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

Comparing libev/ev.pod (file contents):
Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs.
Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC

 If you have a watcher you never unregister that should not keep C<ev_loop>
 from returning, call ev_unref() after starting, and ev_ref() before
 stopping it.
-As an example, libev itself uses this for its internal signal pipe: It is
+As an example, libev itself uses this for its internal signal pipe: It
-not visible to the libev user and should not keep C<ev_loop> from exiting
+is not visible to the libev user and should not keep C<ev_loop> from
-if no event watchers registered by it are active. It is also an excellent
+exiting if no event watchers registered by it are active. It is also an
-way to do this for generic recurring timers or from within third-party
+excellent way to do this for generic recurring timers or from within
-libraries. Just remember to I<unref after start> and I<ref before stop>
+third-party libraries. Just remember to I<unref after start> and I<ref
-(but only if the watcher wasn't active before, or was active before,
+before stop> (but only if the watcher wasn't active before, or was active
-respectively).
+before, respectively. Note also that libev might stop watchers itself
+(e.g. non-repeating timers) in which case you have to C<ev_ref>
+in the callback).
 Example: Create a signal watcher, but keep it from keeping C<ev_loop>
 running when nothing else is active.
    ev_signal exitsig;
 C<ev_fork>).
 =item C<EV_ASYNC>
 The given async watcher has been asynchronously notified (see C<ev_async>).
+=item C<EV_CUSTOM>
+Not ever sent (or otherwise used) by libev itself, but can be freely used
+by libev users to signal watchers (e.g. via C<ev_feed_event>).
 =item C<EV_ERROR>
 An unspecified error has occurred, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 year, it will still time out after (roughly) one hour. "Roughly" because
 detecting time jumps is hard, and some inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
 The callback is guaranteed to be invoked only I<after> its timeout has
-passed, but if multiple timers become ready during the same loop iteration
+passed. If multiple timers become ready during the same loop iteration
-then order of execution is undefined.
+then the ones with earlier time-out values are invoked before ones with
+later time-out values (but this is no longer true when a callback calls
+C<ev_loop> recursively).
 =head3 Be smart about timeouts
 Many real-world problems involve some kind of timeout, usually for error
 recovery. A typical example is an HTTP request - if the other side hangs,
 =head2 C<ev_periodic> - to cron or not to cron?
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
-Unlike C<ev_timer>'s, they are not based on real time (or relative time)
+Unlike C<ev_timer>, periodic watchers are not based on real time (or
-but on wall clock time (absolute time). You can tell a periodic watcher
+relative time, the physical time that passes) but on wall clock time
-to trigger after some specific point in time. For example, if you tell a
+(absolute time, the thing you can read on your calender or clock). The
-periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
+difference is that wall clock time can run faster or slower than real
-+ 10.>, that is, an absolute time not a delay) and then reset your system
+time, and time jumps are not uncommon (e.g. when you adjust your
-clock to January of the previous year, then it will take more than year
+wrist-watch).
-to trigger the event (unlike an C<ev_timer>, which would still trigger
-roughly 10 seconds later as it uses a relative timeout).
+You can tell a periodic watcher to trigger after some specific point
+in time: for example, if you tell a periodic watcher to trigger "in 10
+seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
+not a delay) and then reset your system clock to January of the previous
+year, then it will take a year or more to trigger the event (unlike an
+C<ev_timer>, which would still trigger roughly 10 seconds after starting
+it, as it uses a relative timeout).
-C<ev_periodic>s can also be used to implement vastly more complex timers,
+C<ev_periodic> watchers can also be used to implement vastly more complex
-such as triggering an event on each "midnight, local time", or other
+timers, such as triggering an event on each "midnight, local time", or
-complicated rules.
+other complicated rules. This cannot be done with C<ev_timer> watchers, as
+those cannot react to time jumps.
 As with timers, the callback is guaranteed to be invoked only when the
-time (C<at>) has passed, but if multiple periodic timers become ready
+point in time where it is supposed to trigger has passed. If multiple
-during the same loop iteration, then order of execution is undefined.
+timers become ready during the same loop iteration then the ones with
+earlier time-out values are invoked before ones with later time-out values
+(but this is no longer true when a callback calls C<ev_loop> recursively).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
-=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
+=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
-=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
+=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
-Lots of arguments, lets sort it out... There are basically three modes of
+Lots of arguments, let's sort it out... There are basically three modes of
 operation, and we will explain them from simplest to most complex:
 =over 4
-=item * absolute timer (at = time, interval = reschedule_cb = 0)
+=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
 In this configuration the watcher triggers an event after the wall clock
-time C<at> has passed. It will not repeat and will not adjust when a time
+time C<offset> has passed. It will not repeat and will not adjust when a
-jump occurs, that is, if it is to be run at January 1st 2011 then it will
+time jump occurs, that is, if it is to be run at January 1st 2011 then it
-only run when the system clock reaches or surpasses this time.
+will be stopped and invoked when the system clock reaches or surpasses
+this point in time.
-=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
+=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
 In this mode the watcher will always be scheduled to time out at the next
-C<at + N * interval> time (for some integer N, which can also be negative)
+C<offset + N * interval> time (for some integer N, which can also be
-and then repeat, regardless of any time jumps.
+negative) and then repeat, regardless of any time jumps. The C<offset>
+argument is merely an offset into the C<interval> periods.
 This can be used to create timers that do not drift with respect to the
-system clock, for example, here is a C<ev_periodic> that triggers each
+system clock, for example, here is an C<ev_periodic> that triggers each
-hour, on the hour:
+hour, on the hour (with respect to UTC):
    ev_periodic_set (&periodic, 0., 3600., 0);
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the callback will be called when the system time shows a
 full hour (UTC), or more correctly, when the system time is evenly divisible
 by 3600.
 Another way to think about it (for the mathematically inclined) is that
 C<ev_periodic> will try to run the callback in this mode at the next possible
-time where C<time = at (mod interval)>, regardless of any time jumps.
+time where C<time = offset (mod interval)>, regardless of any time jumps.
-For numerical stability it is preferable that the C<at> value is near
+For numerical stability it is preferable that the C<offset> value is near
 C<ev_now ()> (the current time), but there is no range requirement for
 this value, and in fact is often specified as zero.
 Note also that there is an upper limit to how often a timer can fire (CPU
 speed for example), so if C<interval> is very small then timing stability
 will of course deteriorate. Libev itself tries to be exact to be about one
 millisecond (if the OS supports it and the machine is fast enough).
-=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
+=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
-In this mode the values for C<interval> and C<at> are both being
+In this mode the values for C<interval> and C<offset> are both being
 ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
-NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
+NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
-ever, or make ANY event loop modifications whatsoever>.
+or make ANY other event loop modifications whatsoever, unless explicitly
+allowed by documentation here>.
 If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
 it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
 only event loop modification you are allowed to do).
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
 =item ev_tstamp ev_periodic_at (ev_periodic *)
-When active, returns the absolute time that the watcher is supposed to
+When active, returns the absolute time that the watcher is supposed
-trigger next.
+to trigger next. This is not the same as the C<offset> argument to
+C<ev_periodic_set>, but indeed works even in interval and manual
+rescheduling modes.
 =item ev_tstamp offset [read-write]
 When repeating, this contains the offset value, otherwise this is the
-absolute point in time (the C<at> value passed to C<ev_periodic_set>).
+absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
+although libev might modify this value for better numerical stability).
 Can be modified any time, but changes only take effect when the periodic
 timer fires or C<ev_periodic_again> is being called.
 =item ev_tstamp interval [read-write]
 =head3 Watcher-Specific Functions and Data Members
 =over 4
-=item ev_idle_init (ev_signal *, callback)
+=item ev_idle_init (ev_idle *, callback)
 Initialises and configures the idle watcher - it has no parameters of any
 kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
 believe me.
 an C<EV_ASYNC> event on the watcher into the event loop. Unlike
 C<ev_feed_event>, this call is safe to do from other threads, signal or
 similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
 section below on what exactly this means).
+Note that, as with other watchers in libev, multiple events might get
+compressed into a single callback invocation (another way to look at this
+is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
+reset when the event loop detects that).
-This call incurs the overhead of a system call only once per loop iteration,
+This call incurs the overhead of a system call only once per event loop
-so while the overhead might be noticeable, it doesn't apply to repeated
+iteration, so while the overhead might be noticeable, it doesn't apply to
-calls to C<ev_async_send>.
+repeated calls to C<ev_async_send> for the same event loop.
 =item bool = ev_async_pending (ev_async *)
 Returns a non-zero value when C<ev_async_send> has been called on the
 watcher but the event has not yet been processed (or even noted) by the
 C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
 the loop iterates next and checks for the watcher to have become active,
 it will reset the flag again. C<ev_async_pending> can be used to very
 quickly check whether invoking the loop might be a good idea.
-Not that this does I<not> check whether the watcher itself is pending, only
+Not that this does I<not> check whether the watcher itself is pending,
-whether it has been requested to make this watcher pending.
+only whether it has been requested to make this watcher pending: there
+is a time window between the event loop checking and resetting the async
+notification, and the callback being invoked.
 =back
 =head1 OTHER FUNCTIONS
 L<http://software.schmorp.de/pkg/EV>.
 =item Python
 Python bindings can be found at L<http://code.google.com/p/pyev/>. It
-seems to be quite complete and well-documented. Note, however, that the
+seems to be quite complete and well-documented.
-patch they require for libev is outright dangerous as it breaks the ABI
-for everybody else, and therefore, should never be applied in an installed
-libev (if python requires an incompatible ABI then it needs to embed
-libev).
 =item Ruby
 Tony Arcieri has written a ruby extension that offers access to a subset
 of the libev API and adds file handle abstractions, asynchronous DNS and
 more on top of it. It can be found via gem servers. Its homepage is at
 L<http://rev.rubyforge.org/>.
 Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
 makes rev work even on mingw.
+=item Haskell
+A haskell binding to libev is available at
+L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
 =item D
 Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
 be found at L<http://proj.llucax.com.ar/wiki/evd>.

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Comparing libev/ev.pod (file contents): Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs. Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs.
Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC