[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 1.39 by root, Sat Apr 6 22:39:37 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 can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head2 COMPARISON TO OTHER MODULES
		46
		47	There is an abundance of modules on CPAN that do "something fork", such as
		48	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		49	or L<AnyEvent::Subprocess>. There are modules that implement their own
		50	process management, such as L<AnyEvent::DBI>.
		51
		52	The problems that all these modules try to solve are real, however, none
		53	of them (from what I have seen) tackle the very real problems of unwanted
		54	memory sharing, efficiency, not being able to use event processing or
		55	similar modules in the processes they create.
		56
		57	This module doesn't try to replace any of them - instead it tries to solve
		58	the problem of creating processes with a minimum of fuss and overhead (and
		59	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		60	except they were written before AnyEvent:Fork was available, so obviously
		61	had to roll their own.
		62
24	=head1 PROBLEM STATEMENT	63	=head2 PROBLEM STATEMENT
25		64
26	There are two ways to implement parallel processing on UNIX like operating	65	There are two traditional ways to implement parallel processing on UNIX
27	systems - fork and process, and fork+exec and process. They have different	66	like operating systems - fork and process, and fork+exec and process. They
28	advantages and disadvantages that I describe below, together with how this	67	have different advantages and disadvantages that I describe below,
29	module tries to mitigate the disadvantages.	68	together with how this module tries to mitigate the disadvantages.
30		69
31	=over 4	70	=over 4
32		71
33	=item Forking from a big process can be very slow (a 5GB process needs	72	=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	73
		74	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	75	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.	76	in some circumstances (e.g. when vfork is used), fork+exec can be much
		77	faster.
37		78
38	This module can help here by telling a small(er) helper process to fork,	79	This module can help here by telling a small(er) helper process to fork,
39	or fork+exec instead.	80	which is faster then forking the main process, and also uses vfork where
		81	possible. This gives the speed of vfork, with the flexibility of fork.
40		82
41	=item Forking usually creates a copy-on-write copy of the parent	83	=item Forking usually creates a copy-on-write copy of the parent
42	process. Memory (for example, modules or data files that have been	84	process.
43	will not take additional memory). When exec'ing a new process, modules	85
44	and data files might need to be loaded again, at extra cpu and memory	86	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	87	memory after a fork. When exec'ing a new process, modules and data files
		88	might need to be loaded again, at extra CPU and memory cost. But when
		89	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	90	them and replaces them by new data, the child processes will retain the
47	will retain the memory even if it isn't used.	91	old version even if it isn't used, which can suddenly and unexpectedly
		92	increase memory usage when freeing memory.
		93
		94	The trade-off is between more sharing with fork (which can be good or
		95	bad), and no sharing with exec.
48		96
49	This module allows the main program to do a controlled fork, and allows	97	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	98	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	99	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	100	risking to share large dynamic data structures that will blow up child
53	memory usage.	101	memory usage.
54		102
		103	In other words, this module puts you into control over what is being
		104	shared and what isn't, at all times.
		105
55	=item Exec'ing a new perl process might be difficult and slow. For	106	=item Exec'ing a new perl process might be difficult.
		107
56	example, it is not easy to find the correct path to the perl interpreter,	108	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	109	interpreter - C<$^X> might not be a perl interpreter at all.
58	might run into problems when perl is upgraded for example.
59		110
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	111	This module tries hard to identify the correct path to the perl
62	interpreter. With a cooperative main program, exec'ing the interpreter	112	interpreter. With a cooperative main program, exec'ing the interpreter
63	might not even be necessary.	113	might not even be necessary, but even without help from the main program,
		114	it will still work when used from a module.
64		115
		116	=item Exec'ing a new perl process might be slow, as all necessary modules
		117	have to be loaded from disk again, with no guarantees of success.
		118
		119	Long running processes might run into problems when perl is upgraded
		120	and modules are no longer loadable because they refer to a different
		121	perl version, or parts of a distribution are newer than the ones already
		122	loaded.
		123
		124	This module supports creating pre-initialised perl processes to be used as
		125	a template for new processes.
		126
65	=item Forking might be impossible when a program is running. For example,	127	=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		128
		129	For example, POSIX makes it almost impossible to fork from a
		130	multi-threaded program while doing anything useful in the child - in
		131	fact, if your perl program uses POSIX threads (even indirectly via
		132	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		133	anymore without risking corruption issues on a number of operating
		134	systems.
		135
71	This module can safely fork helper processes at any time, by caling	136	This module can safely fork helper processes at any time, by calling
72	fork+exec in C, in a POSIX-compatible way.	137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
73		138
74	=item Parallel processing with fork might be inconvenient or difficult	139	=item Parallel processing with fork might be inconvenient or difficult
		140	to implement. Modules might not work in both parent and child.
		141
75	to implement. For example, when a program uses an event loop and creates	142	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	143	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	144	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	145	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.	146	or the main program also does, leading to problems.
80		147
81	This module only lets the main program create pools by forking (because	148	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	149	"unsafe module" category, or just about anything that communicates with
83	pools are created by fork+exec, after which such modules can again be	150	the external world, such as network libraries and file I/O modules, which
84	loaded.	151	usually don't like being copied and then allowed to continue in two
		152	processes.
		153
		154	With this module only the main program is allowed to create new processes
		155	by forking (because only the main program can know when it is still safe
		156	to do so) - all other processes are created via fork+exec, which makes it
		157	possible to use modules such as event loops or window interfaces safely.
85		158
86	=back	159	=back
		160
		161	=head1 EXAMPLES
		162
		163	=head2 Create a single new process, tell it to run your worker function.
		164
		165	AnyEvent::Fork
		166	->new
		167	->require ("MyModule")
		168	->run ("MyModule::worker, sub {
		169	my ($master_filehandle) = @_;
		170
		171	# now $master_filehandle is connected to the
		172	# $slave_filehandle in the new process.
		173	});
		174
		175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
		179	sub worker {
		180	my ($slave_filehandle) = @_;
		181
		182	# now $slave_filehandle is connected to the $master_filehandle
		183	# in the original prorcess. have fun!
		184	}
		185
		186	=head2 Create a pool of server processes all accepting on the same socket.
		187
		188	# create listener socket
		189	my $listener = ...;
		190
		191	# create a pool template, initialise it and give it the socket
		192	my $pool = AnyEvent::Fork
		193	->new
		194	->require ("Some::Stuff", "My::Server")
		195	->send_fh ($listener);
		196
		197	# now create 10 identical workers
		198	for my $id (1..10) {
		199	$pool
		200	->fork
		201	->send_arg ($id)
		202	->run ("My::Server::run");
		203	}
		204
		205	# now do other things - maybe use the filehandle provided by run
		206	# to wait for the processes to die. or whatever.
		207
		208	C<My::Server> might look like this:
		209
		210	package My::Server;
		211
		212	sub run {
		213	my ($slave, $listener, $id) = @_;
		214
		215	close $slave; # we do not use the socket, so close it to save resources
		216
		217	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		218	# or anything we usually couldn't do in a process forked normally.
		219	while (my $socket = $listener->accept) {
		220	# do sth. with new socket
		221	}
		222	}
		223
		224	=head2 use AnyEvent::Fork as a faster fork+exec
		225
		226	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
		227	and standard error redirected to the communications socket. It is usually
		228	faster than fork+exec, but still lets you prepare the environment.
		229
		230	open my $output, ">/tmp/log" or die "$!";
		231
		232	AnyEvent::Fork
		233	->new
		234	->eval ('
		235	sub run {
		236	my ($fh, $output, @cmd) = @_;
		237
		238	# perl will clear close-on-exec on STDOUT/STDERR
		239	open STDOUT, ">&", $output or die;
		240	open STDERR, ">&", $fh or die;
		241
		242	exec @cmd;
		243	}
		244	')
		245	->send_fh ($output)
		246	->send_arg ("/bin/echo", "hi")
		247	->run ("run", my $cv = AE::cv);
		248
		249	my $stderr = $cv->recv;
87		250
88	=head1 CONCEPTS	251	=head1 CONCEPTS
89		252
90	This module can create new processes either by executing a new perl	253	This module can create new processes either by executing a new perl
91	process, or by forking from an existing "template" process.	254	process, or by forking from an existing "template" process.
108	needed the first time. Forking from this process shares the memory used	271	needed the first time. Forking from this process shares the memory used
109	for the perl interpreter with the new process, but loading modules takes	272	for the perl interpreter with the new process, but loading modules takes
110	time, and the memory is not shared with anything else.	273	time, and the memory is not shared with anything else.
111		274
112	This is ideal for when you only need one extra process of a kind, with the	275	This is ideal for when you only need one extra process of a kind, with the
113	option of starting and stipping it on demand.	276	option of starting and stopping it on demand.
		277
		278	Example:
		279
		280	AnyEvent::Fork
		281	->new
		282	->require ("Some::Module")
		283	->run ("Some::Module::run", sub {
		284	my ($fork_fh) = @_;
		285	});
114		286
115	=item fork a new template process, load code, then fork processes off of	287	=item fork a new template process, load code, then fork processes off of
116	it and run the code	288	it and run the code
117		289
118	When you need to have a bunch of processes that all execute the same (or	290	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	296	modules you loaded) is shared between the processes, and each new process
125	consumes relatively little memory of its own.	297	consumes relatively little memory of its own.
126		298
127	The disadvantage of this approach is that you need to create a template	299	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	300	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	301	only need a fixed number of processes you can create them, and then destroy
130	the template process.	302	the template process.
		303
		304	Example:
		305
		306	my $template = AnyEvent::Fork->new->require ("Some::Module");
		307
		308	for (1..10) {
		309	$template->fork->run ("Some::Module::run", sub {
		310	my ($fork_fh) = @_;
		311	});
		312	}
		313
		314	# at this point, you can keep $template around to fork new processes
		315	# later, or you can destroy it, which causes it to vanish.
131		316
132	=item execute a new perl interpreter, load some code, run it	317	=item execute a new perl interpreter, load some code, run it
133		318
134	This is relatively slow, and doesn't allow you to share memory between	319	This is relatively slow, and doesn't allow you to share memory between
135	multiple processes.	320	multiple processes.
…		…
137	The only advantage is that you don't have to have a template process	322	The only advantage is that you don't have to have a template process
138	hanging around all the time to fork off some new processes, which might be	323	hanging around all the time to fork off some new processes, which might be
139	an advantage when there are long time spans where no extra processes are	324	an advantage when there are long time spans where no extra processes are
140	needed.	325	needed.
141		326
		327	Example:
		328
		329	AnyEvent::Fork
		330	->new_exec
		331	->require ("Some::Module")
		332	->run ("Some::Module::run", sub {
		333	my ($fork_fh) = @_;
		334	});
		335
142	=back	336	=back
143		337
144	=head1 FUNCTIONS	338	=head1 THE C<AnyEvent::Fork> CLASS
		339
		340	This module exports nothing, and only implements a single class -
		341	C<AnyEvent::Fork>.
		342
		343	There are two class constructors that both create new processes - C<new>
		344	and C<new_exec>. The C<fork> method creates a new process by forking an
		345	existing one and could be considered a third constructor.
		346
		347	Most of the remaining methods deal with preparing the new process, by
		348	loading code, evaluating code and sending data to the new process. They
		349	usually return the process object, so you can chain method calls.
		350
		351	If a process object is destroyed before calling its C<run> method, then
		352	the process simply exits. After C<run> is called, all responsibility is
		353	passed to the specified function.
		354
		355	As long as there is any outstanding work to be done, process objects
		356	resist being destroyed, so there is no reason to store them unless you
		357	need them later - configure and forget works just fine.
145		358
146	=over 4	359	=over 4
147		360
148	=cut	361	=cut
149		362
150	package AnyEvent::ProcessPool;	363	package AnyEvent::Fork;
151		364
152	use common::sense;	365	use common::sense;
153		366
154	use Socket ();	367	use Errno ();
155		368
156	use Proc::FastSpawn;
157	use AnyEvent;	369	use AnyEvent;
158	use AnyEvent::ProcessPool::Util;
159	use AnyEvent::Util ();	370	use AnyEvent::Util ();
160		371
161	BEGIN {	372	use IO::FDPass;
162	# require Exporter;
163	}
164		373
165	=item my $pool = new AnyEvent::ProcessPool key => value...	374	our $VERSION = 0.5;
166		375
167	Create a new process pool. The following named parameters are supported:	376	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
168		377
169	=over 4	378	=over 4
170		379
171	=back	380	=back
172		381
173	=cut	382	=cut
174		383
		384	# the early fork template process
		385	our $EARLY;
		386
175	# the template process	387	# the empty template process
176	our $template;	388	our $TEMPLATE;
177		389
178	sub _queue {	390	sub _cmd {
179	my ($pid, $fh) = @_;	391	my $self = shift;
180		392
181	[	393	# ideally, we would want to use "a (w/a)*" as format string, but perl
		394	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		395	# it.
		396	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
		397
		398	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		399	do {
		400	# send the next "thing" in the queue - either a reference to an fh,
		401	# or a plain string.
		402
		403	if (ref $self->[2][0]) {
		404	# send fh
		405	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		406	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		407	undef $self->[3];
		408	die "AnyEvent::Fork: file descriptor send failure: $!";
		409	}
		410
		411	shift @{ $self->[2] };
		412
		413	} else {
		414	# send string
		415	my $len = syswrite $self->[1], $self->[2][0];
		416
		417	unless ($len) {
		418	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		419	undef $self->[3];
		420	die "AnyEvent::Fork: command write failure: $!";
		421	}
		422
		423	substr $self->[2][0], 0, $len, "";
		424	shift @{ $self->[2] } unless length $self->[2][0];
		425	}
		426	} while @{ $self->[2] };
		427
		428	# everything written
		429	undef $self->[3];
		430
		431	# invoke run callback, if any
		432	$self->[4]->($self->[1]) if $self->[4];
		433	};
		434
		435	() # make sure we don't leak the watcher
		436	}
		437
		438	sub _new {
		439	my ($self, $fh, $pid) = @_;
		440
		441	AnyEvent::Util::fh_nonblocking $fh, 1;
		442
		443	$self = bless [
182	$pid,	444	$pid,
183	$fh,	445	$fh,
184	[],	446	[], # write queue - strings or fd's
185	undef	447	undef, # AE watcher
186	]	448	], $self;
187	}
188		449
189	sub queue_cmd {	450	$self
190	my $queue = shift;
191
192	push @{ $queue->[2] }, pack "N/a", pack "a (w/a)*", @_;
193
194	$queue->[3] \|\|= AE::io $queue->[1], 1, sub {
195	if (ref $queue->[2][0]) {
196	AnyEvent::ProcessPool::Util::fd_send fileno $queue->[1], fileno ${ $queue->[2][0] }
197	and shift @{ $queue->[2] };
198	} else {
199	my $len = syswrite $queue->[1], $queue->[2][0]
200	or do { undef $queue->[3]; die "AnyEvent::ProcessPool::queue write failure: $!" };
201	substr $queue->[2][0], 0, $len, "";
202	shift @{ $queue->[2] } unless length $queue->[2][0];
203	}
204
205	undef $queue->[3] unless @{ $queue->[2] };
206	};
207	}	451	}
208		452
209	sub run_template {	453	# fork template from current process, used by AnyEvent::Fork::Early/Template
210	return if $template;	454	sub _new_fork {
211
212	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	455	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
213	AnyEvent::Util::fh_nonblocking $fh, 1;	456	my $parent = $$;
214	fd_inherit fileno $slave;
215		457
216	my %env = %ENV;	458	my $pid = fork;
217	$env{PERL5LIB} = join ":", grep !ref, @INC;
218		459
219	my $pid = spawn	460	if ($pid eq 0) {
220	$^X,	461	require AnyEvent::Fork::Serve;
221	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	462	$AnyEvent::Fork::Serve::OWNER = $parent;
222	[map "$_=$env{$_}", keys %env],	463	close $fh;
223	or die "unable to spawn AnyEvent::ProcessPool server: $!";	464	$0 = "$_[1] of $parent";
		465	$SIG{CHLD} = 'IGNORE';
		466	AnyEvent::Fork::Serve::serve ($slave);
		467	exit 0;
		468	} elsif (!$pid) {
		469	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		470	}
224		471
225	close $slave;	472	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	}	473	}
		474
		475	=item my $proc = new AnyEvent::Fork
		476
		477	Create a new "empty" perl interpreter process and returns its process
		478	object for further manipulation.
		479
		480	The new process is forked from a template process that is kept around
		481	for this purpose. When it doesn't exist yet, it is created by a call to
		482	C<new_exec> first and then stays around for future calls.
		483
		484	=cut
238		485
239	sub new {	486	sub new {
240	my $class = shift;	487	my $class = shift;
241		488
242	my $self = bless {	489	$TEMPLATE \|\|= $class->new_exec;
243	@_	490	$TEMPLATE->fork
244	}, $class;	491	}
245		492
246	run_template;	493	=item $new_proc = $proc->fork
		494
		495	Forks C<$proc>, creating a new process, and returns the process object
		496	of the new process.
		497
		498	If any of the C<send_> functions have been called before fork, then they
		499	will be cloned in the child. For example, in a pre-forked server, you
		500	might C<send_fh> the listening socket into the template process, and then
		501	keep calling C<fork> and C<run>.
		502
		503	=cut
		504
		505	sub fork {
		506	my ($self) = @_;
		507
		508	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		509
		510	$self->send_fh ($slave);
		511	$self->_cmd ("f");
		512
		513	AnyEvent::Fork->_new ($fh)
		514	}
		515
		516	=item my $proc = new_exec AnyEvent::Fork
		517
		518	Create a new "empty" perl interpreter process and returns its process
		519	object for further manipulation.
		520
		521	Unlike the C<new> method, this method I<always> spawns a new perl process
		522	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
		523	reduces the amount of memory sharing that is possible, and is also slower.
		524
		525	You should use C<new> whenever possible, except when having a template
		526	process around is unacceptable.
		527
		528	The path to the perl interpreter is divined using various methods - first
		529	C<$^X> is investigated to see if the path ends with something that sounds
		530	as if it were the perl interpreter. Failing this, the module falls back to
		531	using C<$Config::Config{perlpath}>.
		532
		533	=cut
		534
		535	sub new_exec {
		536	my ($self) = @_;
		537
		538	return $EARLY->fork
		539	if $EARLY;
		540
		541	# first find path of perl
		542	my $perl = $;
		543
		544	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		545	# that looks like perl. this obviously only works for posix and win32
		546	unless (
		547	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		548	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		549	) {
		550	# if it doesn't look perlish enough, try Config
		551	require Config;
		552	$perl = $Config::Config{perlpath};
		553	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		554	}
		555
		556	require Proc::FastSpawn;
		557
		558	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		559	Proc::FastSpawn::fd_inherit (fileno $slave);
		560
		561	# new fh's should always be set cloexec (due to $^F),
		562	# but hey, not on win32, so we always clear the inherit flag.
		563	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		564
		565	# quick. also doesn't work in win32. of course. what did you expect
		566	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		567	my %env = %ENV;
		568	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		569
		570	my $pid = Proc::FastSpawn::spawn (
		571	$perl,
		572	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		573	[map "$_=$env{$_}", keys %env],
		574	) or die "unable to spawn AnyEvent::Fork server: $!";
		575
		576	$self->_new ($fh, $pid)
		577	}
		578
		579	=item $pid = $proc->pid
		580
		581	Returns the process id of the process I<iff it is a direct child of the
		582	process running AnyEvent::Fork>, and C<undef> otherwise.
		583
		584	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		585	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		586	to clean up their zombies when they die.
		587
		588	All other processes are not direct children, and will be cleaned up by
		589	AnyEvent::Fork itself.
		590
		591	=cut
		592
		593	sub pid {
		594	$_[0][0]
		595	}
		596
		597	=item $proc = $proc->eval ($perlcode, @args)
		598
		599	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		600	the strings specified by C<@args>, in the "main" package.
		601
		602	This call is meant to do any custom initialisation that might be required
		603	(for example, the C<require> method uses it). It's not supposed to be used
		604	to completely take over the process, use C<run> for that.
		605
		606	The code will usually be executed after this call returns, and there is no
		607	way to pass anything back to the calling process. Any evaluation errors
		608	will be reported to stderr and cause the process to exit.
		609
		610	If you want to execute some code (that isn't in a module) to take over the
		611	process, you should compile a function via C<eval> first, and then call
		612	it via C<run>. This also gives you access to any arguments passed via the
		613	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		614	a faster fork+exec> example to see it in action.
		615
		616	Returns the process object for easy chaining of method calls.
		617
		618	=cut
		619
		620	sub eval {
		621	my ($self, $code, @args) = @_;
		622
		623	$self->_cmd (e => pack "(w/a)", $code, @args);
247		624
248	$self	625	$self
249	}	626	}
250		627
		628	=item $proc = $proc->require ($module, ...)
		629
		630	Tries to load the given module(s) into the process
		631
		632	Returns the process object for easy chaining of method calls.
		633
		634	=cut
		635
		636	sub require {
		637	my ($self, @modules) = @_;
		638
		639	s%::%/%g for @modules;
		640	$self->eval ('require "$_.pm" for @_', @modules);
		641
		642	$self
		643	}
		644
		645	=item $proc = $proc->send_fh ($handle, ...)
		646
		647	Send one or more file handles (I<not> file descriptors) to the process,
		648	to prepare a call to C<run>.
		649
		650	The process object keeps a reference to the handles until they have
		651	been passed over to the process, so you must not explicitly close the
		652	handles. This is most easily accomplished by simply not storing the file
		653	handles anywhere after passing them to this method - when AnyEvent::Fork
		654	is finished using them, perl will automatically close them.
		655
		656	Returns the process object for easy chaining of method calls.
		657
		658	Example: pass a file handle to a process, and release it without
		659	closing. It will be closed automatically when it is no longer used.
		660
		661	$proc->send_fh ($my_fh);
		662	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		663
		664	=cut
		665
		666	sub send_fh {
		667	my ($self, @fh) = @_;
		668
		669	for my $fh (@fh) {
		670	$self->_cmd ("h");
		671	push @{ $self->[2] }, \$fh;
		672	}
		673
		674	$self
		675	}
		676
		677	=item $proc = $proc->send_arg ($string, ...)
		678
		679	Send one or more argument strings to the process, to prepare a call to
		680	C<run>. The strings can be any octet strings.
		681
		682	The protocol is optimised to pass a moderate number of relatively short
		683	strings - while you can pass up to 4GB of data in one go, this is more
		684	meant to pass some ID information or other startup info, not big chunks of
		685	data.
		686
		687	Returns the process object for easy chaining of method calls.
		688
		689	=cut
		690
		691	sub send_arg {
		692	my ($self, @arg) = @_;
		693
		694	$self->_cmd (a => pack "(w/a)", @arg);
		695
		696	$self
		697	}
		698
		699	=item $proc->run ($func, $cb->($fh))
		700
		701	Enter the function specified by the function name in C<$func> in the
		702	process. The function is called with the communication socket as first
		703	argument, followed by all file handles and string arguments sent earlier
		704	via C<send_fh> and C<send_arg> methods, in the order they were called.
		705
		706	The process object becomes unusable on return from this function - any
		707	further method calls result in undefined behaviour.
		708
		709	The function name should be fully qualified, but if it isn't, it will be
		710	looked up in the C<main> package.
		711
		712	If the called function returns, doesn't exist, or any error occurs, the
		713	process exits.
		714
		715	Preparing the process is done in the background - when all commands have
		716	been sent, the callback is invoked with the local communications socket
		717	as argument. At this point you can start using the socket in any way you
		718	like.
		719
		720	If the communication socket isn't used, it should be closed on both sides,
		721	to save on kernel memory.
		722
		723	The socket is non-blocking in the parent, and blocking in the newly
		724	created process. The close-on-exec flag is set in both.
		725
		726	Even if not used otherwise, the socket can be a good indicator for the
		727	existence of the process - if the other process exits, you get a readable
		728	event on it, because exiting the process closes the socket (if it didn't
		729	create any children using fork).
		730
		731	Example: create a template for a process pool, pass a few strings, some
		732	file handles, then fork, pass one more string, and run some code.
		733
		734	my $pool = AnyEvent::Fork
		735	->new
		736	->send_arg ("str1", "str2")
		737	->send_fh ($fh1, $fh2);
		738
		739	for (1..2) {
		740	$pool
		741	->fork
		742	->send_arg ("str3")
		743	->run ("Some::function", sub {
		744	my ($fh) = @_;
		745
		746	# fh is nonblocking, but we trust that the OS can accept these
		747	# few octets anyway.
		748	syswrite $fh, "hi #$_\n";
		749
		750	# $fh is being closed here, as we don't store it anywhere
		751	});
		752	}
		753
		754	# Some::function might look like this - all parameters passed before fork
		755	# and after will be passed, in order, after the communications socket.
		756	sub Some::function {
		757	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		758
		759	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		760	}
		761
		762	=cut
		763
		764	sub run {
		765	my ($self, $func, $cb) = @_;
		766
		767	$self->[4] = $cb;
		768	$self->_cmd (r => $func);
		769	}
		770
251	=back	771	=back
		772
		773	=head1 PERFORMANCE
		774
		775	Now for some unscientific benchmark numbers (all done on an amd64
		776	GNU/Linux box). These are intended to give you an idea of the relative
		777	performance you can expect, they are not meant to be absolute performance
		778	numbers.
		779
		780	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		781	exit in the child and waits for the socket to close in the parent. I did
		782	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		783
		784	2079 new processes per second, using manual socketpair + fork
		785
		786	Then I did the same thing, but instead of calling fork, I called
		787	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		788	socket form the child to close on exit. This does the same thing as manual
		789	socket pair + fork, except that what is forked is the template process
		790	(2440kB), and the socket needs to be passed to the server at the other end
		791	of the socket first.
		792
		793	2307 new processes per second, using AnyEvent::Fork->new
		794
		795	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		796	a new perl interpreter and compile the small server each time, I get:
		797
		798	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		799
		800	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		801	though it uses the same operations, but adds a lot of overhead?
		802
		803	The difference is simply the process size: forking the 5MB process takes
		804	so much longer than forking the 2.5MB template process that the extra
		805	overhead introduced is canceled out.
		806
		807	If the benchmark process grows, the normal fork becomes even slower:
		808
		809	1340 new processes, manual fork of a 20MB process
		810	731 new processes, manual fork of a 200MB process
		811	235 new processes, manual fork of a 2000MB process
		812
		813	What that means (to me) is that I can use this module without having a bad
		814	conscience because of the extra overhead required to start new processes.
		815
		816	=head1 TYPICAL PROBLEMS
		817
		818	This section lists typical problems that remain. I hope by recognising
		819	them, most can be avoided.
		820
		821	=over 4
		822
		823	=item leaked file descriptors for exec'ed processes
		824
		825	POSIX systems inherit file descriptors by default when exec'ing a new
		826	process. While perl itself laudably sets the close-on-exec flags on new
		827	file handles, most C libraries don't care, and even if all cared, it's
		828	often not possible to set the flag in a race-free manner.
		829
		830	That means some file descriptors can leak through. And since it isn't
		831	possible to know which file descriptors are "good" and "necessary" (or
		832	even to know which file descriptors are open), there is no good way to
		833	close the ones that might harm.
		834
		835	As an example of what "harm" can be done consider a web server that
		836	accepts connections and afterwards some module uses AnyEvent::Fork for the
		837	first time, causing it to fork and exec a new process, which might inherit
		838	the network socket. When the server closes the socket, it is still open
		839	in the child (which doesn't even know that) and the client might conclude
		840	that the connection is still fine.
		841
		842	For the main program, there are multiple remedies available -
		843	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		844	C<new_exec> is another, as in both cases, the first process can be exec'ed
		845	well before many random file descriptors are open.
		846
		847	In general, the solution for these kind of problems is to fix the
		848	libraries or the code that leaks those file descriptors.
		849
		850	Fortunately, most of these leaked descriptors do no harm, other than
		851	sitting on some resources.
		852
		853	=item leaked file descriptors for fork'ed processes
		854
		855	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		856	which closes file descriptors not marked for being inherited.
		857
		858	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		859	a way to create these processes by forking, and this leaks more file
		860	descriptors than exec'ing them, as there is no way to mark descriptors as
		861	"close on fork".
		862
		863	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		864	pipes for internal uses, and L<Gtk2> might open a connection to the X
		865	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		866	trouble with a fork.
		867
		868	The solution is to either not load these modules before use'ing
		869	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		870	initialising them, for example, by calling C<init Gtk2> manually.
		871
		872	=item exiting calls object destructors
		873
		874	This only applies to users of L<AnyEvent::Fork:Early> and
		875	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		876	that reference external resources.
		877
		878	When a process created by AnyEvent::Fork exits, it might do so by calling
		879	exit, or simply letting perl reach the end of the program. At which point
		880	Perl runs all destructors.
		881
		882	Not all destructors are fork-safe - for example, an object that represents
		883	the connection to an X display might tell the X server to free resources,
		884	which is inconvenient when the "real" object in the parent still needs to
		885	use them.
		886
		887	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		888	it as the very first thing, right?
		889
		890	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		891	is to not create objects with nontrivial destructors that might have an
		892	effect outside of Perl.
		893
		894	=back
		895
		896	=head1 PORTABILITY NOTES
		897
		898	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		899	and ::Template is not going to work), and it cost a lot of blood and sweat
		900	to make it so, mostly due to the bloody broken perl that nobody seems to
		901	care about. The fork emulation is a bad joke - I have yet to see something
		902	useful that you can do with it without running into memory corruption
		903	issues or other braindamage. Hrrrr.
		904
		905	Cygwin perl is not supported at the moment due to some hilarious
		906	shortcomings of its API - see L<IO::FDPoll> for more details.
		907
		908	=head1 SEE ALSO
		909
		910	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		911	L<AnyEvent::Fork::Template> (to create a process by forking the main
		912	program at a convenient time).
252		913
253	=head1 AUTHOR	914	=head1 AUTHOR
254		915
255	Marc Lehmann <schmorp@schmorp.de>	916	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	917	http://home.schmorp.de/

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs. Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC