[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 1.46 by root, Thu Apr 18 11:18:23 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;
…		…
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		254
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
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.
		259
		260	All these processes are called "child processes" (whether they are direct
		261	children or not), while the process that manages them is called the
		262	"parent process".
197		263
198	Each such process comes with its own file handle that can be used to	264	Each such process comes with its own file handle that can be used to
199	communicate with it (it's actually a socket - one end in the new process,	265	communicate with it (it's actually a socket - one end in the new process,
200	one end in the main process), and among the things you can do in it are	266	one end in the main process), and among the things you can do in it are
201	load modules, fork new processes, send file handles to it, and execute	267	load modules, fork new processes, send file handles to it, and execute
…		…
275	my ($fork_fh) = @_;	341	my ($fork_fh) = @_;
276	});	342	});
277		343
278	=back	344	=back
279		345
280	=head1 FUNCTIONS	346	=head1 THE C<AnyEvent::Fork> CLASS
		347
		348	This module exports nothing, and only implements a single class -
		349	C<AnyEvent::Fork>.
		350
		351	There are two class constructors that both create new processes - C<new>
		352	and C<new_exec>. The C<fork> method creates a new process by forking an
		353	existing one and could be considered a third constructor.
		354
		355	Most of the remaining methods deal with preparing the new process, by
		356	loading code, evaluating code and sending data to the new process. They
		357	usually return the process object, so you can chain method calls.
		358
		359	If a process object is destroyed before calling its C<run> method, then
		360	the process simply exits. After C<run> is called, all responsibility is
		361	passed to the specified function.
		362
		363	As long as there is any outstanding work to be done, process objects
		364	resist being destroyed, so there is no reason to store them unless you
		365	need them later - configure and forget works just fine.
281		366
282	=over 4	367	=over 4
283		368
284	=cut	369	=cut
285		370
…		…
292	use AnyEvent;	377	use AnyEvent;
293	use AnyEvent::Util ();	378	use AnyEvent::Util ();
294		379
295	use IO::FDPass;	380	use IO::FDPass;
296		381
297	our $VERSION = 0.5;	382	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		383
311	# the early fork template process	384	# the early fork template process
312	our $EARLY;	385	our $EARLY;
313		386
314	# the empty template process	387	# the empty template process
315	our $TEMPLATE;	388	our $TEMPLATE;
		389
		390	sub QUEUE() { 0 }
		391	sub FH() { 1 }
		392	sub WW() { 2 }
		393	sub PID() { 3 }
		394	sub CB() { 4 }
		395
		396	sub _new {
		397	my ($self, $fh, $pid) = @_;
		398
		399	AnyEvent::Util::fh_nonblocking $fh, 1;
		400
		401	$self = bless [
		402	[], # write queue - strings or fd's
		403	$fh,
		404	undef, # AE watcher
		405	$pid,
		406	], $self;
		407
		408	$self
		409	}
316		410
317	sub _cmd {	411	sub _cmd {
318	my $self = shift;	412	my $self = shift;
319		413
320	# ideally, we would want to use "a (w/a)*" as format string, but perl	414	# 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	415	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
322	# it.	416	# it.
323	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	417	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
324		418
325	$self->[3] \|\|= AE::io $self->[1], 1, sub {	419	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
326	do {	420	do {
327	# send the next "thing" in the queue - either a reference to an fh,	421	# send the next "thing" in the queue - either a reference to an fh,
328	# or a plain string.	422	# or a plain string.
329		423
330	if (ref $self->[2][0]) {	424	if (ref $self->[QUEUE][0]) {
331	# send fh	425	# send fh
332	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	426	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
333	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	427	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
334	undef $self->[3];	428	undef $self->[WW];
335	die "AnyEvent::Fork: file descriptor send failure: $!";	429	die "AnyEvent::Fork: file descriptor send failure: $!";
336	}	430	}
337		431
338	shift @{ $self->[2] };	432	shift @{ $self->[QUEUE] };
339		433
340	} else {	434	} else {
341	# send string	435	# send string
342	my $len = syswrite $self->[1], $self->[2][0];	436	my $len = syswrite $self->[FH], $self->[QUEUE][0];
343		437
344	unless ($len) {	438	unless ($len) {
345	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	439	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
346	undef $self->[3];	440	undef $self->[3];
347	die "AnyEvent::Fork: command write failure: $!";	441	die "AnyEvent::Fork: command write failure: $!";
348	}	442	}
349		443
350	substr $self->[2][0], 0, $len, "";	444	substr $self->[QUEUE][0], 0, $len, "";
351	shift @{ $self->[2] } unless length $self->[2][0];	445	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
352	}	446	}
353	} while @{ $self->[2] };	447	} while @{ $self->[QUEUE] };
354		448
355	# everything written	449	# everything written
356	undef $self->[3];	450	undef $self->[WW];
357		451
358	# invoke run callback, if any	452	# invoke run callback, if any
359	$self->[4]->($self->[1]) if $self->[4];	453	$self->[CB]->($self->[FH]) if $self->[CB];
360	};	454	};
361		455
362	() # make sure we don't leak the watcher	456	() # make sure we don't leak the watcher
363	}
364
365	sub _new {
366	my ($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	$self
378	}	457	}
379		458
380	# fork template from current process, used by AnyEvent::Fork::Early/Template	459	# fork template from current process, used by AnyEvent::Fork::Early/Template
381	sub _new_fork {	460	sub _new_fork {
382	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	461	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
387	if ($pid eq 0) {	466	if ($pid eq 0) {
388	require AnyEvent::Fork::Serve;	467	require AnyEvent::Fork::Serve;
389	$AnyEvent::Fork::Serve::OWNER = $parent;	468	$AnyEvent::Fork::Serve::OWNER = $parent;
390	close $fh;	469	close $fh;
391	$0 = "$_[1] of $parent";	470	$0 = "$_[1] of $parent";
392	$SIG{CHLD} = 'IGNORE';
393	AnyEvent::Fork::Serve::serve ($slave);	471	AnyEvent::Fork::Serve::serve ($slave);
394	exit 0;	472	exit 0;
395	} elsif (!$pid) {	473	} elsif (!$pid) {
396	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	474	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
397	}	475	}
…		…
404	Create a new "empty" perl interpreter process and returns its process	482	Create a new "empty" perl interpreter process and returns its process
405	object for further manipulation.	483	object for further manipulation.
406		484
407	The new process is forked from a template process that is kept around	485	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	486	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.	487	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		488
416	=cut	489	=cut
417		490
418	sub new {	491	sub new {
419	my $class = shift;	492	my $class = shift;
…		…
509	}	582	}
510		583
511	=item $pid = $proc->pid	584	=item $pid = $proc->pid
512		585
513	Returns the process id of the process I<iff it is a direct child of the	586	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.	587	process running AnyEvent::Fork>, and C<undef> otherwise.
515		588
516	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	589	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
517	L<AnyEvent::Fork::Template> are direct children, and you are responsible	590	L<AnyEvent::Fork::Template> are direct children, and you are responsible
518	to clean up their zombies when they die.	591	to clean up their zombies when they die.
519		592
520	All other processes are not direct children, and will be cleaned up by	593	All other processes are not direct children, and will be cleaned up by
521	AnyEvent::Fork.	594	AnyEvent::Fork itself.
522		595
523	=cut	596	=cut
524		597
525	sub pid {	598	sub pid {
526	$_[0][0]	599	$_[0][PID]
527	}	600	}
528		601
529	=item $proc = $proc->eval ($perlcode, @args)	602	=item $proc = $proc->eval ($perlcode, @args)
530		603
531	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	604	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
532	the strings specified by C<@args>, in the "main" package.	605	the strings specified by C<@args>, in the "main" package.
533		606
534	This call is meant to do any custom initialisation that might be required	607	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	608	(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.	609	to completely take over the process, use C<run> for that.
537		610
538	The code will usually be executed after this call returns, and there is no	611	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	612	way to pass anything back to the calling process. Any evaluation errors
540	will be reported to stderr and cause the process to exit.	613	will be reported to stderr and cause the process to exit.
541		614
542	If you want to execute some code to take over the process (see the	615	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	616	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	617	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.	618	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		619	a faster fork+exec> example to see it in action.
546		620
547	Returns the process object for easy chaining of method calls.	621	Returns the process object for easy chaining of method calls.
548		622
549	=cut	623	=cut
550		624
…		…
576	=item $proc = $proc->send_fh ($handle, ...)	650	=item $proc = $proc->send_fh ($handle, ...)
577		651
578	Send one or more file handles (I<not> file descriptors) to the process,	652	Send one or more file handles (I<not> file descriptors) to the process,
579	to prepare a call to C<run>.	653	to prepare a call to C<run>.
580		654
581	The process object keeps a reference to the handles until this is done,	655	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	656	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	657	handles. This is most easily accomplished by simply not storing the file
584	them to this method.	658	handles anywhere after passing them to this method - when AnyEvent::Fork
		659	is finished using them, perl will automatically close them.
585		660
586	Returns the process object for easy chaining of method calls.	661	Returns the process object for easy chaining of method calls.
587		662
588	Example: pass a file handle to a process, and release it without	663	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.	664	closing. It will be closed automatically when it is no longer used.
…		…
596	sub send_fh {	671	sub send_fh {
597	my ($self, @fh) = @_;	672	my ($self, @fh) = @_;
598		673
599	for my $fh (@fh) {	674	for my $fh (@fh) {
600	$self->_cmd ("h");	675	$self->_cmd ("h");
601	push @{ $self->[2] }, \$fh;	676	push @{ $self->[QUEUE] }, \$fh;
602	}	677	}
603		678
604	$self	679	$self
605	}	680	}
606		681
607	=item $proc = $proc->send_arg ($string, ...)	682	=item $proc = $proc->send_arg ($string, ...)
608		683
609	Send one or more argument strings to the process, to prepare a call to	684	Send one or more argument strings to the process, to prepare a call to
610	C<run>. The strings can be any octet string.	685	C<run>. The strings can be any octet strings.
611		686
612	The protocol is optimised to pass a moderate number of relatively short	687	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	688	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	689	meant to pass some ID information or other startup info, not big chunks of
615	data.	690	data.
…		…
631	Enter the function specified by the function name in C<$func> in the	706	Enter the function specified by the function name in C<$func> in the
632	process. The function is called with the communication socket as first	707	process. The function is called with the communication socket as first
633	argument, followed by all file handles and string arguments sent earlier	708	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.	709	via C<send_fh> and C<send_arg> methods, in the order they were called.
635		710
		711	The process object becomes unusable on return from this function - any
		712	further method calls result in undefined behaviour.
		713
636	The function name should be fully qualified, but if it isn't, it will be	714	The function name should be fully qualified, but if it isn't, it will be
637	looked up in the main package.	715	looked up in the C<main> package.
638		716
639	If the called function returns, doesn't exist, or any error occurs, the	717	If the called function returns, doesn't exist, or any error occurs, the
640	process exits.	718	process exits.
641		719
642	Preparing the process is done in the background - when all commands have	720	Preparing the process is done in the background - when all commands have
643	been sent, the callback is invoked with the local communications socket	721	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	722	as argument. At this point you can start using the socket in any way you
645	like.	723	like.
646
647	The process object becomes unusable on return from this function - any
648	further method calls result in undefined behaviour.
649		724
650	If the communication socket isn't used, it should be closed on both sides,	725	If the communication socket isn't used, it should be closed on both sides,
651	to save on kernel memory.	726	to save on kernel memory.
652		727
653	The socket is non-blocking in the parent, and blocking in the newly	728	The socket is non-blocking in the parent, and blocking in the newly
…		…
692	=cut	767	=cut
693		768
694	sub run {	769	sub run {
695	my ($self, $func, $cb) = @_;	770	my ($self, $func, $cb) = @_;
696		771
697	$self->[4] = $cb;	772	$self->[CB] = $cb;
698	$self->_cmd (r => $func);	773	$self->_cmd (r => $func);
699	}	774	}
700		775
701	=back	776	=back
702		777
…		…
728	479 vfork+execs per second, using AnyEvent::Fork->new_exec	803	479 vfork+execs per second, using AnyEvent::Fork->new_exec
729		804
730	So how can C<< AnyEvent->new >> be faster than a standard fork, even	805	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?	806	though it uses the same operations, but adds a lot of overhead?
732		807
733	The difference is simply the process size: forking the 6MB process takes	808	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	809	so much longer than forking the 2.5MB template process that the extra
735	introduced is canceled out.	810	overhead is canceled out.
736		811
737	If the benchmark process grows, the normal fork becomes even slower:	812	If the benchmark process grows, the normal fork becomes even slower:
738		813
739	1340 new processes, manual fork in a 20MB process	814	1340 new processes, manual fork of a 20MB process
740	731 new processes, manual fork in a 200MB process	815	731 new processes, manual fork of a 200MB process
741	235 new processes, manual fork in a 2000MB process	816	235 new processes, manual fork of a 2000MB process
742		817
743	What that means (to me) is that I can use this module without having a	818	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	819	conscience because of the extra overhead required to start new processes.
745	processes.
746		820
747	=head1 TYPICAL PROBLEMS	821	=head1 TYPICAL PROBLEMS
748		822
749	This section lists typical problems that remain. I hope by recognising	823	This section lists typical problems that remain. I hope by recognising
750	them, most can be avoided.	824	them, most can be avoided.
751		825
752	=over 4	826	=over 4
753		827
754	=item "leaked" file descriptors for exec'ed processes	828	=item leaked file descriptors for exec'ed processes
755		829
756	POSIX systems inherit file descriptors by default when exec'ing a new	830	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	831	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	832	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.	833	often not possible to set the flag in a race-free manner.
…		…
779	libraries or the code that leaks those file descriptors.	853	libraries or the code that leaks those file descriptors.
780		854
781	Fortunately, most of these leaked descriptors do no harm, other than	855	Fortunately, most of these leaked descriptors do no harm, other than
782	sitting on some resources.	856	sitting on some resources.
783		857
784	=item "leaked" file descriptors for fork'ed processes	858	=item leaked file descriptors for fork'ed processes
785		859
786	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	860	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
787	which closes file descriptors not marked for being inherited.	861	which closes file descriptors not marked for being inherited.
788		862
789	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	863	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
798		872
799	The solution is to either not load these modules before use'ing	873	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	874	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
801	initialising them, for example, by calling C<init Gtk2> manually.	875	initialising them, for example, by calling C<init Gtk2> manually.
802		876
803	=item exit runs destructors	877	=item exiting calls object destructors
804		878
805	This only applies to users of Lc<AnyEvent::Fork:Early> and	879	This only applies to users of L<AnyEvent::Fork:Early> and
806	L<AnyEvent::Fork::Template>.	880	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		881	that reference external resources.
807		882
808	When a process created by AnyEvent::Fork exits, it might do so by calling	883	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	884	exit, or simply letting perl reach the end of the program. At which point
810	Perl runs all destructors.	885	Perl runs all destructors.
811		886
…		…
830	to make it so, mostly due to the bloody broken perl that nobody seems to	905	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	906	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	907	useful that you can do with it without running into memory corruption
833	issues or other braindamage. Hrrrr.	908	issues or other braindamage. Hrrrr.
834		909
835	Cygwin perl is not supported at the moment, as it should implement fd	910	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	911	shortcomings of its API - see L<IO::FDPoll> for more details.
837	support enough functionality to do it.
838		912
839	=head1 SEE ALSO	913	=head1 SEE ALSO
840		914
841	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	915	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		916	(part of this distribution).
		917
842	L<AnyEvent::Fork::Template> (to create a process by forking the main	918	L<AnyEvent::Fork::Template>, to create a process by forking the main
843	program at a convenient time).	919	program at a convenient time (part of this distribution).
844		920
845	=head1 AUTHOR	921	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		922
		923	=head1 AUTHOR AND CONTACT INFORMATION
846		924
847	Marc Lehmann <schmorp@schmorp.de>	925	Marc Lehmann <schmorp@schmorp.de>
848	http://home.schmorp.de/	926	http://software.schmorp.de/pkg/AnyEvent-Fork
849		927
850	=cut	928	=cut
851		929
852	1	930	1
853		931

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Revision 1.46 by root, Thu Apr 18 11:18:23 2013 UTC