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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.23 by root, Sat Apr 6 08:29:43 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	##################################################################
67	# use AnyEvent::Fork as a faster fork+exec	227	=head2 use AnyEvent::Fork as a faster fork+exec
68		228
69	# this runs /bin/echo hi, with stdout redirected to /tmp/log	229	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
70	# and stderr to the communications socket. it is usually faster	230	and standard error redirected to the communications socket. It is usually
71	# than fork+exec, but still let's you prepare the environment.	231	faster than fork+exec, but still lets you prepare the environment.
72		232
73	open my $output, ">/tmp/log" or die "$!";	233	open my $output, ">/tmp/log" or die "$!";
74		234
75	AnyEvent::Fork	235	AnyEvent::Fork
76	->new	236	->new
77	->eval ('	237	->eval ('
		238	# compile a helper function for later use
78	sub run {	239	sub run {
79	my ($fh, $output, @cmd) = @_;	240	my ($fh, $output, @cmd) = @_;
80		241
81	# perl will clear close-on-exec on STDOUT/STDERR	242	# perl will clear close-on-exec on STDOUT/STDERR
82	open STDOUT, ">&", $output or die;	243	open STDOUT, ">&", $output or die;
…		…
88	->send_fh ($output)	249	->send_fh ($output)
89	->send_arg ("/bin/echo", "hi")	250	->send_arg ("/bin/echo", "hi")
90	->run ("run", my $cv = AE::cv);	251	->run ("run", my $cv = AE::cv);
91		252
92	my $stderr = $cv->recv;	253	my $stderr = $cv->recv;
93
94	=head1 DESCRIPTION
95
96	This module allows you to create new processes, without actually forking
97	them from your current process (avoiding the problems of forking), but
98	preserving most of the advantages of fork.
99
100	It can be used to create new worker processes or new independent
101	subprocesses for short- and long-running jobs, process pools (e.g. for use
102	in pre-forked servers) but also to spawn new external processes (such as
103	CGI scripts from a web server), which can be faster (and more well behaved)
104	than using fork+exec in big processes.
105
106	Special care has been taken to make this module useful from other modules,
107	while still supporting specialised environments such as L<App::Staticperl>
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.
122
123	=head1 PROBLEM STATEMENT
124
125	There are two ways to implement parallel processing on UNIX like operating
126	systems - fork and process, and fork+exec and process. They have different
127	advantages and disadvantages that I describe below, together with how this
128	module tries to mitigate the disadvantages.
129
130	=over 4
131
132	=item Forking from a big process can be very slow (a 5GB process needs
133	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
134	is often shared with exec (because you have to fork first), but in some
135	circumstances (e.g. when vfork is used), fork+exec can be much faster.
136
137	This module can help here by telling a small(er) helper process to fork,
138	or fork+exec instead.
139
140	=item Forking usually creates a copy-on-write copy of the parent
141	process. Memory (for example, modules or data files that have been
142	will not take additional memory). When exec'ing a new process, modules
143	and data files might need to be loaded again, at extra CPU and memory
144	cost. Likewise when forking, all data structures are copied as well - if
145	the program frees them and replaces them by new data, the child processes
146	will retain the memory even if it isn't used.
147
148	This module allows the main program to do a controlled fork, and allows
149	modules to exec processes safely at any time. When creating a custom
150	process pool you can take advantage of data sharing via fork without
151	risking to share large dynamic data structures that will blow up child
152	memory usage.
153
154	=item Exec'ing a new perl process might be difficult and slow. For
155	example, it is not easy to find the correct path to the perl interpreter,
156	and all modules have to be loaded from disk again. Long running processes
157	might run into problems when perl is upgraded for example.
158
159	This module supports creating pre-initialised perl processes to be used
160	as template, and also tries hard to identify the correct path to the perl
161	interpreter. With a cooperative main program, exec'ing the interpreter
162	might not even be necessary.
163
164	=item Forking might be impossible when a program is running. For example,
165	POSIX makes it almost impossible to fork from a multi-threaded program and
166	do anything useful in the child - strictly speaking, if your perl program
167	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
168	you cannot call fork on the perl level anymore, at all.
169
170	This module can safely fork helper processes at any time, by calling
171	fork+exec in C, in a POSIX-compatible way.
172
173	=item Parallel processing with fork might be inconvenient or difficult
174	to implement. For example, when a program uses an event loop and creates
175	watchers it becomes very hard to use the event loop from a child
176	program, as the watchers already exist but are only meaningful in the
177	parent. Worse, a module might want to use such a system, not knowing
178	whether another module or the main program also does, leading to problems.
179
180	This module only lets the main program create pools by forking (because
181	only the main program can know when it is still safe to do so) - all other
182	pools are created by fork+exec, after which such modules can again be
183	loaded.
184
185	=back
186		254
187	=head1 CONCEPTS	255	=head1 CONCEPTS
188		256
189	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
190	process, or by forking from an existing "template" process.	258	process, or by forking from an existing "template" process.
…		…
269	my ($fork_fh) = @_;	337	my ($fork_fh) = @_;
270	});	338	});
271		339
272	=back	340	=back
273		341
274	=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.
275		362
276	=over 4	363	=over 4
277		364
278	=cut	365	=cut
279		366
…		…
286	use AnyEvent;	373	use AnyEvent;
287	use AnyEvent::Util ();	374	use AnyEvent::Util ();
288		375
289	use IO::FDPass;	376	use IO::FDPass;
290		377
291	our $VERSION = 0.5;	378	our $VERSION = 0.6;
292
293	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
294
295	=item my $pool = new AnyEvent::Fork key => value...
296
297	Create a new process pool. The following named parameters are supported:
298
299	=over 4
300
301	=back
302
303	=cut
304		379
305	# the early fork template process	380	# the early fork template process
306	our $EARLY;	381	our $EARLY;
307		382
308	# the empty template process	383	# the empty template process
309	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	}
310		406
311	sub _cmd {	407	sub _cmd {
312	my $self = shift;	408	my $self = shift;
313		409
314	# 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
315	# 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
316	# it.	412	# it.
317	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	413	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
318		414
319	$self->[3] \|\|= AE::io $self->[1], 1, sub {	415	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
320	do {	416	do {
321	# 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,
322	# or a plain string.	418	# or a plain string.
323		419
324	if (ref $self->[2][0]) {	420	if (ref $self->[QUEUE][0]) {
325	# send fh	421	# send fh
326	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	422	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
327	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	423	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
328	undef $self->[3];	424	undef $self->[WW];
329	die "AnyEvent::Fork: file descriptor send failure: $!";	425	die "AnyEvent::Fork: file descriptor send failure: $!";
330	}	426	}
331		427
332	shift @{ $self->[2] };	428	shift @{ $self->[QUEUE] };
333		429
334	} else {	430	} else {
335	# send string	431	# send string
336	my $len = syswrite $self->[1], $self->[2][0];	432	my $len = syswrite $self->[FH], $self->[QUEUE][0];
337		433
338	unless ($len) {	434	unless ($len) {
339	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	435	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
340	undef $self->[3];	436	undef $self->[3];
341	die "AnyEvent::Fork: command write failure: $!";	437	die "AnyEvent::Fork: command write failure: $!";
342	}	438	}
343		439
344	substr $self->[2][0], 0, $len, "";	440	substr $self->[QUEUE][0], 0, $len, "";
345	shift @{ $self->[2] } unless length $self->[2][0];	441	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
346	}	442	}
347	} while @{ $self->[2] };	443	} while @{ $self->[QUEUE] };
348		444
349	# everything written	445	# everything written
350	undef $self->[3];	446	undef $self->[WW];
351		447
352	# invoke run callback, if any	448	# invoke run callback, if any
353	$self->[4]->($self->[1]) if $self->[4];	449	$self->[CB]->($self->[FH]) if $self->[CB];
354	};	450	};
355		451
356	() # make sure we don't leak the watcher	452	() # make sure we don't leak the watcher
357	}
358
359	sub _new {
360	my ($self, $fh, $pid) = @_;
361
362	AnyEvent::Util::fh_nonblocking $fh, 1;
363
364	$self = bless [
365	$pid,
366	$fh,
367	[], # write queue - strings or fd's
368	undef, # AE watcher
369	], $self;
370
371	$self
372	}	453	}
373		454
374	# fork template from current process, used by AnyEvent::Fork::Early/Template	455	# fork template from current process, used by AnyEvent::Fork::Early/Template
375	sub _new_fork {	456	sub _new_fork {
376	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	457	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
381	if ($pid eq 0) {	462	if ($pid eq 0) {
382	require AnyEvent::Fork::Serve;	463	require AnyEvent::Fork::Serve;
383	$AnyEvent::Fork::Serve::OWNER = $parent;	464	$AnyEvent::Fork::Serve::OWNER = $parent;
384	close $fh;	465	close $fh;
385	$0 = "$_[1] of $parent";	466	$0 = "$_[1] of $parent";
386	$SIG{CHLD} = 'IGNORE';
387	AnyEvent::Fork::Serve::serve ($slave);	467	AnyEvent::Fork::Serve::serve ($slave);
388	exit 0;	468	exit 0;
389	} elsif (!$pid) {	469	} elsif (!$pid) {
390	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	470	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
391	}	471	}
…		…
398	Create a new "empty" perl interpreter process and returns its process	478	Create a new "empty" perl interpreter process and returns its process
399	object for further manipulation.	479	object for further manipulation.
400		480
401	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
402	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
403	C<new_exec> and kept around for future calls.	483	C<new_exec> first and then stays 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.
409		484
410	=cut	485	=cut
411		486
412	sub new {	487	sub new {
413	my $class = shift;	488	my $class = shift;
…		…
503	}	578	}
504		579
505	=item $pid = $proc->pid	580	=item $pid = $proc->pid
506		581
507	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
508	process> running AnyEvent::Fork, and C<undef> otherwise.	583	process running AnyEvent::Fork>, and C<undef> otherwise.
509		584
510	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	585	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
511	L<AnyEvent::Fork::Template> are direct children, and you are responsible	586	L<AnyEvent::Fork::Template> are direct children, and you are responsible
512	to clean up their zombies when they die.	587	to clean up their zombies when they die.
513		588
514	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
515	AnyEvent::Fork.	590	AnyEvent::Fork itself.
516		591
517	=cut	592	=cut
518		593
519	sub pid {	594	sub pid {
520	$_[0][0]	595	$_[0][PID]
521	}	596	}
522		597
523	=item $proc = $proc->eval ($perlcode, @args)	598	=item $proc = $proc->eval ($perlcode, @args)
524		599
525	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
526	the strings specified by C<@args>, in the "main" package.	601	the strings specified by C<@args>, in the "main" package.
527		602
528	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
529	(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
530	to completely take over the process, use C<run> for that.	605	to completely take over the process, use C<run> for that.
531		606
532	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
533	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
534	will be reported to stderr and cause the process to exit.	609	will be reported to stderr and cause the process to exit.
535		610
536	If you want to execute some code to take over the process (see the	611	If you want to execute some code (that isn't in a module) to take over the
537	"fork+exec" example in the SYNOPSIS), you should compile a function via	612	process, you should compile a function via C<eval> first, and then call
538	C<eval> first, and then call it via C<run>. This also gives you access to	613	it via C<run>. This also gives you access to any arguments passed via the
539	any arguments passed via the C<send_xxx> methods, such as file handles.	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.
540		616
541	Returns the process object for easy chaining of method calls.	617	Returns the process object for easy chaining of method calls.
542		618
543	=cut	619	=cut
544		620
…		…
570	=item $proc = $proc->send_fh ($handle, ...)	646	=item $proc = $proc->send_fh ($handle, ...)
571		647
572	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,
573	to prepare a call to C<run>.	649	to prepare a call to C<run>.
574		650
575	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
576	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
577	accomplished by simply not storing the file handles anywhere after passing	653	handles. This is most easily accomplished by simply not storing the file
578	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.
579		656
580	Returns the process object for easy chaining of method calls.	657	Returns the process object for easy chaining of method calls.
581		658
582	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
583	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.
…		…
590	sub send_fh {	667	sub send_fh {
591	my ($self, @fh) = @_;	668	my ($self, @fh) = @_;
592		669
593	for my $fh (@fh) {	670	for my $fh (@fh) {
594	$self->_cmd ("h");	671	$self->_cmd ("h");
595	push @{ $self->[2] }, \$fh;	672	push @{ $self->[QUEUE] }, \$fh;
596	}	673	}
597		674
598	$self	675	$self
599	}	676	}
600		677
601	=item $proc = $proc->send_arg ($string, ...)	678	=item $proc = $proc->send_arg ($string, ...)
602		679
603	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
604	C<run>. The strings can be any octet string.	681	C<run>. The strings can be any octet strings.
605		682
606	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
607	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
608	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
609	data.	686	data.
…		…
625	Enter the function specified by the function name in C<$func> in the	702	Enter the function specified by the function name in C<$func> in the
626	process. The function is called with the communication socket as first	703	process. The function is called with the communication socket as first
627	argument, followed by all file handles and string arguments sent earlier	704	argument, followed by all file handles and string arguments sent earlier
628	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.
629		706
		707	The process object becomes unusable on return from this function - any
		708	further method calls result in undefined behaviour.
		709
630	The function name should be fully qualified, but if it isn't, it will be	710	The function name should be fully qualified, but if it isn't, it will be
631	looked up in the main package.	711	looked up in the C<main> package.
632		712
633	If the called function returns, doesn't exist, or any error occurs, the	713	If the called function returns, doesn't exist, or any error occurs, the
634	process exits.	714	process exits.
635		715
636	Preparing the process is done in the background - when all commands have	716	Preparing the process is done in the background - when all commands have
637	been sent, the callback is invoked with the local communications socket	717	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	718	as argument. At this point you can start using the socket in any way you
639	like.	719	like.
640
641	The process object becomes unusable on return from this function - any
642	further method calls result in undefined behaviour.
643		720
644	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,
645	to save on kernel memory.	722	to save on kernel memory.
646		723
647	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
…		…
686	=cut	763	=cut
687		764
688	sub run {	765	sub run {
689	my ($self, $func, $cb) = @_;	766	my ($self, $func, $cb) = @_;
690		767
691	$self->[4] = $cb;	768	$self->[CB] = $cb;
692	$self->_cmd (r => $func);	769	$self->_cmd (r => $func);
693	}	770	}
694		771
695	=back	772	=back
696		773
…		…
722	479 vfork+execs per second, using AnyEvent::Fork->new_exec	799	479 vfork+execs per second, using AnyEvent::Fork->new_exec
723		800
724	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
725	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?
726		803
727	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
728	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
729	introduced is canceled out.	806	overhead is canceled out.
730		807
731	If the benchmark process grows, the normal fork becomes even slower:	808	If the benchmark process grows, the normal fork becomes even slower:
732		809
733	1340 new processes, manual fork in a 20MB process	810	1340 new processes, manual fork of a 20MB process
734	731 new processes, manual fork in a 200MB process	811	731 new processes, manual fork of a 200MB process
735	235 new processes, manual fork in a 2000MB process	812	235 new processes, manual fork of a 2000MB process
736		813
737	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
738	very bad conscience because of the extra overhead required to start new	815	conscience because of the extra overhead required to start new processes.
739	processes.
740		816
741	=head1 TYPICAL PROBLEMS	817	=head1 TYPICAL PROBLEMS
742		818
743	This section lists typical problems that remain. I hope by recognising	819	This section lists typical problems that remain. I hope by recognising
744	them, most can be avoided.	820	them, most can be avoided.
745		821
746	=over 4	822	=over 4
747		823
748	=item "leaked" file descriptors for exec'ed processes	824	=item leaked file descriptors for exec'ed processes
749		825
750	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
751	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
752	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
753	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.
…		…
773	libraries or the code that leaks those file descriptors.	849	libraries or the code that leaks those file descriptors.
774		850
775	Fortunately, most of these leaked descriptors do no harm, other than	851	Fortunately, most of these leaked descriptors do no harm, other than
776	sitting on some resources.	852	sitting on some resources.
777		853
778	=item "leaked" file descriptors for fork'ed processes	854	=item leaked file descriptors for fork'ed processes
779		855
780	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,
781	which closes file descriptors not marked for being inherited.	857	which closes file descriptors not marked for being inherited.
782		858
783	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	859	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
792		868
793	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
794	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
795	initialising them, for example, by calling C<init Gtk2> manually.	871	initialising them, for example, by calling C<init Gtk2> manually.
796		872
797	=item exit runs destructors	873	=item exiting calls object destructors
798		874
799	This only applies to users of Lc<AnyEvent::Fork:Early> and	875	This only applies to users of L<AnyEvent::Fork:Early> and
800	L<AnyEvent::Fork::Template>.	876	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		877	that reference external resources.
801		878
802	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
803	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
804	Perl runs all destructors.	881	Perl runs all destructors.
805		882
…		…
824	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
825	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
826	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
827	issues or other braindamage. Hrrrr.	904	issues or other braindamage. Hrrrr.
828		905
829	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
830	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.
831	support enough functionality to do it.
832		908
833	=head1 SEE ALSO	909	=head1 SEE ALSO
834		910
835	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	911	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
836	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
837	program at a convenient time).	913	program at a convenient time), L<AnyEvent::Fork::RPC> (for simple RPC to
		914	child processes).
838		915
839	=head1 AUTHOR	916	=head1 AUTHOR AND CONTACT INFORMATION
840		917
841	Marc Lehmann <schmorp@schmorp.de>	918	Marc Lehmann <schmorp@schmorp.de>
842	http://home.schmorp.de/	919	http://software.schmorp.de/pkg/AnyEvent-Fork
843		920
844	=cut	921	=cut
845		922
846	1	923	1
847		924

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Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs.
Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC