… | |
… | |
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 | |
… | |
… | |
110 | name C<loop> (which is always of type C<ev_loop *>) will not have |
122 | name C<loop> (which is always of type C<ev_loop *>) will not have |
111 | this argument. |
123 | this argument. |
112 | |
124 | |
113 | =head2 TIME REPRESENTATION |
125 | =head2 TIME REPRESENTATION |
114 | |
126 | |
115 | Libev represents time as a single floating point number, representing the |
127 | Libev represents time as a single floating point number, representing |
116 | (fractional) number of seconds since the (POSIX) epoch (somewhere near |
128 | the (fractional) number of seconds since the (POSIX) epoch (somewhere |
117 | the beginning of 1970, details are complicated, don't ask). This type is |
129 | near the beginning of 1970, details are complicated, don't ask). This |
118 | called C<ev_tstamp>, which is what you should use too. It usually aliases |
130 | type is called C<ev_tstamp>, which is what you should use too. It usually |
119 | to the C<double> type in C, and when you need to do any calculations on |
131 | aliases to the C<double> type in C. When you need to do any calculations |
120 | it, you should treat it as some floating point value. Unlike the name |
132 | on it, you should treat it as some floating point value. Unlike the name |
121 | component C<stamp> might indicate, it is also used for time differences |
133 | component C<stamp> might indicate, it is also used for time differences |
122 | throughout libev. |
134 | throughout libev. |
123 | |
135 | |
124 | =head1 ERROR HANDLING |
136 | =head1 ERROR HANDLING |
125 | |
137 | |
… | |
… | |
632 | |
644 | |
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 L<The special problem of time updates> in the C<ev_timer> section. |
638 | |
650 | |
639 | =item ev_suspend (loop) |
651 | =item ev_suspend (loop) |
640 | |
652 | |
641 | =item ev_resume (loop) |
653 | =item ev_resume (loop) |
642 | |
654 | |
… | |
… | |
799 | |
811 | |
800 | By setting a higher I<io collect interval> you allow libev to spend more |
812 | By setting a higher I<io collect interval> you allow libev to spend more |
801 | time collecting I/O events, so you can handle more events per iteration, |
813 | time collecting I/O events, so you can handle more events per iteration, |
802 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
814 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
803 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
815 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
804 | introduce an additional C<ev_sleep ()> call into most loop iterations. |
816 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
|
|
817 | sleep time ensures that libev will not poll for I/O events more often then |
|
|
818 | once per this interval, on average. |
805 | |
819 | |
806 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
820 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
807 | to spend more time collecting timeouts, at the expense of increased |
821 | to spend more time collecting timeouts, at the expense of increased |
808 | latency/jitter/inexactness (the watcher callback will be called |
822 | latency/jitter/inexactness (the watcher callback will be called |
809 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
823 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
… | |
… | |
811 | |
825 | |
812 | Many (busy) programs can usually benefit by setting the I/O collect |
826 | Many (busy) programs can usually benefit by setting the I/O collect |
813 | interval to a value near C<0.1> or so, which is often enough for |
827 | interval to a value near C<0.1> or so, which is often enough for |
814 | interactive servers (of course not for games), likewise for timeouts. It |
828 | interactive servers (of course not for games), likewise for timeouts. It |
815 | usually doesn't make much sense to set it to a lower value than C<0.01>, |
829 | usually doesn't make much sense to set it to a lower value than C<0.01>, |
816 | as this approaches the timing granularity of most systems. |
830 | as this approaches the timing granularity of most systems. Note that if |
|
|
831 | you do transactions with the outside world and you can't increase the |
|
|
832 | parallelity, then this setting will limit your transaction rate (if you |
|
|
833 | need to poll once per transaction and the I/O collect interval is 0.01, |
|
|
834 | then you can't do more than 100 transations per second). |
817 | |
835 | |
818 | Setting the I<timeout collect interval> can improve the opportunity for |
836 | Setting the I<timeout collect interval> can improve the opportunity for |
819 | saving power, as the program will "bundle" timer callback invocations that |
837 | saving power, as the program will "bundle" timer callback invocations that |
820 | are "near" in time together, by delaying some, thus reducing the number of |
838 | are "near" in time together, by delaying some, thus reducing the number of |
821 | times the process sleeps and wakes up again. Another useful technique to |
839 | times the process sleeps and wakes up again. Another useful technique to |
822 | reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure |
840 | reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure |
823 | they fire on, say, one-second boundaries only. |
841 | they fire on, say, one-second boundaries only. |
|
|
842 | |
|
|
843 | Example: we only need 0.1s timeout granularity, and we wish not to poll |
|
|
844 | more often than 100 times per second: |
|
|
845 | |
|
|
846 | ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1); |
|
|
847 | ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01); |
824 | |
848 | |
825 | =item ev_loop_verify (loop) |
849 | =item ev_loop_verify (loop) |
826 | |
850 | |
827 | This function only does something when C<EV_VERIFY> support has been |
851 | This function only does something when C<EV_VERIFY> support has been |
828 | compiled in, which is the default for non-minimal builds. It tries to go |
852 | compiled in, which is the default for non-minimal builds. It tries to go |
… | |
… | |
1083 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1107 | integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
1084 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1108 | (default: C<-2>). Pending watchers with higher priority will be invoked |
1085 | before watchers with lower priority, but priority will not keep watchers |
1109 | before watchers with lower priority, but priority will not keep watchers |
1086 | from being executed (except for C<ev_idle> watchers). |
1110 | from being executed (except for C<ev_idle> watchers). |
1087 | |
1111 | |
1088 | See L< |
|
|
1089 | |
|
|
1090 | This means that priorities are I<only> used for ordering callback |
|
|
1091 | invocation after new events have been received. This is useful, for |
|
|
1092 | example, to reduce latency after idling, or more often, to bind two |
|
|
1093 | watchers on the same event and make sure one is called first. |
|
|
1094 | |
|
|
1095 | If you need to suppress invocation when higher priority events are pending |
1112 | If you need to suppress invocation when higher priority events are pending |
1096 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1113 | you need to look at C<ev_idle> watchers, which provide this functionality. |
1097 | |
1114 | |
1098 | You I<must not> change the priority of a watcher as long as it is active or |
1115 | You I<must not> change the priority of a watcher as long as it is active or |
1099 | pending. |
1116 | pending. |
1100 | |
|
|
1101 | The default priority used by watchers when no priority has been set is |
|
|
1102 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1103 | |
1117 | |
1104 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1118 | Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
1105 | fine, as long as you do not mind that the priority value you query might |
1119 | fine, as long as you do not mind that the priority value you query might |
1106 | or might not have been clamped to the valid range. |
1120 | or might not have been clamped to the valid range. |
|
|
1121 | |
|
|
1122 | The default priority used by watchers when no priority has been set is |
|
|
1123 | always C<0>, which is supposed to not be too high and not be too low :). |
|
|
1124 | |
|
|
1125 | See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of |
|
|
1126 | priorities. |
1107 | |
1127 | |
1108 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1128 | =item ev_invoke (loop, ev_TYPE *watcher, int revents) |
1109 | |
1129 | |
1110 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1130 | Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
1111 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
1131 | C<loop> nor C<revents> need to be valid as long as the watcher callback |
… | |
… | |
1176 | #include <stddef.h> |
1196 | #include <stddef.h> |
1177 | |
1197 | |
1178 | static void |
1198 | static void |
1179 | t1_cb (EV_P_ ev_timer *w, int revents) |
1199 | t1_cb (EV_P_ ev_timer *w, int revents) |
1180 | { |
1200 | { |
1181 | struct my_biggy big = (struct my_biggy * |
1201 | struct my_biggy big = (struct my_biggy *) |
1182 | (((char *)w) - offsetof (struct my_biggy, t1)); |
1202 | (((char *)w) - offsetof (struct my_biggy, t1)); |
1183 | } |
1203 | } |
1184 | |
1204 | |
1185 | static void |
1205 | static void |
1186 | t2_cb (EV_P_ ev_timer *w, int revents) |
1206 | t2_cb (EV_P_ ev_timer *w, int revents) |
1187 | { |
1207 | { |
1188 | struct my_biggy big = (struct my_biggy * |
1208 | struct my_biggy big = (struct my_biggy *) |
1189 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1209 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1190 | } |
1210 | } |
|
|
1211 | |
|
|
1212 | =head2 WATCHER PRIORITY MODELS |
|
|
1213 | |
|
|
1214 | Many event loops support I<watcher priorities>, which are usually small |
|
|
1215 | integers that influence the ordering of event callback invocation |
|
|
1216 | between watchers in some way, all else being equal. |
|
|
1217 | |
|
|
1218 | In libev, Watcher priorities can be set using C<ev_set_priority>. See its |
|
|
1219 | description for the more technical details such as the actual priority |
|
|
1220 | range. |
|
|
1221 | |
|
|
1222 | There are two common ways how these these priorities are being interpreted |
|
|
1223 | by event loops: |
|
|
1224 | |
|
|
1225 | In the more common lock-out model, higher priorities "lock out" invocation |
|
|
1226 | of lower priority watchers, which means as long as higher priority |
|
|
1227 | watchers receive events, lower priority watchers are not being invoked. |
|
|
1228 | |
|
|
1229 | The less common only-for-ordering model uses priorities solely to order |
|
|
1230 | callback invocation within a single event loop iteration: Higher priority |
|
|
1231 | watchers are invoked before lower priority ones, but they all get invoked |
|
|
1232 | before polling for new events. |
|
|
1233 | |
|
|
1234 | Libev uses the second (only-for-ordering) model for all its watchers |
|
|
1235 | except for idle watchers (which use the lock-out model). |
|
|
1236 | |
|
|
1237 | The rationale behind this is that implementing the lock-out model for |
|
|
1238 | watchers is not well supported by most kernel interfaces, and most event |
|
|
1239 | libraries will just poll for the same events again and again as long as |
|
|
1240 | their callbacks have not been executed, which is very inefficient in the |
|
|
1241 | common case of one high-priority watcher locking out a mass of lower |
|
|
1242 | priority ones. |
|
|
1243 | |
|
|
1244 | Static (ordering) priorities are most useful when you have two or more |
|
|
1245 | watchers handling the same resource: a typical usage example is having an |
|
|
1246 | C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle |
|
|
1247 | timeouts. Under load, data might be received while the program handles |
|
|
1248 | other jobs, but since timers normally get invoked first, the timeout |
|
|
1249 | handler will be executed before checking for data. In that case, giving |
|
|
1250 | the timer a lower priority than the I/O watcher ensures that I/O will be |
|
|
1251 | handled first even under adverse conditions (which is usually, but not |
|
|
1252 | always, what you want). |
|
|
1253 | |
|
|
1254 | Since idle watchers use the "lock-out" model, meaning that idle watchers |
|
|
1255 | will only be executed when no same or higher priority watchers have |
|
|
1256 | received events, they can be used to implement the "lock-out" model when |
|
|
1257 | required. |
|
|
1258 | |
|
|
1259 | For example, to emulate how many other event libraries handle priorities, |
|
|
1260 | you can associate an C<ev_idle> watcher to each such watcher, and in |
|
|
1261 | the normal watcher callback, you just start the idle watcher. The real |
|
|
1262 | processing is done in the idle watcher callback. This causes libev to |
|
|
1263 | continously poll and process kernel event data for the watcher, but when |
|
|
1264 | the lock-out case is known to be rare (which in turn is rare :), this is |
|
|
1265 | workable. |
|
|
1266 | |
|
|
1267 | Usually, however, the lock-out model implemented that way will perform |
|
|
1268 | miserably under the type of load it was designed to handle. In that case, |
|
|
1269 | it might be preferable to stop the real watcher before starting the |
|
|
1270 | idle watcher, so the kernel will not have to process the event in case |
|
|
1271 | the actual processing will be delayed for considerable time. |
|
|
1272 | |
|
|
1273 | Here is an example of an I/O watcher that should run at a strictly lower |
|
|
1274 | priority than the default, and which should only process data when no |
|
|
1275 | other events are pending: |
|
|
1276 | |
|
|
1277 | ev_idle idle; // actual processing watcher |
|
|
1278 | ev_io io; // actual event watcher |
|
|
1279 | |
|
|
1280 | static void |
|
|
1281 | io_cb (EV_P_ ev_io *w, int revents) |
|
|
1282 | { |
|
|
1283 | // stop the I/O watcher, we received the event, but |
|
|
1284 | // are not yet ready to handle it. |
|
|
1285 | ev_io_stop (EV_A_ w); |
|
|
1286 | |
|
|
1287 | // start the idle watcher to ahndle the actual event. |
|
|
1288 | // it will not be executed as long as other watchers |
|
|
1289 | // with the default priority are receiving events. |
|
|
1290 | ev_idle_start (EV_A_ &idle); |
|
|
1291 | } |
|
|
1292 | |
|
|
1293 | static void |
|
|
1294 | idle_cb (EV_P_ ev_idle *w, int revents) |
|
|
1295 | { |
|
|
1296 | // actual processing |
|
|
1297 | read (STDIN_FILENO, ...); |
|
|
1298 | |
|
|
1299 | // have to start the I/O watcher again, as |
|
|
1300 | // we have handled the event |
|
|
1301 | ev_io_start (EV_P_ &io); |
|
|
1302 | } |
|
|
1303 | |
|
|
1304 | // initialisation |
|
|
1305 | ev_idle_init (&idle, idle_cb); |
|
|
1306 | ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ); |
|
|
1307 | ev_io_start (EV_DEFAULT_ &io); |
|
|
1308 | |
|
|
1309 | In the "real" world, it might also be beneficial to start a timer, so that |
|
|
1310 | low-priority connections can not be locked out forever under load. This |
|
|
1311 | enables your program to keep a lower latency for important connections |
|
|
1312 | during short periods of high load, while not completely locking out less |
|
|
1313 | important ones. |
1191 | |
1314 | |
1192 | |
1315 | |
1193 | =head1 WATCHER TYPES |
1316 | =head1 WATCHER TYPES |
1194 | |
1317 | |
1195 | This section describes each watcher in detail, but will not repeat |
1318 | This section describes each watcher in detail, but will not repeat |
… | |
… | |
1221 | descriptors to non-blocking mode is also usually a good idea (but not |
1344 | descriptors to non-blocking mode is also usually a good idea (but not |
1222 | required if you know what you are doing). |
1345 | required if you know what you are doing). |
1223 | |
1346 | |
1224 | If you cannot use non-blocking mode, then force the use of a |
1347 | If you cannot use non-blocking mode, then force the use of a |
1225 | known-to-be-good backend (at the time of this writing, this includes only |
1348 | known-to-be-good backend (at the time of this writing, this includes only |
1226 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). |
1349 | C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file |
|
|
1350 | descriptors for which non-blocking operation makes no sense (such as |
|
|
1351 | files) - libev doesn't guarentee any specific behaviour in that case. |
1227 | |
1352 | |
1228 | Another thing you have to watch out for is that it is quite easy to |
1353 | Another thing you have to watch out for is that it is quite easy to |
1229 | receive "spurious" readiness notifications, that is your callback might |
1354 | receive "spurious" readiness notifications, that is your callback might |
1230 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1355 | be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1231 | because there is no data. Not only are some backends known to create a |
1356 | because there is no data. Not only are some backends known to create a |
… | |
… | |
1352 | year, it will still time out after (roughly) one hour. "Roughly" because |
1477 | year, it will still time out after (roughly) one hour. "Roughly" because |
1353 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1478 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1354 | monotonic clock option helps a lot here). |
1479 | monotonic clock option helps a lot here). |
1355 | |
1480 | |
1356 | The callback is guaranteed to be invoked only I<after> its timeout has |
1481 | The callback is guaranteed to be invoked only I<after> its timeout has |
1357 | passed. If multiple timers become ready during the same loop iteration |
1482 | passed (not I<at>, so on systems with very low-resolution clocks this |
1358 | then the ones with earlier time-out values are invoked before ones with |
1483 | might introduce a small delay). If multiple timers become ready during the |
|
|
1484 | same loop iteration then the ones with earlier time-out values are invoked |
1359 | later time-out values (but this is no longer true when a callback calls |
1485 | before ones with later time-out values (but this is no longer true when a |
1360 | C<ev_loop> recursively). |
1486 | callback calls C<ev_loop> recursively). |
1361 | |
1487 | |
1362 | =head3 Be smart about timeouts |
1488 | =head3 Be smart about timeouts |
1363 | |
1489 | |
1364 | Many real-world problems involve some kind of timeout, usually for error |
1490 | Many real-world problems involve some kind of timeout, usually for error |
1365 | recovery. A typical example is an HTTP request - if the other side hangs, |
1491 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1409 | C<after> argument to C<ev_timer_set>, and only ever use the C<repeat> |
1535 | C<after> argument to C<ev_timer_set>, and only ever use the C<repeat> |
1410 | member and C<ev_timer_again>. |
1536 | member and C<ev_timer_again>. |
1411 | |
1537 | |
1412 | At start: |
1538 | At start: |
1413 | |
1539 | |
1414 | ev_timer_init (timer, callback); |
1540 | ev_init (timer, callback); |
1415 | timer->repeat = 60.; |
1541 | timer->repeat = 60.; |
1416 | ev_timer_again (loop, timer); |
1542 | ev_timer_again (loop, timer); |
1417 | |
1543 | |
1418 | Each time there is some activity: |
1544 | Each time there is some activity: |
1419 | |
1545 | |
… | |
… | |
1481 | |
1607 | |
1482 | To start the timer, simply initialise the watcher and set C<last_activity> |
1608 | To start the timer, simply initialise the watcher and set C<last_activity> |
1483 | to the current time (meaning we just have some activity :), then call the |
1609 | to the current time (meaning we just have some activity :), then call the |
1484 | callback, which will "do the right thing" and start the timer: |
1610 | callback, which will "do the right thing" and start the timer: |
1485 | |
1611 | |
1486 | ev_timer_init (timer, callback); |
1612 | ev_init (timer, callback); |
1487 | last_activity = ev_now (loop); |
1613 | last_activity = ev_now (loop); |
1488 | callback (loop, timer, EV_TIMEOUT); |
1614 | callback (loop, timer, EV_TIMEOUT); |
1489 | |
1615 | |
1490 | And when there is some activity, simply store the current time in |
1616 | And when there is some activity, simply store the current time in |
1491 | C<last_activity>, no libev calls at all: |
1617 | C<last_activity>, no libev calls at all: |
… | |
… | |
1888 | some child status changes (most typically when a child of yours dies or |
2014 | some child status changes (most typically when a child of yours dies or |
1889 | exits). It is permissible to install a child watcher I<after> the child |
2015 | exits). It is permissible to install a child watcher I<after> the child |
1890 | has been forked (which implies it might have already exited), as long |
2016 | has been forked (which implies it might have already exited), as long |
1891 | as the event loop isn't entered (or is continued from a watcher), i.e., |
2017 | as the event loop isn't entered (or is continued from a watcher), i.e., |
1892 | forking and then immediately registering a watcher for the child is fine, |
2018 | forking and then immediately registering a watcher for the child is fine, |
1893 | but forking and registering a watcher a few event loop iterations later is |
2019 | but forking and registering a watcher a few event loop iterations later or |
1894 | not. |
2020 | in the next callback invocation is not. |
1895 | |
2021 | |
1896 | Only the default event loop is capable of handling signals, and therefore |
2022 | Only the default event loop is capable of handling signals, and therefore |
1897 | you can only register child watchers in the default event loop. |
2023 | you can only register child watchers in the default event loop. |
1898 | |
2024 | |
1899 | =head3 Process Interaction |
2025 | =head3 Process Interaction |
… | |
… | |
2254 | // no longer anything immediate to do. |
2380 | // no longer anything immediate to do. |
2255 | } |
2381 | } |
2256 | |
2382 | |
2257 | ev_idle *idle_watcher = malloc (sizeof (ev_idle)); |
2383 | ev_idle *idle_watcher = malloc (sizeof (ev_idle)); |
2258 | ev_idle_init (idle_watcher, idle_cb); |
2384 | ev_idle_init (idle_watcher, idle_cb); |
2259 | ev_idle_start (loop, idle_cb); |
2385 | ev_idle_start (loop, idle_watcher); |
2260 | |
2386 | |
2261 | |
2387 | |
2262 | =head2 C<ev_prepare> and C<ev_check> - customise your event loop! |
2388 | =head2 C<ev_prepare> and C<ev_check> - customise your event loop! |
2263 | |
2389 | |
2264 | Prepare and check watchers are usually (but not always) used in pairs: |
2390 | Prepare and check watchers are usually (but not always) used in pairs: |
… | |
… | |
2357 | struct pollfd fds [nfd]; |
2483 | struct pollfd fds [nfd]; |
2358 | // actual code will need to loop here and realloc etc. |
2484 | // actual code will need to loop here and realloc etc. |
2359 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
2485 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
2360 | |
2486 | |
2361 | /* the callback is illegal, but won't be called as we stop during check */ |
2487 | /* the callback is illegal, but won't be called as we stop during check */ |
2362 | ev_timer_init (&tw, 0, timeout * 1e-3); |
2488 | ev_timer_init (&tw, 0, timeout * 1e-3, 0.); |
2363 | ev_timer_start (loop, &tw); |
2489 | ev_timer_start (loop, &tw); |
2364 | |
2490 | |
2365 | // create one ev_io per pollfd |
2491 | // create one ev_io per pollfd |
2366 | for (int i = 0; i < nfd; ++i) |
2492 | for (int i = 0; i < nfd; ++i) |
2367 | { |
2493 | { |
… | |
… | |
2597 | event loop blocks next and before C<ev_check> watchers are being called, |
2723 | event loop blocks next and before C<ev_check> watchers are being called, |
2598 | and only in the child after the fork. If whoever good citizen calling |
2724 | and only in the child after the fork. If whoever good citizen calling |
2599 | C<ev_default_fork> cheats and calls it in the wrong process, the fork |
2725 | C<ev_default_fork> cheats and calls it in the wrong process, the fork |
2600 | handlers will be invoked, too, of course. |
2726 | handlers will be invoked, too, of course. |
2601 | |
2727 | |
|
|
2728 | =head3 The special problem of life after fork - how is it possible? |
|
|
2729 | |
|
|
2730 | Most uses of C<fork()> consist of forking, then some simple calls to ste |
|
|
2731 | up/change the process environment, followed by a call to C<exec()>. This |
|
|
2732 | sequence should be handled by libev without any problems. |
|
|
2733 | |
|
|
2734 | This changes when the application actually wants to do event handling |
|
|
2735 | in the child, or both parent in child, in effect "continuing" after the |
|
|
2736 | fork. |
|
|
2737 | |
|
|
2738 | The default mode of operation (for libev, with application help to detect |
|
|
2739 | forks) is to duplicate all the state in the child, as would be expected |
|
|
2740 | when I<either> the parent I<or> the child process continues. |
|
|
2741 | |
|
|
2742 | When both processes want to continue using libev, then this is usually the |
|
|
2743 | wrong result. In that case, usually one process (typically the parent) is |
|
|
2744 | supposed to continue with all watchers in place as before, while the other |
|
|
2745 | process typically wants to start fresh, i.e. without any active watchers. |
|
|
2746 | |
|
|
2747 | The cleanest and most efficient way to achieve that with libev is to |
|
|
2748 | simply create a new event loop, which of course will be "empty", and |
|
|
2749 | use that for new watchers. This has the advantage of not touching more |
|
|
2750 | memory than necessary, and thus avoiding the copy-on-write, and the |
|
|
2751 | disadvantage of having to use multiple event loops (which do not support |
|
|
2752 | signal watchers). |
|
|
2753 | |
|
|
2754 | When this is not possible, or you want to use the default loop for |
|
|
2755 | other reasons, then in the process that wants to start "fresh", call |
|
|
2756 | C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying |
|
|
2757 | the default loop will "orphan" (not stop) all registered watchers, so you |
|
|
2758 | have to be careful not to execute code that modifies those watchers. Note |
|
|
2759 | also that in that case, you have to re-register any signal watchers. |
|
|
2760 | |
2602 | =head3 Watcher-Specific Functions and Data Members |
2761 | =head3 Watcher-Specific Functions and Data Members |
2603 | |
2762 | |
2604 | =over 4 |
2763 | =over 4 |
2605 | |
2764 | |
2606 | =item ev_fork_init (ev_signal *, callback) |
2765 | =item ev_fork_init (ev_signal *, callback) |
… | |
… | |
3788 | way (note also that glib is the slowest event library known to man). |
3947 | way (note also that glib is the slowest event library known to man). |
3789 | |
3948 | |
3790 | There is no supported compilation method available on windows except |
3949 | There is no supported compilation method available on windows except |
3791 | embedding it into other applications. |
3950 | embedding it into other applications. |
3792 | |
3951 | |
|
|
3952 | Sensible signal handling is officially unsupported by Microsoft - libev |
|
|
3953 | tries its best, but under most conditions, signals will simply not work. |
|
|
3954 | |
3793 | Not a libev limitation but worth mentioning: windows apparently doesn't |
3955 | Not a libev limitation but worth mentioning: windows apparently doesn't |
3794 | accept large writes: instead of resulting in a partial write, windows will |
3956 | accept large writes: instead of resulting in a partial write, windows will |
3795 | either accept everything or return C<ENOBUFS> if the buffer is too large, |
3957 | either accept everything or return C<ENOBUFS> if the buffer is too large, |
3796 | so make sure you only write small amounts into your sockets (less than a |
3958 | so make sure you only write small amounts into your sockets (less than a |
3797 | megabyte seems safe, but this apparently depends on the amount of memory |
3959 | megabyte seems safe, but this apparently depends on the amount of memory |
… | |
… | |
3801 | the abysmal performance of winsockets, using a large number of sockets |
3963 | the abysmal performance of winsockets, using a large number of sockets |
3802 | is not recommended (and not reasonable). If your program needs to use |
3964 | is not recommended (and not reasonable). If your program needs to use |
3803 | more than a hundred or so sockets, then likely it needs to use a totally |
3965 | more than a hundred or so sockets, then likely it needs to use a totally |
3804 | different implementation for windows, as libev offers the POSIX readiness |
3966 | different implementation for windows, as libev offers the POSIX readiness |
3805 | notification model, which cannot be implemented efficiently on windows |
3967 | notification model, which cannot be implemented efficiently on windows |
3806 | (Microsoft monopoly games). |
3968 | (due to Microsoft monopoly games). |
3807 | |
3969 | |
3808 | A typical way to use libev under windows is to embed it (see the embedding |
3970 | A typical way to use libev under windows is to embed it (see the embedding |
3809 | section for details) and use the following F<evwrap.h> header file instead |
3971 | section for details) and use the following F<evwrap.h> header file instead |
3810 | of F<ev.h>: |
3972 | of F<ev.h>: |
3811 | |
3973 | |
… | |
… | |
3847 | |
4009 | |
3848 | Early versions of winsocket's select only supported waiting for a maximum |
4010 | Early versions of winsocket's select only supported waiting for a maximum |
3849 | of C<64> handles (probably owning to the fact that all windows kernels |
4011 | of C<64> handles (probably owning to the fact that all windows kernels |
3850 | can only wait for C<64> things at the same time internally; Microsoft |
4012 | can only wait for C<64> things at the same time internally; Microsoft |
3851 | recommends spawning a chain of threads and wait for 63 handles and the |
4013 | recommends spawning a chain of threads and wait for 63 handles and the |
3852 | previous thread in each. Great). |
4014 | previous thread in each. Sounds great!). |
3853 | |
4015 | |
3854 | Newer versions support more handles, but you need to define C<FD_SETSIZE> |
4016 | Newer versions support more handles, but you need to define C<FD_SETSIZE> |
3855 | to some high number (e.g. C<2048>) before compiling the winsocket select |
4017 | to some high number (e.g. C<2048>) before compiling the winsocket select |
3856 | call (which might be in libev or elsewhere, for example, perl does its own |
4018 | call (which might be in libev or elsewhere, for example, perl and many |
3857 | select emulation on windows). |
4019 | other interpreters do their own select emulation on windows). |
3858 | |
4020 | |
3859 | Another limit is the number of file descriptors in the Microsoft runtime |
4021 | Another limit is the number of file descriptors in the Microsoft runtime |
3860 | libraries, which by default is C<64> (there must be a hidden I<64> fetish |
4022 | libraries, which by default is C<64> (there must be a hidden I<64> |
3861 | or something like this inside Microsoft). You can increase this by calling |
4023 | fetish or something like this inside Microsoft). You can increase this |
3862 | C<_setmaxstdio>, which can increase this limit to C<2048> (another |
4024 | by calling C<_setmaxstdio>, which can increase this limit to C<2048> |
3863 | arbitrary limit), but is broken in many versions of the Microsoft runtime |
4025 | (another arbitrary limit), but is broken in many versions of the Microsoft |
3864 | libraries. |
|
|
3865 | |
|
|
3866 | This might get you to about C<512> or C<2048> sockets (depending on |
4026 | runtime libraries. This might get you to about C<512> or C<2048> sockets |
3867 | windows version and/or the phase of the moon). To get more, you need to |
4027 | (depending on windows version and/or the phase of the moon). To get more, |
3868 | wrap all I/O functions and provide your own fd management, but the cost of |
4028 | you need to wrap all I/O functions and provide your own fd management, but |
3869 | calling select (O(n²)) will likely make this unworkable. |
4029 | the cost of calling select (O(n²)) will likely make this unworkable. |
3870 | |
4030 | |
3871 | =back |
4031 | =back |
3872 | |
4032 | |
3873 | =head2 PORTABILITY REQUIREMENTS |
4033 | =head2 PORTABILITY REQUIREMENTS |
3874 | |
4034 | |
… | |
… | |
3995 | involves iterating over all running async watchers or all signal numbers. |
4155 | involves iterating over all running async watchers or all signal numbers. |
3996 | |
4156 | |
3997 | =back |
4157 | =back |
3998 | |
4158 | |
3999 | |
4159 | |
|
|
4160 | =head1 GLOSSARY |
|
|
4161 | |
|
|
4162 | =over 4 |
|
|
4163 | |
|
|
4164 | =item active |
|
|
4165 | |
|
|
4166 | A watcher is active as long as it has been started (has been attached to |
|
|
4167 | an event loop) but not yet stopped (disassociated from the event loop). |
|
|
4168 | |
|
|
4169 | =item application |
|
|
4170 | |
|
|
4171 | In this document, an application is whatever is using libev. |
|
|
4172 | |
|
|
4173 | =item callback |
|
|
4174 | |
|
|
4175 | The address of a function that is called when some event has been |
|
|
4176 | detected. Callbacks are being passed the event loop, the watcher that |
|
|
4177 | received the event, and the actual event bitset. |
|
|
4178 | |
|
|
4179 | =item callback invocation |
|
|
4180 | |
|
|
4181 | The act of calling the callback associated with a watcher. |
|
|
4182 | |
|
|
4183 | =item event |
|
|
4184 | |
|
|
4185 | A change of state of some external event, such as data now being available |
|
|
4186 | for reading on a file descriptor, time having passed or simply not having |
|
|
4187 | any other events happening anymore. |
|
|
4188 | |
|
|
4189 | In libev, events are represented as single bits (such as C<EV_READ> or |
|
|
4190 | C<EV_TIMEOUT>). |
|
|
4191 | |
|
|
4192 | =item event library |
|
|
4193 | |
|
|
4194 | A software package implementing an event model and loop. |
|
|
4195 | |
|
|
4196 | =item event loop |
|
|
4197 | |
|
|
4198 | An entity that handles and processes external events and converts them |
|
|
4199 | into callback invocations. |
|
|
4200 | |
|
|
4201 | =item event model |
|
|
4202 | |
|
|
4203 | The model used to describe how an event loop handles and processes |
|
|
4204 | watchers and events. |
|
|
4205 | |
|
|
4206 | =item pending |
|
|
4207 | |
|
|
4208 | A watcher is pending as soon as the corresponding event has been detected, |
|
|
4209 | and stops being pending as soon as the watcher will be invoked or its |
|
|
4210 | pending status is explicitly cleared by the application. |
|
|
4211 | |
|
|
4212 | A watcher can be pending, but not active. Stopping a watcher also clears |
|
|
4213 | its pending status. |
|
|
4214 | |
|
|
4215 | =item real time |
|
|
4216 | |
|
|
4217 | The physical time that is observed. It is apparently strictly monotonic :) |
|
|
4218 | |
|
|
4219 | =item wall-clock time |
|
|
4220 | |
|
|
4221 | The time and date as shown on clocks. Unlike real time, it can actually |
|
|
4222 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
|
|
4223 | clock. |
|
|
4224 | |
|
|
4225 | =item watcher |
|
|
4226 | |
|
|
4227 | A data structure that describes interest in certain events. Watchers need |
|
|
4228 | to be started (attached to an event loop) before they can receive events. |
|
|
4229 | |
|
|
4230 | =item watcher invocation |
|
|
4231 | |
|
|
4232 | The act of calling the callback associated with a watcher. |
|
|
4233 | |
|
|
4234 | =back |
|
|
4235 | |
4000 | =head1 AUTHOR |
4236 | =head1 AUTHOR |
4001 | |
4237 | |
4002 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4238 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. |
4003 | |
4239 | |