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

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
		15
		16	=head1 DESCRIPTION
		17
		18	This module allows you to create new processes, without actually forking
		19	them from your current process (avoiding the problems of forking), but
		20	preserving most of the advantages of fork.
		21
		22	It can be used to create new worker processes or new independent
		23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
		27
		28	Special care has been taken to make this module useful from other modules,
		29	while still supporting specialised environments such as L<App::Staticperl>
		30	or L<PAR::Packer>.
		31
		32	=head2 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you could use the L<AnyEvent::Fork::RPC>
		40	companion module, which adds simple RPC/job queueing to a process created
		41	by this module.
		42
		43	Or you can implement it yourself in whatever way you like, use some
		44	message-passing module such as L<AnyEvent::MP>, some pipe such as
		45	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		46	e.g. JSON or Storable messages, and so on.
		47
		48	=head2 COMPARISON TO OTHER MODULES
		49
		50	There is an abundance of modules on CPAN that do "something fork", such as
		51	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		52	or L<AnyEvent::Subprocess>. There are modules that implement their own
		53	process management, such as L<AnyEvent::DBI>.
		54
		55	The problems that all these modules try to solve are real, however, none
		56	of them (from what I have seen) tackle the very real problems of unwanted
		57	memory sharing, efficiency, not being able to use event processing or
		58	similar modules in the processes they create.
		59
		60	This module doesn't try to replace any of them - instead it tries to solve
		61	the problem of creating processes with a minimum of fuss and overhead (and
		62	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		63	except they were written before AnyEvent:Fork was available, so obviously
		64	had to roll their own.
		65
		66	=head2 PROBLEM STATEMENT
		67
		68	There are two traditional ways to implement parallel processing on UNIX
		69	like operating systems - fork and process, and fork+exec and process. They
		70	have different advantages and disadvantages that I describe below,
		71	together with how this module tries to mitigate the disadvantages.
		72
		73	=over 4
		74
		75	=item Forking from a big process can be very slow.
		76
		77	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		78	overhead is often shared with exec (because you have to fork first), but
		79	in some circumstances (e.g. when vfork is used), fork+exec can be much
		80	faster.
		81
		82	This module can help here by telling a small(er) helper process to fork,
		83	which is faster then forking the main process, and also uses vfork where
		84	possible. This gives the speed of vfork, with the flexibility of fork.
		85
		86	=item Forking usually creates a copy-on-write copy of the parent
		87	process.
		88
		89	For example, modules or data files that are loaded will not use additional
		90	memory after a fork. When exec'ing a new process, modules and data files
		91	might need to be loaded again, at extra CPU and memory cost. But when
		92	forking, literally all data structures are copied - if the program frees
		93	them and replaces them by new data, the child processes will retain the
		94	old version even if it isn't used, which can suddenly and unexpectedly
		95	increase memory usage when freeing memory.
		96
		97	The trade-off is between more sharing with fork (which can be good or
		98	bad), and no sharing with exec.
		99
		100	This module allows the main program to do a controlled fork, and allows
		101	modules to exec processes safely at any time. When creating a custom
		102	process pool you can take advantage of data sharing via fork without
		103	risking to share large dynamic data structures that will blow up child
		104	memory usage.
		105
		106	In other words, this module puts you into control over what is being
		107	shared and what isn't, at all times.
		108
		109	=item Exec'ing a new perl process might be difficult.
		110
		111	For example, it is not easy to find the correct path to the perl
		112	interpreter - C<$^X> might not be a perl interpreter at all.
		113
		114	This module tries hard to identify the correct path to the perl
		115	interpreter. With a cooperative main program, exec'ing the interpreter
		116	might not even be necessary, but even without help from the main program,
		117	it will still work when used from a module.
		118
		119	=item Exec'ing a new perl process might be slow, as all necessary modules
		120	have to be loaded from disk again, with no guarantees of success.
		121
		122	Long running processes might run into problems when perl is upgraded
		123	and modules are no longer loadable because they refer to a different
		124	perl version, or parts of a distribution are newer than the ones already
		125	loaded.
		126
		127	This module supports creating pre-initialised perl processes to be used as
		128	a template for new processes.
		129
		130	=item Forking might be impossible when a program is running.
		131
		132	For example, POSIX makes it almost impossible to fork from a
		133	multi-threaded program while doing anything useful in the child - in
		134	fact, if your perl program uses POSIX threads (even indirectly via
		135	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		136	anymore without risking corruption issues on a number of operating
		137	systems.
		138
		139	This module can safely fork helper processes at any time, by calling
		140	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		141
		142	=item Parallel processing with fork might be inconvenient or difficult
		143	to implement. Modules might not work in both parent and child.
		144
		145	For example, when a program uses an event loop and creates watchers it
		146	becomes very hard to use the event loop from a child program, as the
		147	watchers already exist but are only meaningful in the parent. Worse, a
		148	module might want to use such a module, not knowing whether another module
		149	or the main program also does, leading to problems.
		150
		151	Apart from event loops, graphical toolkits also commonly fall into the
		152	"unsafe module" category, or just about anything that communicates with
		153	the external world, such as network libraries and file I/O modules, which
		154	usually don't like being copied and then allowed to continue in two
		155	processes.
		156
		157	With this module only the main program is allowed to create new processes
		158	by forking (because only the main program can know when it is still safe
		159	to do so) - all other processes are created via fork+exec, which makes it
		160	possible to use modules such as event loops or window interfaces safely.
		161
		162	=back
		163
		164	=head1 EXAMPLES
		165
10	# create a single new process, tell it to run your worker function	166	=head2 Create a single new process, tell it to run your worker function.
11		167
12	AnyEvent::Fork	168	AnyEvent::Fork
13	->new	169	->new
14	->require ("MyModule")	170	->require ("MyModule")
15	->run ("MyModule::worker, sub {	171	->run ("MyModule::worker, sub {
…		…
17		173
18	# now $master_filehandle is connected to the	174	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	175	# $slave_filehandle in the new process.
20	});	176	});
21		177
22	# MyModule::worker might look like this	178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
23	sub MyModule::worker {	182	sub worker {
24	my ($slave_filehandle) = @_;	183	my ($slave_filehandle) = @_;
25		184
26	# now $slave_filehandle is connected to the $master_filehandle	185	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	186	# in the original prorcess. have fun!
28	}	187	}
29		188
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	189	=head2 Create a pool of server processes all accepting on the same socket.
32		190
33	# create listener socket	191	# create listener socket
34	my $listener = ...;	192	my $listener = ...;
35		193
36	# create a pool template, initialise it and give it the socket	194	# create a pool template, initialise it and give it the socket
…		…
48	}	206	}
49		207
50	# now do other things - maybe use the filehandle provided by run	208	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	209	# to wait for the processes to die. or whatever.
52		210
53	# My::Server::run might look like this	211	C<My::Server> might look like this:
54	sub My::Server::run {	212
		213	package My::Server;
		214
		215	sub run {
55	my ($slave, $listener, $id) = @_;	216	my ($slave, $listener, $id) = @_;
56		217
57	close $slave; # we do not use the socket, so close it to save resources	218	close $slave; # we do not use the socket, so close it to save resources
58		219
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	220	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	222	while (my $socket = $listener->accept) {
62	# do sth. with new socket	223	# do sth. with new socket
63	}	224	}
64	}	225	}
65		226
66	=head1 DESCRIPTION	227	=head2 use AnyEvent::Fork as a faster fork+exec
67		228
68	This module allows you to create new processes, without actually forking	229	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
69	them from your current process (avoiding the problems of forking), but	230	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	231	faster than fork+exec, but still lets you prepare the environment.
71		232
72	It can be used to create new worker processes or new independent	233	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		234
78	Special care has been taken to make this module useful from other modules,	235	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	236	->new
80	or L<PAR::Packer>.	237	->eval ('
		238	# compile a helper function for later use
		239	sub run {
		240	my ($fh, $output, @cmd) = @_;
81		241
82	=head1 WHAT THIS MODULE IS NOT	242	# perl will clear close-on-exec on STDOUT/STDERR
		243	open STDOUT, ">&", $output or die;
		244	open STDERR, ">&", $fh or die;
83		245
84	This module only creates processes and lets you pass file handles and	246	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	247	}
86	there is no back channel from the process back to you, and there is no RPC	248	')
87	or message passing going on.	249	->send_fh ($output)
		250	->send_arg ("/bin/echo", "hi")
		251	->run ("run", my $cv = AE::cv);
88		252
89	If you need some form of RPC, you can either implement it yourself	253	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		254
159	=head1 CONCEPTS	255	=head1 CONCEPTS
160		256
161	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
162	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".
163		263
164	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
165	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,
166	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
167	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
…		…
241	my ($fork_fh) = @_;	341	my ($fork_fh) = @_;
242	});	342	});
243		343
244	=back	344	=back
245		345
246	=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.
247		366
248	=over 4	367	=over 4
249		368
250	=cut	369	=cut
251		370
252	package AnyEvent::Fork;	371	package AnyEvent::Fork;
253		372
254	use common::sense;	373	use common::sense;
255		374
256	use Socket ();	375	use Errno ();
257		376
258	use AnyEvent;	377	use AnyEvent;
259	use AnyEvent::Util ();	378	use AnyEvent::Util ();
260		379
261	use IO::FDPass;	380	use IO::FDPass;
262		381
263	our $VERSION = 0.2;	382	our $VERSION = 0.6;
264
265	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
271	=over 4
272
273	=back
274
275	=cut
276		383
277	# the early fork template process	384	# the early fork template process
278	our $EARLY;	385	our $EARLY;
279		386
280	# the empty template process	387	# the empty template process
281	our $TEMPLATE;	388	our $TEMPLATE;
282		389
		390	sub QUEUE() { 0 }
		391	sub FH() { 1 }
		392	sub WW() { 2 }
		393	sub PID() { 3 }
		394	sub CB() { 4 }
		395
		396	sub _new {
		397	my ($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	}
		410
283	sub _cmd {	411	sub _cmd {
284	my $self = shift;	412	my $self = shift;
285		413
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	414	# 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.	415	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
290	push @{ $self->[2] }, pack "L/a", pack "(w/a)*", @_;	416	# it.
		417	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
291		418
292	$self->[3] \|\|= AE::io $self->[1], 1, sub {	419	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		420	do {
293	# 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,
294	# or a plain string.	422	# or a plain string.
295		423
296	if (ref $self->[2][0]) {	424	if (ref $self->[QUEUE][0]) {
297	# send fh	425	# send fh
298	IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }	426	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
		427	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		428	undef $self->[WW];
		429	die "AnyEvent::Fork: file descriptor send failure: $!";
		430	}
		431
299	and shift @{ $self->[2] };	432	shift @{ $self->[QUEUE] };
300		433
301	} else {	434	} else {
302	# send string	435	# send string
303	my $len = syswrite $self->[1], $self->[2][0]	436	my $len = syswrite $self->[FH], $self->[QUEUE][0];
		437
		438	unless ($len) {
		439	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		440	undef $self->[3];
304	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	441	die "AnyEvent::Fork: command write failure: $!";
		442	}
305		443
306	substr $self->[2][0], 0, $len, "";	444	substr $self->[QUEUE][0], 0, $len, "";
307	shift @{ $self->[2] } unless length $self->[2][0];	445	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
308	}	446	}
		447	} while @{ $self->[QUEUE] };
309		448
310	unless (@{ $self->[2] }) {	449	# everything written
311	undef $self->[3];	450	undef $self->[WW];
		451
312	# invoke run callback	452	# invoke run callback, if any
313	$self->[0]->($self->[1]) if $self->[0];	453	$self->[CB]->($self->[FH]) if $self->[CB];
314	}
315	};	454	};
316		455
317	() # make sure we don't leak the watcher	456	() # make sure we don't leak the watcher
318	}
319
320	sub _new {
321	my ($self, $fh) = @_;
322
323	AnyEvent::Util::fh_nonblocking $fh, 1;
324
325	$self = bless [
326	undef, # run callback
327	$fh,
328	[], # write queue - strings or fd's
329	undef, # AE watcher
330	], $self;
331
332	$self
333	}	457	}
334		458
335	# fork template from current process, used by AnyEvent::Fork::Early/Template	459	# fork template from current process, used by AnyEvent::Fork::Early/Template
336	sub _new_fork {	460	sub _new_fork {
337	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	461	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
342	if ($pid eq 0) {	466	if ($pid eq 0) {
343	require AnyEvent::Fork::Serve;	467	require AnyEvent::Fork::Serve;
344	$AnyEvent::Fork::Serve::OWNER = $parent;	468	$AnyEvent::Fork::Serve::OWNER = $parent;
345	close $fh;	469	close $fh;
346	$0 = "$_[1] of $parent";	470	$0 = "$_[1] of $parent";
347	$SIG{CHLD} = 'IGNORE';
348	AnyEvent::Fork::Serve::serve ($slave);	471	AnyEvent::Fork::Serve::serve ($slave);
349	exit 0;	472	exit 0;
350	} elsif (!$pid) {	473	} elsif (!$pid) {
351	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	474	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
352	}	475	}
353		476
354	AnyEvent::Fork->_new ($fh)	477	AnyEvent::Fork->_new ($fh, $pid)
355	}	478	}
356		479
357	=item my $proc = new AnyEvent::Fork	480	=item my $proc = new AnyEvent::Fork
358		481
359	Create a new "empty" perl interpreter process and returns its process	482	Create a new "empty" perl interpreter process and returns its process
360	object for further manipulation.	483	object for further manipulation.
361		484
362	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
363	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
364	C<new_exec> and kept around for future calls.	487	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		488
371	=cut	489	=cut
372		490
373	sub new {	491	sub new {
374	my $class = shift;	492	my $class = shift;
…		…
452	# quick. also doesn't work in win32. of course. what did you expect	570	# quick. also doesn't work in win32. of course. what did you expect
453	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	571	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
454	my %env = %ENV;	572	my %env = %ENV;
455	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	573	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
456		574
457	Proc::FastSpawn::spawn (	575	my $pid = Proc::FastSpawn::spawn (
458	$perl,	576	$perl,
459	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	577	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
460	[map "$_=$env{$_}", keys %env],	578	[map "$_=$env{$_}", keys %env],
461	) or die "unable to spawn AnyEvent::Fork server: $!";	579	) or die "unable to spawn AnyEvent::Fork server: $!";
462		580
463	$self->_new ($fh)	581	$self->_new ($fh, $pid)
		582	}
		583
		584	=item $pid = $proc->pid
		585
		586	Returns the process id of the process I<iff it is a direct child of the
		587	process running AnyEvent::Fork>, and C<undef> otherwise.
		588
		589	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		590	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		591	to clean up their zombies when they die.
		592
		593	All other processes are not direct children, and will be cleaned up by
		594	AnyEvent::Fork itself.
		595
		596	=cut
		597
		598	sub pid {
		599	$_[0][PID]
464	}	600	}
465		601
466	=item $proc = $proc->eval ($perlcode, @args)	602	=item $proc = $proc->eval ($perlcode, @args)
467		603
468	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
469	the strings specified by C<@args>.	605	the strings specified by C<@args>, in the "main" package.
470		606
471	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
472	(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
473	to completely take over the process, use C<run> for that.	609	to completely take over the process, use C<run> for that.
474		610
475	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
476	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
477	will be reported to stderr and cause the process to exit.	613	will be reported to stderr and cause the process to exit.
478		614
		615	If you want to execute some code (that isn't in a module) to take over the
		616	process, you should compile a function via C<eval> first, and then call
		617	it via C<run>. This also gives you access to any arguments passed via the
		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.
		620
479	Returns the process object for easy chaining of method calls.	621	Returns the process object for easy chaining of method calls.
480		622
481	=cut	623	=cut
482		624
483	sub eval {	625	sub eval {
484	my ($self, $code, @args) = @_;	626	my ($self, $code, @args) = @_;
485		627
486	$self->_cmd (e => $code, @args);	628	$self->_cmd (e => pack "(w/a)", $code, @args);
487		629
488	$self	630	$self
489	}	631	}
490		632
491	=item $proc = $proc->require ($module, ...)	633	=item $proc = $proc->require ($module, ...)
…		…
508	=item $proc = $proc->send_fh ($handle, ...)	650	=item $proc = $proc->send_fh ($handle, ...)
509		651
510	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,
511	to prepare a call to C<run>.	653	to prepare a call to C<run>.
512		654
513	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
514	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
515	accomplished by simply not storing the file handles anywhere after passing	657	handles. This is most easily accomplished by simply not storing the file
516	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.
517		660
518	Returns the process object for easy chaining of method calls.	661	Returns the process object for easy chaining of method calls.
519		662
520	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
521	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.
…		…
528	sub send_fh {	671	sub send_fh {
529	my ($self, @fh) = @_;	672	my ($self, @fh) = @_;
530		673
531	for my $fh (@fh) {	674	for my $fh (@fh) {
532	$self->_cmd ("h");	675	$self->_cmd ("h");
533	push @{ $self->[2] }, \$fh;	676	push @{ $self->[QUEUE] }, \$fh;
534	}	677	}
535		678
536	$self	679	$self
537	}	680	}
538		681
539	=item $proc = $proc->send_arg ($string, ...)	682	=item $proc = $proc->send_arg ($string, ...)
540		683
541	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
542	C<run>. The strings can be any octet string.	685	C<run>. The strings can be any octet strings.
		686
		687	The protocol is optimised to pass a moderate number of relatively short
		688	strings - while you can pass up to 4GB of data in one go, this is more
		689	meant to pass some ID information or other startup info, not big chunks of
		690	data.
543		691
544	Returns the process object for easy chaining of method calls.	692	Returns the process object for easy chaining of method calls.
545		693
546	=cut	694	=cut
547		695
548	sub send_arg {	696	sub send_arg {
549	my ($self, @arg) = @_;	697	my ($self, @arg) = @_;
550		698
551	$self->_cmd (a => @arg);	699	$self->_cmd (a => pack "(w/a)", @arg);
552		700
553	$self	701	$self
554	}	702	}
555		703
556	=item $proc->run ($func, $cb->($fh))	704	=item $proc->run ($func, $cb->($fh))
557		705
558	Enter the function specified by the fully qualified name in C<$func> in	706	Enter the function specified by the function name in C<$func> in the
559	the process. The function is called with the communication socket as first	707	process. The function is called with the communication socket as first
560	argument, followed by all file handles and string arguments sent earlier	708	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.	709	via C<send_fh> and C<send_arg> methods, in the order they were called.
562		710
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.	711	The process object becomes unusable on return from this function - any
		712	further method calls result in undefined behaviour.
		713
		714	The function name should be fully qualified, but if it isn't, it will be
		715	looked up in the C<main> package.
		716
		717	If the called function returns, doesn't exist, or any error occurs, the
		718	process exits.
		719
		720	Preparing the process is done in the background - when all commands have
		721	been sent, the callback is invoked with the local communications socket
		722	as argument. At this point you can start using the socket in any way you
		723	like.
569		724
570	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,
571	to save on kernel memory.	726	to save on kernel memory.
572		727
573	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
574	created process. The close-on-exec flag is set on both. Even if not used	729	created process. The close-on-exec flag is set in both.
		730
575	otherwise, the socket can be a good indicator for the existence of the	731	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,	732	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	733	event on it, because exiting the process closes the socket (if it didn't
578	children using fork).	734	create any children using fork).
579		735
580	Example: create a template for a process pool, pass a few strings, some	736	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.	737	file handles, then fork, pass one more string, and run some code.
582		738
583	my $pool = AnyEvent::Fork	739	my $pool = AnyEvent::Fork
…		…
591	->send_arg ("str3")	747	->send_arg ("str3")
592	->run ("Some::function", sub {	748	->run ("Some::function", sub {
593	my ($fh) = @_;	749	my ($fh) = @_;
594		750
595	# fh is nonblocking, but we trust that the OS can accept these	751	# fh is nonblocking, but we trust that the OS can accept these
596	# extra 3 octets anyway.	752	# few octets anyway.
597	syswrite $fh, "hi #$_\n";	753	syswrite $fh, "hi #$_\n";
598		754
599	# $fh is being closed here, as we don't store it anywhere	755	# $fh is being closed here, as we don't store it anywhere
600	});	756	});
601	}	757	}
…		…
603	# Some::function might look like this - all parameters passed before fork	759	# Some::function might look like this - all parameters passed before fork
604	# and after will be passed, in order, after the communications socket.	760	# and after will be passed, in order, after the communications socket.
605	sub Some::function {	761	sub Some::function {
606	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	762	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
607		763
608	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	764	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
609	}	765	}
610		766
611	=cut	767	=cut
612		768
613	sub run {	769	sub run {
614	my ($self, $func, $cb) = @_;	770	my ($self, $func, $cb) = @_;
615		771
616	$self->[0] = $cb;	772	$self->[CB] = $cb;
617	$self->_cmd (r => $func);	773	$self->_cmd (r => $func);
618	}	774	}
619		775
620	=back	776	=back
621		777
622	=head1 PERFORMANCE	778	=head1 PERFORMANCE
623		779
624	Now for some unscientific benchmark numbers (all done on an amd64	780	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	781	GNU/Linux box). These are intended to give you an idea of the relative
626	performance you can expect.	782	performance you can expect, they are not meant to be absolute performance
		783	numbers.
627		784
628	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls	785	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	786	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.	787	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
631		788
632	2079 new processes per second, using socketpair + fork manually	789	2079 new processes per second, using manual socketpair + fork
633		790
634	Then I did the same thing, but instead of calling fork, I called	791	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	792	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	793	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	794	socket pair + fork, except that what is forked is the template process
…		…
646	479 vfork+execs per second, using AnyEvent::Fork->new_exec	803	479 vfork+execs per second, using AnyEvent::Fork->new_exec
647		804
648	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
649	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?
650		807
651	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
652	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
653	introduced is canceled out.	810	overhead is canceled out.
654		811
655	If the benchmark process grows, the normal fork becomes even slower:	812	If the benchmark process grows, the normal fork becomes even slower:
656		813
657	1340 new processes, manual fork in a 20MB process	814	1340 new processes, manual fork of a 20MB process
658	731 new processes, manual fork in a 200MB process	815	731 new processes, manual fork of a 200MB process
659	235 new processes, manual fork in a 2000MB process	816	235 new processes, manual fork of a 2000MB process
660		817
661	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
662	very bad conscience because of the extra overhead required to start new	819	conscience because of the extra overhead required to start new processes.
663	processes.
664		820
665	=head1 TYPICAL PROBLEMS	821	=head1 TYPICAL PROBLEMS
666		822
667	This section lists typical problems that remain. I hope by recognising	823	This section lists typical problems that remain. I hope by recognising
668	them, most can be avoided.	824	them, most can be avoided.
669		825
670	=over 4	826	=over 4
671		827
672	=item exit runs destructors
673
674	=item "leaked" file descriptors for exec'ed processes	828	=item leaked file descriptors for exec'ed processes
675		829
676	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
677	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
678	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
679	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.
…		…
699	libraries or the code that leaks those file descriptors.	853	libraries or the code that leaks those file descriptors.
700		854
701	Fortunately, most of these leaked descriptors do no harm, other than	855	Fortunately, most of these leaked descriptors do no harm, other than
702	sitting on some resources.	856	sitting on some resources.
703		857
704	=item "leaked" file descriptors for fork'ed processes	858	=item leaked file descriptors for fork'ed processes
705		859
706	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,
707	which closes file descriptors not marked for being inherited.	861	which closes file descriptors not marked for being inherited.
708		862
709	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	863	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
717	trouble with a fork.	871	trouble with a fork.
718		872
719	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
720	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
721	initialising them, for example, by calling C<init Gtk2> manually.	875	initialising them, for example, by calling C<init Gtk2> manually.
		876
		877	=item exiting calls object destructors
		878
		879	This only applies to users of L<AnyEvent::Fork:Early> and
		880	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		881	that reference external resources.
		882
		883	When a process created by AnyEvent::Fork exits, it might do so by calling
		884	exit, or simply letting perl reach the end of the program. At which point
		885	Perl runs all destructors.
		886
		887	Not all destructors are fork-safe - for example, an object that represents
		888	the connection to an X display might tell the X server to free resources,
		889	which is inconvenient when the "real" object in the parent still needs to
		890	use them.
		891
		892	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		893	it as the very first thing, right?
		894
		895	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		896	is to not create objects with nontrivial destructors that might have an
		897	effect outside of Perl.
722		898
723	=back	899	=back
724		900
725	=head1 PORTABILITY NOTES	901	=head1 PORTABILITY NOTES
726		902
…		…
729	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
730	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
731	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
732	issues or other braindamage. Hrrrr.	908	issues or other braindamage. Hrrrr.
733		909
734	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
735	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.
736	support enough functionality to do it.
737		912
738	=head1 SEE ALSO	913	=head1 SEE ALSO
739		914
740	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
741	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
742	program at a convenient time).	919	program at a convenient time (part of this distribution).
743		920
744	=head1 AUTHOR	921	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		922
		923	=head1 AUTHOR AND CONTACT INFORMATION
745		924
746	Marc Lehmann <schmorp@schmorp.de>	925	Marc Lehmann <schmorp@schmorp.de>
747	http://home.schmorp.de/	926	http://software.schmorp.de/pkg/AnyEvent-Fork
748		927
749	=cut	928	=cut
750		929
751	1	930	1
752		931

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