--- libev/ev.pod 2007/11/23 04:36:03 1.30 +++ libev/ev.pod 2007/11/23 15:26:08 1.33 @@ -77,6 +77,22 @@ compatible to older versions, so a larger minor version alone is usually not a problem. +=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. + +=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 ev_set_allocator (void *(*cb)(void *ptr, long size)) Sets the allocation function to use (the prototype is similar to the @@ -121,15 +137,15 @@ 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 +163,7 @@ 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 +171,14 @@ 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 +191,18 @@ 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 +210,24 @@ 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 +236,22 @@ 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 @@ -246,15 +287,19 @@ 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) @@ -271,8 +316,8 @@ 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. 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 +326,31 @@ 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 *. =item ev_unloop (loop, how) @@ -370,7 +417,7 @@ 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 @@ -497,8 +544,8 @@ 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 @@ -510,6 +557,17 @@ 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 =head2 C - relative and optionally recurring timeouts