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

Comparing libev/ev.pod (file contents):
Revision 1.402 by root, Wed Apr 18 06:09:29 2012 UTC vs.
Revision 1.406 by root, Thu May 3 16:00:47 2012 UTC

 =item C<EV_PREPARE>
 =item C<EV_CHECK>
-All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
+All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
-to gather new events, and all C<ev_check> watchers are invoked just after
+gather new events, and all C<ev_check> watchers are queued (not invoked)
-C<ev_run> has gathered them, but before it invokes any callbacks for any
+just after C<ev_run> has gathered them, but before it queues any callbacks
+for any received events. That means C<ev_prepare> watchers are the last
+watchers invoked before the event loop sleeps or polls for new events, and
+C<ev_check> watchers will be invoked before any other watchers of the same
+or lower priority within an event loop iteration.
-received events. Callbacks of both watcher types can start and stop as
+Callbacks of both watcher types can start and stop as many watchers as
-many watchers as they want, and all of them will be taken into account
+they want, and all of them will be taken into account (for example, a
-(for example, a C<ev_prepare> watcher might start an idle watcher to keep
+C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
-C<ev_run> from blocking).
+blocking).
 =item C<EV_EMBED>
 The embedded event loop specified in the C<ev_embed> watcher needs attention.
    callback (EV_P_ ev_timer *w, int revents)
    {
      // calculate when the timeout would happen
      ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
-     // if negative, it means we the timeout already occured
+     // if negative, it means we the timeout already occurred
      if (after < 0.)
        {
          // timeout occurred, take action
        }
      else
 Otherwise, we now the earliest time at which the timeout would trigger,
 and simply start the timer with this timeout value.
 In other words, each time the callback is invoked it will check whether
-the timeout cocured. If not, it will simply reschedule itself to check
+the timeout occurred. If not, it will simply reschedule itself to check
 again at the earliest time it could time out. Rinse. Repeat.
 This scheme causes more callback invocations (about one every 60 seconds
 minus half the average time between activity), but virtually no calls to
 libev to change the timeout.
    if (activity detected)
      last_activity = ev_now (EV_A);
 When your timeout value changes, then the timeout can be changed by simply
 providing a new value, stopping the timer and calling the callback, which
-will agaion do the right thing (for example, time out immediately :).
+will again do the right thing (for example, time out immediately :).
    timeout = new_value;
    ev_timer_stop (EV_A_ &timer);
    callback (EV_A_ &timer, 0);
 Apart from keeping your process non-blocking (which is a useful
 effect on its own sometimes), idle watchers are a good place to do
 "pseudo-background processing", or delay processing stuff to after the
 event loop has handled all outstanding events.
+=head3 Abusing an C<ev_idle> watcher for its side-effect
+As long as there is at least one active idle watcher, libev will never
+sleep unnecessarily. Or in other words, it will loop as fast as possible.
+For this to work, the idle watcher doesn't need to be invoked at all - the
+lowest priority will do.
+This mode of operation can be useful together with an C<ev_check> watcher,
+to do something on each event loop iteration - for example to balance load
+between different connections.
+See L<Abusing an C<ev_check> watcher for its side-effect> for a longer
+example.
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_idle_init (ev_idle *, callback)
    ev_idle_start (loop, idle_watcher);
 =head2 C<ev_prepare> and C<ev_check> - customise your event loop!
-Prepare and check watchers are usually (but not always) used in pairs:
+Prepare and check watchers are often (but not always) used in pairs:
 prepare watchers get invoked before the process blocks and check watchers
 afterwards.
 You I<must not> call C<ev_run> or similar functions that enter
 the current event loop from either C<ev_prepare> or C<ev_check>
 with priority higher than or equal to the event loop and one coroutine
 of lower priority, but only once, using idle watchers to keep the event
 loop from blocking if lower-priority coroutines are active, thus mapping
 low-priority coroutines to idle/background tasks).
-It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
+When used for this purpose, it is recommended to give C<ev_check> watchers
-priority, to ensure that they are being run before any other watchers
+highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
-after the poll (this doesn't matter for C<ev_prepare> watchers).
+any other watchers after the poll (this doesn't matter for C<ev_prepare>
+watchers).
 Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
 activate ("feed") events into libev. While libev fully supports this, they
 might get executed before other C<ev_check> watchers did their job. As
 C<ev_check> watchers are often used to embed other (non-libev) event
 loops those other event loops might be in an unusable state until their
 C<ev_check> watcher ran (always remind yourself to coexist peacefully with
 others).
+=head3 Abusing an C<ev_check> watcher for its side-effect
+C<ev_check> (and less often also C<ev_prepare>) watchers can also be
+useful because they are called once per event loop iteration. For
+example, if you want to handle a large number of connections fairly, you
+normally only do a bit of work for each active connection, and if there
+is more work to do, you wait for the next event loop iteration, so other
+connections have a chance of making progress.
+Using an C<ev_check> watcher is almost enough: it will be called on the
+next event loop iteration. However, that isn't as soon as possible -
+without external events, your C<ev_check> watcher will not be invoked.
+This is where C<ev_idle> watchers come in handy - all you need is a
+single global idle watcher that is active as long as you have one active
+C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
+will not sleep, and the C<ev_check> watcher makes sure a callback gets
+invoked. Neither watcher alone can do that.
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 it by calling C<ev_async_send>, which is thread- and signal safe.
 This functionality is very similar to C<ev_signal> watchers, as signals,
 too, are asynchronous in nature, and signals, too, will be compressed
 (i.e. the number of callback invocations may be less than the number of
-C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
+C<ev_async_send> calls). In fact, you could use signal watchers as a kind
 of "global async watchers" by using a watcher on an otherwise unused
 signal, and C<ev_feed_signal> to signal this watcher from another thread,
 even without knowing which loop owns the signal.
 =head3 Queueing
    ...
    ev_set_syserr_cb (fatal_error);
 The only API functions that can currently throw exceptions are C<ev_run>,
-C<ev_inoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
+C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
 because it runs cleanup watchers).
 Throwing exceptions in watcher callbacks is only supported if libev itself
 is compiled with a C++ compiler or your C and C++ environments allow
 throwing exceptions through C libraries (most do).

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Comparing libev/ev.pod (file contents): Revision 1.402 by root, Wed Apr 18 06:09:29 2012 UTC vs. Revision 1.406 by root, Thu May 3 16:00:47 2012 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.402 by root, Wed Apr 18 06:09:29 2012 UTC vs.
Revision 1.406 by root, Thu May 3 16:00:47 2012 UTC