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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs.
Revision 1.56 by root, Sun Apr 28 13:47:52 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
		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	$cv->recv;
87		327
88	=head1 CONCEPTS	328	=head1 CONCEPTS
89		329
90	This module can create new processes either by executing a new perl	330	This module can create new processes either by executing a new perl
91	process, or by forking from an existing "template" process.	331	process, or by forking from an existing "template" process.
		332
		333	All these processes are called "child processes" (whether they are direct
		334	children or not), while the process that manages them is called the
		335	"parent process".
92		336
93	Each such process comes with its own file handle that can be used to	337	Each such process comes with its own file handle that can be used to
94	communicate with it (it's actually a socket - one end in the new process,	338	communicate with it (it's actually a socket - one end in the new process,
95	one end in the main process), and among the things you can do in it are	339	one end in the main process), and among the things you can do in it are
96	load modules, fork new processes, send file handles to it, and execute	340	load modules, fork new processes, send file handles to it, and execute
108	needed the first time. Forking from this process shares the memory used	352	needed the first time. Forking from this process shares the memory used
109	for the perl interpreter with the new process, but loading modules takes	353	for the perl interpreter with the new process, but loading modules takes
110	time, and the memory is not shared with anything else.	354	time, and the memory is not shared with anything else.
111		355
112	This is ideal for when you only need one extra process of a kind, with the	356	This is ideal for when you only need one extra process of a kind, with the
113	option of starting and stipping it on demand.	357	option of starting and stopping it on demand.
		358
		359	Example:
		360
		361	AnyEvent::Fork
		362	->new
		363	->require ("Some::Module")
		364	->run ("Some::Module::run", sub {
		365	my ($fork_fh) = @_;
		366	});
114		367
115	=item fork a new template process, load code, then fork processes off of	368	=item fork a new template process, load code, then fork processes off of
116	it and run the code	369	it and run the code
117		370
118	When you need to have a bunch of processes that all execute the same (or	371	When you need to have a bunch of processes that all execute the same (or
…		…
124	modules you loaded) is shared between the processes, and each new process	377	modules you loaded) is shared between the processes, and each new process
125	consumes relatively little memory of its own.	378	consumes relatively little memory of its own.
126		379
127	The disadvantage of this approach is that you need to create a template	380	The disadvantage of this approach is that you need to create a template
128	process for the sole purpose of forking new processes from it, but if you	381	process for the sole purpose of forking new processes from it, but if you
129	only need a fixed number of proceses you can create them, and then destroy	382	only need a fixed number of processes you can create them, and then destroy
130	the template process.	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 $template around to fork new processes
		396	# later, or you can destroy it, which causes it to vanish.
131		397
132	=item execute a new perl interpreter, load some code, run it	398	=item execute a new perl interpreter, load some code, run it
133		399
134	This is relatively slow, and doesn't allow you to share memory between	400	This is relatively slow, and doesn't allow you to share memory between
135	multiple processes.	401	multiple processes.
…		…
137	The only advantage is that you don't have to have a template process	403	The only advantage is that you don't have to have a template process
138	hanging around all the time to fork off some new processes, which might be	404	hanging around all the time to fork off some new processes, which might be
139	an advantage when there are long time spans where no extra processes are	405	an advantage when there are long time spans where no extra processes are
140	needed.	406	needed.
141		407
		408	Example:
		409
		410	AnyEvent::Fork
		411	->new_exec
		412	->require ("Some::Module")
		413	->run ("Some::Module::run", sub {
		414	my ($fork_fh) = @_;
		415	});
		416
142	=back	417	=back
143		418
144	=head1 FUNCTIONS	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.
145		439
146	=over 4	440	=over 4
147		441
148	=cut	442	=cut
149		443
150	package AnyEvent::ProcessPool;	444	package AnyEvent::Fork;
151		445
152	use common::sense;	446	use common::sense;
153		447
154	use Socket ();	448	use Errno ();
155		449
156	use Proc::FastSpawn;
157	use AnyEvent;	450	use AnyEvent;
158	use AnyEvent::ProcessPool::Util;
159	use AnyEvent::Util ();	451	use AnyEvent::Util ();
160		452
161	BEGIN {	453	use IO::FDPass;
162	# require Exporter;
163	}
164		454
165	=item my $pool = new AnyEvent::ProcessPool key => value...	455	our $VERSION = 1.1;
166		456
167	Create a new process pool. The following named parameters are supported:	457	# the early fork template process
		458	our $EARLY;
168		459
169	=over 4
170
171	=back
172
173	=cut
174
175	# the template process	460	# the empty template process
176	our $template;	461	our $TEMPLATE;
177		462
178	sub _queue {	463	sub QUEUE() { 0 }
179	my ($pid, $fh) = @_;	464	sub FH() { 1 }
		465	sub WW() { 2 }
		466	sub PID() { 3 }
		467	sub CB() { 4 }
180		468
181	[	469	sub _new {
		470	my ($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
182	$pid,	478	$pid,
183	$fh,	479	], $self;
184	[],
185	undef
186	]
187	}
188		480
		481	$self
		482	}
		483
189	sub queue_cmd {	484	sub _cmd {
190	my $queue = shift;	485	my $self = shift;
191		486
192	push @{ $queue->[2] }, pack "N/a", pack "a (w/a)*", @_;	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 L/a*", $_[0], $_[1];
193		491
194	$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
195	if (ref $queue->[2][0]) {	497	if (ref $self->[QUEUE][0]) {
196	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
197	and shift @{ $queue->[2] };	505	shift @{ $self->[QUEUE] };
		506
198	} else {	507	} else {
		508	# send string
199	my $len = syswrite $queue->[1], $queue->[2][0]	509	my $len = syswrite $self->[FH], $self->[QUEUE][0];
200	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
201	substr $queue->[2][0], 0, $len, "";	517	substr $self->[QUEUE][0], 0, $len, "";
202	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 = ();
203	}	529	}
204
205	undef $queue->[3] unless @{ $queue->[2] };
206	};	530	};
207	}
208		531
209	sub run_template {	532	() # make sure we don't leak the watcher
210	return if $template;	533	}
211		534
		535	# fork template from current process, used by AnyEvent::Fork::Early/Template
		536	sub _new_fork {
212	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	537	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
213	AnyEvent::Util::fh_nonblocking $fh, 1;	538	my $parent = $$;
214	fd_inherit fileno $slave;
215		539
216	my %env = %ENV;	540	my $pid = fork;
217	$env{PERL5LIB} = join ":", grep !ref, @INC;
218		541
219	my $pid = spawn	542	if ($pid eq 0) {
220	$^X,	543	require AnyEvent::Fork::Serve;
221	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	544	$AnyEvent::Fork::Serve::OWNER = $parent;
222	[map "$_=$env{$_}", keys %env],	545	close $fh;
223	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	}
224		552
225	close $slave;	553	AnyEvent::Fork->_new ($fh, $pid)
226
227	$template = _queue $pid, $fh;
228
229	my ($a, $b) = AnyEvent::Util::portable_socketpair;
230
231	queue_cmd $template, "Iabc";
232	push @{ $template->[2] }, \$b;
233
234	use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
235	undef $b;
236	die "x" . <$a>;
237	}	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
238		566
239	sub new {	567	sub new {
240	my $class = shift;	568	my $class = shift;
241		569
242	my $self = bless {	570	$TEMPLATE \|\|= $class->new_exec;
		571	$TEMPLATE->fork
		572	}
		573
		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	The path to perl can also be overriden by setting the global variable
		615	C<$AnyEvent::Fork::PERL> - it's value will be used for all subsequent
		616	invocations.
		617
		618	=cut
		619
		620	our $PERL;
		621
		622	sub new_exec {
		623	my ($self) = @_;
		624
		625	return $EARLY->fork
		626	if $EARLY;
		627
		628	unless (defined $PERL) {
		629	# first find path of perl
		630	my $perl = $;
		631
		632	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		633	# that looks like perl. this obviously only works for posix and win32
		634	unless (
		635	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		636	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		637	) {
		638	# if it doesn't look perlish enough, try Config
		639	require Config;
		640	$perl = $Config::Config{perlpath};
		641	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
243	@_	642	}
244	}, $class;
245		643
246	run_template;	644	$PERL = $perl;
		645	}
		646
		647	require Proc::FastSpawn;
		648
		649	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		650	Proc::FastSpawn::fd_inherit (fileno $slave);
		651
		652	# new fh's should always be set cloexec (due to $^F),
		653	# but hey, not on win32, so we always clear the inherit flag.
		654	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		655
		656	# quick. also doesn't work in win32. of course. what did you expect
		657	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		658	my %env = %ENV;
		659	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		660
		661	my $pid = Proc::FastSpawn::spawn (
		662	$PERL,
		663	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		664	[map "$_=$env{$_}", keys %env],
		665	) or die "unable to spawn AnyEvent::Fork server: $!";
		666
		667	$self->_new ($fh, $pid)
		668	}
		669
		670	=item $pid = $proc->pid
		671
		672	Returns the process id of the process I<iff it is a direct child of the
		673	process running AnyEvent::Fork>, and C<undef> otherwise.
		674
		675	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		676	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		677	to clean up their zombies when they die.
		678
		679	All other processes are not direct children, and will be cleaned up by
		680	AnyEvent::Fork itself.
		681
		682	=cut
		683
		684	sub pid {
		685	$_[0][PID]
		686	}
		687
		688	=item $proc = $proc->eval ($perlcode, @args)
		689
		690	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
		691	the strings specified by C<@args>, in the "main" package.
		692
		693	This call is meant to do any custom initialisation that might be required
		694	(for example, the C<require> method uses it). It's not supposed to be used
		695	to completely take over the process, use C<run> for that.
		696
		697	The code will usually be executed after this call returns, and there is no
		698	way to pass anything back to the calling process. Any evaluation errors
		699	will be reported to stderr and cause the process to exit.
		700
		701	If you want to execute some code (that isn't in a module) to take over the
		702	process, you should compile a function via C<eval> first, and then call
		703	it via C<run>. This also gives you access to any arguments passed via the
		704	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		705	a faster fork+exec> example to see it in action.
		706
		707	Returns the process object for easy chaining of method calls.
		708
		709	=cut
		710
		711	sub eval {
		712	my ($self, $code, @args) = @_;
		713
		714	$self->_cmd (e => pack "(w/a)", $code, @args);
247		715
248	$self	716	$self
249	}	717	}
250		718
		719	=item $proc = $proc->require ($module, ...)
		720
		721	Tries to load the given module(s) into the process
		722
		723	Returns the process object for easy chaining of method calls.
		724
		725	=cut
		726
		727	sub require {
		728	my ($self, @modules) = @_;
		729
		730	s%::%/%g for @modules;
		731	$self->eval ('require "$_.pm" for @_', @modules);
		732
		733	$self
		734	}
		735
		736	=item $proc = $proc->send_fh ($handle, ...)
		737
		738	Send one or more file handles (I<not> file descriptors) to the process,
		739	to prepare a call to C<run>.
		740
		741	The process object keeps a reference to the handles until they have
		742	been passed over to the process, so you must not explicitly close the
		743	handles. This is most easily accomplished by simply not storing the file
		744	handles anywhere after passing them to this method - when AnyEvent::Fork
		745	is finished using them, perl will automatically close them.
		746
		747	Returns the process object for easy chaining of method calls.
		748
		749	Example: pass a file handle to a process, and release it without
		750	closing. It will be closed automatically when it is no longer used.
		751
		752	$proc->send_fh ($my_fh);
		753	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		754
		755	=cut
		756
		757	sub send_fh {
		758	my ($self, @fh) = @_;
		759
		760	for my $fh (@fh) {
		761	$self->_cmd ("h");
		762	push @{ $self->[QUEUE] }, \$fh;
		763	}
		764
		765	$self
		766	}
		767
		768	=item $proc = $proc->send_arg ($string, ...)
		769
		770	Send one or more argument strings to the process, to prepare a call to
		771	C<run>. The strings can be any octet strings.
		772
		773	The protocol is optimised to pass a moderate number of relatively short
		774	strings - while you can pass up to 4GB of data in one go, this is more
		775	meant to pass some ID information or other startup info, not big chunks of
		776	data.
		777
		778	Returns the process object for easy chaining of method calls.
		779
		780	=cut
		781
		782	sub send_arg {
		783	my ($self, @arg) = @_;
		784
		785	$self->_cmd (a => pack "(w/a)", @arg);
		786
		787	$self
		788	}
		789
		790	=item $proc->run ($func, $cb->($fh))
		791
		792	Enter the function specified by the function name in C<$func> in the
		793	process. The function is called with the communication socket as first
		794	argument, followed by all file handles and string arguments sent earlier
		795	via C<send_fh> and C<send_arg> methods, in the order they were called.
		796
		797	The process object becomes unusable on return from this function - any
		798	further method calls result in undefined behaviour.
		799
		800	The function name should be fully qualified, but if it isn't, it will be
		801	looked up in the C<main> package.
		802
		803	If the called function returns, doesn't exist, or any error occurs, the
		804	process exits.
		805
		806	Preparing the process is done in the background - when all commands have
		807	been sent, the callback is invoked with the local communications socket
		808	as argument. At this point you can start using the socket in any way you
		809	like.
		810
		811	If the communication socket isn't used, it should be closed on both sides,
		812	to save on kernel memory.
		813
		814	The socket is non-blocking in the parent, and blocking in the newly
		815	created process. The close-on-exec flag is set in both.
		816
		817	Even if not used otherwise, the socket can be a good indicator for the
		818	existence of the process - if the other process exits, you get a readable
		819	event on it, because exiting the process closes the socket (if it didn't
		820	create any children using fork).
		821
		822	Example: create a template for a process pool, pass a few strings, some
		823	file handles, then fork, pass one more string, and run some code.
		824
		825	my $pool = AnyEvent::Fork
		826	->new
		827	->send_arg ("str1", "str2")
		828	->send_fh ($fh1, $fh2);
		829
		830	for (1..2) {
		831	$pool
		832	->fork
		833	->send_arg ("str3")
		834	->run ("Some::function", sub {
		835	my ($fh) = @_;
		836
		837	# fh is nonblocking, but we trust that the OS can accept these
		838	# few octets anyway.
		839	syswrite $fh, "hi #$_\n";
		840
		841	# $fh is being closed here, as we don't store it anywhere
		842	});
		843	}
		844
		845	# Some::function might look like this - all parameters passed before fork
		846	# and after will be passed, in order, after the communications socket.
		847	sub Some::function {
		848	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		849
		850	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		851	}
		852
		853	=cut
		854
		855	sub run {
		856	my ($self, $func, $cb) = @_;
		857
		858	$self->[CB] = $cb;
		859	$self->_cmd (r => $func);
		860	}
		861
251	=back	862	=back
252		863
253	=head1 AUTHOR	864	=head2 EXPERIMENTAL METHODS
		865
		866	These methods might go away completely or change behaviour, at any time.
		867
		868	=over 4
		869
		870	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		871
		872	Flushes all commands out to the process and then calls the callback with
		873	the communications socket.
		874
		875	The process object becomes unusable on return from this function - any
		876	further method calls result in undefined behaviour.
		877
		878	The point of this method is to give you a file handle thta you cna pass
		879	to another process. In that other process, you can call C<new_from_fh
		880	AnyEvent::Fork> to create a new C<AnyEvent::Fork> object from it, thereby
		881	effectively passing a fork object to another process.
		882
		883	=cut
		884
		885	sub to_fh {
		886	my ($self, $cb) = @_;
		887
		888	$self->[CB] = $cb;
		889
		890	unless ($self->[WW]) {
		891	$self->[CB]->($self->[FH]);
		892	@$self = ();
		893	}
		894	}
		895
		896	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		897
		898	Takes a file handle originally rceeived by the C<to_fh> method and creates
		899	a new C<AnyEvent:Fork> object. The child process itself will not change in
		900	any way, i.e. it will keep all the modifications done to it before calling
		901	C<to_fh>.
		902
		903	The new object is very much like the original object, except that the
		904	C<pid> method will return C<undef> even if the process is a direct child.
		905
		906	=cut
		907
		908	sub new_from_fh {
		909	my ($class, $fh) = @_;
		910
		911	$class->_new ($fh)
		912	}
		913
		914	=back
		915
		916	=head1 PERFORMANCE
		917
		918	Now for some unscientific benchmark numbers (all done on an amd64
		919	GNU/Linux box). These are intended to give you an idea of the relative
		920	performance you can expect, they are not meant to be absolute performance
		921	numbers.
		922
		923	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		924	exit in the child and waits for the socket to close in the parent. I did
		925	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		926
		927	2079 new processes per second, using manual socketpair + fork
		928
		929	Then I did the same thing, but instead of calling fork, I called
		930	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		931	socket from the child to close on exit. This does the same thing as manual
		932	socket pair + fork, except that what is forked is the template process
		933	(2440kB), and the socket needs to be passed to the server at the other end
		934	of the socket first.
		935
		936	2307 new processes per second, using AnyEvent::Fork->new
		937
		938	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		939	a new perl interpreter and compile the small server each time, I get:
		940
		941	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		942
		943	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		944	though it uses the same operations, but adds a lot of overhead?
		945
		946	The difference is simply the process size: forking the 5MB process takes
		947	so much longer than forking the 2.5MB template process that the extra
		948	overhead is canceled out.
		949
		950	If the benchmark process grows, the normal fork becomes even slower:
		951
		952	1340 new processes, manual fork of a 20MB process
		953	731 new processes, manual fork of a 200MB process
		954	235 new processes, manual fork of a 2000MB process
		955
		956	What that means (to me) is that I can use this module without having a bad
		957	conscience because of the extra overhead required to start new processes.
		958
		959	=head1 TYPICAL PROBLEMS
		960
		961	This section lists typical problems that remain. I hope by recognising
		962	them, most can be avoided.
		963
		964	=over 4
		965
		966	=item leaked file descriptors for exec'ed processes
		967
		968	POSIX systems inherit file descriptors by default when exec'ing a new
		969	process. While perl itself laudably sets the close-on-exec flags on new
		970	file handles, most C libraries don't care, and even if all cared, it's
		971	often not possible to set the flag in a race-free manner.
		972
		973	That means some file descriptors can leak through. And since it isn't
		974	possible to know which file descriptors are "good" and "necessary" (or
		975	even to know which file descriptors are open), there is no good way to
		976	close the ones that might harm.
		977
		978	As an example of what "harm" can be done consider a web server that
		979	accepts connections and afterwards some module uses AnyEvent::Fork for the
		980	first time, causing it to fork and exec a new process, which might inherit
		981	the network socket. When the server closes the socket, it is still open
		982	in the child (which doesn't even know that) and the client might conclude
		983	that the connection is still fine.
		984
		985	For the main program, there are multiple remedies available -
		986	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		987	C<new_exec> is another, as in both cases, the first process can be exec'ed
		988	well before many random file descriptors are open.
		989
		990	In general, the solution for these kind of problems is to fix the
		991	libraries or the code that leaks those file descriptors.
		992
		993	Fortunately, most of these leaked descriptors do no harm, other than
		994	sitting on some resources.
		995
		996	=item leaked file descriptors for fork'ed processes
		997
		998	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		999	which closes file descriptors not marked for being inherited.
		1000
		1001	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		1002	a way to create these processes by forking, and this leaks more file
		1003	descriptors than exec'ing them, as there is no way to mark descriptors as
		1004	"close on fork".
		1005
		1006	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		1007	pipes for internal uses, and L<Gtk2> might open a connection to the X
		1008	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		1009	trouble with a fork.
		1010
		1011	The solution is to either not load these modules before use'ing
		1012	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		1013	initialising them, for example, by calling C<init Gtk2> manually.
		1014
		1015	=item exiting calls object destructors
		1016
		1017	This only applies to users of L<AnyEvent::Fork:Early> and
		1018	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1019	that reference external resources.
		1020
		1021	When a process created by AnyEvent::Fork exits, it might do so by calling
		1022	exit, or simply letting perl reach the end of the program. At which point
		1023	Perl runs all destructors.
		1024
		1025	Not all destructors are fork-safe - for example, an object that represents
		1026	the connection to an X display might tell the X server to free resources,
		1027	which is inconvenient when the "real" object in the parent still needs to
		1028	use them.
		1029
		1030	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		1031	it as the very first thing, right?
		1032
		1033	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		1034	is to not create objects with nontrivial destructors that might have an
		1035	effect outside of Perl.
		1036
		1037	=back
		1038
		1039	=head1 PORTABILITY NOTES
		1040
		1041	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		1042	and ::Template is not going to work), and it cost a lot of blood and sweat
		1043	to make it so, mostly due to the bloody broken perl that nobody seems to
		1044	care about. The fork emulation is a bad joke - I have yet to see something
		1045	useful that you can do with it without running into memory corruption
		1046	issues or other braindamage. Hrrrr.
		1047
		1048	Since fork is endlessly broken on win32 perls (it doesn't even remotely
		1049	work within it's documented limits) and quite obviously it's not getting
		1050	improved any time soon, the best way to proceed on windows would be to
		1051	always use C<new_exec> and thus never rely on perl's fork "emulation".
		1052
		1053	Cygwin perl is not supported at the moment due to some hilarious
		1054	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1055	use C<send_fh> and always use C<new_exec> to create processes, it should
		1056	work though.
		1057
		1058	=head1 SEE ALSO
		1059
		1060	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1061	(part of this distribution).
		1062
		1063	L<AnyEvent::Fork::Template>, to create a process by forking the main
		1064	program at a convenient time (part of this distribution).
		1065
		1066	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1067
		1068	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1069
		1070	=head1 AUTHOR AND CONTACT INFORMATION
254		1071
255	Marc Lehmann <schmorp@schmorp.de>	1072	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	1073	http://software.schmorp.de/pkg/AnyEvent-Fork
257		1074
258	=cut	1075	=cut
259		1076
260	1	1077	1
261		1078

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs. Revision 1.56 by root, Sun Apr 28 13:47:52 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs.
Revision 1.56 by root, Sun Apr 28 13:47:52 2013 UTC