[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 1.54 by root, Fri Apr 26 17:24:05 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	=head2 WHAT THIS MODULE IS NOT
23		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 could use the L<AnyEvent::Fork::RPC>
		40	companion module, which adds simple RPC/job queueing to a process created
		41	by this module.
		42
		43	And if you need some automatic process pool management on top of
		44	L<AnyEvent::Fork::RPC>, you can look at the L<AnyEvent::Fork::Pool>
		45	companion module.
		46
		47	Or you can implement it yourself in whatever way you like: use some
		48	message-passing module such as L<AnyEvent::MP>, some pipe such as
		49	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		50	e.g. JSON or Storable messages, and so on.
		51
		52	=head2 COMPARISON TO OTHER MODULES
		53
		54	There is an abundance of modules on CPAN that do "something fork", such as
		55	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		56	or L<AnyEvent::Subprocess>. There are modules that implement their own
		57	process management, such as L<AnyEvent::DBI>.
		58
		59	The problems that all these modules try to solve are real, however, none
		60	of them (from what I have seen) tackle the very real problems of unwanted
		61	memory sharing, efficiency, not being able to use event processing or
		62	similar modules in the processes they create.
		63
		64	This module doesn't try to replace any of them - instead it tries to solve
		65	the problem of creating processes with a minimum of fuss and overhead (and
		66	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		67	except they were written before AnyEvent:Fork was available, so obviously
		68	had to roll their own.
		69
24	=head1 PROBLEM STATEMENT	70	=head2 PROBLEM STATEMENT
25		71
26	There are two ways to implement parallel processing on UNIX like operating	72	There are two traditional ways to implement parallel processing on UNIX
27	systems - fork and process, and fork+exec and process. They have different	73	like operating systems - fork and process, and fork+exec and process. They
28	advantages and disadvantages that I describe below, together with how this	74	have different advantages and disadvantages that I describe below,
29	module tries to mitigate the disadvantages.	75	together with how this module tries to mitigate the disadvantages.
30		76
31	=over 4	77	=over 4
32		78
33	=item Forking from a big process can be very slow (a 5GB process needs	79	=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	80
		81	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	82	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.	83	in some circumstances (e.g. when vfork is used), fork+exec can be much
		84	faster.
37		85
38	This module can help here by telling a small(er) helper process to fork,	86	This module can help here by telling a small(er) helper process to fork,
39	or fork+exec instead.	87	which is faster then forking the main process, and also uses vfork where
		88	possible. This gives the speed of vfork, with the flexibility of fork.
40		89
41	=item Forking usually creates a copy-on-write copy of the parent	90	=item Forking usually creates a copy-on-write copy of the parent
42	process. Memory (for example, modules or data files that have been	91	process.
43	will not take additional memory). When exec'ing a new process, modules	92
44	and data files might need to be loaded again, at extra cpu and memory	93	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	94	memory after a fork. When exec'ing a new process, modules and data files
		95	might need to be loaded again, at extra CPU and memory cost. But when
		96	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	97	them and replaces them by new data, the child processes will retain the
47	will retain the memory even if it isn't used.	98	old version even if it isn't used, which can suddenly and unexpectedly
		99	increase memory usage when freeing memory.
		100
		101	The trade-off is between more sharing with fork (which can be good or
		102	bad), and no sharing with exec.
48		103
49	This module allows the main program to do a controlled fork, and allows	104	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	105	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	106	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	107	risking to share large dynamic data structures that will blow up child
53	memory usage.	108	memory usage.
54		109
		110	In other words, this module puts you into control over what is being
		111	shared and what isn't, at all times.
		112
55	=item Exec'ing a new perl process might be difficult and slow. For	113	=item Exec'ing a new perl process might be difficult.
		114
56	example, it is not easy to find the correct path to the perl interpreter,	115	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	116	interpreter - C<$^X> might not be a perl interpreter at all.
58	might run into problems when perl is upgraded for example.
59		117
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	118	This module tries hard to identify the correct path to the perl
62	interpreter. With a cooperative main program, exec'ing the interpreter	119	interpreter. With a cooperative main program, exec'ing the interpreter
63	might not even be necessary.	120	might not even be necessary, but even without help from the main program,
		121	it will still work when used from a module.
64		122
		123	=item Exec'ing a new perl process might be slow, as all necessary modules
		124	have to be loaded from disk again, with no guarantees of success.
		125
		126	Long running processes might run into problems when perl is upgraded
		127	and modules are no longer loadable because they refer to a different
		128	perl version, or parts of a distribution are newer than the ones already
		129	loaded.
		130
		131	This module supports creating pre-initialised perl processes to be used as
		132	a template for new processes.
		133
65	=item Forking might be impossible when a program is running. For example,	134	=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		135
		136	For example, POSIX makes it almost impossible to fork from a
		137	multi-threaded program while doing anything useful in the child - in
		138	fact, if your perl program uses POSIX threads (even indirectly via
		139	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		140	anymore without risking corruption issues on a number of operating
		141	systems.
		142
71	This module can safely fork helper processes at any time, by caling	143	This module can safely fork helper processes at any time, by calling
72	fork+exec in C, in a POSIX-compatible way.	144	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
73		145
74	=item Parallel processing with fork might be inconvenient or difficult	146	=item Parallel processing with fork might be inconvenient or difficult
		147	to implement. Modules might not work in both parent and child.
		148
75	to implement. For example, when a program uses an event loop and creates	149	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	150	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	151	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	152	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.	153	or the main program also does, leading to problems.
80		154
81	This module only lets the main program create pools by forking (because	155	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	156	"unsafe module" category, or just about anything that communicates with
83	pools are created by fork+exec, after which such modules can again be	157	the external world, such as network libraries and file I/O modules, which
84	loaded.	158	usually don't like being copied and then allowed to continue in two
		159	processes.
		160
		161	With this module only the main program is allowed to create new processes
		162	by forking (because only the main program can know when it is still safe
		163	to do so) - all other processes are created via fork+exec, which makes it
		164	possible to use modules such as event loops or window interfaces safely.
85		165
86	=back	166	=back
87		167
		168	=head1 EXAMPLES
		169
		170	=head2 Create a single new process, tell it to run your worker function.
		171
		172	AnyEvent::Fork
		173	->new
		174	->require ("MyModule")
		175	->run ("MyModule::worker, sub {
		176	my ($master_filehandle) = @_;
		177
		178	# now $master_filehandle is connected to the
		179	# $slave_filehandle in the new process.
		180	});
		181
		182	C<MyModule> might look like this:
		183
		184	package MyModule;
		185
		186	sub worker {
		187	my ($slave_filehandle) = @_;
		188
		189	# now $slave_filehandle is connected to the $master_filehandle
		190	# in the original prorcess. have fun!
		191	}
		192
		193	=head2 Create a pool of server processes all accepting on the same socket.
		194
		195	# create listener socket
		196	my $listener = ...;
		197
		198	# create a pool template, initialise it and give it the socket
		199	my $pool = AnyEvent::Fork
		200	->new
		201	->require ("Some::Stuff", "My::Server")
		202	->send_fh ($listener);
		203
		204	# now create 10 identical workers
		205	for my $id (1..10) {
		206	$pool
		207	->fork
		208	->send_arg ($id)
		209	->run ("My::Server::run");
		210	}
		211
		212	# now do other things - maybe use the filehandle provided by run
		213	# to wait for the processes to die. or whatever.
		214
		215	C<My::Server> might look like this:
		216
		217	package My::Server;
		218
		219	sub run {
		220	my ($slave, $listener, $id) = @_;
		221
		222	close $slave; # we do not use the socket, so close it to save resources
		223
		224	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		225	# or anything we usually couldn't do in a process forked normally.
		226	while (my $socket = $listener->accept) {
		227	# do sth. with new socket
		228	}
		229	}
		230
		231	=head2 use AnyEvent::Fork as a faster fork+exec
		232
		233	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
		234	and standard error redirected to the communications socket. It is usually
		235	faster than fork+exec, but still lets you prepare the environment.
		236
		237	open my $output, ">/tmp/log" or die "$!";
		238
		239	AnyEvent::Fork
		240	->new
		241	->eval ('
		242	# compile a helper function for later use
		243	sub run {
		244	my ($fh, $output, @cmd) = @_;
		245
		246	# perl will clear close-on-exec on STDOUT/STDERR
		247	open STDOUT, ">&", $output or die;
		248	open STDERR, ">&", $fh or die;
		249
		250	exec @cmd;
		251	}
		252	')
		253	->send_fh ($output)
		254	->send_arg ("/bin/echo", "hi")
		255	->run ("run", my $cv = AE::cv);
		256
		257	my $stderr = $cv->recv;
		258
		259	=head2 For stingy users: put the worker code into a C<DATA> section.
		260
		261	When you want to be stingy with files, you cna put your code into the
		262	C<DATA> section of your module (or program):
		263
		264	use AnyEvent::Fork;
		265
		266	AnyEvent::Fork
		267	->new
		268	->eval (do { local $/; <DATA> })
		269	->run ("doit", sub { ... });
		270
		271	__DATA__
		272
		273	sub doit {
		274	... do something!
		275	}
		276
		277	=head2 For stingy standalone programs: do not rely on external files at
		278	all.
		279
		280	For single-file scripts it can be inconvenient to rely on external
		281	files - even when using < C<DATA> section, you still need to C<exec>
		282	an external perl interpreter, which might not be available when using
		283	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
		284
		285	Two modules help here - L<AnyEvent::Fork::Early> forks a template process
		286	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
		287	forks the main program as a template process.
		288
		289	Here is how your main program should look like:
		290
		291	#! perl
		292
		293	# optional, as the very first thing.
		294	# in case modules want to create their own processes.
		295	use AnyEvent::Fork::Early;
		296
		297	# next, load all modules you need in your template process
		298	use Example::My::Module
		299	use Example::Whatever;
		300
		301	# next, put your run function definition and anything else you
		302	# need, but do not use code outside of BEGIN blocks.
		303	sub worker_run {
		304	my ($fh, @args) = @_;
		305	...
		306	}
		307
		308	# now preserve everything so far as AnyEvent::Fork object
		309	# in §TEMPLATE.
		310	use AnyEvent::Fork::Template;
		311
		312	# do not put code outside of BEGIN blocks until here
		313
		314	# now use the $TEMPLATE process in any way you like
		315
		316	# for example: create 10 worker processes
		317	my @worker;
		318	my $cv = AE::cv;
		319	for (1..10) {
		320	$cv->begin;
		321	$TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub {
		322	push @worker, shift;
		323	$cv->end;
		324	});
		325	}
		326	$cv->recv;
		327
		328	=head1 CONCEPTS
		329
		330	This module can create new processes either by executing a new perl
		331	process, or by forking from an existing "template" process.
		332
		333	All these processes are called "child processes" (whether they are direct
		334	children or not), while the process that manages them is called the
		335	"parent process".
		336
		337	Each such process comes with its own file handle that can be used to
		338	communicate with it (it's actually a socket - one end in the new process,
		339	one end in the main process), and among the things you can do in it are
		340	load modules, fork new processes, send file handles to it, and execute
		341	functions.
		342
		343	There are multiple ways to create additional processes to execute some
		344	jobs:
		345
88	=over 4	346	=over 4
89		347
90	=cut	348	=item fork a new process from the "default" template process, load code,
		349	run it
91		350
		351	This module has a "default" template process which it executes when it is
		352	needed the first time. Forking from this process shares the memory used
		353	for the perl interpreter with the new process, but loading modules takes
		354	time, and the memory is not shared with anything else.
		355
		356	This is ideal for when you only need one extra process of a kind, with the
		357	option of starting and stopping it on demand.
		358
		359	Example:
		360
		361	AnyEvent::Fork
		362	->new
		363	->require ("Some::Module")
		364	->run ("Some::Module::run", sub {
		365	my ($fork_fh) = @_;
		366	});
		367
		368	=item fork a new template process, load code, then fork processes off of
		369	it and run the code
		370
		371	When you need to have a bunch of processes that all execute the same (or
		372	very similar) tasks, then a good way is to create a new template process
		373	for them, loading all the modules you need, and then create your worker
		374	processes from this new template process.
		375
		376	This way, all code (and data structures) that can be shared (e.g. the
		377	modules you loaded) is shared between the processes, and each new process
		378	consumes relatively little memory of its own.
		379
		380	The disadvantage of this approach is that you need to create a template
		381	process for the sole purpose of forking new processes from it, but if you
		382	only need a fixed number of processes you can create them, and then destroy
		383	the template process.
		384
		385	Example:
		386
		387	my $template = AnyEvent::Fork->new->require ("Some::Module");
		388
		389	for (1..10) {
		390	$template->fork->run ("Some::Module::run", sub {
		391	my ($fork_fh) = @_;
		392	});
		393	}
		394
		395	# at this point, you can keep $template around to fork new processes
		396	# later, or you can destroy it, which causes it to vanish.
		397
		398	=item execute a new perl interpreter, load some code, run it
		399
		400	This is relatively slow, and doesn't allow you to share memory between
		401	multiple processes.
		402
		403	The only advantage is that you don't have to have a template process
		404	hanging around all the time to fork off some new processes, which might be
		405	an advantage when there are long time spans where no extra processes are
		406	needed.
		407
		408	Example:
		409
		410	AnyEvent::Fork
		411	->new_exec
		412	->require ("Some::Module")
		413	->run ("Some::Module::run", sub {
		414	my ($fork_fh) = @_;
		415	});
		416
		417	=back
		418
		419	=head1 THE C<AnyEvent::Fork> CLASS
		420
		421	This module exports nothing, and only implements a single class -
		422	C<AnyEvent::Fork>.
		423
		424	There are two class constructors that both create new processes - C<new>
		425	and C<new_exec>. The C<fork> method creates a new process by forking an
		426	existing one and could be considered a third constructor.
		427
		428	Most of the remaining methods deal with preparing the new process, by
		429	loading code, evaluating code and sending data to the new process. They
		430	usually return the process object, so you can chain method calls.
		431
		432	If a process object is destroyed before calling its C<run> method, then
		433	the process simply exits. After C<run> is called, all responsibility is
		434	passed to the specified function.
		435
		436	As long as there is any outstanding work to be done, process objects
		437	resist being destroyed, so there is no reason to store them unless you
		438	need them later - configure and forget works just fine.
		439
		440	=over 4
		441
		442	=cut
		443
92	package AnyEvent::ProcessPool;	444	package AnyEvent::Fork;
93		445
94	use common::sense;	446	use common::sense;
95		447
96	use Socket ();	448	use Errno ();
97		449
98	use Proc::FastSpawn;
99	use AnyEvent;	450	use AnyEvent;
100	use AnyEvent::ProcessPool::Util;
101	use AnyEvent::Util ();	451	use AnyEvent::Util ();
102		452
103	BEGIN {	453	use IO::FDPass;
104	# require Exporter;
105	}
106		454
107	=item my $pool = new AnyEvent::ProcessPool key => value...	455	our $VERSION = '1.0';
108		456
109	Create a new process pool. The following named parameters are supported:	457	# the early fork template process
		458	our $EARLY;
110		459
111	=over 4
112
113	=back
114
115	=cut
116
117	# the template process	460	# the empty template process
118	our $template;	461	our $TEMPLATE;
119		462
120	sub _queue {	463	sub QUEUE() { 0 }
121	my ($pid, $fh) = @_;	464	sub FH() { 1 }
		465	sub WW() { 2 }
		466	sub PID() { 3 }
		467	sub CB() { 4 }
122		468
123	[	469	sub _new {
		470	my ($self, $fh, $pid) = @_;
		471
		472	AnyEvent::Util::fh_nonblocking $fh, 1;
		473
		474	$self = bless [
		475	[], # write queue - strings or fd's
		476	$fh,
		477	undef, # AE watcher
124	$pid,	478	$pid,
125	$fh,	479	], $self;
126	[],
127	undef
128	]
129	}
130		480
		481	$self
		482	}
		483
131	sub queue_cmd {	484	sub _cmd {
132	my ($queue, $cmd) = @_;	485	my $self = shift;
133		486
134	push @{ $queue->[2] }, pack "N/a", $cmd;	487	# ideally, we would want to use "a (w/a)*" as format string, but perl
		488	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		489	# it.
		490	push @{ $self->[QUEUE] }, pack "a N/a*", $_[0], $_[1];
135		491
136	$queue->[3] \|\|= AE::io $queue->[1], 1, sub {	492	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		493	do {
		494	# send the next "thing" in the queue - either a reference to an fh,
		495	# or a plain string.
		496
137	if (ref $queue->[2][0]) {	497	if (ref $self->[QUEUE][0]) {
138	AnyEvent::ProcessPool::Util::fd_send fileno $queue->[1], fileno ${ $queue->[2][0] }	498	# send fh
		499	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
		500	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		501	undef $self->[WW];
		502	die "AnyEvent::Fork: file descriptor send failure: $!";
		503	}
		504
139	and shift @{ $queue->[2] };	505	shift @{ $self->[QUEUE] };
		506
140	} else {	507	} else {
		508	# send string
141	my $len = syswrite $queue->[1], $queue->[2][0]	509	my $len = syswrite $self->[FH], $self->[QUEUE][0];
142	or do { undef $queue->[3]; die "AnyEvent::ProcessPool::queue write failure: $!" };	510
		511	unless ($len) {
		512	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		513	undef $self->[WW];
		514	die "AnyEvent::Fork: command write failure: $!";
		515	}
		516
143	substr $queue->[2][0], 0, $len, "";	517	substr $self->[QUEUE][0], 0, $len, "";
144	shift @{ $queue->[2] } unless length $queue->[2][0];	518	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
		519	}
		520	} while @{ $self->[QUEUE] };
		521
		522	# everything written
		523	undef $self->[WW];
		524
		525	# invoke run callback, if any
		526	if ($self->[CB]) {
		527	$self->[CB]->($self->[FH]);
		528	@$self = ();
145	}	529	}
146
147	undef $queue->[3] unless @{ $queue->[2] };
148	};	530	};
149	}
150		531
151	sub run_template {	532	() # make sure we don't leak the watcher
152	return if $template;	533	}
153		534
		535	# fork template from current process, used by AnyEvent::Fork::Early/Template
		536	sub _new_fork {
154	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	537	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
155	AnyEvent::Util::fh_nonblocking $fh, 1;	538	my $parent = $$;
156	fd_inherit fileno $slave;
157		539
158	my %env = %ENV;	540	my $pid = fork;
159	$env{PERL5LIB} = join ":", grep !ref, @INC;
160		541
161	my $pid = spawn	542	if ($pid eq 0) {
162	$^X,	543	require AnyEvent::Fork::Serve;
163	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	544	$AnyEvent::Fork::Serve::OWNER = $parent;
164	[map "$_=$env{$_}", keys %env],	545	close $fh;
165	or die "unable to spawn AnyEvent::ProcessPool server: $!";	546	$0 = "$_[1] of $parent";
		547	AnyEvent::Fork::Serve::serve ($slave);
		548	exit 0;
		549	} elsif (!$pid) {
		550	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		551	}
166		552
167	close $slave;	553	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	}	554	}
		555
		556	=item my $proc = new AnyEvent::Fork
		557
		558	Create a new "empty" perl interpreter process and returns its process
		559	object for further manipulation.
		560
		561	The new process is forked from a template process that is kept around
		562	for this purpose. When it doesn't exist yet, it is created by a call to
		563	C<new_exec> first and then stays around for future calls.
		564
		565	=cut
180		566
181	sub new {	567	sub new {
182	my $class = shift;	568	my $class = shift;
183		569
184	my $self = bless {	570	$TEMPLATE \|\|= $class->new_exec;
185	@_	571	$TEMPLATE->fork
186	}, $class;	572	}
187		573
188	run_template;	574	=item $new_proc = $proc->fork
		575
		576	Forks C<$proc>, creating a new process, and returns the process object
		577	of the new process.
		578
		579	If any of the C<send_> functions have been called before fork, then they
		580	will be cloned in the child. For example, in a pre-forked server, you
		581	might C<send_fh> the listening socket into the template process, and then
		582	keep calling C<fork> and C<run>.
		583
		584	=cut
		585
		586	sub fork {
		587	my ($self) = @_;
		588
		589	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		590
		591	$self->send_fh ($slave);
		592	$self->_cmd ("f");
		593
		594	AnyEvent::Fork->_new ($fh)
		595	}
		596
		597	=item my $proc = new_exec AnyEvent::Fork
		598
		599	Create a new "empty" perl interpreter process and returns its process
		600	object for further manipulation.
		601
		602	Unlike the C<new> method, this method I<always> spawns a new perl process
		603	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
		604	reduces the amount of memory sharing that is possible, and is also slower.
		605
		606	You should use C<new> whenever possible, except when having a template
		607	process around is unacceptable.
		608
		609	The path to the perl interpreter is divined using various methods - first
		610	C<$^X> is investigated to see if the path ends with something that sounds
		611	as if it were the perl interpreter. Failing this, the module falls back to
		612	using C<$Config::Config{perlpath}>.
		613
		614	=cut
		615
		616	sub new_exec {
		617	my ($self) = @_;
		618
		619	return $EARLY->fork
		620	if $EARLY;
		621
		622	# first find path of perl
		623	my $perl = $;
		624
		625	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		626	# that looks like perl. this obviously only works for posix and win32
		627	unless (
		628	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		629	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		630	) {
		631	# if it doesn't look perlish enough, try Config
		632	require Config;
		633	$perl = $Config::Config{perlpath};
		634	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		635	}
		636
		637	require Proc::FastSpawn;
		638
		639	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		640	Proc::FastSpawn::fd_inherit (fileno $slave);
		641
		642	# new fh's should always be set cloexec (due to $^F),
		643	# but hey, not on win32, so we always clear the inherit flag.
		644	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		645
		646	# quick. also doesn't work in win32. of course. what did you expect
		647	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		648	my %env = %ENV;
		649	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		650
		651	my $pid = Proc::FastSpawn::spawn (
		652	$perl,
		653	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		654	[map "$_=$env{$_}", keys %env],
		655	) or die "unable to spawn AnyEvent::Fork server: $!";
		656
		657	$self->_new ($fh, $pid)
		658	}
		659
		660	=item $pid = $proc->pid
		661
		662	Returns the process id of the process I<iff it is a direct child of the
		663	process running AnyEvent::Fork>, and C<undef> otherwise.
		664
		665	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		666	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		667	to clean up their zombies when they die.
		668
		669	All other processes are not direct children, and will be cleaned up by
		670	AnyEvent::Fork itself.
		671
		672	=cut
		673
		674	sub pid {
		675	$_[0][PID]
		676	}
		677
		678	=item $proc = $proc->eval ($perlcode, @args)
		679
		680	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
		681	the strings specified by C<@args>, in the "main" package.
		682
		683	This call is meant to do any custom initialisation that might be required
		684	(for example, the C<require> method uses it). It's not supposed to be used
		685	to completely take over the process, use C<run> for that.
		686
		687	The code will usually be executed after this call returns, and there is no
		688	way to pass anything back to the calling process. Any evaluation errors
		689	will be reported to stderr and cause the process to exit.
		690
		691	If you want to execute some code (that isn't in a module) to take over the
		692	process, you should compile a function via C<eval> first, and then call
		693	it via C<run>. This also gives you access to any arguments passed via the
		694	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		695	a faster fork+exec> example to see it in action.
		696
		697	Returns the process object for easy chaining of method calls.
		698
		699	=cut
		700
		701	sub eval {
		702	my ($self, $code, @args) = @_;
		703
		704	$self->_cmd (e => pack "(w/a)", $code, @args);
189		705
190	$self	706	$self
191	}	707	}
192		708
		709	=item $proc = $proc->require ($module, ...)
		710
		711	Tries to load the given module(s) into the process
		712
		713	Returns the process object for easy chaining of method calls.
		714
		715	=cut
		716
		717	sub require {
		718	my ($self, @modules) = @_;
		719
		720	s%::%/%g for @modules;
		721	$self->eval ('require "$_.pm" for @_', @modules);
		722
		723	$self
		724	}
		725
		726	=item $proc = $proc->send_fh ($handle, ...)
		727
		728	Send one or more file handles (I<not> file descriptors) to the process,
		729	to prepare a call to C<run>.
		730
		731	The process object keeps a reference to the handles until they have
		732	been passed over to the process, so you must not explicitly close the
		733	handles. This is most easily accomplished by simply not storing the file
		734	handles anywhere after passing them to this method - when AnyEvent::Fork
		735	is finished using them, perl will automatically close them.
		736
		737	Returns the process object for easy chaining of method calls.
		738
		739	Example: pass a file handle to a process, and release it without
		740	closing. It will be closed automatically when it is no longer used.
		741
		742	$proc->send_fh ($my_fh);
		743	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		744
		745	=cut
		746
		747	sub send_fh {
		748	my ($self, @fh) = @_;
		749
		750	for my $fh (@fh) {
		751	$self->_cmd ("h");
		752	push @{ $self->[QUEUE] }, \$fh;
		753	}
		754
		755	$self
		756	}
		757
		758	=item $proc = $proc->send_arg ($string, ...)
		759
		760	Send one or more argument strings to the process, to prepare a call to
		761	C<run>. The strings can be any octet strings.
		762
		763	The protocol is optimised to pass a moderate number of relatively short
		764	strings - while you can pass up to 4GB of data in one go, this is more
		765	meant to pass some ID information or other startup info, not big chunks of
		766	data.
		767
		768	Returns the process object for easy chaining of method calls.
		769
		770	=cut
		771
		772	sub send_arg {
		773	my ($self, @arg) = @_;
		774
		775	$self->_cmd (a => pack "(w/a)", @arg);
		776
		777	$self
		778	}
		779
		780	=item $proc->run ($func, $cb->($fh))
		781
		782	Enter the function specified by the function name in C<$func> in the
		783	process. The function is called with the communication socket as first
		784	argument, followed by all file handles and string arguments sent earlier
		785	via C<send_fh> and C<send_arg> methods, in the order they were called.
		786
		787	The process object becomes unusable on return from this function - any
		788	further method calls result in undefined behaviour.
		789
		790	The function name should be fully qualified, but if it isn't, it will be
		791	looked up in the C<main> package.
		792
		793	If the called function returns, doesn't exist, or any error occurs, the
		794	process exits.
		795
		796	Preparing the process is done in the background - when all commands have
		797	been sent, the callback is invoked with the local communications socket
		798	as argument. At this point you can start using the socket in any way you
		799	like.
		800
		801	If the communication socket isn't used, it should be closed on both sides,
		802	to save on kernel memory.
		803
		804	The socket is non-blocking in the parent, and blocking in the newly
		805	created process. The close-on-exec flag is set in both.
		806
		807	Even if not used otherwise, the socket can be a good indicator for the
		808	existence of the process - if the other process exits, you get a readable
		809	event on it, because exiting the process closes the socket (if it didn't
		810	create any children using fork).
		811
		812	Example: create a template for a process pool, pass a few strings, some
		813	file handles, then fork, pass one more string, and run some code.
		814
		815	my $pool = AnyEvent::Fork
		816	->new
		817	->send_arg ("str1", "str2")
		818	->send_fh ($fh1, $fh2);
		819
		820	for (1..2) {
		821	$pool
		822	->fork
		823	->send_arg ("str3")
		824	->run ("Some::function", sub {
		825	my ($fh) = @_;
		826
		827	# fh is nonblocking, but we trust that the OS can accept these
		828	# few octets anyway.
		829	syswrite $fh, "hi #$_\n";
		830
		831	# $fh is being closed here, as we don't store it anywhere
		832	});
		833	}
		834
		835	# Some::function might look like this - all parameters passed before fork
		836	# and after will be passed, in order, after the communications socket.
		837	sub Some::function {
		838	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		839
		840	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		841	}
		842
		843	=cut
		844
		845	sub run {
		846	my ($self, $func, $cb) = @_;
		847
		848	$self->[CB] = $cb;
		849	$self->_cmd (r => $func);
		850	}
		851
193	=back	852	=back
194		853
195	=head1 AUTHOR	854	=head2 ADVANCED METHODS
		855
		856	=over 4
		857
		858	=item new_from_stdio AnyEvent::Fork $fh
		859
		860	Assume that you have a perl interpreter running (without any special
		861	options or a program) somewhere and it has it's STDIN and STDOUT connected
		862	to the C<$fh> somehow. I.e. exactly the state perl is in when you start it
		863	without any arguments:
		864
		865	perl
		866
		867	Then you can create an C<AnyEvent::Fork> object out of this perl
		868	interpreter with this constructor.
		869
		870	When the usefulness of this isn't immediately clear, imagine you manage to
		871	run a perl interpreter remotely (F<ssh remotemachine perl>), then you can
		872	manage it mostly like a local C<AnyEvent::Fork> child.
		873
		874	This works without any module support, i.e. the remote F<perl> does not
		875	need to have any special modules installed.
		876
		877	There are a number of limitations though: C<send_fh> will only work if the
		878	L<IO::FDPass> module is loadable by the remote perl and the two processes
		879	are connected in a way that let's L<IO::FDPass> do it's work.
		880
		881	This will therefore not work over a network connection. From this follows
		882	that C<fork> will also not work under these circumstances, as it relies on
		883	C<send_fh> internally.
		884
		885	Although not a limitation of this module, keep in mind that the
		886	"communications socket" is simply C<STDIN>, and depending on how you
		887	started F<perl> (e.g. via F<ssh>), it might only be half-duplex. This is
		888	fine for C<AnyEvent::Fork>, but your C<run> function might want to use
		889	C<STDIN> (or the "communications socket") for input and C<STDOUT> for
		890	output.
		891
		892	You can support both cases by checking the C<fileno> of the handle passed
		893	to your run function:
		894
		895	sub run {
		896	my ($rfh) = @_;
		897
		898	my $wfh = fileno $rfh ? $rfh : *STDOUT;
		899
		900	# now use $rfh for reading and $wfh for writing
		901	}
		902
		903	=cut
		904
		905	sub new_from_stdio {
		906	my ($class, $fh) = @_;
		907
		908	my $self = $class->_new ($fh);
		909
		910	# send startup code
		911	push @{ $self->[QUEUE] },
		912	(do "AnyEvent/Fork/serve.pl")
		913	. <<'EOF';
		914
		915	$OWNER = "another process";
		916	$0 = "AnyEvent::Fork/stdio of $OWNER";
		917
		918	serve *STDIN;
		919	__END__
		920	EOF
		921
		922	# the data is only sent when the user requests additional things, which
		923	# is likely early enough for our purposes.
		924
		925	$self
		926	}
		927
		928	=back
		929
		930	=head2 EXPERIMENTAL METHODS
		931
		932	These methods might go away completely or change behaviour, a any time.
		933
		934	=over 4
		935
		936	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		937
		938	Flushes all commands out to the process and then calls the callback with
		939	the communications socket.
		940
		941	The process object becomes unusable on return from this function - any
		942	further method calls result in undefined behaviour.
		943
		944	The point of this method is to give you a file handle thta you cna pass
		945	to another process. In that other process, you can call C<new_from_fh
		946	AnyEvent::Fork> to create a new C<AnyEvent::Fork> object from it, thereby
		947	effectively passing a fork object to another process.
		948
		949	=cut
		950
		951	sub to_fh {
		952	my ($self, $cb) = @_;
		953
		954	$self->[CB] = $cb;
		955
		956	unless ($self->[WW]) {
		957	$self->[CB]->($self->[FH]);
		958	@$self = ();
		959	}
		960	}
		961
		962	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		963
		964	Takes a file handle originally rceeived by the C<to_fh> method and creates
		965	a new C<AnyEvent:Fork> object. The child process itself will not change in
		966	any way, i.e. it will keep all the modifications done to it before calling
		967	C<to_fh>.
		968
		969	The new object is very much like the original object, except that the
		970	C<pid> method will return C<undef> even if the process is a direct child.
		971
		972	=cut
		973
		974	sub new_from_fh {
		975	my ($class, $fh) = @_;
		976
		977	$class->_new ($fh)
		978	}
		979
		980	=back
		981
		982	=head1 PERFORMANCE
		983
		984	Now for some unscientific benchmark numbers (all done on an amd64
		985	GNU/Linux box). These are intended to give you an idea of the relative
		986	performance you can expect, they are not meant to be absolute performance
		987	numbers.
		988
		989	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		990	exit in the child and waits for the socket to close in the parent. I did
		991	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		992
		993	2079 new processes per second, using manual socketpair + fork
		994
		995	Then I did the same thing, but instead of calling fork, I called
		996	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		997	socket from the child to close on exit. This does the same thing as manual
		998	socket pair + fork, except that what is forked is the template process
		999	(2440kB), and the socket needs to be passed to the server at the other end
		1000	of the socket first.
		1001
		1002	2307 new processes per second, using AnyEvent::Fork->new
		1003
		1004	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		1005	a new perl interpreter and compile the small server each time, I get:
		1006
		1007	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		1008
		1009	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		1010	though it uses the same operations, but adds a lot of overhead?
		1011
		1012	The difference is simply the process size: forking the 5MB process takes
		1013	so much longer than forking the 2.5MB template process that the extra
		1014	overhead is canceled out.
		1015
		1016	If the benchmark process grows, the normal fork becomes even slower:
		1017
		1018	1340 new processes, manual fork of a 20MB process
		1019	731 new processes, manual fork of a 200MB process
		1020	235 new processes, manual fork of a 2000MB process
		1021
		1022	What that means (to me) is that I can use this module without having a bad
		1023	conscience because of the extra overhead required to start new processes.
		1024
		1025	=head1 TYPICAL PROBLEMS
		1026
		1027	This section lists typical problems that remain. I hope by recognising
		1028	them, most can be avoided.
		1029
		1030	=over 4
		1031
		1032	=item leaked file descriptors for exec'ed processes
		1033
		1034	POSIX systems inherit file descriptors by default when exec'ing a new
		1035	process. While perl itself laudably sets the close-on-exec flags on new
		1036	file handles, most C libraries don't care, and even if all cared, it's
		1037	often not possible to set the flag in a race-free manner.
		1038
		1039	That means some file descriptors can leak through. And since it isn't
		1040	possible to know which file descriptors are "good" and "necessary" (or
		1041	even to know which file descriptors are open), there is no good way to
		1042	close the ones that might harm.
		1043
		1044	As an example of what "harm" can be done consider a web server that
		1045	accepts connections and afterwards some module uses AnyEvent::Fork for the
		1046	first time, causing it to fork and exec a new process, which might inherit
		1047	the network socket. When the server closes the socket, it is still open
		1048	in the child (which doesn't even know that) and the client might conclude
		1049	that the connection is still fine.
		1050
		1051	For the main program, there are multiple remedies available -
		1052	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		1053	C<new_exec> is another, as in both cases, the first process can be exec'ed
		1054	well before many random file descriptors are open.
		1055
		1056	In general, the solution for these kind of problems is to fix the
		1057	libraries or the code that leaks those file descriptors.
		1058
		1059	Fortunately, most of these leaked descriptors do no harm, other than
		1060	sitting on some resources.
		1061
		1062	=item leaked file descriptors for fork'ed processes
		1063
		1064	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		1065	which closes file descriptors not marked for being inherited.
		1066
		1067	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		1068	a way to create these processes by forking, and this leaks more file
		1069	descriptors than exec'ing them, as there is no way to mark descriptors as
		1070	"close on fork".
		1071
		1072	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		1073	pipes for internal uses, and L<Gtk2> might open a connection to the X
		1074	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		1075	trouble with a fork.
		1076
		1077	The solution is to either not load these modules before use'ing
		1078	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		1079	initialising them, for example, by calling C<init Gtk2> manually.
		1080
		1081	=item exiting calls object destructors
		1082
		1083	This only applies to users of L<AnyEvent::Fork:Early> and
		1084	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1085	that reference external resources.
		1086
		1087	When a process created by AnyEvent::Fork exits, it might do so by calling
		1088	exit, or simply letting perl reach the end of the program. At which point
		1089	Perl runs all destructors.
		1090
		1091	Not all destructors are fork-safe - for example, an object that represents
		1092	the connection to an X display might tell the X server to free resources,
		1093	which is inconvenient when the "real" object in the parent still needs to
		1094	use them.
		1095
		1096	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		1097	it as the very first thing, right?
		1098
		1099	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		1100	is to not create objects with nontrivial destructors that might have an
		1101	effect outside of Perl.
		1102
		1103	=back
		1104
		1105	=head1 PORTABILITY NOTES
		1106
		1107	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		1108	and ::Template is not going to work), and it cost a lot of blood and sweat
		1109	to make it so, mostly due to the bloody broken perl that nobody seems to
		1110	care about. The fork emulation is a bad joke - I have yet to see something
		1111	useful that you can do with it without running into memory corruption
		1112	issues or other braindamage. Hrrrr.
		1113
		1114	Since fork is endlessly broken on win32 perls (it doesn't even remotely
		1115	work within it's documented limits) and quite obviously it's not getting
		1116	improved any time soon, the best way to proceed on windows would be to
		1117	always use C<new_exec> and thus never rely on perl's fork "emulation".
		1118
		1119	Cygwin perl is not supported at the moment due to some hilarious
		1120	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1121	use C<send_fh> and always use C<new_exec> to create processes, it should
		1122	work though.
		1123
		1124	=head1 SEE ALSO
		1125
		1126	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1127	(part of this distribution).
		1128
		1129	L<AnyEvent::Fork::Template>, to create a process by forking the main
		1130	program at a convenient time (part of this distribution).
		1131
		1132	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1133
		1134	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1135
		1136	=head1 AUTHOR AND CONTACT INFORMATION
196		1137
197	Marc Lehmann <schmorp@schmorp.de>	1138	Marc Lehmann <schmorp@schmorp.de>
198	http://home.schmorp.de/	1139	http://software.schmorp.de/pkg/AnyEvent-Fork
199		1140
200	=cut	1141	=cut
201		1142
202	1	1143	1
203		1144

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.2 by root, Sun Mar 31 03:26:50 2013 UTC vs. Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.2 by root, Sun Mar 31 03:26:50 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC