AnyEvent-Fork-RPC/RPC.pm

=head1 NAME

AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork

=head1 SYNOPSIS

   use AnyEvent::Fork;
   use AnyEvent::Fork::RPC;

   my $rpc = AnyEvent::Fork
      ->new
      ->require ("MyModule")
      ->AnyEvent::Fork::RPC::run (
         "MyModule::server",
      );

   my $cv = AE::cv;

   $rpc->(1, 2, 3, sub {
      print "MyModule::server returned @_\n";
      $cv->send;
   });

   $cv->recv;

=head1 DESCRIPTION

This module implements a simple RPC protocol and backend for processes
created via L<AnyEvent::Fork>, allowing you to call a function in the
child process and receive its return values (up to 4GB serialised).

It implements two different backends: a synchronous one that works like a
normal function call, and an asynchronous one that can run multiple jobs
concurrently in the child, using AnyEvent.

It also implements an asynchronous event mechanism from the child to the
parent, that could be used for progress indications or other information.

=head1 EXAMPLES

=head2 Synchronous Backend

Here is a simple example that implements a backend that executes C<unlink>
and C<rmdir> calls, and reports their status back. It also reports the
number of requests it has processed every three requests, which is clearly
silly, but illustrates the use of events.

First the parent process:

   use AnyEvent;
   use AnyEvent::Fork;
   use AnyEvent::Fork::RPC;

   my $done = AE::cv;

   my $rpc = AnyEvent::Fork
      ->new
      ->require ("MyWorker")
      ->AnyEvent::Fork::RPC::run ("MyWorker::run",
         on_event   => sub { warn "$_[0] requests handled\n" },
         on_destroy => $done,
      );

   for my $id (1..6) {
      $rpc->(rmdir => "/tmp/somepath/$id", sub {
         $_[0]
            or warn "/tmp/somepath/$id: $_[1]\n";
      });
   }

   undef $rpc;

   $done->recv;

The parent creates the process, queues a few rmdir's. It then forgets
about the C<$rpc> object, so that the child exits after it has handled the
requests, and then it waits till the requests have been handled.

The child is implemented using a separate module, C<MyWorker>, shown here:

   package MyWorker;

   my $count;

   sub run {
      my ($cmd, $path) = @_;

      AnyEvent::Fork::RPC::event ($count)
         unless ++$count % 3;

      my $status = $cmd eq "rmdir"  ? rmdir  $path
                 : $cmd eq "unlink" ? unlink $path
                 : die "fatal error, illegal command '$cmd'";

      $status or (0, "$!")
   }

   1

The C<run> function first sends a "progress" event every three calls, and
then executes C<rmdir> or C<unlink>, depending on the first parameter (or
dies with a fatal error - obviously, you must never let this happen :).

Eventually it returns the status value true if the command was successful,
or the status value 0 and the stringified error message.

On my system, running the first cdoe fragment with the given
F<MyWorker.pm> in the current directory yields:

   /tmp/somepath/1: No such file or directory
   /tmp/somepath/2: No such file or directory
   3  requests handled
   /tmp/somepath/3: No such file or directory
   /tmp/somepath/4: No such file or directory
   /tmp/somepath/5: No such file or directory
   6  requests handled
   /tmp/somepath/6: No such file or directory

Obviously, none of the directories I am trying to delete even exist. Also,
the events and responses are processed in exactly the same order as
they were created in the child, which is true for both synchronous and
asynchronous backends.

Note that the parentheses in the call to C<AnyEvent::Fork::RPC::event> are
not optional. That is because the function isn't defined when the code is
compiled. You can make sure it is visible by pre-loading the correct
backend module in the call to C<require>:

      ->require ("AnyEvent::Fork::RPC::Sync", "MyWorker")

Since the backend module declares the C<event> function, loading it first
ensures that perl will correctly interpret calls to it.

And as a final remark, there is a fine module on CPAN that can
asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
than this example, namely L<IO::AIO>.

=head1 PARENT PROCESS USAGE

This module exports nothing, and only implements a single function:

=over 4

=cut

package AnyEvent::Fork::RPC;

use common::sense;

use Errno ();
use Guard ();

use AnyEvent;
#use AnyEvent::Fork;

our $VERSION = 0.1;

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

This C<run> function/method can be used in place of the
L<AnyEvent::Fork::run> method. Just like that method, it takes over
the L<AnyEvent::Fork> process, but instead of calling the specified
C<$function> directly, it runs a server that accepts RPC calls and handles
responses.

It returns a function reference that can be used to call the function in
the child process, handling serialisation and data transfers.

The following key/value pairs are allowed. It is recommended to have at
least an C<on_error> or C<on_event> handler set.

=over 4

=item on_error => $cb->($msg)

Called on (fatal) errors, with a descriptive (hopefully) message. If
this callback is not provided, but C<on_event> is, then the C<on_event>
callback is called with the first argument being the string C<error>,
followed by the error message.

If neither handler is provided it prints the error to STDERR and will
start failing badly.

=item on_event => $cb->(...)

Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
child, with the arguments of that function passed to the callback.

Also called on errors when no C<on_error> handler is provided.

=item on_destroy => $cb->()

Called when the C<$rpc> object has been destroyed and all requests have
been successfully handled. This is useful when you queue some requests and
want the child to go away after it has handled them. The problem is that
the parent must not exit either until all requests have been handled, and
this cna be accomplished by waiting for this callback.

=item init => $function (default none)

When specified (by name), this function is called in the child as the very
first thing when taking over the process, with all the arguments normally
passed to the C<AnyEvent::Fork::run> function, except the communications
socket.

It can be used to do one-time things in the child such as storing passed
parameters or opening database connections.

It is called very early - before the serialisers are created or the
C<$function> name is resolved into a function reference, so it could be
used to load any modules that provide the serialiser or function. It can
not, however, create events.

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

The default server used in the child does all I/O blockingly, and only
allows a single RPC call to execute concurrently.

Setting C<async> to a true value switches to another implementation that
uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.

The actual API in the child is documented in the section that describes
the calling semantics of the returned C<$rpc> function.

If you want to pre-load the actual back-end modules to enable memory
sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.

If you use a template process and want to fork both sync and async
children, then it is permissible to laod both modules.

=item serialiser => $string (default: '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })')

All arguments, result data and event data have to be serialised to be
transferred between the processes. For this, they have to be frozen and
thawed in both parent and child processes.

By default, only octet strings can be passed between the processes, which
is reasonably fast and efficient.

For more complicated use cases, you can provide your own freeze and thaw
functions, by specifying a string with perl source code. It's supposed to
return two code references when evaluated: the first receives a list of
perl values and must return an octet string. The second receives the octet
string and must return the original list of values.

If you need an external module for serialisation, then you can either
pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
or C<require> statement into the serialiser string. Or both.

=back

=cut

our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })';

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

   my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER;
   my $on_event   = delete $arg{on_event};
   my $on_error   = delete $arg{on_error};
   my $on_destroy = delete $arg{on_destroy};
   
   # default for on_error is to on_event, if specified
   $on_error ||= $on_event
               ? sub { $on_event->(error => shift) }
               : sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };

   # default for on_event is to raise an error
   $on_event ||= sub { $on_error->("event received, but no on_event handler") };

   my ($f, $t) = eval $serialiser; die $@ if $@;

   my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);
   my ($rlen, $rbuf) = 512 - 16;

   my $wcb = sub {
      my $len = syswrite $fh, $wbuf;

      if (!defined $len) {
         if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
            undef $rw; undef $ww; # it ends here
            $on_error->("$!");
         }
      }

      substr $wbuf, 0, $len, "";

      unless (length $wbuf) {
         undef $ww;
         $shutdown and shutdown $fh, 1;
      }
   };

   my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");

   $self->require ($module)
        ->send_arg ($function, $arg{init}, $serialiser)
        ->run ("$module\::run", sub {
      $fh = shift;
      $rw = AE::io $fh, 0, sub {
         $rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
         my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;

         if ($len) {
            while (5 <= length $rbuf) {
               $len = unpack "L", $rbuf;
               4 + $len <= length $rbuf
                  or last;

               my @r = $t->(substr $rbuf, 4, $len);
               substr $rbuf, 0, $len + 4, "";
               
               if (pop @r) {
                  $on_event->(@r);
               } elsif (@rcb) {
                  (shift @rcb)->(@r);
               } else {
                  undef $rw; undef $ww;
                  $on_error->("unexpected data from child");
               }
            }
         } elsif (defined $len) {
            undef $rw; undef $ww; # it ends here

            if (@rcb) {
               $on_error->("unexpected eof");
            } else {
               $on_destroy->();
            }
         } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
            undef $rw; undef $ww; # it ends here
            $on_error->("read: $!");
         }
      };

      $ww ||= AE::io $fh, 1, $wcb;
   });

   my $guard = Guard::guard {
      $shutdown = 1;
      $ww ||= $fh && AE::io $fh, 1, $wcb;
   };

   sub {
      push @rcb, pop;

      $guard; # keep it alive

      $wbuf .= pack "L/a*", &$f;
      $ww ||= $fh && AE::io $fh, 1, $wcb;
   }
}

=item $rpc->(..., $cb->(...))

The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
reference. There are two things you can do with it: call it, and let it go
out of scope (let it get destroyed).

If C<async> was false when C<$rpc> was created (the default), then, if you
call C<$rpc>, the C<$function> is invoked with all arguments passed to
C<$rpc> except the last one (the callback). When the function returns, the
callback will be invoked with all the return values.

If C<async> was true, then the C<$function> receives an additional
initial argument, the result callback. In this case, returning from
C<$function> does nothing - the function only counts as "done" when the
result callback is called, and any arguments passed to it are considered
the return values. This makes it possible to "return" from event handlers
or e.g. Coro threads.

The other thing that can be done with the RPC object is to destroy it. In
this case, the child process will execute all remaining RPC calls, report
their results, and then exit.

=back

=head1 CHILD PROCESS USAGE

The following function is not available in this module. They are only
available in the namespace of this module when the child is running,
without having to load any extra modules. They are part of the child-side
API of L<AnyEvent::Fork::RPC>.

=over 4

=item AnyEvent::Fork::RPC::event ...

Send an event to the parent. Events are a bit like RPC calls made by the
child process to the parent, except that there is no notion of return
values.

=back

=head1 SEE ALSO

L<AnyEvent::Fork> (to create the processes in the first place),
L<AnyEvent::Fork::Pool> (to manage whole pools of processes).

=head1 AUTHOR AND CONTACT INFORMATION

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

=cut

1

Revision:	1.4
Committed:	Wed Apr 17 19:38:25 2013 UTC (11 years, 2 months ago) by root
Branch:	MAIN
Changes since 1.3:	+152 -11 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork
4
5			=head1 SYNOPSIS
6
7			use AnyEvent::Fork;
8			use AnyEvent::Fork::RPC;
9
10			my $rpc = AnyEvent::Fork
11			->new
12			->require ("MyModule")
13			->AnyEvent::Fork::RPC::run (
14			"MyModule::server",
15			);
16
17			my $cv = AE::cv;
18
19			$rpc->(1, 2, 3, sub {
20			print "MyModule::server returned @_\n";
21			$cv->send;
22			});
23
24			$cv->recv;
25
26			=head1 DESCRIPTION
27
28			This module implements a simple RPC protocol and backend for processes
29			created via L<AnyEvent::Fork>, allowing you to call a function in the
30			child process and receive its return values (up to 4GB serialised).
31
32			It implements two different backends: a synchronous one that works like a
33			normal function call, and an asynchronous one that can run multiple jobs
34			concurrently in the child, using AnyEvent.
35
36			It also implements an asynchronous event mechanism from the child to the
37			parent, that could be used for progress indications or other information.
38
39	root	1.4	=head1 EXAMPLES
40
41			=head2 Synchronous Backend
42
43			Here is a simple example that implements a backend that executes C<unlink>
44			and C<rmdir> calls, and reports their status back. It also reports the
45			number of requests it has processed every three requests, which is clearly
46			silly, but illustrates the use of events.
47
48			First the parent process:
49
50			use AnyEvent;
51			use AnyEvent::Fork;
52			use AnyEvent::Fork::RPC;
53
54			my $done = AE::cv;
55
56			my $rpc = AnyEvent::Fork
57			->new
58			->require ("MyWorker")
59			->AnyEvent::Fork::RPC::run ("MyWorker::run",
60			on_event => sub { warn "$_[0] requests handled\n" },
61			on_destroy => $done,
62			);
63
64			for my $id (1..6) {
65			$rpc->(rmdir => "/tmp/somepath/$id", sub {
66			$_[0]
67			or warn "/tmp/somepath/$id: $_[1]\n";
68			});
69			}
70
71			undef $rpc;
72
73			$done->recv;
74
75			The parent creates the process, queues a few rmdir's. It then forgets
76			about the C<$rpc> object, so that the child exits after it has handled the
77			requests, and then it waits till the requests have been handled.
78
79			The child is implemented using a separate module, C<MyWorker>, shown here:
80
81			package MyWorker;
82
83			my $count;
84
85			sub run {
86			my ($cmd, $path) = @_;
87
88			AnyEvent::Fork::RPC::event ($count)
89			unless ++$count % 3;
90
91			my $status = $cmd eq "rmdir" ? rmdir $path
92			: $cmd eq "unlink" ? unlink $path
93			: die "fatal error, illegal command '$cmd'";
94
95			$status or (0, "$!")
96			}
97
98			1
99
100			The C<run> function first sends a "progress" event every three calls, and
101			then executes C<rmdir> or C<unlink>, depending on the first parameter (or
102			dies with a fatal error - obviously, you must never let this happen :).
103
104			Eventually it returns the status value true if the command was successful,
105			or the status value 0 and the stringified error message.
106
107			On my system, running the first cdoe fragment with the given
108			F<MyWorker.pm> in the current directory yields:
109
110			/tmp/somepath/1: No such file or directory
111			/tmp/somepath/2: No such file or directory
112			3 requests handled
113			/tmp/somepath/3: No such file or directory
114			/tmp/somepath/4: No such file or directory
115			/tmp/somepath/5: No such file or directory
116			6 requests handled
117			/tmp/somepath/6: No such file or directory
118
119			Obviously, none of the directories I am trying to delete even exist. Also,
120			the events and responses are processed in exactly the same order as
121			they were created in the child, which is true for both synchronous and
122			asynchronous backends.
123
124			Note that the parentheses in the call to C<AnyEvent::Fork::RPC::event> are
125			not optional. That is because the function isn't defined when the code is
126			compiled. You can make sure it is visible by pre-loading the correct
127			backend module in the call to C<require>:
128
129			->require ("AnyEvent::Fork::RPC::Sync", "MyWorker")
130
131			Since the backend module declares the C<event> function, loading it first
132			ensures that perl will correctly interpret calls to it.
133
134			And as a final remark, there is a fine module on CPAN that can
135			asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
136			than this example, namely L<IO::AIO>.
137
138	root	1.1	=head1 PARENT PROCESS USAGE
139
140			This module exports nothing, and only implements a single function:
141
142			=over 4
143
144			=cut
145
146			package AnyEvent::Fork::RPC;
147
148			use common::sense;
149
150			use Errno ();
151			use Guard ();
152
153			use AnyEvent;
154			#use AnyEvent::Fork;
155
156			our $VERSION = 0.1;
157
158			=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
159
160			The traditional way to call it. But it is way cooler to call it in the
161			following way:
162
163			=item my $rpc = $fork->AnyEvent::Fork::RPC::run ($function, [key => value...])
164
165			This C<run> function/method can be used in place of the
166			L<AnyEvent::Fork::run> method. Just like that method, it takes over
167			the L<AnyEvent::Fork> process, but instead of calling the specified
168			C<$function> directly, it runs a server that accepts RPC calls and handles
169			responses.
170
171			It returns a function reference that can be used to call the function in
172			the child process, handling serialisation and data transfers.
173
174			The following key/value pairs are allowed. It is recommended to have at
175			least an C<on_error> or C<on_event> handler set.
176
177			=over 4
178
179			=item on_error => $cb->($msg)
180
181			Called on (fatal) errors, with a descriptive (hopefully) message. If
182			this callback is not provided, but C<on_event> is, then the C<on_event>
183			callback is called with the first argument being the string C<error>,
184			followed by the error message.
185
186			If neither handler is provided it prints the error to STDERR and will
187			start failing badly.
188
189			=item on_event => $cb->(...)
190
191			Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
192			child, with the arguments of that function passed to the callback.
193
194			Also called on errors when no C<on_error> handler is provided.
195
196	root	1.4	=item on_destroy => $cb->()
197
198			Called when the C<$rpc> object has been destroyed and all requests have
199			been successfully handled. This is useful when you queue some requests and
200			want the child to go away after it has handled them. The problem is that
201			the parent must not exit either until all requests have been handled, and
202			this cna be accomplished by waiting for this callback.
203
204	root	1.1	=item init => $function (default none)
205
206			When specified (by name), this function is called in the child as the very
207			first thing when taking over the process, with all the arguments normally
208			passed to the C<AnyEvent::Fork::run> function, except the communications
209			socket.
210
211			It can be used to do one-time things in the child such as storing passed
212			parameters or opening database connections.
213
214	root	1.4	It is called very early - before the serialisers are created or the
215			C<$function> name is resolved into a function reference, so it could be
216			used to load any modules that provide the serialiser or function. It can
217			not, however, create events.
218
219	root	1.1	=item async => $boolean (default: 0)
220
221			The default server used in the child does all I/O blockingly, and only
222			allows a single RPC call to execute concurrently.
223
224			Setting C<async> to a true value switches to another implementation that
225			uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.
226
227			The actual API in the child is documented in the section that describes
228			the calling semantics of the returned C<$rpc> function.
229
230	root	1.2	If you want to pre-load the actual back-end modules to enable memory
231			sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
232			synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
233
234	root	1.4	If you use a template process and want to fork both sync and async
235			children, then it is permissible to laod both modules.
236
237	root	1.1	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')
238
239			All arguments, result data and event data have to be serialised to be
240			transferred between the processes. For this, they have to be frozen and
241			thawed in both parent and child processes.
242
243			By default, only octet strings can be passed between the processes, which
244			is reasonably fast and efficient.
245
246			For more complicated use cases, you can provide your own freeze and thaw
247			functions, by specifying a string with perl source code. It's supposed to
248			return two code references when evaluated: the first receives a list of
249			perl values and must return an octet string. The second receives the octet
250			string and must return the original list of values.
251
252	root	1.2	If you need an external module for serialisation, then you can either
253			pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
254			or C<require> statement into the serialiser string. Or both.
255
256	root	1.1	=back
257
258			=cut
259
260	root	1.2	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
261
262	root	1.1	sub run {
263			my ($self, $function, %arg) = @_;
264
265	root	1.2	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
266	root	1.1	my $on_event = delete $arg{on_event};
267			my $on_error = delete $arg{on_error};
268	root	1.4	my $on_destroy = delete $arg{on_destroy};
269	root	1.1
270			# default for on_error is to on_event, if specified
271			$on_error \|\|= $on_event
272			? sub { $on_event->(error => shift) }
273			: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };
274
275			# default for on_event is to raise an error
276			$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
277
278			my ($f, $t) = eval $serialiser; die $@ if $@;
279
280	root	1.4	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);
281			my ($rlen, $rbuf) = 512 - 16;
282	root	1.1
283			my $wcb = sub {
284			my $len = syswrite $fh, $wbuf;
285
286			if (!defined $len) {
287			if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
288			undef $rw; undef $ww; # it ends here
289			$on_error->("$!");
290			}
291			}
292
293			substr $wbuf, 0, $len, "";
294
295			unless (length $wbuf) {
296			undef $ww;
297			$shutdown and shutdown $fh, 1;
298			}
299			};
300
301			my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");
302
303			$self->require ($module)
304			->send_arg ($function, $arg{init}, $serialiser)
305			->run ("$module\::run", sub {
306			$fh = shift;
307			$rw = AE::io $fh, 0, sub {
308	root	1.4	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
309			my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
310	root	1.1
311			if ($len) {
312			while (5 <= length $rbuf) {
313			$len = unpack "L", $rbuf;
314	root	1.2	4 + $len <= length $rbuf
315			or last;
316
317			my @r = $t->(substr $rbuf, 4, $len);
318			substr $rbuf, 0, $len + 4, "";
319
320			if (pop @r) {
321			$on_event->(@r);
322			} elsif (@rcb) {
323			(shift @rcb)->(@r);
324			} else {
325			undef $rw; undef $ww;
326			$on_error->("unexpected data from child");
327	root	1.1	}
328			}
329			} elsif (defined $len) {
330			undef $rw; undef $ww; # it ends here
331	root	1.4
332			if (@rcb) {
333			$on_error->("unexpected eof");
334			} else {
335			$on_destroy->();
336			}
337	root	1.1	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
338			undef $rw; undef $ww; # it ends here
339			$on_error->("read: $!");
340			}
341			};
342
343			$ww \|\|= AE::io $fh, 1, $wcb;
344			});
345
346			my $guard = Guard::guard {
347			$shutdown = 1;
348			$ww \|\|= $fh && AE::io $fh, 1, $wcb;
349			};
350
351			sub {
352			push @rcb, pop;
353
354			$guard; # keep it alive
355
356			$wbuf .= pack "L/a*", &$f;
357			$ww \|\|= $fh && AE::io $fh, 1, $wcb;
358			}
359			}
360
361	root	1.4	=item $rpc->(..., $cb->(...))
362
363			The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
364			reference. There are two things you can do with it: call it, and let it go
365			out of scope (let it get destroyed).
366
367			If C<async> was false when C<$rpc> was created (the default), then, if you
368			call C<$rpc>, the C<$function> is invoked with all arguments passed to
369			C<$rpc> except the last one (the callback). When the function returns, the
370			callback will be invoked with all the return values.
371
372			If C<async> was true, then the C<$function> receives an additional
373			initial argument, the result callback. In this case, returning from
374			C<$function> does nothing - the function only counts as "done" when the
375			result callback is called, and any arguments passed to it are considered
376			the return values. This makes it possible to "return" from event handlers
377			or e.g. Coro threads.
378
379			The other thing that can be done with the RPC object is to destroy it. In
380			this case, the child process will execute all remaining RPC calls, report
381			their results, and then exit.
382
383	root	1.1	=back
384
385			=head1 CHILD PROCESS USAGE
386
387	root	1.4	The following function is not available in this module. They are only
388			available in the namespace of this module when the child is running,
389			without having to load any extra modules. They are part of the child-side
390			API of L<AnyEvent::Fork::RPC>.
391	root	1.1
392			=over 4
393
394			=item AnyEvent::Fork::RPC::event ...
395
396			Send an event to the parent. Events are a bit like RPC calls made by the
397			child process to the parent, except that there is no notion of return
398			values.
399
400			=back
401
402			=head1 SEE ALSO
403
404			L<AnyEvent::Fork> (to create the processes in the first place),
405			L<AnyEvent::Fork::Pool> (to manage whole pools of processes).
406
407			=head1 AUTHOR AND CONTACT INFORMATION
408
409			Marc Lehmann <schmorp@schmorp.de>
410			http://software.schmorp.de/pkg/AnyEvent-Fork-RPC
411
412			=cut
413
414			1
415