document the embed watchers

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 81da7eac02530a176f5edfeae4d0e85fa83770d1..3104747349d0f8dab97492e76e36b958a6fc49d9 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -41,19 +41,28 @@ 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 this argument.
 
 argument of name C<loop> (which is always of type C<struct ev_loop *>)
 will not have this argument.
 

-=head1 TIME AND OTHER GLOBAL FUNCTIONS
+=head1 TIME REPRESENTATION

 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near
 the beginning of 1970, details are complicated, don't ask). This type is
 called C<ev_tstamp>, which is what you should use too. It usually aliases
 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near
 the beginning of 1970, details are complicated, don't ask). This type is
 called C<ev_tstamp>, which is what you should use too. It usually aliases

-to the double type in C.
+to the C<double> type in C, and when you need to do any calculations on
+it, you should treat it as such.
+
+
+=head1 GLOBAL FUNCTIONS
+
+These functions can be called anytime, even before initialising the
+library in any way.

 
 =over 4
 
 =item ev_tstamp ev_time ()
 
 
 =over 4
 
 =item ev_tstamp ev_time ()
 

-Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+C<ev_now> function is usually faster and also often returns the timestamp
+you actually want to know.

 
 =item int ev_version_major ()
 
 
 =item int ev_version_major ()
 


@@ -70,6 +79,45 @@ as this indicates an incompatible change.  Minor versions are usually
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 

+Example: make sure we haven't accidentally been linked against the wrong
+version:
+
+  assert (("libev version mismatch",
+           ev_version_major () == EV_VERSION_MAJOR
+           && ev_version_minor () >= EV_VERSION_MINOR));
+
+=item unsigned int ev_supported_backends ()
+
+Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See C<ev_default_loop> for
+a description of the set values.
+
+Example: make sure we have the epoll method, because yeah this is cool and
+a must have and can we have a torrent of it please!!!11
+
+  assert (("sorry, no epoll, no sex",
+           ev_supported_backends () & EVBACKEND_EPOLL));
+
+=item unsigned int ev_recommended_backends ()
+
+Return the set of all backends compiled into this binary of libev and also
+recommended for this platform. This set is often smaller than the one
+returned by C<ev_supported_backends>, as for example kqueue is broken on
+most BSDs and will not be autodetected unless you explicitly request it
+(assuming you know what you are doing). This is the set of backends that
+libev will probe for if you specify no backends explicitly.
+
+=item unsigned int ev_embeddable_backends ()
+
+Returns the set of backends that are embeddable in other event loops. This
+is the theoretical, all-platform, value. To find which backends
+might be supported on 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))
 
 Sets the allocation function to use (the prototype is similar to the
 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
 
 Sets the allocation function to use (the prototype is similar to the


@@ -82,6 +130,26 @@ You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,
 or even to sleep a while and retry until some memory is available.
 
 free some memory if it cannot allocate memory, to use a special allocator,
 or even to sleep a while and retry until some memory is available.
 

+Example: replace the libev allocator with one that waits a bit and then
+retries: better than mine).
+
+   static void *
+   persistent_realloc (void *ptr, long size)
+   {
+     for (;;)
+       {
+         void *newptr = realloc (ptr, size);
+
+         if (newptr)
+           return newptr;
+
+         sleep (60);
+       }
+   }
+
+   ...
+   ev_set_allocator (persistent_realloc);
+

 =item ev_set_syserr_cb (void (*cb)(const char *msg));
 
 Set the callback function to call on a retryable syscall error (such
 =item ev_set_syserr_cb (void (*cb)(const char *msg));
 
 Set the callback function to call on a retryable syscall error (such


@@ -92,6 +160,18 @@ matter what, when it returns. That is, libev will generally retry the
 requested operation, or, if the condition doesn't go away, do bad stuff
 (such as abort).
 
 requested operation, or, if the condition doesn't go away, do bad stuff
 (such as abort).
 

+Example: do the same thing as libev does internally:
+
+   static void
+   fatal_error (const char *msg)
+   {
+     perror (msg);
+     abort ();
+   }
+
+   ...
+   ev_set_syserr_cb (fatal_error);
+

 =back
 
 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
 =back
 
 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP


@@ -101,7 +181,7 @@ types of such loops, the I<default> loop, which supports signals and child
 events, and dynamically created loops which do not.
 
 If you use threads, a common model is to run the default event loop
 events, and dynamically created loops which do not.
 
 If you use threads, a common model is to run the default event loop

-in your main thread (or in a separate thrad) and for each thread you
+in your main thread (or in a separate thread) and for each thread you

 create, you also create another event loop. Libev itself does no locking
 whatsoever, so if you mix calls to the same event loop in different
 threads, make sure you lock (this is usually a bad idea, though, even if
 create, you also create another event loop. Libev itself does no locking
 whatsoever, so if you mix calls to the same event loop in different
 threads, make sure you lock (this is usually a bad idea, though, even if


@@ -114,24 +194,24 @@ done correctly, because it's hideous and inefficient).
 This will initialise the default event loop if it hasn't been initialised
 yet and return it. If the default loop could not be initialised, returns
 false. If it already was initialised it simply returns it (and ignores the
 This will initialise the default event loop if it hasn't been initialised
 yet and return it. If the default loop could not be initialised, returns
 false. If it already was initialised it simply returns it (and ignores the

-flags).
+flags. If that is troubling you, check C<ev_backend ()> afterwards).

 
 If you don't know what event loop to use, use the one returned from this
 function.
 
 The flags argument can be used to specify special behaviour or specific
 
 If you don't know what event loop to use, use the one returned from this
 function.
 
 The flags argument can be used to specify special behaviour or specific

-backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
+backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).

 
 

-It supports the following flags:
+The following flags are supported:

 
 =over 4
 
 
 =over 4
 

-=item EVFLAG_AUTO
+=item C<EVFLAG_AUTO>

 
 The default flags value. Use this if you have no clue (it's the right
 thing, believe me).
 
 
 The default flags value. Use this if you have no clue (it's the right
 thing, believe me).
 

-=item EVFLAG_NOENV
+=item C<EVFLAG_NOENV>

 
 If this flag bit is ored into the flag value (or the program runs setuid
 or setgid) then libev will I<not> look at the environment variable
 
 If this flag bit is ored into the flag value (or the program runs setuid
 or setgid) then libev will I<not> look at the environment variable


@@ -140,24 +220,95 @@ override the flags completely if it is found in the environment. This is
 useful to try out specific backends to test their performance, or to work
 around bugs.
 
 useful to try out specific backends to test their performance, or to work
 around bugs.
 

-=item EVMETHOD_SELECT  (portable select backend)
+=item C<EVBACKEND_SELECT>  (value 1, portable select backend)

 
 

-=item EVMETHOD_POLL    (poll backend, available everywhere except on windows)
+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,
+but if that fails, expect a fairly low limit on the number of fds when
+using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+the fastest backend for a low number of fds.

 
 

-=item EVMETHOD_EPOLL   (linux only)
+=item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)

 
 

-=item EVMETHOD_KQUEUE  (some bsds only)
+And this is your standard poll(2) backend. It's more complicated than
+select, but handles sparse fds better and has no artificial limit on the
+number of fds you can use (except it will slow down considerably with a
+lot of inactive fds). It scales similarly to select, i.e. O(total_fds).

 
 

-=item EVMETHOD_DEVPOLL (solaris 8 only)
+=item C<EVBACKEND_EPOLL>   (value 4, Linux)

 
 

-=item EVMETHOD_PORT    (solaris 10 only)
+For few fds, this backend is a bit little slower than poll and select,
+but it scales phenomenally better. While poll and select usually scale like
+O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+either O(1) or O(active_fds).

 
 

-If one or more of these are ored into the flags value, then only these
-backends will be tried (in the reverse order as given here). If one are
-specified, any backend will do.
+While stopping and starting an I/O watcher in the same iteration will
+result in some caching, there is still a syscall per such incident
+(because the fd could point to a different file description now), so its
+best to avoid that. Also, dup()ed file descriptors might not work very
+well if you register events for both fds.
+
+Please note that epoll sometimes generates spurious notifications, so you
+need to use non-blocking I/O or other means to avoid blocking when no data
+(or space) is available.
+
+=item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
+
+Kqueue deserves special mention, as at the time of this writing, it
+was broken on all BSDs except NetBSD (usually it doesn't work with
+anything but sockets and pipes, except on Darwin, where of course its
+completely useless). For this reason its not being "autodetected"
+unless you explicitly specify it explicitly in the flags (i.e. using
+C<EVBACKEND_KQUEUE>).
+
+It scales in the same way as the epoll backend, but the interface to the
+kernel is more efficient (which says nothing about its actual speed, of
+course). While starting and stopping an I/O watcher does not cause an
+extra syscall as with epoll, it still adds up to four event changes per
+incident, so its best to avoid that.
+
+=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
+
+This is not implemented yet (and might never be).
+
+=item C<EVBACKEND_PORT>    (value 32, Solaris 10)
+
+This uses the Solaris 10 port mechanism. As with everything on Solaris,
+it's really slow, but it still scales very well (O(active_fds)).
+
+Please note that solaris ports can result in 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.
+
+=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>.

 
 =back
 
 
 =back
 

+If one or more of these are ored into the flags value, then only these
+backends will be tried (in the reverse order as given here). If none are
+specified, most compiled-in backend will be tried, usually in reverse
+order of their flag values :)
+
+The most typical usage is like this:
+
+  if (!ev_default_loop (0))
+    fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+
+Restrict libev to the select and poll backends, and do not allow
+environment settings to be taken into account:
+
+  ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
+
+Use whatever libev has to offer, but make sure that kqueue is used if
+available (warning, breaks stuff, best use only with your own private
+event loop and only if you know the OS supports your types of fds):
+
+  ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
+

 =item struct ev_loop *ev_loop_new (unsigned int flags)
 
 Similar to C<ev_default_loop>, but always creates a new event loop that is
 =item struct ev_loop *ev_loop_new (unsigned int flags)
 
 Similar to C<ev_default_loop>, but always creates a new event loop that is


@@ -165,6 +316,12 @@ always distinct from the default loop. Unlike the default loop, it cannot
 handle signal and child watchers, and attempts to do so will be greeted by
 undefined behaviour (or a failed assertion if assertions are enabled).
 
 handle signal and child watchers, and attempts to do so will be greeted by
 undefined behaviour (or a failed assertion if assertions are enabled).
 

+Example: try to create a event loop that uses epoll and nothing else.
+
+  struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
+  if (!epoller)
+    fatal ("no epoll found here, maybe it hides under your chair");
+

 =item ev_default_destroy ()
 
 Destroys the default loop again (frees all memory and kernel state
 =item ev_default_destroy ()
 
 Destroys the default loop again (frees all memory and kernel state


@@ -183,9 +340,9 @@ one. Despite the name, you can call it anytime, but it makes most sense
 after forking, in either the parent or child process (or both, but that
 again makes little sense).
 
 after forking, in either the parent or child process (or both, but that
 again makes little sense).
 

-You I<must> call this function after forking if and only if you want to
-use the event library in both processes. If you just fork+exec, you don't
-have to call it.
+You I<must> call this function in the child process after forking if and
+only if you want to use the event library in both processes. If you just
+fork+exec, you don't have to call it.

 
 The function itself is quite fast and it's usually not a problem to call
 it just in case after a fork. To make this easy, the function will fit in
 
 The function itself is quite fast and it's usually not a problem to call
 it just in case after a fork. To make this easy, the function will fit in


@@ -193,24 +350,28 @@ quite nicely into a call to C<pthread_atfork>:
 
     pthread_atfork (0, 0, ev_default_fork);
 
 
     pthread_atfork (0, 0, ev_default_fork);
 

+At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
+

 =item ev_loop_fork (loop)
 
 Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
 
 =item ev_loop_fork (loop)
 
 Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
 

-=item unsigned int ev_method (loop)
+=item unsigned int ev_backend (loop)

 
 

-Returns one of the C<EVMETHOD_*> flags indicating the event backend in
+Returns one of the C<EVBACKEND_*> flags indicating the event backend in

 use.
 
 =item ev_tstamp ev_now (loop)
 
 Returns the current "event loop time", which is the time the event loop
 use.
 
 =item ev_tstamp ev_now (loop)
 
 Returns the current "event loop time", which is the time the event loop

-got events and started processing them. This timestamp does not change
-as long as callbacks are being processed, and this is also the base time
-used for relative timers. You can treat it as the timestamp of the event
-occuring (or more correctly, the mainloop finding out about it).
+received events and started processing them. This timestamp does not
+change as long as callbacks are being processed, and this is also the base
+time used for relative timers. You can treat it as the timestamp of the
+event occuring (or more correctly, libev finding out about it).

 
 =item ev_loop (loop, int flags)
 
 
 =item ev_loop (loop, int flags)
 


@@ -218,8 +379,14 @@ Finally, this is it, the event handler. This function usually is called
 after you initialised all your watchers and you want to start handling
 events.
 
 after you initialised all your watchers and you want to start handling
 events.
 

-If the flags argument is specified as 0, it will not return until either
-no event watchers are active anymore or C<ev_unloop> was called.
+If the flags argument is specified as C<0>, it will not return until
+either no event watchers are active anymore or C<ev_unloop> was called.
+
+Please note that an explicit C<ev_unloop> is usually better than
+relying on all watchers to be stopped when deciding when a program has
+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 is a thing of beauty.

 
 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
 those events and any outstanding ones, but will not block your process in
 
 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
 those events and any outstanding ones, but will not block your process in


@@ -228,17 +395,45 @@ case there are no events and will return after one iteration of the loop.
 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
 neccessary) and will handle those and any outstanding ones. It will block
 your process until at least one new event arrives, and will return after
 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
 neccessary) and will handle those and any outstanding ones. It will block
 your process until at least one new event arrives, and will return after

-one iteration of the loop.
-
-This flags value could be used to implement alternative looping
-constructs, but the C<prepare> and C<check> watchers provide a better and
-more generic mechanism.
+one iteration of the loop. This is useful if you are waiting for some
+external event in conjunction with something not expressible using other
+libev watchers. 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_loop> does:
+
+   * If there are no active watchers (reference count is zero), return.
+   - Queue prepare watchers and then call all outstanding watchers.
+   - If we have been forked, recreate the kernel state.
+   - Update the kernel state with all outstanding changes.
+   - Update the "event loop time".
+   - Calculate for how long to block.
+   - Block the process, waiting for any events.
+   - Queue all outstanding I/O (fd) events.
+   - Update the "event loop time" and do time jump handling.
+   - Queue all outstanding timers.
+   - Queue all outstanding periodics.
+   - If no events are pending now, queue all idle watchers.
+   - Queue all check watchers.
+   - Call all queued watchers in reverse order (i.e. check watchers first).
+     Signals and child watchers are implemented as I/O watchers, and will
+     be handled here by queueing them when their watcher gets executed.
+   - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+     were used, return, otherwise continue with step *.
+
+Example: queue some jobs and then loop until no events are outsanding
+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_loop (my_loop, 0);
+   ... jobs done. yeah!

 
 =item ev_unloop (loop, how)
 
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 
 =item ev_unloop (loop, how)
 
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either

-C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
+C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or

 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
 
 =item ev_ref (loop)
 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
 
 =item ev_ref (loop)


@@ -256,13 +451,26 @@ no event watchers registered by it are active. It is also an excellent
 way to do this for generic recurring timers or from within third-party
 libraries. Just remember to I<unref after start> and I<ref before stop>.
 
 way to do this for generic recurring timers or from within third-party
 libraries. Just remember to I<unref after start> and I<ref before stop>.
 

+Example: create a signal watcher, but keep it from keeping C<ev_loop>
+running when nothing else is active.
+
+  struct dv_signal exitsig;
+  ev_signal_init (&exitsig, sig_cb, SIGINT);
+  ev_signal_start (myloop, &exitsig);
+  evf_unref (myloop);
+
+Example: for some weird reason, unregister the above signal handler again.
+
+  ev_ref (myloop);
+  ev_signal_stop (myloop, &exitsig);
+

 =back
 
 =head1 ANATOMY OF A WATCHER
 
 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
 =back
 
 =head1 ANATOMY OF A WATCHER
 
 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 ev_io watcher for that:
+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, struct ev_io *w, int revents)
   {


@@ -299,63 +507,63 @@ corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
 
 As long as your watcher is active (has been started but not stopped) you
 must not touch the values stored in it. Most specifically you must never
 
 As long as your watcher is active (has been started but not stopped) you
 must not touch the values stored in it. Most specifically you must never

-reinitialise it or call its set method.
+reinitialise it or call its set macro.

 
 

-You cna check whether an event is active by calling the C<ev_is_active
+You can check whether an event is active by calling the C<ev_is_active

 (watcher *)> macro. To see whether an event is outstanding (but the
 (watcher *)> macro. To see whether an event is outstanding (but the

-callback for it has not been called yet) you cna use the C<ev_is_pending
+callback for it has not been called yet) you can use the C<ev_is_pending

 (watcher *)> macro.
 
 Each and every callback receives the event loop pointer as first, the
 registered watcher structure as second, and a bitset of received events as
 third argument.
 
 (watcher *)> macro.
 
 Each and every callback receives the event loop pointer as first, the
 registered watcher structure as second, and a bitset of received events as
 third argument.
 

-The rceeived events usually include a single bit per event type received
+The received events usually include a single bit per event type received

 (you can receive multiple events at the same time). The possible bit masks
 are:
 
 =over 4
 
 (you can receive multiple events at the same time). The possible bit masks
 are:
 
 =over 4
 

-=item EV_READ
+=item C<EV_READ>

 
 

-=item EV_WRITE
+=item C<EV_WRITE>

 
 

-The file descriptor in the ev_io watcher has become readable and/or
+The file descriptor in the C<ev_io> watcher has become readable and/or

 writable.
 
 writable.
 

-=item EV_TIMEOUT
+=item C<EV_TIMEOUT>

 
 

-The ev_timer watcher has timed out.
+The C<ev_timer> watcher has timed out.

 
 

-=item EV_PERIODIC
+=item C<EV_PERIODIC>

 
 

-The ev_periodic watcher has timed out.
+The C<ev_periodic> watcher has timed out.

 
 

-=item EV_SIGNAL
+=item C<EV_SIGNAL>

 
 

-The signal specified in the ev_signal watcher has been received by a thread.
+The signal specified in the C<ev_signal> watcher has been received by a thread.

 
 

-=item EV_CHILD
+=item C<EV_CHILD>

 
 

-The pid specified in the ev_child watcher has received a status change.
+The pid specified in the C<ev_child> watcher has received a status change.

 
 

-=item EV_IDLE
+=item C<EV_IDLE>

 
 

-The ev_idle watcher has determined that you have nothing better to do.
+The C<ev_idle> watcher has determined that you have nothing better to do.

 
 

-=item EV_PREPARE
+=item C<EV_PREPARE>

 
 

-=item EV_CHECK
+=item C<EV_CHECK>

 
 

-All ev_prepare watchers are invoked just I<before> C<ev_loop> starts
-to gather new events, and all ev_check watchers are invoked just after
+All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
+to gather new events, and all C<ev_check> watchers are invoked just after

 C<ev_loop> has gathered them, but before it invokes any callbacks for any
 received events. Callbacks of both watcher types can start and stop as
 many watchers as they want, and all of them will be taken into account
 C<ev_loop> has gathered them, but before it invokes any callbacks for any
 received events. Callbacks of both watcher types can start and stop as
 many watchers as they want, and all of them will be taken into account

-(for example, a ev_prepare watcher might start an idle watcher to keep
+(for example, a C<ev_prepare> watcher might start an idle watcher to keep

 C<ev_loop> from blocking).
 
 C<ev_loop> from blocking).
 

-=item EV_ERROR
+=item C<EV_ERROR>

 
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev


@@ -374,7 +582,7 @@ programs, though, so beware.
 =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
 
 Each watcher has, by default, a member C<void *data> that you can change
 =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 cna be used
+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
 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


@@ -406,15 +614,16 @@ have been omitted....
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
 
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
 

-=head2 struct ev_io - is my file descriptor readable or writable
+
+=head2 C<ev_io> - is this file descriptor readable or writable

 
 I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 level-triggering because you keep receiving events as long as the
 
 I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 level-triggering because you keep receiving events as long as the

-condition persists. Remember you cna stop the watcher if you don't want to
+condition persists. Remember you can stop the watcher if you don't want to

 act on the event and neither want to receive future events).
 
 act on the event and neither want to receive future events).
 

-In general you can register as many read and/or write event watchers oer
+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).
 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).


@@ -422,11 +631,12 @@ required if you know what you are doing).
 You have to be careful with dup'ed file descriptors, though. Some backends
 (the linux epoll backend is a notable example) cannot handle dup'ed file
 descriptors correctly if you register interest in two or more fds pointing
 You have to be careful with dup'ed file descriptors, though. Some backends
 (the linux epoll backend is a notable example) cannot handle dup'ed file
 descriptors correctly if you register interest in two or more fds pointing

-to the same file/socket etc. description.
+to the same underlying file/socket etc. description (that is, they share
+the same underlying "file open").

 
 If you must do this, then force the use of a known-to-be-good backend
 
 If you must do this, then force the use of a known-to-be-good backend

-(at the time of this writing, this includes only EVMETHOD_SELECT and
-EVMETHOD_POLL).
+(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
+C<EVBACKEND_POLL>).

 
 =over 4
 
 
 =over 4
 


@@ -434,31 +644,65 @@ EVMETHOD_POLL).
 
 =item ev_io_set (ev_io *, int fd, int events)
 
 
 =item ev_io_set (ev_io *, int fd, int events)
 

-Configures an ev_io watcher. The fd is the file descriptor to rceeive
+Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive

 events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
 EV_WRITE> to receive the given events.
 
 events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
 EV_WRITE> to receive the given events.
 

+Please note that most of the more scalable backend mechanisms (for example
+epoll and solaris ports) can result in spurious readyness notifications
+for file descriptors, so you practically need to use non-blocking I/O (and
+treat callback invocation as hint only), or retest separately with a safe
+interface before doing I/O (XLib can do this), or force the use of either
+C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
+problem. Also note that it is quite easy to have your callback invoked
+when the readyness condition is no longer valid even when employing
+typical ways of handling events, so its a good idea to use non-blocking
+I/O unconditionally.
+

 =back
 
 =back
 

-=head2 struct ev_timer - relative and optionally recurring timeouts
+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)
+  {
+     ev_io_stop (loop, w);
+    .. read from stdin here (or from w->fd) and haqndle any I/O errors
+  }
+
+  ...
+  struct ev_loop *loop = ev_default_init (0);
+  struct 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);
+
+
+=head2 C<ev_timer> - relative and optionally recurring timeouts

 
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 
 The timers are based on real time, that is, if you register an event that
 
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 
 The timers are based on real time, that is, if you register an event that

-times out after an hour and youreset your system clock to last years
+times out after an hour and you reset your system clock to last years

 time, it will still time out after (roughly) and hour. "Roughly" because
 time, it will still time out after (roughly) and hour. "Roughly" because

-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some inaccuracies are unavoidable (the

 monotonic clock option helps a lot here).
 
 The relative timeouts are calculated relative to the C<ev_now ()>
 time. This is usually the right thing as this timestamp refers to the time
 monotonic clock option helps a lot here).
 
 The relative timeouts are calculated relative to the C<ev_now ()>
 time. This is usually the right thing as this timestamp refers to the time

-of the event triggering whatever timeout you are modifying/starting.  If
-you suspect event processing to be delayed and you *need* to base the timeout
-ion the current time, use something like this to adjust for this:
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you I<need> to base the timeout
+on the current time, use something like this to adjust for this:

 
    ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
 
 
    ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
 

+The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.
+

 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)


@@ -473,7 +717,7 @@ later, again, and again, until stopped manually.
 The timer itself will do a best-effort at avoiding drift, that is, if you
 configure a timer to trigger every 10 seconds, then it will trigger at
 exactly 10 second intervals. If, however, your program cannot keep up with
 The timer itself will do a best-effort at avoiding drift, that is, if you
 configure a timer to trigger every 10 seconds, then it will trigger at
 exactly 10 second intervals. If, however, your program cannot keep up with

-the timer (ecause it takes longer than those 10 seconds to do stuff) the
+the timer (because it takes longer than those 10 seconds to do stuff) the

 timer will not fire more than once per event loop iteration.
 
 =item ev_timer_again (loop)
 timer will not fire more than once per event loop iteration.
 
 =item ev_timer_again (loop)


@@ -490,30 +734,65 @@ This sounds a bit complicated, but here is a useful and typical
 example: Imagine you have a tcp connection and you want a so-called idle
 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
 example: Imagine you have a tcp connection and you want a so-called idle
 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 ev_timer with after=repeat=60 and calling ev_timer_again each
+configure an C<ev_timer> with after=repeat=60 and calling 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 stop
 the timer, and again will automatically restart it if need be.
 
 =back
 
 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 stop
 the timer, and again will automatically restart it if need be.
 
 =back
 

-=head2 ev_periodic - to cron or not to cron it
+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 over, w is actually stopped right here
+  }
+
+  struct 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)
+  {
+    .. ten seconds without any activity
+  }
+
+  struct 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":
+  // reset the timeout to start ticking again at 10 seconds
+  ev_timer_again (&mytimer);
+
+
+=head2 C<ev_periodic> - to cron or not to cron

 
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 
 
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 

-Unlike ev_timer's, they are not based on real time (or relative time)
+Unlike C<ev_timer>'s, they are not based on real time (or relative time)

 but on wallclock time (absolute time). You can tell a periodic watcher
 to trigger "at" some specific point in time. For example, if you tell a
 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
 + 10.>) and then reset your system clock to the last year, then it will
 but on wallclock time (absolute time). You can tell a periodic watcher
 to trigger "at" some specific point in time. For example, if you tell a
 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
 + 10.>) and then reset your system clock to the last year, then it will

-take a year to trigger the event (unlike an ev_timer, which would trigger
+take a year to trigger the event (unlike an C<ev_timer>, which would trigger

 roughly 10 seconds later and of course not if you reset your system time
 again).
 
 They can also be used to implement vastly more complex timers, such as
 triggering an event on eahc midnight, local time.
 
 roughly 10 seconds later and of course not if you reset your system time
 again).
 
 They can also be used to implement vastly more complex timers, such as
 triggering an event on eahc midnight, local time.
 

+As with timers, the callback is guarenteed to be invoked only when the
+time (C<at>) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
+

 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)


@@ -523,7 +802,6 @@ triggering an event on eahc midnight, local time.
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 

-

 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)
 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)


@@ -546,11 +824,11 @@ time:
 
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a
 
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a

-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible

 by 3600.
 
 Another way to think about it (for the mathematically inclined) is that
 by 3600.
 
 Another way to think about it (for the mathematically inclined) is that

-ev_periodic will try to run the callback in this mode at the next possible
+C<ev_periodic> will try to run the callback in this mode at the next possible

 time where C<time = at (mod interval)>, regardless of any time jumps.
 
 =item * manual reschedule mode (reschedule_cb = callback)
 time where C<time = at (mod interval)>, regardless of any time jumps.
 
 =item * manual reschedule mode (reschedule_cb = callback)


@@ -560,11 +838,12 @@ ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 

-NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions>. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
+NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
+ever, or make any event loop modifications>. If you need to stop it,
+return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
+starting a prepare watcher).

 
 

-Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,

 ev_tstamp now)>, e.g.:
 
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
 ev_tstamp now)>, e.g.:
 
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)


@@ -577,10 +856,14 @@ It must return the next time to trigger, based on the passed time value
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 

+NOTE: I<< This callback must always return a time that is later than the
+passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
+

 This can be used to create very complex timers, such as a timer that
 triggers on each midnight, local time. To do this, you would calculate the
 This can be used to create very complex timers, such as a timer that
 triggers on each midnight, local time. To do this, you would calculate the

-next midnight after C<now> and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
+next midnight after C<now> and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).

 
 =back
 
 
 =back
 


@@ -593,14 +876,48 @@ program when the crontabs have changed).
 
 =back
 
 
 =back
 

-=head2 ev_signal - signal me when a signal gets signalled
+Example: call a callback every hour, or, more precisely, whenever the
+system clock is divisible by 3600. The callback invocation times have
+potentially a lot of jittering, but good long-term stability.
+
+  static void
+  clock_cb (struct ev_loop *loop, struct 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_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)
+  {
+    return fmod (now, 3600.) + 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_init (&hourly_tick, clock_cb,
+                    fmod (ev_now (loop), 3600.), 3600., 0);
+  ev_periodic_start (loop, &hourly_tick);
+  
+
+=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
 normal event processing, like any other event.
 
 
 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
 normal event processing, like any other event.
 

-You cna configure as many watchers as you like per signal. Only when the
+You can configure as many watchers as you like per signal. Only when the

 first watcher gets started will libev actually register a signal watcher
 with the kernel (thus it coexists with your own signal handlers as long
 as you don't register any with libev). Similarly, when the last signal
 first watcher gets started will libev actually register a signal watcher
 with the kernel (thus it coexists with your own signal handlers as long
 as you don't register any with libev). Similarly, when the last signal


@@ -618,7 +935,8 @@ of the C<SIGxxx> constants).
 
 =back
 
 
 =back
 

-=head2 ev_child - wait for pid status changes
+
+=head2 C<ev_child> - wait for pid status changes

 
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).
 
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).


@@ -632,18 +950,34 @@ some child status changes (most typically when a child of yours dies).
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see

-the status word (use the macros from C<sys/wait.h>). The C<rpid> member
-contains the pid of the process causing the status change.
+the status word (use the macros from C<sys/wait.h> and see your systems
+C<waitpid> documentation). The C<rpid> member contains the pid of the
+process causing the status change.

 
 =back
 
 
 =back
 

-=head2 ev_idle - when you've got nothing better to do
+Example: try to exit cleanly on SIGINT and SIGTERM.
+
+  static void
+  sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+  {
+    ev_unloop (loop, EVUNLOOP_ALL);
+  }
+
+  struct ev_signal signal_watcher;
+  ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
+  ev_signal_start (loop, &sigint_cb);

 
 

-Idle watchers trigger events when there are no other I/O or timer (or
-periodic) events pending. That is, as long as your process is busy
-handling sockets or timeouts it will not be called. But when your process
-is idle all idle watchers are being called again and again - until
-stopped, that is, or your process receives more events.
+
+=head2 C<ev_idle> - when you've got nothing better to do
+
+Idle watchers trigger events when there are no other events are pending
+(prepare, check and other idle watchers do not count). That is, as long
+as your process is busy handling sockets or timeouts (or even signals,
+imagine) it will not be triggered. But when your process is idle all idle
+watchers are being called again and again, once per event loop iteration -
+until stopped, that is, or your process receives more events and becomes
+busy.

 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.
 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.


@@ -663,27 +997,50 @@ believe me.
 
 =back
 
 
 =back
 

-=head2 prepare and check - your hooks into the event loop
+Example: dynamically allocate an C<ev_idle>, start it, and in the
+callback, free it. Alos, use no error checking, as usual.

 
 

-Prepare and check watchers usually (but not always) are used in
-tandom. Prepare watchers get invoked before the process blocks and check
-watchers afterwards.
+  static void
+  idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+  {
+    free (w);
+    // now do something you wanted to do when the program has
+    // no longer asnything immediate to do.
+  }

 
 

-Their main purpose is to integrate other event mechanisms into libev. This
-could be used, for example, to track variable changes, implement your own
-watchers, integrate net-snmp or a coroutine library and lots more.
+  struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+  ev_idle_init (idle_watcher, idle_cb);
+  ev_idle_start (loop, idle_cb);

 
 

-This is done by examining in each prepare call which file descriptors need
-to be watched by the other library, registering ev_io watchers for them
-and starting an ev_timer watcher for any timeouts (many libraries provide
-just this functionality). Then, in the check watcher you check for any
-events that occured (by making your callbacks set soem flags for example)
-and call back into the library.

 
 

-As another example, the perl Coro module uses these hooks to integrate
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop
+
+Prepare and check watchers are usually (but not always) used in tandem:
+prepare watchers get invoked before the process blocks and check watchers
+afterwards.
+
+Their main purpose is to integrate other event mechanisms into libev and
+their use is somewhat advanced. This could be used, for example, to track
+variable changes, implement your own watchers, integrate net-snmp or a
+coroutine library and lots more.
+
+This is done by examining in each prepare call which file descriptors need
+to be watched by the other library, registering C<ev_io> watchers for
+them and starting an C<ev_timer> watcher for any timeouts (many libraries
+provide just this functionality). Then, in the check watcher you check for
+any events that occured (by checking the pending status of all watchers
+and stopping them) and call back into the library. The I/O and timer
+callbacks will never actually be called (but must be valid nevertheless,
+because you never know, you know?).
+
+As another example, the Perl Coro module uses these hooks to integrate

 coroutines into libev programs, by yielding to other active coroutines
 during each prepare and only letting the process block if no coroutines
 coroutines into libev programs, by yielding to other active coroutines
 during each prepare and only letting the process block if no coroutines

-are ready to run.
+are ready to run (it's actually more complicated: it only runs coroutines
+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).

 
 =over 4
 
 
 =over 4
 


@@ -693,13 +1050,87 @@ are ready to run.
 
 Initialises and configures the prepare or check watcher - they have no
 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
 
 Initialises and configures the prepare or check watcher - they have no
 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>

-macros, but using them is utterly, utterly pointless.
+macros, but using them is utterly, utterly and completely pointless.
+
+=back
+
+Example: *TODO*.
+
+
+=head2 C<ev_embed> - when one backend isn't enough
+
+This is a rather advanced watcher type that lets you embed one event loop
+into another.
+
+There are primarily two reasons you would want that: work around bugs and
+prioritise I/O.
+
+As an example for a bug workaround, the kqueue backend might only support
+sockets on some platform, so it is unusable as generic backend, but you
+still want to make use of it because you have many sockets and it scales
+so nicely. In this case, you would create a kqueue-based loop and embed it
+into your default loop (which might use e.g. poll). Overall operation will
+be a bit slower because first libev has to poll and then call kevent, but
+at least you can use both at what they are best.
+
+As for prioritising I/O: rarely you have the case where some fds have
+to be watched and handled very quickly (with low latency), and even
+priorities and idle watchers might have too much overhead. In this case
+you would put all the high priority stuff in one loop and all the rest in
+a second one, and embed the second one in the first.
+
+As long as the watcher is started it will automatically handle events. The
+callback will be invoked whenever some events have been handled. You can
+set the callback to C<0> to avoid having to specify one if you are not
+interested in that.
+
+Also, there have not currently been made special provisions for forking:
+when you fork, you not only have to call C<ev_loop_fork> on both loops,
+but you will also have to stop and restart any C<ev_embed> watchers
+yourself.
+
+Unfortunately, not all backends are embeddable, only the ones returned by
+C<ev_embeddable_backends> are, which, unfortunately, does not include any
+portable one.
+
+So when you want to use this feature you will always have to be prepared
+that you cannot get an embeddable loop. The recommended way to get around
+this is to have a separate variables for your embeddable loop, try to
+create it, and if that fails, use the normal loop for everything:
+
+  struct ev_loop *loop_hi = ev_default_init (0);
+  struct ev_loop *loop_lo = 0;
+  struct 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 ())
+    : 0;
+
+  // if we got one, then embed it, otherwise default to loop_hi
+  if (loop_lo)
+    {
+      ev_embed_init (&embed, 0, loop_lo);
+      ev_embed_start (loop_hi, &embed);
+    }
+  else
+    loop_lo = loop_hi;
+
+=over 4
+
+=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)
+
+=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)
+
+Configures the watcher to embed the given loop, which must be embeddable.

 
 =back
 
 
 =back
 

+

 =head1 OTHER FUNCTIONS
 
 =head1 OTHER FUNCTIONS
 

-There are some other fucntions of possible interest. Described. Here. Now.
+There are some other functions of possible interest. Described. Here. Now.

 
 =over 4
 
 
 =over 4
 


@@ -708,40 +1139,43 @@ There are some other fucntions of possible interest. Described. Here. Now.
 This function combines a simple timer and an I/O watcher, calls your
 callback on whichever event happens first and automatically stop both
 watchers. This is useful if you want to wait for a single event on an fd
 This function combines a simple timer and an I/O watcher, calls your
 callback on whichever event happens first and automatically stop both
 watchers. This is useful if you want to wait for a single event on an fd

-or timeout without havign to allocate/configure/start/stop/free one or
+or timeout without having to allocate/configure/start/stop/free one or

 more watchers yourself.
 
 more watchers yourself.
 

-If C<fd> is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set
-will be craeted and started.
+If C<fd> is less than 0, then no I/O watcher will be started and events
+is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
+C<events> set will be craeted and started.

 
 If C<timeout> is less than 0, then no timeout watcher will be
 
 If C<timeout> is less than 0, then no timeout watcher will be

-started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat
-= 0) will be started.
+started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
+repeat = 0) will be started. While C<0> is a valid timeout, it is of
+dubious value.

 
 

-The callback has the type C<void (*cb)(int revents, void *arg)> and
-gets passed an events set (normally a combination of EV_ERROR, EV_READ,
-EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:
+The callback has the type C<void (*cb)(int revents, void *arg)> and gets
+passed an C<revents> set like normal event callbacks (a combination of
+C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
+value passed to C<ev_once>:

 
   static void stdin_ready (int revents, void *arg)
   {
     if (revents & EV_TIMEOUT)
 
   static void stdin_ready (int revents, void *arg)
   {
     if (revents & EV_TIMEOUT)

-      /* doh, nothing entered */
+      /* doh, nothing entered */;

     else if (revents & EV_READ)
     else if (revents & EV_READ)

-      /* stdin might have data for us, joy! */
+      /* stdin might have data for us, joy! */;

   }
 
   }
 

-  ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+  ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);

 
 =item ev_feed_event (loop, watcher, int events)
 
 Feeds the given event set into the event loop, as if the specified event
 
 =item ev_feed_event (loop, watcher, int events)
 
 Feeds the given event set into the event loop, as if the specified event

-has happened for the specified watcher (which must be a pointer to an
-initialised but not necessarily active event watcher).
+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 (loop, int fd, int revents)
 
 
 =item ev_feed_fd_event (loop, int fd, int revents)
 

-Feed an event on the given fd, as if a file descriptor backend detected it.
+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)
 
 
 =item ev_feed_signal_event (loop, int signum)
 


@@ -749,6 +1183,38 @@ Feed an event as if the given signal occured (loop must be the default loop!).
 
 =back
 
 
 =back
 

+
+=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 * 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 * Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).
+
+=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 * 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.
+
+=back
+
+=head1 C++ SUPPORT
+
+TBD.
+

 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.
 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.