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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.20 by root, Sat Apr 6 03:35:36 2013 UTC vs.
Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
		15
		16	=head1 DESCRIPTION
		17
		18	This module allows you to create new processes, without actually forking
		19	them from your current process (avoiding the problems of forking), but
		20	preserving most of the advantages of fork.
		21
		22	It can be used to create new worker processes or new independent
		23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
		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 could use the L<AnyEvent::Fork::RPC>
		40	companion module, which adds simple RPC/job queueing to a process created
		41	by this module.
		42
		43	Or you can implement it yourself in whatever way you like, use some
		44	message-passing module such as L<AnyEvent::MP>, some pipe such as
		45	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		46	e.g. JSON or Storable messages, and so on.
		47
		48	=head2 COMPARISON TO OTHER MODULES
		49
		50	There is an abundance of modules on CPAN that do "something fork", such as
		51	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		52	or L<AnyEvent::Subprocess>. There are modules that implement their own
		53	process management, such as L<AnyEvent::DBI>.
		54
		55	The problems that all these modules try to solve are real, however, none
		56	of them (from what I have seen) tackle the very real problems of unwanted
		57	memory sharing, efficiency, not being able to use event processing or
		58	similar modules in the processes they create.
		59
		60	This module doesn't try to replace any of them - instead it tries to solve
		61	the problem of creating processes with a minimum of fuss and overhead (and
		62	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		63	except they were written before AnyEvent:Fork was available, so obviously
		64	had to roll their own.
		65
		66	=head2 PROBLEM STATEMENT
		67
		68	There are two traditional ways to implement parallel processing on UNIX
		69	like operating systems - fork and process, and fork+exec and process. They
		70	have different advantages and disadvantages that I describe below,
		71	together with how this module tries to mitigate the disadvantages.
		72
		73	=over 4
		74
		75	=item Forking from a big process can be very slow.
		76
		77	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		78	overhead is often shared with exec (because you have to fork first), but
		79	in some circumstances (e.g. when vfork is used), fork+exec can be much
		80	faster.
		81
		82	This module can help here by telling a small(er) helper process to fork,
		83	which is faster then forking the main process, and also uses vfork where
		84	possible. This gives the speed of vfork, with the flexibility of fork.
		85
		86	=item Forking usually creates a copy-on-write copy of the parent
		87	process.
		88
		89	For example, modules or data files that are loaded will not use additional
		90	memory after a fork. When exec'ing a new process, modules and data files
		91	might need to be loaded again, at extra CPU and memory cost. But when
		92	forking, literally all data structures are copied - if the program frees
		93	them and replaces them by new data, the child processes will retain the
		94	old version even if it isn't used, which can suddenly and unexpectedly
		95	increase memory usage when freeing memory.
		96
		97	The trade-off is between more sharing with fork (which can be good or
		98	bad), and no sharing with exec.
		99
		100	This module allows the main program to do a controlled fork, and allows
		101	modules to exec processes safely at any time. When creating a custom
		102	process pool you can take advantage of data sharing via fork without
		103	risking to share large dynamic data structures that will blow up child
		104	memory usage.
		105
		106	In other words, this module puts you into control over what is being
		107	shared and what isn't, at all times.
		108
		109	=item Exec'ing a new perl process might be difficult.
		110
		111	For example, it is not easy to find the correct path to the perl
		112	interpreter - C<$^X> might not be a perl interpreter at all.
		113
		114	This module tries hard to identify the correct path to the perl
		115	interpreter. With a cooperative main program, exec'ing the interpreter
		116	might not even be necessary, but even without help from the main program,
		117	it will still work when used from a module.
		118
		119	=item Exec'ing a new perl process might be slow, as all necessary modules
		120	have to be loaded from disk again, with no guarantees of success.
		121
		122	Long running processes might run into problems when perl is upgraded
		123	and modules are no longer loadable because they refer to a different
		124	perl version, or parts of a distribution are newer than the ones already
		125	loaded.
		126
		127	This module supports creating pre-initialised perl processes to be used as
		128	a template for new processes.
		129
		130	=item Forking might be impossible when a program is running.
		131
		132	For example, POSIX makes it almost impossible to fork from a
		133	multi-threaded program while doing anything useful in the child - in
		134	fact, if your perl program uses POSIX threads (even indirectly via
		135	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		136	anymore without risking corruption issues on a number of operating
		137	systems.
		138
		139	This module can safely fork helper processes at any time, by calling
		140	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		141
		142	=item Parallel processing with fork might be inconvenient or difficult
		143	to implement. Modules might not work in both parent and child.
		144
		145	For example, when a program uses an event loop and creates watchers it
		146	becomes very hard to use the event loop from a child program, as the
		147	watchers already exist but are only meaningful in the parent. Worse, a
		148	module might want to use such a module, not knowing whether another module
		149	or the main program also does, leading to problems.
		150
		151	Apart from event loops, graphical toolkits also commonly fall into the
		152	"unsafe module" category, or just about anything that communicates with
		153	the external world, such as network libraries and file I/O modules, which
		154	usually don't like being copied and then allowed to continue in two
		155	processes.
		156
		157	With this module only the main program is allowed to create new processes
		158	by forking (because only the main program can know when it is still safe
		159	to do so) - all other processes are created via fork+exec, which makes it
		160	possible to use modules such as event loops or window interfaces safely.
		161
		162	=back
		163
		164	=head1 EXAMPLES
		165
10	# create a single new process, tell it to run your worker function	166	=head2 Create a single new process, tell it to run your worker function.
11		167
12	AnyEvent::Fork	168	AnyEvent::Fork
13	->new	169	->new
14	->require ("MyModule")	170	->require ("MyModule")
15	->run ("MyModule::worker, sub {	171	->run ("MyModule::worker, sub {
…		…
17		173
18	# now $master_filehandle is connected to the	174	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	175	# $slave_filehandle in the new process.
20	});	176	});
21		177
22	# MyModule::worker might look like this	178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
23	sub MyModule::worker {	182	sub worker {
24	my ($slave_filehandle) = @_;	183	my ($slave_filehandle) = @_;
25		184
26	# now $slave_filehandle is connected to the $master_filehandle	185	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	186	# in the original prorcess. have fun!
28	}	187	}
29		188
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	189	=head2 Create a pool of server processes all accepting on the same socket.
32		190
33	# create listener socket	191	# create listener socket
34	my $listener = ...;	192	my $listener = ...;
35		193
36	# create a pool template, initialise it and give it the socket	194	# create a pool template, initialise it and give it the socket
…		…
48	}	206	}
49		207
50	# now do other things - maybe use the filehandle provided by run	208	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	209	# to wait for the processes to die. or whatever.
52		210
53	# My::Server::run might look like this	211	C<My::Server> might look like this:
54	sub My::Server::run {	212
		213	package My::Server;
		214
		215	sub run {
55	my ($slave, $listener, $id) = @_;	216	my ($slave, $listener, $id) = @_;
56		217
57	close $slave; # we do not use the socket, so close it to save resources	218	close $slave; # we do not use the socket, so close it to save resources
58		219
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	220	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	222	while (my $socket = $listener->accept) {
62	# do sth. with new socket	223	# do sth. with new socket
63	}	224	}
64	}	225	}
65		226
66	=head1 DESCRIPTION	227	=head2 use AnyEvent::Fork as a faster fork+exec
67		228
68	This module allows you to create new processes, without actually forking	229	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
69	them from your current process (avoiding the problems of forking), but	230	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	231	faster than fork+exec, but still lets you prepare the environment.
71		232
72	It can be used to create new worker processes or new independent	233	open my $output, ">/tmp/log" or die "$!";
73	subprocesses for short- and long-running jobs, process pools (e.g. for use
74	in pre-forked servers) but also to spawn new external processes (such as
75	CGI scripts from a web server), which can be faster (and more well behaved)
76	than using fork+exec in big processes.
77		234
78	Special care has been taken to make this module useful from other modules,	235	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	236	->new
80	or L<PAR::Packer>.	237	->eval ('
		238	# compile a helper function for later use
		239	sub run {
		240	my ($fh, $output, @cmd) = @_;
81		241
82	=head1 WHAT THIS MODULE IS NOT	242	# perl will clear close-on-exec on STDOUT/STDERR
		243	open STDOUT, ">&", $output or die;
		244	open STDERR, ">&", $fh or die;
83		245
84	This module only creates processes and lets you pass file handles and	246	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	247	}
86	there is no back channel from the process back to you, and there is no RPC	248	')
87	or message passing going on.	249	->send_fh ($output)
		250	->send_arg ("/bin/echo", "hi")
		251	->run ("run", my $cv = AE::cv);
88		252
89	If you need some form of RPC, you can either implement it yourself	253	my $stderr = $cv->recv;
90	in whatever way you like, use some message-passing module such
91	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
92	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
93	and so on.
94
95	=head1 PROBLEM STATEMENT
96
97	There are two ways to implement parallel processing on UNIX like operating
98	systems - fork and process, and fork+exec and process. They have different
99	advantages and disadvantages that I describe below, together with how this
100	module tries to mitigate the disadvantages.
101
102	=over 4
103
104	=item Forking from a big process can be very slow (a 5GB process needs
105	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
106	is often shared with exec (because you have to fork first), but in some
107	circumstances (e.g. when vfork is used), fork+exec can be much faster.
108
109	This module can help here by telling a small(er) helper process to fork,
110	or fork+exec instead.
111
112	=item Forking usually creates a copy-on-write copy of the parent
113	process. Memory (for example, modules or data files that have been
114	will not take additional memory). When exec'ing a new process, modules
115	and data files might need to be loaded again, at extra CPU and memory
116	cost. Likewise when forking, all data structures are copied as well - if
117	the program frees them and replaces them by new data, the child processes
118	will retain the memory even if it isn't used.
119
120	This module allows the main program to do a controlled fork, and allows
121	modules to exec processes safely at any time. When creating a custom
122	process pool you can take advantage of data sharing via fork without
123	risking to share large dynamic data structures that will blow up child
124	memory usage.
125
126	=item Exec'ing a new perl process might be difficult and slow. For
127	example, it is not easy to find the correct path to the perl interpreter,
128	and all modules have to be loaded from disk again. Long running processes
129	might run into problems when perl is upgraded for example.
130
131	This module supports creating pre-initialised perl processes to be used
132	as template, and also tries hard to identify the correct path to the perl
133	interpreter. With a cooperative main program, exec'ing the interpreter
134	might not even be necessary.
135
136	=item Forking might be impossible when a program is running. For example,
137	POSIX makes it almost impossible to fork from a multi-threaded program and
138	do anything useful in the child - strictly speaking, if your perl program
139	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
140	you cannot call fork on the perl level anymore, at all.
141
142	This module can safely fork helper processes at any time, by calling
143	fork+exec in C, in a POSIX-compatible way.
144
145	=item Parallel processing with fork might be inconvenient or difficult
146	to implement. For example, when a program uses an event loop and creates
147	watchers it becomes very hard to use the event loop from a child
148	program, as the watchers already exist but are only meaningful in the
149	parent. Worse, a module might want to use such a system, not knowing
150	whether another module or the main program also does, leading to problems.
151
152	This module only lets the main program create pools by forking (because
153	only the main program can know when it is still safe to do so) - all other
154	pools are created by fork+exec, after which such modules can again be
155	loaded.
156
157	=back
158		254
159	=head1 CONCEPTS	255	=head1 CONCEPTS
160		256
161	This module can create new processes either by executing a new perl	257	This module can create new processes either by executing a new perl
162	process, or by forking from an existing "template" process.	258	process, or by forking from an existing "template" process.
…		…
241	my ($fork_fh) = @_;	337	my ($fork_fh) = @_;
242	});	338	});
243		339
244	=back	340	=back
245		341
246	=head1 FUNCTIONS	342	=head1 THE C<AnyEvent::Fork> CLASS
		343
		344	This module exports nothing, and only implements a single class -
		345	C<AnyEvent::Fork>.
		346
		347	There are two class constructors that both create new processes - C<new>
		348	and C<new_exec>. The C<fork> method creates a new process by forking an
		349	existing one and could be considered a third constructor.
		350
		351	Most of the remaining methods deal with preparing the new process, by
		352	loading code, evaluating code and sending data to the new process. They
		353	usually return the process object, so you can chain method calls.
		354
		355	If a process object is destroyed before calling its C<run> method, then
		356	the process simply exits. After C<run> is called, all responsibility is
		357	passed to the specified function.
		358
		359	As long as there is any outstanding work to be done, process objects
		360	resist being destroyed, so there is no reason to store them unless you
		361	need them later - configure and forget works just fine.
247		362
248	=over 4	363	=over 4
249		364
250	=cut	365	=cut
251		366
…		…
258	use AnyEvent;	373	use AnyEvent;
259	use AnyEvent::Util ();	374	use AnyEvent::Util ();
260		375
261	use IO::FDPass;	376	use IO::FDPass;
262		377
263	our $VERSION = 0.2;	378	our $VERSION = 0.6;
264
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267	=item my $pool = new AnyEvent::Fork key => value...
268
269	Create a new process pool. The following named parameters are supported:
270
271	=over 4
272
273	=back
274
275	=cut
276		379
277	# the early fork template process	380	# the early fork template process
278	our $EARLY;	381	our $EARLY;
279		382
280	# the empty template process	383	# the empty template process
281	our $TEMPLATE;	384	our $TEMPLATE;
		385
		386	sub QUEUE() { 0 }
		387	sub FH() { 1 }
		388	sub WW() { 2 }
		389	sub PID() { 3 }
		390	sub CB() { 4 }
		391
		392	sub _new {
		393	my ($self, $fh, $pid) = @_;
		394
		395	AnyEvent::Util::fh_nonblocking $fh, 1;
		396
		397	$self = bless [
		398	[], # write queue - strings or fd's
		399	$fh,
		400	undef, # AE watcher
		401	$pid,
		402	], $self;
		403
		404	$self
		405	}
282		406
283	sub _cmd {	407	sub _cmd {
284	my $self = shift;	408	my $self = shift;
285		409
286	# ideally, we would want to use "a (w/a)*" as format string, but perl	410	# ideally, we would want to use "a (w/a)*" as format string, but perl
287	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack	411	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
288	# it.	412	# it.
289	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	413	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
290		414
291	$self->[3] \|\|= AE::io $self->[1], 1, sub {	415	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
292	do {	416	do {
293	# send the next "thing" in the queue - either a reference to an fh,	417	# send the next "thing" in the queue - either a reference to an fh,
294	# or a plain string.	418	# or a plain string.
295		419
296	if (ref $self->[2][0]) {	420	if (ref $self->[QUEUE][0]) {
297	# send fh	421	# send fh
298	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	422	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
299	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	423	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
300	undef $self->[3];	424	undef $self->[WW];
301	die "AnyEvent::Fork: file descriptor send failure: $!";	425	die "AnyEvent::Fork: file descriptor send failure: $!";
302	}	426	}
303		427
304	shift @{ $self->[2] };	428	shift @{ $self->[QUEUE] };
305		429
306	} else {	430	} else {
307	# send string	431	# send string
308	my $len = syswrite $self->[1], $self->[2][0];	432	my $len = syswrite $self->[FH], $self->[QUEUE][0];
309		433
310	unless ($len) {	434	unless ($len) {
311	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	435	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
312	undef $self->[3];	436	undef $self->[3];
313	die "AnyEvent::Fork: command write failure: $!";	437	die "AnyEvent::Fork: command write failure: $!";
314	}	438	}
315		439
316	substr $self->[2][0], 0, $len, "";	440	substr $self->[QUEUE][0], 0, $len, "";
317	shift @{ $self->[2] } unless length $self->[2][0];	441	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
318	}	442	}
319	} while @{ $self->[2] };	443	} while @{ $self->[QUEUE] };
320		444
321	# everything written	445	# everything written
322	undef $self->[3];	446	undef $self->[WW];
323		447
324	# invoke run callback, if any	448	# invoke run callback, if any
325	$self->[4]->($self->[1]) if $self->[4];	449	$self->[CB]->($self->[FH]) if $self->[CB];
326	};	450	};
327		451
328	() # make sure we don't leak the watcher	452	() # make sure we don't leak the watcher
329	}
330
331	sub _new {
332	my ($self, $fh, $pid) = @_;
333
334	AnyEvent::Util::fh_nonblocking $fh, 1;
335
336	$self = bless [
337	$pid,
338	$fh,
339	[], # write queue - strings or fd's
340	undef, # AE watcher
341	], $self;
342
343	$self
344	}	453	}
345		454
346	# fork template from current process, used by AnyEvent::Fork::Early/Template	455	# fork template from current process, used by AnyEvent::Fork::Early/Template
347	sub _new_fork {	456	sub _new_fork {
348	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	457	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
353	if ($pid eq 0) {	462	if ($pid eq 0) {
354	require AnyEvent::Fork::Serve;	463	require AnyEvent::Fork::Serve;
355	$AnyEvent::Fork::Serve::OWNER = $parent;	464	$AnyEvent::Fork::Serve::OWNER = $parent;
356	close $fh;	465	close $fh;
357	$0 = "$_[1] of $parent";	466	$0 = "$_[1] of $parent";
358	$SIG{CHLD} = 'IGNORE';
359	AnyEvent::Fork::Serve::serve ($slave);	467	AnyEvent::Fork::Serve::serve ($slave);
360	exit 0;	468	exit 0;
361	} elsif (!$pid) {	469	} elsif (!$pid) {
362	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	470	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
363	}	471	}
…		…
370	Create a new "empty" perl interpreter process and returns its process	478	Create a new "empty" perl interpreter process and returns its process
371	object for further manipulation.	479	object for further manipulation.
372		480
373	The new process is forked from a template process that is kept around	481	The new process is forked from a template process that is kept around
374	for this purpose. When it doesn't exist yet, it is created by a call to	482	for this purpose. When it doesn't exist yet, it is created by a call to
375	C<new_exec> and kept around for future calls.	483	C<new_exec> first and then stays around for future calls.
376
377	When the process object is destroyed, it will release the file handle
378	that connects it with the new process. When the new process has not yet
379	called C<run>, then the process will exit. Otherwise, what happens depends
380	entirely on the code that is executed.
381		484
382	=cut	485	=cut
383		486
384	sub new {	487	sub new {
385	my $class = shift;	488	my $class = shift;
…		…
475	}	578	}
476		579
477	=item $pid = $proc->pid	580	=item $pid = $proc->pid
478		581
479	Returns the process id of the process I<iff it is a direct child of the	582	Returns the process id of the process I<iff it is a direct child of the
480	process> running AnyEvent::Fork, and C<undef> otherwise.	583	process running AnyEvent::Fork>, and C<undef> otherwise.
481		584
482	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	585	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
483	L<AnyEvent::Fork::Template> are direct children, and you are responsible	586	L<AnyEvent::Fork::Template> are direct children, and you are responsible
484	to clean up their zombies when they die.	587	to clean up their zombies when they die.
485		588
486	All other processes are not direct children, and will be cleaned up by	589	All other processes are not direct children, and will be cleaned up by
487	AnyEvent::Fork.	590	AnyEvent::Fork itself.
488		591
489	=cut	592	=cut
490		593
491	sub pid {	594	sub pid {
492	$_[0][0]	595	$_[0][PID]
493	}	596	}
494		597
495	=item $proc = $proc->eval ($perlcode, @args)	598	=item $proc = $proc->eval ($perlcode, @args)
496		599
497	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	600	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
498	the strings specified by C<@args>.	601	the strings specified by C<@args>, in the "main" package.
499		602
500	This call is meant to do any custom initialisation that might be required	603	This call is meant to do any custom initialisation that might be required
501	(for example, the C<require> method uses it). It's not supposed to be used	604	(for example, the C<require> method uses it). It's not supposed to be used
502	to completely take over the process, use C<run> for that.	605	to completely take over the process, use C<run> for that.
503		606
504	The code will usually be executed after this call returns, and there is no	607	The code will usually be executed after this call returns, and there is no
505	way to pass anything back to the calling process. Any evaluation errors	608	way to pass anything back to the calling process. Any evaluation errors
506	will be reported to stderr and cause the process to exit.	609	will be reported to stderr and cause the process to exit.
507		610
		611	If you want to execute some code (that isn't in a module) to take over the
		612	process, you should compile a function via C<eval> first, and then call
		613	it via C<run>. This also gives you access to any arguments passed via the
		614	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		615	a faster fork+exec> example to see it in action.
		616
508	Returns the process object for easy chaining of method calls.	617	Returns the process object for easy chaining of method calls.
509		618
510	=cut	619	=cut
511		620
512	sub eval {	621	sub eval {
…		…
537	=item $proc = $proc->send_fh ($handle, ...)	646	=item $proc = $proc->send_fh ($handle, ...)
538		647
539	Send one or more file handles (I<not> file descriptors) to the process,	648	Send one or more file handles (I<not> file descriptors) to the process,
540	to prepare a call to C<run>.	649	to prepare a call to C<run>.
541		650
542	The process object keeps a reference to the handles until this is done,	651	The process object keeps a reference to the handles until they have
543	so you must not explicitly close the handles. This is most easily	652	been passed over to the process, so you must not explicitly close the
544	accomplished by simply not storing the file handles anywhere after passing	653	handles. This is most easily accomplished by simply not storing the file
545	them to this method.	654	handles anywhere after passing them to this method - when AnyEvent::Fork
		655	is finished using them, perl will automatically close them.
546		656
547	Returns the process object for easy chaining of method calls.	657	Returns the process object for easy chaining of method calls.
548		658
549	Example: pass a file handle to a process, and release it without	659	Example: pass a file handle to a process, and release it without
550	closing. It will be closed automatically when it is no longer used.	660	closing. It will be closed automatically when it is no longer used.
…		…
557	sub send_fh {	667	sub send_fh {
558	my ($self, @fh) = @_;	668	my ($self, @fh) = @_;
559		669
560	for my $fh (@fh) {	670	for my $fh (@fh) {
561	$self->_cmd ("h");	671	$self->_cmd ("h");
562	push @{ $self->[2] }, \$fh;	672	push @{ $self->[QUEUE] }, \$fh;
563	}	673	}
564		674
565	$self	675	$self
566	}	676	}
567		677
568	=item $proc = $proc->send_arg ($string, ...)	678	=item $proc = $proc->send_arg ($string, ...)
569		679
570	Send one or more argument strings to the process, to prepare a call to	680	Send one or more argument strings to the process, to prepare a call to
571	C<run>. The strings can be any octet string.	681	C<run>. The strings can be any octet strings.
572		682
573	The protocol is optimised to pass a moderate number of relatively short	683	The protocol is optimised to pass a moderate number of relatively short
574	strings - while you can pass up to 4GB of data in one go, this is more	684	strings - while you can pass up to 4GB of data in one go, this is more
575	meant to pass some ID information or other startup info, not big chunks of	685	meant to pass some ID information or other startup info, not big chunks of
576	data.	686	data.
…		…
587	$self	697	$self
588	}	698	}
589		699
590	=item $proc->run ($func, $cb->($fh))	700	=item $proc->run ($func, $cb->($fh))
591		701
592	Enter the function specified by the fully qualified name in C<$func> in	702	Enter the function specified by the function name in C<$func> in the
593	the process. The function is called with the communication socket as first	703	process. The function is called with the communication socket as first
594	argument, followed by all file handles and string arguments sent earlier	704	argument, followed by all file handles and string arguments sent earlier
595	via C<send_fh> and C<send_arg> methods, in the order they were called.	705	via C<send_fh> and C<send_arg> methods, in the order they were called.
596		706
597	If the called function returns, the process exits.
598
599	Preparing the process can take time - when the process is ready, the
600	callback is invoked with the local communications socket as argument.
601
602	The process object becomes unusable on return from this function.	707	The process object becomes unusable on return from this function - any
		708	further method calls result in undefined behaviour.
		709
		710	The function name should be fully qualified, but if it isn't, it will be
		711	looked up in the C<main> package.
		712
		713	If the called function returns, doesn't exist, or any error occurs, the
		714	process exits.
		715
		716	Preparing the process is done in the background - when all commands have
		717	been sent, the callback is invoked with the local communications socket
		718	as argument. At this point you can start using the socket in any way you
		719	like.
603		720
604	If the communication socket isn't used, it should be closed on both sides,	721	If the communication socket isn't used, it should be closed on both sides,
605	to save on kernel memory.	722	to save on kernel memory.
606		723
607	The socket is non-blocking in the parent, and blocking in the newly	724	The socket is non-blocking in the parent, and blocking in the newly
608	created process. The close-on-exec flag is set on both. Even if not used	725	created process. The close-on-exec flag is set in both.
		726
609	otherwise, the socket can be a good indicator for the existence of the	727	Even if not used otherwise, the socket can be a good indicator for the
610	process - if the other process exits, you get a readable event on it,	728	existence of the process - if the other process exits, you get a readable
611	because exiting the process closes the socket (if it didn't create any	729	event on it, because exiting the process closes the socket (if it didn't
612	children using fork).	730	create any children using fork).
613		731
614	Example: create a template for a process pool, pass a few strings, some	732	Example: create a template for a process pool, pass a few strings, some
615	file handles, then fork, pass one more string, and run some code.	733	file handles, then fork, pass one more string, and run some code.
616		734
617	my $pool = AnyEvent::Fork	735	my $pool = AnyEvent::Fork
…		…
625	->send_arg ("str3")	743	->send_arg ("str3")
626	->run ("Some::function", sub {	744	->run ("Some::function", sub {
627	my ($fh) = @_;	745	my ($fh) = @_;
628		746
629	# fh is nonblocking, but we trust that the OS can accept these	747	# fh is nonblocking, but we trust that the OS can accept these
630	# extra 3 octets anyway.	748	# few octets anyway.
631	syswrite $fh, "hi #$_\n";	749	syswrite $fh, "hi #$_\n";
632		750
633	# $fh is being closed here, as we don't store it anywhere	751	# $fh is being closed here, as we don't store it anywhere
634	});	752	});
635	}	753	}
…		…
637	# Some::function might look like this - all parameters passed before fork	755	# Some::function might look like this - all parameters passed before fork
638	# and after will be passed, in order, after the communications socket.	756	# and after will be passed, in order, after the communications socket.
639	sub Some::function {	757	sub Some::function {
640	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	758	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
641		759
642	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	760	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
643	}	761	}
644		762
645	=cut	763	=cut
646		764
647	sub run {	765	sub run {
648	my ($self, $func, $cb) = @_;	766	my ($self, $func, $cb) = @_;
649		767
650	$self->[4] = $cb;	768	$self->[CB] = $cb;
651	$self->_cmd (r => $func);	769	$self->_cmd (r => $func);
652	}	770	}
653		771
654	=back	772	=back
655		773
…		…
681	479 vfork+execs per second, using AnyEvent::Fork->new_exec	799	479 vfork+execs per second, using AnyEvent::Fork->new_exec
682		800
683	So how can C<< AnyEvent->new >> be faster than a standard fork, even	801	So how can C<< AnyEvent->new >> be faster than a standard fork, even
684	though it uses the same operations, but adds a lot of overhead?	802	though it uses the same operations, but adds a lot of overhead?
685		803
686	The difference is simply the process size: forking the 6MB process takes	804	The difference is simply the process size: forking the 5MB process takes
687	so much longer than forking the 2.5MB template process that the overhead	805	so much longer than forking the 2.5MB template process that the extra
688	introduced is canceled out.	806	overhead is canceled out.
689		807
690	If the benchmark process grows, the normal fork becomes even slower:	808	If the benchmark process grows, the normal fork becomes even slower:
691		809
692	1340 new processes, manual fork in a 20MB process	810	1340 new processes, manual fork of a 20MB process
693	731 new processes, manual fork in a 200MB process	811	731 new processes, manual fork of a 200MB process
694	235 new processes, manual fork in a 2000MB process	812	235 new processes, manual fork of a 2000MB process
695		813
696	What that means (to me) is that I can use this module without having a	814	What that means (to me) is that I can use this module without having a bad
697	very bad conscience because of the extra overhead required to start new	815	conscience because of the extra overhead required to start new processes.
698	processes.
699		816
700	=head1 TYPICAL PROBLEMS	817	=head1 TYPICAL PROBLEMS
701		818
702	This section lists typical problems that remain. I hope by recognising	819	This section lists typical problems that remain. I hope by recognising
703	them, most can be avoided.	820	them, most can be avoided.
704		821
705	=over 4	822	=over 4
706		823
707	=item "leaked" file descriptors for exec'ed processes	824	=item leaked file descriptors for exec'ed processes
708		825
709	POSIX systems inherit file descriptors by default when exec'ing a new	826	POSIX systems inherit file descriptors by default when exec'ing a new
710	process. While perl itself laudably sets the close-on-exec flags on new	827	process. While perl itself laudably sets the close-on-exec flags on new
711	file handles, most C libraries don't care, and even if all cared, it's	828	file handles, most C libraries don't care, and even if all cared, it's
712	often not possible to set the flag in a race-free manner.	829	often not possible to set the flag in a race-free manner.
…		…
732	libraries or the code that leaks those file descriptors.	849	libraries or the code that leaks those file descriptors.
733		850
734	Fortunately, most of these leaked descriptors do no harm, other than	851	Fortunately, most of these leaked descriptors do no harm, other than
735	sitting on some resources.	852	sitting on some resources.
736		853
737	=item "leaked" file descriptors for fork'ed processes	854	=item leaked file descriptors for fork'ed processes
738		855
739	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	856	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
740	which closes file descriptors not marked for being inherited.	857	which closes file descriptors not marked for being inherited.
741		858
742	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	859	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
751		868
752	The solution is to either not load these modules before use'ing	869	The solution is to either not load these modules before use'ing
753	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	870	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
754	initialising them, for example, by calling C<init Gtk2> manually.	871	initialising them, for example, by calling C<init Gtk2> manually.
755		872
756	=item exit runs destructors	873	=item exiting calls object destructors
757		874
758	This only applies to users of Lc<AnyEvent::Fork:Early> and	875	This only applies to users of L<AnyEvent::Fork:Early> and
759	L<AnyEvent::Fork::Template>.	876	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		877	that reference external resources.
760		878
761	When a process created by AnyEvent::Fork exits, it might do so by calling	879	When a process created by AnyEvent::Fork exits, it might do so by calling
762	exit, or simply letting perl reach the end of the program. At which point	880	exit, or simply letting perl reach the end of the program. At which point
763	Perl runs all destructors.	881	Perl runs all destructors.
764		882
…		…
783	to make it so, mostly due to the bloody broken perl that nobody seems to	901	to make it so, mostly due to the bloody broken perl that nobody seems to
784	care about. The fork emulation is a bad joke - I have yet to see something	902	care about. The fork emulation is a bad joke - I have yet to see something
785	useful that you can do with it without running into memory corruption	903	useful that you can do with it without running into memory corruption
786	issues or other braindamage. Hrrrr.	904	issues or other braindamage. Hrrrr.
787		905
788	Cygwin perl is not supported at the moment, as it should implement fd	906	Cygwin perl is not supported at the moment due to some hilarious
789	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	907	shortcomings of its API - see L<IO::FDPoll> for more details.
790	support enough functionality to do it.
791		908
792	=head1 SEE ALSO	909	=head1 SEE ALSO
793		910
794	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	911	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
795	L<AnyEvent::Fork::Template> (to create a process by forking the main	912	L<AnyEvent::Fork::Template> (to create a process by forking the main
796	program at a convenient time).	913	program at a convenient time), L<AnyEvent::Fork::RPC> (for simple RPC to
		914	child processes).
797		915
798	=head1 AUTHOR	916	=head1 AUTHOR AND CONTACT INFORMATION
799		917
800	Marc Lehmann <schmorp@schmorp.de>	918	Marc Lehmann <schmorp@schmorp.de>
801	http://home.schmorp.de/	919	http://software.schmorp.de/pkg/AnyEvent-Fork
802		920
803	=cut	921	=cut
804		922
805	1	923	1
806		924

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.20 by root, Sat Apr 6 03:35:36 2013 UTC vs. Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC

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Revision 1.20 by root, Sat Apr 6 03:35:36 2013 UTC vs.
Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC