[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::loop_done 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::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_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. "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, $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 $at are both being ignored. Instead,
            each time the periodic watcher gets scheduled, the first
            callback ($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>, L<EV::AnyEvent>.

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

Revision:	1.9
Committed:	Mon Nov 12 01:23:21 2007 UTC (16 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_8
Changes since 1.8:	+4 -9 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	1.9	EV::loop; # loop until EV::loop_done 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			$method = EV::ev_method
70			Returns an integer describing the backend used by libev
71			(EV::METHOD_SELECT or EV::METHOD_EPOLL).
72
73			EV::loop [$flags]
74			Begin checking for events and calling callbacks. It returns when a
75			callback calls EV::loop_done.
76
77			The $flags argument can be one of the following:
78
79			0 as above
80			EV::LOOP_ONESHOT block at most once (wait, but do not loop)
81			EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
82
83			EV::loop_done [$how]
84			When called with no arguments or an argument of 1, makes the
85			innermost call to EV::loop return.
86
87			When called with an agrument of 2, all calls to EV::loop will return
88			as fast as possible.
89
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			seconds, and then every $repeat seconds. "Roughly" because the time
208			of callback processing is not taken into account, so the timer will
209			slowly drift. If that isn't acceptable, look at EV::periodic.
210
211			The timer is based on a monotonic clock, that is if somebody is
212			sitting in front of the machine while the timer is running and
213			changes the system clock, the timer will nevertheless run (roughly)
214			the same time.
215
216			The "timer_ns" variant doesn't start (activate) the newly created
217			watcher.
218
219			$w->set ($after, $repeat)
220			Reconfigures the watcher, see the constructor above for details. Can
221			be at any time.
222
223			$w->again
224			Similar to the "start" method, but has special semantics for
225			repeating timers:
226	root	1.2
227	root	1.6	If the timer is active and repeating, reset the timeout to occur
228			$repeat seconds after now.
229	root	1.2
230	root	1.6	If the timer is active and non-repeating, it will be stopped.
231	root	1.2
232	root	1.6	If the timer is in active and repeating, start it.
233
234			Otherwise do nothing.
235
236			This behaviour is useful when you have a timeout for some IO
237			operation. You create a timer object with the same value for $after
238			and $repeat, and then, in the read/write watcher, run the "again"
239			method on the timeout.
240
241	root	1.8	$w = EV::periodic $at, $interval, $reschedule_cb, $callback
242			$w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
243			Similar to EV::timer, but is not based on relative timeouts but on
244			absolute times. Apart from creating "simple" timers that trigger
245			"at" the specified time, it can also be used for non-drifting
246			absolute timers and more complex, cron-like, setups that are not
247			adversely affected by time jumps (i.e. when the system clock is
248			changed by explicit date -s or other means such as ntpd). It is also
249			the most complex watcher type in EV.
250
251			It has three distinct "modes":
252
253			* absolute timer ($interval = $reschedule_cb = 0)
254			This time simply fires at the wallclock time $at and doesn't
255			repeat. It will not adjust when a time jump occurs, that is, if
256			it is to be run at January 1st 2011 then it will run when the
257			system time reaches or surpasses this time.
258
259			* non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
260			In this mode the watcher will always be scheduled to time out at
261			the next "$at + N * $interval" time (for some integer N) and
262			then repeat, regardless of any time jumps.
263
264			This can be used to create timers that do not drift with respect
265			to system time:
266
267			my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
268
269			That doesn't mean there will always be 3600 seconds in between
270			triggers, but only that the the clalback will be called when the
271			system time shows a full hour (UTC).
272
273			Another way to think about it (for the mathematically inclined)
274			is that EV::periodic will try to run the callback in this mode
275			at the next possible time where "$time = $at (mod $interval)",
276			regardless of any time jumps.
277
278			* manual reschedule mode ($reschedule_cb = coderef)
279			In this mode $interval and $at are both being ignored. Instead,
280			each time the periodic watcher gets scheduled, the first
281			callback ($reschedule_cb) will be called with the watcher as
282			first, and the current time as second argument.
283
284			*This callback MUST NOT stop or destroy this or any other
285			periodic watcher, ever*. If you need to stop it, return 1e30 and
286			stop it afterwards.
287
288			It must return the next time to trigger, based on the passed
289			time value (that is, the lowest time value larger than to the
290			second argument). It will usually be called just before the
291			callback will be triggered, but might be called at other times,
292			too.
293
294			This can be used to create very complex timers, such as a timer
295			that triggers on each midnight, local time (actually 24 hours
296			after the last midnight, to keep the example simple. If you know
297			a way to do it correctly in about the same space (without
298			requiring elaborate modules), drop me a note :):
299
300			my $daily = EV::periodic 0, 0, sub {
301			my ($w, $now) = @_;
302
303			use Time::Local ();
304			my (undef, undef, undef, $d, $m, $y) = localtime $now;
305			86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
306			}, sub {
307			print "it's midnight or likely shortly after, now\n";
308			};
309	root	1.6
310			The "periodic_ns" variant doesn't start (activate) the newly created
311	root	1.2	watcher.
312
313	root	1.8	$w->set ($at, $interval, $reschedule_cb)
314	root	1.6	Reconfigures the watcher, see the constructor above for details. Can
315			be at any time.
316
317	root	1.8	$w->again
318			Simply stops and starts the watcher again.
319
320	root	1.6	$w = EV::signal $signal, $callback
321			$w = EV::signal_ns $signal, $callback
322	root	1.4	Call the callback when $signal is received (the signal can be
323	root	1.6	specified by number or by name, just as with kill or %SIG).
324	root	1.4
325			EV will grab the signal for the process (the kernel only allows one
326	root	1.6	component to receive a signal at a time) when you start a signal
327			watcher, and removes it again when you stop it. Perl does the same
328			when you add/remove callbacks to %SIG, so watch out.
329
330			You can have as many signal watchers per signal as you want.
331	root	1.1
332	root	1.6	The "signal_ns" variant doesn't start (activate) the newly created
333			watcher.
334
335			$w->set ($signal)
336			Reconfigures the watcher, see the constructor above for details. Can
337			be at any time.
338
339	root	1.7	$current_signum = $w->signal
340			$old_signum = $w->signal ($new_signal)
341			Returns the previously set signal (always as a number not name) and
342			optionally set a new one.
343
344	root	1.6	$w = EV::child $pid, $callback
345			$w = EV::child_ns $pid, $callback
346			Call the callback when a status change for pid $pid (or any pid if
347			$pid is 0) has been received. More precisely: when the process
348			receives a SIGCHLD, EV will fetch the outstanding exit/wait status
349			for all changed/zombie children and call the callback.
350
351	root	1.7	You can access both status and pid by using the "rstatus" and "rpid"
352			methods on the watcher object.
353	root	1.6
354			You can have as many pid watchers per pid as you want.
355
356			The "child_ns" variant doesn't start (activate) the newly created
357			watcher.
358	root	1.1
359	root	1.6	$w->set ($pid)
360			Reconfigures the watcher, see the constructor above for details. Can
361			be at any time.
362
363	root	1.7	$current_pid = $w->pid
364			$old_pid = $w->pid ($new_pid)
365			Returns the previously set process id and optionally set a new one.
366
367			$exit_status = $w->rstatus
368			Return the exit/wait status (as returned by waitpid, see the waitpid
369			entry in perlfunc).
370
371			$pid = $w->rpid
372			Return the pid of the awaited child (useful when you have installed
373			a watcher for all pids).
374
375	root	1.6	$w = EV::idle $callback
376			$w = EV::idle_ns $callback
377			Call the callback when there are no pending io, timer/periodic,
378			signal or child events, i.e. when the process is idle.
379	root	1.1
380	root	1.6	The process will not block as long as any idle watchers are active,
381			and they will be called repeatedly until stopped.
382	root	1.1
383	root	1.6	The "idle_ns" variant doesn't start (activate) the newly created
384			watcher.
385	root	1.4
386	root	1.6	$w = EV::prepare $callback
387			$w = EV::prepare_ns $callback
388			Call the callback just before the process would block. You can still
389			create/modify any watchers at this point.
390	root	1.1
391	root	1.6	See the EV::check watcher, below, for explanations and an example.
392	root	1.1
393	root	1.6	The "prepare_ns" variant doesn't start (activate) the newly created
394			watcher.
395	root	1.1
396	root	1.6	$w = EV::check $callback
397			$w = EV::check_ns $callback
398			Call the callback just after the process wakes up again (after it
399			has gathered events), but before any other callbacks have been
400			invoked.
401
402			This is used to integrate other event-based software into the EV
403			mainloop: You register a prepare callback and in there, you create
404			io and timer watchers as required by the other software. Here is a
405			real-world example of integrating Net::SNMP (with some details left
406			out):
407
408			our @snmp_watcher;
409
410			our $snmp_prepare = EV::prepare sub {
411			# do nothing unless active
412			$dispatcher->{_event_queue_h}
413			or return;
414
415			# make the dispatcher handle any outstanding stuff
416
417			# create an IO watcher for each and every socket
418			@snmp_watcher = (
419			(map { EV::io $_, EV::READ, sub { } }
420			keys %{ $dispatcher->{_descriptors} }),
421			);
422
423			# if there are any timeouts, also create a timer
424			push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
425			if $event->[Net::SNMP::Dispatcher::_ACTIVE];
426			};
427
428			The callbacks are irrelevant, the only purpose of those watchers is
429			to wake up the process as soon as one of those events occurs (socket
430			readable, or timer timed out). The corresponding EV::check watcher
431			will then clean up:
432
433			our $snmp_check = EV::check sub {
434			# destroy all watchers
435			@snmp_watcher = ();
436
437			# make the dispatcher handle any new stuff
438			};
439
440			The callbacks of the created watchers will not be called as the
441			watchers are destroyed before this cna happen (remember EV::check
442			gets called first).
443	root	1.1
444	root	1.6	The "check_ns" variant doesn't start (activate) the newly created
445			watcher.
446	root	1.1
447	root	1.5	THREADS
448			Threads are not supported by this in any way. Perl pseudo-threads is
449	root	1.6	evil stuff and must die.
450	root	1.2
451			SEE ALSO
452	root	1.6	L<EV::DNS>, L<EV::AnyEvent>.
453	root	1.1
454			AUTHOR
455			Marc Lehmann <schmorp@schmorp.de>
456			http://home.schmorp.de/
457