… | |
… | |
506 | employing an additional generation counter and comparing that against the |
506 | employing an additional generation counter and comparing that against the |
507 | events to filter out spurious ones, recreating the set when required. Last |
507 | events to filter out spurious ones, recreating the set when required. Last |
508 | not least, it also refuses to work with some file descriptors which work |
508 | not least, it also refuses to work with some file descriptors which work |
509 | perfectly fine with C<select> (files, many character devices...). |
509 | perfectly fine with C<select> (files, many character devices...). |
510 | |
510 | |
511 | Epoll is truly the train wreck analog among event poll mechanisms. |
511 | Epoll is truly the train wreck analog among event poll mechanisms, |
|
|
512 | a frankenpoll, cobbled together in a hurry, no thought to design or |
|
|
513 | interaction with others. |
512 | |
514 | |
513 | While stopping, setting and starting an I/O watcher in the same iteration |
515 | 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 |
516 | 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 |
517 | 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 |
518 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
… | |
… | |
582 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
584 | =item C<EVBACKEND_PORT> (value 32, Solaris 10) |
583 | |
585 | |
584 | This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
586 | 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)). |
587 | it's really slow, but it still scales very well (O(active_fds)). |
586 | |
588 | |
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 |
589 | 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 |
590 | file descriptor per loop iteration. For small and medium numbers of file |
593 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
591 | descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
594 | might perform better. |
592 | might perform better. |
595 | |
593 | |
596 | On the positive side, with the exception of the spurious readiness |
594 | 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 |
595 | specification in all tests and is fully embeddable, which is a rare feat |
599 | OS-specific backends (I vastly prefer correctness over speed hacks). |
596 | among the OS-specific backends (I vastly prefer correctness over speed |
|
|
597 | hacks). |
|
|
598 | |
|
|
599 | On the negative side, the interface is I<bizarre> - so bizarre that |
|
|
600 | even sun itself gets it wrong in their code examples: The event polling |
|
|
601 | function sometimes returning events to the caller even though an error |
|
|
602 | occurred, but with no indication whether it has done so or not (yes, it's |
|
|
603 | even documented that way) - deadly for edge-triggered interfaces where |
|
|
604 | you absolutely have to know whether an event occurred or not because you |
|
|
605 | have to re-arm the watcher. |
|
|
606 | |
|
|
607 | Fortunately libev seems to be able to work around these idiocies. |
600 | |
608 | |
601 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
609 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
602 | C<EVBACKEND_POLL>. |
610 | C<EVBACKEND_POLL>. |
603 | |
611 | |
604 | =item C<EVBACKEND_ALL> |
612 | =item C<EVBACKEND_ALL> |
… | |
… | |
1349 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1357 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1350 | functions that do not need a watcher. |
1358 | functions that do not need a watcher. |
1351 | |
1359 | |
1352 | =back |
1360 | =back |
1353 | |
1361 | |
1354 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1362 | See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR |
1355 | |
1363 | 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 | |
1364 | |
1419 | =head2 WATCHER STATES |
1365 | =head2 WATCHER STATES |
1420 | |
1366 | |
1421 | There are various watcher states mentioned throughout this manual - |
1367 | There are various watcher states mentioned throughout this manual - |
1422 | active, pending and so on. In this section these states and the rules to |
1368 | active, pending and so on. In this section these states and the rules to |
… | |
… | |
1608 | In general you can register as many read and/or write event watchers per |
1554 | 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 |
1555 | 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 |
1556 | descriptors to non-blocking mode is also usually a good idea (but not |
1611 | required if you know what you are doing). |
1557 | required if you know what you are doing). |
1612 | |
1558 | |
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 |
1559 | 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 |
1560 | 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 |
1561 | 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 |
1562 | 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 |
1563 | with a relatively standard program structure. Thus it is best to always |
1624 | this situation even with a relatively standard program structure. Thus |
1564 | 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. |
1565 | preferable to a program hanging until some data arrives. |
1627 | |
1566 | |
1628 | If you cannot run the fd in non-blocking mode (for example you should |
1567 | 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 |
1568 | 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 |
1569 | 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 |
1570 | 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 |
1571 | 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 |
1572 | use C<SIGALRM> and an interval timer, just to be sure you won't block |
1634 | indefinitely. |
1573 | indefinitely. |
1635 | |
1574 | |
1636 | But really, best use non-blocking mode. |
1575 | But really, best use non-blocking mode. |
1637 | |
1576 | |
… | |
… | |
1665 | |
1604 | |
1666 | There is no workaround possible except not registering events |
1605 | There is no workaround possible except not registering events |
1667 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1606 | for potentially C<dup ()>'ed file descriptors, or to resort to |
1668 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1607 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1669 | |
1608 | |
|
|
1609 | =head3 The special problem of files |
|
|
1610 | |
|
|
1611 | Many people try to use C<select> (or libev) on file descriptors |
|
|
1612 | representing files, and expect it to become ready when their program |
|
|
1613 | doesn't block on disk accesses (which can take a long time on their own). |
|
|
1614 | |
|
|
1615 | However, this cannot ever work in the "expected" way - you get a readiness |
|
|
1616 | notification as soon as the kernel knows whether and how much data is |
|
|
1617 | there, and in the case of open files, that's always the case, so you |
|
|
1618 | always get a readiness notification instantly, and your read (or possibly |
|
|
1619 | write) will still block on the disk I/O. |
|
|
1620 | |
|
|
1621 | Another way to view it is that in the case of sockets, pipes, character |
|
|
1622 | devices and so on, there is another party (the sender) that delivers data |
|
|
1623 | on its own, but in the case of files, there is no such thing: the disk |
|
|
1624 | will not send data on its own, simply because it doesn't know what you |
|
|
1625 | wish to read - you would first have to request some data. |
|
|
1626 | |
|
|
1627 | Since files are typically not-so-well supported by advanced notification |
|
|
1628 | mechanism, libev tries hard to emulate POSIX behaviour with respect |
|
|
1629 | to files, even though you should not use it. The reason for this is |
|
|
1630 | convenience: sometimes you want to watch STDIN or STDOUT, which is |
|
|
1631 | usually a tty, often a pipe, but also sometimes files or special devices |
|
|
1632 | (for example, C<epoll> on Linux works with F</dev/random> but not with |
|
|
1633 | F</dev/urandom>), and even though the file might better be served with |
|
|
1634 | asynchronous I/O instead of with non-blocking I/O, it is still useful when |
|
|
1635 | it "just works" instead of freezing. |
|
|
1636 | |
|
|
1637 | So avoid file descriptors pointing to files when you know it (e.g. use |
|
|
1638 | libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or |
|
|
1639 | when you rarely read from a file instead of from a socket, and want to |
|
|
1640 | reuse the same code path. |
|
|
1641 | |
1670 | =head3 The special problem of fork |
1642 | =head3 The special problem of fork |
1671 | |
1643 | |
1672 | Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1644 | 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 |
1645 | useless behaviour. Libev fully supports fork, but needs to be told about |
1674 | it in the child. |
1646 | it in the child if you want to continue to use it in the child. |
1675 | |
1647 | |
1676 | To support fork in your programs, you either have to call |
1648 | 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, |
1649 | ()> 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 |
1650 | C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1679 | C<EVBACKEND_POLL>. |
|
|
1680 | |
1651 | |
1681 | =head3 The special problem of SIGPIPE |
1652 | =head3 The special problem of SIGPIPE |
1682 | |
1653 | |
1683 | While not really specific to libev, it is easy to forget about C<SIGPIPE>: |
1654 | 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 |
1655 | when writing to a pipe whose other end has been closed, your program gets |
… | |
… | |
3423 | |
3394 | |
3424 | This section explains some common idioms that are not immediately |
3395 | This section explains some common idioms that are not immediately |
3425 | obvious. Note that examples are sprinkled over the whole manual, and this |
3396 | obvious. Note that examples are sprinkled over the whole manual, and this |
3426 | section only contains stuff that wouldn't fit anywhere else. |
3397 | section only contains stuff that wouldn't fit anywhere else. |
3427 | |
3398 | |
3428 | =over 4 |
3399 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
3429 | |
3400 | |
3430 | =item Model/nested event loop invocations and exit conditions. |
3401 | Each watcher has, by default, a C<void *data> member that you can read |
|
|
3402 | or modify at any time: libev will completely ignore it. This can be used |
|
|
3403 | to associate arbitrary data with your watcher. If you need more data and |
|
|
3404 | don't want to allocate memory separately and store a pointer to it in that |
|
|
3405 | data member, you can also "subclass" the watcher type and provide your own |
|
|
3406 | data: |
|
|
3407 | |
|
|
3408 | struct my_io |
|
|
3409 | { |
|
|
3410 | ev_io io; |
|
|
3411 | int otherfd; |
|
|
3412 | void *somedata; |
|
|
3413 | struct whatever *mostinteresting; |
|
|
3414 | }; |
|
|
3415 | |
|
|
3416 | ... |
|
|
3417 | struct my_io w; |
|
|
3418 | ev_io_init (&w.io, my_cb, fd, EV_READ); |
|
|
3419 | |
|
|
3420 | And since your callback will be called with a pointer to the watcher, you |
|
|
3421 | can cast it back to your own type: |
|
|
3422 | |
|
|
3423 | static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) |
|
|
3424 | { |
|
|
3425 | struct my_io *w = (struct my_io *)w_; |
|
|
3426 | ... |
|
|
3427 | } |
|
|
3428 | |
|
|
3429 | More interesting and less C-conformant ways of casting your callback |
|
|
3430 | function type instead have been omitted. |
|
|
3431 | |
|
|
3432 | =head2 BUILDING YOUR OWN COMPOSITE WATCHERS |
|
|
3433 | |
|
|
3434 | Another common scenario is to use some data structure with multiple |
|
|
3435 | embedded watchers, in effect creating your own watcher that combines |
|
|
3436 | multiple libev event sources into one "super-watcher": |
|
|
3437 | |
|
|
3438 | struct my_biggy |
|
|
3439 | { |
|
|
3440 | int some_data; |
|
|
3441 | ev_timer t1; |
|
|
3442 | ev_timer t2; |
|
|
3443 | } |
|
|
3444 | |
|
|
3445 | In this case getting the pointer to C<my_biggy> is a bit more |
|
|
3446 | complicated: Either you store the address of your C<my_biggy> struct in |
|
|
3447 | the C<data> member of the watcher (for woozies or C++ coders), or you need |
|
|
3448 | to use some pointer arithmetic using C<offsetof> inside your watchers (for |
|
|
3449 | real programmers): |
|
|
3450 | |
|
|
3451 | #include <stddef.h> |
|
|
3452 | |
|
|
3453 | static void |
|
|
3454 | t1_cb (EV_P_ ev_timer *w, int revents) |
|
|
3455 | { |
|
|
3456 | struct my_biggy big = (struct my_biggy *) |
|
|
3457 | (((char *)w) - offsetof (struct my_biggy, t1)); |
|
|
3458 | } |
|
|
3459 | |
|
|
3460 | static void |
|
|
3461 | t2_cb (EV_P_ ev_timer *w, int revents) |
|
|
3462 | { |
|
|
3463 | struct my_biggy big = (struct my_biggy *) |
|
|
3464 | (((char *)w) - offsetof (struct my_biggy, t2)); |
|
|
3465 | } |
|
|
3466 | |
|
|
3467 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3431 | |
3468 | |
3432 | Often (especially in GUI toolkits) there are places where you have |
3469 | Often (especially in GUI toolkits) there are places where you have |
3433 | I<modal> interaction, which is most easily implemented by recursively |
3470 | I<modal> interaction, which is most easily implemented by recursively |
3434 | invoking C<ev_run>. |
3471 | invoking C<ev_run>. |
3435 | |
3472 | |
… | |
… | |
3464 | exit_main_loop = 1; |
3501 | exit_main_loop = 1; |
3465 | |
3502 | |
3466 | // exit both |
3503 | // exit both |
3467 | exit_main_loop = exit_nested_loop = 1; |
3504 | exit_main_loop = exit_nested_loop = 1; |
3468 | |
3505 | |
3469 | =back |
3506 | =head2 THREAD LOCKING EXAMPLE |
|
|
3507 | |
|
|
3508 | Here is a fictitious example of how to run an event loop in a different |
|
|
3509 | thread than where callbacks are being invoked and watchers are |
|
|
3510 | created/added/removed. |
|
|
3511 | |
|
|
3512 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
3513 | which uses exactly this technique (which is suited for many high-level |
|
|
3514 | languages). |
|
|
3515 | |
|
|
3516 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
3517 | variable to wait for callback invocations, an async watcher to notify the |
|
|
3518 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
3519 | |
|
|
3520 | First, you need to associate some data with the event loop: |
|
|
3521 | |
|
|
3522 | typedef struct { |
|
|
3523 | mutex_t lock; /* global loop lock */ |
|
|
3524 | ev_async async_w; |
|
|
3525 | thread_t tid; |
|
|
3526 | cond_t invoke_cv; |
|
|
3527 | } userdata; |
|
|
3528 | |
|
|
3529 | void prepare_loop (EV_P) |
|
|
3530 | { |
|
|
3531 | // for simplicity, we use a static userdata struct. |
|
|
3532 | static userdata u; |
|
|
3533 | |
|
|
3534 | ev_async_init (&u->async_w, async_cb); |
|
|
3535 | ev_async_start (EV_A_ &u->async_w); |
|
|
3536 | |
|
|
3537 | pthread_mutex_init (&u->lock, 0); |
|
|
3538 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
3539 | |
|
|
3540 | // now associate this with the loop |
|
|
3541 | ev_set_userdata (EV_A_ u); |
|
|
3542 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
3543 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
3544 | |
|
|
3545 | // then create the thread running ev_loop |
|
|
3546 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
3547 | } |
|
|
3548 | |
|
|
3549 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
3550 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
3551 | that might have been added: |
|
|
3552 | |
|
|
3553 | static void |
|
|
3554 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
3555 | { |
|
|
3556 | // just used for the side effects |
|
|
3557 | } |
|
|
3558 | |
|
|
3559 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
3560 | protecting the loop data, respectively. |
|
|
3561 | |
|
|
3562 | static void |
|
|
3563 | l_release (EV_P) |
|
|
3564 | { |
|
|
3565 | userdata *u = ev_userdata (EV_A); |
|
|
3566 | pthread_mutex_unlock (&u->lock); |
|
|
3567 | } |
|
|
3568 | |
|
|
3569 | static void |
|
|
3570 | l_acquire (EV_P) |
|
|
3571 | { |
|
|
3572 | userdata *u = ev_userdata (EV_A); |
|
|
3573 | pthread_mutex_lock (&u->lock); |
|
|
3574 | } |
|
|
3575 | |
|
|
3576 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
3577 | into C<ev_run>: |
|
|
3578 | |
|
|
3579 | void * |
|
|
3580 | l_run (void *thr_arg) |
|
|
3581 | { |
|
|
3582 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
3583 | |
|
|
3584 | l_acquire (EV_A); |
|
|
3585 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
3586 | ev_run (EV_A_ 0); |
|
|
3587 | l_release (EV_A); |
|
|
3588 | |
|
|
3589 | return 0; |
|
|
3590 | } |
|
|
3591 | |
|
|
3592 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
3593 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
3594 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
3595 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
3596 | and b) skipping inter-thread-communication when there are no pending |
|
|
3597 | watchers is very beneficial): |
|
|
3598 | |
|
|
3599 | static void |
|
|
3600 | l_invoke (EV_P) |
|
|
3601 | { |
|
|
3602 | userdata *u = ev_userdata (EV_A); |
|
|
3603 | |
|
|
3604 | while (ev_pending_count (EV_A)) |
|
|
3605 | { |
|
|
3606 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
3607 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
3608 | } |
|
|
3609 | } |
|
|
3610 | |
|
|
3611 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
3612 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
3613 | thread to continue: |
|
|
3614 | |
|
|
3615 | static void |
|
|
3616 | real_invoke_pending (EV_P) |
|
|
3617 | { |
|
|
3618 | userdata *u = ev_userdata (EV_A); |
|
|
3619 | |
|
|
3620 | pthread_mutex_lock (&u->lock); |
|
|
3621 | ev_invoke_pending (EV_A); |
|
|
3622 | pthread_cond_signal (&u->invoke_cv); |
|
|
3623 | pthread_mutex_unlock (&u->lock); |
|
|
3624 | } |
|
|
3625 | |
|
|
3626 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
3627 | event loop, you will now have to lock: |
|
|
3628 | |
|
|
3629 | ev_timer timeout_watcher; |
|
|
3630 | userdata *u = ev_userdata (EV_A); |
|
|
3631 | |
|
|
3632 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
3633 | |
|
|
3634 | pthread_mutex_lock (&u->lock); |
|
|
3635 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
3636 | ev_async_send (EV_A_ &u->async_w); |
|
|
3637 | pthread_mutex_unlock (&u->lock); |
|
|
3638 | |
|
|
3639 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
3640 | an event loop currently blocking in the kernel will have no knowledge |
|
|
3641 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
3642 | watchers in the next event loop iteration. |
|
|
3643 | |
|
|
3644 | =head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS |
|
|
3645 | |
|
|
3646 | While the overhead of a callback that e.g. schedules a thread is small, it |
|
|
3647 | is still an overhead. If you embed libev, and your main usage is with some |
|
|
3648 | kind of threads or coroutines, you might want to customise libev so that |
|
|
3649 | doesn't need callbacks anymore. |
|
|
3650 | |
|
|
3651 | Imagine you have coroutines that you can switch to using a function |
|
|
3652 | C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro> |
|
|
3653 | and that due to some magic, the currently active coroutine is stored in a |
|
|
3654 | global called C<current_coro>. Then you can build your own "wait for libev |
|
|
3655 | event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note |
|
|
3656 | the differing C<;> conventions): |
|
|
3657 | |
|
|
3658 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3659 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb) |
|
|
3660 | |
|
|
3661 | That means instead of having a C callback function, you store the |
|
|
3662 | coroutine to switch to in each watcher, and instead of having libev call |
|
|
3663 | your callback, you instead have it switch to that coroutine. |
|
|
3664 | |
|
|
3665 | A coroutine might now wait for an event with a function called |
|
|
3666 | C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't |
|
|
3667 | matter when, or whether the watcher is active or not when this function is |
|
|
3668 | called): |
|
|
3669 | |
|
|
3670 | void |
|
|
3671 | wait_for_event (ev_watcher *w) |
|
|
3672 | { |
|
|
3673 | ev_cb_set (w) = current_coro; |
|
|
3674 | switch_to (libev_coro); |
|
|
3675 | } |
|
|
3676 | |
|
|
3677 | That basically suspends the coroutine inside C<wait_for_event> and |
|
|
3678 | continues the libev coroutine, which, when appropriate, switches back to |
|
|
3679 | this or any other coroutine. I am sure if you sue this your own :) |
|
|
3680 | |
|
|
3681 | You can do similar tricks if you have, say, threads with an event queue - |
|
|
3682 | instead of storing a coroutine, you store the queue object and instead of |
|
|
3683 | switching to a coroutine, you push the watcher onto the queue and notify |
|
|
3684 | any waiters. |
|
|
3685 | |
|
|
3686 | To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two |
|
|
3687 | files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: |
|
|
3688 | |
|
|
3689 | // my_ev.h |
|
|
3690 | #define EV_CB_DECLARE(type) struct my_coro *cb; |
|
|
3691 | #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); |
|
|
3692 | #include "../libev/ev.h" |
|
|
3693 | |
|
|
3694 | // my_ev.c |
|
|
3695 | #define EV_H "my_ev.h" |
|
|
3696 | #include "../libev/ev.c" |
|
|
3697 | |
|
|
3698 | And then use F<my_ev.h> when you would normally use F<ev.h>, and compile |
|
|
3699 | F<my_ev.c> into your project. When properly specifying include paths, you |
|
|
3700 | can even use F<ev.h> as header file name directly. |
3470 | |
3701 | |
3471 | |
3702 | |
3472 | =head1 LIBEVENT EMULATION |
3703 | =head1 LIBEVENT EMULATION |
3473 | |
3704 | |
3474 | Libev offers a compatibility emulation layer for libevent. It cannot |
3705 | Libev offers a compatibility emulation layer for libevent. It cannot |
… | |
… | |
4404 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4635 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4405 | |
4636 | |
4406 | #include "ev_cpp.h" |
4637 | #include "ev_cpp.h" |
4407 | #include "ev.c" |
4638 | #include "ev.c" |
4408 | |
4639 | |
4409 | =head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES |
4640 | =head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT |
4410 | |
4641 | |
4411 | =head2 THREADS AND COROUTINES |
4642 | =head2 THREADS AND COROUTINES |
4412 | |
4643 | |
4413 | =head3 THREADS |
4644 | =head3 THREADS |
4414 | |
4645 | |
… | |
… | |
4465 | default loop and triggering an C<ev_async> watcher from the default loop |
4696 | default loop and triggering an C<ev_async> watcher from the default loop |
4466 | watcher callback into the event loop interested in the signal. |
4697 | watcher callback into the event loop interested in the signal. |
4467 | |
4698 | |
4468 | =back |
4699 | =back |
4469 | |
4700 | |
4470 | =head4 THREAD LOCKING EXAMPLE |
4701 | 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 | |
4702 | |
4608 | =head3 COROUTINES |
4703 | =head3 COROUTINES |
4609 | |
4704 | |
4610 | Libev is very accommodating to coroutines ("cooperative threads"): |
4705 | Libev is very accommodating to coroutines ("cooperative threads"): |
4611 | libev fully supports nesting calls to its functions from different |
4706 | libev fully supports nesting calls to its functions from different |