X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/54a57c74105dc818388cec05e6fc874cdbfebf7f..d42cbf5de98e3dfe102ad9e2acbb57c401bafadc:/ev.pod?ds=sidebyside diff --git a/ev.pod b/ev.pod index 9845aff..3104747 100644 --- a/ev.pod +++ b/ev.pod @@ -47,7 +47,9 @@ Libev represents time as a single floating point number, representing the (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 +79,45 @@ as this indicates an incompatible change. Minor versions are usually 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 +value) compiled into this binary of libev (independent of their +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 +recommended for this platform. This set is often smaller than the one +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 +libev will probe for if you specify no backends explicitly. + +=item unsigned int ev_embeddable_backends () + +Returns the set of backends that are embeddable in other event loops. This +is the theoretical, all-platform, value. To find which backends +might be supported on the current system, you would need to look at +C, likewise for +recommended ones. + +See the description of C watchers for more info. + =item ev_set_allocator (void *(*cb)(void *ptr, long size)) Sets the allocation function to use (the prototype is similar to the @@ -89,6 +130,26 @@ You could override this function in high-availability programs to, say, 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 @@ -99,6 +160,18 @@ matter what, when it returns. That is, libev will generally retry the 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 @@ -121,15 +194,15 @@ done correctly, because it's hideous and inefficient). This will initialise the default event loop if it hasn't been initialised yet and return it. If the default loop could not be initialised, returns false. If it already was initialised it simply returns it (and ignores the -flags). +flags. If that is troubling you, check C afterwards). If you don't know what event loop to use, use the one returned from this function. The flags argument can be used to specify special behaviour or specific -backends to use, and is usually specified as 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 @@ -147,7 +220,7 @@ override the flags completely if it is found in the environment. This is useful to try out specific backends to test their performance, or to work around bugs. -=item C (value 1, portable select backend) +=item C (value 1, portable select backend) This is your standard select(2) backend. Not I standard, as libev tries to roll its own fd_set with no limits on the number of fds, @@ -155,14 +228,14 @@ but if that fails, expect a fairly low limit on the number of fds when using this backend. It doesn't scale too well (O(highest_fd)), but its usually the fastest backend for a low number of fds. -=item C (value 2, poll backend, available everywhere except on windows) +=item C (value 2, poll backend, available everywhere except on windows) And this is your standard poll(2) backend. It's more complicated than select, but handles sparse fds better and has no artificial limit on the number of fds you can use (except it will slow down considerably with a lot of inactive fds). It scales similarly to select, i.e. O(total_fds). -=item C (value 4, Linux) +=item C (value 4, Linux) For few fds, this backend is a bit little slower than poll and select, but it scales phenomenally better. While poll and select usually scale like @@ -175,13 +248,18 @@ result in some caching, there is still a syscall per such incident best to avoid that. Also, dup()ed file descriptors might not work very well if you register events for both fds. -=item C (value 8, most BSD clones) +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 @@ -189,20 +267,24 @@ course). While starting and stopping an I/O watcher does not cause an extra syscall as with epoll, it still adds up to four event changes per incident, so its best to avoid that. -=item C (value 16, Solaris 8) +=item C (value 16, Solaris 8) This is not implemented yet (and might never be). -=item C (value 32, Solaris 10) +=item C (value 32, Solaris 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)). -=item C +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 with C). Since this is a mask, you can do stuff such as -C. +C. =back @@ -211,6 +293,22 @@ backends will be tried (in the reverse order as given here). If none are 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 @@ -218,6 +316,12 @@ always distinct from the default loop. Unlike the default loop, it cannot 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 @@ -236,9 +340,9 @@ one. Despite the name, you can call it anytime, but it makes most sense after forking, in either the parent or child process (or both, but that again makes little sense). -You I call this function after forking if and only if you want to -use the event library in both processes. If you just fork+exec, you don't -have to call it. +You I call this function in the child process after forking if and +only if you want to use the event library in both processes. If you just +fork+exec, you don't have to call it. The function itself is quite fast and it's usually not a problem to call it just in case after a fork. To make this easy, the function will fit in @@ -246,24 +350,28 @@ quite nicely into a call to C: pthread_atfork (0, 0, ev_default_fork); +At the moment, C and C are safe to use +without calling this function, so if you force one of those backends you +do not need to care. + =item ev_loop_fork (loop) Like C, but acts on an event loop created by C. Yes, you have to call this on every allocated event loop after fork, and how you do this is entirely your own problem. -=item unsigned int ev_method (loop) +=item unsigned int ev_backend (loop) -Returns one of the C flags indicating the event backend in +Returns one of the C flags indicating the event backend in use. =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) @@ -271,8 +379,14 @@ Finally, this is it, the event handler. This function usually is called 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 @@ -281,29 +395,39 @@ case there are no events and will return after one iteration of the loop. 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) @@ -327,6 +451,19 @@ no event watchers registered by it are active. It is also an excellent 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 @@ -370,7 +507,7 @@ corresponding stop function (C<< ev__stop (loop, watcher *) >>. As long as your watcher is active (has been started but not stopped) you must not touch the values stored in it. Most specifically you must never -reinitialise it or call its set method. +reinitialise it or call its set macro. You can check whether an event is active by calling the C macro. To see whether an event is outstanding (but the @@ -477,6 +614,7 @@ have been omitted.... 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 @@ -497,8 +635,8 @@ to the same underlying file/socket etc. description (that is, they share the same underlying "file open"). If you must do this, then force the use of a known-to-be-good backend -(at the time of this writing, this includes only EVMETHOD_SELECT and -EVMETHOD_POLL). +(at the time of this writing, this includes only C and +C). =over 4 @@ -510,8 +648,38 @@ Configures an C watcher. The fd is the file descriptor to rceeive 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 @@ -573,6 +741,37 @@ the timer, and again will automatically restart it if need be. =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 @@ -677,6 +876,40 @@ program when the crontabs have changed). =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 @@ -702,6 +935,7 @@ of the C constants). =back + =head2 C - wait for pid status changes Child watchers trigger when your process receives a SIGCHLD in response to @@ -722,6 +956,19 @@ process causing the status change. =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 @@ -750,15 +997,32 @@ believe me. =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: prepare watchers get invoked before the process blocks and check watchers afterwards. -Their main purpose is to integrate other event mechanisms into libev. This -could be used, for example, to track variable changes, implement your own -watchers, integrate net-snmp or a coroutine library and lots more. +Their main purpose is to integrate other event mechanisms into libev and +their use is somewhat advanced. This could be used, for example, to track +variable changes, implement your own watchers, integrate net-snmp or a +coroutine library and lots more. This is done by examining in each prepare call which file descriptors need to be watched by the other library, registering C watchers for @@ -790,6 +1054,80 @@ macros, but using them is utterly, utterly and completely pointless. =back +Example: *TODO*. + + +=head2 C - when one backend isn't enough + +This is a rather advanced watcher type that lets you embed one event loop +into another. + +There are primarily two reasons you would want that: work around bugs and +prioritise I/O. + +As an example for a bug workaround, the kqueue backend might only support +sockets on some platform, so it is unusable as generic backend, but you +still want to make use of it because you have many sockets and it scales +so nicely. In this case, you would create a kqueue-based loop and embed it +into your default loop (which might use e.g. poll). Overall operation will +be a bit slower because first libev has to poll and then call kevent, but +at least you can use both at what they are best. + +As for prioritising I/O: rarely you have the case where some fds have +to be watched and handled very quickly (with low latency), and even +priorities and idle watchers might have too much overhead. In this case +you would put all the high priority stuff in one loop and all the rest in +a second one, and embed the second one in the first. + +As long as the watcher is started it will automatically handle events. The +callback will be invoked whenever some events have been handled. You can +set the callback to C<0> to avoid having to specify one if you are not +interested in that. + +Also, there have not currently been made special provisions for forking: +when you fork, you not only have to call C on both loops, +but you will also have to stop and restart any C watchers +yourself. + +Unfortunately, not all backends are embeddable, only the ones returned by +C are, which, unfortunately, does not include any +portable one. + +So when you want to use this feature you will always have to be prepared +that you cannot get an embeddable loop. The recommended way to get around +this is to have a separate variables for your embeddable loop, try to +create it, and if that fails, use the normal loop for everything: + + struct ev_loop *loop_hi = ev_default_init (0); + struct ev_loop *loop_lo = 0; + struct ev_embed embed; + + // see if there is a chance of getting one that works + // (remember that a flags value of 0 means autodetection) + loop_lo = ev_embeddable_backends () & ev_recommended_backends () + ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) + : 0; + + // if we got one, then embed it, otherwise default to loop_hi + if (loop_lo) + { + ev_embed_init (&embed, 0, loop_lo); + ev_embed_start (loop_hi, &embed); + } + else + loop_lo = loop_hi; + +=over 4 + +=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop) + +=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop) + +Configures the watcher to embed the given loop, which must be embeddable. + +=back + + =head1 OTHER FUNCTIONS There are some other functions of possible interest. Described. Here. Now. @@ -845,6 +1183,7 @@ Feed an event as if the given signal occured (loop must be the default loop!). =back + =head1 LIBEVENT EMULATION Libev offers a compatibility emulation layer for libevent. It cannot