X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/f2f56d433ed4bf97e96e4d1df5fb9f3795b768b3..ebc0759db57ff79951aa13a23c97c5846a78a67d:/ev.pod

diff --git a/ev.pod b/ev.pod
index be0128a..2fd1307 100644
--- a/ev.pod
+++ b/ev.pod
@@ -6,8 +6,54 @@ libev - a high performance full-featured event loop written in C
 
   #include <ev.h>
 
+=head1 EXAMPLE PROGRAM
+
+  #include <ev.h>
+
+  ev_io stdin_watcher;
+  ev_timer timeout_watcher;
+
+  /* called when data readable on stdin */
+  static void
+  stdin_cb (EV_P_ struct ev_io *w, int revents)
+  {
+    /* puts ("stdin ready"); */
+    ev_io_stop (EV_A_ w); /* just a syntax example */
+    ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
+  }
+
+  static void
+  timeout_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    /* puts ("timeout"); */
+    ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
+  }
+
+  int
+  main (void)
+  {
+    struct ev_loop *loop = ev_default_loop (0);
+
+    /* initialise an io watcher, then start it */
+    ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
+    ev_io_start (loop, &stdin_watcher);
+
+    /* simple non-repeating 5.5 second timeout */
+    ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+    ev_timer_start (loop, &timeout_watcher);
+
+    /* loop till timeout or data ready */
+    ev_loop (loop, 0);
+
+    return 0;
+  }
+
 =head1 DESCRIPTION
 
+The newest version of this document is also available as a html-formatted
+web page you might find easier to navigate when reading it for the first
+time: L<http://cvs.schmorp.de/libev/ev.html>.
+
 Libev is an event loop: you register interest in certain events (such as a
 file descriptor being readable or a timeout occuring), and it will manage
 these event sources and provide your program with events.
@@ -23,75 +69,166 @@ watcher.
 
 =head1 FEATURES
 
-Libev supports select, poll, the linux-specific epoll and the bsd-specific
-kqueue mechanisms for file descriptor events, relative timers, absolute
-timers with customised rescheduling, signal events, process status change
-events (related to SIGCHLD), and event watchers dealing with the event
-loop mechanism itself (idle, prepare and check watchers). It also is quite
-fast (see a L<http://libev.schmorp.de/bench.html|benchmark> comparing it
-to libevent).
+Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
+BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
+for file descriptor events (C<ev_io>), the Linux C<inotify> interface
+(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
+with customised rescheduling (C<ev_periodic>), synchronous signals
+(C<ev_signal>), process status change events (C<ev_child>), and event
+watchers dealing with the event loop mechanism itself (C<ev_idle>,
+C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
+file watchers (C<ev_stat>) and even limited support for fork events
+(C<ev_fork>).
+
+It also is quite fast (see this
+L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
+for example).
 
 =head1 CONVENTIONS
 
-Libev is very configurable. In this manual the default configuration
-will be described, which supports multiple event loops. For more info
-about various configuraiton options please have a look at the file
-F<README.embed> in the libev distribution. If libev was configured without
-support for multiple event loops, then all functions taking an initial
-argument of name C<loop> (which is always of type C<struct ev_loop *>)
-will not have this argument.
+Libev is very configurable. In this manual the default configuration will
+be described, which supports multiple event loops. For more info about
+various configuration options please have a look at B<EMBED> section in
+this manual. If libev was configured without support for multiple event
+loops, then all functions taking an initial argument of name C<loop>
+(which is always of type C<struct ev_loop *>) will not have 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
-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 some floatingpoint value. Unlike the name
+component C<stamp> might indicate, it is also used for time differences
+throughout libev.
+
+=head1 GLOBAL FUNCTIONS
+
+These functions can be called anytime, even before initialising the
+library in any way.
 
 =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_minor ()
 
-You can find out the major and minor version numbers of the library
+You can find out the major and minor ABI version numbers of the library
 you linked against by calling the functions C<ev_version_major> and
 C<ev_version_minor>. If you want, you can compare against the global
 symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
 version of the library your program was compiled against.
 
-Usually, its a good idea to terminate if the major versions mismatch,
-as this indicates an incompatible change.  Minor versions are usually
+These version numbers refer to the ABI version of the library, not the
+release version.
+
+Usually, it's a good idea to terminate if the major versions mismatch,
+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.
 
+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
-realloc function). It is used to allocate and free memory (no surprises
-here). If it returns zero when memory needs to be allocated, the library
-might abort or take some potentially destructive action. The default is
-your system realloc function.
+Sets the allocation function to use (the prototype is similar - the
+semantics is identical - to the realloc C function). It is used to
+allocate and free memory (no surprises here). If it returns zero when
+memory needs to be allocated, the library might abort or take some
+potentially destructive action. The default is your system realloc
+function.
 
 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.
 
+Example: Replace the libev allocator with one that waits a bit and then
+retries).
+
+   static void *
+   persistent_realloc (void *ptr, size_t 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
 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 sitution, no
-matter what, when it returns. That is, libev will geenrally retry the
+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).
 
+Example: This is basically the same thing that libev does internally, too.
+
+   static void
+   fatal_error (const char *msg)
+   {
+     perror (msg);
+     abort ();
+   }
+
+   ...
+   ev_set_syserr_cb (fatal_error);
+
 =back
 
 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
@@ -101,10 +238,11 @@ 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
-in your main thread (or in a separate thrad) and for each thread you
-create, you also create another event loop. Libev itself does no lockign
-whatsoever, so if you mix calls to different event loops, make sure you
-lock (this is usually a bad idea, though, even if done right).
+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
+done correctly, because it's hideous and inefficient).
 
 =over 4
 
@@ -113,49 +251,141 @@ lock (this is usually a bad idea, though, even if done right).
 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
-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
 
-=item EVFLAG_AUTO
+=item C<EVFLAG_AUTO>
 
-The default flags value. Use this if you have no clue (its the right
+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 then libev will I<not> look
-at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this
-environment variable will override the flags completely. This is useful
-to try out specific backends to tets their performance, or to work around
-bugs.
+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
+C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
+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.
 
-=item EVMETHOD_SELECT  portable select backend
+=item C<EVFLAG_FORKCHECK>
 
-=item EVMETHOD_POLL    poll backend (everywhere except windows)
+Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
 
-=item EVMETHOD_EPOLL   linux only
+This works by calling C<getpid ()> on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, C<getpid> is actually a simple 5-insn sequence
+without a syscall and thus I<very> fast, but my Linux system also has
+C<pthread_atfork> which is even faster).
 
-=item EVMETHOD_KQUEUE  some bsds only
+The big advantage of this flag is that you can forget about fork (and
+forget about forgetting to tell libev about forking) when you use this
+flag.
 
-=item EVMETHOD_DEVPOLL solaris 8 only
+This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
+environment variable.
 
-=item EVMETHOD_PORT    solaris 10 only
+=item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 
-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.
+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 C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)
+
+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 C<EVBACKEND_EPOLL>   (value 4, Linux)
+
+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).
+
+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 it's
+completely useless). For this reason it's 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
 
+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
@@ -163,11 +393,30 @@ 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).
 
+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
-etc.). This stops all registered event watchers (by not touching them in
-any way whatsoever, although you cnanot rely on this :).
+etc.). None of the active event watchers will be stopped in the normal
+sense, so e.g. C<ev_is_active> might still return true. It is your
+responsibility to either stop all watchers cleanly yoursef I<before>
+calling this function, or cope with the fact afterwards (which is usually
+the easiest thing, you can just ignore the watchers and/or C<free ()> them
+for example).
+
+Note that certain global state, such as signal state, will not be freed by
+this function, and related watchers (such as signal and child watchers)
+would need to be stopped manually.
+
+In general it is not advisable to call this function except in the
+rare occasion where you really need to free e.g. the signal handling
+pipe fds. If you need dynamically allocated loops it is better to use
+C<ev_loop_new> and C<ev_loop_destroy>).
 
 =item ev_loop_destroy (loop)
 
@@ -181,34 +430,48 @@ 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).
 
-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 its usually not a problem to call
+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
 quite nicely into a call to C<pthread_atfork>:
 
     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 unsigned int ev_method (loop)
+=item unsigned int ev_loop_count (loop)
+
+Returns the count of loop iterations for the loop, which is identical to
+the number of times libev did poll for new events. It starts at C<0> and
+happily wraps around with enough iterations.
+
+This value can sometimes be useful as a generation counter of sorts (it
+"ticks" the number of loop iterations), as it roughly corresponds with
+C<ev_prepare> and C<ev_check> calls.
+
+=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)
+=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)
 
@@ -216,49 +479,100 @@ 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.
 
-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
-case there are no events.
+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.
-
-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.
+your process until at least one new event arrives, and will return after
+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:
+
+   - Before the first iteration, call any pending watchers.
+   * If there are no active watchers (reference count is zero), return.
+   - Queue all 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. The C<how> argument
-must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>
-call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>
-calls return.
+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_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)
 
 =item ev_unref (loop)
 
-Ref/unref can be used to add or remove a refcount on the event loop: Every
-watcher keeps one reference. If you have a long-runing watcher you never
-unregister that should not keep ev_loop from running, ev_unref() after
-starting, and ev_ref() before stopping it. Libev itself uses this for
-example for its internal signal pipe: It is not visible to you as a user
-and should not keep C<ev_loop> from exiting if the work is done. It is
-also an excellent way to do this for generic recurring timers or from
-within third-party libraries. Just remember to unref after start and ref
-before stop.
+Ref/unref can be used to add or remove a reference count on the event
+loop: Every watcher keeps one reference, and as long as the reference
+count is nonzero, C<ev_loop> will not return on its own. If you have
+a watcher you never unregister that should not keep C<ev_loop> from
+returning, ev_unref() after starting, and ev_ref() before stopping it. For
+example, libev itself uses this for its internal signal pipe: It is not
+visible to the libev user and should not keep C<ev_loop> from exiting if
+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>.
+
+Example: Create a signal watcher, but keep it from keeping C<ev_loop>
+running when nothing else is active.
+
+  struct ev_signal exitsig;
+  ev_signal_init (&exitsig, sig_cb, SIGINT);
+  ev_signal_start (loop, &exitsig);
+  evf_unref (loop);
+
+Example: For some weird reason, unregister the above signal handler again.
+
+  ev_ref (loop);
+  ev_signal_stop (loop, &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
-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)
   {
@@ -295,63 +609,71 @@ 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
-reinitialise it or call its set method.
-
-You cna check whether an event is active by calling the C<ev_is_active
-(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
-(watcher *)> macro.
+reinitialise it or call its C<set> 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
 
-=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.
 
-=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_STAT>
 
-The ev_idle watcher has determined that you have nothing better to do.
+The path specified in the C<ev_stat> watcher changed its attributes somehow.
 
-=item EV_PREPARE
+=item C<EV_IDLE>
 
-=item EV_CHECK
+The C<ev_idle> watcher has determined that you have nothing better to do.
 
-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
+=item C<EV_PREPARE>
+
+=item C<EV_CHECK>
+
+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
-(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).
 
-=item EV_ERROR
+=item C<EV_EMBED>
+
+The embedded event loop specified in the C<ev_embed> watcher needs attention.
+
+=item C<EV_FORK>
+
+The event loop has been resumed in the child process after fork (see
+C<ev_fork>).
+
+=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
@@ -367,10 +689,130 @@ programs, though, so beware.
 
 =back
 
+=head2 GENERIC WATCHER FUNCTIONS
+
+In the following description, C<TYPE> stands for the watcher type,
+e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
+
+=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 (*)(ev_loop *loop, ev_TYPE *watcher,
+int revents)>.
+
+=item C<ev_TYPE_set> (ev_TYPE *, [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.
+
+=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
+
+This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
+calls into a single call. This is the most convinient method to initialise
+a watcher. The same limitations apply, of course.
+
+=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.
+
+=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
+
+Stops the given watcher again (if active) and clears the pending
+status. It is possible that stopped watchers are pending (for example,
+non-repeating timers are being stopped when they become pending), but
+C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
+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, 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).
+
+This means that priorities are I<only> used for ordering callback
+invocation after new events have been received. This is useful, for
+example, to reduce latency after idling, or more often, to bind two
+watchers on the same event and make sure one is called first.
+
+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.
+
+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 :).
+
+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 adjusted to be within valid range.
+
+=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.
+
+=item int ev_clear_pending (loop, ev_TYPE *watcher)
+
+If the watcher is pending, this function returns 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>.
+
+=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 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
@@ -393,22 +835,118 @@ can cast it back to your own type:
     ...
   }
 
-More interesting and less C-conformant ways of catsing your callback type
-have been omitted....
+More interesting and less C-conformant ways of casting your callback type
+instead have been omitted.
+
+Another common scenario is having some data structure with multiple
+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,
+you need to use C<offsetof>:
+
+  #include <stddef.h>
+
+  static void
+  t1_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t1));
+  }
+
+  static void
+  t2_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t2));
+  }
 
 
 =head1 WATCHER TYPES
 
 This section describes each watcher in detail, but will not repeat
-information given in the last section.
+information given in the last section. Any initialisation/set macros,
+functions and members specific to the watcher type are explained.
+
+Members are additionally marked with either I<[read-only]>, meaning that,
+while the watcher is active, you can look at the member and expect some
+sensible content, but you must not modify it (you can modify it while the
+watcher is stopped to your hearts content), or I<[read-write]>, which
+means you can expect it to have some sensible content while the watcher
+is active, but you can also modify it. Modifying it may not do something
+sensible or take immediate effect (or do anything at all), but libev will
+not crash or malfunction in any way.
+
 
-=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
-condition persists. Remember you cna stop the watcher if you don't want to
-act on the event and neither want to receive future events).
+in each iteration of the event loop, or, more precisely, when reading
+would not block the process and writing would at least be able to write
+some data. This behaviour is called level-triggering because you keep
+receiving events as long as the 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.
+
+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).
+
+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 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
+(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
+C<EVBACKEND_POLL>).
+
+Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness 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
+lot of those (for example solaris ports), it is very easy to get into
+this situation even with a relatively standard program structure. Thus
+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.
+
+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 seperately 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 does this on
+its own, so its quite safe to use).
+
+=head3 The special problem of disappearing file descriptors
+
+Some backends (e.g kqueue, epoll) need to be told about closing a file
+descriptor (either by calling C<close> explicitly or by any other means,
+such as C<dup>). The reason is that you register interest in some file
+descriptor, but when it goes away, the operating system will silently drop
+this interest. If another file descriptor with the same number then is
+registered with libev, there is no efficient way to see that this is, in
+fact, a different file descriptor.
+
+To avoid having to explicitly tell libev about such cases, libev follows
+the following policy:  Each time C<ev_io_set> is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
+descriptor even if the file descriptor number itself did not change.
+
+This is how one would do it normally anyway, the important point is that
+the libev application should not optimise around libev but should leave
+optimisations to libev.
+
+
+=head3 Watcher-Specific Functions
 
 =over 4
 
@@ -416,23 +954,64 @@ act on the event and neither want to receive future events).
 
 =item ev_io_set (ev_io *, int fd, int events)
 
-Configures an 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.
+Configures an C<ev_io> watcher. The C<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.
+
+=item int fd [read-only]
+
+The file descriptor being watched.
+
+=item int events [read-only]
+
+The events being watched.
 
 =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 repeating 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
-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
-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
+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.);
+
+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.
+
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
@@ -447,7 +1026,7 @@ 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 (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)
@@ -455,38 +1034,99 @@ timer will not fire more than once per event loop iteration.
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 
-If the timer is started but nonrepeating, stop it.
+If the timer is pending, its pending status is cleared.
+
+If the timer is started but nonrepeating, stop it (as if it timed out).
 
-If the timer is repeating, either start it if necessary (with the repeat
-value), or reset the running timer to the repeat value.
+If the timer is repeating, either start it if necessary (with the
+C<repeat> value), or reset the running timer to the C<repeat> value.
 
 This sounds a bit complicated, but here is a useful and typical
 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
-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.
+configure an C<ev_timer> with a C<repeat> value of C<60> and then call
+C<ev_timer_again> each time you successfully read or write some data. If
+you go into an idle state where you do not expect data to travel on the
+socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
+automatically restart it if need be.
+
+That means you can ignore the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>:
+
+   ev_timer_init (timer, callback, 0., 5.);
+   ev_timer_again (loop, timer);
+   ...
+   timer->again = 17.;
+   ev_timer_again (loop, timer);
+   ...
+   timer->again = 10.;
+   ev_timer_again (loop, timer);
+
+This is more slightly efficient then stopping/starting the timer each time
+you want to modify its timeout value.
+
+=item ev_tstamp repeat [read-write]
+
+The current C<repeat> value. Will be used each time the watcher times out
+or C<ev_timer_again> is called and determines the next timeout (if any),
+which is also when any modifications are taken into account.
 
 =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).
 
-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 ()
+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
-roughly 10 seconds later and of course not if you reset your system time
-again).
+take a year to trigger the event (unlike an C<ev_timer>, which would trigger
+roughly 10 seconds later).
 
 They can also be used to implement vastly more complex timers, such as
-triggering an event on eahc midnight, local time.
+triggering an event on each midnight, local time or other, complicated,
+rules.
+
+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.
+
+=head3 Watcher-Specific Functions and Data Members
 
 =over 4
 
@@ -497,21 +1137,20 @@ 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:
 
-
 =over 4
 
-=item * absolute timer (interval = reschedule_cb = 0)
+=item * absolute timer (at = time, interval = reschedule_cb = 0)
 
 In this configuration the watcher triggers an event at the wallclock time
 C<at> and doesn't repeat. It will not adjust when a time jump occurs,
 that is, if it is to be run at January 1st 2011 then it will run when the
 system time reaches or surpasses this time.
 
-=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)
+=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
 
 In this mode the watcher will always be scheduled to time out at the next
-C<at + N * interval> time (for some integer N) and then repeat, regardless
-of any time jumps.
+C<at + N * interval> time (for some integer N, which can also be negative)
+and then repeat, regardless of any time jumps.
 
 This can be used to create timers that do not drift with respect to system
 time:
@@ -520,25 +1159,30 @@ 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
-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
-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)
+For numerical stability it is preferable that the C<at> value is near
+C<ev_now ()> (the current time), but there is no range requirement for
+this value.
+
+=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
 
 In this mode the values for C<interval> and C<at> are both being
 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.
 
-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 an C<ev_prepare> watcher, which is legal).
 
-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)
@@ -551,10 +1195,14 @@ 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.
 
+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
-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
 
@@ -565,22 +1213,83 @@ when you changed some parameters or the reschedule callback would return
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
 
+=item ev_tstamp offset [read-write]
+
+When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the C<at> value passed to C<ev_periodic_set>).
+
+Can be modified any time, but changes only take effect when the periodic
+timer fires or C<ev_periodic_again> is being called.
+
+=item ev_tstamp interval [read-write]
+
+The current interval value. Can be modified any time, but changes only
+take effect when the periodic timer fires or C<ev_periodic_again> is being
+called.
+
+=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
+
+The current reschedule callback, or C<0>, if this functionality is
+switched off. Can be changed any time, but changes only take effect when
+the periodic timer fires or C<ev_periodic_again> is being called.
+
+=item ev_tstamp at [read-only]
+
+When active, contains the absolute time that the watcher is supposed to
+trigger next.
+
 =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 its best to deliver signals synchronously, i.e. as part of the
+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
 watcher for a signal is stopped libev will reset the signal handler to
 SIG_DFL (regardless of what it was set to before).
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_signal_init (ev_signal *, callback, int signum)
@@ -590,13 +1299,20 @@ SIG_DFL (regardless of what it was set to before).
 Configures the watcher to trigger on the given signal number (usually one
 of the C<SIGxxx> constants).
 
+=item int signum [read-only]
+
+The signal the watcher watches out for.
+
 =back
 
-=head2 ev_child - wait for pid status changes
+
+=head2 C<ev_child> - watch out for process 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).
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_child_init (ev_child *, callback, int pid)
@@ -606,123 +1322,1241 @@ 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
-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.
-
-=back
+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.
 
-=head2 ev_idle - when you've got nothing better to do
+=item int pid [read-only]
 
-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.
+The process id this watcher watches out for, or C<0>, meaning any process id.
 
-The most noteworthy effect is that as long as any idle watchers are
-active, the process will not block when waiting for new events.
-
-Apart from keeping your process non-blocking (which is a useful
-effect on its own sometimes), idle watchers are a good place to do
-"pseudo-background processing", or delay processing stuff to after the
-event loop has handled all outstanding events.
+=item int rpid [read-write]
 
-=over 4
+The process id that detected a status change.
 
-=item ev_idle_init (ev_signal *, callback)
+=item int rstatus [read-write]
 
-Initialises and configures the idle watcher - it has no parameters of any
-kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
-believe me.
+The process exit/trace status caused by C<rpid> (see your systems
+C<waitpid> and C<sys/wait.h> documentation for details).
 
 =back
 
-=head2 prepare and check - your hooks into the event loop
+Example: Try to exit cleanly on SIGINT and SIGTERM.
 
-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
+  sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+  {
+    ev_unloop (loop, EVUNLOOP_ALL);
+  }
 
-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_signal signal_watcher;
+  ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
+  ev_signal_start (loop, &sigint_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
-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.
+=head2 C<ev_stat> - did the file attributes just change?
 
-=over 4
+This watches a filesystem path for attribute changes. That is, it calls
+C<stat> regularly (or when the OS says it changed) and sees if it changed
+compared to the last time, invoking the callback if it did.
 
-=item ev_prepare_init (ev_prepare *, callback)
+The path does not need to exist: changing from "path exists" to "path does
+not exist" is a status change like any other. The condition "path does
+not exist" is signified by the C<st_nlink> field being zero (which is
+otherwise always forced to be at least one) and all the other fields of
+the stat buffer having unspecified contents.
 
-=item ev_check_init (ev_check *, callback)
+The path I<should> be absolute and I<must not> end in a slash. If it is
+relative and your working directory changes, the behaviour is undefined.
 
-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.
+Since there is no standard to do this, the portable implementation simply
+calls C<stat (2)> regularly on the path to see if it changed somehow. You
+can specify a recommended polling interval for this case. If you specify
+a polling interval of C<0> (highly recommended!) then a I<suitable,
+unspecified default> value will be used (which you can expect to be around
+five seconds, although this might change dynamically). Libev will also
+impose a minimum interval which is currently around C<0.1>, but thats
+usually overkill.
 
-=back
+This watcher type is not meant for massive numbers of stat watchers,
+as even with OS-supported change notifications, this can be
+resource-intensive.
 
-=head1 OTHER FUNCTIONS
+At the time of this writing, only the Linux inotify interface is
+implemented (implementing kqueue support is left as an exercise for the
+reader). Inotify will be used to give hints only and should not change the
+semantics of C<ev_stat> watchers, which means that libev sometimes needs
+to fall back to regular polling again even with inotify, but changes are
+usually detected immediately, and if the file exists there will be no
+polling.
 
-There are some other fucntions of possible interest. Described. Here. Now.
+=head3 Watcher-Specific Functions and Data Members
 
 =over 4
 
-=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
+=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
 
-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
-more watchers yourself.
+=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
 
-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.
+Configures the watcher to wait for status changes of the given
+C<path>. The C<interval> is a hint on how quickly a change is expected to
+be detected and should normally be specified as C<0> to let libev choose
+a suitable value. The memory pointed to by C<path> must point to the same
+path for as long as the watcher is active.
 
-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.
+The callback will be receive C<EV_STAT> when a change was detected,
+relative to the attributes at the time the watcher was started (or the
+last change was detected).
 
-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>:
+=item ev_stat_stat (ev_stat *)
 
-  static void stdin_ready (int revents, void *arg)
-  {
-    if (revents & EV_TIMEOUT)
-      /* doh, nothing entered */
-    else if (revents & EV_READ)
-      /* stdin might have data for us, joy! */
-  }
+Updates the stat buffer immediately with new values. If you change the
+watched path in your callback, you could call this fucntion to avoid
+detecting this change (while introducing a race condition). Can also be
+useful simply to find out the new values.
 
-  ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+=item ev_statdata attr [read-only]
 
-=item ev_feed_event (loop, watcher, int events)
+The most-recently detected attributes of the file. Although the type is of
+C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
+suitable for your system. If the C<st_nlink> member is C<0>, then there
+was some error while C<stat>ing the file.
 
-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).
+=item ev_statdata prev [read-only]
+
+The previous attributes of the file. The callback gets invoked whenever
+C<prev> != C<attr>.
 
-=item ev_feed_fd_event (loop, int fd, int revents)
+=item ev_tstamp interval [read-only]
 
-Feed an event on the given fd, as if a file descriptor backend detected it.
+The specified interval.
 
-=item ev_feed_signal_event (loop, int signum)
+=item const char *path [read-only]
 
-Feed an event as if the given signal occured (loop must be the default loop!).
+The filesystem path that is being watched.
 
 =back
 
+Example: Watch C</etc/passwd> for attribute changes.
+
+  static void
+  passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
+  {
+    /* /etc/passwd changed in some way */
+    if (w->attr.st_nlink)
+      {
+        printf ("passwd current size  %ld\n", (long)w->attr.st_size);
+        printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
+        printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
+      }
+    else
+      /* you shalt not abuse printf for puts */
+      puts ("wow, /etc/passwd is not there, expect problems. "
+            "if this is windows, they already arrived\n");
+  }
+
+  ...
+  ev_stat passwd;
+
+  ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
+  ev_stat_start (loop, &passwd);
+
+
+=head2 C<ev_idle> - when you've got nothing better to do...
+
+Idle watchers trigger events when no other events of the same or higher
+priority 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) of the same or higher priority it will not be
+triggered. But when your process is idle (or only lower-priority watchers
+are pending), the idle watchers are being called once per event loop
+iteration - until stopped, that is, or your process receives more events
+and becomes busy again with higher priority stuff.
+
+The most noteworthy effect is that as long as any idle watchers are
+active, the process will not block when waiting for new events.
+
+Apart from keeping your process non-blocking (which is a useful
+effect on its own sometimes), idle watchers are a good place to do
+"pseudo-background processing", or delay processing stuff to after the
+event loop has handled all outstanding events.
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_idle_init (ev_signal *, callback)
+
+Initialises and configures the idle watcher - it has no parameters of any
+kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
+believe me.
+
+=back
+
+Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
+callback, free it. Also, use no error checking, as usual.
+
+  static void
+  idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+  {
+    free (w);
+    // now do something you wanted to do when the program has
+    // no longer asnything immediate to do.
+  }
+
+  struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+  ev_idle_init (idle_watcher, idle_cb);
+  ev_idle_start (loop, idle_cb);
+
+
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
+
+Prepare and check watchers are usually (but not always) used in tandem:
+prepare watchers get invoked before the process blocks and check watchers
+afterwards.
+
+You I<must not> call C<ev_loop> or similar functions that enter
+the current event loop from either C<ev_prepare> or C<ev_check>
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
+C<ev_check> so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.
+
+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. They are also occasionally useful if
+you cache some data and want to flush it before blocking (for example,
+in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
+watcher).
+
+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
+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).
+
+It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
+too) should not activate ("feed") events into libev. While libev fully
+supports this, they will be called before other C<ev_check> watchers did
+their job. As C<ev_check> watchers are often used to embed other event
+loops those other event loops might be in an unusable state until their
+C<ev_check> watcher ran (always remind yourself to coexist peacefully with
+others).
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_prepare_init (ev_prepare *, callback)
+
+=item ev_check_init (ev_check *, callback)
+
+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 and completely pointless.
+
+=back
+
+There are a number of principal ways to embed other event loops or modules
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named C<EV::ADNS> that does this, which you could
+use for an actually working example. Another Perl module named C<EV::Glib>
+embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
+into the Glib event loop).
+
+Method 1: Add IO watchers and a timeout watcher in a prepare handler,
+and in a check watcher, destroy them and call into libadns. What follows
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use C<ev_clear_pending> explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
+
+  static ev_io iow [nfd];
+  static ev_timer tw;
+
+  static void
+  io_cb (ev_loop *loop, ev_io *w, int revents)
+  {
+  }
+
+  // create io watchers for each fd and a timer before blocking
+  static void
+  adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+  {
+    int timeout = 3600000;
+    struct pollfd fds [nfd];
+    // actual code will need to loop here and realloc etc.
+    adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+    /* the callback is illegal, but won't be called as we stop during check */
+    ev_timer_init (&tw, 0, timeout * 1e-3);
+    ev_timer_start (loop, &tw);
+
+    // create one ev_io per pollfd
+    for (int i = 0; i < nfd; ++i)
+      {
+        ev_io_init (iow + i, io_cb, fds [i].fd,
+          ((fds [i].events & POLLIN ? EV_READ : 0)
+           | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+        fds [i].revents = 0;
+        ev_io_start (loop, iow + i);
+      }
+  }
+
+  // stop all watchers after blocking
+  static void
+  adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+  {
+    ev_timer_stop (loop, &tw);
+
+    for (int i = 0; i < nfd; ++i)
+      {
+        // set the relevant poll flags
+        // could also call adns_processreadable etc. here
+        struct pollfd *fd = fds + i;
+        int revents = ev_clear_pending (iow + i);
+        if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+        if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+
+        // now stop the watcher
+        ev_io_stop (loop, iow + i);
+      }
+
+    adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+  }
+
+Method 2: This would be just like method 1, but you run C<adns_afterpoll>
+in the prepare watcher and would dispose of the check watcher.
+
+Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.
+
+  static void
+  timer_cb (EV_P_ ev_timer *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    adns_processtimeouts (ads, &tv_now);
+  }
+
+  static void
+  io_cb (EV_P_ ev_io *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    if (revents & EV_READ ) adns_processreadable  (ads, w->fd, &tv_now);
+    if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+  }
+
+  // do not ever call adns_afterpoll
+
+Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function.  The drawback with this solution is that the main
+loop is now no longer controllable by EV. The C<Glib::EV> module does
+this.
+
+  static gint
+  event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+  {
+    int got_events = 0;
+
+    for (n = 0; n < nfds; ++n)
+      // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+
+    if (timeout >= 0)
+      // create/start timer
+
+    // poll
+    ev_loop (EV_A_ 0);
+
+    // stop timer again
+    if (timeout >= 0)
+      ev_timer_stop (EV_A_ &to);
+
+    // stop io watchers again - their callbacks should have set
+    for (n = 0; n < nfds; ++n)
+      ev_io_stop (EV_A_ iow [n]);
+
+    return got_events;
+  }
+
+
+=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 (currently only C<ev_io> events are supported in the embedded
+loop, other types of watchers might be handled in a delayed or incorrect
+fashion and must not be used).
+
+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 active, the callback will be invoked every time
+there might be events pending in the embedded loop. The callback must then
+call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
+their callbacks (you could also start an idle watcher to give the embedded
+loop strictly lower priority for example). You can also set the callback
+to C<0>, in which case the embed watcher will automatically execute the
+embedded loop sweep.
+
+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;
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
+
+=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
+
+Configures the watcher to embed the given loop, which must be
+embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
+invoked automatically, otherwise it is the responsibility of the callback
+to invoke it (it will continue to be called until the sweep has been done,
+if you do not want thta, you need to temporarily stop the embed watcher).
+
+=item ev_embed_sweep (loop, ev_embed *)
+
+Make a single, non-blocking sweep over the embedded loop. This works
+similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
+apropriate way for embedded loops.
+
+=item struct ev_loop *other [read-only]
+
+The embedded event loop.
+
+=back
+
+
+=head2 C<ev_fork> - the audacity to resume the event loop after a fork
+
+Fork watchers are called when a C<fork ()> was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
+event loop blocks next and before C<ev_check> watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+C<ev_default_fork> cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_fork_init (ev_signal *, 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.
+
+=back
+
+
+=head1 OTHER FUNCTIONS
+
+There are some other functions of possible interest. Described. Here. Now.
+
+=over 4
+
+=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
+
+This function combines a simple timer and an I/O watcher, calls your
+callback on whichever event happens first and automatically stop both
+watchers. This is useful if you want to wait for a single event on an fd
+or timeout without having to allocate/configure/start/stop/free one or
+more watchers yourself.
+
+If C<fd> is less than 0, then no I/O watcher will be started and events
+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
+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 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)
+      /* doh, nothing entered */;
+    else if (revents & EV_READ)
+      /* stdin might have data for us, joy! */;
+  }
+
+  ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
+
+=item ev_feed_event (ev_loop *, watcher *, int revents)
+
+Feeds the given event set into the event loop, as if the specified event
+had happened for the specified watcher (which must be a pointer to an
+initialised but not necessarily started event watcher).
+
+=item ev_feed_fd_event (ev_loop *, int fd, int revents)
+
+Feed an event on the given fd, as if a file descriptor backend detected
+the given events it.
+
+=item ev_feed_signal_event (ev_loop *loop, int signum)
+
+Feed an event as if the given signal occured (C<loop> must be the default
+loop!).
+
+=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
+
+Libev comes with some simplistic wrapper classes for C++ that mainly allow
+you to use some convinience methods to start/stop watchers and also change
+the callback model to a model using method callbacks on objects.
+
+To use it,
+   
+  #include <ev++.h>
+
+This automatically includes F<ev.h> and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the C<ev> namespace. It should support all the same embedding
+options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
+
+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
+used as callbacks. Other types should be easy to add as long as they only
+need one additional pointer for context. If you need support for other
+types of functors please contact the author (preferably after implementing
+it).
+
+Here is a list of things available in the C<ev> namespace:
+
+=over 4
+
+=item C<ev::READ>, C<ev::WRITE> etc.
+
+These are just enum values with the same values as the C<EV_READ> etc.
+macros from F<ev.h>.
+
+=item C<ev::tstamp>, C<ev::now>
+
+Aliases to the same types/functions as with the C<ev_> prefix.
+
+=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
+
+For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
+the same name in the C<ev> namespace, with the exception of C<ev_signal>
+which is called C<ev::sig> to avoid clashes with the C<signal> macro
+defines by many implementations.
+
+All of those classes have these methods:
+
+=over 4
+
+=item ev::TYPE::TYPE ()
+
+=item ev::TYPE::TYPE (struct ev_loop *)
+
+=item ev::TYPE::~TYPE
+
+The constructor (optionally) takes an event loop to associate the watcher
+with. If it is omitted, it will use C<EV_DEFAULT>.
+
+The constructor calls C<ev_init> for you, which means you have to call the
+C<set> method before starting it.
+
+It will not set a callback, however: You have to call the templated C<set>
+method to set a callback before you can start the watcher.
+
+(The reason why you have to use a method is a limitation in C++ which does
+not allow explicit template arguments for constructors).
+
+The destructor automatically stops the watcher if it is active.
+
+=item w->set<class, &class::method> (object *)
+
+This method sets the callback method to call. The method has to have a
+signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
+first argument and the C<revents> as second. The object must be given as
+parameter and is stored in the C<data> member of the watcher.
+
+This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the C<set> call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.
+
+Example: simple class declaration and watcher initialisation
+
+  struct myclass
+  {
+    void io_cb (ev::io &w, int revents) { }
+  }
+
+  myclass obj;
+  ev::io iow;
+  iow.set <myclass, &myclass::io_cb> (&obj);
+
+=item w->set<function> (void *data = 0)
+
+Also sets a callback, but uses a static method or plain function as
+callback. The optional C<data> argument will be stored in the watcher's
+C<data> member and is free for you to use.
+
+The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
+
+See the method-C<set> above for more details.
+
+Example:
+
+  static void io_cb (ev::io &w, int revents) { }
+  iow.set <io_cb> ();
+
+=item w->set (struct ev_loop *)
+
+Associates a different C<struct ev_loop> with this watcher. You can only
+do this when the watcher is inactive (and not pending either).
+
+=item w->set ([args])
+
+Basically the same as C<ev_TYPE_set>, with the same args. Must be
+called at least once. Unlike the C counterpart, an active watcher gets
+automatically stopped and restarted when reconfiguring it with this
+method.
+
+=item w->start ()
+
+Starts the watcher. Note that there is no C<loop> argument, as the
+constructor already stores the event loop.
+
+=item w->stop ()
+
+Stops the watcher if it is active. Again, no C<loop> argument.
+
+=item w->again () (C<ev::timer>, C<ev::periodic> only)
+
+For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
+C<ev_TYPE_again> function.
+
+=item w->sweep () (C<ev::embed> only)
+
+Invokes C<ev_embed_sweep>.
+
+=item w->update () (C<ev::stat> only)
+
+Invokes C<ev_stat_stat>.
+
+=back
+
+=back
+
+Example: Define a class with an IO and idle watcher, start one of them in
+the constructor.
+
+  class myclass
+  {
+    ev_io   io;   void io_cb   (ev::io   &w, int revents);
+    ev_idle idle  void idle_cb (ev::idle &w, int revents);
+
+    myclass ();
+  }
+
+  myclass::myclass (int fd)
+  {
+    io  .set <myclass, &myclass::io_cb  > (this);
+    idle.set <myclass, &myclass::idle_cb> (this);
+
+    io.start (fd, ev::READ);
+  }
+
+
+=head1 MACRO MAGIC
+
+Libev can be compiled with a variety of options, the most fundamantal
+of which is C<EV_MULTIPLICITY>. This option determines whether (most)
+functions and callbacks have an initial C<struct ev_loop *> argument.
+
+To make it easier to write programs that cope with either variant, the
+following macros are defined:
+
+=over 4
+
+=item C<EV_A>, C<EV_A_>
+
+This provides the loop I<argument> for functions, if one is required ("ev
+loop argument"). The C<EV_A> form is used when this is the sole argument,
+C<EV_A_> is used when other arguments are following. Example:
+
+  ev_unref (EV_A);
+  ev_timer_add (EV_A_ watcher);
+  ev_loop (EV_A_ 0);
+
+It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
+which is often provided by the following macro.
+
+=item C<EV_P>, C<EV_P_>
+
+This provides the loop I<parameter> for functions, if one is required ("ev
+loop parameter"). The C<EV_P> form is used when this is the sole parameter,
+C<EV_P_> is used when other parameters are following. Example:
+
+  // this is how ev_unref is being declared
+  static void ev_unref (EV_P);
+
+  // this is how you can declare your typical callback
+  static void cb (EV_P_ ev_timer *w, int revents)
+
+It declares a parameter C<loop> of type C<struct ev_loop *>, quite
+suitable for use with C<EV_A>.
+
+=item C<EV_DEFAULT>, C<EV_DEFAULT_>
+
+Similar to the other two macros, this gives you the value of the default
+loop, if multiple loops are supported ("ev loop default").
+
+=back
+
+Example: Declare and initialise a check watcher, utilising the above
+macros so it will work regardless of whether multiple loops are supported
+or not.
+
+  static void
+  check_cb (EV_P_ ev_timer *w, int revents)
+  {
+    ev_check_stop (EV_A_ w);
+  }
+
+  ev_check check;
+  ev_check_init (&check, check_cb);
+  ev_check_start (EV_DEFAULT_ &check);
+  ev_loop (EV_DEFAULT_ 0);
+
+=head1 EMBEDDING
+
+Libev can (and often is) directly embedded into host
+applications. Examples of applications that embed it include the Deliantra
+Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
+and rxvt-unicode.
+
+The goal is to enable you to just copy the necessary files into your
+source directory without having to change even a single line in them, so
+you can easily upgrade by simply copying (or having a checked-out copy of
+libev somewhere in your source tree).
+
+=head2 FILESETS
+
+Depending on what features you need you need to include one or more sets of files
+in your app.
+
+=head3 CORE EVENT LOOP
+
+To include only the libev core (all the C<ev_*> functions), with manual
+configuration (no autoconf):
+
+  #define EV_STANDALONE 1
+  #include "ev.c"
+
+This will automatically include F<ev.h>, too, and should be done in a
+single C source file only to provide the function implementations. To use
+it, do the same for F<ev.h> in all files wishing to use this API (best
+done by writing a wrapper around F<ev.h> that you can include instead and
+where you can put other configuration options):
+
+  #define EV_STANDALONE 1
+  #include "ev.h"
+
+Both header files and implementation files can be compiled with a C++
+compiler (at least, thats a stated goal, and breakage will be treated
+as a bug).
+
+You need the following files in your source tree, or in a directory
+in your include path (e.g. in libev/ when using -Ilibev):
+
+  ev.h
+  ev.c
+  ev_vars.h
+  ev_wrap.h
+
+  ev_win32.c      required on win32 platforms only
+
+  ev_select.c     only when select backend is enabled (which is enabled by default)
+  ev_poll.c       only when poll backend is enabled (disabled by default)
+  ev_epoll.c      only when the epoll backend is enabled (disabled by default)
+  ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
+  ev_port.c       only when the solaris port backend is enabled (disabled by default)
+
+F<ev.c> includes the backend files directly when enabled, so you only need
+to compile this single file.
+
+=head3 LIBEVENT COMPATIBILITY API
+
+To include the libevent compatibility API, also include:
+
+  #include "event.c"
+
+in the file including F<ev.c>, and:
+
+  #include "event.h"
+
+in the files that want to use the libevent API. This also includes F<ev.h>.
+
+You need the following additional files for this:
+
+  event.h
+  event.c
+
+=head3 AUTOCONF SUPPORT
+
+Instead of using C<EV_STANDALONE=1> and providing your config in
+whatever way you want, you can also C<m4_include([libev.m4])> in your
+F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
+include F<config.h> and configure itself accordingly.
+
+For this of course you need the m4 file:
+
+  libev.m4
+
+=head2 PREPROCESSOR SYMBOLS/MACROS
+
+Libev can be configured via a variety of preprocessor symbols you have to define
+before including any of its files. The default is not to build for multiplicity
+and only include the select backend.
+
+=over 4
+
+=item EV_STANDALONE
+
+Must always be C<1> if you do not use autoconf configuration, which
+keeps libev from including F<config.h>, and it also defines dummy
+implementations for some libevent functions (such as logging, which is not
+supported). It will also not define any of the structs usually found in
+F<event.h> that are not directly supported by the libev core alone.
+
+=item EV_USE_MONOTONIC
+
+If defined to be C<1>, libev will try to detect the availability of the
+monotonic clock option at both compiletime and runtime. Otherwise no use
+of the monotonic clock option will be attempted. If you enable this, you
+usually have to link against librt or something similar. Enabling it when
+the functionality isn't available is safe, though, althoguh you have
+to make sure you link against any libraries where the C<clock_gettime>
+function is hiding in (often F<-lrt>).
+
+=item EV_USE_REALTIME
+
+If defined to be C<1>, libev will try to detect the availability of the
+realtime clock option at compiletime (and assume its availability at
+runtime if successful). Otherwise no use of the realtime clock option will
+be attempted. This effectively replaces C<gettimeofday> by C<clock_get
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
+note about libraries in the description of C<EV_USE_MONOTONIC>, though.
+
+=item EV_USE_SELECT
+
+If undefined or defined to be C<1>, libev will compile in support for the
+C<select>(2) backend. No attempt at autodetection will be done: if no
+other method takes over, select will be it. Otherwise the select backend
+will not be compiled in.
+
+=item EV_SELECT_USE_FD_SET
+
+If defined to C<1>, then the select backend will use the system C<fd_set>
+structure. This is useful if libev doesn't compile due to a missing
+C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
+exotic systems. This usually limits the range of file descriptors to some
+low limit such as 1024 or might have other limitations (winsocket only
+allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
+influence the size of the C<fd_set> used.
+
+=item EV_SELECT_IS_WINSOCKET
+
+When defined to C<1>, the select backend will assume that
+select/socket/connect etc. don't understand file descriptors but
+wants osf handles on win32 (this is the case when the select to
+be used is the winsock select). This means that it will call
+C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
+it is assumed that all these functions actually work on fds, even
+on win32. Should not be defined on non-win32 platforms.
+
+=item EV_USE_POLL
+
+If defined to be C<1>, libev will compile in support for the C<poll>(2)
+backend. Otherwise it will be enabled on non-win32 platforms. It
+takes precedence over select.
+
+=item EV_USE_EPOLL
+
+If defined to be C<1>, libev will compile in support for the Linux
+C<epoll>(7) backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the
+preferred backend for GNU/Linux systems.
+
+=item EV_USE_KQUEUE
+
+If defined to be C<1>, libev will compile in support for the BSD style
+C<kqueue>(2) backend. Its actual availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for BSD and BSD-like systems, although on most BSDs kqueue only
+supports some types of fds correctly (the only platform we found that
+supports ptys for example was NetBSD), so kqueue might be compiled in, but
+not be used unless explicitly requested. The best way to use it is to find
+out whether kqueue supports your type of fd properly and use an embedded
+kqueue loop.
+
+=item EV_USE_PORT
+
+If defined to be C<1>, libev will compile in support for the Solaris
+10 port style backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for Solaris 10 systems.
+
+=item EV_USE_DEVPOLL
+
+reserved for future expansion, works like the USE symbols above.
+
+=item EV_USE_INOTIFY
+
+If defined to be C<1>, libev will compile in support for the Linux inotify
+interface to speed up C<ev_stat> watchers. Its actual availability will
+be detected at runtime.
+
+=item EV_H
+
+The name of the F<ev.h> header file used to include it. The default if
+undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
+can be used to virtually rename the F<ev.h> header file in case of conflicts.
+
+=item EV_CONFIG_H
+
+If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
+F<ev.c>'s idea of where to find the F<config.h> file, similarly to
+C<EV_H>, above.
+
+=item EV_EVENT_H
+
+Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
+of how the F<event.h> header can be found.
+
+=item EV_PROTOTYPES
+
+If defined to be C<0>, then F<ev.h> will not define any function
+prototypes, but still define all the structs and other symbols. This is
+occasionally useful if you want to provide your own wrapper functions
+around libev functions.
+
+=item EV_MULTIPLICITY
+
+If undefined or defined to C<1>, then all event-loop-specific functions
+will have the C<struct ev_loop *> as first argument, and you can create
+additional independent event loops. Otherwise there will be no support
+for multiple event loops and there is no first event loop pointer
+argument. Instead, all functions act on the single default loop.
+
+=item EV_MINPRI
+
+=item EV_MAXPRI
+
+The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
+C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be C<-2> and C<2>, respectively).
+
+When doing priority-based operations, libev usually has to linearly search
+all the priorities, so having many of them (hundreds) uses a lot of space
+and time, so using the defaults of five priorities (-2 .. +2) is usually
+fine.
+
+If your embedding app does not need any priorities, defining these both to
+C<0> will save some memory and cpu.
+
+=item EV_PERIODIC_ENABLE
+
+If undefined or defined to be C<1>, then periodic timers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_IDLE_ENABLE
+
+If undefined or defined to be C<1>, then idle watchers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_EMBED_ENABLE
+
+If undefined or defined to be C<1>, then embed watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_STAT_ENABLE
+
+If undefined or defined to be C<1>, then stat watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_FORK_ENABLE
+
+If undefined or defined to be C<1>, then fork watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_MINIMAL
+
+If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to C<1>. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.
+
+=item EV_PID_HASHSIZE
+
+C<ev_child> watchers use a small hash table to distribute workload by
+pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
+than enough. If you need to manage thousands of children you might want to
+increase this value (I<must> be a power of two).
+
+=item EV_INOTIFY_HASHSIZE
+
+C<ev_staz> watchers use a small hash table to distribute workload by
+inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
+usually more than enough. If you need to manage thousands of C<ev_stat>
+watchers you might want to increase this value (I<must> be a power of
+two).
+
+=item EV_COMMON
+
+By default, all watchers have a C<void *data> member. By redefining
+this macro to a something else you can include more and other types of
+members. You have to define it each time you include one of the files,
+though, and it must be identical each time.
+
+For example, the perl EV module uses something like this:
+
+  #define EV_COMMON                       \
+    SV *self; /* contains this struct */  \
+    SV *cb_sv, *fh /* note no trailing ";" */
+
+=item EV_CB_DECLARE (type)
+
+=item EV_CB_INVOKE (watcher, revents)
+
+=item ev_set_cb (ev, cb)
+
+Can be used to change the callback member declaration in each watcher,
+and the way callbacks are invoked and set. Must expand to a struct member
+definition and a statement, respectively. See the F<ev.v> header file for
+their default definitions. One possible use for overriding these is to
+avoid the C<struct ev_loop *> as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
+
+=head2 EXPORTED API SYMBOLS
+
+If you need to re-export the API (e.g. via a dll) and you need a list of
+exported symbols, you can use the provided F<Symbol.*> files which list
+all public symbols, one per line:
+
+  Symbols.ev      for libev proper
+  Symbols.event   for the libevent emulation
+
+This can also be used to rename all public symbols to avoid clashes with
+multiple versions of libev linked together (which is obviously bad in
+itself, but sometimes it is inconvinient to avoid this).
+
+A sed comamnd like this will create wrapper C<#define>'s that you need to
+include before including F<ev.h>:
+
+   <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
+
+This would create a file F<wrap.h> which essentially looks like this:
+
+   #define ev_backend     myprefix_ev_backend
+   #define ev_check_start myprefix_ev_check_start
+   #define ev_check_stop  myprefix_ev_check_stop
+   ...
+
+=head2 EXAMPLES
+
+For a real-world example of a program the includes libev
+verbatim, you can have a look at the EV perl module
+(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
+the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
+interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
+will be compiled. It is pretty complex because it provides its own header
+file.
+
+The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
+that everybody includes and which overrides some configure choices:
+
+  #define EV_MINIMAL 1
+  #define EV_USE_POLL 0
+  #define EV_MULTIPLICITY 0
+  #define EV_PERIODIC_ENABLE 0
+  #define EV_STAT_ENABLE 0
+  #define EV_FORK_ENABLE 0
+  #define EV_CONFIG_H <config.h>
+  #define EV_MINPRI 0
+  #define EV_MAXPRI 0
+
+  #include "ev++.h"
+
+And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
+
+  #include "ev_cpp.h"
+  #include "ev.c"
+
+
+=head1 COMPLEXITIES
+
+In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for C<ev_default_init>.
+
+All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
+
+=over 4
+
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+
+This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.
+
+=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+
+That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.
+
+=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+
+These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)
+
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+
+These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).
+
+=item Finding the next timer per loop iteration: O(1)
+
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+
+A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
+
+=item Activating one watcher: O(1)
+
+=item Priority handling: O(number_of_priorities)
+
+Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
+
+=back
+
+
 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.