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

Comparing libev/ev.pod (file contents):
Revision 1.189 by root, Tue Sep 30 19:33:33 2008 UTC vs.
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC

    ev_timer timeout_watcher;
    // all watcher callbacks have a similar signature
    // this callback is called when data is readable on stdin
    static void
-   stdin_cb (EV_P_ struct ev_io *w, int revents)
+   stdin_cb (EV_P_ ev_io *w, int revents)
    {
      puts ("stdin ready");
      // for one-shot events, one must manually stop the watcher
      // with its corresponding stop function.
      ev_io_stop (EV_A_ w);
      ev_unloop (EV_A_ EVUNLOOP_ALL);
    }
    // another callback, this time for a time-out
    static void
-   timeout_cb (EV_P_ struct ev_timer *w, int revents)
+   timeout_cb (EV_P_ ev_timer *w, int revents)
    {
      puts ("timeout");
      // this causes the innermost ev_loop to stop iterating
      ev_unloop (EV_A_ EVUNLOOP_ONE);
    }
    int
    main (void)
    {
      // use the default event loop unless you have special needs
-     struct ev_loop *loop = ev_default_loop (0);
+     ev_loop *loop = ev_default_loop (0);
      // initialise an io watcher, then start it
      // this one will watch for stdin to become readable
      ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
      ev_io_start (loop, &stdin_watcher);
 Libev is very configurable. In this manual the default (and most common)
 configuration will be described, which supports multiple event loops. For
 more info about various configuration options please have a look at
 B<EMBED> section in this manual. If libev was configured without support
 for multiple event loops, then all functions taking an initial argument of
-name C<loop> (which is always of type C<struct ev_loop *>) will not have
+name C<loop> (which is always of type C<ev_loop *>) will not have
 this argument.
 =head2 TIME REPRESENTATION
 Libev represents time as a single floating point number, representing the
 =back
 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
-An event loop is described by a C<struct ev_loop *>. The library knows two
+An event loop is described by a C<ev_loop *>. The library knows two
 types of such loops, the I<default> loop, which supports signals and child
 events, and dynamically created loops which do not.
 =over 4
 C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
 This "unloop state" will be cleared when entering C<ev_loop> again.
+It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
 =item ev_ref (loop)
 =item ev_unref (loop)
 Ref/unref can be used to add or remove a reference count on the event
 respectively).
 Example: Create a signal watcher, but keep it from keeping C<ev_loop>
 running when nothing else is active.
-   struct ev_signal exitsig;
+   ev_signal exitsig;
    ev_signal_init (&exitsig, sig_cb, SIGINT);
    ev_signal_start (loop, &exitsig);
    evf_unref (loop);
 Example: For some weird reason, unregister the above signal handler again.
 A watcher is a structure that you create and register to record your
 interest in some event. For instance, if you want to wait for STDIN to
 become readable, you would create an C<ev_io> watcher for that:
-   static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+   static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
    {
      ev_io_stop (w);
      ev_unloop (loop, EVUNLOOP_ALL);
    }
    struct ev_loop *loop = ev_default_loop (0);
-   struct ev_io stdin_watcher;
+   ev_io stdin_watcher;
    ev_init (&stdin_watcher, my_cb);
    ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
    ev_io_start (loop, &stdin_watcher);
    ev_loop (loop, 0);
 =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
 ran out of memory, a file descriptor was found to be closed or any other
+problem. Libev considers these application bugs.
-problem. You best act on it by reporting the problem and somehow coping
+You best act on it by reporting the problem and somehow coping with the
-with the watcher being stopped.
+watcher being stopped. Note that well-written programs should not receive
+an error ever, so when your watcher receives it, this usually indicates a
+bug in your program.
 Libev will usually signal a few "dummy" events together with an error, for
 example it might indicate that a fd is readable or writable, and if your
 callbacks is well-written it can just attempt the operation and cope with
 the error from read() or write(). This will not work in multi-threaded
 which rolls both calls into one.
 You can reinitialise a watcher at any time as long as it has been stopped
 (or never started) and there are no pending events outstanding.
-The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
+The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
 int revents)>.
 Example: Initialise an C<ev_io> watcher in two steps.
    ev_io w;
    ev_io_start (EV_DEFAULT_UC, &w);
 =item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
-Stops the given watcher again (if active) and clears the pending
+Stops the given watcher if active, and clears the pending status (whether
+the watcher was active or not).
-status. It is possible that stopped watchers are pending (for example,
+It is possible that stopped watchers are pending - for example,
-non-repeating timers are being stopped when they become pending), but
+non-repeating timers are being stopped when they become pending - but
-C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
+calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
-you want to free or reuse the memory used by the watcher it is therefore a
+pending. If you want to free or reuse the memory used by the watcher it is
-good idea to always call its C<ev_TYPE_stop> function.
+therefore a good idea to always call its C<ev_TYPE_stop> function.
 =item bool ev_is_active (ev_TYPE *watcher)
 Returns a true value iff the watcher is active (i.e. it has been started
 and not yet been stopped). As long as a watcher is active you must not modify
 member, you can also "subclass" the watcher type and provide your own
 data:
    struct my_io
    {
-     struct ev_io io;
+     ev_io io;
      int otherfd;
      void *somedata;
      struct whatever *mostinteresting;
    };
    ev_io_init (&w.io, my_cb, fd, EV_READ);
 And since your callback will be called with a pointer to the watcher, you
 can cast it back to your own type:
-   static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
+   static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
    {
      struct my_io *w = (struct my_io *)w_;
      ...
    }
 programmers):
    #include <stddef.h>
    static void
-   t1_cb (EV_P_ struct ev_timer *w, int revents)
+   t1_cb (EV_P_ ev_timer *w, int revents)
    {
      struct my_biggy big = (struct my_biggy *
        (((char *)w) - offsetof (struct my_biggy, t1));
    }
    static void
-   t2_cb (EV_P_ struct ev_timer *w, int revents)
+   t2_cb (EV_P_ ev_timer *w, int revents)
    {
      struct my_biggy big = (struct my_biggy *
        (((char *)w) - offsetof (struct my_biggy, t2));
    }
 Example: Call C<stdin_readable_cb> 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)
+   stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
    {
       ev_io_stop (loop, w);
      .. read from stdin here (or from w->fd) and handle any I/O errors
    }
    ...
    struct ev_loop *loop = ev_default_init (0);
-   struct ev_io stdin_readable;
+   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);
 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
 then order of execution is undefined.
+=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,
+you want to raise some error after a while.
+What follows are some ways to handle this problem, from obvious and
+inefficient to smart and efficient.
+In the following, a 60 second activity timeout is assumed - a timeout that
+gets reset to 60 seconds each time there is activity (e.g. each time some
+data or other life sign was received).
+=over 4
+=item 1. Use a timer and stop, reinitialise and start it on activity.
+This is the most obvious, but not the most simple way: In the beginning,
+start the watcher:
+   ev_timer_init (timer, callback, 60., 0.);
+   ev_timer_start (loop, timer);
+Then, each time there is some activity, C<ev_timer_stop> it, initialise it
+and start it again:
+   ev_timer_stop (loop, timer);
+   ev_timer_set (timer, 60., 0.);
+   ev_timer_start (loop, timer);
+This is relatively simple to implement, but means that each time there is
+some activity, libev will first have to remove the timer from its internal
+data structure and then add it again. Libev tries to be fast, but it's
+still not a constant-time operation.
+=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
+This is the easiest way, and involves using C<ev_timer_again> instead of
+C<ev_timer_start>.
+To implement this, configure an C<ev_timer> with a C<repeat> value
+of C<60> and then call C<ev_timer_again> at start and each time you
+successfully read or write some data. If you go into an idle state where
+you do not expect data to travel on the socket, you can C<ev_timer_stop>
+the timer, and C<ev_timer_again> will automatically restart it if need be.
+That means you can ignore both the C<ev_timer_start> function and the
+C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
+member and C<ev_timer_again>.
+At start:
+   ev_timer_init (timer, callback);
+   timer->repeat = 60.;
+   ev_timer_again (loop, timer);
+Each time there is some activity:
+   ev_timer_again (loop, timer);
+It is even possible to change the time-out on the fly, regardless of
+whether the watcher is active or not:
+   timer->repeat = 30.;
+   ev_timer_again (loop, timer);
+This is slightly more efficient then stopping/starting the timer each time
+you want to modify its timeout value, as libev does not have to completely
+remove and re-insert the timer from/into its internal data structure.
+It is, however, even simpler than the "obvious" way to do it.
+=item 3. Let the timer time out, but then re-arm it as required.
+This method is more tricky, but usually most efficient: Most timeouts are
+relatively long compared to the intervals between other activity - in
+our example, within 60 seconds, there are usually many I/O events with
+associated activity resets.
+In this case, it would be more efficient to leave the C<ev_timer> alone,
+but remember the time of last activity, and check for a real timeout only
+within the callback:
+   ev_tstamp last_activity; // time of last activity
+   static void
+   callback (EV_P_ ev_timer *w, int revents)
+   {
+     ev_tstamp now     = ev_now (EV_A);
+     ev_tstamp timeout = last_activity + 60.;
+     // if last_activity + 60. is older than now, we did time out
+     if (timeout < now)
+       {
+         // timeout occured, take action
+       }
+     else
+       {
+         // callback was invoked, but there was some activity, re-arm
+         // the watcher to fire in last_activity + 60, which is
+         // guaranteed to be in the future, so "again" is positive:
+         w->again = timeout - now;
+         ev_timer_again (EV_A_ w);
+       }
+   }
+To summarise the callback: first calculate the real timeout (defined
+as "60 seconds after the last activity"), then check if that time has
+been reached, which means something I<did>, in fact, time out. Otherwise
+the callback was invoked too early (C<timeout> is in the future), so
+re-schedule the timer to fire at that future time, to see if maybe we have
+a timeout then.
+Note how C<ev_timer_again> is used, taking advantage of the
+C<ev_timer_again> optimisation when the timer is already running.
+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.
+To start the timer, simply initialise the watcher and set C<last_activity>
+to the current time (meaning we just have some activity :), then call the
+callback, which will "do the right thing" and start the timer:
+   ev_timer_init (timer, callback);
+   last_activity = ev_now (loop);
+   callback (loop, timer, EV_TIMEOUT);
+And when there is some activity, simply store the current time in
+C<last_activity>, no libev calls at all:
+   last_actiivty = ev_now (loop);
+This technique is slightly more complex, but in most cases where the
+time-out is unlikely to be triggered, much more efficient.
+Changing the timeout is trivial as well (if it isn't hard-coded in the
+callback :) - just change the timeout and invoke the callback, which will
+fix things for you.
+=item 4. Whee, use a double-linked list for your timeouts.
+If there is not one request, but many thousands, all employing some kind
+of timeout with the same timeout value, then one can do even better:
+When starting the timeout, calculate the timeout value and put the timeout
+at the I<end> of the list.
+Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
+the list is expected to fire (for example, using the technique #3).
+When there is some activity, remove the timer from the list, recalculate
+the timeout, append it to the end of the list again, and make sure to
+update the C<ev_timer> if it was taken from the beginning of the list.
+This way, one can manage an unlimited number of timeouts in O(1) time for
+starting, stopping and updating the timers, at the expense of a major
+complication, and having to use a constant timeout. The constant timeout
+ensures that the list stays sorted.
+=back
+So what method is the best?
+The method #2 is a simple no-brain-required solution that is adequate in
+most situations. Method #3 requires a bit more thinking, but handles many
+cases better, and isn't very complicated either. In most case, choosing
+either one is fine.
+Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
+rather complicated, but extremely efficient, something that really pays
+off after the first or so million of active timers, i.e. it's usually
+overkill :)
 =head3 The special problem of time updates
 Establishing the current time is a costly operation (it usually takes at
 least two system calls): EV therefore updates its idea of the current
 time only before and after C<ev_loop> collects new events, which causes a
 If the timer is started but non-repeating, stop it (as if it timed out).
 If the timer is repeating, either start it if necessary (with the
 C<repeat> value), or reset the running timer to the C<repeat> value.
-This sounds a bit complicated, but here is a useful and typical
+This sounds a bit complicated, see "Be smart about timeouts", above, for a
-example: Imagine you have a TCP connection and you want a so-called idle
+usage example.
-timeout, that is, you want to be called when there have been, say, 60
-seconds of inactivity on the socket. The easiest way to do this is to
-configure an C<ev_timer> with a C<repeat> value of C<60> and then call
-C<ev_timer_again> each time you successfully read or write some data. If
-you go into an idle state where you do not expect data to travel on the
-socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
-automatically restart it if need be.
-That means you can ignore the C<after> value and C<ev_timer_start>
-altogether and only ever use the C<repeat> value and C<ev_timer_again>:
-   ev_timer_init (timer, callback, 0., 5.);
-   ev_timer_again (loop, timer);
-   ...
-   timer->again = 17.;
-   ev_timer_again (loop, timer);
-   ...
-   timer->again = 10.;
-   ev_timer_again (loop, timer);
-This is more slightly efficient then stopping/starting the timer each time
-you want to modify its timeout value.
-Note, however, that it is often even more efficient to remember the
-time of the last activity and let the timer time-out naturally. In the
-callback, you then check whether the time-out is real, or, if there was
-some activity, you reschedule the watcher to time-out in "last_activity +
-timeout - ev_now ()" seconds.
 =item ev_tstamp repeat [read-write]
 The current C<repeat> value. Will be used each time the watcher times out
 or C<ev_timer_again> is called, and determines the next timeout (if any),
 =head3 Examples
 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_cb (struct ev_loop *loop, ev_timer *w, int revents)
    {
      .. one minute over, w is actually stopped right here
    }
-   struct ev_timer mytimer;
+   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)
+   timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
    {
      .. ten seconds without any activity
    }
-   struct ev_timer mytimer;
+   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":
 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).
-The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
+The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
 *w, ev_tstamp now)>, e.g.:
+   static ev_tstamp
-   static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
+   my_rescheduler (ev_periodic *w, ev_tstamp now)
    {
      return now + 60.;
    }
 It must return the next time to trigger, based on the passed time value
 The current interval value. 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 (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
+=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
 The current reschedule callback, or C<0>, if this functionality is
 switched off. Can be changed any time, but changes only take effect when
 the periodic timer fires or C<ev_periodic_again> is being called.
 Example: Call a callback every hour, or, more precisely, whenever the
 system time is divisible by 3600. The callback invocation times have
 potentially a lot of jitter, but good long-term stability.
    static void
-   clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+   clock_cb (struct ev_loop *loop, 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 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 <math.h>
    static ev_tstamp
-   my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
+   my_scheduler_cb (ev_periodic *w, ev_tstamp now)
    {
      return now + (3600. - fmod (now, 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 hourly_tick;
    ev_periodic_init (&hourly_tick, clock_cb,
                      fmod (ev_now (loop), 3600.), 3600., 0);
    ev_periodic_start (loop, &hourly_tick);
 =head3 Examples
 Example: Try to exit cleanly on SIGINT.
    static void
-   sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+   sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
    {
      ev_unloop (loop, EVUNLOOP_ALL);
    }
-   struct ev_signal signal_watcher;
+   ev_signal signal_watcher;
    ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
    ev_signal_start (loop, &signal_watcher);
 =head2 C<ev_child> - watch out for process status changes
 its completion.
    ev_child cw;
    static void
-   child_cb (EV_P_ struct ev_child *w, int revents)
+   child_cb (EV_P_ ev_child *w, int revents)
    {
      ev_child_stop (EV_A_ w);
      printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
    }
 to exchange stat structures with application programs compiled using the
 default compilation environment.
 =head3 Inotify and Kqueue
-When C<inotify (7)> support has been compiled into libev (generally only
+When C<inotify (7)> support has been compiled into libev (generally
+only available with Linux 2.6.25 or above due to bugs in earlier
-available with Linux) and present at runtime, it will be used to speed up
+implementations) and present at runtime, it will be used to speed up
-change detection where possible. The inotify descriptor will be created lazily
+change detection where possible. The inotify descriptor will be created
-when the first C<ev_stat> watcher is being started.
+lazily when the first C<ev_stat> watcher is being started.
 Inotify presence does not change the semantics of C<ev_stat> watchers
 except that changes might be detected earlier, and in some cases, to avoid
 making regular C<stat> calls. Even in the presence of inotify support
 there are many cases where libev has to resort to regular C<stat> polling,
 Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
 callback, free it. Also, use no error checking, as usual.
    static void
-   idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+   idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
    {
      free (w);
      // now do something you wanted to do when the program has
      // no longer anything immediate to do.
    }
-   struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+   ev_idle *idle_watcher = malloc (sizeof (ev_idle));
    ev_idle_init (idle_watcher, idle_cb);
    ev_idle_start (loop, idle_cb);
 =head2 C<ev_prepare> and C<ev_check> - customise your event loop!
    static ev_io iow [nfd];
    static ev_timer tw;
    static void
-   io_cb (ev_loop *loop, ev_io *w, int revents)
+   io_cb (struct ev_loop *loop, ev_io *w, int revents)
    {
    }
    // create io watchers for each fd and a timer before blocking
    static void
-   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+   adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
    {
      int timeout = 3600000;
      struct pollfd fds [nfd];
      // actual code will need to loop here and realloc etc.
      adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
        }
    }
    // stop all watchers after blocking
    static void
-   adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+   adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
    {
      ev_timer_stop (loop, &tw);
      for (int i = 0; i < nfd; ++i)
        {
 C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
 used).
    struct ev_loop *loop_hi = ev_default_init (0);
    struct ev_loop *loop_lo = 0;
-   struct ev_embed embed;
+   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 ())
 kqueue implementation). Store the kqueue/socket-only event loop in
 C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
    struct ev_loop *loop = ev_default_init (0);
    struct ev_loop *loop_socket = 0;
-   struct ev_embed embed;
+   ev_embed embed;
    if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
      if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
        {
          ev_embed_init (&embed, 0, loop_socket);
 =over 4
 =item queueing from a signal handler context
 To implement race-free queueing, you simply add to the queue in the signal
-handler but you block the signal handler in the watcher callback. Here is an example that does that for
+handler but you block the signal handler in the watcher callback. Here is
-some fictitious SIGUSR1 handler:
+an example that does that for some fictitious SIGUSR1 handler:
    static ev_async mysig;
    static void
    sigusr1_handler (void)
 =over 4
 =item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
 This function combines a simple timer and an I/O watcher, calls your
-callback on whichever event happens first and automatically stop both
+callback on whichever event happens first and automatically stops both
 watchers. This is useful if you want to wait for a single event on an fd
 or timeout without having to allocate/configure/start/stop/free one or
 more watchers yourself.
-If C<fd> is less than 0, then no I/O watcher will be started and events
+If C<fd> is less than 0, then no I/O watcher will be started and the
-is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
+C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
-C<events> set will be created and started.
+the given C<fd> and C<events> set will be created and started.
 If C<timeout> is less than 0, then no timeout watcher will be
 started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
-repeat = 0) will be started. While C<0> is a valid timeout, it is of
+repeat = 0) will be started. C<0> is a valid timeout.
-dubious value.
 The callback has the type C<void (*cb)(int revents, void *arg)> and gets
 passed an C<revents> set like normal event callbacks (a combination of
 C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
-value passed to C<ev_once>:
+value passed to C<ev_once>. Note that it is possible to receive I<both>
+a timeout and an io event at the same time - you probably should give io
+events precedence.
+Example: wait up to ten seconds for data to appear on STDIN_FILENO.
    static void stdin_ready (int revents, void *arg)
    {
+     if (revents & EV_READ)
+       /* stdin might have data for us, joy! */;
-     if (revents & EV_TIMEOUT)
+     else if (revents & EV_TIMEOUT)
        /* doh, nothing entered */;
-     else if (revents & EV_READ)
-       /* stdin might have data for us, joy! */;
    }
    ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
-=item ev_feed_event (ev_loop *, watcher *, int revents)
+=item ev_feed_event (struct ev_loop *, watcher *, int revents)
 Feeds the given event set into the event loop, as if the specified event
 had happened for the specified watcher (which must be a pointer to an
 initialised but not necessarily started event watcher).
-=item ev_feed_fd_event (ev_loop *, int fd, int revents)
+=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
 Feed an event on the given fd, as if a file descriptor backend detected
 the given events it.
-=item ev_feed_signal_event (ev_loop *loop, int signum)
+=item ev_feed_signal_event (struct ev_loop *loop, int signum)
 Feed an event as if the given signal occurred (C<loop> must be the default
 loop!).
 =back
 =head2 THREADS AND COROUTINES
 =head3 THREADS
 All libev functions are reentrant and thread-safe unless explicitly
-documented otherwise, but it uses no locking itself. This means that you
+documented otherwise, but libev implements no locking itself. This means
-can use as many loops as you want in parallel, as long as there are no
+that you can use as many loops as you want in parallel, as long as there
-concurrent calls into any libev function with the same loop parameter
+are no concurrent calls into any libev function with the same loop
-(C<ev_default_*> calls have an implicit default loop parameter, of
+parameter (C<ev_default_*> calls have an implicit default loop parameter,
-course): libev guarantees that different event loops share no data
+of course): libev guarantees that different event loops share no data
 structures that need any locking.
 Or to put it differently: calls with different loop parameters can be done
 concurrently from multiple threads, calls with the same loop parameter
 must be done serially (but can be done from different threads, as long as
 =back
 =head3 COROUTINES
-Libev is much more accommodating to coroutines ("cooperative threads"):
+Libev is very accommodating to coroutines ("cooperative threads"):
-libev fully supports nesting calls to it's functions from different
+libev fully supports nesting calls to its functions from different
 coroutines (e.g. you can call C<ev_loop> on the same loop from two
-different coroutines and switch freely between both coroutines running the
+different coroutines, and switch freely between both coroutines running the
 loop, as long as you don't confuse yourself). The only exception is that
 you must not do this from C<ev_periodic> reschedule callbacks.
 Care has been taken to ensure that libev does not keep local state inside
-C<ev_loop>, and other calls do not usually allow coroutine switches.
+C<ev_loop>, and other calls do not usually allow for coroutine switches as
+they do not clal any callbacks.
 =head2 COMPILER WARNINGS
 Depending on your compiler and compiler settings, you might get no or a
 lot of warnings when compiling libev code. Some people are apparently
 with any compiler warnings enabled unless you are prepared to cope with
 them (e.g. by ignoring them). Remember that warnings are just that:
 warnings, not errors, or proof of bugs.
-=head1 VALGRIND
+=head2 VALGRIND
 Valgrind has a special section here because it is a popular tool that is
 highly useful. Unfortunately, valgrind reports are very hard to interpret.
 If you think you found a bug (memory leak, uninitialised data access etc.)
 If you need, for some reason, empty reports from valgrind for your project
 I suggest using suppression lists.
-=head1 COMPLEXITIES
-In this section the complexities of (many of) the algorithms used inside
-libev will be explained. For complexity discussions about backends see the
-documentation for C<ev_default_init>.
-All of the following are about amortised time: If an array needs to be
-extended, libev needs to realloc and move the whole array, but this
-happens asymptotically never with higher number of elements, so O(1) might
-mean it might do a lengthy realloc operation in rare cases, but on average
-it is much faster and asymptotically approaches constant time.
-=over 4
-=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
-This means that, when you have a watcher that triggers in one hour and
-there are 100 watchers that would trigger before that then inserting will
-have to skip roughly seven (C<ld 100>) of these watchers.
-=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
-That means that changing a timer costs less than removing/adding them
-as only the relative motion in the event queue has to be paid for.
-=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
-These just add the watcher into an array or at the head of a list.
-=item Stopping check/prepare/idle/fork/async watchers: O(1)
-=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
-These watchers are stored in lists then need to be walked to find the
-correct watcher to remove. The lists are usually short (you don't usually
-have many watchers waiting for the same fd or signal).
-=item Finding the next timer in each loop iteration: O(1)
-By virtue of using a binary or 4-heap, the next timer is always found at a
-fixed position in the storage array.
-=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
-A change means an I/O watcher gets started or stopped, which requires
-libev to recalculate its status (and possibly tell the kernel, depending
-on backend and whether C<ev_io_set> was used).
-=item Activating one watcher (putting it into the pending state): O(1)
-=item Priority handling: O(number_of_priorities)
-Priorities are implemented by allocating some space for each
-priority. When doing priority-based operations, libev usually has to
-linearly search all the priorities, but starting/stopping and activating
-watchers becomes O(1) with respect to priority handling.
-=item Sending an ev_async: O(1)
-=item Processing ev_async_send: O(number_of_async_watchers)
-=item Processing signals: O(max_signal_number)
-Sending involves a system call I<iff> there were no other C<ev_async_send>
-calls in the current loop iteration. Checking for async and signal events
-involves iterating over all running async watchers or all signal numbers.
-=back
-=head1 PORTABILITY
+=head1 PORTABILITY NOTES
 =head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
 Win32 doesn't support any of the standards (e.g. POSIX) that libev
 requires, and its I/O model is fundamentally incompatible with the POSIX
 =back
 If you know of other additional requirements drop me a note.
+=head1 ALGORITHMIC COMPLEXITIES
+In this section the complexities of (many of) the algorithms used inside
+libev will be documented. For complexity discussions about backends see
+the documentation for C<ev_default_init>.
+All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically rarer with higher number of elements, so O(1) might
+mean that libev does a lengthy realloc operation in rare cases, but on
+average it is much faster and asymptotically approaches constant time.
+=over 4
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that, then inserting will
+have to skip roughly seven (C<ld 100>) of these watchers.
+=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
+That means that changing a timer costs less than removing/adding them,
+as only the relative motion in the event queue has to be paid for.
+=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
+These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle/fork/async watchers: O(1)
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+These watchers are stored in lists, so they need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal: one is typical, two
+is rare).
+=item Finding the next timer in each loop iteration: O(1)
+By virtue of using a binary or 4-heap, the next timer is always found at a
+fixed position in the storage array.
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel, depending
+on backend and whether C<ev_io_set> was used).
+=item Activating one watcher (putting it into the pending state): O(1)
+=item Priority handling: O(number_of_priorities)
+Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities, but starting/stopping and activating
+watchers becomes O(1) with respect to priority handling.
+=item Sending an ev_async: O(1)
+=item Processing ev_async_send: O(number_of_async_watchers)
+=item Processing signals: O(max_signal_number)
+Sending involves a system call I<iff> there were no other C<ev_async_send>
+calls in the current loop iteration. Checking for async and signal events
+involves iterating over all running async watchers or all signal numbers.
+=back
 =head1 AUTHOR
 Marc Lehmann <libev@schmorp.de>.

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Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC