--- libev/ev.pod 2007/11/23 05:00:45 1.31 +++ libev/ev.pod 2007/11/23 16:17:12 1.34 @@ -47,7 +47,9 @@ (fractional) number of seconds since the (POSIX) epoch (somewhere near the beginning of 1970, details are complicated, don't ask). This type is called C, which is what you should use too. It usually aliases -to the double type in C. +to the C type in C, and when you need to do any calculations on +it, you should treat it as such. + =head1 GLOBAL FUNCTIONS @@ -77,6 +79,13 @@ compatible to older versions, so a larger minor version alone is usually not a problem. +Example: make sure we haven't accidentally been linked against the wrong +version: + + assert (("libev version mismatch", + ev_version_major () == EV_VERSION_MAJOR + && ev_version_minor () >= EV_VERSION_MINOR)); + =item unsigned int ev_supported_backends () Return the set of all backends (i.e. their corresponding C @@ -84,6 +93,12 @@ availability on the system you are running on). See C for a description of the set values. +Example: make sure we have the epoll method, because yeah this is cool and +a must have and can we have a torrent of it please!!!11 + + assert (("sorry, no epoll, no sex", + ev_supported_backends () & EVBACKEND_EPOLL)); + =item unsigned int ev_recommended_backends () Return the set of all backends compiled into this binary of libev and also @@ -91,7 +106,7 @@ returned by C, as for example kqueue is broken on most BSDs and will not be autodetected unless you explicitly request it (assuming you know what you are doing). This is the set of backends that -C will probe for. +libev will probe for if you specify no backends explicitly. =item ev_set_allocator (void *(*cb)(void *ptr, long size)) @@ -105,6 +120,26 @@ free some memory if it cannot allocate memory, to use a special allocator, or even to sleep a while and retry until some memory is available. +Example: replace the libev allocator with one that waits a bit and then +retries: better than mine). + + static void * + persistent_realloc (void *ptr, long size) + { + for (;;) + { + void *newptr = realloc (ptr, size); + + if (newptr) + return newptr; + + sleep (60); + } + } + + ... + ev_set_allocator (persistent_realloc); + =item ev_set_syserr_cb (void (*cb)(const char *msg)); Set the callback function to call on a retryable syscall error (such @@ -115,6 +150,18 @@ requested operation, or, if the condition doesn't go away, do bad stuff (such as abort). +Example: do the same thing as libev does internally: + + static void + fatal_error (const char *msg) + { + perror (msg); + abort (); + } + + ... + ev_set_syserr_cb (fatal_error); + =back =head1 FUNCTIONS CONTROLLING THE EVENT LOOP @@ -143,9 +190,9 @@ function. The flags argument can be used to specify special behaviour or specific -backends to use, and is usually specified as C<0> (or EVFLAG_AUTO). +backends to use, and is usually specified as C<0> (or C). -It supports the following flags: +The following flags are supported: =over 4 @@ -191,13 +238,18 @@ best to avoid that. Also, dup()ed file descriptors might not work very well if you register events for both fds. +Please note that epoll sometimes generates spurious notifications, so you +need to use non-blocking I/O or other means to avoid blocking when no data +(or space) is available. + =item C (value 8, most BSD clones) Kqueue deserves special mention, as at the time of this writing, it was broken on all BSDs except NetBSD (usually it doesn't work with anything but sockets and pipes, except on Darwin, where of course its -completely useless). For this reason its not being "autodetected" unless -you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO). +completely useless). For this reason its not being "autodetected" +unless you explicitly specify it explicitly in the flags (i.e. using +C). It scales in the same way as the epoll backend, but the interface to the kernel is more efficient (which says nothing about its actual speed, of @@ -214,6 +266,10 @@ This uses the Solaris 10 port mechanism. As with everything on Solaris, it's really slow, but it still scales very well (O(active_fds)). +Please note that solaris ports can result in a lot of spurious +notifications, so you need to use non-blocking I/O or other means to avoid +blocking when no data (or space) is available. + =item C Try all backends (even potentially broken ones that wouldn't be tried @@ -227,6 +283,22 @@ specified, most compiled-in backend will be tried, usually in reverse order of their flag values :) +The most typical usage is like this: + + if (!ev_default_loop (0)) + fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); + +Restrict libev to the select and poll backends, and do not allow +environment settings to be taken into account: + + ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); + +Use whatever libev has to offer, but make sure that kqueue is used if +available (warning, breaks stuff, best use only with your own private +event loop and only if you know the OS supports your types of fds): + + ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); + =item struct ev_loop *ev_loop_new (unsigned int flags) Similar to C, but always creates a new event loop that is @@ -234,6 +306,12 @@ handle signal and child watchers, and attempts to do so will be greeted by undefined behaviour (or a failed assertion if assertions are enabled). +Example: try to create a event loop that uses epoll and nothing else. + + struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); + if (!epoller) + fatal ("no epoll found here, maybe it hides under your chair"); + =item ev_default_destroy () Destroys the default loop again (frees all memory and kernel state @@ -280,10 +358,10 @@ =item ev_tstamp ev_now (loop) Returns the current "event loop time", which is the time the event loop -got events and started processing them. This timestamp does not change -as long as callbacks are being processed, and this is also the base time -used for relative timers. You can treat it as the timestamp of the event -occuring (or more correctly, the mainloop finding out about it). +received events and started processing them. This timestamp does not +change as long as callbacks are being processed, and this is also the base +time used for relative timers. You can treat it as the timestamp of the +event occuring (or more correctly, libev finding out about it). =item ev_loop (loop, int flags) @@ -291,8 +369,14 @@ after you initialised all your watchers and you want to start handling events. -If the flags argument is specified as 0, it will not return until either -no event watchers are active anymore or C was called. +If the flags argument is specified as C<0>, it will not return until +either no event watchers are active anymore or C was called. + +Please note that an explicit C is usually better than +relying on all watchers to be stopped when deciding when a program has +finished (especially in interactive programs), but having a program that +automatically loops as long as it has to and no longer by virtue of +relying on its watchers stopping correctly is a thing of beauty. A flags value of C will look for new events, will handle those events and any outstanding ones, but will not block your process in @@ -301,29 +385,39 @@ A flags value of C will look for new events (waiting if neccessary) and will handle those and any outstanding ones. It will block your process until at least one new event arrives, and will return after -one iteration of the loop. - -This flags value could be used to implement alternative looping -constructs, but the C and C watchers provide a better and -more generic mechanism. - -Here are the gory details of what ev_loop does: - - 1. If there are no active watchers (reference count is zero), return. - 2. Queue and immediately call all prepare watchers. - 3. If we have been forked, recreate the kernel state. - 4. Update the kernel state with all outstanding changes. - 5. Update the "event loop time". - 6. Calculate for how long to block. - 7. Block the process, waiting for events. - 8. Update the "event loop time" and do time jump handling. - 9. Queue all outstanding timers. - 10. Queue all outstanding periodics. - 11. If no events are pending now, queue all idle watchers. - 12. Queue all check watchers. - 13. Call all queued watchers in reverse order (i.e. check watchers first). - 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK - was used, return, otherwise continue with step #1. +one iteration of the loop. This is useful if you are waiting for some +external event in conjunction with something not expressible using other +libev watchers. However, a pair of C/C watchers is +usually a better approach for this kind of thing. + +Here are the gory details of what C does: + + * If there are no active watchers (reference count is zero), return. + - Queue prepare watchers and then call all outstanding watchers. + - If we have been forked, recreate the kernel state. + - Update the kernel state with all outstanding changes. + - Update the "event loop time". + - Calculate for how long to block. + - Block the process, waiting for any events. + - Queue all outstanding I/O (fd) events. + - Update the "event loop time" and do time jump handling. + - Queue all outstanding timers. + - Queue all outstanding periodics. + - If no events are pending now, queue all idle watchers. + - Queue all check watchers. + - Call all queued watchers in reverse order (i.e. check watchers first). + Signals and child watchers are implemented as I/O watchers, and will + be handled here by queueing them when their watcher gets executed. + - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK + were used, return, otherwise continue with step *. + +Example: queue some jobs and then loop until no events are outsanding +anymore. + + ... queue jobs here, make sure they register event watchers as long + ... as they still have work to do (even an idle watcher will do..) + ev_loop (my_loop, 0); + ... jobs done. yeah! =item ev_unloop (loop, how) @@ -347,6 +441,19 @@ way to do this for generic recurring timers or from within third-party libraries. Just remember to I and I. +Example: create a signal watcher, but keep it from keeping C +running when nothing else is active. + + struct dv_signal exitsig; + ev_signal_init (&exitsig, sig_cb, SIGINT); + ev_signal_start (myloop, &exitsig); + evf_unref (myloop); + +Example: for some weird reason, unregister the above signal handler again. + + ev_ref (myloop); + ev_signal_stop (myloop, &exitsig); + =back =head1 ANATOMY OF A WATCHER @@ -497,6 +604,7 @@ This section describes each watcher in detail, but will not repeat information given in the last section. + =head2 C - is this file descriptor readable or writable I/O watchers check whether a file descriptor is readable or writable @@ -530,8 +638,38 @@ events for and events is either C, C or C to receive the given events. +Please note that most of the more scalable backend mechanisms (for example +epoll and solaris ports) can result in spurious readyness notifications +for file descriptors, so you practically need to use non-blocking I/O (and +treat callback invocation as hint only), or retest separately with a safe +interface before doing I/O (XLib can do this), or force the use of either +C or C, which don't suffer from this +problem. Also note that it is quite easy to have your callback invoked +when the readyness condition is no longer valid even when employing +typical ways of handling events, so its a good idea to use non-blocking +I/O unconditionally. + =back +Example: call C when STDIN_FILENO has become, well +readable, but only once. Since it is likely line-buffered, you could +attempt to read a whole line in the callback: + + static void + stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) + { + ev_io_stop (loop, w); + .. read from stdin here (or from w->fd) and haqndle any I/O errors + } + + ... + struct ev_loop *loop = ev_default_init (0); + struct ev_io stdin_readable; + ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); + ev_io_start (loop, &stdin_readable); + ev_loop (loop, 0); + + =head2 C - relative and optionally recurring timeouts Timer watchers are simple relative timers that generate an event after a @@ -593,6 +731,37 @@ =back +Example: create a timer that fires after 60 seconds. + + static void + one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + { + .. one minute over, w is actually stopped right here + } + + struct ev_timer mytimer; + ev_timer_init (&mytimer, one_minute_cb, 60., 0.); + ev_timer_start (loop, &mytimer); + +Example: create a timeout timer that times out after 10 seconds of +inactivity. + + static void + timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + { + .. ten seconds without any activity + } + + struct ev_timer mytimer; + ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ + ev_timer_again (&mytimer); /* start timer */ + ev_loop (loop, 0); + + // and in some piece of code that gets executed on any "activity": + // reset the timeout to start ticking again at 10 seconds + ev_timer_again (&mytimer); + + =head2 C - to cron or not to cron Periodic watchers are also timers of a kind, but they are very versatile @@ -697,6 +866,40 @@ =back +Example: call a callback every hour, or, more precisely, whenever the +system clock is divisible by 3600. The callback invocation times have +potentially a lot of jittering, but good long-term stability. + + static void + clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) + { + ... its now a full hour (UTC, or TAI or whatever your clock follows) + } + + struct ev_periodic hourly_tick; + ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); + ev_periodic_start (loop, &hourly_tick); + +Example: the same as above, but use a reschedule callback to do it: + + #include + + static ev_tstamp + my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) + { + return fmod (now, 3600.) + 3600.; + } + + ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); + +Example: call a callback every hour, starting now: + + struct ev_periodic hourly_tick; + ev_periodic_init (&hourly_tick, clock_cb, + fmod (ev_now (loop), 3600.), 3600., 0); + ev_periodic_start (loop, &hourly_tick); + + =head2 C - signal me when a signal gets signalled Signal watchers will trigger an event when the process receives a specific @@ -742,6 +945,19 @@ =back +Example: try to exit cleanly on SIGINT and SIGTERM. + + static void + sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) + { + ev_unloop (loop, EVUNLOOP_ALL); + } + + struct ev_signal signal_watcher; + ev_signal_init (&signal_watcher, sigint_cb, SIGINT); + ev_signal_start (loop, &sigint_cb); + + =head2 C - when you've got nothing better to do Idle watchers trigger events when there are no other events are pending @@ -770,6 +986,22 @@ =back +Example: dynamically allocate an C, start it, and in the +callback, free it. Alos, use no error checking, as usual. + + static void + idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) + { + free (w); + // now do something you wanted to do when the program has + // no longer asnything immediate to do. + } + + struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); + ev_idle_init (idle_watcher, idle_cb); + ev_idle_start (loop, idle_cb); + + =head2 C and C - customise your event loop Prepare and check watchers are usually (but not always) used in tandem: @@ -810,6 +1042,9 @@ =back +Example: *TODO*. + + =head1 OTHER FUNCTIONS There are some other functions of possible interest. Described. Here. Now. @@ -865,6 +1100,7 @@ =back + =head1 LIBEVENT EMULATION Libev offers a compatibility emulation layer for libevent. It cannot