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

Comparing libev/ev.pod (file contents):
Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs.
Revision 1.198 by root, Thu Oct 23 06:30:48 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
 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 invole some kind of time-out, 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.
+Here are some ways on how to handle this problem, from simple and
+inefficient to very efficient.
+In the following examples a 60 second activity timeout is assumed - a
+timeout that gets reset to 60 seconds each time some data ("a lifesign")
+was received.
+=over 4
+=item 1. Use a timer and stop, reinitialise, 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> the timer,
+initialise it again, and start it:
+   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 it's
+internal data strcuture and then add it again.
+=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>.
+For 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 the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>.
+At start:
+   ev_timer_init (timer, callback, 0., 60.);
+   ev_timer_again (loop, timer);
+Each time you receive some data:
+   ev_timer_again (loop, timer);
+It is even possible to change the time-out on the fly:
+   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 it's internal data structure.
+=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 loop iteration time - 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 is older than now - timeout, we did time out
+     if (timeout < now)
+       {
+         // timeout occured, take action
+       }
+     else
+       {
+         // callback was invoked, but there was some activity, re-arm
+         // to fire in last_activity + 60.
+         w->again = timeout - now;
+         ev_timer_again (EV_A_ w);
+       }
+   }
+To summarise the callback: first calculate the real time-out (defined as
+"60 seconds after the last activity"), then check if that time has been
+reached, which means there was a real timeout. Otherwise the callback was
+invoked too early (timeout is in the future), so re-schedule the timer to
+fire at that future time.
+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),
+but virtually no calls to libev to change the timeout.
+To start the timer, simply intiialise the watcher and C<last_activity>,
+then call the callback:
+   ev_timer_init (timer, callback);
+   last_activity = ev_now (loop);
+   callback (loop, timer, EV_TIMEOUT);
+And when there is some activity, simply remember the time in
+C<last_activity>:
+   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.
+=back
 =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);
        /* doh, nothing entered */;
    }
    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

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Comparing libev/ev.pod (file contents): Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs. Revision 1.198 by root, Thu Oct 23 06:30:48 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs.
Revision 1.198 by root, Thu Oct 23 06:30:48 2008 UTC