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Revision 1.33 by root, Fri Nov 23 15:26:08 2007 UTC vs.
Revision 1.36 by root, Sat Nov 24 07:14:26 2007 UTC

45 45
46Libev represents time as a single floating point number, representing the 46Libev represents time as a single floating point number, representing the
47(fractional) number of seconds since the (POSIX) epoch (somewhere near 47(fractional) number of seconds since the (POSIX) epoch (somewhere near
48the beginning of 1970, details are complicated, don't ask). This type is 48the beginning of 1970, details are complicated, don't ask). This type is
49called C<ev_tstamp>, which is what you should use too. It usually aliases 49called C<ev_tstamp>, which is what you should use too. It usually aliases
50to the double type in C. 50to the C<double> type in C, and when you need to do any calculations on
51it, you should treat it as such.
52
51 53
52=head1 GLOBAL FUNCTIONS 54=head1 GLOBAL FUNCTIONS
53 55
54These functions can be called anytime, even before initialising the 56These functions can be called anytime, even before initialising the
55library in any way. 57library in any way.
75Usually, it's a good idea to terminate if the major versions mismatch, 77Usually, it's a good idea to terminate if the major versions mismatch,
76as this indicates an incompatible change. Minor versions are usually 78as this indicates an incompatible change. Minor versions are usually
77compatible to older versions, so a larger minor version alone is usually 79compatible to older versions, so a larger minor version alone is usually
78not a problem. 80not a problem.
79 81
82Example: make sure we haven't accidentally been linked against the wrong
83version:
84
85 assert (("libev version mismatch",
86 ev_version_major () == EV_VERSION_MAJOR
87 && ev_version_minor () >= EV_VERSION_MINOR));
88
80=item unsigned int ev_supported_backends () 89=item unsigned int ev_supported_backends ()
81 90
82Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*> 91Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
83value) compiled into this binary of libev (independent of their 92value) compiled into this binary of libev (independent of their
84availability on the system you are running on). See C<ev_default_loop> for 93availability on the system you are running on). See C<ev_default_loop> for
85a description of the set values. 94a description of the set values.
95
96Example: make sure we have the epoll method, because yeah this is cool and
97a must have and can we have a torrent of it please!!!11
98
99 assert (("sorry, no epoll, no sex",
100 ev_supported_backends () & EVBACKEND_EPOLL));
86 101
87=item unsigned int ev_recommended_backends () 102=item unsigned int ev_recommended_backends ()
88 103
89Return the set of all backends compiled into this binary of libev and also 104Return the set of all backends compiled into this binary of libev and also
90recommended for this platform. This set is often smaller than the one 105recommended for this platform. This set is often smaller than the one
91returned by C<ev_supported_backends>, as for example kqueue is broken on 106returned by C<ev_supported_backends>, as for example kqueue is broken on
92most BSDs and will not be autodetected unless you explicitly request it 107most BSDs and will not be autodetected unless you explicitly request it
93(assuming you know what you are doing). This is the set of backends that 108(assuming you know what you are doing). This is the set of backends that
94libev will probe for if you specify no backends explicitly. 109libev will probe for if you specify no backends explicitly.
95 110
111=item unsigned int ev_embeddable_backends ()
112
113Returns the set of backends that are embeddable in other event loops. This
114is the theoretical, all-platform, value. To find which backends
115might be supported on the current system, you would need to look at
116C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
117recommended ones.
118
119See the description of C<ev_embed> watchers for more info.
120
96=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 121=item ev_set_allocator (void *(*cb)(void *ptr, long size))
97 122
98Sets the allocation function to use (the prototype is similar to the 123Sets the allocation function to use (the prototype is similar to the
99realloc C function, the semantics are identical). It is used to allocate 124realloc C function, the semantics are identical). It is used to allocate
100and free memory (no surprises here). If it returns zero when memory 125and free memory (no surprises here). If it returns zero when memory
102destructive action. The default is your system realloc function. 127destructive action. The default is your system realloc function.
103 128
104You could override this function in high-availability programs to, say, 129You could override this function in high-availability programs to, say,
105free some memory if it cannot allocate memory, to use a special allocator, 130free some memory if it cannot allocate memory, to use a special allocator,
106or even to sleep a while and retry until some memory is available. 131or even to sleep a while and retry until some memory is available.
132
133Example: replace the libev allocator with one that waits a bit and then
134retries: better than mine).
135
136 static void *
137 persistent_realloc (void *ptr, long size)
138 {
139 for (;;)
140 {
141 void *newptr = realloc (ptr, size);
142
143 if (newptr)
144 return newptr;
145
146 sleep (60);
147 }
148 }
149
150 ...
151 ev_set_allocator (persistent_realloc);
107 152
108=item ev_set_syserr_cb (void (*cb)(const char *msg)); 153=item ev_set_syserr_cb (void (*cb)(const char *msg));
109 154
110Set the callback function to call on a retryable syscall error (such 155Set the callback function to call on a retryable syscall error (such
111as failed select, poll, epoll_wait). The message is a printable string 156as failed select, poll, epoll_wait). The message is a printable string
113callback is set, then libev will expect it to remedy the sitution, no 158callback is set, then libev will expect it to remedy the sitution, no
114matter what, when it returns. That is, libev will generally retry the 159matter what, when it returns. That is, libev will generally retry the
115requested operation, or, if the condition doesn't go away, do bad stuff 160requested operation, or, if the condition doesn't go away, do bad stuff
116(such as abort). 161(such as abort).
117 162
163Example: do the same thing as libev does internally:
164
165 static void
166 fatal_error (const char *msg)
167 {
168 perror (msg);
169 abort ();
170 }
171
172 ...
173 ev_set_syserr_cb (fatal_error);
174
118=back 175=back
119 176
120=head1 FUNCTIONS CONTROLLING THE EVENT LOOP 177=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
121 178
122An event loop is described by a C<struct ev_loop *>. The library knows two 179An event loop is described by a C<struct ev_loop *>. The library knows two
257Similar to C<ev_default_loop>, but always creates a new event loop that is 314Similar to C<ev_default_loop>, but always creates a new event loop that is
258always distinct from the default loop. Unlike the default loop, it cannot 315always distinct from the default loop. Unlike the default loop, it cannot
259handle signal and child watchers, and attempts to do so will be greeted by 316handle signal and child watchers, and attempts to do so will be greeted by
260undefined behaviour (or a failed assertion if assertions are enabled). 317undefined behaviour (or a failed assertion if assertions are enabled).
261 318
319Example: try to create a event loop that uses epoll and nothing else.
320
321 struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322 if (!epoller)
323 fatal ("no epoll found here, maybe it hides under your chair");
324
262=item ev_default_destroy () 325=item ev_default_destroy ()
263 326
264Destroys the default loop again (frees all memory and kernel state 327Destroys the default loop again (frees all memory and kernel state
265etc.). This stops all registered event watchers (by not touching them in 328etc.). This stops all registered event watchers (by not touching them in
266any way whatsoever, although you cannot rely on this :). 329any way whatsoever, although you cannot rely on this :).
303use. 366use.
304 367
305=item ev_tstamp ev_now (loop) 368=item ev_tstamp ev_now (loop)
306 369
307Returns the current "event loop time", which is the time the event loop 370Returns the current "event loop time", which is the time the event loop
308got events and started processing them. This timestamp does not change 371received events and started processing them. This timestamp does not
309as long as callbacks are being processed, and this is also the base time 372change as long as callbacks are being processed, and this is also the base
310used for relative timers. You can treat it as the timestamp of the event 373time used for relative timers. You can treat it as the timestamp of the
311occuring (or more correctly, the mainloop finding out about it). 374event occuring (or more correctly, libev finding out about it).
312 375
313=item ev_loop (loop, int flags) 376=item ev_loop (loop, int flags)
314 377
315Finally, this is it, the event handler. This function usually is called 378Finally, this is it, the event handler. This function usually is called
316after you initialised all your watchers and you want to start handling 379after you initialised all your watchers and you want to start handling
317events. 380events.
318 381
319If the flags argument is specified as C<0>, it will not return until 382If the flags argument is specified as C<0>, it will not return until
320either no event watchers are active anymore or C<ev_unloop> was called. 383either no event watchers are active anymore or C<ev_unloop> was called.
384
385Please note that an explicit C<ev_unloop> is usually better than
386relying on all watchers to be stopped when deciding when a program has
387finished (especially in interactive programs), but having a program that
388automatically loops as long as it has to and no longer by virtue of
389relying on its watchers stopping correctly is a thing of beauty.
321 390
322A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle 391A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
323those events and any outstanding ones, but will not block your process in 392those events and any outstanding ones, but will not block your process in
324case there are no events and will return after one iteration of the loop. 393case there are no events and will return after one iteration of the loop.
325 394
350 Signals and child watchers are implemented as I/O watchers, and will 419 Signals and child watchers are implemented as I/O watchers, and will
351 be handled here by queueing them when their watcher gets executed. 420 be handled here by queueing them when their watcher gets executed.
352 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 421 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
353 were used, return, otherwise continue with step *. 422 were used, return, otherwise continue with step *.
354 423
424Example: queue some jobs and then loop until no events are outsanding
425anymore.
426
427 ... queue jobs here, make sure they register event watchers as long
428 ... as they still have work to do (even an idle watcher will do..)
429 ev_loop (my_loop, 0);
430 ... jobs done. yeah!
431
355=item ev_unloop (loop, how) 432=item ev_unloop (loop, how)
356 433
357Can be used to make a call to C<ev_loop> return early (but only after it 434Can be used to make a call to C<ev_loop> return early (but only after it
358has processed all outstanding events). The C<how> argument must be either 435has processed all outstanding events). The C<how> argument must be either
359C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or 436C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
372visible to the libev user and should not keep C<ev_loop> from exiting if 449visible to the libev user and should not keep C<ev_loop> from exiting if
373no event watchers registered by it are active. It is also an excellent 450no event watchers registered by it are active. It is also an excellent
374way to do this for generic recurring timers or from within third-party 451way to do this for generic recurring timers or from within third-party
375libraries. Just remember to I<unref after start> and I<ref before stop>. 452libraries. Just remember to I<unref after start> and I<ref before stop>.
376 453
454Example: create a signal watcher, but keep it from keeping C<ev_loop>
455running when nothing else is active.
456
457 struct dv_signal exitsig;
458 ev_signal_init (&exitsig, sig_cb, SIGINT);
459 ev_signal_start (myloop, &exitsig);
460 evf_unref (myloop);
461
462Example: for some weird reason, unregister the above signal handler again.
463
464 ev_ref (myloop);
465 ev_signal_stop (myloop, &exitsig);
466
377=back 467=back
378 468
379=head1 ANATOMY OF A WATCHER 469=head1 ANATOMY OF A WATCHER
380 470
381A watcher is a structure that you create and register to record your 471A watcher is a structure that you create and register to record your
415*) >>), and you can stop watching for events at any time by calling the 505*) >>), and you can stop watching for events at any time by calling the
416corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. 506corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
417 507
418As long as your watcher is active (has been started but not stopped) you 508As long as your watcher is active (has been started but not stopped) you
419must not touch the values stored in it. Most specifically you must never 509must not touch the values stored in it. Most specifically you must never
420reinitialise it or call its set macro. 510reinitialise it or call its C<set> macro.
421
422You can check whether an event is active by calling the C<ev_is_active
423(watcher *)> macro. To see whether an event is outstanding (but the
424callback for it has not been called yet) you can use the C<ev_is_pending
425(watcher *)> macro.
426 511
427Each and every callback receives the event loop pointer as first, the 512Each and every callback receives the event loop pointer as first, the
428registered watcher structure as second, and a bitset of received events as 513registered watcher structure as second, and a bitset of received events as
429third argument. 514third argument.
430 515
487with the error from read() or write(). This will not work in multithreaded 572with the error from read() or write(). This will not work in multithreaded
488programs, though, so beware. 573programs, though, so beware.
489 574
490=back 575=back
491 576
577=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS
578
579In the following description, C<TYPE> stands for the watcher type,
580e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
581
582=over 4
583
584=item C<ev_init> (ev_TYPE *watcher, callback)
585
586This macro initialises the generic portion of a watcher. The contents
587of the watcher object can be arbitrary (so C<malloc> will do). Only
588the generic parts of the watcher are initialised, you I<need> to call
589the type-specific C<ev_TYPE_set> macro afterwards to initialise the
590type-specific parts. For each type there is also a C<ev_TYPE_init> macro
591which rolls both calls into one.
592
593You can reinitialise a watcher at any time as long as it has been stopped
594(or never started) and there are no pending events outstanding.
595
596The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
597int revents)>.
598
599=item C<ev_TYPE_set> (ev_TYPE *, [args])
600
601This macro initialises the type-specific parts of a watcher. You need to
602call C<ev_init> at least once before you call this macro, but you can
603call C<ev_TYPE_set> any number of times. You must not, however, call this
604macro on a watcher that is active (it can be pending, however, which is a
605difference to the C<ev_init> macro).
606
607Although some watcher types do not have type-specific arguments
608(e.g. C<ev_prepare>) you still need to call its C<set> macro.
609
610=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
611
612This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
613calls into a single call. This is the most convinient method to initialise
614a watcher. The same limitations apply, of course.
615
616=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
617
618Starts (activates) the given watcher. Only active watchers will receive
619events. If the watcher is already active nothing will happen.
620
621=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
622
623Stops the given watcher again (if active) and clears the pending
624status. It is possible that stopped watchers are pending (for example,
625non-repeating timers are being stopped when they become pending), but
626C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
627you want to free or reuse the memory used by the watcher it is therefore a
628good idea to always call its C<ev_TYPE_stop> function.
629
630=item bool ev_is_active (ev_TYPE *watcher)
631
632Returns a true value iff the watcher is active (i.e. it has been started
633and not yet been stopped). As long as a watcher is active you must not modify
634it.
635
636=item bool ev_is_pending (ev_TYPE *watcher)
637
638Returns a true value iff the watcher is pending, (i.e. it has outstanding
639events but its callback has not yet been invoked). As long as a watcher
640is pending (but not active) you must not call an init function on it (but
641C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
642libev (e.g. you cnanot C<free ()> it).
643
644=item callback = ev_cb (ev_TYPE *watcher)
645
646Returns the callback currently set on the watcher.
647
648=item ev_cb_set (ev_TYPE *watcher, callback)
649
650Change the callback. You can change the callback at virtually any time
651(modulo threads).
652
653=back
654
655
492=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 656=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
493 657
494Each watcher has, by default, a member C<void *data> that you can change 658Each watcher has, by default, a member C<void *data> that you can change
495and read at any time, libev will completely ignore it. This can be used 659and read at any time, libev will completely ignore it. This can be used
496to associate arbitrary data with your watcher. If you need more data and 660to associate arbitrary data with your watcher. If you need more data and
521 685
522=head1 WATCHER TYPES 686=head1 WATCHER TYPES
523 687
524This section describes each watcher in detail, but will not repeat 688This section describes each watcher in detail, but will not repeat
525information given in the last section. 689information given in the last section.
690
526 691
527=head2 C<ev_io> - is this file descriptor readable or writable 692=head2 C<ev_io> - is this file descriptor readable or writable
528 693
529I/O watchers check whether a file descriptor is readable or writable 694I/O watchers check whether a file descriptor is readable or writable
530in each iteration of the event loop (This behaviour is called 695in each iteration of the event loop (This behaviour is called
568typical ways of handling events, so its a good idea to use non-blocking 733typical ways of handling events, so its a good idea to use non-blocking
569I/O unconditionally. 734I/O unconditionally.
570 735
571=back 736=back
572 737
738Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
739readable, but only once. Since it is likely line-buffered, you could
740attempt to read a whole line in the callback:
741
742 static void
743 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
744 {
745 ev_io_stop (loop, w);
746 .. read from stdin here (or from w->fd) and haqndle any I/O errors
747 }
748
749 ...
750 struct ev_loop *loop = ev_default_init (0);
751 struct ev_io stdin_readable;
752 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
753 ev_io_start (loop, &stdin_readable);
754 ev_loop (loop, 0);
755
756
573=head2 C<ev_timer> - relative and optionally recurring timeouts 757=head2 C<ev_timer> - relative and optionally recurring timeouts
574 758
575Timer watchers are simple relative timers that generate an event after a 759Timer watchers are simple relative timers that generate an event after a
576given time, and optionally repeating in regular intervals after that. 760given time, and optionally repeating in regular intervals after that.
577 761
629state where you do not expect data to travel on the socket, you can stop 813state where you do not expect data to travel on the socket, you can stop
630the timer, and again will automatically restart it if need be. 814the timer, and again will automatically restart it if need be.
631 815
632=back 816=back
633 817
818Example: create a timer that fires after 60 seconds.
819
820 static void
821 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
822 {
823 .. one minute over, w is actually stopped right here
824 }
825
826 struct ev_timer mytimer;
827 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
828 ev_timer_start (loop, &mytimer);
829
830Example: create a timeout timer that times out after 10 seconds of
831inactivity.
832
833 static void
834 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
835 {
836 .. ten seconds without any activity
837 }
838
839 struct ev_timer mytimer;
840 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
841 ev_timer_again (&mytimer); /* start timer */
842 ev_loop (loop, 0);
843
844 // and in some piece of code that gets executed on any "activity":
845 // reset the timeout to start ticking again at 10 seconds
846 ev_timer_again (&mytimer);
847
848
634=head2 C<ev_periodic> - to cron or not to cron 849=head2 C<ev_periodic> - to cron or not to cron
635 850
636Periodic watchers are also timers of a kind, but they are very versatile 851Periodic watchers are also timers of a kind, but they are very versatile
637(and unfortunately a bit complex). 852(and unfortunately a bit complex).
638 853
733a different time than the last time it was called (e.g. in a crond like 948a different time than the last time it was called (e.g. in a crond like
734program when the crontabs have changed). 949program when the crontabs have changed).
735 950
736=back 951=back
737 952
953Example: call a callback every hour, or, more precisely, whenever the
954system clock is divisible by 3600. The callback invocation times have
955potentially a lot of jittering, but good long-term stability.
956
957 static void
958 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
959 {
960 ... its now a full hour (UTC, or TAI or whatever your clock follows)
961 }
962
963 struct ev_periodic hourly_tick;
964 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
965 ev_periodic_start (loop, &hourly_tick);
966
967Example: the same as above, but use a reschedule callback to do it:
968
969 #include <math.h>
970
971 static ev_tstamp
972 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
973 {
974 return fmod (now, 3600.) + 3600.;
975 }
976
977 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
978
979Example: call a callback every hour, starting now:
980
981 struct ev_periodic hourly_tick;
982 ev_periodic_init (&hourly_tick, clock_cb,
983 fmod (ev_now (loop), 3600.), 3600., 0);
984 ev_periodic_start (loop, &hourly_tick);
985
986
738=head2 C<ev_signal> - signal me when a signal gets signalled 987=head2 C<ev_signal> - signal me when a signal gets signalled
739 988
740Signal watchers will trigger an event when the process receives a specific 989Signal watchers will trigger an event when the process receives a specific
741signal one or more times. Even though signals are very asynchronous, libev 990signal one or more times. Even though signals are very asynchronous, libev
742will try it's best to deliver signals synchronously, i.e. as part of the 991will try it's best to deliver signals synchronously, i.e. as part of the
758Configures the watcher to trigger on the given signal number (usually one 1007Configures the watcher to trigger on the given signal number (usually one
759of the C<SIGxxx> constants). 1008of the C<SIGxxx> constants).
760 1009
761=back 1010=back
762 1011
1012
763=head2 C<ev_child> - wait for pid status changes 1013=head2 C<ev_child> - wait for pid status changes
764 1014
765Child watchers trigger when your process receives a SIGCHLD in response to 1015Child watchers trigger when your process receives a SIGCHLD in response to
766some child status changes (most typically when a child of yours dies). 1016some child status changes (most typically when a child of yours dies).
767 1017
777the status word (use the macros from C<sys/wait.h> and see your systems 1027the status word (use the macros from C<sys/wait.h> and see your systems
778C<waitpid> documentation). The C<rpid> member contains the pid of the 1028C<waitpid> documentation). The C<rpid> member contains the pid of the
779process causing the status change. 1029process causing the status change.
780 1030
781=back 1031=back
1032
1033Example: try to exit cleanly on SIGINT and SIGTERM.
1034
1035 static void
1036 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1037 {
1038 ev_unloop (loop, EVUNLOOP_ALL);
1039 }
1040
1041 struct ev_signal signal_watcher;
1042 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1043 ev_signal_start (loop, &sigint_cb);
1044
782 1045
783=head2 C<ev_idle> - when you've got nothing better to do 1046=head2 C<ev_idle> - when you've got nothing better to do
784 1047
785Idle watchers trigger events when there are no other events are pending 1048Idle watchers trigger events when there are no other events are pending
786(prepare, check and other idle watchers do not count). That is, as long 1049(prepare, check and other idle watchers do not count). That is, as long
806kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 1069kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
807believe me. 1070believe me.
808 1071
809=back 1072=back
810 1073
1074Example: dynamically allocate an C<ev_idle>, start it, and in the
1075callback, free it. Alos, use no error checking, as usual.
1076
1077 static void
1078 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1079 {
1080 free (w);
1081 // now do something you wanted to do when the program has
1082 // no longer asnything immediate to do.
1083 }
1084
1085 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1086 ev_idle_init (idle_watcher, idle_cb);
1087 ev_idle_start (loop, idle_cb);
1088
1089
811=head2 C<ev_prepare> and C<ev_check> - customise your event loop 1090=head2 C<ev_prepare> and C<ev_check> - customise your event loop
812 1091
813Prepare and check watchers are usually (but not always) used in tandem: 1092Prepare and check watchers are usually (but not always) used in tandem:
814prepare watchers get invoked before the process blocks and check watchers 1093prepare watchers get invoked before the process blocks and check watchers
815afterwards. 1094afterwards.
816 1095
817Their main purpose is to integrate other event mechanisms into libev. This 1096Their main purpose is to integrate other event mechanisms into libev and
818could be used, for example, to track variable changes, implement your own 1097their use is somewhat advanced. This could be used, for example, to track
819watchers, integrate net-snmp or a coroutine library and lots more. 1098variable changes, implement your own watchers, integrate net-snmp or a
1099coroutine library and lots more.
820 1100
821This is done by examining in each prepare call which file descriptors need 1101This is done by examining in each prepare call which file descriptors need
822to be watched by the other library, registering C<ev_io> watchers for 1102to be watched by the other library, registering C<ev_io> watchers for
823them and starting an C<ev_timer> watcher for any timeouts (many libraries 1103them and starting an C<ev_timer> watcher for any timeouts (many libraries
824provide just this functionality). Then, in the check watcher you check for 1104provide just this functionality). Then, in the check watcher you check for
846parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 1126parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
847macros, but using them is utterly, utterly and completely pointless. 1127macros, but using them is utterly, utterly and completely pointless.
848 1128
849=back 1129=back
850 1130
1131Example: *TODO*.
1132
1133
1134=head2 C<ev_embed> - when one backend isn't enough
1135
1136This is a rather advanced watcher type that lets you embed one event loop
1137into another (currently only C<ev_io> events are supported in the embedded
1138loop, other types of watchers might be handled in a delayed or incorrect
1139fashion and must not be used).
1140
1141There are primarily two reasons you would want that: work around bugs and
1142prioritise I/O.
1143
1144As an example for a bug workaround, the kqueue backend might only support
1145sockets on some platform, so it is unusable as generic backend, but you
1146still want to make use of it because you have many sockets and it scales
1147so nicely. In this case, you would create a kqueue-based loop and embed it
1148into your default loop (which might use e.g. poll). Overall operation will
1149be a bit slower because first libev has to poll and then call kevent, but
1150at least you can use both at what they are best.
1151
1152As for prioritising I/O: rarely you have the case where some fds have
1153to be watched and handled very quickly (with low latency), and even
1154priorities and idle watchers might have too much overhead. In this case
1155you would put all the high priority stuff in one loop and all the rest in
1156a second one, and embed the second one in the first.
1157
1158As long as the watcher is active, the callback will be invoked every time
1159there might be events pending in the embedded loop. The callback must then
1160call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1161their callbacks (you could also start an idle watcher to give the embedded
1162loop strictly lower priority for example). You can also set the callback
1163to C<0>, in which case the embed watcher will automatically execute the
1164embedded loop sweep.
1165
1166As long as the watcher is started it will automatically handle events. The
1167callback will be invoked whenever some events have been handled. You can
1168set the callback to C<0> to avoid having to specify one if you are not
1169interested in that.
1170
1171Also, there have not currently been made special provisions for forking:
1172when you fork, you not only have to call C<ev_loop_fork> on both loops,
1173but you will also have to stop and restart any C<ev_embed> watchers
1174yourself.
1175
1176Unfortunately, not all backends are embeddable, only the ones returned by
1177C<ev_embeddable_backends> are, which, unfortunately, does not include any
1178portable one.
1179
1180So when you want to use this feature you will always have to be prepared
1181that you cannot get an embeddable loop. The recommended way to get around
1182this is to have a separate variables for your embeddable loop, try to
1183create it, and if that fails, use the normal loop for everything:
1184
1185 struct ev_loop *loop_hi = ev_default_init (0);
1186 struct ev_loop *loop_lo = 0;
1187 struct ev_embed embed;
1188
1189 // see if there is a chance of getting one that works
1190 // (remember that a flags value of 0 means autodetection)
1191 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1192 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1193 : 0;
1194
1195 // if we got one, then embed it, otherwise default to loop_hi
1196 if (loop_lo)
1197 {
1198 ev_embed_init (&embed, 0, loop_lo);
1199 ev_embed_start (loop_hi, &embed);
1200 }
1201 else
1202 loop_lo = loop_hi;
1203
1204=over 4
1205
1206=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1207
1208=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1209
1210Configures the watcher to embed the given loop, which must be
1211embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1212invoked automatically, otherwise it is the responsibility of the callback
1213to invoke it (it will continue to be called until the sweep has been done,
1214if you do not want thta, you need to temporarily stop the embed watcher).
1215
1216=item ev_embed_sweep (loop, ev_embed *)
1217
1218Make a single, non-blocking sweep over the embedded loop. This works
1219similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1220apropriate way for embedded loops.
1221
1222=back
1223
1224
851=head1 OTHER FUNCTIONS 1225=head1 OTHER FUNCTIONS
852 1226
853There are some other functions of possible interest. Described. Here. Now. 1227There are some other functions of possible interest. Described. Here. Now.
854 1228
855=over 4 1229=over 4
884 /* stdin might have data for us, joy! */; 1258 /* stdin might have data for us, joy! */;
885 } 1259 }
886 1260
887 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 1261 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
888 1262
889=item ev_feed_event (loop, watcher, int events) 1263=item ev_feed_event (ev_loop *, watcher *, int revents)
890 1264
891Feeds the given event set into the event loop, as if the specified event 1265Feeds the given event set into the event loop, as if the specified event
892had happened for the specified watcher (which must be a pointer to an 1266had happened for the specified watcher (which must be a pointer to an
893initialised but not necessarily started event watcher). 1267initialised but not necessarily started event watcher).
894 1268
895=item ev_feed_fd_event (loop, int fd, int revents) 1269=item ev_feed_fd_event (ev_loop *, int fd, int revents)
896 1270
897Feed an event on the given fd, as if a file descriptor backend detected 1271Feed an event on the given fd, as if a file descriptor backend detected
898the given events it. 1272the given events it.
899 1273
900=item ev_feed_signal_event (loop, int signum) 1274=item ev_feed_signal_event (ev_loop *loop, int signum)
901 1275
902Feed an event as if the given signal occured (loop must be the default loop!). 1276Feed an event as if the given signal occured (C<loop> must be the default
1277loop!).
903 1278
904=back 1279=back
1280
905 1281
906=head1 LIBEVENT EMULATION 1282=head1 LIBEVENT EMULATION
907 1283
908Libev offers a compatibility emulation layer for libevent. It cannot 1284Libev offers a compatibility emulation layer for libevent. It cannot
909emulate the internals of libevent, so here are some usage hints: 1285emulate the internals of libevent, so here are some usage hints:

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