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4 | <head> |
4 | <head> |
5 | <title>libev</title> |
5 | <title>libev</title> |
6 | <meta name="description" content="Pod documentation for libev" /> |
6 | <meta name="description" content="Pod documentation for libev" /> |
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14 | <!-- INDEX START --> |
14 | <!-- INDEX START --> |
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529 | one iteration of the loop. This is useful if you are waiting for some |
529 | one iteration of the loop. This is useful if you are waiting for some |
530 | external event in conjunction with something not expressible using other |
530 | external event in conjunction with something not expressible using other |
531 | libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is |
531 | libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is |
532 | usually a better approach for this kind of thing.</p> |
532 | usually a better approach for this kind of thing.</p> |
533 | <p>Here are the gory details of what <code>ev_loop</code> does:</p> |
533 | <p>Here are the gory details of what <code>ev_loop</code> does:</p> |
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534 | <pre> - Before the first iteration, call any pending watchers. |
534 | <pre> * If there are no active watchers (reference count is zero), return. |
535 | * If there are no active watchers (reference count is zero), return. |
535 | - Queue prepare watchers and then call all outstanding watchers. |
536 | - Queue all prepare watchers and then call all outstanding watchers. |
536 | - If we have been forked, recreate the kernel state. |
537 | - If we have been forked, recreate the kernel state. |
537 | - Update the kernel state with all outstanding changes. |
538 | - Update the kernel state with all outstanding changes. |
538 | - Update the "event loop time". |
539 | - Update the "event loop time". |
539 | - Calculate for how long to block. |
540 | - Calculate for how long to block. |
540 | - Block the process, waiting for any events. |
541 | - Block the process, waiting for any events. |
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1483 | are ready to run (it's actually more complicated: it only runs coroutines |
1484 | are ready to run (it's actually more complicated: it only runs coroutines |
1484 | with priority higher than or equal to the event loop and one coroutine |
1485 | with priority higher than or equal to the event loop and one coroutine |
1485 | of lower priority, but only once, using idle watchers to keep the event |
1486 | of lower priority, but only once, using idle watchers to keep the event |
1486 | loop from blocking if lower-priority coroutines are active, thus mapping |
1487 | loop from blocking if lower-priority coroutines are active, thus mapping |
1487 | low-priority coroutines to idle/background tasks).</p> |
1488 | low-priority coroutines to idle/background tasks).</p> |
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1489 | <p>It is recommended to give <code>ev_check</code> watchers highest (<code>EV_MAXPRI</code>) |
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1490 | priority, to ensure that they are being run before any other watchers |
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1491 | after the poll. Also, <code>ev_check</code> watchers (and <code>ev_prepare</code> watchers, |
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1492 | too) should not activate ("feed") events into libev. While libev fully |
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1493 | supports this, they will be called before other <code>ev_check</code> watchers did |
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1494 | their job. As <code>ev_check</code> watchers are often used to embed other event |
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1495 | loops those other event loops might be in an unusable state until their |
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1496 | <code>ev_check</code> watcher ran (always remind yourself to coexist peacefully with |
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1497 | others).</p> |
1488 | <dl> |
1498 | <dl> |
1489 | <dt>ev_prepare_init (ev_prepare *, callback)</dt> |
1499 | <dt>ev_prepare_init (ev_prepare *, callback)</dt> |
1490 | <dt>ev_check_init (ev_check *, callback)</dt> |
1500 | <dt>ev_check_init (ev_check *, callback)</dt> |
1491 | <dd> |
1501 | <dd> |
1492 | <p>Initialises and configures the prepare or check watcher - they have no |
1502 | <p>Initialises and configures the prepare or check watcher - they have no |
1493 | parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> |
1503 | parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> |
1494 | macros, but using them is utterly, utterly and completely pointless.</p> |
1504 | macros, but using them is utterly, utterly and completely pointless.</p> |
1495 | </dd> |
1505 | </dd> |
1496 | </dl> |
1506 | </dl> |
1497 | <p>Example: To include a library such as adns, you would add IO watchers |
1507 | <p>There are a number of principal ways to embed other event loops or modules |
1498 | and a timeout watcher in a prepare handler, as required by libadns, and |
1508 | into libev. Here are some ideas on how to include libadns into libev |
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1509 | (there is a Perl module named <code>EV::ADNS</code> that does this, which you could |
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1510 | use for an actually working example. Another Perl module named <code>EV::Glib</code> |
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1511 | embeds a Glib main context into libev, and finally, <code>Glib::EV</code> embeds EV |
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1512 | into the Glib event loop).</p> |
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1513 | <p>Method 1: Add IO watchers and a timeout watcher in a prepare handler, |
1499 | in a check watcher, destroy them and call into libadns. What follows is |
1514 | and in a check watcher, destroy them and call into libadns. What follows |
1500 | pseudo-code only of course:</p> |
1515 | is pseudo-code only of course. This requires you to either use a low |
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1516 | priority for the check watcher or use <code>ev_clear_pending</code> explicitly, as |
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1517 | the callbacks for the IO/timeout watchers might not have been called yet.</p> |
1501 | <pre> static ev_io iow [nfd]; |
1518 | <pre> static ev_io iow [nfd]; |
1502 | static ev_timer tw; |
1519 | static ev_timer tw; |
1503 | |
1520 | |
1504 | static void |
1521 | static void |
1505 | io_cb (ev_loop *loop, ev_io *w, int revents) |
1522 | io_cb (ev_loop *loop, ev_io *w, int revents) |
1506 | { |
1523 | { |
1507 | // set the relevant poll flags |
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1508 | // could also call adns_processreadable etc. here |
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1509 | struct pollfd *fd = (struct pollfd *)w->data; |
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1510 | if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; |
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1511 | if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; |
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1512 | } |
1524 | } |
1513 | |
1525 | |
1514 | // create io watchers for each fd and a timer before blocking |
1526 | // create io watchers for each fd and a timer before blocking |
1515 | static void |
1527 | static void |
1516 | adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) |
1528 | adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) |
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1522 | |
1534 | |
1523 | /* the callback is illegal, but won't be called as we stop during check */ |
1535 | /* the callback is illegal, but won't be called as we stop during check */ |
1524 | ev_timer_init (&tw, 0, timeout * 1e-3); |
1536 | ev_timer_init (&tw, 0, timeout * 1e-3); |
1525 | ev_timer_start (loop, &tw); |
1537 | ev_timer_start (loop, &tw); |
1526 | |
1538 | |
1527 | // create on ev_io per pollfd |
1539 | // create one ev_io per pollfd |
1528 | for (int i = 0; i < nfd; ++i) |
1540 | for (int i = 0; i < nfd; ++i) |
1529 | { |
1541 | { |
1530 | ev_io_init (iow + i, io_cb, fds [i].fd, |
1542 | ev_io_init (iow + i, io_cb, fds [i].fd, |
1531 | ((fds [i].events & POLLIN ? EV_READ : 0) |
1543 | ((fds [i].events & POLLIN ? EV_READ : 0) |
1532 | | (fds [i].events & POLLOUT ? EV_WRITE : 0))); |
1544 | | (fds [i].events & POLLOUT ? EV_WRITE : 0))); |
1533 | |
1545 | |
1534 | fds [i].revents = 0; |
1546 | fds [i].revents = 0; |
1535 | iow [i].data = fds + i; |
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1536 | ev_io_start (loop, iow + i); |
1547 | ev_io_start (loop, iow + i); |
1537 | } |
1548 | } |
1538 | } |
1549 | } |
1539 | |
1550 | |
1540 | // stop all watchers after blocking |
1551 | // stop all watchers after blocking |
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1542 | adns_check_cb (ev_loop *loop, ev_check *w, int revents) |
1553 | adns_check_cb (ev_loop *loop, ev_check *w, int revents) |
1543 | { |
1554 | { |
1544 | ev_timer_stop (loop, &tw); |
1555 | ev_timer_stop (loop, &tw); |
1545 | |
1556 | |
1546 | for (int i = 0; i < nfd; ++i) |
1557 | for (int i = 0; i < nfd; ++i) |
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1558 | { |
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1559 | // set the relevant poll flags |
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1560 | // could also call adns_processreadable etc. here |
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1561 | struct pollfd *fd = fds + i; |
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1562 | int revents = ev_clear_pending (iow + i); |
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1563 | if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; |
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1564 | if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; |
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1565 | |
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1566 | // now stop the watcher |
1547 | ev_io_stop (loop, iow + i); |
1567 | ev_io_stop (loop, iow + i); |
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1568 | } |
1548 | |
1569 | |
1549 | adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); |
1570 | adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); |
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1571 | } |
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1572 | |
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1573 | </pre> |
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1574 | <p>Method 2: This would be just like method 1, but you run <code>adns_afterpoll</code> |
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1575 | in the prepare watcher and would dispose of the check watcher.</p> |
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1576 | <p>Method 3: If the module to be embedded supports explicit event |
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1577 | notification (adns does), you can also make use of the actual watcher |
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1578 | callbacks, and only destroy/create the watchers in the prepare watcher.</p> |
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1579 | <pre> static void |
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1580 | timer_cb (EV_P_ ev_timer *w, int revents) |
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1581 | { |
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1582 | adns_state ads = (adns_state)w->data; |
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1583 | update_now (EV_A); |
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1584 | |
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1585 | adns_processtimeouts (ads, &tv_now); |
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1586 | } |
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1587 | |
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1588 | static void |
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1589 | io_cb (EV_P_ ev_io *w, int revents) |
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1590 | { |
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1591 | adns_state ads = (adns_state)w->data; |
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1592 | update_now (EV_A); |
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1593 | |
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1594 | if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); |
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1595 | if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); |
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1596 | } |
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1597 | |
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1598 | // do not ever call adns_afterpoll |
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1599 | |
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1600 | </pre> |
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1601 | <p>Method 4: Do not use a prepare or check watcher because the module you |
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1602 | want to embed is too inflexible to support it. Instead, youc na override |
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1603 | their poll function. The drawback with this solution is that the main |
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1604 | loop is now no longer controllable by EV. The <code>Glib::EV</code> module does |
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1605 | this.</p> |
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1606 | <pre> static gint |
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1607 | event_poll_func (GPollFD *fds, guint nfds, gint timeout) |
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1608 | { |
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1609 | int got_events = 0; |
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1610 | |
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1611 | for (n = 0; n < nfds; ++n) |
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1612 | // create/start io watcher that sets the relevant bits in fds[n] and increment got_events |
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1613 | |
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1614 | if (timeout >= 0) |
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1615 | // create/start timer |
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1616 | |
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1617 | // poll |
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1618 | ev_loop (EV_A_ 0); |
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1619 | |
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1620 | // stop timer again |
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1621 | if (timeout >= 0) |
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1622 | ev_timer_stop (EV_A_ &to); |
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1623 | |
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1624 | // stop io watchers again - their callbacks should have set |
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1625 | for (n = 0; n < nfds; ++n) |
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1626 | ev_io_stop (EV_A_ iow [n]); |
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1627 | |
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1628 | return got_events; |
1550 | } |
1629 | } |
1551 | |
1630 | |
1552 | |
1631 | |
1553 | |
1632 | |
1554 | |
1633 | |