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1=encoding utf-8
2
1=head1 NAME 3=head1 NAME
2 4
3libev - a high performance full-featured event loop written in C 5libev - a high performance full-featured event loop written in C
4 6
5=head1 SYNOPSIS 7=head1 SYNOPSIS
82 84
83=head1 WHAT TO READ WHEN IN A HURRY 85=head1 WHAT TO READ WHEN IN A HURRY
84 86
85This manual tries to be very detailed, but unfortunately, this also makes 87This manual tries to be very detailed, but unfortunately, this also makes
86it very long. If you just want to know the basics of libev, I suggest 88it very long. If you just want to know the basics of libev, I suggest
87reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and 89reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and 90look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89C<ev_timer> sections in L<WATCHER TYPES>. 91C<ev_timer> sections in L</WATCHER TYPES>.
90 92
91=head1 ABOUT LIBEV 93=head1 ABOUT LIBEV
92 94
93Libev is an event loop: you register interest in certain events (such as a 95Libev is an event loop: you register interest in certain events (such as a
94file descriptor being readable or a timeout occurring), and it will manage 96file descriptor being readable or a timeout occurring), and it will manage
396 398
397If this flag bit is or'ed into the flag value (or the program runs setuid 399If this flag bit is or'ed into the flag value (or the program runs setuid
398or setgid) then libev will I<not> look at the environment variable 400or setgid) then libev will I<not> look at the environment variable
399C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will 401C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
400override the flags completely if it is found in the environment. This is 402override the flags completely if it is found in the environment. This is
401useful to try out specific backends to test their performance, or to work 403useful to try out specific backends to test their performance, to work
402around bugs. 404around bugs, or to make libev threadsafe (accessing environment variables
405cannot be done in a threadsafe way, but usually it works if no other
406thread modifies them).
403 407
404=item C<EVFLAG_FORKCHECK> 408=item C<EVFLAG_FORKCHECK>
405 409
406Instead of calling C<ev_loop_fork> manually after a fork, you can also 410Instead of calling C<ev_loop_fork> manually after a fork, you can also
407make libev check for a fork in each iteration by enabling this flag. 411make libev check for a fork in each iteration by enabling this flag.
569kernel is more efficient (which says nothing about its actual speed, of 573kernel is more efficient (which says nothing about its actual speed, of
570course). While stopping, setting and starting an I/O watcher does never 574course). While stopping, setting and starting an I/O watcher does never
571cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to 575cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
572two event changes per incident. Support for C<fork ()> is very bad (you 576two event changes per incident. Support for C<fork ()> is very bad (you
573might have to leak fd's on fork, but it's more sane than epoll) and it 577might have to leak fd's on fork, but it's more sane than epoll) and it
574drops fds silently in similarly hard-to-detect cases 578drops fds silently in similarly hard-to-detect cases.
575 579
576This backend usually performs well under most conditions. 580This backend usually performs well under most conditions.
577 581
578While nominally embeddable in other event loops, this doesn't work 582While nominally embeddable in other event loops, this doesn't work
579everywhere, so you might need to test for this. And since it is broken 583everywhere, so you might need to test for this. And since it is broken
678If you need dynamically allocated loops it is better to use C<ev_loop_new> 682If you need dynamically allocated loops it is better to use C<ev_loop_new>
679and C<ev_loop_destroy>. 683and C<ev_loop_destroy>.
680 684
681=item ev_loop_fork (loop) 685=item ev_loop_fork (loop)
682 686
683This function sets a flag that causes subsequent C<ev_run> iterations to 687This function sets a flag that causes subsequent C<ev_run> iterations
684reinitialise the kernel state for backends that have one. Despite the 688to reinitialise the kernel state for backends that have one. Despite
685name, you can call it anytime, but it makes most sense after forking, in 689the name, you can call it anytime you are allowed to start or stop
686the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the 690watchers (except inside an C<ev_prepare> callback), but it makes most
691sense after forking, in the child process. You I<must> call it (or use
687child before resuming or calling C<ev_run>. 692C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
688 693
689Again, you I<have> to call it on I<any> loop that you want to re-use after 694Again, you I<have> to call it on I<any> loop that you want to re-use after
690a fork, I<even if you do not plan to use the loop in the parent>. This is 695a fork, I<even if you do not plan to use the loop in the parent>. This is
691because some kernel interfaces *cough* I<kqueue> *cough* do funny things 696because some kernel interfaces *cough* I<kqueue> *cough* do funny things
692during fork. 697during fork.
693 698
694On the other hand, you only need to call this function in the child 699On the other hand, you only need to call this function in the child
764 769
765This function is rarely useful, but when some event callback runs for a 770This function is rarely useful, but when some event callback runs for a
766very long time without entering the event loop, updating libev's idea of 771very long time without entering the event loop, updating libev's idea of
767the current time is a good idea. 772the current time is a good idea.
768 773
769See also L<The special problem of time updates> in the C<ev_timer> section. 774See also L</The special problem of time updates> in the C<ev_timer> section.
770 775
771=item ev_suspend (loop) 776=item ev_suspend (loop)
772 777
773=item ev_resume (loop) 778=item ev_resume (loop)
774 779
1318 1323
1319=item callback ev_cb (ev_TYPE *watcher) 1324=item callback ev_cb (ev_TYPE *watcher)
1320 1325
1321Returns the callback currently set on the watcher. 1326Returns the callback currently set on the watcher.
1322 1327
1323=item ev_cb_set (ev_TYPE *watcher, callback) 1328=item ev_set_cb (ev_TYPE *watcher, callback)
1324 1329
1325Change the callback. You can change the callback at virtually any time 1330Change the callback. You can change the callback at virtually any time
1326(modulo threads). 1331(modulo threads).
1327 1332
1328=item ev_set_priority (ev_TYPE *watcher, int priority) 1333=item ev_set_priority (ev_TYPE *watcher, int priority)
1346or might not have been clamped to the valid range. 1351or might not have been clamped to the valid range.
1347 1352
1348The default priority used by watchers when no priority has been set is 1353The default priority used by watchers when no priority has been set is
1349always C<0>, which is supposed to not be too high and not be too low :). 1354always C<0>, which is supposed to not be too high and not be too low :).
1350 1355
1351See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of 1356See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1352priorities. 1357priorities.
1353 1358
1354=item ev_invoke (loop, ev_TYPE *watcher, int revents) 1359=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1355 1360
1356Invoke the C<watcher> with the given C<loop> and C<revents>. Neither 1361Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1381See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related 1386See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1382functions that do not need a watcher. 1387functions that do not need a watcher.
1383 1388
1384=back 1389=back
1385 1390
1386See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR 1391See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1387OWN COMPOSITE WATCHERS> idioms. 1392OWN COMPOSITE WATCHERS> idioms.
1388 1393
1389=head2 WATCHER STATES 1394=head2 WATCHER STATES
1390 1395
1391There are various watcher states mentioned throughout this manual - 1396There are various watcher states mentioned throughout this manual -
1393transition between them will be described in more detail - and while these 1398transition between them will be described in more detail - and while these
1394rules might look complicated, they usually do "the right thing". 1399rules might look complicated, they usually do "the right thing".
1395 1400
1396=over 4 1401=over 4
1397 1402
1398=item initialiased 1403=item initialised
1399 1404
1400Before a watcher can be registered with the event loop it has to be 1405Before a watcher can be registered with the event loop it has to be
1401initialised. This can be done with a call to C<ev_TYPE_init>, or calls to 1406initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1402C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. 1407C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1403 1408
2024 2029
2025The relative timeouts are calculated relative to the C<ev_now ()> 2030The relative timeouts are calculated relative to the C<ev_now ()>
2026time. This is usually the right thing as this timestamp refers to the time 2031time. This is usually the right thing as this timestamp refers to the time
2027of the event triggering whatever timeout you are modifying/starting. If 2032of the event triggering whatever timeout you are modifying/starting. If
2028you suspect event processing to be delayed and you I<need> to base the 2033you suspect event processing to be delayed and you I<need> to base the
2029timeout on the current time, use something like this to adjust for this: 2034timeout on the current time, use something like the following to adjust
2035for it:
2030 2036
2031 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2037 ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
2032 2038
2033If the event loop is suspended for a long time, you can also force an 2039If the event loop is suspended for a long time, you can also force an
2034update of the time returned by C<ev_now ()> by calling C<ev_now_update 2040update of the time returned by C<ev_now ()> by calling C<ev_now_update
2035()>. 2041()>, although that will push the event time of all outstanding events
2042further into the future.
2036 2043
2037=head3 The special problem of unsynchronised clocks 2044=head3 The special problem of unsynchronised clocks
2038 2045
2039Modern systems have a variety of clocks - libev itself uses the normal 2046Modern systems have a variety of clocks - libev itself uses the normal
2040"wall clock" clock and, if available, the monotonic clock (to avoid time 2047"wall clock" clock and, if available, the monotonic clock (to avoid time
2136=item If the timer is repeating, make the C<repeat> value the new timeout 2143=item If the timer is repeating, make the C<repeat> value the new timeout
2137and start the timer, if necessary. 2144and start the timer, if necessary.
2138 2145
2139=back 2146=back
2140 2147
2141This sounds a bit complicated, see L<Be smart about timeouts>, above, for a 2148This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2142usage example. 2149usage example.
2143 2150
2144=item ev_tstamp ev_timer_remaining (loop, ev_timer *) 2151=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2145 2152
2146Returns the remaining time until a timer fires. If the timer is active, 2153Returns the remaining time until a timer fires. If the timer is active,
2389 2396
2390 ev_periodic hourly_tick; 2397 ev_periodic hourly_tick;
2391 ev_periodic_init (&hourly_tick, clock_cb, 2398 ev_periodic_init (&hourly_tick, clock_cb,
2392 fmod (ev_now (loop), 3600.), 3600., 0); 2399 fmod (ev_now (loop), 3600.), 3600., 0);
2393 ev_periodic_start (loop, &hourly_tick); 2400 ev_periodic_start (loop, &hourly_tick);
2394 2401
2395 2402
2396=head2 C<ev_signal> - signal me when a signal gets signalled! 2403=head2 C<ev_signal> - signal me when a signal gets signalled!
2397 2404
2398Signal watchers will trigger an event when the process receives a specific 2405Signal watchers will trigger an event when the process receives a specific
2399signal one or more times. Even though signals are very asynchronous, libev 2406signal one or more times. Even though signals are very asynchronous, libev
2409only within the same loop, i.e. you can watch for C<SIGINT> in your 2416only within the same loop, i.e. you can watch for C<SIGINT> in your
2410default loop and for C<SIGIO> in another loop, but you cannot watch for 2417default loop and for C<SIGIO> in another loop, but you cannot watch for
2411C<SIGINT> in both the default loop and another loop at the same time. At 2418C<SIGINT> in both the default loop and another loop at the same time. At
2412the moment, C<SIGCHLD> is permanently tied to the default loop. 2419the moment, C<SIGCHLD> is permanently tied to the default loop.
2413 2420
2414When the first watcher gets started will libev actually register something 2421Only after the first watcher for a signal is started will libev actually
2415with the kernel (thus it coexists with your own signal handlers as long as 2422register something with the kernel. It thus coexists with your own signal
2416you don't register any with libev for the same signal). 2423handlers as long as you don't register any with libev for the same signal.
2417 2424
2418If possible and supported, libev will install its handlers with 2425If possible and supported, libev will install its handlers with
2419C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should 2426C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2420not be unduly interrupted. If you have a problem with system calls getting 2427not be unduly interrupted. If you have a problem with system calls getting
2421interrupted by signals you can block all signals in an C<ev_check> watcher 2428interrupted by signals you can block all signals in an C<ev_check> watcher
2606 2613
2607=head2 C<ev_stat> - did the file attributes just change? 2614=head2 C<ev_stat> - did the file attributes just change?
2608 2615
2609This watches a file system path for attribute changes. That is, it calls 2616This watches a file system path for attribute changes. That is, it calls
2610C<stat> on that path in regular intervals (or when the OS says it changed) 2617C<stat> on that path in regular intervals (or when the OS says it changed)
2611and sees if it changed compared to the last time, invoking the callback if 2618and sees if it changed compared to the last time, invoking the callback
2612it did. 2619if it did. Starting the watcher C<stat>'s the file, so only changes that
2620happen after the watcher has been started will be reported.
2613 2621
2614The path does not need to exist: changing from "path exists" to "path does 2622The path does not need to exist: changing from "path exists" to "path does
2615not exist" is a status change like any other. The condition "path does not 2623not exist" is a status change like any other. The condition "path does not
2616exist" (or more correctly "path cannot be stat'ed") is signified by the 2624exist" (or more correctly "path cannot be stat'ed") is signified by the
2617C<st_nlink> field being zero (which is otherwise always forced to be at 2625C<st_nlink> field being zero (which is otherwise always forced to be at
2847Apart from keeping your process non-blocking (which is a useful 2855Apart from keeping your process non-blocking (which is a useful
2848effect on its own sometimes), idle watchers are a good place to do 2856effect on its own sometimes), idle watchers are a good place to do
2849"pseudo-background processing", or delay processing stuff to after the 2857"pseudo-background processing", or delay processing stuff to after the
2850event loop has handled all outstanding events. 2858event loop has handled all outstanding events.
2851 2859
2860=head3 Abusing an C<ev_idle> watcher for its side-effect
2861
2862As long as there is at least one active idle watcher, libev will never
2863sleep unnecessarily. Or in other words, it will loop as fast as possible.
2864For this to work, the idle watcher doesn't need to be invoked at all - the
2865lowest priority will do.
2866
2867This mode of operation can be useful together with an C<ev_check> watcher,
2868to do something on each event loop iteration - for example to balance load
2869between different connections.
2870
2871See L</Abusing an ev_check watcher for its side-effect> for a longer
2872example.
2873
2852=head3 Watcher-Specific Functions and Data Members 2874=head3 Watcher-Specific Functions and Data Members
2853 2875
2854=over 4 2876=over 4
2855 2877
2856=item ev_idle_init (ev_idle *, callback) 2878=item ev_idle_init (ev_idle *, callback)
2867callback, free it. Also, use no error checking, as usual. 2889callback, free it. Also, use no error checking, as usual.
2868 2890
2869 static void 2891 static void
2870 idle_cb (struct ev_loop *loop, ev_idle *w, int revents) 2892 idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2871 { 2893 {
2894 // stop the watcher
2895 ev_idle_stop (loop, w);
2896
2897 // now we can free it
2872 free (w); 2898 free (w);
2899
2873 // now do something you wanted to do when the program has 2900 // now do something you wanted to do when the program has
2874 // no longer anything immediate to do. 2901 // no longer anything immediate to do.
2875 } 2902 }
2876 2903
2877 ev_idle *idle_watcher = malloc (sizeof (ev_idle)); 2904 ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2879 ev_idle_start (loop, idle_watcher); 2906 ev_idle_start (loop, idle_watcher);
2880 2907
2881 2908
2882=head2 C<ev_prepare> and C<ev_check> - customise your event loop! 2909=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2883 2910
2884Prepare and check watchers are usually (but not always) used in pairs: 2911Prepare and check watchers are often (but not always) used in pairs:
2885prepare watchers get invoked before the process blocks and check watchers 2912prepare watchers get invoked before the process blocks and check watchers
2886afterwards. 2913afterwards.
2887 2914
2888You I<must not> call C<ev_run> or similar functions that enter 2915You I<must not> call C<ev_run> (or similar functions that enter the
2889the current event loop from either C<ev_prepare> or C<ev_check> 2916current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2890watchers. Other loops than the current one are fine, however. The 2917C<ev_check> watchers. Other loops than the current one are fine,
2891rationale behind this is that you do not need to check for recursion in 2918however. The rationale behind this is that you do not need to check
2892those watchers, i.e. the sequence will always be C<ev_prepare>, blocking, 2919for recursion in those watchers, i.e. the sequence will always be
2893C<ev_check> so if you have one watcher of each kind they will always be 2920C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2894called in pairs bracketing the blocking call. 2921kind they will always be called in pairs bracketing the blocking call.
2895 2922
2896Their main purpose is to integrate other event mechanisms into libev and 2923Their main purpose is to integrate other event mechanisms into libev and
2897their use is somewhat advanced. They could be used, for example, to track 2924their use is somewhat advanced. They could be used, for example, to track
2898variable changes, implement your own watchers, integrate net-snmp or a 2925variable changes, implement your own watchers, integrate net-snmp or a
2899coroutine library and lots more. They are also occasionally useful if 2926coroutine library and lots more. They are also occasionally useful if
2917with priority higher than or equal to the event loop and one coroutine 2944with priority higher than or equal to the event loop and one coroutine
2918of lower priority, but only once, using idle watchers to keep the event 2945of lower priority, but only once, using idle watchers to keep the event
2919loop from blocking if lower-priority coroutines are active, thus mapping 2946loop from blocking if lower-priority coroutines are active, thus mapping
2920low-priority coroutines to idle/background tasks). 2947low-priority coroutines to idle/background tasks).
2921 2948
2922It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>) 2949When used for this purpose, it is recommended to give C<ev_check> watchers
2923priority, to ensure that they are being run before any other watchers 2950highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2924after the poll (this doesn't matter for C<ev_prepare> watchers). 2951any other watchers after the poll (this doesn't matter for C<ev_prepare>
2952watchers).
2925 2953
2926Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not 2954Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2927activate ("feed") events into libev. While libev fully supports this, they 2955activate ("feed") events into libev. While libev fully supports this, they
2928might get executed before other C<ev_check> watchers did their job. As 2956might get executed before other C<ev_check> watchers did their job. As
2929C<ev_check> watchers are often used to embed other (non-libev) event 2957C<ev_check> watchers are often used to embed other (non-libev) event
2930loops those other event loops might be in an unusable state until their 2958loops those other event loops might be in an unusable state until their
2931C<ev_check> watcher ran (always remind yourself to coexist peacefully with 2959C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2932others). 2960others).
2961
2962=head3 Abusing an C<ev_check> watcher for its side-effect
2963
2964C<ev_check> (and less often also C<ev_prepare>) watchers can also be
2965useful because they are called once per event loop iteration. For
2966example, if you want to handle a large number of connections fairly, you
2967normally only do a bit of work for each active connection, and if there
2968is more work to do, you wait for the next event loop iteration, so other
2969connections have a chance of making progress.
2970
2971Using an C<ev_check> watcher is almost enough: it will be called on the
2972next event loop iteration. However, that isn't as soon as possible -
2973without external events, your C<ev_check> watcher will not be invoked.
2974
2975This is where C<ev_idle> watchers come in handy - all you need is a
2976single global idle watcher that is active as long as you have one active
2977C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
2978will not sleep, and the C<ev_check> watcher makes sure a callback gets
2979invoked. Neither watcher alone can do that.
2933 2980
2934=head3 Watcher-Specific Functions and Data Members 2981=head3 Watcher-Specific Functions and Data Members
2935 2982
2936=over 4 2983=over 4
2937 2984
3138 3185
3139=over 4 3186=over 4
3140 3187
3141=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop) 3188=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3142 3189
3143=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop) 3190=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3144 3191
3145Configures the watcher to embed the given loop, which must be 3192Configures the watcher to embed the given loop, which must be
3146embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be 3193embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3147invoked automatically, otherwise it is the responsibility of the callback 3194invoked automatically, otherwise it is the responsibility of the callback
3148to invoke it (it will continue to be called until the sweep has been done, 3195to invoke it (it will continue to be called until the sweep has been done,
3169used). 3216used).
3170 3217
3171 struct ev_loop *loop_hi = ev_default_init (0); 3218 struct ev_loop *loop_hi = ev_default_init (0);
3172 struct ev_loop *loop_lo = 0; 3219 struct ev_loop *loop_lo = 0;
3173 ev_embed embed; 3220 ev_embed embed;
3174 3221
3175 // see if there is a chance of getting one that works 3222 // see if there is a chance of getting one that works
3176 // (remember that a flags value of 0 means autodetection) 3223 // (remember that a flags value of 0 means autodetection)
3177 loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3224 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3178 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3225 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3179 : 0; 3226 : 0;
3193C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too). 3240C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3194 3241
3195 struct ev_loop *loop = ev_default_init (0); 3242 struct ev_loop *loop = ev_default_init (0);
3196 struct ev_loop *loop_socket = 0; 3243 struct ev_loop *loop_socket = 0;
3197 ev_embed embed; 3244 ev_embed embed;
3198 3245
3199 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) 3246 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3200 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) 3247 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3201 { 3248 {
3202 ev_embed_init (&embed, 0, loop_socket); 3249 ev_embed_init (&embed, 0, loop_socket);
3203 ev_embed_start (loop, &embed); 3250 ev_embed_start (loop, &embed);
3211 3258
3212=head2 C<ev_fork> - the audacity to resume the event loop after a fork 3259=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3213 3260
3214Fork watchers are called when a C<fork ()> was detected (usually because 3261Fork watchers are called when a C<fork ()> was detected (usually because
3215whoever is a good citizen cared to tell libev about it by calling 3262whoever is a good citizen cared to tell libev about it by calling
3216C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the 3263C<ev_loop_fork>). The invocation is done before the event loop blocks next
3217event loop blocks next and before C<ev_check> watchers are being called, 3264and before C<ev_check> watchers are being called, and only in the child
3218and only in the child after the fork. If whoever good citizen calling 3265after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3219C<ev_default_fork> cheats and calls it in the wrong process, the fork 3266and calls it in the wrong process, the fork handlers will be invoked, too,
3220handlers will be invoked, too, of course. 3267of course.
3221 3268
3222=head3 The special problem of life after fork - how is it possible? 3269=head3 The special problem of life after fork - how is it possible?
3223 3270
3224Most uses of C<fork()> consist of forking, then some simple calls to set 3271Most uses of C<fork ()> consist of forking, then some simple calls to set
3225up/change the process environment, followed by a call to C<exec()>. This 3272up/change the process environment, followed by a call to C<exec()>. This
3226sequence should be handled by libev without any problems. 3273sequence should be handled by libev without any problems.
3227 3274
3228This changes when the application actually wants to do event handling 3275This changes when the application actually wants to do event handling
3229in the child, or both parent in child, in effect "continuing" after the 3276in the child, or both parent in child, in effect "continuing" after the
3619already been invoked. 3666already been invoked.
3620 3667
3621A common way around all these issues is to make sure that 3668A common way around all these issues is to make sure that
3622C<start_new_request> I<always> returns before the callback is invoked. If 3669C<start_new_request> I<always> returns before the callback is invoked. If
3623C<start_new_request> immediately knows the result, it can artificially 3670C<start_new_request> immediately knows the result, it can artificially
3624delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher 3671delay invoking the callback by using a C<prepare> or C<idle> watcher for
3625for example, or more sneakily, by reusing an existing (stopped) watcher 3672example, or more sneakily, by reusing an existing (stopped) watcher and
3626and pushing it into the pending queue: 3673pushing it into the pending queue:
3627 3674
3628 ev_set_cb (watcher, callback); 3675 ev_set_cb (watcher, callback);
3629 ev_feed_event (EV_A_ watcher, 0); 3676 ev_feed_event (EV_A_ watcher, 0);
3630 3677
3631This way, C<start_new_request> can safely return before the callback is 3678This way, C<start_new_request> can safely return before the callback is
3639 3686
3640This brings the problem of exiting - a callback might want to finish the 3687This brings the problem of exiting - a callback might want to finish the
3641main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but 3688main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3642a modal "Are you sure?" dialog is still waiting), or just the nested one 3689a modal "Are you sure?" dialog is still waiting), or just the nested one
3643and not the main one (e.g. user clocked "Ok" in a modal dialog), or some 3690and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3644other combination: In these cases, C<ev_break> will not work alone. 3691other combination: In these cases, a simple C<ev_break> will not work.
3645 3692
3646The solution is to maintain "break this loop" variable for each C<ev_run> 3693The solution is to maintain "break this loop" variable for each C<ev_run>
3647invocation, and use a loop around C<ev_run> until the condition is 3694invocation, and use a loop around C<ev_run> until the condition is
3648triggered, using C<EVRUN_ONCE>: 3695triggered, using C<EVRUN_ONCE>:
3649 3696
3835called): 3882called):
3836 3883
3837 void 3884 void
3838 wait_for_event (ev_watcher *w) 3885 wait_for_event (ev_watcher *w)
3839 { 3886 {
3840 ev_cb_set (w) = current_coro; 3887 ev_set_cb (w, current_coro);
3841 switch_to (libev_coro); 3888 switch_to (libev_coro);
3842 } 3889 }
3843 3890
3844That basically suspends the coroutine inside C<wait_for_event> and 3891That basically suspends the coroutine inside C<wait_for_event> and
3845continues the libev coroutine, which, when appropriate, switches back to 3892continues the libev coroutine, which, when appropriate, switches back to
3848You can do similar tricks if you have, say, threads with an event queue - 3895You can do similar tricks if you have, say, threads with an event queue -
3849instead of storing a coroutine, you store the queue object and instead of 3896instead of storing a coroutine, you store the queue object and instead of
3850switching to a coroutine, you push the watcher onto the queue and notify 3897switching to a coroutine, you push the watcher onto the queue and notify
3851any waiters. 3898any waiters.
3852 3899
3853To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two 3900To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
3854files, F<my_ev.h> and F<my_ev.c> that include the respective libev files: 3901files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
3855 3902
3856 // my_ev.h 3903 // my_ev.h
3857 #define EV_CB_DECLARE(type) struct my_coro *cb; 3904 #define EV_CB_DECLARE(type) struct my_coro *cb;
3858 #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb); 3905 #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
3859 #include "../libev/ev.h" 3906 #include "../libev/ev.h"
3860 3907
3861 // my_ev.c 3908 // my_ev.c
3862 #define EV_H "my_ev.h" 3909 #define EV_H "my_ev.h"
3863 #include "../libev/ev.c" 3910 #include "../libev/ev.c"
3910libev sources can be compiled as C++. Therefore, code that uses the C API 3957libev sources can be compiled as C++. Therefore, code that uses the C API
3911will work fine. 3958will work fine.
3912 3959
3913Proper exception specifications might have to be added to callbacks passed 3960Proper exception specifications might have to be added to callbacks passed
3914to libev: exceptions may be thrown only from watcher callbacks, all 3961to libev: exceptions may be thrown only from watcher callbacks, all
3915other callbacks (allocator, syserr, loop acquire/release and periodioc 3962other callbacks (allocator, syserr, loop acquire/release and periodic
3916reschedule callbacks) must not throw exceptions, and might need a C<throw 3963reschedule callbacks) must not throw exceptions, and might need a C<throw
3917()> specification. If you have code that needs to be compiled as both C 3964()> specification. If you have code that needs to be compiled as both C
3918and C++ you can use the C<EV_THROW> macro for this: 3965and C++ you can use the C<EV_THROW> macro for this:
3919 3966
3920 static void 3967 static void
3940Libev comes with some simplistic wrapper classes for C++ that mainly allow 3987Libev comes with some simplistic wrapper classes for C++ that mainly allow
3941you to use some convenience methods to start/stop watchers and also change 3988you to use some convenience methods to start/stop watchers and also change
3942the callback model to a model using method callbacks on objects. 3989the callback model to a model using method callbacks on objects.
3943 3990
3944To use it, 3991To use it,
3945 3992
3946 #include <ev++.h> 3993 #include <ev++.h>
3947 3994
3948This automatically includes F<ev.h> and puts all of its definitions (many 3995This automatically includes F<ev.h> and puts all of its definitions (many
3949of them macros) into the global namespace. All C++ specific things are 3996of them macros) into the global namespace. All C++ specific things are
3950put into the C<ev> namespace. It should support all the same embedding 3997put into the C<ev> namespace. It should support all the same embedding
4053 void operator() (ev::io &w, int revents) 4100 void operator() (ev::io &w, int revents)
4054 { 4101 {
4055 ... 4102 ...
4056 } 4103 }
4057 } 4104 }
4058 4105
4059 myfunctor f; 4106 myfunctor f;
4060 4107
4061 ev::io w; 4108 ev::io w;
4062 w.set (&f); 4109 w.set (&f);
4063 4110
4081Associates a different C<struct ev_loop> with this watcher. You can only 4128Associates a different C<struct ev_loop> with this watcher. You can only
4082do this when the watcher is inactive (and not pending either). 4129do this when the watcher is inactive (and not pending either).
4083 4130
4084=item w->set ([arguments]) 4131=item w->set ([arguments])
4085 4132
4086Basically the same as C<ev_TYPE_set>, with the same arguments. Either this 4133Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
4087method or a suitable start method must be called at least once. Unlike the 4134with the same arguments. Either this method or a suitable start method
4088C counterpart, an active watcher gets automatically stopped and restarted 4135must be called at least once. Unlike the C counterpart, an active watcher
4089when reconfiguring it with this method. 4136gets automatically stopped and restarted when reconfiguring it with this
4137method.
4138
4139For C<ev::embed> watchers this method is called C<set_embed>, to avoid
4140clashing with the C<set (loop)> method.
4090 4141
4091=item w->start () 4142=item w->start ()
4092 4143
4093Starts the watcher. Note that there is no C<loop> argument, as the 4144Starts the watcher. Note that there is no C<loop> argument, as the
4094constructor already stores the event loop. 4145constructor already stores the event loop.
4197=item Lua 4248=item Lua
4198 4249
4199Brian Maher has written a partial interface to libev for lua (at the 4250Brian Maher has written a partial interface to libev for lua (at the
4200time of this writing, only C<ev_io> and C<ev_timer>), to be found at 4251time of this writing, only C<ev_io> and C<ev_timer>), to be found at
4201L<http://github.com/brimworks/lua-ev>. 4252L<http://github.com/brimworks/lua-ev>.
4253
4254=item Javascript
4255
4256Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
4257
4258=item Others
4259
4260There are others, and I stopped counting.
4202 4261
4203=back 4262=back
4204 4263
4205 4264
4206=head1 MACRO MAGIC 4265=head1 MACRO MAGIC
4505 4564
4506If programs implement their own fd to handle mapping on win32, then this 4565If programs implement their own fd to handle mapping on win32, then this
4507macro can be used to override the C<close> function, useful to unregister 4566macro can be used to override the C<close> function, useful to unregister
4508file descriptors again. Note that the replacement function has to close 4567file descriptors again. Note that the replacement function has to close
4509the underlying OS handle. 4568the underlying OS handle.
4569
4570=item EV_USE_WSASOCKET
4571
4572If defined to be C<1>, libev will use C<WSASocket> to create its internal
4573communication socket, which works better in some environments. Otherwise,
4574the normal C<socket> function will be used, which works better in other
4575environments.
4510 4576
4511=item EV_USE_POLL 4577=item EV_USE_POLL
4512 4578
4513If defined to be C<1>, libev will compile in support for the C<poll>(2) 4579If defined to be C<1>, libev will compile in support for the C<poll>(2)
4514backend. Otherwise it will be enabled on non-win32 platforms. It 4580backend. Otherwise it will be enabled on non-win32 platforms. It
4559different cpus (or different cpu cores). This reduces dependencies 4625different cpus (or different cpu cores). This reduces dependencies
4560and makes libev faster. 4626and makes libev faster.
4561 4627
4562=item EV_NO_THREADS 4628=item EV_NO_THREADS
4563 4629
4564If defined to be C<1>, libev will assume that it will never be called 4630If defined to be C<1>, libev will assume that it will never be called from
4565from different threads, which is a stronger assumption than C<EV_NO_SMP>, 4631different threads (that includes signal handlers), which is a stronger
4566above. This reduces dependencies and makes libev faster. 4632assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
4633libev faster.
4567 4634
4568=item EV_ATOMIC_T 4635=item EV_ATOMIC_T
4569 4636
4570Libev requires an integer type (suitable for storing C<0> or C<1>) whose 4637Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4571access is atomic and serialised with respect to other threads or signal 4638access is atomic with respect to other threads or signal contexts. No
4572contexts. No such type is easily found in the C language, so you can 4639such type is easily found in the C language, so you can provide your own
4573provide your own type that you know is safe for your purposes. It is used 4640type that you know is safe for your purposes. It is used both for signal
4574both for signal handler "locking" as well as for signal and thread safety 4641handler "locking" as well as for signal and thread safety in C<ev_async>
4575in C<ev_async> watchers. 4642watchers.
4576 4643
4577In the absence of this define, libev will use C<sig_atomic_t volatile> 4644In the absence of this define, libev will use C<sig_atomic_t volatile>
4578(from F<signal.h>), which is usually good enough on most platforms, 4645(from F<signal.h>), which is usually good enough on most platforms.
4579although strictly speaking using a type that also implies a memory fence
4580is required.
4581 4646
4582=item EV_H (h) 4647=item EV_H (h)
4583 4648
4584The name of the F<ev.h> header file used to include it. The default if 4649The name of the F<ev.h> header file used to include it. The default if
4585undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be 4650undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
4953default loop and triggering an C<ev_async> watcher from the default loop 5018default loop and triggering an C<ev_async> watcher from the default loop
4954watcher callback into the event loop interested in the signal. 5019watcher callback into the event loop interested in the signal.
4955 5020
4956=back 5021=back
4957 5022
4958See also L<THREAD LOCKING EXAMPLE>. 5023See also L</THREAD LOCKING EXAMPLE>.
4959 5024
4960=head3 COROUTINES 5025=head3 COROUTINES
4961 5026
4962Libev is very accommodating to coroutines ("cooperative threads"): 5027Libev is very accommodating to coroutines ("cooperative threads"):
4963libev fully supports nesting calls to its functions from different 5028libev fully supports nesting calls to its functions from different
5254thread" or will block signals process-wide, both behaviours would 5319thread" or will block signals process-wide, both behaviours would
5255be compatible with libev. Interaction between C<sigprocmask> and 5320be compatible with libev. Interaction between C<sigprocmask> and
5256C<pthread_sigmask> could complicate things, however. 5321C<pthread_sigmask> could complicate things, however.
5257 5322
5258The most portable way to handle signals is to block signals in all threads 5323The most portable way to handle signals is to block signals in all threads
5259except the initial one, and run the default loop in the initial thread as 5324except the initial one, and run the signal handling loop in the initial
5260well. 5325thread as well.
5261 5326
5262=item C<long> must be large enough for common memory allocation sizes 5327=item C<long> must be large enough for common memory allocation sizes
5263 5328
5264To improve portability and simplify its API, libev uses C<long> internally 5329To improve portability and simplify its API, libev uses C<long> internally
5265instead of C<size_t> when allocating its data structures. On non-POSIX 5330instead of C<size_t> when allocating its data structures. On non-POSIX
5369=over 4 5434=over 4
5370 5435
5371=item C<EV_COMPAT3> backwards compatibility mechanism 5436=item C<EV_COMPAT3> backwards compatibility mechanism
5372 5437
5373The backward compatibility mechanism can be controlled by 5438The backward compatibility mechanism can be controlled by
5374C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING> 5439C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5375section. 5440section.
5376 5441
5377=item C<ev_default_destroy> and C<ev_default_fork> have been removed 5442=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5378 5443
5379These calls can be replaced easily by their C<ev_loop_xxx> counterparts: 5444These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
5422=over 4 5487=over 4
5423 5488
5424=item active 5489=item active
5425 5490
5426A watcher is active as long as it has been started and not yet stopped. 5491A watcher is active as long as it has been started and not yet stopped.
5427See L<WATCHER STATES> for details. 5492See L</WATCHER STATES> for details.
5428 5493
5429=item application 5494=item application
5430 5495
5431In this document, an application is whatever is using libev. 5496In this document, an application is whatever is using libev.
5432 5497
5468watchers and events. 5533watchers and events.
5469 5534
5470=item pending 5535=item pending
5471 5536
5472A watcher is pending as soon as the corresponding event has been 5537A watcher is pending as soon as the corresponding event has been
5473detected. See L<WATCHER STATES> for details. 5538detected. See L</WATCHER STATES> for details.
5474 5539
5475=item real time 5540=item real time
5476 5541
5477The physical time that is observed. It is apparently strictly monotonic :) 5542The physical time that is observed. It is apparently strictly monotonic :)
5478 5543

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