… | |
… | |
463 | epoll scales either O(1) or O(active_fds). |
463 | epoll scales either O(1) or O(active_fds). |
464 | |
464 | |
465 | The epoll mechanism deserves honorable mention as the most misdesigned |
465 | The epoll mechanism deserves honorable mention as the most misdesigned |
466 | of the more advanced event mechanisms: mere annoyances include silently |
466 | of the more advanced event mechanisms: mere annoyances include silently |
467 | dropping file descriptors, requiring a system call per change per file |
467 | dropping file descriptors, requiring a system call per change per file |
468 | descriptor (and unnecessary guessing of parameters), problems with dup and |
468 | descriptor (and unnecessary guessing of parameters), problems with dup, |
|
|
469 | returning before the timeout value, resulting in additional iterations |
|
|
470 | (and only giving 5ms accuracy while select on the same platform gives |
469 | so on. The biggest issue is fork races, however - if a program forks then |
471 | 0.1ms) and so on. The biggest issue is fork races, however - if a program |
470 | I<both> parent and child process have to recreate the epoll set, which can |
472 | forks then I<both> parent and child process have to recreate the epoll |
471 | take considerable time (one syscall per file descriptor) and is of course |
473 | set, which can take considerable time (one syscall per file descriptor) |
472 | hard to detect. |
474 | and is of course hard to detect. |
473 | |
475 | |
474 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
476 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
475 | of course I<doesn't>, and epoll just loves to report events for totally |
477 | of course I<doesn't>, and epoll just loves to report events for totally |
476 | I<different> file descriptors (even already closed ones, so one cannot |
478 | I<different> file descriptors (even already closed ones, so one cannot |
477 | even remove them from the set) than registered in the set (especially |
479 | even remove them from the set) than registered in the set (especially |
478 | on SMP systems). Libev tries to counter these spurious notifications by |
480 | on SMP systems). Libev tries to counter these spurious notifications by |
479 | employing an additional generation counter and comparing that against the |
481 | employing an additional generation counter and comparing that against the |
480 | events to filter out spurious ones, recreating the set when required. Last |
482 | events to filter out spurious ones, recreating the set when required. Last |
481 | not least, it also refuses to work with some file descriptors which work |
483 | not least, it also refuses to work with some file descriptors which work |
482 | perfectly fine with C<select> (files, many character devices...). |
484 | perfectly fine with C<select> (files, many character devices...). |
|
|
485 | |
|
|
486 | Epoll is truly the train wreck analog among event poll mechanisms. |
483 | |
487 | |
484 | While stopping, setting and starting an I/O watcher in the same iteration |
488 | While stopping, setting and starting an I/O watcher in the same iteration |
485 | will result in some caching, there is still a system call per such |
489 | will result in some caching, there is still a system call per such |
486 | incident (because the same I<file descriptor> could point to a different |
490 | incident (because the same I<file descriptor> could point to a different |
487 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
491 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
… | |
… | |
823 | Can be used to make a call to C<ev_run> return early (but only after it |
827 | Can be used to make a call to C<ev_run> return early (but only after it |
824 | has processed all outstanding events). The C<how> argument must be either |
828 | has processed all outstanding events). The C<how> argument must be either |
825 | C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or |
829 | C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or |
826 | C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return. |
830 | C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return. |
827 | |
831 | |
828 | This "unloop state" will be cleared when entering C<ev_run> again. |
832 | This "break state" will be cleared when entering C<ev_run> again. |
829 | |
833 | |
830 | It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO## |
834 | It is safe to call C<ev_break> from outside any C<ev_run> calls, too. |
831 | |
835 | |
832 | =item ev_ref (loop) |
836 | =item ev_ref (loop) |
833 | |
837 | |
834 | =item ev_unref (loop) |
838 | =item ev_unref (loop) |
835 | |
839 | |
… | |
… | |
1154 | programs, though, as the fd could already be closed and reused for another |
1158 | programs, though, as the fd could already be closed and reused for another |
1155 | thing, so beware. |
1159 | thing, so beware. |
1156 | |
1160 | |
1157 | =back |
1161 | =back |
1158 | |
1162 | |
1159 | =head2 WATCHER STATES |
|
|
1160 | |
|
|
1161 | There are various watcher states mentioned throughout this manual - |
|
|
1162 | active, pending and so on. In this section these states and the rules to |
|
|
1163 | transition between them will be described in more detail - and while these |
|
|
1164 | rules might look complicated, they usually do "the right thing". |
|
|
1165 | |
|
|
1166 | =over 4 |
|
|
1167 | |
|
|
1168 | =item initialiased |
|
|
1169 | |
|
|
1170 | Before a watcher can be registered with the event looop it has to be |
|
|
1171 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
|
|
1172 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
|
|
1173 | |
|
|
1174 | In this state it is simply some block of memory that is suitable for use |
|
|
1175 | in an event loop. It can be moved around, freed, reused etc. at will. |
|
|
1176 | |
|
|
1177 | =item started/running/active |
|
|
1178 | |
|
|
1179 | Once a watcher has been started with a call to C<ev_TYPE_start> it becomes |
|
|
1180 | property of the event loop, and is actively waiting for events. While in |
|
|
1181 | this state it cannot be accessed (except in a few documented ways), moved, |
|
|
1182 | freed or anything else - the only legal thing is to keep a pointer to it, |
|
|
1183 | and call libev functions on it that are documented to work on active watchers. |
|
|
1184 | |
|
|
1185 | =item pending |
|
|
1186 | |
|
|
1187 | If a watcher is active and libev determines that an event it is interested |
|
|
1188 | in has occurred (such as a timer expiring), it will become pending. It will |
|
|
1189 | stay in this pending state until either it is stopped or its callback is |
|
|
1190 | about to be invoked, so it is not normally pending inside the watcher |
|
|
1191 | callback. |
|
|
1192 | |
|
|
1193 | The watcher might or might not be active while it is pending (for example, |
|
|
1194 | an expired non-repeating timer can be pending but no longer active). If it |
|
|
1195 | is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>), |
|
|
1196 | but it is still property of the event loop at this time, so cannot be |
|
|
1197 | moved, freed or reused. And if it is active the rules described in the |
|
|
1198 | previous item still apply. |
|
|
1199 | |
|
|
1200 | It is also possible to feed an event on a watcher that is not active (e.g. |
|
|
1201 | via C<ev_feed_event>), in which case it becomes pending without being |
|
|
1202 | active. |
|
|
1203 | |
|
|
1204 | =item stopped |
|
|
1205 | |
|
|
1206 | A watcher can be stopped implicitly by libev (in which case it might still |
|
|
1207 | be pending), or explicitly by calling its C<ev_TYPE_stop> function. The |
|
|
1208 | latter will clear any pending state the watcher might be in, regardless |
|
|
1209 | of whether it was active or not, so stopping a watcher explicitly before |
|
|
1210 | freeing it is often a good idea. |
|
|
1211 | |
|
|
1212 | While stopped (and not pending) the watcher is essentially in the |
|
|
1213 | initialised state, that is it can be reused, moved, modified in any way |
|
|
1214 | you wish. |
|
|
1215 | |
|
|
1216 | =back |
|
|
1217 | |
|
|
1218 | =head2 GENERIC WATCHER FUNCTIONS |
1163 | =head2 GENERIC WATCHER FUNCTIONS |
1219 | |
1164 | |
1220 | =over 4 |
1165 | =over 4 |
1221 | |
1166 | |
1222 | =item C<ev_init> (ev_TYPE *watcher, callback) |
1167 | =item C<ev_init> (ev_TYPE *watcher, callback) |
… | |
… | |
1363 | |
1308 | |
1364 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1309 | See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related |
1365 | functions that do not need a watcher. |
1310 | functions that do not need a watcher. |
1366 | |
1311 | |
1367 | =back |
1312 | =back |
1368 | |
|
|
1369 | |
1313 | |
1370 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1314 | =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
1371 | |
1315 | |
1372 | Each watcher has, by default, a member C<void *data> that you can change |
1316 | Each watcher has, by default, a member C<void *data> that you can change |
1373 | and read at any time: libev will completely ignore it. This can be used |
1317 | and read at any time: libev will completely ignore it. This can be used |
… | |
… | |
1429 | t2_cb (EV_P_ ev_timer *w, int revents) |
1373 | t2_cb (EV_P_ ev_timer *w, int revents) |
1430 | { |
1374 | { |
1431 | struct my_biggy big = (struct my_biggy *) |
1375 | struct my_biggy big = (struct my_biggy *) |
1432 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1376 | (((char *)w) - offsetof (struct my_biggy, t2)); |
1433 | } |
1377 | } |
|
|
1378 | |
|
|
1379 | =head2 WATCHER STATES |
|
|
1380 | |
|
|
1381 | There are various watcher states mentioned throughout this manual - |
|
|
1382 | active, pending and so on. In this section these states and the rules to |
|
|
1383 | transition between them will be described in more detail - and while these |
|
|
1384 | rules might look complicated, they usually do "the right thing". |
|
|
1385 | |
|
|
1386 | =over 4 |
|
|
1387 | |
|
|
1388 | =item initialiased |
|
|
1389 | |
|
|
1390 | Before a watcher can be registered with the event looop it has to be |
|
|
1391 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
|
|
1392 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
|
|
1393 | |
|
|
1394 | In this state it is simply some block of memory that is suitable for use |
|
|
1395 | in an event loop. It can be moved around, freed, reused etc. at will. |
|
|
1396 | |
|
|
1397 | =item started/running/active |
|
|
1398 | |
|
|
1399 | Once a watcher has been started with a call to C<ev_TYPE_start> it becomes |
|
|
1400 | property of the event loop, and is actively waiting for events. While in |
|
|
1401 | this state it cannot be accessed (except in a few documented ways), moved, |
|
|
1402 | freed or anything else - the only legal thing is to keep a pointer to it, |
|
|
1403 | and call libev functions on it that are documented to work on active watchers. |
|
|
1404 | |
|
|
1405 | =item pending |
|
|
1406 | |
|
|
1407 | If a watcher is active and libev determines that an event it is interested |
|
|
1408 | in has occurred (such as a timer expiring), it will become pending. It will |
|
|
1409 | stay in this pending state until either it is stopped or its callback is |
|
|
1410 | about to be invoked, so it is not normally pending inside the watcher |
|
|
1411 | callback. |
|
|
1412 | |
|
|
1413 | The watcher might or might not be active while it is pending (for example, |
|
|
1414 | an expired non-repeating timer can be pending but no longer active). If it |
|
|
1415 | is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>), |
|
|
1416 | but it is still property of the event loop at this time, so cannot be |
|
|
1417 | moved, freed or reused. And if it is active the rules described in the |
|
|
1418 | previous item still apply. |
|
|
1419 | |
|
|
1420 | It is also possible to feed an event on a watcher that is not active (e.g. |
|
|
1421 | via C<ev_feed_event>), in which case it becomes pending without being |
|
|
1422 | active. |
|
|
1423 | |
|
|
1424 | =item stopped |
|
|
1425 | |
|
|
1426 | A watcher can be stopped implicitly by libev (in which case it might still |
|
|
1427 | be pending), or explicitly by calling its C<ev_TYPE_stop> function. The |
|
|
1428 | latter will clear any pending state the watcher might be in, regardless |
|
|
1429 | of whether it was active or not, so stopping a watcher explicitly before |
|
|
1430 | freeing it is often a good idea. |
|
|
1431 | |
|
|
1432 | While stopped (and not pending) the watcher is essentially in the |
|
|
1433 | initialised state, that is it can be reused, moved, modified in any way |
|
|
1434 | you wish. |
|
|
1435 | |
|
|
1436 | =back |
1434 | |
1437 | |
1435 | =head2 WATCHER PRIORITY MODELS |
1438 | =head2 WATCHER PRIORITY MODELS |
1436 | |
1439 | |
1437 | Many event loops support I<watcher priorities>, which are usually small |
1440 | Many event loops support I<watcher priorities>, which are usually small |
1438 | integers that influence the ordering of event callback invocation |
1441 | integers that influence the ordering of event callback invocation |