[ViewVC] Contents 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 *
#	Content
1	NAME
2	EV - perl interface to libev, a high performance full-featured event
3	loop
4
5	SYNOPSIS
6	use EV;
7
8	# TIMERS
9
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	my $w = EV::periodic 0, 60, sub {
21	warn "is called every minute, on the minute, exactly";
22	};
23
24	# IO
25
26	my $w = EV::io *STDIN, EV::READ, sub {
27	my ($w, $revents) = @_; # all callbacks get the watcher object and event mask
28	warn "stdin is readable, you entered: ", <STDIN>;
29	};
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
41	# CHILD/PID STATUS CHANGES
42
43	my $w = EV::child 666, sub {
44	my ($w, $revents) = @_;
45	# my $pid = $w->rpid;
46	my $status = $w->rstatus;
47	};
48
49	# MAINLOOP
50	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
54	DESCRIPTION
55	This module provides an interface to libev
56	(<http://software.schmorp.de/pkg/libev.html>).
57
58	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	$time = EV::time
67	Returns the current time in (fractional) seconds since the epoch.
68
69	$time = EV::now
70	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
105	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	watcher object is destroyed, so you need to keep the watcher objects
123	returned by the constructors.
124
125	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	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
137	$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	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
167	$w->trigger ($revents)
168	Call the callback now with the given event mask.
169
170	$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
175	The $eventmask can be one or more of these constants ORed together:
176
177	EV::READ wait until read() wouldn't block anymore
178	EV::WRITE wait until write() wouldn't block anymore
179
180	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
222	If the timer is active and repeating, reset the timeout to occur
223	$repeat seconds after now.
224
225	If the timer is active and non-repeating, it will be stopped.
226
227	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, $callback
238	Similar to EV::timer, but the time is given as an absolute point in
239	time ($at), plus an optional $interval.
240
241	If the $interval is zero, then the callback will be called at the
242	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
245	If the $interval is nonzero, then the watcher will always be
246	scheduled to time out at the next "$at + N * $interval" time.
247
248	This can be used to schedule a callback to run at very regular
249	intervals, as long as the processing time is less then the interval
250	(otherwise obviously events will be skipped).
251
252	Another way to think about it (for the mathematically inclined) is
253	that EV::periodic will try to run the callback at the next possible
254	time where "$time = $at (mod $interval)", regardless of any time
255	jumps.
256
257	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	watcher.
264
265	$w->set ($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	Call the callback when $signal is received (the signal can be
272	specified by number or by name, just as with kill or %SIG).
273
274	EV will grab the signal for the process (the kernel only allows one
275	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
281	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	$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	$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	You can access both status and pid by using the "rstatus" and "rpid"
301	methods on the watcher object.
302
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
308	$w->set ($pid)
309	Reconfigures the watcher, see the constructor above for details. Can
310	be at any time.
311
312	$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	$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
329	The process will not block as long as any idle watchers are active,
330	and they will be called repeatedly until stopped.
331
332	The "idle_ns" variant doesn't start (activate) the newly created
333	watcher.
334
335	$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
340	See the EV::check watcher, below, for explanations and an example.
341
342	The "prepare_ns" variant doesn't start (activate) the newly created
343	watcher.
344
345	$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
393	The "check_ns" variant doesn't start (activate) the newly created
394	watcher.
395
396	THREADS
397	Threads are not supported by this in any way. Perl pseudo-threads is
398	evil stuff and must die.
399
400	SEE ALSO
401	L<EV::DNS>, L<EV::AnyEvent>.
402
403	AUTHOR
404	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/
406