… | |
… | |
633 | This function is rarely useful, but when some event callback runs for a |
633 | 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 |
634 | very long time without entering the event loop, updating libev's idea of |
635 | the current time is a good idea. |
635 | the current time is a good idea. |
636 | |
636 | |
637 | See also "The special problem of time updates" in the C<ev_timer> section. |
637 | See also "The special problem of time updates" in the C<ev_timer> section. |
|
|
638 | |
|
|
639 | =item ev_suspend (loop) |
|
|
640 | |
|
|
641 | =item ev_resume (loop) |
|
|
642 | |
|
|
643 | These two functions suspend and resume a loop, for use when the loop is |
|
|
644 | not used for a while and timeouts should not be processed. |
|
|
645 | |
|
|
646 | A typical use case would be an interactive program such as a game: When |
|
|
647 | the user presses C<^Z> to suspend the game and resumes it an hour later it |
|
|
648 | would be best to handle timeouts as if no time had actually passed while |
|
|
649 | the program was suspended. This can be achieved by calling C<ev_suspend> |
|
|
650 | in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling |
|
|
651 | C<ev_resume> directly afterwards to resume timer processing. |
|
|
652 | |
|
|
653 | Effectively, all C<ev_timer> watchers will be delayed by the time spend |
|
|
654 | between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers |
|
|
655 | will be rescheduled (that is, they will lose any events that would have |
|
|
656 | occured while suspended). |
|
|
657 | |
|
|
658 | After calling C<ev_suspend> you B<must not> call I<any> function on the |
|
|
659 | given loop other than C<ev_resume>, and you B<must not> call C<ev_resume> |
|
|
660 | without a previous call to C<ev_suspend>. |
|
|
661 | |
|
|
662 | Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the |
|
|
663 | event loop time (see C<ev_now_update>). |
638 | |
664 | |
639 | =item ev_loop (loop, int flags) |
665 | =item ev_loop (loop, int flags) |
640 | |
666 | |
641 | Finally, this is it, the event handler. This function usually is called |
667 | 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 |
668 | after you initialised all your watchers and you want to start handling |
… | |
… | |
1057 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1083 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1058 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1084 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1059 | before watchers with lower priority, but priority will not keep watchers |
1085 | before watchers with lower priority, but priority will not keep watchers |
1060 | from being executed (except for C<ev_idle> watchers). |
1086 | from being executed (except for C<ev_idle> watchers). |
1061 | |
1087 | |
1062 | This means that priorities are I<only> used for ordering callback |
|
|
1063 | invocation after new events have been received. This is useful, for |
|
|
1064 | example, to reduce latency after idling, or more often, to bind two |
|
|
1065 | watchers on the same event and make sure one is called first. |
|
|
1066 | |
|
|
1067 | If you need to suppress invocation when higher priority events are pending |
1088 | If you need to suppress invocation when higher priority events are pending |
1068 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1089 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1069 | |
1090 | |
1070 | You I<must not> change the priority of a watcher as long as it is active or |
1091 | You I<must not> change the priority of a watcher as long as it is active or |
1071 | pending. |
1092 | pending. |
1072 | |
|
|
1073 | The default priority used by watchers when no priority has been set is |
|
|
1074 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1075 | |
1093 | |
1076 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1094 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1077 | fine, as long as you do not mind that the priority value you query might |
1095 | fine, as long as you do not mind that the priority value you query might |
1078 | or might not have been clamped to the valid range. |
1096 | or might not have been clamped to the valid range. |
|
|
1097 | |
|
|
1098 | The default priority used by watchers when no priority has been set is |
|
|
1099 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1100 | |
|
|
1101 | See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of |
|
|
1102 | priorities. |
1079 | |
1103 | |
1080 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1104 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1081 | |
1105 | |
1082 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1106 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1083 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1107 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
… | |
… | |
1158 | t2_cb (EV_P_ ev_timer *w, int revents) |
1182 | t2_cb (EV_P_ ev_timer *w, int revents) |
1159 | { |
1183 | { |
1160 | struct my_biggy big = (struct my_biggy * |
1184 | struct my_biggy big = (struct my_biggy * |
1161 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1185 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1162 | } |
1186 | } |
|
|
1187 | |
|
|
1188 | =head2 WATCHER PRIORITY MODELS |
|
|
1189 | |
|
|
1190 | Many event loops support I<watcher priorities>, which are usually small |
|
|
1191 | integers that influence the ordering of event callback invocation |
|
|
1192 | between watchers in some way, all else being equal. |
|
|
1193 | |
|
|
1194 | In libev, Watcher priorities can be set using C<ev_set_priority>. See its |
|
|
1195 | description for the more technical details such as the actual priority |
|
|
1196 | range. |
|
|
1197 | |
|
|
1198 | There are two common ways how these these priorities are being interpreted |
|
|
1199 | by event loops: |
|
|
1200 | |
|
|
1201 | In the more common lock-out model, higher priorities "lock out" invocation |
|
|
1202 | of lower priority watchers, which means as long as higher priority |
|
|
1203 | watchers receive events, lower priority watchers are not being invoked. |
|
|
1204 | |
|
|
1205 | The less common only-for-ordering model uses priorities solely to order |
|
|
1206 | callback invocation within a single event loop iteration: Higher priority |
|
|
1207 | watchers are invoked before lower priority ones, but they all get invoked |
|
|
1208 | before polling for new events. |
|
|
1209 | |
|
|
1210 | Libev uses the second (only-for-ordering) model for all its watchers |
|
|
1211 | except for idle watchers (which use the lock-out model). |
|
|
1212 | |
|
|
1213 | The rationale behind this is that implementing the lock-out model for |
|
|
1214 | watchers is not well supported by most kernel interfaces, and most event |
|
|
1215 | libraries will just poll for the same events again and again as long as |
|
|
1216 | their callbacks have not been executed, which is very inefficient in the |
|
|
1217 | common case of one high-priority watcher locking out a mass of lower |
|
|
1218 | priority ones. |
|
|
1219 | |
|
|
1220 | Static (ordering) priorities are most useful when you have two or more |
|
|
1221 | watchers handling the same resource: a typical usage example is having an |
|
|
1222 | C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle |
|
|
1223 | timeouts. Under load, data might be received while the program handles |
|
|
1224 | other jobs, but since timers normally get invoked first, the timeout |
|
|
1225 | handler will be executed before checking for data. In that case, giving |
|
|
1226 | the timer a lower priority than the I/O watcher ensures that I/O will be |
|
|
1227 | handled first even under adverse conditions (which is usually, but not |
|
|
1228 | always, what you want). |
|
|
1229 | |
|
|
1230 | Since idle watchers use the "lock-out" model, meaning that idle watchers |
|
|
1231 | will only be executed when no same or higher priority watchers have |
|
|
1232 | received events, they can be used to implement the "lock-out" model when |
|
|
1233 | required. |
|
|
1234 | |
|
|
1235 | For example, to emulate how many other event libraries handle priorities, |
|
|
1236 | you can associate an C<ev_idle> watcher to each such watcher, and in |
|
|
1237 | the normal watcher callback, you just start the idle watcher. The real |
|
|
1238 | processing is done in the idle watcher callback. This causes libev to |
|
|
1239 | continously poll and process kernel event data for the watcher, but when |
|
|
1240 | the lock-out case is known to be rare (which in turn is rare :), this is |
|
|
1241 | workable. |
|
|
1242 | |
|
|
1243 | Usually, however, the lock-out model implemented that way will perform |
|
|
1244 | miserably under the type of load it was designed to handle. In that case, |
|
|
1245 | it might be preferable to stop the real watcher before starting the |
|
|
1246 | idle watcher, so the kernel will not have to process the event in case |
|
|
1247 | the actual processing will be delayed for considerable time. |
|
|
1248 | |
|
|
1249 | Here is an example of an I/O watcher that should run at a strictly lower |
|
|
1250 | priority than the default, and which should only process data when no |
|
|
1251 | other events are pending: |
|
|
1252 | |
|
|
1253 | ev_idle idle; // actual processing watcher |
|
|
1254 | ev_io io; // actual event watcher |
|
|
1255 | |
|
|
1256 | static void |
|
|
1257 | io_cb (EV_P_ ev_io *w, int revents) |
|
|
1258 | { |
|
|
1259 | // stop the I/O watcher, we received the event, but |
|
|
1260 | // are not yet ready to handle it. |
|
|
1261 | ev_io_stop (EV_A_ w); |
|
|
1262 | |
|
|
1263 | // start the idle watcher to ahndle the actual event. |
|
|
1264 | // it will not be executed as long as other watchers |
|
|
1265 | // with the default priority are receiving events. |
|
|
1266 | ev_idle_start (EV_A_ &idle); |
|
|
1267 | } |
|
|
1268 | |
|
|
1269 | static void |
|
|
1270 | idle-cb (EV_P_ ev_idle *w, int revents) |
|
|
1271 | { |
|
|
1272 | // actual processing |
|
|
1273 | read (STDIN_FILENO, ...); |
|
|
1274 | |
|
|
1275 | // have to start the I/O watcher again, as |
|
|
1276 | // we have handled the event |
|
|
1277 | ev_io_start (EV_P_ &io); |
|
|
1278 | } |
|
|
1279 | |
|
|
1280 | // initialisation |
|
|
1281 | ev_idle_init (&idle, idle_cb); |
|
|
1282 | ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ); |
|
|
1283 | ev_io_start (EV_DEFAULT_ &io); |
|
|
1284 | |
|
|
1285 | In the "real" world, it might also be beneficial to start a timer, so that |
|
|
1286 | low-priority connections can not be locked out forever under load. This |
|
|
1287 | enables your program to keep a lower latency for important connections |
|
|
1288 | during short periods of high load, while not completely locking out less |
|
|
1289 | important ones. |
1163 | |
1290 | |
1164 | |
1291 | |
1165 | =head1 WATCHER TYPES |
1292 | =head1 WATCHER TYPES |
1166 | |
1293 | |
1167 | This section describes each watcher in detail, but will not repeat |
1294 | This section describes each watcher in detail, but will not repeat |
… | |
… | |
1324 | year, it will still time out after (roughly) one hour. "Roughly" because |
1451 | year, it will still time out after (roughly) one hour. "Roughly" because |
1325 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1452 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1326 | monotonic clock option helps a lot here). |
1453 | monotonic clock option helps a lot here). |
1327 | |
1454 | |
1328 | The callback is guaranteed to be invoked only I<after> its timeout has |
1455 | The callback is guaranteed to be invoked only I<after> its timeout has |
1329 | passed, but if multiple timers become ready during the same loop iteration |
1456 | passed. If multiple timers become ready during the same loop iteration |
1330 | then order of execution is undefined. |
1457 | then the ones with earlier time-out values are invoked before ones with |
|
|
1458 | later time-out values (but this is no longer true when a callback calls |
|
|
1459 | C<ev_loop> recursively). |
1331 | |
1460 | |
1332 | =head3 Be smart about timeouts |
1461 | =head3 Be smart about timeouts |
1333 | |
1462 | |
1334 | Many real-world problems involve some kind of timeout, usually for error |
1463 | Many real-world problems involve some kind of timeout, usually for error |
1335 | recovery. A typical example is an HTTP request - if the other side hangs, |
1464 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1554 | If the timer is started but non-repeating, stop it (as if it timed out). |
1683 | If the timer is started but non-repeating, stop it (as if it timed out). |
1555 | |
1684 | |
1556 | If the timer is repeating, either start it if necessary (with the |
1685 | If the timer is repeating, either start it if necessary (with the |
1557 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1686 | C<repeat> value), or reset the running timer to the C<repeat> value. |
1558 | |
1687 | |
1559 | This sounds a bit complicated, see "Be smart about timeouts", above, for a |
1688 | This sounds a bit complicated, see L<Be smart about timeouts>, above, for a |
1560 | usage example. |
1689 | usage example. |
1561 | |
1690 | |
1562 | =item ev_tstamp repeat [read-write] |
1691 | =item ev_tstamp repeat [read-write] |
1563 | |
1692 | |
1564 | The current C<repeat> value. Will be used each time the watcher times out |
1693 | The current C<repeat> value. Will be used each time the watcher times out |
… | |
… | |
1624 | timers, such as triggering an event on each "midnight, local time", or |
1753 | timers, such as triggering an event on each "midnight, local time", or |
1625 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
1754 | other complicated rules. This cannot be done with C<ev_timer> watchers, as |
1626 | those cannot react to time jumps. |
1755 | those cannot react to time jumps. |
1627 | |
1756 | |
1628 | As with timers, the callback is guaranteed to be invoked only when the |
1757 | As with timers, the callback is guaranteed to be invoked only when the |
1629 | point in time where it is supposed to trigger has passed, but if multiple |
1758 | point in time where it is supposed to trigger has passed. If multiple |
1630 | periodic timers become ready during the same loop iteration, then order of |
1759 | timers become ready during the same loop iteration then the ones with |
1631 | execution is undefined. |
1760 | earlier time-out values are invoked before ones with later time-out values |
|
|
1761 | (but this is no longer true when a callback calls C<ev_loop> recursively). |
1632 | |
1762 | |
1633 | =head3 Watcher-Specific Functions and Data Members |
1763 | =head3 Watcher-Specific Functions and Data Members |
1634 | |
1764 | |
1635 | =over 4 |
1765 | =over 4 |
1636 | |
1766 | |
… | |
… | |
3964 | involves iterating over all running async watchers or all signal numbers. |
4094 | involves iterating over all running async watchers or all signal numbers. |
3965 | |
4095 | |
3966 | =back |
4096 | =back |
3967 | |
4097 | |
3968 | |
4098 | |
|
|
4099 | =head1 GLOSSARY |
|
|
4100 | |
|
|
4101 | =over 4 |
|
|
4102 | |
|
|
4103 | =item active |
|
|
4104 | |
|
|
4105 | A watcher is active as long as it has been started (has been attached to |
|
|
4106 | an event loop) but not yet stopped (disassociated from the event loop). |
|
|
4107 | |
|
|
4108 | =item application |
|
|
4109 | |
|
|
4110 | In this document, an application is whatever is using libev. |
|
|
4111 | |
|
|
4112 | =item callback |
|
|
4113 | |
|
|
4114 | The address of a function that is called when some event has been |
|
|
4115 | detected. Callbacks are being passed the event loop, the watcher that |
|
|
4116 | received the event, and the actual event bitset. |
|
|
4117 | |
|
|
4118 | =item callback invocation |
|
|
4119 | |
|
|
4120 | The act of calling the callback associated with a watcher. |
|
|
4121 | |
|
|
4122 | =item event |
|
|
4123 | |
|
|
4124 | A change of state of some external event, such as data now being available |
|
|
4125 | for reading on a file descriptor, time having passed or simply not having |
|
|
4126 | any other events happening anymore. |
|
|
4127 | |
|
|
4128 | In libev, events are represented as single bits (such as C<EV_READ> or |
|
|
4129 | C<EV_TIMEOUT>). |
|
|
4130 | |
|
|
4131 | =item event library |
|
|
4132 | |
|
|
4133 | A software package implementing an event model and loop. |
|
|
4134 | |
|
|
4135 | =item event loop |
|
|
4136 | |
|
|
4137 | An entity that handles and processes external events and converts them |
|
|
4138 | into callback invocations. |
|
|
4139 | |
|
|
4140 | =item event model |
|
|
4141 | |
|
|
4142 | The model used to describe how an event loop handles and processes |
|
|
4143 | watchers and events. |
|
|
4144 | |
|
|
4145 | =item pending |
|
|
4146 | |
|
|
4147 | A watcher is pending as soon as the corresponding event has been detected, |
|
|
4148 | and stops being pending as soon as the watcher will be invoked or its |
|
|
4149 | pending status is explicitly cleared by the application. |
|
|
4150 | |
|
|
4151 | A watcher can be pending, but not active. Stopping a watcher also clears |
|
|
4152 | its pending status. |
|
|
4153 | |
|
|
4154 | =item real time |
|
|
4155 | |
|
|
4156 | The physical time that is observed. It is apparently strictly monotonic :) |
|
|
4157 | |
|
|
4158 | =item wall-clock time |
|
|
4159 | |
|
|
4160 | The time and date as shown on clocks. Unlike real time, it can actually |
|
|
4161 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
|
|
4162 | clock. |
|
|
4163 | |
|
|
4164 | =item watcher |
|
|
4165 | |
|
|
4166 | A data structure that describes interest in certain events. Watchers need |
|
|
4167 | to be started (attached to an event loop) before they can receive events. |
|
|
4168 | |
|
|
4169 | =item watcher invocation |
|
|
4170 | |
|
|
4171 | The act of calling the callback associated with a watcher. |
|
|
4172 | |
|
|
4173 | =back |
|
|
4174 | |
3969 | =head1 AUTHOR |
4175 | =head1 AUTHOR |
3970 | |
4176 | |
3971 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4177 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
3972 | |
4178 | |