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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.5 by root, Wed Apr 3 08:29:21 2013 UTC vs.
Revision 1.23 by root, Sat Apr 6 08:29:43 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	##################################################################
		10	# create a single new process, tell it to run your worker function
		11
		12	AnyEvent::Fork
		13	->new
		14	->require ("MyModule")
		15	->run ("MyModule::worker, sub {
		16	my ($master_filehandle) = @_;
		17
		18	# now $master_filehandle is connected to the
		19	# $slave_filehandle in the new process.
		20	});
		21
		22	# MyModule::worker might look like this
		23	sub MyModule::worker {
		24	my ($slave_filehandle) = @_;
		25
		26	# now $slave_filehandle is connected to the $master_filehandle
		27	# in the original prorcess. have fun!
		28	}
		29
		30	##################################################################
		31	# create a pool of server processes all accepting on the same socket
		32
		33	# create listener socket
		34	my $listener = ...;
		35
		36	# create a pool template, initialise it and give it the socket
		37	my $pool = AnyEvent::Fork
		38	->new
		39	->require ("Some::Stuff", "My::Server")
		40	->send_fh ($listener);
		41
		42	# now create 10 identical workers
		43	for my $id (1..10) {
		44	$pool
		45	->fork
		46	->send_arg ($id)
		47	->run ("My::Server::run");
		48	}
		49
		50	# now do other things - maybe use the filehandle provided by run
		51	# to wait for the processes to die. or whatever.
		52
		53	# My::Server::run might look like this
		54	sub My::Server::run {
		55	my ($slave, $listener, $id) = @_;
		56
		57	close $slave; # we do not use the socket, so close it to save resources
		58
		59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		60	# or anything we usually couldn't do in a process forked normally.
		61	while (my $socket = $listener->accept) {
		62	# do sth. with new socket
		63	}
		64	}
		65
		66	##################################################################
		67	# use AnyEvent::Fork as a faster fork+exec
		68
		69	# this runs /bin/echo hi, with stdout redirected to /tmp/log
		70	# and stderr to the communications socket. it is usually faster
		71	# than fork+exec, but still let's you prepare the environment.
		72
		73	open my $output, ">/tmp/log" or die "$!";
		74
		75	AnyEvent::Fork
		76	->new
		77	->eval ('
		78	sub run {
		79	my ($fh, $output, @cmd) = @_;
		80
		81	# perl will clear close-on-exec on STDOUT/STDERR
		82	open STDOUT, ">&", $output or die;
		83	open STDERR, ">&", $fh or die;
		84
		85	exec @cmd;
		86	}
		87	')
		88	->send_fh ($output)
		89	->send_arg ("/bin/echo", "hi")
		90	->run ("run", my $cv = AE::cv);
		91
		92	my $stderr = $cv->recv;
8		93
9	=head1 DESCRIPTION	94	=head1 DESCRIPTION
10		95
11	This module allows you to create new processes, without actually forking	96	This module allows you to create new processes, without actually forking
12	them from your current process (avoiding the problems of forking), but	97	them from your current process (avoiding the problems of forking), but
13	preserving most of the advantages of fork.	98	preserving most of the advantages of fork.
14		99
15	It can be used to create new worker processes or new independent	100	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	101	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	102	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)	103	CGI scripts from a web server), which can be faster (and more well behaved)
19	than using fork+exec in big processes.	104	than using fork+exec in big processes.
20		105
21	Special care has been taken to make this module useful from other modules,	106	Special care has been taken to make this module useful from other modules,
22	while still supporting specialised environments such as L<App::Staticperl>	107	while still supporting specialised environments such as L<App::Staticperl>
23	or L<PAR::Packer>.	108	or L<PAR::Packer>.
		109
		110	=head1 WHAT THIS MODULE IS NOT
		111
		112	This module only creates processes and lets you pass file handles and
		113	strings to it, and run perl code. It does not implement any kind of RPC -
		114	there is no back channel from the process back to you, and there is no RPC
		115	or message passing going on.
		116
		117	If you need some form of RPC, you can either implement it yourself
		118	in whatever way you like, use some message-passing module such
		119	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		120	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		121	and so on.
24		122
25	=head1 PROBLEM STATEMENT	123	=head1 PROBLEM STATEMENT
26		124
27	There are two ways to implement parallel processing on UNIX like operating	125	There are two ways to implement parallel processing on UNIX like operating
28	systems - fork and process, and fork+exec and process. They have different	126	systems - fork and process, and fork+exec and process. They have different
…		…
40	or fork+exec instead.	138	or fork+exec instead.
41		139
42	=item Forking usually creates a copy-on-write copy of the parent	140	=item Forking usually creates a copy-on-write copy of the parent
43	process. Memory (for example, modules or data files that have been	141	process. Memory (for example, modules or data files that have been
44	will not take additional memory). When exec'ing a new process, modules	142	will not take additional memory). When exec'ing a new process, modules
45	and data files might need to be loaded again, at extra cpu and memory	143	and data files might need to be loaded again, at extra CPU and memory
46	cost. Likewise when forking, all data structures are copied as well - if	144	cost. Likewise when forking, all data structures are copied as well - if
47	the program frees them and replaces them by new data, the child processes	145	the program frees them and replaces them by new data, the child processes
48	will retain the memory even if it isn't used.	146	will retain the memory even if it isn't used.
49		147
50	This module allows the main program to do a controlled fork, and allows	148	This module allows the main program to do a controlled fork, and allows
…		…
62	as template, and also tries hard to identify the correct path to the perl	160	as template, and also tries hard to identify the correct path to the perl
63	interpreter. With a cooperative main program, exec'ing the interpreter	161	interpreter. With a cooperative main program, exec'ing the interpreter
64	might not even be necessary.	162	might not even be necessary.
65		163
66	=item Forking might be impossible when a program is running. For example,	164	=item Forking might be impossible when a program is running. For example,
67	POSIX makes it almost impossible to fork from a multithreaded program and	165	POSIX makes it almost impossible to fork from a multi-threaded program and
68	do anything useful in the child - strictly speaking, if your perl program	166	do anything useful in the child - strictly speaking, if your perl program
69	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),	167	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
70	you cannot call fork on the perl level anymore, at all.	168	you cannot call fork on the perl level anymore, at all.
71		169
72	This module can safely fork helper processes at any time, by caling	170	This module can safely fork helper processes at any time, by calling
73	fork+exec in C, in a POSIX-compatible way.	171	fork+exec in C, in a POSIX-compatible way.
74		172
75	=item Parallel processing with fork might be inconvenient or difficult	173	=item Parallel processing with fork might be inconvenient or difficult
76	to implement. For example, when a program uses an event loop and creates	174	to implement. For example, when a program uses an event loop and creates
77	watchers it becomes very hard to use the event loop from a child	175	watchers it becomes very hard to use the event loop from a child
…		…
109	needed the first time. Forking from this process shares the memory used	207	needed the first time. Forking from this process shares the memory used
110	for the perl interpreter with the new process, but loading modules takes	208	for the perl interpreter with the new process, but loading modules takes
111	time, and the memory is not shared with anything else.	209	time, and the memory is not shared with anything else.
112		210
113	This is ideal for when you only need one extra process of a kind, with the	211	This is ideal for when you only need one extra process of a kind, with the
114	option of starting and stipping it on demand.	212	option of starting and stopping it on demand.
		213
		214	Example:
		215
		216	AnyEvent::Fork
		217	->new
		218	->require ("Some::Module")
		219	->run ("Some::Module::run", sub {
		220	my ($fork_fh) = @_;
		221	});
115		222
116	=item fork a new template process, load code, then fork processes off of	223	=item fork a new template process, load code, then fork processes off of
117	it and run the code	224	it and run the code
118		225
119	When you need to have a bunch of processes that all execute the same (or	226	When you need to have a bunch of processes that all execute the same (or
…		…
125	modules you loaded) is shared between the processes, and each new process	232	modules you loaded) is shared between the processes, and each new process
126	consumes relatively little memory of its own.	233	consumes relatively little memory of its own.
127		234
128	The disadvantage of this approach is that you need to create a template	235	The disadvantage of this approach is that you need to create a template
129	process for the sole purpose of forking new processes from it, but if you	236	process for the sole purpose of forking new processes from it, but if you
130	only need a fixed number of proceses you can create them, and then destroy	237	only need a fixed number of processes you can create them, and then destroy
131	the template process.	238	the template process.
		239
		240	Example:
		241
		242	my $template = AnyEvent::Fork->new->require ("Some::Module");
		243
		244	for (1..10) {
		245	$template->fork->run ("Some::Module::run", sub {
		246	my ($fork_fh) = @_;
		247	});
		248	}
		249
		250	# at this point, you can keep $template around to fork new processes
		251	# later, or you can destroy it, which causes it to vanish.
132		252
133	=item execute a new perl interpreter, load some code, run it	253	=item execute a new perl interpreter, load some code, run it
134		254
135	This is relatively slow, and doesn't allow you to share memory between	255	This is relatively slow, and doesn't allow you to share memory between
136	multiple processes.	256	multiple processes.
…		…
138	The only advantage is that you don't have to have a template process	258	The only advantage is that you don't have to have a template process
139	hanging around all the time to fork off some new processes, which might be	259	hanging around all the time to fork off some new processes, which might be
140	an advantage when there are long time spans where no extra processes are	260	an advantage when there are long time spans where no extra processes are
141	needed.	261	needed.
142		262
		263	Example:
		264
		265	AnyEvent::Fork
		266	->new_exec
		267	->require ("Some::Module")
		268	->run ("Some::Module::run", sub {
		269	my ($fork_fh) = @_;
		270	});
		271
143	=back	272	=back
144		273
145	=head1 FUNCTIONS	274	=head1 FUNCTIONS
146		275
147	=over 4	276	=over 4
…		…
150		279
151	package AnyEvent::Fork;	280	package AnyEvent::Fork;
152		281
153	use common::sense;	282	use common::sense;
154		283
155	use Socket ();	284	use Errno ();
156		285
157	use AnyEvent;	286	use AnyEvent;
158	use AnyEvent::Fork::Util;
159	use AnyEvent::Util ();	287	use AnyEvent::Util ();
		288
		289	use IO::FDPass;
		290
		291	our $VERSION = 0.5;
160		292
161	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	293	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
162		294
163	=item my $pool = new AnyEvent::Fork key => value...	295	=item my $pool = new AnyEvent::Fork key => value...
164		296
…		…
177	our $TEMPLATE;	309	our $TEMPLATE;
178		310
179	sub _cmd {	311	sub _cmd {
180	my $self = shift;	312	my $self = shift;
181		313
182	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	314	# ideally, we would want to use "a (w/a)*" as format string, but perl
183	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	315	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
184	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	316	# it.
		317	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
185		318
186	$self->[3] \|\|= AE::io $self->[1], 1, sub {	319	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		320	do {
		321	# send the next "thing" in the queue - either a reference to an fh,
		322	# or a plain string.
		323
187	if (ref $self->[2][0]) {	324	if (ref $self->[2][0]) {
		325	# send fh
188	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	326	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		327	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		328	undef $self->[3];
		329	die "AnyEvent::Fork: file descriptor send failure: $!";
		330	}
		331
189	and shift @{ $self->[2] };	332	shift @{ $self->[2] };
190		333
191	} else {	334	} else {
		335	# send string
192	my $len = syswrite $self->[1], $self->[2][0]	336	my $len = syswrite $self->[1], $self->[2][0];
		337
		338	unless ($len) {
		339	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		340	undef $self->[3];
193	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	341	die "AnyEvent::Fork: command write failure: $!";
		342	}
194		343
195	substr $self->[2][0], 0, $len, "";	344	substr $self->[2][0], 0, $len, "";
196	shift @{ $self->[2] } unless length $self->[2][0];	345	shift @{ $self->[2] } unless length $self->[2][0];
197	}	346	}
		347	} while @{ $self->[2] };
198		348
199	unless (@{ $self->[2] }) {	349	# everything written
200	undef $self->[3];	350	undef $self->[3];
		351
		352	# invoke run callback, if any
201	$self->[0]->($self->[1]) if $self->[0];	353	$self->[4]->($self->[1]) if $self->[4];
202	}
203	};	354	};
		355
		356	() # make sure we don't leak the watcher
204	}	357	}
205		358
206	sub _new {	359	sub _new {
207	my ($self, $fh) = @_;	360	my ($self, $fh, $pid) = @_;
		361
		362	AnyEvent::Util::fh_nonblocking $fh, 1;
208		363
209	$self = bless [	364	$self = bless [
210	undef, # run callback	365	$pid,
211	$fh,	366	$fh,
212	[], # write queue - strings or fd's	367	[], # write queue - strings or fd's
213	undef, # AE watcher	368	undef, # AE watcher
214	], $self;	369	], $self;
215		370
216	# my ($a, $b) = AnyEvent::Util::portable_socketpair;
217
218	# queue_cmd $template, "Iabc";
219	# push @{ $template->[2] }, \$b;
220
221	# use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
222	# undef $b;
223	# die "x" . <$a>;
224
225	$self	371	$self
		372	}
		373
		374	# fork template from current process, used by AnyEvent::Fork::Early/Template
		375	sub _new_fork {
		376	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		377	my $parent = $$;
		378
		379	my $pid = fork;
		380
		381	if ($pid eq 0) {
		382	require AnyEvent::Fork::Serve;
		383	$AnyEvent::Fork::Serve::OWNER = $parent;
		384	close $fh;
		385	$0 = "$_[1] of $parent";
		386	$SIG{CHLD} = 'IGNORE';
		387	AnyEvent::Fork::Serve::serve ($slave);
		388	exit 0;
		389	} elsif (!$pid) {
		390	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		391	}
		392
		393	AnyEvent::Fork->_new ($fh, $pid)
226	}	394	}
227		395
228	=item my $proc = new AnyEvent::Fork	396	=item my $proc = new AnyEvent::Fork
229		397
230	Create a new "empty" perl interpreter process and returns its process	398	Create a new "empty" perl interpreter process and returns its process
231	object for further manipulation.	399	object for further manipulation.
232		400
233	The new process is forked from a template process that is kept around	401	The new process is forked from a template process that is kept around
234	for this purpose. When it doesn't exist yet, it is created by a call to	402	for this purpose. When it doesn't exist yet, it is created by a call to
235	C<new_exec> and kept around for future calls.	403	C<new_exec> and kept around for future calls.
		404
		405	When the process object is destroyed, it will release the file handle
		406	that connects it with the new process. When the new process has not yet
		407	called C<run>, then the process will exit. Otherwise, what happens depends
		408	entirely on the code that is executed.
236		409
237	=cut	410	=cut
238		411
239	sub new {	412	sub new {
240	my $class = shift;	413	my $class = shift;
…		…
261	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	434	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
262		435
263	$self->send_fh ($slave);	436	$self->send_fh ($slave);
264	$self->_cmd ("f");	437	$self->_cmd ("f");
265		438
266	AnyEvent::Util::fh_nonblocking $fh, 1;
267
268	AnyEvent::Fork->_new ($fh)	439	AnyEvent::Fork->_new ($fh)
269	}	440	}
270		441
271	=item my $proc = new_exec AnyEvent::Fork	442	=item my $proc = new_exec AnyEvent::Fork
272		443
…		…
278	reduces the amount of memory sharing that is possible, and is also slower.	449	reduces the amount of memory sharing that is possible, and is also slower.
279		450
280	You should use C<new> whenever possible, except when having a template	451	You should use C<new> whenever possible, except when having a template
281	process around is unacceptable.	452	process around is unacceptable.
282		453
283	The path to the perl interpreter is divined usign various methods - first	454	The path to the perl interpreter is divined using various methods - first
284	C<$^X> is investigated to see if the path ends with something that sounds	455	C<$^X> is investigated to see if the path ends with something that sounds
285	as if it were the perl interpreter. Failing this, the module falls back to	456	as if it were the perl interpreter. Failing this, the module falls back to
286	using C<$Config::Config{perlpath}>.	457	using C<$Config::Config{perlpath}>.
287		458
288	=cut	459	=cut
…		…
297	my $perl = $;	468	my $perl = $;
298		469
299	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	470	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
300	# that looks like perl. this obviously only works for posix and win32	471	# that looks like perl. this obviously only works for posix and win32
301	unless (	472	unless (
302	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	473	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
303	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	474	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
304	) {	475	) {
305	# if it doesn't look perlish enough, try Config	476	# if it doesn't look perlish enough, try Config
306	require Config;	477	require Config;
307	$perl = $Config::Config{perlpath};	478	$perl = $Config::Config{perlpath};
…		…
309	}	480	}
310		481
311	require Proc::FastSpawn;	482	require Proc::FastSpawn;
312		483
313	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	484	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
314	AnyEvent::Util::fh_nonblocking $fh, 1;
315	Proc::FastSpawn::fd_inherit (fileno $slave);	485	Proc::FastSpawn::fd_inherit (fileno $slave);
		486
		487	# new fh's should always be set cloexec (due to $^F),
		488	# but hey, not on win32, so we always clear the inherit flag.
		489	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
316		490
317	# quick. also doesn't work in win32. of course. what did you expect	491	# quick. also doesn't work in win32. of course. what did you expect
318	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	492	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
319	my %env = %ENV;	493	my %env = %ENV;
320	$env{PERL5LIB} = join ":", grep !ref, @INC;	494	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
321		495
322	Proc::FastSpawn::spawn (	496	my $pid = Proc::FastSpawn::spawn (
323	$perl,	497	$perl,
324	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],	498	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
325	[map "$_=$env{$_}", keys %env],	499	[map "$_=$env{$_}", keys %env],
326	) or die "unable to spawn AnyEvent::Fork server: $!";	500	) or die "unable to spawn AnyEvent::Fork server: $!";
327		501
328	$self->_new ($fh)	502	$self->_new ($fh, $pid)
		503	}
		504
		505	=item $pid = $proc->pid
		506
		507	Returns the process id of the process I<iff it is a direct child of the
		508	process> running AnyEvent::Fork, and C<undef> otherwise.
		509
		510	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		511	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		512	to clean up their zombies when they die.
		513
		514	All other processes are not direct children, and will be cleaned up by
		515	AnyEvent::Fork.
		516
		517	=cut
		518
		519	sub pid {
		520	$_[0][0]
		521	}
		522
		523	=item $proc = $proc->eval ($perlcode, @args)
		524
		525	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		526	the strings specified by C<@args>, in the "main" package.
		527
		528	This call is meant to do any custom initialisation that might be required
		529	(for example, the C<require> method uses it). It's not supposed to be used
		530	to completely take over the process, use C<run> for that.
		531
		532	The code will usually be executed after this call returns, and there is no
		533	way to pass anything back to the calling process. Any evaluation errors
		534	will be reported to stderr and cause the process to exit.
		535
		536	If you want to execute some code to take over the process (see the
		537	"fork+exec" example in the SYNOPSIS), you should compile a function via
		538	C<eval> first, and then call it via C<run>. This also gives you access to
		539	any arguments passed via the C<send_xxx> methods, such as file handles.
		540
		541	Returns the process object for easy chaining of method calls.
		542
		543	=cut
		544
		545	sub eval {
		546	my ($self, $code, @args) = @_;
		547
		548	$self->_cmd (e => pack "(w/a)", $code, @args);
		549
		550	$self
329	}	551	}
330		552
331	=item $proc = $proc->require ($module, ...)	553	=item $proc = $proc->require ($module, ...)
332		554
333	Tries to load the given modules into the process	555	Tries to load the given module(s) into the process
334		556
335	Returns the process object for easy chaining of method calls.	557	Returns the process object for easy chaining of method calls.
		558
		559	=cut
		560
		561	sub require {
		562	my ($self, @modules) = @_;
		563
		564	s%::%/%g for @modules;
		565	$self->eval ('require "$_.pm" for @_', @modules);
		566
		567	$self
		568	}
336		569
337	=item $proc = $proc->send_fh ($handle, ...)	570	=item $proc = $proc->send_fh ($handle, ...)
338		571
339	Send one or more file handles (I<not> file descriptors) to the process,	572	Send one or more file handles (I<not> file descriptors) to the process,
340	to prepare a call to C<run>.	573	to prepare a call to C<run>.
…		…
344	accomplished by simply not storing the file handles anywhere after passing	577	accomplished by simply not storing the file handles anywhere after passing
345	them to this method.	578	them to this method.
346		579
347	Returns the process object for easy chaining of method calls.	580	Returns the process object for easy chaining of method calls.
348		581
		582	Example: pass a file handle to a process, and release it without
		583	closing. It will be closed automatically when it is no longer used.
		584
		585	$proc->send_fh ($my_fh);
		586	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		587
349	=cut	588	=cut
350		589
351	sub send_fh {	590	sub send_fh {
352	my ($self, @fh) = @_;	591	my ($self, @fh) = @_;
353		592
…		…
362	=item $proc = $proc->send_arg ($string, ...)	601	=item $proc = $proc->send_arg ($string, ...)
363		602
364	Send one or more argument strings to the process, to prepare a call to	603	Send one or more argument strings to the process, to prepare a call to
365	C<run>. The strings can be any octet string.	604	C<run>. The strings can be any octet string.
366		605
		606	The protocol is optimised to pass a moderate number of relatively short
		607	strings - while you can pass up to 4GB of data in one go, this is more
		608	meant to pass some ID information or other startup info, not big chunks of
		609	data.
		610
367	Returns the process object for easy chaining of emthod calls.	611	Returns the process object for easy chaining of method calls.
368		612
369	=cut	613	=cut
370		614
371	sub send_arg {	615	sub send_arg {
372	my ($self, @arg) = @_;	616	my ($self, @arg) = @_;
373		617
374	$self->_cmd (a => @arg);	618	$self->_cmd (a => pack "(w/a)", @arg);
375		619
376	$self	620	$self
377	}	621	}
378		622
379	=item $proc->run ($func, $cb->($fh))	623	=item $proc->run ($func, $cb->($fh))
380		624
381	Enter the function specified by the fully qualified name in C<$func> in	625	Enter the function specified by the function name in C<$func> in the
382	the process. The function is called with the communication socket as first	626	process. The function is called with the communication socket as first
383	argument, followed by all file handles and string arguments sent earlier	627	argument, followed by all file handles and string arguments sent earlier
384	via C<send_fh> and C<send_arg> methods, in the order they were called.	628	via C<send_fh> and C<send_arg> methods, in the order they were called.
385		629
386	If the called function returns, the process exits.	630	The function name should be fully qualified, but if it isn't, it will be
		631	looked up in the main package.
387		632
388	Preparing the process can take time - when the process is ready, the	633	If the called function returns, doesn't exist, or any error occurs, the
		634	process exits.
		635
		636	Preparing the process is done in the background - when all commands have
389	callback is invoked with the local communications socket as argument.	637	been sent, the callback is invoked with the local communications socket
		638	as argument. At this point you can start using the socket in any way you
		639	like.
390		640
391	The process object becomes unusable on return from this function.	641	The process object becomes unusable on return from this function - any
		642	further method calls result in undefined behaviour.
392		643
393	If the communication socket isn't used, it should be closed on both sides,	644	If the communication socket isn't used, it should be closed on both sides,
394	to save on kernel memory.	645	to save on kernel memory.
395		646
396	The socket is non-blocking in the parent, and blocking in the newly	647	The socket is non-blocking in the parent, and blocking in the newly
397	created process. The close-on-exec flag is set on both. Even if not used	648	created process. The close-on-exec flag is set in both.
		649
398	otherwise, the socket can be a good indicator for the existance of the	650	Even if not used otherwise, the socket can be a good indicator for the
399	process - if the othe rprocess exits, you get a readable event on it,	651	existence of the process - if the other process exits, you get a readable
400	because exiting the process closes the socket (if it didn't create any	652	event on it, because exiting the process closes the socket (if it didn't
401	children using fork).	653	create any children using fork).
		654
		655	Example: create a template for a process pool, pass a few strings, some
		656	file handles, then fork, pass one more string, and run some code.
		657
		658	my $pool = AnyEvent::Fork
		659	->new
		660	->send_arg ("str1", "str2")
		661	->send_fh ($fh1, $fh2);
		662
		663	for (1..2) {
		664	$pool
		665	->fork
		666	->send_arg ("str3")
		667	->run ("Some::function", sub {
		668	my ($fh) = @_;
		669
		670	# fh is nonblocking, but we trust that the OS can accept these
		671	# few octets anyway.
		672	syswrite $fh, "hi #$_\n";
		673
		674	# $fh is being closed here, as we don't store it anywhere
		675	});
		676	}
		677
		678	# Some::function might look like this - all parameters passed before fork
		679	# and after will be passed, in order, after the communications socket.
		680	sub Some::function {
		681	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		682
		683	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		684	}
402		685
403	=cut	686	=cut
404		687
405	sub run {	688	sub run {
406	my ($self, $func, $cb) = @_;	689	my ($self, $func, $cb) = @_;
407		690
408	$self->[0] = $cb;	691	$self->[4] = $cb;
409	$self->_cmd ("r", $func);	692	$self->_cmd (r => $func);
410	}	693	}
411		694
412	=back	695	=back
		696
		697	=head1 PERFORMANCE
		698
		699	Now for some unscientific benchmark numbers (all done on an amd64
		700	GNU/Linux box). These are intended to give you an idea of the relative
		701	performance you can expect, they are not meant to be absolute performance
		702	numbers.
		703
		704	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		705	exit in the child and waits for the socket to close in the parent. I did
		706	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		707
		708	2079 new processes per second, using manual socketpair + fork
		709
		710	Then I did the same thing, but instead of calling fork, I called
		711	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		712	socket form the child to close on exit. This does the same thing as manual
		713	socket pair + fork, except that what is forked is the template process
		714	(2440kB), and the socket needs to be passed to the server at the other end
		715	of the socket first.
		716
		717	2307 new processes per second, using AnyEvent::Fork->new
		718
		719	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		720	a new perl interpreter and compile the small server each time, I get:
		721
		722	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		723
		724	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		725	though it uses the same operations, but adds a lot of overhead?
		726
		727	The difference is simply the process size: forking the 6MB process takes
		728	so much longer than forking the 2.5MB template process that the overhead
		729	introduced is canceled out.
		730
		731	If the benchmark process grows, the normal fork becomes even slower:
		732
		733	1340 new processes, manual fork in a 20MB process
		734	731 new processes, manual fork in a 200MB process
		735	235 new processes, manual fork in a 2000MB process
		736
		737	What that means (to me) is that I can use this module without having a
		738	very bad conscience because of the extra overhead required to start new
		739	processes.
		740
		741	=head1 TYPICAL PROBLEMS
		742
		743	This section lists typical problems that remain. I hope by recognising
		744	them, most can be avoided.
		745
		746	=over 4
		747
		748	=item "leaked" file descriptors for exec'ed processes
		749
		750	POSIX systems inherit file descriptors by default when exec'ing a new
		751	process. While perl itself laudably sets the close-on-exec flags on new
		752	file handles, most C libraries don't care, and even if all cared, it's
		753	often not possible to set the flag in a race-free manner.
		754
		755	That means some file descriptors can leak through. And since it isn't
		756	possible to know which file descriptors are "good" and "necessary" (or
		757	even to know which file descriptors are open), there is no good way to
		758	close the ones that might harm.
		759
		760	As an example of what "harm" can be done consider a web server that
		761	accepts connections and afterwards some module uses AnyEvent::Fork for the
		762	first time, causing it to fork and exec a new process, which might inherit
		763	the network socket. When the server closes the socket, it is still open
		764	in the child (which doesn't even know that) and the client might conclude
		765	that the connection is still fine.
		766
		767	For the main program, there are multiple remedies available -
		768	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		769	C<new_exec> is another, as in both cases, the first process can be exec'ed
		770	well before many random file descriptors are open.
		771
		772	In general, the solution for these kind of problems is to fix the
		773	libraries or the code that leaks those file descriptors.
		774
		775	Fortunately, most of these leaked descriptors do no harm, other than
		776	sitting on some resources.
		777
		778	=item "leaked" file descriptors for fork'ed processes
		779
		780	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		781	which closes file descriptors not marked for being inherited.
		782
		783	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		784	a way to create these processes by forking, and this leaks more file
		785	descriptors than exec'ing them, as there is no way to mark descriptors as
		786	"close on fork".
		787
		788	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		789	pipes for internal uses, and L<Gtk2> might open a connection to the X
		790	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		791	trouble with a fork.
		792
		793	The solution is to either not load these modules before use'ing
		794	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		795	initialising them, for example, by calling C<init Gtk2> manually.
		796
		797	=item exit runs destructors
		798
		799	This only applies to users of Lc<AnyEvent::Fork:Early> and
		800	L<AnyEvent::Fork::Template>.
		801
		802	When a process created by AnyEvent::Fork exits, it might do so by calling
		803	exit, or simply letting perl reach the end of the program. At which point
		804	Perl runs all destructors.
		805
		806	Not all destructors are fork-safe - for example, an object that represents
		807	the connection to an X display might tell the X server to free resources,
		808	which is inconvenient when the "real" object in the parent still needs to
		809	use them.
		810
		811	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		812	it as the very first thing, right?
		813
		814	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		815	is to not create objects with nontrivial destructors that might have an
		816	effect outside of Perl.
		817
		818	=back
		819
		820	=head1 PORTABILITY NOTES
		821
		822	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		823	and ::Template is not going to work), and it cost a lot of blood and sweat
		824	to make it so, mostly due to the bloody broken perl that nobody seems to
		825	care about. The fork emulation is a bad joke - I have yet to see something
		826	useful that you can do with it without running into memory corruption
		827	issues or other braindamage. Hrrrr.
		828
		829	Cygwin perl is not supported at the moment, as it should implement fd
		830	passing, but doesn't, and rolling my own is hard, as cygwin doesn't
		831	support enough functionality to do it.
		832
		833	=head1 SEE ALSO
		834
		835	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		836	L<AnyEvent::Fork::Template> (to create a process by forking the main
		837	program at a convenient time).
413		838
414	=head1 AUTHOR	839	=head1 AUTHOR
415		840
416	Marc Lehmann <schmorp@schmorp.de>	841	Marc Lehmann <schmorp@schmorp.de>
417	http://home.schmorp.de/	842	http://home.schmorp.de/

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Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC