[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.27 by root, Wed Nov 14 05:02:07 2007 UTC vs.
Revision 1.33 by root, Fri Nov 23 15:26:08 2007 UTC

 Usually, it's a good idea to terminate if the major versions mismatch,
 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.
+=item unsigned int ev_supported_backends ()
+Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See C<ev_default_loop> 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<ev_supported_backends>, 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
 realloc C function, the semantics are identical). It is used to allocate
 and free memory (no surprises here). If it returns zero when memory
 =item struct ev_loop *ev_default_loop (unsigned int flags)
 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<ev_backend ()> 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<EVFLAG_AUTO>).
-It supports the following flags:
+The following flags are supported:
 =over 4
 =item C<EVFLAG_AUTO>
 C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
 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<EVMETHOD_SELECT>  (portable select backend)
+=item C<EVBACKEND_SELECT>  (value 1, portable select backend)
+This is your standard select(2) backend. Not I<completely> standard, as
+libev tries to roll its own fd_set with no limits on the number of fds,
+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<EVMETHOD_POLL>    (poll backend, available everywhere except on windows)
+=item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)
-=item C<EVMETHOD_EPOLL>   (linux only)
+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<EVMETHOD_KQUEUE>  (some bsds only)
+=item C<EVBACKEND_EPOLL>   (value 4, Linux)
-=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
+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
+O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+either O(1) or O(active_fds).
-=item C<EVMETHOD_PORT>    (solaris 10 only)
+While stopping and starting an I/O watcher in the same iteration will
+result in some caching, there is still a syscall per such incident
+(because the fd could point to a different file description now), so its
+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<EVBACKEND_KQUEUE>  (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 it explicitly in the flags (i.e. using
+C<EVBACKEND_KQUEUE>).
+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
+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<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
+This is not implemented yet (and might never be).
+=item C<EVBACKEND_PORT>    (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)).
+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<EVBACKEND_ALL>
+Try all backends (even potentially broken ones that wouldn't be tried
+with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
+C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
+=back
 If one or more of these are ored into the flags value, then only these
-backends will be tried (in the reverse order as given here). If one are
+backends will be tried (in the reverse order as given here). If none are
-specified, any backend will do.
+specified, most compiled-in backend will be tried, usually in reverse
+order of their flag values :)
-=back
+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<ev_default_loop>, but always creates a new event loop that is
 always distinct from the default loop. Unlike the default loop, it cannot
 This function reinitialises the kernel state for backends that have
 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<must> call this function after forking if and only if you want to
+You I<must> call this function in the child process after forking if and
-use the event library in both processes. If you just fork+exec, you don't
+only if you want to use the event library in both processes. If you just
-have to call it.
+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
 quite nicely into a call to C<pthread_atfork>:
     pthread_atfork (0, 0, ev_default_fork);
+At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> 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<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. 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<EVMETHOD_*> flags indicating the event backend in
+Returns one of the C<EVBACKEND_*> 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
 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
+If the flags argument is specified as C<0>, it will not return until
-no event watchers are active anymore or C<ev_unloop> was called.
+either no event watchers are active anymore or C<ev_unloop> was called.
 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
 those events and any outstanding ones, but will not block your process in
 case there are no events and will return after one iteration of the loop.
 A flags value of C<EVLOOP_ONESHOT> 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.
+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<ev_prepare>/C<ev_check> watchers is
+usually a better approach for this kind of thing.
-This flags value could be used to implement alternative looping
-constructs, but the C<prepare> and C<check> watchers provide a better and
-more generic mechanism.
-Here are the gory details of what ev_loop does:
+Here are the gory details of what C<ev_loop> does:
-   1. If there are no active watchers (reference count is zero), return.
+   * If there are no active watchers (reference count is zero), return.
-   2. Queue and immediately call all prepare watchers.
+   - Queue prepare watchers and then call all outstanding watchers.
-   3. If we have been forked, recreate the kernel state.
+   - If we have been forked, recreate the kernel state.
-   4. Update the kernel state with all outstanding changes.
+   - Update the kernel state with all outstanding changes.
-   5. Update the "event loop time".
+   - Update the "event loop time".
-   6. Calculate for how long to block.
+   - Calculate for how long to block.
-   7. Block the process, waiting for events.
+   - Block the process, waiting for any events.
+   - Queue all outstanding I/O (fd) events.
-   8. Update the "event loop time" and do time jump handling.
+   - Update the "event loop time" and do time jump handling.
-   9. Queue all outstanding timers.
+   - Queue all outstanding timers.
-  10. Queue all outstanding periodics.
+   - Queue all outstanding periodics.
-  11. If no events are pending now, queue all idle watchers.
+   - If no events are pending now, queue all idle watchers.
-  12. Queue all check watchers.
+   - Queue all check watchers.
-  13. Call all queued watchers in reverse order (i.e. check watchers first).
+   - 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.
-  14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+   - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
-      was used, return, otherwise continue with step #1.
+     were used, return, otherwise continue with step *.
 =item ev_unloop (loop, how)
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 *) >>), and you can stop watching for events at any time by calling the
 corresponding stop function (C<< ev_<type>_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<ev_is_active
 (watcher *)> macro. To see whether an event is outstanding (but the
 callback for it has not been called yet) you can use the C<ev_is_pending
 (watcher *)> macro.
 descriptors correctly if you register interest in two or more fds pointing
 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
+(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
-EVMETHOD_POLL).
+C<EVBACKEND_POLL>).
 =over 4
 =item ev_io_init (ev_io *, callback, int fd, int events)
 Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
 events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
 EV_WRITE> 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<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, 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<ev_timer> - relative and optionally recurring timeouts
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 The timers are based on real time, that is, if you register an event that
 times out after an hour and you reset your system clock to last years
 time, it will still time out after (roughly) and hour. "Roughly" because
-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
 The relative timeouts are calculated relative to the C<ev_now ()>
 time. This is usually the right thing as this timestamp refers to the time
-of the event triggering whatever timeout you are modifying/starting.  If
+of the event triggering whatever timeout you are modifying/starting. If
-you suspect event processing to be delayed and you *need* to base the timeout
+you suspect event processing to be delayed and you I<need> to base the timeout
 on the current time, use something like this to adjust for this:
    ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.
 =over 4
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 again).
 They can also be used to implement vastly more complex timers, such as
 triggering an event on eahc midnight, local time.
+As with timers, the callback is guarenteed to be invoked only when the
+time (C<at>) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
 =over 4
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 =over 4
 =item * absolute timer (interval = reschedule_cb = 0)

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Comparing libev/ev.pod (file contents): Revision 1.27 by root, Wed Nov 14 05:02:07 2007 UTC vs. Revision 1.33 by root, Fri Nov 23 15:26:08 2007 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.27 by root, Wed Nov 14 05:02:07 2007 UTC vs.
Revision 1.33 by root, Fri Nov 23 15:26:08 2007 UTC