AnyEvent-Fork-Pool/Pool.pm

=head1 NAME

AnyEvent::Fork::Pool - simple process pool manager on top of AnyEvent::Fork

=head1 SYNOPSIS

   use AnyEvent;
   use AnyEvent::Fork::Pool;
   # use AnyEvent::Fork is not needed

   # all parameters with default values
   my $pool = AnyEvent::Fork
      ->new
      ->require ("MyWorker")
      ->AnyEvent::Fork::Pool::run (
           "MyWorker::run", # the worker function

           # pool management
           max        => 4,   # absolute maximum # of processes
           idle       => 2,   # minimum # of idle processes
           load       => 2,   # queue at most this number of jobs per process
           start      => 0.1, # wait this many seconds before starting a new process
           stop       => 1,   # wait this many seconds before stopping an idle process
           on_destroy => (my $finish = AE::cv), # called when object is destroyed

           # parameters passed to AnyEvent::Fork::RPC
           async      => 0,
           on_error   => sub { die "FATAL: $_[0]\n" },
           on_event   => sub { my @ev = @_ },
           init       => "MyWorker::init",
           serialiser => $AnyEvent::Fork::RPC::STRING_SERIALISER,
        );

   for (1..10) {
      $pool->(doit => $_, sub {
         print "MyWorker::run returned @_\n";
      });
   }

   undef $pool;

   $finish->recv;

=head1 DESCRIPTION

This module uses processes created via L<AnyEvent::Fork> and the RPC
protocol implement in L<AnyEvent::Fork::RPC> to create a load-balanced
pool of processes that handles jobs.

Understanding of L<AnyEvent::Fork> is helpful but not critical to be able
to use this module, but a thorough understanding of L<AnyEvent::Fork::RPC>
is, as it defines the actual API that needs to be implemented in the
children.

=head1 EXAMPLES

=head1 PARENT USAGE

=over 4

=cut

package AnyEvent::Fork::Pool;

use common::sense;

use Scalar::Util ();

use Guard ();
use Array::Heap ();

use AnyEvent;
use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
use AnyEvent::Fork::RPC;

# these are used for the first and last argument of events
# in the hope of not colliding. yes, I don't like it either,
# but didn't come up with an obviously better alternative.
my $magic0 = ':t6Z@HK1N%Dx@_7?=~-7NQgWDdAs6a,jFN=wLO0*jD*1%P';
my $magic1 = '<~53rexz.U`!]X[A235^"fyEoiTF\T~oH1l/N6+Djep9b~bI9`\1x%B~vWO1q*';

our $VERSION = 0.1;

=item my $rpc = AnyEvent::Fork::Pool::run $fork, $function, [key => value...]

The traditional way to call it. But it is way cooler to call it in the
following way:

=item my $rpc = $fork->AnyEvent::Fork::Pool::run ($function, [key => value...])

Creates a new pool object with the specified C<$function> as function
(name) to call for each request. The pool uses the C<$fork> object as the
template when creating worker processes.

You can supply your own template process, or tell C<AnyEvent::Fork::Pool>
to create one.

A relatively large number of key/value pairs can be specified to influence
the behaviour. They are grouped into the categories "pool management",
"template process" and "rpc parameters".

=over 4

=item Pool Management

The pool consists of a certain number of worker processes. These options
decide how many of these processes exist and when they are started and
stopp.ed

=over 4

=item idle => $count (default: 0)

The minimum amount of idle processes in the pool - when there are fewer
than this many idle workers, C<AnyEvent::Fork::Pool> will try to start new
ones, subject to C<max> and C<start>.

This is also the initial/minimum amount of workers in the pool. The
default of zero means that the pool starts empty and can shrink back to
zero workers over time.

=item max => $count (default: 4)

The maximum number of processes in the pool, in addition to the template
process. C<AnyEvent::Fork::Pool> will never create more than this number
of worker processes, although there can be more temporarily when a worker
is shut down and hasn't exited yet.

=item load => $count (default: 2)

The maximum number of concurrent jobs sent to a single worker
process. Worker processes that handle this number of jobs already are
called "busy".

Jobs that cannot be sent to a worker immediately (because all workers are
busy) will be queued until a worker is available.

=item start => $seconds (default: 0.1)

When a job is queued and all workers are busy, a timer is started. If the
timer elapses and there are still jobs that cannot be queued to a worker,
a new worker is started.

This configurs the time that all workers must be busy before a new worker
is started. Or, put differently, the minimum delay betwene starting new
workers.

The delay is zero by default, which means new workers will be started
without delay.

=item stop => $seconds (default: 1)

When a worker has no jobs to execute it becomes idle. An idle worker that
hasn't executed a job within this amount of time will be stopped, unless
the other parameters say otherwise.

=item on_destroy => $callback->() (default: none)

When a pool object goes out of scope, it will still handle all outstanding
jobs. After that, it will destroy all workers (and also the template
process if it isn't referenced otherwise).

=back

=item Template Process

The worker processes are all forked from a single template
process. Ideally, all modules and all cdoe used by the worker, as well as
any shared data structures should be loaded into the template process, to
take advantage of data sharing via fork.

You can create your own template process by creating a L<AnyEvent::Fork>
object yourself and passing it as the C<template> parameter, but
C<AnyEvent::Fork::Pool> can create one for you, including some standard
options.

=over 4

=item template => $fork (default: C<< AnyEvent::Fork->new >>)

The template process to use, if you want to create your own.

=item require => \@modules (default: C<[]>)

The modules in this list will be laoded into the template process.

=item eval => "# perl code to execute in template" (default: none)

This is a perl string that is evaluated after creating the template
process and after requiring the modules. It can do whatever it wants to
configure the process, but it must not do anything that would keep a later
fork from working (so must not create event handlers or (real) threads for
example).

=back

=item AnyEvent::Fork::RPC Parameters

These parameters are all passed directly to L<AnyEvent::Fork::RPC>. They
are only briefly mentioned here, for their full documentation
please refer to the L<AnyEvent::Fork::RPC> documentation. Also, the
default values mentioned here are only documented as a best effort -
L<AnyEvent::Fork::RPC> documentation is binding.

=over 4

=item async => $boolean (default: 0)

Whether to sue the synchronous or asynchronous RPC backend.

=item on_error => $callback->($message) (default: die with message)

The callback to call on any (fatal) errors.

=item on_event => $callback->(...) (default: C<sub { }>, unlike L<AnyEvent::Fork::RPC>)

The callback to invoke on events.

=item init => $initfunction (default: none)

The function to call in the child, once before handling requests.

=item serialiser => $serialiser (defailt: $AnyEvent::Fork::RPC::STRING_SERIALISER)

The serialiser to use.

=back

=back

=cut

sub run {
   my ($template, $function, %arg) = @_;

   my $max        = $arg{max}        || 4;
   my $idle       = $arg{idle}       || 0,
   my $load       = $arg{load}       || 2,
   my $start      = $arg{start}      || 0.1,
   my $stop       = $arg{stop}       || 1,
   my $on_event   = $arg{on_event}   || sub { },
   my $on_destroy = $arg{on_destroy};

   my @rpc = (
      async      => $arg{async},
      init       => $arg{init},
      serialiser => $arg{serialiser},
      on_error   => $arg{on_error},
   );

   my (@pool, @queue, $nidle, $start_w, $stop_w, $shutdown);
   my ($start, $stop, $want_start, $want_stop, $scheduler);

   my $destroy_guard = Guard::guard {
      $on_destroy->()
         if $on_destroy;
   };

   my $busy;#d#

   $template
      ->require ("AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync"))
      ->eval ('
           my ($magic0, $magic1) = @_;
           sub AnyEvent::Fork::Pool::quit() {
              AnyEvent::Fork::RPC::on_event $magic0, "quit", $magic1;
           }
        ', $magic0, $magic1)
      ->eval (delete $arg{eval});

   $start = sub {
      my $proc = [0, 0, undef]; # load, index, rpc

      warn "start a worker\n";#d#

      $proc->[2] = $template
         ->fork
         ->AnyEvent::Fork::RPC::run ($function,
              @rpc,
              on_event => sub {
                 if (@_ == 3 && $_[0] eq $magic0 && $_[2] eq $magic1) {
                    $destroy_guard if 0; # keep it alive

                    $_[1] eq "quit" and $stop->($proc);
                    return;
                 }

                 &$on_event;
              },
           )
      ;

      ++$nidle;
      Array::Heap::push_heap @pool, $proc;

      Scalar::Util::weaken $proc;
   };

   $stop = sub {
      my $proc = shift;

      $proc->[0]
         or --$nidle;

      Array::Heap::splice_heap_idx @pool, $proc->[1]
         if defined $proc->[1];
   };

   $want_start = sub {
      undef $stop_w;

      $start_w ||= AE::timer $start, 0, sub {
         undef $start_w;

         if (@queue) {
            $start->();
            $scheduler->();
         }
      };
   };

   $want_stop = sub {
      $stop_w ||= AE::timer $stop, 0, sub {
         undef $stop_w;

         $stop->($pool[0])
            if $nidle;
      };
   };

   $scheduler = sub {
      if (@queue) {
         while (@queue) {
            my $proc = $pool[0];

            if ($proc->[0] < $load) {
         warn "free $proc $proc->[0]\n";#d#
               # found free worker
               $proc->[0]++
                  or --$nidle >= $idle
                  or $want_start->();

               Array::Heap::adjust_heap @pool, 0;

               my $job = shift @queue;
               my $ocb = pop @$job;

               $proc->[2]->(@$job, sub {
                  --$busy; warn "busy now $busy\n";#d#
                  # reduce queue counter
                  --$pool[$_][0]
                     or ++$nidle > $idle
                     or $want_stop->();

                  Array::Heap::adjust_heap @pool, $_;

                  $scheduler->();

                  &$ocb;
               });
            } else {
         warn "busy $proc->[0]\n";#d#
               # all busy, delay

               $want_start->();
               last;
            }
         }
      } elsif ($shutdown) {
         @pool = ();
         undef $start_w;
         undef $start; # frees $destroy_guard reference

         $stop->($pool[0])
            while $nidle;
      }
   };

   my $shutdown_guard = Guard::guard {
      $shutdown = 1;
      $scheduler->();
   };

   $start->()
      while @pool < $idle;

   sub {
      $shutdown_guard if 0; # keep it alive

      ++$busy;#d#

      $start->()
         unless @pool;

      push @queue, [@_];
      $scheduler->();
   }
}

=item $pool->call (..., $cb->(...))

Call the RPC function of a worker with the given arguments, and when the
worker is done, call the C<$cb> with the results, like just calling the
L<AnyEvent::Fork::RPC> object directly.

If there is no free worker, the call will be queued.

Note that there can be considerable time between calling this method and
the call actually being executed. During this time, the parameters passed
to this function are effectively read-only - modifying them after the call
and before the callback is invoked causes undefined behaviour.

=cut

=back

=head1 SEE ALSO

L<AnyEvent::Fork>, to create the processes in the first place.

L<AnyEvent::Fork::RPC>, which implements the RPC protocol and API.

=head1 AUTHOR AND CONTACT INFORMATION

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/AnyEvent-Fork-Pool

=cut

1

Revision:	1.3
Committed:	Sat Apr 20 16:38:10 2013 UTC (11 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.2:	+206 -204 lines
Log Message:	api mostly finalised
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			AnyEvent::Fork::Pool - simple process pool manager on top of AnyEvent::Fork
4
5			=head1 SYNOPSIS
6
7			use AnyEvent;
8			use AnyEvent::Fork::Pool;
9			# use AnyEvent::Fork is not needed
10
11			# all parameters with default values
12	root	1.3	my $pool = AnyEvent::Fork
13			->new
14			->require ("MyWorker")
15			->AnyEvent::Fork::Pool::run (
16			"MyWorker::run", # the worker function
17
18			# pool management
19			max => 4, # absolute maximum # of processes
20			idle => 2, # minimum # of idle processes
21			load => 2, # queue at most this number of jobs per process
22			start => 0.1, # wait this many seconds before starting a new process
23			stop => 1, # wait this many seconds before stopping an idle process
24			on_destroy => (my $finish = AE::cv), # called when object is destroyed
25
26			# parameters passed to AnyEvent::Fork::RPC
27			async => 0,
28			on_error => sub { die "FATAL: $_[0]\n" },
29			on_event => sub { my @ev = @_ },
30			init => "MyWorker::init",
31			serialiser => $AnyEvent::Fork::RPC::STRING_SERIALISER,
32			);
33	root	1.1
34			for (1..10) {
35	root	1.3	$pool->(doit => $_, sub {
36	root	1.1	print "MyWorker::run returned @_\n";
37			});
38			}
39
40			undef $pool;
41
42			$finish->recv;
43
44			=head1 DESCRIPTION
45
46			This module uses processes created via L<AnyEvent::Fork> and the RPC
47			protocol implement in L<AnyEvent::Fork::RPC> to create a load-balanced
48			pool of processes that handles jobs.
49
50			Understanding of L<AnyEvent::Fork> is helpful but not critical to be able
51			to use this module, but a thorough understanding of L<AnyEvent::Fork::RPC>
52			is, as it defines the actual API that needs to be implemented in the
53			children.
54
55			=head1 EXAMPLES
56
57	root	1.2	=head1 PARENT USAGE
58	root	1.1
59			=over 4
60
61			=cut
62
63			package AnyEvent::Fork::Pool;
64
65			use common::sense;
66
67	root	1.2	use Scalar::Util ();
68
69	root	1.3	use Guard ();
70	root	1.2	use Array::Heap ();
71	root	1.1
72			use AnyEvent;
73			use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
74			use AnyEvent::Fork::RPC;
75
76	root	1.3	# these are used for the first and last argument of events
77			# in the hope of not colliding. yes, I don't like it either,
78			# but didn't come up with an obviously better alternative.
79	root	1.2	my $magic0 = ':t6Z@HK1N%Dx@_7?=~-7NQgWDdAs6a,jFN=wLO0jD1%P';
80	root	1.3	my $magic1 = '<~53rexz.U`!]X[A235^"fyEoiTF\T~oH1l/N6+Djep9b~bI9`\1x%B~vWO1q*';
81	root	1.2
82	root	1.1	our $VERSION = 0.1;
83
84	root	1.3	=item my $rpc = AnyEvent::Fork::Pool::run $fork, $function, [key => value...]
85
86			The traditional way to call it. But it is way cooler to call it in the
87			following way:
88
89			=item my $rpc = $fork->AnyEvent::Fork::Pool::run ($function, [key => value...])
90	root	1.2
91			Creates a new pool object with the specified C<$function> as function
92	root	1.3	(name) to call for each request. The pool uses the C<$fork> object as the
93			template when creating worker processes.
94	root	1.2
95			You can supply your own template process, or tell C<AnyEvent::Fork::Pool>
96			to create one.
97
98			A relatively large number of key/value pairs can be specified to influence
99			the behaviour. They are grouped into the categories "pool management",
100			"template process" and "rpc parameters".
101	root	1.1
102			=over 4
103
104	root	1.2	=item Pool Management
105
106			The pool consists of a certain number of worker processes. These options
107			decide how many of these processes exist and when they are started and
108			stopp.ed
109
110			=over 4
111
112	root	1.3	=item idle => $count (default: 0)
113	root	1.2
114	root	1.3	The minimum amount of idle processes in the pool - when there are fewer
115			than this many idle workers, C<AnyEvent::Fork::Pool> will try to start new
116			ones, subject to C<max> and C<start>.
117
118			This is also the initial/minimum amount of workers in the pool. The
119			default of zero means that the pool starts empty and can shrink back to
120			zero workers over time.
121	root	1.2
122			=item max => $count (default: 4)
123
124			The maximum number of processes in the pool, in addition to the template
125			process. C<AnyEvent::Fork::Pool> will never create more than this number
126	root	1.3	of worker processes, although there can be more temporarily when a worker
127			is shut down and hasn't exited yet.
128	root	1.2
129	root	1.3	=item load => $count (default: 2)
130	root	1.2
131	root	1.3	The maximum number of concurrent jobs sent to a single worker
132			process. Worker processes that handle this number of jobs already are
133			called "busy".
134	root	1.1
135	root	1.2	Jobs that cannot be sent to a worker immediately (because all workers are
136			busy) will be queued until a worker is available.
137	root	1.1
138	root	1.3	=item start => $seconds (default: 0.1)
139	root	1.1
140	root	1.2	When a job is queued and all workers are busy, a timer is started. If the
141			timer elapses and there are still jobs that cannot be queued to a worker,
142			a new worker is started.
143	root	1.1
144	root	1.2	This configurs the time that all workers must be busy before a new worker
145			is started. Or, put differently, the minimum delay betwene starting new
146			workers.
147	root	1.1
148	root	1.2	The delay is zero by default, which means new workers will be started
149			without delay.
150	root	1.1
151	root	1.3	=item stop => $seconds (default: 1)
152	root	1.1
153	root	1.2	When a worker has no jobs to execute it becomes idle. An idle worker that
154			hasn't executed a job within this amount of time will be stopped, unless
155			the other parameters say otherwise.
156
157			=item on_destroy => $callback->() (default: none)
158
159			When a pool object goes out of scope, it will still handle all outstanding
160			jobs. After that, it will destroy all workers (and also the template
161			process if it isn't referenced otherwise).
162
163			=back
164
165			=item Template Process
166
167			The worker processes are all forked from a single template
168			process. Ideally, all modules and all cdoe used by the worker, as well as
169			any shared data structures should be loaded into the template process, to
170			take advantage of data sharing via fork.
171
172			You can create your own template process by creating a L<AnyEvent::Fork>
173			object yourself and passing it as the C<template> parameter, but
174			C<AnyEvent::Fork::Pool> can create one for you, including some standard
175			options.
176
177			=over 4
178
179			=item template => $fork (default: C<< AnyEvent::Fork->new >>)
180
181			The template process to use, if you want to create your own.
182
183			=item require => \@modules (default: C<[]>)
184
185			The modules in this list will be laoded into the template process.
186
187			=item eval => "# perl code to execute in template" (default: none)
188
189			This is a perl string that is evaluated after creating the template
190			process and after requiring the modules. It can do whatever it wants to
191			configure the process, but it must not do anything that would keep a later
192			fork from working (so must not create event handlers or (real) threads for
193			example).
194
195			=back
196
197			=item AnyEvent::Fork::RPC Parameters
198
199			These parameters are all passed directly to L<AnyEvent::Fork::RPC>. They
200			are only briefly mentioned here, for their full documentation
201			please refer to the L<AnyEvent::Fork::RPC> documentation. Also, the
202			default values mentioned here are only documented as a best effort -
203			L<AnyEvent::Fork::RPC> documentation is binding.
204
205			=over 4
206	root	1.1
207			=item async => $boolean (default: 0)
208
209	root	1.2	Whether to sue the synchronous or asynchronous RPC backend.
210	root	1.1
211	root	1.2	=item on_error => $callback->($message) (default: die with message)
212	root	1.1
213	root	1.2	The callback to call on any (fatal) errors.
214	root	1.1
215	root	1.2	=item on_event => $callback->(...) (default: C<sub { }>, unlike L<AnyEvent::Fork::RPC>)
216	root	1.1
217	root	1.2	The callback to invoke on events.
218	root	1.1
219	root	1.2	=item init => $initfunction (default: none)
220	root	1.1
221	root	1.2	The function to call in the child, once before handling requests.
222	root	1.1
223	root	1.2	=item serialiser => $serialiser (defailt: $AnyEvent::Fork::RPC::STRING_SERIALISER)
224	root	1.1
225	root	1.2	The serialiser to use.
226	root	1.1
227	root	1.2	=back
228	root	1.1
229			=back
230
231			=cut
232
233	root	1.3	sub run {
234			my ($template, $function, %arg) = @_;
235
236			my $max = $arg{max} \|\| 4;
237			my $idle = $arg{idle} \|\| 0,
238			my $load = $arg{load} \|\| 2,
239			my $start = $arg{start} \|\| 0.1,
240			my $stop = $arg{stop} \|\| 1,
241			my $on_event = $arg{on_event} \|\| sub { },
242			my $on_destroy = $arg{on_destroy};
243
244			my @rpc = (
245			async => $arg{async},
246			init => $arg{init},
247			serialiser => $arg{serialiser},
248			on_error => $arg{on_error},
249			);
250
251			my (@pool, @queue, $nidle, $start_w, $stop_w, $shutdown);
252			my ($start, $stop, $want_start, $want_stop, $scheduler);
253
254			my $destroy_guard = Guard::guard {
255			$on_destroy->()
256			if $on_destroy;
257			};
258	root	1.2
259	root	1.3	my $busy;#d#
260
261			$template
262			->require ("AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync"))
263	root	1.2	->eval ('
264	root	1.3	my ($magic0, $magic1) = @_;
265	root	1.2	sub AnyEvent::Fork::Pool::quit() {
266	root	1.3	AnyEvent::Fork::RPC::on_event $magic0, "quit", $magic1;
267	root	1.2	}
268	root	1.3	', $magic0, $magic1)
269			->eval (delete $arg{eval});
270
271			$start = sub {
272			my $proc = [0, 0, undef]; # load, index, rpc
273	root	1.2
274	root	1.3	warn "start a worker\n";#d#
275	root	1.1
276	root	1.3	$proc->[2] = $template
277			->fork
278			->AnyEvent::Fork::RPC::run ($function,
279			@rpc,
280			on_event => sub {
281			if (@_ == 3 && $_[0] eq $magic0 && $_[2] eq $magic1) {
282			$destroy_guard if 0; # keep it alive
283	root	1.2
284	root	1.3	$_[1] eq "quit" and $stop->($proc);
285			return;
286	root	1.2	}
287
288	root	1.3	&$on_event;
289			},
290			)
291			;
292
293			++$nidle;
294			Array::Heap::push_heap @pool, $proc;
295
296			Scalar::Util::weaken $proc;
297			};
298
299			$stop = sub {
300			my $proc = shift;
301
302			$proc->[0]
303			or --$nidle;
304
305			Array::Heap::splice_heap_idx @pool, $proc->[1]
306			if defined $proc->[1];
307			};
308
309			$want_start = sub {
310			undef $stop_w;
311
312			$start_w \|\|= AE::timer $start, 0, sub {
313			undef $start_w;
314
315			if (@queue) {
316			$start->();
317			$scheduler->();
318			}
319			};
320			};
321
322			$want_stop = sub {
323			$stop_w \|\|= AE::timer $stop, 0, sub {
324			undef $stop_w;
325
326			$stop->($pool[0])
327			if $nidle;
328			};
329			};
330
331			$scheduler = sub {
332			if (@queue) {
333			while (@queue) {
334			my $proc = $pool[0];
335
336			if ($proc->[0] < $load) {
337			warn "free $proc $proc->[0]\n";#d#
338			# found free worker
339			$proc->[0]++
340			or --$nidle >= $idle
341			or $want_start->();
342
343			Array::Heap::adjust_heap @pool, 0;
344
345			my $job = shift @queue;
346			my $ocb = pop @$job;
347
348			$proc->[2]->(@$job, sub {
349			--$busy; warn "busy now $busy\n";#d#
350			# reduce queue counter
351			--$pool[$_][0]
352			or ++$nidle > $idle
353			or $want_stop->();
354
355			Array::Heap::adjust_heap @pool, $_;
356
357			$scheduler->();
358
359			&$ocb;
360			});
361			} else {
362			warn "busy $proc->[0]\n";#d#
363			# all busy, delay
364
365			$want_start->();
366			last;
367			}
368			}
369			} elsif ($shutdown) {
370			@pool = ();
371			undef $start_w;
372			undef $start; # frees $destroy_guard reference
373
374			$stop->($pool[0])
375			while $nidle;
376			}
377			};
378
379			my $shutdown_guard = Guard::guard {
380			$shutdown = 1;
381			$scheduler->();
382			};
383
384			$start->()
385			while @pool < $idle;
386
387			sub {
388			$shutdown_guard if 0; # keep it alive
389	root	1.2
390	root	1.3	++$busy;#d#
391
392			$start->()
393			unless @pool;
394
395			push @queue, [@_];
396			$scheduler->();
397			}
398	root	1.2	}
399
400			=item $pool->call (..., $cb->(...))
401
402			Call the RPC function of a worker with the given arguments, and when the
403			worker is done, call the C<$cb> with the results, like just calling the
404			L<AnyEvent::Fork::RPC> object directly.
405
406			If there is no free worker, the call will be queued.
407
408			Note that there can be considerable time between calling this method and
409			the call actually being executed. During this time, the parameters passed
410			to this function are effectively read-only - modifying them after the call
411			and before the callback is invoked causes undefined behaviour.
412
413			=cut
414	root	1.1
415			=back
416
417			=head1 SEE ALSO
418
419			L<AnyEvent::Fork>, to create the processes in the first place.
420
421			L<AnyEvent::Fork::RPC>, which implements the RPC protocol and API.
422
423			=head1 AUTHOR AND CONTACT INFORMATION
424
425			Marc Lehmann <schmorp@schmorp.de>
426			http://software.schmorp.de/pkg/AnyEvent-Fork-Pool
427
428			=cut
429
430			1
431