… | |
… | |
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 | |
… | |
… | |
435 | example) that can't properly initialise their signal masks. |
441 | example) that can't properly initialise their signal masks. |
436 | |
442 | |
437 | =item C<EVFLAG_NOSIGMASK> |
443 | =item C<EVFLAG_NOSIGMASK> |
438 | |
444 | |
439 | When this flag is specified, then libev will avoid to modify the signal |
445 | 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 |
446 | mask. Specifically, this means you have to make sure signals are unblocked |
441 | when you want to receive them. |
447 | when you want to receive them. |
442 | |
448 | |
443 | This behaviour is useful when you want to do your own signal handling, or |
449 | 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 |
450 | want to handle signals only in specific threads and want to avoid libev |
445 | unblocking the signals. |
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. |
446 | |
455 | |
447 | This flag's behaviour will become the default in future versions of libev. |
456 | This flag's behaviour will become the default in future versions of libev. |
448 | |
457 | |
449 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
458 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
450 | |
459 | |
… | |
… | |
480 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
489 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
481 | |
490 | |
482 | 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 |
483 | kernels). |
492 | kernels). |
484 | |
493 | |
485 | 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 |
486 | but it scales phenomenally better. While poll and select usually scale |
495 | it scales phenomenally better. While poll and select usually scale like |
487 | 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 |
488 | epoll scales either O(1) or O(active_fds). |
497 | fd), epoll scales either O(1) or O(active_fds). |
489 | |
498 | |
490 | The epoll mechanism deserves honorable mention as the most misdesigned |
499 | The epoll mechanism deserves honorable mention as the most misdesigned |
491 | of the more advanced event mechanisms: mere annoyances include silently |
500 | of the more advanced event mechanisms: mere annoyances include silently |
492 | dropping file descriptors, requiring a system call per change per file |
501 | dropping file descriptors, requiring a system call per change per file |
493 | descriptor (and unnecessary guessing of parameters), problems with dup, |
502 | descriptor (and unnecessary guessing of parameters), problems with dup, |
… | |
… | |
496 | 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 |
497 | 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 |
498 | set, which can take considerable time (one syscall per file descriptor) |
507 | set, which can take considerable time (one syscall per file descriptor) |
499 | and is of course hard to detect. |
508 | and is of course hard to detect. |
500 | |
509 | |
501 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
510 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, |
502 | 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 |
503 | I<different> file descriptors (even already closed ones, so one cannot |
512 | totally I<different> file descriptors (even already closed ones, so |
504 | 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 |
505 | on SMP systems). Libev tries to counter these spurious notifications by |
514 | (especially on SMP systems). Libev tries to counter these spurious |
506 | employing an additional generation counter and comparing that against the |
515 | notifications by employing an additional generation counter and comparing |
507 | 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 |
508 | 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 |
509 | perfectly fine with C<select> (files, many character devices...). |
521 | perfectly fine with C<select> (files, many character devices...). |
510 | |
522 | |
511 | 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... |
512 | |
526 | |
513 | 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 |
514 | 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 |
515 | 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 |
516 | 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 |
… | |
… | |
592 | On the positive side, this backend actually performed fully to |
606 | On the positive side, this backend actually performed fully to |
593 | specification in all tests and is fully embeddable, which is a rare feat |
607 | specification in all tests and is fully embeddable, which is a rare feat |
594 | among the OS-specific backends (I vastly prefer correctness over speed |
608 | among the OS-specific backends (I vastly prefer correctness over speed |
595 | hacks). |
609 | hacks). |
596 | |
610 | |
597 | On the negative side, the interface is I<bizarre>, with the event polling |
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 |
598 | function sometimes returning events to the caller even though an error |
613 | function sometimes returns events to the caller even though an error |
599 | occured, but with no indication whether it has done so or not (yes, it's |
614 | occurred, but with no indication whether it has done so or not (yes, it's |
600 | even documented that way) - deadly for edge-triggered interfaces, but |
615 | even documented that way) - deadly for edge-triggered interfaces where you |
|
|
616 | absolutely have to know whether an event occurred or not because you have |
|
|
617 | to re-arm the watcher. |
|
|
618 | |
601 | fortunately libev seems to be able to work around it. |
619 | Fortunately libev seems to be able to work around these idiocies. |
602 | |
620 | |
603 | 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 |
604 | C<EVBACKEND_POLL>. |
622 | C<EVBACKEND_POLL>. |
605 | |
623 | |
606 | =item C<EVBACKEND_ALL> |
624 | =item C<EVBACKEND_ALL> |
… | |
… | |
816 | 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 |
817 | 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 |
818 | 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 |
819 | usually a better approach for this kind of thing. |
837 | usually a better approach for this kind of thing. |
820 | |
838 | |
821 | 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): |
822 | |
842 | |
823 | - Increment loop depth. |
843 | - Increment loop depth. |
824 | - Reset the ev_break status. |
844 | - Reset the ev_break status. |
825 | - Before the first iteration, call any pending watchers. |
845 | - Before the first iteration, call any pending watchers. |
826 | LOOP: |
846 | LOOP: |
… | |
… | |
859 | anymore. |
879 | anymore. |
860 | |
880 | |
861 | ... queue jobs here, make sure they register event watchers as long |
881 | ... queue jobs here, make sure they register event watchers as long |
862 | ... 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..) |
863 | ev_run (my_loop, 0); |
883 | ev_run (my_loop, 0); |
864 | ... jobs done or somebody called unloop. yeah! |
884 | ... jobs done or somebody called break. yeah! |
865 | |
885 | |
866 | =item ev_break (loop, how) |
886 | =item ev_break (loop, how) |
867 | |
887 | |
868 | 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 |
869 | 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 |
… | |
… | |
932 | 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. |
933 | |
953 | |
934 | 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 |
935 | 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, |
936 | 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 |
937 | 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 |
938 | 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 |
939 | 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 |
940 | once per this interval, on average. |
960 | once per this interval, on average (as long as the host time resolution is |
|
|
961 | good enough). |
941 | |
962 | |
942 | 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 |
943 | to spend more time collecting timeouts, at the expense of increased |
964 | to spend more time collecting timeouts, at the expense of increased |
944 | latency/jitter/inexactness (the watcher callback will be called |
965 | latency/jitter/inexactness (the watcher callback will be called |
945 | 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 |
… | |
… | |
1351 | 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 |
1352 | functions that do not need a watcher. |
1373 | functions that do not need a watcher. |
1353 | |
1374 | |
1354 | =back |
1375 | =back |
1355 | |
1376 | |
1356 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1377 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1357 | |
1378 | OWN COMPOSITE WATCHERS> idioms. |
1358 | Each watcher has, by default, a member C<void *data> that you can change |
|
|
1359 | and read at any time: libev will completely ignore it. This can be used |
|
|
1360 | to associate arbitrary data with your watcher. If you need more data and |
|
|
1361 | don't want to allocate memory and store a pointer to it in that data |
|
|
1362 | member, you can also "subclass" the watcher type and provide your own |
|
|
1363 | data: |
|
|
1364 | |
|
|
1365 | struct my_io |
|
|
1366 | { |
|
|
1367 | ev_io io; |
|
|
1368 | int otherfd; |
|
|
1369 | void *somedata; |
|
|
1370 | struct whatever *mostinteresting; |
|
|
1371 | }; |
|
|
1372 | |
|
|
1373 | ... |
|
|
1374 | struct my_io w; |
|
|
1375 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
1376 | |
|
|
1377 | And since your callback will be called with a pointer to the watcher, you |
|
|
1378 | can cast it back to your own type: |
|
|
1379 | |
|
|
1380 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
1381 | { |
|
|
1382 | struct my_io *w = (struct my_io *)w_; |
|
|
1383 | ... |
|
|
1384 | } |
|
|
1385 | |
|
|
1386 | More interesting and less C-conformant ways of casting your callback type |
|
|
1387 | instead have been omitted. |
|
|
1388 | |
|
|
1389 | Another common scenario is to use some data structure with multiple |
|
|
1390 | embedded watchers: |
|
|
1391 | |
|
|
1392 | struct my_biggy |
|
|
1393 | { |
|
|
1394 | int some_data; |
|
|
1395 | ev_timer t1; |
|
|
1396 | ev_timer t2; |
|
|
1397 | } |
|
|
1398 | |
|
|
1399 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
1400 | complicated: Either you store the address of your C<my_biggy> struct |
|
|
1401 | in the C<data> member of the watcher (for woozies), or you need to use |
|
|
1402 | some pointer arithmetic using C<offsetof> inside your watchers (for real |
|
|
1403 | programmers): |
|
|
1404 | |
|
|
1405 | #include <stddef.h> |
|
|
1406 | |
|
|
1407 | static void |
|
|
1408 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
1409 | { |
|
|
1410 | struct my_biggy big = (struct my_biggy *) |
|
|
1411 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
1412 | } |
|
|
1413 | |
|
|
1414 | static void |
|
|
1415 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
1416 | { |
|
|
1417 | struct my_biggy big = (struct my_biggy *) |
|
|
1418 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
1419 | } |
|
|
1420 | |
1379 | |
1421 | =head2 WATCHER STATES |
1380 | =head2 WATCHER STATES |
1422 | |
1381 | |
1423 | There are various watcher states mentioned throughout this manual - |
1382 | There are various watcher states mentioned throughout this manual - |
1424 | 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 |
… | |
… | |
1427 | |
1386 | |
1428 | =over 4 |
1387 | =over 4 |
1429 | |
1388 | |
1430 | =item initialiased |
1389 | =item initialiased |
1431 | |
1390 | |
1432 | 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 |
1433 | 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 |
1434 | 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. |
1435 | |
1394 | |
1436 | 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 |
1437 | 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. |
1438 | |
1399 | |
1439 | =item started/running/active |
1400 | =item started/running/active |
1440 | |
1401 | |
1441 | 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 |
1442 | 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 |
… | |
… | |
1470 | 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 |
1471 | 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 |
1472 | freeing it is often a good idea. |
1433 | freeing it is often a good idea. |
1473 | |
1434 | |
1474 | While stopped (and not pending) the watcher is essentially in the |
1435 | While stopped (and not pending) the watcher is essentially in the |
1475 | 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 |
1476 | you wish. |
1437 | you wish (but when you trash the memory block, you need to C<ev_TYPE_init> |
|
|
1438 | it again). |
1477 | |
1439 | |
1478 | =back |
1440 | =back |
1479 | |
1441 | |
1480 | =head2 WATCHER PRIORITY MODELS |
1442 | =head2 WATCHER PRIORITY MODELS |
1481 | |
1443 | |
… | |
… | |
1610 | 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 |
1611 | 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 |
1612 | 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 |
1613 | required if you know what you are doing). |
1575 | required if you know what you are doing). |
1614 | |
1576 | |
1615 | If you cannot use non-blocking mode, then force the use of a |
|
|
1616 | known-to-be-good backend (at the time of this writing, this includes only |
|
|
1617 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file |
|
|
1618 | descriptors for which non-blocking operation makes no sense (such as |
|
|
1619 | files) - libev doesn't guarantee any specific behaviour in that case. |
|
|
1620 | |
|
|
1621 | 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 |
1622 | receive "spurious" readiness notifications, that is your callback might |
1578 | receive "spurious" readiness notifications, that is, your callback might |
1623 | 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 |
1624 | 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 |
1625 | 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 |
1626 | 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 |
1627 | it is best to always use non-blocking I/O: An extra C<read>(2) returning |
|
|
1628 | C<EAGAIN> is far preferable to a program hanging until some data arrives. |
1583 | preferable to a program hanging until some data arrives. |
1629 | |
1584 | |
1630 | 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 |
1631 | 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 |
1632 | 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 |
1633 | 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 |
1634 | 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 |
1635 | 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 |
1636 | indefinitely. |
1591 | indefinitely. |
1637 | |
1592 | |
1638 | But really, best use non-blocking mode. |
1593 | But really, best use non-blocking mode. |
1639 | |
1594 | |
… | |
… | |
1667 | |
1622 | |
1668 | There is no workaround possible except not registering events |
1623 | There is no workaround possible except not registering events |
1669 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1624 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1670 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1625 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1671 | |
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 | |
1672 | =head3 The special problem of fork |
1660 | =head3 The special problem of fork |
1673 | |
1661 | |
1674 | 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 |
1675 | 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 |
1676 | it in the child. |
1664 | it in the child if you want to continue to use it in the child. |
1677 | |
1665 | |
1678 | 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 |
1679 | 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 |
1680 | enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or |
1668 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1681 | C<EVBACKEND_POLL>. |
|
|
1682 | |
1669 | |
1683 | =head3 The special problem of SIGPIPE |
1670 | =head3 The special problem of SIGPIPE |
1684 | |
1671 | |
1685 | 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>: |
1686 | 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 |
… | |
… | |
2036 | keep up with the timer (because it takes longer than those 10 seconds to |
2023 | keep up with the timer (because it takes longer than those 10 seconds to |
2037 | do stuff) the timer will not fire more than once per event loop iteration. |
2024 | do stuff) the timer will not fire more than once per event loop iteration. |
2038 | |
2025 | |
2039 | =item ev_timer_again (loop, ev_timer *) |
2026 | =item ev_timer_again (loop, ev_timer *) |
2040 | |
2027 | |
2041 | This will act as if the timer timed out and restart it again if it is |
2028 | This will act as if the timer timed out and restarts it again if it is |
2042 | repeating. The exact semantics are: |
2029 | repeating. The exact semantics are: |
2043 | |
2030 | |
2044 | If the timer is pending, its pending status is cleared. |
2031 | If the timer is pending, its pending status is cleared. |
2045 | |
2032 | |
2046 | If the timer is started but non-repeating, stop it (as if it timed out). |
2033 | If the timer is started but non-repeating, stop it (as if it timed out). |
… | |
… | |
2176 | |
2163 | |
2177 | 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 |
2178 | 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 |
2179 | 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. |
2180 | |
2167 | |
2181 | 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 |
2182 | 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 |
2183 | 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. |
2184 | |
2174 | |
2185 | 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 |
2186 | 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 |
2187 | 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 |
2188 | 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). |
… | |
… | |
2331 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2321 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2332 | |
2322 | |
2333 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2323 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2334 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2324 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2335 | 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, |
2336 | 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>). |
2337 | |
2328 | |
2338 | While this does not matter for the signal disposition (libev never |
2329 | While this does not matter for the signal disposition (libev never |
2339 | 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 |
2340 | 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 |
2341 | certain signals to be blocked. |
2332 | certain signals to be blocked. |
… | |
… | |
3212 | atexit (program_exits); |
3203 | atexit (program_exits); |
3213 | |
3204 | |
3214 | |
3205 | |
3215 | =head2 C<ev_async> - how to wake up an event loop |
3206 | =head2 C<ev_async> - how to wake up an event loop |
3216 | |
3207 | |
3217 | 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 |
3218 | asynchronous sources such as signal handlers (as opposed to multiple event |
3209 | asynchronous sources such as signal handlers (as opposed to multiple event |
3219 | loops - those are of course safe to use in different threads). |
3210 | loops - those are of course safe to use in different threads). |
3220 | |
3211 | |
3221 | 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, |
3222 | 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> |
… | |
… | |
3229 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3220 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3230 | of "global async watchers" by using a watcher on an otherwise unused |
3221 | of "global async watchers" by using a watcher on an otherwise unused |
3231 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3222 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3232 | even without knowing which loop owns the signal. |
3223 | even without knowing which loop owns the signal. |
3233 | |
3224 | |
3234 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
|
|
3235 | just the default loop. |
|
|
3236 | |
|
|
3237 | =head3 Queueing |
3225 | =head3 Queueing |
3238 | |
3226 | |
3239 | C<ev_async> does not support queueing of data in any way. The reason |
3227 | C<ev_async> does not support queueing of data in any way. The reason |
3240 | is that the author does not know of a simple (or any) algorithm for a |
3228 | is that the author does not know of a simple (or any) algorithm for a |
3241 | multiple-writer-single-reader queue that works in all cases and doesn't |
3229 | multiple-writer-single-reader queue that works in all cases and doesn't |
… | |
… | |
3332 | trust me. |
3320 | trust me. |
3333 | |
3321 | |
3334 | =item ev_async_send (loop, ev_async *) |
3322 | =item ev_async_send (loop, ev_async *) |
3335 | |
3323 | |
3336 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3324 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3337 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
3325 | an C<EV_ASYNC> event on the watcher into the event loop, and instantly |
|
|
3326 | returns. |
|
|
3327 | |
3338 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
3328 | Unlike C<ev_feed_event>, this call is safe to do from other threads, |
3339 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
3329 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3340 | section below on what exactly this means). |
3330 | embedding section below on what exactly this means). |
3341 | |
3331 | |
3342 | Note that, as with other watchers in libev, multiple events might get |
3332 | Note that, as with other watchers in libev, multiple events might get |
3343 | compressed into a single callback invocation (another way to look at this |
3333 | compressed into a single callback invocation (another way to look at |
3344 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3334 | this is that C<ev_async> watchers are level-triggered: they are set on |
3345 | reset when the event loop detects that). |
3335 | C<ev_async_send>, reset when the event loop detects that). |
3346 | |
3336 | |
3347 | This call incurs the overhead of a system call only once per event loop |
3337 | This call incurs the overhead of at most one extra system call per event |
3348 | iteration, so while the overhead might be noticeable, it doesn't apply to |
3338 | loop iteration, if the event loop is blocked, and no syscall at all if |
3349 | repeated calls to C<ev_async_send> for the same event loop. |
3339 | the event loop (or your program) is processing events. That means that |
|
|
3340 | repeated calls are basically free (there is no need to avoid calls for |
|
|
3341 | performance reasons) and that the overhead becomes smaller (typically |
|
|
3342 | zero) under load. |
3350 | |
3343 | |
3351 | =item bool = ev_async_pending (ev_async *) |
3344 | =item bool = ev_async_pending (ev_async *) |
3352 | |
3345 | |
3353 | Returns a non-zero value when C<ev_async_send> has been called on the |
3346 | Returns a non-zero value when C<ev_async_send> has been called on the |
3354 | watcher but the event has not yet been processed (or even noted) by the |
3347 | watcher but the event has not yet been processed (or even noted) by the |
… | |
… | |
3425 | |
3418 | |
3426 | This section explains some common idioms that are not immediately |
3419 | This section explains some common idioms that are not immediately |
3427 | obvious. Note that examples are sprinkled over the whole manual, and this |
3420 | obvious. Note that examples are sprinkled over the whole manual, and this |
3428 | section only contains stuff that wouldn't fit anywhere else. |
3421 | section only contains stuff that wouldn't fit anywhere else. |
3429 | |
3422 | |
3430 | =over 4 |
3423 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
3431 | |
3424 | |
3432 | =item Model/nested event loop invocations and exit conditions. |
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 |
3433 | |
3492 | |
3434 | Often (especially in GUI toolkits) there are places where you have |
3493 | Often (especially in GUI toolkits) there are places where you have |
3435 | I<modal> interaction, which is most easily implemented by recursively |
3494 | I<modal> interaction, which is most easily implemented by recursively |
3436 | invoking C<ev_run>. |
3495 | invoking C<ev_run>. |
3437 | |
3496 | |
… | |
… | |
3466 | exit_main_loop = 1; |
3525 | exit_main_loop = 1; |
3467 | |
3526 | |
3468 | // exit both |
3527 | // exit both |
3469 | exit_main_loop = exit_nested_loop = 1; |
3528 | exit_main_loop = exit_nested_loop = 1; |
3470 | |
3529 | |
3471 | =back |
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. |
3472 | |
3725 | |
3473 | |
3726 | |
3474 | =head1 LIBEVENT EMULATION |
3727 | =head1 LIBEVENT EMULATION |
3475 | |
3728 | |
3476 | Libev offers a compatibility emulation layer for libevent. It cannot |
3729 | Libev offers a compatibility emulation layer for libevent. It cannot |
… | |
… | |
3691 | watchers in the constructor. |
3944 | watchers in the constructor. |
3692 | |
3945 | |
3693 | class myclass |
3946 | class myclass |
3694 | { |
3947 | { |
3695 | ev::io io ; void io_cb (ev::io &w, int revents); |
3948 | ev::io io ; void io_cb (ev::io &w, int revents); |
3696 | ev::io2 io2 ; void io2_cb (ev::io &w, int revents); |
3949 | ev::io io2 ; void io2_cb (ev::io &w, int revents); |
3697 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
3950 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
3698 | |
3951 | |
3699 | myclass (int fd) |
3952 | myclass (int fd) |
3700 | { |
3953 | { |
3701 | io .set <myclass, &myclass::io_cb > (this); |
3954 | io .set <myclass, &myclass::io_cb > (this); |
… | |
… | |
3752 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
4005 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
3753 | |
4006 | |
3754 | =item D |
4007 | =item D |
3755 | |
4008 | |
3756 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
4009 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
3757 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
4010 | be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>. |
3758 | |
4011 | |
3759 | =item Ocaml |
4012 | =item Ocaml |
3760 | |
4013 | |
3761 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4014 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
3762 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
4015 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
… | |
… | |
3810 | suitable for use with C<EV_A>. |
4063 | suitable for use with C<EV_A>. |
3811 | |
4064 | |
3812 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4065 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
3813 | |
4066 | |
3814 | Similar to the other two macros, this gives you the value of the default |
4067 | Similar to the other two macros, this gives you the value of the default |
3815 | loop, if multiple loops are supported ("ev loop default"). |
4068 | loop, if multiple loops are supported ("ev loop default"). The default loop |
|
|
4069 | will be initialised if it isn't already initialised. |
|
|
4070 | |
|
|
4071 | For non-multiplicity builds, these macros do nothing, so you always have |
|
|
4072 | to initialise the loop somewhere. |
3816 | |
4073 | |
3817 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4074 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
3818 | |
4075 | |
3819 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4076 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
3820 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
4077 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
… | |
… | |
3965 | supported). It will also not define any of the structs usually found in |
4222 | supported). It will also not define any of the structs usually found in |
3966 | F<event.h> that are not directly supported by the libev core alone. |
4223 | F<event.h> that are not directly supported by the libev core alone. |
3967 | |
4224 | |
3968 | In standalone mode, libev will still try to automatically deduce the |
4225 | In standalone mode, libev will still try to automatically deduce the |
3969 | configuration, but has to be more conservative. |
4226 | configuration, but has to be more conservative. |
|
|
4227 | |
|
|
4228 | =item EV_USE_FLOOR |
|
|
4229 | |
|
|
4230 | If defined to be C<1>, libev will use the C<floor ()> function for its |
|
|
4231 | periodic reschedule calculations, otherwise libev will fall back on a |
|
|
4232 | portable (slower) implementation. If you enable this, you usually have to |
|
|
4233 | link against libm or something equivalent. Enabling this when the C<floor> |
|
|
4234 | function is not available will fail, so the safe default is to not enable |
|
|
4235 | this. |
3970 | |
4236 | |
3971 | =item EV_USE_MONOTONIC |
4237 | =item EV_USE_MONOTONIC |
3972 | |
4238 | |
3973 | If defined to be C<1>, libev will try to detect the availability of the |
4239 | If defined to be C<1>, libev will try to detect the availability of the |
3974 | monotonic clock option at both compile time and runtime. Otherwise no |
4240 | monotonic clock option at both compile time and runtime. Otherwise no |
… | |
… | |
4107 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4373 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4108 | |
4374 | |
4109 | =item EV_ATOMIC_T |
4375 | =item EV_ATOMIC_T |
4110 | |
4376 | |
4111 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4377 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4112 | access is atomic with respect to other threads or signal contexts. No such |
4378 | access is atomic and serialised with respect to other threads or signal |
4113 | type is easily found in the C language, so you can provide your own type |
4379 | contexts. No such type is easily found in the C language, so you can |
4114 | that you know is safe for your purposes. It is used both for signal handler "locking" |
4380 | provide your own type that you know is safe for your purposes. It is used |
4115 | as well as for signal and thread safety in C<ev_async> watchers. |
4381 | both for signal handler "locking" as well as for signal and thread safety |
|
|
4382 | in C<ev_async> watchers. |
4116 | |
4383 | |
4117 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4384 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4118 | (from F<signal.h>), which is usually good enough on most platforms. |
4385 | (from F<signal.h>), which is usually good enough on most platforms, |
|
|
4386 | although strictly speaking using a type that also implies a memory fence |
|
|
4387 | is required. |
4119 | |
4388 | |
4120 | =item EV_H (h) |
4389 | =item EV_H (h) |
4121 | |
4390 | |
4122 | The name of the F<ev.h> header file used to include it. The default if |
4391 | The name of the F<ev.h> header file used to include it. The default if |
4123 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
4392 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
… | |
… | |
4146 | If undefined or defined to C<1>, then all event-loop-specific functions |
4415 | If undefined or defined to C<1>, then all event-loop-specific functions |
4147 | will have the C<struct ev_loop *> as first argument, and you can create |
4416 | will have the C<struct ev_loop *> as first argument, and you can create |
4148 | additional independent event loops. Otherwise there will be no support |
4417 | additional independent event loops. Otherwise there will be no support |
4149 | for multiple event loops and there is no first event loop pointer |
4418 | for multiple event loops and there is no first event loop pointer |
4150 | argument. Instead, all functions act on the single default loop. |
4419 | argument. Instead, all functions act on the single default loop. |
|
|
4420 | |
|
|
4421 | Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a |
|
|
4422 | default loop when multiplicity is switched off - you always have to |
|
|
4423 | initialise the loop manually in this case. |
4151 | |
4424 | |
4152 | =item EV_MINPRI |
4425 | =item EV_MINPRI |
4153 | |
4426 | |
4154 | =item EV_MAXPRI |
4427 | =item EV_MAXPRI |
4155 | |
4428 | |
… | |
… | |
4406 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4679 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4407 | |
4680 | |
4408 | #include "ev_cpp.h" |
4681 | #include "ev_cpp.h" |
4409 | #include "ev.c" |
4682 | #include "ev.c" |
4410 | |
4683 | |
4411 | =head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES |
4684 | =head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT |
4412 | |
4685 | |
4413 | =head2 THREADS AND COROUTINES |
4686 | =head2 THREADS AND COROUTINES |
4414 | |
4687 | |
4415 | =head3 THREADS |
4688 | =head3 THREADS |
4416 | |
4689 | |
… | |
… | |
4467 | default loop and triggering an C<ev_async> watcher from the default loop |
4740 | default loop and triggering an C<ev_async> watcher from the default loop |
4468 | watcher callback into the event loop interested in the signal. |
4741 | watcher callback into the event loop interested in the signal. |
4469 | |
4742 | |
4470 | =back |
4743 | =back |
4471 | |
4744 | |
4472 | =head4 THREAD LOCKING EXAMPLE |
4745 | See also L<THREAD LOCKING EXAMPLE>. |
4473 | |
|
|
4474 | Here is a fictitious example of how to run an event loop in a different |
|
|
4475 | thread than where callbacks are being invoked and watchers are |
|
|
4476 | created/added/removed. |
|
|
4477 | |
|
|
4478 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
4479 | which uses exactly this technique (which is suited for many high-level |
|
|
4480 | languages). |
|
|
4481 | |
|
|
4482 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
4483 | variable to wait for callback invocations, an async watcher to notify the |
|
|
4484 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
4485 | |
|
|
4486 | First, you need to associate some data with the event loop: |
|
|
4487 | |
|
|
4488 | typedef struct { |
|
|
4489 | mutex_t lock; /* global loop lock */ |
|
|
4490 | ev_async async_w; |
|
|
4491 | thread_t tid; |
|
|
4492 | cond_t invoke_cv; |
|
|
4493 | } userdata; |
|
|
4494 | |
|
|
4495 | void prepare_loop (EV_P) |
|
|
4496 | { |
|
|
4497 | // for simplicity, we use a static userdata struct. |
|
|
4498 | static userdata u; |
|
|
4499 | |
|
|
4500 | ev_async_init (&u->async_w, async_cb); |
|
|
4501 | ev_async_start (EV_A_ &u->async_w); |
|
|
4502 | |
|
|
4503 | pthread_mutex_init (&u->lock, 0); |
|
|
4504 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
4505 | |
|
|
4506 | // now associate this with the loop |
|
|
4507 | ev_set_userdata (EV_A_ u); |
|
|
4508 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
4509 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
4510 | |
|
|
4511 | // then create the thread running ev_loop |
|
|
4512 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
4513 | } |
|
|
4514 | |
|
|
4515 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
4516 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
4517 | that might have been added: |
|
|
4518 | |
|
|
4519 | static void |
|
|
4520 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
4521 | { |
|
|
4522 | // just used for the side effects |
|
|
4523 | } |
|
|
4524 | |
|
|
4525 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
4526 | protecting the loop data, respectively. |
|
|
4527 | |
|
|
4528 | static void |
|
|
4529 | l_release (EV_P) |
|
|
4530 | { |
|
|
4531 | userdata *u = ev_userdata (EV_A); |
|
|
4532 | pthread_mutex_unlock (&u->lock); |
|
|
4533 | } |
|
|
4534 | |
|
|
4535 | static void |
|
|
4536 | l_acquire (EV_P) |
|
|
4537 | { |
|
|
4538 | userdata *u = ev_userdata (EV_A); |
|
|
4539 | pthread_mutex_lock (&u->lock); |
|
|
4540 | } |
|
|
4541 | |
|
|
4542 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
4543 | into C<ev_run>: |
|
|
4544 | |
|
|
4545 | void * |
|
|
4546 | l_run (void *thr_arg) |
|
|
4547 | { |
|
|
4548 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
4549 | |
|
|
4550 | l_acquire (EV_A); |
|
|
4551 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
4552 | ev_run (EV_A_ 0); |
|
|
4553 | l_release (EV_A); |
|
|
4554 | |
|
|
4555 | return 0; |
|
|
4556 | } |
|
|
4557 | |
|
|
4558 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
4559 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
4560 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
4561 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
4562 | and b) skipping inter-thread-communication when there are no pending |
|
|
4563 | watchers is very beneficial): |
|
|
4564 | |
|
|
4565 | static void |
|
|
4566 | l_invoke (EV_P) |
|
|
4567 | { |
|
|
4568 | userdata *u = ev_userdata (EV_A); |
|
|
4569 | |
|
|
4570 | while (ev_pending_count (EV_A)) |
|
|
4571 | { |
|
|
4572 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
4573 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
4574 | } |
|
|
4575 | } |
|
|
4576 | |
|
|
4577 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
4578 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
4579 | thread to continue: |
|
|
4580 | |
|
|
4581 | static void |
|
|
4582 | real_invoke_pending (EV_P) |
|
|
4583 | { |
|
|
4584 | userdata *u = ev_userdata (EV_A); |
|
|
4585 | |
|
|
4586 | pthread_mutex_lock (&u->lock); |
|
|
4587 | ev_invoke_pending (EV_A); |
|
|
4588 | pthread_cond_signal (&u->invoke_cv); |
|
|
4589 | pthread_mutex_unlock (&u->lock); |
|
|
4590 | } |
|
|
4591 | |
|
|
4592 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
4593 | event loop, you will now have to lock: |
|
|
4594 | |
|
|
4595 | ev_timer timeout_watcher; |
|
|
4596 | userdata *u = ev_userdata (EV_A); |
|
|
4597 | |
|
|
4598 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
4599 | |
|
|
4600 | pthread_mutex_lock (&u->lock); |
|
|
4601 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
4602 | ev_async_send (EV_A_ &u->async_w); |
|
|
4603 | pthread_mutex_unlock (&u->lock); |
|
|
4604 | |
|
|
4605 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
4606 | an event loop currently blocking in the kernel will have no knowledge |
|
|
4607 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
4608 | watchers in the next event loop iteration. |
|
|
4609 | |
4746 | |
4610 | =head3 COROUTINES |
4747 | =head3 COROUTINES |
4611 | |
4748 | |
4612 | Libev is very accommodating to coroutines ("cooperative threads"): |
4749 | Libev is very accommodating to coroutines ("cooperative threads"): |
4613 | libev fully supports nesting calls to its functions from different |
4750 | libev fully supports nesting calls to its functions from different |
… | |
… | |
4778 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4915 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4779 | model. Libev still offers limited functionality on this platform in |
4916 | model. Libev still offers limited functionality on this platform in |
4780 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4917 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4781 | descriptors. This only applies when using Win32 natively, not when using |
4918 | descriptors. This only applies when using Win32 natively, not when using |
4782 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4919 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4783 | as every compielr comes with a slightly differently broken/incompatible |
4920 | as every compiler comes with a slightly differently broken/incompatible |
4784 | environment. |
4921 | environment. |
4785 | |
4922 | |
4786 | Lifting these limitations would basically require the full |
4923 | Lifting these limitations would basically require the full |
4787 | re-implementation of the I/O system. If you are into this kind of thing, |
4924 | re-implementation of the I/O system. If you are into this kind of thing, |
4788 | then note that glib does exactly that for you in a very portable way (note |
4925 | then note that glib does exactly that for you in a very portable way (note |
… | |
… | |
4921 | |
5058 | |
4922 | The type C<double> is used to represent timestamps. It is required to |
5059 | The type C<double> is used to represent timestamps. It is required to |
4923 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5060 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
4924 | good enough for at least into the year 4000 with millisecond accuracy |
5061 | good enough for at least into the year 4000 with millisecond accuracy |
4925 | (the design goal for libev). This requirement is overfulfilled by |
5062 | (the design goal for libev). This requirement is overfulfilled by |
4926 | implementations using IEEE 754, which is basically all existing ones. With |
5063 | implementations using IEEE 754, which is basically all existing ones. |
|
|
5064 | |
4927 | IEEE 754 doubles, you get microsecond accuracy until at least 2200. |
5065 | With IEEE 754 doubles, you get microsecond accuracy until at least the |
|
|
5066 | year 2255 (and millisecond accuray till the year 287396 - by then, libev |
|
|
5067 | is either obsolete or somebody patched it to use C<long double> or |
|
|
5068 | something like that, just kidding). |
4928 | |
5069 | |
4929 | =back |
5070 | =back |
4930 | |
5071 | |
4931 | If you know of other additional requirements drop me a note. |
5072 | If you know of other additional requirements drop me a note. |
4932 | |
5073 | |
… | |
… | |
4994 | =item Processing ev_async_send: O(number_of_async_watchers) |
5135 | =item Processing ev_async_send: O(number_of_async_watchers) |
4995 | |
5136 | |
4996 | =item Processing signals: O(max_signal_number) |
5137 | =item Processing signals: O(max_signal_number) |
4997 | |
5138 | |
4998 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
5139 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
4999 | calls in the current loop iteration. Checking for async and signal events |
5140 | calls in the current loop iteration and the loop is currently |
|
|
5141 | blocked. Checking for async and signal events involves iterating over all |
5000 | involves iterating over all running async watchers or all signal numbers. |
5142 | running async watchers or all signal numbers. |
5001 | |
5143 | |
5002 | =back |
5144 | =back |
5003 | |
5145 | |
5004 | |
5146 | |
5005 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
5147 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
… | |
… | |
5122 | The physical time that is observed. It is apparently strictly monotonic :) |
5264 | The physical time that is observed. It is apparently strictly monotonic :) |
5123 | |
5265 | |
5124 | =item wall-clock time |
5266 | =item wall-clock time |
5125 | |
5267 | |
5126 | The time and date as shown on clocks. Unlike real time, it can actually |
5268 | The time and date as shown on clocks. Unlike real time, it can actually |
5127 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
5269 | be wrong and jump forwards and backwards, e.g. when you adjust your |
5128 | clock. |
5270 | clock. |
5129 | |
5271 | |
5130 | =item watcher |
5272 | =item watcher |
5131 | |
5273 | |
5132 | A data structure that describes interest in certain events. Watchers need |
5274 | A data structure that describes interest in certain events. Watchers need |
… | |
… | |
5135 | =back |
5277 | =back |
5136 | |
5278 | |
5137 | =head1 AUTHOR |
5279 | =head1 AUTHOR |
5138 | |
5280 | |
5139 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5281 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5140 | Magnusson and Emanuele Giaquinta. |
5282 | Magnusson and Emanuele Giaquinta, and minor corrections by many others. |
5141 | |
5283 | |