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Revision 1.205 by root, Mon Oct 27 12:20:32 2008 UTC

10 10
11 // a single header file is required 11 // a single header file is required
12 #include <ev.h> 12 #include <ev.h>
13 13
14 // every watcher type has its own typedef'd struct 14 // every watcher type has its own typedef'd struct
15 // with the name ev_<type> 15 // with the name ev_TYPE
16 ev_io stdin_watcher; 16 ev_io stdin_watcher;
17 ev_timer timeout_watcher; 17 ev_timer timeout_watcher;
18 18
19 // all watcher callbacks have a similar signature 19 // all watcher callbacks have a similar signature
20 // this callback is called when data is readable on stdin 20 // this callback is called when data is readable on stdin
21 static void 21 static void
22 stdin_cb (EV_P_ struct ev_io *w, int revents) 22 stdin_cb (EV_P_ ev_io *w, int revents)
23 { 23 {
24 puts ("stdin ready"); 24 puts ("stdin ready");
25 // for one-shot events, one must manually stop the watcher 25 // for one-shot events, one must manually stop the watcher
26 // with its corresponding stop function. 26 // with its corresponding stop function.
27 ev_io_stop (EV_A_ w); 27 ev_io_stop (EV_A_ w);
30 ev_unloop (EV_A_ EVUNLOOP_ALL); 30 ev_unloop (EV_A_ EVUNLOOP_ALL);
31 } 31 }
32 32
33 // another callback, this time for a time-out 33 // another callback, this time for a time-out
34 static void 34 static void
35 timeout_cb (EV_P_ struct ev_timer *w, int revents) 35 timeout_cb (EV_P_ ev_timer *w, int revents)
36 { 36 {
37 puts ("timeout"); 37 puts ("timeout");
38 // this causes the innermost ev_loop to stop iterating 38 // this causes the innermost ev_loop to stop iterating
39 ev_unloop (EV_A_ EVUNLOOP_ONE); 39 ev_unloop (EV_A_ EVUNLOOP_ONE);
40 } 40 }
41 41
42 int 42 int
43 main (void) 43 main (void)
44 { 44 {
45 // use the default event loop unless you have special needs 45 // use the default event loop unless you have special needs
46 struct ev_loop *loop = ev_default_loop (0); 46 ev_loop *loop = ev_default_loop (0);
47 47
48 // initialise an io watcher, then start it 48 // initialise an io watcher, then start it
49 // this one will watch for stdin to become readable 49 // this one will watch for stdin to become readable
50 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 50 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51 ev_io_start (loop, &stdin_watcher); 51 ev_io_start (loop, &stdin_watcher);
103Libev is very configurable. In this manual the default (and most common) 103Libev is very configurable. In this manual the default (and most common)
104configuration will be described, which supports multiple event loops. For 104configuration will be described, which supports multiple event loops. For
105more info about various configuration options please have a look at 105more info about various configuration options please have a look at
106B<EMBED> section in this manual. If libev was configured without support 106B<EMBED> section in this manual. If libev was configured without support
107for multiple event loops, then all functions taking an initial argument of 107for multiple event loops, then all functions taking an initial argument of
108name C<loop> (which is always of type C<struct ev_loop *>) will not have 108name C<loop> (which is always of type C<ev_loop *>) will not have
109this argument. 109this argument.
110 110
111=head2 TIME REPRESENTATION 111=head2 TIME REPRESENTATION
112 112
113Libev represents time as a single floating point number, representing the 113Libev represents time as a single floating point number, representing the
276 276
277=back 277=back
278 278
279=head1 FUNCTIONS CONTROLLING THE EVENT LOOP 279=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280 280
281An event loop is described by a C<struct ev_loop *>. The library knows two 281An event loop is described by a C<struct ev_loop *> (the C<struct>
282types of such loops, the I<default> loop, which supports signals and child 282is I<not> optional in this case, as there is also an C<ev_loop>
283events, and dynamically created loops which do not. 283I<function>).
284
285The library knows two types of such loops, the I<default> loop, which
286supports signals and child events, and dynamically created loops which do
287not.
284 288
285=over 4 289=over 4
286 290
287=item struct ev_loop *ev_default_loop (unsigned int flags) 291=item struct ev_loop *ev_default_loop (unsigned int flags)
288 292
380=item C<EVBACKEND_EPOLL> (value 4, Linux) 384=item C<EVBACKEND_EPOLL> (value 4, Linux)
381 385
382For few fds, this backend is a bit little slower than poll and select, 386For few fds, this backend is a bit little slower than poll and select,
383but it scales phenomenally better. While poll and select usually scale 387but it scales phenomenally better. While poll and select usually scale
384like O(total_fds) where n is the total number of fds (or the highest fd), 388like O(total_fds) where n is the total number of fds (or the highest fd),
385epoll scales either O(1) or O(active_fds). The epoll design has a number 389epoll scales either O(1) or O(active_fds).
386of shortcomings, such as silently dropping events in some hard-to-detect 390
387cases and requiring a system call per fd change, no fork support and bad 391The epoll syscalls are the most misdesigned of the more advanced
388support for dup. 392event mechanisms: probelsm include silently dropping events in some
393hard-to-detect cases, requiring a system call per fd change, no fork
394support, problems with dup and so on.
395
396Epoll is also notoriously buggy - embedding epoll fds should work, but
397of course doesn't, and epoll just loves to report events for totally
398I<different> file descriptors (even already closed ones, so one cannot
399even remove them from the set) than registered in the set (especially
400on SMP systems). Libev tries to counter these spurious notifications by
401employing an additional generation counter and comparing that against the
402events to filter out spurious ones.
389 403
390While stopping, setting and starting an I/O watcher in the same iteration 404While stopping, setting and starting an I/O watcher in the same iteration
391will result in some caching, there is still a system call per such incident 405will result in some caching, there is still a system call per such incident
392(because the fd could point to a different file description now), so its 406(because the fd could point to a different file description now), so its
393best to avoid that. Also, C<dup ()>'ed file descriptors might not work 407best to avoid that. Also, C<dup ()>'ed file descriptors might not work
394very well if you register events for both fds. 408very well if you register events for both fds.
395
396Please note that epoll sometimes generates spurious notifications, so you
397need to use non-blocking I/O or other means to avoid blocking when no data
398(or space) is available.
399 409
400Best performance from this backend is achieved by not unregistering all 410Best performance from this backend is achieved by not unregistering all
401watchers for a file descriptor until it has been closed, if possible, 411watchers for a file descriptor until it has been closed, if possible,
402i.e. keep at least one watcher active per fd at all times. Stopping and 412i.e. keep at least one watcher active per fd at all times. Stopping and
403starting a watcher (without re-setting it) also usually doesn't cause 413starting a watcher (without re-setting it) also usually doesn't cause
527responsibility to either stop all watchers cleanly yourself I<before> 537responsibility to either stop all watchers cleanly yourself I<before>
528calling this function, or cope with the fact afterwards (which is usually 538calling this function, or cope with the fact afterwards (which is usually
529the easiest thing, you can just ignore the watchers and/or C<free ()> them 539the easiest thing, you can just ignore the watchers and/or C<free ()> them
530for example). 540for example).
531 541
532Note that certain global state, such as signal state, will not be freed by 542Note that certain global state, such as signal state (and installed signal
533this function, and related watchers (such as signal and child watchers) 543handlers), will not be freed by this function, and related watchers (such
534would need to be stopped manually. 544as signal and child watchers) would need to be stopped manually.
535 545
536In general it is not advisable to call this function except in the 546In general it is not advisable to call this function except in the
537rare occasion where you really need to free e.g. the signal handling 547rare occasion where you really need to free e.g. the signal handling
538pipe fds. If you need dynamically allocated loops it is better to use 548pipe fds. If you need dynamically allocated loops it is better to use
539C<ev_loop_new> and C<ev_loop_destroy>). 549C<ev_loop_new> and C<ev_loop_destroy>).
710respectively). 720respectively).
711 721
712Example: Create a signal watcher, but keep it from keeping C<ev_loop> 722Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713running when nothing else is active. 723running when nothing else is active.
714 724
715 struct ev_signal exitsig; 725 ev_signal exitsig;
716 ev_signal_init (&exitsig, sig_cb, SIGINT); 726 ev_signal_init (&exitsig, sig_cb, SIGINT);
717 ev_signal_start (loop, &exitsig); 727 ev_signal_start (loop, &exitsig);
718 evf_unref (loop); 728 evf_unref (loop);
719 729
720Example: For some weird reason, unregister the above signal handler again. 730Example: For some weird reason, unregister the above signal handler again.
768they fire on, say, one-second boundaries only. 778they fire on, say, one-second boundaries only.
769 779
770=item ev_loop_verify (loop) 780=item ev_loop_verify (loop)
771 781
772This function only does something when C<EV_VERIFY> support has been 782This function only does something when C<EV_VERIFY> support has been
773compiled in. which is the default for non-minimal builds. It tries to go 783compiled in, which is the default for non-minimal builds. It tries to go
774through all internal structures and checks them for validity. If anything 784through all internal structures and checks them for validity. If anything
775is found to be inconsistent, it will print an error message to standard 785is found to be inconsistent, it will print an error message to standard
776error and call C<abort ()>. 786error and call C<abort ()>.
777 787
778This can be used to catch bugs inside libev itself: under normal 788This can be used to catch bugs inside libev itself: under normal
782=back 792=back
783 793
784 794
785=head1 ANATOMY OF A WATCHER 795=head1 ANATOMY OF A WATCHER
786 796
797In the following description, uppercase C<TYPE> in names stands for the
798watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
799watchers and C<ev_io_start> for I/O watchers.
800
787A watcher is a structure that you create and register to record your 801A watcher is a structure that you create and register to record your
788interest in some event. For instance, if you want to wait for STDIN to 802interest in some event. For instance, if you want to wait for STDIN to
789become readable, you would create an C<ev_io> watcher for that: 803become readable, you would create an C<ev_io> watcher for that:
790 804
791 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 805 static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
792 { 806 {
793 ev_io_stop (w); 807 ev_io_stop (w);
794 ev_unloop (loop, EVUNLOOP_ALL); 808 ev_unloop (loop, EVUNLOOP_ALL);
795 } 809 }
796 810
797 struct ev_loop *loop = ev_default_loop (0); 811 struct ev_loop *loop = ev_default_loop (0);
812
798 struct ev_io stdin_watcher; 813 ev_io stdin_watcher;
814
799 ev_init (&stdin_watcher, my_cb); 815 ev_init (&stdin_watcher, my_cb);
800 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 816 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801 ev_io_start (loop, &stdin_watcher); 817 ev_io_start (loop, &stdin_watcher);
818
802 ev_loop (loop, 0); 819 ev_loop (loop, 0);
803 820
804As you can see, you are responsible for allocating the memory for your 821As you can see, you are responsible for allocating the memory for your
805watcher structures (and it is usually a bad idea to do this on the stack, 822watcher structures (and it is I<usually> a bad idea to do this on the
806although this can sometimes be quite valid). 823stack).
824
825Each watcher has an associated watcher structure (called C<struct ev_TYPE>
826or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807 827
808Each watcher structure must be initialised by a call to C<ev_init 828Each watcher structure must be initialised by a call to C<ev_init
809(watcher *, callback)>, which expects a callback to be provided. This 829(watcher *, callback)>, which expects a callback to be provided. This
810callback gets invoked each time the event occurs (or, in the case of I/O 830callback gets invoked each time the event occurs (or, in the case of I/O
811watchers, each time the event loop detects that the file descriptor given 831watchers, each time the event loop detects that the file descriptor given
812is readable and/or writable). 832is readable and/or writable).
813 833
814Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro 834Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815with arguments specific to this watcher type. There is also a macro 835macro to configure it, with arguments specific to the watcher type. There
816to combine initialisation and setting in one call: C<< ev_<type>_init 836is also a macro to combine initialisation and setting in one call: C<<
817(watcher *, callback, ...) >>. 837ev_TYPE_init (watcher *, callback, ...) >>.
818 838
819To make the watcher actually watch out for events, you have to start it 839To make the watcher actually watch out for events, you have to start it
820with a watcher-specific start function (C<< ev_<type>_start (loop, watcher 840with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821*) >>), and you can stop watching for events at any time by calling the 841*) >>), and you can stop watching for events at any time by calling the
822corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. 842corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823 843
824As long as your watcher is active (has been started but not stopped) you 844As long as your watcher is active (has been started but not stopped) you
825must not touch the values stored in it. Most specifically you must never 845must not touch the values stored in it. Most specifically you must never
826reinitialise it or call its C<set> macro. 846reinitialise it or call its C<ev_TYPE_set> macro.
827 847
828Each and every callback receives the event loop pointer as first, the 848Each and every callback receives the event loop pointer as first, the
829registered watcher structure as second, and a bitset of received events as 849registered watcher structure as second, and a bitset of received events as
830third argument. 850third argument.
831 851
894=item C<EV_ERROR> 914=item C<EV_ERROR>
895 915
896An unspecified error has occurred, the watcher has been stopped. This might 916An unspecified error has occurred, the watcher has been stopped. This might
897happen because the watcher could not be properly started because libev 917happen because the watcher could not be properly started because libev
898ran out of memory, a file descriptor was found to be closed or any other 918ran out of memory, a file descriptor was found to be closed or any other
919problem. Libev considers these application bugs.
920
899problem. You best act on it by reporting the problem and somehow coping 921You best act on it by reporting the problem and somehow coping with the
900with the watcher being stopped. 922watcher being stopped. Note that well-written programs should not receive
923an error ever, so when your watcher receives it, this usually indicates a
924bug in your program.
901 925
902Libev will usually signal a few "dummy" events together with an error, for 926Libev will usually signal a few "dummy" events together with an error, for
903example it might indicate that a fd is readable or writable, and if your 927example it might indicate that a fd is readable or writable, and if your
904callbacks is well-written it can just attempt the operation and cope with 928callbacks is well-written it can just attempt the operation and cope with
905the error from read() or write(). This will not work in multi-threaded 929the error from read() or write(). This will not work in multi-threaded
908 932
909=back 933=back
910 934
911=head2 GENERIC WATCHER FUNCTIONS 935=head2 GENERIC WATCHER FUNCTIONS
912 936
913In the following description, C<TYPE> stands for the watcher type,
914e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
915
916=over 4 937=over 4
917 938
918=item C<ev_init> (ev_TYPE *watcher, callback) 939=item C<ev_init> (ev_TYPE *watcher, callback)
919 940
920This macro initialises the generic portion of a watcher. The contents 941This macro initialises the generic portion of a watcher. The contents
925which rolls both calls into one. 946which rolls both calls into one.
926 947
927You can reinitialise a watcher at any time as long as it has been stopped 948You can reinitialise a watcher at any time as long as it has been stopped
928(or never started) and there are no pending events outstanding. 949(or never started) and there are no pending events outstanding.
929 950
930The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher, 951The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
931int revents)>. 952int revents)>.
932 953
933Example: Initialise an C<ev_io> watcher in two steps. 954Example: Initialise an C<ev_io> watcher in two steps.
934 955
935 ev_io w; 956 ev_io w;
969 990
970 ev_io_start (EV_DEFAULT_UC, &w); 991 ev_io_start (EV_DEFAULT_UC, &w);
971 992
972=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher) 993=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
973 994
974Stops the given watcher again (if active) and clears the pending 995Stops the given watcher if active, and clears the pending status (whether
996the watcher was active or not).
997
975status. It is possible that stopped watchers are pending (for example, 998It is possible that stopped watchers are pending - for example,
976non-repeating timers are being stopped when they become pending), but 999non-repeating timers are being stopped when they become pending - but
977C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If 1000calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
978you want to free or reuse the memory used by the watcher it is therefore a 1001pending. If you want to free or reuse the memory used by the watcher it is
979good idea to always call its C<ev_TYPE_stop> function. 1002therefore a good idea to always call its C<ev_TYPE_stop> function.
980 1003
981=item bool ev_is_active (ev_TYPE *watcher) 1004=item bool ev_is_active (ev_TYPE *watcher)
982 1005
983Returns a true value iff the watcher is active (i.e. it has been started 1006Returns a true value iff the watcher is active (i.e. it has been started
984and not yet been stopped). As long as a watcher is active you must not modify 1007and not yet been stopped). As long as a watcher is active you must not modify
1026The default priority used by watchers when no priority has been set is 1049The default priority used by watchers when no priority has been set is
1027always C<0>, which is supposed to not be too high and not be too low :). 1050always C<0>, which is supposed to not be too high and not be too low :).
1028 1051
1029Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is 1052Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1030fine, as long as you do not mind that the priority value you query might 1053fine, as long as you do not mind that the priority value you query might
1031or might not have been adjusted to be within valid range. 1054or might not have been clamped to the valid range.
1032 1055
1033=item ev_invoke (loop, ev_TYPE *watcher, int revents) 1056=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1034 1057
1035Invoke the C<watcher> with the given C<loop> and C<revents>. Neither 1058Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1036C<loop> nor C<revents> need to be valid as long as the watcher callback 1059C<loop> nor C<revents> need to be valid as long as the watcher callback
1058member, you can also "subclass" the watcher type and provide your own 1081member, you can also "subclass" the watcher type and provide your own
1059data: 1082data:
1060 1083
1061 struct my_io 1084 struct my_io
1062 { 1085 {
1063 struct ev_io io; 1086 ev_io io;
1064 int otherfd; 1087 int otherfd;
1065 void *somedata; 1088 void *somedata;
1066 struct whatever *mostinteresting; 1089 struct whatever *mostinteresting;
1067 }; 1090 };
1068 1091
1071 ev_io_init (&w.io, my_cb, fd, EV_READ); 1094 ev_io_init (&w.io, my_cb, fd, EV_READ);
1072 1095
1073And since your callback will be called with a pointer to the watcher, you 1096And since your callback will be called with a pointer to the watcher, you
1074can cast it back to your own type: 1097can cast it back to your own type:
1075 1098
1076 static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1099 static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1077 { 1100 {
1078 struct my_io *w = (struct my_io *)w_; 1101 struct my_io *w = (struct my_io *)w_;
1079 ... 1102 ...
1080 } 1103 }
1081 1104
1099programmers): 1122programmers):
1100 1123
1101 #include <stddef.h> 1124 #include <stddef.h>
1102 1125
1103 static void 1126 static void
1104 t1_cb (EV_P_ struct ev_timer *w, int revents) 1127 t1_cb (EV_P_ ev_timer *w, int revents)
1105 { 1128 {
1106 struct my_biggy big = (struct my_biggy * 1129 struct my_biggy big = (struct my_biggy *
1107 (((char *)w) - offsetof (struct my_biggy, t1)); 1130 (((char *)w) - offsetof (struct my_biggy, t1));
1108 } 1131 }
1109 1132
1110 static void 1133 static void
1111 t2_cb (EV_P_ struct ev_timer *w, int revents) 1134 t2_cb (EV_P_ ev_timer *w, int revents)
1112 { 1135 {
1113 struct my_biggy big = (struct my_biggy * 1136 struct my_biggy big = (struct my_biggy *
1114 (((char *)w) - offsetof (struct my_biggy, t2)); 1137 (((char *)w) - offsetof (struct my_biggy, t2));
1115 } 1138 }
1116 1139
1251Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well 1274Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1252readable, but only once. Since it is likely line-buffered, you could 1275readable, but only once. Since it is likely line-buffered, you could
1253attempt to read a whole line in the callback. 1276attempt to read a whole line in the callback.
1254 1277
1255 static void 1278 static void
1256 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1279 stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1257 { 1280 {
1258 ev_io_stop (loop, w); 1281 ev_io_stop (loop, w);
1259 .. read from stdin here (or from w->fd) and handle any I/O errors 1282 .. read from stdin here (or from w->fd) and handle any I/O errors
1260 } 1283 }
1261 1284
1262 ... 1285 ...
1263 struct ev_loop *loop = ev_default_init (0); 1286 struct ev_loop *loop = ev_default_init (0);
1264 struct ev_io stdin_readable; 1287 ev_io stdin_readable;
1265 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1288 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1266 ev_io_start (loop, &stdin_readable); 1289 ev_io_start (loop, &stdin_readable);
1267 ev_loop (loop, 0); 1290 ev_loop (loop, 0);
1268 1291
1269 1292
1280 1303
1281The callback is guaranteed to be invoked only I<after> its timeout has 1304The callback is guaranteed to be invoked only I<after> its timeout has
1282passed, but if multiple timers become ready during the same loop iteration 1305passed, but if multiple timers become ready during the same loop iteration
1283then order of execution is undefined. 1306then order of execution is undefined.
1284 1307
1308=head3 Be smart about timeouts
1309
1310Many real-world problems involve some kind of timeout, usually for error
1311recovery. A typical example is an HTTP request - if the other side hangs,
1312you want to raise some error after a while.
1313
1314What follows are some ways to handle this problem, from obvious and
1315inefficient to smart and efficient.
1316
1317In the following, a 60 second activity timeout is assumed - a timeout that
1318gets reset to 60 seconds each time there is activity (e.g. each time some
1319data or other life sign was received).
1320
1321=over 4
1322
1323=item 1. Use a timer and stop, reinitialise and start it on activity.
1324
1325This is the most obvious, but not the most simple way: In the beginning,
1326start the watcher:
1327
1328 ev_timer_init (timer, callback, 60., 0.);
1329 ev_timer_start (loop, timer);
1330
1331Then, each time there is some activity, C<ev_timer_stop> it, initialise it
1332and start it again:
1333
1334 ev_timer_stop (loop, timer);
1335 ev_timer_set (timer, 60., 0.);
1336 ev_timer_start (loop, timer);
1337
1338This is relatively simple to implement, but means that each time there is
1339some activity, libev will first have to remove the timer from its internal
1340data structure and then add it again. Libev tries to be fast, but it's
1341still not a constant-time operation.
1342
1343=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
1344
1345This is the easiest way, and involves using C<ev_timer_again> instead of
1346C<ev_timer_start>.
1347
1348To implement this, configure an C<ev_timer> with a C<repeat> value
1349of C<60> and then call C<ev_timer_again> at start and each time you
1350successfully read or write some data. If you go into an idle state where
1351you do not expect data to travel on the socket, you can C<ev_timer_stop>
1352the timer, and C<ev_timer_again> will automatically restart it if need be.
1353
1354That means you can ignore both the C<ev_timer_start> function and the
1355C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1356member and C<ev_timer_again>.
1357
1358At start:
1359
1360 ev_timer_init (timer, callback);
1361 timer->repeat = 60.;
1362 ev_timer_again (loop, timer);
1363
1364Each time there is some activity:
1365
1366 ev_timer_again (loop, timer);
1367
1368It is even possible to change the time-out on the fly, regardless of
1369whether the watcher is active or not:
1370
1371 timer->repeat = 30.;
1372 ev_timer_again (loop, timer);
1373
1374This is slightly more efficient then stopping/starting the timer each time
1375you want to modify its timeout value, as libev does not have to completely
1376remove and re-insert the timer from/into its internal data structure.
1377
1378It is, however, even simpler than the "obvious" way to do it.
1379
1380=item 3. Let the timer time out, but then re-arm it as required.
1381
1382This method is more tricky, but usually most efficient: Most timeouts are
1383relatively long compared to the intervals between other activity - in
1384our example, within 60 seconds, there are usually many I/O events with
1385associated activity resets.
1386
1387In this case, it would be more efficient to leave the C<ev_timer> alone,
1388but remember the time of last activity, and check for a real timeout only
1389within the callback:
1390
1391 ev_tstamp last_activity; // time of last activity
1392
1393 static void
1394 callback (EV_P_ ev_timer *w, int revents)
1395 {
1396 ev_tstamp now = ev_now (EV_A);
1397 ev_tstamp timeout = last_activity + 60.;
1398
1399 // if last_activity + 60. is older than now, we did time out
1400 if (timeout < now)
1401 {
1402 // timeout occured, take action
1403 }
1404 else
1405 {
1406 // callback was invoked, but there was some activity, re-arm
1407 // the watcher to fire in last_activity + 60, which is
1408 // guaranteed to be in the future, so "again" is positive:
1409 w->again = timeout - now;
1410 ev_timer_again (EV_A_ w);
1411 }
1412 }
1413
1414To summarise the callback: first calculate the real timeout (defined
1415as "60 seconds after the last activity"), then check if that time has
1416been reached, which means something I<did>, in fact, time out. Otherwise
1417the callback was invoked too early (C<timeout> is in the future), so
1418re-schedule the timer to fire at that future time, to see if maybe we have
1419a timeout then.
1420
1421Note how C<ev_timer_again> is used, taking advantage of the
1422C<ev_timer_again> optimisation when the timer is already running.
1423
1424This scheme causes more callback invocations (about one every 60 seconds
1425minus half the average time between activity), but virtually no calls to
1426libev to change the timeout.
1427
1428To start the timer, simply initialise the watcher and set C<last_activity>
1429to the current time (meaning we just have some activity :), then call the
1430callback, which will "do the right thing" and start the timer:
1431
1432 ev_timer_init (timer, callback);
1433 last_activity = ev_now (loop);
1434 callback (loop, timer, EV_TIMEOUT);
1435
1436And when there is some activity, simply store the current time in
1437C<last_activity>, no libev calls at all:
1438
1439 last_actiivty = ev_now (loop);
1440
1441This technique is slightly more complex, but in most cases where the
1442time-out is unlikely to be triggered, much more efficient.
1443
1444Changing the timeout is trivial as well (if it isn't hard-coded in the
1445callback :) - just change the timeout and invoke the callback, which will
1446fix things for you.
1447
1448=item 4. Wee, just use a double-linked list for your timeouts.
1449
1450If there is not one request, but many thousands (millions...), all
1451employing some kind of timeout with the same timeout value, then one can
1452do even better:
1453
1454When starting the timeout, calculate the timeout value and put the timeout
1455at the I<end> of the list.
1456
1457Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
1458the list is expected to fire (for example, using the technique #3).
1459
1460When there is some activity, remove the timer from the list, recalculate
1461the timeout, append it to the end of the list again, and make sure to
1462update the C<ev_timer> if it was taken from the beginning of the list.
1463
1464This way, one can manage an unlimited number of timeouts in O(1) time for
1465starting, stopping and updating the timers, at the expense of a major
1466complication, and having to use a constant timeout. The constant timeout
1467ensures that the list stays sorted.
1468
1469=back
1470
1471So which method the best?
1472
1473Method #2 is a simple no-brain-required solution that is adequate in most
1474situations. Method #3 requires a bit more thinking, but handles many cases
1475better, and isn't very complicated either. In most case, choosing either
1476one is fine, with #3 being better in typical situations.
1477
1478Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1479rather complicated, but extremely efficient, something that really pays
1480off after the first million or so of active timers, i.e. it's usually
1481overkill :)
1482
1285=head3 The special problem of time updates 1483=head3 The special problem of time updates
1286 1484
1287Establishing the current time is a costly operation (it usually takes at 1485Establishing the current time is a costly operation (it usually takes at
1288least two system calls): EV therefore updates its idea of the current 1486least two system calls): EV therefore updates its idea of the current
1289time only before and after C<ev_loop> collects new events, which causes a 1487time only before and after C<ev_loop> collects new events, which causes a
1332If the timer is started but non-repeating, stop it (as if it timed out). 1530If the timer is started but non-repeating, stop it (as if it timed out).
1333 1531
1334If the timer is repeating, either start it if necessary (with the 1532If the timer is repeating, either start it if necessary (with the
1335C<repeat> value), or reset the running timer to the C<repeat> value. 1533C<repeat> value), or reset the running timer to the C<repeat> value.
1336 1534
1337This sounds a bit complicated, but here is a useful and typical 1535This sounds a bit complicated, see "Be smart about timeouts", above, for a
1338example: Imagine you have a TCP connection and you want a so-called idle 1536usage example.
1339timeout, that is, you want to be called when there have been, say, 60
1340seconds of inactivity on the socket. The easiest way to do this is to
1341configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1342C<ev_timer_again> each time you successfully read or write some data. If
1343you go into an idle state where you do not expect data to travel on the
1344socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1345automatically restart it if need be.
1346
1347That means you can ignore the C<after> value and C<ev_timer_start>
1348altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1349
1350 ev_timer_init (timer, callback, 0., 5.);
1351 ev_timer_again (loop, timer);
1352 ...
1353 timer->again = 17.;
1354 ev_timer_again (loop, timer);
1355 ...
1356 timer->again = 10.;
1357 ev_timer_again (loop, timer);
1358
1359This is more slightly efficient then stopping/starting the timer each time
1360you want to modify its timeout value.
1361
1362Note, however, that it is often even more efficient to remember the
1363time of the last activity and let the timer time-out naturally. In the
1364callback, you then check whether the time-out is real, or, if there was
1365some activity, you reschedule the watcher to time-out in "last_activity +
1366timeout - ev_now ()" seconds.
1367 1537
1368=item ev_tstamp repeat [read-write] 1538=item ev_tstamp repeat [read-write]
1369 1539
1370The current C<repeat> value. Will be used each time the watcher times out 1540The current C<repeat> value. Will be used each time the watcher times out
1371or C<ev_timer_again> is called, and determines the next timeout (if any), 1541or C<ev_timer_again> is called, and determines the next timeout (if any),
1376=head3 Examples 1546=head3 Examples
1377 1547
1378Example: Create a timer that fires after 60 seconds. 1548Example: Create a timer that fires after 60 seconds.
1379 1549
1380 static void 1550 static void
1381 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1551 one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1382 { 1552 {
1383 .. one minute over, w is actually stopped right here 1553 .. one minute over, w is actually stopped right here
1384 } 1554 }
1385 1555
1386 struct ev_timer mytimer; 1556 ev_timer mytimer;
1387 ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 1557 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1388 ev_timer_start (loop, &mytimer); 1558 ev_timer_start (loop, &mytimer);
1389 1559
1390Example: Create a timeout timer that times out after 10 seconds of 1560Example: Create a timeout timer that times out after 10 seconds of
1391inactivity. 1561inactivity.
1392 1562
1393 static void 1563 static void
1394 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1564 timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1395 { 1565 {
1396 .. ten seconds without any activity 1566 .. ten seconds without any activity
1397 } 1567 }
1398 1568
1399 struct ev_timer mytimer; 1569 ev_timer mytimer;
1400 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 1570 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1401 ev_timer_again (&mytimer); /* start timer */ 1571 ev_timer_again (&mytimer); /* start timer */
1402 ev_loop (loop, 0); 1572 ev_loop (loop, 0);
1403 1573
1404 // and in some piece of code that gets executed on any "activity": 1574 // and in some piece of code that gets executed on any "activity":
1490 1660
1491If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop 1661If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1492it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the 1662it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1493only event loop modification you are allowed to do). 1663only event loop modification you are allowed to do).
1494 1664
1495The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic 1665The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1496*w, ev_tstamp now)>, e.g.: 1666*w, ev_tstamp now)>, e.g.:
1497 1667
1668 static ev_tstamp
1498 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1669 my_rescheduler (ev_periodic *w, ev_tstamp now)
1499 { 1670 {
1500 return now + 60.; 1671 return now + 60.;
1501 } 1672 }
1502 1673
1503It must return the next time to trigger, based on the passed time value 1674It must return the next time to trigger, based on the passed time value
1540 1711
1541The current interval value. Can be modified any time, but changes only 1712The current interval value. Can be modified any time, but changes only
1542take effect when the periodic timer fires or C<ev_periodic_again> is being 1713take effect when the periodic timer fires or C<ev_periodic_again> is being
1543called. 1714called.
1544 1715
1545=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write] 1716=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1546 1717
1547The current reschedule callback, or C<0>, if this functionality is 1718The current reschedule callback, or C<0>, if this functionality is
1548switched off. Can be changed any time, but changes only take effect when 1719switched off. Can be changed any time, but changes only take effect when
1549the periodic timer fires or C<ev_periodic_again> is being called. 1720the periodic timer fires or C<ev_periodic_again> is being called.
1550 1721
1555Example: Call a callback every hour, or, more precisely, whenever the 1726Example: Call a callback every hour, or, more precisely, whenever the
1556system time is divisible by 3600. The callback invocation times have 1727system time is divisible by 3600. The callback invocation times have
1557potentially a lot of jitter, but good long-term stability. 1728potentially a lot of jitter, but good long-term stability.
1558 1729
1559 static void 1730 static void
1560 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1731 clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1561 { 1732 {
1562 ... its now a full hour (UTC, or TAI or whatever your clock follows) 1733 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1563 } 1734 }
1564 1735
1565 struct ev_periodic hourly_tick; 1736 ev_periodic hourly_tick;
1566 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 1737 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1567 ev_periodic_start (loop, &hourly_tick); 1738 ev_periodic_start (loop, &hourly_tick);
1568 1739
1569Example: The same as above, but use a reschedule callback to do it: 1740Example: The same as above, but use a reschedule callback to do it:
1570 1741
1571 #include <math.h> 1742 #include <math.h>
1572 1743
1573 static ev_tstamp 1744 static ev_tstamp
1574 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 1745 my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1575 { 1746 {
1576 return now + (3600. - fmod (now, 3600.)); 1747 return now + (3600. - fmod (now, 3600.));
1577 } 1748 }
1578 1749
1579 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 1750 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1580 1751
1581Example: Call a callback every hour, starting now: 1752Example: Call a callback every hour, starting now:
1582 1753
1583 struct ev_periodic hourly_tick; 1754 ev_periodic hourly_tick;
1584 ev_periodic_init (&hourly_tick, clock_cb, 1755 ev_periodic_init (&hourly_tick, clock_cb,
1585 fmod (ev_now (loop), 3600.), 3600., 0); 1756 fmod (ev_now (loop), 3600.), 3600., 0);
1586 ev_periodic_start (loop, &hourly_tick); 1757 ev_periodic_start (loop, &hourly_tick);
1587 1758
1588 1759
1630=head3 Examples 1801=head3 Examples
1631 1802
1632Example: Try to exit cleanly on SIGINT. 1803Example: Try to exit cleanly on SIGINT.
1633 1804
1634 static void 1805 static void
1635 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 1806 sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1636 { 1807 {
1637 ev_unloop (loop, EVUNLOOP_ALL); 1808 ev_unloop (loop, EVUNLOOP_ALL);
1638 } 1809 }
1639 1810
1640 struct ev_signal signal_watcher; 1811 ev_signal signal_watcher;
1641 ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 1812 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1642 ev_signal_start (loop, &signal_watcher); 1813 ev_signal_start (loop, &signal_watcher);
1643 1814
1644 1815
1645=head2 C<ev_child> - watch out for process status changes 1816=head2 C<ev_child> - watch out for process status changes
1720its completion. 1891its completion.
1721 1892
1722 ev_child cw; 1893 ev_child cw;
1723 1894
1724 static void 1895 static void
1725 child_cb (EV_P_ struct ev_child *w, int revents) 1896 child_cb (EV_P_ ev_child *w, int revents)
1726 { 1897 {
1727 ev_child_stop (EV_A_ w); 1898 ev_child_stop (EV_A_ w);
1728 printf ("process %d exited with status %x\n", w->rpid, w->rstatus); 1899 printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1729 } 1900 }
1730 1901
1794to exchange stat structures with application programs compiled using the 1965to exchange stat structures with application programs compiled using the
1795default compilation environment. 1966default compilation environment.
1796 1967
1797=head3 Inotify and Kqueue 1968=head3 Inotify and Kqueue
1798 1969
1799When C<inotify (7)> support has been compiled into libev (generally only 1970When C<inotify (7)> support has been compiled into libev (generally
1971only available with Linux 2.6.25 or above due to bugs in earlier
1800available with Linux) and present at runtime, it will be used to speed up 1972implementations) and present at runtime, it will be used to speed up
1801change detection where possible. The inotify descriptor will be created lazily 1973change detection where possible. The inotify descriptor will be created
1802when the first C<ev_stat> watcher is being started. 1974lazily when the first C<ev_stat> watcher is being started.
1803 1975
1804Inotify presence does not change the semantics of C<ev_stat> watchers 1976Inotify presence does not change the semantics of C<ev_stat> watchers
1805except that changes might be detected earlier, and in some cases, to avoid 1977except that changes might be detected earlier, and in some cases, to avoid
1806making regular C<stat> calls. Even in the presence of inotify support 1978making regular C<stat> calls. Even in the presence of inotify support
1807there are many cases where libev has to resort to regular C<stat> polling, 1979there are many cases where libev has to resort to regular C<stat> polling,
1981 2153
1982Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the 2154Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1983callback, free it. Also, use no error checking, as usual. 2155callback, free it. Also, use no error checking, as usual.
1984 2156
1985 static void 2157 static void
1986 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2158 idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1987 { 2159 {
1988 free (w); 2160 free (w);
1989 // now do something you wanted to do when the program has 2161 // now do something you wanted to do when the program has
1990 // no longer anything immediate to do. 2162 // no longer anything immediate to do.
1991 } 2163 }
1992 2164
1993 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 2165 ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1994 ev_idle_init (idle_watcher, idle_cb); 2166 ev_idle_init (idle_watcher, idle_cb);
1995 ev_idle_start (loop, idle_cb); 2167 ev_idle_start (loop, idle_cb);
1996 2168
1997 2169
1998=head2 C<ev_prepare> and C<ev_check> - customise your event loop! 2170=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2079 2251
2080 static ev_io iow [nfd]; 2252 static ev_io iow [nfd];
2081 static ev_timer tw; 2253 static ev_timer tw;
2082 2254
2083 static void 2255 static void
2084 io_cb (ev_loop *loop, ev_io *w, int revents) 2256 io_cb (struct ev_loop *loop, ev_io *w, int revents)
2085 { 2257 {
2086 } 2258 }
2087 2259
2088 // create io watchers for each fd and a timer before blocking 2260 // create io watchers for each fd and a timer before blocking
2089 static void 2261 static void
2090 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 2262 adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2091 { 2263 {
2092 int timeout = 3600000; 2264 int timeout = 3600000;
2093 struct pollfd fds [nfd]; 2265 struct pollfd fds [nfd];
2094 // actual code will need to loop here and realloc etc. 2266 // actual code will need to loop here and realloc etc.
2095 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 2267 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2110 } 2282 }
2111 } 2283 }
2112 2284
2113 // stop all watchers after blocking 2285 // stop all watchers after blocking
2114 static void 2286 static void
2115 adns_check_cb (ev_loop *loop, ev_check *w, int revents) 2287 adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2116 { 2288 {
2117 ev_timer_stop (loop, &tw); 2289 ev_timer_stop (loop, &tw);
2118 2290
2119 for (int i = 0; i < nfd; ++i) 2291 for (int i = 0; i < nfd; ++i)
2120 { 2292 {
2288C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be 2460C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2289used). 2461used).
2290 2462
2291 struct ev_loop *loop_hi = ev_default_init (0); 2463 struct ev_loop *loop_hi = ev_default_init (0);
2292 struct ev_loop *loop_lo = 0; 2464 struct ev_loop *loop_lo = 0;
2293 struct ev_embed embed; 2465 ev_embed embed;
2294 2466
2295 // see if there is a chance of getting one that works 2467 // see if there is a chance of getting one that works
2296 // (remember that a flags value of 0 means autodetection) 2468 // (remember that a flags value of 0 means autodetection)
2297 loop_lo = ev_embeddable_backends () & ev_recommended_backends () 2469 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2298 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 2470 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2312kqueue implementation). Store the kqueue/socket-only event loop in 2484kqueue implementation). Store the kqueue/socket-only event loop in
2313C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too). 2485C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2314 2486
2315 struct ev_loop *loop = ev_default_init (0); 2487 struct ev_loop *loop = ev_default_init (0);
2316 struct ev_loop *loop_socket = 0; 2488 struct ev_loop *loop_socket = 0;
2317 struct ev_embed embed; 2489 ev_embed embed;
2318 2490
2319 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) 2491 if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2320 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) 2492 if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2321 { 2493 {
2322 ev_embed_init (&embed, 0, loop_socket); 2494 ev_embed_init (&embed, 0, loop_socket);
2536 /* doh, nothing entered */; 2708 /* doh, nothing entered */;
2537 } 2709 }
2538 2710
2539 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 2711 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2540 2712
2541=item ev_feed_event (ev_loop *, watcher *, int revents) 2713=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2542 2714
2543Feeds the given event set into the event loop, as if the specified event 2715Feeds the given event set into the event loop, as if the specified event
2544had happened for the specified watcher (which must be a pointer to an 2716had happened for the specified watcher (which must be a pointer to an
2545initialised but not necessarily started event watcher). 2717initialised but not necessarily started event watcher).
2546 2718
2547=item ev_feed_fd_event (ev_loop *, int fd, int revents) 2719=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2548 2720
2549Feed an event on the given fd, as if a file descriptor backend detected 2721Feed an event on the given fd, as if a file descriptor backend detected
2550the given events it. 2722the given events it.
2551 2723
2552=item ev_feed_signal_event (ev_loop *loop, int signum) 2724=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2553 2725
2554Feed an event as if the given signal occurred (C<loop> must be the default 2726Feed an event as if the given signal occurred (C<loop> must be the default
2555loop!). 2727loop!).
2556 2728
2557=back 2729=back
2791 2963
2792=item D 2964=item D
2793 2965
2794Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to 2966Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2795be found at L<http://proj.llucax.com.ar/wiki/evd>. 2967be found at L<http://proj.llucax.com.ar/wiki/evd>.
2968
2969=item Ocaml
2970
2971Erkki Seppala has written Ocaml bindings for libev, to be found at
2972L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2796 2973
2797=back 2974=back
2798 2975
2799 2976
2800=head1 MACRO MAGIC 2977=head1 MACRO MAGIC

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