… | |
… | |
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 |
|
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68 | |
|
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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>. |
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74 | |
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75 | While this document tries to be as complete as possible in documenting |
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76 | libev, its usage and the rationale behind its design, it is not a tutorial |
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77 | on event-based programming, nor will it introduce event-based programming |
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78 | with libev. |
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79 | |
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80 | Familarity with event based programming techniques in general is assumed |
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81 | throughout this document. |
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82 | |
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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 | |
… | |
… | |
1083 | 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> |
1084 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1096 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1085 | before watchers with lower priority, but priority will not keep watchers |
1097 | before watchers with lower priority, but priority will not keep watchers |
1086 | from being executed (except for C<ev_idle> watchers). |
1098 | from being executed (except for C<ev_idle> watchers). |
1087 | |
1099 | |
1088 | This means that priorities are I<only> used for ordering callback |
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1089 | invocation after new events have been received. This is useful, for |
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1090 | example, to reduce latency after idling, or more often, to bind two |
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1091 | watchers on the same event and make sure one is called first. |
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1092 | |
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1093 | 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 |
1094 | 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. |
1095 | |
1102 | |
1096 | 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 |
1097 | pending. |
1104 | pending. |
1098 | |
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1099 | The default priority used by watchers when no priority has been set is |
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1100 | always C<0>, which is supposed to not be too high and not be too low :). |
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1101 | |
1105 | |
1102 | 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 |
1103 | 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 |
1104 | or might not have been clamped to the valid range. |
1108 | or might not have been clamped to the valid range. |
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1109 | |
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1110 | The default priority used by watchers when no priority has been set is |
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1111 | always C<0>, which is supposed to not be too high and not be too low :). |
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1112 | |
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1113 | See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of |
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1114 | priorities. |
1105 | |
1115 | |
1106 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1116 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1107 | |
1117 | |
1108 | 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 |
1109 | 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 |
… | |
… | |
1184 | t2_cb (EV_P_ ev_timer *w, int revents) |
1194 | t2_cb (EV_P_ ev_timer *w, int revents) |
1185 | { |
1195 | { |
1186 | struct my_biggy big = (struct my_biggy * |
1196 | struct my_biggy big = (struct my_biggy * |
1187 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1197 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1188 | } |
1198 | } |
|
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1199 | |
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1200 | =head2 WATCHER PRIORITY MODELS |
|
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1201 | |
|
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1202 | Many event loops support I<watcher priorities>, which are usually small |
|
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1203 | integers that influence the ordering of event callback invocation |
|
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1204 | between watchers in some way, all else being equal. |
|
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1205 | |
|
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1206 | In libev, Watcher priorities can be set using C<ev_set_priority>. See its |
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1207 | description for the more technical details such as the actual priority |
|
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1208 | range. |
|
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1209 | |
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1210 | There are two common ways how these these priorities are being interpreted |
|
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1211 | by event loops: |
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1212 | |
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1213 | In the more common lock-out model, higher priorities "lock out" invocation |
|
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1214 | of lower priority watchers, which means as long as higher priority |
|
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1215 | watchers receive events, lower priority watchers are not being invoked. |
|
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1216 | |
|
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1217 | The less common only-for-ordering model uses priorities solely to order |
|
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1218 | callback invocation within a single event loop iteration: Higher priority |
|
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1219 | watchers are invoked before lower priority ones, but they all get invoked |
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1220 | before polling for new events. |
|
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1221 | |
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1222 | Libev uses the second (only-for-ordering) model for all its watchers |
|
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1223 | except for idle watchers (which use the lock-out model). |
|
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1224 | |
|
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1225 | The rationale behind this is that implementing the lock-out model for |
|
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1226 | watchers is not well supported by most kernel interfaces, and most event |
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1227 | libraries will just poll for the same events again and again as long as |
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1228 | their callbacks have not been executed, which is very inefficient in the |
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1229 | common case of one high-priority watcher locking out a mass of lower |
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1230 | priority ones. |
|
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1231 | |
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1232 | Static (ordering) priorities are most useful when you have two or more |
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1233 | watchers handling the same resource: a typical usage example is having an |
|
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1234 | C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle |
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1235 | timeouts. Under load, data might be received while the program handles |
|
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1236 | other jobs, but since timers normally get invoked first, the timeout |
|
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1237 | handler will be executed before checking for data. In that case, giving |
|
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1238 | the timer a lower priority than the I/O watcher ensures that I/O will be |
|
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1239 | handled first even under adverse conditions (which is usually, but not |
|
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1240 | always, what you want). |
|
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1241 | |
|
|
1242 | Since idle watchers use the "lock-out" model, meaning that idle watchers |
|
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1243 | will only be executed when no same or higher priority watchers have |
|
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1244 | received events, they can be used to implement the "lock-out" model when |
|
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1245 | required. |
|
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1246 | |
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1247 | For example, to emulate how many other event libraries handle priorities, |
|
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1248 | you can associate an C<ev_idle> watcher to each such watcher, and in |
|
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1249 | the normal watcher callback, you just start the idle watcher. The real |
|
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1250 | processing is done in the idle watcher callback. This causes libev to |
|
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1251 | continously poll and process kernel event data for the watcher, but when |
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1252 | the lock-out case is known to be rare (which in turn is rare :), this is |
|
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1253 | workable. |
|
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1254 | |
|
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1255 | Usually, however, the lock-out model implemented that way will perform |
|
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1256 | miserably under the type of load it was designed to handle. In that case, |
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1257 | it might be preferable to stop the real watcher before starting the |
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1258 | idle watcher, so the kernel will not have to process the event in case |
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1259 | the actual processing will be delayed for considerable time. |
|
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1260 | |
|
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1261 | Here is an example of an I/O watcher that should run at a strictly lower |
|
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1262 | priority than the default, and which should only process data when no |
|
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1263 | other events are pending: |
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1264 | |
|
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1265 | ev_idle idle; // actual processing watcher |
|
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1266 | ev_io io; // actual event watcher |
|
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1267 | |
|
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1268 | static void |
|
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1269 | io_cb (EV_P_ ev_io *w, int revents) |
|
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1270 | { |
|
|
1271 | // stop the I/O watcher, we received the event, but |
|
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1272 | // are not yet ready to handle it. |
|
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1273 | ev_io_stop (EV_A_ w); |
|
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1274 | |
|
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1275 | // start the idle watcher to ahndle the actual event. |
|
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1276 | // it will not be executed as long as other watchers |
|
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1277 | // with the default priority are receiving events. |
|
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1278 | ev_idle_start (EV_A_ &idle); |
|
|
1279 | } |
|
|
1280 | |
|
|
1281 | static void |
|
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1282 | idle-cb (EV_P_ ev_idle *w, int revents) |
|
|
1283 | { |
|
|
1284 | // actual processing |
|
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1285 | read (STDIN_FILENO, ...); |
|
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1286 | |
|
|
1287 | // have to start the I/O watcher again, as |
|
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1288 | // we have handled the event |
|
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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); |
|
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1295 | ev_io_start (EV_DEFAULT_ &io); |
|
|
1296 | |
|
|
1297 | In the "real" world, it might also be beneficial to start a timer, so that |
|
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1298 | low-priority connections can not be locked out forever under load. This |
|
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1299 | enables your program to keep a lower latency for important connections |
|
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1300 | during short periods of high load, while not completely locking out less |
|
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1301 | important ones. |
1189 | |
1302 | |
1190 | |
1303 | |
1191 | =head1 WATCHER TYPES |
1304 | =head1 WATCHER TYPES |
1192 | |
1305 | |
1193 | This section describes each watcher in detail, but will not repeat |
1306 | This section describes each watcher in detail, but will not repeat |
… | |
… | |
1582 | 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). |
1583 | |
1696 | |
1584 | 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 |
1585 | 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. |
1586 | |
1699 | |
1587 | 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 |
1588 | usage example. |
1701 | usage example. |
1589 | |
1702 | |
1590 | =item ev_tstamp repeat [read-write] |
1703 | =item ev_tstamp repeat [read-write] |
1591 | |
1704 | |
1592 | 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 |
… | |
… | |
3993 | involves iterating over all running async watchers or all signal numbers. |
4106 | involves iterating over all running async watchers or all signal numbers. |
3994 | |
4107 | |
3995 | =back |
4108 | =back |
3996 | |
4109 | |
3997 | |
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 | |
3998 | =head1 AUTHOR |
4187 | =head1 AUTHOR |
3999 | |
4188 | |
4000 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4189 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4001 | |
4190 | |