[ViewVC] Annotation of: cvs/EV/README

NAME
    EV - perl interface to libev, a high performance full-featured event
    loop

SYNOPSIS
      use EV;
  
      # TIMERS
  
      my $w = EV::timer 2, 0, sub {
         warn "is called after 2s";
      };
  
      my $w = EV::timer 2, 1, sub {
         warn "is called roughly every 2s (repeat = 1)";
      };
  
      undef $w; # destroy event watcher again
  
      my $w = EV::periodic 0, 60, sub {
         warn "is called every minute, on the minute, exactly";
      };
  
      # IO
  
      my $w = EV::io *STDIN, EV::READ, sub {
         my ($w, $revents) = @_; # all callbacks get the watcher object and event mask
         warn "stdin is readable, you entered: ", <STDIN>;
      };
  
      # SIGNALS
  
      my $w = EV::signal 'QUIT', sub {
         warn "sigquit received\n";
      };
  
      my $w = EV::signal 3, sub {
         warn "sigquit received (this is GNU/Linux, right?)\n";
      };

      # CHILD/PID STATUS CHANGES

      my $w = EV::child 666, sub {
         my ($w, $revents) = @_;
         # my $pid = $w->rpid;
         my $status = $w->rstatus;
      };
  
      # MAINLOOP
      EV::loop;                   # loop until EV::loop_done is called
      EV::loop EV::LOOP_ONESHOT;  # block until at least one event could be handled
      EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block

DESCRIPTION
    This module provides an interface to libev
    (<http://software.schmorp.de/pkg/libev.html>).

BASIC INTERFACE
    $EV::DIED
        Must contain a reference to a function that is called when a
        callback throws an exception (with $@ containing thr error). The
        default prints an informative message and continues.

        If this callback throws an exception it will be silently ignored.

    $time = EV::time
        Returns the current time in (fractional) seconds since the epoch.

    $time = EV::now
        Returns the time the last event loop iteration has been started.
        This is the time that (relative) timers are based on, and refering
        to it is usually faster then calling EV::time.

    $method = EV::ev_method
        Returns an integer describing the backend used by libev
        (EV::METHOD_SELECT or EV::METHOD_EPOLL).

    EV::loop [$flags]
        Begin checking for events and calling callbacks. It returns when a
        callback calls EV::loop_done.

        The $flags argument can be one of the following:

           0                  as above
           EV::LOOP_ONESHOT   block at most once (wait, but do not loop)
           EV::LOOP_NONBLOCK  do not block at all (fetch/handle events but do not wait)

    EV::loop_done [$how]
        When called with no arguments or an argument of 1, makes the
        innermost call to EV::loop return.

        When called with an agrument of 2, all calls to EV::loop will return
        as fast as possible.

  WATCHER
    A watcher is an object that gets created 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:

      my $watcher = EV::io *STDIN, EV::READ, sub {
         my ($watcher, $revents) = @_;
         warn "yeah, STDIN should not be readable without blocking!\n"
      };

    All watchers can be active (waiting for events) or inactive (paused).
    Only active watchers will have their callbacks invoked. All callbacks
    will be called with at least two arguments: the watcher and a bitmask of
    received events.

    Each watcher type has its associated bit in revents, so you can use the
    same callback for multiple watchers. The event mask is named after the
    type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE,
    EV::periodic sets EV::PERIODIC and so on, with the exception of IO
    events (which can set both EV::READ and EV::WRITE bits), and EV::timer
    (which uses EV::TIMEOUT).

    In the rare case where one wants to create a watcher but not start it at
    the same time, each constructor has a variant with a trailing "_ns" in
    its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.

    Please note that a watcher will automatically be stopped when the
    watcher object is destroyed, so you *need* to keep the watcher objects
    returned by the constructors.

    Also, all methods changing some aspect of a watcher (->set, ->priority,
    ->fh and so on) automatically stop and start it again if it is active,
    which means pending events get lost.

  WATCHER TYPES
    Now lets move to the existing watcher types and asociated methods.

    The following methods are available for all watchers. Then followes a
    description of each watcher constructor (EV::io, EV::timer,
    EV::periodic, EV::signal, EV::child, EV::idle, EV::prepare and
    EV::check), followed by any type-specific methods (if any).

    $w->start
        Starts a watcher if it isn't active already. Does nothing to an
        already active watcher. By default, all watchers start out in the
        active state (see the description of the "_ns" variants if you need
        stopped watchers).

    $w->stop
        Stop a watcher if it is active. Also clear any pending events
        (events that have been received but that didn't yet result in a
        callback invocation), regardless of wether the watcher was active or
        not.

    $bool = $w->is_active
        Returns true if the watcher is active, false otherwise.

    $current_cb = $w->cb
    $old_cb = $w->cb ($new_cb)
        Queries the callback on the watcher and optionally changes it. You
        can do this at any time without the watcher restarting.

    $current_priority = $w->priority
    $old_priority = $w->priority ($new_priority)
        Queries the priority on the watcher and optionally changes it.
        Pending watchers with higher priority will be invoked first. The
        valid range of priorities lies between EV::MAXPRI (default 2) and
        EV::MINPRI (default -2). If the priority is outside this range it
        will automatically be normalised to the nearest valid priority.

        The default priority of any newly-created weatcher is 0.

    $w->trigger ($revents)
        Call the callback *now* with the given event mask.

    $w = EV::io $fileno_or_fh, $eventmask, $callback
    $w = EV::io_ns $fileno_or_fh, $eventmask, $callback
        As long as the returned watcher object is alive, call the $callback
        when the events specified in $eventmask.

        The $eventmask can be one or more of these constants ORed together:

          EV::READ     wait until read() wouldn't block anymore
          EV::WRITE    wait until write() wouldn't block anymore

        The "io_ns" variant doesn't start (activate) the newly created
        watcher.

    $w->set ($fileno_or_fh, $eventmask)
        Reconfigures the watcher, see the constructor above for details. Can
        be called at any time.

    $current_fh = $w->fh
    $old_fh = $w->fh ($new_fh)
        Returns the previously set filehandle and optionally set a new one.

    $current_eventmask = $w->events
    $old_eventmask = $w->events ($new_eventmask)
        Returns the previously set event mask and optionally set a new one.

    $w = EV::timer $after, $repeat, $callback
    $w = EV::timer_ns $after, $repeat, $callback
        Calls the callback after $after seconds. If $repeat is non-zero, the
        timer will be restarted (with the $repeat value as $after) after the
        callback returns.

        This means that the callback would be called roughly after $after
        seconds, and then every $repeat seconds. "Roughly" because the time
        of callback processing is not taken into account, so the timer will
        slowly drift. If that isn't acceptable, look at EV::periodic.

        The timer is based on a monotonic clock, that is if somebody is
        sitting in front of the machine while the timer is running and
        changes the system clock, the timer will nevertheless run (roughly)
        the same time.

        The "timer_ns" variant doesn't start (activate) the newly created
        watcher.

    $w->set ($after, $repeat)
        Reconfigures the watcher, see the constructor above for details. Can
        be at any time.

    $w->again
        Similar to the "start" method, but has special semantics for
        repeating timers:

        If the timer is active and repeating, reset the timeout to occur
        $repeat seconds after now.

        If the timer is active and non-repeating, it will be stopped.

        If the timer is in active and repeating, start it.

        Otherwise do nothing.

        This behaviour is useful when you have a timeout for some IO
        operation. You create a timer object with the same value for $after
        and $repeat, and then, in the read/write watcher, run the "again"
        method on the timeout.

    $w = EV::periodic $at, $interval, $callback
    $w = EV::periodic_ns $at, $interval, $callback
        Similar to EV::timer, but the time is given as an absolute point in
        time ($at), plus an optional $interval.

        If the $interval is zero, then the callback will be called at the
        time $at if that is in the future, or as soon as possible if it is
        in the past. It will not automatically repeat.

        If the $interval is nonzero, then the watcher will always be
        scheduled to time out at the next "$at + N * $interval" time.

        This can be used to schedule a callback to run at very regular
        intervals, as long as the processing time is less then the interval
        (otherwise obviously events will be skipped).

        Another way to think about it (for the mathematically inclined) is
        that EV::periodic will try to run the callback at the next possible
        time where "$time = $at (mod $interval)", regardless of any time
        jumps.

        This periodic timer is based on "wallclock time", that is, if the
        clock changes ("ntp", "date -s" etc.), then the timer will
        nevertheless run at the specified time. This means it will never
        drift (it might jitter, but it will not drift).

        The "periodic_ns" variant doesn't start (activate) the newly created
        watcher.

    $w->set ($at, $interval)
        Reconfigures the watcher, see the constructor above for details. Can
        be at any time.

    $w = EV::signal $signal, $callback
    $w = EV::signal_ns $signal, $callback
        Call the callback when $signal is received (the signal can be
        specified by number or by name, just as with kill or %SIG).

        EV will grab the signal for the process (the kernel only allows one
        component to receive a signal at a time) when you start a signal
        watcher, and removes it again when you stop it. Perl does the same
        when you add/remove callbacks to %SIG, so watch out.

        You can have as many signal watchers per signal as you want.

        The "signal_ns" variant doesn't start (activate) the newly created
        watcher.

    $w->set ($signal)
        Reconfigures the watcher, see the constructor above for details. Can
        be at any time.

    $current_signum = $w->signal
    $old_signum = $w->signal ($new_signal)
        Returns the previously set signal (always as a number not name) and
        optionally set a new one.

    $w = EV::child $pid, $callback
    $w = EV::child_ns $pid, $callback
        Call the callback when a status change for pid $pid (or any pid if
        $pid is 0) has been received. More precisely: when the process
        receives a SIGCHLD, EV will fetch the outstanding exit/wait status
        for all changed/zombie children and call the callback.

        You can access both status and pid by using the "rstatus" and "rpid"
        methods on the watcher object.

        You can have as many pid watchers per pid as you want.

        The "child_ns" variant doesn't start (activate) the newly created
        watcher.

    $w->set ($pid)
        Reconfigures the watcher, see the constructor above for details. Can
        be at any time.

    $current_pid = $w->pid
    $old_pid = $w->pid ($new_pid)
        Returns the previously set process id and optionally set a new one.

    $exit_status = $w->rstatus
        Return the exit/wait status (as returned by waitpid, see the waitpid
        entry in perlfunc).

    $pid = $w->rpid
        Return the pid of the awaited child (useful when you have installed
        a watcher for all pids).

    $w = EV::idle $callback
    $w = EV::idle_ns $callback
        Call the callback when there are no pending io, timer/periodic,
        signal or child events, i.e. when the process is idle.

        The process will not block as long as any idle watchers are active,
        and they will be called repeatedly until stopped.

        The "idle_ns" variant doesn't start (activate) the newly created
        watcher.

    $w = EV::prepare $callback
    $w = EV::prepare_ns $callback
        Call the callback just before the process would block. You can still
        create/modify any watchers at this point.

        See the EV::check watcher, below, for explanations and an example.

        The "prepare_ns" variant doesn't start (activate) the newly created
        watcher.

    $w = EV::check $callback
    $w = EV::check_ns $callback
        Call the callback just after the process wakes up again (after it
        has gathered events), but before any other callbacks have been
        invoked.

        This is used to integrate other event-based software into the EV
        mainloop: You register a prepare callback and in there, you create
        io and timer watchers as required by the other software. Here is a
        real-world example of integrating Net::SNMP (with some details left
        out):

           our @snmp_watcher;

           our $snmp_prepare = EV::prepare sub {
              # do nothing unless active
              $dispatcher->{_event_queue_h}
                 or return;

              # make the dispatcher handle any outstanding stuff

              # create an IO watcher for each and every socket
              @snmp_watcher = (
                 (map { EV::io $_, EV::READ, sub { } }
                     keys %{ $dispatcher->{_descriptors} }),
              );

              # if there are any timeouts, also create a timer
              push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
                 if $event->[Net::SNMP::Dispatcher::_ACTIVE];
           };

        The callbacks are irrelevant, the only purpose of those watchers is
        to wake up the process as soon as one of those events occurs (socket
        readable, or timer timed out). The corresponding EV::check watcher
        will then clean up:

           our $snmp_check = EV::check sub {
              # destroy all watchers
              @snmp_watcher = ();

              # make the dispatcher handle any new stuff
           };

        The callbacks of the created watchers will not be called as the
        watchers are destroyed before this cna happen (remember EV::check
        gets called first).

        The "check_ns" variant doesn't start (activate) the newly created
        watcher.

THREADS
    Threads are not supported by this in any way. Perl pseudo-threads is
    evil stuff and must die.

SEE ALSO
      L<EV::DNS>, L<EV::AnyEvent>.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.7
Committed:	Sat Nov 3 16:25:49 2007 UTC (16 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_5, rel-0_51
Changes since 1.6:	+38 -6 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	NAME
2	root	1.6	EV - perl interface to libev, a high performance full-featured event
3			loop
4	root	1.1
5	root	1.2	SYNOPSIS
6	root	1.4	use EV;
7
8	root	1.6	# TIMERS
9	root	1.4
10			my $w = EV::timer 2, 0, sub {
11			warn "is called after 2s";
12			};
13
14			my $w = EV::timer 2, 1, sub {
15			warn "is called roughly every 2s (repeat = 1)";
16			};
17
18			undef $w; # destroy event watcher again
19
20	root	1.6	my $w = EV::periodic 0, 60, sub {
21	root	1.4	warn "is called every minute, on the minute, exactly";
22			};
23
24			# IO
25
26	root	1.6	my $w = EV::io *STDIN, EV::READ, sub {
27	root	1.5	my ($w, $revents) = @_; # all callbacks get the watcher object and event mask
28	root	1.6	warn "stdin is readable, you entered: ", <STDIN>;
29	root	1.4	};
30
31			# SIGNALS
32
33			my $w = EV::signal 'QUIT', sub {
34			warn "sigquit received\n";
35			};
36
37			my $w = EV::signal 3, sub {
38			warn "sigquit received (this is GNU/Linux, right?)\n";
39			};
40	root	1.5
41			# CHILD/PID STATUS CHANGES
42
43			my $w = EV::child 666, sub {
44	root	1.7	my ($w, $revents) = @_;
45			# my $pid = $w->rpid;
46			my $status = $w->rstatus;
47	root	1.5	};
48	root	1.4
49			# MAINLOOP
50	root	1.6	EV::loop; # loop until EV::loop_done is called
51			EV::loop EV::LOOP_ONESHOT; # block until at least one event could be handled
52			EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block
53	root	1.2
54			DESCRIPTION
55	root	1.5	This module provides an interface to libev
56	root	1.6	(<http://software.schmorp.de/pkg/libev.html>).
57	root	1.2
58	root	1.3	BASIC INTERFACE
59			$EV::DIED
60			Must contain a reference to a function that is called when a
61			callback throws an exception (with $@ containing thr error). The
62			default prints an informative message and continues.
63
64			If this callback throws an exception it will be silently ignored.
65
66	root	1.6	$time = EV::time
67			Returns the current time in (fractional) seconds since the epoch.
68
69	root	1.2	$time = EV::now
70	root	1.6	Returns the time the last event loop iteration has been started.
71			This is the time that (relative) timers are based on, and refering
72			to it is usually faster then calling EV::time.
73
74			$method = EV::ev_method
75			Returns an integer describing the backend used by libev
76			(EV::METHOD_SELECT or EV::METHOD_EPOLL).
77
78			EV::loop [$flags]
79			Begin checking for events and calling callbacks. It returns when a
80			callback calls EV::loop_done.
81
82			The $flags argument can be one of the following:
83
84			0 as above
85			EV::LOOP_ONESHOT block at most once (wait, but do not loop)
86			EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
87
88			EV::loop_done [$how]
89			When called with no arguments or an argument of 1, makes the
90			innermost call to EV::loop return.
91
92			When called with an agrument of 2, all calls to EV::loop will return
93			as fast as possible.
94
95			WATCHER
96			A watcher is an object that gets created to record your interest in some
97			event. For instance, if you want to wait for STDIN to become readable,
98			you would create an EV::io watcher for that:
99
100			my $watcher = EV::io *STDIN, EV::READ, sub {
101			my ($watcher, $revents) = @_;
102			warn "yeah, STDIN should not be readable without blocking!\n"
103			};
104	root	1.2
105	root	1.6	All watchers can be active (waiting for events) or inactive (paused).
106			Only active watchers will have their callbacks invoked. All callbacks
107			will be called with at least two arguments: the watcher and a bitmask of
108			received events.
109
110			Each watcher type has its associated bit in revents, so you can use the
111			same callback for multiple watchers. The event mask is named after the
112			type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE,
113			EV::periodic sets EV::PERIODIC and so on, with the exception of IO
114			events (which can set both EV::READ and EV::WRITE bits), and EV::timer
115			(which uses EV::TIMEOUT).
116
117			In the rare case where one wants to create a watcher but not start it at
118			the same time, each constructor has a variant with a trailing "_ns" in
119			its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.
120
121			Please note that a watcher will automatically be stopped when the
122	root	1.7	watcher object is destroyed, so you need to keep the watcher objects
123	root	1.6	returned by the constructors.
124
125	root	1.7	Also, all methods changing some aspect of a watcher (->set, ->priority,
126			->fh and so on) automatically stop and start it again if it is active,
127			which means pending events get lost.
128
129	root	1.6	WATCHER TYPES
130			Now lets move to the existing watcher types and asociated methods.
131
132			The following methods are available for all watchers. Then followes a
133			description of each watcher constructor (EV::io, EV::timer,
134			EV::periodic, EV::signal, EV::child, EV::idle, EV::prepare and
135			EV::check), followed by any type-specific methods (if any).
136	root	1.2
137	root	1.6	$w->start
138			Starts a watcher if it isn't active already. Does nothing to an
139			already active watcher. By default, all watchers start out in the
140			active state (see the description of the "_ns" variants if you need
141			stopped watchers).
142
143			$w->stop
144			Stop a watcher if it is active. Also clear any pending events
145			(events that have been received but that didn't yet result in a
146			callback invocation), regardless of wether the watcher was active or
147			not.
148
149			$bool = $w->is_active
150			Returns true if the watcher is active, false otherwise.
151
152			$current_cb = $w->cb
153			$old_cb = $w->cb ($new_cb)
154			Queries the callback on the watcher and optionally changes it. You
155	root	1.7	can do this at any time without the watcher restarting.
156
157			$current_priority = $w->priority
158			$old_priority = $w->priority ($new_priority)
159			Queries the priority on the watcher and optionally changes it.
160			Pending watchers with higher priority will be invoked first. The
161			valid range of priorities lies between EV::MAXPRI (default 2) and
162			EV::MINPRI (default -2). If the priority is outside this range it
163			will automatically be normalised to the nearest valid priority.
164
165			The default priority of any newly-created weatcher is 0.
166	root	1.2
167	root	1.6	$w->trigger ($revents)
168			Call the callback now with the given event mask.
169	root	1.2
170	root	1.6	$w = EV::io $fileno_or_fh, $eventmask, $callback
171			$w = EV::io_ns $fileno_or_fh, $eventmask, $callback
172			As long as the returned watcher object is alive, call the $callback
173			when the events specified in $eventmask.
174	root	1.2
175	root	1.6	The $eventmask can be one or more of these constants ORed together:
176	root	1.1
177	root	1.2	EV::READ wait until read() wouldn't block anymore
178			EV::WRITE wait until write() wouldn't block anymore
179
180	root	1.6	The "io_ns" variant doesn't start (activate) the newly created
181			watcher.
182
183			$w->set ($fileno_or_fh, $eventmask)
184			Reconfigures the watcher, see the constructor above for details. Can
185			be called at any time.
186
187			$current_fh = $w->fh
188			$old_fh = $w->fh ($new_fh)
189			Returns the previously set filehandle and optionally set a new one.
190
191			$current_eventmask = $w->events
192			$old_eventmask = $w->events ($new_eventmask)
193			Returns the previously set event mask and optionally set a new one.
194
195			$w = EV::timer $after, $repeat, $callback
196			$w = EV::timer_ns $after, $repeat, $callback
197			Calls the callback after $after seconds. If $repeat is non-zero, the
198			timer will be restarted (with the $repeat value as $after) after the
199			callback returns.
200
201			This means that the callback would be called roughly after $after
202			seconds, and then every $repeat seconds. "Roughly" because the time
203			of callback processing is not taken into account, so the timer will
204			slowly drift. If that isn't acceptable, look at EV::periodic.
205
206			The timer is based on a monotonic clock, that is if somebody is
207			sitting in front of the machine while the timer is running and
208			changes the system clock, the timer will nevertheless run (roughly)
209			the same time.
210
211			The "timer_ns" variant doesn't start (activate) the newly created
212			watcher.
213
214			$w->set ($after, $repeat)
215			Reconfigures the watcher, see the constructor above for details. Can
216			be at any time.
217
218			$w->again
219			Similar to the "start" method, but has special semantics for
220			repeating timers:
221	root	1.2
222	root	1.6	If the timer is active and repeating, reset the timeout to occur
223			$repeat seconds after now.
224	root	1.2
225	root	1.6	If the timer is active and non-repeating, it will be stopped.
226	root	1.2
227	root	1.6	If the timer is in active and repeating, start it.
228
229			Otherwise do nothing.
230
231			This behaviour is useful when you have a timeout for some IO
232			operation. You create a timer object with the same value for $after
233			and $repeat, and then, in the read/write watcher, run the "again"
234			method on the timeout.
235
236			$w = EV::periodic $at, $interval, $callback
237			$w = EV::periodic_ns $at, $interval, $callback
238	root	1.2	Similar to EV::timer, but the time is given as an absolute point in
239			time ($at), plus an optional $interval.
240
241			If the $interval is zero, then the callback will be called at the
242	root	1.6	time $at if that is in the future, or as soon as possible if it is
243			in the past. It will not automatically repeat.
244	root	1.2
245			If the $interval is nonzero, then the watcher will always be
246	root	1.6	scheduled to time out at the next "$at + N * $interval" time.
247	root	1.2
248			This can be used to schedule a callback to run at very regular
249			intervals, as long as the processing time is less then the interval
250			(otherwise obviously events will be skipped).
251
252			Another way to think about it (for the mathematically inclined) is
253	root	1.6	that EV::periodic will try to run the callback at the next possible
254	root	1.2	time where "$time = $at (mod $interval)", regardless of any time
255			jumps.
256
257	root	1.6	This periodic timer is based on "wallclock time", that is, if the
258			clock changes ("ntp", "date -s" etc.), then the timer will
259			nevertheless run at the specified time. This means it will never
260			drift (it might jitter, but it will not drift).
261
262			The "periodic_ns" variant doesn't start (activate) the newly created
263	root	1.2	watcher.
264
265	root	1.6	$w->set ($at, $interval)
266			Reconfigures the watcher, see the constructor above for details. Can
267			be at any time.
268
269			$w = EV::signal $signal, $callback
270			$w = EV::signal_ns $signal, $callback
271	root	1.4	Call the callback when $signal is received (the signal can be
272	root	1.6	specified by number or by name, just as with kill or %SIG).
273	root	1.4
274			EV will grab the signal for the process (the kernel only allows one
275	root	1.6	component to receive a signal at a time) when you start a signal
276			watcher, and removes it again when you stop it. Perl does the same
277			when you add/remove callbacks to %SIG, so watch out.
278
279			You can have as many signal watchers per signal as you want.
280	root	1.1
281	root	1.6	The "signal_ns" variant doesn't start (activate) the newly created
282			watcher.
283
284			$w->set ($signal)
285			Reconfigures the watcher, see the constructor above for details. Can
286			be at any time.
287
288	root	1.7	$current_signum = $w->signal
289			$old_signum = $w->signal ($new_signal)
290			Returns the previously set signal (always as a number not name) and
291			optionally set a new one.
292
293	root	1.6	$w = EV::child $pid, $callback
294			$w = EV::child_ns $pid, $callback
295			Call the callback when a status change for pid $pid (or any pid if
296			$pid is 0) has been received. More precisely: when the process
297			receives a SIGCHLD, EV will fetch the outstanding exit/wait status
298			for all changed/zombie children and call the callback.
299
300	root	1.7	You can access both status and pid by using the "rstatus" and "rpid"
301			methods on the watcher object.
302	root	1.6
303			You can have as many pid watchers per pid as you want.
304
305			The "child_ns" variant doesn't start (activate) the newly created
306			watcher.
307	root	1.1
308	root	1.6	$w->set ($pid)
309			Reconfigures the watcher, see the constructor above for details. Can
310			be at any time.
311
312	root	1.7	$current_pid = $w->pid
313			$old_pid = $w->pid ($new_pid)
314			Returns the previously set process id and optionally set a new one.
315
316			$exit_status = $w->rstatus
317			Return the exit/wait status (as returned by waitpid, see the waitpid
318			entry in perlfunc).
319
320			$pid = $w->rpid
321			Return the pid of the awaited child (useful when you have installed
322			a watcher for all pids).
323
324	root	1.6	$w = EV::idle $callback
325			$w = EV::idle_ns $callback
326			Call the callback when there are no pending io, timer/periodic,
327			signal or child events, i.e. when the process is idle.
328	root	1.1
329	root	1.6	The process will not block as long as any idle watchers are active,
330			and they will be called repeatedly until stopped.
331	root	1.1
332	root	1.6	The "idle_ns" variant doesn't start (activate) the newly created
333			watcher.
334	root	1.4
335	root	1.6	$w = EV::prepare $callback
336			$w = EV::prepare_ns $callback
337			Call the callback just before the process would block. You can still
338			create/modify any watchers at this point.
339	root	1.1
340	root	1.6	See the EV::check watcher, below, for explanations and an example.
341	root	1.1
342	root	1.6	The "prepare_ns" variant doesn't start (activate) the newly created
343			watcher.
344	root	1.1
345	root	1.6	$w = EV::check $callback
346			$w = EV::check_ns $callback
347			Call the callback just after the process wakes up again (after it
348			has gathered events), but before any other callbacks have been
349			invoked.
350
351			This is used to integrate other event-based software into the EV
352			mainloop: You register a prepare callback and in there, you create
353			io and timer watchers as required by the other software. Here is a
354			real-world example of integrating Net::SNMP (with some details left
355			out):
356
357			our @snmp_watcher;
358
359			our $snmp_prepare = EV::prepare sub {
360			# do nothing unless active
361			$dispatcher->{_event_queue_h}
362			or return;
363
364			# make the dispatcher handle any outstanding stuff
365
366			# create an IO watcher for each and every socket
367			@snmp_watcher = (
368			(map { EV::io $_, EV::READ, sub { } }
369			keys %{ $dispatcher->{_descriptors} }),
370			);
371
372			# if there are any timeouts, also create a timer
373			push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
374			if $event->[Net::SNMP::Dispatcher::_ACTIVE];
375			};
376
377			The callbacks are irrelevant, the only purpose of those watchers is
378			to wake up the process as soon as one of those events occurs (socket
379			readable, or timer timed out). The corresponding EV::check watcher
380			will then clean up:
381
382			our $snmp_check = EV::check sub {
383			# destroy all watchers
384			@snmp_watcher = ();
385
386			# make the dispatcher handle any new stuff
387			};
388
389			The callbacks of the created watchers will not be called as the
390			watchers are destroyed before this cna happen (remember EV::check
391			gets called first).
392	root	1.1
393	root	1.6	The "check_ns" variant doesn't start (activate) the newly created
394			watcher.
395	root	1.1
396	root	1.5	THREADS
397			Threads are not supported by this in any way. Perl pseudo-threads is
398	root	1.6	evil stuff and must die.
399	root	1.2
400			SEE ALSO
401	root	1.6	L<EV::DNS>, L<EV::AnyEvent>.
402	root	1.1
403			AUTHOR
404			Marc Lehmann <schmorp@schmorp.de>
405			http://home.schmorp.de/
406