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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.17 by root, Fri Apr 5 23:42:24 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
		15
		16	=head1 DESCRIPTION
		17
		18	This module allows you to create new processes, without actually forking
		19	them from your current process (avoiding the problems of forking), but
		20	preserving most of the advantages of fork.
		21
		22	It can be used to create new worker processes or new independent
		23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
		27
		28	Special care has been taken to make this module useful from other modules,
		29	while still supporting specialised environments such as L<App::Staticperl>
		30	or L<PAR::Packer>.
		31
		32	=head2 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you 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	=head2 COMPARISON TO OTHER MODULES
		46
		47	There is an abundance of modules on CPAN that do "something fork", such as
		48	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		49	or L<AnyEvent::Subprocess>. There are modules that implement their own
		50	process management, such as L<AnyEvent::DBI>.
		51
		52	The problems that all these modules try to solve are real, however, none
		53	of them (from what I have seen) tackle the very real problems of unwanted
		54	memory sharing, efficiency, not being able to use event processing or
		55	similar modules in the processes they create.
		56
		57	This module doesn't try to replace any of them - instead it tries to solve
		58	the problem of creating processes with a minimum of fuss and overhead (and
		59	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		60	except they were written before AnyEvent:Fork was available, so obviously
		61	had to roll their own.
		62
		63	=head2 PROBLEM STATEMENT
		64
		65	There are two traditional ways to implement parallel processing on UNIX
		66	like operating systems - fork and process, and fork+exec and process. They
		67	have different advantages and disadvantages that I describe below,
		68	together with how this module tries to mitigate the disadvantages.
		69
		70	=over 4
		71
		72	=item Forking from a big process can be very slow.
		73
		74	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		75	overhead is often shared with exec (because you have to fork first), but
		76	in some circumstances (e.g. when vfork is used), fork+exec can be much
		77	faster.
		78
		79	This module can help here by telling a small(er) helper process to fork,
		80	which is faster then forking the main process, and also uses vfork where
		81	possible. This gives the speed of vfork, with the flexibility of fork.
		82
		83	=item Forking usually creates a copy-on-write copy of the parent
		84	process.
		85
		86	For example, modules or data files that are loaded will not use additional
		87	memory after a fork. When exec'ing a new process, modules and data files
		88	might need to be loaded again, at extra CPU and memory cost. But when
		89	forking, literally all data structures are copied - if the program frees
		90	them and replaces them by new data, the child processes will retain the
		91	old version even if it isn't used, which can suddenly and unexpectedly
		92	increase memory usage when freeing memory.
		93
		94	The trade-off is between more sharing with fork (which can be good or
		95	bad), and no sharing with exec.
		96
		97	This module allows the main program to do a controlled fork, and allows
		98	modules to exec processes safely at any time. When creating a custom
		99	process pool you can take advantage of data sharing via fork without
		100	risking to share large dynamic data structures that will blow up child
		101	memory usage.
		102
		103	In other words, this module puts you into control over what is being
		104	shared and what isn't, at all times.
		105
		106	=item Exec'ing a new perl process might be difficult.
		107
		108	For example, it is not easy to find the correct path to the perl
		109	interpreter - C<$^X> might not be a perl interpreter at all.
		110
		111	This module tries hard to identify the correct path to the perl
		112	interpreter. With a cooperative main program, exec'ing the interpreter
		113	might not even be necessary, but even without help from the main program,
		114	it will still work when used from a module.
		115
		116	=item Exec'ing a new perl process might be slow, as all necessary modules
		117	have to be loaded from disk again, with no guarantees of success.
		118
		119	Long running processes might run into problems when perl is upgraded
		120	and modules are no longer loadable because they refer to a different
		121	perl version, or parts of a distribution are newer than the ones already
		122	loaded.
		123
		124	This module supports creating pre-initialised perl processes to be used as
		125	a template for new processes.
		126
		127	=item Forking might be impossible when a program is running.
		128
		129	For example, POSIX makes it almost impossible to fork from a
		130	multi-threaded program while doing anything useful in the child - in
		131	fact, if your perl program uses POSIX threads (even indirectly via
		132	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		133	anymore without risking corruption issues on a number of operating
		134	systems.
		135
		136	This module can safely fork helper processes at any time, by calling
		137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		138
		139	=item Parallel processing with fork might be inconvenient or difficult
		140	to implement. Modules might not work in both parent and child.
		141
		142	For example, when a program uses an event loop and creates watchers it
		143	becomes very hard to use the event loop from a child program, as the
		144	watchers already exist but are only meaningful in the parent. Worse, a
		145	module might want to use such a module, not knowing whether another module
		146	or the main program also does, leading to problems.
		147
		148	Apart from event loops, graphical toolkits also commonly fall into the
		149	"unsafe module" category, or just about anything that communicates with
		150	the external world, such as network libraries and file I/O modules, which
		151	usually don't like being copied and then allowed to continue in two
		152	processes.
		153
		154	With this module only the main program is allowed to create new processes
		155	by forking (because only the main program can know when it is still safe
		156	to do so) - all other processes are created via fork+exec, which makes it
		157	possible to use modules such as event loops or window interfaces safely.
		158
		159	=back
		160
		161	=head1 EXAMPLES
		162
10	# create a single new process, tell it to run your worker function	163	=head2 Create a single new process, tell it to run your worker function.
11		164
12	AnyEvent::Fork	165	AnyEvent::Fork
13	->new	166	->new
14	->require ("MyModule")	167	->require ("MyModule")
15	->run ("MyModule::worker, sub {	168	->run ("MyModule::worker, sub {
…		…
17		170
18	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
20	});	173	});
21		174
22	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
23	sub MyModule::worker {	179	sub worker {
24	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
25		181
26	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
28	}	184	}
29		185
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	186	=head2 Create a pool of server processes all accepting on the same socket.
32		187
33	# create listener socket	188	# create listener socket
34	my $listener = ...;	189	my $listener = ...;
35		190
36	# create a pool template, initialise it and give it the socket	191	# create a pool template, initialise it and give it the socket
…		…
48	}	203	}
49		204
50	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
52		207
53	# My::Server::run might look like this	208	C<My::Server> might look like this:
54	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
55	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
56		214
57	close $slave; # we do not use the socket, so close it to save resources	215	close $slave; # we do not use the socket, so close it to save resources
58		216
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	217	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	219	while (my $socket = $listener->accept) {
62	# do sth. with new socket	220	# do sth. with new socket
63	}	221	}
64	}	222	}
65		223
66	=head1 DESCRIPTION	224	=head2 use AnyEvent::Fork as a faster fork+exec
67		225
68	This module allows you to create new processes, without actually forking	226	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	227	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	228	faster than fork+exec, but still lets you prepare the environment.
71		229
72	It can be used to create new worker processes or new independent	230	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		231
78	Special care has been taken to make this module useful from other modules,	232	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	233	->new
80	or L<PAR::Packer>.	234	->eval ('
		235	sub run {
		236	my ($fh, $output, @cmd) = @_;
81		237
82	=head1 WHAT THIS MODULE IS NOT	238	# perl will clear close-on-exec on STDOUT/STDERR
		239	open STDOUT, ">&", $output or die;
		240	open STDERR, ">&", $fh or die;
83		241
84	This module only creates processes and lets you pass file handles and	242	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	243	}
86	there is no back channel from the process back to you, and there is no RPC	244	')
87	or message passing going on.	245	->send_fh ($output)
		246	->send_arg ("/bin/echo", "hi")
		247	->run ("run", my $cv = AE::cv);
88		248
89	If you need some form of RPC, you can either implement it yourself	249	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		250
159	=head1 CONCEPTS	251	=head1 CONCEPTS
160		252
161	This module can create new processes either by executing a new perl	253	This module can create new processes either by executing a new perl
162	process, or by forking from an existing "template" process.	254	process, or by forking from an existing "template" process.
…		…
241	my ($fork_fh) = @_;	333	my ($fork_fh) = @_;
242	});	334	});
243		335
244	=back	336	=back
245		337
246	=head1 FUNCTIONS	338	=head1 THE C<AnyEvent::Fork> CLASS
		339
		340	This module exports nothing, and only implements a single class -
		341	C<AnyEvent::Fork>.
		342
		343	There are two class constructors that both create new processes - C<new>
		344	and C<new_exec>. The C<fork> method creates a new process by forking an
		345	existing one and could be considered a third constructor.
		346
		347	Most of the remaining methods deal with preparing the new process, by
		348	loading code, evaluating code and sending data to the new process. They
		349	usually return the process object, so you can chain method calls.
		350
		351	If a process object is destroyed before calling its C<run> method, then
		352	the process simply exits. After C<run> is called, all responsibility is
		353	passed to the specified function.
		354
		355	As long as there is any outstanding work to be done, process objects
		356	resist being destroyed, so there is no reason to store them unless you
		357	need them later - configure and forget works just fine.
247		358
248	=over 4	359	=over 4
249		360
250	=cut	361	=cut
251		362
252	package AnyEvent::Fork;	363	package AnyEvent::Fork;
253		364
254	use common::sense;	365	use common::sense;
255		366
256	use Socket ();	367	use Errno ();
257		368
258	use AnyEvent;	369	use AnyEvent;
259	use AnyEvent::Util ();	370	use AnyEvent::Util ();
260		371
261	use IO::FDPass;	372	use IO::FDPass;
262		373
263	our $VERSION = 0.2;	374	our $VERSION = 0.5;
264		375
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	376	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		377
271	=over 4	378	=over 4
272		379
273	=back	380	=back
274		381
…		…
281	our $TEMPLATE;	388	our $TEMPLATE;
282		389
283	sub _cmd {	390	sub _cmd {
284	my $self = shift;	391	my $self = shift;
285		392
286	#TODO: maybe append the packet to any existing string command already in the queue
287
288	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	393	# ideally, we would want to use "a (w/a)*" as format string, but perl
289	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	394	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		395	# it.
290	push @{ $self->[2] }, pack "L/a", pack "(w/a)*", @_;	396	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
291		397
292	$self->[3] \|\|= AE::io $self->[1], 1, sub {	398	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		399	do {
293	# send the next "thing" in the queue - either a reference to an fh,	400	# send the next "thing" in the queue - either a reference to an fh,
294	# or a plain string.	401	# or a plain string.
295		402
296	if (ref $self->[2][0]) {	403	if (ref $self->[2][0]) {
297	# send fh	404	# send fh
298	IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }	405	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		406	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		407	undef $self->[3];
		408	die "AnyEvent::Fork: file descriptor send failure: $!";
		409	}
		410
299	and shift @{ $self->[2] };	411	shift @{ $self->[2] };
300		412
301	} else {	413	} else {
302	# send string	414	# send string
303	my $len = syswrite $self->[1], $self->[2][0]	415	my $len = syswrite $self->[1], $self->[2][0];
		416
		417	unless ($len) {
		418	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		419	undef $self->[3];
304	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	420	die "AnyEvent::Fork: command write failure: $!";
		421	}
305		422
306	substr $self->[2][0], 0, $len, "";	423	substr $self->[2][0], 0, $len, "";
307	shift @{ $self->[2] } unless length $self->[2][0];	424	shift @{ $self->[2] } unless length $self->[2][0];
308	}	425	}
		426	} while @{ $self->[2] };
309		427
310	unless (@{ $self->[2] }) {	428	# everything written
311	undef $self->[3];	429	undef $self->[3];
		430
312	# invoke run callback	431	# invoke run callback, if any
313	$self->[0]->($self->[1]) if $self->[0];	432	$self->[4]->($self->[1]) if $self->[4];
314	}
315	};	433	};
316		434
317	() # make sure we don't leak the watcher	435	() # make sure we don't leak the watcher
318	}	436	}
319		437
320	sub _new {	438	sub _new {
321	my ($self, $fh) = @_;	439	my ($self, $fh, $pid) = @_;
322		440
323	AnyEvent::Util::fh_nonblocking $fh, 1;	441	AnyEvent::Util::fh_nonblocking $fh, 1;
324		442
325	$self = bless [	443	$self = bless [
326	undef, # run callback	444	$pid,
327	$fh,	445	$fh,
328	[], # write queue - strings or fd's	446	[], # write queue - strings or fd's
329	undef, # AE watcher	447	undef, # AE watcher
330	], $self;	448	], $self;
331		449
…		…
349	exit 0;	467	exit 0;
350	} elsif (!$pid) {	468	} elsif (!$pid) {
351	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	469	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
352	}	470	}
353		471
354	AnyEvent::Fork->_new ($fh)	472	AnyEvent::Fork->_new ($fh, $pid)
355	}	473	}
356		474
357	=item my $proc = new AnyEvent::Fork	475	=item my $proc = new AnyEvent::Fork
358		476
359	Create a new "empty" perl interpreter process and returns its process	477	Create a new "empty" perl interpreter process and returns its process
360	object for further manipulation.	478	object for further manipulation.
361		479
362	The new process is forked from a template process that is kept around	480	The new process is forked from a template process that is kept around
363	for this purpose. When it doesn't exist yet, it is created by a call to	481	for this purpose. When it doesn't exist yet, it is created by a call to
364	C<new_exec> and kept around for future calls.	482	C<new_exec> first and then stays around for future calls.
365
366	When the process object is destroyed, it will release the file handle
367	that connects it with the new process. When the new process has not yet
368	called C<run>, then the process will exit. Otherwise, what happens depends
369	entirely on the code that is executed.
370		483
371	=cut	484	=cut
372		485
373	sub new {	486	sub new {
374	my $class = shift;	487	my $class = shift;
…		…
452	# quick. also doesn't work in win32. of course. what did you expect	565	# quick. also doesn't work in win32. of course. what did you expect
453	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	566	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
454	my %env = %ENV;	567	my %env = %ENV;
455	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	568	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
456		569
457	Proc::FastSpawn::spawn (	570	my $pid = Proc::FastSpawn::spawn (
458	$perl,	571	$perl,
459	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	572	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
460	[map "$_=$env{$_}", keys %env],	573	[map "$_=$env{$_}", keys %env],
461	) or die "unable to spawn AnyEvent::Fork server: $!";	574	) or die "unable to spawn AnyEvent::Fork server: $!";
462		575
463	$self->_new ($fh)	576	$self->_new ($fh, $pid)
		577	}
		578
		579	=item $pid = $proc->pid
		580
		581	Returns the process id of the process I<iff it is a direct child of the
		582	process running AnyEvent::Fork>, and C<undef> otherwise.
		583
		584	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		585	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		586	to clean up their zombies when they die.
		587
		588	All other processes are not direct children, and will be cleaned up by
		589	AnyEvent::Fork itself.
		590
		591	=cut
		592
		593	sub pid {
		594	$_[0][0]
464	}	595	}
465		596
466	=item $proc = $proc->eval ($perlcode, @args)	597	=item $proc = $proc->eval ($perlcode, @args)
467		598
468	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	599	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
469	the strings specified by C<@args>.	600	the strings specified by C<@args>, in the "main" package.
470		601
471	This call is meant to do any custom initialisation that might be required	602	This call is meant to do any custom initialisation that might be required
472	(for example, the C<require> method uses it). It's not supposed to be used	603	(for example, the C<require> method uses it). It's not supposed to be used
473	to completely take over the process, use C<run> for that.	604	to completely take over the process, use C<run> for that.
474		605
475	The code will usually be executed after this call returns, and there is no	606	The code will usually be executed after this call returns, and there is no
476	way to pass anything back to the calling process. Any evaluation errors	607	way to pass anything back to the calling process. Any evaluation errors
477	will be reported to stderr and cause the process to exit.	608	will be reported to stderr and cause the process to exit.
478		609
		610	If you want to execute some code (that isn't in a module) to take over the
		611	process, you should compile a function via C<eval> first, and then call
		612	it via C<run>. This also gives you access to any arguments passed via the
		613	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		614	a faster fork+exec> example to see it in action.
		615
479	Returns the process object for easy chaining of method calls.	616	Returns the process object for easy chaining of method calls.
480		617
481	=cut	618	=cut
482		619
483	sub eval {	620	sub eval {
484	my ($self, $code, @args) = @_;	621	my ($self, $code, @args) = @_;
485		622
486	$self->_cmd (e => $code, @args);	623	$self->_cmd (e => pack "(w/a)", $code, @args);
487		624
488	$self	625	$self
489	}	626	}
490		627
491	=item $proc = $proc->require ($module, ...)	628	=item $proc = $proc->require ($module, ...)
…		…
508	=item $proc = $proc->send_fh ($handle, ...)	645	=item $proc = $proc->send_fh ($handle, ...)
509		646
510	Send one or more file handles (I<not> file descriptors) to the process,	647	Send one or more file handles (I<not> file descriptors) to the process,
511	to prepare a call to C<run>.	648	to prepare a call to C<run>.
512		649
513	The process object keeps a reference to the handles until this is done,	650	The process object keeps a reference to the handles until they have
514	so you must not explicitly close the handles. This is most easily	651	been passed over to the process, so you must not explicitly close the
515	accomplished by simply not storing the file handles anywhere after passing	652	handles. This is most easily accomplished by simply not storing the file
516	them to this method.	653	handles anywhere after passing them to this method - when AnyEvent::Fork
		654	is finished using them, perl will automatically close them.
517		655
518	Returns the process object for easy chaining of method calls.	656	Returns the process object for easy chaining of method calls.
519		657
520	Example: pass a file handle to a process, and release it without	658	Example: pass a file handle to a process, and release it without
521	closing. It will be closed automatically when it is no longer used.	659	closing. It will be closed automatically when it is no longer used.
…		…
537	}	675	}
538		676
539	=item $proc = $proc->send_arg ($string, ...)	677	=item $proc = $proc->send_arg ($string, ...)
540		678
541	Send one or more argument strings to the process, to prepare a call to	679	Send one or more argument strings to the process, to prepare a call to
542	C<run>. The strings can be any octet string.	680	C<run>. The strings can be any octet strings.
		681
		682	The protocol is optimised to pass a moderate number of relatively short
		683	strings - while you can pass up to 4GB of data in one go, this is more
		684	meant to pass some ID information or other startup info, not big chunks of
		685	data.
543		686
544	Returns the process object for easy chaining of method calls.	687	Returns the process object for easy chaining of method calls.
545		688
546	=cut	689	=cut
547		690
548	sub send_arg {	691	sub send_arg {
549	my ($self, @arg) = @_;	692	my ($self, @arg) = @_;
550		693
551	$self->_cmd (a => @arg);	694	$self->_cmd (a => pack "(w/a)", @arg);
552		695
553	$self	696	$self
554	}	697	}
555		698
556	=item $proc->run ($func, $cb->($fh))	699	=item $proc->run ($func, $cb->($fh))
557		700
558	Enter the function specified by the fully qualified name in C<$func> in	701	Enter the function specified by the function name in C<$func> in the
559	the process. The function is called with the communication socket as first	702	process. The function is called with the communication socket as first
560	argument, followed by all file handles and string arguments sent earlier	703	argument, followed by all file handles and string arguments sent earlier
561	via C<send_fh> and C<send_arg> methods, in the order they were called.	704	via C<send_fh> and C<send_arg> methods, in the order they were called.
562		705
563	If the called function returns, the process exits.
564
565	Preparing the process can take time - when the process is ready, the
566	callback is invoked with the local communications socket as argument.
567
568	The process object becomes unusable on return from this function.	706	The process object becomes unusable on return from this function - any
		707	further method calls result in undefined behaviour.
		708
		709	The function name should be fully qualified, but if it isn't, it will be
		710	looked up in the C<main> package.
		711
		712	If the called function returns, doesn't exist, or any error occurs, the
		713	process exits.
		714
		715	Preparing the process is done in the background - when all commands have
		716	been sent, the callback is invoked with the local communications socket
		717	as argument. At this point you can start using the socket in any way you
		718	like.
569		719
570	If the communication socket isn't used, it should be closed on both sides,	720	If the communication socket isn't used, it should be closed on both sides,
571	to save on kernel memory.	721	to save on kernel memory.
572		722
573	The socket is non-blocking in the parent, and blocking in the newly	723	The socket is non-blocking in the parent, and blocking in the newly
574	created process. The close-on-exec flag is set on both. Even if not used	724	created process. The close-on-exec flag is set in both.
		725
575	otherwise, the socket can be a good indicator for the existence of the	726	Even if not used otherwise, the socket can be a good indicator for the
576	process - if the other process exits, you get a readable event on it,	727	existence of the process - if the other process exits, you get a readable
577	because exiting the process closes the socket (if it didn't create any	728	event on it, because exiting the process closes the socket (if it didn't
578	children using fork).	729	create any children using fork).
579		730
580	Example: create a template for a process pool, pass a few strings, some	731	Example: create a template for a process pool, pass a few strings, some
581	file handles, then fork, pass one more string, and run some code.	732	file handles, then fork, pass one more string, and run some code.
582		733
583	my $pool = AnyEvent::Fork	734	my $pool = AnyEvent::Fork
…		…
591	->send_arg ("str3")	742	->send_arg ("str3")
592	->run ("Some::function", sub {	743	->run ("Some::function", sub {
593	my ($fh) = @_;	744	my ($fh) = @_;
594		745
595	# fh is nonblocking, but we trust that the OS can accept these	746	# fh is nonblocking, but we trust that the OS can accept these
596	# extra 3 octets anyway.	747	# few octets anyway.
597	syswrite $fh, "hi #$_\n";	748	syswrite $fh, "hi #$_\n";
598		749
599	# $fh is being closed here, as we don't store it anywhere	750	# $fh is being closed here, as we don't store it anywhere
600	});	751	});
601	}	752	}
…		…
603	# Some::function might look like this - all parameters passed before fork	754	# Some::function might look like this - all parameters passed before fork
604	# and after will be passed, in order, after the communications socket.	755	# and after will be passed, in order, after the communications socket.
605	sub Some::function {	756	sub Some::function {
606	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	757	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
607		758
608	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	759	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
609	}	760	}
610		761
611	=cut	762	=cut
612		763
613	sub run {	764	sub run {
614	my ($self, $func, $cb) = @_;	765	my ($self, $func, $cb) = @_;
615		766
616	$self->[0] = $cb;	767	$self->[4] = $cb;
617	$self->_cmd (r => $func);	768	$self->_cmd (r => $func);
618	}	769	}
619		770
620	=back	771	=back
621		772
622	=head1 PERFORMANCE	773	=head1 PERFORMANCE
623		774
624	Now for some unscientific benchmark numbers (all done on an amd64	775	Now for some unscientific benchmark numbers (all done on an amd64
625	GNU/Linux box). These are intended to give you an idea of the relative	776	GNU/Linux box). These are intended to give you an idea of the relative
626	performance you can expect.	777	performance you can expect, they are not meant to be absolute performance
		778	numbers.
627		779
628	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls	780	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
629	exit in the child and waits for the socket to close in the parent. I did	781	exit in the child and waits for the socket to close in the parent. I did
630	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 6312kB.	782	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
631		783
632	2079 new processes per second, using socketpair + fork manually	784	2079 new processes per second, using manual socketpair + fork
633		785
634	Then I did the same thing, but instead of calling fork, I called	786	Then I did the same thing, but instead of calling fork, I called
635	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the	787	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
636	socket form the child to close on exit. This does the same thing as manual	788	socket form the child to close on exit. This does the same thing as manual
637	socket pair + fork, except that what is forked is the template process	789	socket pair + fork, except that what is forked is the template process
…		…
646	479 vfork+execs per second, using AnyEvent::Fork->new_exec	798	479 vfork+execs per second, using AnyEvent::Fork->new_exec
647		799
648	So how can C<< AnyEvent->new >> be faster than a standard fork, even	800	So how can C<< AnyEvent->new >> be faster than a standard fork, even
649	though it uses the same operations, but adds a lot of overhead?	801	though it uses the same operations, but adds a lot of overhead?
650		802
651	The difference is simply the process size: forking the 6MB process takes	803	The difference is simply the process size: forking the 5MB process takes
652	so much longer than forking the 2.5MB template process that the overhead	804	so much longer than forking the 2.5MB template process that the extra
653	introduced is canceled out.	805	overhead introduced is canceled out.
654		806
655	If the benchmark process grows, the normal fork becomes even slower:	807	If the benchmark process grows, the normal fork becomes even slower:
656		808
657	1340 new processes, manual fork in a 20MB process	809	1340 new processes, manual fork of a 20MB process
658	731 new processes, manual fork in a 200MB process	810	731 new processes, manual fork of a 200MB process
659	235 new processes, manual fork in a 2000MB process	811	235 new processes, manual fork of a 2000MB process
660		812
661	What that means (to me) is that I can use this module without having a	813	What that means (to me) is that I can use this module without having a bad
662	very bad conscience because of the extra overhead required to start new	814	conscience because of the extra overhead required to start new processes.
663	processes.
664		815
665	=head1 TYPICAL PROBLEMS	816	=head1 TYPICAL PROBLEMS
666		817
667	This section lists typical problems that remain. I hope by recognising	818	This section lists typical problems that remain. I hope by recognising
668	them, most can be avoided.	819	them, most can be avoided.
669		820
670	=over 4	821	=over 4
671		822
672	=item exit runs destructors
673
674	=item "leaked" file descriptors for exec'ed processes	823	=item leaked file descriptors for exec'ed processes
675		824
676	POSIX systems inherit file descriptors by default when exec'ing a new	825	POSIX systems inherit file descriptors by default when exec'ing a new
677	process. While perl itself laudably sets the close-on-exec flags on new	826	process. While perl itself laudably sets the close-on-exec flags on new
678	file handles, most C libraries don't care, and even if all cared, it's	827	file handles, most C libraries don't care, and even if all cared, it's
679	often not possible to set the flag in a race-free manner.	828	often not possible to set the flag in a race-free manner.
…		…
699	libraries or the code that leaks those file descriptors.	848	libraries or the code that leaks those file descriptors.
700		849
701	Fortunately, most of these leaked descriptors do no harm, other than	850	Fortunately, most of these leaked descriptors do no harm, other than
702	sitting on some resources.	851	sitting on some resources.
703		852
704	=item "leaked" file descriptors for fork'ed processes	853	=item leaked file descriptors for fork'ed processes
705		854
706	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	855	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
707	which closes file descriptors not marked for being inherited.	856	which closes file descriptors not marked for being inherited.
708		857
709	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	858	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
717	trouble with a fork.	866	trouble with a fork.
718		867
719	The solution is to either not load these modules before use'ing	868	The solution is to either not load these modules before use'ing
720	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	869	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
721	initialising them, for example, by calling C<init Gtk2> manually.	870	initialising them, for example, by calling C<init Gtk2> manually.
		871
		872	=item exiting calls object destructors
		873
		874	This only applies to users of L<AnyEvent::Fork:Early> and
		875	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		876	that reference external resources.
		877
		878	When a process created by AnyEvent::Fork exits, it might do so by calling
		879	exit, or simply letting perl reach the end of the program. At which point
		880	Perl runs all destructors.
		881
		882	Not all destructors are fork-safe - for example, an object that represents
		883	the connection to an X display might tell the X server to free resources,
		884	which is inconvenient when the "real" object in the parent still needs to
		885	use them.
		886
		887	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		888	it as the very first thing, right?
		889
		890	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		891	is to not create objects with nontrivial destructors that might have an
		892	effect outside of Perl.
722		893
723	=back	894	=back
724		895
725	=head1 PORTABILITY NOTES	896	=head1 PORTABILITY NOTES
726		897
…		…
729	to make it so, mostly due to the bloody broken perl that nobody seems to	900	to make it so, mostly due to the bloody broken perl that nobody seems to
730	care about. The fork emulation is a bad joke - I have yet to see something	901	care about. The fork emulation is a bad joke - I have yet to see something
731	useful that you can do with it without running into memory corruption	902	useful that you can do with it without running into memory corruption
732	issues or other braindamage. Hrrrr.	903	issues or other braindamage. Hrrrr.
733		904
734	Cygwin perl is not supported at the moment, as it should implement fd	905	Cygwin perl is not supported at the moment due to some hilarious
735	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	906	shortcomings of its API - see L<IO::FDPoll> for more details.
736	support enough functionality to do it.
737		907
738	=head1 SEE ALSO	908	=head1 SEE ALSO
739		909
740	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	910	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
741	L<AnyEvent::Fork::Template> (to create a process by forking the main	911	L<AnyEvent::Fork::Template> (to create a process by forking the main

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.17 by root, Fri Apr 5 23:42:24 2013 UTC vs. Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.17 by root, Fri Apr 5 23:42:24 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC