AnyEvent-Fork/Fork.pm

=head1 NAME

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

ATTENTION, this is a very early release, and very untested. Consider it a
technology preview.

=head1 SYNOPSIS

   use AnyEvent::Fork;

   ##################################################################
   # create a single new process, tell it to run your worker function

   AnyEvent::Fork
      ->new
      ->require ("MyModule")
      ->run ("MyModule::worker, sub {
         my ($master_filehandle) = @_;

         # now $master_filehandle is connected to the
         # $slave_filehandle in the new process.
      });

   # MyModule::worker might look like this
   sub MyModule::worker {
      my ($slave_filehandle) = @_;

      # now $slave_filehandle is connected to the $master_filehandle
      # in the original prorcess. have fun!
   }

   ##################################################################
   # create a pool of server processes all accepting on the same socket

   # create listener socket
   my $listener = ...;

   # create a pool template, initialise it and give it the socket
   my $pool = AnyEvent::Fork
                 ->new
                 ->require ("Some::Stuff", "My::Server")
                 ->send_fh ($listener);

   # now create 10 identical workers
   for my $id (1..10) {
      $pool
         ->fork
         ->send_arg ($id)
         ->run ("My::Server::run");
   }

   # now do other things - maybe use the filehandle provided by run
   # to wait for the processes to die. or whatever.

   # My::Server::run might look like this
   sub My::Server::run {
      my ($slave, $listener, $id) = @_;

      close $slave; # we do not use the socket, so close it to save resources

      # we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
      # or anything we usually couldn't do in a process forked normally.
      while (my $socket = $listener->accept) {
         # do sth. with new socket
      }
   }

=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.

Example:

   AnyEvent::Fork
      ->new
      ->require ("Some::Module")
      ->run ("Some::Module::run", sub {
         my ($fork_fh) = @_;
      });

=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.

Example:

   my $template = AnyEvent::Fork->new->require ("Some::Module");
   
   for (1..10) {
      $template->fork->run ("Some::Module::run", sub {
         my ($fork_fh) = @_;
      });
   }

   # at this point, you can keep $template around to fork new processes
   # later, or you can destroy it, which causes it to vanish.

=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.

Example:

   AnyEvent::Fork
      ->new_exec
      ->require ("Some::Module")
      ->run ("Some::Module::run", sub {
         my ($fork_fh) = @_;
      });

=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;

   #TODO: maybe append the packet to any existing string command already in the queue

   # 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 {
      # send the next "thing" in the queue - either a reference to an fh,
      # or a plain string.

      if (ref $self->[2][0]) {
         # send fh
         AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }
            and shift @{ $self->[2] };

      } else {
         # send string
         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];
         # invoke run callback
         $self->[0]->($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;

   $self
}

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

   my $pid = fork;

   if ($pid eq 0) {
      require AnyEvent::Fork::Serve;
      $AnyEvent::Fork::Serve::OWNER = $parent;
      close $fh;
      $0 = "$_[1] of $parent";
      AnyEvent::Fork::Serve::serve ($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.

When the process object is destroyed, it will release the file handle
that connects it with the new process. When the new process has not yet
called C<run>, then the process will exit. Otherwise, what happens depends
entirely on the code that is executed.

=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);

   # new fh's should always be set cloexec (due to $^F),
   # but hey, not on win32, so we always clear the inherit flag.
   Proc::FastSpawn::fd_inherit (fileno $fh, 0);

   # 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 +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), 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 = $proc->eval ($perlcode, @args)

Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
the strings specified by C<@args>.

This call is meant to do any custom initialisation that might be required
(for example, the C<require> method uses it). It's not supposed to be used
to completely take over the process, use C<run> for that.

The code will usually be executed after this call returns, and there is no
way to pass anything back to the calling process. Any evaluation errors
will be reported to stderr and cause the process to exit.

Returns the process object for easy chaining of method calls.

=cut

sub eval {
   my ($self, $code, @args) = @_;

   $self->_cmd (e => $code, @args);

   $self
}

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

Tries to load the given module(s) into the process

Returns the process object for easy chaining of method calls.

=cut

sub require {
   my ($self, @modules) = @_;

   s%::%/%g for @modules;
   $self->eval ('require "$_.pm" for @_', @modules);

   $self
}

=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.

Example: pass an fh to a process, and release it without closing. it will
be closed automatically when it is no longer used.

   $proc->send_fh ($my_fh);
   undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT

=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 other process exits, you get a readable event on it,
because exiting the process closes the socket (if it didn't create any
children using fork).

Example: create a template for a process pool, pass a few strings, some
file handles, then fork, pass one more string, and run some code.

   my $pool = AnyEvent::Fork
                 ->new
                 ->send_arg ("str1", "str2")
                 ->send_fh ($fh1, $fh2);

   for (1..2) {
      $pool
         ->fork
         ->send_arg ("str3")
         ->run ("Some::function", sub {
            my ($fh) = @_;

            # fh is nonblocking, but we trust that the OS can accept these
            # extra 3 octets anyway.
            syswrite $fh, "hi #$_\n";

            # $fh is being closed here, as we don't store it anywhere
         });
   }

   # Some::function might look like this - all parameters passed before fork
   # and after will be passed, in order, after the communications socket.
   sub Some::function {
      my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;

      print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"
   }

=cut

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

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

=back

=head1 PORTABILITY NOTES

Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
and ::Template is not going to work), and it cost a lot of blood and sweat
to make it so, mostly due to the bloody broken perl that nobody seems to
care about. The fork emulation is a bad joke - I have yet to see something
useful that you cna do with it without running into memory corruption
issues or other braindamage. Hrrrr.

Cygwin perl is not supported at the moment, as it should implement fd
passing, but doesn't, and rolling my own is hard, as cygwin doesn't
support enough functionality to do it.

=head1 AUTHOR

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

=cut

1

Revision:	1.11
Committed:	Thu Apr 4 07:22:44 2013 UTC (11 years, 2 months ago) by root
Branch:	MAIN
Changes since 1.10:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
4
5	ATTENTION, this is a very early release, and very untested. Consider it a
6	technology preview.
7
8	=head1 SYNOPSIS
9
10	use AnyEvent::Fork;
11
12	##################################################################
13	# create a single new process, tell it to run your worker function
14
15	AnyEvent::Fork
16	->new
17	->require ("MyModule")
18	->run ("MyModule::worker, sub {
19	my ($master_filehandle) = @_;
20
21	# now $master_filehandle is connected to the
22	# $slave_filehandle in the new process.
23	});
24
25	# MyModule::worker might look like this
26	sub MyModule::worker {
27	my ($slave_filehandle) = @_;
28
29	# now $slave_filehandle is connected to the $master_filehandle
30	# in the original prorcess. have fun!
31	}
32
33	##################################################################
34	# create a pool of server processes all accepting on the same socket
35
36	# create listener socket
37	my $listener = ...;
38
39	# create a pool template, initialise it and give it the socket
40	my $pool = AnyEvent::Fork
41	->new
42	->require ("Some::Stuff", "My::Server")
43	->send_fh ($listener);
44
45	# now create 10 identical workers
46	for my $id (1..10) {
47	$pool
48	->fork
49	->send_arg ($id)
50	->run ("My::Server::run");
51	}
52
53	# now do other things - maybe use the filehandle provided by run
54	# to wait for the processes to die. or whatever.
55
56	# My::Server::run might look like this
57	sub My::Server::run {
58	my ($slave, $listener, $id) = @_;
59
60	close $slave; # we do not use the socket, so close it to save resources
61
62	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
63	# or anything we usually couldn't do in a process forked normally.
64	while (my $socket = $listener->accept) {
65	# do sth. with new socket
66	}
67	}
68
69	=head1 DESCRIPTION
70
71	This module allows you to create new processes, without actually forking
72	them from your current process (avoiding the problems of forking), but
73	preserving most of the advantages of fork.
74
75	It can be used to create new worker processes or new independent
76	subprocesses for short- and long-running jobs, process pools (e.g. for use
77	in pre-forked servers) but also to spawn new external processes (such as
78	CGI scripts from a webserver), which can be faster (and more well behaved)
79	than using fork+exec in big processes.
80
81	Special care has been taken to make this module useful from other modules,
82	while still supporting specialised environments such as L<App::Staticperl>
83	or L<PAR::Packer>.
84
85	=head1 PROBLEM STATEMENT
86
87	There are two ways to implement parallel processing on UNIX like operating
88	systems - fork and process, and fork+exec and process. They have different
89	advantages and disadvantages that I describe below, together with how this
90	module tries to mitigate the disadvantages.
91
92	=over 4
93
94	=item Forking from a big process can be very slow (a 5GB process needs
95	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
96	is often shared with exec (because you have to fork first), but in some
97	circumstances (e.g. when vfork is used), fork+exec can be much faster.
98
99	This module can help here by telling a small(er) helper process to fork,
100	or fork+exec instead.
101
102	=item Forking usually creates a copy-on-write copy of the parent
103	process. Memory (for example, modules or data files that have been
104	will not take additional memory). When exec'ing a new process, modules
105	and data files might need to be loaded again, at extra cpu and memory
106	cost. Likewise when forking, all data structures are copied as well - if
107	the program frees them and replaces them by new data, the child processes
108	will retain the memory even if it isn't used.
109
110	This module allows the main program to do a controlled fork, and allows
111	modules to exec processes safely at any time. When creating a custom
112	process pool you can take advantage of data sharing via fork without
113	risking to share large dynamic data structures that will blow up child
114	memory usage.
115
116	=item Exec'ing a new perl process might be difficult and slow. For
117	example, it is not easy to find the correct path to the perl interpreter,
118	and all modules have to be loaded from disk again. Long running processes
119	might run into problems when perl is upgraded for example.
120
121	This module supports creating pre-initialised perl processes to be used
122	as template, and also tries hard to identify the correct path to the perl
123	interpreter. With a cooperative main program, exec'ing the interpreter
124	might not even be necessary.
125
126	=item Forking might be impossible when a program is running. For example,
127	POSIX makes it almost impossible to fork from a multithreaded program and
128	do anything useful in the child - strictly speaking, if your perl program
129	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
130	you cannot call fork on the perl level anymore, at all.
131
132	This module can safely fork helper processes at any time, by caling
133	fork+exec in C, in a POSIX-compatible way.
134
135	=item Parallel processing with fork might be inconvenient or difficult
136	to implement. For example, when a program uses an event loop and creates
137	watchers it becomes very hard to use the event loop from a child
138	program, as the watchers already exist but are only meaningful in the
139	parent. Worse, a module might want to use such a system, not knowing
140	whether another module or the main program also does, leading to problems.
141
142	This module only lets the main program create pools by forking (because
143	only the main program can know when it is still safe to do so) - all other
144	pools are created by fork+exec, after which such modules can again be
145	loaded.
146
147	=back
148
149	=head1 CONCEPTS
150
151	This module can create new processes either by executing a new perl
152	process, or by forking from an existing "template" process.
153
154	Each such process comes with its own file handle that can be used to
155	communicate with it (it's actually a socket - one end in the new process,
156	one end in the main process), and among the things you can do in it are
157	load modules, fork new processes, send file handles to it, and execute
158	functions.
159
160	There are multiple ways to create additional processes to execute some
161	jobs:
162
163	=over 4
164
165	=item fork a new process from the "default" template process, load code,
166	run it
167
168	This module has a "default" template process which it executes when it is
169	needed the first time. Forking from this process shares the memory used
170	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.
172
173	This is ideal for when you only need one extra process of a kind, with the
174	option of starting and stipping it on demand.
175
176	Example:
177
178	AnyEvent::Fork
179	->new
180	->require ("Some::Module")
181	->run ("Some::Module::run", sub {
182	my ($fork_fh) = @_;
183	});
184
185	=item fork a new template process, load code, then fork processes off of
186	it and run the code
187
188	When you need to have a bunch of processes that all execute the same (or
189	very similar) tasks, then a good way is to create a new template process
190	for them, loading all the modules you need, and then create your worker
191	processes from this new template process.
192
193	This way, all code (and data structures) that can be shared (e.g. the
194	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.
196
197	The disadvantage of this approach is that you need to create a template
198	process for the sole purpose of forking new processes from it, but if you
199	only need a fixed number of proceses you can create them, and then destroy
200	the template process.
201
202	Example:
203
204	my $template = AnyEvent::Fork->new->require ("Some::Module");
205
206	for (1..10) {
207	$template->fork->run ("Some::Module::run", sub {
208	my ($fork_fh) = @_;
209	});
210	}
211
212	# at this point, you can keep $template around to fork new processes
213	# later, or you can destroy it, which causes it to vanish.
214
215	=item execute a new perl interpreter, load some code, run it
216
217	This is relatively slow, and doesn't allow you to share memory between
218	multiple processes.
219
220	The only advantage is that you don't have to have a template process
221	hanging around all the time to fork off some new processes, which might be
222	an advantage when there are long time spans where no extra processes are
223	needed.
224
225	Example:
226
227	AnyEvent::Fork
228	->new_exec
229	->require ("Some::Module")
230	->run ("Some::Module::run", sub {
231	my ($fork_fh) = @_;
232	});
233
234	=back
235
236	=head1 FUNCTIONS
237
238	=over 4
239
240	=cut
241
242	package AnyEvent::Fork;
243
244	use common::sense;
245
246	use Socket ();
247
248	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();
251
252	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
253
254	=item my $pool = new AnyEvent::Fork key => value...
255
256	Create a new process pool. The following named parameters are supported:
257
258	=over 4
259
260	=back
261
262	=cut
263
264	# the early fork template process
265	our $EARLY;
266
267	# the empty template process
268	our $TEMPLATE;
269
270	sub _cmd {
271	my $self = shift;
272
273	#TODO: maybe append the packet to any existing string command already in the queue
274
275	# ideally, we would want to use "a (w/a)*" as format string, but perl versions
276	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.
277	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;
278
279	$self->[3] \|\|= AE::io $self->[1], 1, sub {
280	# send the next "thing" in the queue - either a reference to an fh,
281	# or a plain string.
282
283	if (ref $self->[2][0]) {
284	# send fh
285	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }
286	and shift @{ $self->[2] };
287
288	} else {
289	# send string
290	my $len = syswrite $self->[1], $self->[2][0]
291	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };
292
293	substr $self->[2][0], 0, $len, "";
294	shift @{ $self->[2] } unless length $self->[2][0];
295	}
296
297	unless (@{ $self->[2] }) {
298	undef $self->[3];
299	# invoke run callback
300	$self->[0]->($self->[1]) if $self->[0];
301	}
302	};
303	}
304
305	sub _new {
306	my ($self, $fh) = @_;
307
308	AnyEvent::Util::fh_nonblocking $fh, 1;
309
310	$self = bless [
311	undef, # run callback
312	$fh,
313	[], # write queue - strings or fd's
314	undef, # AE watcher
315	], $self;
316
317	$self
318	}
319
320	# fork template from current process, used by AnyEvent::Fork::Early/Template
321	sub _new_fork {
322	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
323	my $parent = $$;
324
325	my $pid = fork;
326
327	if ($pid eq 0) {
328	require AnyEvent::Fork::Serve;
329	$AnyEvent::Fork::Serve::OWNER = $parent;
330	close $fh;
331	$0 = "$_[1] of $parent";
332	AnyEvent::Fork::Serve::serve ($slave);
333	AnyEvent::Fork::Util::_exit 0;
334	} elsif (!$pid) {
335	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
336	}
337
338	AnyEvent::Fork->_new ($fh)
339	}
340
341	=item my $proc = new AnyEvent::Fork
342
343	Create a new "empty" perl interpreter process and returns its process
344	object for further manipulation.
345
346	The new process is forked from a template process that is kept around
347	for this purpose. When it doesn't exist yet, it is created by a call to
348	C<new_exec> and kept around for future calls.
349
350	When the process object is destroyed, it will release the file handle
351	that connects it with the new process. When the new process has not yet
352	called C<run>, then the process will exit. Otherwise, what happens depends
353	entirely on the code that is executed.
354
355	=cut
356
357	sub new {
358	my $class = shift;
359
360	$TEMPLATE \|\|= $class->new_exec;
361	$TEMPLATE->fork
362	}
363
364	=item $new_proc = $proc->fork
365
366	Forks C<$proc>, creating a new process, and returns the process object
367	of the new process.
368
369	If any of the C<send_> functions have been called before fork, then they
370	will be cloned in the child. For example, in a pre-forked server, you
371	might C<send_fh> the listening socket into the template process, and then
372	keep calling C<fork> and C<run>.
373
374	=cut
375
376	sub fork {
377	my ($self) = @_;
378
379	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
380
381	$self->send_fh ($slave);
382	$self->_cmd ("f");
383
384	AnyEvent::Fork->_new ($fh)
385	}
386
387	=item my $proc = new_exec AnyEvent::Fork
388
389	Create a new "empty" perl interpreter process and returns its process
390	object for further manipulation.
391
392	Unlike the C<new> method, this method I<always> spawns a new perl process
393	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
394	reduces the amount of memory sharing that is possible, and is also slower.
395
396	You should use C<new> whenever possible, except when having a template
397	process around is unacceptable.
398
399	The path to the perl interpreter is divined usign various methods - first
400	C<$^X> is investigated to see if the path ends with something that sounds
401	as if it were the perl interpreter. Failing this, the module falls back to
402	using C<$Config::Config{perlpath}>.
403
404	=cut
405
406	sub new_exec {
407	my ($self) = @_;
408
409	return $EARLY->fork
410	if $EARLY;
411
412	# first find path of perl
413	my $perl = $;
414
415	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
416	# that looks like perl. this obviously only works for posix and win32
417	unless (
418	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)
419	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
420	) {
421	# if it doesn't look perlish enough, try Config
422	require Config;
423	$perl = $Config::Config{perlpath};
424	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
425	}
426
427	require Proc::FastSpawn;
428
429	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
430	Proc::FastSpawn::fd_inherit (fileno $slave);
431
432	# new fh's should always be set cloexec (due to $^F),
433	# but hey, not on win32, so we always clear the inherit flag.
434	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
435
436	# quick. also doesn't work in win32. of course. what did you expect
437	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
438	my %env = %ENV;
439	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;
440
441	Proc::FastSpawn::spawn (
442	$perl,
443	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
444	[map "$_=$env{$_}", keys %env],
445	) or die "unable to spawn AnyEvent::Fork server: $!";
446
447	$self->_new ($fh)
448	}
449
450	=item $proc = $proc->eval ($perlcode, @args)
451
452	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
453	the strings specified by C<@args>.
454
455	This call is meant to do any custom initialisation that might be required
456	(for example, the C<require> method uses it). It's not supposed to be used
457	to completely take over the process, use C<run> for that.
458
459	The code will usually be executed after this call returns, and there is no
460	way to pass anything back to the calling process. Any evaluation errors
461	will be reported to stderr and cause the process to exit.
462
463	Returns the process object for easy chaining of method calls.
464
465	=cut
466
467	sub eval {
468	my ($self, $code, @args) = @_;
469
470	$self->_cmd (e => $code, @args);
471
472	$self
473	}
474
475	=item $proc = $proc->require ($module, ...)
476
477	Tries to load the given module(s) into the process
478
479	Returns the process object for easy chaining of method calls.
480
481	=cut
482
483	sub require {
484	my ($self, @modules) = @_;
485
486	s%::%/%g for @modules;
487	$self->eval ('require "$_.pm" for @_', @modules);
488
489	$self
490	}
491
492	=item $proc = $proc->send_fh ($handle, ...)
493
494	Send one or more file handles (I<not> file descriptors) to the process,
495	to prepare a call to C<run>.
496
497	The process object keeps a reference to the handles until this is done,
498	so you must not explicitly close the handles. This is most easily
499	accomplished by simply not storing the file handles anywhere after passing
500	them to this method.
501
502	Returns the process object for easy chaining of method calls.
503
504	Example: pass an fh to a process, and release it without closing. it will
505	be closed automatically when it is no longer used.
506
507	$proc->send_fh ($my_fh);
508	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
509
510	=cut
511
512	sub send_fh {
513	my ($self, @fh) = @_;
514
515	for my $fh (@fh) {
516	$self->_cmd ("h");
517	push @{ $self->[2] }, \$fh;
518	}
519
520	$self
521	}
522
523	=item $proc = $proc->send_arg ($string, ...)
524
525	Send one or more argument strings to the process, to prepare a call to
526	C<run>. The strings can be any octet string.
527
528	Returns the process object for easy chaining of emthod calls.
529
530	=cut
531
532	sub send_arg {
533	my ($self, @arg) = @_;
534
535	$self->_cmd (a => @arg);
536
537	$self
538	}
539
540	=item $proc->run ($func, $cb->($fh))
541
542	Enter the function specified by the fully qualified name in C<$func> in
543	the process. The function is called with the communication socket as first
544	argument, followed by all file handles and string arguments sent earlier
545	via C<send_fh> and C<send_arg> methods, in the order they were called.
546
547	If the called function returns, the process exits.
548
549	Preparing the process can take time - when the process is ready, the
550	callback is invoked with the local communications socket as argument.
551
552	The process object becomes unusable on return from this function.
553
554	If the communication socket isn't used, it should be closed on both sides,
555	to save on kernel memory.
556
557	The socket is non-blocking in the parent, and blocking in the newly
558	created process. The close-on-exec flag is set on both. Even if not used
559	otherwise, the socket can be a good indicator for the existance of the
560	process - if the other process exits, you get a readable event on it,
561	because exiting the process closes the socket (if it didn't create any
562	children using fork).
563
564	Example: create a template for a process pool, pass a few strings, some
565	file handles, then fork, pass one more string, and run some code.
566
567	my $pool = AnyEvent::Fork
568	->new
569	->send_arg ("str1", "str2")
570	->send_fh ($fh1, $fh2);
571
572	for (1..2) {
573	$pool
574	->fork
575	->send_arg ("str3")
576	->run ("Some::function", sub {
577	my ($fh) = @_;
578
579	# fh is nonblocking, but we trust that the OS can accept these
580	# extra 3 octets anyway.
581	syswrite $fh, "hi #$_\n";
582
583	# $fh is being closed here, as we don't store it anywhere
584	});
585	}
586
587	# Some::function might look like this - all parameters passed before fork
588	# and after will be passed, in order, after the communications socket.
589	sub Some::function {
590	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
591
592	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"
593	}
594
595	=cut
596
597	sub run {
598	my ($self, $func, $cb) = @_;
599
600	$self->[0] = $cb;
601	$self->_cmd (r => $func);
602	}
603
604	=back
605
606	=head1 PORTABILITY NOTES
607
608	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
609	and ::Template is not going to work), and it cost a lot of blood and sweat
610	to make it so, mostly due to the bloody broken perl that nobody seems to
611	care about. The fork emulation is a bad joke - I have yet to see something
612	useful that you cna do with it without running into memory corruption
613	issues or other braindamage. Hrrrr.
614
615	Cygwin perl is not supported at the moment, as it should implement fd
616	passing, but doesn't, and rolling my own is hard, as cygwin doesn't
617	support enough functionality to do it.
618
619	=head1 AUTHOR
620
621	Marc Lehmann <schmorp@schmorp.de>
622	http://home.schmorp.de/
623
624	=cut
625
626	1
627