AnyEvent-Fork-RPC/RPC.pm

=head1 NAME

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

=head1 SYNOPSIS

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

   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.

Loading this module also always loads L<AnyEvent::Fork>, so you can make a
separate C<use AnyEvent::Fork> if you wish, but you don't have to.

=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_error   => sub { warn "FATAL: $_[0]"; exit 1 },
         on_event   => sub { warn "$_[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 code 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; # we don't actually depend on it, this is for convenience

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 can 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 load 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 (4 <= 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:	1.7
Committed:	Wed Apr 17 20:19:41 2013 UTC (11 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.6:	+6 -3 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::RPC;
8	root	1.7	# use AnyEvent::Fork is not needed
9	root	1.1
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	1.7	Loading this module also always loads L<AnyEvent::Fork>, so you can make a
40			separate C<use AnyEvent::Fork> if you wish, but you don't have to.
41
42	root	1.4	=head1 EXAMPLES
43
44			=head2 Synchronous Backend
45
46			Here is a simple example that implements a backend that executes C<unlink>
47			and C<rmdir> calls, and reports their status back. It also reports the
48			number of requests it has processed every three requests, which is clearly
49			silly, but illustrates the use of events.
50
51			First the parent process:
52
53			use AnyEvent;
54			use AnyEvent::Fork;
55			use AnyEvent::Fork::RPC;
56
57			my $done = AE::cv;
58
59			my $rpc = AnyEvent::Fork
60			->new
61			->require ("MyWorker")
62			->AnyEvent::Fork::RPC::run ("MyWorker::run",
63	root	1.5	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
64	root	1.4	on_event => sub { warn "$_[0] requests handled\n" },
65			on_destroy => $done,
66			);
67
68			for my $id (1..6) {
69			$rpc->(rmdir => "/tmp/somepath/$id", sub {
70			$_[0]
71			or warn "/tmp/somepath/$id: $_[1]\n";
72			});
73			}
74
75			undef $rpc;
76
77			$done->recv;
78
79			The parent creates the process, queues a few rmdir's. It then forgets
80			about the C<$rpc> object, so that the child exits after it has handled the
81			requests, and then it waits till the requests have been handled.
82
83			The child is implemented using a separate module, C<MyWorker>, shown here:
84
85			package MyWorker;
86
87			my $count;
88
89			sub run {
90			my ($cmd, $path) = @_;
91
92			AnyEvent::Fork::RPC::event ($count)
93			unless ++$count % 3;
94
95			my $status = $cmd eq "rmdir" ? rmdir $path
96			: $cmd eq "unlink" ? unlink $path
97			: die "fatal error, illegal command '$cmd'";
98
99			$status or (0, "$!")
100			}
101
102			1
103
104			The C<run> function first sends a "progress" event every three calls, and
105			then executes C<rmdir> or C<unlink>, depending on the first parameter (or
106			dies with a fatal error - obviously, you must never let this happen :).
107
108			Eventually it returns the status value true if the command was successful,
109			or the status value 0 and the stringified error message.
110
111	root	1.6	On my system, running the first code fragment with the given
112	root	1.4	F<MyWorker.pm> in the current directory yields:
113
114			/tmp/somepath/1: No such file or directory
115			/tmp/somepath/2: No such file or directory
116			3 requests handled
117			/tmp/somepath/3: No such file or directory
118			/tmp/somepath/4: No such file or directory
119			/tmp/somepath/5: No such file or directory
120			6 requests handled
121			/tmp/somepath/6: No such file or directory
122
123			Obviously, none of the directories I am trying to delete even exist. Also,
124			the events and responses are processed in exactly the same order as
125			they were created in the child, which is true for both synchronous and
126			asynchronous backends.
127
128			Note that the parentheses in the call to C<AnyEvent::Fork::RPC::event> are
129			not optional. That is because the function isn't defined when the code is
130			compiled. You can make sure it is visible by pre-loading the correct
131			backend module in the call to C<require>:
132
133			->require ("AnyEvent::Fork::RPC::Sync", "MyWorker")
134
135			Since the backend module declares the C<event> function, loading it first
136			ensures that perl will correctly interpret calls to it.
137
138			And as a final remark, there is a fine module on CPAN that can
139			asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
140			than this example, namely L<IO::AIO>.
141
142	root	1.1	=head1 PARENT PROCESS USAGE
143
144			This module exports nothing, and only implements a single function:
145
146			=over 4
147
148			=cut
149
150			package AnyEvent::Fork::RPC;
151
152			use common::sense;
153
154			use Errno ();
155			use Guard ();
156
157			use AnyEvent;
158	root	1.7	use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
159	root	1.1
160			our $VERSION = 0.1;
161
162			=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
163
164			The traditional way to call it. But it is way cooler to call it in the
165			following way:
166
167			=item my $rpc = $fork->AnyEvent::Fork::RPC::run ($function, [key => value...])
168
169			This C<run> function/method can be used in place of the
170			L<AnyEvent::Fork::run> method. Just like that method, it takes over
171			the L<AnyEvent::Fork> process, but instead of calling the specified
172			C<$function> directly, it runs a server that accepts RPC calls and handles
173			responses.
174
175			It returns a function reference that can be used to call the function in
176			the child process, handling serialisation and data transfers.
177
178			The following key/value pairs are allowed. It is recommended to have at
179			least an C<on_error> or C<on_event> handler set.
180
181			=over 4
182
183			=item on_error => $cb->($msg)
184
185			Called on (fatal) errors, with a descriptive (hopefully) message. If
186			this callback is not provided, but C<on_event> is, then the C<on_event>
187			callback is called with the first argument being the string C<error>,
188			followed by the error message.
189
190			If neither handler is provided it prints the error to STDERR and will
191			start failing badly.
192
193			=item on_event => $cb->(...)
194
195			Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
196			child, with the arguments of that function passed to the callback.
197
198			Also called on errors when no C<on_error> handler is provided.
199
200	root	1.4	=item on_destroy => $cb->()
201
202			Called when the C<$rpc> object has been destroyed and all requests have
203			been successfully handled. This is useful when you queue some requests and
204			want the child to go away after it has handled them. The problem is that
205			the parent must not exit either until all requests have been handled, and
206	root	1.6	this can be accomplished by waiting for this callback.
207	root	1.4
208	root	1.1	=item init => $function (default none)
209
210			When specified (by name), this function is called in the child as the very
211			first thing when taking over the process, with all the arguments normally
212			passed to the C<AnyEvent::Fork::run> function, except the communications
213			socket.
214
215			It can be used to do one-time things in the child such as storing passed
216			parameters or opening database connections.
217
218	root	1.4	It is called very early - before the serialisers are created or the
219			C<$function> name is resolved into a function reference, so it could be
220			used to load any modules that provide the serialiser or function. It can
221			not, however, create events.
222
223	root	1.1	=item async => $boolean (default: 0)
224
225			The default server used in the child does all I/O blockingly, and only
226			allows a single RPC call to execute concurrently.
227
228			Setting C<async> to a true value switches to another implementation that
229			uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.
230
231			The actual API in the child is documented in the section that describes
232			the calling semantics of the returned C<$rpc> function.
233
234	root	1.2	If you want to pre-load the actual back-end modules to enable memory
235			sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
236			synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
237
238	root	1.4	If you use a template process and want to fork both sync and async
239	root	1.6	children, then it is permissible to load both modules.
240	root	1.4
241	root	1.1	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')
242
243			All arguments, result data and event data have to be serialised to be
244			transferred between the processes. For this, they have to be frozen and
245			thawed in both parent and child processes.
246
247			By default, only octet strings can be passed between the processes, which
248			is reasonably fast and efficient.
249
250			For more complicated use cases, you can provide your own freeze and thaw
251			functions, by specifying a string with perl source code. It's supposed to
252			return two code references when evaluated: the first receives a list of
253			perl values and must return an octet string. The second receives the octet
254			string and must return the original list of values.
255
256	root	1.2	If you need an external module for serialisation, then you can either
257			pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
258			or C<require> statement into the serialiser string. Or both.
259
260	root	1.1	=back
261
262			=cut
263
264	root	1.2	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
265
266	root	1.1	sub run {
267			my ($self, $function, %arg) = @_;
268
269	root	1.2	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
270	root	1.1	my $on_event = delete $arg{on_event};
271			my $on_error = delete $arg{on_error};
272	root	1.4	my $on_destroy = delete $arg{on_destroy};
273	root	1.1
274			# default for on_error is to on_event, if specified
275			$on_error \|\|= $on_event
276			? sub { $on_event->(error => shift) }
277			: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };
278
279			# default for on_event is to raise an error
280			$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
281
282			my ($f, $t) = eval $serialiser; die $@ if $@;
283
284	root	1.4	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);
285			my ($rlen, $rbuf) = 512 - 16;
286	root	1.1
287			my $wcb = sub {
288			my $len = syswrite $fh, $wbuf;
289
290			if (!defined $len) {
291			if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
292			undef $rw; undef $ww; # it ends here
293			$on_error->("$!");
294			}
295			}
296
297			substr $wbuf, 0, $len, "";
298
299			unless (length $wbuf) {
300			undef $ww;
301			$shutdown and shutdown $fh, 1;
302			}
303			};
304
305			my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");
306
307			$self->require ($module)
308			->send_arg ($function, $arg{init}, $serialiser)
309			->run ("$module\::run", sub {
310			$fh = shift;
311			$rw = AE::io $fh, 0, sub {
312	root	1.4	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
313			my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
314	root	1.1
315			if ($len) {
316	root	1.7	while (4 <= length $rbuf) {
317	root	1.1	$len = unpack "L", $rbuf;
318	root	1.2	4 + $len <= length $rbuf
319			or last;
320
321			my @r = $t->(substr $rbuf, 4, $len);
322			substr $rbuf, 0, $len + 4, "";
323
324			if (pop @r) {
325			$on_event->(@r);
326			} elsif (@rcb) {
327			(shift @rcb)->(@r);
328			} else {
329			undef $rw; undef $ww;
330			$on_error->("unexpected data from child");
331	root	1.1	}
332			}
333			} elsif (defined $len) {
334			undef $rw; undef $ww; # it ends here
335	root	1.4
336			if (@rcb) {
337			$on_error->("unexpected eof");
338			} else {
339			$on_destroy->();
340			}
341	root	1.1	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
342			undef $rw; undef $ww; # it ends here
343			$on_error->("read: $!");
344			}
345			};
346
347			$ww \|\|= AE::io $fh, 1, $wcb;
348			});
349
350			my $guard = Guard::guard {
351			$shutdown = 1;
352			$ww \|\|= $fh && AE::io $fh, 1, $wcb;
353			};
354
355			sub {
356			push @rcb, pop;
357
358			$guard; # keep it alive
359
360			$wbuf .= pack "L/a*", &$f;
361			$ww \|\|= $fh && AE::io $fh, 1, $wcb;
362			}
363			}
364
365	root	1.4	=item $rpc->(..., $cb->(...))
366
367			The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
368			reference. There are two things you can do with it: call it, and let it go
369			out of scope (let it get destroyed).
370
371			If C<async> was false when C<$rpc> was created (the default), then, if you
372			call C<$rpc>, the C<$function> is invoked with all arguments passed to
373			C<$rpc> except the last one (the callback). When the function returns, the
374			callback will be invoked with all the return values.
375
376			If C<async> was true, then the C<$function> receives an additional
377			initial argument, the result callback. In this case, returning from
378			C<$function> does nothing - the function only counts as "done" when the
379			result callback is called, and any arguments passed to it are considered
380			the return values. This makes it possible to "return" from event handlers
381			or e.g. Coro threads.
382
383			The other thing that can be done with the RPC object is to destroy it. In
384			this case, the child process will execute all remaining RPC calls, report
385			their results, and then exit.
386
387	root	1.1	=back
388
389			=head1 CHILD PROCESS USAGE
390
391	root	1.4	The following function is not available in this module. They are only
392			available in the namespace of this module when the child is running,
393			without having to load any extra modules. They are part of the child-side
394			API of L<AnyEvent::Fork::RPC>.
395	root	1.1
396			=over 4
397
398			=item AnyEvent::Fork::RPC::event ...
399
400			Send an event to the parent. Events are a bit like RPC calls made by the
401			child process to the parent, except that there is no notion of return
402			values.
403
404			=back
405
406			=head1 SEE ALSO
407
408			L<AnyEvent::Fork> (to create the processes in the first place),
409			L<AnyEvent::Fork::Pool> (to manage whole pools of processes).
410
411			=head1 AUTHOR AND CONTACT INFORMATION
412
413			Marc Lehmann <schmorp@schmorp.de>
414			http://software.schmorp.de/pkg/AnyEvent-Fork-RPC
415
416			=cut
417
418			1
419