… | |
… | |
174 | =item ev_tstamp ev_time () |
174 | =item ev_tstamp ev_time () |
175 | |
175 | |
176 | Returns the current time as libev would use it. Please note that the |
176 | Returns the current time as libev would use it. Please note that the |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
178 | you actually want to know. Also interesting is the combination of |
178 | you actually want to know. Also interesting is the combination of |
179 | C<ev_update_now> and C<ev_now>. |
179 | C<ev_now_update> and C<ev_now>. |
180 | |
180 | |
181 | =item ev_sleep (ev_tstamp interval) |
181 | =item ev_sleep (ev_tstamp interval) |
182 | |
182 | |
183 | Sleep for the given interval: The current thread will be blocked until |
183 | Sleep for the given interval: The current thread will be blocked |
184 | either it is interrupted or the given time interval has passed. Basically |
184 | until either it is interrupted or the given time interval has |
|
|
185 | passed (approximately - it might return a bit earlier even if not |
|
|
186 | interrupted). Returns immediately if C<< interval <= 0 >>. |
|
|
187 | |
185 | this is a sub-second-resolution C<sleep ()>. |
188 | Basically this is a sub-second-resolution C<sleep ()>. |
|
|
189 | |
|
|
190 | The range of the C<interval> is limited - libev only guarantees to work |
|
|
191 | with sleep times of up to one day (C<< interval <= 86400 >>). |
186 | |
192 | |
187 | =item int ev_version_major () |
193 | =item int ev_version_major () |
188 | |
194 | |
189 | =item int ev_version_minor () |
195 | =item int ev_version_minor () |
190 | |
196 | |
… | |
… | |
435 | example) that can't properly initialise their signal masks. |
441 | example) that can't properly initialise their signal masks. |
436 | |
442 | |
437 | =item C<EVFLAG_NOSIGMASK> |
443 | =item C<EVFLAG_NOSIGMASK> |
438 | |
444 | |
439 | When this flag is specified, then libev will avoid to modify the signal |
445 | When this flag is specified, then libev will avoid to modify the signal |
440 | mask. Specifically, this means you ahve to make sure signals are unblocked |
446 | mask. Specifically, this means you have to make sure signals are unblocked |
441 | when you want to receive them. |
447 | when you want to receive them. |
442 | |
448 | |
443 | This behaviour is useful when you want to do your own signal handling, or |
449 | This behaviour is useful when you want to do your own signal handling, or |
444 | want to handle signals only in specific threads and want to avoid libev |
450 | want to handle signals only in specific threads and want to avoid libev |
445 | unblocking the signals. |
451 | unblocking the signals. |
… | |
… | |
483 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
489 | =item C<EVBACKEND_EPOLL> (value 4, Linux) |
484 | |
490 | |
485 | Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
491 | Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9 |
486 | kernels). |
492 | kernels). |
487 | |
493 | |
488 | For few fds, this backend is a bit little slower than poll and select, |
494 | For few fds, this backend is a bit little slower than poll and select, but |
489 | but it scales phenomenally better. While poll and select usually scale |
495 | it scales phenomenally better. While poll and select usually scale like |
490 | like O(total_fds) where n is the total number of fds (or the highest fd), |
496 | O(total_fds) where total_fds is the total number of fds (or the highest |
491 | epoll scales either O(1) or O(active_fds). |
497 | fd), epoll scales either O(1) or O(active_fds). |
492 | |
498 | |
493 | The epoll mechanism deserves honorable mention as the most misdesigned |
499 | The epoll mechanism deserves honorable mention as the most misdesigned |
494 | of the more advanced event mechanisms: mere annoyances include silently |
500 | of the more advanced event mechanisms: mere annoyances include silently |
495 | dropping file descriptors, requiring a system call per change per file |
501 | dropping file descriptors, requiring a system call per change per file |
496 | descriptor (and unnecessary guessing of parameters), problems with dup, |
502 | descriptor (and unnecessary guessing of parameters), problems with dup, |
… | |
… | |
499 | 0.1ms) and so on. The biggest issue is fork races, however - if a program |
505 | 0.1ms) and so on. The biggest issue is fork races, however - if a program |
500 | forks then I<both> parent and child process have to recreate the epoll |
506 | forks then I<both> parent and child process have to recreate the epoll |
501 | set, which can take considerable time (one syscall per file descriptor) |
507 | set, which can take considerable time (one syscall per file descriptor) |
502 | and is of course hard to detect. |
508 | and is of course hard to detect. |
503 | |
509 | |
504 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, but |
510 | Epoll is also notoriously buggy - embedding epoll fds I<should> work, |
505 | of course I<doesn't>, and epoll just loves to report events for totally |
511 | but of course I<doesn't>, and epoll just loves to report events for |
506 | I<different> file descriptors (even already closed ones, so one cannot |
512 | totally I<different> file descriptors (even already closed ones, so |
507 | even remove them from the set) than registered in the set (especially |
513 | one cannot even remove them from the set) than registered in the set |
508 | on SMP systems). Libev tries to counter these spurious notifications by |
514 | (especially on SMP systems). Libev tries to counter these spurious |
509 | employing an additional generation counter and comparing that against the |
515 | notifications by employing an additional generation counter and comparing |
510 | events to filter out spurious ones, recreating the set when required. Last |
516 | that against the events to filter out spurious ones, recreating the set |
|
|
517 | when required. Epoll also erroneously rounds down timeouts, but gives you |
|
|
518 | no way to know when and by how much, so sometimes you have to busy-wait |
|
|
519 | because epoll returns immediately despite a nonzero timeout. And last |
511 | not least, it also refuses to work with some file descriptors which work |
520 | not least, it also refuses to work with some file descriptors which work |
512 | perfectly fine with C<select> (files, many character devices...). |
521 | perfectly fine with C<select> (files, many character devices...). |
513 | |
522 | |
514 | Epoll is truly the train wreck analog among event poll mechanisms, |
523 | Epoll is truly the train wreck among event poll mechanisms, a frankenpoll, |
515 | a frankenpoll, cobbled together in a hurry, no thought to design or |
524 | cobbled together in a hurry, no thought to design or interaction with |
516 | interaction with others. |
525 | others. Oh, the pain, will it ever stop... |
517 | |
526 | |
518 | While stopping, setting and starting an I/O watcher in the same iteration |
527 | While stopping, setting and starting an I/O watcher in the same iteration |
519 | will result in some caching, there is still a system call per such |
528 | will result in some caching, there is still a system call per such |
520 | incident (because the same I<file descriptor> could point to a different |
529 | incident (because the same I<file descriptor> could point to a different |
521 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
530 | I<file description> now), so its best to avoid that. Also, C<dup ()>'ed |
… | |
… | |
558 | |
567 | |
559 | It scales in the same way as the epoll backend, but the interface to the |
568 | It scales in the same way as the epoll backend, but the interface to the |
560 | kernel is more efficient (which says nothing about its actual speed, of |
569 | kernel is more efficient (which says nothing about its actual speed, of |
561 | course). While stopping, setting and starting an I/O watcher does never |
570 | course). While stopping, setting and starting an I/O watcher does never |
562 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
571 | cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to |
563 | two event changes per incident. Support for C<fork ()> is very bad (but |
572 | two event changes per incident. Support for C<fork ()> is very bad (you |
564 | sane, unlike epoll) and it drops fds silently in similarly hard-to-detect |
573 | might have to leak fd's on fork, but it's more sane than epoll) and it |
565 | cases |
574 | drops fds silently in similarly hard-to-detect cases |
566 | |
575 | |
567 | This backend usually performs well under most conditions. |
576 | This backend usually performs well under most conditions. |
568 | |
577 | |
569 | While nominally embeddable in other event loops, this doesn't work |
578 | While nominally embeddable in other event loops, this doesn't work |
570 | everywhere, so you might need to test for this. And since it is broken |
579 | everywhere, so you might need to test for this. And since it is broken |
… | |
… | |
599 | among the OS-specific backends (I vastly prefer correctness over speed |
608 | among the OS-specific backends (I vastly prefer correctness over speed |
600 | hacks). |
609 | hacks). |
601 | |
610 | |
602 | On the negative side, the interface is I<bizarre> - so bizarre that |
611 | On the negative side, the interface is I<bizarre> - so bizarre that |
603 | even sun itself gets it wrong in their code examples: The event polling |
612 | even sun itself gets it wrong in their code examples: The event polling |
604 | function sometimes returning events to the caller even though an error |
613 | function sometimes returns events to the caller even though an error |
605 | occurred, but with no indication whether it has done so or not (yes, it's |
614 | occurred, but with no indication whether it has done so or not (yes, it's |
606 | even documented that way) - deadly for edge-triggered interfaces where |
615 | even documented that way) - deadly for edge-triggered interfaces where you |
607 | you absolutely have to know whether an event occurred or not because you |
616 | absolutely have to know whether an event occurred or not because you have |
608 | have to re-arm the watcher. |
617 | to re-arm the watcher. |
609 | |
618 | |
610 | Fortunately libev seems to be able to work around these idiocies. |
619 | Fortunately libev seems to be able to work around these idiocies. |
611 | |
620 | |
612 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
621 | This backend maps C<EV_READ> and C<EV_WRITE> in the same way as |
613 | C<EVBACKEND_POLL>. |
622 | C<EVBACKEND_POLL>. |
… | |
… | |
825 | This is useful if you are waiting for some external event in conjunction |
834 | This is useful if you are waiting for some external event in conjunction |
826 | with something not expressible using other libev watchers (i.e. "roll your |
835 | with something not expressible using other libev watchers (i.e. "roll your |
827 | own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is |
836 | own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is |
828 | usually a better approach for this kind of thing. |
837 | usually a better approach for this kind of thing. |
829 | |
838 | |
830 | Here are the gory details of what C<ev_run> does: |
839 | Here are the gory details of what C<ev_run> does (this is for your |
|
|
840 | understanding, not a guarantee that things will work exactly like this in |
|
|
841 | future versions): |
831 | |
842 | |
832 | - Increment loop depth. |
843 | - Increment loop depth. |
833 | - Reset the ev_break status. |
844 | - Reset the ev_break status. |
834 | - Before the first iteration, call any pending watchers. |
845 | - Before the first iteration, call any pending watchers. |
835 | LOOP: |
846 | LOOP: |
… | |
… | |
941 | overhead for the actual polling but can deliver many events at once. |
952 | overhead for the actual polling but can deliver many events at once. |
942 | |
953 | |
943 | By setting a higher I<io collect interval> you allow libev to spend more |
954 | By setting a higher I<io collect interval> you allow libev to spend more |
944 | time collecting I/O events, so you can handle more events per iteration, |
955 | time collecting I/O events, so you can handle more events per iteration, |
945 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
956 | at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
946 | C<ev_timer>) will be not affected. Setting this to a non-null value will |
957 | C<ev_timer>) will not be affected. Setting this to a non-null value will |
947 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
958 | introduce an additional C<ev_sleep ()> call into most loop iterations. The |
948 | sleep time ensures that libev will not poll for I/O events more often then |
959 | sleep time ensures that libev will not poll for I/O events more often then |
949 | once per this interval, on average. |
960 | once per this interval, on average (as long as the host time resolution is |
|
|
961 | good enough). |
950 | |
962 | |
951 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
963 | Likewise, by setting a higher I<timeout collect interval> you allow libev |
952 | to spend more time collecting timeouts, at the expense of increased |
964 | to spend more time collecting timeouts, at the expense of increased |
953 | latency/jitter/inexactness (the watcher callback will be called |
965 | latency/jitter/inexactness (the watcher callback will be called |
954 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
966 | later). C<ev_io> watchers will not be affected. Setting this to a non-null |
… | |
… | |
1008 | can be done relatively simply by putting mutex_lock/unlock calls around |
1020 | can be done relatively simply by putting mutex_lock/unlock calls around |
1009 | each call to a libev function. |
1021 | each call to a libev function. |
1010 | |
1022 | |
1011 | However, C<ev_run> can run an indefinite time, so it is not feasible |
1023 | However, C<ev_run> can run an indefinite time, so it is not feasible |
1012 | to wait for it to return. One way around this is to wake up the event |
1024 | to wait for it to return. One way around this is to wake up the event |
1013 | loop via C<ev_break> and C<av_async_send>, another way is to set these |
1025 | loop via C<ev_break> and C<ev_async_send>, another way is to set these |
1014 | I<release> and I<acquire> callbacks on the loop. |
1026 | I<release> and I<acquire> callbacks on the loop. |
1015 | |
1027 | |
1016 | When set, then C<release> will be called just before the thread is |
1028 | When set, then C<release> will be called just before the thread is |
1017 | suspended waiting for new events, and C<acquire> is called just |
1029 | suspended waiting for new events, and C<acquire> is called just |
1018 | afterwards. |
1030 | afterwards. |
… | |
… | |
1374 | |
1386 | |
1375 | =over 4 |
1387 | =over 4 |
1376 | |
1388 | |
1377 | =item initialiased |
1389 | =item initialiased |
1378 | |
1390 | |
1379 | Before a watcher can be registered with the event looop it has to be |
1391 | Before a watcher can be registered with the event loop it has to be |
1380 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
1392 | initialised. This can be done with a call to C<ev_TYPE_init>, or calls to |
1381 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
1393 | C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function. |
1382 | |
1394 | |
1383 | In this state it is simply some block of memory that is suitable for |
1395 | In this state it is simply some block of memory that is suitable for |
1384 | use in an event loop. It can be moved around, freed, reused etc. at |
1396 | use in an event loop. It can be moved around, freed, reused etc. at |
… | |
… | |
1759 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1771 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1760 | monotonic clock option helps a lot here). |
1772 | monotonic clock option helps a lot here). |
1761 | |
1773 | |
1762 | The callback is guaranteed to be invoked only I<after> its timeout has |
1774 | The callback is guaranteed to be invoked only I<after> its timeout has |
1763 | passed (not I<at>, so on systems with very low-resolution clocks this |
1775 | passed (not I<at>, so on systems with very low-resolution clocks this |
1764 | might introduce a small delay). If multiple timers become ready during the |
1776 | might introduce a small delay, see "the special problem of being too |
|
|
1777 | early", below). If multiple timers become ready during the same loop |
1765 | same loop iteration then the ones with earlier time-out values are invoked |
1778 | iteration then the ones with earlier time-out values are invoked before |
1766 | before ones of the same priority with later time-out values (but this is |
1779 | ones of the same priority with later time-out values (but this is no |
1767 | no longer true when a callback calls C<ev_run> recursively). |
1780 | longer true when a callback calls C<ev_run> recursively). |
1768 | |
1781 | |
1769 | =head3 Be smart about timeouts |
1782 | =head3 Be smart about timeouts |
1770 | |
1783 | |
1771 | Many real-world problems involve some kind of timeout, usually for error |
1784 | Many real-world problems involve some kind of timeout, usually for error |
1772 | recovery. A typical example is an HTTP request - if the other side hangs, |
1785 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1847 | |
1860 | |
1848 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1861 | In this case, it would be more efficient to leave the C<ev_timer> alone, |
1849 | but remember the time of last activity, and check for a real timeout only |
1862 | but remember the time of last activity, and check for a real timeout only |
1850 | within the callback: |
1863 | within the callback: |
1851 | |
1864 | |
|
|
1865 | ev_tstamp timeout = 60.; |
1852 | ev_tstamp last_activity; // time of last activity |
1866 | ev_tstamp last_activity; // time of last activity |
|
|
1867 | ev_timer timer; |
1853 | |
1868 | |
1854 | static void |
1869 | static void |
1855 | callback (EV_P_ ev_timer *w, int revents) |
1870 | callback (EV_P_ ev_timer *w, int revents) |
1856 | { |
1871 | { |
1857 | ev_tstamp now = ev_now (EV_A); |
1872 | // calculate when the timeout would happen |
1858 | ev_tstamp timeout = last_activity + 60.; |
1873 | ev_tstamp after = last_activity - ev_now (EV_A) + timeout; |
1859 | |
1874 | |
1860 | // if last_activity + 60. is older than now, we did time out |
1875 | // if negative, it means we the timeout already occured |
1861 | if (timeout < now) |
1876 | if (after < 0.) |
1862 | { |
1877 | { |
1863 | // timeout occurred, take action |
1878 | // timeout occurred, take action |
1864 | } |
1879 | } |
1865 | else |
1880 | else |
1866 | { |
1881 | { |
1867 | // callback was invoked, but there was some activity, re-arm |
1882 | // callback was invoked, but there was some recent |
1868 | // the watcher to fire in last_activity + 60, which is |
1883 | // activity. simply restart the timer to time out |
1869 | // guaranteed to be in the future, so "again" is positive: |
1884 | // after "after" seconds, which is the earliest time |
1870 | w->repeat = timeout - now; |
1885 | // the timeout can occur. |
|
|
1886 | ev_timer_set (w, after, 0.); |
1871 | ev_timer_again (EV_A_ w); |
1887 | ev_timer_start (EV_A_ w); |
1872 | } |
1888 | } |
1873 | } |
1889 | } |
1874 | |
1890 | |
1875 | To summarise the callback: first calculate the real timeout (defined |
1891 | To summarise the callback: first calculate in how many seconds the |
1876 | as "60 seconds after the last activity"), then check if that time has |
1892 | timeout will occur (by calculating the absolute time when it would occur, |
1877 | been reached, which means something I<did>, in fact, time out. Otherwise |
1893 | C<last_activity + timeout>, and subtracting the current time, C<ev_now |
1878 | the callback was invoked too early (C<timeout> is in the future), so |
1894 | (EV_A)> from that). |
1879 | re-schedule the timer to fire at that future time, to see if maybe we have |
|
|
1880 | a timeout then. |
|
|
1881 | |
1895 | |
1882 | Note how C<ev_timer_again> is used, taking advantage of the |
1896 | If this value is negative, then we are already past the timeout, i.e. we |
1883 | C<ev_timer_again> optimisation when the timer is already running. |
1897 | timed out, and need to do whatever is needed in this case. |
|
|
1898 | |
|
|
1899 | Otherwise, we now the earliest time at which the timeout would trigger, |
|
|
1900 | and simply start the timer with this timeout value. |
|
|
1901 | |
|
|
1902 | In other words, each time the callback is invoked it will check whether |
|
|
1903 | the timeout cocured. If not, it will simply reschedule itself to check |
|
|
1904 | again at the earliest time it could time out. Rinse. Repeat. |
1884 | |
1905 | |
1885 | This scheme causes more callback invocations (about one every 60 seconds |
1906 | This scheme causes more callback invocations (about one every 60 seconds |
1886 | minus half the average time between activity), but virtually no calls to |
1907 | minus half the average time between activity), but virtually no calls to |
1887 | libev to change the timeout. |
1908 | libev to change the timeout. |
1888 | |
1909 | |
1889 | To start the timer, simply initialise the watcher and set C<last_activity> |
1910 | To start the machinery, simply initialise the watcher and set |
1890 | to the current time (meaning we just have some activity :), then call the |
1911 | C<last_activity> to the current time (meaning there was some activity just |
1891 | callback, which will "do the right thing" and start the timer: |
1912 | now), then call the callback, which will "do the right thing" and start |
|
|
1913 | the timer: |
1892 | |
1914 | |
|
|
1915 | last_activity = ev_now (EV_A); |
1893 | ev_init (timer, callback); |
1916 | ev_init (&timer, callback); |
1894 | last_activity = ev_now (loop); |
1917 | callback (EV_A_ &timer, 0); |
1895 | callback (loop, timer, EV_TIMER); |
|
|
1896 | |
1918 | |
1897 | And when there is some activity, simply store the current time in |
1919 | When there is some activity, simply store the current time in |
1898 | C<last_activity>, no libev calls at all: |
1920 | C<last_activity>, no libev calls at all: |
1899 | |
1921 | |
|
|
1922 | if (activity detected) |
1900 | last_activity = ev_now (loop); |
1923 | last_activity = ev_now (EV_A); |
|
|
1924 | |
|
|
1925 | When your timeout value changes, then the timeout can be changed by simply |
|
|
1926 | providing a new value, stopping the timer and calling the callback, which |
|
|
1927 | will agaion do the right thing (for example, time out immediately :). |
|
|
1928 | |
|
|
1929 | timeout = new_value; |
|
|
1930 | ev_timer_stop (EV_A_ &timer); |
|
|
1931 | callback (EV_A_ &timer, 0); |
1901 | |
1932 | |
1902 | This technique is slightly more complex, but in most cases where the |
1933 | This technique is slightly more complex, but in most cases where the |
1903 | time-out is unlikely to be triggered, much more efficient. |
1934 | time-out is unlikely to be triggered, much more efficient. |
1904 | |
|
|
1905 | Changing the timeout is trivial as well (if it isn't hard-coded in the |
|
|
1906 | callback :) - just change the timeout and invoke the callback, which will |
|
|
1907 | fix things for you. |
|
|
1908 | |
1935 | |
1909 | =item 4. Wee, just use a double-linked list for your timeouts. |
1936 | =item 4. Wee, just use a double-linked list for your timeouts. |
1910 | |
1937 | |
1911 | If there is not one request, but many thousands (millions...), all |
1938 | If there is not one request, but many thousands (millions...), all |
1912 | employing some kind of timeout with the same timeout value, then one can |
1939 | employing some kind of timeout with the same timeout value, then one can |
… | |
… | |
1939 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1966 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1940 | rather complicated, but extremely efficient, something that really pays |
1967 | rather complicated, but extremely efficient, something that really pays |
1941 | off after the first million or so of active timers, i.e. it's usually |
1968 | off after the first million or so of active timers, i.e. it's usually |
1942 | overkill :) |
1969 | overkill :) |
1943 | |
1970 | |
|
|
1971 | =head3 The special problem of being too early |
|
|
1972 | |
|
|
1973 | If you ask a timer to call your callback after three seconds, then |
|
|
1974 | you expect it to be invoked after three seconds - but of course, this |
|
|
1975 | cannot be guaranteed to infinite precision. Less obviously, it cannot be |
|
|
1976 | guaranteed to any precision by libev - imagine somebody suspending the |
|
|
1977 | process with a STOP signal for a few hours for example. |
|
|
1978 | |
|
|
1979 | So, libev tries to invoke your callback as soon as possible I<after> the |
|
|
1980 | delay has occurred, but cannot guarantee this. |
|
|
1981 | |
|
|
1982 | A less obvious failure mode is calling your callback too early: many event |
|
|
1983 | loops compare timestamps with a "elapsed delay >= requested delay", but |
|
|
1984 | this can cause your callback to be invoked much earlier than you would |
|
|
1985 | expect. |
|
|
1986 | |
|
|
1987 | To see why, imagine a system with a clock that only offers full second |
|
|
1988 | resolution (think windows if you can't come up with a broken enough OS |
|
|
1989 | yourself). If you schedule a one-second timer at the time 500.9, then the |
|
|
1990 | event loop will schedule your timeout to elapse at a system time of 500 |
|
|
1991 | (500.9 truncated to the resolution) + 1, or 501. |
|
|
1992 | |
|
|
1993 | If an event library looks at the timeout 0.1s later, it will see "501 >= |
|
|
1994 | 501" and invoke the callback 0.1s after it was started, even though a |
|
|
1995 | one-second delay was requested - this is being "too early", despite best |
|
|
1996 | intentions. |
|
|
1997 | |
|
|
1998 | This is the reason why libev will never invoke the callback if the elapsed |
|
|
1999 | delay equals the requested delay, but only when the elapsed delay is |
|
|
2000 | larger than the requested delay. In the example above, libev would only invoke |
|
|
2001 | the callback at system time 502, or 1.1s after the timer was started. |
|
|
2002 | |
|
|
2003 | So, while libev cannot guarantee that your callback will be invoked |
|
|
2004 | exactly when requested, it I<can> and I<does> guarantee that the requested |
|
|
2005 | delay has actually elapsed, or in other words, it always errs on the "too |
|
|
2006 | late" side of things. |
|
|
2007 | |
1944 | =head3 The special problem of time updates |
2008 | =head3 The special problem of time updates |
1945 | |
2009 | |
1946 | Establishing the current time is a costly operation (it usually takes at |
2010 | Establishing the current time is a costly operation (it usually takes |
1947 | least two system calls): EV therefore updates its idea of the current |
2011 | at least one system call): EV therefore updates its idea of the current |
1948 | time only before and after C<ev_run> collects new events, which causes a |
2012 | time only before and after C<ev_run> collects new events, which causes a |
1949 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
2013 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
1950 | lots of events in one iteration. |
2014 | lots of events in one iteration. |
1951 | |
2015 | |
1952 | The relative timeouts are calculated relative to the C<ev_now ()> |
2016 | The relative timeouts are calculated relative to the C<ev_now ()> |
… | |
… | |
1958 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
2022 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
1959 | |
2023 | |
1960 | If the event loop is suspended for a long time, you can also force an |
2024 | If the event loop is suspended for a long time, you can also force an |
1961 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
2025 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
1962 | ()>. |
2026 | ()>. |
|
|
2027 | |
|
|
2028 | =head3 The special problem of unsynchronised clocks |
|
|
2029 | |
|
|
2030 | Modern systems have a variety of clocks - libev itself uses the normal |
|
|
2031 | "wall clock" clock and, if available, the monotonic clock (to avoid time |
|
|
2032 | jumps). |
|
|
2033 | |
|
|
2034 | Neither of these clocks is synchronised with each other or any other clock |
|
|
2035 | on the system, so C<ev_time ()> might return a considerably different time |
|
|
2036 | than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example, |
|
|
2037 | a call to C<gettimeofday> might return a second count that is one higher |
|
|
2038 | than a directly following call to C<time>. |
|
|
2039 | |
|
|
2040 | The moral of this is to only compare libev-related timestamps with |
|
|
2041 | C<ev_time ()> and C<ev_now ()>, at least if you want better precision than |
|
|
2042 | a second or so. |
|
|
2043 | |
|
|
2044 | One more problem arises due to this lack of synchronisation: if libev uses |
|
|
2045 | the system monotonic clock and you compare timestamps from C<ev_time> |
|
|
2046 | or C<ev_now> from when you started your timer and when your callback is |
|
|
2047 | invoked, you will find that sometimes the callback is a bit "early". |
|
|
2048 | |
|
|
2049 | This is because C<ev_timer>s work in real time, not wall clock time, so |
|
|
2050 | libev makes sure your callback is not invoked before the delay happened, |
|
|
2051 | I<measured according to the real time>, not the system clock. |
|
|
2052 | |
|
|
2053 | If your timeouts are based on a physical timescale (e.g. "time out this |
|
|
2054 | connection after 100 seconds") then this shouldn't bother you as it is |
|
|
2055 | exactly the right behaviour. |
|
|
2056 | |
|
|
2057 | If you want to compare wall clock/system timestamps to your timers, then |
|
|
2058 | you need to use C<ev_periodic>s, as these are based on the wall clock |
|
|
2059 | time, where your comparisons will always generate correct results. |
1963 | |
2060 | |
1964 | =head3 The special problems of suspended animation |
2061 | =head3 The special problems of suspended animation |
1965 | |
2062 | |
1966 | When you leave the server world it is quite customary to hit machines that |
2063 | When you leave the server world it is quite customary to hit machines that |
1967 | can suspend/hibernate - what happens to the clocks during such a suspend? |
2064 | can suspend/hibernate - what happens to the clocks during such a suspend? |
… | |
… | |
2011 | keep up with the timer (because it takes longer than those 10 seconds to |
2108 | keep up with the timer (because it takes longer than those 10 seconds to |
2012 | do stuff) the timer will not fire more than once per event loop iteration. |
2109 | do stuff) the timer will not fire more than once per event loop iteration. |
2013 | |
2110 | |
2014 | =item ev_timer_again (loop, ev_timer *) |
2111 | =item ev_timer_again (loop, ev_timer *) |
2015 | |
2112 | |
2016 | This will act as if the timer timed out and restart it again if it is |
2113 | This will act as if the timer timed out, and restarts it again if it is |
2017 | repeating. The exact semantics are: |
2114 | repeating. It basically works like calling C<ev_timer_stop>, updating the |
|
|
2115 | timeout to the C<repeat> value and calling C<ev_timer_start>. |
2018 | |
2116 | |
|
|
2117 | The exact semantics are as in the following rules, all of which will be |
|
|
2118 | applied to the watcher: |
|
|
2119 | |
|
|
2120 | =over 4 |
|
|
2121 | |
2019 | If the timer is pending, its pending status is cleared. |
2122 | =item If the timer is pending, the pending status is always cleared. |
2020 | |
2123 | |
2021 | If the timer is started but non-repeating, stop it (as if it timed out). |
2124 | =item If the timer is started but non-repeating, stop it (as if it timed |
|
|
2125 | out, without invoking it). |
2022 | |
2126 | |
2023 | If the timer is repeating, either start it if necessary (with the |
2127 | =item If the timer is repeating, make the C<repeat> value the new timeout |
2024 | C<repeat> value), or reset the running timer to the C<repeat> value. |
2128 | and start the timer, if necessary. |
|
|
2129 | |
|
|
2130 | =back |
2025 | |
2131 | |
2026 | This sounds a bit complicated, see L<Be smart about timeouts>, above, for a |
2132 | This sounds a bit complicated, see L<Be smart about timeouts>, above, for a |
2027 | usage example. |
2133 | usage example. |
2028 | |
2134 | |
2029 | =item ev_tstamp ev_timer_remaining (loop, ev_timer *) |
2135 | =item ev_tstamp ev_timer_remaining (loop, ev_timer *) |
… | |
… | |
2151 | |
2257 | |
2152 | Another way to think about it (for the mathematically inclined) is that |
2258 | Another way to think about it (for the mathematically inclined) is that |
2153 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2259 | C<ev_periodic> will try to run the callback in this mode at the next possible |
2154 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2260 | time where C<time = offset (mod interval)>, regardless of any time jumps. |
2155 | |
2261 | |
2156 | For numerical stability it is preferable that the C<offset> value is near |
2262 | The C<interval> I<MUST> be positive, and for numerical stability, the |
2157 | C<ev_now ()> (the current time), but there is no range requirement for |
2263 | interval value should be higher than C<1/8192> (which is around 100 |
2158 | this value, and in fact is often specified as zero. |
2264 | microseconds) and C<offset> should be higher than C<0> and should have |
|
|
2265 | at most a similar magnitude as the current time (say, within a factor of |
|
|
2266 | ten). Typical values for offset are, in fact, C<0> or something between |
|
|
2267 | C<0> and C<interval>, which is also the recommended range. |
2159 | |
2268 | |
2160 | Note also that there is an upper limit to how often a timer can fire (CPU |
2269 | Note also that there is an upper limit to how often a timer can fire (CPU |
2161 | speed for example), so if C<interval> is very small then timing stability |
2270 | speed for example), so if C<interval> is very small then timing stability |
2162 | will of course deteriorate. Libev itself tries to be exact to be about one |
2271 | will of course deteriorate. Libev itself tries to be exact to be about one |
2163 | millisecond (if the OS supports it and the machine is fast enough). |
2272 | millisecond (if the OS supports it and the machine is fast enough). |
… | |
… | |
3205 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3314 | C<ev_async_sent> calls). In fact, you could use signal watchers as a kind |
3206 | of "global async watchers" by using a watcher on an otherwise unused |
3315 | of "global async watchers" by using a watcher on an otherwise unused |
3207 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3316 | signal, and C<ev_feed_signal> to signal this watcher from another thread, |
3208 | even without knowing which loop owns the signal. |
3317 | even without knowing which loop owns the signal. |
3209 | |
3318 | |
3210 | Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
|
|
3211 | just the default loop. |
|
|
3212 | |
|
|
3213 | =head3 Queueing |
3319 | =head3 Queueing |
3214 | |
3320 | |
3215 | C<ev_async> does not support queueing of data in any way. The reason |
3321 | C<ev_async> does not support queueing of data in any way. The reason |
3216 | is that the author does not know of a simple (or any) algorithm for a |
3322 | is that the author does not know of a simple (or any) algorithm for a |
3217 | multiple-writer-single-reader queue that works in all cases and doesn't |
3323 | multiple-writer-single-reader queue that works in all cases and doesn't |
… | |
… | |
3308 | trust me. |
3414 | trust me. |
3309 | |
3415 | |
3310 | =item ev_async_send (loop, ev_async *) |
3416 | =item ev_async_send (loop, ev_async *) |
3311 | |
3417 | |
3312 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3418 | Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
3313 | an C<EV_ASYNC> event on the watcher into the event loop, and instanlty |
3419 | an C<EV_ASYNC> event on the watcher into the event loop, and instantly |
3314 | returns. |
3420 | returns. |
3315 | |
3421 | |
3316 | Unlike C<ev_feed_event>, this call is safe to do from other threads, |
3422 | Unlike C<ev_feed_event>, this call is safe to do from other threads, |
3317 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3423 | signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the |
3318 | embedding section below on what exactly this means). |
3424 | embedding section below on what exactly this means). |
3319 | |
3425 | |
3320 | Note that, as with other watchers in libev, multiple events might get |
3426 | Note that, as with other watchers in libev, multiple events might get |
3321 | compressed into a single callback invocation (another way to look at this |
3427 | compressed into a single callback invocation (another way to look at |
3322 | is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>, |
3428 | this is that C<ev_async> watchers are level-triggered: they are set on |
3323 | reset when the event loop detects that). |
3429 | C<ev_async_send>, reset when the event loop detects that). |
3324 | |
3430 | |
3325 | This call incurs the overhead of a system call only once per event loop |
3431 | This call incurs the overhead of at most one extra system call per event |
3326 | iteration, so while the overhead might be noticeable, it doesn't apply to |
3432 | loop iteration, if the event loop is blocked, and no syscall at all if |
3327 | repeated calls to C<ev_async_send> for the same event loop. |
3433 | the event loop (or your program) is processing events. That means that |
|
|
3434 | repeated calls are basically free (there is no need to avoid calls for |
|
|
3435 | performance reasons) and that the overhead becomes smaller (typically |
|
|
3436 | zero) under load. |
3328 | |
3437 | |
3329 | =item bool = ev_async_pending (ev_async *) |
3438 | =item bool = ev_async_pending (ev_async *) |
3330 | |
3439 | |
3331 | Returns a non-zero value when C<ev_async_send> has been called on the |
3440 | Returns a non-zero value when C<ev_async_send> has been called on the |
3332 | watcher but the event has not yet been processed (or even noted) by the |
3441 | watcher but the event has not yet been processed (or even noted) by the |
… | |
… | |
3387 | ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
3496 | ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
3388 | |
3497 | |
3389 | =item ev_feed_fd_event (loop, int fd, int revents) |
3498 | =item ev_feed_fd_event (loop, int fd, int revents) |
3390 | |
3499 | |
3391 | Feed an event on the given fd, as if a file descriptor backend detected |
3500 | Feed an event on the given fd, as if a file descriptor backend detected |
3392 | the given events it. |
3501 | the given events. |
3393 | |
3502 | |
3394 | =item ev_feed_signal_event (loop, int signum) |
3503 | =item ev_feed_signal_event (loop, int signum) |
3395 | |
3504 | |
3396 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3505 | Feed an event as if the given signal occurred. See also C<ev_feed_signal>, |
3397 | which is async-safe. |
3506 | which is async-safe. |
… | |
… | |
3471 | { |
3580 | { |
3472 | struct my_biggy big = (struct my_biggy *) |
3581 | struct my_biggy big = (struct my_biggy *) |
3473 | (((char *)w) - offsetof (struct my_biggy, t2)); |
3582 | (((char *)w) - offsetof (struct my_biggy, t2)); |
3474 | } |
3583 | } |
3475 | |
3584 | |
|
|
3585 | =head2 AVOIDING FINISHING BEFORE RETURNING |
|
|
3586 | |
|
|
3587 | Often you have structures like this in event-based programs: |
|
|
3588 | |
|
|
3589 | callback () |
|
|
3590 | { |
|
|
3591 | free (request); |
|
|
3592 | } |
|
|
3593 | |
|
|
3594 | request = start_new_request (..., callback); |
|
|
3595 | |
|
|
3596 | The intent is to start some "lengthy" operation. The C<request> could be |
|
|
3597 | used to cancel the operation, or do other things with it. |
|
|
3598 | |
|
|
3599 | It's not uncommon to have code paths in C<start_new_request> that |
|
|
3600 | immediately invoke the callback, for example, to report errors. Or you add |
|
|
3601 | some caching layer that finds that it can skip the lengthy aspects of the |
|
|
3602 | operation and simply invoke the callback with the result. |
|
|
3603 | |
|
|
3604 | The problem here is that this will happen I<before> C<start_new_request> |
|
|
3605 | has returned, so C<request> is not set. |
|
|
3606 | |
|
|
3607 | Even if you pass the request by some safer means to the callback, you |
|
|
3608 | might want to do something to the request after starting it, such as |
|
|
3609 | canceling it, which probably isn't working so well when the callback has |
|
|
3610 | already been invoked. |
|
|
3611 | |
|
|
3612 | A common way around all these issues is to make sure that |
|
|
3613 | C<start_new_request> I<always> returns before the callback is invoked. If |
|
|
3614 | C<start_new_request> immediately knows the result, it can artificially |
|
|
3615 | delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher |
|
|
3616 | for example, or more sneakily, by reusing an existing (stopped) watcher |
|
|
3617 | and pushing it into the pending queue: |
|
|
3618 | |
|
|
3619 | ev_set_cb (watcher, callback); |
|
|
3620 | ev_feed_event (EV_A_ watcher, 0); |
|
|
3621 | |
|
|
3622 | This way, C<start_new_request> can safely return before the callback is |
|
|
3623 | invoked, while not delaying callback invocation too much. |
|
|
3624 | |
3476 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3625 | =head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS |
3477 | |
3626 | |
3478 | Often (especially in GUI toolkits) there are places where you have |
3627 | Often (especially in GUI toolkits) there are places where you have |
3479 | I<modal> interaction, which is most easily implemented by recursively |
3628 | I<modal> interaction, which is most easily implemented by recursively |
3480 | invoking C<ev_run>. |
3629 | invoking C<ev_run>. |
… | |
… | |
3493 | int exit_main_loop = 0; |
3642 | int exit_main_loop = 0; |
3494 | |
3643 | |
3495 | while (!exit_main_loop) |
3644 | while (!exit_main_loop) |
3496 | ev_run (EV_DEFAULT_ EVRUN_ONCE); |
3645 | ev_run (EV_DEFAULT_ EVRUN_ONCE); |
3497 | |
3646 | |
3498 | // in a model watcher |
3647 | // in a modal watcher |
3499 | int exit_nested_loop = 0; |
3648 | int exit_nested_loop = 0; |
3500 | |
3649 | |
3501 | while (!exit_nested_loop) |
3650 | while (!exit_nested_loop) |
3502 | ev_run (EV_A_ EVRUN_ONCE); |
3651 | ev_run (EV_A_ EVRUN_ONCE); |
3503 | |
3652 | |
… | |
… | |
3683 | switch_to (libev_coro); |
3832 | switch_to (libev_coro); |
3684 | } |
3833 | } |
3685 | |
3834 | |
3686 | That basically suspends the coroutine inside C<wait_for_event> and |
3835 | That basically suspends the coroutine inside C<wait_for_event> and |
3687 | continues the libev coroutine, which, when appropriate, switches back to |
3836 | continues the libev coroutine, which, when appropriate, switches back to |
3688 | this or any other coroutine. I am sure if you sue this your own :) |
3837 | this or any other coroutine. |
3689 | |
3838 | |
3690 | You can do similar tricks if you have, say, threads with an event queue - |
3839 | You can do similar tricks if you have, say, threads with an event queue - |
3691 | instead of storing a coroutine, you store the queue object and instead of |
3840 | instead of storing a coroutine, you store the queue object and instead of |
3692 | switching to a coroutine, you push the watcher onto the queue and notify |
3841 | switching to a coroutine, you push the watcher onto the queue and notify |
3693 | any waiters. |
3842 | any waiters. |
… | |
… | |
3768 | with C<operator ()> can be used as callbacks. Other types should be easy |
3917 | with C<operator ()> can be used as callbacks. Other types should be easy |
3769 | to add as long as they only need one additional pointer for context. If |
3918 | to add as long as they only need one additional pointer for context. If |
3770 | you need support for other types of functors please contact the author |
3919 | you need support for other types of functors please contact the author |
3771 | (preferably after implementing it). |
3920 | (preferably after implementing it). |
3772 | |
3921 | |
|
|
3922 | For all this to work, your C++ compiler either has to use the same calling |
|
|
3923 | conventions as your C compiler (for static member functions), or you have |
|
|
3924 | to embed libev and compile libev itself as C++. |
|
|
3925 | |
3773 | Here is a list of things available in the C<ev> namespace: |
3926 | Here is a list of things available in the C<ev> namespace: |
3774 | |
3927 | |
3775 | =over 4 |
3928 | =over 4 |
3776 | |
3929 | |
3777 | =item C<ev::READ>, C<ev::WRITE> etc. |
3930 | =item C<ev::READ>, C<ev::WRITE> etc. |
… | |
… | |
3786 | =item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc. |
3939 | =item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc. |
3787 | |
3940 | |
3788 | For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of |
3941 | For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of |
3789 | the same name in the C<ev> namespace, with the exception of C<ev_signal> |
3942 | the same name in the C<ev> namespace, with the exception of C<ev_signal> |
3790 | which is called C<ev::sig> to avoid clashes with the C<signal> macro |
3943 | which is called C<ev::sig> to avoid clashes with the C<signal> macro |
3791 | defines by many implementations. |
3944 | defined by many implementations. |
3792 | |
3945 | |
3793 | All of those classes have these methods: |
3946 | All of those classes have these methods: |
3794 | |
3947 | |
3795 | =over 4 |
3948 | =over 4 |
3796 | |
3949 | |
… | |
… | |
3929 | watchers in the constructor. |
4082 | watchers in the constructor. |
3930 | |
4083 | |
3931 | class myclass |
4084 | class myclass |
3932 | { |
4085 | { |
3933 | ev::io io ; void io_cb (ev::io &w, int revents); |
4086 | ev::io io ; void io_cb (ev::io &w, int revents); |
3934 | ev::io2 io2 ; void io2_cb (ev::io &w, int revents); |
4087 | ev::io io2 ; void io2_cb (ev::io &w, int revents); |
3935 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
4088 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
3936 | |
4089 | |
3937 | myclass (int fd) |
4090 | myclass (int fd) |
3938 | { |
4091 | { |
3939 | io .set <myclass, &myclass::io_cb > (this); |
4092 | io .set <myclass, &myclass::io_cb > (this); |
… | |
… | |
3990 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
4143 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
3991 | |
4144 | |
3992 | =item D |
4145 | =item D |
3993 | |
4146 | |
3994 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
4147 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
3995 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
4148 | be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>. |
3996 | |
4149 | |
3997 | =item Ocaml |
4150 | =item Ocaml |
3998 | |
4151 | |
3999 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4152 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4000 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
4153 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
… | |
… | |
4048 | suitable for use with C<EV_A>. |
4201 | suitable for use with C<EV_A>. |
4049 | |
4202 | |
4050 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4203 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4051 | |
4204 | |
4052 | Similar to the other two macros, this gives you the value of the default |
4205 | Similar to the other two macros, this gives you the value of the default |
4053 | loop, if multiple loops are supported ("ev loop default"). |
4206 | loop, if multiple loops are supported ("ev loop default"). The default loop |
|
|
4207 | will be initialised if it isn't already initialised. |
|
|
4208 | |
|
|
4209 | For non-multiplicity builds, these macros do nothing, so you always have |
|
|
4210 | to initialise the loop somewhere. |
4054 | |
4211 | |
4055 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4212 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4056 | |
4213 | |
4057 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4214 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4058 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
4215 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
… | |
… | |
4203 | supported). It will also not define any of the structs usually found in |
4360 | supported). It will also not define any of the structs usually found in |
4204 | F<event.h> that are not directly supported by the libev core alone. |
4361 | F<event.h> that are not directly supported by the libev core alone. |
4205 | |
4362 | |
4206 | In standalone mode, libev will still try to automatically deduce the |
4363 | In standalone mode, libev will still try to automatically deduce the |
4207 | configuration, but has to be more conservative. |
4364 | configuration, but has to be more conservative. |
|
|
4365 | |
|
|
4366 | =item EV_USE_FLOOR |
|
|
4367 | |
|
|
4368 | If defined to be C<1>, libev will use the C<floor ()> function for its |
|
|
4369 | periodic reschedule calculations, otherwise libev will fall back on a |
|
|
4370 | portable (slower) implementation. If you enable this, you usually have to |
|
|
4371 | link against libm or something equivalent. Enabling this when the C<floor> |
|
|
4372 | function is not available will fail, so the safe default is to not enable |
|
|
4373 | this. |
4208 | |
4374 | |
4209 | =item EV_USE_MONOTONIC |
4375 | =item EV_USE_MONOTONIC |
4210 | |
4376 | |
4211 | If defined to be C<1>, libev will try to detect the availability of the |
4377 | If defined to be C<1>, libev will try to detect the availability of the |
4212 | monotonic clock option at both compile time and runtime. Otherwise no |
4378 | monotonic clock option at both compile time and runtime. Otherwise no |
… | |
… | |
4342 | If defined to be C<1>, libev will compile in support for the Linux inotify |
4508 | If defined to be C<1>, libev will compile in support for the Linux inotify |
4343 | interface to speed up C<ev_stat> watchers. Its actual availability will |
4509 | interface to speed up C<ev_stat> watchers. Its actual availability will |
4344 | be detected at runtime. If undefined, it will be enabled if the headers |
4510 | be detected at runtime. If undefined, it will be enabled if the headers |
4345 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4511 | indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
4346 | |
4512 | |
|
|
4513 | =item EV_NO_SMP |
|
|
4514 | |
|
|
4515 | If defined to be C<1>, libev will assume that memory is always coherent |
|
|
4516 | between threads, that is, threads can be used, but threads never run on |
|
|
4517 | different cpus (or different cpu cores). This reduces dependencies |
|
|
4518 | and makes libev faster. |
|
|
4519 | |
|
|
4520 | =item EV_NO_THREADS |
|
|
4521 | |
|
|
4522 | If defined to be C<1>, libev will assume that it will never be called |
|
|
4523 | from different threads, which is a stronger assumption than C<EV_NO_SMP>, |
|
|
4524 | above. This reduces dependencies and makes libev faster. |
|
|
4525 | |
4347 | =item EV_ATOMIC_T |
4526 | =item EV_ATOMIC_T |
4348 | |
4527 | |
4349 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4528 | Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
4350 | access is atomic with respect to other threads or signal contexts. No such |
4529 | access is atomic and serialised with respect to other threads or signal |
4351 | type is easily found in the C language, so you can provide your own type |
4530 | contexts. No such type is easily found in the C language, so you can |
4352 | that you know is safe for your purposes. It is used both for signal handler "locking" |
4531 | provide your own type that you know is safe for your purposes. It is used |
4353 | as well as for signal and thread safety in C<ev_async> watchers. |
4532 | both for signal handler "locking" as well as for signal and thread safety |
|
|
4533 | in C<ev_async> watchers. |
4354 | |
4534 | |
4355 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4535 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4356 | (from F<signal.h>), which is usually good enough on most platforms. |
4536 | (from F<signal.h>), which is usually good enough on most platforms, |
|
|
4537 | although strictly speaking using a type that also implies a memory fence |
|
|
4538 | is required. |
4357 | |
4539 | |
4358 | =item EV_H (h) |
4540 | =item EV_H (h) |
4359 | |
4541 | |
4360 | The name of the F<ev.h> header file used to include it. The default if |
4542 | The name of the F<ev.h> header file used to include it. The default if |
4361 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
4543 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
… | |
… | |
4385 | will have the C<struct ev_loop *> as first argument, and you can create |
4567 | will have the C<struct ev_loop *> as first argument, and you can create |
4386 | additional independent event loops. Otherwise there will be no support |
4568 | additional independent event loops. Otherwise there will be no support |
4387 | for multiple event loops and there is no first event loop pointer |
4569 | for multiple event loops and there is no first event loop pointer |
4388 | argument. Instead, all functions act on the single default loop. |
4570 | argument. Instead, all functions act on the single default loop. |
4389 | |
4571 | |
|
|
4572 | Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a |
|
|
4573 | default loop when multiplicity is switched off - you always have to |
|
|
4574 | initialise the loop manually in this case. |
|
|
4575 | |
4390 | =item EV_MINPRI |
4576 | =item EV_MINPRI |
4391 | |
4577 | |
4392 | =item EV_MAXPRI |
4578 | =item EV_MAXPRI |
4393 | |
4579 | |
4394 | The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to |
4580 | The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to |
… | |
… | |
4491 | |
4677 | |
4492 | With an intelligent-enough linker (gcc+binutils are intelligent enough |
4678 | With an intelligent-enough linker (gcc+binutils are intelligent enough |
4493 | when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by |
4679 | when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by |
4494 | your program might be left out as well - a binary starting a timer and an |
4680 | your program might be left out as well - a binary starting a timer and an |
4495 | I/O watcher then might come out at only 5Kb. |
4681 | I/O watcher then might come out at only 5Kb. |
|
|
4682 | |
|
|
4683 | =item EV_API_STATIC |
|
|
4684 | |
|
|
4685 | If this symbol is defined (by default it is not), then all identifiers |
|
|
4686 | will have static linkage. This means that libev will not export any |
|
|
4687 | identifiers, and you cannot link against libev anymore. This can be useful |
|
|
4688 | when you embed libev, only want to use libev functions in a single file, |
|
|
4689 | and do not want its identifiers to be visible. |
|
|
4690 | |
|
|
4691 | To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that |
|
|
4692 | wants to use libev. |
|
|
4693 | |
|
|
4694 | This option only works when libev is compiled with a C compiler, as C++ |
|
|
4695 | doesn't support the required declaration syntax. |
4496 | |
4696 | |
4497 | =item EV_AVOID_STDIO |
4697 | =item EV_AVOID_STDIO |
4498 | |
4698 | |
4499 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
4699 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
4500 | functions (printf, scanf, perror etc.). This will increase the code size |
4700 | functions (printf, scanf, perror etc.). This will increase the code size |
… | |
… | |
4880 | requires, and its I/O model is fundamentally incompatible with the POSIX |
5080 | requires, and its I/O model is fundamentally incompatible with the POSIX |
4881 | model. Libev still offers limited functionality on this platform in |
5081 | model. Libev still offers limited functionality on this platform in |
4882 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
5082 | the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
4883 | descriptors. This only applies when using Win32 natively, not when using |
5083 | descriptors. This only applies when using Win32 natively, not when using |
4884 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
5084 | e.g. cygwin. Actually, it only applies to the microsofts own compilers, |
4885 | as every compielr comes with a slightly differently broken/incompatible |
5085 | as every compiler comes with a slightly differently broken/incompatible |
4886 | environment. |
5086 | environment. |
4887 | |
5087 | |
4888 | Lifting these limitations would basically require the full |
5088 | Lifting these limitations would basically require the full |
4889 | re-implementation of the I/O system. If you are into this kind of thing, |
5089 | re-implementation of the I/O system. If you are into this kind of thing, |
4890 | then note that glib does exactly that for you in a very portable way (note |
5090 | then note that glib does exactly that for you in a very portable way (note |
… | |
… | |
5023 | |
5223 | |
5024 | The type C<double> is used to represent timestamps. It is required to |
5224 | The type C<double> is used to represent timestamps. It is required to |
5025 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5225 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5026 | good enough for at least into the year 4000 with millisecond accuracy |
5226 | good enough for at least into the year 4000 with millisecond accuracy |
5027 | (the design goal for libev). This requirement is overfulfilled by |
5227 | (the design goal for libev). This requirement is overfulfilled by |
5028 | implementations using IEEE 754, which is basically all existing ones. With |
5228 | implementations using IEEE 754, which is basically all existing ones. |
|
|
5229 | |
5029 | IEEE 754 doubles, you get microsecond accuracy until at least 2200. |
5230 | With IEEE 754 doubles, you get microsecond accuracy until at least the |
|
|
5231 | year 2255 (and millisecond accuracy till the year 287396 - by then, libev |
|
|
5232 | is either obsolete or somebody patched it to use C<long double> or |
|
|
5233 | something like that, just kidding). |
5030 | |
5234 | |
5031 | =back |
5235 | =back |
5032 | |
5236 | |
5033 | If you know of other additional requirements drop me a note. |
5237 | If you know of other additional requirements drop me a note. |
5034 | |
5238 | |
… | |
… | |
5096 | =item Processing ev_async_send: O(number_of_async_watchers) |
5300 | =item Processing ev_async_send: O(number_of_async_watchers) |
5097 | |
5301 | |
5098 | =item Processing signals: O(max_signal_number) |
5302 | =item Processing signals: O(max_signal_number) |
5099 | |
5303 | |
5100 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
5304 | Sending involves a system call I<iff> there were no other C<ev_async_send> |
5101 | calls in the current loop iteration. Checking for async and signal events |
5305 | calls in the current loop iteration and the loop is currently |
|
|
5306 | blocked. Checking for async and signal events involves iterating over all |
5102 | involves iterating over all running async watchers or all signal numbers. |
5307 | running async watchers or all signal numbers. |
5103 | |
5308 | |
5104 | =back |
5309 | =back |
5105 | |
5310 | |
5106 | |
5311 | |
5107 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
5312 | =head1 PORTING FROM LIBEV 3.X TO 4.X |
… | |
… | |
5224 | The physical time that is observed. It is apparently strictly monotonic :) |
5429 | The physical time that is observed. It is apparently strictly monotonic :) |
5225 | |
5430 | |
5226 | =item wall-clock time |
5431 | =item wall-clock time |
5227 | |
5432 | |
5228 | The time and date as shown on clocks. Unlike real time, it can actually |
5433 | The time and date as shown on clocks. Unlike real time, it can actually |
5229 | be wrong and jump forwards and backwards, e.g. when the you adjust your |
5434 | be wrong and jump forwards and backwards, e.g. when you adjust your |
5230 | clock. |
5435 | clock. |
5231 | |
5436 | |
5232 | =item watcher |
5437 | =item watcher |
5233 | |
5438 | |
5234 | A data structure that describes interest in certain events. Watchers need |
5439 | A data structure that describes interest in certain events. Watchers need |
… | |
… | |
5237 | =back |
5442 | =back |
5238 | |
5443 | |
5239 | =head1 AUTHOR |
5444 | =head1 AUTHOR |
5240 | |
5445 | |
5241 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5446 | Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael |
5242 | Magnusson and Emanuele Giaquinta. |
5447 | Magnusson and Emanuele Giaquinta, and minor corrections by many others. |
5243 | |
5448 | |