[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, $status) = @_;
      };
  
      # 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 returned, so you *need* to keep the watcher objects
    returned by the constructors.

  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
        cna do this at any time.

    $w->trigger ($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.

    $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.

        Unlike all other callbacks, this callback will be called with an
        additional third argument which is the exit status. See the
        "waitpid" function for details.

        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.

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