[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 1.33 by root, Sat Apr 6 09:34:11 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	=head1 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
21	=head1 PROBLEM STATEMENT	45	=head1 PROBLEM STATEMENT
22		46
23	There are two ways to implement parallel processing on UNIX like operating	47	There are two traditional ways to implement parallel processing on UNIX
24	systems - fork and process, and fork+exec and process. They have different	48	like operating systems - fork and process, and fork+exec and process. They
25	advantages and disadvantages that I describe below, together with how this	49	have different advantages and disadvantages that I describe below,
26	module tries to mitigate the disadvantages.	50	together with how this module tries to mitigate the disadvantages.
27		51
28	=over 4	52	=over 4
29		53
30	=item Forking from a big process can be very slow (a 5GB process needs	54	=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	55
		56	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	57	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.	58	in some circumstances (e.g. when vfork is used), fork+exec can be much
		59	faster.
34		60
35	This module can help here by telling a small(er) helper process to fork,	61	This module can help here by telling a small(er) helper process to fork,
36	or fork+exec instead.	62	which is faster then forking the main process, and also uses vfork where
		63	possible. This gives the speed of vfork, with the flexibility of fork.
37		64
38	=item Forking usually creates a copy-on-write copy of the parent	65	=item Forking usually creates a copy-on-write copy of the parent
39	process. Memory (for example, modules or data files that have been	66	process.
40	will not take additional memory). When exec'ing a new process, modules	67
41	and data files might need to be loaded again, at extra cpu and memory	68	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	69	memory after a fork. When exec'ing a new process, modules and data files
		70	might need to be loaded again, at extra CPU and memory cost. But when
		71	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	72	them and replaces them by new data, the child processes will retain the
44	will retain the memory even if it isn't used.	73	old version even if it isn't used, which can suddenly and unexpectedly
		74	increase memory usage when freeing memory.
		75
		76	The trade-off is between more sharing with fork (which can be good or
		77	bad), and no sharing with exec.
45		78
46	This module allows the main program to do a controlled fork, and allows	79	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	80	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	81	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	82	risking to share large dynamic data structures that will blow up child
50	memory usage.	83	memory usage.
51		84
		85	In other words, this module puts you into control over what is being
		86	shared and what isn't, at all times.
		87
52	=item Exec'ing a new perl process might be difficult and slow. For	88	=item Exec'ing a new perl process might be difficult.
		89
53	example, it is not easy to find the correct path to the perl interpreter,	90	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	91	interpreter - C<$^X> might not be a perl interpreter at all.
55	might run into problems when perl is upgraded for example.
56		92
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	93	This module tries hard to identify the correct path to the perl
59	interpreter. With a cooperative main program, exec'ing the interpreter	94	interpreter. With a cooperative main program, exec'ing the interpreter
60	might not even be necessary.	95	might not even be necessary, but even without help from the main program,
		96	it will still work when used from a module.
61		97
		98	=item Exec'ing a new perl process might be slow, as all necessary modules
		99	have to be loaded from disk again, with no guarantees of success.
		100
		101	Long running processes might run into problems when perl is upgraded
		102	and modules are no longer loadable because they refer to a different
		103	perl version, or parts of a distribution are newer than the ones already
		104	loaded.
		105
		106	This module supports creating pre-initialised perl processes to be used as
		107	a template for new processes.
		108
62	=item Forking might be impossible when a program is running. For example,	109	=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		110
		111	For example, POSIX makes it almost impossible to fork from a
		112	multi-threaded program while doing anything useful in the child - in
		113	fact, if your perl program uses POSIX threads (even indirectly via
		114	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		115	anymore without risking corruption issues on a number of operating
		116	systems.
		117
68	This module can safely fork helper processes at any time, by caling	118	This module can safely fork helper processes at any time, by calling
69	fork+exec in C, in a POSIX-compatible way.	119	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
70		120
71	=item Parallel processing with fork might be inconvenient or difficult	121	=item Parallel processing with fork might be inconvenient or difficult
		122	to implement. Modules might not work in both parent and child.
		123
72	to implement. For example, when a program uses an event loop and creates	124	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	125	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	126	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	127	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.	128	or the main program also does, leading to problems.
77		129
78	This module only lets the main program create pools by forking (because	130	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	131	"unsafe module" category, or just about anything that communicates with
80	pools are created by fork+exec, after which such modules can again be	132	the external world, such as network libraries and file I/O modules, which
81	loaded.	133	usually don't like being copied and then allowed to continue in two
		134	processes.
		135
		136	With this module only the main program is allowed to create new processes
		137	by forking (because only the main program can know when it is still safe
		138	to do so) - all other processes are created via fork+exec, which makes it
		139	possible to use modules such as event loops or window interfaces safely.
82		140
83	=back	141	=back
		142
		143	=head1 EXAMPLES
		144
		145	=head2 Create a single new process, tell it to run your worker function.
		146
		147	AnyEvent::Fork
		148	->new
		149	->require ("MyModule")
		150	->run ("MyModule::worker, sub {
		151	my ($master_filehandle) = @_;
		152
		153	# now $master_filehandle is connected to the
		154	# $slave_filehandle in the new process.
		155	});
		156
		157	C<MyModule> might look like this:
		158
		159	package MyModule;
		160
		161	sub worker {
		162	my ($slave_filehandle) = @_;
		163
		164	# now $slave_filehandle is connected to the $master_filehandle
		165	# in the original prorcess. have fun!
		166	}
		167
		168	=head2 Create a pool of server processes all accepting on the same socket.
		169
		170	# create listener socket
		171	my $listener = ...;
		172
		173	# create a pool template, initialise it and give it the socket
		174	my $pool = AnyEvent::Fork
		175	->new
		176	->require ("Some::Stuff", "My::Server")
		177	->send_fh ($listener);
		178
		179	# now create 10 identical workers
		180	for my $id (1..10) {
		181	$pool
		182	->fork
		183	->send_arg ($id)
		184	->run ("My::Server::run");
		185	}
		186
		187	# now do other things - maybe use the filehandle provided by run
		188	# to wait for the processes to die. or whatever.
		189
		190	C<My::Server> might look like this:
		191
		192	package My::Server;
		193
		194	sub run {
		195	my ($slave, $listener, $id) = @_;
		196
		197	close $slave; # we do not use the socket, so close it to save resources
		198
		199	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		200	# or anything we usually couldn't do in a process forked normally.
		201	while (my $socket = $listener->accept) {
		202	# do sth. with new socket
		203	}
		204	}
		205
		206	=head2 use AnyEvent::Fork as a faster fork+exec
		207
		208	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
		209	and standard error redirected to the communications socket. It is usually
		210	faster than fork+exec, but still lets you prepare the environment.
		211
		212	open my $output, ">/tmp/log" or die "$!";
		213
		214	AnyEvent::Fork
		215	->new
		216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
		219
		220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
		223
		224	exec @cmd;
		225	}
		226	')
		227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
		230
		231	my $stderr = $cv->recv;
84		232
85	=head1 CONCEPTS	233	=head1 CONCEPTS
86		234
87	This module can create new processes either by executing a new perl	235	This module can create new processes either by executing a new perl
88	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
105	needed the first time. Forking from this process shares the memory used	253	needed the first time. Forking from this process shares the memory used
106	for the perl interpreter with the new process, but loading modules takes	254	for the perl interpreter with the new process, but loading modules takes
107	time, and the memory is not shared with anything else.	255	time, and the memory is not shared with anything else.
108		256
109	This is ideal for when you only need one extra process of a kind, with the	257	This is ideal for when you only need one extra process of a kind, with the
110	option of starting and stipping it on demand.	258	option of starting and stopping it on demand.
		259
		260	Example:
		261
		262	AnyEvent::Fork
		263	->new
		264	->require ("Some::Module")
		265	->run ("Some::Module::run", sub {
		266	my ($fork_fh) = @_;
		267	});
111		268
112	=item fork a new template process, load code, then fork processes off of	269	=item fork a new template process, load code, then fork processes off of
113	it and run the code	270	it and run the code
114		271
115	When you need to have a bunch of processes that all execute the same (or	272	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	278	modules you loaded) is shared between the processes, and each new process
122	consumes relatively little memory of its own.	279	consumes relatively little memory of its own.
123		280
124	The disadvantage of this approach is that you need to create a template	281	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	282	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	283	only need a fixed number of processes you can create them, and then destroy
127	the template process.	284	the template process.
		285
		286	Example:
		287
		288	my $template = AnyEvent::Fork->new->require ("Some::Module");
		289
		290	for (1..10) {
		291	$template->fork->run ("Some::Module::run", sub {
		292	my ($fork_fh) = @_;
		293	});
		294	}
		295
		296	# at this point, you can keep $template around to fork new processes
		297	# later, or you can destroy it, which causes it to vanish.
128		298
129	=item execute a new perl interpreter, load some code, run it	299	=item execute a new perl interpreter, load some code, run it
130		300
131	This is relatively slow, and doesn't allow you to share memory between	301	This is relatively slow, and doesn't allow you to share memory between
132	multiple processes.	302	multiple processes.
…		…
134	The only advantage is that you don't have to have a template process	304	The only advantage is that you don't have to have a template process
135	hanging around all the time to fork off some new processes, which might be	305	hanging around all the time to fork off some new processes, which might be
136	an advantage when there are long time spans where no extra processes are	306	an advantage when there are long time spans where no extra processes are
137	needed.	307	needed.
138		308
		309	Example:
		310
		311	AnyEvent::Fork
		312	->new_exec
		313	->require ("Some::Module")
		314	->run ("Some::Module::run", sub {
		315	my ($fork_fh) = @_;
		316	});
		317
139	=back	318	=back
140		319
141	=head1 FUNCTIONS	320	=head1 THE C<AnyEvent::Fork> CLASS
		321
		322	This module exports nothing, and only implements a single class -
		323	C<AnyEvent::Fork>.
		324
		325	There are two class constructors that both create new processes - C<new>
		326	and C<new_exec>. The C<fork> method creates a new process by forking an
		327	existing one and could be considered a third constructor.
		328
		329	Most of the remaining methods deal with preparing the new process, by
		330	loading code, evaluating code and sending data to the new process. They
		331	usually return the process object, so you can chain method calls.
		332
		333	If a process object is destroyed before calling its C<run> method, then
		334	the process simply exits. After C<run> is called, all responsibility is
		335	passed to the specified function.
		336
		337	As long as there is any outstanding work to be done, process objects
		338	resist being destroyed, so there is no reason to store them unless you
		339	need them later - configure and forget works just fine.
142		340
143	=over 4	341	=over 4
144		342
145	=cut	343	=cut
146		344
147	package AnyEvent::Fork;	345	package AnyEvent::Fork;
148		346
149	use common::sense;	347	use common::sense;
150		348
151	use Socket ();	349	use Errno ();
152		350
153	use AnyEvent;	351	use AnyEvent;
154	use AnyEvent::Fork::Util;
155	use AnyEvent::Util ();	352	use AnyEvent::Util ();
156		353
		354	use IO::FDPass;
		355
		356	our $VERSION = 0.5;
		357
157	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	358	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
158		359
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	360	=over 4
164		361
165	=back	362	=back
166		363
167	=cut	364	=cut
		365
		366	# the early fork template process
		367	our $EARLY;
168		368
169	# the empty template process	369	# the empty template process
170	our $TEMPLATE;	370	our $TEMPLATE;
171		371
172	sub _cmd {	372	sub _cmd {
173	my $self = shift;	373	my $self = shift;
174		374
175	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	375	# 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.	376	# 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)*", @_;	377	# it.
		378	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
178		379
179	$self->[3] \|\|= AE::io $self->[1], 1, sub {	380	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		381	do {
		382	# send the next "thing" in the queue - either a reference to an fh,
		383	# or a plain string.
		384
180	if (ref $self->[2][0]) {	385	if (ref $self->[2][0]) {
		386	# send fh
181	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	387	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		388	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		389	undef $self->[3];
		390	die "AnyEvent::Fork: file descriptor send failure: $!";
		391	}
		392
182	and shift @{ $self->[2] };	393	shift @{ $self->[2] };
		394
183	} else {	395	} else {
		396	# send string
184	my $len = syswrite $self->[1], $self->[2][0]	397	my $len = syswrite $self->[1], $self->[2][0];
		398
		399	unless ($len) {
		400	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		401	undef $self->[3];
185	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	402	die "AnyEvent::Fork: command write failure: $!";
		403	}
		404
186	substr $self->[2][0], 0, $len, "";	405	substr $self->[2][0], 0, $len, "";
187	shift @{ $self->[2] } unless length $self->[2][0];	406	shift @{ $self->[2] } unless length $self->[2][0];
188	}	407	}
		408	} while @{ $self->[2] };
189		409
190	unless (@{ $self->[2] }) {	410	# everything written
191	undef $self->[3];	411	undef $self->[3];
		412
		413	# invoke run callback, if any
192	$self->[0]->($self->[1]) if $self->[0];	414	$self->[4]->($self->[1]) if $self->[4];
193	}
194	};	415	};
		416
		417	() # make sure we don't leak the watcher
195	}	418	}
196		419
197	sub _new {	420	sub _new {
198	my ($self, $fh) = @_;	421	my ($self, $fh, $pid) = @_;
		422
		423	AnyEvent::Util::fh_nonblocking $fh, 1;
199		424
200	$self = bless [	425	$self = bless [
201	undef, # run callback	426	$pid,
202	$fh,	427	$fh,
203	[], # write queue - strings or fd's	428	[], # write queue - strings or fd's
204	undef, # AE watcher	429	undef, # AE watcher
205	], $self;	430	], $self;
206		431
207	# my ($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	432	$self
		433	}
		434
		435	# fork template from current process, used by AnyEvent::Fork::Early/Template
		436	sub _new_fork {
		437	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		438	my $parent = $$;
		439
		440	my $pid = fork;
		441
		442	if ($pid eq 0) {
		443	require AnyEvent::Fork::Serve;
		444	$AnyEvent::Fork::Serve::OWNER = $parent;
		445	close $fh;
		446	$0 = "$_[1] of $parent";
		447	$SIG{CHLD} = 'IGNORE';
		448	AnyEvent::Fork::Serve::serve ($slave);
		449	exit 0;
		450	} elsif (!$pid) {
		451	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		452	}
		453
		454	AnyEvent::Fork->_new ($fh, $pid)
217	}	455	}
218		456
219	=item my $proc = new AnyEvent::Fork	457	=item my $proc = new AnyEvent::Fork
220		458
221	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
222	object for further manipulation.	460	object for further manipulation.
223		461
224	The new process is forked from a template process that is kept around	462	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	463	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.	464	C<new_exec> first and then stays around for future calls.
227		465
228	=cut	466	=cut
229		467
230	sub new {	468	sub new {
231	my $class = shift;	469	my $class = shift;
…		…
252	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	490	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
253		491
254	$self->send_fh ($slave);	492	$self->send_fh ($slave);
255	$self->_cmd ("f");	493	$self->_cmd ("f");
256		494
257	AnyEvent::Util::fh_nonblocking $fh, 1;
258
259	AnyEvent::Fork->_new ($fh)	495	AnyEvent::Fork->_new ($fh)
260	}	496	}
261		497
262	=item my $proc = new_exec AnyEvent::Fork	498	=item my $proc = new_exec AnyEvent::Fork
263		499
…		…
269	reduces the amount of memory sharing that is possible, and is also slower.	505	reduces the amount of memory sharing that is possible, and is also slower.
270		506
271	You should use C<new> whenever possible, except when having a template	507	You should use C<new> whenever possible, except when having a template
272	process around is unacceptable.	508	process around is unacceptable.
273		509
274	The path to the perl interpreter is divined usign various methods - first	510	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	511	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	512	as if it were the perl interpreter. Failing this, the module falls back to
277	using C<$Config::Config{perlpath}>.	513	using C<$Config::Config{perlpath}>.
278		514
279	=cut	515	=cut
280		516
281	sub new_exec {	517	sub new_exec {
282	my ($self) = @_;	518	my ($self) = @_;
283		519
		520	return $EARLY->fork
		521	if $EARLY;
		522
284	# first find path of perl	523	# first find path of perl
285	my $perl = $;	524	my $perl = $;
286		525
287	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	526	# 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	527	# that looks like perl. this obviously only works for posix and win32
289	unless (	528	unless (
290	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	529	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
291	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	530	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
292	) {	531	) {
293	# if it doesn't look perlish enough, try Config	532	# if it doesn't look perlish enough, try Config
294	require Config;	533	require Config;
295	$perl = $Config::Config{perlpath};	534	$perl = $Config::Config{perlpath};
…		…
297	}	536	}
298		537
299	require Proc::FastSpawn;	538	require Proc::FastSpawn;
300		539
301	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	540	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
302	AnyEvent::Util::fh_nonblocking $fh, 1;
303	Proc::FastSpawn::fd_inherit (fileno $slave);	541	Proc::FastSpawn::fd_inherit (fileno $slave);
		542
		543	# new fh's should always be set cloexec (due to $^F),
		544	# but hey, not on win32, so we always clear the inherit flag.
		545	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
304		546
305	# quick. also doesn't work in win32. of course. what did you expect	547	# quick. also doesn't work in win32. of course. what did you expect
306	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	548	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
307	my %env = %ENV;	549	my %env = %ENV;
308	$env{PERL5LIB} = join ":", grep !ref, @INC;	550	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
309		551
310	Proc::FastSpawn::spawn (	552	my $pid = Proc::FastSpawn::spawn (
311	$perl,	553	$perl,
312	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],	554	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
313	[map "$_=$env{$_}", keys %env],	555	[map "$_=$env{$_}", keys %env],
314	) or die "unable to spawn AnyEvent::Fork server: $!";	556	) or die "unable to spawn AnyEvent::Fork server: $!";
315		557
316	$self->_new ($fh)	558	$self->_new ($fh, $pid)
		559	}
		560
		561	=item $pid = $proc->pid
		562
		563	Returns the process id of the process I<iff it is a direct child of the
		564	process running AnyEvent::Fork>, and C<undef> otherwise.
		565
		566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		568	to clean up their zombies when they die.
		569
		570	All other processes are not direct children, and will be cleaned up by
		571	AnyEvent::Fork itself.
		572
		573	=cut
		574
		575	sub pid {
		576	$_[0][0]
		577	}
		578
		579	=item $proc = $proc->eval ($perlcode, @args)
		580
		581	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		582	the strings specified by C<@args>, in the "main" package.
		583
		584	This call is meant to do any custom initialisation that might be required
		585	(for example, the C<require> method uses it). It's not supposed to be used
		586	to completely take over the process, use C<run> for that.
		587
		588	The code will usually be executed after this call returns, and there is no
		589	way to pass anything back to the calling process. Any evaluation errors
		590	will be reported to stderr and cause the process to exit.
		591
		592	If you want to execute some code (that isn't in a module) to take over the
		593	process, you should compile a function via C<eval> first, and then call
		594	it via C<run>. This also gives you access to any arguments passed via the
		595	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		596	a faster fork+exec> example.
		597
		598	Returns the process object for easy chaining of method calls.
		599
		600	=cut
		601
		602	sub eval {
		603	my ($self, $code, @args) = @_;
		604
		605	$self->_cmd (e => pack "(w/a)", $code, @args);
		606
		607	$self
317	}	608	}
318		609
319	=item $proc = $proc->require ($module, ...)	610	=item $proc = $proc->require ($module, ...)
320		611
321	Tries to load the given modules into the process	612	Tries to load the given module(s) into the process
322		613
323	Returns the process object for easy chaining of method calls.	614	Returns the process object for easy chaining of method calls.
		615
		616	=cut
		617
		618	sub require {
		619	my ($self, @modules) = @_;
		620
		621	s%::%/%g for @modules;
		622	$self->eval ('require "$_.pm" for @_', @modules);
		623
		624	$self
		625	}
324		626
325	=item $proc = $proc->send_fh ($handle, ...)	627	=item $proc = $proc->send_fh ($handle, ...)
326		628
327	Send one or more file handles (I<not> file descriptors) to the process,	629	Send one or more file handles (I<not> file descriptors) to the process,
328	to prepare a call to C<run>.	630	to prepare a call to C<run>.
…		…
332	accomplished by simply not storing the file handles anywhere after passing	634	accomplished by simply not storing the file handles anywhere after passing
333	them to this method.	635	them to this method.
334		636
335	Returns the process object for easy chaining of method calls.	637	Returns the process object for easy chaining of method calls.
336		638
		639	Example: pass a file handle to a process, and release it without
		640	closing. It will be closed automatically when it is no longer used.
		641
		642	$proc->send_fh ($my_fh);
		643	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		644
337	=cut	645	=cut
338		646
339	sub send_fh {	647	sub send_fh {
340	my ($self, @fh) = @_;	648	my ($self, @fh) = @_;
341		649
…		…
350	=item $proc = $proc->send_arg ($string, ...)	658	=item $proc = $proc->send_arg ($string, ...)
351		659
352	Send one or more argument strings to the process, to prepare a call to	660	Send one or more argument strings to the process, to prepare a call to
353	C<run>. The strings can be any octet string.	661	C<run>. The strings can be any octet string.
354		662
		663	The protocol is optimised to pass a moderate number of relatively short
		664	strings - while you can pass up to 4GB of data in one go, this is more
		665	meant to pass some ID information or other startup info, not big chunks of
		666	data.
		667
355	Returns the process object for easy chaining of emthod calls.	668	Returns the process object for easy chaining of method calls.
356		669
357	=cut	670	=cut
358		671
359	sub send_arg {	672	sub send_arg {
360	my ($self, @arg) = @_;	673	my ($self, @arg) = @_;
361		674
362	$self->_cmd (a => @arg);	675	$self->_cmd (a => pack "(w/a)", @arg);
363		676
364	$self	677	$self
365	}	678	}
366		679
367	=item $proc->run ($func, $cb->($fh))	680	=item $proc->run ($func, $cb->($fh))
368		681
369	Enter the function specified by the fully qualified name in C<$func> in	682	Enter the function specified by the function name in C<$func> in the
370	the process. The function is called with the communication socket as first	683	process. The function is called with the communication socket as first
371	argument, followed by all file handles and string arguments sent earlier	684	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.	685	via C<send_fh> and C<send_arg> methods, in the order they were called.
373		686
374	If the called function returns, the process exits.	687	The function name should be fully qualified, but if it isn't, it will be
		688	looked up in the main package.
375		689
376	Preparing the process can take time - when the process is ready, the	690	If the called function returns, doesn't exist, or any error occurs, the
		691	process exits.
		692
		693	Preparing the process is done in the background - when all commands have
377	callback is invoked with the local communications socket as argument.	694	been sent, the callback is invoked with the local communications socket
		695	as argument. At this point you can start using the socket in any way you
		696	like.
378		697
379	The process object becomes unusable on return from this function.	698	The process object becomes unusable on return from this function - any
		699	further method calls result in undefined behaviour.
380		700
381	If the communication socket isn't used, it should be closed on both sides,	701	If the communication socket isn't used, it should be closed on both sides,
382	to save on kernel memory.	702	to save on kernel memory.
383		703
384	The socket is non-blocking in the parent, and blocking in the newly	704	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	705	created process. The close-on-exec flag is set in both.
		706
386	otherwise, the socket can be a good indicator for the existance of the	707	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,	708	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	709	event on it, because exiting the process closes the socket (if it didn't
389	children using fork).	710	create any children using fork).
		711
		712	Example: create a template for a process pool, pass a few strings, some
		713	file handles, then fork, pass one more string, and run some code.
		714
		715	my $pool = AnyEvent::Fork
		716	->new
		717	->send_arg ("str1", "str2")
		718	->send_fh ($fh1, $fh2);
		719
		720	for (1..2) {
		721	$pool
		722	->fork
		723	->send_arg ("str3")
		724	->run ("Some::function", sub {
		725	my ($fh) = @_;
		726
		727	# fh is nonblocking, but we trust that the OS can accept these
		728	# few octets anyway.
		729	syswrite $fh, "hi #$_\n";
		730
		731	# $fh is being closed here, as we don't store it anywhere
		732	});
		733	}
		734
		735	# Some::function might look like this - all parameters passed before fork
		736	# and after will be passed, in order, after the communications socket.
		737	sub Some::function {
		738	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		739
		740	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		741	}
390		742
391	=cut	743	=cut
392		744
393	sub run {	745	sub run {
394	my ($self, $func, $cb) = @_;	746	my ($self, $func, $cb) = @_;
395		747
396	$self->[0] = $cb;	748	$self->[4] = $cb;
397	$self->_cmd ("r", $func);	749	$self->_cmd (r => $func);
398	}	750	}
399		751
400	=back	752	=back
		753
		754	=head1 PERFORMANCE
		755
		756	Now for some unscientific benchmark numbers (all done on an amd64
		757	GNU/Linux box). These are intended to give you an idea of the relative
		758	performance you can expect, they are not meant to be absolute performance
		759	numbers.
		760
		761	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		762	exit in the child and waits for the socket to close in the parent. I did
		763	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		764
		765	2079 new processes per second, using manual socketpair + fork
		766
		767	Then I did the same thing, but instead of calling fork, I called
		768	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		769	socket form the child to close on exit. This does the same thing as manual
		770	socket pair + fork, except that what is forked is the template process
		771	(2440kB), and the socket needs to be passed to the server at the other end
		772	of the socket first.
		773
		774	2307 new processes per second, using AnyEvent::Fork->new
		775
		776	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		777	a new perl interpreter and compile the small server each time, I get:
		778
		779	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		780
		781	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		782	though it uses the same operations, but adds a lot of overhead?
		783
		784	The difference is simply the process size: forking the 6MB process takes
		785	so much longer than forking the 2.5MB template process that the overhead
		786	introduced is canceled out.
		787
		788	If the benchmark process grows, the normal fork becomes even slower:
		789
		790	1340 new processes, manual fork in a 20MB process
		791	731 new processes, manual fork in a 200MB process
		792	235 new processes, manual fork in a 2000MB process
		793
		794	What that means (to me) is that I can use this module without having a
		795	very bad conscience because of the extra overhead required to start new
		796	processes.
		797
		798	=head1 TYPICAL PROBLEMS
		799
		800	This section lists typical problems that remain. I hope by recognising
		801	them, most can be avoided.
		802
		803	=over 4
		804
		805	=item "leaked" file descriptors for exec'ed processes
		806
		807	POSIX systems inherit file descriptors by default when exec'ing a new
		808	process. While perl itself laudably sets the close-on-exec flags on new
		809	file handles, most C libraries don't care, and even if all cared, it's
		810	often not possible to set the flag in a race-free manner.
		811
		812	That means some file descriptors can leak through. And since it isn't
		813	possible to know which file descriptors are "good" and "necessary" (or
		814	even to know which file descriptors are open), there is no good way to
		815	close the ones that might harm.
		816
		817	As an example of what "harm" can be done consider a web server that
		818	accepts connections and afterwards some module uses AnyEvent::Fork for the
		819	first time, causing it to fork and exec a new process, which might inherit
		820	the network socket. When the server closes the socket, it is still open
		821	in the child (which doesn't even know that) and the client might conclude
		822	that the connection is still fine.
		823
		824	For the main program, there are multiple remedies available -
		825	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		826	C<new_exec> is another, as in both cases, the first process can be exec'ed
		827	well before many random file descriptors are open.
		828
		829	In general, the solution for these kind of problems is to fix the
		830	libraries or the code that leaks those file descriptors.
		831
		832	Fortunately, most of these leaked descriptors do no harm, other than
		833	sitting on some resources.
		834
		835	=item "leaked" file descriptors for fork'ed processes
		836
		837	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		838	which closes file descriptors not marked for being inherited.
		839
		840	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		841	a way to create these processes by forking, and this leaks more file
		842	descriptors than exec'ing them, as there is no way to mark descriptors as
		843	"close on fork".
		844
		845	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		846	pipes for internal uses, and L<Gtk2> might open a connection to the X
		847	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		848	trouble with a fork.
		849
		850	The solution is to either not load these modules before use'ing
		851	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		852	initialising them, for example, by calling C<init Gtk2> manually.
		853
		854	=item exit runs destructors
		855
		856	This only applies to users of Lc<AnyEvent::Fork:Early> and
		857	L<AnyEvent::Fork::Template>.
		858
		859	When a process created by AnyEvent::Fork exits, it might do so by calling
		860	exit, or simply letting perl reach the end of the program. At which point
		861	Perl runs all destructors.
		862
		863	Not all destructors are fork-safe - for example, an object that represents
		864	the connection to an X display might tell the X server to free resources,
		865	which is inconvenient when the "real" object in the parent still needs to
		866	use them.
		867
		868	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		869	it as the very first thing, right?
		870
		871	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		872	is to not create objects with nontrivial destructors that might have an
		873	effect outside of Perl.
		874
		875	=back
		876
		877	=head1 PORTABILITY NOTES
		878
		879	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		880	and ::Template is not going to work), and it cost a lot of blood and sweat
		881	to make it so, mostly due to the bloody broken perl that nobody seems to
		882	care about. The fork emulation is a bad joke - I have yet to see something
		883	useful that you can do with it without running into memory corruption
		884	issues or other braindamage. Hrrrr.
		885
		886	Cygwin perl is not supported at the moment, as it should implement fd
		887	passing, but doesn't, and rolling my own is hard, as cygwin doesn't
		888	support enough functionality to do it.
		889
		890	=head1 SEE ALSO
		891
		892	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		893	L<AnyEvent::Fork::Template> (to create a process by forking the main
		894	program at a convenient time).
401		895
402	=head1 AUTHOR	896	=head1 AUTHOR
403		897
404	Marc Lehmann <schmorp@schmorp.de>	898	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/	899	http://home.schmorp.de/

Diff Legend

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

Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.4 by root, Wed Apr 3 07:35:57 2013 UTC vs. Revision 1.33 by root, Sat Apr 6 09:34:11 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.4 by root, Wed Apr 3 07:35:57 2013 UTC vs.
Revision 1.33 by root, Sat Apr 6 09:34:11 2013 UTC