… | |
… | |
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 | |
… | |
… | |
299 | } |
299 | } |
300 | |
300 | |
301 | ... |
301 | ... |
302 | ev_set_syserr_cb (fatal_error); |
302 | ev_set_syserr_cb (fatal_error); |
303 | |
303 | |
|
|
304 | =item ev_feed_signal (int signum) |
|
|
305 | |
|
|
306 | This function can be used to "simulate" a signal receive. It is completely |
|
|
307 | safe to call this function at any time, from any context, including signal |
|
|
308 | handlers or random threads. |
|
|
309 | |
|
|
310 | Its main use is to customise signal handling in your process, especially |
|
|
311 | in the presence of threads. For example, you could block signals |
|
|
312 | by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when |
|
|
313 | creating any loops), and in one thread, use C<sigwait> or any other |
|
|
314 | mechanism to wait for signals, then "deliver" them to libev by calling |
|
|
315 | C<ev_feed_signal>. |
|
|
316 | |
304 | =back |
317 | =back |
305 | |
318 | |
306 | =head1 FUNCTIONS CONTROLLING EVENT LOOPS |
319 | =head1 FUNCTIONS CONTROLLING EVENT LOOPS |
307 | |
320 | |
308 | An event loop is described by a C<struct ev_loop *> (the C<struct> is |
321 | An event loop is described by a C<struct ev_loop *> (the C<struct> is |
… | |
… | |
418 | threads that are not interested in handling them. |
431 | threads that are not interested in handling them. |
419 | |
432 | |
420 | Signalfd will not be used by default as this changes your signal mask, and |
433 | 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 |
434 | there are a lot of shoddy libraries and programs (glib's threadpool for |
422 | example) that can't properly initialise their signal masks. |
435 | example) that can't properly initialise their signal masks. |
|
|
436 | |
|
|
437 | =item C<EVFLAG_NOSIGMASK> |
|
|
438 | |
|
|
439 | When this flag is specified, then libev will avoid to modify the signal |
|
|
440 | mask. Specifically, this means you ahve to make sure signals are unblocked |
|
|
441 | when you want to receive them. |
|
|
442 | |
|
|
443 | This behaviour is useful when you want to do your own signal handling, or |
|
|
444 | want to handle signals only in specific threads and want to avoid libev |
|
|
445 | unblocking the signals. |
|
|
446 | |
|
|
447 | It's also required by POSIX in a threaded program, as libev calls |
|
|
448 | C<sigprocmask>, whose behaviour is officially unspecified. |
|
|
449 | |
|
|
450 | This flag's behaviour will become the default in future versions of libev. |
423 | |
451 | |
424 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
452 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
425 | |
453 | |
426 | This is your standard select(2) backend. Not I<completely> standard, as |
454 | 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, |
455 | libev tries to roll its own fd_set with no limits on the number of fds, |
… | |
… | |
481 | employing an additional generation counter and comparing that against the |
509 | employing an additional generation counter and comparing that against the |
482 | events to filter out spurious ones, recreating the set when required. Last |
510 | events to filter out spurious ones, recreating the set when required. Last |
483 | not least, it also refuses to work with some file descriptors which work |
511 | not least, it also refuses to work with some file descriptors which work |
484 | perfectly fine with C<select> (files, many character devices...). |
512 | perfectly fine with C<select> (files, many character devices...). |
485 | |
513 | |
486 | Epoll is truly the train wreck analog among event poll mechanisms. |
514 | Epoll is truly the train wreck analog among event poll mechanisms, |
|
|
515 | a frankenpoll, cobbled together in a hurry, no thought to design or |
|
|
516 | interaction with others. |
487 | |
517 | |
488 | While stopping, setting and starting an I/O watcher in the same iteration |
518 | 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 |
519 | 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 |
520 | 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 |
521 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
… | |
… | |
557 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
587 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
558 | |
588 | |
559 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
589 | 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)). |
590 | it's really slow, but it still scales very well (O(active_fds)). |
561 | |
591 | |
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 |
592 | 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 |
593 | file descriptor per loop iteration. For small and medium numbers of file |
568 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
594 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
569 | might perform better. |
595 | might perform better. |
570 | |
596 | |
571 | On the positive side, with the exception of the spurious readiness |
597 | 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 |
598 | specification in all tests and is fully embeddable, which is a rare feat |
574 | OS-specific backends (I vastly prefer correctness over speed hacks). |
599 | among the OS-specific backends (I vastly prefer correctness over speed |
|
|
600 | hacks). |
|
|
601 | |
|
|
602 | On the negative side, the interface is I<bizarre> - so bizarre that |
|
|
603 | even sun itself gets it wrong in their code examples: The event polling |
|
|
604 | function sometimes returning events to the caller even though an error |
|
|
605 | occurred, but with no indication whether it has done so or not (yes, it's |
|
|
606 | even documented that way) - deadly for edge-triggered interfaces where |
|
|
607 | you absolutely have to know whether an event occurred or not because you |
|
|
608 | have to re-arm the watcher. |
|
|
609 | |
|
|
610 | Fortunately libev seems to be able to work around these idiocies. |
575 | |
611 | |
576 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
612 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
577 | C<EVBACKEND_POLL>. |
613 | C<EVBACKEND_POLL>. |
578 | |
614 | |
579 | =item C<EVBACKEND_ALL> |
615 | =item C<EVBACKEND_ALL> |
580 | |
616 | |
581 | Try all backends (even potentially broken ones that wouldn't be tried |
617 | 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 |
618 | with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as |
583 | C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
619 | C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
584 | |
620 | |
585 | It is definitely not recommended to use this flag. |
621 | It is definitely not recommended to use this flag, use whatever |
|
|
622 | C<ev_recommended_backends ()> returns, or simply do not specify a backend |
|
|
623 | at all. |
|
|
624 | |
|
|
625 | =item C<EVBACKEND_MASK> |
|
|
626 | |
|
|
627 | Not a backend at all, but a mask to select all backend bits from a |
|
|
628 | C<flags> value, in case you want to mask out any backends from a flags |
|
|
629 | value (e.g. when modifying the C<LIBEV_FLAGS> environment variable). |
586 | |
630 | |
587 | =back |
631 | =back |
588 | |
632 | |
589 | If one or more of the backend flags are or'ed into the flags value, |
633 | 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 |
634 | then only these backends will be tried (in the reverse order as listed |
… | |
… | |
824 | anymore. |
868 | anymore. |
825 | |
869 | |
826 | ... queue jobs here, make sure they register event watchers as long |
870 | ... 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..) |
871 | ... as they still have work to do (even an idle watcher will do..) |
828 | ev_run (my_loop, 0); |
872 | ev_run (my_loop, 0); |
829 | ... jobs done or somebody called unloop. yeah! |
873 | ... jobs done or somebody called break. yeah! |
830 | |
874 | |
831 | =item ev_break (loop, how) |
875 | =item ev_break (loop, how) |
832 | |
876 | |
833 | Can be used to make a call to C<ev_run> return early (but only after it |
877 | 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 |
878 | has processed all outstanding events). The C<how> argument must be either |
… | |
… | |
867 | running when nothing else is active. |
911 | running when nothing else is active. |
868 | |
912 | |
869 | ev_signal exitsig; |
913 | ev_signal exitsig; |
870 | ev_signal_init (&exitsig, sig_cb, SIGINT); |
914 | ev_signal_init (&exitsig, sig_cb, SIGINT); |
871 | ev_signal_start (loop, &exitsig); |
915 | ev_signal_start (loop, &exitsig); |
872 | evf_unref (loop); |
916 | ev_unref (loop); |
873 | |
917 | |
874 | Example: For some weird reason, unregister the above signal handler again. |
918 | Example: For some weird reason, unregister the above signal handler again. |
875 | |
919 | |
876 | ev_ref (loop); |
920 | ev_ref (loop); |
877 | ev_signal_stop (loop, &exitsig); |
921 | ev_signal_stop (loop, &exitsig); |
… | |
… | |
1316 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1360 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1317 | functions that do not need a watcher. |
1361 | functions that do not need a watcher. |
1318 | |
1362 | |
1319 | =back |
1363 | =back |
1320 | |
1364 | |
1321 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1365 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1322 | |
1366 | 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 | |
1367 | |
1386 | =head2 WATCHER STATES |
1368 | =head2 WATCHER STATES |
1387 | |
1369 | |
1388 | There are various watcher states mentioned throughout this manual - |
1370 | There are various watcher states mentioned throughout this manual - |
1389 | active, pending and so on. In this section these states and the rules to |
1371 | active, pending and so on. In this section these states and the rules to |
… | |
… | |
1396 | |
1378 | |
1397 | Before a watcher can be registered with the event looop it has to be |
1379 | Before a watcher can be registered with the event looop it has to be |
1398 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
1380 | 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. |
1381 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
1400 | |
1382 | |
1401 | In this state it is simply some block of memory that is suitable for use |
1383 | 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. |
1384 | use in an event loop. It can be moved around, freed, reused etc. at |
|
|
1385 | will - as long as you either keep the memory contents intact, or call |
|
|
1386 | C<ev_TYPE_init> again. |
1403 | |
1387 | |
1404 | =item started/running/active |
1388 | =item started/running/active |
1405 | |
1389 | |
1406 | Once a watcher has been started with a call to C<ev_TYPE_start> it becomes |
1390 | 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 |
1391 | 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 |
1419 | 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 |
1420 | of whether it was active or not, so stopping a watcher explicitly before |
1437 | freeing it is often a good idea. |
1421 | freeing it is often a good idea. |
1438 | |
1422 | |
1439 | While stopped (and not pending) the watcher is essentially in the |
1423 | 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 |
1424 | initialised state, that is, it can be reused, moved, modified in any way |
1441 | you wish. |
1425 | you wish (but when you trash the memory block, you need to C<ev_TYPE_init> |
|
|
1426 | it again). |
1442 | |
1427 | |
1443 | =back |
1428 | =back |
1444 | |
1429 | |
1445 | =head2 WATCHER PRIORITY MODELS |
1430 | =head2 WATCHER PRIORITY MODELS |
1446 | |
1431 | |
… | |
… | |
1575 | In general you can register as many read and/or write event watchers per |
1560 | 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 |
1561 | 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 |
1562 | descriptors to non-blocking mode is also usually a good idea (but not |
1578 | required if you know what you are doing). |
1563 | required if you know what you are doing). |
1579 | |
1564 | |
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 |
1565 | 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 |
1566 | 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 |
1567 | 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 |
1568 | 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 |
1569 | with a relatively standard program structure. Thus it is best to always |
1591 | this situation even with a relatively standard program structure. Thus |
1570 | 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. |
1571 | preferable to a program hanging until some data arrives. |
1594 | |
1572 | |
1595 | If you cannot run the fd in non-blocking mode (for example you should |
1573 | 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 |
1574 | 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 |
1575 | 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 |
1576 | 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 |
1577 | 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 |
1578 | use C<SIGALRM> and an interval timer, just to be sure you won't block |
1601 | indefinitely. |
1579 | indefinitely. |
1602 | |
1580 | |
1603 | But really, best use non-blocking mode. |
1581 | But really, best use non-blocking mode. |
1604 | |
1582 | |
… | |
… | |
1632 | |
1610 | |
1633 | There is no workaround possible except not registering events |
1611 | There is no workaround possible except not registering events |
1634 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1612 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1635 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1613 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1636 | |
1614 | |
|
|
1615 | =head3 The special problem of files |
|
|
1616 | |
|
|
1617 | Many people try to use C<select> (or libev) on file descriptors |
|
|
1618 | representing files, and expect it to become ready when their program |
|
|
1619 | doesn't block on disk accesses (which can take a long time on their own). |
|
|
1620 | |
|
|
1621 | However, this cannot ever work in the "expected" way - you get a readiness |
|
|
1622 | notification as soon as the kernel knows whether and how much data is |
|
|
1623 | there, and in the case of open files, that's always the case, so you |
|
|
1624 | always get a readiness notification instantly, and your read (or possibly |
|
|
1625 | write) will still block on the disk I/O. |
|
|
1626 | |
|
|
1627 | Another way to view it is that in the case of sockets, pipes, character |
|
|
1628 | devices and so on, there is another party (the sender) that delivers data |
|
|
1629 | on its own, but in the case of files, there is no such thing: the disk |
|
|
1630 | will not send data on its own, simply because it doesn't know what you |
|
|
1631 | wish to read - you would first have to request some data. |
|
|
1632 | |
|
|
1633 | Since files are typically not-so-well supported by advanced notification |
|
|
1634 | mechanism, libev tries hard to emulate POSIX behaviour with respect |
|
|
1635 | to files, even though you should not use it. The reason for this is |
|
|
1636 | convenience: sometimes you want to watch STDIN or STDOUT, which is |
|
|
1637 | usually a tty, often a pipe, but also sometimes files or special devices |
|
|
1638 | (for example, C<epoll> on Linux works with F</dev/random> but not with |
|
|
1639 | F</dev/urandom>), and even though the file might better be served with |
|
|
1640 | asynchronous I/O instead of with non-blocking I/O, it is still useful when |
|
|
1641 | it "just works" instead of freezing. |
|
|
1642 | |
|
|
1643 | So avoid file descriptors pointing to files when you know it (e.g. use |
|
|
1644 | libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or |
|
|
1645 | when you rarely read from a file instead of from a socket, and want to |
|
|
1646 | reuse the same code path. |
|
|
1647 | |
1637 | =head3 The special problem of fork |
1648 | =head3 The special problem of fork |
1638 | |
1649 | |
1639 | Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1650 | 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 |
1651 | useless behaviour. Libev fully supports fork, but needs to be told about |
1641 | it in the child. |
1652 | it in the child if you want to continue to use it in the child. |
1642 | |
1653 | |
1643 | To support fork in your programs, you either have to call |
1654 | 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, |
1655 | ()> 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 |
1656 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1646 | C<EVBACKEND_POLL>. |
|
|
1647 | |
1657 | |
1648 | =head3 The special problem of SIGPIPE |
1658 | =head3 The special problem of SIGPIPE |
1649 | |
1659 | |
1650 | While not really specific to libev, it is easy to forget about C<SIGPIPE>: |
1660 | 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 |
1661 | when writing to a pipe whose other end has been closed, your program gets |
… | |
… | |
2296 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2306 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2297 | |
2307 | |
2298 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2308 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2299 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2309 | (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, |
2310 | 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. |
2311 | and might or might not set or restore the installed signal handler (but |
|
|
2312 | see C<EVFLAG_NOSIGMASK>). |
2302 | |
2313 | |
2303 | While this does not matter for the signal disposition (libev never |
2314 | 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 |
2315 | 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 |
2316 | C<execve>), this matters for the signal mask: many programs do not expect |
2306 | certain signals to be blocked. |
2317 | certain signals to be blocked. |
… | |
… | |
2319 | I<has> to modify the signal mask, at least temporarily. |
2330 | I<has> to modify the signal mask, at least temporarily. |
2320 | |
2331 | |
2321 | So I can't stress this enough: I<If you do not reset your signal mask when |
2332 | 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 |
2333 | 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. |
2334 | is not a libev-specific thing, this is true for most event libraries. |
|
|
2335 | |
|
|
2336 | =head3 The special problem of threads signal handling |
|
|
2337 | |
|
|
2338 | POSIX threads has problematic signal handling semantics, specifically, |
|
|
2339 | a lot of functionality (sigfd, sigwait etc.) only really works if all |
|
|
2340 | threads in a process block signals, which is hard to achieve. |
|
|
2341 | |
|
|
2342 | When you want to use sigwait (or mix libev signal handling with your own |
|
|
2343 | for the same signals), you can tackle this problem by globally blocking |
|
|
2344 | all signals before creating any threads (or creating them with a fully set |
|
|
2345 | sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating |
|
|
2346 | loops. Then designate one thread as "signal receiver thread" which handles |
|
|
2347 | these signals. You can pass on any signals that libev might be interested |
|
|
2348 | in by calling C<ev_feed_signal>. |
2324 | |
2349 | |
2325 | =head3 Watcher-Specific Functions and Data Members |
2350 | =head3 Watcher-Specific Functions and Data Members |
2326 | |
2351 | |
2327 | =over 4 |
2352 | =over 4 |
2328 | |
2353 | |
… | |
… | |
3163 | atexit (program_exits); |
3188 | atexit (program_exits); |
3164 | |
3189 | |
3165 | |
3190 | |
3166 | =head2 C<ev_async> - how to wake up an event loop |
3191 | =head2 C<ev_async> - how to wake up an event loop |
3167 | |
3192 | |
3168 | In general, you cannot use an C<ev_run> from multiple threads or other |
3193 | 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 |
3194 | asynchronous sources such as signal handlers (as opposed to multiple event |
3170 | loops - those are of course safe to use in different threads). |
3195 | loops - those are of course safe to use in different threads). |
3171 | |
3196 | |
3172 | Sometimes, however, you need to wake up an event loop you do not control, |
3197 | 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> |
3198 | 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. |
3200 | it by calling C<ev_async_send>, which is thread- and signal safe. |
3176 | |
3201 | |
3177 | This functionality is very similar to C<ev_signal> watchers, as signals, |
3202 | This functionality is very similar to C<ev_signal> watchers, as signals, |
3178 | too, are asynchronous in nature, and signals, too, will be compressed |
3203 | 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 |
3204 | (i.e. the number of callback invocations may be less than the number of |
3180 | C<ev_async_sent> calls). |
3205 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
|
|
3206 | of "global async watchers" by using a watcher on an otherwise unused |
|
|
3207 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
|
|
3208 | even without knowing which loop owns the signal. |
3181 | |
3209 | |
3182 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
3210 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
3183 | just the default loop. |
3211 | just the default loop. |
3184 | |
3212 | |
3185 | =head3 Queueing |
3213 | =head3 Queueing |
… | |
… | |
3280 | trust me. |
3308 | trust me. |
3281 | |
3309 | |
3282 | =item ev_async_send (loop, ev_async *) |
3310 | =item ev_async_send (loop, ev_async *) |
3283 | |
3311 | |
3284 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3312 | 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 |
3313 | an C<EV_ASYNC> event on the watcher into the event loop, and instantly |
|
|
3314 | returns. |
|
|
3315 | |
3286 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
3316 | 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 |
3317 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3288 | section below on what exactly this means). |
3318 | embedding section below on what exactly this means). |
3289 | |
3319 | |
3290 | Note that, as with other watchers in libev, multiple events might get |
3320 | 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 |
3321 | 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>, |
3322 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3293 | reset when the event loop detects that). |
3323 | reset when the event loop detects that). |
… | |
… | |
3361 | Feed an event on the given fd, as if a file descriptor backend detected |
3391 | Feed an event on the given fd, as if a file descriptor backend detected |
3362 | the given events it. |
3392 | the given events it. |
3363 | |
3393 | |
3364 | =item ev_feed_signal_event (loop, int signum) |
3394 | =item ev_feed_signal_event (loop, int signum) |
3365 | |
3395 | |
3366 | Feed an event as if the given signal occurred (C<loop> must be the default |
3396 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3367 | loop!). |
3397 | which is async-safe. |
3368 | |
3398 | |
3369 | =back |
3399 | =back |
3370 | |
3400 | |
3371 | |
3401 | |
3372 | =head1 COMMON OR USEFUL IDIOMS (OR BOTH) |
3402 | =head1 COMMON OR USEFUL IDIOMS (OR BOTH) |
3373 | |
3403 | |
3374 | This section explains some common idioms that are not immediately |
3404 | This section explains some common idioms that are not immediately |
3375 | obvious. Note that examples are sprinkled over the whole manual, and this |
3405 | obvious. Note that examples are sprinkled over the whole manual, and this |
3376 | section only contains stuff that wouldn't fit anywhere else. |
3406 | section only contains stuff that wouldn't fit anywhere else. |
3377 | |
3407 | |
3378 | =over 4 |
3408 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
3379 | |
3409 | |
3380 | =item Model/nested event loop invocations and exit conditions. |
3410 | Each watcher has, by default, a C<void *data> member that you can read |
|
|
3411 | or modify at any time: libev will completely ignore it. This can be used |
|
|
3412 | to associate arbitrary data with your watcher. If you need more data and |
|
|
3413 | don't want to allocate memory separately and store a pointer to it in that |
|
|
3414 | data member, you can also "subclass" the watcher type and provide your own |
|
|
3415 | data: |
|
|
3416 | |
|
|
3417 | struct my_io |
|
|
3418 | { |
|
|
3419 | ev_io io; |
|
|
3420 | int otherfd; |
|
|
3421 | void *somedata; |
|
|
3422 | struct whatever *mostinteresting; |
|
|
3423 | }; |
|
|
3424 | |
|
|
3425 | ... |
|
|
3426 | struct my_io w; |
|
|
3427 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
3428 | |
|
|
3429 | And since your callback will be called with a pointer to the watcher, you |
|
|
3430 | can cast it back to your own type: |
|
|
3431 | |
|
|
3432 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
3433 | { |
|
|
3434 | struct my_io *w = (struct my_io *)w_; |
|
|
3435 | ... |
|
|
3436 | } |
|
|
3437 | |
|
|
3438 | More interesting and less C-conformant ways of casting your callback |
|
|
3439 | function type instead have been omitted. |
|
|
3440 | |
|
|
3441 | =head2 BUILDING YOUR OWN COMPOSITE WATCHERS |
|
|
3442 | |
|
|
3443 | Another common scenario is to use some data structure with multiple |
|
|
3444 | embedded watchers, in effect creating your own watcher that combines |
|
|
3445 | multiple libev event sources into one "super-watcher": |
|
|
3446 | |
|
|
3447 | struct my_biggy |
|
|
3448 | { |
|
|
3449 | int some_data; |
|
|
3450 | ev_timer t1; |
|
|
3451 | ev_timer t2; |
|
|
3452 | } |
|
|
3453 | |
|
|
3454 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
3455 | complicated: Either you store the address of your C<my_biggy> struct in |
|
|
3456 | the C<data> member of the watcher (for woozies or C++ coders), or you need |
|
|
3457 | to use some pointer arithmetic using C<offsetof> inside your watchers (for |
|
|
3458 | real programmers): |
|
|
3459 | |
|
|
3460 | #include <stddef.h> |
|
|
3461 | |
|
|
3462 | static void |
|
|
3463 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
3464 | { |
|
|
3465 | struct my_biggy big = (struct my_biggy *) |
|
|
3466 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
3467 | } |
|
|
3468 | |
|
|
3469 | static void |
|
|
3470 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
3471 | { |
|
|
3472 | struct my_biggy big = (struct my_biggy *) |
|
|
3473 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
3474 | } |
|
|
3475 | |
|
|
3476 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3381 | |
3477 | |
3382 | Often (especially in GUI toolkits) there are places where you have |
3478 | Often (especially in GUI toolkits) there are places where you have |
3383 | I<modal> interaction, which is most easily implemented by recursively |
3479 | I<modal> interaction, which is most easily implemented by recursively |
3384 | invoking C<ev_run>. |
3480 | invoking C<ev_run>. |
3385 | |
3481 | |
… | |
… | |
3414 | exit_main_loop = 1; |
3510 | exit_main_loop = 1; |
3415 | |
3511 | |
3416 | // exit both |
3512 | // exit both |
3417 | exit_main_loop = exit_nested_loop = 1; |
3513 | exit_main_loop = exit_nested_loop = 1; |
3418 | |
3514 | |
3419 | =back |
3515 | =head2 THREAD LOCKING EXAMPLE |
|
|
3516 | |
|
|
3517 | Here is a fictitious example of how to run an event loop in a different |
|
|
3518 | thread from where callbacks are being invoked and watchers are |
|
|
3519 | created/added/removed. |
|
|
3520 | |
|
|
3521 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
3522 | which uses exactly this technique (which is suited for many high-level |
|
|
3523 | languages). |
|
|
3524 | |
|
|
3525 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
3526 | variable to wait for callback invocations, an async watcher to notify the |
|
|
3527 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
3528 | |
|
|
3529 | First, you need to associate some data with the event loop: |
|
|
3530 | |
|
|
3531 | typedef struct { |
|
|
3532 | mutex_t lock; /* global loop lock */ |
|
|
3533 | ev_async async_w; |
|
|
3534 | thread_t tid; |
|
|
3535 | cond_t invoke_cv; |
|
|
3536 | } userdata; |
|
|
3537 | |
|
|
3538 | void prepare_loop (EV_P) |
|
|
3539 | { |
|
|
3540 | // for simplicity, we use a static userdata struct. |
|
|
3541 | static userdata u; |
|
|
3542 | |
|
|
3543 | ev_async_init (&u->async_w, async_cb); |
|
|
3544 | ev_async_start (EV_A_ &u->async_w); |
|
|
3545 | |
|
|
3546 | pthread_mutex_init (&u->lock, 0); |
|
|
3547 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
3548 | |
|
|
3549 | // now associate this with the loop |
|
|
3550 | ev_set_userdata (EV_A_ u); |
|
|
3551 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
3552 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
3553 | |
|
|
3554 | // then create the thread running ev_run |
|
|
3555 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
3556 | } |
|
|
3557 | |
|
|
3558 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
3559 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
3560 | that might have been added: |
|
|
3561 | |
|
|
3562 | static void |
|
|
3563 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
3564 | { |
|
|
3565 | // just used for the side effects |
|
|
3566 | } |
|
|
3567 | |
|
|
3568 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
3569 | protecting the loop data, respectively. |
|
|
3570 | |
|
|
3571 | static void |
|
|
3572 | l_release (EV_P) |
|
|
3573 | { |
|
|
3574 | userdata *u = ev_userdata (EV_A); |
|
|
3575 | pthread_mutex_unlock (&u->lock); |
|
|
3576 | } |
|
|
3577 | |
|
|
3578 | static void |
|
|
3579 | l_acquire (EV_P) |
|
|
3580 | { |
|
|
3581 | userdata *u = ev_userdata (EV_A); |
|
|
3582 | pthread_mutex_lock (&u->lock); |
|
|
3583 | } |
|
|
3584 | |
|
|
3585 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
3586 | into C<ev_run>: |
|
|
3587 | |
|
|
3588 | void * |
|
|
3589 | l_run (void *thr_arg) |
|
|
3590 | { |
|
|
3591 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
3592 | |
|
|
3593 | l_acquire (EV_A); |
|
|
3594 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
3595 | ev_run (EV_A_ 0); |
|
|
3596 | l_release (EV_A); |
|
|
3597 | |
|
|
3598 | return 0; |
|
|
3599 | } |
|
|
3600 | |
|
|
3601 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
3602 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
3603 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
3604 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
3605 | and b) skipping inter-thread-communication when there are no pending |
|
|
3606 | watchers is very beneficial): |
|
|
3607 | |
|
|
3608 | static void |
|
|
3609 | l_invoke (EV_P) |
|
|
3610 | { |
|
|
3611 | userdata *u = ev_userdata (EV_A); |
|
|
3612 | |
|
|
3613 | while (ev_pending_count (EV_A)) |
|
|
3614 | { |
|
|
3615 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
3616 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
3617 | } |
|
|
3618 | } |
|
|
3619 | |
|
|
3620 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
3621 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
3622 | thread to continue: |
|
|
3623 | |
|
|
3624 | static void |
|
|
3625 | real_invoke_pending (EV_P) |
|
|
3626 | { |
|
|
3627 | userdata *u = ev_userdata (EV_A); |
|
|
3628 | |
|
|
3629 | pthread_mutex_lock (&u->lock); |
|
|
3630 | ev_invoke_pending (EV_A); |
|
|
3631 | pthread_cond_signal (&u->invoke_cv); |
|
|
3632 | pthread_mutex_unlock (&u->lock); |
|
|
3633 | } |
|
|
3634 | |
|
|
3635 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
3636 | event loop, you will now have to lock: |
|
|
3637 | |
|
|
3638 | ev_timer timeout_watcher; |
|
|
3639 | userdata *u = ev_userdata (EV_A); |
|
|
3640 | |
|
|
3641 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
3642 | |
|
|
3643 | pthread_mutex_lock (&u->lock); |
|
|
3644 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
3645 | ev_async_send (EV_A_ &u->async_w); |
|
|
3646 | pthread_mutex_unlock (&u->lock); |
|
|
3647 | |
|
|
3648 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
3649 | an event loop currently blocking in the kernel will have no knowledge |
|
|
3650 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
3651 | watchers in the next event loop iteration. |
|
|
3652 | |
|
|
3653 | =head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS |
|
|
3654 | |
|
|
3655 | While the overhead of a callback that e.g. schedules a thread is small, it |
|
|
3656 | is still an overhead. If you embed libev, and your main usage is with some |
|
|
3657 | kind of threads or coroutines, you might want to customise libev so that |
|
|
3658 | doesn't need callbacks anymore. |
|
|
3659 | |
|
|
3660 | Imagine you have coroutines that you can switch to using a function |
|
|
3661 | C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro> |
|
|
3662 | and that due to some magic, the currently active coroutine is stored in a |
|
|
3663 | global called C<current_coro>. Then you can build your own "wait for libev |
|
|
3664 | event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note |
|
|
3665 | the differing C<;> conventions): |
|
|
3666 | |
|
|
3667 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3668 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb) |
|
|
3669 | |
|
|
3670 | That means instead of having a C callback function, you store the |
|
|
3671 | coroutine to switch to in each watcher, and instead of having libev call |
|
|
3672 | your callback, you instead have it switch to that coroutine. |
|
|
3673 | |
|
|
3674 | A coroutine might now wait for an event with a function called |
|
|
3675 | C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't |
|
|
3676 | matter when, or whether the watcher is active or not when this function is |
|
|
3677 | called): |
|
|
3678 | |
|
|
3679 | void |
|
|
3680 | wait_for_event (ev_watcher *w) |
|
|
3681 | { |
|
|
3682 | ev_cb_set (w) = current_coro; |
|
|
3683 | switch_to (libev_coro); |
|
|
3684 | } |
|
|
3685 | |
|
|
3686 | That basically suspends the coroutine inside C<wait_for_event> and |
|
|
3687 | continues the libev coroutine, which, when appropriate, switches back to |
|
|
3688 | this or any other coroutine. I am sure if you sue this your own :) |
|
|
3689 | |
|
|
3690 | You can do similar tricks if you have, say, threads with an event queue - |
|
|
3691 | instead of storing a coroutine, you store the queue object and instead of |
|
|
3692 | switching to a coroutine, you push the watcher onto the queue and notify |
|
|
3693 | any waiters. |
|
|
3694 | |
|
|
3695 | To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two |
|
|
3696 | files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: |
|
|
3697 | |
|
|
3698 | // my_ev.h |
|
|
3699 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3700 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); |
|
|
3701 | #include "../libev/ev.h" |
|
|
3702 | |
|
|
3703 | // my_ev.c |
|
|
3704 | #define EV_H "my_ev.h" |
|
|
3705 | #include "../libev/ev.c" |
|
|
3706 | |
|
|
3707 | And then use F<my_ev.h> when you would normally use F<ev.h>, and compile |
|
|
3708 | F<my_ev.c> into your project. When properly specifying include paths, you |
|
|
3709 | can even use F<ev.h> as header file name directly. |
3420 | |
3710 | |
3421 | |
3711 | |
3422 | =head1 LIBEVENT EMULATION |
3712 | =head1 LIBEVENT EMULATION |
3423 | |
3713 | |
3424 | Libev offers a compatibility emulation layer for libevent. It cannot |
3714 | Libev offers a compatibility emulation layer for libevent. It cannot |
… | |
… | |
3427 | =over 4 |
3717 | =over 4 |
3428 | |
3718 | |
3429 | =item * Only the libevent-1.4.1-beta API is being emulated. |
3719 | =item * Only the libevent-1.4.1-beta API is being emulated. |
3430 | |
3720 | |
3431 | This was the newest libevent version available when libev was implemented, |
3721 | This was the newest libevent version available when libev was implemented, |
3432 | and is still mostly uncanged in 2010. |
3722 | and is still mostly unchanged in 2010. |
3433 | |
3723 | |
3434 | =item * Use it by including <event.h>, as usual. |
3724 | =item * Use it by including <event.h>, as usual. |
3435 | |
3725 | |
3436 | =item * The following members are fully supported: ev_base, ev_callback, |
3726 | =item * The following members are fully supported: ev_base, ev_callback, |
3437 | ev_arg, ev_fd, ev_res, ev_events. |
3727 | ev_arg, ev_fd, ev_res, ev_events. |
… | |
… | |
3472 | Care has been taken to keep the overhead low. The only data member the C++ |
3762 | Care has been taken to keep the overhead low. The only data member the C++ |
3473 | classes add (compared to plain C-style watchers) is the event loop pointer |
3763 | classes add (compared to plain C-style watchers) is the event loop pointer |
3474 | that the watcher is associated with (or no additional members at all if |
3764 | that the watcher is associated with (or no additional members at all if |
3475 | you disable C<EV_MULTIPLICITY> when embedding libev). |
3765 | you disable C<EV_MULTIPLICITY> when embedding libev). |
3476 | |
3766 | |
3477 | Currently, functions, and static and non-static member functions can be |
3767 | Currently, functions, static and non-static member functions and classes |
3478 | used as callbacks. Other types should be easy to add as long as they only |
3768 | with C<operator ()> can be used as callbacks. Other types should be easy |
3479 | need one additional pointer for context. If you need support for other |
3769 | to add as long as they only need one additional pointer for context. If |
3480 | types of functors please contact the author (preferably after implementing |
3770 | you need support for other types of functors please contact the author |
3481 | it). |
3771 | (preferably after implementing it). |
3482 | |
3772 | |
3483 | Here is a list of things available in the C<ev> namespace: |
3773 | Here is a list of things available in the C<ev> namespace: |
3484 | |
3774 | |
3485 | =over 4 |
3775 | =over 4 |
3486 | |
3776 | |
… | |
… | |
4354 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4644 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4355 | |
4645 | |
4356 | #include "ev_cpp.h" |
4646 | #include "ev_cpp.h" |
4357 | #include "ev.c" |
4647 | #include "ev.c" |
4358 | |
4648 | |
4359 | =head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES |
4649 | =head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT |
4360 | |
4650 | |
4361 | =head2 THREADS AND COROUTINES |
4651 | =head2 THREADS AND COROUTINES |
4362 | |
4652 | |
4363 | =head3 THREADS |
4653 | =head3 THREADS |
4364 | |
4654 | |
… | |
… | |
4415 | default loop and triggering an C<ev_async> watcher from the default loop |
4705 | default loop and triggering an C<ev_async> watcher from the default loop |
4416 | watcher callback into the event loop interested in the signal. |
4706 | watcher callback into the event loop interested in the signal. |
4417 | |
4707 | |
4418 | =back |
4708 | =back |
4419 | |
4709 | |
4420 | =head4 THREAD LOCKING EXAMPLE |
4710 | See also L<THREAD LOCKING EXAMPLE>. |
4421 | |
|
|
4422 | Here is a fictitious example of how to run an event loop in a different |
|
|
4423 | thread than where callbacks are being invoked and watchers are |
|
|
4424 | created/added/removed. |
|
|
4425 | |
|
|
4426 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
4427 | which uses exactly this technique (which is suited for many high-level |
|
|
4428 | languages). |
|
|
4429 | |
|
|
4430 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
4431 | variable to wait for callback invocations, an async watcher to notify the |
|
|
4432 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
4433 | |
|
|
4434 | First, you need to associate some data with the event loop: |
|
|
4435 | |
|
|
4436 | typedef struct { |
|
|
4437 | mutex_t lock; /* global loop lock */ |
|
|
4438 | ev_async async_w; |
|
|
4439 | thread_t tid; |
|
|
4440 | cond_t invoke_cv; |
|
|
4441 | } userdata; |
|
|
4442 | |
|
|
4443 | void prepare_loop (EV_P) |
|
|
4444 | { |
|
|
4445 | // for simplicity, we use a static userdata struct. |
|
|
4446 | static userdata u; |
|
|
4447 | |
|
|
4448 | ev_async_init (&u->async_w, async_cb); |
|
|
4449 | ev_async_start (EV_A_ &u->async_w); |
|
|
4450 | |
|
|
4451 | pthread_mutex_init (&u->lock, 0); |
|
|
4452 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
4453 | |
|
|
4454 | // now associate this with the loop |
|
|
4455 | ev_set_userdata (EV_A_ u); |
|
|
4456 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
4457 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
4458 | |
|
|
4459 | // then create the thread running ev_loop |
|
|
4460 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
4461 | } |
|
|
4462 | |
|
|
4463 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
4464 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
4465 | that might have been added: |
|
|
4466 | |
|
|
4467 | static void |
|
|
4468 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
4469 | { |
|
|
4470 | // just used for the side effects |
|
|
4471 | } |
|
|
4472 | |
|
|
4473 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
4474 | protecting the loop data, respectively. |
|
|
4475 | |
|
|
4476 | static void |
|
|
4477 | l_release (EV_P) |
|
|
4478 | { |
|
|
4479 | userdata *u = ev_userdata (EV_A); |
|
|
4480 | pthread_mutex_unlock (&u->lock); |
|
|
4481 | } |
|
|
4482 | |
|
|
4483 | static void |
|
|
4484 | l_acquire (EV_P) |
|
|
4485 | { |
|
|
4486 | userdata *u = ev_userdata (EV_A); |
|
|
4487 | pthread_mutex_lock (&u->lock); |
|
|
4488 | } |
|
|
4489 | |
|
|
4490 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
4491 | into C<ev_run>: |
|
|
4492 | |
|
|
4493 | void * |
|
|
4494 | l_run (void *thr_arg) |
|
|
4495 | { |
|
|
4496 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
4497 | |
|
|
4498 | l_acquire (EV_A); |
|
|
4499 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
4500 | ev_run (EV_A_ 0); |
|
|
4501 | l_release (EV_A); |
|
|
4502 | |
|
|
4503 | return 0; |
|
|
4504 | } |
|
|
4505 | |
|
|
4506 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
4507 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
4508 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
4509 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
4510 | and b) skipping inter-thread-communication when there are no pending |
|
|
4511 | watchers is very beneficial): |
|
|
4512 | |
|
|
4513 | static void |
|
|
4514 | l_invoke (EV_P) |
|
|
4515 | { |
|
|
4516 | userdata *u = ev_userdata (EV_A); |
|
|
4517 | |
|
|
4518 | while (ev_pending_count (EV_A)) |
|
|
4519 | { |
|
|
4520 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
4521 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
4522 | } |
|
|
4523 | } |
|
|
4524 | |
|
|
4525 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
4526 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
4527 | thread to continue: |
|
|
4528 | |
|
|
4529 | static void |
|
|
4530 | real_invoke_pending (EV_P) |
|
|
4531 | { |
|
|
4532 | userdata *u = ev_userdata (EV_A); |
|
|
4533 | |
|
|
4534 | pthread_mutex_lock (&u->lock); |
|
|
4535 | ev_invoke_pending (EV_A); |
|
|
4536 | pthread_cond_signal (&u->invoke_cv); |
|
|
4537 | pthread_mutex_unlock (&u->lock); |
|
|
4538 | } |
|
|
4539 | |
|
|
4540 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
4541 | event loop, you will now have to lock: |
|
|
4542 | |
|
|
4543 | ev_timer timeout_watcher; |
|
|
4544 | userdata *u = ev_userdata (EV_A); |
|
|
4545 | |
|
|
4546 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
4547 | |
|
|
4548 | pthread_mutex_lock (&u->lock); |
|
|
4549 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
4550 | ev_async_send (EV_A_ &u->async_w); |
|
|
4551 | pthread_mutex_unlock (&u->lock); |
|
|
4552 | |
|
|
4553 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
4554 | an event loop currently blocking in the kernel will have no knowledge |
|
|
4555 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
4556 | watchers in the next event loop iteration. |
|
|
4557 | |
4711 | |
4558 | =head3 COROUTINES |
4712 | =head3 COROUTINES |
4559 | |
4713 | |
4560 | Libev is very accommodating to coroutines ("cooperative threads"): |
4714 | Libev is very accommodating to coroutines ("cooperative threads"): |
4561 | libev fully supports nesting calls to its functions from different |
4715 | libev fully supports nesting calls to its functions from different |
… | |
… | |
5083 | =back |
5237 | =back |
5084 | |
5238 | |
5085 | =head1 AUTHOR |
5239 | =head1 AUTHOR |
5086 | |
5240 | |
5087 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5241 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5088 | Magnusson and Emanuele Giaquinta. |
5242 | Magnusson and Emanuele Giaquinta, and minor corrections by many others. |
5089 | |
5243 | |