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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.4 by root, Wed Apr 3 07:35:57 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

…		…
3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't	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::Fork;	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 new processes, without actually forking	18	This module allows you to create new processes, without actually forking
12	them from your current process (avoiding the problems of forking), but	19	them from your current process (avoiding the problems of forking), but
13	preserving most of the advantages of fork.	20	preserving most of the advantages of fork.
14		21
15	It can be used to create new worker processes or new independent	22	It can be used to create new worker processes or new independent
16	subprocesses for short- and long-running jobs, process pools (e.g. for use	23	subprocesses for short- and long-running jobs, process pools (e.g. for use
17	in pre-forked servers) but also to spawn new external processes (such as	24	in pre-forked servers) but also to spawn new external processes (such as
18	CGI scripts from a webserver), which can be faster (and more well behaved)	25	CGI scripts from a web server), which can be faster (and more well behaved)
19	than using fork+exec in big processes.	26	than using fork+exec in big processes.
20		27
		28	Special care has been taken to make this module useful from other modules,
		29	while still supporting specialised environments such as L<App::Staticperl>
		30	or L<PAR::Packer>.
		31
		32	=head2 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		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
21	=head1 PROBLEM STATEMENT	63	=head2 PROBLEM STATEMENT
22		64
23	There are two ways to implement parallel processing on UNIX like operating	65	There are two traditional ways to implement parallel processing on UNIX
24	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
25	advantages and disadvantages that I describe below, together with how this	67	have different advantages and disadvantages that I describe below,
26	module tries to mitigate the disadvantages.	68	together with how this module tries to mitigate the disadvantages.
27		69
28	=over 4	70	=over 4
29		71
30	=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.
31	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
32	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
33	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.
34		78
35	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,
36	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.
37		82
38	=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
39	process. Memory (for example, modules or data files that have been	84	process.
40	will not take additional memory). When exec'ing a new process, modules	85
41	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
42	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
43	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
44	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.
45		96
46	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
47	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
48	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
49	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
50	memory usage.	101	memory usage.
51		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
52	=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
53	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
54	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.
55	might run into problems when perl is upgraded for example.
56		110
57	This module supports creating pre-initialised perl processes to be used
58	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
59	interpreter. With a cooperative main program, exec'ing the interpreter	112	interpreter. With a cooperative main program, exec'ing the interpreter
60	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.
61		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
62	=item Forking might be impossible when a program is running. For example,	127	=item Forking might be impossible when a program is running.
63	POSIX makes it almost impossible to fork from a multithreaded program and
64	do anything useful in the child - strictly speaking, if your perl program
65	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
66	you cannot call fork on the perl level anymore, at all.
67		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
68	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
69	fork+exec in C, in a POSIX-compatible way.	137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
70		138
71	=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
72	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
73	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
74	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
75	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
76	whether another module or the main program also does, leading to problems.	146	or the main program also does, leading to problems.
77		147
78	This module only lets the main program create pools by forking (because	148	Apart from event loops, graphical toolkits also commonly fall into the
79	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
80	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
81	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.
82		158
83	=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 = $cv->recv;
84		250
85	=head1 CONCEPTS	251	=head1 CONCEPTS
86		252
87	This module can create new processes either by executing a new perl	253	This module can create new processes either by executing a new perl
88	process, or by forking from an existing "template" process.	254	process, or by forking from an existing "template" process.
…		…
105	needed the first time. Forking from this process shares the memory used	271	needed the first time. Forking from this process shares the memory used
106	for the perl interpreter with the new process, but loading modules takes	272	for the perl interpreter with the new process, but loading modules takes
107	time, and the memory is not shared with anything else.	273	time, and the memory is not shared with anything else.
108		274
109	This is ideal for when you only need one extra process of a kind, with the	275	This is ideal for when you only need one extra process of a kind, with the
110	option of starting and stipping it on demand.	276	option of starting and stopping it on demand.
		277
		278	Example:
		279
		280	AnyEvent::Fork
		281	->new
		282	->require ("Some::Module")
		283	->run ("Some::Module::run", sub {
		284	my ($fork_fh) = @_;
		285	});
111		286
112	=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
113	it and run the code	288	it and run the code
114		289
115	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
…		…
121	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
122	consumes relatively little memory of its own.	297	consumes relatively little memory of its own.
123		298
124	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
125	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
126	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
127	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 $template around to fork new processes
		315	# later, or you can destroy it, which causes it to vanish.
128		316
129	=item execute a new perl interpreter, load some code, run it	317	=item execute a new perl interpreter, load some code, run it
130		318
131	This is relatively slow, and doesn't allow you to share memory between	319	This is relatively slow, and doesn't allow you to share memory between
132	multiple processes.	320	multiple processes.
…		…
134	The only advantage is that you don't have to have a template process	322	The only advantage is that you don't have to have a template process
135	hanging around all the time to fork off some new processes, which might be	323	hanging around all the time to fork off some new processes, which might be
136	an advantage when there are long time spans where no extra processes are	324	an advantage when there are long time spans where no extra processes are
137	needed.	325	needed.
138		326
		327	Example:
		328
		329	AnyEvent::Fork
		330	->new_exec
		331	->require ("Some::Module")
		332	->run ("Some::Module::run", sub {
		333	my ($fork_fh) = @_;
		334	});
		335
139	=back	336	=back
140		337
141	=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.
142		358
143	=over 4	359	=over 4
144		360
145	=cut	361	=cut
146		362
147	package AnyEvent::Fork;	363	package AnyEvent::Fork;
148		364
149	use common::sense;	365	use common::sense;
150		366
151	use Socket ();	367	use Errno ();
152		368
153	use AnyEvent;	369	use AnyEvent;
154	use AnyEvent::Fork::Util;
155	use AnyEvent::Util ();	370	use AnyEvent::Util ();
156		371
		372	use IO::FDPass;
		373
		374	our $VERSION = 0.5;
		375
157	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	376	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
158		377
159	=item my $pool = new AnyEvent::Fork key => value...
160
161	Create a new process pool. The following named parameters are supported:
162
163	=over 4	378	=over 4
164		379
165	=back	380	=back
166		381
167	=cut	382	=cut
		383
		384	# the early fork template process
		385	our $EARLY;
168		386
169	# the empty template process	387	# the empty template process
170	our $TEMPLATE;	388	our $TEMPLATE;
171		389
172	sub _cmd {	390	sub _cmd {
173	my $self = shift;	391	my $self = shift;
174		392
175	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	393	# ideally, we would want to use "a (w/a)*" as format string, but perl
176	# form at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	394	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
177	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	395	# it.
		396	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
178		397
179	$self->[3] \|\|= AE::io $self->[1], 1, sub {	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
180	if (ref $self->[2][0]) {	403	if (ref $self->[2][0]) {
		404	# send fh
181	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	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
182	and shift @{ $self->[2] };	411	shift @{ $self->[2] };
		412
183	} else {	413	} else {
		414	# send string
184	my $len = syswrite $self->[1], $self->[2][0]	415	my $len = syswrite $self->[1], $self->[2][0];
		416
		417	unless ($len) {
		418	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		419	undef $self->[3];
185	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	420	die "AnyEvent::Fork: command write failure: $!";
		421	}
		422
186	substr $self->[2][0], 0, $len, "";	423	substr $self->[2][0], 0, $len, "";
187	shift @{ $self->[2] } unless length $self->[2][0];	424	shift @{ $self->[2] } unless length $self->[2][0];
188	}	425	}
		426	} while @{ $self->[2] };
189		427
190	unless (@{ $self->[2] }) {	428	# everything written
191	undef $self->[3];	429	undef $self->[3];
		430
		431	# invoke run callback, if any
192	$self->[0]->($self->[1]) if $self->[0];	432	$self->[4]->($self->[1]) if $self->[4];
193	}
194	};	433	};
		434
		435	() # make sure we don't leak the watcher
195	}	436	}
196		437
197	sub _new {	438	sub _new {
198	my ($self, $fh) = @_;	439	my ($self, $fh, $pid) = @_;
		440
		441	AnyEvent::Util::fh_nonblocking $fh, 1;
199		442
200	$self = bless [	443	$self = bless [
201	undef, # run callback	444	$pid,
202	$fh,	445	$fh,
203	[], # write queue - strings or fd's	446	[], # write queue - strings or fd's
204	undef, # AE watcher	447	undef, # AE watcher
205	], $self;	448	], $self;
206		449
207	# my ($a, $b) = AnyEvent::Util::portable_socketpair;
208
209	# queue_cmd $template, "Iabc";
210	# push @{ $template->[2] }, \$b;
211
212	# use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
213	# undef $b;
214	# die "x" . <$a>;
215
216	$self	450	$self
		451	}
		452
		453	# fork template from current process, used by AnyEvent::Fork::Early/Template
		454	sub _new_fork {
		455	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		456	my $parent = $$;
		457
		458	my $pid = fork;
		459
		460	if ($pid eq 0) {
		461	require AnyEvent::Fork::Serve;
		462	$AnyEvent::Fork::Serve::OWNER = $parent;
		463	close $fh;
		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	}
		471
		472	AnyEvent::Fork->_new ($fh, $pid)
217	}	473	}
218		474
219	=item my $proc = new AnyEvent::Fork	475	=item my $proc = new AnyEvent::Fork
220		476
221	Create a new "empty" perl interpreter process and returns its process	477	Create a new "empty" perl interpreter process and returns its process
222	object for further manipulation.	478	object for further manipulation.
223		479
224	The new process is forked from a template process that is kept around	480	The new process is forked from a template process that is kept around
225	for this purpose. When it doesn't exist yet, it is created by a call to	481	for this purpose. When it doesn't exist yet, it is created by a call to
226	C<new_exec> and kept around for future calls.	482	C<new_exec> first and then stays around for future calls.
227		483
228	=cut	484	=cut
229		485
230	sub new {	486	sub new {
231	my $class = shift;	487	my $class = shift;
…		…
252	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	508	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
253		509
254	$self->send_fh ($slave);	510	$self->send_fh ($slave);
255	$self->_cmd ("f");	511	$self->_cmd ("f");
256		512
257	AnyEvent::Util::fh_nonblocking $fh, 1;
258
259	AnyEvent::Fork->_new ($fh)	513	AnyEvent::Fork->_new ($fh)
260	}	514	}
261		515
262	=item my $proc = new_exec AnyEvent::Fork	516	=item my $proc = new_exec AnyEvent::Fork
263		517
…		…
269	reduces the amount of memory sharing that is possible, and is also slower.	523	reduces the amount of memory sharing that is possible, and is also slower.
270		524
271	You should use C<new> whenever possible, except when having a template	525	You should use C<new> whenever possible, except when having a template
272	process around is unacceptable.	526	process around is unacceptable.
273		527
274	The path to the perl interpreter is divined usign various methods - first	528	The path to the perl interpreter is divined using various methods - first
275	C<$^X> is investigated to see if the path ends with something that sounds	529	C<$^X> is investigated to see if the path ends with something that sounds
276	as if it were the perl interpreter. Failing this, the module falls back to	530	as if it were the perl interpreter. Failing this, the module falls back to
277	using C<$Config::Config{perlpath}>.	531	using C<$Config::Config{perlpath}>.
278		532
279	=cut	533	=cut
280		534
281	sub new_exec {	535	sub new_exec {
282	my ($self) = @_;	536	my ($self) = @_;
283		537
		538	return $EARLY->fork
		539	if $EARLY;
		540
284	# first find path of perl	541	# first find path of perl
285	my $perl = $;	542	my $perl = $;
286		543
287	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	544	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
288	# that looks like perl. this obviously only works for posix and win32	545	# that looks like perl. this obviously only works for posix and win32
289	unless (	546	unless (
290	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	547	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
291	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	548	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
292	) {	549	) {
293	# if it doesn't look perlish enough, try Config	550	# if it doesn't look perlish enough, try Config
294	require Config;	551	require Config;
295	$perl = $Config::Config{perlpath};	552	$perl = $Config::Config{perlpath};
…		…
297	}	554	}
298		555
299	require Proc::FastSpawn;	556	require Proc::FastSpawn;
300		557
301	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	558	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
302	AnyEvent::Util::fh_nonblocking $fh, 1;
303	Proc::FastSpawn::fd_inherit (fileno $slave);	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);
304		564
305	# quick. also doesn't work in win32. of course. what did you expect	565	# quick. also doesn't work in win32. of course. what did you expect
306	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	566	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
307	my %env = %ENV;	567	my %env = %ENV;
308	$env{PERL5LIB} = join ":", grep !ref, @INC;	568	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
309		569
310	Proc::FastSpawn::spawn (	570	my $pid = Proc::FastSpawn::spawn (
311	$perl,	571	$perl,
312	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],	572	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
313	[map "$_=$env{$_}", keys %env],	573	[map "$_=$env{$_}", keys %env],
314	) or die "unable to spawn AnyEvent::Fork server: $!";	574	) or die "unable to spawn AnyEvent::Fork server: $!";
315		575
316	$self->_new ($fh)	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);
		624
		625	$self
317	}	626	}
318		627
319	=item $proc = $proc->require ($module, ...)	628	=item $proc = $proc->require ($module, ...)
320		629
321	Tries to load the given modules into the process	630	Tries to load the given module(s) into the process
322		631
323	Returns the process object for easy chaining of method calls.	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	}
324		644
325	=item $proc = $proc->send_fh ($handle, ...)	645	=item $proc = $proc->send_fh ($handle, ...)
326		646
327	Send one or more file handles (I<not> file descriptors) to the process,	647	Send one or more file handles (I<not> file descriptors) to the process,
328	to prepare a call to C<run>.	648	to prepare a call to C<run>.
329		649
330	The process object keeps a reference to the handles until this is done,	650	The process object keeps a reference to the handles until they have
331	so you must not explicitly close the handles. This is most easily	651	been passed over to the process, so you must not explicitly close the
332	accomplished by simply not storing the file handles anywhere after passing	652	handles. This is most easily accomplished by simply not storing the file
333	them to this method.	653	handles anywhere after passing them to this method - when AnyEvent::Fork
		654	is finished using them, perl will automatically close them.
334		655
335	Returns the process object for easy chaining of method calls.	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 $my_fh; # free the reference if you want, but DO NOT CLOSE IT
336		663
337	=cut	664	=cut
338		665
339	sub send_fh {	666	sub send_fh {
340	my ($self, @fh) = @_;	667	my ($self, @fh) = @_;
…		…
348	}	675	}
349		676
350	=item $proc = $proc->send_arg ($string, ...)	677	=item $proc = $proc->send_arg ($string, ...)
351		678
352	Send one or more argument strings to the process, to prepare a call to	679	Send one or more argument strings to the process, to prepare a call to
353	C<run>. The strings can be any octet string.	680	C<run>. The strings can be any octet strings.
354		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
355	Returns the process object for easy chaining of emthod calls.	687	Returns the process object for easy chaining of method calls.
356		688
357	=cut	689	=cut
358		690
359	sub send_arg {	691	sub send_arg {
360	my ($self, @arg) = @_;	692	my ($self, @arg) = @_;
361		693
362	$self->_cmd (a => @arg);	694	$self->_cmd (a => pack "(w/a)", @arg);
363		695
364	$self	696	$self
365	}	697	}
366		698
367	=item $proc->run ($func, $cb->($fh))	699	=item $proc->run ($func, $cb->($fh))
368		700
369	Enter the function specified by the fully qualified name in C<$func> in	701	Enter the function specified by the function name in C<$func> in the
370	the process. The function is called with the communication socket as first	702	process. The function is called with the communication socket as first
371	argument, followed by all file handles and string arguments sent earlier	703	argument, followed by all file handles and string arguments sent earlier
372	via C<send_fh> and C<send_arg> methods, in the order they were called.	704	via C<send_fh> and C<send_arg> methods, in the order they were called.
373		705
374	If the called function returns, the process exits.
375
376	Preparing the process can take time - when the process is ready, the
377	callback is invoked with the local communications socket as argument.
378
379	The process object becomes unusable on return from this function.	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.
380		719
381	If the communication socket isn't used, it should be closed on both sides,	720	If the communication socket isn't used, it should be closed on both sides,
382	to save on kernel memory.	721	to save on kernel memory.
383		722
384	The socket is non-blocking in the parent, and blocking in the newly	723	The socket is non-blocking in the parent, and blocking in the newly
385	created process. The close-on-exec flag is set on both. Even if not used	724	created process. The close-on-exec flag is set in both.
		725
386	otherwise, the socket can be a good indicator for the existance of the	726	Even if not used otherwise, the socket can be a good indicator for the
387	process - if the othe rprocess exits, you get a readable event on it,	727	existence of the process - if the other process exits, you get a readable
388	because exiting the process closes the socket (if it didn't create any	728	event on it, because exiting the process closes the socket (if it didn't
389	children using fork).	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	}
390		761
391	=cut	762	=cut
392		763
393	sub run {	764	sub run {
394	my ($self, $func, $cb) = @_;	765	my ($self, $func, $cb) = @_;
395		766
396	$self->[0] = $cb;	767	$self->[4] = $cb;
397	$self->_cmd ("r", $func);	768	$self->_cmd (r => $func);
398	}	769	}
399		770
400	=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).
401		913
402	=head1 AUTHOR	914	=head1 AUTHOR
403		915
404	Marc Lehmann <schmorp@schmorp.de>	916	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/	917	http://home.schmorp.de/

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.4 by root, Wed Apr 3 07:35:57 2013 UTC vs. Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

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Revision 1.4 by root, Wed Apr 3 07:35:57 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC