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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.13 by root, Thu Apr 4 07:58:01 2013 UTC vs.
Revision 1.44 by root, Thu Apr 18 10:49:59 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 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
13	# 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.
14		167
15	AnyEvent::Fork	168	AnyEvent::Fork
16	->new	169	->new
17	->require ("MyModule")	170	->require ("MyModule")
18	->run ("MyModule::worker, sub {	171	->run ("MyModule::worker, sub {
20		173
21	# now $master_filehandle is connected to the	174	# now $master_filehandle is connected to the
22	# $slave_filehandle in the new process.	175	# $slave_filehandle in the new process.
23	});	176	});
24		177
25	# MyModule::worker might look like this	178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
26	sub MyModule::worker {	182	sub worker {
27	my ($slave_filehandle) = @_;	183	my ($slave_filehandle) = @_;
28		184
29	# now $slave_filehandle is connected to the $master_filehandle	185	# now $slave_filehandle is connected to the $master_filehandle
30	# in the original prorcess. have fun!	186	# in the original prorcess. have fun!
31	}	187	}
32		188
33	##################################################################
34	# 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.
35		190
36	# create listener socket	191	# create listener socket
37	my $listener = ...;	192	my $listener = ...;
38		193
39	# create a pool template, initialise it and give it the socket	194	# create a pool template, initialise it and give it the socket
…		…
51	}	206	}
52		207
53	# now do other things - maybe use the filehandle provided by run	208	# now do other things - maybe use the filehandle provided by run
54	# to wait for the processes to die. or whatever.	209	# to wait for the processes to die. or whatever.
55		210
56	# My::Server::run might look like this	211	C<My::Server> might look like this:
57	sub My::Server::run {	212
		213	package My::Server;
		214
		215	sub run {
58	my ($slave, $listener, $id) = @_;	216	my ($slave, $listener, $id) = @_;
59		217
60	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
61		219
62	# 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,
…		…
64	while (my $socket = $listener->accept) {	222	while (my $socket = $listener->accept) {
65	# do sth. with new socket	223	# do sth. with new socket
66	}	224	}
67	}	225	}
68		226
69	=head1 DESCRIPTION	227	=head2 use AnyEvent::Fork as a faster fork+exec
70		228
71	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>
72	them from your current process (avoiding the problems of forking), but	230	and standard error redirected to the communications socket. It is usually
73	preserving most of the advantages of fork.	231	faster than fork+exec, but still lets you prepare the environment.
74		232
75	It can be used to create new worker processes or new independent	233	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		234
81	Special care has been taken to make this module useful from other modules,	235	AnyEvent::Fork
82	while still supporting specialised environments such as L<App::Staticperl>	236	->new
83	or L<PAR::Packer>.	237	->eval ('
		238	# compile a helper function for later use
		239	sub run {
		240	my ($fh, $output, @cmd) = @_;
84		241
85	=head1 PROBLEM STATEMENT	242	# perl will clear close-on-exec on STDOUT/STDERR
		243	open STDOUT, ">&", $output or die;
		244	open STDERR, ">&", $fh or die;
86		245
87	There are two ways to implement parallel processing on UNIX like operating	246	exec @cmd;
88	systems - fork and process, and fork+exec and process. They have different	247	}
89	advantages and disadvantages that I describe below, together with how this	248	')
90	module tries to mitigate the disadvantages.	249	->send_fh ($output)
		250	->send_arg ("/bin/echo", "hi")
		251	->run ("run", my $cv = AE::cv);
91		252
92	=over 4	253	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		254
149	=head1 CONCEPTS	255	=head1 CONCEPTS
150		256
151	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
152	process, or by forking from an existing "template" process.	258	process, or by forking from an existing "template" process.
…		…
169	needed the first time. Forking from this process shares the memory used	275	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	276	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.	277	time, and the memory is not shared with anything else.
172		278
173	This is ideal for when you only need one extra process of a kind, with the	279	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.	280	option of starting and stopping it on demand.
175		281
176	Example:	282	Example:
177		283
178	AnyEvent::Fork	284	AnyEvent::Fork
179	->new	285	->new
…		…
194	modules you loaded) is shared between the processes, and each new process	300	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.	301	consumes relatively little memory of its own.
196		302
197	The disadvantage of this approach is that you need to create a template	303	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	304	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	305	only need a fixed number of processes you can create them, and then destroy
200	the template process.	306	the template process.
201		307
202	Example:	308	Example:
203		309
204	my $template = AnyEvent::Fork->new->require ("Some::Module");	310	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
231	my ($fork_fh) = @_;	337	my ($fork_fh) = @_;
232	});	338	});
233		339
234	=back	340	=back
235		341
236	=head1 FUNCTIONS	342	=head1 THE C<AnyEvent::Fork> CLASS
		343
		344	This module exports nothing, and only implements a single class -
		345	C<AnyEvent::Fork>.
		346
		347	There are two class constructors that both create new processes - C<new>
		348	and C<new_exec>. The C<fork> method creates a new process by forking an
		349	existing one and could be considered a third constructor.
		350
		351	Most of the remaining methods deal with preparing the new process, by
		352	loading code, evaluating code and sending data to the new process. They
		353	usually return the process object, so you can chain method calls.
		354
		355	If a process object is destroyed before calling its C<run> method, then
		356	the process simply exits. After C<run> is called, all responsibility is
		357	passed to the specified function.
		358
		359	As long as there is any outstanding work to be done, process objects
		360	resist being destroyed, so there is no reason to store them unless you
		361	need them later - configure and forget works just fine.
237		362
238	=over 4	363	=over 4
239		364
240	=cut	365	=cut
241		366
242	package AnyEvent::Fork;	367	package AnyEvent::Fork;
243		368
244	use common::sense;	369	use common::sense;
245		370
246	use Socket ();	371	use Errno ();
247		372
248	use AnyEvent;	373	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();	374	use AnyEvent::Util ();
251		375
252	our $VERSION = $AnyEvent::Fork::Util::VERSION;	376	use IO::FDPass;
253		377
254	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	378	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
260	=over 4
261
262	=back
263
264	=cut
265		379
266	# the early fork template process	380	# the early fork template process
267	our $EARLY;	381	our $EARLY;
268		382
269	# the empty template process	383	# the empty template process
270	our $TEMPLATE;	384	our $TEMPLATE;
271		385
		386	sub QUEUE() { 0 }
		387	sub FH() { 1 }
		388	sub WW() { 2 }
		389	sub PID() { 3 }
		390	sub CB() { 4 }
		391
		392	sub _new {
		393	my ($self, $fh, $pid) = @_;
		394
		395	AnyEvent::Util::fh_nonblocking $fh, 1;
		396
		397	$self = bless [
		398	[], # write queue - strings or fd's
		399	$fh,
		400	undef, # AE watcher
		401	$pid,
		402	], $self;
		403
		404	$self
		405	}
		406
272	sub _cmd {	407	sub _cmd {
273	my $self = shift;	408	my $self = shift;
274		409
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	410	# 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.	411	# 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)*", @_;	412	# it.
		413	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
280		414
281	$self->[3] \|\|= AE::io $self->[1], 1, sub {	415	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		416	do {
282	# send the next "thing" in the queue - either a reference to an fh,	417	# send the next "thing" in the queue - either a reference to an fh,
283	# or a plain string.	418	# or a plain string.
284		419
285	if (ref $self->[2][0]) {	420	if (ref $self->[QUEUE][0]) {
286	# send fh	421	# send fh
287	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	422	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
		423	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		424	undef $self->[WW];
		425	die "AnyEvent::Fork: file descriptor send failure: $!";
		426	}
		427
288	and shift @{ $self->[2] };	428	shift @{ $self->[QUEUE] };
289		429
290	} else {	430	} else {
291	# send string	431	# send string
292	my $len = syswrite $self->[1], $self->[2][0]	432	my $len = syswrite $self->[FH], $self->[QUEUE][0];
		433
		434	unless ($len) {
		435	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		436	undef $self->[3];
293	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	437	die "AnyEvent::Fork: command write failure: $!";
		438	}
294		439
295	substr $self->[2][0], 0, $len, "";	440	substr $self->[QUEUE][0], 0, $len, "";
296	shift @{ $self->[2] } unless length $self->[2][0];	441	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
297	}	442	}
		443	} while @{ $self->[QUEUE] };
298		444
299	unless (@{ $self->[2] }) {	445	# everything written
300	undef $self->[3];	446	undef $self->[WW];
		447
301	# invoke run callback	448	# invoke run callback, if any
302	$self->[0]->($self->[1]) if $self->[0];	449	$self->[CB]->($self->[FH]) if $self->[CB];
303	}
304	};	450	};
305	}
306		451
307	sub _new {	452	() # make sure we don't leak the watcher
308	my ($self, $fh) = @_;
309
310	AnyEvent::Util::fh_nonblocking $fh, 1;
311
312	$self = bless [
313	undef, # run callback
314	$fh,
315	[], # write queue - strings or fd's
316	undef, # AE watcher
317	], $self;
318
319	$self
320	}	453	}
321		454
322	# fork template from current process, used by AnyEvent::Fork::Early/Template	455	# fork template from current process, used by AnyEvent::Fork::Early/Template
323	sub _new_fork {	456	sub _new_fork {
324	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	457	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
330	require AnyEvent::Fork::Serve;	463	require AnyEvent::Fork::Serve;
331	$AnyEvent::Fork::Serve::OWNER = $parent;	464	$AnyEvent::Fork::Serve::OWNER = $parent;
332	close $fh;	465	close $fh;
333	$0 = "$_[1] of $parent";	466	$0 = "$_[1] of $parent";
334	AnyEvent::Fork::Serve::serve ($slave);	467	AnyEvent::Fork::Serve::serve ($slave);
335	AnyEvent::Fork::Util::_exit 0;	468	exit 0;
336	} elsif (!$pid) {	469	} elsif (!$pid) {
337	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	470	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
338	}	471	}
339		472
340	AnyEvent::Fork->_new ($fh)	473	AnyEvent::Fork->_new ($fh, $pid)
341	}	474	}
342		475
343	=item my $proc = new AnyEvent::Fork	476	=item my $proc = new AnyEvent::Fork
344		477
345	Create a new "empty" perl interpreter process and returns its process	478	Create a new "empty" perl interpreter process and returns its process
346	object for further manipulation.	479	object for further manipulation.
347		480
348	The new process is forked from a template process that is kept around	481	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	482	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.	483	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		484
357	=cut	485	=cut
358		486
359	sub new {	487	sub new {
360	my $class = shift;	488	my $class = shift;
…		…
396	reduces the amount of memory sharing that is possible, and is also slower.	524	reduces the amount of memory sharing that is possible, and is also slower.
397		525
398	You should use C<new> whenever possible, except when having a template	526	You should use C<new> whenever possible, except when having a template
399	process around is unacceptable.	527	process around is unacceptable.
400		528
401	The path to the perl interpreter is divined usign various methods - first	529	The path to the perl interpreter is divined using various methods - first
402	C<$^X> is investigated to see if the path ends with something that sounds	530	C<$^X> is investigated to see if the path ends with something that sounds
403	as if it were the perl interpreter. Failing this, the module falls back to	531	as if it were the perl interpreter. Failing this, the module falls back to
404	using C<$Config::Config{perlpath}>.	532	using C<$Config::Config{perlpath}>.
405		533
406	=cut	534	=cut
…		…
415	my $perl = $;	543	my $perl = $;
416		544
417	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	545	# 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	546	# that looks like perl. this obviously only works for posix and win32
419	unless (	547	unless (
420	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	548	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
421	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	549	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
422	) {	550	) {
423	# if it doesn't look perlish enough, try Config	551	# if it doesn't look perlish enough, try Config
424	require Config;	552	require Config;
425	$perl = $Config::Config{perlpath};	553	$perl = $Config::Config{perlpath};
…		…
436	Proc::FastSpawn::fd_inherit (fileno $fh, 0);	564	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
437		565
438	# quick. also doesn't work in win32. of course. what did you expect	566	# quick. also doesn't work in win32. of course. what did you expect
439	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	567	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
440	my %env = %ENV;	568	my %env = %ENV;
441	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;	569	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
442		570
443	Proc::FastSpawn::spawn (	571	my $pid = Proc::FastSpawn::spawn (
444	$perl,	572	$perl,
445	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	573	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
446	[map "$_=$env{$_}", keys %env],	574	[map "$_=$env{$_}", keys %env],
447	) or die "unable to spawn AnyEvent::Fork server: $!";	575	) or die "unable to spawn AnyEvent::Fork server: $!";
448		576
449	$self->_new ($fh)	577	$self->_new ($fh, $pid)
		578	}
		579
		580	=item $pid = $proc->pid
		581
		582	Returns the process id of the process I<iff it is a direct child of the
		583	process running AnyEvent::Fork>, and C<undef> otherwise.
		584
		585	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		586	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		587	to clean up their zombies when they die.
		588
		589	All other processes are not direct children, and will be cleaned up by
		590	AnyEvent::Fork itself.
		591
		592	=cut
		593
		594	sub pid {
		595	$_[0][PID]
450	}	596	}
451		597
452	=item $proc = $proc->eval ($perlcode, @args)	598	=item $proc = $proc->eval ($perlcode, @args)
453		599
454	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	600	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
455	the strings specified by C<@args>.	601	the strings specified by C<@args>, in the "main" package.
456		602
457	This call is meant to do any custom initialisation that might be required	603	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	604	(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.	605	to completely take over the process, use C<run> for that.
460		606
461	The code will usually be executed after this call returns, and there is no	607	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	608	way to pass anything back to the calling process. Any evaluation errors
463	will be reported to stderr and cause the process to exit.	609	will be reported to stderr and cause the process to exit.
464		610
		611	If you want to execute some code (that isn't in a module) to take over the
		612	process, you should compile a function via C<eval> first, and then call
		613	it via C<run>. This also gives you access to any arguments passed via the
		614	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		615	a faster fork+exec> example to see it in action.
		616
465	Returns the process object for easy chaining of method calls.	617	Returns the process object for easy chaining of method calls.
466		618
467	=cut	619	=cut
468		620
469	sub eval {	621	sub eval {
470	my ($self, $code, @args) = @_;	622	my ($self, $code, @args) = @_;
471		623
472	$self->_cmd (e => $code, @args);	624	$self->_cmd (e => pack "(w/a)", $code, @args);
473		625
474	$self	626	$self
475	}	627	}
476		628
477	=item $proc = $proc->require ($module, ...)	629	=item $proc = $proc->require ($module, ...)
…		…
494	=item $proc = $proc->send_fh ($handle, ...)	646	=item $proc = $proc->send_fh ($handle, ...)
495		647
496	Send one or more file handles (I<not> file descriptors) to the process,	648	Send one or more file handles (I<not> file descriptors) to the process,
497	to prepare a call to C<run>.	649	to prepare a call to C<run>.
498		650
499	The process object keeps a reference to the handles until this is done,	651	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	652	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	653	handles. This is most easily accomplished by simply not storing the file
502	them to this method.	654	handles anywhere after passing them to this method - when AnyEvent::Fork
		655	is finished using them, perl will automatically close them.
503		656
504	Returns the process object for easy chaining of method calls.	657	Returns the process object for easy chaining of method calls.
505		658
506	Example: pass an fh to a process, and release it without closing. it will	659	Example: pass a file handle to a process, and release it without
507	be closed automatically when it is no longer used.	660	closing. It will be closed automatically when it is no longer used.
508		661
509	$proc->send_fh ($my_fh);	662	$proc->send_fh ($my_fh);
510	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	663	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
511		664
512	=cut	665	=cut
…		…
514	sub send_fh {	667	sub send_fh {
515	my ($self, @fh) = @_;	668	my ($self, @fh) = @_;
516		669
517	for my $fh (@fh) {	670	for my $fh (@fh) {
518	$self->_cmd ("h");	671	$self->_cmd ("h");
519	push @{ $self->[2] }, \$fh;	672	push @{ $self->[QUEUE] }, \$fh;
520	}	673	}
521		674
522	$self	675	$self
523	}	676	}
524		677
525	=item $proc = $proc->send_arg ($string, ...)	678	=item $proc = $proc->send_arg ($string, ...)
526		679
527	Send one or more argument strings to the process, to prepare a call to	680	Send one or more argument strings to the process, to prepare a call to
528	C<run>. The strings can be any octet string.	681	C<run>. The strings can be any octet strings.
529		682
		683	The protocol is optimised to pass a moderate number of relatively short
		684	strings - while you can pass up to 4GB of data in one go, this is more
		685	meant to pass some ID information or other startup info, not big chunks of
		686	data.
		687
530	Returns the process object for easy chaining of emthod calls.	688	Returns the process object for easy chaining of method calls.
531		689
532	=cut	690	=cut
533		691
534	sub send_arg {	692	sub send_arg {
535	my ($self, @arg) = @_;	693	my ($self, @arg) = @_;
536		694
537	$self->_cmd (a => @arg);	695	$self->_cmd (a => pack "(w/a)", @arg);
538		696
539	$self	697	$self
540	}	698	}
541		699
542	=item $proc->run ($func, $cb->($fh))	700	=item $proc->run ($func, $cb->($fh))
543		701
544	Enter the function specified by the fully qualified name in C<$func> in	702	Enter the function specified by the function name in C<$func> in the
545	the process. The function is called with the communication socket as first	703	process. The function is called with the communication socket as first
546	argument, followed by all file handles and string arguments sent earlier	704	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.	705	via C<send_fh> and C<send_arg> methods, in the order they were called.
548		706
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.	707	The process object becomes unusable on return from this function - any
		708	further method calls result in undefined behaviour.
		709
		710	The function name should be fully qualified, but if it isn't, it will be
		711	looked up in the C<main> package.
		712
		713	If the called function returns, doesn't exist, or any error occurs, the
		714	process exits.
		715
		716	Preparing the process is done in the background - when all commands have
		717	been sent, the callback is invoked with the local communications socket
		718	as argument. At this point you can start using the socket in any way you
		719	like.
555		720
556	If the communication socket isn't used, it should be closed on both sides,	721	If the communication socket isn't used, it should be closed on both sides,
557	to save on kernel memory.	722	to save on kernel memory.
558		723
559	The socket is non-blocking in the parent, and blocking in the newly	724	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	725	created process. The close-on-exec flag is set in both.
		726
561	otherwise, the socket can be a good indicator for the existance of the	727	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,	728	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	729	event on it, because exiting the process closes the socket (if it didn't
564	children using fork).	730	create any children using fork).
565		731
566	Example: create a template for a process pool, pass a few strings, some	732	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.	733	file handles, then fork, pass one more string, and run some code.
568		734
569	my $pool = AnyEvent::Fork	735	my $pool = AnyEvent::Fork
…		…
577	->send_arg ("str3")	743	->send_arg ("str3")
578	->run ("Some::function", sub {	744	->run ("Some::function", sub {
579	my ($fh) = @_;	745	my ($fh) = @_;
580		746
581	# fh is nonblocking, but we trust that the OS can accept these	747	# fh is nonblocking, but we trust that the OS can accept these
582	# extra 3 octets anyway.	748	# few octets anyway.
583	syswrite $fh, "hi #$_\n";	749	syswrite $fh, "hi #$_\n";
584		750
585	# $fh is being closed here, as we don't store it anywhere	751	# $fh is being closed here, as we don't store it anywhere
586	});	752	});
587	}	753	}
…		…
589	# Some::function might look like this - all parameters passed before fork	755	# Some::function might look like this - all parameters passed before fork
590	# and after will be passed, in order, after the communications socket.	756	# and after will be passed, in order, after the communications socket.
591	sub Some::function {	757	sub Some::function {
592	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	758	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
593		759
594	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	760	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
595	}	761	}
596		762
597	=cut	763	=cut
598		764
599	sub run {	765	sub run {
600	my ($self, $func, $cb) = @_;	766	my ($self, $func, $cb) = @_;
601		767
602	$self->[0] = $cb;	768	$self->[CB] = $cb;
603	$self->_cmd (r => $func);	769	$self->_cmd (r => $func);
604	}	770	}
		771
		772	=back
		773
		774	=head1 PERFORMANCE
		775
		776	Now for some unscientific benchmark numbers (all done on an amd64
		777	GNU/Linux box). These are intended to give you an idea of the relative
		778	performance you can expect, they are not meant to be absolute performance
		779	numbers.
		780
		781	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		782	exit in the child and waits for the socket to close in the parent. I did
		783	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		784
		785	2079 new processes per second, using manual socketpair + fork
		786
		787	Then I did the same thing, but instead of calling fork, I called
		788	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		789	socket form the child to close on exit. This does the same thing as manual
		790	socket pair + fork, except that what is forked is the template process
		791	(2440kB), and the socket needs to be passed to the server at the other end
		792	of the socket first.
		793
		794	2307 new processes per second, using AnyEvent::Fork->new
		795
		796	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		797	a new perl interpreter and compile the small server each time, I get:
		798
		799	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		800
		801	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		802	though it uses the same operations, but adds a lot of overhead?
		803
		804	The difference is simply the process size: forking the 5MB process takes
		805	so much longer than forking the 2.5MB template process that the extra
		806	overhead is canceled out.
		807
		808	If the benchmark process grows, the normal fork becomes even slower:
		809
		810	1340 new processes, manual fork of a 20MB process
		811	731 new processes, manual fork of a 200MB process
		812	235 new processes, manual fork of a 2000MB process
		813
		814	What that means (to me) is that I can use this module without having a bad
		815	conscience because of the extra overhead required to start new processes.
		816
		817	=head1 TYPICAL PROBLEMS
		818
		819	This section lists typical problems that remain. I hope by recognising
		820	them, most can be avoided.
		821
		822	=over 4
		823
		824	=item leaked file descriptors for exec'ed processes
		825
		826	POSIX systems inherit file descriptors by default when exec'ing a new
		827	process. While perl itself laudably sets the close-on-exec flags on new
		828	file handles, most C libraries don't care, and even if all cared, it's
		829	often not possible to set the flag in a race-free manner.
		830
		831	That means some file descriptors can leak through. And since it isn't
		832	possible to know which file descriptors are "good" and "necessary" (or
		833	even to know which file descriptors are open), there is no good way to
		834	close the ones that might harm.
		835
		836	As an example of what "harm" can be done consider a web server that
		837	accepts connections and afterwards some module uses AnyEvent::Fork for the
		838	first time, causing it to fork and exec a new process, which might inherit
		839	the network socket. When the server closes the socket, it is still open
		840	in the child (which doesn't even know that) and the client might conclude
		841	that the connection is still fine.
		842
		843	For the main program, there are multiple remedies available -
		844	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		845	C<new_exec> is another, as in both cases, the first process can be exec'ed
		846	well before many random file descriptors are open.
		847
		848	In general, the solution for these kind of problems is to fix the
		849	libraries or the code that leaks those file descriptors.
		850
		851	Fortunately, most of these leaked descriptors do no harm, other than
		852	sitting on some resources.
		853
		854	=item leaked file descriptors for fork'ed processes
		855
		856	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		857	which closes file descriptors not marked for being inherited.
		858
		859	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		860	a way to create these processes by forking, and this leaks more file
		861	descriptors than exec'ing them, as there is no way to mark descriptors as
		862	"close on fork".
		863
		864	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		865	pipes for internal uses, and L<Gtk2> might open a connection to the X
		866	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		867	trouble with a fork.
		868
		869	The solution is to either not load these modules before use'ing
		870	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		871	initialising them, for example, by calling C<init Gtk2> manually.
		872
		873	=item exiting calls object destructors
		874
		875	This only applies to users of L<AnyEvent::Fork:Early> and
		876	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		877	that reference external resources.
		878
		879	When a process created by AnyEvent::Fork exits, it might do so by calling
		880	exit, or simply letting perl reach the end of the program. At which point
		881	Perl runs all destructors.
		882
		883	Not all destructors are fork-safe - for example, an object that represents
		884	the connection to an X display might tell the X server to free resources,
		885	which is inconvenient when the "real" object in the parent still needs to
		886	use them.
		887
		888	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		889	it as the very first thing, right?
		890
		891	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		892	is to not create objects with nontrivial destructors that might have an
		893	effect outside of Perl.
605		894
606	=back	895	=back
607		896
608	=head1 PORTABILITY NOTES	897	=head1 PORTABILITY NOTES
609		898
610	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	899	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	900	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	901	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	902	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	903	useful that you can do with it without running into memory corruption
615	issues or other braindamage. Hrrrr.	904	issues or other braindamage. Hrrrr.
616		905
617	Cygwin perl is not supported at the moment, as it should implement fd	906	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	907	shortcomings of its API - see L<IO::FDPoll> for more details.
619	support enough functionality to do it.
620		908
621	=head1 SEE ALSO	909	=head1 SEE ALSO
622		910
623	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	911	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
624	L<AnyEvent::Fork::Template> (to create a process by forking the main	912	L<AnyEvent::Fork::Template> (to create a process by forking the main
625	program at a convenient time).	913	program at a convenient time), L<AnyEvent::Fork::RPC> (for simple RPC to
		914	child processes).
626		915
627	=head1 AUTHOR	916	=head1 AUTHOR AND CONTACT INFORMATION
628		917
629	Marc Lehmann <schmorp@schmorp.de>	918	Marc Lehmann <schmorp@schmorp.de>
630	http://home.schmorp.de/	919	http://software.schmorp.de/pkg/AnyEvent-Fork
631		920
632	=cut	921	=cut
633		922
634	1	923	1
635		924

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Revision 1.44 by root, Thu Apr 18 10:49:59 2013 UTC