[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 1.41 by root, Mon Apr 8 03:20:53 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	=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
13	# 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.
14		164
15	AnyEvent::Fork	165	AnyEvent::Fork
16	->new	166	->new
17	->require ("MyModule")	167	->require ("MyModule")
18	->run ("MyModule::worker, sub {	168	->run ("MyModule::worker, sub {
20		170
21	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
22	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
23	});	173	});
24		174
25	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
26	sub MyModule::worker {	179	sub worker {
27	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
28		181
29	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
30	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
31	}	184	}
32		185
33	##################################################################
34	# 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.
35		187
36	# create listener socket	188	# create listener socket
37	my $listener = ...;	189	my $listener = ...;
38		190
39	# create a pool template, initialise it and give it the socket	191	# create a pool template, initialise it and give it the socket
…		…
51	}	203	}
52		204
53	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
54	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
55		207
56	# My::Server::run might look like this	208	C<My::Server> might look like this:
57	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
58	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
59		214
60	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
61		216
62	# 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,
…		…
64	while (my $socket = $listener->accept) {	219	while (my $socket = $listener->accept) {
65	# do sth. with new socket	220	# do sth. with new socket
66	}	221	}
67	}	222	}
68		223
69	=head1 DESCRIPTION	224	=head2 use AnyEvent::Fork as a faster fork+exec
70		225
71	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
72	them from your current process (avoiding the problems of forking), but	227	and standard error redirected to the communications socket. It is usually
73	preserving most of the advantages of fork.	228	faster than fork+exec, but still lets you prepare the environment.
74		229
75	It can be used to create new worker processes or new independent	230	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		231
81	Special care has been taken to make this module useful from other modules,	232	AnyEvent::Fork
82	while still supporting specialised environments such as L<App::Staticperl>	233	->new
83	or L<PAR::Packer>.	234	->eval ('
		235	# compile a helper function for later use
		236	sub run {
		237	my ($fh, $output, @cmd) = @_;
84		238
85	=head1 PROBLEM STATEMENT	239	# perl will clear close-on-exec on STDOUT/STDERR
		240	open STDOUT, ">&", $output or die;
		241	open STDERR, ">&", $fh or die;
86		242
87	There are two ways to implement parallel processing on UNIX like operating	243	exec @cmd;
88	systems - fork and process, and fork+exec and process. They have different	244	}
89	advantages and disadvantages that I describe below, together with how this	245	')
90	module tries to mitigate the disadvantages.	246	->send_fh ($output)
		247	->send_arg ("/bin/echo", "hi")
		248	->run ("run", my $cv = AE::cv);
91		249
92	=over 4	250	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		251
149	=head1 CONCEPTS	252	=head1 CONCEPTS
150		253
151	This module can create new processes either by executing a new perl	254	This module can create new processes either by executing a new perl
152	process, or by forking from an existing "template" process.	255	process, or by forking from an existing "template" process.
…		…
169	needed the first time. Forking from this process shares the memory used	272	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	273	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.	274	time, and the memory is not shared with anything else.
172		275
173	This is ideal for when you only need one extra process of a kind, with the	276	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.	277	option of starting and stopping it on demand.
175		278
176	Example:	279	Example:
177		280
178	AnyEvent::Fork	281	AnyEvent::Fork
179	->new	282	->new
…		…
194	modules you loaded) is shared between the processes, and each new process	297	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.	298	consumes relatively little memory of its own.
196		299
197	The disadvantage of this approach is that you need to create a template	300	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	301	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	302	only need a fixed number of processes you can create them, and then destroy
200	the template process.	303	the template process.
201		304
202	Example:	305	Example:
203		306
204	my $template = AnyEvent::Fork->new->require ("Some::Module");	307	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
231	my ($fork_fh) = @_;	334	my ($fork_fh) = @_;
232	});	335	});
233		336
234	=back	337	=back
235		338
236	=head1 FUNCTIONS	339	=head1 THE C<AnyEvent::Fork> CLASS
		340
		341	This module exports nothing, and only implements a single class -
		342	C<AnyEvent::Fork>.
		343
		344	There are two class constructors that both create new processes - C<new>
		345	and C<new_exec>. The C<fork> method creates a new process by forking an
		346	existing one and could be considered a third constructor.
		347
		348	Most of the remaining methods deal with preparing the new process, by
		349	loading code, evaluating code and sending data to the new process. They
		350	usually return the process object, so you can chain method calls.
		351
		352	If a process object is destroyed before calling its C<run> method, then
		353	the process simply exits. After C<run> is called, all responsibility is
		354	passed to the specified function.
		355
		356	As long as there is any outstanding work to be done, process objects
		357	resist being destroyed, so there is no reason to store them unless you
		358	need them later - configure and forget works just fine.
237		359
238	=over 4	360	=over 4
239		361
240	=cut	362	=cut
241		363
242	package AnyEvent::Fork;	364	package AnyEvent::Fork;
243		365
244	use common::sense;	366	use common::sense;
245		367
246	use Socket ();	368	use Errno ();
247		369
248	use AnyEvent;	370	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();	371	use AnyEvent::Util ();
251		372
252	our $VERSION = $AnyEvent::Fork::Util::VERSION;	373	use IO::FDPass;
253		374
254	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	375	our $VERSION = 0.6;
255
256	=item my $pool = new AnyEvent::Fork key => value...
257
258	Create a new process pool. The following named parameters are supported:
259		376
260	=over 4	377	=over 4
261		378
262	=back	379	=back
263		380
…		…
270	our $TEMPLATE;	387	our $TEMPLATE;
271		388
272	sub _cmd {	389	sub _cmd {
273	my $self = shift;	390	my $self = shift;
274		391
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	392	# 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.	393	# 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)*", @_;	394	# it.
		395	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
280		396
281	$self->[3] \|\|= AE::io $self->[1], 1, sub {	397	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		398	do {
282	# send the next "thing" in the queue - either a reference to an fh,	399	# send the next "thing" in the queue - either a reference to an fh,
283	# or a plain string.	400	# or a plain string.
284		401
285	if (ref $self->[2][0]) {	402	if (ref $self->[2][0]) {
286	# send fh	403	# send fh
287	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	404	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		405	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		406	undef $self->[3];
		407	die "AnyEvent::Fork: file descriptor send failure: $!";
		408	}
		409
288	and shift @{ $self->[2] };	410	shift @{ $self->[2] };
289		411
290	} else {	412	} else {
291	# send string	413	# send string
292	my $len = syswrite $self->[1], $self->[2][0]	414	my $len = syswrite $self->[1], $self->[2][0];
		415
		416	unless ($len) {
		417	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		418	undef $self->[3];
293	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	419	die "AnyEvent::Fork: command write failure: $!";
		420	}
294		421
295	substr $self->[2][0], 0, $len, "";	422	substr $self->[2][0], 0, $len, "";
296	shift @{ $self->[2] } unless length $self->[2][0];	423	shift @{ $self->[2] } unless length $self->[2][0];
297	}	424	}
		425	} while @{ $self->[2] };
298		426
299	unless (@{ $self->[2] }) {	427	# everything written
300	undef $self->[3];	428	undef $self->[3];
		429
301	# invoke run callback	430	# invoke run callback, if any
302	$self->[0]->($self->[1]) if $self->[0];	431	$self->[4]->($self->[1]) if $self->[4];
303	}
304	};	432	};
		433
		434	() # make sure we don't leak the watcher
305	}	435	}
306		436
307	sub _new {	437	sub _new {
308	my ($self, $fh) = @_;	438	my ($self, $fh, $pid) = @_;
309		439
310	AnyEvent::Util::fh_nonblocking $fh, 1;	440	AnyEvent::Util::fh_nonblocking $fh, 1;
311		441
312	$self = bless [	442	$self = bless [
313	undef, # run callback	443	$pid,
314	$fh,	444	$fh,
315	[], # write queue - strings or fd's	445	[], # write queue - strings or fd's
316	undef, # AE watcher	446	undef, # AE watcher
317	], $self;	447	], $self;
318		448
…		…
330	require AnyEvent::Fork::Serve;	460	require AnyEvent::Fork::Serve;
331	$AnyEvent::Fork::Serve::OWNER = $parent;	461	$AnyEvent::Fork::Serve::OWNER = $parent;
332	close $fh;	462	close $fh;
333	$0 = "$_[1] of $parent";	463	$0 = "$_[1] of $parent";
334	AnyEvent::Fork::Serve::serve ($slave);	464	AnyEvent::Fork::Serve::serve ($slave);
335	AnyEvent::Fork::Util::_exit 0;	465	exit 0;
336	} elsif (!$pid) {	466	} elsif (!$pid) {
337	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	467	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
338	}	468	}
339		469
340	AnyEvent::Fork->_new ($fh)	470	AnyEvent::Fork->_new ($fh, $pid)
341	}	471	}
342		472
343	=item my $proc = new AnyEvent::Fork	473	=item my $proc = new AnyEvent::Fork
344		474
345	Create a new "empty" perl interpreter process and returns its process	475	Create a new "empty" perl interpreter process and returns its process
346	object for further manipulation.	476	object for further manipulation.
347		477
348	The new process is forked from a template process that is kept around	478	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	479	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.	480	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		481
357	=cut	482	=cut
358		483
359	sub new {	484	sub new {
360	my $class = shift;	485	my $class = shift;
…		…
396	reduces the amount of memory sharing that is possible, and is also slower.	521	reduces the amount of memory sharing that is possible, and is also slower.
397		522
398	You should use C<new> whenever possible, except when having a template	523	You should use C<new> whenever possible, except when having a template
399	process around is unacceptable.	524	process around is unacceptable.
400		525
401	The path to the perl interpreter is divined usign various methods - first	526	The path to the perl interpreter is divined using various methods - first
402	C<$^X> is investigated to see if the path ends with something that sounds	527	C<$^X> is investigated to see if the path ends with something that sounds
403	as if it were the perl interpreter. Failing this, the module falls back to	528	as if it were the perl interpreter. Failing this, the module falls back to
404	using C<$Config::Config{perlpath}>.	529	using C<$Config::Config{perlpath}>.
405		530
406	=cut	531	=cut
…		…
415	my $perl = $;	540	my $perl = $;
416		541
417	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	542	# 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	543	# that looks like perl. this obviously only works for posix and win32
419	unless (	544	unless (
420	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	545	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
421	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	546	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
422	) {	547	) {
423	# if it doesn't look perlish enough, try Config	548	# if it doesn't look perlish enough, try Config
424	require Config;	549	require Config;
425	$perl = $Config::Config{perlpath};	550	$perl = $Config::Config{perlpath};
…		…
436	Proc::FastSpawn::fd_inherit (fileno $fh, 0);	561	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
437		562
438	# quick. also doesn't work in win32. of course. what did you expect	563	# quick. also doesn't work in win32. of course. what did you expect
439	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	564	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
440	my %env = %ENV;	565	my %env = %ENV;
441	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;	566	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
442		567
443	Proc::FastSpawn::spawn (	568	my $pid = Proc::FastSpawn::spawn (
444	$perl,	569	$perl,
445	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	570	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
446	[map "$_=$env{$_}", keys %env],	571	[map "$_=$env{$_}", keys %env],
447	) or die "unable to spawn AnyEvent::Fork server: $!";	572	) or die "unable to spawn AnyEvent::Fork server: $!";
448		573
449	$self->_new ($fh)	574	$self->_new ($fh, $pid)
		575	}
		576
		577	=item $pid = $proc->pid
		578
		579	Returns the process id of the process I<iff it is a direct child of the
		580	process running AnyEvent::Fork>, and C<undef> otherwise.
		581
		582	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		583	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		584	to clean up their zombies when they die.
		585
		586	All other processes are not direct children, and will be cleaned up by
		587	AnyEvent::Fork itself.
		588
		589	=cut
		590
		591	sub pid {
		592	$_[0][0]
450	}	593	}
451		594
452	=item $proc = $proc->eval ($perlcode, @args)	595	=item $proc = $proc->eval ($perlcode, @args)
453		596
454	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	597	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
455	the strings specified by C<@args>.	598	the strings specified by C<@args>, in the "main" package.
456		599
457	This call is meant to do any custom initialisation that might be required	600	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	601	(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.	602	to completely take over the process, use C<run> for that.
460		603
461	The code will usually be executed after this call returns, and there is no	604	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	605	way to pass anything back to the calling process. Any evaluation errors
463	will be reported to stderr and cause the process to exit.	606	will be reported to stderr and cause the process to exit.
464		607
		608	If you want to execute some code (that isn't in a module) to take over the
		609	process, you should compile a function via C<eval> first, and then call
		610	it via C<run>. This also gives you access to any arguments passed via the
		611	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		612	a faster fork+exec> example to see it in action.
		613
465	Returns the process object for easy chaining of method calls.	614	Returns the process object for easy chaining of method calls.
466		615
467	=cut	616	=cut
468		617
469	sub eval {	618	sub eval {
470	my ($self, $code, @args) = @_;	619	my ($self, $code, @args) = @_;
471		620
472	$self->_cmd (e => $code, @args);	621	$self->_cmd (e => pack "(w/a)", $code, @args);
473		622
474	$self	623	$self
475	}	624	}
476		625
477	=item $proc = $proc->require ($module, ...)	626	=item $proc = $proc->require ($module, ...)
…		…
494	=item $proc = $proc->send_fh ($handle, ...)	643	=item $proc = $proc->send_fh ($handle, ...)
495		644
496	Send one or more file handles (I<not> file descriptors) to the process,	645	Send one or more file handles (I<not> file descriptors) to the process,
497	to prepare a call to C<run>.	646	to prepare a call to C<run>.
498		647
499	The process object keeps a reference to the handles until this is done,	648	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	649	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	650	handles. This is most easily accomplished by simply not storing the file
502	them to this method.	651	handles anywhere after passing them to this method - when AnyEvent::Fork
		652	is finished using them, perl will automatically close them.
503		653
504	Returns the process object for easy chaining of method calls.	654	Returns the process object for easy chaining of method calls.
505		655
506	Example: pass an fh to a process, and release it without closing. it will	656	Example: pass a file handle to a process, and release it without
507	be closed automatically when it is no longer used.	657	closing. It will be closed automatically when it is no longer used.
508		658
509	$proc->send_fh ($my_fh);	659	$proc->send_fh ($my_fh);
510	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	660	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
511		661
512	=cut	662	=cut
…		…
523	}	673	}
524		674
525	=item $proc = $proc->send_arg ($string, ...)	675	=item $proc = $proc->send_arg ($string, ...)
526		676
527	Send one or more argument strings to the process, to prepare a call to	677	Send one or more argument strings to the process, to prepare a call to
528	C<run>. The strings can be any octet string.	678	C<run>. The strings can be any octet strings.
529		679
		680	The protocol is optimised to pass a moderate number of relatively short
		681	strings - while you can pass up to 4GB of data in one go, this is more
		682	meant to pass some ID information or other startup info, not big chunks of
		683	data.
		684
530	Returns the process object for easy chaining of emthod calls.	685	Returns the process object for easy chaining of method calls.
531		686
532	=cut	687	=cut
533		688
534	sub send_arg {	689	sub send_arg {
535	my ($self, @arg) = @_;	690	my ($self, @arg) = @_;
536		691
537	$self->_cmd (a => @arg);	692	$self->_cmd (a => pack "(w/a)", @arg);
538		693
539	$self	694	$self
540	}	695	}
541		696
542	=item $proc->run ($func, $cb->($fh))	697	=item $proc->run ($func, $cb->($fh))
543		698
544	Enter the function specified by the fully qualified name in C<$func> in	699	Enter the function specified by the function name in C<$func> in the
545	the process. The function is called with the communication socket as first	700	process. The function is called with the communication socket as first
546	argument, followed by all file handles and string arguments sent earlier	701	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.	702	via C<send_fh> and C<send_arg> methods, in the order they were called.
548		703
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.	704	The process object becomes unusable on return from this function - any
		705	further method calls result in undefined behaviour.
		706
		707	The function name should be fully qualified, but if it isn't, it will be
		708	looked up in the C<main> package.
		709
		710	If the called function returns, doesn't exist, or any error occurs, the
		711	process exits.
		712
		713	Preparing the process is done in the background - when all commands have
		714	been sent, the callback is invoked with the local communications socket
		715	as argument. At this point you can start using the socket in any way you
		716	like.
555		717
556	If the communication socket isn't used, it should be closed on both sides,	718	If the communication socket isn't used, it should be closed on both sides,
557	to save on kernel memory.	719	to save on kernel memory.
558		720
559	The socket is non-blocking in the parent, and blocking in the newly	721	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	722	created process. The close-on-exec flag is set in both.
		723
561	otherwise, the socket can be a good indicator for the existance of the	724	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,	725	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	726	event on it, because exiting the process closes the socket (if it didn't
564	children using fork).	727	create any children using fork).
565		728
566	Example: create a template for a process pool, pass a few strings, some	729	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.	730	file handles, then fork, pass one more string, and run some code.
568		731
569	my $pool = AnyEvent::Fork	732	my $pool = AnyEvent::Fork
…		…
577	->send_arg ("str3")	740	->send_arg ("str3")
578	->run ("Some::function", sub {	741	->run ("Some::function", sub {
579	my ($fh) = @_;	742	my ($fh) = @_;
580		743
581	# fh is nonblocking, but we trust that the OS can accept these	744	# fh is nonblocking, but we trust that the OS can accept these
582	# extra 3 octets anyway.	745	# few octets anyway.
583	syswrite $fh, "hi #$_\n";	746	syswrite $fh, "hi #$_\n";
584		747
585	# $fh is being closed here, as we don't store it anywhere	748	# $fh is being closed here, as we don't store it anywhere
586	});	749	});
587	}	750	}
…		…
589	# Some::function might look like this - all parameters passed before fork	752	# Some::function might look like this - all parameters passed before fork
590	# and after will be passed, in order, after the communications socket.	753	# and after will be passed, in order, after the communications socket.
591	sub Some::function {	754	sub Some::function {
592	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	755	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
593		756
594	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	757	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
595	}	758	}
596		759
597	=cut	760	=cut
598		761
599	sub run {	762	sub run {
600	my ($self, $func, $cb) = @_;	763	my ($self, $func, $cb) = @_;
601		764
602	$self->[0] = $cb;	765	$self->[4] = $cb;
603	$self->_cmd (r => $func);	766	$self->_cmd (r => $func);
604	}	767	}
		768
		769	=back
		770
		771	=head1 PERFORMANCE
		772
		773	Now for some unscientific benchmark numbers (all done on an amd64
		774	GNU/Linux box). These are intended to give you an idea of the relative
		775	performance you can expect, they are not meant to be absolute performance
		776	numbers.
		777
		778	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		779	exit in the child and waits for the socket to close in the parent. I did
		780	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		781
		782	2079 new processes per second, using manual socketpair + fork
		783
		784	Then I did the same thing, but instead of calling fork, I called
		785	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		786	socket form the child to close on exit. This does the same thing as manual
		787	socket pair + fork, except that what is forked is the template process
		788	(2440kB), and the socket needs to be passed to the server at the other end
		789	of the socket first.
		790
		791	2307 new processes per second, using AnyEvent::Fork->new
		792
		793	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		794	a new perl interpreter and compile the small server each time, I get:
		795
		796	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		797
		798	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		799	though it uses the same operations, but adds a lot of overhead?
		800
		801	The difference is simply the process size: forking the 5MB process takes
		802	so much longer than forking the 2.5MB template process that the extra
		803	overhead introduced is canceled out.
		804
		805	If the benchmark process grows, the normal fork becomes even slower:
		806
		807	1340 new processes, manual fork of a 20MB process
		808	731 new processes, manual fork of a 200MB process
		809	235 new processes, manual fork of a 2000MB process
		810
		811	What that means (to me) is that I can use this module without having a bad
		812	conscience because of the extra overhead required to start new processes.
		813
		814	=head1 TYPICAL PROBLEMS
		815
		816	This section lists typical problems that remain. I hope by recognising
		817	them, most can be avoided.
		818
		819	=over 4
		820
		821	=item leaked file descriptors for exec'ed processes
		822
		823	POSIX systems inherit file descriptors by default when exec'ing a new
		824	process. While perl itself laudably sets the close-on-exec flags on new
		825	file handles, most C libraries don't care, and even if all cared, it's
		826	often not possible to set the flag in a race-free manner.
		827
		828	That means some file descriptors can leak through. And since it isn't
		829	possible to know which file descriptors are "good" and "necessary" (or
		830	even to know which file descriptors are open), there is no good way to
		831	close the ones that might harm.
		832
		833	As an example of what "harm" can be done consider a web server that
		834	accepts connections and afterwards some module uses AnyEvent::Fork for the
		835	first time, causing it to fork and exec a new process, which might inherit
		836	the network socket. When the server closes the socket, it is still open
		837	in the child (which doesn't even know that) and the client might conclude
		838	that the connection is still fine.
		839
		840	For the main program, there are multiple remedies available -
		841	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		842	C<new_exec> is another, as in both cases, the first process can be exec'ed
		843	well before many random file descriptors are open.
		844
		845	In general, the solution for these kind of problems is to fix the
		846	libraries or the code that leaks those file descriptors.
		847
		848	Fortunately, most of these leaked descriptors do no harm, other than
		849	sitting on some resources.
		850
		851	=item leaked file descriptors for fork'ed processes
		852
		853	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		854	which closes file descriptors not marked for being inherited.
		855
		856	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		857	a way to create these processes by forking, and this leaks more file
		858	descriptors than exec'ing them, as there is no way to mark descriptors as
		859	"close on fork".
		860
		861	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		862	pipes for internal uses, and L<Gtk2> might open a connection to the X
		863	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		864	trouble with a fork.
		865
		866	The solution is to either not load these modules before use'ing
		867	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		868	initialising them, for example, by calling C<init Gtk2> manually.
		869
		870	=item exiting calls object destructors
		871
		872	This only applies to users of L<AnyEvent::Fork:Early> and
		873	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		874	that reference external resources.
		875
		876	When a process created by AnyEvent::Fork exits, it might do so by calling
		877	exit, or simply letting perl reach the end of the program. At which point
		878	Perl runs all destructors.
		879
		880	Not all destructors are fork-safe - for example, an object that represents
		881	the connection to an X display might tell the X server to free resources,
		882	which is inconvenient when the "real" object in the parent still needs to
		883	use them.
		884
		885	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		886	it as the very first thing, right?
		887
		888	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		889	is to not create objects with nontrivial destructors that might have an
		890	effect outside of Perl.
605		891
606	=back	892	=back
607		893
608	=head1 PORTABILITY NOTES	894	=head1 PORTABILITY NOTES
609		895
610	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	896	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	897	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	898	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	899	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	900	useful that you can do with it without running into memory corruption
615	issues or other braindamage. Hrrrr.	901	issues or other braindamage. Hrrrr.
616		902
617	Cygwin perl is not supported at the moment, as it should implement fd	903	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	904	shortcomings of its API - see L<IO::FDPoll> for more details.
619	support enough functionality to do it.	905
		906	=head1 SEE ALSO
		907
		908	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		909	L<AnyEvent::Fork::Template> (to create a process by forking the main
		910	program at a convenient time).
620		911
621	=head1 AUTHOR	912	=head1 AUTHOR
622		913
623	Marc Lehmann <schmorp@schmorp.de>	914	Marc Lehmann <schmorp@schmorp.de>
624	http://home.schmorp.de/	915	http://home.schmorp.de/

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.12 by root, Thu Apr 4 07:27:09 2013 UTC vs. Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

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Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC