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

Comparing libev/ev.pod (file contents):
Revision 1.327 by root, Sun Oct 24 20:05:43 2010 UTC vs.
Revision 1.370 by root, Thu Jun 2 23:42:40 2011 UTC

      ev_timer_start (loop, &timeout_watcher);
      // now wait for events to arrive
      ev_run (loop, 0);
-     // unloop was called, so exit
+     // break was called, so exit
      return 0;
    }
 =head1 ABOUT THIS DOCUMENT
 on event-based programming, nor will it introduce event-based programming
 with libev.
 Familiarity with event based programming techniques in general is assumed
 throughout this document.
+=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
+look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
+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
 the current system, you would need to look at C<ev_embeddable_backends ()
 & ev_supported_backends ()>, likewise for recommended ones.
 See the description of C<ev_embed> watchers for more info.
-=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
+=item ev_set_allocator (void *(*cb)(void *ptr, long size))
 Sets the allocation function to use (the prototype is similar - the
 semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
 used to allocate and free memory (no surprises here). If it returns zero
 when memory needs to be allocated (C<size != 0>), the library might abort
    }
    ...
    ev_set_allocator (persistent_realloc);
-=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
+=item ev_set_syserr_cb (void (*cb)(const char *msg))
 Set the callback function to call on a retryable system call error (such
 as failed select, poll, epoll_wait). The message is a printable string
 indicating the system call or subsystem causing the problem. If this
 callback is set, then libev will expect it to remedy the situation, no
    }
    ...
    ev_set_syserr_cb (fatal_error);
+=item ev_feed_signal (int signum)
+This function can be used to "simulate" a signal receive. It is completely
+safe to call this function at any time, from any context, including signal
+handlers or random threads.
+Its main use is to customise signal handling in your process, especially
+in the presence of threads. For example, you could block signals
+by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
+creating any loops), and in one thread, use C<sigwait> or any other
+mechanism to wait for signals, then "deliver" them to libev by calling
+C<ev_feed_signal>.
 =back
 =head1 FUNCTIONS CONTROLLING EVENT LOOPS
 An event loop is described by a C<struct ev_loop *> (the C<struct> is
 I<not> optional in this case unless libev 3 compatibility is disabled, as
 libev 3 had an C<ev_loop> function colliding with the struct name).
 The library knows two types of such loops, the I<default> loop, which
-supports signals and child events, and dynamically created event loops
+supports child process events, and dynamically created event loops which
-which do not.
+do not.
 =over 4
 =item struct ev_loop *ev_default_loop (unsigned int flags)
 =item struct ev_loop *ev_loop_new (unsigned int flags)
 This will create and initialise a new event loop object. If the loop
 could not be initialised, returns false.
-Note that this function I<is> thread-safe, and one common way to use
+This function is thread-safe, and one common way to use libev with
-libev with threads is indeed to create one loop per thread, and using the
+threads is indeed to create one loop per thread, and using the default
-default loop in the "main" or "initial" thread.
+loop in the "main" or "initial" thread.
 The flags argument can be used to specify special behaviour or specific
 backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
 The following flags are supported:
 environment variable.
 =item C<EVFLAG_NOINOTIFY>
 When this flag is specified, then libev will not attempt to use the
-I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
+I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
 testing, this flag can be useful to conserve inotify file descriptors, as
 otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
 =item C<EVFLAG_SIGNALFD>
 When this flag is specified, then libev will attempt to use the
-I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
+I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
 delivers signals synchronously, which makes it both faster and might make
 it possible to get the queued signal data. It can also simplify signal
 handling with threads, as long as you properly block signals in your
 threads that are not interested in handling them.
 Signalfd will not be used by default as this changes your signal mask, and
 there are a lot of shoddy libraries and programs (glib's threadpool for
 example) that can't properly initialise their signal masks.
+=item C<EVFLAG_NOSIGMASK>
+When this flag is specified, then libev will avoid to modify the signal
+mask. Specifically, this means you ahve to make sure signals are unblocked
+when you want to receive them.
+This behaviour is useful when you want to do your own signal handling, or
+want to handle signals only in specific threads and want to avoid libev
+unblocking the signals.
+It's also required by POSIX in a threaded program, as libev calls
+C<sigprocmask>, whose behaviour is officially unspecified.
+This flag's behaviour will become the default in future versions of libev.
 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 This is your standard select(2) backend. Not I<completely> standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 =item C<EVBACKEND_EPOLL>   (value 4, Linux)
 Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
 kernels).
-For few fds, this backend is a bit little slower than poll and select,
+For few fds, this backend is a bit little slower than poll and select, but
-but it scales phenomenally better. While poll and select usually scale
+it scales phenomenally better. While poll and select usually scale like
-like O(total_fds) where n is the total number of fds (or the highest fd),
+O(total_fds) where total_fds is the total number of fds (or the highest
-epoll scales either O(1) or O(active_fds).
+fd), epoll scales either O(1) or O(active_fds).
 The epoll mechanism deserves honorable mention as the most misdesigned
 of the more advanced event mechanisms: mere annoyances include silently
 dropping file descriptors, requiring a system call per change per file
-descriptor (and unnecessary guessing of parameters), problems with dup and
+descriptor (and unnecessary guessing of parameters), problems with dup,
+returning before the timeout value, resulting in additional iterations
+(and only giving 5ms accuracy while select on the same platform gives
-so on. The biggest issue is fork races, however - if a program forks then
+0.1ms) and so on. The biggest issue is fork races, however - if a program
-I<both> parent and child process have to recreate the epoll set, which can
+forks then I<both> parent and child process have to recreate the epoll
-take considerable time (one syscall per file descriptor) and is of course
+set, which can take considerable time (one syscall per file descriptor)
-hard to detect.
+and is of course hard to detect.
-Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
+Epoll is also notoriously buggy - embedding epoll fds I<should> work,
-of course I<doesn't>, and epoll just loves to report events for totally
+but of course I<doesn't>, and epoll just loves to report events for
-I<different> file descriptors (even already closed ones, so one cannot
+totally I<different> file descriptors (even already closed ones, so
-even remove them from the set) than registered in the set (especially
+one cannot even remove them from the set) than registered in the set
-on SMP systems). Libev tries to counter these spurious notifications by
+(especially on SMP systems). Libev tries to counter these spurious
-employing an additional generation counter and comparing that against the
+notifications by employing an additional generation counter and comparing
-events to filter out spurious ones, recreating the set when required. Last
+that against the events to filter out spurious ones, recreating the set
+when required. Epoll also errornously rounds down timeouts, but gives you
+no way to know when and by how much, so sometimes you have to busy-wait
+because epoll returns immediately despite a nonzero timeout. And last
 not least, it also refuses to work with some file descriptors which work
 perfectly fine with C<select> (files, many character devices...).
+Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
+cobbled together in a hurry, no thought to design or interaction with
+others. Oh, the pain, will it ever stop...
 While stopping, setting and starting an I/O watcher in the same iteration
 will result in some caching, there is still a system call per such
 incident (because the same I<file descriptor> could point to a different
 I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
 =item C<EVBACKEND_PORT>    (value 32, Solaris 10)
 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
 it's really slow, but it still scales very well (O(active_fds)).
-Please note that Solaris event ports can deliver a lot of spurious
-notifications, so you need to use non-blocking I/O or other means to avoid
-blocking when no data (or space) is available.
 While this backend scales well, it requires one system call per active
 file descriptor per loop iteration. For small and medium numbers of file
 descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
 might perform better.
-On the positive side, with the exception of the spurious readiness
+On the positive side, this backend actually performed fully to
-notifications, this backend actually performed fully to specification
-in all tests and is fully embeddable, which is a rare feat among the
+specification in all tests and is fully embeddable, which is a rare feat
-OS-specific backends (I vastly prefer correctness over speed hacks).
+among the OS-specific backends (I vastly prefer correctness over speed
+hacks).
+On the negative side, the interface is I<bizarre> - so bizarre that
+even sun itself gets it wrong in their code examples: The event polling
+function sometimes returning events to the caller even though an error
+occurred, but with no indication whether it has done so or not (yes, it's
+even documented that way) - deadly for edge-triggered interfaces where
+you absolutely have to know whether an event occurred or not because you
+have to re-arm the watcher.
+Fortunately libev seems to be able to work around these idiocies.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_ALL>
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
-It is definitely not recommended to use this flag.
+It is definitely not recommended to use this flag, use whatever
+C<ev_recommended_backends ()> returns, or simply do not specify a backend
+at all.
+=item C<EVBACKEND_MASK>
+Not a backend at all, but a mask to select all backend bits from a
+C<flags> value, in case you want to mask out any backends from a flags
+value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
 =back
 If one or more of the backend flags are or'ed into the flags value,
 then only these backends will be tried (in the reverse order as listed
 This function is normally used on loop objects allocated by
 C<ev_loop_new>, but it can also be used on the default loop returned by
 C<ev_default_loop>, in which case it is not thread-safe.
 Note that it is not advisable to call this function on the default loop
-except in the rare occasion where you really need to free it's resources.
+except in the rare occasion where you really need to free its resources.
 If you need dynamically allocated loops it is better to use C<ev_loop_new>
 and C<ev_loop_destroy>.
 =item ev_loop_fork (loop)
 prepare and check phases.
 =item unsigned int ev_depth (loop)
 Returns the number of times C<ev_run> was entered minus the number of
-times C<ev_run> was exited, in other words, the recursion depth.
+times C<ev_run> was exited normally, in other words, the recursion depth.
 Outside C<ev_run>, this number is zero. In a callback, this number is
 C<1>, unless C<ev_run> was invoked recursively (or from another thread),
 in which case it is higher.
-Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
+Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
-etc.), doesn't count as "exit" - consider this as a hint to avoid such
+throwing an exception etc.), doesn't count as "exit" - consider this
-ungentleman-like behaviour unless it's really convenient.
+as a hint to avoid such ungentleman-like behaviour unless it's really
+convenient, in which case it is fully supported.
 =item unsigned int ev_backend (loop)
 Returns one of the C<EVBACKEND_*> flags indicating the event backend in
 use.
 finished (especially in interactive programs), but having a program
 that automatically loops as long as it has to and no longer by virtue
 of relying on its watchers stopping correctly, that is truly a thing of
 beauty.
+This function is also I<mostly> exception-safe - you can break out of
+a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
+exception and so on. This does not decrement the C<ev_depth> value, nor
+will it clear any outstanding C<EVBREAK_ONE> breaks.
 A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
 those events and any already outstanding ones, but will not wait and
 block your process in case there are no events and will return after one
 iteration of the loop. This is sometimes useful to poll and handle new
 events while doing lengthy calculations, to keep the program responsive.
 This is useful if you are waiting for some external event in conjunction
 with something not expressible using other libev watchers (i.e. "roll your
 own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
 usually a better approach for this kind of thing.
-Here are the gory details of what C<ev_run> does:
+Here are the gory details of what C<ev_run> does (this is for your
+understanding, not a guarantee that things will work exactly like this in
+future versions):
    - Increment loop depth.
    - Reset the ev_break status.
    - Before the first iteration, call any pending watchers.
    LOOP:
 anymore.
    ... queue jobs here, make sure they register event watchers as long
    ... as they still have work to do (even an idle watcher will do..)
    ev_run (my_loop, 0);
-   ... jobs done or somebody called unloop. yeah!
+   ... jobs done or somebody called break. yeah!
 =item ev_break (loop, how)
 Can be used to make a call to C<ev_run> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
 C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
-This "unloop state" will be cleared when entering C<ev_run> again.
+This "break state" will be cleared on the next call to C<ev_run>.
-It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
+It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
+which case it will have no effect.
 =item ev_ref (loop)
 =item ev_unref (loop)
 running when nothing else is active.
    ev_signal exitsig;
    ev_signal_init (&exitsig, sig_cb, SIGINT);
    ev_signal_start (loop, &exitsig);
-   evf_unref (loop);
+   ev_unref (loop);
 Example: For some weird reason, unregister the above signal handler again.
    ev_ref (loop);
    ev_signal_stop (loop, &exitsig);
 See also the locking example in the C<THREADS> section later in this
 document.
 =item ev_set_userdata (loop, void *data)
-=item ev_userdata (loop)
+=item void *ev_userdata (loop)
 Set and retrieve a single C<void *> associated with a loop. When
 C<ev_set_userdata> has never been called, then C<ev_userdata> returns
-C<0.>
+C<0>.
 These two functions can be used to associate arbitrary data with a loop,
 and are intended solely for the C<invoke_pending_cb>, C<release> and
 C<acquire> callbacks described above, but of course can be (ab-)used for
 any other purpose as well.
 The event loop has been resumed in the child process after fork (see
 C<ev_fork>).
 =item C<EV_CLEANUP>
-The event loop is abotu to be destroyed (see C<ev_cleanup>).
+The event loop is about to be destroyed (see C<ev_cleanup>).
 =item C<EV_ASYNC>
 The given async watcher has been asynchronously notified (see C<ev_async>).
 programs, though, as the fd could already be closed and reused for another
 thing, so beware.
 =back
+=head2 GENERIC WATCHER FUNCTIONS
+=over 4
+=item C<ev_init> (ev_TYPE *watcher, callback)
+This macro initialises the generic portion of a watcher. The contents
+of the watcher object can be arbitrary (so C<malloc> will do). Only
+the generic parts of the watcher are initialised, you I<need> to call
+the type-specific C<ev_TYPE_set> macro afterwards to initialise the
+type-specific parts. For each type there is also a C<ev_TYPE_init> macro
+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 (*)(struct ev_loop *loop, ev_TYPE *watcher,
+int revents)>.
+Example: Initialise an C<ev_io> watcher in two steps.
+   ev_io w;
+   ev_init (&w, my_cb);
+   ev_io_set (&w, STDIN_FILENO, EV_READ);
+=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
+This macro initialises the type-specific parts of a watcher. You need to
+call C<ev_init> at least once before you call this macro, but you can
+call C<ev_TYPE_set> any number of times. You must not, however, call this
+macro on a watcher that is active (it can be pending, however, which is a
+difference to the C<ev_init> macro).
+Although some watcher types do not have type-specific arguments
+(e.g. C<ev_prepare>) you still need to call its C<set> macro.
+See C<ev_init>, above, for an example.
+=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
+This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
+calls into a single call. This is the most convenient method to initialise
+a watcher. The same limitations apply, of course.
+Example: Initialise and set an C<ev_io> watcher in one step.
+   ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
+=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
+Starts (activates) the given watcher. Only active watchers will receive
+events. If the watcher is already active nothing will happen.
+Example: Start the C<ev_io> watcher that is being abused as example in this
+whole section.
+   ev_io_start (EV_DEFAULT_UC, &w);
+=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
+Stops the given watcher if active, and clears the pending status (whether
+the watcher was active or not).
+It is possible that stopped watchers are pending - for example,
+non-repeating timers are being stopped when they become pending - but
+calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
+pending. If you want to free or reuse the memory used by the watcher it is
+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
+it.
+=item bool ev_is_pending (ev_TYPE *watcher)
+Returns a true value iff the watcher is pending, (i.e. it has outstanding
+events but its callback has not yet been invoked). As long as a watcher
+is pending (but not active) you must not call an init function on it (but
+C<ev_TYPE_set> is safe), you must not change its priority, and you must
+make sure the watcher is available to libev (e.g. you cannot C<free ()>
+it).
+=item callback ev_cb (ev_TYPE *watcher)
+Returns the callback currently set on the watcher.
+=item ev_cb_set (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)
+=item int ev_priority (ev_TYPE *watcher)
+Set and query the priority of the watcher. The priority is a small
+integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
+(default: C<-2>). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for C<ev_idle> watchers).
+If you need to suppress invocation when higher priority events are pending
+you need to look at C<ev_idle> watchers, which provide this functionality.
+You I<must not> change the priority of a watcher as long as it is active or
+pending.
+Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
+fine, as long as you do not mind that the priority value you query might
+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
+priorities.
+=item ev_invoke (loop, ev_TYPE *watcher, int revents)
+Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
+C<loop> nor C<revents> need to be valid as long as the watcher callback
+can deal with that fact, as both are simply passed through to the
+callback.
+=item int ev_clear_pending (loop, ev_TYPE *watcher)
+If the watcher is pending, this function clears its pending status and
+returns its C<revents> bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns C<0>.
+Sometimes it can be useful to "poll" a watcher instead of waiting for its
+callback to be invoked, which can be accomplished with this function.
+=item ev_feed_event (loop, ev_TYPE *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). Obviously you must
+not free the watcher as long as it has pending events.
+Stopping the watcher, letting libev invoke it, or calling
+C<ev_clear_pending> will clear the pending event, even if the watcher was
+not started in the first place.
+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
+OWN COMPOSITE WATCHERS> idioms.
 =head2 WATCHER STATES
 There are various watcher states mentioned throughout this manual -
 active, pending and so on. In this section these states and the rules to
 transition between them will be described in more detail - and while these
 Before a watcher can be registered with the event looop it has to be
 initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
 C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
-In this state it is simply some block of memory that is suitable for use
+In this state it is simply some block of memory that is suitable for
-in an event loop. It can be moved around, freed, reused etc. at will.
+use in an event loop. It can be moved around, freed, reused etc. at
+will - as long as you either keep the memory contents intact, or call
+C<ev_TYPE_init> again.
 =item started/running/active
 Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
 property of the event loop, and is actively waiting for events. While in
 latter will clear any pending state the watcher might be in, regardless
 of whether it was active or not, so stopping a watcher explicitly before
 freeing it is often a good idea.
 While stopped (and not pending) the watcher is essentially in the
-initialised state, that is it can be reused, moved, modified in any way
+initialised state, that is, it can be reused, moved, modified in any way
-you wish.
+you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
+it again).
 =back
-=head2 GENERIC WATCHER FUNCTIONS
-=over 4
-=item C<ev_init> (ev_TYPE *watcher, callback)
-This macro initialises the generic portion of a watcher. The contents
-of the watcher object can be arbitrary (so C<malloc> will do). Only
-the generic parts of the watcher are initialised, you I<need> to call
-the type-specific C<ev_TYPE_set> macro afterwards to initialise the
-type-specific parts. For each type there is also a C<ev_TYPE_init> macro
-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 (*)(struct ev_loop *loop, ev_TYPE *watcher,
-int revents)>.
-Example: Initialise an C<ev_io> watcher in two steps.
-   ev_io w;
-   ev_init (&w, my_cb);
-   ev_io_set (&w, STDIN_FILENO, EV_READ);
-=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
-This macro initialises the type-specific parts of a watcher. You need to
-call C<ev_init> at least once before you call this macro, but you can
-call C<ev_TYPE_set> any number of times. You must not, however, call this
-macro on a watcher that is active (it can be pending, however, which is a
-difference to the C<ev_init> macro).
-Although some watcher types do not have type-specific arguments
-(e.g. C<ev_prepare>) you still need to call its C<set> macro.
-See C<ev_init>, above, for an example.
-=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
-This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
-calls into a single call. This is the most convenient method to initialise
-a watcher. The same limitations apply, of course.
-Example: Initialise and set an C<ev_io> watcher in one step.
-   ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
-=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
-Starts (activates) the given watcher. Only active watchers will receive
-events. If the watcher is already active nothing will happen.
-Example: Start the C<ev_io> watcher that is being abused as example in this
-whole section.
-   ev_io_start (EV_DEFAULT_UC, &w);
-=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
-Stops the given watcher if active, and clears the pending status (whether
-the watcher was active or not).
-It is possible that stopped watchers are pending - for example,
-non-repeating timers are being stopped when they become pending - but
-calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
-pending. If you want to free or reuse the memory used by the watcher it is
-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
-it.
-=item bool ev_is_pending (ev_TYPE *watcher)
-Returns a true value iff the watcher is pending, (i.e. it has outstanding
-events but its callback has not yet been invoked). As long as a watcher
-is pending (but not active) you must not call an init function on it (but
-C<ev_TYPE_set> is safe), you must not change its priority, and you must
-make sure the watcher is available to libev (e.g. you cannot C<free ()>
-it).
-=item callback ev_cb (ev_TYPE *watcher)
-Returns the callback currently set on the watcher.
-=item ev_cb_set (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)
-=item int ev_priority (ev_TYPE *watcher)
-Set and query the priority of the watcher. The priority is a small
-integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
-(default: C<-2>). Pending watchers with higher priority will be invoked
-before watchers with lower priority, but priority will not keep watchers
-from being executed (except for C<ev_idle> watchers).
-If you need to suppress invocation when higher priority events are pending
-you need to look at C<ev_idle> watchers, which provide this functionality.
-You I<must not> change the priority of a watcher as long as it is active or
-pending.
-Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
-fine, as long as you do not mind that the priority value you query might
-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
-priorities.
-=item ev_invoke (loop, ev_TYPE *watcher, int revents)
-Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
-C<loop> nor C<revents> need to be valid as long as the watcher callback
-can deal with that fact, as both are simply passed through to the
-callback.
-=item int ev_clear_pending (loop, ev_TYPE *watcher)
-If the watcher is pending, this function clears its pending status and
-returns its C<revents> bitset (as if its callback was invoked). If the
-watcher isn't pending it does nothing and returns C<0>.
-Sometimes it can be useful to "poll" a watcher instead of waiting for its
-callback to be invoked, which can be accomplished with this function.
-=item ev_feed_event (loop, ev_TYPE *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). Obviously you must
-not free the watcher as long as it has pending events.
-Stopping the watcher, letting libev invoke it, or calling
-C<ev_clear_pending> will clear the pending event, even if the watcher was
-not started in the first place.
-See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
-functions that do not need a watcher.
-=back
-=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
-Each watcher has, by default, a member C<void *data> that you can change
-and read at any time: libev will completely ignore it. This can be used
-to associate arbitrary data with your watcher. If you need more data and
-don't want to allocate memory and store a pointer to it in that data
-member, you can also "subclass" the watcher type and provide your own
-data:
-   struct my_io
-   {
-     ev_io io;
-     int otherfd;
-     void *somedata;
-     struct whatever *mostinteresting;
-   };
-   ...
-   struct my_io w;
-   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, ev_io *w_, int revents)
-   {
-     struct my_io *w = (struct my_io *)w_;
-     ...
-   }
-More interesting and less C-conformant ways of casting your callback type
-instead have been omitted.
-Another common scenario is to use some data structure with multiple
-embedded watchers:
-   struct my_biggy
-   {
-     int some_data;
-     ev_timer t1;
-     ev_timer t2;
-   }
-In this case getting the pointer to C<my_biggy> is a bit more
-complicated: Either you store the address of your C<my_biggy> struct
-in the C<data> member of the watcher (for woozies), or you need to use
-some pointer arithmetic using C<offsetof> inside your watchers (for real
-programmers):
-   #include <stddef.h>
-   static void
-   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_ ev_timer *w, int revents)
-   {
-     struct my_biggy big = (struct my_biggy *)
-       (((char *)w) - offsetof (struct my_biggy, t2));
-   }
 =head2 WATCHER PRIORITY MODELS
 Many event loops support I<watcher priorities>, which are usually small
 integers that influence the ordering of event callback invocation
 In general you can register as many read and/or write event watchers per
 fd as you want (as long as you don't confuse yourself). Setting all file
 descriptors to non-blocking mode is also usually a good idea (but not
 required if you know what you are doing).
-If you cannot use non-blocking mode, then force the use of a
-known-to-be-good backend (at the time of this writing, this includes only
-C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
-descriptors for which non-blocking operation makes no sense (such as
-files) - libev doesn't guarantee any specific behaviour in that case.
 Another thing you have to watch out for is that it is quite easy to
-receive "spurious" readiness notifications, that is your callback might
+receive "spurious" readiness notifications, that is, your callback might
 be called with C<EV_READ> but a subsequent C<read>(2) will actually block
-because there is no data. Not only are some backends known to create a
+because there is no data. It is very easy to get into this situation even
-lot of those (for example Solaris ports), it is very easy to get into
+with a relatively standard program structure. Thus it is best to always
-this situation even with a relatively standard program structure. Thus
+use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
-it is best to always use non-blocking I/O: An extra C<read>(2) returning
-C<EAGAIN> is far preferable to a program hanging until some data arrives.
+preferable to a program hanging until some data arrives.
 If you cannot run the fd in non-blocking mode (for example you should
 not play around with an Xlib connection), then you have to separately
 re-test whether a file descriptor is really ready with a known-to-be good
-interface such as poll (fortunately in our Xlib example, Xlib already
+interface such as poll (fortunately in the case of Xlib, it already does
-does this on its own, so its quite safe to use). Some people additionally
+this on its own, so its quite safe to use). Some people additionally
 use C<SIGALRM> and an interval timer, just to be sure you won't block
 indefinitely.
 But really, best use non-blocking mode.
 There is no workaround possible except not registering events
 for potentially C<dup ()>'ed file descriptors, or to resort to
 C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
+=head3 The special problem of files
+Many people try to use C<select> (or libev) on file descriptors
+representing files, and expect it to become ready when their program
+doesn't block on disk accesses (which can take a long time on their own).
+However, this cannot ever work in the "expected" way - you get a readiness
+notification as soon as the kernel knows whether and how much data is
+there, and in the case of open files, that's always the case, so you
+always get a readiness notification instantly, and your read (or possibly
+write) will still block on the disk I/O.
+Another way to view it is that in the case of sockets, pipes, character
+devices and so on, there is another party (the sender) that delivers data
+on its own, but in the case of files, there is no such thing: the disk
+will not send data on its own, simply because it doesn't know what you
+wish to read - you would first have to request some data.
+Since files are typically not-so-well supported by advanced notification
+mechanism, libev tries hard to emulate POSIX behaviour with respect
+to files, even though you should not use it. The reason for this is
+convenience: sometimes you want to watch STDIN or STDOUT, which is
+usually a tty, often a pipe, but also sometimes files or special devices
+(for example, C<epoll> on Linux works with F</dev/random> but not with
+F</dev/urandom>), and even though the file might better be served with
+asynchronous I/O instead of with non-blocking I/O, it is still useful when
+it "just works" instead of freezing.
+So avoid file descriptors pointing to files when you know it (e.g. use
+libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
+when you rarely read from a file instead of from a socket, and want to
+reuse the same code path.
 =head3 The special problem of fork
 Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
 useless behaviour. Libev fully supports fork, but needs to be told about
-it in the child.
+it in the child if you want to continue to use it in the child.
-To support fork in your programs, you either have to call
+To support fork in your child processes, you have to call C<ev_loop_fork
-C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
+()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
-enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
+C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
-C<EVBACKEND_POLL>.
 =head3 The special problem of SIGPIPE
 While not really specific to libev, it is easy to forget about C<SIGPIPE>:
 when writing to a pipe whose other end has been closed, your program gets
 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 = offset (mod interval)>, regardless of any time jumps.
-For numerical stability it is preferable that the C<offset> value is near
+The C<interval> I<MUST> be positive, and for numerical stability, the
-C<ev_now ()> (the current time), but there is no range requirement for
+interval value should be higher than C<1/8192> (which is around 100
-this value, and in fact is often specified as zero.
+microseconds) and C<offset> should be higher than C<0> and should have
+at most a similar magnitude as the current time (say, within a factor of
+ten). Typical values for offset are, in fact, C<0> or something between
+C<0> and C<interval>, which is also the recommended range.
 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).
 =head2 C<ev_signal> - signal me when a signal gets signalled!
 Signal watchers will trigger an event when the process receives a specific
 signal one or more times. Even though signals are very asynchronous, libev
-will try it's best to deliver signals synchronously, i.e. as part of the
+will try its best to deliver signals synchronously, i.e. as part of the
 normal event processing, like any other event.
 If you want signals to be delivered truly asynchronously, just use
 C<sigaction> as you would do without libev and forget about sharing
 the signal. You can even use C<ev_async> from a signal handler to
 =head3 The special problem of inheritance over fork/execve/pthread_create
 Both the signal mask (C<sigprocmask>) and the signal disposition
 (C<sigaction>) are unspecified after starting a signal watcher (and after
 stopping it again), that is, libev might or might not block the signal,
-and might or might not set or restore the installed signal handler.
+and might or might not set or restore the installed signal handler (but
+see C<EVFLAG_NOSIGMASK>).
 While this does not matter for the signal disposition (libev never
 sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
 C<execve>), this matters for the signal mask: many programs do not expect
 certain signals to be blocked.
 I<has> to modify the signal mask, at least temporarily.
 So I can't stress this enough: I<If you do not reset your signal mask when
 you expect it to be empty, you have a race condition in your code>. This
 is not a libev-specific thing, this is true for most event libraries.
+=head3 The special problem of threads signal handling
+POSIX threads has problematic signal handling semantics, specifically,
+a lot of functionality (sigfd, sigwait etc.) only really works if all
+threads in a process block signals, which is hard to achieve.
+When you want to use sigwait (or mix libev signal handling with your own
+for the same signals), you can tackle this problem by globally blocking
+all signals before creating any threads (or creating them with a fully set
+sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
+loops. Then designate one thread as "signal receiver thread" which handles
+these signals. You can pass on any signals that libev might be interested
+in by calling C<ev_feed_signal>.
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_fork_init (ev_fork *, callback)
 Initialises and configures the fork watcher - it has no parameters of any
 kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
-believe me.
+really.
 =back
 =head2 C<ev_cleanup> - even the best things end
-Cleanup watchers are called just before the event loop they are registered
+Cleanup watchers are called just before the event loop is being destroyed
-with is being destroyed.
+by a call to C<ev_loop_destroy>.
 While there is no guarantee that the event loop gets destroyed, cleanup
 watchers provide a convenient method to install cleanup hooks for your
 program, worker threads and so on - you just to make sure to destroy the
 loop when you want them to be invoked.
 =item ev_cleanup_init (ev_cleanup *, callback)
 Initialises and configures the cleanup watcher - it has no parameters of
 any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
-pointless, believe me.
+pointless, I assure you.
 =back
 Example: Register an atexit handler to destroy the default loop, so any
 cleanup functions are called.
    atexit (program_exits);
 =head2 C<ev_async> - how to wake up an event loop
-In general, you cannot use an C<ev_run> from multiple threads or other
+In general, you cannot use an C<ev_loop> from multiple threads or other
 asynchronous sources such as signal handlers (as opposed to multiple event
 loops - those are of course safe to use in different threads).
 Sometimes, however, you need to wake up an event loop you do not control,
 for example because it belongs to another thread. This is what C<ev_async>
 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).
+C<ev_async_sent> 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.
 Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
 just the default loop.
 =head3 Queueing
 trust me.
 =item ev_async_send (loop, ev_async *)
 Sends/signals/activates the given C<ev_async> watcher, that is, feeds
-an C<EV_ASYNC> event on the watcher into the event loop. Unlike
+an C<EV_ASYNC> event on the watcher into the event loop, and instantly
+returns.
-C<ev_feed_event>, this call is safe to do from other threads, signal or
+Unlike C<ev_feed_event>, this call is safe to do from other threads,
-similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
+signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
-section below on what exactly this means).
+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).
 Feed an event on the given fd, as if a file descriptor backend detected
 the given events it.
 =item ev_feed_signal_event (loop, int signum)
-Feed an event as if the given signal occurred (C<loop> must be the default
+Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
-loop!).
+which is async-safe.
 =back
+=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
+This section explains some common idioms that are not immediately
+obvious. Note that examples are sprinkled over the whole manual, and this
+section only contains stuff that wouldn't fit anywhere else.
+=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
+Each watcher has, by default, a C<void *data> member that you can read
+or modify at any time: libev will completely ignore it. This can be used
+to associate arbitrary data with your watcher. If you need more data and
+don't want to allocate memory separately and store a pointer to it in that
+data member, you can also "subclass" the watcher type and provide your own
+data:
+   struct my_io
+   {
+     ev_io io;
+     int otherfd;
+     void *somedata;
+     struct whatever *mostinteresting;
+   };
+   ...
+   struct my_io w;
+   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, ev_io *w_, int revents)
+   {
+     struct my_io *w = (struct my_io *)w_;
+     ...
+   }
+More interesting and less C-conformant ways of casting your callback
+function type instead have been omitted.
+=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
+Another common scenario is to use some data structure with multiple
+embedded watchers, in effect creating your own watcher that combines
+multiple libev event sources into one "super-watcher":
+   struct my_biggy
+   {
+     int some_data;
+     ev_timer t1;
+     ev_timer t2;
+   }
+In this case getting the pointer to C<my_biggy> is a bit more
+complicated: Either you store the address of your C<my_biggy> struct in
+the C<data> member of the watcher (for woozies or C++ coders), or you need
+to use some pointer arithmetic using C<offsetof> inside your watchers (for
+real programmers):
+   #include <stddef.h>
+   static void
+   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_ ev_timer *w, int revents)
+   {
+     struct my_biggy big = (struct my_biggy *)
+       (((char *)w) - offsetof (struct my_biggy, t2));
+   }
+=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
+Often (especially in GUI toolkits) there are places where you have
+I<modal> interaction, which is most easily implemented by recursively
+invoking C<ev_run>.
+This brings the problem of exiting - a callback might want to finish the
+main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
+a modal "Are you sure?" dialog is still waiting), or just the nested one
+and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
+other combination: In these cases, C<ev_break> will not work alone.
+The solution is to maintain "break this loop" variable for each C<ev_run>
+invocation, and use a loop around C<ev_run> until the condition is
+triggered, using C<EVRUN_ONCE>:
+   // main loop
+   int exit_main_loop = 0;
+   while (!exit_main_loop)
+     ev_run (EV_DEFAULT_ EVRUN_ONCE);
+   // in a model watcher
+   int exit_nested_loop = 0;
+   while (!exit_nested_loop)
+     ev_run (EV_A_ EVRUN_ONCE);
+To exit from any of these loops, just set the corresponding exit variable:
+   // exit modal loop
+   exit_nested_loop = 1;
+   // exit main program, after modal loop is finished
+   exit_main_loop = 1;
+   // exit both
+   exit_main_loop = exit_nested_loop = 1;
+=head2 THREAD LOCKING EXAMPLE
+Here is a fictitious example of how to run an event loop in a different
+thread from where callbacks are being invoked and watchers are
+created/added/removed.
+For a real-world example, see the C<EV::Loop::Async> perl module,
+which uses exactly this technique (which is suited for many high-level
+languages).
+The example uses a pthread mutex to protect the loop data, a condition
+variable to wait for callback invocations, an async watcher to notify the
+event loop thread and an unspecified mechanism to wake up the main thread.
+First, you need to associate some data with the event loop:
+   typedef struct {
+     mutex_t lock; /* global loop lock */
+     ev_async async_w;
+     thread_t tid;
+     cond_t invoke_cv;
+   } userdata;
+   void prepare_loop (EV_P)
+   {
+      // for simplicity, we use a static userdata struct.
+      static userdata u;
+      ev_async_init (&u->async_w, async_cb);
+      ev_async_start (EV_A_ &u->async_w);
+      pthread_mutex_init (&u->lock, 0);
+      pthread_cond_init (&u->invoke_cv, 0);
+      // now associate this with the loop
+      ev_set_userdata (EV_A_ u);
+      ev_set_invoke_pending_cb (EV_A_ l_invoke);
+      ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
+      // then create the thread running ev_run
+      pthread_create (&u->tid, 0, l_run, EV_A);
+   }
+The callback for the C<ev_async> watcher does nothing: the watcher is used
+solely to wake up the event loop so it takes notice of any new watchers
+that might have been added:
+   static void
+   async_cb (EV_P_ ev_async *w, int revents)
+   {
+      // just used for the side effects
+   }
+The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
+protecting the loop data, respectively.
+   static void
+   l_release (EV_P)
+   {
+     userdata *u = ev_userdata (EV_A);
+     pthread_mutex_unlock (&u->lock);
+   }
+   static void
+   l_acquire (EV_P)
+   {
+     userdata *u = ev_userdata (EV_A);
+     pthread_mutex_lock (&u->lock);
+   }
+The event loop thread first acquires the mutex, and then jumps straight
+into C<ev_run>:
+   void *
+   l_run (void *thr_arg)
+   {
+     struct ev_loop *loop = (struct ev_loop *)thr_arg;
+     l_acquire (EV_A);
+     pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
+     ev_run (EV_A_ 0);
+     l_release (EV_A);
+     return 0;
+   }
+Instead of invoking all pending watchers, the C<l_invoke> callback will
+signal the main thread via some unspecified mechanism (signals? pipe
+writes? C<Async::Interrupt>?) and then waits until all pending watchers
+have been called (in a while loop because a) spurious wakeups are possible
+and b) skipping inter-thread-communication when there are no pending
+watchers is very beneficial):
+   static void
+   l_invoke (EV_P)
+   {
+     userdata *u = ev_userdata (EV_A);
+     while (ev_pending_count (EV_A))
+       {
+         wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
+         pthread_cond_wait (&u->invoke_cv, &u->lock);
+       }
+   }
+Now, whenever the main thread gets told to invoke pending watchers, it
+will grab the lock, call C<ev_invoke_pending> and then signal the loop
+thread to continue:
+   static void
+   real_invoke_pending (EV_P)
+   {
+     userdata *u = ev_userdata (EV_A);
+     pthread_mutex_lock (&u->lock);
+     ev_invoke_pending (EV_A);
+     pthread_cond_signal (&u->invoke_cv);
+     pthread_mutex_unlock (&u->lock);
+   }
+Whenever you want to start/stop a watcher or do other modifications to an
+event loop, you will now have to lock:
+   ev_timer timeout_watcher;
+   userdata *u = ev_userdata (EV_A);
+   ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+   pthread_mutex_lock (&u->lock);
+   ev_timer_start (EV_A_ &timeout_watcher);
+   ev_async_send (EV_A_ &u->async_w);
+   pthread_mutex_unlock (&u->lock);
+Note that sending the C<ev_async> watcher is required because otherwise
+an event loop currently blocking in the kernel will have no knowledge
+about the newly added timer. By waking up the loop it will pick up any new
+watchers in the next event loop iteration.
+=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
+While the overhead of a callback that e.g. schedules a thread is small, it
+is still an overhead. If you embed libev, and your main usage is with some
+kind of threads or coroutines, you might want to customise libev so that
+doesn't need callbacks anymore.
+Imagine you have coroutines that you can switch to using a function
+C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
+and that due to some magic, the currently active coroutine is stored in a
+global called C<current_coro>. Then you can build your own "wait for libev
+event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
+the differing C<;> conventions):
+   #define EV_CB_DECLARE(type)   struct my_coro *cb;
+   #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
+That means instead of having a C callback function, you store the
+coroutine to switch to in each watcher, and instead of having libev call
+your callback, you instead have it switch to that coroutine.
+A coroutine might now wait for an event with a function called
+C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
+matter when, or whether the watcher is active or not when this function is
+called):
+   void
+   wait_for_event (ev_watcher *w)
+   {
+     ev_cb_set (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
+this or any other coroutine. I am sure if you sue this your own :)
+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
+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);
+   #include "../libev/ev.h"
+   // my_ev.c
+   #define EV_H "my_ev.h"
+   #include "../libev/ev.c"
+And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
+F<my_ev.c> into your project. When properly specifying include paths, you
+can even use F<ev.h> as header file name directly.
 =head1 LIBEVENT EMULATION
 Libev offers a compatibility emulation layer for libevent. It cannot
 emulate the internals of libevent, so here are some usage hints:
 =over 4
+=item * Only the libevent-1.4.1-beta API is being emulated.
+This was the newest libevent version available when libev was implemented,
+and is still mostly unchanged in 2010.
 =item * Use it by including <event.h>, as usual.
 =item * The following members are fully supported: ev_base, ev_callback,
 ev_arg, ev_fd, ev_res, ev_events.
 =item * Priorities are not currently supported. Initialising priorities
 will fail and all watchers will have the same priority, even though there
 is an ev_pri field.
 =item * In libevent, the last base created gets the signals, in libev, the
-first base created (== the default loop) gets the signals.
+base that registered the signal gets the signals.
 =item * Other members are not supported.
 =item * The libev emulation is I<not> ABI compatible to libevent, you need
 to use the libev header file and library.
 Care has been taken to keep the overhead low. The only data member the C++
 classes add (compared to plain C-style watchers) is the event loop pointer
 that the watcher is associated with (or no additional members at all if
 you disable C<EV_MULTIPLICITY> when embedding libev).
-Currently, functions, and static and non-static member functions can be
+Currently, functions, static and non-static member functions and classes
-used as callbacks. Other types should be easy to add as long as they only
+with C<operator ()> can be used as callbacks. Other types should be easy
-need one additional pointer for context. If you need support for other
+to add as long as they only need one additional pointer for context. If
-types of functors please contact the author (preferably after implementing
+you need support for other types of functors please contact the author
-it).
+(preferably after implementing it).
 Here is a list of things available in the C<ev> namespace:
 =over 4
 F<event.h> that are not directly supported by the libev core alone.
 In standalone mode, libev will still try to automatically deduce the
 configuration, but has to be more conservative.
+=item EV_USE_FLOOR
+If defined to be C<1>, libev will use the C<floor ()> function for its
+periodic reschedule calculations, otherwise libev will fall back on a
+portable (slower) implementation. If you enable this, you usually have to
+link against libm or something equivalent. Enabling this when the C<floor>
+function is not available will fail, so the safe default is to not enable
+this.
 =item EV_USE_MONOTONIC
 If defined to be C<1>, libev will try to detect the availability of the
 monotonic clock option at both compile time and runtime. Otherwise no
 use of the monotonic clock option will be attempted. If you enable this,
 And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
    #include "ev_cpp.h"
    #include "ev.c"
-=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
+=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
 =head2 THREADS AND COROUTINES
 =head3 THREADS
 default loop and triggering an C<ev_async> watcher from the default loop
 watcher callback into the event loop interested in the signal.
 =back
-=head4 THREAD LOCKING EXAMPLE
+See also L<THREAD LOCKING EXAMPLE>.
-Here is a fictitious example of how to run an event loop in a different
-thread than where callbacks are being invoked and watchers are
-created/added/removed.
-For a real-world example, see the C<EV::Loop::Async> perl module,
-which uses exactly this technique (which is suited for many high-level
-languages).
-The example uses a pthread mutex to protect the loop data, a condition
-variable to wait for callback invocations, an async watcher to notify the
-event loop thread and an unspecified mechanism to wake up the main thread.
-First, you need to associate some data with the event loop:
-   typedef struct {
-     mutex_t lock; /* global loop lock */
-     ev_async async_w;
-     thread_t tid;
-     cond_t invoke_cv;
-   } userdata;
-   void prepare_loop (EV_P)
-   {
-      // for simplicity, we use a static userdata struct.
-      static userdata u;
-      ev_async_init (&u->async_w, async_cb);
-      ev_async_start (EV_A_ &u->async_w);
-      pthread_mutex_init (&u->lock, 0);
-      pthread_cond_init (&u->invoke_cv, 0);
-      // now associate this with the loop
-      ev_set_userdata (EV_A_ u);
-      ev_set_invoke_pending_cb (EV_A_ l_invoke);
-      ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
-      // then create the thread running ev_loop
-      pthread_create (&u->tid, 0, l_run, EV_A);
-   }
-The callback for the C<ev_async> watcher does nothing: the watcher is used
-solely to wake up the event loop so it takes notice of any new watchers
-that might have been added:
-   static void
-   async_cb (EV_P_ ev_async *w, int revents)
-   {
-      // just used for the side effects
-   }
-The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
-protecting the loop data, respectively.
-   static void
-   l_release (EV_P)
-   {
-     userdata *u = ev_userdata (EV_A);
-     pthread_mutex_unlock (&u->lock);
-   }
-   static void
-   l_acquire (EV_P)
-   {
-     userdata *u = ev_userdata (EV_A);
-     pthread_mutex_lock (&u->lock);
-   }
-The event loop thread first acquires the mutex, and then jumps straight
-into C<ev_run>:
-   void *
-   l_run (void *thr_arg)
-   {
-     struct ev_loop *loop = (struct ev_loop *)thr_arg;
-     l_acquire (EV_A);
-     pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
-     ev_run (EV_A_ 0);
-     l_release (EV_A);
-     return 0;
-   }
-Instead of invoking all pending watchers, the C<l_invoke> callback will
-signal the main thread via some unspecified mechanism (signals? pipe
-writes? C<Async::Interrupt>?) and then waits until all pending watchers
-have been called (in a while loop because a) spurious wakeups are possible
-and b) skipping inter-thread-communication when there are no pending
-watchers is very beneficial):
-   static void
-   l_invoke (EV_P)
-   {
-     userdata *u = ev_userdata (EV_A);
-     while (ev_pending_count (EV_A))
-       {
-         wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
-         pthread_cond_wait (&u->invoke_cv, &u->lock);
-       }
-   }
-Now, whenever the main thread gets told to invoke pending watchers, it
-will grab the lock, call C<ev_invoke_pending> and then signal the loop
-thread to continue:
-   static void
-   real_invoke_pending (EV_P)
-   {
-     userdata *u = ev_userdata (EV_A);
-     pthread_mutex_lock (&u->lock);
-     ev_invoke_pending (EV_A);
-     pthread_cond_signal (&u->invoke_cv);
-     pthread_mutex_unlock (&u->lock);
-   }
-Whenever you want to start/stop a watcher or do other modifications to an
-event loop, you will now have to lock:
-   ev_timer timeout_watcher;
-   userdata *u = ev_userdata (EV_A);
-   ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
-   pthread_mutex_lock (&u->lock);
-   ev_timer_start (EV_A_ &timeout_watcher);
-   ev_async_send (EV_A_ &u->async_w);
-   pthread_mutex_unlock (&u->lock);
-Note that sending the C<ev_async> watcher is required because otherwise
-an event loop currently blocking in the kernel will have no knowledge
-about the newly added timer. By waking up the loop it will pick up any new
-watchers in the next event loop iteration.
 =head3 COROUTINES
 Libev is very accommodating to coroutines ("cooperative threads"):
 libev fully supports nesting calls to its functions from different
 structure (guaranteed by POSIX but not by ISO C for example), but it also
 assumes that the same (machine) code can be used to call any watcher
 callback: The watcher callbacks have different type signatures, but libev
 calls them using an C<ev_watcher *> internally.
+=item pointer accesses must be thread-atomic
+Accessing a pointer value must be atomic, it must both be readable and
+writable in one piece - this is the case on all current architectures.
 =item C<sig_atomic_t volatile> must be thread-atomic as well
 The type C<sig_atomic_t volatile> (or whatever is defined as
 C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
 threads. This is not part of the specification for C<sig_atomic_t>, but is
 =back
 =head1 PORTING FROM LIBEV 3.X TO 4.X
-The major version 4 introduced some minor incompatible changes to the API.
+The major version 4 introduced some incompatible changes to the API.
-At the moment, the C<ev.h> header file tries to implement superficial
+At the moment, the C<ev.h> header file provides compatibility definitions
-compatibility, so most programs should still compile. Those might be
+for all changes, so most programs should still compile. The compatibility
-removed in later versions of libev, so better update early than late.
+layer might be removed in later versions of libev, so better update to the
+new API early than late.
 =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>
+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:
 ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
 as all other watcher types. Note that C<ev_loop_fork> is still called
 C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
 typedef.
-=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>
-section.
 =item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
 The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
 mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
 and work, but the library code will of course be larger.
 The physical time that is observed. It is apparently strictly monotonic :)
 =item wall-clock time
 The time and date as shown on clocks. Unlike real time, it can actually
-be wrong and jump forwards and backwards, e.g. when the you adjust your
+be wrong and jump forwards and backwards, e.g. when you adjust your
 clock.
 =item watcher
 A data structure that describes interest in certain events. Watchers need
 =back
 =head1 AUTHOR
-Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
+Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
+Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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Revision 1.370 by root, Thu Jun 2 23:42:40 2011 UTC