[ViewVC] Diff of: cvs/AnyEvent-Fork/Fork.pm

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.2 by root, Sun Mar 31 03:26:50 2013 UTC vs.
Revision 1.37 by root, Sat Apr 6 20:06:39 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::ProcessPool - manage pools of perl worker processes, exec'ed or fork'ed	3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::ProcessPool;	7	use AnyEvent::Fork;
		8
		9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
8		15
9	=head1 DESCRIPTION	16	=head1 DESCRIPTION
10		17
11	This module allows you to create single worker processes but also worker	18	This module allows you to create new processes, without actually forking
12	pool that share memory, by forking from the main program, or exec'ing new	19	them from your current process (avoiding the problems of forking), but
13	perl interpreters from a module.	20	preserving most of the advantages of fork.
14		21
15	You create a new processes in a pool by specifying a function to call	22	It can be used to create new worker processes or new independent
16	with any combination of string values and file handles.	23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
17		27
18	A pool can have initialisation code which is executed before forking. The	28	Special care has been taken to make this module useful from other modules,
19	initialisation code is only executed once and the resulting process is	29	while still supporting specialised environments such as L<App::Staticperl>
20	cached, to be used as a template.	30	or L<PAR::Packer>.
21		31
22	Pools without such initialisation code don't cache an extra process.	32	=head1 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
23		44
24	=head1 PROBLEM STATEMENT	45	=head1 PROBLEM STATEMENT
25		46
26	There are two ways to implement parallel processing on UNIX like operating	47	There are two traditional ways to implement parallel processing on UNIX
27	systems - fork and process, and fork+exec and process. They have different	48	like operating systems - fork and process, and fork+exec and process. They
28	advantages and disadvantages that I describe below, together with how this	49	have different advantages and disadvantages that I describe below,
29	module tries to mitigate the disadvantages.	50	together with how this module tries to mitigate the disadvantages.
30		51
31	=over 4	52	=over 4
32		53
33	=item Forking from a big process can be very slow (a 5GB process needs	54	=item Forking from a big process can be very slow.
34	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead	55
		56	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
35	is often shared with exec (because you have to fork first), but in some	57	overhead is often shared with exec (because you have to fork first), but
36	circumstances (e.g. when vfork is used), fork+exec can be much faster.	58	in some circumstances (e.g. when vfork is used), fork+exec can be much
		59	faster.
37		60
38	This module can help here by telling a small(er) helper process to fork,	61	This module can help here by telling a small(er) helper process to fork,
39	or fork+exec instead.	62	which is faster then forking the main process, and also uses vfork where
		63	possible. This gives the speed of vfork, with the flexibility of fork.
40		64
41	=item Forking usually creates a copy-on-write copy of the parent	65	=item Forking usually creates a copy-on-write copy of the parent
42	process. Memory (for example, modules or data files that have been	66	process.
43	will not take additional memory). When exec'ing a new process, modules	67
44	and data files might need to be loaded again, at extra cpu and memory	68	For example, modules or data files that are loaded will not use additional
45	cost. Likewise when forking, all data structures are copied as well - if	69	memory after a fork. When exec'ing a new process, modules and data files
		70	might need to be loaded again, at extra CPU and memory cost. But when
		71	forking, literally all data structures are copied - if the program frees
46	the program frees them and replaces them by new data, the child processes	72	them and replaces them by new data, the child processes will retain the
47	will retain the memory even if it isn't used.	73	old version even if it isn't used, which can suddenly and unexpectedly
		74	increase memory usage when freeing memory.
		75
		76	The trade-off is between more sharing with fork (which can be good or
		77	bad), and no sharing with exec.
48		78
49	This module allows the main program to do a controlled fork, and allows	79	This module allows the main program to do a controlled fork, and allows
50	modules to exec processes safely at any time. When creating a custom	80	modules to exec processes safely at any time. When creating a custom
51	process pool you can take advantage of data sharing via fork without	81	process pool you can take advantage of data sharing via fork without
52	risking to share large dynamic data structures that will blow up child	82	risking to share large dynamic data structures that will blow up child
53	memory usage.	83	memory usage.
54		84
		85	In other words, this module puts you into control over what is being
		86	shared and what isn't, at all times.
		87
55	=item Exec'ing a new perl process might be difficult and slow. For	88	=item Exec'ing a new perl process might be difficult.
		89
56	example, it is not easy to find the correct path to the perl interpreter,	90	For example, it is not easy to find the correct path to the perl
57	and all modules have to be loaded from disk again. Long running processes	91	interpreter - C<$^X> might not be a perl interpreter at all.
58	might run into problems when perl is upgraded for example.
59		92
60	This module supports creating pre-initialised perl processes to be used
61	as template, and also tries hard to identify the correct path to the perl	93	This module tries hard to identify the correct path to the perl
62	interpreter. With a cooperative main program, exec'ing the interpreter	94	interpreter. With a cooperative main program, exec'ing the interpreter
63	might not even be necessary.	95	might not even be necessary, but even without help from the main program,
		96	it will still work when used from a module.
64		97
		98	=item Exec'ing a new perl process might be slow, as all necessary modules
		99	have to be loaded from disk again, with no guarantees of success.
		100
		101	Long running processes might run into problems when perl is upgraded
		102	and modules are no longer loadable because they refer to a different
		103	perl version, or parts of a distribution are newer than the ones already
		104	loaded.
		105
		106	This module supports creating pre-initialised perl processes to be used as
		107	a template for new processes.
		108
65	=item Forking might be impossible when a program is running. For example,	109	=item Forking might be impossible when a program is running.
66	POSIX makes it almost impossible to fork from a multithreaded program and
67	do anything useful in the child - strictly speaking, if your perl program
68	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
69	you cannot call fork on the perl level anymore, at all.
70		110
		111	For example, POSIX makes it almost impossible to fork from a
		112	multi-threaded program while doing anything useful in the child - in
		113	fact, if your perl program uses POSIX threads (even indirectly via
		114	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		115	anymore without risking corruption issues on a number of operating
		116	systems.
		117
71	This module can safely fork helper processes at any time, by caling	118	This module can safely fork helper processes at any time, by calling
72	fork+exec in C, in a POSIX-compatible way.	119	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
73		120
74	=item Parallel processing with fork might be inconvenient or difficult	121	=item Parallel processing with fork might be inconvenient or difficult
		122	to implement. Modules might not work in both parent and child.
		123
75	to implement. For example, when a program uses an event loop and creates	124	For example, when a program uses an event loop and creates watchers it
76	watchers it becomes very hard to use the event loop from a child	125	becomes very hard to use the event loop from a child program, as the
77	program, as the watchers already exist but are only meaningful in the	126	watchers already exist but are only meaningful in the parent. Worse, a
78	parent. Worse, a module might want to use such a system, not knowing	127	module might want to use such a module, not knowing whether another module
79	whether another module or the main program also does, leading to problems.	128	or the main program also does, leading to problems.
80		129
81	This module only lets the main program create pools by forking (because	130	Apart from event loops, graphical toolkits also commonly fall into the
82	only the main program can know when it is still safe to do so) - all other	131	"unsafe module" category, or just about anything that communicates with
83	pools are created by fork+exec, after which such modules can again be	132	the external world, such as network libraries and file I/O modules, which
84	loaded.	133	usually don't like being copied and then allowed to continue in two
		134	processes.
		135
		136	With this module only the main program is allowed to create new processes
		137	by forking (because only the main program can know when it is still safe
		138	to do so) - all other processes are created via fork+exec, which makes it
		139	possible to use modules such as event loops or window interfaces safely.
85		140
86	=back	141	=back
87		142
		143	=head1 EXAMPLES
		144
		145	=head2 Create a single new process, tell it to run your worker function.
		146
		147	AnyEvent::Fork
		148	->new
		149	->require ("MyModule")
		150	->run ("MyModule::worker, sub {
		151	my ($master_filehandle) = @_;
		152
		153	# now $master_filehandle is connected to the
		154	# $slave_filehandle in the new process.
		155	});
		156
		157	C<MyModule> might look like this:
		158
		159	package MyModule;
		160
		161	sub worker {
		162	my ($slave_filehandle) = @_;
		163
		164	# now $slave_filehandle is connected to the $master_filehandle
		165	# in the original prorcess. have fun!
		166	}
		167
		168	=head2 Create a pool of server processes all accepting on the same socket.
		169
		170	# create listener socket
		171	my $listener = ...;
		172
		173	# create a pool template, initialise it and give it the socket
		174	my $pool = AnyEvent::Fork
		175	->new
		176	->require ("Some::Stuff", "My::Server")
		177	->send_fh ($listener);
		178
		179	# now create 10 identical workers
		180	for my $id (1..10) {
		181	$pool
		182	->fork
		183	->send_arg ($id)
		184	->run ("My::Server::run");
		185	}
		186
		187	# now do other things - maybe use the filehandle provided by run
		188	# to wait for the processes to die. or whatever.
		189
		190	C<My::Server> might look like this:
		191
		192	package My::Server;
		193
		194	sub run {
		195	my ($slave, $listener, $id) = @_;
		196
		197	close $slave; # we do not use the socket, so close it to save resources
		198
		199	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		200	# or anything we usually couldn't do in a process forked normally.
		201	while (my $socket = $listener->accept) {
		202	# do sth. with new socket
		203	}
		204	}
		205
		206	=head2 use AnyEvent::Fork as a faster fork+exec
		207
		208	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
		209	and standard error redirected to the communications socket. It is usually
		210	faster than fork+exec, but still lets you prepare the environment.
		211
		212	open my $output, ">/tmp/log" or die "$!";
		213
		214	AnyEvent::Fork
		215	->new
		216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
		219
		220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
		223
		224	exec @cmd;
		225	}
		226	')
		227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
		230
		231	my $stderr = $cv->recv;
		232
		233	=head1 CONCEPTS
		234
		235	This module can create new processes either by executing a new perl
		236	process, or by forking from an existing "template" process.
		237
		238	Each such process comes with its own file handle that can be used to
		239	communicate with it (it's actually a socket - one end in the new process,
		240	one end in the main process), and among the things you can do in it are
		241	load modules, fork new processes, send file handles to it, and execute
		242	functions.
		243
		244	There are multiple ways to create additional processes to execute some
		245	jobs:
		246
88	=over 4	247	=over 4
89		248
90	=cut	249	=item fork a new process from the "default" template process, load code,
		250	run it
91		251
		252	This module has a "default" template process which it executes when it is
		253	needed the first time. Forking from this process shares the memory used
		254	for the perl interpreter with the new process, but loading modules takes
		255	time, and the memory is not shared with anything else.
		256
		257	This is ideal for when you only need one extra process of a kind, with the
		258	option of starting and stopping it on demand.
		259
		260	Example:
		261
		262	AnyEvent::Fork
		263	->new
		264	->require ("Some::Module")
		265	->run ("Some::Module::run", sub {
		266	my ($fork_fh) = @_;
		267	});
		268
		269	=item fork a new template process, load code, then fork processes off of
		270	it and run the code
		271
		272	When you need to have a bunch of processes that all execute the same (or
		273	very similar) tasks, then a good way is to create a new template process
		274	for them, loading all the modules you need, and then create your worker
		275	processes from this new template process.
		276
		277	This way, all code (and data structures) that can be shared (e.g. the
		278	modules you loaded) is shared between the processes, and each new process
		279	consumes relatively little memory of its own.
		280
		281	The disadvantage of this approach is that you need to create a template
		282	process for the sole purpose of forking new processes from it, but if you
		283	only need a fixed number of processes you can create them, and then destroy
		284	the template process.
		285
		286	Example:
		287
		288	my $template = AnyEvent::Fork->new->require ("Some::Module");
		289
		290	for (1..10) {
		291	$template->fork->run ("Some::Module::run", sub {
		292	my ($fork_fh) = @_;
		293	});
		294	}
		295
		296	# at this point, you can keep $template around to fork new processes
		297	# later, or you can destroy it, which causes it to vanish.
		298
		299	=item execute a new perl interpreter, load some code, run it
		300
		301	This is relatively slow, and doesn't allow you to share memory between
		302	multiple processes.
		303
		304	The only advantage is that you don't have to have a template process
		305	hanging around all the time to fork off some new processes, which might be
		306	an advantage when there are long time spans where no extra processes are
		307	needed.
		308
		309	Example:
		310
		311	AnyEvent::Fork
		312	->new_exec
		313	->require ("Some::Module")
		314	->run ("Some::Module::run", sub {
		315	my ($fork_fh) = @_;
		316	});
		317
		318	=back
		319
		320	=head1 THE C<AnyEvent::Fork> CLASS
		321
		322	This module exports nothing, and only implements a single class -
		323	C<AnyEvent::Fork>.
		324
		325	There are two class constructors that both create new processes - C<new>
		326	and C<new_exec>. The C<fork> method creates a new process by forking an
		327	existing one and could be considered a third constructor.
		328
		329	Most of the remaining methods deal with preparing the new process, by
		330	loading code, evaluating code and sending data to the new process. They
		331	usually return the process object, so you can chain method calls.
		332
		333	If a process object is destroyed before calling its C<run> method, then
		334	the process simply exits. After C<run> is called, all responsibility is
		335	passed to the specified function.
		336
		337	As long as there is any outstanding work to be done, process objects
		338	resist being destroyed, so there is no reason to store them unless you
		339	need them later - configure and forget works just fine.
		340
		341	=over 4
		342
		343	=cut
		344
92	package AnyEvent::ProcessPool;	345	package AnyEvent::Fork;
93		346
94	use common::sense;	347	use common::sense;
95		348
96	use Socket ();	349	use Errno ();
97		350
98	use Proc::FastSpawn;
99	use AnyEvent;	351	use AnyEvent;
100	use AnyEvent::ProcessPool::Util;
101	use AnyEvent::Util ();	352	use AnyEvent::Util ();
102		353
103	BEGIN {	354	use IO::FDPass;
104	# require Exporter;
105	}
106		355
107	=item my $pool = new AnyEvent::ProcessPool key => value...	356	our $VERSION = 0.5;
108		357
109	Create a new process pool. The following named parameters are supported:	358	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
110		359
111	=over 4	360	=over 4
112		361
113	=back	362	=back
114		363
115	=cut	364	=cut
116		365
		366	# the early fork template process
		367	our $EARLY;
		368
117	# the template process	369	# the empty template process
118	our $template;	370	our $TEMPLATE;
119		371
120	sub _queue {	372	sub _cmd {
121	my ($pid, $fh) = @_;	373	my $self = shift;
122		374
123	[	375	# ideally, we would want to use "a (w/a)*" as format string, but perl
		376	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		377	# it.
		378	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
		379
		380	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		381	do {
		382	# send the next "thing" in the queue - either a reference to an fh,
		383	# or a plain string.
		384
		385	if (ref $self->[2][0]) {
		386	# send fh
		387	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		388	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		389	undef $self->[3];
		390	die "AnyEvent::Fork: file descriptor send failure: $!";
		391	}
		392
		393	shift @{ $self->[2] };
		394
		395	} else {
		396	# send string
		397	my $len = syswrite $self->[1], $self->[2][0];
		398
		399	unless ($len) {
		400	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		401	undef $self->[3];
		402	die "AnyEvent::Fork: command write failure: $!";
		403	}
		404
		405	substr $self->[2][0], 0, $len, "";
		406	shift @{ $self->[2] } unless length $self->[2][0];
		407	}
		408	} while @{ $self->[2] };
		409
		410	# everything written
		411	undef $self->[3];
		412
		413	# invoke run callback, if any
		414	$self->[4]->($self->[1]) if $self->[4];
		415	};
		416
		417	() # make sure we don't leak the watcher
		418	}
		419
		420	sub _new {
		421	my ($self, $fh, $pid) = @_;
		422
		423	AnyEvent::Util::fh_nonblocking $fh, 1;
		424
		425	$self = bless [
124	$pid,	426	$pid,
125	$fh,	427	$fh,
126	[],	428	[], # write queue - strings or fd's
127	undef	429	undef, # AE watcher
128	]	430	], $self;
129	}
130		431
131	sub queue_cmd {	432	$self
132	my ($queue, $cmd) = @_;
133
134	push @{ $queue->[2] }, pack "N/a", $cmd;
135
136	$queue->[3] \|\|= AE::io $queue->[1], 1, sub {
137	if (ref $queue->[2][0]) {
138	AnyEvent::ProcessPool::Util::fd_send fileno $queue->[1], fileno ${ $queue->[2][0] }
139	and shift @{ $queue->[2] };
140	} else {
141	my $len = syswrite $queue->[1], $queue->[2][0]
142	or do { undef $queue->[3]; die "AnyEvent::ProcessPool::queue write failure: $!" };
143	substr $queue->[2][0], 0, $len, "";
144	shift @{ $queue->[2] } unless length $queue->[2][0];
145	}
146
147	undef $queue->[3] unless @{ $queue->[2] };
148	};
149	}	433	}
150		434
151	sub run_template {	435	# fork template from current process, used by AnyEvent::Fork::Early/Template
152	return if $template;	436	sub _new_fork {
153
154	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	437	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
155	AnyEvent::Util::fh_nonblocking $fh, 1;	438	my $parent = $$;
156	fd_inherit fileno $slave;
157		439
158	my %env = %ENV;	440	my $pid = fork;
159	$env{PERL5LIB} = join ":", grep !ref, @INC;
160		441
161	my $pid = spawn	442	if ($pid eq 0) {
162	$^X,	443	require AnyEvent::Fork::Serve;
163	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	444	$AnyEvent::Fork::Serve::OWNER = $parent;
164	[map "$_=$env{$_}", keys %env],	445	close $fh;
165	or die "unable to spawn AnyEvent::ProcessPool server: $!";	446	$0 = "$_[1] of $parent";
		447	$SIG{CHLD} = 'IGNORE';
		448	AnyEvent::Fork::Serve::serve ($slave);
		449	exit 0;
		450	} elsif (!$pid) {
		451	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		452	}
166		453
167	close $slave;	454	AnyEvent::Fork->_new ($fh, $pid)
168
169	$template = _queue $pid, $fh;
170
171	my ($a, $b) = AnyEvent::Util::portable_socketpair;
172
173	queue_cmd $template, "Iabc";
174	push @{ $template->[2] }, \$b;
175
176	use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
177	undef $b;
178	die "x" . <$a>;
179	}	455	}
		456
		457	=item my $proc = new AnyEvent::Fork
		458
		459	Create a new "empty" perl interpreter process and returns its process
		460	object for further manipulation.
		461
		462	The new process is forked from a template process that is kept around
		463	for this purpose. When it doesn't exist yet, it is created by a call to
		464	C<new_exec> first and then stays around for future calls.
		465
		466	=cut
180		467
181	sub new {	468	sub new {
182	my $class = shift;	469	my $class = shift;
183		470
184	my $self = bless {	471	$TEMPLATE \|\|= $class->new_exec;
185	@_	472	$TEMPLATE->fork
186	}, $class;	473	}
187		474
188	run_template;	475	=item $new_proc = $proc->fork
		476
		477	Forks C<$proc>, creating a new process, and returns the process object
		478	of the new process.
		479
		480	If any of the C<send_> functions have been called before fork, then they
		481	will be cloned in the child. For example, in a pre-forked server, you
		482	might C<send_fh> the listening socket into the template process, and then
		483	keep calling C<fork> and C<run>.
		484
		485	=cut
		486
		487	sub fork {
		488	my ($self) = @_;
		489
		490	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		491
		492	$self->send_fh ($slave);
		493	$self->_cmd ("f");
		494
		495	AnyEvent::Fork->_new ($fh)
		496	}
		497
		498	=item my $proc = new_exec AnyEvent::Fork
		499
		500	Create a new "empty" perl interpreter process and returns its process
		501	object for further manipulation.
		502
		503	Unlike the C<new> method, this method I<always> spawns a new perl process
		504	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
		505	reduces the amount of memory sharing that is possible, and is also slower.
		506
		507	You should use C<new> whenever possible, except when having a template
		508	process around is unacceptable.
		509
		510	The path to the perl interpreter is divined using various methods - first
		511	C<$^X> is investigated to see if the path ends with something that sounds
		512	as if it were the perl interpreter. Failing this, the module falls back to
		513	using C<$Config::Config{perlpath}>.
		514
		515	=cut
		516
		517	sub new_exec {
		518	my ($self) = @_;
		519
		520	return $EARLY->fork
		521	if $EARLY;
		522
		523	# first find path of perl
		524	my $perl = $;
		525
		526	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		527	# that looks like perl. this obviously only works for posix and win32
		528	unless (
		529	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		530	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		531	) {
		532	# if it doesn't look perlish enough, try Config
		533	require Config;
		534	$perl = $Config::Config{perlpath};
		535	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		536	}
		537
		538	require Proc::FastSpawn;
		539
		540	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		541	Proc::FastSpawn::fd_inherit (fileno $slave);
		542
		543	# new fh's should always be set cloexec (due to $^F),
		544	# but hey, not on win32, so we always clear the inherit flag.
		545	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		546
		547	# quick. also doesn't work in win32. of course. what did you expect
		548	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		549	my %env = %ENV;
		550	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		551
		552	my $pid = Proc::FastSpawn::spawn (
		553	$perl,
		554	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		555	[map "$_=$env{$_}", keys %env],
		556	) or die "unable to spawn AnyEvent::Fork server: $!";
		557
		558	$self->_new ($fh, $pid)
		559	}
		560
		561	=item $pid = $proc->pid
		562
		563	Returns the process id of the process I<iff it is a direct child of the
		564	process running AnyEvent::Fork>, and C<undef> otherwise.
		565
		566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		568	to clean up their zombies when they die.
		569
		570	All other processes are not direct children, and will be cleaned up by
		571	AnyEvent::Fork itself.
		572
		573	=cut
		574
		575	sub pid {
		576	$_[0][0]
		577	}
		578
		579	=item $proc = $proc->eval ($perlcode, @args)
		580
		581	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		582	the strings specified by C<@args>, in the "main" package.
		583
		584	This call is meant to do any custom initialisation that might be required
		585	(for example, the C<require> method uses it). It's not supposed to be used
		586	to completely take over the process, use C<run> for that.
		587
		588	The code will usually be executed after this call returns, and there is no
		589	way to pass anything back to the calling process. Any evaluation errors
		590	will be reported to stderr and cause the process to exit.
		591
		592	If you want to execute some code (that isn't in a module) to take over the
		593	process, you should compile a function via C<eval> first, and then call
		594	it via C<run>. This also gives you access to any arguments passed via the
		595	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		596	a faster fork+exec> example to see it in action.
		597
		598	Returns the process object for easy chaining of method calls.
		599
		600	=cut
		601
		602	sub eval {
		603	my ($self, $code, @args) = @_;
		604
		605	$self->_cmd (e => pack "(w/a)", $code, @args);
189		606
190	$self	607	$self
191	}	608	}
192		609
		610	=item $proc = $proc->require ($module, ...)
		611
		612	Tries to load the given module(s) into the process
		613
		614	Returns the process object for easy chaining of method calls.
		615
		616	=cut
		617
		618	sub require {
		619	my ($self, @modules) = @_;
		620
		621	s%::%/%g for @modules;
		622	$self->eval ('require "$_.pm" for @_', @modules);
		623
		624	$self
		625	}
		626
		627	=item $proc = $proc->send_fh ($handle, ...)
		628
		629	Send one or more file handles (I<not> file descriptors) to the process,
		630	to prepare a call to C<run>.
		631
		632	The process object keeps a reference to the handles until they have
		633	been passed over to the process, so you must not explicitly close the
		634	handles. This is most easily accomplished by simply not storing the file
		635	handles anywhere after passing them to this method - when AnyEvent::Fork
		636	is finished using them, perl will automatically close them.
		637
		638	Returns the process object for easy chaining of method calls.
		639
		640	Example: pass a file handle to a process, and release it without
		641	closing. It will be closed automatically when it is no longer used.
		642
		643	$proc->send_fh ($my_fh);
		644	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		645
		646	=cut
		647
		648	sub send_fh {
		649	my ($self, @fh) = @_;
		650
		651	for my $fh (@fh) {
		652	$self->_cmd ("h");
		653	push @{ $self->[2] }, \$fh;
		654	}
		655
		656	$self
		657	}
		658
		659	=item $proc = $proc->send_arg ($string, ...)
		660
		661	Send one or more argument strings to the process, to prepare a call to
		662	C<run>. The strings can be any octet strings.
		663
		664	The protocol is optimised to pass a moderate number of relatively short
		665	strings - while you can pass up to 4GB of data in one go, this is more
		666	meant to pass some ID information or other startup info, not big chunks of
		667	data.
		668
		669	Returns the process object for easy chaining of method calls.
		670
		671	=cut
		672
		673	sub send_arg {
		674	my ($self, @arg) = @_;
		675
		676	$self->_cmd (a => pack "(w/a)", @arg);
		677
		678	$self
		679	}
		680
		681	=item $proc->run ($func, $cb->($fh))
		682
		683	Enter the function specified by the function name in C<$func> in the
		684	process. The function is called with the communication socket as first
		685	argument, followed by all file handles and string arguments sent earlier
		686	via C<send_fh> and C<send_arg> methods, in the order they were called.
		687
		688	The process object becomes unusable on return from this function - any
		689	further method calls result in undefined behaviour.
		690
		691	The function name should be fully qualified, but if it isn't, it will be
		692	looked up in the C<main> package.
		693
		694	If the called function returns, doesn't exist, or any error occurs, the
		695	process exits.
		696
		697	Preparing the process is done in the background - when all commands have
		698	been sent, the callback is invoked with the local communications socket
		699	as argument. At this point you can start using the socket in any way you
		700	like.
		701
		702	If the communication socket isn't used, it should be closed on both sides,
		703	to save on kernel memory.
		704
		705	The socket is non-blocking in the parent, and blocking in the newly
		706	created process. The close-on-exec flag is set in both.
		707
		708	Even if not used otherwise, the socket can be a good indicator for the
		709	existence of the process - if the other process exits, you get a readable
		710	event on it, because exiting the process closes the socket (if it didn't
		711	create any children using fork).
		712
		713	Example: create a template for a process pool, pass a few strings, some
		714	file handles, then fork, pass one more string, and run some code.
		715
		716	my $pool = AnyEvent::Fork
		717	->new
		718	->send_arg ("str1", "str2")
		719	->send_fh ($fh1, $fh2);
		720
		721	for (1..2) {
		722	$pool
		723	->fork
		724	->send_arg ("str3")
		725	->run ("Some::function", sub {
		726	my ($fh) = @_;
		727
		728	# fh is nonblocking, but we trust that the OS can accept these
		729	# few octets anyway.
		730	syswrite $fh, "hi #$_\n";
		731
		732	# $fh is being closed here, as we don't store it anywhere
		733	});
		734	}
		735
		736	# Some::function might look like this - all parameters passed before fork
		737	# and after will be passed, in order, after the communications socket.
		738	sub Some::function {
		739	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		740
		741	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		742	}
		743
		744	=cut
		745
		746	sub run {
		747	my ($self, $func, $cb) = @_;
		748
		749	$self->[4] = $cb;
		750	$self->_cmd (r => $func);
		751	}
		752
193	=back	753	=back
		754
		755	=head1 PERFORMANCE
		756
		757	Now for some unscientific benchmark numbers (all done on an amd64
		758	GNU/Linux box). These are intended to give you an idea of the relative
		759	performance you can expect, they are not meant to be absolute performance
		760	numbers.
		761
		762	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		763	exit in the child and waits for the socket to close in the parent. I did
		764	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		765
		766	2079 new processes per second, using manual socketpair + fork
		767
		768	Then I did the same thing, but instead of calling fork, I called
		769	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		770	socket form the child to close on exit. This does the same thing as manual
		771	socket pair + fork, except that what is forked is the template process
		772	(2440kB), and the socket needs to be passed to the server at the other end
		773	of the socket first.
		774
		775	2307 new processes per second, using AnyEvent::Fork->new
		776
		777	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		778	a new perl interpreter and compile the small server each time, I get:
		779
		780	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		781
		782	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		783	though it uses the same operations, but adds a lot of overhead?
		784
		785	The difference is simply the process size: forking the 5MB process takes
		786	so much longer than forking the 2.5MB template process that the extra
		787	overhead introduced is canceled out.
		788
		789	If the benchmark process grows, the normal fork becomes even slower:
		790
		791	1340 new processes, manual fork of a 20MB process
		792	731 new processes, manual fork of a 200MB process
		793	235 new processes, manual fork of a 2000MB process
		794
		795	What that means (to me) is that I can use this module without having a bad
		796	conscience because of the extra overhead required to start new processes.
		797
		798	=head1 TYPICAL PROBLEMS
		799
		800	This section lists typical problems that remain. I hope by recognising
		801	them, most can be avoided.
		802
		803	=over 4
		804
		805	=item leaked file descriptors for exec'ed processes
		806
		807	POSIX systems inherit file descriptors by default when exec'ing a new
		808	process. While perl itself laudably sets the close-on-exec flags on new
		809	file handles, most C libraries don't care, and even if all cared, it's
		810	often not possible to set the flag in a race-free manner.
		811
		812	That means some file descriptors can leak through. And since it isn't
		813	possible to know which file descriptors are "good" and "necessary" (or
		814	even to know which file descriptors are open), there is no good way to
		815	close the ones that might harm.
		816
		817	As an example of what "harm" can be done consider a web server that
		818	accepts connections and afterwards some module uses AnyEvent::Fork for the
		819	first time, causing it to fork and exec a new process, which might inherit
		820	the network socket. When the server closes the socket, it is still open
		821	in the child (which doesn't even know that) and the client might conclude
		822	that the connection is still fine.
		823
		824	For the main program, there are multiple remedies available -
		825	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		826	C<new_exec> is another, as in both cases, the first process can be exec'ed
		827	well before many random file descriptors are open.
		828
		829	In general, the solution for these kind of problems is to fix the
		830	libraries or the code that leaks those file descriptors.
		831
		832	Fortunately, most of these leaked descriptors do no harm, other than
		833	sitting on some resources.
		834
		835	=item leaked file descriptors for fork'ed processes
		836
		837	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		838	which closes file descriptors not marked for being inherited.
		839
		840	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		841	a way to create these processes by forking, and this leaks more file
		842	descriptors than exec'ing them, as there is no way to mark descriptors as
		843	"close on fork".
		844
		845	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		846	pipes for internal uses, and L<Gtk2> might open a connection to the X
		847	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		848	trouble with a fork.
		849
		850	The solution is to either not load these modules before use'ing
		851	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		852	initialising them, for example, by calling C<init Gtk2> manually.
		853
		854	=item exiting calls object destructors
		855
		856	This only applies to users of Lc<AnyEvent::Fork:Early> and
		857	L<AnyEvent::Fork::Template>.
		858
		859	When a process created by AnyEvent::Fork exits, it might do so by calling
		860	exit, or simply letting perl reach the end of the program. At which point
		861	Perl runs all destructors.
		862
		863	Not all destructors are fork-safe - for example, an object that represents
		864	the connection to an X display might tell the X server to free resources,
		865	which is inconvenient when the "real" object in the parent still needs to
		866	use them.
		867
		868	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		869	it as the very first thing, right?
		870
		871	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		872	is to not create objects with nontrivial destructors that might have an
		873	effect outside of Perl.
		874
		875	=back
		876
		877	=head1 PORTABILITY NOTES
		878
		879	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		880	and ::Template is not going to work), and it cost a lot of blood and sweat
		881	to make it so, mostly due to the bloody broken perl that nobody seems to
		882	care about. The fork emulation is a bad joke - I have yet to see something
		883	useful that you can do with it without running into memory corruption
		884	issues or other braindamage. Hrrrr.
		885
		886	Cygwin perl is not supported at the moment due to some hilarious
		887	shortcomings of its API - see L<IO::FDPoll> for more details.
		888
		889	=head1 SEE ALSO
		890
		891	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		892	L<AnyEvent::Fork::Template> (to create a process by forking the main
		893	program at a convenient time).
194		894
195	=head1 AUTHOR	895	=head1 AUTHOR
196		896
197	Marc Lehmann <schmorp@schmorp.de>	897	Marc Lehmann <schmorp@schmorp.de>
198	http://home.schmorp.de/	898	http://home.schmorp.de/

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Revision 1.37 by root, Sat Apr 6 20:06:39 2013 UTC