… | |
… | |
62 | |
62 | |
63 | // unloop was called, so exit |
63 | // unloop was called, so exit |
64 | return 0; |
64 | return 0; |
65 | } |
65 | } |
66 | |
66 | |
67 | =head1 DESCRIPTION |
67 | =head1 ABOUT THIS DOCUMENT |
|
|
68 | |
|
|
69 | This document documents the libev software package. |
68 | |
70 | |
69 | The newest version of this document is also available as an html-formatted |
71 | The newest version of this document is also available as an html-formatted |
70 | web page you might find easier to navigate when reading it for the first |
72 | web page you might find easier to navigate when reading it for the first |
71 | time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. |
73 | time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. |
|
|
74 | |
|
|
75 | While this document tries to be as complete as possible in documenting |
|
|
76 | libev, its usage and the rationale behind its design, it is not a tutorial |
|
|
77 | on event-based programming, nor will it introduce event-based programming |
|
|
78 | with libev. |
|
|
79 | |
|
|
80 | Familarity with event based programming techniques in general is assumed |
|
|
81 | throughout this document. |
|
|
82 | |
|
|
83 | =head1 ABOUT LIBEV |
72 | |
84 | |
73 | Libev is an event loop: you register interest in certain events (such as a |
85 | Libev is an event loop: you register interest in certain events (such as a |
74 | file descriptor being readable or a timeout occurring), and it will manage |
86 | file descriptor being readable or a timeout occurring), and it will manage |
75 | these event sources and provide your program with events. |
87 | these event sources and provide your program with events. |
76 | |
88 | |
… | |
… | |
633 | This function is rarely useful, but when some event callback runs for a |
645 | This function is rarely useful, but when some event callback runs for a |
634 | very long time without entering the event loop, updating libev's idea of |
646 | very long time without entering the event loop, updating libev's idea of |
635 | the current time is a good idea. |
647 | the current time is a good idea. |
636 | |
648 | |
637 | See also "The special problem of time updates" in the C<ev_timer> section. |
649 | See also "The special problem of time updates" in the C<ev_timer> section. |
|
|
650 | |
|
|
651 | =item ev_suspend (loop) |
|
|
652 | |
|
|
653 | =item ev_resume (loop) |
|
|
654 | |
|
|
655 | These two functions suspend and resume a loop, for use when the loop is |
|
|
656 | not used for a while and timeouts should not be processed. |
|
|
657 | |
|
|
658 | A typical use case would be an interactive program such as a game: When |
|
|
659 | the user presses C<^Z> to suspend the game and resumes it an hour later it |
|
|
660 | would be best to handle timeouts as if no time had actually passed while |
|
|
661 | the program was suspended. This can be achieved by calling C<ev_suspend> |
|
|
662 | in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling |
|
|
663 | C<ev_resume> directly afterwards to resume timer processing. |
|
|
664 | |
|
|
665 | Effectively, all C<ev_timer> watchers will be delayed by the time spend |
|
|
666 | between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers |
|
|
667 | will be rescheduled (that is, they will lose any events that would have |
|
|
668 | occured while suspended). |
|
|
669 | |
|
|
670 | After calling C<ev_suspend> you B<must not> call I<any> function on the |
|
|
671 | given loop other than C<ev_resume>, and you B<must not> call C<ev_resume> |
|
|
672 | without a previous call to C<ev_suspend>. |
|
|
673 | |
|
|
674 | Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the |
|
|
675 | event loop time (see C<ev_now_update>). |
638 | |
676 | |
639 | =item ev_loop (loop, int flags) |
677 | =item ev_loop (loop, int flags) |
640 | |
678 | |
641 | Finally, this is it, the event handler. This function usually is called |
679 | Finally, this is it, the event handler. This function usually is called |
642 | after you initialised all your watchers and you want to start handling |
680 | after you initialised all your watchers and you want to start handling |
… | |
… | |
726 | |
764 | |
727 | If you have a watcher you never unregister that should not keep C<ev_loop> |
765 | If you have a watcher you never unregister that should not keep C<ev_loop> |
728 | from returning, call ev_unref() after starting, and ev_ref() before |
766 | from returning, call ev_unref() after starting, and ev_ref() before |
729 | stopping it. |
767 | stopping it. |
730 | |
768 | |
731 | As an example, libev itself uses this for its internal signal pipe: It is |
769 | As an example, libev itself uses this for its internal signal pipe: It |
732 | not visible to the libev user and should not keep C<ev_loop> from exiting |
770 | is not visible to the libev user and should not keep C<ev_loop> from |
733 | if no event watchers registered by it are active. It is also an excellent |
771 | exiting if no event watchers registered by it are active. It is also an |
734 | way to do this for generic recurring timers or from within third-party |
772 | excellent way to do this for generic recurring timers or from within |
735 | libraries. Just remember to I<unref after start> and I<ref before stop> |
773 | third-party libraries. Just remember to I<unref after start> and I<ref |
736 | (but only if the watcher wasn't active before, or was active before, |
774 | before stop> (but only if the watcher wasn't active before, or was active |
737 | respectively). |
775 | before, respectively. Note also that libev might stop watchers itself |
|
|
776 | (e.g. non-repeating timers) in which case you have to C<ev_ref> |
|
|
777 | in the callback). |
738 | |
778 | |
739 | Example: Create a signal watcher, but keep it from keeping C<ev_loop> |
779 | Example: Create a signal watcher, but keep it from keeping C<ev_loop> |
740 | running when nothing else is active. |
780 | running when nothing else is active. |
741 | |
781 | |
742 | ev_signal exitsig; |
782 | ev_signal exitsig; |
… | |
… | |
926 | |
966 | |
927 | =item C<EV_ASYNC> |
967 | =item C<EV_ASYNC> |
928 | |
968 | |
929 | The given async watcher has been asynchronously notified (see C<ev_async>). |
969 | The given async watcher has been asynchronously notified (see C<ev_async>). |
930 | |
970 | |
|
|
971 | =item C<EV_CUSTOM> |
|
|
972 | |
|
|
973 | Not ever sent (or otherwise used) by libev itself, but can be freely used |
|
|
974 | by libev users to signal watchers (e.g. via C<ev_feed_event>). |
|
|
975 | |
931 | =item C<EV_ERROR> |
976 | =item C<EV_ERROR> |
932 | |
977 | |
933 | An unspecified error has occurred, the watcher has been stopped. This might |
978 | An unspecified error has occurred, the watcher has been stopped. This might |
934 | happen because the watcher could not be properly started because libev |
979 | happen because the watcher could not be properly started because libev |
935 | ran out of memory, a file descriptor was found to be closed or any other |
980 | ran out of memory, a file descriptor was found to be closed or any other |
… | |
… | |
1050 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1095 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1051 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1096 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1052 | before watchers with lower priority, but priority will not keep watchers |
1097 | before watchers with lower priority, but priority will not keep watchers |
1053 | from being executed (except for C<ev_idle> watchers). |
1098 | from being executed (except for C<ev_idle> watchers). |
1054 | |
1099 | |
1055 | This means that priorities are I<only> used for ordering callback |
|
|
1056 | invocation after new events have been received. This is useful, for |
|
|
1057 | example, to reduce latency after idling, or more often, to bind two |
|
|
1058 | watchers on the same event and make sure one is called first. |
|
|
1059 | |
|
|
1060 | If you need to suppress invocation when higher priority events are pending |
1100 | If you need to suppress invocation when higher priority events are pending |
1061 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1101 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1062 | |
1102 | |
1063 | You I<must not> change the priority of a watcher as long as it is active or |
1103 | You I<must not> change the priority of a watcher as long as it is active or |
1064 | pending. |
1104 | pending. |
1065 | |
|
|
1066 | The default priority used by watchers when no priority has been set is |
|
|
1067 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1068 | |
1105 | |
1069 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1106 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1070 | fine, as long as you do not mind that the priority value you query might |
1107 | fine, as long as you do not mind that the priority value you query might |
1071 | or might not have been clamped to the valid range. |
1108 | or might not have been clamped to the valid range. |
|
|
1109 | |
|
|
1110 | The default priority used by watchers when no priority has been set is |
|
|
1111 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1112 | |
|
|
1113 | See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of |
|
|
1114 | priorities. |
1072 | |
1115 | |
1073 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1116 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1074 | |
1117 | |
1075 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1118 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1076 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1119 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
… | |
… | |
1151 | t2_cb (EV_P_ ev_timer *w, int revents) |
1194 | t2_cb (EV_P_ ev_timer *w, int revents) |
1152 | { |
1195 | { |
1153 | struct my_biggy big = (struct my_biggy * |
1196 | struct my_biggy big = (struct my_biggy * |
1154 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1197 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1155 | } |
1198 | } |
|
|
1199 | |
|
|
1200 | =head2 WATCHER PRIORITY MODELS |
|
|
1201 | |
|
|
1202 | Many event loops support I<watcher priorities>, which are usually small |
|
|
1203 | integers that influence the ordering of event callback invocation |
|
|
1204 | between watchers in some way, all else being equal. |
|
|
1205 | |
|
|
1206 | In libev, Watcher priorities can be set using C<ev_set_priority>. See its |
|
|
1207 | description for the more technical details such as the actual priority |
|
|
1208 | range. |
|
|
1209 | |
|
|
1210 | There are two common ways how these these priorities are being interpreted |
|
|
1211 | by event loops: |
|
|
1212 | |
|
|
1213 | In the more common lock-out model, higher priorities "lock out" invocation |
|
|
1214 | of lower priority watchers, which means as long as higher priority |
|
|
1215 | watchers receive events, lower priority watchers are not being invoked. |
|
|
1216 | |
|
|
1217 | The less common only-for-ordering model uses priorities solely to order |
|
|
1218 | callback invocation within a single event loop iteration: Higher priority |
|
|
1219 | watchers are invoked before lower priority ones, but they all get invoked |
|
|
1220 | before polling for new events. |
|
|
1221 | |
|
|
1222 | Libev uses the second (only-for-ordering) model for all its watchers |
|
|
1223 | except for idle watchers (which use the lock-out model). |
|
|
1224 | |
|
|
1225 | The rationale behind this is that implementing the lock-out model for |
|
|
1226 | watchers is not well supported by most kernel interfaces, and most event |
|
|
1227 | libraries will just poll for the same events again and again as long as |
|
|
1228 | their callbacks have not been executed, which is very inefficient in the |
|
|
1229 | common case of one high-priority watcher locking out a mass of lower |
|
|
1230 | priority ones. |
|
|
1231 | |
|
|
1232 | Static (ordering) priorities are most useful when you have two or more |
|
|
1233 | watchers handling the same resource: a typical usage example is having an |
|
|
1234 | C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle |
|
|
1235 | timeouts. Under load, data might be received while the program handles |
|
|
1236 | other jobs, but since timers normally get invoked first, the timeout |
|
|
1237 | handler will be executed before checking for data. In that case, giving |
|
|
1238 | the timer a lower priority than the I/O watcher ensures that I/O will be |
|
|
1239 | handled first even under adverse conditions (which is usually, but not |
|
|
1240 | always, what you want). |
|
|
1241 | |
|
|
1242 | Since idle watchers use the "lock-out" model, meaning that idle watchers |
|
|
1243 | will only be executed when no same or higher priority watchers have |
|
|
1244 | received events, they can be used to implement the "lock-out" model when |
|
|
1245 | required. |
|
|
1246 | |
|
|
1247 | For example, to emulate how many other event libraries handle priorities, |
|
|
1248 | you can associate an C<ev_idle> watcher to each such watcher, and in |
|
|
1249 | the normal watcher callback, you just start the idle watcher. The real |
|
|
1250 | processing is done in the idle watcher callback. This causes libev to |
|
|
1251 | continously poll and process kernel event data for the watcher, but when |
|
|
1252 | the lock-out case is known to be rare (which in turn is rare :), this is |
|
|
1253 | workable. |
|
|
1254 | |
|
|
1255 | Usually, however, the lock-out model implemented that way will perform |
|
|
1256 | miserably under the type of load it was designed to handle. In that case, |
|
|
1257 | it might be preferable to stop the real watcher before starting the |
|
|
1258 | idle watcher, so the kernel will not have to process the event in case |
|
|
1259 | the actual processing will be delayed for considerable time. |
|
|
1260 | |
|
|
1261 | Here is an example of an I/O watcher that should run at a strictly lower |
|
|
1262 | priority than the default, and which should only process data when no |
|
|
1263 | other events are pending: |
|
|
1264 | |
|
|
1265 | ev_idle idle; // actual processing watcher |
|
|
1266 | ev_io io; // actual event watcher |
|
|
1267 | |
|
|
1268 | static void |
|
|
1269 | io_cb (EV_P_ ev_io *w, int revents) |
|
|
1270 | { |
|
|
1271 | // stop the I/O watcher, we received the event, but |
|
|
1272 | // are not yet ready to handle it. |
|
|
1273 | ev_io_stop (EV_A_ w); |
|
|
1274 | |
|
|
1275 | // start the idle watcher to ahndle the actual event. |
|
|
1276 | // it will not be executed as long as other watchers |
|
|
1277 | // with the default priority are receiving events. |
|
|
1278 | ev_idle_start (EV_A_ &idle); |
|
|
1279 | } |
|
|
1280 | |
|
|
1281 | static void |
|
|
1282 | idle-cb (EV_P_ ev_idle *w, int revents) |
|
|
1283 | { |
|
|
1284 | // actual processing |
|
|
1285 | read (STDIN_FILENO, ...); |
|
|
1286 | |
|
|
1287 | // have to start the I/O watcher again, as |
|
|
1288 | // we have handled the event |
|
|
1289 | ev_io_start (EV_P_ &io); |
|
|
1290 | } |
|
|
1291 | |
|
|
1292 | // initialisation |
|
|
1293 | ev_idle_init (&idle, idle_cb); |
|
|
1294 | ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ); |
|
|
1295 | ev_io_start (EV_DEFAULT_ &io); |
|
|
1296 | |
|
|
1297 | In the "real" world, it might also be beneficial to start a timer, so that |
|
|
1298 | low-priority connections can not be locked out forever under load. This |
|
|
1299 | enables your program to keep a lower latency for important connections |
|
|
1300 | during short periods of high load, while not completely locking out less |
|
|
1301 | important ones. |
1156 | |
1302 | |
1157 | |
1303 | |
1158 | =head1 WATCHER TYPES |
1304 | =head1 WATCHER TYPES |
1159 | |
1305 | |
1160 | This section describes each watcher in detail, but will not repeat |
1306 | This section describes each watcher in detail, but will not repeat |
… | |
… | |
1317 | year, it will still time out after (roughly) one hour. "Roughly" because |
1463 | year, it will still time out after (roughly) one hour. "Roughly" because |
1318 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1464 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1319 | monotonic clock option helps a lot here). |
1465 | monotonic clock option helps a lot here). |
1320 | |
1466 | |
1321 | The callback is guaranteed to be invoked only I<after> its timeout has |
1467 | The callback is guaranteed to be invoked only I<after> its timeout has |
1322 | passed, but if multiple timers become ready during the same loop iteration |
1468 | passed. If multiple timers become ready during the same loop iteration |
1323 | then order of execution is undefined. |
1469 | then the ones with earlier time-out values are invoked before ones with |
|
|
1470 | later time-out values (but this is no longer true when a callback calls |
|
|
1471 | C<ev_loop> recursively). |
1324 | |
1472 | |
1325 | =head3 Be smart about timeouts |
1473 | =head3 Be smart about timeouts |
1326 | |
1474 | |
1327 | Many real-world problems involve some kind of timeout, usually for error |
1475 | Many real-world problems involve some kind of timeout, usually for error |
1328 | recovery. A typical example is an HTTP request - if the other side hangs, |
1476 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1547 | If the timer is started but non-repeating, stop it (as if it timed out). |
1695 | If the timer is started but non-repeating, stop it (as if it timed out). |
1548 | |
1696 | |
1549 | If the timer is repeating, either start it if necessary (with the |
1697 | If the timer is repeating, either start it if necessary (with the |
1550 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1698 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1551 | |
1699 | |
1552 | This sounds a bit complicated, see "Be smart about timeouts", above, for a |
1700 | This sounds a bit complicated, see L<Be smart about timeouts>, above, for a |
1553 | usage example. |
1701 | usage example. |
1554 | |
1702 | |
1555 | =item ev_tstamp repeat [read-write] |
1703 | =item ev_tstamp repeat [read-write] |
1556 | |
1704 | |
1557 | The current C<repeat> value. Will be used each time the watcher times out |
1705 | The current C<repeat> value. Will be used each time the watcher times out |
… | |
… | |
1617 | timers, such as triggering an event on each "midnight, local time", or |
1765 | timers, such as triggering an event on each "midnight, local time", or |
1618 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
1766 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
1619 | those cannot react to time jumps. |
1767 | those cannot react to time jumps. |
1620 | |
1768 | |
1621 | As with timers, the callback is guaranteed to be invoked only when the |
1769 | As with timers, the callback is guaranteed to be invoked only when the |
1622 | point in time where it is supposed to trigger has passed, but if multiple |
1770 | point in time where it is supposed to trigger has passed. If multiple |
1623 | periodic timers become ready during the same loop iteration, then order of |
1771 | timers become ready during the same loop iteration then the ones with |
1624 | execution is undefined. |
1772 | earlier time-out values are invoked before ones with later time-out values |
|
|
1773 | (but this is no longer true when a callback calls C<ev_loop> recursively). |
1625 | |
1774 | |
1626 | =head3 Watcher-Specific Functions and Data Members |
1775 | =head3 Watcher-Specific Functions and Data Members |
1627 | |
1776 | |
1628 | =over 4 |
1777 | =over 4 |
1629 | |
1778 | |
… | |
… | |
3957 | involves iterating over all running async watchers or all signal numbers. |
4106 | involves iterating over all running async watchers or all signal numbers. |
3958 | |
4107 | |
3959 | =back |
4108 | =back |
3960 | |
4109 | |
3961 | |
4110 | |
|
|
4111 | =head1 GLOSSARY |
|
|
4112 | |
|
|
4113 | =over 4 |
|
|
4114 | |
|
|
4115 | =item active |
|
|
4116 | |
|
|
4117 | A watcher is active as long as it has been started (has been attached to |
|
|
4118 | an event loop) but not yet stopped (disassociated from the event loop). |
|
|
4119 | |
|
|
4120 | =item application |
|
|
4121 | |
|
|
4122 | In this document, an application is whatever is using libev. |
|
|
4123 | |
|
|
4124 | =item callback |
|
|
4125 | |
|
|
4126 | The address of a function that is called when some event has been |
|
|
4127 | detected. Callbacks are being passed the event loop, the watcher that |
|
|
4128 | received the event, and the actual event bitset. |
|
|
4129 | |
|
|
4130 | =item callback invocation |
|
|
4131 | |
|
|
4132 | The act of calling the callback associated with a watcher. |
|
|
4133 | |
|
|
4134 | =item event |
|
|
4135 | |
|
|
4136 | A change of state of some external event, such as data now being available |
|
|
4137 | for reading on a file descriptor, time having passed or simply not having |
|
|
4138 | any other events happening anymore. |
|
|
4139 | |
|
|
4140 | In libev, events are represented as single bits (such as C<EV_READ> or |
|
|
4141 | C<EV_TIMEOUT>). |
|
|
4142 | |
|
|
4143 | =item event library |
|
|
4144 | |
|
|
4145 | A software package implementing an event model and loop. |
|
|
4146 | |
|
|
4147 | =item event loop |
|
|
4148 | |
|
|
4149 | An entity that handles and processes external events and converts them |
|
|
4150 | into callback invocations. |
|
|
4151 | |
|
|
4152 | =item event model |
|
|
4153 | |
|
|
4154 | The model used to describe how an event loop handles and processes |
|
|
4155 | watchers and events. |
|
|
4156 | |
|
|
4157 | =item pending |
|
|
4158 | |
|
|
4159 | A watcher is pending as soon as the corresponding event has been detected, |
|
|
4160 | and stops being pending as soon as the watcher will be invoked or its |
|
|
4161 | pending status is explicitly cleared by the application. |
|
|
4162 | |
|
|
4163 | A watcher can be pending, but not active. Stopping a watcher also clears |
|
|
4164 | its pending status. |
|
|
4165 | |
|
|
4166 | =item real time |
|
|
4167 | |
|
|
4168 | The physical time that is observed. It is apparently strictly monotonic :) |
|
|
4169 | |
|
|
4170 | =item wall-clock time |
|
|
4171 | |
|
|
4172 | The time and date as shown on clocks. Unlike real time, it can actually |
|
|
4173 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
|
|
4174 | clock. |
|
|
4175 | |
|
|
4176 | =item watcher |
|
|
4177 | |
|
|
4178 | A data structure that describes interest in certain events. Watchers need |
|
|
4179 | to be started (attached to an event loop) before they can receive events. |
|
|
4180 | |
|
|
4181 | =item watcher invocation |
|
|
4182 | |
|
|
4183 | The act of calling the callback associated with a watcher. |
|
|
4184 | |
|
|
4185 | =back |
|
|
4186 | |
3962 | =head1 AUTHOR |
4187 | =head1 AUTHOR |
3963 | |
4188 | |
3964 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4189 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
3965 | |
4190 | |