+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.
+
+=item ev_statdata attr [read-only]
+
+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.
+
+=item ev_statdata prev [read-only]
+
+The previous attributes of the file. The callback gets invoked whenever
+C<prev> != C<attr>.
+
+=item ev_tstamp interval [read-only]
+
+The specified interval.
+
+=item const char *path [read-only]
+
+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). (See portability notes, below).
+
+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;
+
+=head2 Portability notes
+
+Kqueue is nominally embeddable, but this is broken on all BSDs that I
+tried, in various ways. Usually the embedded event loop will simply never
+receive events, sometimes it will only trigger a few times, sometimes in a
+loop. Epoll is also nominally embeddable, but many Linux kernel versions
+will always eport the epoll fd as ready, even when no events are pending.
+
+While libev allows embedding these backends (they are contained in
+C<ev_embeddable_backends ()>), take extreme care that it will actually
+work.
+
+When in doubt, create a dynamic event loop forced to use sockets (this
+usually works) and possibly another thread and a pipe or so to report to
+your main event loop.
+
+=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)
+ {
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