[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, 2, sub {
         warn "is called roughly every 2s (repeat = 2)";
      };
  
      undef $w; # destroy event watcher again
  
      my $w = EV::periodic 0, 60, 0, sub {
         warn "is called every minute, on the minute, exactly";
      };
  
      # IO
  
      my $w = EV::io *STDIN, EV::READ, sub {
         my ($w, $revents) = @_; # all callbacks receive the watcher and event mask
         warn "stdin is readable, you entered: ", <STDIN>;
      };
  
      # SIGNALS
  
      my $w = EV::signal 'QUIT', sub {
         warn "sigquit received\n";
      };
  
      # CHILD/PID STATUS CHANGES

      my $w = EV::child 666, sub {
         my ($w, $revents) = @_;
         my $status = $w->rstatus;
      };
  
      # MAINLOOP
      EV::loop;           # loop until EV::unloop is called or all watchers stop
      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::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::unloop.

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

        When called with an argument of EV::UNLOOP_ALL, 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_data = $w->data
    $old_data = $w->data ($new_data)
        Queries a freely usable data scalar on the watcher and optionally
        changes it. This is a way to associate custom data with a watcher:

           my $w = EV::timer 60, 0, sub {
              warn $_[0]->data;
           };
           $w->data ("print me!");

    $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. The timer does his best not
        to drift, but it will not invoke the timer more often then once per
        event loop iteration, and might drift in other cases. If that isn't
        acceptable, look at EV::periodic, which can provide long-term stable
        timers.

        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 non-repeating, it will be stopped.

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

        If the timer is inactive and repeating, start it using the repeat
        value.

        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, $reschedule_cb, $callback
    $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
        Similar to EV::timer, but is not based on relative timeouts but on
        absolute times. Apart from creating "simple" timers that trigger
        "at" the specified time, it can also be used for non-drifting
        absolute timers and more complex, cron-like, setups that are not
        adversely affected by time jumps (i.e. when the system clock is
        changed by explicit date -s or other means such as ntpd). It is also
        the most complex watcher type in EV.

        It has three distinct "modes":

        * absolute timer ($interval = $reschedule_cb = 0)
            This time simply fires at the wallclock time $at and doesn't
            repeat. It will not adjust when a time jump occurs, that is, if
            it is to be run at January 1st 2011 then it will run when the
            system time reaches or surpasses this time.

        * non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
            In this mode the watcher will always be scheduled to time out at
            the next "$at + N * $interval" time (for some integer N) and
            then repeat, regardless of any time jumps.

            This can be used to create timers that do not drift with respect
            to system time:

               my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };

            That doesn't mean there will always be 3600 seconds in between
            triggers, but only that the the clalback will be called when the
            system time shows a full hour (UTC).

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

        * manual reschedule mode ($reschedule_cb = coderef)
            In this mode $interval and $at are both being ignored. Instead,
            each time the periodic watcher gets scheduled, the reschedule
            callback ($reschedule_cb) will be called with the watcher as
            first, and the current time as second argument.

            *This callback MUST NOT stop or destroy this or any other
            periodic watcher, ever*. If you need to stop it, return 1e30 and
            stop it afterwards.

            It must return the next time to trigger, based on the passed
            time value (that is, the lowest time value larger than to the
            second argument). It will usually be called just before the
            callback will be triggered, but might be called at other times,
            too.

            This can be used to create very complex timers, such as a timer
            that triggers on each midnight, local time (actually 24 hours
            after the last midnight, to keep the example simple. If you know
            a way to do it correctly in about the same space (without
            requiring elaborate modules), drop me a note :):

               my $daily = EV::periodic 0, 0, sub {
                  my ($w, $now) = @_;

                  use Time::Local ();
                  my (undef, undef, undef, $d, $m, $y) = localtime $now;
                  86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
               }, sub {
                  print "it's midnight or likely shortly after, now\n";
               };

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

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

    $w->again
        Simply stops and starts the watcher again.

    $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>.

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

Revision:	1.11
Committed:	Sat Nov 17 01:41:33 2007 UTC (16 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_1, rel-1_3, rel-1_2
Changes since 1.10:	+2 -2 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	root	1.9	my $w = EV::timer 2, 2, sub {
15			warn "is called roughly every 2s (repeat = 2)";
16	root	1.4	};
17
18			undef $w; # destroy event watcher again
19
20	root	1.8	my $w = EV::periodic 0, 60, 0, sub {
21	root	1.4	warn "is called every minute, on the minute, exactly";
22			};
23
24			# IO
25
26	root	1.6	my $w = EV::io *STDIN, EV::READ, sub {
27	root	1.9	my ($w, $revents) = @_; # all callbacks receive the watcher 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	root	1.5	# CHILD/PID STATUS CHANGES
38
39			my $w = EV::child 666, sub {
40	root	1.7	my ($w, $revents) = @_;
41			my $status = $w->rstatus;
42	root	1.5	};
43	root	1.4
44			# MAINLOOP
45	root	1.10	EV::loop; # loop until EV::unloop is called or all watchers stop
46	root	1.6	EV::loop EV::LOOP_ONESHOT; # block until at least one event could be handled
47			EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block
48	root	1.2
49			DESCRIPTION
50	root	1.5	This module provides an interface to libev
51	root	1.6	(<http://software.schmorp.de/pkg/libev.html>).
52	root	1.2
53	root	1.3	BASIC INTERFACE
54			$EV::DIED
55			Must contain a reference to a function that is called when a
56			callback throws an exception (with $@ containing thr error). The
57			default prints an informative message and continues.
58
59			If this callback throws an exception it will be silently ignored.
60
61	root	1.6	$time = EV::time
62			Returns the current time in (fractional) seconds since the epoch.
63
64	root	1.2	$time = EV::now
65	root	1.6	Returns the time the last event loop iteration has been started.
66			This is the time that (relative) timers are based on, and refering
67			to it is usually faster then calling EV::time.
68
69	root	1.11	$method = EV::method
70	root	1.6	Returns an integer describing the backend used by libev
71			(EV::METHOD_SELECT or EV::METHOD_EPOLL).
72
73			EV::loop [$flags]
74			Begin checking for events and calling callbacks. It returns when a
75	root	1.10	callback calls EV::unloop.
76	root	1.6
77			The $flags argument can be one of the following:
78
79			0 as above
80			EV::LOOP_ONESHOT block at most once (wait, but do not loop)
81			EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
82
83	root	1.10	EV::unloop [$how]
84			When called with no arguments or an argument of EV::UNLOOP_ONE,
85			makes the innermost call to EV::loop return.
86	root	1.6
87	root	1.10	When called with an argument of EV::UNLOOP_ALL, all calls to
88			EV::loop will return as fast as possible.
89	root	1.6
90			WATCHER
91			A watcher is an object that gets created to record your interest in some
92			event. For instance, if you want to wait for STDIN to become readable,
93			you would create an EV::io watcher for that:
94
95			my $watcher = EV::io *STDIN, EV::READ, sub {
96			my ($watcher, $revents) = @_;
97			warn "yeah, STDIN should not be readable without blocking!\n"
98			};
99	root	1.2
100	root	1.6	All watchers can be active (waiting for events) or inactive (paused).
101			Only active watchers will have their callbacks invoked. All callbacks
102			will be called with at least two arguments: the watcher and a bitmask of
103			received events.
104
105			Each watcher type has its associated bit in revents, so you can use the
106			same callback for multiple watchers. The event mask is named after the
107			type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE,
108			EV::periodic sets EV::PERIODIC and so on, with the exception of IO
109			events (which can set both EV::READ and EV::WRITE bits), and EV::timer
110			(which uses EV::TIMEOUT).
111
112			In the rare case where one wants to create a watcher but not start it at
113			the same time, each constructor has a variant with a trailing "_ns" in
114			its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.
115
116			Please note that a watcher will automatically be stopped when the
117	root	1.7	watcher object is destroyed, so you need to keep the watcher objects
118	root	1.6	returned by the constructors.
119
120	root	1.7	Also, all methods changing some aspect of a watcher (->set, ->priority,
121			->fh and so on) automatically stop and start it again if it is active,
122			which means pending events get lost.
123
124	root	1.6	WATCHER TYPES
125			Now lets move to the existing watcher types and asociated methods.
126
127			The following methods are available for all watchers. Then followes a
128			description of each watcher constructor (EV::io, EV::timer,
129			EV::periodic, EV::signal, EV::child, EV::idle, EV::prepare and
130			EV::check), followed by any type-specific methods (if any).
131	root	1.2
132	root	1.6	$w->start
133			Starts a watcher if it isn't active already. Does nothing to an
134			already active watcher. By default, all watchers start out in the
135			active state (see the description of the "_ns" variants if you need
136			stopped watchers).
137
138			$w->stop
139			Stop a watcher if it is active. Also clear any pending events
140			(events that have been received but that didn't yet result in a
141			callback invocation), regardless of wether the watcher was active or
142			not.
143
144			$bool = $w->is_active
145			Returns true if the watcher is active, false otherwise.
146
147	root	1.8	$current_data = $w->data
148			$old_data = $w->data ($new_data)
149			Queries a freely usable data scalar on the watcher and optionally
150			changes it. This is a way to associate custom data with a watcher:
151
152			my $w = EV::timer 60, 0, sub {
153			warn $_[0]->data;
154			};
155			$w->data ("print me!");
156
157	root	1.6	$current_cb = $w->cb
158			$old_cb = $w->cb ($new_cb)
159			Queries the callback on the watcher and optionally changes it. You
160	root	1.7	can do this at any time without the watcher restarting.
161
162			$current_priority = $w->priority
163			$old_priority = $w->priority ($new_priority)
164			Queries the priority on the watcher and optionally changes it.
165			Pending watchers with higher priority will be invoked first. The
166			valid range of priorities lies between EV::MAXPRI (default 2) and
167			EV::MINPRI (default -2). If the priority is outside this range it
168			will automatically be normalised to the nearest valid priority.
169
170			The default priority of any newly-created weatcher is 0.
171	root	1.2
172	root	1.6	$w->trigger ($revents)
173			Call the callback now with the given event mask.
174	root	1.2
175	root	1.6	$w = EV::io $fileno_or_fh, $eventmask, $callback
176			$w = EV::io_ns $fileno_or_fh, $eventmask, $callback
177			As long as the returned watcher object is alive, call the $callback
178			when the events specified in $eventmask.
179	root	1.2
180	root	1.6	The $eventmask can be one or more of these constants ORed together:
181	root	1.1
182	root	1.2	EV::READ wait until read() wouldn't block anymore
183			EV::WRITE wait until write() wouldn't block anymore
184
185	root	1.6	The "io_ns" variant doesn't start (activate) the newly created
186			watcher.
187
188			$w->set ($fileno_or_fh, $eventmask)
189			Reconfigures the watcher, see the constructor above for details. Can
190			be called at any time.
191
192			$current_fh = $w->fh
193			$old_fh = $w->fh ($new_fh)
194			Returns the previously set filehandle and optionally set a new one.
195
196			$current_eventmask = $w->events
197			$old_eventmask = $w->events ($new_eventmask)
198			Returns the previously set event mask and optionally set a new one.
199
200			$w = EV::timer $after, $repeat, $callback
201			$w = EV::timer_ns $after, $repeat, $callback
202			Calls the callback after $after seconds. If $repeat is non-zero, the
203			timer will be restarted (with the $repeat value as $after) after the
204			callback returns.
205
206			This means that the callback would be called roughly after $after
207	root	1.10	seconds, and then every $repeat seconds. The timer does his best not
208			to drift, but it will not invoke the timer more often then once per
209			event loop iteration, and might drift in other cases. If that isn't
210			acceptable, look at EV::periodic, which can provide long-term stable
211			timers.
212	root	1.6
213	root	1.10	The timer is based on a monotonic clock, that is, if somebody is
214	root	1.6	sitting in front of the machine while the timer is running and
215			changes the system clock, the timer will nevertheless run (roughly)
216			the same time.
217
218			The "timer_ns" variant doesn't start (activate) the newly created
219			watcher.
220
221			$w->set ($after, $repeat)
222			Reconfigures the watcher, see the constructor above for details. Can
223			be at any time.
224
225			$w->again
226			Similar to the "start" method, but has special semantics for
227			repeating timers:
228	root	1.2
229	root	1.10	If the timer is active and non-repeating, it will be stopped.
230
231	root	1.6	If the timer is active and repeating, reset the timeout to occur
232			$repeat seconds after now.
233	root	1.2
234	root	1.10	If the timer is inactive and repeating, start it using the repeat
235			value.
236	root	1.6
237			Otherwise do nothing.
238
239			This behaviour is useful when you have a timeout for some IO
240			operation. You create a timer object with the same value for $after
241			and $repeat, and then, in the read/write watcher, run the "again"
242			method on the timeout.
243
244	root	1.8	$w = EV::periodic $at, $interval, $reschedule_cb, $callback
245			$w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
246			Similar to EV::timer, but is not based on relative timeouts but on
247			absolute times. Apart from creating "simple" timers that trigger
248			"at" the specified time, it can also be used for non-drifting
249			absolute timers and more complex, cron-like, setups that are not
250			adversely affected by time jumps (i.e. when the system clock is
251			changed by explicit date -s or other means such as ntpd). It is also
252			the most complex watcher type in EV.
253
254			It has three distinct "modes":
255
256			* absolute timer ($interval = $reschedule_cb = 0)
257			This time simply fires at the wallclock time $at and doesn't
258			repeat. It will not adjust when a time jump occurs, that is, if
259			it is to be run at January 1st 2011 then it will run when the
260			system time reaches or surpasses this time.
261
262			* non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
263			In this mode the watcher will always be scheduled to time out at
264			the next "$at + N * $interval" time (for some integer N) and
265			then repeat, regardless of any time jumps.
266
267			This can be used to create timers that do not drift with respect
268			to system time:
269
270			my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
271
272			That doesn't mean there will always be 3600 seconds in between
273			triggers, but only that the the clalback will be called when the
274			system time shows a full hour (UTC).
275
276			Another way to think about it (for the mathematically inclined)
277			is that EV::periodic will try to run the callback in this mode
278			at the next possible time where "$time = $at (mod $interval)",
279			regardless of any time jumps.
280
281			* manual reschedule mode ($reschedule_cb = coderef)
282			In this mode $interval and $at are both being ignored. Instead,
283	root	1.10	each time the periodic watcher gets scheduled, the reschedule
284	root	1.8	callback ($reschedule_cb) will be called with the watcher as
285			first, and the current time as second argument.
286
287			*This callback MUST NOT stop or destroy this or any other
288			periodic watcher, ever*. If you need to stop it, return 1e30 and
289			stop it afterwards.
290
291			It must return the next time to trigger, based on the passed
292			time value (that is, the lowest time value larger than to the
293			second argument). It will usually be called just before the
294			callback will be triggered, but might be called at other times,
295			too.
296
297			This can be used to create very complex timers, such as a timer
298			that triggers on each midnight, local time (actually 24 hours
299			after the last midnight, to keep the example simple. If you know
300			a way to do it correctly in about the same space (without
301			requiring elaborate modules), drop me a note :):
302
303			my $daily = EV::periodic 0, 0, sub {
304			my ($w, $now) = @_;
305
306			use Time::Local ();
307			my (undef, undef, undef, $d, $m, $y) = localtime $now;
308			86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
309			}, sub {
310			print "it's midnight or likely shortly after, now\n";
311			};
312	root	1.6
313			The "periodic_ns" variant doesn't start (activate) the newly created
314	root	1.2	watcher.
315
316	root	1.8	$w->set ($at, $interval, $reschedule_cb)
317	root	1.6	Reconfigures the watcher, see the constructor above for details. Can
318			be at any time.
319
320	root	1.8	$w->again
321			Simply stops and starts the watcher again.
322
323	root	1.6	$w = EV::signal $signal, $callback
324			$w = EV::signal_ns $signal, $callback
325	root	1.4	Call the callback when $signal is received (the signal can be
326	root	1.6	specified by number or by name, just as with kill or %SIG).
327	root	1.4
328			EV will grab the signal for the process (the kernel only allows one
329	root	1.6	component to receive a signal at a time) when you start a signal
330			watcher, and removes it again when you stop it. Perl does the same
331			when you add/remove callbacks to %SIG, so watch out.
332
333			You can have as many signal watchers per signal as you want.
334	root	1.1
335	root	1.6	The "signal_ns" variant doesn't start (activate) the newly created
336			watcher.
337
338			$w->set ($signal)
339			Reconfigures the watcher, see the constructor above for details. Can
340			be at any time.
341
342	root	1.7	$current_signum = $w->signal
343			$old_signum = $w->signal ($new_signal)
344			Returns the previously set signal (always as a number not name) and
345			optionally set a new one.
346
347	root	1.6	$w = EV::child $pid, $callback
348			$w = EV::child_ns $pid, $callback
349			Call the callback when a status change for pid $pid (or any pid if
350			$pid is 0) has been received. More precisely: when the process
351			receives a SIGCHLD, EV will fetch the outstanding exit/wait status
352			for all changed/zombie children and call the callback.
353
354	root	1.7	You can access both status and pid by using the "rstatus" and "rpid"
355			methods on the watcher object.
356	root	1.6
357			You can have as many pid watchers per pid as you want.
358
359			The "child_ns" variant doesn't start (activate) the newly created
360			watcher.
361	root	1.1
362	root	1.6	$w->set ($pid)
363			Reconfigures the watcher, see the constructor above for details. Can
364			be at any time.
365
366	root	1.7	$current_pid = $w->pid
367			$old_pid = $w->pid ($new_pid)
368			Returns the previously set process id and optionally set a new one.
369
370			$exit_status = $w->rstatus
371			Return the exit/wait status (as returned by waitpid, see the waitpid
372			entry in perlfunc).
373
374			$pid = $w->rpid
375			Return the pid of the awaited child (useful when you have installed
376			a watcher for all pids).
377
378	root	1.6	$w = EV::idle $callback
379			$w = EV::idle_ns $callback
380			Call the callback when there are no pending io, timer/periodic,
381			signal or child events, i.e. when the process is idle.
382	root	1.1
383	root	1.6	The process will not block as long as any idle watchers are active,
384			and they will be called repeatedly until stopped.
385	root	1.1
386	root	1.6	The "idle_ns" variant doesn't start (activate) the newly created
387			watcher.
388	root	1.4
389	root	1.6	$w = EV::prepare $callback
390			$w = EV::prepare_ns $callback
391			Call the callback just before the process would block. You can still
392			create/modify any watchers at this point.
393	root	1.1
394	root	1.6	See the EV::check watcher, below, for explanations and an example.
395	root	1.1
396	root	1.6	The "prepare_ns" variant doesn't start (activate) the newly created
397			watcher.
398	root	1.1
399	root	1.6	$w = EV::check $callback
400			$w = EV::check_ns $callback
401			Call the callback just after the process wakes up again (after it
402			has gathered events), but before any other callbacks have been
403			invoked.
404
405			This is used to integrate other event-based software into the EV
406			mainloop: You register a prepare callback and in there, you create
407			io and timer watchers as required by the other software. Here is a
408			real-world example of integrating Net::SNMP (with some details left
409			out):
410
411			our @snmp_watcher;
412
413			our $snmp_prepare = EV::prepare sub {
414			# do nothing unless active
415			$dispatcher->{_event_queue_h}
416			or return;
417
418			# make the dispatcher handle any outstanding stuff
419
420			# create an IO watcher for each and every socket
421			@snmp_watcher = (
422			(map { EV::io $_, EV::READ, sub { } }
423			keys %{ $dispatcher->{_descriptors} }),
424			);
425
426			# if there are any timeouts, also create a timer
427			push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
428			if $event->[Net::SNMP::Dispatcher::_ACTIVE];
429			};
430
431			The callbacks are irrelevant, the only purpose of those watchers is
432			to wake up the process as soon as one of those events occurs (socket
433			readable, or timer timed out). The corresponding EV::check watcher
434			will then clean up:
435
436			our $snmp_check = EV::check sub {
437			# destroy all watchers
438			@snmp_watcher = ();
439
440			# make the dispatcher handle any new stuff
441			};
442
443			The callbacks of the created watchers will not be called as the
444			watchers are destroyed before this cna happen (remember EV::check
445			gets called first).
446	root	1.1
447	root	1.6	The "check_ns" variant doesn't start (activate) the newly created
448			watcher.
449	root	1.1
450	root	1.5	THREADS
451			Threads are not supported by this in any way. Perl pseudo-threads is
452	root	1.6	evil stuff and must die.
453	root	1.2
454			SEE ALSO
455	root	1.11	L<EV::DNS>.
456	root	1.1
457			AUTHOR
458			Marc Lehmann <schmorp@schmorp.de>
459			http://home.schmorp.de/
460