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

Comparing libev/ev.pod (file contents):
Revision 1.405 by root, Thu May 3 15:07:15 2012 UTC vs.
Revision 1.421 by root, Thu Aug 2 11:55:28 2012 UTC

 =head1 WHAT TO READ WHEN IN A HURRY
 This manual tries to be very detailed, but unfortunately, this also makes
 it very long. If you just want to know the basics of libev, I suggest
-reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
+reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
-look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
+look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
-C<ev_timer> sections in L<WATCHER TYPES>.
+C<ev_timer> sections in L</WATCHER TYPES>.
 =head1 ABOUT LIBEV
 Libev is an event loop: you register interest in certain events (such as a
 file descriptor being readable or a timeout occurring), and it will manage
 This function is rarely useful, but when some event callback runs for a
 very long time without entering the event loop, updating libev's idea of
 the current time is a good idea.
-See also L<The special problem of time updates> in the C<ev_timer> section.
+See also L</The special problem of time updates> in the C<ev_timer> section.
 =item ev_suspend (loop)
 =item ev_resume (loop)
 =item callback ev_cb (ev_TYPE *watcher)
 Returns the callback currently set on the watcher.
-=item ev_cb_set (ev_TYPE *watcher, callback)
+=item ev_set_cb (ev_TYPE *watcher, callback)
 Change the callback. You can change the callback at virtually any time
 (modulo threads).
 =item ev_set_priority (ev_TYPE *watcher, int priority)
 or might not have been clamped to the valid range.
 The default priority used by watchers when no priority has been set is
 always C<0>, which is supposed to not be too high and not be too low :).
-See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
+See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
 priorities.
 =item ev_invoke (loop, ev_TYPE *watcher, int revents)
 Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
 See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
 functions that do not need a watcher.
 =back
-See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
+See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
 OWN COMPOSITE WATCHERS> idioms.
 =head2 WATCHER STATES
 There are various watcher states mentioned throughout this manual -
 =item If the timer is repeating, make the C<repeat> value the new timeout
 and start the timer, if necessary.
 =back
-This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
+This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
 usage example.
 =item ev_tstamp ev_timer_remaining (loop, ev_timer *)
 Returns the remaining time until a timer fires. If the timer is active,
 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 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)
 callback, free it. Also, use no error checking, as usual.
    static void
    idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
    {
+     // stop the watcher
+     ev_idle_stop (loop, w);
+     // now we can free it
      free (w);
      // now do something you wanted to do when the program has
      // no longer anything immediate to do.
    }
    ev_idle *idle_watcher = malloc (sizeof (ev_idle));
    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
 =head2 C<ev_fork> - the audacity to resume the event loop after a fork
 Fork watchers are called when a C<fork ()> was detected (usually because
 whoever is a good citizen cared to tell libev about it by calling
-C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
+C<ev_loop_fork>). The invocation is done before the event loop blocks next
-event loop blocks next and before C<ev_check> watchers are being called,
+and before C<ev_check> watchers are being called, and only in the child
-and only in the child after the fork. If whoever good citizen calling
+after the fork. If whoever good citizen calling C<ev_default_fork> cheats
-C<ev_default_fork> cheats and calls it in the wrong process, the fork
+and calls it in the wrong process, the fork handlers will be invoked, too,
-handlers will be invoked, too, of course.
+of course.
 =head3 The special problem of life after fork - how is it possible?
 Most uses of C<fork()> consist of forking, then some simple calls to set
 up/change the process environment, followed by a call to C<exec()>. This
 called):
    void
    wait_for_event (ev_watcher *w)
    {
-     ev_cb_set (w) = current_coro;
+     ev_set_cb (w, current_coro);
      switch_to (libev_coro);
    }
 That basically suspends the coroutine inside C<wait_for_event> and
 continues the libev coroutine, which, when appropriate, switches back to
 You can do similar tricks if you have, say, threads with an event queue -
 instead of storing a coroutine, you store the queue object and instead of
 switching to a coroutine, you push the watcher onto the queue and notify
 any waiters.
-To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
+To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
 files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
    // my_ev.h
    #define EV_CB_DECLARE(type)   struct my_coro *cb;
    #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
 libev sources can be compiled as C++. Therefore, code that uses the C API
 will work fine.
 Proper exception specifications might have to be added to callbacks passed
 to libev: exceptions may be thrown only from watcher callbacks, all
-other callbacks (allocator, syserr, loop acquire/release and periodioc
+other callbacks (allocator, syserr, loop acquire/release and periodic
 reschedule callbacks) must not throw exceptions, and might need a C<throw
 ()> specification. If you have code that needs to be compiled as both C
 and C++ you can use the C<EV_THROW> macro for this:
    static void
 Associates a different C<struct ev_loop> with this watcher. You can only
 do this when the watcher is inactive (and not pending either).
 =item w->set ([arguments])
-Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
+Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
-method or a suitable start method must be called at least once. Unlike the
+with the same arguments. Either this method or a suitable start method
-C counterpart, an active watcher gets automatically stopped and restarted
+must be called at least once. Unlike the C counterpart, an active watcher
-when reconfiguring it with this method.
+gets automatically stopped and restarted when reconfiguring it with this
+method.
+For C<ev::embed> watchers this method is called C<set_embed>, to avoid
+clashing with the C<set (loop)> method.
 =item w->start ()
 Starts the watcher. Note that there is no C<loop> argument, as the
 constructor already stores the event loop.
 =item Lua
 Brian Maher has written a partial interface to libev for lua (at the
 time of this writing, only C<ev_io> and C<ev_timer>), to be found at
 L<http://github.com/brimworks/lua-ev>.
+=item Javascript
+Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
+=item Others
+There are others, and I stopped counting.
 =back
 =head1 MACRO MAGIC
 If programs implement their own fd to handle mapping on win32, then this
 macro can be used to override the C<close> function, useful to unregister
 file descriptors again. Note that the replacement function has to close
 the underlying OS handle.
+=item EV_USE_WSASOCKET
+If defined to be C<1>, libev will use C<WSASocket> to create its internal
+communication socket, which works better in some environments. Otherwise,
+the normal C<socket> function will be used, which works better in other
+environments.
 =item EV_USE_POLL
 If defined to be C<1>, libev will compile in support for the C<poll>(2)
 backend. Otherwise it will be enabled on non-win32 platforms. It
 above. This reduces dependencies and makes libev faster.
 =item EV_ATOMIC_T
 Libev requires an integer type (suitable for storing C<0> or C<1>) whose
-access is atomic and serialised with respect to other threads or signal
+access is atomic with respect to other threads or signal contexts. No
-contexts. No such type is easily found in the C language, so you can
+such type is easily found in the C language, so you can provide your own
-provide your own type that you know is safe for your purposes. It is used
+type that you know is safe for your purposes. It is used both for signal
-both for signal handler "locking" as well as for signal and thread safety
+handler "locking" as well as for signal and thread safety in C<ev_async>
-in C<ev_async> watchers.
+watchers.
 In the absence of this define, libev will use C<sig_atomic_t volatile>
-(from F<signal.h>), which is usually good enough on most platforms,
+(from F<signal.h>), which is usually good enough on most platforms.
-although strictly speaking using a type that also implies a memory fence
-is required.
 =item EV_H (h)
 The name of the F<ev.h> header file used to include it. The default if
 undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
 default loop and triggering an C<ev_async> watcher from the default loop
 watcher callback into the event loop interested in the signal.
 =back
-See also L<THREAD LOCKING EXAMPLE>.
+See also L</THREAD LOCKING EXAMPLE>.
 =head3 COROUTINES
 Libev is very accommodating to coroutines ("cooperative threads"):
 libev fully supports nesting calls to its functions from different
 thread" or will block signals process-wide, both behaviours would
 be compatible with libev. Interaction between C<sigprocmask> and
 C<pthread_sigmask> could complicate things, however.
 The most portable way to handle signals is to block signals in all threads
-except the initial one, and run the default loop in the initial thread as
+except the initial one, and run the signal handling loop in the initial
-well.
+thread as well.
 =item C<long> must be large enough for common memory allocation sizes
 To improve portability and simplify its API, libev uses C<long> internally
 instead of C<size_t> when allocating its data structures. On non-POSIX
 =over 4
 =item C<EV_COMPAT3> backwards compatibility mechanism
 The backward compatibility mechanism can be controlled by
-C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
+C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
 section.
 =item C<ev_default_destroy> and C<ev_default_fork> have been removed
 These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
 =over 4
 =item active
 A watcher is active as long as it has been started and not yet stopped.
-See L<WATCHER STATES> for details.
+See L</WATCHER STATES> for details.
 =item application
 In this document, an application is whatever is using libev.
 watchers and events.
 =item pending
 A watcher is pending as soon as the corresponding event has been
-detected. See L<WATCHER STATES> for details.
+detected. See L</WATCHER STATES> for details.
 =item real time
 The physical time that is observed. It is apparently strictly monotonic :)

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Comparing libev/ev.pod (file contents): Revision 1.405 by root, Thu May 3 15:07:15 2012 UTC vs. Revision 1.421 by root, Thu Aug 2 11:55:28 2012 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.405 by root, Thu May 3 15:07:15 2012 UTC vs.
Revision 1.421 by root, Thu Aug 2 11:55:28 2012 UTC