[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 1.47 by root, Thu Apr 18 20:17:34 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.
		259
		260	All these processes are called "child processes" (whether they are direct
		261	children or not), while the process that manages them is called the
		262	"parent process".
153		263
154	Each such process comes with its own file handle that can be used to	264	Each such process comes with its own file handle that can be used to
155	communicate with it (it's actually a socket - one end in the new process,	265	communicate with it (it's actually a socket - one end in the new process,
156	one end in the main process), and among the things you can do in it are	266	one end in the main process), and among the things you can do in it are
157	load modules, fork new processes, send file handles to it, and execute	267	load modules, fork new processes, send file handles to it, and execute
…		…
169	needed the first time. Forking from this process shares the memory used	279	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	280	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.	281	time, and the memory is not shared with anything else.
172		282
173	This is ideal for when you only need one extra process of a kind, with the	283	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.	284	option of starting and stopping it on demand.
175		285
176	Example:	286	Example:
177		287
178	AnyEvent::Fork	288	AnyEvent::Fork
179	->new	289	->new
…		…
194	modules you loaded) is shared between the processes, and each new process	304	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.	305	consumes relatively little memory of its own.
196		306
197	The disadvantage of this approach is that you need to create a template	307	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	308	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	309	only need a fixed number of processes you can create them, and then destroy
200	the template process.	310	the template process.
201		311
202	Example:	312	Example:
203		313
204	my $template = AnyEvent::Fork->new->require ("Some::Module");	314	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
231	my ($fork_fh) = @_;	341	my ($fork_fh) = @_;
232	});	342	});
233		343
234	=back	344	=back
235		345
236	=head1 FUNCTIONS	346	=head1 THE C<AnyEvent::Fork> CLASS
		347
		348	This module exports nothing, and only implements a single class -
		349	C<AnyEvent::Fork>.
		350
		351	There are two class constructors that both create new processes - C<new>
		352	and C<new_exec>. The C<fork> method creates a new process by forking an
		353	existing one and could be considered a third constructor.
		354
		355	Most of the remaining methods deal with preparing the new process, by
		356	loading code, evaluating code and sending data to the new process. They
		357	usually return the process object, so you can chain method calls.
		358
		359	If a process object is destroyed before calling its C<run> method, then
		360	the process simply exits. After C<run> is called, all responsibility is
		361	passed to the specified function.
		362
		363	As long as there is any outstanding work to be done, process objects
		364	resist being destroyed, so there is no reason to store them unless you
		365	need them later - configure and forget works just fine.
237		366
238	=over 4	367	=over 4
239		368
240	=cut	369	=cut
241		370
242	package AnyEvent::Fork;	371	package AnyEvent::Fork;
243		372
244	use common::sense;	373	use common::sense;
245		374
246	use Socket ();	375	use Errno ();
247		376
248	use AnyEvent;	377	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();	378	use AnyEvent::Util ();
251		379
252	our $VERSION = $AnyEvent::Fork::Util::VERSION;	380	use IO::FDPass;
253		381
254	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	382	our $VERSION = 0.7;
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		383
266	# the early fork template process	384	# the early fork template process
267	our $EARLY;	385	our $EARLY;
268		386
269	# the empty template process	387	# the empty template process
270	our $TEMPLATE;	388	our $TEMPLATE;
271		389
		390	sub QUEUE() { 0 }
		391	sub FH() { 1 }
		392	sub WW() { 2 }
		393	sub PID() { 3 }
		394	sub CB() { 4 }
		395
		396	sub _new {
		397	my ($self, $fh, $pid) = @_;
		398
		399	AnyEvent::Util::fh_nonblocking $fh, 1;
		400
		401	$self = bless [
		402	[], # write queue - strings or fd's
		403	$fh,
		404	undef, # AE watcher
		405	$pid,
		406	], $self;
		407
		408	$self
		409	}
		410
272	sub _cmd {	411	sub _cmd {
273	my $self = shift;	412	my $self = shift;
274		413
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	414	# 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.	415	# 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)*", @_;	416	# it.
		417	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
280		418
281	$self->[3] \|\|= AE::io $self->[1], 1, sub {	419	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		420	do {
282	# send the next "thing" in the queue - either a reference to an fh,	421	# send the next "thing" in the queue - either a reference to an fh,
283	# or a plain string.	422	# or a plain string.
284		423
285	if (ref $self->[2][0]) {	424	if (ref $self->[QUEUE][0]) {
286	# send fh	425	# send fh
287	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	426	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
		427	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		428	undef $self->[WW];
		429	die "AnyEvent::Fork: file descriptor send failure: $!";
		430	}
		431
288	and shift @{ $self->[2] };	432	shift @{ $self->[QUEUE] };
289		433
290	} else {	434	} else {
291	# send string	435	# send string
292	my $len = syswrite $self->[1], $self->[2][0]	436	my $len = syswrite $self->[FH], $self->[QUEUE][0];
		437
		438	unless ($len) {
		439	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		440	undef $self->[3];
293	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	441	die "AnyEvent::Fork: command write failure: $!";
		442	}
294		443
295	substr $self->[2][0], 0, $len, "";	444	substr $self->[QUEUE][0], 0, $len, "";
296	shift @{ $self->[2] } unless length $self->[2][0];	445	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
297	}	446	}
		447	} while @{ $self->[QUEUE] };
298		448
299	unless (@{ $self->[2] }) {	449	# everything written
300	undef $self->[3];	450	undef $self->[WW];
		451
301	# invoke run callback	452	# invoke run callback, if any
302	$self->[0]->($self->[1]) if $self->[0];	453	$self->[CB]->($self->[FH]) if $self->[CB];
303	}
304	};	454	};
305	}
306		455
307	sub _new {	456	() # make sure we don't leak the watcher
308	my ($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	$self
320	}	457	}
321		458
322	# fork template from current process, used by AnyEvent::Fork::Early/Template	459	# fork template from current process, used by AnyEvent::Fork::Early/Template
323	sub _new_fork {	460	sub _new_fork {
324	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	461	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
330	require AnyEvent::Fork::Serve;	467	require AnyEvent::Fork::Serve;
331	$AnyEvent::Fork::Serve::OWNER = $parent;	468	$AnyEvent::Fork::Serve::OWNER = $parent;
332	close $fh;	469	close $fh;
333	$0 = "$_[1] of $parent";	470	$0 = "$_[1] of $parent";
334	AnyEvent::Fork::Serve::serve ($slave);	471	AnyEvent::Fork::Serve::serve ($slave);
335	AnyEvent::Fork::Util::_exit 0;	472	exit 0;
336	} elsif (!$pid) {	473	} elsif (!$pid) {
337	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	474	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
338	}	475	}
339		476
340	AnyEvent::Fork->_new ($fh)	477	AnyEvent::Fork->_new ($fh, $pid)
341	}	478	}
342		479
343	=item my $proc = new AnyEvent::Fork	480	=item my $proc = new AnyEvent::Fork
344		481
345	Create a new "empty" perl interpreter process and returns its process	482	Create a new "empty" perl interpreter process and returns its process
346	object for further manipulation.	483	object for further manipulation.
347		484
348	The new process is forked from a template process that is kept around	485	The new process is forked from a template process that is kept around
349	for this purpose. When it doesn't exist yet, it is created by a call to	486	for this purpose. When it doesn't exist yet, it is created by a call to
350	C<new_exec> and kept around for future calls.	487	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		488
357	=cut	489	=cut
358		490
359	sub new {	491	sub new {
360	my $class = shift;	492	my $class = shift;
…		…
396	reduces the amount of memory sharing that is possible, and is also slower.	528	reduces the amount of memory sharing that is possible, and is also slower.
397		529
398	You should use C<new> whenever possible, except when having a template	530	You should use C<new> whenever possible, except when having a template
399	process around is unacceptable.	531	process around is unacceptable.
400		532
401	The path to the perl interpreter is divined usign various methods - first	533	The path to the perl interpreter is divined using various methods - first
402	C<$^X> is investigated to see if the path ends with something that sounds	534	C<$^X> is investigated to see if the path ends with something that sounds
403	as if it were the perl interpreter. Failing this, the module falls back to	535	as if it were the perl interpreter. Failing this, the module falls back to
404	using C<$Config::Config{perlpath}>.	536	using C<$Config::Config{perlpath}>.
405		537
406	=cut	538	=cut
…		…
415	my $perl = $;	547	my $perl = $;
416		548
417	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	549	# 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	550	# that looks like perl. this obviously only works for posix and win32
419	unless (	551	unless (
420	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	552	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
421	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	553	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
422	) {	554	) {
423	# if it doesn't look perlish enough, try Config	555	# if it doesn't look perlish enough, try Config
424	require Config;	556	require Config;
425	$perl = $Config::Config{perlpath};	557	$perl = $Config::Config{perlpath};
…		…
436	Proc::FastSpawn::fd_inherit (fileno $fh, 0);	568	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
437		569
438	# quick. also doesn't work in win32. of course. what did you expect	570	# quick. also doesn't work in win32. of course. what did you expect
439	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	571	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
440	my %env = %ENV;	572	my %env = %ENV;
441	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;	573	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
442		574
443	Proc::FastSpawn::spawn (	575	my $pid = Proc::FastSpawn::spawn (
444	$perl,	576	$perl,
445	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	577	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
446	[map "$_=$env{$_}", keys %env],	578	[map "$_=$env{$_}", keys %env],
447	) or die "unable to spawn AnyEvent::Fork server: $!";	579	) or die "unable to spawn AnyEvent::Fork server: $!";
448		580
449	$self->_new ($fh)	581	$self->_new ($fh, $pid)
		582	}
		583
		584	=item $pid = $proc->pid
		585
		586	Returns the process id of the process I<iff it is a direct child of the
		587	process running AnyEvent::Fork>, and C<undef> otherwise.
		588
		589	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		590	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		591	to clean up their zombies when they die.
		592
		593	All other processes are not direct children, and will be cleaned up by
		594	AnyEvent::Fork itself.
		595
		596	=cut
		597
		598	sub pid {
		599	$_[0][PID]
450	}	600	}
451		601
452	=item $proc = $proc->eval ($perlcode, @args)	602	=item $proc = $proc->eval ($perlcode, @args)
453		603
454	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	604	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
455	the strings specified by C<@args>.	605	the strings specified by C<@args>, in the "main" package.
456		606
457	This call is meant to do any custom initialisation that might be required	607	This call is meant to do any custom initialisation that might be required
458	(for example, the C<require> method uses it). It's not supposed to be used	608	(for example, the C<require> method uses it). It's not supposed to be used
459	to completely take over the process, use C<run> for that.	609	to completely take over the process, use C<run> for that.
460		610
461	The code will usually be executed after this call returns, and there is no	611	The code will usually be executed after this call returns, and there is no
462	way to pass anything back to the calling process. Any evaluation errors	612	way to pass anything back to the calling process. Any evaluation errors
463	will be reported to stderr and cause the process to exit.	613	will be reported to stderr and cause the process to exit.
464		614
		615	If you want to execute some code (that isn't in a module) to take over the
		616	process, you should compile a function via C<eval> first, and then call
		617	it via C<run>. This also gives you access to any arguments passed via the
		618	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		619	a faster fork+exec> example to see it in action.
		620
465	Returns the process object for easy chaining of method calls.	621	Returns the process object for easy chaining of method calls.
466		622
467	=cut	623	=cut
468		624
469	sub eval {	625	sub eval {
470	my ($self, $code, @args) = @_;	626	my ($self, $code, @args) = @_;
471		627
472	$self->_cmd (e => $code, @args);	628	$self->_cmd (e => pack "(w/a)", $code, @args);
473		629
474	$self	630	$self
475	}	631	}
476		632
477	=item $proc = $proc->require ($module, ...)	633	=item $proc = $proc->require ($module, ...)
…		…
494	=item $proc = $proc->send_fh ($handle, ...)	650	=item $proc = $proc->send_fh ($handle, ...)
495		651
496	Send one or more file handles (I<not> file descriptors) to the process,	652	Send one or more file handles (I<not> file descriptors) to the process,
497	to prepare a call to C<run>.	653	to prepare a call to C<run>.
498		654
499	The process object keeps a reference to the handles until this is done,	655	The process object keeps a reference to the handles until they have
500	so you must not explicitly close the handles. This is most easily	656	been passed over to the process, so you must not explicitly close the
501	accomplished by simply not storing the file handles anywhere after passing	657	handles. This is most easily accomplished by simply not storing the file
502	them to this method.	658	handles anywhere after passing them to this method - when AnyEvent::Fork
		659	is finished using them, perl will automatically close them.
503		660
504	Returns the process object for easy chaining of method calls.	661	Returns the process object for easy chaining of method calls.
505		662
506	Example: pass an fh to a process, and release it without closing. it will	663	Example: pass a file handle to a process, and release it without
507	be closed automatically when it is no longer used.	664	closing. It will be closed automatically when it is no longer used.
508		665
509	$proc->send_fh ($my_fh);	666	$proc->send_fh ($my_fh);
510	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	667	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
511		668
512	=cut	669	=cut
…		…
514	sub send_fh {	671	sub send_fh {
515	my ($self, @fh) = @_;	672	my ($self, @fh) = @_;
516		673
517	for my $fh (@fh) {	674	for my $fh (@fh) {
518	$self->_cmd ("h");	675	$self->_cmd ("h");
519	push @{ $self->[2] }, \$fh;	676	push @{ $self->[QUEUE] }, \$fh;
520	}	677	}
521		678
522	$self	679	$self
523	}	680	}
524		681
525	=item $proc = $proc->send_arg ($string, ...)	682	=item $proc = $proc->send_arg ($string, ...)
526		683
527	Send one or more argument strings to the process, to prepare a call to	684	Send one or more argument strings to the process, to prepare a call to
528	C<run>. The strings can be any octet string.	685	C<run>. The strings can be any octet strings.
529		686
		687	The protocol is optimised to pass a moderate number of relatively short
		688	strings - while you can pass up to 4GB of data in one go, this is more
		689	meant to pass some ID information or other startup info, not big chunks of
		690	data.
		691
530	Returns the process object for easy chaining of emthod calls.	692	Returns the process object for easy chaining of method calls.
531		693
532	=cut	694	=cut
533		695
534	sub send_arg {	696	sub send_arg {
535	my ($self, @arg) = @_;	697	my ($self, @arg) = @_;
536		698
537	$self->_cmd (a => @arg);	699	$self->_cmd (a => pack "(w/a)", @arg);
538		700
539	$self	701	$self
540	}	702	}
541		703
542	=item $proc->run ($func, $cb->($fh))	704	=item $proc->run ($func, $cb->($fh))
543		705
544	Enter the function specified by the fully qualified name in C<$func> in	706	Enter the function specified by the function name in C<$func> in the
545	the process. The function is called with the communication socket as first	707	process. The function is called with the communication socket as first
546	argument, followed by all file handles and string arguments sent earlier	708	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.	709	via C<send_fh> and C<send_arg> methods, in the order they were called.
548		710
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.	711	The process object becomes unusable on return from this function - any
		712	further method calls result in undefined behaviour.
		713
		714	The function name should be fully qualified, but if it isn't, it will be
		715	looked up in the C<main> package.
		716
		717	If the called function returns, doesn't exist, or any error occurs, the
		718	process exits.
		719
		720	Preparing the process is done in the background - when all commands have
		721	been sent, the callback is invoked with the local communications socket
		722	as argument. At this point you can start using the socket in any way you
		723	like.
555		724
556	If the communication socket isn't used, it should be closed on both sides,	725	If the communication socket isn't used, it should be closed on both sides,
557	to save on kernel memory.	726	to save on kernel memory.
558		727
559	The socket is non-blocking in the parent, and blocking in the newly	728	The socket is non-blocking in the parent, and blocking in the newly
560	created process. The close-on-exec flag is set on both. Even if not used	729	created process. The close-on-exec flag is set in both.
		730
561	otherwise, the socket can be a good indicator for the existance of the	731	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,	732	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	733	event on it, because exiting the process closes the socket (if it didn't
564	children using fork).	734	create any children using fork).
565		735
566	Example: create a template for a process pool, pass a few strings, some	736	Example: create a template for a process pool, pass a few strings, some
567	file handles, then fork, pass one more string, and run some code.	737	file handles, then fork, pass one more string, and run some code.
568		738
569	my $pool = AnyEvent::Fork	739	my $pool = AnyEvent::Fork
…		…
577	->send_arg ("str3")	747	->send_arg ("str3")
578	->run ("Some::function", sub {	748	->run ("Some::function", sub {
579	my ($fh) = @_;	749	my ($fh) = @_;
580		750
581	# fh is nonblocking, but we trust that the OS can accept these	751	# fh is nonblocking, but we trust that the OS can accept these
582	# extra 3 octets anyway.	752	# few octets anyway.
583	syswrite $fh, "hi #$_\n";	753	syswrite $fh, "hi #$_\n";
584		754
585	# $fh is being closed here, as we don't store it anywhere	755	# $fh is being closed here, as we don't store it anywhere
586	});	756	});
587	}	757	}
…		…
589	# Some::function might look like this - all parameters passed before fork	759	# Some::function might look like this - all parameters passed before fork
590	# and after will be passed, in order, after the communications socket.	760	# and after will be passed, in order, after the communications socket.
591	sub Some::function {	761	sub Some::function {
592	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	762	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
593		763
594	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	764	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
595	}	765	}
596		766
597	=cut	767	=cut
598		768
599	sub run {	769	sub run {
600	my ($self, $func, $cb) = @_;	770	my ($self, $func, $cb) = @_;
601		771
602	$self->[0] = $cb;	772	$self->[CB] = $cb;
603	$self->_cmd (r => $func);	773	$self->_cmd (r => $func);
604	}	774	}
		775
		776	=back
		777
		778	=head1 PERFORMANCE
		779
		780	Now for some unscientific benchmark numbers (all done on an amd64
		781	GNU/Linux box). These are intended to give you an idea of the relative
		782	performance you can expect, they are not meant to be absolute performance
		783	numbers.
		784
		785	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		786	exit in the child and waits for the socket to close in the parent. I did
		787	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		788
		789	2079 new processes per second, using manual socketpair + fork
		790
		791	Then I did the same thing, but instead of calling fork, I called
		792	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		793	socket form the child to close on exit. This does the same thing as manual
		794	socket pair + fork, except that what is forked is the template process
		795	(2440kB), and the socket needs to be passed to the server at the other end
		796	of the socket first.
		797
		798	2307 new processes per second, using AnyEvent::Fork->new
		799
		800	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		801	a new perl interpreter and compile the small server each time, I get:
		802
		803	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		804
		805	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		806	though it uses the same operations, but adds a lot of overhead?
		807
		808	The difference is simply the process size: forking the 5MB process takes
		809	so much longer than forking the 2.5MB template process that the extra
		810	overhead is canceled out.
		811
		812	If the benchmark process grows, the normal fork becomes even slower:
		813
		814	1340 new processes, manual fork of a 20MB process
		815	731 new processes, manual fork of a 200MB process
		816	235 new processes, manual fork of a 2000MB process
		817
		818	What that means (to me) is that I can use this module without having a bad
		819	conscience because of the extra overhead required to start new processes.
		820
		821	=head1 TYPICAL PROBLEMS
		822
		823	This section lists typical problems that remain. I hope by recognising
		824	them, most can be avoided.
		825
		826	=over 4
		827
		828	=item leaked file descriptors for exec'ed processes
		829
		830	POSIX systems inherit file descriptors by default when exec'ing a new
		831	process. While perl itself laudably sets the close-on-exec flags on new
		832	file handles, most C libraries don't care, and even if all cared, it's
		833	often not possible to set the flag in a race-free manner.
		834
		835	That means some file descriptors can leak through. And since it isn't
		836	possible to know which file descriptors are "good" and "necessary" (or
		837	even to know which file descriptors are open), there is no good way to
		838	close the ones that might harm.
		839
		840	As an example of what "harm" can be done consider a web server that
		841	accepts connections and afterwards some module uses AnyEvent::Fork for the
		842	first time, causing it to fork and exec a new process, which might inherit
		843	the network socket. When the server closes the socket, it is still open
		844	in the child (which doesn't even know that) and the client might conclude
		845	that the connection is still fine.
		846
		847	For the main program, there are multiple remedies available -
		848	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		849	C<new_exec> is another, as in both cases, the first process can be exec'ed
		850	well before many random file descriptors are open.
		851
		852	In general, the solution for these kind of problems is to fix the
		853	libraries or the code that leaks those file descriptors.
		854
		855	Fortunately, most of these leaked descriptors do no harm, other than
		856	sitting on some resources.
		857
		858	=item leaked file descriptors for fork'ed processes
		859
		860	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		861	which closes file descriptors not marked for being inherited.
		862
		863	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		864	a way to create these processes by forking, and this leaks more file
		865	descriptors than exec'ing them, as there is no way to mark descriptors as
		866	"close on fork".
		867
		868	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		869	pipes for internal uses, and L<Gtk2> might open a connection to the X
		870	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		871	trouble with a fork.
		872
		873	The solution is to either not load these modules before use'ing
		874	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		875	initialising them, for example, by calling C<init Gtk2> manually.
		876
		877	=item exiting calls object destructors
		878
		879	This only applies to users of L<AnyEvent::Fork:Early> and
		880	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		881	that reference external resources.
		882
		883	When a process created by AnyEvent::Fork exits, it might do so by calling
		884	exit, or simply letting perl reach the end of the program. At which point
		885	Perl runs all destructors.
		886
		887	Not all destructors are fork-safe - for example, an object that represents
		888	the connection to an X display might tell the X server to free resources,
		889	which is inconvenient when the "real" object in the parent still needs to
		890	use them.
		891
		892	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		893	it as the very first thing, right?
		894
		895	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		896	is to not create objects with nontrivial destructors that might have an
		897	effect outside of Perl.
605		898
606	=back	899	=back
607		900
608	=head1 PORTABILITY NOTES	901	=head1 PORTABILITY NOTES
609		902
610	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	903	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	904	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	905	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	906	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	907	useful that you can do with it without running into memory corruption
615	issues or other braindamage. Hrrrr.	908	issues or other braindamage. Hrrrr.
616		909
617	Cygwin perl is not supported at the moment, as it should implement fd	910	Cygwin perl is not supported at the moment due to some hilarious
618	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	911	shortcomings of its API - see L<IO::FDPoll> for more details.
619	support enough functionality to do it.
620		912
621	=head1 SEE ALSO	913	=head1 SEE ALSO
622		914
623	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	915	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		916	(part of this distribution).
		917
624	L<AnyEvent::Fork::Template> (to create a process by forking the main	918	L<AnyEvent::Fork::Template>, to create a process by forking the main
625	program at a convenient time).	919	program at a convenient time (part of this distribution).
626		920
627	=head1 AUTHOR	921	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		922
		923	=head1 AUTHOR AND CONTACT INFORMATION
628		924
629	Marc Lehmann <schmorp@schmorp.de>	925	Marc Lehmann <schmorp@schmorp.de>
630	http://home.schmorp.de/	926	http://software.schmorp.de/pkg/AnyEvent-Fork
631		927
632	=cut	928	=cut
633		929
634	1	930	1
635		931

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Revision 1.47 by root, Thu Apr 18 20:17:34 2013 UTC