… | |
… | |
620 | happily wraps around with enough iterations. |
620 | happily wraps around with enough iterations. |
621 | |
621 | |
622 | This value can sometimes be useful as a generation counter of sorts (it |
622 | This value can sometimes be useful as a generation counter of sorts (it |
623 | "ticks" the number of loop iterations), as it roughly corresponds with |
623 | "ticks" the number of loop iterations), as it roughly corresponds with |
624 | C<ev_prepare> and C<ev_check> calls. |
624 | C<ev_prepare> and C<ev_check> calls. |
|
|
625 | |
|
|
626 | =item unsigned int ev_loop_depth (loop) |
|
|
627 | |
|
|
628 | Returns the number of times C<ev_loop> was entered minus the number of |
|
|
629 | times C<ev_loop> was exited, in other words, the recursion depth. |
|
|
630 | |
|
|
631 | Outside C<ev_loop>, this number is zero. In a callback, this number is |
|
|
632 | C<1>, unless C<ev_loop> was invoked recursively (or from another thread), |
|
|
633 | in which case it is higher. |
|
|
634 | |
|
|
635 | Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread |
|
|
636 | etc.), doesn't count as exit. |
625 | |
637 | |
626 | =item unsigned int ev_backend (loop) |
638 | =item unsigned int ev_backend (loop) |
627 | |
639 | |
628 | Returns one of the C<EVBACKEND_*> flags indicating the event backend in |
640 | Returns one of the C<EVBACKEND_*> flags indicating the event backend in |
629 | use. |
641 | use. |
… | |
… | |
811 | |
823 | |
812 | By setting a higher I<io collect interval> you allow libev to spend more |
824 | By setting a higher I<io collect interval> you allow libev to spend more |
813 | time collecting I/O events, so you can handle more events per iteration, |
825 | time collecting I/O events, so you can handle more events per iteration, |
814 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
826 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
815 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
827 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
816 | introduce an additional C<ev_sleep ()> call into most loop iterations. |
828 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
|
|
829 | sleep time ensures that libev will not poll for I/O events more often then |
|
|
830 | once per this interval, on average. |
817 | |
831 | |
818 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
832 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
819 | to spend more time collecting timeouts, at the expense of increased |
833 | to spend more time collecting timeouts, at the expense of increased |
820 | latency/jitter/inexactness (the watcher callback will be called |
834 | latency/jitter/inexactness (the watcher callback will be called |
821 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
835 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
… | |
… | |
823 | |
837 | |
824 | Many (busy) programs can usually benefit by setting the I/O collect |
838 | Many (busy) programs can usually benefit by setting the I/O collect |
825 | interval to a value near C<0.1> or so, which is often enough for |
839 | interval to a value near C<0.1> or so, which is often enough for |
826 | interactive servers (of course not for games), likewise for timeouts. It |
840 | interactive servers (of course not for games), likewise for timeouts. It |
827 | usually doesn't make much sense to set it to a lower value than C<0.01>, |
841 | usually doesn't make much sense to set it to a lower value than C<0.01>, |
828 | as this approaches the timing granularity of most systems. |
842 | as this approaches the timing granularity of most systems. Note that if |
|
|
843 | you do transactions with the outside world and you can't increase the |
|
|
844 | parallelity, then this setting will limit your transaction rate (if you |
|
|
845 | need to poll once per transaction and the I/O collect interval is 0.01, |
|
|
846 | then you can't do more than 100 transations per second). |
829 | |
847 | |
830 | Setting the I<timeout collect interval> can improve the opportunity for |
848 | Setting the I<timeout collect interval> can improve the opportunity for |
831 | saving power, as the program will "bundle" timer callback invocations that |
849 | saving power, as the program will "bundle" timer callback invocations that |
832 | are "near" in time together, by delaying some, thus reducing the number of |
850 | are "near" in time together, by delaying some, thus reducing the number of |
833 | times the process sleeps and wakes up again. Another useful technique to |
851 | times the process sleeps and wakes up again. Another useful technique to |
834 | reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure |
852 | reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure |
835 | they fire on, say, one-second boundaries only. |
853 | they fire on, say, one-second boundaries only. |
|
|
854 | |
|
|
855 | Example: we only need 0.1s timeout granularity, and we wish not to poll |
|
|
856 | more often than 100 times per second: |
|
|
857 | |
|
|
858 | ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1); |
|
|
859 | ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01); |
836 | |
860 | |
837 | =item ev_loop_verify (loop) |
861 | =item ev_loop_verify (loop) |
838 | |
862 | |
839 | This function only does something when C<EV_VERIFY> support has been |
863 | This function only does something when C<EV_VERIFY> support has been |
840 | compiled in, which is the default for non-minimal builds. It tries to go |
864 | compiled in, which is the default for non-minimal builds. It tries to go |
… | |
… | |
1468 | |
1492 | |
1469 | The callback is guaranteed to be invoked only I<after> its timeout has |
1493 | The callback is guaranteed to be invoked only I<after> its timeout has |
1470 | passed (not I<at>, so on systems with very low-resolution clocks this |
1494 | passed (not I<at>, so on systems with very low-resolution clocks this |
1471 | might introduce a small delay). If multiple timers become ready during the |
1495 | might introduce a small delay). If multiple timers become ready during the |
1472 | same loop iteration then the ones with earlier time-out values are invoked |
1496 | same loop iteration then the ones with earlier time-out values are invoked |
1473 | before ones with later time-out values (but this is no longer true when a |
1497 | before ones of the same priority with later time-out values (but this is |
1474 | callback calls C<ev_loop> recursively). |
1498 | no longer true when a callback calls C<ev_loop> recursively). |
1475 | |
1499 | |
1476 | =head3 Be smart about timeouts |
1500 | =head3 Be smart about timeouts |
1477 | |
1501 | |
1478 | Many real-world problems involve some kind of timeout, usually for error |
1502 | Many real-world problems involve some kind of timeout, usually for error |
1479 | recovery. A typical example is an HTTP request - if the other side hangs, |
1503 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
2002 | some child status changes (most typically when a child of yours dies or |
2026 | some child status changes (most typically when a child of yours dies or |
2003 | exits). It is permissible to install a child watcher I<after> the child |
2027 | exits). It is permissible to install a child watcher I<after> the child |
2004 | has been forked (which implies it might have already exited), as long |
2028 | has been forked (which implies it might have already exited), as long |
2005 | as the event loop isn't entered (or is continued from a watcher), i.e., |
2029 | as the event loop isn't entered (or is continued from a watcher), i.e., |
2006 | forking and then immediately registering a watcher for the child is fine, |
2030 | forking and then immediately registering a watcher for the child is fine, |
2007 | but forking and registering a watcher a few event loop iterations later is |
2031 | but forking and registering a watcher a few event loop iterations later or |
2008 | not. |
2032 | in the next callback invocation is not. |
2009 | |
2033 | |
2010 | Only the default event loop is capable of handling signals, and therefore |
2034 | Only the default event loop is capable of handling signals, and therefore |
2011 | you can only register child watchers in the default event loop. |
2035 | you can only register child watchers in the default event loop. |
|
|
2036 | |
|
|
2037 | Due to some design glitches inside libev, child watchers will always be |
|
|
2038 | handled at maximum priority (their priority is set to EV_MAXPRI by libev) |
2012 | |
2039 | |
2013 | =head3 Process Interaction |
2040 | =head3 Process Interaction |
2014 | |
2041 | |
2015 | Libev grabs C<SIGCHLD> as soon as the default event loop is |
2042 | Libev grabs C<SIGCHLD> as soon as the default event loop is |
2016 | initialised. This is necessary to guarantee proper behaviour even if |
2043 | initialised. This is necessary to guarantee proper behaviour even if |
… | |
… | |
4065 | =item C<double> must hold a time value in seconds with enough accuracy |
4092 | =item C<double> must hold a time value in seconds with enough accuracy |
4066 | |
4093 | |
4067 | The type C<double> is used to represent timestamps. It is required to |
4094 | The type C<double> is used to represent timestamps. It is required to |
4068 | have at least 51 bits of mantissa (and 9 bits of exponent), which is good |
4095 | have at least 51 bits of mantissa (and 9 bits of exponent), which is good |
4069 | enough for at least into the year 4000. This requirement is fulfilled by |
4096 | enough for at least into the year 4000. This requirement is fulfilled by |
4070 | implementations implementing IEEE 754 (basically all existing ones). |
4097 | implementations implementing IEEE 754, which is basically all existing |
|
|
4098 | ones. With IEEE 754 doubles, you get microsecond accuracy until at least |
|
|
4099 | 2200. |
4071 | |
4100 | |
4072 | =back |
4101 | =back |
4073 | |
4102 | |
4074 | If you know of other additional requirements drop me a note. |
4103 | If you know of other additional requirements drop me a note. |
4075 | |
4104 | |