… | |
… | |
10 | |
10 | |
11 | // a single header file is required |
11 | // a single header file is required |
12 | #include <ev.h> |
12 | #include <ev.h> |
13 | |
13 | |
14 | // every watcher type has its own typedef'd struct |
14 | // every watcher type has its own typedef'd struct |
15 | // with the name ev_<type> |
15 | // with the name ev_TYPE |
16 | ev_io stdin_watcher; |
16 | ev_io stdin_watcher; |
17 | ev_timer timeout_watcher; |
17 | ev_timer timeout_watcher; |
18 | |
18 | |
19 | // all watcher callbacks have a similar signature |
19 | // all watcher callbacks have a similar signature |
20 | // this callback is called when data is readable on stdin |
20 | // this callback is called when data is readable on stdin |
… | |
… | |
276 | |
276 | |
277 | =back |
277 | =back |
278 | |
278 | |
279 | =head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
279 | =head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
280 | |
280 | |
281 | An event loop is described by a C<ev_loop *>. The library knows two |
281 | An event loop is described by a C<struct ev_loop *> (the C<struct> |
282 | types of such loops, the I<default> loop, which supports signals and child |
282 | is I<not> optional in this case, as there is also an C<ev_loop> |
283 | events, and dynamically created loops which do not. |
283 | I<function>). |
|
|
284 | |
|
|
285 | The library knows two types of such loops, the I<default> loop, which |
|
|
286 | supports signals and child events, and dynamically created loops which do |
|
|
287 | not. |
284 | |
288 | |
285 | =over 4 |
289 | =over 4 |
286 | |
290 | |
287 | =item struct ev_loop *ev_default_loop (unsigned int flags) |
291 | =item struct ev_loop *ev_default_loop (unsigned int flags) |
288 | |
292 | |
… | |
… | |
768 | they fire on, say, one-second boundaries only. |
772 | they fire on, say, one-second boundaries only. |
769 | |
773 | |
770 | =item ev_loop_verify (loop) |
774 | =item ev_loop_verify (loop) |
771 | |
775 | |
772 | This function only does something when C<EV_VERIFY> support has been |
776 | This function only does something when C<EV_VERIFY> support has been |
773 | compiled in. which is the default for non-minimal builds. It tries to go |
777 | compiled in, which is the default for non-minimal builds. It tries to go |
774 | through all internal structures and checks them for validity. If anything |
778 | through all internal structures and checks them for validity. If anything |
775 | is found to be inconsistent, it will print an error message to standard |
779 | is found to be inconsistent, it will print an error message to standard |
776 | error and call C<abort ()>. |
780 | error and call C<abort ()>. |
777 | |
781 | |
778 | This can be used to catch bugs inside libev itself: under normal |
782 | This can be used to catch bugs inside libev itself: under normal |
… | |
… | |
781 | |
785 | |
782 | =back |
786 | =back |
783 | |
787 | |
784 | |
788 | |
785 | =head1 ANATOMY OF A WATCHER |
789 | =head1 ANATOMY OF A WATCHER |
|
|
790 | |
|
|
791 | In the following description, uppercase C<TYPE> in names stands for the |
|
|
792 | watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer |
|
|
793 | watchers and C<ev_io_start> for I/O watchers. |
786 | |
794 | |
787 | A watcher is a structure that you create and register to record your |
795 | A watcher is a structure that you create and register to record your |
788 | interest in some event. For instance, if you want to wait for STDIN to |
796 | interest in some event. For instance, if you want to wait for STDIN to |
789 | become readable, you would create an C<ev_io> watcher for that: |
797 | become readable, you would create an C<ev_io> watcher for that: |
790 | |
798 | |
… | |
… | |
793 | ev_io_stop (w); |
801 | ev_io_stop (w); |
794 | ev_unloop (loop, EVUNLOOP_ALL); |
802 | ev_unloop (loop, EVUNLOOP_ALL); |
795 | } |
803 | } |
796 | |
804 | |
797 | struct ev_loop *loop = ev_default_loop (0); |
805 | struct ev_loop *loop = ev_default_loop (0); |
|
|
806 | |
798 | ev_io stdin_watcher; |
807 | ev_io stdin_watcher; |
|
|
808 | |
799 | ev_init (&stdin_watcher, my_cb); |
809 | ev_init (&stdin_watcher, my_cb); |
800 | ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
810 | ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
801 | ev_io_start (loop, &stdin_watcher); |
811 | ev_io_start (loop, &stdin_watcher); |
|
|
812 | |
802 | ev_loop (loop, 0); |
813 | ev_loop (loop, 0); |
803 | |
814 | |
804 | As you can see, you are responsible for allocating the memory for your |
815 | As you can see, you are responsible for allocating the memory for your |
805 | watcher structures (and it is usually a bad idea to do this on the stack, |
816 | watcher structures (and it is I<usually> a bad idea to do this on the |
806 | although this can sometimes be quite valid). |
817 | stack). |
|
|
818 | |
|
|
819 | Each watcher has an associated watcher structure (called C<struct ev_TYPE> |
|
|
820 | or simply C<ev_TYPE>, as typedefs are provided for all watcher structs). |
807 | |
821 | |
808 | Each watcher structure must be initialised by a call to C<ev_init |
822 | Each watcher structure must be initialised by a call to C<ev_init |
809 | (watcher *, callback)>, which expects a callback to be provided. This |
823 | (watcher *, callback)>, which expects a callback to be provided. This |
810 | callback gets invoked each time the event occurs (or, in the case of I/O |
824 | callback gets invoked each time the event occurs (or, in the case of I/O |
811 | watchers, each time the event loop detects that the file descriptor given |
825 | watchers, each time the event loop detects that the file descriptor given |
812 | is readable and/or writable). |
826 | is readable and/or writable). |
813 | |
827 | |
814 | Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
828 | Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >> |
815 | with arguments specific to this watcher type. There is also a macro |
829 | macro to configure it, with arguments specific to the watcher type. There |
816 | to combine initialisation and setting in one call: C<< ev_<type>_init |
830 | is also a macro to combine initialisation and setting in one call: C<< |
817 | (watcher *, callback, ...) >>. |
831 | ev_TYPE_init (watcher *, callback, ...) >>. |
818 | |
832 | |
819 | To make the watcher actually watch out for events, you have to start it |
833 | To make the watcher actually watch out for events, you have to start it |
820 | with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
834 | with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher |
821 | *) >>), and you can stop watching for events at any time by calling the |
835 | *) >>), and you can stop watching for events at any time by calling the |
822 | corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
836 | corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>. |
823 | |
837 | |
824 | As long as your watcher is active (has been started but not stopped) you |
838 | As long as your watcher is active (has been started but not stopped) you |
825 | must not touch the values stored in it. Most specifically you must never |
839 | must not touch the values stored in it. Most specifically you must never |
826 | reinitialise it or call its C<set> macro. |
840 | reinitialise it or call its C<ev_TYPE_set> macro. |
827 | |
841 | |
828 | Each and every callback receives the event loop pointer as first, the |
842 | Each and every callback receives the event loop pointer as first, the |
829 | registered watcher structure as second, and a bitset of received events as |
843 | registered watcher structure as second, and a bitset of received events as |
830 | third argument. |
844 | third argument. |
831 | |
845 | |
… | |
… | |
911 | thing, so beware. |
925 | thing, so beware. |
912 | |
926 | |
913 | =back |
927 | =back |
914 | |
928 | |
915 | =head2 GENERIC WATCHER FUNCTIONS |
929 | =head2 GENERIC WATCHER FUNCTIONS |
916 | |
|
|
917 | In the following description, C<TYPE> stands for the watcher type, |
|
|
918 | e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers. |
|
|
919 | |
930 | |
920 | =over 4 |
931 | =over 4 |
921 | |
932 | |
922 | =item C<ev_init> (ev_TYPE *watcher, callback) |
933 | =item C<ev_init> (ev_TYPE *watcher, callback) |
923 | |
934 | |
… | |
… | |
1288 | passed, but if multiple timers become ready during the same loop iteration |
1299 | passed, but if multiple timers become ready during the same loop iteration |
1289 | then order of execution is undefined. |
1300 | then order of execution is undefined. |
1290 | |
1301 | |
1291 | =head3 Be smart about timeouts |
1302 | =head3 Be smart about timeouts |
1292 | |
1303 | |
1293 | Many real-world problems invole some kind of time-out, usually for error |
1304 | Many real-world problems involve some kind of timeout, usually for error |
1294 | recovery. A typical example is an HTTP request - if the other side hangs, |
1305 | recovery. A typical example is an HTTP request - if the other side hangs, |
1295 | you want to raise some error after a while. |
1306 | you want to raise some error after a while. |
1296 | |
1307 | |
1297 | Here are some ways on how to handle this problem, from simple and |
1308 | What follows are some ways to handle this problem, from obvious and |
1298 | inefficient to very efficient. |
1309 | inefficient to smart and efficient. |
1299 | |
1310 | |
1300 | In the following examples a 60 second activity timeout is assumed - a |
1311 | In the following, a 60 second activity timeout is assumed - a timeout that |
1301 | timeout that gets reset to 60 seconds each time some data ("a lifesign") |
1312 | gets reset to 60 seconds each time there is activity (e.g. each time some |
1302 | was received. |
1313 | data or other life sign was received). |
1303 | |
1314 | |
1304 | =over 4 |
1315 | =over 4 |
1305 | |
1316 | |
1306 | =item 1. Use a timer and stop, reinitialise, start it on activity. |
1317 | =item 1. Use a timer and stop, reinitialise and start it on activity. |
1307 | |
1318 | |
1308 | This is the most obvious, but not the most simple way: In the beginning, |
1319 | This is the most obvious, but not the most simple way: In the beginning, |
1309 | start the watcher: |
1320 | start the watcher: |
1310 | |
1321 | |
1311 | ev_timer_init (timer, callback, 60., 0.); |
1322 | ev_timer_init (timer, callback, 60., 0.); |
1312 | ev_timer_start (loop, timer); |
1323 | ev_timer_start (loop, timer); |
1313 | |
1324 | |
1314 | Then, each time there is some activity, C<ev_timer_stop> the timer, |
1325 | Then, each time there is some activity, C<ev_timer_stop> it, initialise it |
1315 | initialise it again, and start it: |
1326 | and start it again: |
1316 | |
1327 | |
1317 | ev_timer_stop (loop, timer); |
1328 | ev_timer_stop (loop, timer); |
1318 | ev_timer_set (timer, 60., 0.); |
1329 | ev_timer_set (timer, 60., 0.); |
1319 | ev_timer_start (loop, timer); |
1330 | ev_timer_start (loop, timer); |
1320 | |
1331 | |
1321 | This is relatively simple to implement, but means that each time there |
1332 | This is relatively simple to implement, but means that each time there is |
1322 | is some activity, libev will first have to remove the timer from it's |
1333 | some activity, libev will first have to remove the timer from its internal |
1323 | internal data strcuture and then add it again. |
1334 | data structure and then add it again. Libev tries to be fast, but it's |
|
|
1335 | still not a constant-time operation. |
1324 | |
1336 | |
1325 | =item 2. Use a timer and re-start it with C<ev_timer_again> inactivity. |
1337 | =item 2. Use a timer and re-start it with C<ev_timer_again> inactivity. |
1326 | |
1338 | |
1327 | This is the easiest way, and involves using C<ev_timer_again> instead of |
1339 | This is the easiest way, and involves using C<ev_timer_again> instead of |
1328 | C<ev_timer_start>. |
1340 | C<ev_timer_start>. |
1329 | |
1341 | |
1330 | For this, configure an C<ev_timer> with a C<repeat> value of C<60> and |
1342 | To implement this, configure an C<ev_timer> with a C<repeat> value |
1331 | then call C<ev_timer_again> at start and each time you successfully read |
1343 | of C<60> and then call C<ev_timer_again> at start and each time you |
1332 | or write some data. If you go into an idle state where you do not expect |
1344 | successfully read or write some data. If you go into an idle state where |
1333 | data to travel on the socket, you can C<ev_timer_stop> the timer, and |
1345 | you do not expect data to travel on the socket, you can C<ev_timer_stop> |
1334 | C<ev_timer_again> will automatically restart it if need be. |
1346 | the timer, and C<ev_timer_again> will automatically restart it if need be. |
1335 | |
1347 | |
1336 | That means you can ignore the C<after> value and C<ev_timer_start> |
1348 | That means you can ignore both the C<ev_timer_start> function and the |
1337 | altogether and only ever use the C<repeat> value and C<ev_timer_again>. |
1349 | C<after> argument to C<ev_timer_set>, and only ever use the C<repeat> |
|
|
1350 | member and C<ev_timer_again>. |
1338 | |
1351 | |
1339 | At start: |
1352 | At start: |
1340 | |
1353 | |
1341 | ev_timer_init (timer, callback, 0., 60.); |
1354 | ev_timer_init (timer, callback); |
|
|
1355 | timer->repeat = 60.; |
1342 | ev_timer_again (loop, timer); |
1356 | ev_timer_again (loop, timer); |
1343 | |
1357 | |
1344 | Each time you receive some data: |
1358 | Each time there is some activity: |
1345 | |
1359 | |
1346 | ev_timer_again (loop, timer); |
1360 | ev_timer_again (loop, timer); |
1347 | |
1361 | |
1348 | It is even possible to change the time-out on the fly: |
1362 | It is even possible to change the time-out on the fly, regardless of |
|
|
1363 | whether the watcher is active or not: |
1349 | |
1364 | |
1350 | timer->repeat = 30.; |
1365 | timer->repeat = 30.; |
1351 | ev_timer_again (loop, timer); |
1366 | ev_timer_again (loop, timer); |
1352 | |
1367 | |
1353 | This is slightly more efficient then stopping/starting the timer each time |
1368 | This is slightly more efficient then stopping/starting the timer each time |
1354 | you want to modify its timeout value, as libev does not have to completely |
1369 | you want to modify its timeout value, as libev does not have to completely |
1355 | remove and re-insert the timer from/into it's internal data structure. |
1370 | remove and re-insert the timer from/into its internal data structure. |
|
|
1371 | |
|
|
1372 | It is, however, even simpler than the "obvious" way to do it. |
1356 | |
1373 | |
1357 | =item 3. Let the timer time out, but then re-arm it as required. |
1374 | =item 3. Let the timer time out, but then re-arm it as required. |
1358 | |
1375 | |
1359 | This method is more tricky, but usually most efficient: Most timeouts are |
1376 | This method is more tricky, but usually most efficient: Most timeouts are |
1360 | relatively long compared to the loop iteration time - in our example, |
1377 | relatively long compared to the intervals between other activity - in |
1361 | within 60 seconds, there are usually many I/O events with associated |
1378 | our example, within 60 seconds, there are usually many I/O events with |
1362 | activity resets. |
1379 | associated activity resets. |
1363 | |
1380 | |
1364 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1381 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1365 | but remember the time of last activity, and check for a real timeout only |
1382 | but remember the time of last activity, and check for a real timeout only |
1366 | within the callback: |
1383 | within the callback: |
1367 | |
1384 | |
1368 | ev_tstamp last_activity; // time of last activity |
1385 | ev_tstamp last_activity; // time of last activity |
1369 | |
1386 | |
1370 | static void |
1387 | static void |
1371 | callback (EV_P_ ev_timer *w, int revents) |
1388 | callback (EV_P_ ev_timer *w, int revents) |
1372 | { |
1389 | { |
1373 | ev_tstamp now = ev_now (EV_A); |
1390 | ev_tstamp now = ev_now (EV_A); |
1374 | ev_tstamp timeout = last_activity + 60.; |
1391 | ev_tstamp timeout = last_activity + 60.; |
1375 | |
1392 | |
1376 | // if last_activity is older than now - timeout, we did time out |
1393 | // if last_activity + 60. is older than now, we did time out |
1377 | if (timeout < now) |
1394 | if (timeout < now) |
1378 | { |
1395 | { |
1379 | // timeout occured, take action |
1396 | // timeout occured, take action |
1380 | } |
1397 | } |
1381 | else |
1398 | else |
1382 | { |
1399 | { |
1383 | // callback was invoked, but there was some activity, re-arm |
1400 | // callback was invoked, but there was some activity, re-arm |
1384 | // to fire in last_activity + 60. |
1401 | // the watcher to fire in last_activity + 60, which is |
|
|
1402 | // guaranteed to be in the future, so "again" is positive: |
1385 | w->again = timeout - now; |
1403 | w->again = timeout - now; |
1386 | ev_timer_again (EV_A_ w); |
1404 | ev_timer_again (EV_A_ w); |
1387 | } |
1405 | } |
1388 | } |
1406 | } |
1389 | |
1407 | |
1390 | To summarise the callback: first calculate the real time-out (defined as |
1408 | To summarise the callback: first calculate the real timeout (defined |
1391 | "60 seconds after the last activity"), then check if that time has been |
1409 | as "60 seconds after the last activity"), then check if that time has |
1392 | reached, which means there was a real timeout. Otherwise the callback was |
1410 | been reached, which means something I<did>, in fact, time out. Otherwise |
1393 | invoked too early (timeout is in the future), so re-schedule the timer to |
1411 | the callback was invoked too early (C<timeout> is in the future), so |
1394 | fire at that future time. |
1412 | re-schedule the timer to fire at that future time, to see if maybe we have |
|
|
1413 | a timeout then. |
1395 | |
1414 | |
1396 | Note how C<ev_timer_again> is used, taking advantage of the |
1415 | Note how C<ev_timer_again> is used, taking advantage of the |
1397 | C<ev_timer_again> optimisation when the timer is already running. |
1416 | C<ev_timer_again> optimisation when the timer is already running. |
1398 | |
1417 | |
1399 | This scheme causes more callback invocations (about one every 60 seconds), |
1418 | This scheme causes more callback invocations (about one every 60 seconds |
1400 | but virtually no calls to libev to change the timeout. |
1419 | minus half the average time between activity), but virtually no calls to |
|
|
1420 | libev to change the timeout. |
1401 | |
1421 | |
1402 | To start the timer, simply intiialise the watcher and C<last_activity>, |
1422 | To start the timer, simply initialise the watcher and set C<last_activity> |
1403 | then call the callback: |
1423 | to the current time (meaning we just have some activity :), then call the |
|
|
1424 | callback, which will "do the right thing" and start the timer: |
1404 | |
1425 | |
1405 | ev_timer_init (timer, callback); |
1426 | ev_timer_init (timer, callback); |
1406 | last_activity = ev_now (loop); |
1427 | last_activity = ev_now (loop); |
1407 | callback (loop, timer, EV_TIMEOUT); |
1428 | callback (loop, timer, EV_TIMEOUT); |
1408 | |
1429 | |
1409 | And when there is some activity, simply remember the time in |
1430 | And when there is some activity, simply store the current time in |
1410 | C<last_activity>: |
1431 | C<last_activity>, no libev calls at all: |
1411 | |
1432 | |
1412 | last_actiivty = ev_now (loop); |
1433 | last_actiivty = ev_now (loop); |
1413 | |
1434 | |
1414 | This technique is slightly more complex, but in most cases where the |
1435 | This technique is slightly more complex, but in most cases where the |
1415 | time-out is unlikely to be triggered, much more efficient. |
1436 | time-out is unlikely to be triggered, much more efficient. |
1416 | |
1437 | |
|
|
1438 | Changing the timeout is trivial as well (if it isn't hard-coded in the |
|
|
1439 | callback :) - just change the timeout and invoke the callback, which will |
|
|
1440 | fix things for you. |
|
|
1441 | |
|
|
1442 | =item 4. Wee, just use a double-linked list for your timeouts. |
|
|
1443 | |
|
|
1444 | If there is not one request, but many thousands (millions...), all |
|
|
1445 | employing some kind of timeout with the same timeout value, then one can |
|
|
1446 | do even better: |
|
|
1447 | |
|
|
1448 | When starting the timeout, calculate the timeout value and put the timeout |
|
|
1449 | at the I<end> of the list. |
|
|
1450 | |
|
|
1451 | Then use an C<ev_timer> to fire when the timeout at the I<beginning> of |
|
|
1452 | the list is expected to fire (for example, using the technique #3). |
|
|
1453 | |
|
|
1454 | When there is some activity, remove the timer from the list, recalculate |
|
|
1455 | the timeout, append it to the end of the list again, and make sure to |
|
|
1456 | update the C<ev_timer> if it was taken from the beginning of the list. |
|
|
1457 | |
|
|
1458 | This way, one can manage an unlimited number of timeouts in O(1) time for |
|
|
1459 | starting, stopping and updating the timers, at the expense of a major |
|
|
1460 | complication, and having to use a constant timeout. The constant timeout |
|
|
1461 | ensures that the list stays sorted. |
|
|
1462 | |
1417 | =back |
1463 | =back |
|
|
1464 | |
|
|
1465 | So which method the best? |
|
|
1466 | |
|
|
1467 | Method #2 is a simple no-brain-required solution that is adequate in most |
|
|
1468 | situations. Method #3 requires a bit more thinking, but handles many cases |
|
|
1469 | better, and isn't very complicated either. In most case, choosing either |
|
|
1470 | one is fine, with #3 being better in typical situations. |
|
|
1471 | |
|
|
1472 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
|
|
1473 | rather complicated, but extremely efficient, something that really pays |
|
|
1474 | off after the first million or so of active timers, i.e. it's usually |
|
|
1475 | overkill :) |
1418 | |
1476 | |
1419 | =head3 The special problem of time updates |
1477 | =head3 The special problem of time updates |
1420 | |
1478 | |
1421 | Establishing the current time is a costly operation (it usually takes at |
1479 | Establishing the current time is a costly operation (it usually takes at |
1422 | least two system calls): EV therefore updates its idea of the current |
1480 | least two system calls): EV therefore updates its idea of the current |
… | |
… | |
2900 | =item D |
2958 | =item D |
2901 | |
2959 | |
2902 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2960 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2903 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2961 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
2904 | |
2962 | |
|
|
2963 | =item Ocaml |
|
|
2964 | |
|
|
2965 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
|
|
2966 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
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2967 | |
2905 | =back |
2968 | =back |
2906 | |
2969 | |
2907 | |
2970 | |
2908 | =head1 MACRO MAGIC |
2971 | =head1 MACRO MAGIC |
2909 | |
2972 | |