… | |
… | |
1596 | =head2 C<ev_periodic> - to cron or not to cron? |
1596 | =head2 C<ev_periodic> - to cron or not to cron? |
1597 | |
1597 | |
1598 | Periodic watchers are also timers of a kind, but they are very versatile |
1598 | Periodic watchers are also timers of a kind, but they are very versatile |
1599 | (and unfortunately a bit complex). |
1599 | (and unfortunately a bit complex). |
1600 | |
1600 | |
1601 | Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
1601 | Unlike C<ev_timer>, periodic watchers are not based on real time (or |
1602 | but on wall clock time (absolute time). You can tell a periodic watcher |
1602 | relative time, the physical time that passes) but on wall clock time |
1603 | to trigger after some specific point in time. For example, if you tell a |
1603 | (absolute time, the thing you can read on your calender or clock). The |
1604 | periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now () |
1604 | difference is that wall clock time can run faster or slower than real |
1605 | + 10.>, that is, an absolute time not a delay) and then reset your system |
1605 | time, and time jumps are not uncommon (e.g. when you adjust your |
1606 | clock to January of the previous year, then it will take more than year |
1606 | wrist-watch). |
1607 | to trigger the event (unlike an C<ev_timer>, which would still trigger |
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1608 | roughly 10 seconds later as it uses a relative timeout). |
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1609 | |
1607 | |
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1608 | You can tell a periodic watcher to trigger after some specific point |
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1609 | in time: for example, if you tell a periodic watcher to trigger "in 10 |
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1610 | seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time |
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1611 | not a delay) and then reset your system clock to January of the previous |
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1612 | year, then it will take a year or more to trigger the event (unlike an |
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1613 | C<ev_timer>, which would still trigger roughly 10 seconds after starting |
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1614 | it, as it uses a relative timeout). |
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1615 | |
1610 | C<ev_periodic>s can also be used to implement vastly more complex timers, |
1616 | C<ev_periodic> watchers can also be used to implement vastly more complex |
1611 | such as triggering an event on each "midnight, local time", or other |
1617 | timers, such as triggering an event on each "midnight, local time", or |
1612 | complicated rules. |
1618 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
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1619 | those cannot react to time jumps. |
1613 | |
1620 | |
1614 | As with timers, the callback is guaranteed to be invoked only when the |
1621 | As with timers, the callback is guaranteed to be invoked only when the |
1615 | time (C<at>) has passed, but if multiple periodic timers become ready |
1622 | point in time where it is supposed to trigger has passed, but if multiple |
1616 | during the same loop iteration, then order of execution is undefined. |
1623 | periodic timers become ready during the same loop iteration, then order of |
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1624 | execution is undefined. |
1617 | |
1625 | |
1618 | =head3 Watcher-Specific Functions and Data Members |
1626 | =head3 Watcher-Specific Functions and Data Members |
1619 | |
1627 | |
1620 | =over 4 |
1628 | =over 4 |
1621 | |
1629 | |
1622 | =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
1630 | =item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb) |
1623 | |
1631 | |
1624 | =item ev_periodic_set (ev_periodic *, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
1632 | =item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb) |
1625 | |
1633 | |
1626 | Lots of arguments, lets sort it out... There are basically three modes of |
1634 | Lots of arguments, let's sort it out... There are basically three modes of |
1627 | operation, and we will explain them from simplest to most complex: |
1635 | operation, and we will explain them from simplest to most complex: |
1628 | |
1636 | |
1629 | =over 4 |
1637 | =over 4 |
1630 | |
1638 | |
1631 | =item * absolute timer (at = time, interval = reschedule_cb = 0) |
1639 | =item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0) |
1632 | |
1640 | |
1633 | In this configuration the watcher triggers an event after the wall clock |
1641 | In this configuration the watcher triggers an event after the wall clock |
1634 | time C<at> has passed. It will not repeat and will not adjust when a time |
1642 | time C<offset> has passed. It will not repeat and will not adjust when a |
1635 | jump occurs, that is, if it is to be run at January 1st 2011 then it will |
1643 | time jump occurs, that is, if it is to be run at January 1st 2011 then it |
1636 | only run when the system clock reaches or surpasses this time. |
1644 | will be stopped and invoked when the system clock reaches or surpasses |
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1645 | this point in time. |
1637 | |
1646 | |
1638 | =item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) |
1647 | =item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0) |
1639 | |
1648 | |
1640 | In this mode the watcher will always be scheduled to time out at the next |
1649 | In this mode the watcher will always be scheduled to time out at the next |
1641 | C<at + N * interval> time (for some integer N, which can also be negative) |
1650 | C<offset + N * interval> time (for some integer N, which can also be |
1642 | and then repeat, regardless of any time jumps. |
1651 | negative) and then repeat, regardless of any time jumps. The C<offset> |
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1652 | argument is merely an offset into the C<interval> periods. |
1643 | |
1653 | |
1644 | This can be used to create timers that do not drift with respect to the |
1654 | This can be used to create timers that do not drift with respect to the |
1645 | system clock, for example, here is a C<ev_periodic> that triggers each |
1655 | system clock, for example, here is an C<ev_periodic> that triggers each |
1646 | hour, on the hour: |
1656 | hour, on the hour (with respect to UTC): |
1647 | |
1657 | |
1648 | ev_periodic_set (&periodic, 0., 3600., 0); |
1658 | ev_periodic_set (&periodic, 0., 3600., 0); |
1649 | |
1659 | |
1650 | This doesn't mean there will always be 3600 seconds in between triggers, |
1660 | This doesn't mean there will always be 3600 seconds in between triggers, |
1651 | but only that the callback will be called when the system time shows a |
1661 | but only that the callback will be called when the system time shows a |
1652 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1662 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1653 | by 3600. |
1663 | by 3600. |
1654 | |
1664 | |
1655 | Another way to think about it (for the mathematically inclined) is that |
1665 | Another way to think about it (for the mathematically inclined) is that |
1656 | C<ev_periodic> will try to run the callback in this mode at the next possible |
1666 | C<ev_periodic> will try to run the callback in this mode at the next possible |
1657 | time where C<time = at (mod interval)>, regardless of any time jumps. |
1667 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
1658 | |
1668 | |
1659 | For numerical stability it is preferable that the C<at> value is near |
1669 | For numerical stability it is preferable that the C<offset> value is near |
1660 | C<ev_now ()> (the current time), but there is no range requirement for |
1670 | C<ev_now ()> (the current time), but there is no range requirement for |
1661 | this value, and in fact is often specified as zero. |
1671 | this value, and in fact is often specified as zero. |
1662 | |
1672 | |
1663 | Note also that there is an upper limit to how often a timer can fire (CPU |
1673 | Note also that there is an upper limit to how often a timer can fire (CPU |
1664 | speed for example), so if C<interval> is very small then timing stability |
1674 | speed for example), so if C<interval> is very small then timing stability |
1665 | will of course deteriorate. Libev itself tries to be exact to be about one |
1675 | will of course deteriorate. Libev itself tries to be exact to be about one |
1666 | millisecond (if the OS supports it and the machine is fast enough). |
1676 | millisecond (if the OS supports it and the machine is fast enough). |
1667 | |
1677 | |
1668 | =item * manual reschedule mode (at and interval ignored, reschedule_cb = callback) |
1678 | =item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback) |
1669 | |
1679 | |
1670 | In this mode the values for C<interval> and C<at> are both being |
1680 | In this mode the values for C<interval> and C<offset> are both being |
1671 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1681 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1672 | reschedule callback will be called with the watcher as first, and the |
1682 | reschedule callback will be called with the watcher as first, and the |
1673 | current time as second argument. |
1683 | current time as second argument. |
1674 | |
1684 | |
1675 | NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
1685 | NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever, |
1676 | ever, or make ANY other event loop modifications whatsoever>. |
1686 | or make ANY other event loop modifications whatsoever, unless explicitly |
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1687 | allowed by documentation here>. |
1677 | |
1688 | |
1678 | If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop |
1689 | If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop |
1679 | it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the |
1690 | it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the |
1680 | only event loop modification you are allowed to do). |
1691 | only event loop modification you are allowed to do). |
1681 | |
1692 | |
… | |
… | |
1711 | a different time than the last time it was called (e.g. in a crond like |
1722 | a different time than the last time it was called (e.g. in a crond like |
1712 | program when the crontabs have changed). |
1723 | program when the crontabs have changed). |
1713 | |
1724 | |
1714 | =item ev_tstamp ev_periodic_at (ev_periodic *) |
1725 | =item ev_tstamp ev_periodic_at (ev_periodic *) |
1715 | |
1726 | |
1716 | When active, returns the absolute time that the watcher is supposed to |
1727 | When active, returns the absolute time that the watcher is supposed |
1717 | trigger next. |
1728 | to trigger next. This is not the same as the C<offset> argument to |
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1729 | C<ev_periodic_set>, but indeed works even in interval and manual |
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1730 | rescheduling modes. |
1718 | |
1731 | |
1719 | =item ev_tstamp offset [read-write] |
1732 | =item ev_tstamp offset [read-write] |
1720 | |
1733 | |
1721 | When repeating, this contains the offset value, otherwise this is the |
1734 | When repeating, this contains the offset value, otherwise this is the |
1722 | absolute point in time (the C<at> value passed to C<ev_periodic_set>). |
1735 | absolute point in time (the C<offset> value passed to C<ev_periodic_set>, |
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1736 | although libev might modify this value for better numerical stability). |
1723 | |
1737 | |
1724 | Can be modified any time, but changes only take effect when the periodic |
1738 | Can be modified any time, but changes only take effect when the periodic |
1725 | timer fires or C<ev_periodic_again> is being called. |
1739 | timer fires or C<ev_periodic_again> is being called. |
1726 | |
1740 | |
1727 | =item ev_tstamp interval [read-write] |
1741 | =item ev_tstamp interval [read-write] |
… | |
… | |
2682 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
2696 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
2683 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
2697 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
2684 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
2698 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
2685 | section below on what exactly this means). |
2699 | section below on what exactly this means). |
2686 | |
2700 | |
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2701 | Note that, as with other watchers in libev, multiple events might get |
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2702 | compressed into a single callback invocation (another way to look at this |
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2703 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
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2704 | reset when the event loop detects that). |
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2705 | |
2687 | This call incurs the overhead of a system call only once per loop iteration, |
2706 | This call incurs the overhead of a system call only once per event loop |
2688 | so while the overhead might be noticeable, it doesn't apply to repeated |
2707 | iteration, so while the overhead might be noticeable, it doesn't apply to |
2689 | calls to C<ev_async_send>. |
2708 | repeated calls to C<ev_async_send> for the same event loop. |
2690 | |
2709 | |
2691 | =item bool = ev_async_pending (ev_async *) |
2710 | =item bool = ev_async_pending (ev_async *) |
2692 | |
2711 | |
2693 | Returns a non-zero value when C<ev_async_send> has been called on the |
2712 | Returns a non-zero value when C<ev_async_send> has been called on the |
2694 | watcher but the event has not yet been processed (or even noted) by the |
2713 | watcher but the event has not yet been processed (or even noted) by the |
… | |
… | |
2697 | C<ev_async_send> sets a flag in the watcher and wakes up the loop. When |
2716 | C<ev_async_send> sets a flag in the watcher and wakes up the loop. When |
2698 | the loop iterates next and checks for the watcher to have become active, |
2717 | the loop iterates next and checks for the watcher to have become active, |
2699 | it will reset the flag again. C<ev_async_pending> can be used to very |
2718 | it will reset the flag again. C<ev_async_pending> can be used to very |
2700 | quickly check whether invoking the loop might be a good idea. |
2719 | quickly check whether invoking the loop might be a good idea. |
2701 | |
2720 | |
2702 | Not that this does I<not> check whether the watcher itself is pending, only |
2721 | Not that this does I<not> check whether the watcher itself is pending, |
2703 | whether it has been requested to make this watcher pending. |
2722 | only whether it has been requested to make this watcher pending: there |
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2723 | is a time window between the event loop checking and resetting the async |
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2724 | notification, and the callback being invoked. |
2704 | |
2725 | |
2705 | =back |
2726 | =back |
2706 | |
2727 | |
2707 | |
2728 | |
2708 | =head1 OTHER FUNCTIONS |
2729 | =head1 OTHER FUNCTIONS |