… | |
… | |
8 | |
8 | |
9 | =head2 EXAMPLE PROGRAM |
9 | =head2 EXAMPLE PROGRAM |
10 | |
10 | |
11 | // a single header file is required |
11 | // a single header file is required |
12 | #include <ev.h> |
12 | #include <ev.h> |
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13 | |
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14 | #include <stdio.h> // for puts |
13 | |
15 | |
14 | // every watcher type has its own typedef'd struct |
16 | // every watcher type has its own typedef'd struct |
15 | // with the name ev_TYPE |
17 | // with the name ev_TYPE |
16 | ev_io stdin_watcher; |
18 | ev_io stdin_watcher; |
17 | ev_timer timeout_watcher; |
19 | ev_timer timeout_watcher; |
… | |
… | |
41 | |
43 | |
42 | int |
44 | int |
43 | main (void) |
45 | main (void) |
44 | { |
46 | { |
45 | // use the default event loop unless you have special needs |
47 | // use the default event loop unless you have special needs |
46 | ev_loop *loop = ev_default_loop (0); |
48 | struct ev_loop *loop = ev_default_loop (0); |
47 | |
49 | |
48 | // initialise an io watcher, then start it |
50 | // initialise an io watcher, then start it |
49 | // this one will watch for stdin to become readable |
51 | // this one will watch for stdin to become readable |
50 | ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); |
52 | ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); |
51 | ev_io_start (loop, &stdin_watcher); |
53 | ev_io_start (loop, &stdin_watcher); |
… | |
… | |
60 | |
62 | |
61 | // unloop was called, so exit |
63 | // unloop was called, so exit |
62 | return 0; |
64 | return 0; |
63 | } |
65 | } |
64 | |
66 | |
65 | =head1 DESCRIPTION |
67 | =head1 ABOUT THIS DOCUMENT |
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68 | |
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69 | This document documents the libev software package. |
66 | |
70 | |
67 | The newest version of this document is also available as an html-formatted |
71 | The newest version of this document is also available as an html-formatted |
68 | web page you might find easier to navigate when reading it for the first |
72 | web page you might find easier to navigate when reading it for the first |
69 | time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. |
73 | time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. |
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74 | |
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75 | While this document tries to be as complete as possible in documenting |
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76 | libev, its usage and the rationale behind its design, it is not a tutorial |
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77 | on event-based programming, nor will it introduce event-based programming |
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78 | with libev. |
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79 | |
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80 | Familarity with event based programming techniques in general is assumed |
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81 | throughout this document. |
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82 | |
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83 | =head1 ABOUT LIBEV |
70 | |
84 | |
71 | Libev is an event loop: you register interest in certain events (such as a |
85 | Libev is an event loop: you register interest in certain events (such as a |
72 | file descriptor being readable or a timeout occurring), and it will manage |
86 | file descriptor being readable or a timeout occurring), and it will manage |
73 | these event sources and provide your program with events. |
87 | these event sources and provide your program with events. |
74 | |
88 | |
… | |
… | |
108 | name C<loop> (which is always of type C<ev_loop *>) will not have |
122 | name C<loop> (which is always of type C<ev_loop *>) will not have |
109 | this argument. |
123 | this argument. |
110 | |
124 | |
111 | =head2 TIME REPRESENTATION |
125 | =head2 TIME REPRESENTATION |
112 | |
126 | |
113 | Libev represents time as a single floating point number, representing the |
127 | Libev represents time as a single floating point number, representing |
114 | (fractional) number of seconds since the (POSIX) epoch (somewhere near |
128 | the (fractional) number of seconds since the (POSIX) epoch (somewhere |
115 | the beginning of 1970, details are complicated, don't ask). This type is |
129 | near the beginning of 1970, details are complicated, don't ask). This |
116 | called C<ev_tstamp>, which is what you should use too. It usually aliases |
130 | type is called C<ev_tstamp>, which is what you should use too. It usually |
117 | to the C<double> type in C, and when you need to do any calculations on |
131 | aliases to the C<double> type in C. When you need to do any calculations |
118 | it, you should treat it as some floating point value. Unlike the name |
132 | on it, you should treat it as some floating point value. Unlike the name |
119 | component C<stamp> might indicate, it is also used for time differences |
133 | component C<stamp> might indicate, it is also used for time differences |
120 | throughout libev. |
134 | throughout libev. |
121 | |
135 | |
122 | =head1 ERROR HANDLING |
136 | =head1 ERROR HANDLING |
123 | |
137 | |
… | |
… | |
458 | |
472 | |
459 | While nominally embeddable in other event loops, this doesn't work |
473 | While nominally embeddable in other event loops, this doesn't work |
460 | everywhere, so you might need to test for this. And since it is broken |
474 | everywhere, so you might need to test for this. And since it is broken |
461 | almost everywhere, you should only use it when you have a lot of sockets |
475 | almost everywhere, you should only use it when you have a lot of sockets |
462 | (for which it usually works), by embedding it into another event loop |
476 | (for which it usually works), by embedding it into another event loop |
463 | (e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it, |
477 | (e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course |
464 | using it only for sockets. |
478 | also broken on OS X)) and, did I mention it, using it only for sockets. |
465 | |
479 | |
466 | This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with |
480 | This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with |
467 | C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with |
481 | C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with |
468 | C<NOTE_EOF>. |
482 | C<NOTE_EOF>. |
469 | |
483 | |
… | |
… | |
607 | |
621 | |
608 | 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 |
609 | "ticks" the number of loop iterations), as it roughly corresponds with |
623 | "ticks" the number of loop iterations), as it roughly corresponds with |
610 | C<ev_prepare> and C<ev_check> calls. |
624 | C<ev_prepare> and C<ev_check> calls. |
611 | |
625 | |
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626 | =item unsigned int ev_loop_depth (loop) |
|
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627 | |
|
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628 | Returns the number of times C<ev_loop> was entered minus the number of |
|
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629 | times C<ev_loop> was exited, in other words, the recursion depth. |
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630 | |
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631 | Outside C<ev_loop>, this number is zero. In a callback, this number is |
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632 | C<1>, unless C<ev_loop> was invoked recursively (or from another thread), |
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633 | in which case it is higher. |
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634 | |
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635 | Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread |
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636 | etc.), doesn't count as exit. |
|
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637 | |
612 | =item unsigned int ev_backend (loop) |
638 | =item unsigned int ev_backend (loop) |
613 | |
639 | |
614 | 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 |
615 | use. |
641 | use. |
616 | |
642 | |
… | |
… | |
630 | |
656 | |
631 | This function is rarely useful, but when some event callback runs for a |
657 | This function is rarely useful, but when some event callback runs for a |
632 | very long time without entering the event loop, updating libev's idea of |
658 | very long time without entering the event loop, updating libev's idea of |
633 | the current time is a good idea. |
659 | the current time is a good idea. |
634 | |
660 | |
635 | See also "The special problem of time updates" in the C<ev_timer> section. |
661 | See also L<The special problem of time updates> in the C<ev_timer> section. |
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662 | |
|
|
663 | =item ev_suspend (loop) |
|
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664 | |
|
|
665 | =item ev_resume (loop) |
|
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666 | |
|
|
667 | These two functions suspend and resume a loop, for use when the loop is |
|
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668 | not used for a while and timeouts should not be processed. |
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|
669 | |
|
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670 | A typical use case would be an interactive program such as a game: When |
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671 | the user presses C<^Z> to suspend the game and resumes it an hour later it |
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672 | would be best to handle timeouts as if no time had actually passed while |
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673 | the program was suspended. This can be achieved by calling C<ev_suspend> |
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674 | in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling |
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675 | C<ev_resume> directly afterwards to resume timer processing. |
|
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676 | |
|
|
677 | Effectively, all C<ev_timer> watchers will be delayed by the time spend |
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678 | between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers |
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679 | will be rescheduled (that is, they will lose any events that would have |
|
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680 | occured while suspended). |
|
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681 | |
|
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682 | After calling C<ev_suspend> you B<must not> call I<any> function on the |
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683 | given loop other than C<ev_resume>, and you B<must not> call C<ev_resume> |
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684 | without a previous call to C<ev_suspend>. |
|
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685 | |
|
|
686 | Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the |
|
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687 | event loop time (see C<ev_now_update>). |
636 | |
688 | |
637 | =item ev_loop (loop, int flags) |
689 | =item ev_loop (loop, int flags) |
638 | |
690 | |
639 | Finally, this is it, the event handler. This function usually is called |
691 | Finally, this is it, the event handler. This function usually is called |
640 | after you initialised all your watchers and you want to start handling |
692 | after you initialised all your watchers and you want to start handling |
… | |
… | |
724 | |
776 | |
725 | If you have a watcher you never unregister that should not keep C<ev_loop> |
777 | If you have a watcher you never unregister that should not keep C<ev_loop> |
726 | from returning, call ev_unref() after starting, and ev_ref() before |
778 | from returning, call ev_unref() after starting, and ev_ref() before |
727 | stopping it. |
779 | stopping it. |
728 | |
780 | |
729 | As an example, libev itself uses this for its internal signal pipe: It is |
781 | As an example, libev itself uses this for its internal signal pipe: It |
730 | not visible to the libev user and should not keep C<ev_loop> from exiting |
782 | is not visible to the libev user and should not keep C<ev_loop> from |
731 | if no event watchers registered by it are active. It is also an excellent |
783 | exiting if no event watchers registered by it are active. It is also an |
732 | way to do this for generic recurring timers or from within third-party |
784 | excellent way to do this for generic recurring timers or from within |
733 | libraries. Just remember to I<unref after start> and I<ref before stop> |
785 | third-party libraries. Just remember to I<unref after start> and I<ref |
734 | (but only if the watcher wasn't active before, or was active before, |
786 | before stop> (but only if the watcher wasn't active before, or was active |
735 | respectively). |
787 | before, respectively. Note also that libev might stop watchers itself |
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|
788 | (e.g. non-repeating timers) in which case you have to C<ev_ref> |
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|
789 | in the callback). |
736 | |
790 | |
737 | Example: Create a signal watcher, but keep it from keeping C<ev_loop> |
791 | Example: Create a signal watcher, but keep it from keeping C<ev_loop> |
738 | running when nothing else is active. |
792 | running when nothing else is active. |
739 | |
793 | |
740 | ev_signal exitsig; |
794 | ev_signal exitsig; |
… | |
… | |
769 | |
823 | |
770 | 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 |
771 | 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, |
772 | 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 |
773 | 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 |
774 | introduce an additional C<ev_sleep ()> call into most loop iterations. |
828 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
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|
829 | sleep time ensures that libev will not poll for I/O events more often then |
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830 | once per this interval, on average. |
775 | |
831 | |
776 | 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 |
777 | to spend more time collecting timeouts, at the expense of increased |
833 | to spend more time collecting timeouts, at the expense of increased |
778 | latency/jitter/inexactness (the watcher callback will be called |
834 | latency/jitter/inexactness (the watcher callback will be called |
779 | 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 |
… | |
… | |
781 | |
837 | |
782 | 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 |
783 | 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 |
784 | interactive servers (of course not for games), likewise for timeouts. It |
840 | interactive servers (of course not for games), likewise for timeouts. It |
785 | 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>, |
786 | as this approaches the timing granularity of most systems. |
842 | as this approaches the timing granularity of most systems. Note that if |
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843 | you do transactions with the outside world and you can't increase the |
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844 | parallelity, then this setting will limit your transaction rate (if you |
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845 | need to poll once per transaction and the I/O collect interval is 0.01, |
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846 | then you can't do more than 100 transations per second). |
787 | |
847 | |
788 | Setting the I<timeout collect interval> can improve the opportunity for |
848 | Setting the I<timeout collect interval> can improve the opportunity for |
789 | saving power, as the program will "bundle" timer callback invocations that |
849 | saving power, as the program will "bundle" timer callback invocations that |
790 | 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 |
791 | 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 |
792 | 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 |
793 | they fire on, say, one-second boundaries only. |
853 | they fire on, say, one-second boundaries only. |
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854 | |
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855 | Example: we only need 0.1s timeout granularity, and we wish not to poll |
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856 | more often than 100 times per second: |
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857 | |
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858 | ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1); |
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859 | ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01); |
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860 | |
|
|
861 | =item ev_invoke_pending (loop) |
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862 | |
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|
863 | This call will simply invoke all pending watchers while resetting their |
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864 | pending state. Normally, C<ev_loop> does this automatically when required, |
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865 | but when overriding the invoke callback this call comes handy. |
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866 | |
|
|
867 | =item int ev_pending_count (loop) |
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|
868 | |
|
|
869 | Returns the number of pending watchers - zero indicates that no watchers |
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870 | are pending. |
|
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871 | |
|
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872 | =item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P)) |
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873 | |
|
|
874 | This overrides the invoke pending functionality of the loop: Instead of |
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875 | invoking all pending watchers when there are any, C<ev_loop> will call |
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876 | this callback instead. This is useful, for example, when you want to |
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877 | invoke the actual watchers inside another context (another thread etc.). |
|
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878 | |
|
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879 | If you want to reset the callback, use C<ev_invoke_pending> as new |
|
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880 | callback. |
|
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881 | |
|
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882 | =item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P)) |
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883 | |
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884 | Sometimes you want to share the same loop between multiple threads. This |
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885 | can be done relatively simply by putting mutex_lock/unlock calls around |
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886 | each call to a libev function. |
|
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887 | |
|
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888 | However, C<ev_loop> can run an indefinite time, so it is not feasible to |
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889 | wait for it to return. One way around this is to wake up the loop via |
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890 | C<ev_unloop> and C<av_async_send>, another way is to set these I<release> |
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891 | and I<acquire> callbacks on the loop. |
|
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892 | |
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893 | When set, then C<release> will be called just before the thread is |
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894 | suspended waiting for new events, and C<acquire> is called just |
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895 | afterwards. |
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896 | |
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897 | Ideally, C<release> will just call your mutex_unlock function, and |
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898 | C<acquire> will just call the mutex_lock function again. |
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899 | |
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900 | While event loop modifications are allowed between invocations of |
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901 | C<release> and C<acquire> (that's their only purpose after all), no |
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902 | modifications done will affect the event loop, i.e. adding watchers will |
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903 | have no effect on the set of file descriptors being watched, or the time |
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904 | waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it |
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905 | to take note of any changes you made. |
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906 | |
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907 | In theory, threads executing C<ev_loop> will be async-cancel safe between |
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908 | invocations of C<release> and C<acquire>. |
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909 | |
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910 | See also the locking example in the C<THREADS> section later in this |
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911 | document. |
|
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912 | |
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913 | =item ev_set_userdata (loop, void *data) |
|
|
914 | |
|
|
915 | =item ev_userdata (loop) |
|
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916 | |
|
|
917 | Set and retrieve a single C<void *> associated with a loop. When |
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918 | C<ev_set_userdata> has never been called, then C<ev_userdata> returns |
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919 | C<0.> |
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920 | |
|
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921 | These two functions can be used to associate arbitrary data with a loop, |
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922 | and are intended solely for the C<invoke_pending_cb>, C<release> and |
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923 | C<acquire> callbacks described above, but of course can be (ab-)used for |
|
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924 | any other purpose as well. |
794 | |
925 | |
795 | =item ev_loop_verify (loop) |
926 | =item ev_loop_verify (loop) |
796 | |
927 | |
797 | This function only does something when C<EV_VERIFY> support has been |
928 | This function only does something when C<EV_VERIFY> support has been |
798 | compiled in, which is the default for non-minimal builds. It tries to go |
929 | compiled in, which is the default for non-minimal builds. It tries to go |
… | |
… | |
924 | |
1055 | |
925 | =item C<EV_ASYNC> |
1056 | =item C<EV_ASYNC> |
926 | |
1057 | |
927 | The given async watcher has been asynchronously notified (see C<ev_async>). |
1058 | The given async watcher has been asynchronously notified (see C<ev_async>). |
928 | |
1059 | |
|
|
1060 | =item C<EV_CUSTOM> |
|
|
1061 | |
|
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1062 | Not ever sent (or otherwise used) by libev itself, but can be freely used |
|
|
1063 | by libev users to signal watchers (e.g. via C<ev_feed_event>). |
|
|
1064 | |
929 | =item C<EV_ERROR> |
1065 | =item C<EV_ERROR> |
930 | |
1066 | |
931 | An unspecified error has occurred, the watcher has been stopped. This might |
1067 | An unspecified error has occurred, the watcher has been stopped. This might |
932 | happen because the watcher could not be properly started because libev |
1068 | happen because the watcher could not be properly started because libev |
933 | ran out of memory, a file descriptor was found to be closed or any other |
1069 | ran out of memory, a file descriptor was found to be closed or any other |
… | |
… | |
1048 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1184 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1049 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1185 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1050 | before watchers with lower priority, but priority will not keep watchers |
1186 | before watchers with lower priority, but priority will not keep watchers |
1051 | from being executed (except for C<ev_idle> watchers). |
1187 | from being executed (except for C<ev_idle> watchers). |
1052 | |
1188 | |
1053 | This means that priorities are I<only> used for ordering callback |
|
|
1054 | invocation after new events have been received. This is useful, for |
|
|
1055 | example, to reduce latency after idling, or more often, to bind two |
|
|
1056 | watchers on the same event and make sure one is called first. |
|
|
1057 | |
|
|
1058 | If you need to suppress invocation when higher priority events are pending |
1189 | If you need to suppress invocation when higher priority events are pending |
1059 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1190 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1060 | |
1191 | |
1061 | You I<must not> change the priority of a watcher as long as it is active or |
1192 | You I<must not> change the priority of a watcher as long as it is active or |
1062 | pending. |
1193 | pending. |
1063 | |
|
|
1064 | The default priority used by watchers when no priority has been set is |
|
|
1065 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1066 | |
1194 | |
1067 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1195 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1068 | fine, as long as you do not mind that the priority value you query might |
1196 | fine, as long as you do not mind that the priority value you query might |
1069 | or might not have been clamped to the valid range. |
1197 | or might not have been clamped to the valid range. |
|
|
1198 | |
|
|
1199 | The default priority used by watchers when no priority has been set is |
|
|
1200 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1201 | |
|
|
1202 | See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of |
|
|
1203 | priorities. |
1070 | |
1204 | |
1071 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1205 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1072 | |
1206 | |
1073 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1207 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1074 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1208 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
… | |
… | |
1139 | #include <stddef.h> |
1273 | #include <stddef.h> |
1140 | |
1274 | |
1141 | static void |
1275 | static void |
1142 | t1_cb (EV_P_ ev_timer *w, int revents) |
1276 | t1_cb (EV_P_ ev_timer *w, int revents) |
1143 | { |
1277 | { |
1144 | struct my_biggy big = (struct my_biggy * |
1278 | struct my_biggy big = (struct my_biggy *) |
1145 | (((char *)w) - offsetof (struct my_biggy, t1)); |
1279 | (((char *)w) - offsetof (struct my_biggy, t1)); |
1146 | } |
1280 | } |
1147 | |
1281 | |
1148 | static void |
1282 | static void |
1149 | t2_cb (EV_P_ ev_timer *w, int revents) |
1283 | t2_cb (EV_P_ ev_timer *w, int revents) |
1150 | { |
1284 | { |
1151 | struct my_biggy big = (struct my_biggy * |
1285 | struct my_biggy big = (struct my_biggy *) |
1152 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1286 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1153 | } |
1287 | } |
|
|
1288 | |
|
|
1289 | =head2 WATCHER PRIORITY MODELS |
|
|
1290 | |
|
|
1291 | Many event loops support I<watcher priorities>, which are usually small |
|
|
1292 | integers that influence the ordering of event callback invocation |
|
|
1293 | between watchers in some way, all else being equal. |
|
|
1294 | |
|
|
1295 | In libev, Watcher priorities can be set using C<ev_set_priority>. See its |
|
|
1296 | description for the more technical details such as the actual priority |
|
|
1297 | range. |
|
|
1298 | |
|
|
1299 | There are two common ways how these these priorities are being interpreted |
|
|
1300 | by event loops: |
|
|
1301 | |
|
|
1302 | In the more common lock-out model, higher priorities "lock out" invocation |
|
|
1303 | of lower priority watchers, which means as long as higher priority |
|
|
1304 | watchers receive events, lower priority watchers are not being invoked. |
|
|
1305 | |
|
|
1306 | The less common only-for-ordering model uses priorities solely to order |
|
|
1307 | callback invocation within a single event loop iteration: Higher priority |
|
|
1308 | watchers are invoked before lower priority ones, but they all get invoked |
|
|
1309 | before polling for new events. |
|
|
1310 | |
|
|
1311 | Libev uses the second (only-for-ordering) model for all its watchers |
|
|
1312 | except for idle watchers (which use the lock-out model). |
|
|
1313 | |
|
|
1314 | The rationale behind this is that implementing the lock-out model for |
|
|
1315 | watchers is not well supported by most kernel interfaces, and most event |
|
|
1316 | libraries will just poll for the same events again and again as long as |
|
|
1317 | their callbacks have not been executed, which is very inefficient in the |
|
|
1318 | common case of one high-priority watcher locking out a mass of lower |
|
|
1319 | priority ones. |
|
|
1320 | |
|
|
1321 | Static (ordering) priorities are most useful when you have two or more |
|
|
1322 | watchers handling the same resource: a typical usage example is having an |
|
|
1323 | C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle |
|
|
1324 | timeouts. Under load, data might be received while the program handles |
|
|
1325 | other jobs, but since timers normally get invoked first, the timeout |
|
|
1326 | handler will be executed before checking for data. In that case, giving |
|
|
1327 | the timer a lower priority than the I/O watcher ensures that I/O will be |
|
|
1328 | handled first even under adverse conditions (which is usually, but not |
|
|
1329 | always, what you want). |
|
|
1330 | |
|
|
1331 | Since idle watchers use the "lock-out" model, meaning that idle watchers |
|
|
1332 | will only be executed when no same or higher priority watchers have |
|
|
1333 | received events, they can be used to implement the "lock-out" model when |
|
|
1334 | required. |
|
|
1335 | |
|
|
1336 | For example, to emulate how many other event libraries handle priorities, |
|
|
1337 | you can associate an C<ev_idle> watcher to each such watcher, and in |
|
|
1338 | the normal watcher callback, you just start the idle watcher. The real |
|
|
1339 | processing is done in the idle watcher callback. This causes libev to |
|
|
1340 | continously poll and process kernel event data for the watcher, but when |
|
|
1341 | the lock-out case is known to be rare (which in turn is rare :), this is |
|
|
1342 | workable. |
|
|
1343 | |
|
|
1344 | Usually, however, the lock-out model implemented that way will perform |
|
|
1345 | miserably under the type of load it was designed to handle. In that case, |
|
|
1346 | it might be preferable to stop the real watcher before starting the |
|
|
1347 | idle watcher, so the kernel will not have to process the event in case |
|
|
1348 | the actual processing will be delayed for considerable time. |
|
|
1349 | |
|
|
1350 | Here is an example of an I/O watcher that should run at a strictly lower |
|
|
1351 | priority than the default, and which should only process data when no |
|
|
1352 | other events are pending: |
|
|
1353 | |
|
|
1354 | ev_idle idle; // actual processing watcher |
|
|
1355 | ev_io io; // actual event watcher |
|
|
1356 | |
|
|
1357 | static void |
|
|
1358 | io_cb (EV_P_ ev_io *w, int revents) |
|
|
1359 | { |
|
|
1360 | // stop the I/O watcher, we received the event, but |
|
|
1361 | // are not yet ready to handle it. |
|
|
1362 | ev_io_stop (EV_A_ w); |
|
|
1363 | |
|
|
1364 | // start the idle watcher to ahndle the actual event. |
|
|
1365 | // it will not be executed as long as other watchers |
|
|
1366 | // with the default priority are receiving events. |
|
|
1367 | ev_idle_start (EV_A_ &idle); |
|
|
1368 | } |
|
|
1369 | |
|
|
1370 | static void |
|
|
1371 | idle_cb (EV_P_ ev_idle *w, int revents) |
|
|
1372 | { |
|
|
1373 | // actual processing |
|
|
1374 | read (STDIN_FILENO, ...); |
|
|
1375 | |
|
|
1376 | // have to start the I/O watcher again, as |
|
|
1377 | // we have handled the event |
|
|
1378 | ev_io_start (EV_P_ &io); |
|
|
1379 | } |
|
|
1380 | |
|
|
1381 | // initialisation |
|
|
1382 | ev_idle_init (&idle, idle_cb); |
|
|
1383 | ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ); |
|
|
1384 | ev_io_start (EV_DEFAULT_ &io); |
|
|
1385 | |
|
|
1386 | In the "real" world, it might also be beneficial to start a timer, so that |
|
|
1387 | low-priority connections can not be locked out forever under load. This |
|
|
1388 | enables your program to keep a lower latency for important connections |
|
|
1389 | during short periods of high load, while not completely locking out less |
|
|
1390 | important ones. |
1154 | |
1391 | |
1155 | |
1392 | |
1156 | =head1 WATCHER TYPES |
1393 | =head1 WATCHER TYPES |
1157 | |
1394 | |
1158 | This section describes each watcher in detail, but will not repeat |
1395 | This section describes each watcher in detail, but will not repeat |
… | |
… | |
1184 | descriptors to non-blocking mode is also usually a good idea (but not |
1421 | descriptors to non-blocking mode is also usually a good idea (but not |
1185 | required if you know what you are doing). |
1422 | required if you know what you are doing). |
1186 | |
1423 | |
1187 | If you cannot use non-blocking mode, then force the use of a |
1424 | If you cannot use non-blocking mode, then force the use of a |
1188 | known-to-be-good backend (at the time of this writing, this includes only |
1425 | known-to-be-good backend (at the time of this writing, this includes only |
1189 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). |
1426 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file |
|
|
1427 | descriptors for which non-blocking operation makes no sense (such as |
|
|
1428 | files) - libev doesn't guarentee any specific behaviour in that case. |
1190 | |
1429 | |
1191 | Another thing you have to watch out for is that it is quite easy to |
1430 | Another thing you have to watch out for is that it is quite easy to |
1192 | receive "spurious" readiness notifications, that is your callback might |
1431 | receive "spurious" readiness notifications, that is your callback might |
1193 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1432 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1194 | because there is no data. Not only are some backends known to create a |
1433 | because there is no data. Not only are some backends known to create a |
… | |
… | |
1315 | year, it will still time out after (roughly) one hour. "Roughly" because |
1554 | year, it will still time out after (roughly) one hour. "Roughly" because |
1316 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1555 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1317 | monotonic clock option helps a lot here). |
1556 | monotonic clock option helps a lot here). |
1318 | |
1557 | |
1319 | The callback is guaranteed to be invoked only I<after> its timeout has |
1558 | The callback is guaranteed to be invoked only I<after> its timeout has |
1320 | passed, but if multiple timers become ready during the same loop iteration |
1559 | passed (not I<at>, so on systems with very low-resolution clocks this |
1321 | then order of execution is undefined. |
1560 | might introduce a small delay). If multiple timers become ready during the |
|
|
1561 | same loop iteration then the ones with earlier time-out values are invoked |
|
|
1562 | before ones of the same priority with later time-out values (but this is |
|
|
1563 | no longer true when a callback calls C<ev_loop> recursively). |
1322 | |
1564 | |
1323 | =head3 Be smart about timeouts |
1565 | =head3 Be smart about timeouts |
1324 | |
1566 | |
1325 | Many real-world problems involve some kind of timeout, usually for error |
1567 | Many real-world problems involve some kind of timeout, usually for error |
1326 | recovery. A typical example is an HTTP request - if the other side hangs, |
1568 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1370 | C<after> argument to C<ev_timer_set>, and only ever use the C<repeat> |
1612 | C<after> argument to C<ev_timer_set>, and only ever use the C<repeat> |
1371 | member and C<ev_timer_again>. |
1613 | member and C<ev_timer_again>. |
1372 | |
1614 | |
1373 | At start: |
1615 | At start: |
1374 | |
1616 | |
1375 | ev_timer_init (timer, callback); |
1617 | ev_init (timer, callback); |
1376 | timer->repeat = 60.; |
1618 | timer->repeat = 60.; |
1377 | ev_timer_again (loop, timer); |
1619 | ev_timer_again (loop, timer); |
1378 | |
1620 | |
1379 | Each time there is some activity: |
1621 | Each time there is some activity: |
1380 | |
1622 | |
… | |
… | |
1442 | |
1684 | |
1443 | To start the timer, simply initialise the watcher and set C<last_activity> |
1685 | To start the timer, simply initialise the watcher and set C<last_activity> |
1444 | to the current time (meaning we just have some activity :), then call the |
1686 | to the current time (meaning we just have some activity :), then call the |
1445 | callback, which will "do the right thing" and start the timer: |
1687 | callback, which will "do the right thing" and start the timer: |
1446 | |
1688 | |
1447 | ev_timer_init (timer, callback); |
1689 | ev_init (timer, callback); |
1448 | last_activity = ev_now (loop); |
1690 | last_activity = ev_now (loop); |
1449 | callback (loop, timer, EV_TIMEOUT); |
1691 | callback (loop, timer, EV_TIMEOUT); |
1450 | |
1692 | |
1451 | And when there is some activity, simply store the current time in |
1693 | And when there is some activity, simply store the current time in |
1452 | C<last_activity>, no libev calls at all: |
1694 | C<last_activity>, no libev calls at all: |
… | |
… | |
1545 | If the timer is started but non-repeating, stop it (as if it timed out). |
1787 | If the timer is started but non-repeating, stop it (as if it timed out). |
1546 | |
1788 | |
1547 | If the timer is repeating, either start it if necessary (with the |
1789 | If the timer is repeating, either start it if necessary (with the |
1548 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1790 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1549 | |
1791 | |
1550 | This sounds a bit complicated, see "Be smart about timeouts", above, for a |
1792 | This sounds a bit complicated, see L<Be smart about timeouts>, above, for a |
1551 | usage example. |
1793 | usage example. |
1552 | |
1794 | |
1553 | =item ev_tstamp repeat [read-write] |
1795 | =item ev_tstamp repeat [read-write] |
1554 | |
1796 | |
1555 | The current C<repeat> value. Will be used each time the watcher times out |
1797 | The current C<repeat> value. Will be used each time the watcher times out |
… | |
… | |
1594 | =head2 C<ev_periodic> - to cron or not to cron? |
1836 | =head2 C<ev_periodic> - to cron or not to cron? |
1595 | |
1837 | |
1596 | Periodic watchers are also timers of a kind, but they are very versatile |
1838 | Periodic watchers are also timers of a kind, but they are very versatile |
1597 | (and unfortunately a bit complex). |
1839 | (and unfortunately a bit complex). |
1598 | |
1840 | |
1599 | Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
1841 | Unlike C<ev_timer>, periodic watchers are not based on real time (or |
1600 | but on wall clock time (absolute time). You can tell a periodic watcher |
1842 | relative time, the physical time that passes) but on wall clock time |
1601 | to trigger after some specific point in time. For example, if you tell a |
1843 | (absolute time, the thing you can read on your calender or clock). The |
1602 | periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now () |
1844 | difference is that wall clock time can run faster or slower than real |
1603 | + 10.>, that is, an absolute time not a delay) and then reset your system |
1845 | time, and time jumps are not uncommon (e.g. when you adjust your |
1604 | clock to January of the previous year, then it will take more than year |
1846 | wrist-watch). |
1605 | to trigger the event (unlike an C<ev_timer>, which would still trigger |
|
|
1606 | roughly 10 seconds later as it uses a relative timeout). |
|
|
1607 | |
1847 | |
|
|
1848 | You can tell a periodic watcher to trigger after some specific point |
|
|
1849 | in time: for example, if you tell a periodic watcher to trigger "in 10 |
|
|
1850 | seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time |
|
|
1851 | not a delay) and then reset your system clock to January of the previous |
|
|
1852 | year, then it will take a year or more to trigger the event (unlike an |
|
|
1853 | C<ev_timer>, which would still trigger roughly 10 seconds after starting |
|
|
1854 | it, as it uses a relative timeout). |
|
|
1855 | |
1608 | C<ev_periodic>s can also be used to implement vastly more complex timers, |
1856 | C<ev_periodic> watchers can also be used to implement vastly more complex |
1609 | such as triggering an event on each "midnight, local time", or other |
1857 | timers, such as triggering an event on each "midnight, local time", or |
1610 | complicated rules. |
1858 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
|
|
1859 | those cannot react to time jumps. |
1611 | |
1860 | |
1612 | As with timers, the callback is guaranteed to be invoked only when the |
1861 | As with timers, the callback is guaranteed to be invoked only when the |
1613 | time (C<at>) has passed, but if multiple periodic timers become ready |
1862 | point in time where it is supposed to trigger has passed. If multiple |
1614 | during the same loop iteration, then order of execution is undefined. |
1863 | timers become ready during the same loop iteration then the ones with |
|
|
1864 | earlier time-out values are invoked before ones with later time-out values |
|
|
1865 | (but this is no longer true when a callback calls C<ev_loop> recursively). |
1615 | |
1866 | |
1616 | =head3 Watcher-Specific Functions and Data Members |
1867 | =head3 Watcher-Specific Functions and Data Members |
1617 | |
1868 | |
1618 | =over 4 |
1869 | =over 4 |
1619 | |
1870 | |
1620 | =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
1871 | =item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb) |
1621 | |
1872 | |
1622 | =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
1873 | =item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb) |
1623 | |
1874 | |
1624 | Lots of arguments, lets sort it out... There are basically three modes of |
1875 | Lots of arguments, let's sort it out... There are basically three modes of |
1625 | operation, and we will explain them from simplest to most complex: |
1876 | operation, and we will explain them from simplest to most complex: |
1626 | |
1877 | |
1627 | =over 4 |
1878 | =over 4 |
1628 | |
1879 | |
1629 | =item * absolute timer (at = time, interval = reschedule_cb = 0) |
1880 | =item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0) |
1630 | |
1881 | |
1631 | In this configuration the watcher triggers an event after the wall clock |
1882 | In this configuration the watcher triggers an event after the wall clock |
1632 | time C<at> has passed. It will not repeat and will not adjust when a time |
1883 | time C<offset> has passed. It will not repeat and will not adjust when a |
1633 | jump occurs, that is, if it is to be run at January 1st 2011 then it will |
1884 | time jump occurs, that is, if it is to be run at January 1st 2011 then it |
1634 | only run when the system clock reaches or surpasses this time. |
1885 | will be stopped and invoked when the system clock reaches or surpasses |
|
|
1886 | this point in time. |
1635 | |
1887 | |
1636 | =item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) |
1888 | =item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0) |
1637 | |
1889 | |
1638 | In this mode the watcher will always be scheduled to time out at the next |
1890 | In this mode the watcher will always be scheduled to time out at the next |
1639 | C<at + N * interval> time (for some integer N, which can also be negative) |
1891 | C<offset + N * interval> time (for some integer N, which can also be |
1640 | and then repeat, regardless of any time jumps. |
1892 | negative) and then repeat, regardless of any time jumps. The C<offset> |
|
|
1893 | argument is merely an offset into the C<interval> periods. |
1641 | |
1894 | |
1642 | This can be used to create timers that do not drift with respect to the |
1895 | This can be used to create timers that do not drift with respect to the |
1643 | system clock, for example, here is a C<ev_periodic> that triggers each |
1896 | system clock, for example, here is an C<ev_periodic> that triggers each |
1644 | hour, on the hour: |
1897 | hour, on the hour (with respect to UTC): |
1645 | |
1898 | |
1646 | ev_periodic_set (&periodic, 0., 3600., 0); |
1899 | ev_periodic_set (&periodic, 0., 3600., 0); |
1647 | |
1900 | |
1648 | This doesn't mean there will always be 3600 seconds in between triggers, |
1901 | This doesn't mean there will always be 3600 seconds in between triggers, |
1649 | but only that the callback will be called when the system time shows a |
1902 | but only that the callback will be called when the system time shows a |
1650 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1903 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1651 | by 3600. |
1904 | by 3600. |
1652 | |
1905 | |
1653 | Another way to think about it (for the mathematically inclined) is that |
1906 | Another way to think about it (for the mathematically inclined) is that |
1654 | C<ev_periodic> will try to run the callback in this mode at the next possible |
1907 | C<ev_periodic> will try to run the callback in this mode at the next possible |
1655 | time where C<time = at (mod interval)>, regardless of any time jumps. |
1908 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
1656 | |
1909 | |
1657 | For numerical stability it is preferable that the C<at> value is near |
1910 | For numerical stability it is preferable that the C<offset> value is near |
1658 | C<ev_now ()> (the current time), but there is no range requirement for |
1911 | C<ev_now ()> (the current time), but there is no range requirement for |
1659 | this value, and in fact is often specified as zero. |
1912 | this value, and in fact is often specified as zero. |
1660 | |
1913 | |
1661 | Note also that there is an upper limit to how often a timer can fire (CPU |
1914 | Note also that there is an upper limit to how often a timer can fire (CPU |
1662 | speed for example), so if C<interval> is very small then timing stability |
1915 | speed for example), so if C<interval> is very small then timing stability |
1663 | will of course deteriorate. Libev itself tries to be exact to be about one |
1916 | will of course deteriorate. Libev itself tries to be exact to be about one |
1664 | millisecond (if the OS supports it and the machine is fast enough). |
1917 | millisecond (if the OS supports it and the machine is fast enough). |
1665 | |
1918 | |
1666 | =item * manual reschedule mode (at and interval ignored, reschedule_cb = callback) |
1919 | =item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback) |
1667 | |
1920 | |
1668 | In this mode the values for C<interval> and C<at> are both being |
1921 | In this mode the values for C<interval> and C<offset> are both being |
1669 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1922 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1670 | reschedule callback will be called with the watcher as first, and the |
1923 | reschedule callback will be called with the watcher as first, and the |
1671 | current time as second argument. |
1924 | current time as second argument. |
1672 | |
1925 | |
1673 | NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
1926 | NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever, |
1674 | ever, or make ANY event loop modifications whatsoever>. |
1927 | or make ANY other event loop modifications whatsoever, unless explicitly |
|
|
1928 | allowed by documentation here>. |
1675 | |
1929 | |
1676 | If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop |
1930 | If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop |
1677 | it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the |
1931 | it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the |
1678 | only event loop modification you are allowed to do). |
1932 | only event loop modification you are allowed to do). |
1679 | |
1933 | |
… | |
… | |
1709 | a different time than the last time it was called (e.g. in a crond like |
1963 | a different time than the last time it was called (e.g. in a crond like |
1710 | program when the crontabs have changed). |
1964 | program when the crontabs have changed). |
1711 | |
1965 | |
1712 | =item ev_tstamp ev_periodic_at (ev_periodic *) |
1966 | =item ev_tstamp ev_periodic_at (ev_periodic *) |
1713 | |
1967 | |
1714 | When active, returns the absolute time that the watcher is supposed to |
1968 | When active, returns the absolute time that the watcher is supposed |
1715 | trigger next. |
1969 | to trigger next. This is not the same as the C<offset> argument to |
|
|
1970 | C<ev_periodic_set>, but indeed works even in interval and manual |
|
|
1971 | rescheduling modes. |
1716 | |
1972 | |
1717 | =item ev_tstamp offset [read-write] |
1973 | =item ev_tstamp offset [read-write] |
1718 | |
1974 | |
1719 | When repeating, this contains the offset value, otherwise this is the |
1975 | When repeating, this contains the offset value, otherwise this is the |
1720 | absolute point in time (the C<at> value passed to C<ev_periodic_set>). |
1976 | absolute point in time (the C<offset> value passed to C<ev_periodic_set>, |
|
|
1977 | although libev might modify this value for better numerical stability). |
1721 | |
1978 | |
1722 | Can be modified any time, but changes only take effect when the periodic |
1979 | Can be modified any time, but changes only take effect when the periodic |
1723 | timer fires or C<ev_periodic_again> is being called. |
1980 | timer fires or C<ev_periodic_again> is being called. |
1724 | |
1981 | |
1725 | =item ev_tstamp interval [read-write] |
1982 | =item ev_tstamp interval [read-write] |
… | |
… | |
1834 | some child status changes (most typically when a child of yours dies or |
2091 | some child status changes (most typically when a child of yours dies or |
1835 | exits). It is permissible to install a child watcher I<after> the child |
2092 | exits). It is permissible to install a child watcher I<after> the child |
1836 | has been forked (which implies it might have already exited), as long |
2093 | has been forked (which implies it might have already exited), as long |
1837 | as the event loop isn't entered (or is continued from a watcher), i.e., |
2094 | as the event loop isn't entered (or is continued from a watcher), i.e., |
1838 | forking and then immediately registering a watcher for the child is fine, |
2095 | forking and then immediately registering a watcher for the child is fine, |
1839 | but forking and registering a watcher a few event loop iterations later is |
2096 | but forking and registering a watcher a few event loop iterations later or |
1840 | not. |
2097 | in the next callback invocation is not. |
1841 | |
2098 | |
1842 | Only the default event loop is capable of handling signals, and therefore |
2099 | Only the default event loop is capable of handling signals, and therefore |
1843 | you can only register child watchers in the default event loop. |
2100 | you can only register child watchers in the default event loop. |
|
|
2101 | |
|
|
2102 | Due to some design glitches inside libev, child watchers will always be |
|
|
2103 | handled at maximum priority (their priority is set to C<EV_MAXPRI> by |
|
|
2104 | libev) |
1844 | |
2105 | |
1845 | =head3 Process Interaction |
2106 | =head3 Process Interaction |
1846 | |
2107 | |
1847 | Libev grabs C<SIGCHLD> as soon as the default event loop is |
2108 | Libev grabs C<SIGCHLD> as soon as the default event loop is |
1848 | initialised. This is necessary to guarantee proper behaviour even if |
2109 | initialised. This is necessary to guarantee proper behaviour even if |
… | |
… | |
2010 | the process. The exception are C<ev_stat> watchers - those call C<stat |
2271 | the process. The exception are C<ev_stat> watchers - those call C<stat |
2011 | ()>, which is a synchronous operation. |
2272 | ()>, which is a synchronous operation. |
2012 | |
2273 | |
2013 | For local paths, this usually doesn't matter: unless the system is very |
2274 | For local paths, this usually doesn't matter: unless the system is very |
2014 | busy or the intervals between stat's are large, a stat call will be fast, |
2275 | busy or the intervals between stat's are large, a stat call will be fast, |
2015 | as the path data is suually in memory already (except when starting the |
2276 | as the path data is usually in memory already (except when starting the |
2016 | watcher). |
2277 | watcher). |
2017 | |
2278 | |
2018 | For networked file systems, calling C<stat ()> can block an indefinite |
2279 | For networked file systems, calling C<stat ()> can block an indefinite |
2019 | time due to network issues, and even under good conditions, a stat call |
2280 | time due to network issues, and even under good conditions, a stat call |
2020 | often takes multiple milliseconds. |
2281 | often takes multiple milliseconds. |
… | |
… | |
2177 | |
2438 | |
2178 | =head3 Watcher-Specific Functions and Data Members |
2439 | =head3 Watcher-Specific Functions and Data Members |
2179 | |
2440 | |
2180 | =over 4 |
2441 | =over 4 |
2181 | |
2442 | |
2182 | =item ev_idle_init (ev_signal *, callback) |
2443 | =item ev_idle_init (ev_idle *, callback) |
2183 | |
2444 | |
2184 | Initialises and configures the idle watcher - it has no parameters of any |
2445 | Initialises and configures the idle watcher - it has no parameters of any |
2185 | kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
2446 | kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
2186 | believe me. |
2447 | believe me. |
2187 | |
2448 | |
… | |
… | |
2200 | // no longer anything immediate to do. |
2461 | // no longer anything immediate to do. |
2201 | } |
2462 | } |
2202 | |
2463 | |
2203 | ev_idle *idle_watcher = malloc (sizeof (ev_idle)); |
2464 | ev_idle *idle_watcher = malloc (sizeof (ev_idle)); |
2204 | ev_idle_init (idle_watcher, idle_cb); |
2465 | ev_idle_init (idle_watcher, idle_cb); |
2205 | ev_idle_start (loop, idle_cb); |
2466 | ev_idle_start (loop, idle_watcher); |
2206 | |
2467 | |
2207 | |
2468 | |
2208 | =head2 C<ev_prepare> and C<ev_check> - customise your event loop! |
2469 | =head2 C<ev_prepare> and C<ev_check> - customise your event loop! |
2209 | |
2470 | |
2210 | Prepare and check watchers are usually (but not always) used in pairs: |
2471 | Prepare and check watchers are usually (but not always) used in pairs: |
… | |
… | |
2303 | struct pollfd fds [nfd]; |
2564 | struct pollfd fds [nfd]; |
2304 | // actual code will need to loop here and realloc etc. |
2565 | // actual code will need to loop here and realloc etc. |
2305 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
2566 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
2306 | |
2567 | |
2307 | /* the callback is illegal, but won't be called as we stop during check */ |
2568 | /* the callback is illegal, but won't be called as we stop during check */ |
2308 | ev_timer_init (&tw, 0, timeout * 1e-3); |
2569 | ev_timer_init (&tw, 0, timeout * 1e-3, 0.); |
2309 | ev_timer_start (loop, &tw); |
2570 | ev_timer_start (loop, &tw); |
2310 | |
2571 | |
2311 | // create one ev_io per pollfd |
2572 | // create one ev_io per pollfd |
2312 | for (int i = 0; i < nfd; ++i) |
2573 | for (int i = 0; i < nfd; ++i) |
2313 | { |
2574 | { |
… | |
… | |
2426 | some fds have to be watched and handled very quickly (with low latency), |
2687 | some fds have to be watched and handled very quickly (with low latency), |
2427 | and even priorities and idle watchers might have too much overhead. In |
2688 | and even priorities and idle watchers might have too much overhead. In |
2428 | this case you would put all the high priority stuff in one loop and all |
2689 | this case you would put all the high priority stuff in one loop and all |
2429 | the rest in a second one, and embed the second one in the first. |
2690 | the rest in a second one, and embed the second one in the first. |
2430 | |
2691 | |
2431 | As long as the watcher is active, the callback will be invoked every time |
2692 | As long as the watcher is active, the callback will be invoked every |
2432 | there might be events pending in the embedded loop. The callback must then |
2693 | time there might be events pending in the embedded loop. The callback |
2433 | call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke |
2694 | must then call C<ev_embed_sweep (mainloop, watcher)> to make a single |
2434 | their callbacks (you could also start an idle watcher to give the embedded |
2695 | sweep and invoke their callbacks (the callback doesn't need to invoke the |
2435 | loop strictly lower priority for example). You can also set the callback |
2696 | C<ev_embed_sweep> function directly, it could also start an idle watcher |
2436 | to C<0>, in which case the embed watcher will automatically execute the |
2697 | to give the embedded loop strictly lower priority for example). |
2437 | embedded loop sweep. |
|
|
2438 | |
2698 | |
2439 | As long as the watcher is started it will automatically handle events. The |
2699 | You can also set the callback to C<0>, in which case the embed watcher |
2440 | callback will be invoked whenever some events have been handled. You can |
2700 | will automatically execute the embedded loop sweep whenever necessary. |
2441 | set the callback to C<0> to avoid having to specify one if you are not |
|
|
2442 | interested in that. |
|
|
2443 | |
2701 | |
2444 | Also, there have not currently been made special provisions for forking: |
2702 | Fork detection will be handled transparently while the C<ev_embed> watcher |
2445 | when you fork, you not only have to call C<ev_loop_fork> on both loops, |
2703 | is active, i.e., the embedded loop will automatically be forked when the |
2446 | but you will also have to stop and restart any C<ev_embed> watchers |
2704 | embedding loop forks. In other cases, the user is responsible for calling |
2447 | yourself - but you can use a fork watcher to handle this automatically, |
2705 | C<ev_loop_fork> on the embedded loop. |
2448 | and future versions of libev might do just that. |
|
|
2449 | |
2706 | |
2450 | Unfortunately, not all backends are embeddable: only the ones returned by |
2707 | Unfortunately, not all backends are embeddable: only the ones returned by |
2451 | C<ev_embeddable_backends> are, which, unfortunately, does not include any |
2708 | C<ev_embeddable_backends> are, which, unfortunately, does not include any |
2452 | portable one. |
2709 | portable one. |
2453 | |
2710 | |
… | |
… | |
2547 | event loop blocks next and before C<ev_check> watchers are being called, |
2804 | event loop blocks next and before C<ev_check> watchers are being called, |
2548 | and only in the child after the fork. If whoever good citizen calling |
2805 | and only in the child after the fork. If whoever good citizen calling |
2549 | C<ev_default_fork> cheats and calls it in the wrong process, the fork |
2806 | C<ev_default_fork> cheats and calls it in the wrong process, the fork |
2550 | handlers will be invoked, too, of course. |
2807 | handlers will be invoked, too, of course. |
2551 | |
2808 | |
|
|
2809 | =head3 The special problem of life after fork - how is it possible? |
|
|
2810 | |
|
|
2811 | Most uses of C<fork()> consist of forking, then some simple calls to ste |
|
|
2812 | up/change the process environment, followed by a call to C<exec()>. This |
|
|
2813 | sequence should be handled by libev without any problems. |
|
|
2814 | |
|
|
2815 | This changes when the application actually wants to do event handling |
|
|
2816 | in the child, or both parent in child, in effect "continuing" after the |
|
|
2817 | fork. |
|
|
2818 | |
|
|
2819 | The default mode of operation (for libev, with application help to detect |
|
|
2820 | forks) is to duplicate all the state in the child, as would be expected |
|
|
2821 | when I<either> the parent I<or> the child process continues. |
|
|
2822 | |
|
|
2823 | When both processes want to continue using libev, then this is usually the |
|
|
2824 | wrong result. In that case, usually one process (typically the parent) is |
|
|
2825 | supposed to continue with all watchers in place as before, while the other |
|
|
2826 | process typically wants to start fresh, i.e. without any active watchers. |
|
|
2827 | |
|
|
2828 | The cleanest and most efficient way to achieve that with libev is to |
|
|
2829 | simply create a new event loop, which of course will be "empty", and |
|
|
2830 | use that for new watchers. This has the advantage of not touching more |
|
|
2831 | memory than necessary, and thus avoiding the copy-on-write, and the |
|
|
2832 | disadvantage of having to use multiple event loops (which do not support |
|
|
2833 | signal watchers). |
|
|
2834 | |
|
|
2835 | When this is not possible, or you want to use the default loop for |
|
|
2836 | other reasons, then in the process that wants to start "fresh", call |
|
|
2837 | C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying |
|
|
2838 | the default loop will "orphan" (not stop) all registered watchers, so you |
|
|
2839 | have to be careful not to execute code that modifies those watchers. Note |
|
|
2840 | also that in that case, you have to re-register any signal watchers. |
|
|
2841 | |
2552 | =head3 Watcher-Specific Functions and Data Members |
2842 | =head3 Watcher-Specific Functions and Data Members |
2553 | |
2843 | |
2554 | =over 4 |
2844 | =over 4 |
2555 | |
2845 | |
2556 | =item ev_fork_init (ev_signal *, callback) |
2846 | =item ev_fork_init (ev_signal *, callback) |
… | |
… | |
2684 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
2974 | an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
2685 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
2975 | C<ev_feed_event>, this call is safe to do from other threads, signal or |
2686 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
2976 | similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding |
2687 | section below on what exactly this means). |
2977 | section below on what exactly this means). |
2688 | |
2978 | |
|
|
2979 | Note that, as with other watchers in libev, multiple events might get |
|
|
2980 | compressed into a single callback invocation (another way to look at this |
|
|
2981 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
|
|
2982 | reset when the event loop detects that). |
|
|
2983 | |
2689 | This call incurs the overhead of a system call only once per loop iteration, |
2984 | This call incurs the overhead of a system call only once per event loop |
2690 | so while the overhead might be noticeable, it doesn't apply to repeated |
2985 | iteration, so while the overhead might be noticeable, it doesn't apply to |
2691 | calls to C<ev_async_send>. |
2986 | repeated calls to C<ev_async_send> for the same event loop. |
2692 | |
2987 | |
2693 | =item bool = ev_async_pending (ev_async *) |
2988 | =item bool = ev_async_pending (ev_async *) |
2694 | |
2989 | |
2695 | Returns a non-zero value when C<ev_async_send> has been called on the |
2990 | Returns a non-zero value when C<ev_async_send> has been called on the |
2696 | watcher but the event has not yet been processed (or even noted) by the |
2991 | watcher but the event has not yet been processed (or even noted) by the |
… | |
… | |
2699 | C<ev_async_send> sets a flag in the watcher and wakes up the loop. When |
2994 | C<ev_async_send> sets a flag in the watcher and wakes up the loop. When |
2700 | the loop iterates next and checks for the watcher to have become active, |
2995 | the loop iterates next and checks for the watcher to have become active, |
2701 | it will reset the flag again. C<ev_async_pending> can be used to very |
2996 | it will reset the flag again. C<ev_async_pending> can be used to very |
2702 | quickly check whether invoking the loop might be a good idea. |
2997 | quickly check whether invoking the loop might be a good idea. |
2703 | |
2998 | |
2704 | Not that this does I<not> check whether the watcher itself is pending, only |
2999 | Not that this does I<not> check whether the watcher itself is pending, |
2705 | whether it has been requested to make this watcher pending. |
3000 | only whether it has been requested to make this watcher pending: there |
|
|
3001 | is a time window between the event loop checking and resetting the async |
|
|
3002 | notification, and the callback being invoked. |
2706 | |
3003 | |
2707 | =back |
3004 | =back |
2708 | |
3005 | |
2709 | |
3006 | |
2710 | =head1 OTHER FUNCTIONS |
3007 | =head1 OTHER FUNCTIONS |
… | |
… | |
2889 | |
3186 | |
2890 | myclass obj; |
3187 | myclass obj; |
2891 | ev::io iow; |
3188 | ev::io iow; |
2892 | iow.set <myclass, &myclass::io_cb> (&obj); |
3189 | iow.set <myclass, &myclass::io_cb> (&obj); |
2893 | |
3190 | |
|
|
3191 | =item w->set (object *) |
|
|
3192 | |
|
|
3193 | This is an B<experimental> feature that might go away in a future version. |
|
|
3194 | |
|
|
3195 | This is a variation of a method callback - leaving out the method to call |
|
|
3196 | will default the method to C<operator ()>, which makes it possible to use |
|
|
3197 | functor objects without having to manually specify the C<operator ()> all |
|
|
3198 | the time. Incidentally, you can then also leave out the template argument |
|
|
3199 | list. |
|
|
3200 | |
|
|
3201 | The C<operator ()> method prototype must be C<void operator ()(watcher &w, |
|
|
3202 | int revents)>. |
|
|
3203 | |
|
|
3204 | See the method-C<set> above for more details. |
|
|
3205 | |
|
|
3206 | Example: use a functor object as callback. |
|
|
3207 | |
|
|
3208 | struct myfunctor |
|
|
3209 | { |
|
|
3210 | void operator() (ev::io &w, int revents) |
|
|
3211 | { |
|
|
3212 | ... |
|
|
3213 | } |
|
|
3214 | } |
|
|
3215 | |
|
|
3216 | myfunctor f; |
|
|
3217 | |
|
|
3218 | ev::io w; |
|
|
3219 | w.set (&f); |
|
|
3220 | |
2894 | =item w->set<function> (void *data = 0) |
3221 | =item w->set<function> (void *data = 0) |
2895 | |
3222 | |
2896 | Also sets a callback, but uses a static method or plain function as |
3223 | Also sets a callback, but uses a static method or plain function as |
2897 | callback. The optional C<data> argument will be stored in the watcher's |
3224 | callback. The optional C<data> argument will be stored in the watcher's |
2898 | C<data> member and is free for you to use. |
3225 | C<data> member and is free for you to use. |
… | |
… | |
2984 | L<http://software.schmorp.de/pkg/EV>. |
3311 | L<http://software.schmorp.de/pkg/EV>. |
2985 | |
3312 | |
2986 | =item Python |
3313 | =item Python |
2987 | |
3314 | |
2988 | Python bindings can be found at L<http://code.google.com/p/pyev/>. It |
3315 | Python bindings can be found at L<http://code.google.com/p/pyev/>. It |
2989 | seems to be quite complete and well-documented. Note, however, that the |
3316 | seems to be quite complete and well-documented. |
2990 | patch they require for libev is outright dangerous as it breaks the ABI |
|
|
2991 | for everybody else, and therefore, should never be applied in an installed |
|
|
2992 | libev (if python requires an incompatible ABI then it needs to embed |
|
|
2993 | libev). |
|
|
2994 | |
3317 | |
2995 | =item Ruby |
3318 | =item Ruby |
2996 | |
3319 | |
2997 | Tony Arcieri has written a ruby extension that offers access to a subset |
3320 | Tony Arcieri has written a ruby extension that offers access to a subset |
2998 | of the libev API and adds file handle abstractions, asynchronous DNS and |
3321 | of the libev API and adds file handle abstractions, asynchronous DNS and |
2999 | more on top of it. It can be found via gem servers. Its homepage is at |
3322 | more on top of it. It can be found via gem servers. Its homepage is at |
3000 | L<http://rev.rubyforge.org/>. |
3323 | L<http://rev.rubyforge.org/>. |
|
|
3324 | |
|
|
3325 | Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190> |
|
|
3326 | makes rev work even on mingw. |
|
|
3327 | |
|
|
3328 | =item Haskell |
|
|
3329 | |
|
|
3330 | A haskell binding to libev is available at |
|
|
3331 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
3001 | |
3332 | |
3002 | =item D |
3333 | =item D |
3003 | |
3334 | |
3004 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
3335 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
3005 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
3336 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
… | |
… | |
3182 | keeps libev from including F<config.h>, and it also defines dummy |
3513 | keeps libev from including F<config.h>, and it also defines dummy |
3183 | implementations for some libevent functions (such as logging, which is not |
3514 | implementations for some libevent functions (such as logging, which is not |
3184 | supported). It will also not define any of the structs usually found in |
3515 | supported). It will also not define any of the structs usually found in |
3185 | F<event.h> that are not directly supported by the libev core alone. |
3516 | F<event.h> that are not directly supported by the libev core alone. |
3186 | |
3517 | |
|
|
3518 | In stanbdalone mode, libev will still try to automatically deduce the |
|
|
3519 | configuration, but has to be more conservative. |
|
|
3520 | |
3187 | =item EV_USE_MONOTONIC |
3521 | =item EV_USE_MONOTONIC |
3188 | |
3522 | |
3189 | If defined to be C<1>, libev will try to detect the availability of the |
3523 | If defined to be C<1>, libev will try to detect the availability of the |
3190 | monotonic clock option at both compile time and runtime. Otherwise no use |
3524 | monotonic clock option at both compile time and runtime. Otherwise no |
3191 | of the monotonic clock option will be attempted. If you enable this, you |
3525 | use of the monotonic clock option will be attempted. If you enable this, |
3192 | usually have to link against librt or something similar. Enabling it when |
3526 | you usually have to link against librt or something similar. Enabling it |
3193 | the functionality isn't available is safe, though, although you have |
3527 | when the functionality isn't available is safe, though, although you have |
3194 | to make sure you link against any libraries where the C<clock_gettime> |
3528 | to make sure you link against any libraries where the C<clock_gettime> |
3195 | function is hiding in (often F<-lrt>). |
3529 | function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>. |
3196 | |
3530 | |
3197 | =item EV_USE_REALTIME |
3531 | =item EV_USE_REALTIME |
3198 | |
3532 | |
3199 | If defined to be C<1>, libev will try to detect the availability of the |
3533 | If defined to be C<1>, libev will try to detect the availability of the |
3200 | real-time clock option at compile time (and assume its availability at |
3534 | real-time clock option at compile time (and assume its availability |
3201 | runtime if successful). Otherwise no use of the real-time clock option will |
3535 | at runtime if successful). Otherwise no use of the real-time clock |
3202 | be attempted. This effectively replaces C<gettimeofday> by C<clock_get |
3536 | option will be attempted. This effectively replaces C<gettimeofday> |
3203 | (CLOCK_REALTIME, ...)> and will not normally affect correctness. See the |
3537 | by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect |
3204 | note about libraries in the description of C<EV_USE_MONOTONIC>, though. |
3538 | correctness. See the note about libraries in the description of |
|
|
3539 | C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of |
|
|
3540 | C<EV_USE_CLOCK_SYSCALL>. |
|
|
3541 | |
|
|
3542 | =item EV_USE_CLOCK_SYSCALL |
|
|
3543 | |
|
|
3544 | If defined to be C<1>, libev will try to use a direct syscall instead |
|
|
3545 | of calling the system-provided C<clock_gettime> function. This option |
|
|
3546 | exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt> |
|
|
3547 | unconditionally pulls in C<libpthread>, slowing down single-threaded |
|
|
3548 | programs needlessly. Using a direct syscall is slightly slower (in |
|
|
3549 | theory), because no optimised vdso implementation can be used, but avoids |
|
|
3550 | the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or |
|
|
3551 | higher, as it simplifies linking (no need for C<-lrt>). |
3205 | |
3552 | |
3206 | =item EV_USE_NANOSLEEP |
3553 | =item EV_USE_NANOSLEEP |
3207 | |
3554 | |
3208 | If defined to be C<1>, libev will assume that C<nanosleep ()> is available |
3555 | If defined to be C<1>, libev will assume that C<nanosleep ()> is available |
3209 | and will use it for delays. Otherwise it will use C<select ()>. |
3556 | and will use it for delays. Otherwise it will use C<select ()>. |
… | |
… | |
3225 | |
3572 | |
3226 | =item EV_SELECT_USE_FD_SET |
3573 | =item EV_SELECT_USE_FD_SET |
3227 | |
3574 | |
3228 | If defined to C<1>, then the select backend will use the system C<fd_set> |
3575 | If defined to C<1>, then the select backend will use the system C<fd_set> |
3229 | structure. This is useful if libev doesn't compile due to a missing |
3576 | structure. This is useful if libev doesn't compile due to a missing |
3230 | C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on |
3577 | C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout |
3231 | exotic systems. This usually limits the range of file descriptors to some |
3578 | on exotic systems. This usually limits the range of file descriptors to |
3232 | low limit such as 1024 or might have other limitations (winsocket only |
3579 | some low limit such as 1024 or might have other limitations (winsocket |
3233 | allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might |
3580 | only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, |
3234 | influence the size of the C<fd_set> used. |
3581 | configures the maximum size of the C<fd_set>. |
3235 | |
3582 | |
3236 | =item EV_SELECT_IS_WINSOCKET |
3583 | =item EV_SELECT_IS_WINSOCKET |
3237 | |
3584 | |
3238 | When defined to C<1>, the select backend will assume that |
3585 | When defined to C<1>, the select backend will assume that |
3239 | select/socket/connect etc. don't understand file descriptors but |
3586 | select/socket/connect etc. don't understand file descriptors but |
… | |
… | |
3389 | defined to be C<0>, then they are not. |
3736 | defined to be C<0>, then they are not. |
3390 | |
3737 | |
3391 | =item EV_MINIMAL |
3738 | =item EV_MINIMAL |
3392 | |
3739 | |
3393 | If you need to shave off some kilobytes of code at the expense of some |
3740 | If you need to shave off some kilobytes of code at the expense of some |
3394 | speed, define this symbol to C<1>. Currently this is used to override some |
3741 | speed (but with the full API), define this symbol to C<1>. Currently this |
3395 | inlining decisions, saves roughly 30% code size on amd64. It also selects a |
3742 | is used to override some inlining decisions, saves roughly 30% code size |
3396 | much smaller 2-heap for timer management over the default 4-heap. |
3743 | on amd64. It also selects a much smaller 2-heap for timer management over |
|
|
3744 | the default 4-heap. |
|
|
3745 | |
|
|
3746 | You can save even more by disabling watcher types you do not need |
|
|
3747 | and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert> |
|
|
3748 | (C<-DNDEBUG>) will usually reduce code size a lot. |
|
|
3749 | |
|
|
3750 | Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to |
|
|
3751 | provide a bare-bones event library. See C<ev.h> for details on what parts |
|
|
3752 | of the API are still available, and do not complain if this subset changes |
|
|
3753 | over time. |
3397 | |
3754 | |
3398 | =item EV_PID_HASHSIZE |
3755 | =item EV_PID_HASHSIZE |
3399 | |
3756 | |
3400 | C<ev_child> watchers use a small hash table to distribute workload by |
3757 | C<ev_child> watchers use a small hash table to distribute workload by |
3401 | pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more |
3758 | pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more |
… | |
… | |
3587 | default loop and triggering an C<ev_async> watcher from the default loop |
3944 | default loop and triggering an C<ev_async> watcher from the default loop |
3588 | watcher callback into the event loop interested in the signal. |
3945 | watcher callback into the event loop interested in the signal. |
3589 | |
3946 | |
3590 | =back |
3947 | =back |
3591 | |
3948 | |
|
|
3949 | =head4 THREAD LOCKING EXAMPLE |
|
|
3950 | |
|
|
3951 | Here is a fictitious example of how to run an event loop in a different |
|
|
3952 | thread than where callbacks are being invoked and watchers are |
|
|
3953 | created/added/removed. |
|
|
3954 | |
|
|
3955 | For a real-world example, see the C<EV::Loop::Async> perl module, |
|
|
3956 | which uses exactly this technique (which is suited for many high-level |
|
|
3957 | languages). |
|
|
3958 | |
|
|
3959 | The example uses a pthread mutex to protect the loop data, a condition |
|
|
3960 | variable to wait for callback invocations, an async watcher to notify the |
|
|
3961 | event loop thread and an unspecified mechanism to wake up the main thread. |
|
|
3962 | |
|
|
3963 | First, you need to associate some data with the event loop: |
|
|
3964 | |
|
|
3965 | typedef struct { |
|
|
3966 | mutex_t lock; /* global loop lock */ |
|
|
3967 | ev_async async_w; |
|
|
3968 | thread_t tid; |
|
|
3969 | cond_t invoke_cv; |
|
|
3970 | } userdata; |
|
|
3971 | |
|
|
3972 | void prepare_loop (EV_P) |
|
|
3973 | { |
|
|
3974 | // for simplicity, we use a static userdata struct. |
|
|
3975 | static userdata u; |
|
|
3976 | |
|
|
3977 | ev_async_init (&u->async_w, async_cb); |
|
|
3978 | ev_async_start (EV_A_ &u->async_w); |
|
|
3979 | |
|
|
3980 | pthread_mutex_init (&u->lock, 0); |
|
|
3981 | pthread_cond_init (&u->invoke_cv, 0); |
|
|
3982 | |
|
|
3983 | // now associate this with the loop |
|
|
3984 | ev_set_userdata (EV_A_ u); |
|
|
3985 | ev_set_invoke_pending_cb (EV_A_ l_invoke); |
|
|
3986 | ev_set_loop_release_cb (EV_A_ l_release, l_acquire); |
|
|
3987 | |
|
|
3988 | // then create the thread running ev_loop |
|
|
3989 | pthread_create (&u->tid, 0, l_run, EV_A); |
|
|
3990 | } |
|
|
3991 | |
|
|
3992 | The callback for the C<ev_async> watcher does nothing: the watcher is used |
|
|
3993 | solely to wake up the event loop so it takes notice of any new watchers |
|
|
3994 | that might have been added: |
|
|
3995 | |
|
|
3996 | static void |
|
|
3997 | async_cb (EV_P_ ev_async *w, int revents) |
|
|
3998 | { |
|
|
3999 | // just used for the side effects |
|
|
4000 | } |
|
|
4001 | |
|
|
4002 | The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex |
|
|
4003 | protecting the loop data, respectively. |
|
|
4004 | |
|
|
4005 | static void |
|
|
4006 | l_release (EV_P) |
|
|
4007 | { |
|
|
4008 | userdata *u = ev_userdata (EV_A); |
|
|
4009 | pthread_mutex_unlock (&u->lock); |
|
|
4010 | } |
|
|
4011 | |
|
|
4012 | static void |
|
|
4013 | l_acquire (EV_P) |
|
|
4014 | { |
|
|
4015 | userdata *u = ev_userdata (EV_A); |
|
|
4016 | pthread_mutex_lock (&u->lock); |
|
|
4017 | } |
|
|
4018 | |
|
|
4019 | The event loop thread first acquires the mutex, and then jumps straight |
|
|
4020 | into C<ev_loop>: |
|
|
4021 | |
|
|
4022 | void * |
|
|
4023 | l_run (void *thr_arg) |
|
|
4024 | { |
|
|
4025 | struct ev_loop *loop = (struct ev_loop *)thr_arg; |
|
|
4026 | |
|
|
4027 | l_acquire (EV_A); |
|
|
4028 | pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); |
|
|
4029 | ev_loop (EV_A_ 0); |
|
|
4030 | l_release (EV_A); |
|
|
4031 | |
|
|
4032 | return 0; |
|
|
4033 | } |
|
|
4034 | |
|
|
4035 | Instead of invoking all pending watchers, the C<l_invoke> callback will |
|
|
4036 | signal the main thread via some unspecified mechanism (signals? pipe |
|
|
4037 | writes? C<Async::Interrupt>?) and then waits until all pending watchers |
|
|
4038 | have been called (in a while loop because a) spurious wakeups are possible |
|
|
4039 | and b) skipping inter-thread-communication when there are no pending |
|
|
4040 | watchers is very beneficial): |
|
|
4041 | |
|
|
4042 | static void |
|
|
4043 | l_invoke (EV_P) |
|
|
4044 | { |
|
|
4045 | userdata *u = ev_userdata (EV_A); |
|
|
4046 | |
|
|
4047 | while (ev_pending_count (EV_A)) |
|
|
4048 | { |
|
|
4049 | wake_up_other_thread_in_some_magic_or_not_so_magic_way (); |
|
|
4050 | pthread_cond_wait (&u->invoke_cv, &u->lock); |
|
|
4051 | } |
|
|
4052 | } |
|
|
4053 | |
|
|
4054 | Now, whenever the main thread gets told to invoke pending watchers, it |
|
|
4055 | will grab the lock, call C<ev_invoke_pending> and then signal the loop |
|
|
4056 | thread to continue: |
|
|
4057 | |
|
|
4058 | static void |
|
|
4059 | real_invoke_pending (EV_P) |
|
|
4060 | { |
|
|
4061 | userdata *u = ev_userdata (EV_A); |
|
|
4062 | |
|
|
4063 | pthread_mutex_lock (&u->lock); |
|
|
4064 | ev_invoke_pending (EV_A); |
|
|
4065 | pthread_cond_signal (&u->invoke_cv); |
|
|
4066 | pthread_mutex_unlock (&u->lock); |
|
|
4067 | } |
|
|
4068 | |
|
|
4069 | Whenever you want to start/stop a watcher or do other modifications to an |
|
|
4070 | event loop, you will now have to lock: |
|
|
4071 | |
|
|
4072 | ev_timer timeout_watcher; |
|
|
4073 | userdata *u = ev_userdata (EV_A); |
|
|
4074 | |
|
|
4075 | ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
|
|
4076 | |
|
|
4077 | pthread_mutex_lock (&u->lock); |
|
|
4078 | ev_timer_start (EV_A_ &timeout_watcher); |
|
|
4079 | ev_async_send (EV_A_ &u->async_w); |
|
|
4080 | pthread_mutex_unlock (&u->lock); |
|
|
4081 | |
|
|
4082 | Note that sending the C<ev_async> watcher is required because otherwise |
|
|
4083 | an event loop currently blocking in the kernel will have no knowledge |
|
|
4084 | about the newly added timer. By waking up the loop it will pick up any new |
|
|
4085 | watchers in the next event loop iteration. |
|
|
4086 | |
3592 | =head3 COROUTINES |
4087 | =head3 COROUTINES |
3593 | |
4088 | |
3594 | Libev is very accommodating to coroutines ("cooperative threads"): |
4089 | Libev is very accommodating to coroutines ("cooperative threads"): |
3595 | libev fully supports nesting calls to its functions from different |
4090 | libev fully supports nesting calls to its functions from different |
3596 | coroutines (e.g. you can call C<ev_loop> on the same loop from two |
4091 | coroutines (e.g. you can call C<ev_loop> on the same loop from two |
3597 | different coroutines, and switch freely between both coroutines running the |
4092 | different coroutines, and switch freely between both coroutines running |
3598 | loop, as long as you don't confuse yourself). The only exception is that |
4093 | the loop, as long as you don't confuse yourself). The only exception is |
3599 | you must not do this from C<ev_periodic> reschedule callbacks. |
4094 | that you must not do this from C<ev_periodic> reschedule callbacks. |
3600 | |
4095 | |
3601 | Care has been taken to ensure that libev does not keep local state inside |
4096 | Care has been taken to ensure that libev does not keep local state inside |
3602 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
4097 | C<ev_loop>, and other calls do not usually allow for coroutine switches as |
3603 | they do not call any callbacks. |
4098 | they do not call any callbacks. |
3604 | |
4099 | |
… | |
… | |
3681 | way (note also that glib is the slowest event library known to man). |
4176 | way (note also that glib is the slowest event library known to man). |
3682 | |
4177 | |
3683 | There is no supported compilation method available on windows except |
4178 | There is no supported compilation method available on windows except |
3684 | embedding it into other applications. |
4179 | embedding it into other applications. |
3685 | |
4180 | |
|
|
4181 | Sensible signal handling is officially unsupported by Microsoft - libev |
|
|
4182 | tries its best, but under most conditions, signals will simply not work. |
|
|
4183 | |
3686 | Not a libev limitation but worth mentioning: windows apparently doesn't |
4184 | Not a libev limitation but worth mentioning: windows apparently doesn't |
3687 | accept large writes: instead of resulting in a partial write, windows will |
4185 | accept large writes: instead of resulting in a partial write, windows will |
3688 | either accept everything or return C<ENOBUFS> if the buffer is too large, |
4186 | either accept everything or return C<ENOBUFS> if the buffer is too large, |
3689 | so make sure you only write small amounts into your sockets (less than a |
4187 | so make sure you only write small amounts into your sockets (less than a |
3690 | megabyte seems safe, but this apparently depends on the amount of memory |
4188 | megabyte seems safe, but this apparently depends on the amount of memory |
… | |
… | |
3694 | the abysmal performance of winsockets, using a large number of sockets |
4192 | the abysmal performance of winsockets, using a large number of sockets |
3695 | is not recommended (and not reasonable). If your program needs to use |
4193 | is not recommended (and not reasonable). If your program needs to use |
3696 | more than a hundred or so sockets, then likely it needs to use a totally |
4194 | more than a hundred or so sockets, then likely it needs to use a totally |
3697 | different implementation for windows, as libev offers the POSIX readiness |
4195 | different implementation for windows, as libev offers the POSIX readiness |
3698 | notification model, which cannot be implemented efficiently on windows |
4196 | notification model, which cannot be implemented efficiently on windows |
3699 | (Microsoft monopoly games). |
4197 | (due to Microsoft monopoly games). |
3700 | |
4198 | |
3701 | A typical way to use libev under windows is to embed it (see the embedding |
4199 | A typical way to use libev under windows is to embed it (see the embedding |
3702 | section for details) and use the following F<evwrap.h> header file instead |
4200 | section for details) and use the following F<evwrap.h> header file instead |
3703 | of F<ev.h>: |
4201 | of F<ev.h>: |
3704 | |
4202 | |
… | |
… | |
3740 | |
4238 | |
3741 | Early versions of winsocket's select only supported waiting for a maximum |
4239 | Early versions of winsocket's select only supported waiting for a maximum |
3742 | of C<64> handles (probably owning to the fact that all windows kernels |
4240 | of C<64> handles (probably owning to the fact that all windows kernels |
3743 | can only wait for C<64> things at the same time internally; Microsoft |
4241 | can only wait for C<64> things at the same time internally; Microsoft |
3744 | recommends spawning a chain of threads and wait for 63 handles and the |
4242 | recommends spawning a chain of threads and wait for 63 handles and the |
3745 | previous thread in each. Great). |
4243 | previous thread in each. Sounds great!). |
3746 | |
4244 | |
3747 | Newer versions support more handles, but you need to define C<FD_SETSIZE> |
4245 | Newer versions support more handles, but you need to define C<FD_SETSIZE> |
3748 | to some high number (e.g. C<2048>) before compiling the winsocket select |
4246 | to some high number (e.g. C<2048>) before compiling the winsocket select |
3749 | call (which might be in libev or elsewhere, for example, perl does its own |
4247 | call (which might be in libev or elsewhere, for example, perl and many |
3750 | select emulation on windows). |
4248 | other interpreters do their own select emulation on windows). |
3751 | |
4249 | |
3752 | Another limit is the number of file descriptors in the Microsoft runtime |
4250 | Another limit is the number of file descriptors in the Microsoft runtime |
3753 | libraries, which by default is C<64> (there must be a hidden I<64> fetish |
4251 | libraries, which by default is C<64> (there must be a hidden I<64> |
3754 | or something like this inside Microsoft). You can increase this by calling |
4252 | fetish or something like this inside Microsoft). You can increase this |
3755 | C<_setmaxstdio>, which can increase this limit to C<2048> (another |
4253 | by calling C<_setmaxstdio>, which can increase this limit to C<2048> |
3756 | arbitrary limit), but is broken in many versions of the Microsoft runtime |
4254 | (another arbitrary limit), but is broken in many versions of the Microsoft |
3757 | libraries. |
|
|
3758 | |
|
|
3759 | This might get you to about C<512> or C<2048> sockets (depending on |
4255 | runtime libraries. This might get you to about C<512> or C<2048> sockets |
3760 | windows version and/or the phase of the moon). To get more, you need to |
4256 | (depending on windows version and/or the phase of the moon). To get more, |
3761 | wrap all I/O functions and provide your own fd management, but the cost of |
4257 | you need to wrap all I/O functions and provide your own fd management, but |
3762 | calling select (O(n²)) will likely make this unworkable. |
4258 | the cost of calling select (O(n²)) will likely make this unworkable. |
3763 | |
4259 | |
3764 | =back |
4260 | =back |
3765 | |
4261 | |
3766 | =head2 PORTABILITY REQUIREMENTS |
4262 | =head2 PORTABILITY REQUIREMENTS |
3767 | |
4263 | |
… | |
… | |
3810 | =item C<double> must hold a time value in seconds with enough accuracy |
4306 | =item C<double> must hold a time value in seconds with enough accuracy |
3811 | |
4307 | |
3812 | The type C<double> is used to represent timestamps. It is required to |
4308 | The type C<double> is used to represent timestamps. It is required to |
3813 | have at least 51 bits of mantissa (and 9 bits of exponent), which is good |
4309 | have at least 51 bits of mantissa (and 9 bits of exponent), which is good |
3814 | enough for at least into the year 4000. This requirement is fulfilled by |
4310 | enough for at least into the year 4000. This requirement is fulfilled by |
3815 | implementations implementing IEEE 754 (basically all existing ones). |
4311 | implementations implementing IEEE 754, which is basically all existing |
|
|
4312 | ones. With IEEE 754 doubles, you get microsecond accuracy until at least |
|
|
4313 | 2200. |
3816 | |
4314 | |
3817 | =back |
4315 | =back |
3818 | |
4316 | |
3819 | If you know of other additional requirements drop me a note. |
4317 | If you know of other additional requirements drop me a note. |
3820 | |
4318 | |
… | |
… | |
3888 | involves iterating over all running async watchers or all signal numbers. |
4386 | involves iterating over all running async watchers or all signal numbers. |
3889 | |
4387 | |
3890 | =back |
4388 | =back |
3891 | |
4389 | |
3892 | |
4390 | |
|
|
4391 | =head1 GLOSSARY |
|
|
4392 | |
|
|
4393 | =over 4 |
|
|
4394 | |
|
|
4395 | =item active |
|
|
4396 | |
|
|
4397 | A watcher is active as long as it has been started (has been attached to |
|
|
4398 | an event loop) but not yet stopped (disassociated from the event loop). |
|
|
4399 | |
|
|
4400 | =item application |
|
|
4401 | |
|
|
4402 | In this document, an application is whatever is using libev. |
|
|
4403 | |
|
|
4404 | =item callback |
|
|
4405 | |
|
|
4406 | The address of a function that is called when some event has been |
|
|
4407 | detected. Callbacks are being passed the event loop, the watcher that |
|
|
4408 | received the event, and the actual event bitset. |
|
|
4409 | |
|
|
4410 | =item callback invocation |
|
|
4411 | |
|
|
4412 | The act of calling the callback associated with a watcher. |
|
|
4413 | |
|
|
4414 | =item event |
|
|
4415 | |
|
|
4416 | A change of state of some external event, such as data now being available |
|
|
4417 | for reading on a file descriptor, time having passed or simply not having |
|
|
4418 | any other events happening anymore. |
|
|
4419 | |
|
|
4420 | In libev, events are represented as single bits (such as C<EV_READ> or |
|
|
4421 | C<EV_TIMEOUT>). |
|
|
4422 | |
|
|
4423 | =item event library |
|
|
4424 | |
|
|
4425 | A software package implementing an event model and loop. |
|
|
4426 | |
|
|
4427 | =item event loop |
|
|
4428 | |
|
|
4429 | An entity that handles and processes external events and converts them |
|
|
4430 | into callback invocations. |
|
|
4431 | |
|
|
4432 | =item event model |
|
|
4433 | |
|
|
4434 | The model used to describe how an event loop handles and processes |
|
|
4435 | watchers and events. |
|
|
4436 | |
|
|
4437 | =item pending |
|
|
4438 | |
|
|
4439 | A watcher is pending as soon as the corresponding event has been detected, |
|
|
4440 | and stops being pending as soon as the watcher will be invoked or its |
|
|
4441 | pending status is explicitly cleared by the application. |
|
|
4442 | |
|
|
4443 | A watcher can be pending, but not active. Stopping a watcher also clears |
|
|
4444 | its pending status. |
|
|
4445 | |
|
|
4446 | =item real time |
|
|
4447 | |
|
|
4448 | The physical time that is observed. It is apparently strictly monotonic :) |
|
|
4449 | |
|
|
4450 | =item wall-clock time |
|
|
4451 | |
|
|
4452 | The time and date as shown on clocks. Unlike real time, it can actually |
|
|
4453 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
|
|
4454 | clock. |
|
|
4455 | |
|
|
4456 | =item watcher |
|
|
4457 | |
|
|
4458 | A data structure that describes interest in certain events. Watchers need |
|
|
4459 | to be started (attached to an event loop) before they can receive events. |
|
|
4460 | |
|
|
4461 | =item watcher invocation |
|
|
4462 | |
|
|
4463 | The act of calling the callback associated with a watcher. |
|
|
4464 | |
|
|
4465 | =back |
|
|
4466 | |
3893 | =head1 AUTHOR |
4467 | =head1 AUTHOR |
3894 | |
4468 | |
3895 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4469 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
3896 | |
4470 | |