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.

Special care has been taken to make this module useful from other modules,
while still supporting specialised environments such as L<App::Staticperl>
or L<PAR::Packer>.

=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 early fork template process
our $EARLY;

# 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
   # from 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) = @_;

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

   $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
}

# fork template from current process, used by AnyEvent::Fork::Early/Template
sub _new_fork {
   my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
   my $pid = fork;

   if ($pid eq 0) {
      require AnyEvent::Fork::Serve;
      close $fh;
      AnyEvent::Fork::Serve::serve ($slave);
      AnyEvent::Fork::Util::_exit 0;
   } elsif (!$pid) {
      die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
   }

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

=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::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) = @_;

   return $EARLY->fork
      if $EARLY;

   # 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;
   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:	1.6
Committed:	Wed Apr 3 08:47:44 2013 UTC (11 years, 2 months ago) by root
Branch:	MAIN
Changes since 1.5:	+19 -3 lines
Log Message:	* empty log message *
#	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	root	1.5	Special care has been taken to make this module useful from other modules,
22			while still supporting specialised environments such as L<App::Staticperl>
23			or L<PAR::Packer>.
24
25	root	1.1	=head1 PROBLEM STATEMENT
26
27			There are two ways to implement parallel processing on UNIX like operating
28			systems - fork and process, and fork+exec and process. They have different
29			advantages and disadvantages that I describe below, together with how this
30			module tries to mitigate the disadvantages.
31
32			=over 4
33
34			=item Forking from a big process can be very slow (a 5GB process needs
35			0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
36			is often shared with exec (because you have to fork first), but in some
37			circumstances (e.g. when vfork is used), fork+exec can be much faster.
38
39			This module can help here by telling a small(er) helper process to fork,
40			or fork+exec instead.
41
42			=item Forking usually creates a copy-on-write copy of the parent
43			process. Memory (for example, modules or data files that have been
44			will not take additional memory). When exec'ing a new process, modules
45			and data files might need to be loaded again, at extra cpu and memory
46			cost. Likewise when forking, all data structures are copied as well - if
47			the program frees them and replaces them by new data, the child processes
48			will retain the memory even if it isn't used.
49
50			This module allows the main program to do a controlled fork, and allows
51			modules to exec processes safely at any time. When creating a custom
52			process pool you can take advantage of data sharing via fork without
53			risking to share large dynamic data structures that will blow up child
54			memory usage.
55
56			=item Exec'ing a new perl process might be difficult and slow. For
57			example, it is not easy to find the correct path to the perl interpreter,
58			and all modules have to be loaded from disk again. Long running processes
59			might run into problems when perl is upgraded for example.
60
61			This module supports creating pre-initialised perl processes to be used
62			as template, and also tries hard to identify the correct path to the perl
63			interpreter. With a cooperative main program, exec'ing the interpreter
64			might not even be necessary.
65
66			=item Forking might be impossible when a program is running. For example,
67			POSIX makes it almost impossible to fork from a multithreaded program and
68			do anything useful in the child - strictly speaking, if your perl program
69			uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
70			you cannot call fork on the perl level anymore, at all.
71
72			This module can safely fork helper processes at any time, by caling
73			fork+exec in C, in a POSIX-compatible way.
74
75			=item Parallel processing with fork might be inconvenient or difficult
76			to implement. For example, when a program uses an event loop and creates
77			watchers it becomes very hard to use the event loop from a child
78			program, as the watchers already exist but are only meaningful in the
79			parent. Worse, a module might want to use such a system, not knowing
80			whether another module or the main program also does, leading to problems.
81
82			This module only lets the main program create pools by forking (because
83			only the main program can know when it is still safe to do so) - all other
84			pools are created by fork+exec, after which such modules can again be
85			loaded.
86
87			=back
88
89	root	1.3	=head1 CONCEPTS
90
91			This module can create new processes either by executing a new perl
92			process, or by forking from an existing "template" process.
93
94			Each such process comes with its own file handle that can be used to
95			communicate with it (it's actually a socket - one end in the new process,
96			one end in the main process), and among the things you can do in it are
97			load modules, fork new processes, send file handles to it, and execute
98			functions.
99
100			There are multiple ways to create additional processes to execute some
101			jobs:
102
103			=over 4
104
105			=item fork a new process from the "default" template process, load code,
106			run it
107
108			This module has a "default" template process which it executes when it is
109			needed the first time. Forking from this process shares the memory used
110			for the perl interpreter with the new process, but loading modules takes
111			time, and the memory is not shared with anything else.
112
113			This is ideal for when you only need one extra process of a kind, with the
114			option of starting and stipping it on demand.
115
116			=item fork a new template process, load code, then fork processes off of
117			it and run the code
118
119			When you need to have a bunch of processes that all execute the same (or
120			very similar) tasks, then a good way is to create a new template process
121			for them, loading all the modules you need, and then create your worker
122			processes from this new template process.
123
124			This way, all code (and data structures) that can be shared (e.g. the
125			modules you loaded) is shared between the processes, and each new process
126			consumes relatively little memory of its own.
127
128			The disadvantage of this approach is that you need to create a template
129			process for the sole purpose of forking new processes from it, but if you
130			only need a fixed number of proceses you can create them, and then destroy
131			the template process.
132
133			=item execute a new perl interpreter, load some code, run it
134
135			This is relatively slow, and doesn't allow you to share memory between
136			multiple processes.
137
138			The only advantage is that you don't have to have a template process
139			hanging around all the time to fork off some new processes, which might be
140			an advantage when there are long time spans where no extra processes are
141			needed.
142
143			=back
144
145			=head1 FUNCTIONS
146
147	root	1.1	=over 4
148
149			=cut
150
151	root	1.4	package AnyEvent::Fork;
152	root	1.1
153			use common::sense;
154
155			use Socket ();
156
157			use AnyEvent;
158	root	1.4	use AnyEvent::Fork::Util;
159	root	1.1	use AnyEvent::Util ();
160
161	root	1.4	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
162	root	1.1
163	root	1.4	=item my $pool = new AnyEvent::Fork key => value...
164	root	1.1
165			Create a new process pool. The following named parameters are supported:
166
167			=over 4
168
169			=back
170
171			=cut
172
173	root	1.5	# the early fork template process
174			our $EARLY;
175
176	root	1.4	# the empty template process
177			our $TEMPLATE;
178
179			sub _cmd {
180			my $self = shift;
181
182			# ideally, we would want to use "a (w/a)*" as format string, but perl versions
183	root	1.5	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.
184	root	1.4	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;
185
186			$self->[3] \|\|= AE::io $self->[1], 1, sub {
187			if (ref $self->[2][0]) {
188			AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }
189			and shift @{ $self->[2] };
190	root	1.5
191	root	1.4	} else {
192			my $len = syswrite $self->[1], $self->[2][0]
193			or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };
194	root	1.5
195	root	1.4	substr $self->[2][0], 0, $len, "";
196			shift @{ $self->[2] } unless length $self->[2][0];
197			}
198
199			unless (@{ $self->[2] }) {
200			undef $self->[3];
201			$self->[0]->($self->[1]) if $self->[0];
202			}
203			};
204			}
205	root	1.1
206	root	1.4	sub _new {
207			my ($self, $fh) = @_;
208	root	1.1
209	root	1.6	AnyEvent::Util::fh_nonblocking $fh, 1;
210
211	root	1.4	$self = bless [
212			undef, # run callback
213	root	1.1	$fh,
214	root	1.4	[], # write queue - strings or fd's
215			undef, # AE watcher
216			], $self;
217
218			# my ($a, $b) = AnyEvent::Util::portable_socketpair;
219
220			# queue_cmd $template, "Iabc";
221			# push @{ $template->[2] }, \$b;
222
223			# use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
224			# undef $b;
225			# die "x" . <$a>;
226
227			$self
228	root	1.1	}
229
230	root	1.6	# fork template from current process, used by AnyEvent::Fork::Early/Template
231			sub _new_fork {
232			my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
233			my $pid = fork;
234
235			if ($pid eq 0) {
236			require AnyEvent::Fork::Serve;
237			close $fh;
238			AnyEvent::Fork::Serve::serve ($slave);
239			AnyEvent::Fork::Util::_exit 0;
240			} elsif (!$pid) {
241			die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
242			}
243
244			AnyEvent::Fork->_new ($fh)
245			}
246
247	root	1.4	=item my $proc = new AnyEvent::Fork
248	root	1.1
249	root	1.4	Create a new "empty" perl interpreter process and returns its process
250			object for further manipulation.
251	root	1.1
252	root	1.4	The new process is forked from a template process that is kept around
253			for this purpose. When it doesn't exist yet, it is created by a call to
254			C<new_exec> and kept around for future calls.
255
256			=cut
257
258			sub new {
259			my $class = shift;
260	root	1.1
261	root	1.4	$TEMPLATE \|\|= $class->new_exec;
262			$TEMPLATE->fork
263	root	1.1	}
264
265	root	1.4	=item $new_proc = $proc->fork
266
267			Forks C<$proc>, creating a new process, and returns the process object
268			of the new process.
269
270			If any of the C<send_> functions have been called before fork, then they
271			will be cloned in the child. For example, in a pre-forked server, you
272			might C<send_fh> the listening socket into the template process, and then
273			keep calling C<fork> and C<run>.
274
275			=cut
276
277			sub fork {
278			my ($self) = @_;
279	root	1.1
280			my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
281	root	1.4
282			$self->send_fh ($slave);
283			$self->_cmd ("f");
284
285			AnyEvent::Fork->_new ($fh)
286			}
287
288			=item my $proc = new_exec AnyEvent::Fork
289
290			Create a new "empty" perl interpreter process and returns its process
291			object for further manipulation.
292
293			Unlike the C<new> method, this method I<always> spawns a new perl process
294			(except in some cases, see L<AnyEvent::Fork::Early> for details). This
295			reduces the amount of memory sharing that is possible, and is also slower.
296
297			You should use C<new> whenever possible, except when having a template
298			process around is unacceptable.
299
300			The path to the perl interpreter is divined usign various methods - first
301			C<$^X> is investigated to see if the path ends with something that sounds
302			as if it were the perl interpreter. Failing this, the module falls back to
303			using C<$Config::Config{perlpath}>.
304
305			=cut
306
307			sub new_exec {
308			my ($self) = @_;
309
310	root	1.5	return $EARLY->fork
311			if $EARLY;
312
313	root	1.4	# first find path of perl
314			my $perl = $;
315
316			# first we try $^X, but the path must be absolute (always on win32), and end in sth.
317			# that looks like perl. this obviously only works for posix and win32
318			unless (
319			(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)
320			&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
321			) {
322			# if it doesn't look perlish enough, try Config
323			require Config;
324			$perl = $Config::Config{perlpath};
325			$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
326			}
327
328			require Proc::FastSpawn;
329
330			my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
331			Proc::FastSpawn::fd_inherit (fileno $slave);
332
333			# quick. also doesn't work in win32. of course. what did you expect
334			#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
335	root	1.1	my %env = %ENV;
336			$env{PERL5LIB} = join ":", grep !ref, @INC;
337
338	root	1.4	Proc::FastSpawn::spawn (
339			$perl,
340			["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],
341			[map "$_=$env{$_}", keys %env],
342			) or die "unable to spawn AnyEvent::Fork server: $!";
343
344			$self->_new ($fh)
345			}
346
347			=item $proc = $proc->require ($module, ...)
348	root	1.1
349	root	1.4	Tries to load the given modules into the process
350	root	1.1
351	root	1.4	Returns the process object for easy chaining of method calls.
352	root	1.1
353	root	1.4	=item $proc = $proc->send_fh ($handle, ...)
354	root	1.1
355	root	1.4	Send one or more file handles (I<not> file descriptors) to the process,
356			to prepare a call to C<run>.
357	root	1.1
358	root	1.4	The process object keeps a reference to the handles until this is done,
359			so you must not explicitly close the handles. This is most easily
360			accomplished by simply not storing the file handles anywhere after passing
361			them to this method.
362
363			Returns the process object for easy chaining of method calls.
364
365			=cut
366
367			sub send_fh {
368			my ($self, @fh) = @_;
369
370			for my $fh (@fh) {
371			$self->_cmd ("h");
372			push @{ $self->[2] }, \$fh;
373			}
374
375			$self
376	root	1.1	}
377
378	root	1.4	=item $proc = $proc->send_arg ($string, ...)
379
380			Send one or more argument strings to the process, to prepare a call to
381			C<run>. The strings can be any octet string.
382
383			Returns the process object for easy chaining of emthod calls.
384
385			=cut
386	root	1.1
387	root	1.4	sub send_arg {
388			my ($self, @arg) = @_;
389	root	1.1
390	root	1.4	$self->_cmd (a => @arg);
391	root	1.1
392			$self
393			}
394
395	root	1.4	=item $proc->run ($func, $cb->($fh))
396
397			Enter the function specified by the fully qualified name in C<$func> in
398			the process. The function is called with the communication socket as first
399			argument, followed by all file handles and string arguments sent earlier
400			via C<send_fh> and C<send_arg> methods, in the order they were called.
401
402			If the called function returns, the process exits.
403
404			Preparing the process can take time - when the process is ready, the
405			callback is invoked with the local communications socket as argument.
406
407			The process object becomes unusable on return from this function.
408
409			If the communication socket isn't used, it should be closed on both sides,
410			to save on kernel memory.
411
412			The socket is non-blocking in the parent, and blocking in the newly
413			created process. The close-on-exec flag is set on both. Even if not used
414			otherwise, the socket can be a good indicator for the existance of the
415			process - if the othe rprocess exits, you get a readable event on it,
416			because exiting the process closes the socket (if it didn't create any
417			children using fork).
418
419			=cut
420
421			sub run {
422			my ($self, $func, $cb) = @_;
423
424			$self->[0] = $cb;
425			$self->_cmd ("r", $func);
426			}
427
428	root	1.1	=back
429
430			=head1 AUTHOR
431
432			Marc Lehmann <schmorp@schmorp.de>
433			http://home.schmorp.de/
434
435			=cut
436
437			1
438