AnyEvent-Fork/Fork.pm

=head1 NAME

AnyEvent::Fork - everything you wanted to use fork() for, but couldn't

=head1 SYNOPSIS

   use AnyEvent::Fork;

=head1 DESCRIPTION

This module allows you to create new processes, without actually forking
them from your current process (avoiding the problems of forking), but
preserving most of the advantages of fork.

It can be used to create new worker processes or new independent
subprocesses for short- and long-running jobs, process pools (e.g. for use
in pre-forked servers) but also to spawn new external processes (such as
CGI scripts from a webserver), which can be faster (and more well behaved)
than using fork+exec in big processes.

=head1 PROBLEM STATEMENT

There are two ways to implement parallel processing on UNIX like operating
systems - fork and process, and fork+exec and process. They have different
advantages and disadvantages that I describe below, together with how this
module tries to mitigate the disadvantages.

=over 4

=item Forking from a big process can be very slow (a 5GB process needs
0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
is often shared with exec (because you have to fork first), but in some
circumstances (e.g. when vfork is used), fork+exec can be much faster.

This module can help here by telling a small(er) helper process to fork,
or fork+exec instead.

=item Forking usually creates a copy-on-write copy of the parent
process. Memory (for example, modules or data files that have been
will not take additional memory). When exec'ing a new process, modules
and data files might need to be loaded again, at extra cpu and memory
cost. Likewise when forking, all data structures are copied as well - if
the program frees them and replaces them by new data, the child processes
will retain the memory even if it isn't used.

This module allows the main program to do a controlled fork, and allows
modules to exec processes safely at any time. When creating a custom
process pool you can take advantage of data sharing via fork without
risking to share large dynamic data structures that will blow up child
memory usage.

=item Exec'ing a new perl process might be difficult and slow. For
example, it is not easy to find the correct path to the perl interpreter,
and all modules have to be loaded from disk again. Long running processes
might run into problems when perl is upgraded for example.

This module supports creating pre-initialised perl processes to be used
as template, and also tries hard to identify the correct path to the perl
interpreter. With a cooperative main program, exec'ing the interpreter
might not even be necessary.

=item Forking might be impossible when a program is running. For example,
POSIX makes it almost impossible to fork from a multithreaded program and
do anything useful in the child - strictly speaking, if your perl program
uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
you cannot call fork on the perl level anymore, at all.

This module can safely fork helper processes at any time, by caling
fork+exec in C, in a POSIX-compatible way.

=item Parallel processing with fork might be inconvenient or difficult
to implement. For example, when a program uses an event loop and creates
watchers it becomes very hard to use the event loop from a child
program, as the watchers already exist but are only meaningful in the
parent. Worse, a module might want to use such a system, not knowing
whether another module or the main program also does, leading to problems.

This module only lets the main program create pools by forking (because
only the main program can know when it is still safe to do so) - all other
pools are created by fork+exec, after which such modules can again be
loaded.

=back

=head1 CONCEPTS

This module can create new processes either by executing a new perl
process, or by forking from an existing "template" process.

Each such process comes with its own file handle that can be used to
communicate with it (it's actually a socket - one end in the new process,
one end in the main process), and among the things you can do in it are
load modules, fork new processes, send file handles to it, and execute
functions.

There are multiple ways to create additional processes to execute some
jobs:

=over 4

=item fork a new process from the "default" template process, load code,
run it

This module has a "default" template process which it executes when it is
needed the first time. Forking from this process shares the memory used
for the perl interpreter with the new process, but loading modules takes
time, and the memory is not shared with anything else.

This is ideal for when you only need one extra process of a kind, with the
option of starting and stipping it on demand.

=item fork a new template process, load code, then fork processes off of
it and run the code

When you need to have a bunch of processes that all execute the same (or
very similar) tasks, then a good way is to create a new template process
for them, loading all the modules you need, and then create your worker
processes from this new template process.

This way, all code (and data structures) that can be shared (e.g. the
modules you loaded) is shared between the processes, and each new process
consumes relatively little memory of its own.

The disadvantage of this approach is that you need to create a template
process for the sole purpose of forking new processes from it, but if you
only need a fixed number of proceses you can create them, and then destroy
the template process.

=item execute a new perl interpreter, load some code, run it

This is relatively slow, and doesn't allow you to share memory between
multiple processes.

The only advantage is that you don't have to have a template process
hanging around all the time to fork off some new processes, which might be
an advantage when there are long time spans where no extra processes are
needed.

=back

=head1 FUNCTIONS

=over 4

=cut

package AnyEvent::Fork;

use common::sense;

use Socket ();

use AnyEvent;
use AnyEvent::Fork::Util;
use AnyEvent::Util ();

our $PERL; # the path to the perl interpreter, deduces with various forms of magic

=item my $pool = new AnyEvent::Fork key => value...

Create a new process pool. The following named parameters are supported:

=over 4

=back

=cut

# the empty template process
our $TEMPLATE;

sub _cmd {
   my $self = shift;

   # ideally, we would want to use "a (w/a)*" as format string, but perl versions
   # form at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.
   push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;

   $self->[3] ||= AE::io $self->[1], 1, sub {
      if (ref $self->[2][0]) {
         AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }
            and shift @{ $self->[2] };
      } else {
         my $len = syswrite $self->[1], $self->[2][0]
            or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };
         substr $self->[2][0], 0, $len, "";
         shift @{ $self->[2] } unless length $self->[2][0];
      }

      unless (@{ $self->[2] }) {
         undef $self->[3];
         $self->[0]->($self->[1]) if $self->[0];
      }
   };
}

sub _new {
   my ($self, $fh) = @_;

   $self = bless [
      undef, # run callback
      $fh,
      [],    # write queue - strings or fd's
      undef, # AE watcher
   ], $self;

#   my ($a, $b) = AnyEvent::Util::portable_socketpair;

#   queue_cmd $template, "Iabc";
#   push @{ $template->[2] }, \$b;

#   use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
#   undef $b;
#   die "x" . <$a>;

   $self
}

=item my $proc = new AnyEvent::Fork

Create a new "empty" perl interpreter process and returns its process
object for further manipulation.

The new process is forked from a template process that is kept around
for this purpose. When it doesn't exist yet, it is created by a call to
C<new_exec> and kept around for future calls.

=cut

sub new {
   my $class = shift;

   $TEMPLATE ||= $class->new_exec;
   $TEMPLATE->fork
}

=item $new_proc = $proc->fork

Forks C<$proc>, creating a new process, and returns the process object
of the new process.

If any of the C<send_> functions have been called before fork, then they
will be cloned in the child. For example, in a pre-forked server, you
might C<send_fh> the listening socket into the template process, and then
keep calling C<fork> and C<run>.

=cut

sub fork {
   my ($self) = @_;

   my ($fh, $slave) = AnyEvent::Util::portable_socketpair;

   $self->send_fh ($slave);
   $self->_cmd ("f");

   AnyEvent::Util::fh_nonblocking $fh, 1;

   AnyEvent::Fork->_new ($fh)
}

=item my $proc = new_exec AnyEvent::Fork

Create a new "empty" perl interpreter process and returns its process
object for further manipulation.

Unlike the C<new> method, this method I<always> spawns a new perl process
(except in some cases, see L<AnyEvent::Fork::Early> for details). This
reduces the amount of memory sharing that is possible, and is also slower.

You should use C<new> whenever possible, except when having a template
process around is unacceptable.

The path to the perl interpreter is divined usign various methods - first
C<$^X> is investigated to see if the path ends with something that sounds
as if it were the perl interpreter. Failing this, the module falls back to
using C<$Config::Config{perlpath}>.

=cut

sub new_exec {
   my ($self) = @_;

   # first find path of perl
   my $perl = $;

   # first we try $^X, but the path must be absolute (always on win32), and end in sth.
   # that looks like perl. this obviously only works for posix and win32
   unless (
      (AnyEvent::Fork::Util::WIN32 || $perl =~ m%^/%)
      && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
   ) {
      # if it doesn't look perlish enough, try Config
      require Config;
      $perl = $Config::Config{perlpath};
      $perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
   }

   require Proc::FastSpawn;

   my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
   AnyEvent::Util::fh_nonblocking $fh, 1;
   Proc::FastSpawn::fd_inherit (fileno $slave);

   # quick. also doesn't work in win32. of course. what did you expect
   #local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
   my %env = %ENV;
   $env{PERL5LIB} = join ":", grep !ref, @INC;

   Proc::FastSpawn::spawn (
      $perl,
      ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],
      [map "$_=$env{$_}", keys %env],
   ) or die "unable to spawn AnyEvent::Fork server: $!";

   $self->_new ($fh)
}

=item $proc = $proc->require ($module, ...)

Tries to load the given modules into the process

Returns the process object for easy chaining of method calls.

=item $proc = $proc->send_fh ($handle, ...)

Send one or more file handles (I<not> file descriptors) to the process,
to prepare a call to C<run>.

The process object keeps a reference to the handles until this is done,
so you must not explicitly close the handles. This is most easily
accomplished by simply not storing the file handles anywhere after passing
them to this method.

Returns the process object for easy chaining of method calls.

=cut

sub send_fh {
   my ($self, @fh) = @_;

   for my $fh (@fh) {
      $self->_cmd ("h");
      push @{ $self->[2] }, \$fh;
   }

   $self
}

=item $proc = $proc->send_arg ($string, ...)

Send one or more argument strings to the process, to prepare a call to
C<run>. The strings can be any octet string.

Returns the process object for easy chaining of emthod calls.

=cut

sub send_arg {
   my ($self, @arg) = @_;

   $self->_cmd (a => @arg);

   $self
}

=item $proc->run ($func, $cb->($fh))

Enter the function specified by the fully qualified name in C<$func> in
the process. The function is called with the communication socket as first
argument, followed by all file handles and string arguments sent earlier
via C<send_fh> and C<send_arg> methods, in the order they were called.

If the called function returns, the process exits.

Preparing the process can take time - when the process is ready, the
callback is invoked with the local communications socket as argument.

The process object becomes unusable on return from this function.

If the communication socket isn't used, it should be closed on both sides,
to save on kernel memory.

The socket is non-blocking in the parent, and blocking in the newly
created process. The close-on-exec flag is set on both. Even if not used
otherwise, the socket can be a good indicator for the existance of the
process - if the othe rprocess exits, you get a readable event on it,
because exiting the process closes the socket (if it didn't create any
children using fork).

=cut

sub run {
   my ($self, $func, $cb) = @_;

   $self->[0] = $cb;
   $self->_cmd ("r", $func);
}

=back

=head1 AUTHOR

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

=cut

1

Revision:	1.4
Committed:	Wed Apr 3 07:35:57 2013 UTC (11 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.3:	+216 -67 lines
Log Message:	phew
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.4	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
4	root	1.1
5			=head1 SYNOPSIS
6
7	root	1.4	use AnyEvent::Fork;
8	root	1.1
9			=head1 DESCRIPTION
10
11	root	1.4	This module allows you to create new processes, without actually forking
12			them from your current process (avoiding the problems of forking), but
13			preserving most of the advantages of fork.
14
15			It can be used to create new worker processes or new independent
16			subprocesses for short- and long-running jobs, process pools (e.g. for use
17			in pre-forked servers) but also to spawn new external processes (such as
18			CGI scripts from a webserver), which can be faster (and more well behaved)
19			than using fork+exec in big processes.
20	root	1.1
21			=head1 PROBLEM STATEMENT
22
23			There are two ways to implement parallel processing on UNIX like operating
24			systems - fork and process, and fork+exec and process. They have different
25			advantages and disadvantages that I describe below, together with how this
26			module tries to mitigate the disadvantages.
27
28			=over 4
29
30			=item Forking from a big process can be very slow (a 5GB process needs
31			0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
32			is often shared with exec (because you have to fork first), but in some
33			circumstances (e.g. when vfork is used), fork+exec can be much faster.
34
35			This module can help here by telling a small(er) helper process to fork,
36			or fork+exec instead.
37
38			=item Forking usually creates a copy-on-write copy of the parent
39			process. Memory (for example, modules or data files that have been
40			will not take additional memory). When exec'ing a new process, modules
41			and data files might need to be loaded again, at extra cpu and memory
42			cost. Likewise when forking, all data structures are copied as well - if
43			the program frees them and replaces them by new data, the child processes
44			will retain the memory even if it isn't used.
45
46			This module allows the main program to do a controlled fork, and allows
47			modules to exec processes safely at any time. When creating a custom
48			process pool you can take advantage of data sharing via fork without
49			risking to share large dynamic data structures that will blow up child
50			memory usage.
51
52			=item Exec'ing a new perl process might be difficult and slow. For
53			example, it is not easy to find the correct path to the perl interpreter,
54			and all modules have to be loaded from disk again. Long running processes
55			might run into problems when perl is upgraded for example.
56
57			This module supports creating pre-initialised perl processes to be used
58			as template, and also tries hard to identify the correct path to the perl
59			interpreter. With a cooperative main program, exec'ing the interpreter
60			might not even be necessary.
61
62			=item Forking might be impossible when a program is running. For example,
63			POSIX makes it almost impossible to fork from a multithreaded program and
64			do anything useful in the child - strictly speaking, if your perl program
65			uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
66			you cannot call fork on the perl level anymore, at all.
67
68			This module can safely fork helper processes at any time, by caling
69			fork+exec in C, in a POSIX-compatible way.
70
71			=item Parallel processing with fork might be inconvenient or difficult
72			to implement. For example, when a program uses an event loop and creates
73			watchers it becomes very hard to use the event loop from a child
74			program, as the watchers already exist but are only meaningful in the
75			parent. Worse, a module might want to use such a system, not knowing
76			whether another module or the main program also does, leading to problems.
77
78			This module only lets the main program create pools by forking (because
79			only the main program can know when it is still safe to do so) - all other
80			pools are created by fork+exec, after which such modules can again be
81			loaded.
82
83			=back
84
85	root	1.3	=head1 CONCEPTS
86
87			This module can create new processes either by executing a new perl
88			process, or by forking from an existing "template" process.
89
90			Each such process comes with its own file handle that can be used to
91			communicate with it (it's actually a socket - one end in the new process,
92			one end in the main process), and among the things you can do in it are
93			load modules, fork new processes, send file handles to it, and execute
94			functions.
95
96			There are multiple ways to create additional processes to execute some
97			jobs:
98
99			=over 4
100
101			=item fork a new process from the "default" template process, load code,
102			run it
103
104			This module has a "default" template process which it executes when it is
105			needed the first time. Forking from this process shares the memory used
106			for the perl interpreter with the new process, but loading modules takes
107			time, and the memory is not shared with anything else.
108
109			This is ideal for when you only need one extra process of a kind, with the
110			option of starting and stipping it on demand.
111
112			=item fork a new template process, load code, then fork processes off of
113			it and run the code
114
115			When you need to have a bunch of processes that all execute the same (or
116			very similar) tasks, then a good way is to create a new template process
117			for them, loading all the modules you need, and then create your worker
118			processes from this new template process.
119
120			This way, all code (and data structures) that can be shared (e.g. the
121			modules you loaded) is shared between the processes, and each new process
122			consumes relatively little memory of its own.
123
124			The disadvantage of this approach is that you need to create a template
125			process for the sole purpose of forking new processes from it, but if you
126			only need a fixed number of proceses you can create them, and then destroy
127			the template process.
128
129			=item execute a new perl interpreter, load some code, run it
130
131			This is relatively slow, and doesn't allow you to share memory between
132			multiple processes.
133
134			The only advantage is that you don't have to have a template process
135			hanging around all the time to fork off some new processes, which might be
136			an advantage when there are long time spans where no extra processes are
137			needed.
138
139			=back
140
141			=head1 FUNCTIONS
142
143	root	1.1	=over 4
144
145			=cut
146
147	root	1.4	package AnyEvent::Fork;
148	root	1.1
149			use common::sense;
150
151			use Socket ();
152
153			use AnyEvent;
154	root	1.4	use AnyEvent::Fork::Util;
155	root	1.1	use AnyEvent::Util ();
156
157	root	1.4	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
158	root	1.1
159	root	1.4	=item my $pool = new AnyEvent::Fork key => value...
160	root	1.1
161			Create a new process pool. The following named parameters are supported:
162
163			=over 4
164
165			=back
166
167			=cut
168
169	root	1.4	# the empty template process
170			our $TEMPLATE;
171
172			sub _cmd {
173			my $self = shift;
174
175			# ideally, we would want to use "a (w/a)*" as format string, but perl versions
176			# form at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.
177			push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;
178
179			$self->[3] \|\|= AE::io $self->[1], 1, sub {
180			if (ref $self->[2][0]) {
181			AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }
182			and shift @{ $self->[2] };
183			} else {
184			my $len = syswrite $self->[1], $self->[2][0]
185			or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };
186			substr $self->[2][0], 0, $len, "";
187			shift @{ $self->[2] } unless length $self->[2][0];
188			}
189
190			unless (@{ $self->[2] }) {
191			undef $self->[3];
192			$self->[0]->($self->[1]) if $self->[0];
193			}
194			};
195			}
196	root	1.1
197	root	1.4	sub _new {
198			my ($self, $fh) = @_;
199	root	1.1
200	root	1.4	$self = bless [
201			undef, # run callback
202	root	1.1	$fh,
203	root	1.4	[], # write queue - strings or fd's
204			undef, # AE watcher
205			], $self;
206
207			# my ($a, $b) = AnyEvent::Util::portable_socketpair;
208
209			# queue_cmd $template, "Iabc";
210			# push @{ $template->[2] }, \$b;
211
212			# use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
213			# undef $b;
214			# die "x" . <$a>;
215
216			$self
217	root	1.1	}
218
219	root	1.4	=item my $proc = new AnyEvent::Fork
220	root	1.1
221	root	1.4	Create a new "empty" perl interpreter process and returns its process
222			object for further manipulation.
223	root	1.1
224	root	1.4	The new process is forked from a template process that is kept around
225			for this purpose. When it doesn't exist yet, it is created by a call to
226			C<new_exec> and kept around for future calls.
227
228			=cut
229
230			sub new {
231			my $class = shift;
232	root	1.1
233	root	1.4	$TEMPLATE \|\|= $class->new_exec;
234			$TEMPLATE->fork
235	root	1.1	}
236
237	root	1.4	=item $new_proc = $proc->fork
238
239			Forks C<$proc>, creating a new process, and returns the process object
240			of the new process.
241
242			If any of the C<send_> functions have been called before fork, then they
243			will be cloned in the child. For example, in a pre-forked server, you
244			might C<send_fh> the listening socket into the template process, and then
245			keep calling C<fork> and C<run>.
246
247			=cut
248
249			sub fork {
250			my ($self) = @_;
251	root	1.1
252			my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
253	root	1.4
254			$self->send_fh ($slave);
255			$self->_cmd ("f");
256
257	root	1.1	AnyEvent::Util::fh_nonblocking $fh, 1;
258
259	root	1.4	AnyEvent::Fork->_new ($fh)
260			}
261
262			=item my $proc = new_exec AnyEvent::Fork
263
264			Create a new "empty" perl interpreter process and returns its process
265			object for further manipulation.
266
267			Unlike the C<new> method, this method I<always> spawns a new perl process
268			(except in some cases, see L<AnyEvent::Fork::Early> for details). This
269			reduces the amount of memory sharing that is possible, and is also slower.
270
271			You should use C<new> whenever possible, except when having a template
272			process around is unacceptable.
273
274			The path to the perl interpreter is divined usign various methods - first
275			C<$^X> is investigated to see if the path ends with something that sounds
276			as if it were the perl interpreter. Failing this, the module falls back to
277			using C<$Config::Config{perlpath}>.
278
279			=cut
280
281			sub new_exec {
282			my ($self) = @_;
283
284			# first find path of perl
285			my $perl = $;
286
287			# first we try $^X, but the path must be absolute (always on win32), and end in sth.
288			# that looks like perl. this obviously only works for posix and win32
289			unless (
290			(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)
291			&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
292			) {
293			# if it doesn't look perlish enough, try Config
294			require Config;
295			$perl = $Config::Config{perlpath};
296			$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
297			}
298
299			require Proc::FastSpawn;
300
301			my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
302			AnyEvent::Util::fh_nonblocking $fh, 1;
303			Proc::FastSpawn::fd_inherit (fileno $slave);
304
305			# quick. also doesn't work in win32. of course. what did you expect
306			#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
307	root	1.1	my %env = %ENV;
308			$env{PERL5LIB} = join ":", grep !ref, @INC;
309
310	root	1.4	Proc::FastSpawn::spawn (
311			$perl,
312			["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],
313			[map "$_=$env{$_}", keys %env],
314			) or die "unable to spawn AnyEvent::Fork server: $!";
315
316			$self->_new ($fh)
317			}
318
319			=item $proc = $proc->require ($module, ...)
320	root	1.1
321	root	1.4	Tries to load the given modules into the process
322	root	1.1
323	root	1.4	Returns the process object for easy chaining of method calls.
324	root	1.1
325	root	1.4	=item $proc = $proc->send_fh ($handle, ...)
326	root	1.1
327	root	1.4	Send one or more file handles (I<not> file descriptors) to the process,
328			to prepare a call to C<run>.
329	root	1.1
330	root	1.4	The process object keeps a reference to the handles until this is done,
331			so you must not explicitly close the handles. This is most easily
332			accomplished by simply not storing the file handles anywhere after passing
333			them to this method.
334
335			Returns the process object for easy chaining of method calls.
336
337			=cut
338
339			sub send_fh {
340			my ($self, @fh) = @_;
341
342			for my $fh (@fh) {
343			$self->_cmd ("h");
344			push @{ $self->[2] }, \$fh;
345			}
346
347			$self
348	root	1.1	}
349
350	root	1.4	=item $proc = $proc->send_arg ($string, ...)
351
352			Send one or more argument strings to the process, to prepare a call to
353			C<run>. The strings can be any octet string.
354
355			Returns the process object for easy chaining of emthod calls.
356
357			=cut
358	root	1.1
359	root	1.4	sub send_arg {
360			my ($self, @arg) = @_;
361	root	1.1
362	root	1.4	$self->_cmd (a => @arg);
363	root	1.1
364			$self
365			}
366
367	root	1.4	=item $proc->run ($func, $cb->($fh))
368
369			Enter the function specified by the fully qualified name in C<$func> in
370			the process. The function is called with the communication socket as first
371			argument, followed by all file handles and string arguments sent earlier
372			via C<send_fh> and C<send_arg> methods, in the order they were called.
373
374			If the called function returns, the process exits.
375
376			Preparing the process can take time - when the process is ready, the
377			callback is invoked with the local communications socket as argument.
378
379			The process object becomes unusable on return from this function.
380
381			If the communication socket isn't used, it should be closed on both sides,
382			to save on kernel memory.
383
384			The socket is non-blocking in the parent, and blocking in the newly
385			created process. The close-on-exec flag is set on both. Even if not used
386			otherwise, the socket can be a good indicator for the existance of the
387			process - if the othe rprocess exits, you get a readable event on it,
388			because exiting the process closes the socket (if it didn't create any
389			children using fork).
390
391			=cut
392
393			sub run {
394			my ($self, $func, $cb) = @_;
395
396			$self->[0] = $cb;
397			$self->_cmd ("r", $func);
398			}
399
400	root	1.1	=back
401
402			=head1 AUTHOR
403
404			Marc Lehmann <schmorp@schmorp.de>
405			http://home.schmorp.de/
406
407			=cut
408
409			1
410