… | |
… | |
441 | when you want to receive them. |
441 | when you want to receive them. |
442 | |
442 | |
443 | This behaviour is useful when you want to do your own signal handling, or |
443 | This behaviour is useful when you want to do your own signal handling, or |
444 | want to handle signals only in specific threads and want to avoid libev |
444 | want to handle signals only in specific threads and want to avoid libev |
445 | unblocking the signals. |
445 | unblocking the signals. |
|
|
446 | |
|
|
447 | It's also required by POSIX in a threaded program, as libev calls |
|
|
448 | C<sigprocmask>, whose behaviour is officially unspecified. |
446 | |
449 | |
447 | This flag's behaviour will become the default in future versions of libev. |
450 | This flag's behaviour will become the default in future versions of libev. |
448 | |
451 | |
449 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
452 | =item C<EVBACKEND_SELECT> (value 1, portable select backend) |
450 | |
453 | |
… | |
… | |
1357 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1360 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1358 | functions that do not need a watcher. |
1361 | functions that do not need a watcher. |
1359 | |
1362 | |
1360 | =back |
1363 | =back |
1361 | |
1364 | |
1362 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1365 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1363 | |
1366 | OWN COMPOSITE WATCHERS> idioms. |
1364 | Each watcher has, by default, a member C<void *data> that you can change |
|
|
1365 | and read at any time: libev will completely ignore it. This can be used |
|
|
1366 | to associate arbitrary data with your watcher. If you need more data and |
|
|
1367 | don't want to allocate memory and store a pointer to it in that data |
|
|
1368 | member, you can also "subclass" the watcher type and provide your own |
|
|
1369 | data: |
|
|
1370 | |
|
|
1371 | struct my_io |
|
|
1372 | { |
|
|
1373 | ev_io io; |
|
|
1374 | int otherfd; |
|
|
1375 | void *somedata; |
|
|
1376 | struct whatever *mostinteresting; |
|
|
1377 | }; |
|
|
1378 | |
|
|
1379 | ... |
|
|
1380 | struct my_io w; |
|
|
1381 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
1382 | |
|
|
1383 | And since your callback will be called with a pointer to the watcher, you |
|
|
1384 | can cast it back to your own type: |
|
|
1385 | |
|
|
1386 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
1387 | { |
|
|
1388 | struct my_io *w = (struct my_io *)w_; |
|
|
1389 | ... |
|
|
1390 | } |
|
|
1391 | |
|
|
1392 | More interesting and less C-conformant ways of casting your callback type |
|
|
1393 | instead have been omitted. |
|
|
1394 | |
|
|
1395 | Another common scenario is to use some data structure with multiple |
|
|
1396 | embedded watchers: |
|
|
1397 | |
|
|
1398 | struct my_biggy |
|
|
1399 | { |
|
|
1400 | int some_data; |
|
|
1401 | ev_timer t1; |
|
|
1402 | ev_timer t2; |
|
|
1403 | } |
|
|
1404 | |
|
|
1405 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
1406 | complicated: Either you store the address of your C<my_biggy> struct |
|
|
1407 | in the C<data> member of the watcher (for woozies), or you need to use |
|
|
1408 | some pointer arithmetic using C<offsetof> inside your watchers (for real |
|
|
1409 | programmers): |
|
|
1410 | |
|
|
1411 | #include <stddef.h> |
|
|
1412 | |
|
|
1413 | static void |
|
|
1414 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
1415 | { |
|
|
1416 | struct my_biggy big = (struct my_biggy *) |
|
|
1417 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
1418 | } |
|
|
1419 | |
|
|
1420 | static void |
|
|
1421 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
1422 | { |
|
|
1423 | struct my_biggy big = (struct my_biggy *) |
|
|
1424 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
1425 | } |
|
|
1426 | |
1367 | |
1427 | =head2 WATCHER STATES |
1368 | =head2 WATCHER STATES |
1428 | |
1369 | |
1429 | There are various watcher states mentioned throughout this manual - |
1370 | There are various watcher states mentioned throughout this manual - |
1430 | active, pending and so on. In this section these states and the rules to |
1371 | active, pending and so on. In this section these states and the rules to |
… | |
… | |
1680 | always get a readiness notification instantly, and your read (or possibly |
1621 | always get a readiness notification instantly, and your read (or possibly |
1681 | write) will still block on the disk I/O. |
1622 | write) will still block on the disk I/O. |
1682 | |
1623 | |
1683 | Another way to view it is that in the case of sockets, pipes, character |
1624 | Another way to view it is that in the case of sockets, pipes, character |
1684 | devices and so on, there is another party (the sender) that delivers data |
1625 | devices and so on, there is another party (the sender) that delivers data |
1685 | on it's own, but in the case of files, there is no such thing: the disk |
1626 | on its own, but in the case of files, there is no such thing: the disk |
1686 | will not send data on it's own, simply because it doesn't know what you |
1627 | will not send data on its own, simply because it doesn't know what you |
1687 | wish to read - you would first have to request some data. |
1628 | wish to read - you would first have to request some data. |
1688 | |
1629 | |
1689 | Since files are typically not-so-well supported by advanced notification |
1630 | Since files are typically not-so-well supported by advanced notification |
1690 | mechanism, libev tries hard to emulate POSIX behaviour with respect |
1631 | mechanism, libev tries hard to emulate POSIX behaviour with respect |
1691 | to files, even though you should not use it. The reason for this is |
1632 | to files, even though you should not use it. The reason for this is |
… | |
… | |
2362 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2303 | =head3 The special problem of inheritance over fork/execve/pthread_create |
2363 | |
2304 | |
2364 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2305 | Both the signal mask (C<sigprocmask>) and the signal disposition |
2365 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2306 | (C<sigaction>) are unspecified after starting a signal watcher (and after |
2366 | stopping it again), that is, libev might or might not block the signal, |
2307 | stopping it again), that is, libev might or might not block the signal, |
2367 | and might or might not set or restore the installed signal handler. |
2308 | and might or might not set or restore the installed signal handler (but |
|
|
2309 | see C<EVFLAG_NOSIGMASK>). |
2368 | |
2310 | |
2369 | While this does not matter for the signal disposition (libev never |
2311 | While this does not matter for the signal disposition (libev never |
2370 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2312 | sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on |
2371 | C<execve>), this matters for the signal mask: many programs do not expect |
2313 | C<execve>), this matters for the signal mask: many programs do not expect |
2372 | certain signals to be blocked. |
2314 | certain signals to be blocked. |
… | |
… | |
3456 | |
3398 | |
3457 | This section explains some common idioms that are not immediately |
3399 | This section explains some common idioms that are not immediately |
3458 | obvious. Note that examples are sprinkled over the whole manual, and this |
3400 | obvious. Note that examples are sprinkled over the whole manual, and this |
3459 | section only contains stuff that wouldn't fit anywhere else. |
3401 | section only contains stuff that wouldn't fit anywhere else. |
3460 | |
3402 | |
|
|
3403 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
|
|
3404 | |
|
|
3405 | Each watcher has, by default, a C<void *data> member that you can read |
|
|
3406 | or modify at any time: libev will completely ignore it. This can be used |
|
|
3407 | to associate arbitrary data with your watcher. If you need more data and |
|
|
3408 | don't want to allocate memory separately and store a pointer to it in that |
|
|
3409 | data member, you can also "subclass" the watcher type and provide your own |
|
|
3410 | data: |
|
|
3411 | |
|
|
3412 | struct my_io |
|
|
3413 | { |
|
|
3414 | ev_io io; |
|
|
3415 | int otherfd; |
|
|
3416 | void *somedata; |
|
|
3417 | struct whatever *mostinteresting; |
|
|
3418 | }; |
|
|
3419 | |
|
|
3420 | ... |
|
|
3421 | struct my_io w; |
|
|
3422 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
3423 | |
|
|
3424 | And since your callback will be called with a pointer to the watcher, you |
|
|
3425 | can cast it back to your own type: |
|
|
3426 | |
|
|
3427 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
3428 | { |
|
|
3429 | struct my_io *w = (struct my_io *)w_; |
|
|
3430 | ... |
|
|
3431 | } |
|
|
3432 | |
|
|
3433 | More interesting and less C-conformant ways of casting your callback |
|
|
3434 | function type instead have been omitted. |
|
|
3435 | |
|
|
3436 | =head2 BUILDING YOUR OWN COMPOSITE WATCHERS |
|
|
3437 | |
|
|
3438 | Another common scenario is to use some data structure with multiple |
|
|
3439 | embedded watchers, in effect creating your own watcher that combines |
|
|
3440 | multiple libev event sources into one "super-watcher": |
|
|
3441 | |
|
|
3442 | struct my_biggy |
|
|
3443 | { |
|
|
3444 | int some_data; |
|
|
3445 | ev_timer t1; |
|
|
3446 | ev_timer t2; |
|
|
3447 | } |
|
|
3448 | |
|
|
3449 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
3450 | complicated: Either you store the address of your C<my_biggy> struct in |
|
|
3451 | the C<data> member of the watcher (for woozies or C++ coders), or you need |
|
|
3452 | to use some pointer arithmetic using C<offsetof> inside your watchers (for |
|
|
3453 | real programmers): |
|
|
3454 | |
|
|
3455 | #include <stddef.h> |
|
|
3456 | |
|
|
3457 | static void |
|
|
3458 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
3459 | { |
|
|
3460 | struct my_biggy big = (struct my_biggy *) |
|
|
3461 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
3462 | } |
|
|
3463 | |
|
|
3464 | static void |
|
|
3465 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
3466 | { |
|
|
3467 | struct my_biggy big = (struct my_biggy *) |
|
|
3468 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
3469 | } |
|
|
3470 | |
3461 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3471 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3462 | |
3472 | |
3463 | Often (especially in GUI toolkits) there are places where you have |
3473 | Often (especially in GUI toolkits) there are places where you have |
3464 | I<modal> interaction, which is most easily implemented by recursively |
3474 | I<modal> interaction, which is most easily implemented by recursively |
3465 | invoking C<ev_run>. |
3475 | invoking C<ev_run>. |
… | |
… | |
3498 | exit_main_loop = exit_nested_loop = 1; |
3508 | exit_main_loop = exit_nested_loop = 1; |
3499 | |
3509 | |
3500 | =head2 THREAD LOCKING EXAMPLE |
3510 | =head2 THREAD LOCKING EXAMPLE |
3501 | |
3511 | |
3502 | Here is a fictitious example of how to run an event loop in a different |
3512 | Here is a fictitious example of how to run an event loop in a different |
3503 | thread than where callbacks are being invoked and watchers are |
3513 | thread from where callbacks are being invoked and watchers are |
3504 | created/added/removed. |
3514 | created/added/removed. |
3505 | |
3515 | |
3506 | For a real-world example, see the C<EV::Loop::Async> perl module, |
3516 | For a real-world example, see the C<EV::Loop::Async> perl module, |
3507 | which uses exactly this technique (which is suited for many high-level |
3517 | which uses exactly this technique (which is suited for many high-level |
3508 | languages). |
3518 | languages). |
… | |
… | |
3632 | |
3642 | |
3633 | Note that sending the C<ev_async> watcher is required because otherwise |
3643 | Note that sending the C<ev_async> watcher is required because otherwise |
3634 | an event loop currently blocking in the kernel will have no knowledge |
3644 | an event loop currently blocking in the kernel will have no knowledge |
3635 | about the newly added timer. By waking up the loop it will pick up any new |
3645 | about the newly added timer. By waking up the loop it will pick up any new |
3636 | watchers in the next event loop iteration. |
3646 | watchers in the next event loop iteration. |
|
|
3647 | |
|
|
3648 | =head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS |
|
|
3649 | |
|
|
3650 | While the overhead of a callback that e.g. schedules a thread is small, it |
|
|
3651 | is still an overhead. If you embed libev, and your main usage is with some |
|
|
3652 | kind of threads or coroutines, you might want to customise libev so that |
|
|
3653 | doesn't need callbacks anymore. |
|
|
3654 | |
|
|
3655 | Imagine you have coroutines that you can switch to using a function |
|
|
3656 | C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro> |
|
|
3657 | and that due to some magic, the currently active coroutine is stored in a |
|
|
3658 | global called C<current_coro>. Then you can build your own "wait for libev |
|
|
3659 | event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note |
|
|
3660 | the differing C<;> conventions): |
|
|
3661 | |
|
|
3662 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3663 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb) |
|
|
3664 | |
|
|
3665 | That means instead of having a C callback function, you store the |
|
|
3666 | coroutine to switch to in each watcher, and instead of having libev call |
|
|
3667 | your callback, you instead have it switch to that coroutine. |
|
|
3668 | |
|
|
3669 | A coroutine might now wait for an event with a function called |
|
|
3670 | C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't |
|
|
3671 | matter when, or whether the watcher is active or not when this function is |
|
|
3672 | called): |
|
|
3673 | |
|
|
3674 | void |
|
|
3675 | wait_for_event (ev_watcher *w) |
|
|
3676 | { |
|
|
3677 | ev_cb_set (w) = current_coro; |
|
|
3678 | switch_to (libev_coro); |
|
|
3679 | } |
|
|
3680 | |
|
|
3681 | That basically suspends the coroutine inside C<wait_for_event> and |
|
|
3682 | continues the libev coroutine, which, when appropriate, switches back to |
|
|
3683 | this or any other coroutine. I am sure if you sue this your own :) |
|
|
3684 | |
|
|
3685 | You can do similar tricks if you have, say, threads with an event queue - |
|
|
3686 | instead of storing a coroutine, you store the queue object and instead of |
|
|
3687 | switching to a coroutine, you push the watcher onto the queue and notify |
|
|
3688 | any waiters. |
|
|
3689 | |
|
|
3690 | To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two |
|
|
3691 | files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: |
|
|
3692 | |
|
|
3693 | // my_ev.h |
|
|
3694 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3695 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); |
|
|
3696 | #include "../libev/ev.h" |
|
|
3697 | |
|
|
3698 | // my_ev.c |
|
|
3699 | #define EV_H "my_ev.h" |
|
|
3700 | #include "../libev/ev.c" |
|
|
3701 | |
|
|
3702 | And then use F<my_ev.h> when you would normally use F<ev.h>, and compile |
|
|
3703 | F<my_ev.c> into your project. When properly specifying include paths, you |
|
|
3704 | can even use F<ev.h> as header file name directly. |
3637 | |
3705 | |
3638 | |
3706 | |
3639 | =head1 LIBEVENT EMULATION |
3707 | =head1 LIBEVENT EMULATION |
3640 | |
3708 | |
3641 | Libev offers a compatibility emulation layer for libevent. It cannot |
3709 | Libev offers a compatibility emulation layer for libevent. It cannot |