EV

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Note that this function is I<not> thread-safe, so if you want to use it
from multiple threads, you have to employ some kind of mutex (note also
that this case is unlikely, as loops cannot be shared easily between
threads anyway).

The default loop is the only loop that can handle C<ev_child> watchers,
and to do this, it always registers a handler for C<SIGCHLD>. If this is
a problem for your application you can either create a dynamic loop with
C<ev_loop_new> which doesn't do that, or you can simply overwrite the
C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.

Example: This is the most typical usage.

   if (!ev_default_loop (0))
     fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");

Example: 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);

=item struct ev_loop *ev_loop_new (unsigned int flags)

This will create and initialise a new event loop object. If the loop
could not be initialised, returns false.

This function is thread-safe, and one common way to use libev with
threads is indeed to create one loop per thread, and using the default
loop in the "main" or "initial" thread.

The flags argument can be used to specify special behaviour or specific
backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).

The following flags are supported:

=over 4

=item C<EVFLAG_AUTO>

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

=item C<EVFLAG_NOENV>

If this flag bit is or'ed 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, to work
around bugs, or to make libev threadsafe (accessing environment variables
cannot be done in a threadsafe way, but usually it works if no other
thread modifies them).

=item C<EVFLAG_FORKCHECK>

Instead of calling C<ev_loop_fork> manually after a fork, you can also
make libev check for a fork in each iteration by enabling this flag.

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
GNU/Linux system for example, C<getpid> is actually a simple 5-insn
sequence without a system call and thus I<very> fast, but my GNU/Linux
system also has C<pthread_atfork> which is even faster). (Update: glibc
versions 2.25 apparently removed the C<getpid> optimisation again).

The big advantage of this flag is that you can forget about fork (and
forget about forgetting to tell libev about forking, although you still
have to ignore C<SIGPIPE>) when you use this flag.

This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
environment variable.

=item C<EVFLAG_NOINOTIFY>

When this flag is specified, then libev will not attempt to use the
I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
testing, this flag can be useful to conserve inotify file descriptors, as
otherwise each loop using C<ev_stat> watchers consumes one inotify handle.

=item C<EVFLAG_SIGNALFD>

When this flag is specified, then libev will attempt to use the
I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
delivers signals synchronously, which makes it both faster and might make
it possible to get the queued signal data. It can also simplify signal
handling with threads, as long as you properly block signals in your
threads that are not interested in handling them.

Signalfd will not be used by default as this changes your signal mask, and
there are a lot of shoddy libraries and programs (glib's threadpool for
example) that can't properly initialise their signal masks.

=item C<EVFLAG_NOSIGMASK>

When this flag is specified, then libev will avoid to modify the signal
mask. Specifically, this means you have to make sure signals are unblocked
when you want to receive them.

This behaviour is useful when you want to do your own signal handling, or
want to handle signals only in specific threads and want to avoid libev
unblocking the signals.

It's also required by POSIX in a threaded program, as libev calls
C<sigprocmask>, whose behaviour is officially unspecified.

=item C<EVFLAG_NOTIMERFD>

When this flag is specified, the libev will avoid using a C<timerfd> to
detect time jumps. It will still be able to detect time jumps, but takes
longer and has a lower accuracy in doing so, but saves a file descriptor
per loop.

The current implementation only tries to use a C<timerfd> when the first
C<ev_periodic> watcher is started and falls back on other methods if it
cannot be created, but this behaviour might change in the future.

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

This is your standard select(2) backend. Not I<completely> standard, as
libev tries to roll its own fd_set with no limits on the number of fds,
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 (low-numbered :) fds.

To get good performance out of this backend you need a high amount of
parallelism (most of the file descriptors should be busy). If you are
writing a server, you should C<accept ()> in a loop to accept as many
connections as possible during one iteration. You might also want to have
a look at C<ev_set_io_collect_interval ()> to increase the amount of
readiness notifications you get per iteration.

This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
C<writefds> set (and to work around Microsoft Windows bugs, also onto the
C<exceptfds> set on that platform).

=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). See the entry for C<EVBACKEND_SELECT>, above, for
performance tips.

This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.

=item C<EVBACKEND_EPOLL>   (value 4, Linux)

Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
kernels).

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

The epoll mechanism deserves honorable mention as the most misdesigned
of the more advanced event mechanisms: mere annoyances include silently
dropping file descriptors, requiring a system call per change per file
descriptor (and unnecessary guessing of parameters), problems with dup,
returning before the timeout value, resulting in additional iterations
(and only giving 5ms accuracy while select on the same platform gives
0.1ms) and so on. The biggest issue is fork races, however - if a program
forks then I<both> parent and child process have to recreate the epoll
set, which can take considerable time (one syscall per file descriptor)
and is of course hard to detect.

Epoll is also notoriously buggy - embedding epoll fds I<should> work,
but of course I<doesn't>, and epoll just loves to report events for
totally I<different> file descriptors (even already closed ones, so
one cannot even remove them from the set) than registered in the set
(especially on SMP systems). Libev tries to counter these spurious
notifications by employing an additional generation counter and comparing
that against the events to filter out spurious ones, recreating the set
when required. Epoll also erroneously rounds down timeouts, but gives you
no way to know when and by how much, so sometimes you have to busy-wait
because epoll returns immediately despite a nonzero timeout. And last
not least, it also refuses to work with some file descriptors which work
perfectly fine with C<select> (files, many character devices...).

Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
cobbled together in a hurry, no thought to design or interaction with
others. Oh, the pain, will it ever stop...

While stopping, setting and starting an I/O watcher in the same iteration
will result in some caching, there is still a system call per such
incident (because the same I<file descriptor> could point to a different
I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
file descriptors might not work very well if you register events for both
file descriptors.

Best performance from this backend is achieved by not unregistering all
watchers for a file descriptor until it has been closed, if possible,
i.e. keep at least one watcher active per fd at all times. Stopping and
starting a watcher (without re-setting it) also usually doesn't cause
extra overhead. A fork can both result in spurious notifications as well
as in libev having to destroy and recreate the epoll object, which can
take considerable time and thus should be avoided.

All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
faster than epoll for maybe up to a hundred file descriptors, depending on
the usage. So sad.

While nominally embeddable in other event loops, this feature is broken in
a lot of kernel revisions, but probably(!) works in current versions.

This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
C<EVBACKEND_POLL>.

=item C<EVBACKEND_IOURING>    (value 128, linux)

Use the linux-specific io_uring backend. It offers an enourmous amount
of features other than just I/O events, but suffers from an extreme
feature-first, correctness-later approach, and is slower than epoll, so
it is not used by default.

One important misdesign is that when sleeping in io_uring, the kernel
wrongly counts that as disk I/O wait, keeping loadavg and a cpu core
"virtually" busy, even if nothing actually waits for disk or uses CPU.

If your application forks frequently, then this backend might be faster,

libev/ev.pod  view on Meta::CPAN

It is definitely not recommended to use this flag, use whatever
C<ev_recommended_backends ()> returns, or simply do not specify a backend
at all.

=item C<EVBACKEND_MASK>

Not a backend at all, but a mask to select all backend bits from a
C<flags> value, in case you want to mask out any backends from a flags
value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).

=back

If one or more of the backend flags are or'ed into the flags value,
then only these backends will be tried (in the reverse order as listed
here). If none are specified, all backends in C<ev_recommended_backends
()> will be tried.

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");

Example: Use whatever libev has to offer, but make sure that kqueue is
used if available.

   struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);

Example: Similarly, on linux, you mgiht want to take advantage of the
linux aio backend if possible, but fall back to something else if that
isn't available.

   struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);

=item ev_loop_destroy (loop)

Destroys an event loop object (frees all memory and kernel state
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 yourself 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 (and installed signal
handlers), will not be freed by this function, and related watchers (such
as signal and child watchers) would need to be stopped manually.

This function is normally used on loop objects allocated by
C<ev_loop_new>, but it can also be used on the default loop returned by
C<ev_default_loop>, in which case it is not thread-safe.

Note that it is not advisable to call this function on the default loop
except in the rare occasion where you really need to free its resources.
If you need dynamically allocated loops it is better to use C<ev_loop_new>
and C<ev_loop_destroy>.

=item ev_loop_fork (loop)

This function sets a flag that causes subsequent C<ev_run> iterations
to reinitialise the kernel state for backends that have one. Despite
the name, you can call it anytime you are allowed to start or stop
watchers (except inside an C<ev_prepare> callback), but it makes most
sense after forking, in the child process. You I<must> call it (or use
C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.

In addition, if you want to reuse a loop (via this function or
C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.

Again, you I<have> to call it on I<any> loop that you want to re-use after
a fork, I<even if you do not plan to use the loop in the parent>. This is
because some kernel interfaces *cough* I<kqueue> *cough* do funny things
during fork.

On the other hand, you only need to call this function in the child
process if and only if you want to use the event loop in the child. If
you just fork+exec or create a new loop in the child, you don't have to
call it at all (in fact, C<epoll> is so badly broken that it makes a
difference, but libev will usually detect this case on its own and do a
costly reset of the backend).

The function itself is quite fast and it's usually not a problem to call
it just in case after a fork.

Example: Automate calling C<ev_loop_fork> on the default loop when
using pthreads.

   static void
   post_fork_child (void)
   {
     ev_loop_fork (EV_DEFAULT);
   }

   ...
   pthread_atfork (0, 0, post_fork_child);

=item int ev_is_default_loop (loop)

Returns true when the given loop is, in fact, the default loop, and false
otherwise.

=item unsigned int ev_iteration (loop)

Returns the current iteration count for the event 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 - and is incremented between the
prepare and check phases.

=item unsigned int ev_depth (loop)

Returns the number of times C<ev_run> was entered minus the number of
times C<ev_run> was exited normally, in other words, the recursion depth.

Outside C<ev_run>, this number is zero. In a callback, this number is
C<1>, unless C<ev_run> was invoked recursively (or from another thread),
in which case it is higher.

Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
throwing an exception etc.), doesn't count as "exit" - consider this
as a hint to avoid such ungentleman-like behaviour unless it's really
convenient, in which case it is fully supported.

=item unsigned int ev_backend (loop)

Returns one of the C<EVBACKEND_*> flags indicating the event backend in
use.

=item ev_tstamp ev_now (loop)

Returns the current "event loop time", which is the time the event loop
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 occurring (or more correctly, libev finding out about it).

=item ev_now_update (loop)

Establishes the current time by querying the kernel, updating the time
returned by C<ev_now ()> in the progress. This is a costly operation and
is usually done automatically within C<ev_run ()>.

This function is rarely useful, but when some event callback runs for a
very long time without entering the event loop, updating libev's idea of
the current time is a good idea.

See also L</The special problem of time updates> in the C<ev_timer> section.

=item ev_suspend (loop)

=item ev_resume (loop)

These two functions suspend and resume an event loop, for use when the
loop is not used for a while and timeouts should not be processed.

A typical use case would be an interactive program such as a game:  When
the user presses C<^Z> to suspend the game and resumes it an hour later it
would be best to handle timeouts as if no time had actually passed while
the program was suspended. This can be achieved by calling C<ev_suspend>
in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
C<ev_resume> directly afterwards to resume timer processing.

Effectively, all C<ev_timer> watchers will be delayed by the time spend
between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
will be rescheduled (that is, they will lose any events that would have
occurred while suspended).

libev/ev.pod  view on Meta::CPAN

=item ev_break (loop, how)

Can be used to make a call to C<ev_run> return early (but only after it
has processed all outstanding events). The C<how> argument must be either
C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.

This "break state" will be cleared on the next call to C<ev_run>.

It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
which case it will have no effect.

=item ev_ref (loop)

=item ev_unref (loop)

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_run> will not return on its own.

This is useful when you have a watcher that you never intend to
unregister, but that nevertheless should not keep C<ev_run> from
returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
before stopping it.

As an example, libev itself uses this for its internal signal pipe: It
is not visible to the libev user and should not keep C<ev_run> 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> (but only if the watcher wasn't active before, or was active
before, respectively. Note also that libev might stop watchers itself
(e.g. non-repeating timers) in which case you have to C<ev_ref>
in the callback).

Example: Create a signal watcher, but keep it from keeping C<ev_run>
running when nothing else is active.

   ev_signal exitsig;
   ev_signal_init (&exitsig, sig_cb, SIGINT);
   ev_signal_start (loop, &exitsig);
   ev_unref (loop);

Example: For some weird reason, unregister the above signal handler again.

   ev_ref (loop);
   ev_signal_stop (loop, &exitsig);

=item ev_set_io_collect_interval (loop, ev_tstamp interval)

=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)

These advanced functions influence the time that libev will spend waiting
for events. Both time intervals are by default C<0>, meaning that libev
will try to invoke timer/periodic callbacks and I/O callbacks with minimum
latency.

Setting these to a higher value (the C<interval> I<must> be >= C<0>)
allows libev to delay invocation of I/O and timer/periodic callbacks
to increase efficiency of loop iterations (or to increase power-saving
opportunities).

The idea is that sometimes your program runs just fast enough to handle
one (or very few) event(s) per loop iteration. While this makes the
program responsive, it also wastes a lot of CPU time to poll for new
events, especially with backends like C<select ()> which have a high
overhead for the actual polling but can deliver many events at once.

By setting a higher I<io collect interval> you allow libev to spend more
time collecting I/O events, so you can handle more events per iteration,
at the cost of increasing latency. Timeouts (both C<ev_periodic> and
C<ev_timer>) will not be affected. Setting this to a non-null value will
introduce an additional C<ev_sleep ()> call into most loop iterations. The
sleep time ensures that libev will not poll for I/O events more often then
once per this interval, on average (as long as the host time resolution is
good enough).

Likewise, by setting a higher I<timeout collect interval> you allow libev
to spend more time collecting timeouts, at the expense of increased
latency/jitter/inexactness (the watcher callback will be called
later). C<ev_io> watchers will not be affected. Setting this to a non-null
value will not introduce any overhead in libev.

Many (busy) programs can usually benefit by setting the I/O collect
interval to a value near C<0.1> or so, which is often enough for
interactive servers (of course not for games), likewise for timeouts. It
usually doesn't make much sense to set it to a lower value than C<0.01>,
as this approaches the timing granularity of most systems. Note that if
you do transactions with the outside world and you can't increase the
parallelity, then this setting will limit your transaction rate (if you
need to poll once per transaction and the I/O collect interval is 0.01,
then you can't do more than 100 transactions per second).

Setting the I<timeout collect interval> can improve the opportunity for
saving power, as the program will "bundle" timer callback invocations that
are "near" in time together, by delaying some, thus reducing the number of
times the process sleeps and wakes up again. Another useful technique to
reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
they fire on, say, one-second boundaries only.

Example: we only need 0.1s timeout granularity, and we wish not to poll
more often than 100 times per second:

   ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
   ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);

=item ev_invoke_pending (loop)

This call will simply invoke all pending watchers while resetting their
pending state. Normally, C<ev_run> does this automatically when required,
but when overriding the invoke callback this call comes handy. This
function can be invoked from a watcher - this can be useful for example
when you want to do some lengthy calculation and want to pass further
event handling to another thread (you still have to make sure only one
thread executes within C<ev_invoke_pending> or C<ev_run> of course).

=item int ev_pending_count (loop)

Returns the number of pending watchers - zero indicates that no watchers
are pending.

=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))

This overrides the invoke pending functionality of the loop: Instead of
invoking all pending watchers when there are any, C<ev_run> will call
this callback instead. This is useful, for example, when you want to
invoke the actual watchers inside another context (another thread etc.).

If you want to reset the callback, use C<ev_invoke_pending> as new
callback.

=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())

Sometimes you want to share the same loop between multiple threads. This
can be done relatively simply by putting mutex_lock/unlock calls around
each call to a libev function.

However, C<ev_run> can run an indefinite time, so it is not feasible
to wait for it to return. One way around this is to wake up the event
loop via C<ev_break> and C<ev_async_send>, another way is to set these
I<release> and I<acquire> callbacks on the loop.

When set, then C<release> will be called just before the thread is
suspended waiting for new events, and C<acquire> is called just
afterwards.

Ideally, C<release> will just call your mutex_unlock function, and
C<acquire> will just call the mutex_lock function again.

While event loop modifications are allowed between invocations of
C<release> and C<acquire> (that's their only purpose after all), no
modifications done will affect the event loop, i.e. adding watchers will
have no effect on the set of file descriptors being watched, or the time
waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
to take note of any changes you made.

In theory, threads executing C<ev_run> will be async-cancel safe between
invocations of C<release> and C<acquire>.

libev/ev.pod  view on Meta::CPAN

I<has> to modify the signal mask, at least temporarily.

So I can't stress this enough: I<If you do not reset your signal mask when
you expect it to be empty, you have a race condition in your code>. This
is not a libev-specific thing, this is true for most event libraries.

=head3 The special problem of threads signal handling

POSIX threads has problematic signal handling semantics, specifically,
a lot of functionality (sigfd, sigwait etc.) only really works if all
threads in a process block signals, which is hard to achieve.

When you want to use sigwait (or mix libev signal handling with your own
for the same signals), you can tackle this problem by globally blocking
all signals before creating any threads (or creating them with a fully set
sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
loops. Then designate one thread as "signal receiver thread" which handles
these signals. You can pass on any signals that libev might be interested
in by calling C<ev_feed_signal>.

=head3 Watcher-Specific Functions and Data Members

=over 4

=item ev_signal_init (ev_signal *, callback, int signum)

=item ev_signal_set (ev_signal *, int signum)

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

=head3 Examples

Example: Try to exit cleanly on SIGINT.

   static void
   sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
   {
     ev_break (loop, EVBREAK_ALL);
   }

   ev_signal signal_watcher;
   ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
   ev_signal_start (loop, &signal_watcher);


=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 or
exits). It is permissible to install a child watcher I<after> the child
has been forked (which implies it might have already exited), as long
as the event loop isn't entered (or is continued from a watcher), i.e.,
forking and then immediately registering a watcher for the child is fine,
but forking and registering a watcher a few event loop iterations later or
in the next callback invocation is not.

Only the default event loop is capable of handling signals, and therefore
you can only register child watchers in the default event loop.

Due to some design glitches inside libev, child watchers will always be
handled at maximum priority (their priority is set to C<EV_MAXPRI> by
libev)

=head3 Process Interaction

Libev grabs C<SIGCHLD> as soon as the default event loop is
initialised. This is necessary to guarantee proper behaviour even if the
first child watcher is started after the child exits. The occurrence
of C<SIGCHLD> is recorded asynchronously, but child reaping is done
synchronously as part of the event loop processing. Libev always reaps all
children, even ones not watched.

=head3 Overriding the Built-In Processing

Libev offers no special support for overriding the built-in child
processing, but if your application collides with libev's default child
handler, you can override it easily by installing your own handler for
C<SIGCHLD> after initialising the default loop, and making sure the
default loop never gets destroyed. You are encouraged, however, to use an
event-based approach to child reaping and thus use libev's support for
that, so other libev users can use C<ev_child> watchers freely.

=head3 Stopping the Child Watcher

Currently, the child watcher never gets stopped, even when the
child terminates, so normally one needs to stop the watcher in the
callback. Future versions of libev might stop the watcher automatically
when a child exit is detected (calling C<ev_child_stop> twice is not a
problem).

=head3 Watcher-Specific Functions and Data Members

=over 4

=item ev_child_init (ev_child *, callback, int pid, int trace)

=item ev_child_set (ev_child *, int pid, int trace)

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> and see your systems
C<waitpid> documentation). The C<rpid> member contains the pid of the
process causing the status change. C<trace> must be either C<0> (only
activate the watcher when the process terminates) or C<1> (additionally
activate the watcher when the process is stopped or continued).

=item int pid [read-only]

The process id this watcher watches out for, or C<0>, meaning any process id.

=item int rpid [read-write]

The process id that detected a status change.