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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.12 by root, Thu Apr 4 07:27:09 2013 UTC vs.
Revision 1.38 by root, Sat Apr 6 20:07:30 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't	3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
4		4
5	ATTENTION, this is a very early release, and very untested. Consider it a
6	technology preview.
7
8	=head1 SYNOPSIS	5	=head1 SYNOPSIS
9		6
10	use AnyEvent::Fork;	7	use AnyEvent::Fork;
11		8
12	##################################################################	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
13	# 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.
14		146
15	AnyEvent::Fork	147	AnyEvent::Fork
16	->new	148	->new
17	->require ("MyModule")	149	->require ("MyModule")
18	->run ("MyModule::worker, sub {	150	->run ("MyModule::worker, sub {
20		152
21	# now $master_filehandle is connected to the	153	# now $master_filehandle is connected to the
22	# $slave_filehandle in the new process.	154	# $slave_filehandle in the new process.
23	});	155	});
24		156
25	# MyModule::worker might look like this	157	C<MyModule> might look like this:
		158
		159	package MyModule;
		160
26	sub MyModule::worker {	161	sub worker {
27	my ($slave_filehandle) = @_;	162	my ($slave_filehandle) = @_;
28		163
29	# now $slave_filehandle is connected to the $master_filehandle	164	# now $slave_filehandle is connected to the $master_filehandle
30	# in the original prorcess. have fun!	165	# in the original prorcess. have fun!
31	}	166	}
32		167
33	##################################################################
34	# 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.
35		169
36	# create listener socket	170	# create listener socket
37	my $listener = ...;	171	my $listener = ...;
38		172
39	# create a pool template, initialise it and give it the socket	173	# create a pool template, initialise it and give it the socket
…		…
51	}	185	}
52		186
53	# now do other things - maybe use the filehandle provided by run	187	# now do other things - maybe use the filehandle provided by run
54	# to wait for the processes to die. or whatever.	188	# to wait for the processes to die. or whatever.
55		189
56	# My::Server::run might look like this	190	C<My::Server> might look like this:
57	sub My::Server::run {	191
		192	package My::Server;
		193
		194	sub run {
58	my ($slave, $listener, $id) = @_;	195	my ($slave, $listener, $id) = @_;
59		196
60	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
61		198
62	# 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,
…		…
64	while (my $socket = $listener->accept) {	201	while (my $socket = $listener->accept) {
65	# do sth. with new socket	202	# do sth. with new socket
66	}	203	}
67	}	204	}
68		205
69	=head1 DESCRIPTION	206	=head2 use AnyEvent::Fork as a faster fork+exec
70		207
71	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
72	them from your current process (avoiding the problems of forking), but	209	and standard error redirected to the communications socket. It is usually
73	preserving most of the advantages of fork.	210	faster than fork+exec, but still lets you prepare the environment.
74		211
75	It can be used to create new worker processes or new independent	212	open my $output, ">/tmp/log" or die "$!";
76	subprocesses for short- and long-running jobs, process pools (e.g. for use
77	in pre-forked servers) but also to spawn new external processes (such as
78	CGI scripts from a webserver), which can be faster (and more well behaved)
79	than using fork+exec in big processes.
80		213
81	Special care has been taken to make this module useful from other modules,	214	AnyEvent::Fork
82	while still supporting specialised environments such as L<App::Staticperl>	215	->new
83	or L<PAR::Packer>.	216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
84		219
85	=head1 PROBLEM STATEMENT	220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
86		223
87	There are two ways to implement parallel processing on UNIX like operating	224	exec @cmd;
88	systems - fork and process, and fork+exec and process. They have different	225	}
89	advantages and disadvantages that I describe below, together with how this	226	')
90	module tries to mitigate the disadvantages.	227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
91		230
92	=over 4	231	my $stderr = $cv->recv;
93
94	=item Forking from a big process can be very slow (a 5GB process needs
95	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
96	is often shared with exec (because you have to fork first), but in some
97	circumstances (e.g. when vfork is used), fork+exec can be much faster.
98
99	This module can help here by telling a small(er) helper process to fork,
100	or fork+exec instead.
101
102	=item Forking usually creates a copy-on-write copy of the parent
103	process. Memory (for example, modules or data files that have been
104	will not take additional memory). When exec'ing a new process, modules
105	and data files might need to be loaded again, at extra cpu and memory
106	cost. Likewise when forking, all data structures are copied as well - if
107	the program frees them and replaces them by new data, the child processes
108	will retain the memory even if it isn't used.
109
110	This module allows the main program to do a controlled fork, and allows
111	modules to exec processes safely at any time. When creating a custom
112	process pool you can take advantage of data sharing via fork without
113	risking to share large dynamic data structures that will blow up child
114	memory usage.
115
116	=item Exec'ing a new perl process might be difficult and slow. For
117	example, it is not easy to find the correct path to the perl interpreter,
118	and all modules have to be loaded from disk again. Long running processes
119	might run into problems when perl is upgraded for example.
120
121	This module supports creating pre-initialised perl processes to be used
122	as template, and also tries hard to identify the correct path to the perl
123	interpreter. With a cooperative main program, exec'ing the interpreter
124	might not even be necessary.
125
126	=item Forking might be impossible when a program is running. For example,
127	POSIX makes it almost impossible to fork from a multithreaded program and
128	do anything useful in the child - strictly speaking, if your perl program
129	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
130	you cannot call fork on the perl level anymore, at all.
131
132	This module can safely fork helper processes at any time, by caling
133	fork+exec in C, in a POSIX-compatible way.
134
135	=item Parallel processing with fork might be inconvenient or difficult
136	to implement. For example, when a program uses an event loop and creates
137	watchers it becomes very hard to use the event loop from a child
138	program, as the watchers already exist but are only meaningful in the
139	parent. Worse, a module might want to use such a system, not knowing
140	whether another module or the main program also does, leading to problems.
141
142	This module only lets the main program create pools by forking (because
143	only the main program can know when it is still safe to do so) - all other
144	pools are created by fork+exec, after which such modules can again be
145	loaded.
146
147	=back
148		232
149	=head1 CONCEPTS	233	=head1 CONCEPTS
150		234
151	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
152	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
169	needed the first time. Forking from this process shares the memory used	253	needed the first time. Forking from this process shares the memory used
170	for the perl interpreter with the new process, but loading modules takes	254	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.	255	time, and the memory is not shared with anything else.
172		256
173	This is ideal for when you only need one extra process of a kind, with the	257	This is ideal for when you only need one extra process of a kind, with the
174	option of starting and stipping it on demand.	258	option of starting and stopping it on demand.
175		259
176	Example:	260	Example:
177		261
178	AnyEvent::Fork	262	AnyEvent::Fork
179	->new	263	->new
…		…
194	modules you loaded) is shared between the processes, and each new process	278	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.	279	consumes relatively little memory of its own.
196		280
197	The disadvantage of this approach is that you need to create a template	281	The disadvantage of this approach is that you need to create a template
198	process for the sole purpose of forking new processes from it, but if you	282	process for the sole purpose of forking new processes from it, but if you
199	only need a fixed number of proceses you can create them, and then destroy	283	only need a fixed number of processes you can create them, and then destroy
200	the template process.	284	the template process.
201		285
202	Example:	286	Example:
203		287
204	my $template = AnyEvent::Fork->new->require ("Some::Module");	288	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
231	my ($fork_fh) = @_;	315	my ($fork_fh) = @_;
232	});	316	});
233		317
234	=back	318	=back
235		319
236	=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.
237		340
238	=over 4	341	=over 4
239		342
240	=cut	343	=cut
241		344
242	package AnyEvent::Fork;	345	package AnyEvent::Fork;
243		346
244	use common::sense;	347	use common::sense;
245		348
246	use Socket ();	349	use Errno ();
247		350
248	use AnyEvent;	351	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();	352	use AnyEvent::Util ();
251		353
252	our $VERSION = $AnyEvent::Fork::Util::VERSION;	354	use IO::FDPass;
		355
		356	our $VERSION = 0.5;
253		357
254	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
255
256	=item my $pool = new AnyEvent::Fork key => value...
257
258	Create a new process pool. The following named parameters are supported:
259		359
260	=over 4	360	=over 4
261		361
262	=back	362	=back
263		363
…		…
270	our $TEMPLATE;	370	our $TEMPLATE;
271		371
272	sub _cmd {	372	sub _cmd {
273	my $self = shift;	373	my $self = shift;
274		374
275	#TODO: maybe append the packet to any existing string command already in the queue
276
277	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	375	# ideally, we would want to use "a (w/a)*" as format string, but perl
278	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	376	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
279	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	377	# it.
		378	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
280		379
281	$self->[3] \|\|= AE::io $self->[1], 1, sub {	380	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		381	do {
282	# 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,
283	# or a plain string.	383	# or a plain string.
284		384
285	if (ref $self->[2][0]) {	385	if (ref $self->[2][0]) {
286	# send fh	386	# send fh
287	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	387	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		388	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		389	undef $self->[3];
		390	die "AnyEvent::Fork: file descriptor send failure: $!";
		391	}
		392
288	and shift @{ $self->[2] };	393	shift @{ $self->[2] };
289		394
290	} else {	395	} else {
291	# send string	396	# send string
292	my $len = syswrite $self->[1], $self->[2][0]	397	my $len = syswrite $self->[1], $self->[2][0];
		398
		399	unless ($len) {
		400	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		401	undef $self->[3];
293	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	402	die "AnyEvent::Fork: command write failure: $!";
		403	}
294		404
295	substr $self->[2][0], 0, $len, "";	405	substr $self->[2][0], 0, $len, "";
296	shift @{ $self->[2] } unless length $self->[2][0];	406	shift @{ $self->[2] } unless length $self->[2][0];
297	}	407	}
		408	} while @{ $self->[2] };
298		409
299	unless (@{ $self->[2] }) {	410	# everything written
300	undef $self->[3];	411	undef $self->[3];
		412
301	# invoke run callback	413	# invoke run callback, if any
302	$self->[0]->($self->[1]) if $self->[0];	414	$self->[4]->($self->[1]) if $self->[4];
303	}
304	};	415	};
		416
		417	() # make sure we don't leak the watcher
305	}	418	}
306		419
307	sub _new {	420	sub _new {
308	my ($self, $fh) = @_;	421	my ($self, $fh, $pid) = @_;
309		422
310	AnyEvent::Util::fh_nonblocking $fh, 1;	423	AnyEvent::Util::fh_nonblocking $fh, 1;
311		424
312	$self = bless [	425	$self = bless [
313	undef, # run callback	426	$pid,
314	$fh,	427	$fh,
315	[], # write queue - strings or fd's	428	[], # write queue - strings or fd's
316	undef, # AE watcher	429	undef, # AE watcher
317	], $self;	430	], $self;
318		431
…		…
329	if ($pid eq 0) {	442	if ($pid eq 0) {
330	require AnyEvent::Fork::Serve;	443	require AnyEvent::Fork::Serve;
331	$AnyEvent::Fork::Serve::OWNER = $parent;	444	$AnyEvent::Fork::Serve::OWNER = $parent;
332	close $fh;	445	close $fh;
333	$0 = "$_[1] of $parent";	446	$0 = "$_[1] of $parent";
		447	$SIG{CHLD} = 'IGNORE';
334	AnyEvent::Fork::Serve::serve ($slave);	448	AnyEvent::Fork::Serve::serve ($slave);
335	AnyEvent::Fork::Util::_exit 0;	449	exit 0;
336	} elsif (!$pid) {	450	} elsif (!$pid) {
337	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	451	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
338	}	452	}
339		453
340	AnyEvent::Fork->_new ($fh)	454	AnyEvent::Fork->_new ($fh, $pid)
341	}	455	}
342		456
343	=item my $proc = new AnyEvent::Fork	457	=item my $proc = new AnyEvent::Fork
344		458
345	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
346	object for further manipulation.	460	object for further manipulation.
347		461
348	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
349	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
350	C<new_exec> and kept around for future calls.	464	C<new_exec> first and then stays around for future calls.
351
352	When the process object is destroyed, it will release the file handle
353	that connects it with the new process. When the new process has not yet
354	called C<run>, then the process will exit. Otherwise, what happens depends
355	entirely on the code that is executed.
356		465
357	=cut	466	=cut
358		467
359	sub new {	468	sub new {
360	my $class = shift;	469	my $class = shift;
…		…
396	reduces the amount of memory sharing that is possible, and is also slower.	505	reduces the amount of memory sharing that is possible, and is also slower.
397		506
398	You should use C<new> whenever possible, except when having a template	507	You should use C<new> whenever possible, except when having a template
399	process around is unacceptable.	508	process around is unacceptable.
400		509
401	The path to the perl interpreter is divined usign various methods - first	510	The path to the perl interpreter is divined using various methods - first
402	C<$^X> is investigated to see if the path ends with something that sounds	511	C<$^X> is investigated to see if the path ends with something that sounds
403	as if it were the perl interpreter. Failing this, the module falls back to	512	as if it were the perl interpreter. Failing this, the module falls back to
404	using C<$Config::Config{perlpath}>.	513	using C<$Config::Config{perlpath}>.
405		514
406	=cut	515	=cut
…		…
415	my $perl = $;	524	my $perl = $;
416		525
417	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	526	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
418	# that looks like perl. this obviously only works for posix and win32	527	# that looks like perl. this obviously only works for posix and win32
419	unless (	528	unless (
420	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	529	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
421	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	530	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
422	) {	531	) {
423	# if it doesn't look perlish enough, try Config	532	# if it doesn't look perlish enough, try Config
424	require Config;	533	require Config;
425	$perl = $Config::Config{perlpath};	534	$perl = $Config::Config{perlpath};
…		…
436	Proc::FastSpawn::fd_inherit (fileno $fh, 0);	545	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
437		546
438	# 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
439	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	548	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
440	my %env = %ENV;	549	my %env = %ENV;
441	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;	550	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
442		551
443	Proc::FastSpawn::spawn (	552	my $pid = Proc::FastSpawn::spawn (
444	$perl,	553	$perl,
445	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	554	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
446	[map "$_=$env{$_}", keys %env],	555	[map "$_=$env{$_}", keys %env],
447	) or die "unable to spawn AnyEvent::Fork server: $!";	556	) or die "unable to spawn AnyEvent::Fork server: $!";
448		557
449	$self->_new ($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]
450	}	577	}
451		578
452	=item $proc = $proc->eval ($perlcode, @args)	579	=item $proc = $proc->eval ($perlcode, @args)
453		580
454	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
455	the strings specified by C<@args>.	582	the strings specified by C<@args>, in the "main" package.
456		583
457	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
458	(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
459	to completely take over the process, use C<run> for that.	586	to completely take over the process, use C<run> for that.
460		587
461	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
462	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
463	will be reported to stderr and cause the process to exit.	590	will be reported to stderr and cause the process to exit.
464		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
465	Returns the process object for easy chaining of method calls.	598	Returns the process object for easy chaining of method calls.
466		599
467	=cut	600	=cut
468		601
469	sub eval {	602	sub eval {
470	my ($self, $code, @args) = @_;	603	my ($self, $code, @args) = @_;
471		604
472	$self->_cmd (e => $code, @args);	605	$self->_cmd (e => pack "(w/a)", $code, @args);
473		606
474	$self	607	$self
475	}	608	}
476		609
477	=item $proc = $proc->require ($module, ...)	610	=item $proc = $proc->require ($module, ...)
…		…
494	=item $proc = $proc->send_fh ($handle, ...)	627	=item $proc = $proc->send_fh ($handle, ...)
495		628
496	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,
497	to prepare a call to C<run>.	630	to prepare a call to C<run>.
498		631
499	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
500	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
501	accomplished by simply not storing the file handles anywhere after passing	634	handles. This is most easily accomplished by simply not storing the file
502	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.
503		637
504	Returns the process object for easy chaining of method calls.	638	Returns the process object for easy chaining of method calls.
505		639
506	Example: pass an fh to a process, and release it without closing. it will	640	Example: pass a file handle to a process, and release it without
507	be closed automatically when it is no longer used.	641	closing. It will be closed automatically when it is no longer used.
508		642
509	$proc->send_fh ($my_fh);	643	$proc->send_fh ($my_fh);
510	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	644	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
511		645
512	=cut	646	=cut
…		…
523	}	657	}
524		658
525	=item $proc = $proc->send_arg ($string, ...)	659	=item $proc = $proc->send_arg ($string, ...)
526		660
527	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
528	C<run>. The strings can be any octet string.	662	C<run>. The strings can be any octet strings.
529		663
		664	The protocol is optimised to pass a moderate number of relatively short
		665	strings - while you can pass up to 4GB of data in one go, this is more
		666	meant to pass some ID information or other startup info, not big chunks of
		667	data.
		668
530	Returns the process object for easy chaining of emthod calls.	669	Returns the process object for easy chaining of method calls.
531		670
532	=cut	671	=cut
533		672
534	sub send_arg {	673	sub send_arg {
535	my ($self, @arg) = @_;	674	my ($self, @arg) = @_;
536		675
537	$self->_cmd (a => @arg);	676	$self->_cmd (a => pack "(w/a)", @arg);
538		677
539	$self	678	$self
540	}	679	}
541		680
542	=item $proc->run ($func, $cb->($fh))	681	=item $proc->run ($func, $cb->($fh))
543		682
544	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
545	the process. The function is called with the communication socket as first	684	process. The function is called with the communication socket as first
546	argument, followed by all file handles and string arguments sent earlier	685	argument, followed by all file handles and string arguments sent earlier
547	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.
548		687
549	If the called function returns, the process exits.
550
551	Preparing the process can take time - when the process is ready, the
552	callback is invoked with the local communications socket as argument.
553
554	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.
555		701
556	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,
557	to save on kernel memory.	703	to save on kernel memory.
558		704
559	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
560	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
561	otherwise, the socket can be a good indicator for the existance of the	708	Even if not used otherwise, the socket can be a good indicator for the
562	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
563	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
564	children using fork).	711	create any children using fork).
565		712
566	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
567	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.
568		715
569	my $pool = AnyEvent::Fork	716	my $pool = AnyEvent::Fork
…		…
577	->send_arg ("str3")	724	->send_arg ("str3")
578	->run ("Some::function", sub {	725	->run ("Some::function", sub {
579	my ($fh) = @_;	726	my ($fh) = @_;
580		727
581	# 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
582	# extra 3 octets anyway.	729	# few octets anyway.
583	syswrite $fh, "hi #$_\n";	730	syswrite $fh, "hi #$_\n";
584		731
585	# $fh is being closed here, as we don't store it anywhere	732	# $fh is being closed here, as we don't store it anywhere
586	});	733	});
587	}	734	}
…		…
589	# Some::function might look like this - all parameters passed before fork	736	# Some::function might look like this - all parameters passed before fork
590	# and after will be passed, in order, after the communications socket.	737	# and after will be passed, in order, after the communications socket.
591	sub Some::function {	738	sub Some::function {
592	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	739	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
593		740
594	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	741	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
595	}	742	}
596		743
597	=cut	744	=cut
598		745
599	sub run {	746	sub run {
600	my ($self, $func, $cb) = @_;	747	my ($self, $func, $cb) = @_;
601		748
602	$self->[0] = $cb;	749	$self->[4] = $cb;
603	$self->_cmd (r => $func);	750	$self->_cmd (r => $func);
604	}	751	}
		752
		753	=back
		754
		755	=head1 PERFORMANCE
		756
		757	Now for some unscientific benchmark numbers (all done on an amd64
		758	GNU/Linux box). These are intended to give you an idea of the relative
		759	performance you can expect, they are not meant to be absolute performance
		760	numbers.
		761
		762	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		763	exit in the child and waits for the socket to close in the parent. I did
		764	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		765
		766	2079 new processes per second, using manual socketpair + fork
		767
		768	Then I did the same thing, but instead of calling fork, I called
		769	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		770	socket form the child to close on exit. This does the same thing as manual
		771	socket pair + fork, except that what is forked is the template process
		772	(2440kB), and the socket needs to be passed to the server at the other end
		773	of the socket first.
		774
		775	2307 new processes per second, using AnyEvent::Fork->new
		776
		777	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		778	a new perl interpreter and compile the small server each time, I get:
		779
		780	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		781
		782	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		783	though it uses the same operations, but adds a lot of overhead?
		784
		785	The difference is simply the process size: forking the 5MB process takes
		786	so much longer than forking the 2.5MB template process that the extra
		787	overhead introduced is canceled out.
		788
		789	If the benchmark process grows, the normal fork becomes even slower:
		790
		791	1340 new processes, manual fork of a 20MB process
		792	731 new processes, manual fork of a 200MB process
		793	235 new processes, manual fork of a 2000MB process
		794
		795	What that means (to me) is that I can use this module without having a bad
		796	conscience because of the extra overhead required to start new processes.
		797
		798	=head1 TYPICAL PROBLEMS
		799
		800	This section lists typical problems that remain. I hope by recognising
		801	them, most can be avoided.
		802
		803	=over 4
		804
		805	=item leaked file descriptors for exec'ed processes
		806
		807	POSIX systems inherit file descriptors by default when exec'ing a new
		808	process. While perl itself laudably sets the close-on-exec flags on new
		809	file handles, most C libraries don't care, and even if all cared, it's
		810	often not possible to set the flag in a race-free manner.
		811
		812	That means some file descriptors can leak through. And since it isn't
		813	possible to know which file descriptors are "good" and "necessary" (or
		814	even to know which file descriptors are open), there is no good way to
		815	close the ones that might harm.
		816
		817	As an example of what "harm" can be done consider a web server that
		818	accepts connections and afterwards some module uses AnyEvent::Fork for the
		819	first time, causing it to fork and exec a new process, which might inherit
		820	the network socket. When the server closes the socket, it is still open
		821	in the child (which doesn't even know that) and the client might conclude
		822	that the connection is still fine.
		823
		824	For the main program, there are multiple remedies available -
		825	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		826	C<new_exec> is another, as in both cases, the first process can be exec'ed
		827	well before many random file descriptors are open.
		828
		829	In general, the solution for these kind of problems is to fix the
		830	libraries or the code that leaks those file descriptors.
		831
		832	Fortunately, most of these leaked descriptors do no harm, other than
		833	sitting on some resources.
		834
		835	=item leaked file descriptors for fork'ed processes
		836
		837	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		838	which closes file descriptors not marked for being inherited.
		839
		840	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		841	a way to create these processes by forking, and this leaks more file
		842	descriptors than exec'ing them, as there is no way to mark descriptors as
		843	"close on fork".
		844
		845	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		846	pipes for internal uses, and L<Gtk2> might open a connection to the X
		847	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		848	trouble with a fork.
		849
		850	The solution is to either not load these modules before use'ing
		851	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		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 L<AnyEvent::Fork:Early> and
		857	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		858	that reference external resources.
		859
		860	When a process created by AnyEvent::Fork exits, it might do so by calling
		861	exit, or simply letting perl reach the end of the program. At which point
		862	Perl runs all destructors.
		863
		864	Not all destructors are fork-safe - for example, an object that represents
		865	the connection to an X display might tell the X server to free resources,
		866	which is inconvenient when the "real" object in the parent still needs to
		867	use them.
		868
		869	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		870	it as the very first thing, right?
		871
		872	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		873	is to not create objects with nontrivial destructors that might have an
		874	effect outside of Perl.
605		875
606	=back	876	=back
607		877
608	=head1 PORTABILITY NOTES	878	=head1 PORTABILITY NOTES
609		879
610	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	880	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
611	and ::Template is not going to work), and it cost a lot of blood and sweat	881	and ::Template is not going to work), and it cost a lot of blood and sweat
612	to make it so, mostly due to the bloody broken perl that nobody seems to	882	to make it so, mostly due to the bloody broken perl that nobody seems to
613	care about. The fork emulation is a bad joke - I have yet to see something	883	care about. The fork emulation is a bad joke - I have yet to see something
614	useful that you cna do with it without running into memory corruption	884	useful that you can do with it without running into memory corruption
615	issues or other braindamage. Hrrrr.	885	issues or other braindamage. Hrrrr.
616		886
617	Cygwin perl is not supported at the moment, as it should implement fd	887	Cygwin perl is not supported at the moment due to some hilarious
618	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	888	shortcomings of its API - see L<IO::FDPoll> for more details.
619	support enough functionality to do it.	889
		890	=head1 SEE ALSO
		891
		892	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		893	L<AnyEvent::Fork::Template> (to create a process by forking the main
		894	program at a convenient time).
620		895
621	=head1 AUTHOR	896	=head1 AUTHOR
622		897
623	Marc Lehmann <schmorp@schmorp.de>	898	Marc Lehmann <schmorp@schmorp.de>
624	http://home.schmorp.de/	899	http://home.schmorp.de/

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Revision 1.38 by root, Sat Apr 6 20:07:30 2013 UTC