… | |
… | |
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 | |
… | |
… | |
174 | =item ev_tstamp ev_time () |
174 | =item ev_tstamp ev_time () |
175 | |
175 | |
176 | Returns the current time as libev would use it. Please note that the |
176 | Returns the current time as libev would use it. Please note that the |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
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_now_update> 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 |
… | |
… | |
582 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
596 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
583 | |
597 | |
584 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
598 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
585 | it's really slow, but it still scales very well (O(active_fds)). |
599 | it's really slow, but it still scales very well (O(active_fds)). |
586 | |
600 | |
587 | Please note that Solaris event ports can deliver a lot of spurious |
|
|
588 | notifications, so you need to use non-blocking I/O or other means to avoid |
|
|
589 | blocking when no data (or space) is available. |
|
|
590 | |
|
|
591 | While this backend scales well, it requires one system call per active |
601 | While this backend scales well, it requires one system call per active |
592 | file descriptor per loop iteration. For small and medium numbers of file |
602 | file descriptor per loop iteration. For small and medium numbers of file |
593 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
603 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
594 | might perform better. |
604 | might perform better. |
595 | |
605 | |
596 | On the positive side, with the exception of the spurious readiness |
606 | On the positive side, this backend actually performed fully to |
597 | notifications, this backend actually performed fully to specification |
|
|
598 | in all tests and is fully embeddable, which is a rare feat among the |
607 | specification in all tests and is fully embeddable, which is a rare feat |
599 | OS-specific backends (I vastly prefer correctness over speed hacks). |
608 | among the OS-specific backends (I vastly prefer correctness over speed |
|
|
609 | hacks). |
|
|
610 | |
|
|
611 | On the negative side, the interface is I<bizarre> - so bizarre that |
|
|
612 | even sun itself gets it wrong in their code examples: The event polling |
|
|
613 | function sometimes returns events to the caller even though an error |
|
|
614 | occurred, but with no indication whether it has done so or not (yes, it's |
|
|
615 | even documented that way) - deadly for edge-triggered interfaces where you |
|
|
616 | absolutely have to know whether an event occurred or not because you have |
|
|
617 | to re-arm the watcher. |
|
|
618 | |
|
|
619 | Fortunately libev seems to be able to work around these idiocies. |
600 | |
620 | |
601 | 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 |
602 | C<EVBACKEND_POLL>. |
622 | C<EVBACKEND_POLL>. |
603 | |
623 | |
604 | =item C<EVBACKEND_ALL> |
624 | =item C<EVBACKEND_ALL> |
… | |
… | |
814 | 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 |
815 | 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 |
816 | 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 |
817 | usually a better approach for this kind of thing. |
837 | usually a better approach for this kind of thing. |
818 | |
838 | |
819 | 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): |
820 | |
842 | |
821 | - Increment loop depth. |
843 | - Increment loop depth. |
822 | - Reset the ev_break status. |
844 | - Reset the ev_break status. |
823 | - Before the first iteration, call any pending watchers. |
845 | - Before the first iteration, call any pending watchers. |
824 | LOOP: |
846 | LOOP: |
… | |
… | |
857 | anymore. |
879 | anymore. |
858 | |
880 | |
859 | ... queue jobs here, make sure they register event watchers as long |
881 | ... queue jobs here, make sure they register event watchers as long |
860 | ... 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..) |
861 | ev_run (my_loop, 0); |
883 | ev_run (my_loop, 0); |
862 | ... jobs done or somebody called unloop. yeah! |
884 | ... jobs done or somebody called break. yeah! |
863 | |
885 | |
864 | =item ev_break (loop, how) |
886 | =item ev_break (loop, how) |
865 | |
887 | |
866 | 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 |
867 | 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 |
… | |
… | |
930 | 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. |
931 | |
953 | |
932 | 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 |
933 | 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, |
934 | 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 |
935 | 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 |
936 | 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 |
937 | 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 |
938 | once per this interval, on average. |
960 | once per this interval, on average (as long as the host time resolution is |
|
|
961 | good enough). |
939 | |
962 | |
940 | 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 |
941 | to spend more time collecting timeouts, at the expense of increased |
964 | to spend more time collecting timeouts, at the expense of increased |
942 | latency/jitter/inexactness (the watcher callback will be called |
965 | latency/jitter/inexactness (the watcher callback will be called |
943 | 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 |
… | |
… | |
997 | can be done relatively simply by putting mutex_lock/unlock calls around |
1020 | can be done relatively simply by putting mutex_lock/unlock calls around |
998 | each call to a libev function. |
1021 | each call to a libev function. |
999 | |
1022 | |
1000 | However, C<ev_run> can run an indefinite time, so it is not feasible |
1023 | However, C<ev_run> can run an indefinite time, so it is not feasible |
1001 | to wait for it to return. One way around this is to wake up the event |
1024 | to wait for it to return. One way around this is to wake up the event |
1002 | loop via C<ev_break> and C<av_async_send>, another way is to set these |
1025 | loop via C<ev_break> and C<ev_async_send>, another way is to set these |
1003 | I<release> and I<acquire> callbacks on the loop. |
1026 | I<release> and I<acquire> callbacks on the loop. |
1004 | |
1027 | |
1005 | When set, then C<release> will be called just before the thread is |
1028 | When set, then C<release> will be called just before the thread is |
1006 | suspended waiting for new events, and C<acquire> is called just |
1029 | suspended waiting for new events, and C<acquire> is called just |
1007 | afterwards. |
1030 | afterwards. |
… | |
… | |
1349 | 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 |
1350 | functions that do not need a watcher. |
1373 | functions that do not need a watcher. |
1351 | |
1374 | |
1352 | =back |
1375 | =back |
1353 | |
1376 | |
1354 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1377 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1355 | |
1378 | OWN COMPOSITE WATCHERS> idioms. |
1356 | Each watcher has, by default, a member C<void *data> that you can change |
|
|
1357 | and read at any time: libev will completely ignore it. This can be used |
|
|
1358 | to associate arbitrary data with your watcher. If you need more data and |
|
|
1359 | don't want to allocate memory and store a pointer to it in that data |
|
|
1360 | member, you can also "subclass" the watcher type and provide your own |
|
|
1361 | data: |
|
|
1362 | |
|
|
1363 | struct my_io |
|
|
1364 | { |
|
|
1365 | ev_io io; |
|
|
1366 | int otherfd; |
|
|
1367 | void *somedata; |
|
|
1368 | struct whatever *mostinteresting; |
|
|
1369 | }; |
|
|
1370 | |
|
|
1371 | ... |
|
|
1372 | struct my_io w; |
|
|
1373 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
1374 | |
|
|
1375 | And since your callback will be called with a pointer to the watcher, you |
|
|
1376 | can cast it back to your own type: |
|
|
1377 | |
|
|
1378 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
1379 | { |
|
|
1380 | struct my_io *w = (struct my_io *)w_; |
|
|
1381 | ... |
|
|
1382 | } |
|
|
1383 | |
|
|
1384 | More interesting and less C-conformant ways of casting your callback type |
|
|
1385 | instead have been omitted. |
|
|
1386 | |
|
|
1387 | Another common scenario is to use some data structure with multiple |
|
|
1388 | embedded watchers: |
|
|
1389 | |
|
|
1390 | struct my_biggy |
|
|
1391 | { |
|
|
1392 | int some_data; |
|
|
1393 | ev_timer t1; |
|
|
1394 | ev_timer t2; |
|
|
1395 | } |
|
|
1396 | |
|
|
1397 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
1398 | complicated: Either you store the address of your C<my_biggy> struct |
|
|
1399 | in the C<data> member of the watcher (for woozies), or you need to use |
|
|
1400 | some pointer arithmetic using C<offsetof> inside your watchers (for real |
|
|
1401 | programmers): |
|
|
1402 | |
|
|
1403 | #include <stddef.h> |
|
|
1404 | |
|
|
1405 | static void |
|
|
1406 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
1407 | { |
|
|
1408 | struct my_biggy big = (struct my_biggy *) |
|
|
1409 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
1410 | } |
|
|
1411 | |
|
|
1412 | static void |
|
|
1413 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
1414 | { |
|
|
1415 | struct my_biggy big = (struct my_biggy *) |
|
|
1416 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
1417 | } |
|
|
1418 | |
1379 | |
1419 | =head2 WATCHER STATES |
1380 | =head2 WATCHER STATES |
1420 | |
1381 | |
1421 | There are various watcher states mentioned throughout this manual - |
1382 | There are various watcher states mentioned throughout this manual - |
1422 | 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 |
… | |
… | |
1425 | |
1386 | |
1426 | =over 4 |
1387 | =over 4 |
1427 | |
1388 | |
1428 | =item initialiased |
1389 | =item initialiased |
1429 | |
1390 | |
1430 | 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 |
1431 | 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 |
1432 | 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. |
1433 | |
1394 | |
1434 | 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 |
1435 | 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. |
1436 | |
1399 | |
1437 | =item started/running/active |
1400 | =item started/running/active |
1438 | |
1401 | |
1439 | 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 |
1440 | 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 |
… | |
… | |
1468 | 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 |
1469 | 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 |
1470 | freeing it is often a good idea. |
1433 | freeing it is often a good idea. |
1471 | |
1434 | |
1472 | While stopped (and not pending) the watcher is essentially in the |
1435 | While stopped (and not pending) the watcher is essentially in the |
1473 | 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 |
1474 | you wish. |
1437 | you wish (but when you trash the memory block, you need to C<ev_TYPE_init> |
|
|
1438 | it again). |
1475 | |
1439 | |
1476 | =back |
1440 | =back |
1477 | |
1441 | |
1478 | =head2 WATCHER PRIORITY MODELS |
1442 | =head2 WATCHER PRIORITY MODELS |
1479 | |
1443 | |
… | |
… | |
1608 | 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 |
1609 | 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 |
1610 | 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 |
1611 | required if you know what you are doing). |
1575 | required if you know what you are doing). |
1612 | |
1576 | |
1613 | If you cannot use non-blocking mode, then force the use of a |
|
|
1614 | known-to-be-good backend (at the time of this writing, this includes only |
|
|
1615 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file |
|
|
1616 | descriptors for which non-blocking operation makes no sense (such as |
|
|
1617 | files) - libev doesn't guarantee any specific behaviour in that case. |
|
|
1618 | |
|
|
1619 | 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 |
1620 | receive "spurious" readiness notifications, that is your callback might |
1578 | receive "spurious" readiness notifications, that is, your callback might |
1621 | 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 |
1622 | 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 |
1623 | 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 |
1624 | 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 |
1625 | it is best to always use non-blocking I/O: An extra C<read>(2) returning |
|
|
1626 | C<EAGAIN> is far preferable to a program hanging until some data arrives. |
1583 | preferable to a program hanging until some data arrives. |
1627 | |
1584 | |
1628 | 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 |
1629 | 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 |
1630 | 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 |
1631 | 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 |
1632 | 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 |
1633 | 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 |
1634 | indefinitely. |
1591 | indefinitely. |
1635 | |
1592 | |
1636 | But really, best use non-blocking mode. |
1593 | But really, best use non-blocking mode. |
1637 | |
1594 | |
… | |
… | |
1665 | |
1622 | |
1666 | There is no workaround possible except not registering events |
1623 | There is no workaround possible except not registering events |
1667 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1624 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1668 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1625 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1669 | |
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 | |
1670 | =head3 The special problem of fork |
1660 | =head3 The special problem of fork |
1671 | |
1661 | |
1672 | 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 |
1673 | 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 |
1674 | it in the child. |
1664 | it in the child if you want to continue to use it in the child. |
1675 | |
1665 | |
1676 | 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 |
1677 | 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 |
1678 | enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or |
1668 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1679 | C<EVBACKEND_POLL>. |
|
|
1680 | |
1669 | |
1681 | =head3 The special problem of SIGPIPE |
1670 | =head3 The special problem of SIGPIPE |
1682 | |
1671 | |
1683 | 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>: |
1684 | 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 |
… | |
… | |
1782 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1771 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1783 | monotonic clock option helps a lot here). |
1772 | monotonic clock option helps a lot here). |
1784 | |
1773 | |
1785 | The callback is guaranteed to be invoked only I<after> its timeout has |
1774 | The callback is guaranteed to be invoked only I<after> its timeout has |
1786 | passed (not I<at>, so on systems with very low-resolution clocks this |
1775 | passed (not I<at>, so on systems with very low-resolution clocks this |
1787 | might introduce a small delay). If multiple timers become ready during the |
1776 | might introduce a small delay, see "the special problem of being too |
|
|
1777 | early", below). If multiple timers become ready during the same loop |
1788 | same loop iteration then the ones with earlier time-out values are invoked |
1778 | iteration then the ones with earlier time-out values are invoked before |
1789 | before ones of the same priority with later time-out values (but this is |
1779 | ones of the same priority with later time-out values (but this is no |
1790 | no longer true when a callback calls C<ev_run> recursively). |
1780 | longer true when a callback calls C<ev_run> recursively). |
1791 | |
1781 | |
1792 | =head3 Be smart about timeouts |
1782 | =head3 Be smart about timeouts |
1793 | |
1783 | |
1794 | Many real-world problems involve some kind of timeout, usually for error |
1784 | Many real-world problems involve some kind of timeout, usually for error |
1795 | recovery. A typical example is an HTTP request - if the other side hangs, |
1785 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1870 | |
1860 | |
1871 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1861 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1872 | but remember the time of last activity, and check for a real timeout only |
1862 | but remember the time of last activity, and check for a real timeout only |
1873 | within the callback: |
1863 | within the callback: |
1874 | |
1864 | |
|
|
1865 | ev_tstamp timeout = 60.; |
1875 | ev_tstamp last_activity; // time of last activity |
1866 | ev_tstamp last_activity; // time of last activity |
|
|
1867 | ev_timer timer; |
1876 | |
1868 | |
1877 | static void |
1869 | static void |
1878 | callback (EV_P_ ev_timer *w, int revents) |
1870 | callback (EV_P_ ev_timer *w, int revents) |
1879 | { |
1871 | { |
1880 | ev_tstamp now = ev_now (EV_A); |
1872 | // calculate when the timeout would happen |
1881 | ev_tstamp timeout = last_activity + 60.; |
1873 | ev_tstamp after = last_activity - ev_now (EV_A) + timeout; |
1882 | |
1874 | |
1883 | // if last_activity + 60. is older than now, we did time out |
1875 | // if negative, it means we the timeout already occured |
1884 | if (timeout < now) |
1876 | if (after < 0.) |
1885 | { |
1877 | { |
1886 | // timeout occurred, take action |
1878 | // timeout occurred, take action |
1887 | } |
1879 | } |
1888 | else |
1880 | else |
1889 | { |
1881 | { |
1890 | // callback was invoked, but there was some activity, re-arm |
1882 | // callback was invoked, but there was some recent |
1891 | // the watcher to fire in last_activity + 60, which is |
1883 | // activity. simply restart the timer to time out |
1892 | // guaranteed to be in the future, so "again" is positive: |
1884 | // after "after" seconds, which is the earliest time |
1893 | w->repeat = timeout - now; |
1885 | // the timeout can occur. |
|
|
1886 | ev_timer_set (w, after, 0.); |
1894 | ev_timer_again (EV_A_ w); |
1887 | ev_timer_start (EV_A_ w); |
1895 | } |
1888 | } |
1896 | } |
1889 | } |
1897 | |
1890 | |
1898 | To summarise the callback: first calculate the real timeout (defined |
1891 | To summarise the callback: first calculate in how many seconds the |
1899 | as "60 seconds after the last activity"), then check if that time has |
1892 | timeout will occur (by calculating the absolute time when it would occur, |
1900 | been reached, which means something I<did>, in fact, time out. Otherwise |
1893 | C<last_activity + timeout>, and subtracting the current time, C<ev_now |
1901 | the callback was invoked too early (C<timeout> is in the future), so |
1894 | (EV_A)> from that). |
1902 | re-schedule the timer to fire at that future time, to see if maybe we have |
|
|
1903 | a timeout then. |
|
|
1904 | |
1895 | |
1905 | Note how C<ev_timer_again> is used, taking advantage of the |
1896 | If this value is negative, then we are already past the timeout, i.e. we |
1906 | C<ev_timer_again> optimisation when the timer is already running. |
1897 | timed out, and need to do whatever is needed in this case. |
|
|
1898 | |
|
|
1899 | Otherwise, we now the earliest time at which the timeout would trigger, |
|
|
1900 | and simply start the timer with this timeout value. |
|
|
1901 | |
|
|
1902 | In other words, each time the callback is invoked it will check whether |
|
|
1903 | the timeout cocured. If not, it will simply reschedule itself to check |
|
|
1904 | again at the earliest time it could time out. Rinse. Repeat. |
1907 | |
1905 | |
1908 | This scheme causes more callback invocations (about one every 60 seconds |
1906 | This scheme causes more callback invocations (about one every 60 seconds |
1909 | minus half the average time between activity), but virtually no calls to |
1907 | minus half the average time between activity), but virtually no calls to |
1910 | libev to change the timeout. |
1908 | libev to change the timeout. |
1911 | |
1909 | |
1912 | To start the timer, simply initialise the watcher and set C<last_activity> |
1910 | To start the machinery, simply initialise the watcher and set |
1913 | to the current time (meaning we just have some activity :), then call the |
1911 | C<last_activity> to the current time (meaning there was some activity just |
1914 | callback, which will "do the right thing" and start the timer: |
1912 | now), then call the callback, which will "do the right thing" and start |
|
|
1913 | the timer: |
1915 | |
1914 | |
|
|
1915 | last_activity = ev_now (EV_A); |
1916 | ev_init (timer, callback); |
1916 | ev_init (&timer, callback); |
1917 | last_activity = ev_now (loop); |
1917 | callback (EV_A_ &timer, 0); |
1918 | callback (loop, timer, EV_TIMER); |
|
|
1919 | |
1918 | |
1920 | And when there is some activity, simply store the current time in |
1919 | When there is some activity, simply store the current time in |
1921 | C<last_activity>, no libev calls at all: |
1920 | C<last_activity>, no libev calls at all: |
1922 | |
1921 | |
|
|
1922 | if (activity detected) |
1923 | last_activity = ev_now (loop); |
1923 | last_activity = ev_now (EV_A); |
|
|
1924 | |
|
|
1925 | When your timeout value changes, then the timeout can be changed by simply |
|
|
1926 | providing a new value, stopping the timer and calling the callback, which |
|
|
1927 | will agaion do the right thing (for example, time out immediately :). |
|
|
1928 | |
|
|
1929 | timeout = new_value; |
|
|
1930 | ev_timer_stop (EV_A_ &timer); |
|
|
1931 | callback (EV_A_ &timer, 0); |
1924 | |
1932 | |
1925 | This technique is slightly more complex, but in most cases where the |
1933 | This technique is slightly more complex, but in most cases where the |
1926 | time-out is unlikely to be triggered, much more efficient. |
1934 | time-out is unlikely to be triggered, much more efficient. |
1927 | |
|
|
1928 | Changing the timeout is trivial as well (if it isn't hard-coded in the |
|
|
1929 | callback :) - just change the timeout and invoke the callback, which will |
|
|
1930 | fix things for you. |
|
|
1931 | |
1935 | |
1932 | =item 4. Wee, just use a double-linked list for your timeouts. |
1936 | =item 4. Wee, just use a double-linked list for your timeouts. |
1933 | |
1937 | |
1934 | If there is not one request, but many thousands (millions...), all |
1938 | If there is not one request, but many thousands (millions...), all |
1935 | employing some kind of timeout with the same timeout value, then one can |
1939 | employing some kind of timeout with the same timeout value, then one can |
… | |
… | |
1962 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1966 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1963 | rather complicated, but extremely efficient, something that really pays |
1967 | rather complicated, but extremely efficient, something that really pays |
1964 | off after the first million or so of active timers, i.e. it's usually |
1968 | off after the first million or so of active timers, i.e. it's usually |
1965 | overkill :) |
1969 | overkill :) |
1966 | |
1970 | |
|
|
1971 | =head3 The special problem of being too early |
|
|
1972 | |
|
|
1973 | If you ask a timer to call your callback after three seconds, then |
|
|
1974 | you expect it to be invoked after three seconds - but of course, this |
|
|
1975 | cannot be guaranteed to infinite precision. Less obviously, it cannot be |
|
|
1976 | guaranteed to any precision by libev - imagine somebody suspending the |
|
|
1977 | process with a STOP signal for a few hours for example. |
|
|
1978 | |
|
|
1979 | So, libev tries to invoke your callback as soon as possible I<after> the |
|
|
1980 | delay has occurred, but cannot guarantee this. |
|
|
1981 | |
|
|
1982 | A less obvious failure mode is calling your callback too early: many event |
|
|
1983 | loops compare timestamps with a "elapsed delay >= requested delay", but |
|
|
1984 | this can cause your callback to be invoked much earlier than you would |
|
|
1985 | expect. |
|
|
1986 | |
|
|
1987 | To see why, imagine a system with a clock that only offers full second |
|
|
1988 | resolution (think windows if you can't come up with a broken enough OS |
|
|
1989 | yourself). If you schedule a one-second timer at the time 500.9, then the |
|
|
1990 | event loop will schedule your timeout to elapse at a system time of 500 |
|
|
1991 | (500.9 truncated to the resolution) + 1, or 501. |
|
|
1992 | |
|
|
1993 | If an event library looks at the timeout 0.1s later, it will see "501 >= |
|
|
1994 | 501" and invoke the callback 0.1s after it was started, even though a |
|
|
1995 | one-second delay was requested - this is being "too early", despite best |
|
|
1996 | intentions. |
|
|
1997 | |
|
|
1998 | This is the reason why libev will never invoke the callback if the elapsed |
|
|
1999 | delay equals the requested delay, but only when the elapsed delay is |
|
|
2000 | larger than the requested delay. In the example above, libev would only invoke |
|
|
2001 | the callback at system time 502, or 1.1s after the timer was started. |
|
|
2002 | |
|
|
2003 | So, while libev cannot guarantee that your callback will be invoked |
|
|
2004 | exactly when requested, it I<can> and I<does> guarantee that the requested |
|
|
2005 | delay has actually elapsed, or in other words, it always errs on the "too |
|
|
2006 | late" side of things. |
|
|
2007 | |
1967 | =head3 The special problem of time updates |
2008 | =head3 The special problem of time updates |
1968 | |
2009 | |
1969 | Establishing the current time is a costly operation (it usually takes at |
2010 | Establishing the current time is a costly operation (it usually takes |
1970 | least two system calls): EV therefore updates its idea of the current |
2011 | at least one system call): EV therefore updates its idea of the current |
1971 | time only before and after C<ev_run> collects new events, which causes a |
2012 | time only before and after C<ev_run> collects new events, which causes a |
1972 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
2013 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
1973 | lots of events in one iteration. |
2014 | lots of events in one iteration. |
1974 | |
2015 | |
1975 | The relative timeouts are calculated relative to the C<ev_now ()> |
2016 | The relative timeouts are calculated relative to the C<ev_now ()> |
… | |
… | |
1981 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
2022 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
1982 | |
2023 | |
1983 | If the event loop is suspended for a long time, you can also force an |
2024 | If the event loop is suspended for a long time, you can also force an |
1984 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
2025 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
1985 | ()>. |
2026 | ()>. |
|
|
2027 | |
|
|
2028 | =head3 The special problem of unsynchronised clocks |
|
|
2029 | |
|
|
2030 | Modern systems have a variety of clocks - libev itself uses the normal |
|
|
2031 | "wall clock" clock and, if available, the monotonic clock (to avoid time |
|
|
2032 | jumps). |
|
|
2033 | |
|
|
2034 | Neither of these clocks is synchronised with each other or any other clock |
|
|
2035 | on the system, so C<ev_time ()> might return a considerably different time |
|
|
2036 | than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example, |
|
|
2037 | a call to C<gettimeofday> might return a second count that is one higher |
|
|
2038 | than a directly following call to C<time>. |
|
|
2039 | |
|
|
2040 | The moral of this is to only compare libev-related timestamps with |
|
|
2041 | C<ev_time ()> and C<ev_now ()>, at least if you want better precision than |
|
|
2042 | a second or so. |
|
|
2043 | |
|
|
2044 | One more problem arises due to this lack of synchronisation: if libev uses |
|
|
2045 | the system monotonic clock and you compare timestamps from C<ev_time> |
|
|
2046 | or C<ev_now> from when you started your timer and when your callback is |
|
|
2047 | invoked, you will find that sometimes the callback is a bit "early". |
|
|
2048 | |
|
|
2049 | This is because C<ev_timer>s work in real time, not wall clock time, so |
|
|
2050 | libev makes sure your callback is not invoked before the delay happened, |
|
|
2051 | I<measured according to the real time>, not the system clock. |
|
|
2052 | |
|
|
2053 | If your timeouts are based on a physical timescale (e.g. "time out this |
|
|
2054 | connection after 100 seconds") then this shouldn't bother you as it is |
|
|
2055 | exactly the right behaviour. |
|
|
2056 | |
|
|
2057 | If you want to compare wall clock/system timestamps to your timers, then |
|
|
2058 | you need to use C<ev_periodic>s, as these are based on the wall clock |
|
|
2059 | time, where your comparisons will always generate correct results. |
1986 | |
2060 | |
1987 | =head3 The special problems of suspended animation |
2061 | =head3 The special problems of suspended animation |
1988 | |
2062 | |
1989 | When you leave the server world it is quite customary to hit machines that |
2063 | When you leave the server world it is quite customary to hit machines that |
1990 | can suspend/hibernate - what happens to the clocks during such a suspend? |
2064 | can suspend/hibernate - what happens to the clocks during such a suspend? |
… | |
… | |
2034 | keep up with the timer (because it takes longer than those 10 seconds to |
2108 | keep up with the timer (because it takes longer than those 10 seconds to |
2035 | do stuff) the timer will not fire more than once per event loop iteration. |
2109 | do stuff) the timer will not fire more than once per event loop iteration. |
2036 | |
2110 | |
2037 | =item ev_timer_again (loop, ev_timer *) |
2111 | =item ev_timer_again (loop, ev_timer *) |
2038 | |
2112 | |
2039 | This will act as if the timer timed out and restart it again if it is |
2113 | This will act as if the timer timed out and restarts it again if it is |
2040 | repeating. The exact semantics are: |
2114 | repeating. The exact semantics are: |
2041 | |
2115 | |
2042 | If the timer is pending, its pending status is cleared. |
2116 | If the timer is pending, its pending status is cleared. |
2043 | |
2117 | |
2044 | If the timer is started but non-repeating, stop it (as if it timed out). |
2118 | If the timer is started but non-repeating, stop it (as if it timed out). |
… | |
… | |
2174 | |
2248 | |
2175 | Another way to think about it (for the mathematically inclined) is that |
2249 | Another way to think about it (for the mathematically inclined) is that |
2176 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2250 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2177 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2251 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2178 | |
2252 | |
2179 | For numerical stability it is preferable that the C<offset> value is near |
2253 | The C<interval> I<MUST> be positive, and for numerical stability, the |
2180 | C<ev_now ()> (the current time), but there is no range requirement for |
2254 | interval value should be higher than C<1/8192> (which is around 100 |
2181 | this value, and in fact is often specified as zero. |
2255 | microseconds) and C<offset> should be higher than C<0> and should have |
|
|
2256 | at most a similar magnitude as the current time (say, within a factor of |
|
|
2257 | ten). Typical values for offset are, in fact, C<0> or something between |
|
|
2258 | C<0> and C<interval>, which is also the recommended range. |
2182 | |
2259 | |
2183 | Note also that there is an upper limit to how often a timer can fire (CPU |
2260 | Note also that there is an upper limit to how often a timer can fire (CPU |
2184 | speed for example), so if C<interval> is very small then timing stability |
2261 | speed for example), so if C<interval> is very small then timing stability |
2185 | will of course deteriorate. Libev itself tries to be exact to be about one |
2262 | will of course deteriorate. Libev itself tries to be exact to be about one |
2186 | millisecond (if the OS supports it and the machine is fast enough). |
2263 | millisecond (if the OS supports it and the machine is fast enough). |
… | |
… | |
2329 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2406 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2330 | |
2407 | |
2331 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2408 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2332 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2409 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2333 | stopping it again), that is, libev might or might not block the signal, |
2410 | stopping it again), that is, libev might or might not block the signal, |
2334 | and might or might not set or restore the installed signal handler. |
2411 | and might or might not set or restore the installed signal handler (but |
|
|
2412 | see C<EVFLAG_NOSIGMASK>). |
2335 | |
2413 | |
2336 | While this does not matter for the signal disposition (libev never |
2414 | While this does not matter for the signal disposition (libev never |
2337 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2415 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2338 | C<execve>), this matters for the signal mask: many programs do not expect |
2416 | C<execve>), this matters for the signal mask: many programs do not expect |
2339 | certain signals to be blocked. |
2417 | certain signals to be blocked. |
… | |
… | |
3210 | atexit (program_exits); |
3288 | atexit (program_exits); |
3211 | |
3289 | |
3212 | |
3290 | |
3213 | =head2 C<ev_async> - how to wake up an event loop |
3291 | =head2 C<ev_async> - how to wake up an event loop |
3214 | |
3292 | |
3215 | In general, you cannot use an C<ev_run> from multiple threads or other |
3293 | In general, you cannot use an C<ev_loop> from multiple threads or other |
3216 | asynchronous sources such as signal handlers (as opposed to multiple event |
3294 | asynchronous sources such as signal handlers (as opposed to multiple event |
3217 | loops - those are of course safe to use in different threads). |
3295 | loops - those are of course safe to use in different threads). |
3218 | |
3296 | |
3219 | Sometimes, however, you need to wake up an event loop you do not control, |
3297 | Sometimes, however, you need to wake up an event loop you do not control, |
3220 | for example because it belongs to another thread. This is what C<ev_async> |
3298 | for example because it belongs to another thread. This is what C<ev_async> |
… | |
… | |
3227 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3305 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3228 | of "global async watchers" by using a watcher on an otherwise unused |
3306 | of "global async watchers" by using a watcher on an otherwise unused |
3229 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3307 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3230 | even without knowing which loop owns the signal. |
3308 | even without knowing which loop owns the signal. |
3231 | |
3309 | |
3232 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
|
|
3233 | just the default loop. |
|
|
3234 | |
|
|
3235 | =head3 Queueing |
3310 | =head3 Queueing |
3236 | |
3311 | |
3237 | C<ev_async> does not support queueing of data in any way. The reason |
3312 | C<ev_async> does not support queueing of data in any way. The reason |
3238 | is that the author does not know of a simple (or any) algorithm for a |
3313 | is that the author does not know of a simple (or any) algorithm for a |
3239 | multiple-writer-single-reader queue that works in all cases and doesn't |
3314 | multiple-writer-single-reader queue that works in all cases and doesn't |
… | |
… | |
3330 | trust me. |
3405 | trust me. |
3331 | |
3406 | |
3332 | =item ev_async_send (loop, ev_async *) |
3407 | =item ev_async_send (loop, ev_async *) |
3333 | |
3408 | |
3334 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3409 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3335 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
3410 | an C<EV_ASYNC> event on the watcher into the event loop, and instantly |
|
|
3411 | returns. |
|
|
3412 | |
3336 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
3413 | Unlike C<ev_feed_event>, this call is safe to do from other threads, |
3337 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
3414 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3338 | section below on what exactly this means). |
3415 | embedding section below on what exactly this means). |
3339 | |
3416 | |
3340 | Note that, as with other watchers in libev, multiple events might get |
3417 | Note that, as with other watchers in libev, multiple events might get |
3341 | compressed into a single callback invocation (another way to look at this |
3418 | compressed into a single callback invocation (another way to look at |
3342 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3419 | this is that C<ev_async> watchers are level-triggered: they are set on |
3343 | reset when the event loop detects that). |
3420 | C<ev_async_send>, reset when the event loop detects that). |
3344 | |
3421 | |
3345 | This call incurs the overhead of a system call only once per event loop |
3422 | This call incurs the overhead of at most one extra system call per event |
3346 | iteration, so while the overhead might be noticeable, it doesn't apply to |
3423 | loop iteration, if the event loop is blocked, and no syscall at all if |
3347 | repeated calls to C<ev_async_send> for the same event loop. |
3424 | the event loop (or your program) is processing events. That means that |
|
|
3425 | repeated calls are basically free (there is no need to avoid calls for |
|
|
3426 | performance reasons) and that the overhead becomes smaller (typically |
|
|
3427 | zero) under load. |
3348 | |
3428 | |
3349 | =item bool = ev_async_pending (ev_async *) |
3429 | =item bool = ev_async_pending (ev_async *) |
3350 | |
3430 | |
3351 | Returns a non-zero value when C<ev_async_send> has been called on the |
3431 | Returns a non-zero value when C<ev_async_send> has been called on the |
3352 | watcher but the event has not yet been processed (or even noted) by the |
3432 | watcher but the event has not yet been processed (or even noted) by the |
… | |
… | |
3407 | ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
3487 | ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
3408 | |
3488 | |
3409 | =item ev_feed_fd_event (loop, int fd, int revents) |
3489 | =item ev_feed_fd_event (loop, int fd, int revents) |
3410 | |
3490 | |
3411 | Feed an event on the given fd, as if a file descriptor backend detected |
3491 | Feed an event on the given fd, as if a file descriptor backend detected |
3412 | the given events it. |
3492 | the given events. |
3413 | |
3493 | |
3414 | =item ev_feed_signal_event (loop, int signum) |
3494 | =item ev_feed_signal_event (loop, int signum) |
3415 | |
3495 | |
3416 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3496 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3417 | which is async-safe. |
3497 | which is async-safe. |
… | |
… | |
3423 | |
3503 | |
3424 | This section explains some common idioms that are not immediately |
3504 | This section explains some common idioms that are not immediately |
3425 | obvious. Note that examples are sprinkled over the whole manual, and this |
3505 | obvious. Note that examples are sprinkled over the whole manual, and this |
3426 | section only contains stuff that wouldn't fit anywhere else. |
3506 | section only contains stuff that wouldn't fit anywhere else. |
3427 | |
3507 | |
3428 | =over 4 |
3508 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
3429 | |
3509 | |
3430 | =item Model/nested event loop invocations and exit conditions. |
3510 | Each watcher has, by default, a C<void *data> member that you can read |
|
|
3511 | or modify at any time: libev will completely ignore it. This can be used |
|
|
3512 | to associate arbitrary data with your watcher. If you need more data and |
|
|
3513 | don't want to allocate memory separately and store a pointer to it in that |
|
|
3514 | data member, you can also "subclass" the watcher type and provide your own |
|
|
3515 | data: |
|
|
3516 | |
|
|
3517 | struct my_io |
|
|
3518 | { |
|
|
3519 | ev_io io; |
|
|
3520 | int otherfd; |
|
|
3521 | void *somedata; |
|
|
3522 | struct whatever *mostinteresting; |
|
|
3523 | }; |
|
|
3524 | |
|
|
3525 | ... |
|
|
3526 | struct my_io w; |
|
|
3527 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
3528 | |
|
|
3529 | And since your callback will be called with a pointer to the watcher, you |
|
|
3530 | can cast it back to your own type: |
|
|
3531 | |
|
|
3532 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
3533 | { |
|
|
3534 | struct my_io *w = (struct my_io *)w_; |
|
|
3535 | ... |
|
|
3536 | } |
|
|
3537 | |
|
|
3538 | More interesting and less C-conformant ways of casting your callback |
|
|
3539 | function type instead have been omitted. |
|
|
3540 | |
|
|
3541 | =head2 BUILDING YOUR OWN COMPOSITE WATCHERS |
|
|
3542 | |
|
|
3543 | Another common scenario is to use some data structure with multiple |
|
|
3544 | embedded watchers, in effect creating your own watcher that combines |
|
|
3545 | multiple libev event sources into one "super-watcher": |
|
|
3546 | |
|
|
3547 | struct my_biggy |
|
|
3548 | { |
|
|
3549 | int some_data; |
|
|
3550 | ev_timer t1; |
|
|
3551 | ev_timer t2; |
|
|
3552 | } |
|
|
3553 | |
|
|
3554 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
3555 | complicated: Either you store the address of your C<my_biggy> struct in |
|
|
3556 | the C<data> member of the watcher (for woozies or C++ coders), or you need |
|
|
3557 | to use some pointer arithmetic using C<offsetof> inside your watchers (for |
|
|
3558 | real programmers): |
|
|
3559 | |
|
|
3560 | #include <stddef.h> |
|
|
3561 | |
|
|
3562 | static void |
|
|
3563 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
3564 | { |
|
|
3565 | struct my_biggy big = (struct my_biggy *) |
|
|
3566 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
3567 | } |
|
|
3568 | |
|
|
3569 | static void |
|
|
3570 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
3571 | { |
|
|
3572 | struct my_biggy big = (struct my_biggy *) |
|
|
3573 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
3574 | } |
|
|
3575 | |
|
|
3576 | =head2 AVOIDING FINISHING BEFORE RETURNING |
|
|
3577 | |
|
|
3578 | Often you have structures like this in event-based programs: |
|
|
3579 | |
|
|
3580 | callback () |
|
|
3581 | { |
|
|
3582 | free (request); |
|
|
3583 | } |
|
|
3584 | |
|
|
3585 | request = start_new_request (..., callback); |
|
|
3586 | |
|
|
3587 | The intent is to start some "lengthy" operation. The C<request> could be |
|
|
3588 | used to cancel the operation, or do other things with it. |
|
|
3589 | |
|
|
3590 | It's not uncommon to have code paths in C<start_new_request> that |
|
|
3591 | immediately invoke the callback, for example, to report errors. Or you add |
|
|
3592 | some caching layer that finds that it can skip the lengthy aspects of the |
|
|
3593 | operation and simply invoke the callback with the result. |
|
|
3594 | |
|
|
3595 | The problem here is that this will happen I<before> C<start_new_request> |
|
|
3596 | has returned, so C<request> is not set. |
|
|
3597 | |
|
|
3598 | Even if you pass the request by some safer means to the callback, you |
|
|
3599 | might want to do something to the request after starting it, such as |
|
|
3600 | canceling it, which probably isn't working so well when the callback has |
|
|
3601 | already been invoked. |
|
|
3602 | |
|
|
3603 | A common way around all these issues is to make sure that |
|
|
3604 | C<start_new_request> I<always> returns before the callback is invoked. If |
|
|
3605 | C<start_new_request> immediately knows the result, it can artificially |
|
|
3606 | delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher |
|
|
3607 | for example, or more sneakily, by reusing an existing (stopped) watcher |
|
|
3608 | and pushing it into the pending queue: |
|
|
3609 | |
|
|
3610 | ev_set_cb (watcher, callback); |
|
|
3611 | ev_feed_event (EV_A_ watcher, 0); |
|
|
3612 | |
|
|
3613 | This way, C<start_new_request> can safely return before the callback is |
|
|
3614 | invoked, while not delaying callback invocation too much. |
|
|
3615 | |
|
|
3616 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3431 | |
3617 | |
3432 | Often (especially in GUI toolkits) there are places where you have |
3618 | Often (especially in GUI toolkits) there are places where you have |
3433 | I<modal> interaction, which is most easily implemented by recursively |
3619 | I<modal> interaction, which is most easily implemented by recursively |
3434 | invoking C<ev_run>. |
3620 | invoking C<ev_run>. |
3435 | |
3621 | |
… | |
… | |
3447 | int exit_main_loop = 0; |
3633 | int exit_main_loop = 0; |
3448 | |
3634 | |
3449 | while (!exit_main_loop) |
3635 | while (!exit_main_loop) |
3450 | ev_run (EV_DEFAULT_ EVRUN_ONCE); |
3636 | ev_run (EV_DEFAULT_ EVRUN_ONCE); |
3451 | |
3637 | |
3452 | // in a model watcher |
3638 | // in a modal watcher |
3453 | int exit_nested_loop = 0; |
3639 | int exit_nested_loop = 0; |
3454 | |
3640 | |
3455 | while (!exit_nested_loop) |
3641 | while (!exit_nested_loop) |
3456 | ev_run (EV_A_ EVRUN_ONCE); |
3642 | ev_run (EV_A_ EVRUN_ONCE); |
3457 | |
3643 | |
… | |
… | |
3464 | exit_main_loop = 1; |
3650 | exit_main_loop = 1; |
3465 | |
3651 | |
3466 | // exit both |
3652 | // exit both |
3467 | exit_main_loop = exit_nested_loop = 1; |
3653 | exit_main_loop = exit_nested_loop = 1; |
3468 | |
3654 | |
3469 | =back |
3655 | =head2 THREAD LOCKING EXAMPLE |
|
|
3656 | |
|
|
3657 | Here is a fictitious example of how to run an event loop in a different |
|
|
3658 | thread from where callbacks are being invoked and watchers are |
|
|
3659 | created/added/removed. |
|
|
3660 | |
|
|
3661 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
3662 | which uses exactly this technique (which is suited for many high-level |
|
|
3663 | languages). |
|
|
3664 | |
|
|
3665 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
3666 | variable to wait for callback invocations, an async watcher to notify the |
|
|
3667 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
3668 | |
|
|
3669 | First, you need to associate some data with the event loop: |
|
|
3670 | |
|
|
3671 | typedef struct { |
|
|
3672 | mutex_t lock; /* global loop lock */ |
|
|
3673 | ev_async async_w; |
|
|
3674 | thread_t tid; |
|
|
3675 | cond_t invoke_cv; |
|
|
3676 | } userdata; |
|
|
3677 | |
|
|
3678 | void prepare_loop (EV_P) |
|
|
3679 | { |
|
|
3680 | // for simplicity, we use a static userdata struct. |
|
|
3681 | static userdata u; |
|
|
3682 | |
|
|
3683 | ev_async_init (&u->async_w, async_cb); |
|
|
3684 | ev_async_start (EV_A_ &u->async_w); |
|
|
3685 | |
|
|
3686 | pthread_mutex_init (&u->lock, 0); |
|
|
3687 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
3688 | |
|
|
3689 | // now associate this with the loop |
|
|
3690 | ev_set_userdata (EV_A_ u); |
|
|
3691 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
3692 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
3693 | |
|
|
3694 | // then create the thread running ev_run |
|
|
3695 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
3696 | } |
|
|
3697 | |
|
|
3698 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
3699 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
3700 | that might have been added: |
|
|
3701 | |
|
|
3702 | static void |
|
|
3703 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
3704 | { |
|
|
3705 | // just used for the side effects |
|
|
3706 | } |
|
|
3707 | |
|
|
3708 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
3709 | protecting the loop data, respectively. |
|
|
3710 | |
|
|
3711 | static void |
|
|
3712 | l_release (EV_P) |
|
|
3713 | { |
|
|
3714 | userdata *u = ev_userdata (EV_A); |
|
|
3715 | pthread_mutex_unlock (&u->lock); |
|
|
3716 | } |
|
|
3717 | |
|
|
3718 | static void |
|
|
3719 | l_acquire (EV_P) |
|
|
3720 | { |
|
|
3721 | userdata *u = ev_userdata (EV_A); |
|
|
3722 | pthread_mutex_lock (&u->lock); |
|
|
3723 | } |
|
|
3724 | |
|
|
3725 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
3726 | into C<ev_run>: |
|
|
3727 | |
|
|
3728 | void * |
|
|
3729 | l_run (void *thr_arg) |
|
|
3730 | { |
|
|
3731 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
3732 | |
|
|
3733 | l_acquire (EV_A); |
|
|
3734 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
3735 | ev_run (EV_A_ 0); |
|
|
3736 | l_release (EV_A); |
|
|
3737 | |
|
|
3738 | return 0; |
|
|
3739 | } |
|
|
3740 | |
|
|
3741 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
3742 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
3743 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
3744 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
3745 | and b) skipping inter-thread-communication when there are no pending |
|
|
3746 | watchers is very beneficial): |
|
|
3747 | |
|
|
3748 | static void |
|
|
3749 | l_invoke (EV_P) |
|
|
3750 | { |
|
|
3751 | userdata *u = ev_userdata (EV_A); |
|
|
3752 | |
|
|
3753 | while (ev_pending_count (EV_A)) |
|
|
3754 | { |
|
|
3755 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
3756 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
3757 | } |
|
|
3758 | } |
|
|
3759 | |
|
|
3760 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
3761 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
3762 | thread to continue: |
|
|
3763 | |
|
|
3764 | static void |
|
|
3765 | real_invoke_pending (EV_P) |
|
|
3766 | { |
|
|
3767 | userdata *u = ev_userdata (EV_A); |
|
|
3768 | |
|
|
3769 | pthread_mutex_lock (&u->lock); |
|
|
3770 | ev_invoke_pending (EV_A); |
|
|
3771 | pthread_cond_signal (&u->invoke_cv); |
|
|
3772 | pthread_mutex_unlock (&u->lock); |
|
|
3773 | } |
|
|
3774 | |
|
|
3775 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
3776 | event loop, you will now have to lock: |
|
|
3777 | |
|
|
3778 | ev_timer timeout_watcher; |
|
|
3779 | userdata *u = ev_userdata (EV_A); |
|
|
3780 | |
|
|
3781 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
3782 | |
|
|
3783 | pthread_mutex_lock (&u->lock); |
|
|
3784 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
3785 | ev_async_send (EV_A_ &u->async_w); |
|
|
3786 | pthread_mutex_unlock (&u->lock); |
|
|
3787 | |
|
|
3788 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
3789 | an event loop currently blocking in the kernel will have no knowledge |
|
|
3790 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
3791 | watchers in the next event loop iteration. |
|
|
3792 | |
|
|
3793 | =head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS |
|
|
3794 | |
|
|
3795 | While the overhead of a callback that e.g. schedules a thread is small, it |
|
|
3796 | is still an overhead. If you embed libev, and your main usage is with some |
|
|
3797 | kind of threads or coroutines, you might want to customise libev so that |
|
|
3798 | doesn't need callbacks anymore. |
|
|
3799 | |
|
|
3800 | Imagine you have coroutines that you can switch to using a function |
|
|
3801 | C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro> |
|
|
3802 | and that due to some magic, the currently active coroutine is stored in a |
|
|
3803 | global called C<current_coro>. Then you can build your own "wait for libev |
|
|
3804 | event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note |
|
|
3805 | the differing C<;> conventions): |
|
|
3806 | |
|
|
3807 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3808 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb) |
|
|
3809 | |
|
|
3810 | That means instead of having a C callback function, you store the |
|
|
3811 | coroutine to switch to in each watcher, and instead of having libev call |
|
|
3812 | your callback, you instead have it switch to that coroutine. |
|
|
3813 | |
|
|
3814 | A coroutine might now wait for an event with a function called |
|
|
3815 | C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't |
|
|
3816 | matter when, or whether the watcher is active or not when this function is |
|
|
3817 | called): |
|
|
3818 | |
|
|
3819 | void |
|
|
3820 | wait_for_event (ev_watcher *w) |
|
|
3821 | { |
|
|
3822 | ev_cb_set (w) = current_coro; |
|
|
3823 | switch_to (libev_coro); |
|
|
3824 | } |
|
|
3825 | |
|
|
3826 | That basically suspends the coroutine inside C<wait_for_event> and |
|
|
3827 | continues the libev coroutine, which, when appropriate, switches back to |
|
|
3828 | this or any other coroutine. |
|
|
3829 | |
|
|
3830 | You can do similar tricks if you have, say, threads with an event queue - |
|
|
3831 | instead of storing a coroutine, you store the queue object and instead of |
|
|
3832 | switching to a coroutine, you push the watcher onto the queue and notify |
|
|
3833 | any waiters. |
|
|
3834 | |
|
|
3835 | To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two |
|
|
3836 | files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: |
|
|
3837 | |
|
|
3838 | // my_ev.h |
|
|
3839 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3840 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); |
|
|
3841 | #include "../libev/ev.h" |
|
|
3842 | |
|
|
3843 | // my_ev.c |
|
|
3844 | #define EV_H "my_ev.h" |
|
|
3845 | #include "../libev/ev.c" |
|
|
3846 | |
|
|
3847 | And then use F<my_ev.h> when you would normally use F<ev.h>, and compile |
|
|
3848 | F<my_ev.c> into your project. When properly specifying include paths, you |
|
|
3849 | can even use F<ev.h> as header file name directly. |
3470 | |
3850 | |
3471 | |
3851 | |
3472 | =head1 LIBEVENT EMULATION |
3852 | =head1 LIBEVENT EMULATION |
3473 | |
3853 | |
3474 | Libev offers a compatibility emulation layer for libevent. It cannot |
3854 | Libev offers a compatibility emulation layer for libevent. It cannot |
… | |
… | |
3689 | watchers in the constructor. |
4069 | watchers in the constructor. |
3690 | |
4070 | |
3691 | class myclass |
4071 | class myclass |
3692 | { |
4072 | { |
3693 | ev::io io ; void io_cb (ev::io &w, int revents); |
4073 | ev::io io ; void io_cb (ev::io &w, int revents); |
3694 | ev::io2 io2 ; void io2_cb (ev::io &w, int revents); |
4074 | ev::io io2 ; void io2_cb (ev::io &w, int revents); |
3695 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
4075 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
3696 | |
4076 | |
3697 | myclass (int fd) |
4077 | myclass (int fd) |
3698 | { |
4078 | { |
3699 | io .set <myclass, &myclass::io_cb > (this); |
4079 | io .set <myclass, &myclass::io_cb > (this); |
… | |
… | |
3750 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
4130 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
3751 | |
4131 | |
3752 | =item D |
4132 | =item D |
3753 | |
4133 | |
3754 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
4134 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
3755 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
4135 | be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>. |
3756 | |
4136 | |
3757 | =item Ocaml |
4137 | =item Ocaml |
3758 | |
4138 | |
3759 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4139 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
3760 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
4140 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
… | |
… | |
3808 | suitable for use with C<EV_A>. |
4188 | suitable for use with C<EV_A>. |
3809 | |
4189 | |
3810 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4190 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
3811 | |
4191 | |
3812 | Similar to the other two macros, this gives you the value of the default |
4192 | Similar to the other two macros, this gives you the value of the default |
3813 | loop, if multiple loops are supported ("ev loop default"). |
4193 | loop, if multiple loops are supported ("ev loop default"). The default loop |
|
|
4194 | will be initialised if it isn't already initialised. |
|
|
4195 | |
|
|
4196 | For non-multiplicity builds, these macros do nothing, so you always have |
|
|
4197 | to initialise the loop somewhere. |
3814 | |
4198 | |
3815 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4199 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
3816 | |
4200 | |
3817 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4201 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
3818 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
4202 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
… | |
… | |
3963 | supported). It will also not define any of the structs usually found in |
4347 | supported). It will also not define any of the structs usually found in |
3964 | F<event.h> that are not directly supported by the libev core alone. |
4348 | F<event.h> that are not directly supported by the libev core alone. |
3965 | |
4349 | |
3966 | In standalone mode, libev will still try to automatically deduce the |
4350 | In standalone mode, libev will still try to automatically deduce the |
3967 | configuration, but has to be more conservative. |
4351 | configuration, but has to be more conservative. |
|
|
4352 | |
|
|
4353 | =item EV_USE_FLOOR |
|
|
4354 | |
|
|
4355 | If defined to be C<1>, libev will use the C<floor ()> function for its |
|
|
4356 | periodic reschedule calculations, otherwise libev will fall back on a |
|
|
4357 | portable (slower) implementation. If you enable this, you usually have to |
|
|
4358 | link against libm or something equivalent. Enabling this when the C<floor> |
|
|
4359 | function is not available will fail, so the safe default is to not enable |
|
|
4360 | this. |
3968 | |
4361 | |
3969 | =item EV_USE_MONOTONIC |
4362 | =item EV_USE_MONOTONIC |
3970 | |
4363 | |
3971 | If defined to be C<1>, libev will try to detect the availability of the |
4364 | If defined to be C<1>, libev will try to detect the availability of the |
3972 | monotonic clock option at both compile time and runtime. Otherwise no |
4365 | monotonic clock option at both compile time and runtime. Otherwise no |
… | |
… | |
4105 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4498 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4106 | |
4499 | |
4107 | =item EV_ATOMIC_T |
4500 | =item EV_ATOMIC_T |
4108 | |
4501 | |
4109 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4502 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4110 | access is atomic with respect to other threads or signal contexts. No such |
4503 | access is atomic and serialised with respect to other threads or signal |
4111 | type is easily found in the C language, so you can provide your own type |
4504 | contexts. No such type is easily found in the C language, so you can |
4112 | that you know is safe for your purposes. It is used both for signal handler "locking" |
4505 | provide your own type that you know is safe for your purposes. It is used |
4113 | as well as for signal and thread safety in C<ev_async> watchers. |
4506 | both for signal handler "locking" as well as for signal and thread safety |
|
|
4507 | in C<ev_async> watchers. |
4114 | |
4508 | |
4115 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4509 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4116 | (from F<signal.h>), which is usually good enough on most platforms. |
4510 | (from F<signal.h>), which is usually good enough on most platforms, |
|
|
4511 | although strictly speaking using a type that also implies a memory fence |
|
|
4512 | is required. |
4117 | |
4513 | |
4118 | =item EV_H (h) |
4514 | =item EV_H (h) |
4119 | |
4515 | |
4120 | The name of the F<ev.h> header file used to include it. The default if |
4516 | The name of the F<ev.h> header file used to include it. The default if |
4121 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
4517 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
… | |
… | |
4145 | will have the C<struct ev_loop *> as first argument, and you can create |
4541 | will have the C<struct ev_loop *> as first argument, and you can create |
4146 | additional independent event loops. Otherwise there will be no support |
4542 | additional independent event loops. Otherwise there will be no support |
4147 | for multiple event loops and there is no first event loop pointer |
4543 | for multiple event loops and there is no first event loop pointer |
4148 | argument. Instead, all functions act on the single default loop. |
4544 | argument. Instead, all functions act on the single default loop. |
4149 | |
4545 | |
|
|
4546 | Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a |
|
|
4547 | default loop when multiplicity is switched off - you always have to |
|
|
4548 | initialise the loop manually in this case. |
|
|
4549 | |
4150 | =item EV_MINPRI |
4550 | =item EV_MINPRI |
4151 | |
4551 | |
4152 | =item EV_MAXPRI |
4552 | =item EV_MAXPRI |
4153 | |
4553 | |
4154 | The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to |
4554 | The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to |
… | |
… | |
4251 | |
4651 | |
4252 | With an intelligent-enough linker (gcc+binutils are intelligent enough |
4652 | With an intelligent-enough linker (gcc+binutils are intelligent enough |
4253 | when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by |
4653 | when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by |
4254 | your program might be left out as well - a binary starting a timer and an |
4654 | your program might be left out as well - a binary starting a timer and an |
4255 | I/O watcher then might come out at only 5Kb. |
4655 | I/O watcher then might come out at only 5Kb. |
|
|
4656 | |
|
|
4657 | =item EV_API_STATIC |
|
|
4658 | |
|
|
4659 | If this symbol is defined (by default it is not), then all identifiers |
|
|
4660 | will have static linkage. This means that libev will not export any |
|
|
4661 | identifiers, and you cannot link against libev anymore. This can be useful |
|
|
4662 | when you embed libev, only want to use libev functions in a single file, |
|
|
4663 | and do not want its identifiers to be visible. |
|
|
4664 | |
|
|
4665 | To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that |
|
|
4666 | wants to use libev. |
4256 | |
4667 | |
4257 | =item EV_AVOID_STDIO |
4668 | =item EV_AVOID_STDIO |
4258 | |
4669 | |
4259 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
4670 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
4260 | functions (printf, scanf, perror etc.). This will increase the code size |
4671 | functions (printf, scanf, perror etc.). This will increase the code size |
… | |
… | |
4404 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4815 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4405 | |
4816 | |
4406 | #include "ev_cpp.h" |
4817 | #include "ev_cpp.h" |
4407 | #include "ev.c" |
4818 | #include "ev.c" |
4408 | |
4819 | |
4409 | =head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES |
4820 | =head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT |
4410 | |
4821 | |
4411 | =head2 THREADS AND COROUTINES |
4822 | =head2 THREADS AND COROUTINES |
4412 | |
4823 | |
4413 | =head3 THREADS |
4824 | =head3 THREADS |
4414 | |
4825 | |
… | |
… | |
4465 | default loop and triggering an C<ev_async> watcher from the default loop |
4876 | default loop and triggering an C<ev_async> watcher from the default loop |
4466 | watcher callback into the event loop interested in the signal. |
4877 | watcher callback into the event loop interested in the signal. |
4467 | |
4878 | |
4468 | =back |
4879 | =back |
4469 | |
4880 | |
4470 | =head4 THREAD LOCKING EXAMPLE |
4881 | See also L<THREAD LOCKING EXAMPLE>. |
4471 | |
|
|
4472 | Here is a fictitious example of how to run an event loop in a different |
|
|
4473 | thread than where callbacks are being invoked and watchers are |
|
|
4474 | created/added/removed. |
|
|
4475 | |
|
|
4476 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
4477 | which uses exactly this technique (which is suited for many high-level |
|
|
4478 | languages). |
|
|
4479 | |
|
|
4480 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
4481 | variable to wait for callback invocations, an async watcher to notify the |
|
|
4482 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
4483 | |
|
|
4484 | First, you need to associate some data with the event loop: |
|
|
4485 | |
|
|
4486 | typedef struct { |
|
|
4487 | mutex_t lock; /* global loop lock */ |
|
|
4488 | ev_async async_w; |
|
|
4489 | thread_t tid; |
|
|
4490 | cond_t invoke_cv; |
|
|
4491 | } userdata; |
|
|
4492 | |
|
|
4493 | void prepare_loop (EV_P) |
|
|
4494 | { |
|
|
4495 | // for simplicity, we use a static userdata struct. |
|
|
4496 | static userdata u; |
|
|
4497 | |
|
|
4498 | ev_async_init (&u->async_w, async_cb); |
|
|
4499 | ev_async_start (EV_A_ &u->async_w); |
|
|
4500 | |
|
|
4501 | pthread_mutex_init (&u->lock, 0); |
|
|
4502 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
4503 | |
|
|
4504 | // now associate this with the loop |
|
|
4505 | ev_set_userdata (EV_A_ u); |
|
|
4506 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
4507 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
4508 | |
|
|
4509 | // then create the thread running ev_loop |
|
|
4510 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
4511 | } |
|
|
4512 | |
|
|
4513 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
4514 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
4515 | that might have been added: |
|
|
4516 | |
|
|
4517 | static void |
|
|
4518 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
4519 | { |
|
|
4520 | // just used for the side effects |
|
|
4521 | } |
|
|
4522 | |
|
|
4523 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
4524 | protecting the loop data, respectively. |
|
|
4525 | |
|
|
4526 | static void |
|
|
4527 | l_release (EV_P) |
|
|
4528 | { |
|
|
4529 | userdata *u = ev_userdata (EV_A); |
|
|
4530 | pthread_mutex_unlock (&u->lock); |
|
|
4531 | } |
|
|
4532 | |
|
|
4533 | static void |
|
|
4534 | l_acquire (EV_P) |
|
|
4535 | { |
|
|
4536 | userdata *u = ev_userdata (EV_A); |
|
|
4537 | pthread_mutex_lock (&u->lock); |
|
|
4538 | } |
|
|
4539 | |
|
|
4540 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
4541 | into C<ev_run>: |
|
|
4542 | |
|
|
4543 | void * |
|
|
4544 | l_run (void *thr_arg) |
|
|
4545 | { |
|
|
4546 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
4547 | |
|
|
4548 | l_acquire (EV_A); |
|
|
4549 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
4550 | ev_run (EV_A_ 0); |
|
|
4551 | l_release (EV_A); |
|
|
4552 | |
|
|
4553 | return 0; |
|
|
4554 | } |
|
|
4555 | |
|
|
4556 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
4557 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
4558 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
4559 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
4560 | and b) skipping inter-thread-communication when there are no pending |
|
|
4561 | watchers is very beneficial): |
|
|
4562 | |
|
|
4563 | static void |
|
|
4564 | l_invoke (EV_P) |
|
|
4565 | { |
|
|
4566 | userdata *u = ev_userdata (EV_A); |
|
|
4567 | |
|
|
4568 | while (ev_pending_count (EV_A)) |
|
|
4569 | { |
|
|
4570 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
4571 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
4572 | } |
|
|
4573 | } |
|
|
4574 | |
|
|
4575 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
4576 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
4577 | thread to continue: |
|
|
4578 | |
|
|
4579 | static void |
|
|
4580 | real_invoke_pending (EV_P) |
|
|
4581 | { |
|
|
4582 | userdata *u = ev_userdata (EV_A); |
|
|
4583 | |
|
|
4584 | pthread_mutex_lock (&u->lock); |
|
|
4585 | ev_invoke_pending (EV_A); |
|
|
4586 | pthread_cond_signal (&u->invoke_cv); |
|
|
4587 | pthread_mutex_unlock (&u->lock); |
|
|
4588 | } |
|
|
4589 | |
|
|
4590 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
4591 | event loop, you will now have to lock: |
|
|
4592 | |
|
|
4593 | ev_timer timeout_watcher; |
|
|
4594 | userdata *u = ev_userdata (EV_A); |
|
|
4595 | |
|
|
4596 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
4597 | |
|
|
4598 | pthread_mutex_lock (&u->lock); |
|
|
4599 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
4600 | ev_async_send (EV_A_ &u->async_w); |
|
|
4601 | pthread_mutex_unlock (&u->lock); |
|
|
4602 | |
|
|
4603 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
4604 | an event loop currently blocking in the kernel will have no knowledge |
|
|
4605 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
4606 | watchers in the next event loop iteration. |
|
|
4607 | |
4882 | |
4608 | =head3 COROUTINES |
4883 | =head3 COROUTINES |
4609 | |
4884 | |
4610 | Libev is very accommodating to coroutines ("cooperative threads"): |
4885 | Libev is very accommodating to coroutines ("cooperative threads"): |
4611 | libev fully supports nesting calls to its functions from different |
4886 | libev fully supports nesting calls to its functions from different |
… | |
… | |
4776 | requires, and its I/O model is fundamentally incompatible with the POSIX |
5051 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4777 | model. Libev still offers limited functionality on this platform in |
5052 | model. Libev still offers limited functionality on this platform in |
4778 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
5053 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4779 | descriptors. This only applies when using Win32 natively, not when using |
5054 | descriptors. This only applies when using Win32 natively, not when using |
4780 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
5055 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4781 | as every compielr comes with a slightly differently broken/incompatible |
5056 | as every compiler comes with a slightly differently broken/incompatible |
4782 | environment. |
5057 | environment. |
4783 | |
5058 | |
4784 | Lifting these limitations would basically require the full |
5059 | Lifting these limitations would basically require the full |
4785 | re-implementation of the I/O system. If you are into this kind of thing, |
5060 | re-implementation of the I/O system. If you are into this kind of thing, |
4786 | then note that glib does exactly that for you in a very portable way (note |
5061 | then note that glib does exactly that for you in a very portable way (note |
… | |
… | |
4919 | |
5194 | |
4920 | The type C<double> is used to represent timestamps. It is required to |
5195 | The type C<double> is used to represent timestamps. It is required to |
4921 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5196 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
4922 | good enough for at least into the year 4000 with millisecond accuracy |
5197 | good enough for at least into the year 4000 with millisecond accuracy |
4923 | (the design goal for libev). This requirement is overfulfilled by |
5198 | (the design goal for libev). This requirement is overfulfilled by |
4924 | implementations using IEEE 754, which is basically all existing ones. With |
5199 | implementations using IEEE 754, which is basically all existing ones. |
|
|
5200 | |
4925 | IEEE 754 doubles, you get microsecond accuracy until at least 2200. |
5201 | With IEEE 754 doubles, you get microsecond accuracy until at least the |
|
|
5202 | year 2255 (and millisecond accuracy till the year 287396 - by then, libev |
|
|
5203 | is either obsolete or somebody patched it to use C<long double> or |
|
|
5204 | something like that, just kidding). |
4926 | |
5205 | |
4927 | =back |
5206 | =back |
4928 | |
5207 | |
4929 | If you know of other additional requirements drop me a note. |
5208 | If you know of other additional requirements drop me a note. |
4930 | |
5209 | |
… | |
… | |
4992 | =item Processing ev_async_send: O(number_of_async_watchers) |
5271 | =item Processing ev_async_send: O(number_of_async_watchers) |
4993 | |
5272 | |
4994 | =item Processing signals: O(max_signal_number) |
5273 | =item Processing signals: O(max_signal_number) |
4995 | |
5274 | |
4996 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
5275 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
4997 | calls in the current loop iteration. Checking for async and signal events |
5276 | calls in the current loop iteration and the loop is currently |
|
|
5277 | blocked. Checking for async and signal events involves iterating over all |
4998 | involves iterating over all running async watchers or all signal numbers. |
5278 | running async watchers or all signal numbers. |
4999 | |
5279 | |
5000 | =back |
5280 | =back |
5001 | |
5281 | |
5002 | |
5282 | |
5003 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
5283 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
… | |
… | |
5120 | The physical time that is observed. It is apparently strictly monotonic :) |
5400 | The physical time that is observed. It is apparently strictly monotonic :) |
5121 | |
5401 | |
5122 | =item wall-clock time |
5402 | =item wall-clock time |
5123 | |
5403 | |
5124 | The time and date as shown on clocks. Unlike real time, it can actually |
5404 | The time and date as shown on clocks. Unlike real time, it can actually |
5125 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
5405 | be wrong and jump forwards and backwards, e.g. when you adjust your |
5126 | clock. |
5406 | clock. |
5127 | |
5407 | |
5128 | =item watcher |
5408 | =item watcher |
5129 | |
5409 | |
5130 | A data structure that describes interest in certain events. Watchers need |
5410 | A data structure that describes interest in certain events. Watchers need |
… | |
… | |
5133 | =back |
5413 | =back |
5134 | |
5414 | |
5135 | =head1 AUTHOR |
5415 | =head1 AUTHOR |
5136 | |
5416 | |
5137 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5417 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5138 | Magnusson and Emanuele Giaquinta. |
5418 | Magnusson and Emanuele Giaquinta, and minor corrections by many others. |
5139 | |
5419 | |