[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 1.41 by root, Mon Apr 8 03:20:53 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	# compile a helper function for later use
		236	sub run {
		237	my ($fh, $output, @cmd) = @_;
		238
		239	# perl will clear close-on-exec on STDOUT/STDERR
		240	open STDOUT, ">&", $output or die;
		241	open STDERR, ">&", $fh or die;
		242
		243	exec @cmd;
		244	}
		245	')
		246	->send_fh ($output)
		247	->send_arg ("/bin/echo", "hi")
		248	->run ("run", my $cv = AE::cv);
		249
		250	my $stderr = $cv->recv;
87		251
88	=head1 CONCEPTS	252	=head1 CONCEPTS
89		253
90	This module can create new processes either by executing a new perl	254	This module can create new processes either by executing a new perl
91	process, or by forking from an existing "template" process.	255	process, or by forking from an existing "template" process.
108	needed the first time. Forking from this process shares the memory used	272	needed the first time. Forking from this process shares the memory used
109	for the perl interpreter with the new process, but loading modules takes	273	for the perl interpreter with the new process, but loading modules takes
110	time, and the memory is not shared with anything else.	274	time, and the memory is not shared with anything else.
111		275
112	This is ideal for when you only need one extra process of a kind, with the	276	This is ideal for when you only need one extra process of a kind, with the
113	option of starting and stipping it on demand.	277	option of starting and stopping it on demand.
		278
		279	Example:
		280
		281	AnyEvent::Fork
		282	->new
		283	->require ("Some::Module")
		284	->run ("Some::Module::run", sub {
		285	my ($fork_fh) = @_;
		286	});
114		287
115	=item fork a new template process, load code, then fork processes off of	288	=item fork a new template process, load code, then fork processes off of
116	it and run the code	289	it and run the code
117		290
118	When you need to have a bunch of processes that all execute the same (or	291	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	297	modules you loaded) is shared between the processes, and each new process
125	consumes relatively little memory of its own.	298	consumes relatively little memory of its own.
126		299
127	The disadvantage of this approach is that you need to create a template	300	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	301	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	302	only need a fixed number of processes you can create them, and then destroy
130	the template process.	303	the template process.
		304
		305	Example:
		306
		307	my $template = AnyEvent::Fork->new->require ("Some::Module");
		308
		309	for (1..10) {
		310	$template->fork->run ("Some::Module::run", sub {
		311	my ($fork_fh) = @_;
		312	});
		313	}
		314
		315	# at this point, you can keep $template around to fork new processes
		316	# later, or you can destroy it, which causes it to vanish.
131		317
132	=item execute a new perl interpreter, load some code, run it	318	=item execute a new perl interpreter, load some code, run it
133		319
134	This is relatively slow, and doesn't allow you to share memory between	320	This is relatively slow, and doesn't allow you to share memory between
135	multiple processes.	321	multiple processes.
…		…
137	The only advantage is that you don't have to have a template process	323	The only advantage is that you don't have to have a template process
138	hanging around all the time to fork off some new processes, which might be	324	hanging around all the time to fork off some new processes, which might be
139	an advantage when there are long time spans where no extra processes are	325	an advantage when there are long time spans where no extra processes are
140	needed.	326	needed.
141		327
		328	Example:
		329
		330	AnyEvent::Fork
		331	->new_exec
		332	->require ("Some::Module")
		333	->run ("Some::Module::run", sub {
		334	my ($fork_fh) = @_;
		335	});
		336
142	=back	337	=back
143		338
144	=head1 FUNCTIONS	339	=head1 THE C<AnyEvent::Fork> CLASS
		340
		341	This module exports nothing, and only implements a single class -
		342	C<AnyEvent::Fork>.
		343
		344	There are two class constructors that both create new processes - C<new>
		345	and C<new_exec>. The C<fork> method creates a new process by forking an
		346	existing one and could be considered a third constructor.
		347
		348	Most of the remaining methods deal with preparing the new process, by
		349	loading code, evaluating code and sending data to the new process. They
		350	usually return the process object, so you can chain method calls.
		351
		352	If a process object is destroyed before calling its C<run> method, then
		353	the process simply exits. After C<run> is called, all responsibility is
		354	passed to the specified function.
		355
		356	As long as there is any outstanding work to be done, process objects
		357	resist being destroyed, so there is no reason to store them unless you
		358	need them later - configure and forget works just fine.
145		359
146	=over 4	360	=over 4
147		361
148	=cut	362	=cut
149		363
150	package AnyEvent::ProcessPool;	364	package AnyEvent::Fork;
151		365
152	use common::sense;	366	use common::sense;
153		367
154	use Socket ();	368	use Errno ();
155		369
156	use Proc::FastSpawn;
157	use AnyEvent;	370	use AnyEvent;
158	use AnyEvent::ProcessPool::Util;
159	use AnyEvent::Util ();	371	use AnyEvent::Util ();
160		372
161	BEGIN {	373	use IO::FDPass;
162	# require Exporter;
163	}
164		374
165	=item my $pool = new AnyEvent::ProcessPool key => value...	375	our $VERSION = 0.6;
166
167	Create a new process pool. The following named parameters are supported:
168		376
169	=over 4	377	=over 4
170		378
171	=back	379	=back
172		380
173	=cut	381	=cut
174		382
		383	# the early fork template process
		384	our $EARLY;
		385
175	# the template process	386	# the empty template process
176	our $template;	387	our $TEMPLATE;
177		388
178	sub _queue {	389	sub _cmd {
179	my ($pid, $fh) = @_;	390	my $self = shift;
180		391
181	[	392	# ideally, we would want to use "a (w/a)*" as format string, but perl
		393	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		394	# it.
		395	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
		396
		397	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		398	do {
		399	# send the next "thing" in the queue - either a reference to an fh,
		400	# or a plain string.
		401
		402	if (ref $self->[2][0]) {
		403	# send fh
		404	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		405	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		406	undef $self->[3];
		407	die "AnyEvent::Fork: file descriptor send failure: $!";
		408	}
		409
		410	shift @{ $self->[2] };
		411
		412	} else {
		413	# send string
		414	my $len = syswrite $self->[1], $self->[2][0];
		415
		416	unless ($len) {
		417	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		418	undef $self->[3];
		419	die "AnyEvent::Fork: command write failure: $!";
		420	}
		421
		422	substr $self->[2][0], 0, $len, "";
		423	shift @{ $self->[2] } unless length $self->[2][0];
		424	}
		425	} while @{ $self->[2] };
		426
		427	# everything written
		428	undef $self->[3];
		429
		430	# invoke run callback, if any
		431	$self->[4]->($self->[1]) if $self->[4];
		432	};
		433
		434	() # make sure we don't leak the watcher
		435	}
		436
		437	sub _new {
		438	my ($self, $fh, $pid) = @_;
		439
		440	AnyEvent::Util::fh_nonblocking $fh, 1;
		441
		442	$self = bless [
182	$pid,	443	$pid,
183	$fh,	444	$fh,
184	[],	445	[], # write queue - strings or fd's
185	undef	446	undef, # AE watcher
186	]	447	], $self;
187	}
188		448
189	sub queue_cmd {	449	$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	}	450	}
208		451
209	sub run_template {	452	# fork template from current process, used by AnyEvent::Fork::Early/Template
210	return if $template;	453	sub _new_fork {
211
212	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	454	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
213	AnyEvent::Util::fh_nonblocking $fh, 1;	455	my $parent = $$;
214	fd_inherit fileno $slave;
215		456
216	my %env = %ENV;	457	my $pid = fork;
217	$env{PERL5LIB} = join ":", grep !ref, @INC;
218		458
219	my $pid = spawn	459	if ($pid eq 0) {
220	$^X,	460	require AnyEvent::Fork::Serve;
221	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	461	$AnyEvent::Fork::Serve::OWNER = $parent;
222	[map "$_=$env{$_}", keys %env],	462	close $fh;
223	or die "unable to spawn AnyEvent::ProcessPool server: $!";	463	$0 = "$_[1] of $parent";
		464	AnyEvent::Fork::Serve::serve ($slave);
		465	exit 0;
		466	} elsif (!$pid) {
		467	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		468	}
224		469
225	close $slave;	470	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	}	471	}
		472
		473	=item my $proc = new AnyEvent::Fork
		474
		475	Create a new "empty" perl interpreter process and returns its process
		476	object for further manipulation.
		477
		478	The new process is forked from a template process that is kept around
		479	for this purpose. When it doesn't exist yet, it is created by a call to
		480	C<new_exec> first and then stays around for future calls.
		481
		482	=cut
238		483
239	sub new {	484	sub new {
240	my $class = shift;	485	my $class = shift;
241		486
242	my $self = bless {	487	$TEMPLATE \|\|= $class->new_exec;
243	@_	488	$TEMPLATE->fork
244	}, $class;	489	}
245		490
246	run_template;	491	=item $new_proc = $proc->fork
		492
		493	Forks C<$proc>, creating a new process, and returns the process object
		494	of the new process.
		495
		496	If any of the C<send_> functions have been called before fork, then they
		497	will be cloned in the child. For example, in a pre-forked server, you
		498	might C<send_fh> the listening socket into the template process, and then
		499	keep calling C<fork> and C<run>.
		500
		501	=cut
		502
		503	sub fork {
		504	my ($self) = @_;
		505
		506	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		507
		508	$self->send_fh ($slave);
		509	$self->_cmd ("f");
		510
		511	AnyEvent::Fork->_new ($fh)
		512	}
		513
		514	=item my $proc = new_exec AnyEvent::Fork
		515
		516	Create a new "empty" perl interpreter process and returns its process
		517	object for further manipulation.
		518
		519	Unlike the C<new> method, this method I<always> spawns a new perl process
		520	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
		521	reduces the amount of memory sharing that is possible, and is also slower.
		522
		523	You should use C<new> whenever possible, except when having a template
		524	process around is unacceptable.
		525
		526	The path to the perl interpreter is divined using various methods - first
		527	C<$^X> is investigated to see if the path ends with something that sounds
		528	as if it were the perl interpreter. Failing this, the module falls back to
		529	using C<$Config::Config{perlpath}>.
		530
		531	=cut
		532
		533	sub new_exec {
		534	my ($self) = @_;
		535
		536	return $EARLY->fork
		537	if $EARLY;
		538
		539	# first find path of perl
		540	my $perl = $;
		541
		542	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		543	# that looks like perl. this obviously only works for posix and win32
		544	unless (
		545	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		546	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		547	) {
		548	# if it doesn't look perlish enough, try Config
		549	require Config;
		550	$perl = $Config::Config{perlpath};
		551	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		552	}
		553
		554	require Proc::FastSpawn;
		555
		556	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		557	Proc::FastSpawn::fd_inherit (fileno $slave);
		558
		559	# new fh's should always be set cloexec (due to $^F),
		560	# but hey, not on win32, so we always clear the inherit flag.
		561	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		562
		563	# quick. also doesn't work in win32. of course. what did you expect
		564	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		565	my %env = %ENV;
		566	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		567
		568	my $pid = Proc::FastSpawn::spawn (
		569	$perl,
		570	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		571	[map "$_=$env{$_}", keys %env],
		572	) or die "unable to spawn AnyEvent::Fork server: $!";
		573
		574	$self->_new ($fh, $pid)
		575	}
		576
		577	=item $pid = $proc->pid
		578
		579	Returns the process id of the process I<iff it is a direct child of the
		580	process running AnyEvent::Fork>, and C<undef> otherwise.
		581
		582	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		583	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		584	to clean up their zombies when they die.
		585
		586	All other processes are not direct children, and will be cleaned up by
		587	AnyEvent::Fork itself.
		588
		589	=cut
		590
		591	sub pid {
		592	$_[0][0]
		593	}
		594
		595	=item $proc = $proc->eval ($perlcode, @args)
		596
		597	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		598	the strings specified by C<@args>, in the "main" package.
		599
		600	This call is meant to do any custom initialisation that might be required
		601	(for example, the C<require> method uses it). It's not supposed to be used
		602	to completely take over the process, use C<run> for that.
		603
		604	The code will usually be executed after this call returns, and there is no
		605	way to pass anything back to the calling process. Any evaluation errors
		606	will be reported to stderr and cause the process to exit.
		607
		608	If you want to execute some code (that isn't in a module) to take over the
		609	process, you should compile a function via C<eval> first, and then call
		610	it via C<run>. This also gives you access to any arguments passed via the
		611	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		612	a faster fork+exec> example to see it in action.
		613
		614	Returns the process object for easy chaining of method calls.
		615
		616	=cut
		617
		618	sub eval {
		619	my ($self, $code, @args) = @_;
		620
		621	$self->_cmd (e => pack "(w/a)", $code, @args);
247		622
248	$self	623	$self
249	}	624	}
250		625
		626	=item $proc = $proc->require ($module, ...)
		627
		628	Tries to load the given module(s) into the process
		629
		630	Returns the process object for easy chaining of method calls.
		631
		632	=cut
		633
		634	sub require {
		635	my ($self, @modules) = @_;
		636
		637	s%::%/%g for @modules;
		638	$self->eval ('require "$_.pm" for @_', @modules);
		639
		640	$self
		641	}
		642
		643	=item $proc = $proc->send_fh ($handle, ...)
		644
		645	Send one or more file handles (I<not> file descriptors) to the process,
		646	to prepare a call to C<run>.
		647
		648	The process object keeps a reference to the handles until they have
		649	been passed over to the process, so you must not explicitly close the
		650	handles. This is most easily accomplished by simply not storing the file
		651	handles anywhere after passing them to this method - when AnyEvent::Fork
		652	is finished using them, perl will automatically close them.
		653
		654	Returns the process object for easy chaining of method calls.
		655
		656	Example: pass a file handle to a process, and release it without
		657	closing. It will be closed automatically when it is no longer used.
		658
		659	$proc->send_fh ($my_fh);
		660	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		661
		662	=cut
		663
		664	sub send_fh {
		665	my ($self, @fh) = @_;
		666
		667	for my $fh (@fh) {
		668	$self->_cmd ("h");
		669	push @{ $self->[2] }, \$fh;
		670	}
		671
		672	$self
		673	}
		674
		675	=item $proc = $proc->send_arg ($string, ...)
		676
		677	Send one or more argument strings to the process, to prepare a call to
		678	C<run>. The strings can be any octet strings.
		679
		680	The protocol is optimised to pass a moderate number of relatively short
		681	strings - while you can pass up to 4GB of data in one go, this is more
		682	meant to pass some ID information or other startup info, not big chunks of
		683	data.
		684
		685	Returns the process object for easy chaining of method calls.
		686
		687	=cut
		688
		689	sub send_arg {
		690	my ($self, @arg) = @_;
		691
		692	$self->_cmd (a => pack "(w/a)", @arg);
		693
		694	$self
		695	}
		696
		697	=item $proc->run ($func, $cb->($fh))
		698
		699	Enter the function specified by the function name in C<$func> in the
		700	process. The function is called with the communication socket as first
		701	argument, followed by all file handles and string arguments sent earlier
		702	via C<send_fh> and C<send_arg> methods, in the order they were called.
		703
		704	The process object becomes unusable on return from this function - any
		705	further method calls result in undefined behaviour.
		706
		707	The function name should be fully qualified, but if it isn't, it will be
		708	looked up in the C<main> package.
		709
		710	If the called function returns, doesn't exist, or any error occurs, the
		711	process exits.
		712
		713	Preparing the process is done in the background - when all commands have
		714	been sent, the callback is invoked with the local communications socket
		715	as argument. At this point you can start using the socket in any way you
		716	like.
		717
		718	If the communication socket isn't used, it should be closed on both sides,
		719	to save on kernel memory.
		720
		721	The socket is non-blocking in the parent, and blocking in the newly
		722	created process. The close-on-exec flag is set in both.
		723
		724	Even if not used otherwise, the socket can be a good indicator for the
		725	existence of the process - if the other process exits, you get a readable
		726	event on it, because exiting the process closes the socket (if it didn't
		727	create any children using fork).
		728
		729	Example: create a template for a process pool, pass a few strings, some
		730	file handles, then fork, pass one more string, and run some code.
		731
		732	my $pool = AnyEvent::Fork
		733	->new
		734	->send_arg ("str1", "str2")
		735	->send_fh ($fh1, $fh2);
		736
		737	for (1..2) {
		738	$pool
		739	->fork
		740	->send_arg ("str3")
		741	->run ("Some::function", sub {
		742	my ($fh) = @_;
		743
		744	# fh is nonblocking, but we trust that the OS can accept these
		745	# few octets anyway.
		746	syswrite $fh, "hi #$_\n";
		747
		748	# $fh is being closed here, as we don't store it anywhere
		749	});
		750	}
		751
		752	# Some::function might look like this - all parameters passed before fork
		753	# and after will be passed, in order, after the communications socket.
		754	sub Some::function {
		755	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		756
		757	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		758	}
		759
		760	=cut
		761
		762	sub run {
		763	my ($self, $func, $cb) = @_;
		764
		765	$self->[4] = $cb;
		766	$self->_cmd (r => $func);
		767	}
		768
251	=back	769	=back
		770
		771	=head1 PERFORMANCE
		772
		773	Now for some unscientific benchmark numbers (all done on an amd64
		774	GNU/Linux box). These are intended to give you an idea of the relative
		775	performance you can expect, they are not meant to be absolute performance
		776	numbers.
		777
		778	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		779	exit in the child and waits for the socket to close in the parent. I did
		780	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		781
		782	2079 new processes per second, using manual socketpair + fork
		783
		784	Then I did the same thing, but instead of calling fork, I called
		785	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		786	socket form the child to close on exit. This does the same thing as manual
		787	socket pair + fork, except that what is forked is the template process
		788	(2440kB), and the socket needs to be passed to the server at the other end
		789	of the socket first.
		790
		791	2307 new processes per second, using AnyEvent::Fork->new
		792
		793	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		794	a new perl interpreter and compile the small server each time, I get:
		795
		796	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		797
		798	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		799	though it uses the same operations, but adds a lot of overhead?
		800
		801	The difference is simply the process size: forking the 5MB process takes
		802	so much longer than forking the 2.5MB template process that the extra
		803	overhead introduced is canceled out.
		804
		805	If the benchmark process grows, the normal fork becomes even slower:
		806
		807	1340 new processes, manual fork of a 20MB process
		808	731 new processes, manual fork of a 200MB process
		809	235 new processes, manual fork of a 2000MB process
		810
		811	What that means (to me) is that I can use this module without having a bad
		812	conscience because of the extra overhead required to start new processes.
		813
		814	=head1 TYPICAL PROBLEMS
		815
		816	This section lists typical problems that remain. I hope by recognising
		817	them, most can be avoided.
		818
		819	=over 4
		820
		821	=item leaked file descriptors for exec'ed processes
		822
		823	POSIX systems inherit file descriptors by default when exec'ing a new
		824	process. While perl itself laudably sets the close-on-exec flags on new
		825	file handles, most C libraries don't care, and even if all cared, it's
		826	often not possible to set the flag in a race-free manner.
		827
		828	That means some file descriptors can leak through. And since it isn't
		829	possible to know which file descriptors are "good" and "necessary" (or
		830	even to know which file descriptors are open), there is no good way to
		831	close the ones that might harm.
		832
		833	As an example of what "harm" can be done consider a web server that
		834	accepts connections and afterwards some module uses AnyEvent::Fork for the
		835	first time, causing it to fork and exec a new process, which might inherit
		836	the network socket. When the server closes the socket, it is still open
		837	in the child (which doesn't even know that) and the client might conclude
		838	that the connection is still fine.
		839
		840	For the main program, there are multiple remedies available -
		841	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		842	C<new_exec> is another, as in both cases, the first process can be exec'ed
		843	well before many random file descriptors are open.
		844
		845	In general, the solution for these kind of problems is to fix the
		846	libraries or the code that leaks those file descriptors.
		847
		848	Fortunately, most of these leaked descriptors do no harm, other than
		849	sitting on some resources.
		850
		851	=item leaked file descriptors for fork'ed processes
		852
		853	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		854	which closes file descriptors not marked for being inherited.
		855
		856	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		857	a way to create these processes by forking, and this leaks more file
		858	descriptors than exec'ing them, as there is no way to mark descriptors as
		859	"close on fork".
		860
		861	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		862	pipes for internal uses, and L<Gtk2> might open a connection to the X
		863	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		864	trouble with a fork.
		865
		866	The solution is to either not load these modules before use'ing
		867	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		868	initialising them, for example, by calling C<init Gtk2> manually.
		869
		870	=item exiting calls object destructors
		871
		872	This only applies to users of L<AnyEvent::Fork:Early> and
		873	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		874	that reference external resources.
		875
		876	When a process created by AnyEvent::Fork exits, it might do so by calling
		877	exit, or simply letting perl reach the end of the program. At which point
		878	Perl runs all destructors.
		879
		880	Not all destructors are fork-safe - for example, an object that represents
		881	the connection to an X display might tell the X server to free resources,
		882	which is inconvenient when the "real" object in the parent still needs to
		883	use them.
		884
		885	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		886	it as the very first thing, right?
		887
		888	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		889	is to not create objects with nontrivial destructors that might have an
		890	effect outside of Perl.
		891
		892	=back
		893
		894	=head1 PORTABILITY NOTES
		895
		896	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		897	and ::Template is not going to work), and it cost a lot of blood and sweat
		898	to make it so, mostly due to the bloody broken perl that nobody seems to
		899	care about. The fork emulation is a bad joke - I have yet to see something
		900	useful that you can do with it without running into memory corruption
		901	issues or other braindamage. Hrrrr.
		902
		903	Cygwin perl is not supported at the moment due to some hilarious
		904	shortcomings of its API - see L<IO::FDPoll> for more details.
		905
		906	=head1 SEE ALSO
		907
		908	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		909	L<AnyEvent::Fork::Template> (to create a process by forking the main
		910	program at a convenient time).
252		911
253	=head1 AUTHOR	912	=head1 AUTHOR
254		913
255	Marc Lehmann <schmorp@schmorp.de>	914	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	915	http://home.schmorp.de/

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Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC