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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.24 by root, Sat Apr 6 08:32:23 2013 UTC vs.
Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC

…		…
27		27
28	Special care has been taken to make this module useful from other modules,	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>	29	while still supporting specialised environments such as L<App::Staticperl>
30	or L<PAR::Packer>.	30	or L<PAR::Packer>.
31		31
32	=head1 WHAT THIS MODULE IS NOT	32	=head2 WHAT THIS MODULE IS NOT
33		33
34	This module only creates processes and lets you pass file handles and	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 -	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	36	there is no back channel from the process back to you, and there is no RPC
37	or message passing going on.	37	or message passing going on.
38		38
39	If you need some form of RPC, you can either implement it yourself	39	If you need some form of RPC, you could use the L<AnyEvent::Fork::RPC>
40	in whatever way you like, use some message-passing module such	40	companion module, which adds simple RPC/job queueing to a process created
41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use	41	by this module.
42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,	42
43	and so on.	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
44		163
45	=head1 EXAMPLES	164	=head1 EXAMPLES
46		165
47	=head2 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.
48		167
…		…
54		173
55	# now $master_filehandle is connected to the	174	# now $master_filehandle is connected to the
56	# $slave_filehandle in the new process.	175	# $slave_filehandle in the new process.
57	});	176	});
58		177
59	# MyModule::worker might look like this	178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
60	sub MyModule::worker {	182	sub worker {
61	my ($slave_filehandle) = @_;	183	my ($slave_filehandle) = @_;
62		184
63	# now $slave_filehandle is connected to the $master_filehandle	185	# now $slave_filehandle is connected to the $master_filehandle
64	# in the original prorcess. have fun!	186	# in the original prorcess. have fun!
65	}	187	}
…		…
84	}	206	}
85		207
86	# now do other things - maybe use the filehandle provided by run	208	# now do other things - maybe use the filehandle provided by run
87	# to wait for the processes to die. or whatever.	209	# to wait for the processes to die. or whatever.
88		210
89	# My::Server::run might look like this	211	C<My::Server> might look like this:
90	sub My::Server::run {	212
		213	package My::Server;
		214
		215	sub run {
91	my ($slave, $listener, $id) = @_;	216	my ($slave, $listener, $id) = @_;
92		217
93	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
94		219
95	# 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,
…		…
99	}	224	}
100	}	225	}
101		226
102	=head2 use AnyEvent::Fork as a faster fork+exec	227	=head2 use AnyEvent::Fork as a faster fork+exec
103		228
104	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to	229	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
105	the communications socket. It is usually faster than fork+exec, but still	230	and standard error redirected to the communications socket. It is usually
106	let's you prepare the environment.	231	faster than fork+exec, but still lets you prepare the environment.
107		232
108	open my $output, ">/tmp/log" or die "$!";	233	open my $output, ">/tmp/log" or die "$!";
109		234
110	AnyEvent::Fork	235	AnyEvent::Fork
111	->new	236	->new
112	->eval ('	237	->eval ('
		238	# compile a helper function for later use
113	sub run {	239	sub run {
114	my ($fh, $output, @cmd) = @_;	240	my ($fh, $output, @cmd) = @_;
115		241
116	# perl will clear close-on-exec on STDOUT/STDERR	242	# perl will clear close-on-exec on STDOUT/STDERR
117	open STDOUT, ">&", $output or die;	243	open STDOUT, ">&", $output or die;
…		…
123	->send_fh ($output)	249	->send_fh ($output)
124	->send_arg ("/bin/echo", "hi")	250	->send_arg ("/bin/echo", "hi")
125	->run ("run", my $cv = AE::cv);	251	->run ("run", my $cv = AE::cv);
126		252
127	my $stderr = $cv->recv;	253	my $stderr = $cv->recv;
128
129	=head1 PROBLEM STATEMENT
130
131	There are two ways to implement parallel processing on UNIX like operating
132	systems - fork and process, and fork+exec and process. They have different
133	advantages and disadvantages that I describe below, together with how this
134	module tries to mitigate the disadvantages.
135
136	=over 4
137
138	=item Forking from a big process can be very slow (a 5GB process needs
139	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
140	is often shared with exec (because you have to fork first), but in some
141	circumstances (e.g. when vfork is used), fork+exec can be much faster.
142
143	This module can help here by telling a small(er) helper process to fork,
144	or fork+exec instead.
145
146	=item Forking usually creates a copy-on-write copy of the parent
147	process. Memory (for example, modules or data files that have been
148	will not take additional memory). When exec'ing a new process, modules
149	and data files might need to be loaded again, at extra CPU and memory
150	cost. Likewise when forking, all data structures are copied as well - if
151	the program frees them and replaces them by new data, the child processes
152	will retain the memory even if it isn't used.
153
154	This module allows the main program to do a controlled fork, and allows
155	modules to exec processes safely at any time. When creating a custom
156	process pool you can take advantage of data sharing via fork without
157	risking to share large dynamic data structures that will blow up child
158	memory usage.
159
160	=item Exec'ing a new perl process might be difficult and slow. For
161	example, it is not easy to find the correct path to the perl interpreter,
162	and all modules have to be loaded from disk again. Long running processes
163	might run into problems when perl is upgraded for example.
164
165	This module supports creating pre-initialised perl processes to be used
166	as template, and also tries hard to identify the correct path to the perl
167	interpreter. With a cooperative main program, exec'ing the interpreter
168	might not even be necessary.
169
170	=item Forking might be impossible when a program is running. For example,
171	POSIX makes it almost impossible to fork from a multi-threaded program and
172	do anything useful in the child - strictly speaking, if your perl program
173	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
174	you cannot call fork on the perl level anymore, at all.
175
176	This module can safely fork helper processes at any time, by calling
177	fork+exec in C, in a POSIX-compatible way.
178
179	=item Parallel processing with fork might be inconvenient or difficult
180	to implement. For example, when a program uses an event loop and creates
181	watchers it becomes very hard to use the event loop from a child
182	program, as the watchers already exist but are only meaningful in the
183	parent. Worse, a module might want to use such a system, not knowing
184	whether another module or the main program also does, leading to problems.
185
186	This module only lets the main program create pools by forking (because
187	only the main program can know when it is still safe to do so) - all other
188	pools are created by fork+exec, after which such modules can again be
189	loaded.
190
191	=back
192		254
193	=head1 CONCEPTS	255	=head1 CONCEPTS
194		256
195	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
196	process, or by forking from an existing "template" process.	258	process, or by forking from an existing "template" process.
…		…
275	my ($fork_fh) = @_;	337	my ($fork_fh) = @_;
276	});	338	});
277		339
278	=back	340	=back
279		341
280	=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.
281		362
282	=over 4	363	=over 4
283		364
284	=cut	365	=cut
285		366
…		…
292	use AnyEvent;	373	use AnyEvent;
293	use AnyEvent::Util ();	374	use AnyEvent::Util ();
294		375
295	use IO::FDPass;	376	use IO::FDPass;
296		377
297	our $VERSION = 0.5;	378	our $VERSION = 0.6;
298
299	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
300
301	=item my $pool = new AnyEvent::Fork key => value...
302
303	Create a new process pool. The following named parameters are supported:
304
305	=over 4
306
307	=back
308
309	=cut
310		379
311	# the early fork template process	380	# the early fork template process
312	our $EARLY;	381	our $EARLY;
313		382
314	# the empty template process	383	# the empty template process
315	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	}
316		406
317	sub _cmd {	407	sub _cmd {
318	my $self = shift;	408	my $self = shift;
319		409
320	# 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
321	# 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
322	# it.	412	# it.
323	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	413	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
324		414
325	$self->[3] \|\|= AE::io $self->[1], 1, sub {	415	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
326	do {	416	do {
327	# 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,
328	# or a plain string.	418	# or a plain string.
329		419
330	if (ref $self->[2][0]) {	420	if (ref $self->[QUEUE][0]) {
331	# send fh	421	# send fh
332	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	422	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
333	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	423	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
334	undef $self->[3];	424	undef $self->[WW];
335	die "AnyEvent::Fork: file descriptor send failure: $!";	425	die "AnyEvent::Fork: file descriptor send failure: $!";
336	}	426	}
337		427
338	shift @{ $self->[2] };	428	shift @{ $self->[QUEUE] };
339		429
340	} else {	430	} else {
341	# send string	431	# send string
342	my $len = syswrite $self->[1], $self->[2][0];	432	my $len = syswrite $self->[FH], $self->[QUEUE][0];
343		433
344	unless ($len) {	434	unless ($len) {
345	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	435	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
346	undef $self->[3];	436	undef $self->[3];
347	die "AnyEvent::Fork: command write failure: $!";	437	die "AnyEvent::Fork: command write failure: $!";
348	}	438	}
349		439
350	substr $self->[2][0], 0, $len, "";	440	substr $self->[QUEUE][0], 0, $len, "";
351	shift @{ $self->[2] } unless length $self->[2][0];	441	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
352	}	442	}
353	} while @{ $self->[2] };	443	} while @{ $self->[QUEUE] };
354		444
355	# everything written	445	# everything written
356	undef $self->[3];	446	undef $self->[WW];
357		447
358	# invoke run callback, if any	448	# invoke run callback, if any
359	$self->[4]->($self->[1]) if $self->[4];	449	$self->[CB]->($self->[FH]) if $self->[CB];
360	};	450	};
361		451
362	() # make sure we don't leak the watcher	452	() # make sure we don't leak the watcher
363	}
364
365	sub _new {
366	my ($self, $fh, $pid) = @_;
367
368	AnyEvent::Util::fh_nonblocking $fh, 1;
369
370	$self = bless [
371	$pid,
372	$fh,
373	[], # write queue - strings or fd's
374	undef, # AE watcher
375	], $self;
376
377	$self
378	}	453	}
379		454
380	# fork template from current process, used by AnyEvent::Fork::Early/Template	455	# fork template from current process, used by AnyEvent::Fork::Early/Template
381	sub _new_fork {	456	sub _new_fork {
382	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	457	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
387	if ($pid eq 0) {	462	if ($pid eq 0) {
388	require AnyEvent::Fork::Serve;	463	require AnyEvent::Fork::Serve;
389	$AnyEvent::Fork::Serve::OWNER = $parent;	464	$AnyEvent::Fork::Serve::OWNER = $parent;
390	close $fh;	465	close $fh;
391	$0 = "$_[1] of $parent";	466	$0 = "$_[1] of $parent";
392	$SIG{CHLD} = 'IGNORE';
393	AnyEvent::Fork::Serve::serve ($slave);	467	AnyEvent::Fork::Serve::serve ($slave);
394	exit 0;	468	exit 0;
395	} elsif (!$pid) {	469	} elsif (!$pid) {
396	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	470	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
397	}	471	}
…		…
404	Create a new "empty" perl interpreter process and returns its process	478	Create a new "empty" perl interpreter process and returns its process
405	object for further manipulation.	479	object for further manipulation.
406		480
407	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
408	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
409	C<new_exec> and kept around for future calls.	483	C<new_exec> first and then stays around for future calls.
410
411	When the process object is destroyed, it will release the file handle
412	that connects it with the new process. When the new process has not yet
413	called C<run>, then the process will exit. Otherwise, what happens depends
414	entirely on the code that is executed.
415		484
416	=cut	485	=cut
417		486
418	sub new {	487	sub new {
419	my $class = shift;	488	my $class = shift;
…		…
509	}	578	}
510		579
511	=item $pid = $proc->pid	580	=item $pid = $proc->pid
512		581
513	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
514	process> running AnyEvent::Fork, and C<undef> otherwise.	583	process running AnyEvent::Fork>, and C<undef> otherwise.
515		584
516	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	585	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
517	L<AnyEvent::Fork::Template> are direct children, and you are responsible	586	L<AnyEvent::Fork::Template> are direct children, and you are responsible
518	to clean up their zombies when they die.	587	to clean up their zombies when they die.
519		588
520	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
521	AnyEvent::Fork.	590	AnyEvent::Fork itself.
522		591
523	=cut	592	=cut
524		593
525	sub pid {	594	sub pid {
526	$_[0][0]	595	$_[0][PID]
527	}	596	}
528		597
529	=item $proc = $proc->eval ($perlcode, @args)	598	=item $proc = $proc->eval ($perlcode, @args)
530		599
531	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
532	the strings specified by C<@args>, in the "main" package.	601	the strings specified by C<@args>, in the "main" package.
533		602
534	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
535	(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
536	to completely take over the process, use C<run> for that.	605	to completely take over the process, use C<run> for that.
537		606
538	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
539	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
540	will be reported to stderr and cause the process to exit.	609	will be reported to stderr and cause the process to exit.
541		610
542	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
543	"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
544	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
545	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.
546		616
547	Returns the process object for easy chaining of method calls.	617	Returns the process object for easy chaining of method calls.
548		618
549	=cut	619	=cut
550		620
…		…
576	=item $proc = $proc->send_fh ($handle, ...)	646	=item $proc = $proc->send_fh ($handle, ...)
577		647
578	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,
579	to prepare a call to C<run>.	649	to prepare a call to C<run>.
580		650
581	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
582	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
583	accomplished by simply not storing the file handles anywhere after passing	653	handles. This is most easily accomplished by simply not storing the file
584	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.
585		656
586	Returns the process object for easy chaining of method calls.	657	Returns the process object for easy chaining of method calls.
587		658
588	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
589	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.
…		…
596	sub send_fh {	667	sub send_fh {
597	my ($self, @fh) = @_;	668	my ($self, @fh) = @_;
598		669
599	for my $fh (@fh) {	670	for my $fh (@fh) {
600	$self->_cmd ("h");	671	$self->_cmd ("h");
601	push @{ $self->[2] }, \$fh;	672	push @{ $self->[QUEUE] }, \$fh;
602	}	673	}
603		674
604	$self	675	$self
605	}	676	}
606		677
607	=item $proc = $proc->send_arg ($string, ...)	678	=item $proc = $proc->send_arg ($string, ...)
608		679
609	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
610	C<run>. The strings can be any octet string.	681	C<run>. The strings can be any octet strings.
611		682
612	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
613	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
614	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
615	data.	686	data.
…		…
631	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
632	process. The function is called with the communication socket as first	703	process. The function is called with the communication socket as first
633	argument, followed by all file handles and string arguments sent earlier	704	argument, followed by all file handles and string arguments sent earlier
634	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.
635		706
		707	The process object becomes unusable on return from this function - any
		708	further method calls result in undefined behaviour.
		709
636	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
637	looked up in the main package.	711	looked up in the C<main> package.
638		712
639	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
640	process exits.	714	process exits.
641		715
642	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
643	been sent, the callback is invoked with the local communications socket	717	been sent, the callback is invoked with the local communications socket
644	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
645	like.	719	like.
646
647	The process object becomes unusable on return from this function - any
648	further method calls result in undefined behaviour.
649		720
650	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,
651	to save on kernel memory.	722	to save on kernel memory.
652		723
653	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
…		…
692	=cut	763	=cut
693		764
694	sub run {	765	sub run {
695	my ($self, $func, $cb) = @_;	766	my ($self, $func, $cb) = @_;
696		767
697	$self->[4] = $cb;	768	$self->[CB] = $cb;
698	$self->_cmd (r => $func);	769	$self->_cmd (r => $func);
699	}	770	}
700		771
701	=back	772	=back
702		773
…		…
728	479 vfork+execs per second, using AnyEvent::Fork->new_exec	799	479 vfork+execs per second, using AnyEvent::Fork->new_exec
729		800
730	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
731	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?
732		803
733	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
734	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
735	introduced is canceled out.	806	overhead is canceled out.
736		807
737	If the benchmark process grows, the normal fork becomes even slower:	808	If the benchmark process grows, the normal fork becomes even slower:
738		809
739	1340 new processes, manual fork in a 20MB process	810	1340 new processes, manual fork of a 20MB process
740	731 new processes, manual fork in a 200MB process	811	731 new processes, manual fork of a 200MB process
741	235 new processes, manual fork in a 2000MB process	812	235 new processes, manual fork of a 2000MB process
742		813
743	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
744	very bad conscience because of the extra overhead required to start new	815	conscience because of the extra overhead required to start new processes.
745	processes.
746		816
747	=head1 TYPICAL PROBLEMS	817	=head1 TYPICAL PROBLEMS
748		818
749	This section lists typical problems that remain. I hope by recognising	819	This section lists typical problems that remain. I hope by recognising
750	them, most can be avoided.	820	them, most can be avoided.
751		821
752	=over 4	822	=over 4
753		823
754	=item "leaked" file descriptors for exec'ed processes	824	=item leaked file descriptors for exec'ed processes
755		825
756	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
757	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
758	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
759	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.
…		…
779	libraries or the code that leaks those file descriptors.	849	libraries or the code that leaks those file descriptors.
780		850
781	Fortunately, most of these leaked descriptors do no harm, other than	851	Fortunately, most of these leaked descriptors do no harm, other than
782	sitting on some resources.	852	sitting on some resources.
783		853
784	=item "leaked" file descriptors for fork'ed processes	854	=item leaked file descriptors for fork'ed processes
785		855
786	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,
787	which closes file descriptors not marked for being inherited.	857	which closes file descriptors not marked for being inherited.
788		858
789	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	859	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
798		868
799	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
800	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
801	initialising them, for example, by calling C<init Gtk2> manually.	871	initialising them, for example, by calling C<init Gtk2> manually.
802		872
803	=item exit runs destructors	873	=item exiting calls object destructors
804		874
805	This only applies to users of Lc<AnyEvent::Fork:Early> and	875	This only applies to users of L<AnyEvent::Fork:Early> and
806	L<AnyEvent::Fork::Template>.	876	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		877	that reference external resources.
807		878
808	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
809	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
810	Perl runs all destructors.	881	Perl runs all destructors.
811		882
…		…
830	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
831	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
832	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
833	issues or other braindamage. Hrrrr.	904	issues or other braindamage. Hrrrr.
834		905
835	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
836	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.
837	support enough functionality to do it.
838		908
839	=head1 SEE ALSO	909	=head1 SEE ALSO
840		910
841	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	911	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
842	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
843	program at a convenient time).	913	program at a convenient time), L<AnyEvent::Fork::RPC> (for simple RPC to
		914	child processes).
844		915
845	=head1 AUTHOR	916	=head1 AUTHOR AND CONTACT INFORMATION
846		917
847	Marc Lehmann <schmorp@schmorp.de>	918	Marc Lehmann <schmorp@schmorp.de>
848	http://home.schmorp.de/	919	http://software.schmorp.de/pkg/AnyEvent-Fork
849		920
850	=cut	921	=cut
851		922
852	1	923	1
853		924

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Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC