the number of fds when |
462 | but if that fails, expect a fairly low limit on the number of fds when |
… | |
… | |
455 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
489 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
456 | |
490 | |
457 | Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
491 | Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
458 | kernels). |
492 | kernels). |
459 | |
493 | |
460 | For few fds, this backend is a bit little slower than poll and select, |
494 | For few fds, this backend is a bit little slower than poll and select, but |
461 | but it scales phenomenally better. While poll and select usually scale |
495 | it scales phenomenally better. While poll and select usually scale like |
462 | like O(total_fds) where n is the total number of fds (or the highest fd), |
496 | O(total_fds) where total_fds is the total number of fds (or the highest |
463 | epoll scales either O(1) or O(active_fds). |
497 | fd), epoll scales either O(1) or O(active_fds). |
464 | |
498 | |
465 | The epoll mechanism deserves honorable mention as the most misdesigned |
499 | The epoll mechanism deserves honorable mention as the most misdesigned |
466 | of the more advanced event mechanisms: mere annoyances include silently |
500 | of the more advanced event mechanisms: mere annoyances include silently |
467 | dropping file descriptors, requiring a system call per change per file |
501 | dropping file descriptors, requiring a system call per change per file |
468 | descriptor (and unnecessary guessing of parameters), problems with dup, |
502 | descriptor (and unnecessary guessing of parameters), problems with dup, |
… | |
… | |
471 | 0.1ms) and so on. The biggest issue is fork races, however - if a program |
505 | 0.1ms) and so on. The biggest issue is fork races, however - if a program |
472 | forks then I<both> parent and child process have to recreate the epoll |
506 | forks then I<both> parent and child process have to recreate the epoll |
473 | set, which can take considerable time (one syscall per file descriptor) |
507 | set, which can take considerable time (one syscall per file descriptor) |
474 | and is of course hard to detect. |
508 | and is of course hard to detect. |
475 | |
509 | |
476 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
510 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, |
477 | of course I<doesn't>, and epoll just loves to report events for totally |
511 | but of course I<doesn't>, and epoll just loves to report events for |
478 | I<different> file descriptors (even already closed ones, so one cannot |
512 | totally I<different> file descriptors (even already closed ones, so |
479 | even remove them from the set) than registered in the set (especially |
513 | one cannot even remove them from the set) than registered in the set |
480 | on SMP systems). Libev tries to counter these spurious notifications by |
514 | (especially on SMP systems). Libev tries to counter these spurious |
481 | employing an additional generation counter and comparing that against the |
515 | notifications by employing an additional generation counter and comparing |
482 | events to filter out spurious ones, recreating the set when required. Last |
516 | that against the events to filter out spurious ones, recreating the set |
|
|
517 | when required. Epoll also erroneously rounds down timeouts, but gives you |
|
|
518 | no way to know when and by how much, so sometimes you have to busy-wait |
|
|
519 | because epoll returns immediately despite a nonzero timeout. And last |
483 | not least, it also refuses to work with some file descriptors which work |
520 | not least, it also refuses to work with some file descriptors which work |
484 | perfectly fine with C<select> (files, many character devices...). |
521 | perfectly fine with C<select> (files, many character devices...). |
485 | |
522 | |
486 | Epoll is truly the train wreck analog among event poll mechanisms. |
523 | Epoll is truly the train wreck among event poll mechanisms, a frankenpoll, |
|
|
524 | cobbled together in a hurry, no thought to design or interaction with |
|
|
525 | others. Oh, the pain, will it ever stop... |
487 | |
526 | |
488 | While stopping, setting and starting an I/O watcher in the same iteration |
527 | While stopping, setting and starting an I/O watcher in the same iteration |
489 | will result in some caching, there is still a system call per such |
528 | will result in some caching, there is still a system call per such |
490 | incident (because the same I<file descriptor> could point to a different |
529 | incident (because the same I<file descriptor> could point to a different |
491 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
530 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
… | |
… | |
557 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
596 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
558 | |
597 | |
559 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
598 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
560 | it's really slow, but it still scales very well (O(active_fds)). |
599 | it's really slow, but it still scales very well (O(active_fds)). |
561 | |
600 | |
562 | Please note that Solaris event ports can deliver a lot of spurious |
|
|
563 | notifications, so you need to use non-blocking I/O or other means to avoid |
|
|
564 | blocking when no data (or space) is available. |
|
|
565 | |
|
|
566 | While this backend scales well, it requires one system call per active |
601 | While this backend scales well, it requires one system call per active |
567 | file descriptor per loop iteration. For small and medium numbers of file |
602 | file descriptor per loop iteration. For small and medium numbers of file |
568 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
603 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
569 | might perform better. |
604 | might perform better. |
570 | |
605 | |
571 | On the positive side, with the exception of the spurious readiness |
606 | On the positive side, this backend actually performed fully to |
572 | notifications, this backend actually performed fully to specification |
|
|
573 | in all tests and is fully embeddable, which is a rare feat among the |
607 | specification in all tests and is fully embeddable, which is a rare feat |
574 | OS-specific backends (I vastly prefer correctness over speed hacks). |
608 | among the OS-specific backends (I vastly prefer correctness over speed |
|
|
609 | hacks). |
|
|
610 | |
|
|
611 | On the negative side, the interface is I<bizarre> - so bizarre that |
|
|
612 | even sun itself gets it wrong in their code examples: The event polling |
|
|
613 | function sometimes returning events to the caller even though an error |
|
|
614 | occurred, but with no indication whether it has done so or not (yes, it's |
|
|
615 | even documented that way) - deadly for edge-triggered interfaces where |
|
|
616 | you absolutely have to know whether an event occurred or not because you |
|
|
617 | have to re-arm the watcher. |
|
|
618 | |
|
|
619 | Fortunately libev seems to be able to work around these idiocies. |
575 | |
620 | |
576 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
621 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
577 | C<EVBACKEND_POLL>. |
622 | C<EVBACKEND_POLL>. |
578 | |
623 | |
579 | =item C<EVBACKEND_ALL> |
624 | =item C<EVBACKEND_ALL> |
580 | |
625 | |
581 | Try all backends (even potentially broken ones that wouldn't be tried |
626 | Try all backends (even potentially broken ones that wouldn't be tried |
582 | with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as |
627 | with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as |
583 | C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
628 | C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
584 | |
629 | |
585 | It is definitely not recommended to use this flag. |
630 | It is definitely not recommended to use this flag, use whatever |
|
|
631 | C<ev_recommended_backends ()> returns, or simply do not specify a backend |
|
|
632 | at all. |
|
|
633 | |
|
|
634 | =item C<EVBACKEND_MASK> |
|
|
635 | |
|
|
636 | Not a backend at all, but a mask to select all backend bits from a |
|
|
637 | C<flags> value, in case you want to mask out any backends from a flags |
|
|
638 | value (e.g. when modifying the C<LIBEV_FLAGS> environment variable). |
586 | |
639 | |
587 | =back |
640 | =back |
588 | |
641 | |
589 | If one or more of the backend flags are or'ed into the flags value, |
642 | If one or more of the backend flags are or'ed into the flags value, |
590 | then only these backends will be tried (in the reverse order as listed |
643 | then only these backends will be tried (in the reverse order as listed |
… | |
… | |
781 | This is useful if you are waiting for some external event in conjunction |
834 | This is useful if you are waiting for some external event in conjunction |
782 | with something not expressible using other libev watchers (i.e. "roll your |
835 | with something not expressible using other libev watchers (i.e. "roll your |
783 | own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is |
836 | own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is |
784 | usually a better approach for this kind of thing. |
837 | usually a better approach for this kind of thing. |
785 | |
838 | |
786 | Here are the gory details of what C<ev_run> does: |
839 | Here are the gory details of what C<ev_run> does (this is for your |
|
|
840 | understanding, not a guarantee that things will work exactly like this in |
|
|
841 | future versions): |
787 | |
842 | |
788 | - Increment loop depth. |
843 | - Increment loop depth. |
789 | - Reset the ev_break status. |
844 | - Reset the ev_break status. |
790 | - Before the first iteration, call any pending watchers. |
845 | - Before the first iteration, call any pending watchers. |
791 | LOOP: |
846 | LOOP: |
… | |
… | |
824 | anymore. |
879 | anymore. |
825 | |
880 | |
826 | ... queue jobs here, make sure they register event watchers as long |
881 | ... queue jobs here, make sure they register event watchers as long |
827 | ... as they still have work to do (even an idle watcher will do..) |
882 | ... as they still have work to do (even an idle watcher will do..) |
828 | ev_run (my_loop, 0); |
883 | ev_run (my_loop, 0); |
829 | ... jobs done or somebody called unloop. yeah! |
884 | ... jobs done or somebody called break. yeah! |
830 | |
885 | |
831 | =item ev_break (loop, how) |
886 | =item ev_break (loop, how) |
832 | |
887 | |
833 | Can be used to make a call to C<ev_run> return early (but only after it |
888 | Can be used to make a call to C<ev_run> return early (but only after it |
834 | has processed all outstanding events). The C<how> argument must be either |
889 | has processed all outstanding events). The C<how> argument must be either |
… | |
… | |
867 | running when nothing else is active. |
922 | running when nothing else is active. |
868 | |
923 | |
869 | ev_signal exitsig; |
924 | ev_signal exitsig; |
870 | ev_signal_init (&exitsig, sig_cb, SIGINT); |
925 | ev_signal_init (&exitsig, sig_cb, SIGINT); |
871 | ev_signal_start (loop, &exitsig); |
926 | ev_signal_start (loop, &exitsig); |
872 | evf_unref (loop); |
927 | ev_unref (loop); |
873 | |
928 | |
874 | Example: For some weird reason, unregister the above signal handler again. |
929 | Example: For some weird reason, unregister the above signal handler again. |
875 | |
930 | |
876 | ev_ref (loop); |
931 | ev_ref (loop); |
877 | ev_signal_stop (loop, &exitsig); |
932 | ev_signal_stop (loop, &exitsig); |
… | |
… | |
897 | overhead for the actual polling but can deliver many events at once. |
952 | overhead for the actual polling but can deliver many events at once. |
898 | |
953 | |
899 | By setting a higher I<io collect interval> you allow libev to spend more |
954 | By setting a higher I<io collect interval> you allow libev to spend more |
900 | time collecting I/O events, so you can handle more events per iteration, |
955 | time collecting I/O events, so you can handle more events per iteration, |
901 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
956 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
902 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
957 | C<ev_timer>) will not be affected. Setting this to a non-null value will |
903 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
958 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
904 | sleep time ensures that libev will not poll for I/O events more often then |
959 | sleep time ensures that libev will not poll for I/O events more often then |
905 | once per this interval, on average. |
960 | once per this interval, on average (as long as the host time resolution is |
|
|
961 | good enough). |
906 | |
962 | |
907 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
963 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
908 | to spend more time collecting timeouts, at the expense of increased |
964 | to spend more time collecting timeouts, at the expense of increased |
909 | latency/jitter/inexactness (the watcher callback will be called |
965 | latency/jitter/inexactness (the watcher callback will be called |
910 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
966 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
… | |
… | |
989 | See also the locking example in the C<THREADS> section later in this |
1045 | See also the locking example in the C<THREADS> section later in this |
990 | document. |
1046 | document. |
991 | |
1047 | |
992 | =item ev_set_userdata (loop, void *data) |
1048 | =item ev_set_userdata (loop, void *data) |
993 | |
1049 | |
994 | =item ev_userdata (loop) |
1050 | =item void *ev_userdata (loop) |
995 | |
1051 | |
996 | Set and retrieve a single C<void *> associated with a loop. When |
1052 | Set and retrieve a single C<void *> associated with a loop. When |
997 | C<ev_set_userdata> has never been called, then C<ev_userdata> returns |
1053 | C<ev_set_userdata> has never been called, then C<ev_userdata> returns |
998 | C<0>. |
1054 | C<0>. |
999 | |
1055 | |
… | |
… | |
1316 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1372 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1317 | functions that do not need a watcher. |
1373 | functions that do not need a watcher. |
1318 | |
1374 | |
1319 | =back |
1375 | =back |
1320 | |
1376 | |
1321 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1377 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1322 | |
1378 | OWN COMPOSITE WATCHERS> idioms. |
1323 | Each watcher has, by default, a member C<void *data> that you can change |
|
|
1324 | and read at any time: libev will completely ignore it. This can be used |
|
|
1325 | to associate arbitrary data with your watcher. If you need more data and |
|
|
1326 | don't want to allocate memory and store a pointer to it in that data |
|
|
1327 | member, you can also "subclass" the watcher type and provide your own |
|
|
1328 | data: |
|
|
1329 | |
|
|
1330 | struct my_io |
|
|
1331 | { |
|
|
1332 | ev_io io; |
|
|
1333 | int otherfd; |
|
|
1334 | void *somedata; |
|
|
1335 | struct whatever *mostinteresting; |
|
|
1336 | }; |
|
|
1337 | |
|
|
1338 | ... |
|
|
1339 | struct my_io w; |
|
|
1340 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
1341 | |
|
|
1342 | And since your callback will be called with a pointer to the watcher, you |
|
|
1343 | can cast it back to your own type: |
|
|
1344 | |
|
|
1345 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
1346 | { |
|
|
1347 | struct my_io *w = (struct my_io *)w_; |
|
|
1348 | ... |
|
|
1349 | } |
|
|
1350 | |
|
|
1351 | More interesting and less C-conformant ways of casting your callback type |
|
|
1352 | instead have been omitted. |
|
|
1353 | |
|
|
1354 | Another common scenario is to use some data structure with multiple |
|
|
1355 | embedded watchers: |
|
|
1356 | |
|
|
1357 | struct my_biggy |
|
|
1358 | { |
|
|
1359 | int some_data; |
|
|
1360 | ev_timer t1; |
|
|
1361 | ev_timer t2; |
|
|
1362 | } |
|
|
1363 | |
|
|
1364 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
1365 | complicated: Either you store the address of your C<my_biggy> struct |
|
|
1366 | in the C<data> member of the watcher (for woozies), or you need to use |
|
|
1367 | some pointer arithmetic using C<offsetof> inside your watchers (for real |
|
|
1368 | programmers): |
|
|
1369 | |
|
|
1370 | #include <stddef.h> |
|
|
1371 | |
|
|
1372 | static void |
|
|
1373 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
1374 | { |
|
|
1375 | struct my_biggy big = (struct my_biggy *) |
|
|
1376 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
1377 | } |
|
|
1378 | |
|
|
1379 | static void |
|
|
1380 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
1381 | { |
|
|
1382 | struct my_biggy big = (struct my_biggy *) |
|
|
1383 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
1384 | } |
|
|
1385 | |
1379 | |
1386 | =head2 WATCHER STATES |
1380 | =head2 WATCHER STATES |
1387 | |
1381 | |
1388 | There are various watcher states mentioned throughout this manual - |
1382 | There are various watcher states mentioned throughout this manual - |
1389 | active, pending and so on. In this section these states and the rules to |
1383 | active, pending and so on. In this section these states and the rules to |
… | |
… | |
1392 | |
1386 | |
1393 | =over 4 |
1387 | =over 4 |
1394 | |
1388 | |
1395 | =item initialiased |
1389 | =item initialiased |
1396 | |
1390 | |
1397 | Before a watcher can be registered with the event looop it has to be |
1391 | Before a watcher can be registered with the event loop it has to be |
1398 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
1392 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
1399 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
1393 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
1400 | |
1394 | |
1401 | In this state it is simply some block of memory that is suitable for use |
1395 | In this state it is simply some block of memory that is suitable for |
1402 | in an event loop. It can be moved around, freed, reused etc. at will. |
1396 | use in an event loop. It can be moved around, freed, reused etc. at |
|
|
1397 | will - as long as you either keep the memory contents intact, or call |
|
|
1398 | C<ev_TYPE_init> again. |
1403 | |
1399 | |
1404 | =item started/running/active |
1400 | =item started/running/active |
1405 | |
1401 | |
1406 | Once a watcher has been started with a call to C<ev_TYPE_start> it becomes |
1402 | Once a watcher has been started with a call to C<ev_TYPE_start> it becomes |
1407 | property of the event loop, and is actively waiting for events. While in |
1403 | property of the event loop, and is actively waiting for events. While in |
… | |
… | |
1435 | latter will clear any pending state the watcher might be in, regardless |
1431 | latter will clear any pending state the watcher might be in, regardless |
1436 | of whether it was active or not, so stopping a watcher explicitly before |
1432 | of whether it was active or not, so stopping a watcher explicitly before |
1437 | freeing it is often a good idea. |
1433 | freeing it is often a good idea. |
1438 | |
1434 | |
1439 | While stopped (and not pending) the watcher is essentially in the |
1435 | While stopped (and not pending) the watcher is essentially in the |
1440 | initialised state, that is it can be reused, moved, modified in any way |
1436 | initialised state, that is, it can be reused, moved, modified in any way |
1441 | you wish. |
1437 | you wish (but when you trash the memory block, you need to C<ev_TYPE_init> |
|
|
1438 | it again). |
1442 | |
1439 | |
1443 | =back |
1440 | =back |
1444 | |
1441 | |
1445 | =head2 WATCHER PRIORITY MODELS |
1442 | =head2 WATCHER PRIORITY MODELS |
1446 | |
1443 | |
… | |
… | |
1575 | In general you can register as many read and/or write event watchers per |
1572 | In general you can register as many read and/or write event watchers per |
1576 | fd as you want (as long as you don't confuse yourself). Setting all file |
1573 | fd as you want (as long as you don't confuse yourself). Setting all file |
1577 | descriptors to non-blocking mode is also usually a good idea (but not |
1574 | descriptors to non-blocking mode is also usually a good idea (but not |
1578 | required if you know what you are doing). |
1575 | required if you know what you are doing). |
1579 | |
1576 | |
1580 | If you cannot use non-blocking mode, then force the use of a |
|
|
1581 | known-to-be-good backend (at the time of this writing, this includes only |
|
|
1582 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file |
|
|
1583 | descriptors for which non-blocking operation makes no sense (such as |
|
|
1584 | files) - libev doesn't guarantee any specific behaviour in that case. |
|
|
1585 | |
|
|
1586 | Another thing you have to watch out for is that it is quite easy to |
1577 | Another thing you have to watch out for is that it is quite easy to |
1587 | receive "spurious" readiness notifications, that is your callback might |
1578 | receive "spurious" readiness notifications, that is, your callback might |
1588 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1579 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1589 | because there is no data. Not only are some backends known to create a |
1580 | because there is no data. It is very easy to get into this situation even |
1590 | lot of those (for example Solaris ports), it is very easy to get into |
1581 | with a relatively standard program structure. Thus it is best to always |
1591 | this situation even with a relatively standard program structure. Thus |
1582 | use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far |
1592 | it is best to always use non-blocking I/O: An extra C<read>(2) returning |
|
|
1593 | C<EAGAIN> is far preferable to a program hanging until some data arrives. |
1583 | preferable to a program hanging until some data arrives. |
1594 | |
1584 | |
1595 | If you cannot run the fd in non-blocking mode (for example you should |
1585 | If you cannot run the fd in non-blocking mode (for example you should |
1596 | not play around with an Xlib connection), then you have to separately |
1586 | not play around with an Xlib connection), then you have to separately |
1597 | re-test whether a file descriptor is really ready with a known-to-be good |
1587 | re-test whether a file descriptor is really ready with a known-to-be good |
1598 | interface such as poll (fortunately in our Xlib example, Xlib already |
1588 | interface such as poll (fortunately in the case of Xlib, it already does |
1599 | does this on its own, so its quite safe to use). Some people additionally |
1589 | this on its own, so its quite safe to use). Some people additionally |
1600 | use C<SIGALRM> and an interval timer, just to be sure you won't block |
1590 | use C<SIGALRM> and an interval timer, just to be sure you won't block |
1601 | indefinitely. |
1591 | indefinitely. |
1602 | |
1592 | |
1603 | But really, best use non-blocking mode. |
1593 | But really, best use non-blocking mode. |
1604 | |
1594 | |
… | |
… | |
1632 | |
1622 | |
1633 | There is no workaround possible except not registering events |
1623 | There is no workaround possible except not registering events |
1634 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1624 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1635 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1625 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1636 | |
1626 | |
|
|
1627 | =head3 The special problem of files |
|
|
1628 | |
|
|
1629 | Many people try to use C<select> (or libev) on file descriptors |
|
|
1630 | representing files, and expect it to become ready when their program |
|
|
1631 | doesn't block on disk accesses (which can take a long time on their own). |
|
|
1632 | |
|
|
1633 | However, this cannot ever work in the "expected" way - you get a readiness |
|
|
1634 | notification as soon as the kernel knows whether and how much data is |
|
|
1635 | there, and in the case of open files, that's always the case, so you |
|
|
1636 | always get a readiness notification instantly, and your read (or possibly |
|
|
1637 | write) will still block on the disk I/O. |
|
|
1638 | |
|
|
1639 | Another way to view it is that in the case of sockets, pipes, character |
|
|
1640 | devices and so on, there is another party (the sender) that delivers data |
|
|
1641 | on its own, but in the case of files, there is no such thing: the disk |
|
|
1642 | will not send data on its own, simply because it doesn't know what you |
|
|
1643 | wish to read - you would first have to request some data. |
|
|
1644 | |
|
|
1645 | Since files are typically not-so-well supported by advanced notification |
|
|
1646 | mechanism, libev tries hard to emulate POSIX behaviour with respect |
|
|
1647 | to files, even though you should not use it. The reason for this is |
|
|
1648 | convenience: sometimes you want to watch STDIN or STDOUT, which is |
|
|
1649 | usually a tty, often a pipe, but also sometimes files or special devices |
|
|
1650 | (for example, C<epoll> on Linux works with F</dev/random> but not with |
|
|
1651 | F</dev/urandom>), and even though the file might better be served with |
|
|
1652 | asynchronous I/O instead of with non-blocking I/O, it is still useful when |
|
|
1653 | it "just works" instead of freezing. |
|
|
1654 | |
|
|
1655 | So avoid file descriptors pointing to files when you know it (e.g. use |
|
|
1656 | libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or |
|
|
1657 | when you rarely read from a file instead of from a socket, and want to |
|
|
1658 | reuse the same code path. |
|
|
1659 | |
1637 | =head3 The special problem of fork |
1660 | =head3 The special problem of fork |
1638 | |
1661 | |
1639 | Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1662 | Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1640 | useless behaviour. Libev fully supports fork, but needs to be told about |
1663 | useless behaviour. Libev fully supports fork, but needs to be told about |
1641 | it in the child. |
1664 | it in the child if you want to continue to use it in the child. |
1642 | |
1665 | |
1643 | To support fork in your programs, you either have to call |
1666 | To support fork in your child processes, you have to call C<ev_loop_fork |
1644 | C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child, |
1667 | ()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to |
1645 | enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or |
1668 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1646 | C<EVBACKEND_POLL>. |
|
|
1647 | |
1669 | |
1648 | =head3 The special problem of SIGPIPE |
1670 | =head3 The special problem of SIGPIPE |
1649 | |
1671 | |
1650 | While not really specific to libev, it is easy to forget about C<SIGPIPE>: |
1672 | While not really specific to libev, it is easy to forget about C<SIGPIPE>: |
1651 | when writing to a pipe whose other end has been closed, your program gets |
1673 | when writing to a pipe whose other end has been closed, your program gets |
… | |
… | |
2141 | |
2163 | |
2142 | Another way to think about it (for the mathematically inclined) is that |
2164 | Another way to think about it (for the mathematically inclined) is that |
2143 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2165 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2144 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2166 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2145 | |
2167 | |
2146 | For numerical stability it is preferable that the C<offset> value is near |
2168 | The C<interval> I<MUST> be positive, and for numerical stability, the |
2147 | C<ev_now ()> (the current time), but there is no range requirement for |
2169 | interval value should be higher than C<1/8192> (which is around 100 |
2148 | this value, and in fact is often specified as zero. |
2170 | microseconds) and C<offset> should be higher than C<0> and should have |
|
|
2171 | at most a similar magnitude as the current time (say, within a factor of |
|
|
2172 | ten). Typical values for offset are, in fact, C<0> or something between |
|
|
2173 | C<0> and C<interval>, which is also the recommended range. |
2149 | |
2174 | |
2150 | Note also that there is an upper limit to how often a timer can fire (CPU |
2175 | Note also that there is an upper limit to how often a timer can fire (CPU |
2151 | speed for example), so if C<interval> is very small then timing stability |
2176 | speed for example), so if C<interval> is very small then timing stability |
2152 | will of course deteriorate. Libev itself tries to be exact to be about one |
2177 | will of course deteriorate. Libev itself tries to be exact to be about one |
2153 | millisecond (if the OS supports it and the machine is fast enough). |
2178 | millisecond (if the OS supports it and the machine is fast enough). |
… | |
… | |
2296 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2321 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2297 | |
2322 | |
2298 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2323 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2299 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2324 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2300 | stopping it again), that is, libev might or might not block the signal, |
2325 | stopping it again), that is, libev might or might not block the signal, |
2301 | and might or might not set or restore the installed signal handler. |
2326 | and might or might not set or restore the installed signal handler (but |
|
|
2327 | see C<EVFLAG_NOSIGMASK>). |
2302 | |
2328 | |
2303 | While this does not matter for the signal disposition (libev never |
2329 | While this does not matter for the signal disposition (libev never |
2304 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2330 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2305 | C<execve>), this matters for the signal mask: many programs do not expect |
2331 | C<execve>), this matters for the signal mask: many programs do not expect |
2306 | certain signals to be blocked. |
2332 | certain signals to be blocked. |
… | |
… | |
2319 | I<has> to modify the signal mask, at least temporarily. |
2345 | I<has> to modify the signal mask, at least temporarily. |
2320 | |
2346 | |
2321 | So I can't stress this enough: I<If you do not reset your signal mask when |
2347 | So I can't stress this enough: I<If you do not reset your signal mask when |
2322 | you expect it to be empty, you have a race condition in your code>. This |
2348 | you expect it to be empty, you have a race condition in your code>. This |
2323 | is not a libev-specific thing, this is true for most event libraries. |
2349 | is not a libev-specific thing, this is true for most event libraries. |
|
|
2350 | |
|
|
2351 | =head3 The special problem of threads signal handling |
|
|
2352 | |
|
|
2353 | POSIX threads has problematic signal handling semantics, specifically, |
|
|
2354 | a lot of functionality (sigfd, sigwait etc.) only really works if all |
|
|
2355 | threads in a process block signals, which is hard to achieve. |
|
|
2356 | |
|
|
2357 | When you want to use sigwait (or mix libev signal handling with your own |
|
|
2358 | for the same signals), you can tackle this problem by globally blocking |
|
|
2359 | all signals before creating any threads (or creating them with a fully set |
|
|
2360 | sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating |
|
|
2361 | loops. Then designate one thread as "signal receiver thread" which handles |
|
|
2362 | these signals. You can pass on any signals that libev might be interested |
|
|
2363 | in by calling C<ev_feed_signal>. |
2324 | |
2364 | |
2325 | =head3 Watcher-Specific Functions and Data Members |
2365 | =head3 Watcher-Specific Functions and Data Members |
2326 | |
2366 | |
2327 | =over 4 |
2367 | =over 4 |
2328 | |
2368 | |
… | |
… | |
3163 | atexit (program_exits); |
3203 | atexit (program_exits); |
3164 | |
3204 | |
3165 | |
3205 | |
3166 | =head2 C<ev_async> - how to wake up an event loop |
3206 | =head2 C<ev_async> - how to wake up an event loop |
3167 | |
3207 | |
3168 | In general, you cannot use an C<ev_run> from multiple threads or other |
3208 | In general, you cannot use an C<ev_loop> from multiple threads or other |
3169 | asynchronous sources such as signal handlers (as opposed to multiple event |
3209 | asynchronous sources such as signal handlers (as opposed to multiple event |
3170 | loops - those are of course safe to use in different threads). |
3210 | loops - those are of course safe to use in different threads). |
3171 | |
3211 | |
3172 | Sometimes, however, you need to wake up an event loop you do not control, |
3212 | Sometimes, however, you need to wake up an event loop you do not control, |
3173 | for example because it belongs to another thread. This is what C<ev_async> |
3213 | for example because it belongs to another thread. This is what C<ev_async> |
… | |
… | |
3175 | it by calling C<ev_async_send>, which is thread- and signal safe. |
3215 | it by calling C<ev_async_send>, which is thread- and signal safe. |
3176 | |
3216 | |
3177 | This functionality is very similar to C<ev_signal> watchers, as signals, |
3217 | This functionality is very similar to C<ev_signal> watchers, as signals, |
3178 | too, are asynchronous in nature, and signals, too, will be compressed |
3218 | too, are asynchronous in nature, and signals, too, will be compressed |
3179 | (i.e. the number of callback invocations may be less than the number of |
3219 | (i.e. the number of callback invocations may be less than the number of |
3180 | C<ev_async_sent> calls). |
3220 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
|
|
3221 | of "global async watchers" by using a watcher on an otherwise unused |
|
|
3222 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
|
|
3223 | even without knowing which loop owns the signal. |
3181 | |
3224 | |
3182 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
3225 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
3183 | just the default loop. |
3226 | just the default loop. |
3184 | |
3227 | |
3185 | =head3 Queueing |
3228 | =head3 Queueing |
… | |
… | |
3280 | trust me. |
3323 | trust me. |
3281 | |
3324 | |
3282 | =item ev_async_send (loop, ev_async *) |
3325 | =item ev_async_send (loop, ev_async *) |
3283 | |
3326 | |
3284 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3327 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3285 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
3328 | an C<EV_ASYNC> event on the watcher into the event loop, and instantly |
|
|
3329 | returns. |
|
|
3330 | |
3286 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
3331 | Unlike C<ev_feed_event>, this call is safe to do from other threads, |
3287 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
3332 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3288 | section below on what exactly this means). |
3333 | embedding section below on what exactly this means). |
3289 | |
3334 | |
3290 | Note that, as with other watchers in libev, multiple events might get |
3335 | Note that, as with other watchers in libev, multiple events might get |
3291 | compressed into a single callback invocation (another way to look at this |
3336 | compressed into a single callback invocation (another way to look at this |
3292 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3337 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3293 | reset when the event loop detects that). |
3338 | reset when the event loop detects that). |
… | |
… | |
3361 | Feed an event on the given fd, as if a file descriptor backend detected |
3406 | Feed an event on the given fd, as if a file descriptor backend detected |
3362 | the given events it. |
3407 | the given events it. |
3363 | |
3408 | |
3364 | =item ev_feed_signal_event (loop, int signum) |
3409 | =item ev_feed_signal_event (loop, int signum) |
3365 | |
3410 | |
3366 | Feed an event as if the given signal occurred (C<loop> must be the default |
3411 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3367 | loop!). |
3412 | which is async-safe. |
3368 | |
3413 | |
3369 | =back |
3414 | =back |
|
|
3415 | |
|
|
3416 | |
|
|
3417 | =head1 COMMON OR USEFUL IDIOMS (OR BOTH) |
|
|
3418 | |
|
|
3419 | This section explains some common idioms that are not immediately |
|
|
3420 | obvious. Note that examples are sprinkled over the whole manual, and this |
|
|
3421 | section only contains stuff that wouldn't fit anywhere else. |
|
|
3422 | |
|
|
3423 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
|
|
3424 | |
|
|
3425 | Each watcher has, by default, a C<void *data> member that you can read |
|
|
3426 | or modify at any time: libev will completely ignore it. This can be used |
|
|
3427 | to associate arbitrary data with your watcher. If you need more data and |
|
|
3428 | don't want to allocate memory separately and store a pointer to it in that |
|
|
3429 | data member, you can also "subclass" the watcher type and provide your own |
|
|
3430 | data: |
|
|
3431 | |
|
|
3432 | struct my_io |
|
|
3433 | { |
|
|
3434 | ev_io io; |
|
|
3435 | int otherfd; |
|
|
3436 | void *somedata; |
|
|
3437 | struct whatever *mostinteresting; |
|
|
3438 | }; |
|
|
3439 | |
|
|
3440 | ... |
|
|
3441 | struct my_io w; |
|
|
3442 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
3443 | |
|
|
3444 | And since your callback will be called with a pointer to the watcher, you |
|
|
3445 | can cast it back to your own type: |
|
|
3446 | |
|
|
3447 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
3448 | { |
|
|
3449 | struct my_io *w = (struct my_io *)w_; |
|
|
3450 | ... |
|
|
3451 | } |
|
|
3452 | |
|
|
3453 | More interesting and less C-conformant ways of casting your callback |
|
|
3454 | function type instead have been omitted. |
|
|
3455 | |
|
|
3456 | =head2 BUILDING YOUR OWN COMPOSITE WATCHERS |
|
|
3457 | |
|
|
3458 | Another common scenario is to use some data structure with multiple |
|
|
3459 | embedded watchers, in effect creating your own watcher that combines |
|
|
3460 | multiple libev event sources into one "super-watcher": |
|
|
3461 | |
|
|
3462 | struct my_biggy |
|
|
3463 | { |
|
|
3464 | int some_data; |
|
|
3465 | ev_timer t1; |
|
|
3466 | ev_timer t2; |
|
|
3467 | } |
|
|
3468 | |
|
|
3469 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
3470 | complicated: Either you store the address of your C<my_biggy> struct in |
|
|
3471 | the C<data> member of the watcher (for woozies or C++ coders), or you need |
|
|
3472 | to use some pointer arithmetic using C<offsetof> inside your watchers (for |
|
|
3473 | real programmers): |
|
|
3474 | |
|
|
3475 | #include <stddef.h> |
|
|
3476 | |
|
|
3477 | static void |
|
|
3478 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
3479 | { |
|
|
3480 | struct my_biggy big = (struct my_biggy *) |
|
|
3481 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
3482 | } |
|
|
3483 | |
|
|
3484 | static void |
|
|
3485 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
3486 | { |
|
|
3487 | struct my_biggy big = (struct my_biggy *) |
|
|
3488 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
3489 | } |
|
|
3490 | |
|
|
3491 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
|
|
3492 | |
|
|
3493 | Often (especially in GUI toolkits) there are places where you have |
|
|
3494 | I<modal> interaction, which is most easily implemented by recursively |
|
|
3495 | invoking C<ev_run>. |
|
|
3496 | |
|
|
3497 | This brings the problem of exiting - a callback might want to finish the |
|
|
3498 | main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but |
|
|
3499 | a modal "Are you sure?" dialog is still waiting), or just the nested one |
|
|
3500 | and not the main one (e.g. user clocked "Ok" in a modal dialog), or some |
|
|
3501 | other combination: In these cases, C<ev_break> will not work alone. |
|
|
3502 | |
|
|
3503 | The solution is to maintain "break this loop" variable for each C<ev_run> |
|
|
3504 | invocation, and use a loop around C<ev_run> until the condition is |
|
|
3505 | triggered, using C<EVRUN_ONCE>: |
|
|
3506 | |
|
|
3507 | // main loop |
|
|
3508 | int exit_main_loop = 0; |
|
|
3509 | |
|
|
3510 | while (!exit_main_loop) |
|
|
3511 | ev_run (EV_DEFAULT_ EVRUN_ONCE); |
|
|
3512 | |
|
|
3513 | // in a model watcher |
|
|
3514 | int exit_nested_loop = 0; |
|
|
3515 | |
|
|
3516 | while (!exit_nested_loop) |
|
|
3517 | ev_run (EV_A_ EVRUN_ONCE); |
|
|
3518 | |
|
|
3519 | To exit from any of these loops, just set the corresponding exit variable: |
|
|
3520 | |
|
|
3521 | // exit modal loop |
|
|
3522 | exit_nested_loop = 1; |
|
|
3523 | |
|
|
3524 | // exit main program, after modal loop is finished |
|
|
3525 | exit_main_loop = 1; |
|
|
3526 | |
|
|
3527 | // exit both |
|
|
3528 | exit_main_loop = exit_nested_loop = 1; |
|
|
3529 | |
|
|
3530 | =head2 THREAD LOCKING EXAMPLE |
|
|
3531 | |
|
|
3532 | Here is a fictitious example of how to run an event loop in a different |
|
|
3533 | thread from where callbacks are being invoked and watchers are |
|
|
3534 | created/added/removed. |
|
|
3535 | |
|
|
3536 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
3537 | which uses exactly this technique (which is suited for many high-level |
|
|
3538 | languages). |
|
|
3539 | |
|
|
3540 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
3541 | variable to wait for callback invocations, an async watcher to notify the |
|
|
3542 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
3543 | |
|
|
3544 | First, you need to associate some data with the event loop: |
|
|
3545 | |
|
|
3546 | typedef struct { |
|
|
3547 | mutex_t lock; /* global loop lock */ |
|
|
3548 | ev_async async_w; |
|
|
3549 | thread_t tid; |
|
|
3550 | cond_t invoke_cv; |
|
|
3551 | } userdata; |
|
|
3552 | |
|
|
3553 | void prepare_loop (EV_P) |
|
|
3554 | { |
|
|
3555 | // for simplicity, we use a static userdata struct. |
|
|
3556 | static userdata u; |
|
|
3557 | |
|
|
3558 | ev_async_init (&u->async_w, async_cb); |
|
|
3559 | ev_async_start (EV_A_ &u->async_w); |
|
|
3560 | |
|
|
3561 | pthread_mutex_init (&u->lock, 0); |
|
|
3562 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
3563 | |
|
|
3564 | // now associate this with the loop |
|
|
3565 | ev_set_userdata (EV_A_ u); |
|
|
3566 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
3567 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
3568 | |
|
|
3569 | // then create the thread running ev_run |
|
|
3570 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
3571 | } |
|
|
3572 | |
|
|
3573 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
3574 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
3575 | that might have been added: |
|
|
3576 | |
|
|
3577 | static void |
|
|
3578 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
3579 | { |
|
|
3580 | // just used for the side effects |
|
|
3581 | } |
|
|
3582 | |
|
|
3583 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
3584 | protecting the loop data, respectively. |
|
|
3585 | |
|
|
3586 | static void |
|
|
3587 | l_release (EV_P) |
|
|
3588 | { |
|
|
3589 | userdata *u = ev_userdata (EV_A); |
|
|
3590 | pthread_mutex_unlock (&u->lock); |
|
|
3591 | } |
|
|
3592 | |
|
|
3593 | static void |
|
|
3594 | l_acquire (EV_P) |
|
|
3595 | { |
|
|
3596 | userdata *u = ev_userdata (EV_A); |
|
|
3597 | pthread_mutex_lock (&u->lock); |
|
|
3598 | } |
|
|
3599 | |
|
|
3600 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
3601 | into C<ev_run>: |
|
|
3602 | |
|
|
3603 | void * |
|
|
3604 | l_run (void *thr_arg) |
|
|
3605 | { |
|
|
3606 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
3607 | |
|
|
3608 | l_acquire (EV_A); |
|
|
3609 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
3610 | ev_run (EV_A_ 0); |
|
|
3611 | l_release (EV_A); |
|
|
3612 | |
|
|
3613 | return 0; |
|
|
3614 | } |
|
|
3615 | |
|
|
3616 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
3617 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
3618 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
3619 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
3620 | and b) skipping inter-thread-communication when there are no pending |
|
|
3621 | watchers is very beneficial): |
|
|
3622 | |
|
|
3623 | static void |
|
|
3624 | l_invoke (EV_P) |
|
|
3625 | { |
|
|
3626 | userdata *u = ev_userdata (EV_A); |
|
|
3627 | |
|
|
3628 | while (ev_pending_count (EV_A)) |
|
|
3629 | { |
|
|
3630 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
3631 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
3632 | } |
|
|
3633 | } |
|
|
3634 | |
|
|
3635 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
3636 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
3637 | thread to continue: |
|
|
3638 | |
|
|
3639 | static void |
|
|
3640 | real_invoke_pending (EV_P) |
|
|
3641 | { |
|
|
3642 | userdata *u = ev_userdata (EV_A); |
|
|
3643 | |
|
|
3644 | pthread_mutex_lock (&u->lock); |
|
|
3645 | ev_invoke_pending (EV_A); |
|
|
3646 | pthread_cond_signal (&u->invoke_cv); |
|
|
3647 | pthread_mutex_unlock (&u->lock); |
|
|
3648 | } |
|
|
3649 | |
|
|
3650 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
3651 | event loop, you will now have to lock: |
|
|
3652 | |
|
|
3653 | ev_timer timeout_watcher; |
|
|
3654 | userdata *u = ev_userdata (EV_A); |
|
|
3655 | |
|
|
3656 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
3657 | |
|
|
3658 | pthread_mutex_lock (&u->lock); |
|
|
3659 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
3660 | ev_async_send (EV_A_ &u->async_w); |
|
|
3661 | pthread_mutex_unlock (&u->lock); |
|
|
3662 | |
|
|
3663 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
3664 | an event loop currently blocking in the kernel will have no knowledge |
|
|
3665 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
3666 | watchers in the next event loop iteration. |
|
|
3667 | |
|
|
3668 | =head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS |
|
|
3669 | |
|
|
3670 | While the overhead of a callback that e.g. schedules a thread is small, it |
|
|
3671 | is still an overhead. If you embed libev, and your main usage is with some |
|
|
3672 | kind of threads or coroutines, you might want to customise libev so that |
|
|
3673 | doesn't need callbacks anymore. |
|
|
3674 | |
|
|
3675 | Imagine you have coroutines that you can switch to using a function |
|
|
3676 | C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro> |
|
|
3677 | and that due to some magic, the currently active coroutine is stored in a |
|
|
3678 | global called C<current_coro>. Then you can build your own "wait for libev |
|
|
3679 | event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note |
|
|
3680 | the differing C<;> conventions): |
|
|
3681 | |
|
|
3682 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3683 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb) |
|
|
3684 | |
|
|
3685 | That means instead of having a C callback function, you store the |
|
|
3686 | coroutine to switch to in each watcher, and instead of having libev call |
|
|
3687 | your callback, you instead have it switch to that coroutine. |
|
|
3688 | |
|
|
3689 | A coroutine might now wait for an event with a function called |
|
|
3690 | C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't |
|
|
3691 | matter when, or whether the watcher is active or not when this function is |
|
|
3692 | called): |
|
|
3693 | |
|
|
3694 | void |
|
|
3695 | wait_for_event (ev_watcher *w) |
|
|
3696 | { |
|
|
3697 | ev_cb_set (w) = current_coro; |
|
|
3698 | switch_to (libev_coro); |
|
|
3699 | } |
|
|
3700 | |
|
|
3701 | That basically suspends the coroutine inside C<wait_for_event> and |
|
|
3702 | continues the libev coroutine, which, when appropriate, switches back to |
|
|
3703 | this or any other coroutine. I am sure if you sue this your own :) |
|
|
3704 | |
|
|
3705 | You can do similar tricks if you have, say, threads with an event queue - |
|
|
3706 | instead of storing a coroutine, you store the queue object and instead of |
|
|
3707 | switching to a coroutine, you push the watcher onto the queue and notify |
|
|
3708 | any waiters. |
|
|
3709 | |
|
|
3710 | To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two |
|
|
3711 | files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: |
|
|
3712 | |
|
|
3713 | // my_ev.h |
|
|
3714 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3715 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); |
|
|
3716 | #include "../libev/ev.h" |
|
|
3717 | |
|
|
3718 | // my_ev.c |
|
|
3719 | #define EV_H "my_ev.h" |
|
|
3720 | #include "../libev/ev.c" |
|
|
3721 | |
|
|
3722 | And then use F<my_ev.h> when you would normally use F<ev.h>, and compile |
|
|
3723 | F<my_ev.c> into your project. When properly specifying include paths, you |
|
|
3724 | can even use F<ev.h> as header file name directly. |
3370 | |
3725 | |
3371 | |
3726 | |
3372 | =head1 LIBEVENT EMULATION |
3727 | =head1 LIBEVENT EMULATION |
3373 | |
3728 | |
3374 | Libev offers a compatibility emulation layer for libevent. It cannot |
3729 | Libev offers a compatibility emulation layer for libevent. It cannot |
3375 | emulate the internals of libevent, so here are some usage hints: |
3730 | emulate the internals of libevent, so here are some usage hints: |
3376 | |
3731 | |
3377 | =over 4 |
3732 | =over 4 |
|
|
3733 | |
|
|
3734 | =item * Only the libevent-1.4.1-beta API is being emulated. |
|
|
3735 | |
|
|
3736 | This was the newest libevent version available when libev was implemented, |
|
|
3737 | and is still mostly unchanged in 2010. |
3378 | |
3738 | |
3379 | =item * Use it by including <event.h>, as usual. |
3739 | =item * Use it by including <event.h>, as usual. |
3380 | |
3740 | |
3381 | =item * The following members are fully supported: ev_base, ev_callback, |
3741 | =item * The following members are fully supported: ev_base, ev_callback, |
3382 | ev_arg, ev_fd, ev_res, ev_events. |
3742 | ev_arg, ev_fd, ev_res, ev_events. |
… | |
… | |
3417 | Care has been taken to keep the overhead low. The only data member the C++ |
3777 | Care has been taken to keep the overhead low. The only data member the C++ |
3418 | classes add (compared to plain C-style watchers) is the event loop pointer |
3778 | classes add (compared to plain C-style watchers) is the event loop pointer |
3419 | that the watcher is associated with (or no additional members at all if |
3779 | that the watcher is associated with (or no additional members at all if |
3420 | you disable C<EV_MULTIPLICITY> when embedding libev). |
3780 | you disable C<EV_MULTIPLICITY> when embedding libev). |
3421 | |
3781 | |
3422 | Currently, functions, and static and non-static member functions can be |
3782 | Currently, functions, static and non-static member functions and classes |
3423 | used as callbacks. Other types should be easy to add as long as they only |
3783 | with C<operator ()> can be used as callbacks. Other types should be easy |
3424 | need one additional pointer for context. If you need support for other |
3784 | to add as long as they only need one additional pointer for context. If |
3425 | types of functors please contact the author (preferably after implementing |
3785 | you need support for other types of functors please contact the author |
3426 | it). |
3786 | (preferably after implementing it). |
3427 | |
3787 | |
3428 | Here is a list of things available in the C<ev> namespace: |
3788 | Here is a list of things available in the C<ev> namespace: |
3429 | |
3789 | |
3430 | =over 4 |
3790 | =over 4 |
3431 | |
3791 | |
… | |
… | |
3859 | F<event.h> that are not directly supported by the libev core alone. |
4219 | F<event.h> that are not directly supported by the libev core alone. |
3860 | |
4220 | |
3861 | In standalone mode, libev will still try to automatically deduce the |
4221 | In standalone mode, libev will still try to automatically deduce the |
3862 | configuration, but has to be more conservative. |
4222 | configuration, but has to be more conservative. |
3863 | |
4223 | |
|
|
4224 | =item EV_USE_FLOOR |
|
|
4225 | |
|
|
4226 | If defined to be C<1>, libev will use the C<floor ()> function for its |
|
|
4227 | periodic reschedule calculations, otherwise libev will fall back on a |
|
|
4228 | portable (slower) implementation. If you enable this, you usually have to |
|
|
4229 | link against libm or something equivalent. Enabling this when the C<floor> |
|
|
4230 | function is not available will fail, so the safe default is to not enable |
|
|
4231 | this. |
|
|
4232 | |
3864 | =item EV_USE_MONOTONIC |
4233 | =item EV_USE_MONOTONIC |
3865 | |
4234 | |
3866 | If defined to be C<1>, libev will try to detect the availability of the |
4235 | If defined to be C<1>, libev will try to detect the availability of the |
3867 | monotonic clock option at both compile time and runtime. Otherwise no |
4236 | monotonic clock option at both compile time and runtime. Otherwise no |
3868 | use of the monotonic clock option will be attempted. If you enable this, |
4237 | use of the monotonic clock option will be attempted. If you enable this, |
… | |
… | |
4299 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4668 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4300 | |
4669 | |
4301 | #include "ev_cpp.h" |
4670 | #include "ev_cpp.h" |
4302 | #include "ev.c" |
4671 | #include "ev.c" |
4303 | |
4672 | |
4304 | =head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES |
4673 | =head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT |
4305 | |
4674 | |
4306 | =head2 THREADS AND COROUTINES |
4675 | =head2 THREADS AND COROUTINES |
4307 | |
4676 | |
4308 | =head3 THREADS |
4677 | =head3 THREADS |
4309 | |
4678 | |
… | |
… | |
4360 | default loop and triggering an C<ev_async> watcher from the default loop |
4729 | default loop and triggering an C<ev_async> watcher from the default loop |
4361 | watcher callback into the event loop interested in the signal. |
4730 | watcher callback into the event loop interested in the signal. |
4362 | |
4731 | |
4363 | =back |
4732 | =back |
4364 | |
4733 | |
4365 | =head4 THREAD LOCKING EXAMPLE |
4734 | See also L<THREAD LOCKING EXAMPLE>. |
4366 | |
|
|
4367 | Here is a fictitious example of how to run an event loop in a different |
|
|
4368 | thread than where callbacks are being invoked and watchers are |
|
|
4369 | created/added/removed. |
|
|
4370 | |
|
|
4371 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
4372 | which uses exactly this technique (which is suited for many high-level |
|
|
4373 | languages). |
|
|
4374 | |
|
|
4375 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
4376 | variable to wait for callback invocations, an async watcher to notify the |
|
|
4377 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
4378 | |
|
|
4379 | First, you need to associate some data with the event loop: |
|
|
4380 | |
|
|
4381 | typedef struct { |
|
|
4382 | mutex_t lock; /* global loop lock */ |
|
|
4383 | ev_async async_w; |
|
|
4384 | thread_t tid; |
|
|
4385 | cond_t invoke_cv; |
|
|
4386 | } userdata; |
|
|
4387 | |
|
|
4388 | void prepare_loop (EV_P) |
|
|
4389 | { |
|
|
4390 | // for simplicity, we use a static userdata struct. |
|
|
4391 | static userdata u; |
|
|
4392 | |
|
|
4393 | ev_async_init (&u->async_w, async_cb); |
|
|
4394 | ev_async_start (EV_A_ &u->async_w); |
|
|
4395 | |
|
|
4396 | pthread_mutex_init (&u->lock, 0); |
|
|
4397 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
4398 | |
|
|
4399 | // now associate this with the loop |
|
|
4400 | ev_set_userdata (EV_A_ u); |
|
|
4401 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
4402 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
4403 | |
|
|
4404 | // then create the thread running ev_loop |
|
|
4405 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
4406 | } |
|
|
4407 | |
|
|
4408 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
4409 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
4410 | that might have been added: |
|
|
4411 | |
|
|
4412 | static void |
|
|
4413 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
4414 | { |
|
|
4415 | // just used for the side effects |
|
|
4416 | } |
|
|
4417 | |
|
|
4418 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
4419 | protecting the loop data, respectively. |
|
|
4420 | |
|
|
4421 | static void |
|
|
4422 | l_release (EV_P) |
|
|
4423 | { |
|
|
4424 | userdata *u = ev_userdata (EV_A); |
|
|
4425 | pthread_mutex_unlock (&u->lock); |
|
|
4426 | } |
|
|
4427 | |
|
|
4428 | static void |
|
|
4429 | l_acquire (EV_P) |
|
|
4430 | { |
|
|
4431 | userdata *u = ev_userdata (EV_A); |
|
|
4432 | pthread_mutex_lock (&u->lock); |
|
|
4433 | } |
|
|
4434 | |
|
|
4435 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
4436 | into C<ev_run>: |
|
|
4437 | |
|
|
4438 | void * |
|
|
4439 | l_run (void *thr_arg) |
|
|
4440 | { |
|
|
4441 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
4442 | |
|
|
4443 | l_acquire (EV_A); |
|
|
4444 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
4445 | ev_run (EV_A_ 0); |
|
|
4446 | l_release (EV_A); |
|
|
4447 | |
|
|
4448 | return 0; |
|
|
4449 | } |
|
|
4450 | |
|
|
4451 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
4452 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
4453 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
4454 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
4455 | and b) skipping inter-thread-communication when there are no pending |
|
|
4456 | watchers is very beneficial): |
|
|
4457 | |
|
|
4458 | static void |
|
|
4459 | l_invoke (EV_P) |
|
|
4460 | { |
|
|
4461 | userdata *u = ev_userdata (EV_A); |
|
|
4462 | |
|
|
4463 | while (ev_pending_count (EV_A)) |
|
|
4464 | { |
|
|
4465 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
4466 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
4467 | } |
|
|
4468 | } |
|
|
4469 | |
|
|
4470 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
4471 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
4472 | thread to continue: |
|
|
4473 | |
|
|
4474 | static void |
|
|
4475 | real_invoke_pending (EV_P) |
|
|
4476 | { |
|
|
4477 | userdata *u = ev_userdata (EV_A); |
|
|
4478 | |
|
|
4479 | pthread_mutex_lock (&u->lock); |
|
|
4480 | ev_invoke_pending (EV_A); |
|
|
4481 | pthread_cond_signal (&u->invoke_cv); |
|
|
4482 | pthread_mutex_unlock (&u->lock); |
|
|
4483 | } |
|
|
4484 | |
|
|
4485 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
4486 | event loop, you will now have to lock: |
|
|
4487 | |
|
|
4488 | ev_timer timeout_watcher; |
|
|
4489 | userdata *u = ev_userdata (EV_A); |
|
|
4490 | |
|
|
4491 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
4492 | |
|
|
4493 | pthread_mutex_lock (&u->lock); |
|
|
4494 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
4495 | ev_async_send (EV_A_ &u->async_w); |
|
|
4496 | pthread_mutex_unlock (&u->lock); |
|
|
4497 | |
|
|
4498 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
4499 | an event loop currently blocking in the kernel will have no knowledge |
|
|
4500 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
4501 | watchers in the next event loop iteration. |
|
|
4502 | |
4735 | |
4503 | =head3 COROUTINES |
4736 | =head3 COROUTINES |
4504 | |
4737 | |
4505 | Libev is very accommodating to coroutines ("cooperative threads"): |
4738 | Libev is very accommodating to coroutines ("cooperative threads"): |
4506 | libev fully supports nesting calls to its functions from different |
4739 | libev fully supports nesting calls to its functions from different |
… | |
… | |
4671 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4904 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4672 | model. Libev still offers limited functionality on this platform in |
4905 | model. Libev still offers limited functionality on this platform in |
4673 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4906 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4674 | descriptors. This only applies when using Win32 natively, not when using |
4907 | descriptors. This only applies when using Win32 natively, not when using |
4675 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4908 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4676 | as every compielr comes with a slightly differently broken/incompatible |
4909 | as every compiler comes with a slightly differently broken/incompatible |
4677 | environment. |
4910 | environment. |
4678 | |
4911 | |
4679 | Lifting these limitations would basically require the full |
4912 | Lifting these limitations would basically require the full |
4680 | re-implementation of the I/O system. If you are into this kind of thing, |
4913 | re-implementation of the I/O system. If you are into this kind of thing, |
4681 | then note that glib does exactly that for you in a very portable way (note |
4914 | then note that glib does exactly that for you in a very portable way (note |
… | |
… | |
5015 | The physical time that is observed. It is apparently strictly monotonic :) |
5248 | The physical time that is observed. It is apparently strictly monotonic :) |
5016 | |
5249 | |
5017 | =item wall-clock time |
5250 | =item wall-clock time |
5018 | |
5251 | |
5019 | The time and date as shown on clocks. Unlike real time, it can actually |
5252 | The time and date as shown on clocks. Unlike real time, it can actually |
5020 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
5253 | be wrong and jump forwards and backwards, e.g. when you adjust your |
5021 | clock. |
5254 | clock. |
5022 | |
5255 | |
5023 | =item watcher |
5256 | =item watcher |
5024 | |
5257 | |
5025 | A data structure that describes interest in certain events. Watchers need |
5258 | A data structure that describes interest in certain events. Watchers need |
… | |
… | |
5028 | =back |
5261 | =back |
5029 | |
5262 | |
5030 | =head1 AUTHOR |
5263 | =head1 AUTHOR |
5031 | |
5264 | |
5032 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5265 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5033 | Magnusson and Emanuele Giaquinta. |
5266 | Magnusson and Emanuele Giaquinta, and minor corrections by many others. |
5034 | |
5267 | |