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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs.
Revision 1.37 by root, Sat Apr 6 20:06:39 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	=head1 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 can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head1 PROBLEM STATEMENT
		46
		47	There are two traditional ways to implement parallel processing on UNIX
		48	like operating systems - fork and process, and fork+exec and process. They
		49	have different advantages and disadvantages that I describe below,
		50	together with how this module tries to mitigate the disadvantages.
		51
		52	=over 4
		53
		54	=item Forking from a big process can be very slow.
		55
		56	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		57	overhead is often shared with exec (because you have to fork first), but
		58	in some circumstances (e.g. when vfork is used), fork+exec can be much
		59	faster.
		60
		61	This module can help here by telling a small(er) helper process to fork,
		62	which is faster then forking the main process, and also uses vfork where
		63	possible. This gives the speed of vfork, with the flexibility of fork.
		64
		65	=item Forking usually creates a copy-on-write copy of the parent
		66	process.
		67
		68	For example, modules or data files that are loaded will not use additional
		69	memory after a fork. When exec'ing a new process, modules and data files
		70	might need to be loaded again, at extra CPU and memory cost. But when
		71	forking, literally all data structures are copied - if the program frees
		72	them and replaces them by new data, the child processes will retain the
		73	old version even if it isn't used, which can suddenly and unexpectedly
		74	increase memory usage when freeing memory.
		75
		76	The trade-off is between more sharing with fork (which can be good or
		77	bad), and no sharing with exec.
		78
		79	This module allows the main program to do a controlled fork, and allows
		80	modules to exec processes safely at any time. When creating a custom
		81	process pool you can take advantage of data sharing via fork without
		82	risking to share large dynamic data structures that will blow up child
		83	memory usage.
		84
		85	In other words, this module puts you into control over what is being
		86	shared and what isn't, at all times.
		87
		88	=item Exec'ing a new perl process might be difficult.
		89
		90	For example, it is not easy to find the correct path to the perl
		91	interpreter - C<$^X> might not be a perl interpreter at all.
		92
		93	This module tries hard to identify the correct path to the perl
		94	interpreter. With a cooperative main program, exec'ing the interpreter
		95	might not even be necessary, but even without help from the main program,
		96	it will still work when used from a module.
		97
		98	=item Exec'ing a new perl process might be slow, as all necessary modules
		99	have to be loaded from disk again, with no guarantees of success.
		100
		101	Long running processes might run into problems when perl is upgraded
		102	and modules are no longer loadable because they refer to a different
		103	perl version, or parts of a distribution are newer than the ones already
		104	loaded.
		105
		106	This module supports creating pre-initialised perl processes to be used as
		107	a template for new processes.
		108
		109	=item Forking might be impossible when a program is running.
		110
		111	For example, POSIX makes it almost impossible to fork from a
		112	multi-threaded program while doing anything useful in the child - in
		113	fact, if your perl program uses POSIX threads (even indirectly via
		114	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		115	anymore without risking corruption issues on a number of operating
		116	systems.
		117
		118	This module can safely fork helper processes at any time, by calling
		119	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		120
		121	=item Parallel processing with fork might be inconvenient or difficult
		122	to implement. Modules might not work in both parent and child.
		123
		124	For example, when a program uses an event loop and creates watchers it
		125	becomes very hard to use the event loop from a child program, as the
		126	watchers already exist but are only meaningful in the parent. Worse, a
		127	module might want to use such a module, not knowing whether another module
		128	or the main program also does, leading to problems.
		129
		130	Apart from event loops, graphical toolkits also commonly fall into the
		131	"unsafe module" category, or just about anything that communicates with
		132	the external world, such as network libraries and file I/O modules, which
		133	usually don't like being copied and then allowed to continue in two
		134	processes.
		135
		136	With this module only the main program is allowed to create new processes
		137	by forking (because only the main program can know when it is still safe
		138	to do so) - all other processes are created via fork+exec, which makes it
		139	possible to use modules such as event loops or window interfaces safely.
		140
		141	=back
		142
		143	=head1 EXAMPLES
		144
10	# create a single new process, tell it to run your worker function	145	=head2 Create a single new process, tell it to run your worker function.
11		146
12	AnyEvent::Fork	147	AnyEvent::Fork
13	->new	148	->new
14	->require ("MyModule")	149	->require ("MyModule")
15	->run ("MyModule::worker, sub {	150	->run ("MyModule::worker, sub {
…		…
17		152
18	# now $master_filehandle is connected to the	153	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	154	# $slave_filehandle in the new process.
20	});	155	});
21		156
22	# MyModule::worker might look like this	157	C<MyModule> might look like this:
		158
		159	package MyModule;
		160
23	sub MyModule::worker {	161	sub worker {
24	my ($slave_filehandle) = @_;	162	my ($slave_filehandle) = @_;
25		163
26	# now $slave_filehandle is connected to the $master_filehandle	164	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	165	# in the original prorcess. have fun!
28	}	166	}
29		167
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	168	=head2 Create a pool of server processes all accepting on the same socket.
32		169
33	# create listener socket	170	# create listener socket
34	my $listener = ...;	171	my $listener = ...;
35		172
36	# create a pool template, initialise it and give it the socket	173	# create a pool template, initialise it and give it the socket
…		…
48	}	185	}
49		186
50	# now do other things - maybe use the filehandle provided by run	187	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	188	# to wait for the processes to die. or whatever.
52		189
53	# My::Server::run might look like this	190	C<My::Server> might look like this:
54	sub My::Server::run {	191
		192	package My::Server;
		193
		194	sub run {
55	my ($slave, $listener, $id) = @_;	195	my ($slave, $listener, $id) = @_;
56		196
57	close $slave; # we do not use the socket, so close it to save resources	197	close $slave; # we do not use the socket, so close it to save resources
58		198
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	199	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	201	while (my $socket = $listener->accept) {
62	# do sth. with new socket	202	# do sth. with new socket
63	}	203	}
64	}	204	}
65		205
66	=head1 DESCRIPTION	206	=head2 use AnyEvent::Fork as a faster fork+exec
67		207
68	This module allows you to create new processes, without actually forking	208	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
69	them from your current process (avoiding the problems of forking), but	209	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	210	faster than fork+exec, but still lets you prepare the environment.
71		211
72	It can be used to create new worker processes or new independent	212	open my $output, ">/tmp/log" or die "$!";
73	subprocesses for short- and long-running jobs, process pools (e.g. for use
74	in pre-forked servers) but also to spawn new external processes (such as
75	CGI scripts from a web server), which can be faster (and more well behaved)
76	than using fork+exec in big processes.
77		213
78	Special care has been taken to make this module useful from other modules,	214	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	215	->new
80	or L<PAR::Packer>.	216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
81		219
82	=head1 WHAT THIS MODULE IS NOT	220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
83		223
84	This module only creates processes and lets you pass file handles and	224	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	225	}
86	there is no back channel from the process back to you, and there is no RPC	226	')
87	or message passing going on.	227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
88		230
89	If you need some form of RPC, you can either implement it yourself	231	my $stderr = $cv->recv;
90	in whatever way you like, use some message-passing module such
91	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
92	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
93	and so on.
94
95	=head1 PROBLEM STATEMENT
96
97	There are two ways to implement parallel processing on UNIX like operating
98	systems - fork and process, and fork+exec and process. They have different
99	advantages and disadvantages that I describe below, together with how this
100	module tries to mitigate the disadvantages.
101
102	=over 4
103
104	=item Forking from a big process can be very slow (a 5GB process needs
105	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
106	is often shared with exec (because you have to fork first), but in some
107	circumstances (e.g. when vfork is used), fork+exec can be much faster.
108
109	This module can help here by telling a small(er) helper process to fork,
110	or fork+exec instead.
111
112	=item Forking usually creates a copy-on-write copy of the parent
113	process. Memory (for example, modules or data files that have been
114	will not take additional memory). When exec'ing a new process, modules
115	and data files might need to be loaded again, at extra CPU and memory
116	cost. Likewise when forking, all data structures are copied as well - if
117	the program frees them and replaces them by new data, the child processes
118	will retain the memory even if it isn't used.
119
120	This module allows the main program to do a controlled fork, and allows
121	modules to exec processes safely at any time. When creating a custom
122	process pool you can take advantage of data sharing via fork without
123	risking to share large dynamic data structures that will blow up child
124	memory usage.
125
126	=item Exec'ing a new perl process might be difficult and slow. For
127	example, it is not easy to find the correct path to the perl interpreter,
128	and all modules have to be loaded from disk again. Long running processes
129	might run into problems when perl is upgraded for example.
130
131	This module supports creating pre-initialised perl processes to be used
132	as template, and also tries hard to identify the correct path to the perl
133	interpreter. With a cooperative main program, exec'ing the interpreter
134	might not even be necessary.
135
136	=item Forking might be impossible when a program is running. For example,
137	POSIX makes it almost impossible to fork from a multi-threaded program and
138	do anything useful in the child - strictly speaking, if your perl program
139	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
140	you cannot call fork on the perl level anymore, at all.
141
142	This module can safely fork helper processes at any time, by calling
143	fork+exec in C, in a POSIX-compatible way.
144
145	=item Parallel processing with fork might be inconvenient or difficult
146	to implement. For example, when a program uses an event loop and creates
147	watchers it becomes very hard to use the event loop from a child
148	program, as the watchers already exist but are only meaningful in the
149	parent. Worse, a module might want to use such a system, not knowing
150	whether another module or the main program also does, leading to problems.
151
152	This module only lets the main program create pools by forking (because
153	only the main program can know when it is still safe to do so) - all other
154	pools are created by fork+exec, after which such modules can again be
155	loaded.
156
157	=back
158		232
159	=head1 CONCEPTS	233	=head1 CONCEPTS
160		234
161	This module can create new processes either by executing a new perl	235	This module can create new processes either by executing a new perl
162	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
241	my ($fork_fh) = @_;	315	my ($fork_fh) = @_;
242	});	316	});
243		317
244	=back	318	=back
245		319
246	=head1 FUNCTIONS	320	=head1 THE C<AnyEvent::Fork> CLASS
		321
		322	This module exports nothing, and only implements a single class -
		323	C<AnyEvent::Fork>.
		324
		325	There are two class constructors that both create new processes - C<new>
		326	and C<new_exec>. The C<fork> method creates a new process by forking an
		327	existing one and could be considered a third constructor.
		328
		329	Most of the remaining methods deal with preparing the new process, by
		330	loading code, evaluating code and sending data to the new process. They
		331	usually return the process object, so you can chain method calls.
		332
		333	If a process object is destroyed before calling its C<run> method, then
		334	the process simply exits. After C<run> is called, all responsibility is
		335	passed to the specified function.
		336
		337	As long as there is any outstanding work to be done, process objects
		338	resist being destroyed, so there is no reason to store them unless you
		339	need them later - configure and forget works just fine.
247		340
248	=over 4	341	=over 4
249		342
250	=cut	343	=cut
251		344
…		…
258	use AnyEvent;	351	use AnyEvent;
259	use AnyEvent::Util ();	352	use AnyEvent::Util ();
260		353
261	use IO::FDPass;	354	use IO::FDPass;
262		355
263	our $VERSION = 0.2;	356	our $VERSION = 0.5;
264		357
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	358	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267	=item my $pool = new AnyEvent::Fork key => value...
268
269	Create a new process pool. The following named parameters are supported:
270		359
271	=over 4	360	=over 4
272		361
273	=back	362	=back
274		363
…		…
284	my $self = shift;	373	my $self = shift;
285		374
286	# ideally, we would want to use "a (w/a)*" as format string, but perl	375	# ideally, we would want to use "a (w/a)*" as format string, but perl
287	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack	376	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
288	# it.	377	# it.
289	push @{ $self->[2] }, pack "L/a", pack "(w/a)*", @_;	378	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
290		379
291	unless ($self->[3]) {	380	$self->[3] \|\|= AE::io $self->[1], 1, sub {
292	my $wcb = sub {
293	do {	381	do {
294	# send the next "thing" in the queue - either a reference to an fh,	382	# send the next "thing" in the queue - either a reference to an fh,
295	# or a plain string.	383	# or a plain string.
296		384
297	if (ref $self->[2][0]) {	385	if (ref $self->[2][0]) {
298	# send fh	386	# send fh
299	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	387	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
300	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	388	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
301	undef $self->[3];	389	undef $self->[3];
302	die "AnyEvent::Fork: file descriptor send failure: $!";	390	die "AnyEvent::Fork: file descriptor send failure: $!";
303	}
304
305	shift @{ $self->[2] };
306
307	} else {
308	# send string
309	my $len = syswrite $self->[1], $self->[2][0];
310
311	unless ($len) {
312	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
313	undef $self->[3];
314	die "AnyEvent::Fork: command write failure: $!";
315	}
316
317	substr $self->[2][0], 0, $len, "";
318	shift @{ $self->[2] } unless length $self->[2][0];
319	}	391	}
		392
		393	shift @{ $self->[2] };
		394
		395	} else {
		396	# send string
		397	my $len = syswrite $self->[1], $self->[2][0];
		398
		399	unless ($len) {
		400	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		401	undef $self->[3];
		402	die "AnyEvent::Fork: command write failure: $!";
		403	}
		404
		405	substr $self->[2][0], 0, $len, "";
		406	shift @{ $self->[2] } unless length $self->[2][0];
		407	}
320	} while @{ $self->[2] };	408	} while @{ $self->[2] };
321		409
322	# everything written	410	# everything written
323	undef $self->[3];	411	undef $self->[3];
		412
324	# invoke run callback	413	# invoke run callback, if any
325	$self->[0]->($self->[1]) if $self->[0];	414	$self->[4]->($self->[1]) if $self->[4];
326	};
327
328	$wcb->();
329
330	$self->[3] \|\|= AE::io $self->[1], 1, $wcb
331	if @{ $self->[2] };
332	}	415	};
333		416
334	() # make sure we don't leak the watcher	417	() # make sure we don't leak the watcher
335	}	418	}
336		419
337	sub _new {	420	sub _new {
338	my ($self, $fh) = @_;	421	my ($self, $fh, $pid) = @_;
339		422
340	AnyEvent::Util::fh_nonblocking $fh, 1;	423	AnyEvent::Util::fh_nonblocking $fh, 1;
341		424
342	$self = bless [	425	$self = bless [
343	undef, # run callback	426	$pid,
344	$fh,	427	$fh,
345	[], # write queue - strings or fd's	428	[], # write queue - strings or fd's
346	undef, # AE watcher	429	undef, # AE watcher
347	], $self;	430	], $self;
348		431
…		…
366	exit 0;	449	exit 0;
367	} elsif (!$pid) {	450	} elsif (!$pid) {
368	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	451	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
369	}	452	}
370		453
371	AnyEvent::Fork->_new ($fh)	454	AnyEvent::Fork->_new ($fh, $pid)
372	}	455	}
373		456
374	=item my $proc = new AnyEvent::Fork	457	=item my $proc = new AnyEvent::Fork
375		458
376	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
377	object for further manipulation.	460	object for further manipulation.
378		461
379	The new process is forked from a template process that is kept around	462	The new process is forked from a template process that is kept around
380	for this purpose. When it doesn't exist yet, it is created by a call to	463	for this purpose. When it doesn't exist yet, it is created by a call to
381	C<new_exec> and kept around for future calls.	464	C<new_exec> first and then stays around for future calls.
382
383	When the process object is destroyed, it will release the file handle
384	that connects it with the new process. When the new process has not yet
385	called C<run>, then the process will exit. Otherwise, what happens depends
386	entirely on the code that is executed.
387		465
388	=cut	466	=cut
389		467
390	sub new {	468	sub new {
391	my $class = shift;	469	my $class = shift;
…		…
469	# quick. also doesn't work in win32. of course. what did you expect	547	# quick. also doesn't work in win32. of course. what did you expect
470	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	548	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
471	my %env = %ENV;	549	my %env = %ENV;
472	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	550	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
473		551
474	Proc::FastSpawn::spawn (	552	my $pid = Proc::FastSpawn::spawn (
475	$perl,	553	$perl,
476	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	554	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
477	[map "$_=$env{$_}", keys %env],	555	[map "$_=$env{$_}", keys %env],
478	) or die "unable to spawn AnyEvent::Fork server: $!";	556	) or die "unable to spawn AnyEvent::Fork server: $!";
479		557
480	$self->_new ($fh)	558	$self->_new ($fh, $pid)
		559	}
		560
		561	=item $pid = $proc->pid
		562
		563	Returns the process id of the process I<iff it is a direct child of the
		564	process running AnyEvent::Fork>, and C<undef> otherwise.
		565
		566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		568	to clean up their zombies when they die.
		569
		570	All other processes are not direct children, and will be cleaned up by
		571	AnyEvent::Fork itself.
		572
		573	=cut
		574
		575	sub pid {
		576	$_[0][0]
481	}	577	}
482		578
483	=item $proc = $proc->eval ($perlcode, @args)	579	=item $proc = $proc->eval ($perlcode, @args)
484		580
485	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	581	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
486	the strings specified by C<@args>.	582	the strings specified by C<@args>, in the "main" package.
487		583
488	This call is meant to do any custom initialisation that might be required	584	This call is meant to do any custom initialisation that might be required
489	(for example, the C<require> method uses it). It's not supposed to be used	585	(for example, the C<require> method uses it). It's not supposed to be used
490	to completely take over the process, use C<run> for that.	586	to completely take over the process, use C<run> for that.
491		587
492	The code will usually be executed after this call returns, and there is no	588	The code will usually be executed after this call returns, and there is no
493	way to pass anything back to the calling process. Any evaluation errors	589	way to pass anything back to the calling process. Any evaluation errors
494	will be reported to stderr and cause the process to exit.	590	will be reported to stderr and cause the process to exit.
495		591
		592	If you want to execute some code (that isn't in a module) to take over the
		593	process, you should compile a function via C<eval> first, and then call
		594	it via C<run>. This also gives you access to any arguments passed via the
		595	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		596	a faster fork+exec> example to see it in action.
		597
496	Returns the process object for easy chaining of method calls.	598	Returns the process object for easy chaining of method calls.
497		599
498	=cut	600	=cut
499		601
500	sub eval {	602	sub eval {
501	my ($self, $code, @args) = @_;	603	my ($self, $code, @args) = @_;
502		604
503	$self->_cmd (e => $code, @args);	605	$self->_cmd (e => pack "(w/a)", $code, @args);
504		606
505	$self	607	$self
506	}	608	}
507		609
508	=item $proc = $proc->require ($module, ...)	610	=item $proc = $proc->require ($module, ...)
…		…
525	=item $proc = $proc->send_fh ($handle, ...)	627	=item $proc = $proc->send_fh ($handle, ...)
526		628
527	Send one or more file handles (I<not> file descriptors) to the process,	629	Send one or more file handles (I<not> file descriptors) to the process,
528	to prepare a call to C<run>.	630	to prepare a call to C<run>.
529		631
530	The process object keeps a reference to the handles until this is done,	632	The process object keeps a reference to the handles until they have
531	so you must not explicitly close the handles. This is most easily	633	been passed over to the process, so you must not explicitly close the
532	accomplished by simply not storing the file handles anywhere after passing	634	handles. This is most easily accomplished by simply not storing the file
533	them to this method.	635	handles anywhere after passing them to this method - when AnyEvent::Fork
		636	is finished using them, perl will automatically close them.
534		637
535	Returns the process object for easy chaining of method calls.	638	Returns the process object for easy chaining of method calls.
536		639
537	Example: pass a file handle to a process, and release it without	640	Example: pass a file handle to a process, and release it without
538	closing. It will be closed automatically when it is no longer used.	641	closing. It will be closed automatically when it is no longer used.
…		…
554	}	657	}
555		658
556	=item $proc = $proc->send_arg ($string, ...)	659	=item $proc = $proc->send_arg ($string, ...)
557		660
558	Send one or more argument strings to the process, to prepare a call to	661	Send one or more argument strings to the process, to prepare a call to
559	C<run>. The strings can be any octet string.	662	C<run>. The strings can be any octet strings.
560		663
561	The protocol is optimised to pass a moderate number of relatively short	664	The protocol is optimised to pass a moderate number of relatively short
562	strings - while you can pass up to 4GB of data in one go, this is more	665	strings - while you can pass up to 4GB of data in one go, this is more
563	meant to pass some ID information or other startup info, not big chunks of	666	meant to pass some ID information or other startup info, not big chunks of
564	data.	667	data.
…		…
568	=cut	671	=cut
569		672
570	sub send_arg {	673	sub send_arg {
571	my ($self, @arg) = @_;	674	my ($self, @arg) = @_;
572		675
573	$self->_cmd (a => @arg);	676	$self->_cmd (a => pack "(w/a)", @arg);
574		677
575	$self	678	$self
576	}	679	}
577		680
578	=item $proc->run ($func, $cb->($fh))	681	=item $proc->run ($func, $cb->($fh))
579		682
580	Enter the function specified by the fully qualified name in C<$func> in	683	Enter the function specified by the function name in C<$func> in the
581	the process. The function is called with the communication socket as first	684	process. The function is called with the communication socket as first
582	argument, followed by all file handles and string arguments sent earlier	685	argument, followed by all file handles and string arguments sent earlier
583	via C<send_fh> and C<send_arg> methods, in the order they were called.	686	via C<send_fh> and C<send_arg> methods, in the order they were called.
584		687
585	If the called function returns, the process exits.
586
587	Preparing the process can take time - when the process is ready, the
588	callback is invoked with the local communications socket as argument.
589
590	The process object becomes unusable on return from this function.	688	The process object becomes unusable on return from this function - any
		689	further method calls result in undefined behaviour.
		690
		691	The function name should be fully qualified, but if it isn't, it will be
		692	looked up in the C<main> package.
		693
		694	If the called function returns, doesn't exist, or any error occurs, the
		695	process exits.
		696
		697	Preparing the process is done in the background - when all commands have
		698	been sent, the callback is invoked with the local communications socket
		699	as argument. At this point you can start using the socket in any way you
		700	like.
591		701
592	If the communication socket isn't used, it should be closed on both sides,	702	If the communication socket isn't used, it should be closed on both sides,
593	to save on kernel memory.	703	to save on kernel memory.
594		704
595	The socket is non-blocking in the parent, and blocking in the newly	705	The socket is non-blocking in the parent, and blocking in the newly
596	created process. The close-on-exec flag is set on both. Even if not used	706	created process. The close-on-exec flag is set in both.
		707
597	otherwise, the socket can be a good indicator for the existence of the	708	Even if not used otherwise, the socket can be a good indicator for the
598	process - if the other process exits, you get a readable event on it,	709	existence of the process - if the other process exits, you get a readable
599	because exiting the process closes the socket (if it didn't create any	710	event on it, because exiting the process closes the socket (if it didn't
600	children using fork).	711	create any children using fork).
601		712
602	Example: create a template for a process pool, pass a few strings, some	713	Example: create a template for a process pool, pass a few strings, some
603	file handles, then fork, pass one more string, and run some code.	714	file handles, then fork, pass one more string, and run some code.
604		715
605	my $pool = AnyEvent::Fork	716	my $pool = AnyEvent::Fork
…		…
613	->send_arg ("str3")	724	->send_arg ("str3")
614	->run ("Some::function", sub {	725	->run ("Some::function", sub {
615	my ($fh) = @_;	726	my ($fh) = @_;
616		727
617	# fh is nonblocking, but we trust that the OS can accept these	728	# fh is nonblocking, but we trust that the OS can accept these
618	# extra 3 octets anyway.	729	# few octets anyway.
619	syswrite $fh, "hi #$_\n";	730	syswrite $fh, "hi #$_\n";
620		731
621	# $fh is being closed here, as we don't store it anywhere	732	# $fh is being closed here, as we don't store it anywhere
622	});	733	});
623	}	734	}
…		…
625	# Some::function might look like this - all parameters passed before fork	736	# Some::function might look like this - all parameters passed before fork
626	# and after will be passed, in order, after the communications socket.	737	# and after will be passed, in order, after the communications socket.
627	sub Some::function {	738	sub Some::function {
628	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	739	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
629		740
630	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	741	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
631	}	742	}
632		743
633	=cut	744	=cut
634		745
635	sub run {	746	sub run {
636	my ($self, $func, $cb) = @_;	747	my ($self, $func, $cb) = @_;
637		748
638	$self->[0] = $cb;	749	$self->[4] = $cb;
639	$self->_cmd (r => $func);	750	$self->_cmd (r => $func);
640	}	751	}
641		752
642	=back	753	=back
643		754
…		…
669	479 vfork+execs per second, using AnyEvent::Fork->new_exec	780	479 vfork+execs per second, using AnyEvent::Fork->new_exec
670		781
671	So how can C<< AnyEvent->new >> be faster than a standard fork, even	782	So how can C<< AnyEvent->new >> be faster than a standard fork, even
672	though it uses the same operations, but adds a lot of overhead?	783	though it uses the same operations, but adds a lot of overhead?
673		784
674	The difference is simply the process size: forking the 6MB process takes	785	The difference is simply the process size: forking the 5MB process takes
675	so much longer than forking the 2.5MB template process that the overhead	786	so much longer than forking the 2.5MB template process that the extra
676	introduced is canceled out.	787	overhead introduced is canceled out.
677		788
678	If the benchmark process grows, the normal fork becomes even slower:	789	If the benchmark process grows, the normal fork becomes even slower:
679		790
680	1340 new processes, manual fork in a 20MB process	791	1340 new processes, manual fork of a 20MB process
681	731 new processes, manual fork in a 200MB process	792	731 new processes, manual fork of a 200MB process
682	235 new processes, manual fork in a 2000MB process	793	235 new processes, manual fork of a 2000MB process
683		794
684	What that means (to me) is that I can use this module without having a	795	What that means (to me) is that I can use this module without having a bad
685	very bad conscience because of the extra overhead required to start new	796	conscience because of the extra overhead required to start new processes.
686	processes.
687		797
688	=head1 TYPICAL PROBLEMS	798	=head1 TYPICAL PROBLEMS
689		799
690	This section lists typical problems that remain. I hope by recognising	800	This section lists typical problems that remain. I hope by recognising
691	them, most can be avoided.	801	them, most can be avoided.
692		802
693	=over 4	803	=over 4
694		804
695	=item exit runs destructors
696
697	=item "leaked" file descriptors for exec'ed processes	805	=item leaked file descriptors for exec'ed processes
698		806
699	POSIX systems inherit file descriptors by default when exec'ing a new	807	POSIX systems inherit file descriptors by default when exec'ing a new
700	process. While perl itself laudably sets the close-on-exec flags on new	808	process. While perl itself laudably sets the close-on-exec flags on new
701	file handles, most C libraries don't care, and even if all cared, it's	809	file handles, most C libraries don't care, and even if all cared, it's
702	often not possible to set the flag in a race-free manner.	810	often not possible to set the flag in a race-free manner.
…		…
722	libraries or the code that leaks those file descriptors.	830	libraries or the code that leaks those file descriptors.
723		831
724	Fortunately, most of these leaked descriptors do no harm, other than	832	Fortunately, most of these leaked descriptors do no harm, other than
725	sitting on some resources.	833	sitting on some resources.
726		834
727	=item "leaked" file descriptors for fork'ed processes	835	=item leaked file descriptors for fork'ed processes
728		836
729	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	837	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
730	which closes file descriptors not marked for being inherited.	838	which closes file descriptors not marked for being inherited.
731		839
732	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	840	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
740	trouble with a fork.	848	trouble with a fork.
741		849
742	The solution is to either not load these modules before use'ing	850	The solution is to either not load these modules before use'ing
743	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	851	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
744	initialising them, for example, by calling C<init Gtk2> manually.	852	initialising them, for example, by calling C<init Gtk2> manually.
		853
		854	=item exiting calls object destructors
		855
		856	This only applies to users of Lc<AnyEvent::Fork:Early> and
		857	L<AnyEvent::Fork::Template>.
		858
		859	When a process created by AnyEvent::Fork exits, it might do so by calling
		860	exit, or simply letting perl reach the end of the program. At which point
		861	Perl runs all destructors.
		862
		863	Not all destructors are fork-safe - for example, an object that represents
		864	the connection to an X display might tell the X server to free resources,
		865	which is inconvenient when the "real" object in the parent still needs to
		866	use them.
		867
		868	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		869	it as the very first thing, right?
		870
		871	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		872	is to not create objects with nontrivial destructors that might have an
		873	effect outside of Perl.
745		874
746	=back	875	=back
747		876
748	=head1 PORTABILITY NOTES	877	=head1 PORTABILITY NOTES
749		878
…		…
752	to make it so, mostly due to the bloody broken perl that nobody seems to	881	to make it so, mostly due to the bloody broken perl that nobody seems to
753	care about. The fork emulation is a bad joke - I have yet to see something	882	care about. The fork emulation is a bad joke - I have yet to see something
754	useful that you can do with it without running into memory corruption	883	useful that you can do with it without running into memory corruption
755	issues or other braindamage. Hrrrr.	884	issues or other braindamage. Hrrrr.
756		885
757	Cygwin perl is not supported at the moment, as it should implement fd	886	Cygwin perl is not supported at the moment due to some hilarious
758	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	887	shortcomings of its API - see L<IO::FDPoll> for more details.
759	support enough functionality to do it.
760		888
761	=head1 SEE ALSO	889	=head1 SEE ALSO
762		890
763	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	891	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
764	L<AnyEvent::Fork::Template> (to create a process by forking the main	892	L<AnyEvent::Fork::Template> (to create a process by forking the main

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs. Revision 1.37 by root, Sat Apr 6 20:06:39 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs.
Revision 1.37 by root, Sat Apr 6 20:06:39 2013 UTC