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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.5 by root, Wed Apr 3 08:29:21 2013 UTC vs.
Revision 1.31 by root, Sat Apr 6 09:29:26 2013 UTC

…		…
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	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
		8
		9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
8		15
9	=head1 DESCRIPTION	16	=head1 DESCRIPTION
10		17
11	This module allows you to create new processes, without actually forking	18	This module allows you to create new processes, without actually forking
12	them from your current process (avoiding the problems of forking), but	19	them from your current process (avoiding the problems of forking), but
13	preserving most of the advantages of fork.	20	preserving most of the advantages of fork.
14		21
15	It can be used to create new worker processes or new independent	22	It can be used to create new worker processes or new independent
16	subprocesses for short- and long-running jobs, process pools (e.g. for use	23	subprocesses for short- and long-running jobs, process pools (e.g. for use
17	in pre-forked servers) but also to spawn new external processes (such as	24	in pre-forked servers) but also to spawn new external processes (such as
18	CGI scripts from a webserver), which can be faster (and more well behaved)	25	CGI scripts from a web server), which can be faster (and more well behaved)
19	than using fork+exec in big processes.	26	than using fork+exec in big processes.
20		27
21	Special care has been taken to make this module useful from other modules,	28	Special care has been taken to make this module useful from other modules,
22	while still supporting specialised environments such as L<App::Staticperl>	29	while still supporting specialised environments such as L<App::Staticperl>
23	or L<PAR::Packer>.	30	or L<PAR::Packer>.
24		31
		32	=head1 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
25	=head1 PROBLEM STATEMENT	45	=head1 PROBLEM STATEMENT
26		46
27	There are two ways to implement parallel processing on UNIX like operating	47	There are two traditional ways to implement parallel processing on UNIX
28	systems - fork and process, and fork+exec and process. They have different	48	like operating systems - fork and process, and fork+exec and process. They
29	advantages and disadvantages that I describe below, together with how this	49	have different advantages and disadvantages that I describe below,
30	module tries to mitigate the disadvantages.	50	together with how this module tries to mitigate the disadvantages.
31		51
32	=over 4	52	=over 4
33		53
34	=item Forking from a big process can be very slow (a 5GB process needs	54	=item Forking from a big process can be very slow.
35	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead	55
		56	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
36	is often shared with exec (because you have to fork first), but in some	57	overhead is often shared with exec (because you have to fork first), but
37	circumstances (e.g. when vfork is used), fork+exec can be much faster.	58	in some circumstances (e.g. when vfork is used), fork+exec can be much
		59	faster.
38		60
39	This module can help here by telling a small(er) helper process to fork,	61	This module can help here by telling a small(er) helper process to fork,
40	or fork+exec instead.	62	which is faster then forking the main process, and also uses vfork where
		63	possible. This gives the speed of vfork, with the flexibility of fork.
41		64
42	=item Forking usually creates a copy-on-write copy of the parent	65	=item Forking usually creates a copy-on-write copy of the parent
43	process. Memory (for example, modules or data files that have been	66	process.
44	will not take additional memory). When exec'ing a new process, modules	67
45	and data files might need to be loaded again, at extra cpu and memory	68	For example, modules or data files that are loaded will not use additional
46	cost. Likewise when forking, all data structures are copied as well - if	69	memory after a fork. When exec'ing a new process, modules and data files
		70	might need to be loaded again, at extra CPU and memory cost. But when
		71	forking, literally all data structures are copied - if the program frees
47	the program frees them and replaces them by new data, the child processes	72	them and replaces them by new data, the child processes will retain the
48	will retain the memory even if it isn't used.	73	old version even if it isn't used, which can suddenly and unexpectedly
		74	increase memory usage when freeing memory.
		75
		76	The trade-off is between more sharing with fork (which can be good or
		77	bad), and no sharing with exec.
49		78
50	This module allows the main program to do a controlled fork, and allows	79	This module allows the main program to do a controlled fork, and allows
51	modules to exec processes safely at any time. When creating a custom	80	modules to exec processes safely at any time. When creating a custom
52	process pool you can take advantage of data sharing via fork without	81	process pool you can take advantage of data sharing via fork without
53	risking to share large dynamic data structures that will blow up child	82	risking to share large dynamic data structures that will blow up child
54	memory usage.	83	memory usage.
55		84
		85	In other words, this module puts you into control over what is being
		86	shared and what isn't, at all times.
		87
56	=item Exec'ing a new perl process might be difficult and slow. For	88	=item Exec'ing a new perl process might be difficult.
		89
57	example, it is not easy to find the correct path to the perl interpreter,	90	For example, it is not easy to find the correct path to the perl
58	and all modules have to be loaded from disk again. Long running processes	91	interpreter - C<$^X> might not be a perl interpreter at all.
59	might run into problems when perl is upgraded for example.
60		92
61	This module supports creating pre-initialised perl processes to be used
62	as template, and also tries hard to identify the correct path to the perl	93	This module tries hard to identify the correct path to the perl
63	interpreter. With a cooperative main program, exec'ing the interpreter	94	interpreter. With a cooperative main program, exec'ing the interpreter
64	might not even be necessary.	95	might not even be necessary, but even without help from the main program,
		96	it will still work when used from a module.
65		97
		98	=item Exec'ing a new perl process might be slow, as all necessary modules
		99	have to be loaded from disk again, with no guarantees of success.
		100
		101	Long running processes might run into problems when perl is upgraded
		102	and modules are no longer loadable because they refer to a different
		103	perl version, or parts of a distribution are newer than the ones already
		104	loaded.
		105
		106	This module supports creating pre-initialised perl processes to be used as
		107	a template for new processes.
		108
66	=item Forking might be impossible when a program is running. For example,	109	=item Forking might be impossible when a program is running.
67	POSIX makes it almost impossible to fork from a multithreaded program and
68	do anything useful in the child - strictly speaking, if your perl program
69	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
70	you cannot call fork on the perl level anymore, at all.
71		110
		111	For example, POSIX makes it almost impossible to fork from a
		112	multi-threaded program while doing anything useful in the child - in
		113	fact, if your perl program uses POSIX threads (even indirectly via
		114	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		115	anymore without risking corruption issues on a number of operating
		116	systems.
		117
72	This module can safely fork helper processes at any time, by caling	118	This module can safely fork helper processes at any time, by calling
73	fork+exec in C, in a POSIX-compatible way.	119	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
74		120
75	=item Parallel processing with fork might be inconvenient or difficult	121	=item Parallel processing with fork might be inconvenient or difficult
		122	to implement. Modules might not work in both parent and child.
		123
76	to implement. For example, when a program uses an event loop and creates	124	For example, when a program uses an event loop and creates watchers it
77	watchers it becomes very hard to use the event loop from a child	125	becomes very hard to use the event loop from a child program, as the
78	program, as the watchers already exist but are only meaningful in the	126	watchers already exist but are only meaningful in the parent. Worse, a
79	parent. Worse, a module might want to use such a system, not knowing	127	module might want to use such a module, not knowing whether another module
80	whether another module or the main program also does, leading to problems.	128	or the main program also does, leading to problems.
81		129
82	This module only lets the main program create pools by forking (because	130	Apart from event loops, graphical toolkits also commonly fall into the
83	only the main program can know when it is still safe to do so) - all other	131	"unsafe module" category, or just about anything that communicates with
84	pools are created by fork+exec, after which such modules can again be	132	the external world, such as network libraries and file I/O modules, which
85	loaded.	133	usually don't like being copied and then allowed to continue in two
		134	processes.
		135
		136	With this module only the main program is allowed to create new processes
		137	by forking (because only the main program can know when it is still safe
		138	to do so) - all other processes are created via fork+exec, which makes it
		139	possible to use modules such as event loops or window interfaces safely.
86		140
87	=back	141	=back
		142
		143	=head1 EXAMPLES
		144
		145	=head2 Create a single new process, tell it to run your worker function.
		146
		147	AnyEvent::Fork
		148	->new
		149	->require ("MyModule")
		150	->run ("MyModule::worker, sub {
		151	my ($master_filehandle) = @_;
		152
		153	# now $master_filehandle is connected to the
		154	# $slave_filehandle in the new process.
		155	});
		156
		157	MyModule might look like this:
		158
		159	package MyModule;
		160
		161	sub worker {
		162	my ($slave_filehandle) = @_;
		163
		164	# now $slave_filehandle is connected to the $master_filehandle
		165	# in the original prorcess. have fun!
		166	}
		167
		168	=head2 Create a pool of server processes all accepting on the same socket.
		169
		170	# create listener socket
		171	my $listener = ...;
		172
		173	# create a pool template, initialise it and give it the socket
		174	my $pool = AnyEvent::Fork
		175	->new
		176	->require ("Some::Stuff", "My::Server")
		177	->send_fh ($listener);
		178
		179	# now create 10 identical workers
		180	for my $id (1..10) {
		181	$pool
		182	->fork
		183	->send_arg ($id)
		184	->run ("My::Server::run");
		185	}
		186
		187	# now do other things - maybe use the filehandle provided by run
		188	# to wait for the processes to die. or whatever.
		189
		190	My::Server might look like this:
		191
		192	package My::Server;
		193
		194	sub run {
		195	my ($slave, $listener, $id) = @_;
		196
		197	close $slave; # we do not use the socket, so close it to save resources
		198
		199	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		200	# or anything we usually couldn't do in a process forked normally.
		201	while (my $socket = $listener->accept) {
		202	# do sth. with new socket
		203	}
		204	}
		205
		206	=head2 use AnyEvent::Fork as a faster fork+exec
		207
		208	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to
		209	the communications socket. It is usually faster than fork+exec, but still
		210	let's you prepare the environment.
		211
		212	open my $output, ">/tmp/log" or die "$!";
		213
		214	AnyEvent::Fork
		215	->new
		216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
		219
		220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
		223
		224	exec @cmd;
		225	}
		226	')
		227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
		230
		231	my $stderr = $cv->recv;
88		232
89	=head1 CONCEPTS	233	=head1 CONCEPTS
90		234
91	This module can create new processes either by executing a new perl	235	This module can create new processes either by executing a new perl
92	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
109	needed the first time. Forking from this process shares the memory used	253	needed the first time. Forking from this process shares the memory used
110	for the perl interpreter with the new process, but loading modules takes	254	for the perl interpreter with the new process, but loading modules takes
111	time, and the memory is not shared with anything else.	255	time, and the memory is not shared with anything else.
112		256
113	This is ideal for when you only need one extra process of a kind, with the	257	This is ideal for when you only need one extra process of a kind, with the
114	option of starting and stipping it on demand.	258	option of starting and stopping it on demand.
		259
		260	Example:
		261
		262	AnyEvent::Fork
		263	->new
		264	->require ("Some::Module")
		265	->run ("Some::Module::run", sub {
		266	my ($fork_fh) = @_;
		267	});
115		268
116	=item fork a new template process, load code, then fork processes off of	269	=item fork a new template process, load code, then fork processes off of
117	it and run the code	270	it and run the code
118		271
119	When you need to have a bunch of processes that all execute the same (or	272	When you need to have a bunch of processes that all execute the same (or
…		…
125	modules you loaded) is shared between the processes, and each new process	278	modules you loaded) is shared between the processes, and each new process
126	consumes relatively little memory of its own.	279	consumes relatively little memory of its own.
127		280
128	The disadvantage of this approach is that you need to create a template	281	The disadvantage of this approach is that you need to create a template
129	process for the sole purpose of forking new processes from it, but if you	282	process for the sole purpose of forking new processes from it, but if you
130	only need a fixed number of proceses you can create them, and then destroy	283	only need a fixed number of processes you can create them, and then destroy
131	the template process.	284	the template process.
		285
		286	Example:
		287
		288	my $template = AnyEvent::Fork->new->require ("Some::Module");
		289
		290	for (1..10) {
		291	$template->fork->run ("Some::Module::run", sub {
		292	my ($fork_fh) = @_;
		293	});
		294	}
		295
		296	# at this point, you can keep $template around to fork new processes
		297	# later, or you can destroy it, which causes it to vanish.
132		298
133	=item execute a new perl interpreter, load some code, run it	299	=item execute a new perl interpreter, load some code, run it
134		300
135	This is relatively slow, and doesn't allow you to share memory between	301	This is relatively slow, and doesn't allow you to share memory between
136	multiple processes.	302	multiple processes.
…		…
138	The only advantage is that you don't have to have a template process	304	The only advantage is that you don't have to have a template process
139	hanging around all the time to fork off some new processes, which might be	305	hanging around all the time to fork off some new processes, which might be
140	an advantage when there are long time spans where no extra processes are	306	an advantage when there are long time spans where no extra processes are
141	needed.	307	needed.
142		308
		309	Example:
		310
		311	AnyEvent::Fork
		312	->new_exec
		313	->require ("Some::Module")
		314	->run ("Some::Module::run", sub {
		315	my ($fork_fh) = @_;
		316	});
		317
143	=back	318	=back
144		319
145	=head1 FUNCTIONS	320	=head1 THE C<AnyEvent::Fork> CLASS
		321
		322	This module exports nothing, and only implements a single class -
		323	C<AnyEvent::Fork>.
		324
		325	There are two class constructors that both create new processes - C<new>
		326	and C<new_exec>. The C<fork> method creates a new process by forking an
		327	existing one and could be considered a third constructor.
		328
		329	Most of the remaining methods deal with preparing the new process, by
		330	loading code, evaluating code and sending data to the new process. They
		331	usually return the process object, so you can chain method calls.
		332
		333	If a process object is destroyed before calling its C<run> method, then
		334	the process simply exits. After C<run> is called, all responsibility is
		335	passed to the specified function.
		336
		337	As long as there is any outstanding work to be done, process objects
		338	resist being destroyed, so there is no reason to store them unless you
		339	need them later - configure and forget works just fine.
146		340
147	=over 4	341	=over 4
148		342
149	=cut	343	=cut
150		344
151	package AnyEvent::Fork;	345	package AnyEvent::Fork;
152		346
153	use common::sense;	347	use common::sense;
154		348
155	use Socket ();	349	use Errno ();
156		350
157	use AnyEvent;	351	use AnyEvent;
158	use AnyEvent::Fork::Util;
159	use AnyEvent::Util ();	352	use AnyEvent::Util ();
160		353
		354	use IO::FDPass;
		355
		356	our $VERSION = 0.5;
		357
161	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	358	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
162
163	=item my $pool = new AnyEvent::Fork key => value...
164
165	Create a new process pool. The following named parameters are supported:
166		359
167	=over 4	360	=over 4
168		361
169	=back	362	=back
170		363
…		…
177	our $TEMPLATE;	370	our $TEMPLATE;
178		371
179	sub _cmd {	372	sub _cmd {
180	my $self = shift;	373	my $self = shift;
181		374
182	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	375	# ideally, we would want to use "a (w/a)*" as format string, but perl
183	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	376	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
184	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	377	# it.
		378	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
185		379
186	$self->[3] \|\|= AE::io $self->[1], 1, sub {	380	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		381	do {
		382	# send the next "thing" in the queue - either a reference to an fh,
		383	# or a plain string.
		384
187	if (ref $self->[2][0]) {	385	if (ref $self->[2][0]) {
		386	# send fh
188	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	387	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		388	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		389	undef $self->[3];
		390	die "AnyEvent::Fork: file descriptor send failure: $!";
		391	}
		392
189	and shift @{ $self->[2] };	393	shift @{ $self->[2] };
190		394
191	} else {	395	} else {
		396	# send string
192	my $len = syswrite $self->[1], $self->[2][0]	397	my $len = syswrite $self->[1], $self->[2][0];
		398
		399	unless ($len) {
		400	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		401	undef $self->[3];
193	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	402	die "AnyEvent::Fork: command write failure: $!";
		403	}
194		404
195	substr $self->[2][0], 0, $len, "";	405	substr $self->[2][0], 0, $len, "";
196	shift @{ $self->[2] } unless length $self->[2][0];	406	shift @{ $self->[2] } unless length $self->[2][0];
197	}	407	}
		408	} while @{ $self->[2] };
198		409
199	unless (@{ $self->[2] }) {	410	# everything written
200	undef $self->[3];	411	undef $self->[3];
		412
		413	# invoke run callback, if any
201	$self->[0]->($self->[1]) if $self->[0];	414	$self->[4]->($self->[1]) if $self->[4];
202	}
203	};	415	};
		416
		417	() # make sure we don't leak the watcher
204	}	418	}
205		419
206	sub _new {	420	sub _new {
207	my ($self, $fh) = @_;	421	my ($self, $fh, $pid) = @_;
		422
		423	AnyEvent::Util::fh_nonblocking $fh, 1;
208		424
209	$self = bless [	425	$self = bless [
210	undef, # run callback	426	$pid,
211	$fh,	427	$fh,
212	[], # write queue - strings or fd's	428	[], # write queue - strings or fd's
213	undef, # AE watcher	429	undef, # AE watcher
214	], $self;	430	], $self;
215		431
216	# my ($a, $b) = AnyEvent::Util::portable_socketpair;
217
218	# queue_cmd $template, "Iabc";
219	# push @{ $template->[2] }, \$b;
220
221	# use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
222	# undef $b;
223	# die "x" . <$a>;
224
225	$self	432	$self
		433	}
		434
		435	# fork template from current process, used by AnyEvent::Fork::Early/Template
		436	sub _new_fork {
		437	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		438	my $parent = $$;
		439
		440	my $pid = fork;
		441
		442	if ($pid eq 0) {
		443	require AnyEvent::Fork::Serve;
		444	$AnyEvent::Fork::Serve::OWNER = $parent;
		445	close $fh;
		446	$0 = "$_[1] of $parent";
		447	$SIG{CHLD} = 'IGNORE';
		448	AnyEvent::Fork::Serve::serve ($slave);
		449	exit 0;
		450	} elsif (!$pid) {
		451	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		452	}
		453
		454	AnyEvent::Fork->_new ($fh, $pid)
226	}	455	}
227		456
228	=item my $proc = new AnyEvent::Fork	457	=item my $proc = new AnyEvent::Fork
229		458
230	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
231	object for further manipulation.	460	object for further manipulation.
232		461
233	The new process is forked from a template process that is kept around	462	The new process is forked from a template process that is kept around
234	for this purpose. When it doesn't exist yet, it is created by a call to	463	for this purpose. When it doesn't exist yet, it is created by a call to
235	C<new_exec> and kept around for future calls.	464	C<new_exec> first and then stays around for future calls.
236		465
237	=cut	466	=cut
238		467
239	sub new {	468	sub new {
240	my $class = shift;	469	my $class = shift;
…		…
261	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	490	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
262		491
263	$self->send_fh ($slave);	492	$self->send_fh ($slave);
264	$self->_cmd ("f");	493	$self->_cmd ("f");
265		494
266	AnyEvent::Util::fh_nonblocking $fh, 1;
267
268	AnyEvent::Fork->_new ($fh)	495	AnyEvent::Fork->_new ($fh)
269	}	496	}
270		497
271	=item my $proc = new_exec AnyEvent::Fork	498	=item my $proc = new_exec AnyEvent::Fork
272		499
…		…
278	reduces the amount of memory sharing that is possible, and is also slower.	505	reduces the amount of memory sharing that is possible, and is also slower.
279		506
280	You should use C<new> whenever possible, except when having a template	507	You should use C<new> whenever possible, except when having a template
281	process around is unacceptable.	508	process around is unacceptable.
282		509
283	The path to the perl interpreter is divined usign various methods - first	510	The path to the perl interpreter is divined using various methods - first
284	C<$^X> is investigated to see if the path ends with something that sounds	511	C<$^X> is investigated to see if the path ends with something that sounds
285	as if it were the perl interpreter. Failing this, the module falls back to	512	as if it were the perl interpreter. Failing this, the module falls back to
286	using C<$Config::Config{perlpath}>.	513	using C<$Config::Config{perlpath}>.
287		514
288	=cut	515	=cut
…		…
297	my $perl = $;	524	my $perl = $;
298		525
299	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	526	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
300	# that looks like perl. this obviously only works for posix and win32	527	# that looks like perl. this obviously only works for posix and win32
301	unless (	528	unless (
302	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	529	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
303	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	530	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
304	) {	531	) {
305	# if it doesn't look perlish enough, try Config	532	# if it doesn't look perlish enough, try Config
306	require Config;	533	require Config;
307	$perl = $Config::Config{perlpath};	534	$perl = $Config::Config{perlpath};
…		…
309	}	536	}
310		537
311	require Proc::FastSpawn;	538	require Proc::FastSpawn;
312		539
313	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	540	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
314	AnyEvent::Util::fh_nonblocking $fh, 1;
315	Proc::FastSpawn::fd_inherit (fileno $slave);	541	Proc::FastSpawn::fd_inherit (fileno $slave);
		542
		543	# new fh's should always be set cloexec (due to $^F),
		544	# but hey, not on win32, so we always clear the inherit flag.
		545	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
316		546
317	# quick. also doesn't work in win32. of course. what did you expect	547	# quick. also doesn't work in win32. of course. what did you expect
318	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	548	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
319	my %env = %ENV;	549	my %env = %ENV;
320	$env{PERL5LIB} = join ":", grep !ref, @INC;	550	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
321		551
322	Proc::FastSpawn::spawn (	552	my $pid = Proc::FastSpawn::spawn (
323	$perl,	553	$perl,
324	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave],	554	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
325	[map "$_=$env{$_}", keys %env],	555	[map "$_=$env{$_}", keys %env],
326	) or die "unable to spawn AnyEvent::Fork server: $!";	556	) or die "unable to spawn AnyEvent::Fork server: $!";
327		557
328	$self->_new ($fh)	558	$self->_new ($fh, $pid)
		559	}
		560
		561	=item $pid = $proc->pid
		562
		563	Returns the process id of the process I<iff it is a direct child of the
		564	process> running AnyEvent::Fork, and C<undef> otherwise.
		565
		566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		568	to clean up their zombies when they die.
		569
		570	All other processes are not direct children, and will be cleaned up by
		571	AnyEvent::Fork itself.
		572
		573	=cut
		574
		575	sub pid {
		576	$_[0][0]
		577	}
		578
		579	=item $proc = $proc->eval ($perlcode, @args)
		580
		581	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
		582	the strings specified by C<@args>, in the "main" package.
		583
		584	This call is meant to do any custom initialisation that might be required
		585	(for example, the C<require> method uses it). It's not supposed to be used
		586	to completely take over the process, use C<run> for that.
		587
		588	The code will usually be executed after this call returns, and there is no
		589	way to pass anything back to the calling process. Any evaluation errors
		590	will be reported to stderr and cause the process to exit.
		591
		592	If you want to execute some code to take over the process (see the
		593	"fork+exec" example in the SYNOPSIS), you should compile a function via
		594	C<eval> first, and then call it via C<run>. This also gives you access to
		595	any arguments passed via the C<send_xxx> methods, such as file handles.
		596
		597	Returns the process object for easy chaining of method calls.
		598
		599	=cut
		600
		601	sub eval {
		602	my ($self, $code, @args) = @_;
		603
		604	$self->_cmd (e => pack "(w/a)", $code, @args);
		605
		606	$self
329	}	607	}
330		608
331	=item $proc = $proc->require ($module, ...)	609	=item $proc = $proc->require ($module, ...)
332		610
333	Tries to load the given modules into the process	611	Tries to load the given module(s) into the process
334		612
335	Returns the process object for easy chaining of method calls.	613	Returns the process object for easy chaining of method calls.
		614
		615	=cut
		616
		617	sub require {
		618	my ($self, @modules) = @_;
		619
		620	s%::%/%g for @modules;
		621	$self->eval ('require "$_.pm" for @_', @modules);
		622
		623	$self
		624	}
336		625
337	=item $proc = $proc->send_fh ($handle, ...)	626	=item $proc = $proc->send_fh ($handle, ...)
338		627
339	Send one or more file handles (I<not> file descriptors) to the process,	628	Send one or more file handles (I<not> file descriptors) to the process,
340	to prepare a call to C<run>.	629	to prepare a call to C<run>.
…		…
344	accomplished by simply not storing the file handles anywhere after passing	633	accomplished by simply not storing the file handles anywhere after passing
345	them to this method.	634	them to this method.
346		635
347	Returns the process object for easy chaining of method calls.	636	Returns the process object for easy chaining of method calls.
348		637
		638	Example: pass a file handle to a process, and release it without
		639	closing. It will be closed automatically when it is no longer used.
		640
		641	$proc->send_fh ($my_fh);
		642	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		643
349	=cut	644	=cut
350		645
351	sub send_fh {	646	sub send_fh {
352	my ($self, @fh) = @_;	647	my ($self, @fh) = @_;
353		648
…		…
362	=item $proc = $proc->send_arg ($string, ...)	657	=item $proc = $proc->send_arg ($string, ...)
363		658
364	Send one or more argument strings to the process, to prepare a call to	659	Send one or more argument strings to the process, to prepare a call to
365	C<run>. The strings can be any octet string.	660	C<run>. The strings can be any octet string.
366		661
		662	The protocol is optimised to pass a moderate number of relatively short
		663	strings - while you can pass up to 4GB of data in one go, this is more
		664	meant to pass some ID information or other startup info, not big chunks of
		665	data.
		666
367	Returns the process object for easy chaining of emthod calls.	667	Returns the process object for easy chaining of method calls.
368		668
369	=cut	669	=cut
370		670
371	sub send_arg {	671	sub send_arg {
372	my ($self, @arg) = @_;	672	my ($self, @arg) = @_;
373		673
374	$self->_cmd (a => @arg);	674	$self->_cmd (a => pack "(w/a)", @arg);
375		675
376	$self	676	$self
377	}	677	}
378		678
379	=item $proc->run ($func, $cb->($fh))	679	=item $proc->run ($func, $cb->($fh))
380		680
381	Enter the function specified by the fully qualified name in C<$func> in	681	Enter the function specified by the function name in C<$func> in the
382	the process. The function is called with the communication socket as first	682	process. The function is called with the communication socket as first
383	argument, followed by all file handles and string arguments sent earlier	683	argument, followed by all file handles and string arguments sent earlier
384	via C<send_fh> and C<send_arg> methods, in the order they were called.	684	via C<send_fh> and C<send_arg> methods, in the order they were called.
385		685
386	If the called function returns, the process exits.	686	The function name should be fully qualified, but if it isn't, it will be
		687	looked up in the main package.
387		688
388	Preparing the process can take time - when the process is ready, the	689	If the called function returns, doesn't exist, or any error occurs, the
		690	process exits.
		691
		692	Preparing the process is done in the background - when all commands have
389	callback is invoked with the local communications socket as argument.	693	been sent, the callback is invoked with the local communications socket
		694	as argument. At this point you can start using the socket in any way you
		695	like.
390		696
391	The process object becomes unusable on return from this function.	697	The process object becomes unusable on return from this function - any
		698	further method calls result in undefined behaviour.
392		699
393	If the communication socket isn't used, it should be closed on both sides,	700	If the communication socket isn't used, it should be closed on both sides,
394	to save on kernel memory.	701	to save on kernel memory.
395		702
396	The socket is non-blocking in the parent, and blocking in the newly	703	The socket is non-blocking in the parent, and blocking in the newly
397	created process. The close-on-exec flag is set on both. Even if not used	704	created process. The close-on-exec flag is set in both.
		705
398	otherwise, the socket can be a good indicator for the existance of the	706	Even if not used otherwise, the socket can be a good indicator for the
399	process - if the othe rprocess exits, you get a readable event on it,	707	existence of the process - if the other process exits, you get a readable
400	because exiting the process closes the socket (if it didn't create any	708	event on it, because exiting the process closes the socket (if it didn't
401	children using fork).	709	create any children using fork).
		710
		711	Example: create a template for a process pool, pass a few strings, some
		712	file handles, then fork, pass one more string, and run some code.
		713
		714	my $pool = AnyEvent::Fork
		715	->new
		716	->send_arg ("str1", "str2")
		717	->send_fh ($fh1, $fh2);
		718
		719	for (1..2) {
		720	$pool
		721	->fork
		722	->send_arg ("str3")
		723	->run ("Some::function", sub {
		724	my ($fh) = @_;
		725
		726	# fh is nonblocking, but we trust that the OS can accept these
		727	# few octets anyway.
		728	syswrite $fh, "hi #$_\n";
		729
		730	# $fh is being closed here, as we don't store it anywhere
		731	});
		732	}
		733
		734	# Some::function might look like this - all parameters passed before fork
		735	# and after will be passed, in order, after the communications socket.
		736	sub Some::function {
		737	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		738
		739	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		740	}
402		741
403	=cut	742	=cut
404		743
405	sub run {	744	sub run {
406	my ($self, $func, $cb) = @_;	745	my ($self, $func, $cb) = @_;
407		746
408	$self->[0] = $cb;	747	$self->[4] = $cb;
409	$self->_cmd ("r", $func);	748	$self->_cmd (r => $func);
410	}	749	}
411		750
412	=back	751	=back
		752
		753	=head1 PERFORMANCE
		754
		755	Now for some unscientific benchmark numbers (all done on an amd64
		756	GNU/Linux box). These are intended to give you an idea of the relative
		757	performance you can expect, they are not meant to be absolute performance
		758	numbers.
		759
		760	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		761	exit in the child and waits for the socket to close in the parent. I did
		762	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		763
		764	2079 new processes per second, using manual socketpair + fork
		765
		766	Then I did the same thing, but instead of calling fork, I called
		767	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		768	socket form the child to close on exit. This does the same thing as manual
		769	socket pair + fork, except that what is forked is the template process
		770	(2440kB), and the socket needs to be passed to the server at the other end
		771	of the socket first.
		772
		773	2307 new processes per second, using AnyEvent::Fork->new
		774
		775	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		776	a new perl interpreter and compile the small server each time, I get:
		777
		778	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		779
		780	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		781	though it uses the same operations, but adds a lot of overhead?
		782
		783	The difference is simply the process size: forking the 6MB process takes
		784	so much longer than forking the 2.5MB template process that the overhead
		785	introduced is canceled out.
		786
		787	If the benchmark process grows, the normal fork becomes even slower:
		788
		789	1340 new processes, manual fork in a 20MB process
		790	731 new processes, manual fork in a 200MB process
		791	235 new processes, manual fork in a 2000MB process
		792
		793	What that means (to me) is that I can use this module without having a
		794	very bad conscience because of the extra overhead required to start new
		795	processes.
		796
		797	=head1 TYPICAL PROBLEMS
		798
		799	This section lists typical problems that remain. I hope by recognising
		800	them, most can be avoided.
		801
		802	=over 4
		803
		804	=item "leaked" file descriptors for exec'ed processes
		805
		806	POSIX systems inherit file descriptors by default when exec'ing a new
		807	process. While perl itself laudably sets the close-on-exec flags on new
		808	file handles, most C libraries don't care, and even if all cared, it's
		809	often not possible to set the flag in a race-free manner.
		810
		811	That means some file descriptors can leak through. And since it isn't
		812	possible to know which file descriptors are "good" and "necessary" (or
		813	even to know which file descriptors are open), there is no good way to
		814	close the ones that might harm.
		815
		816	As an example of what "harm" can be done consider a web server that
		817	accepts connections and afterwards some module uses AnyEvent::Fork for the
		818	first time, causing it to fork and exec a new process, which might inherit
		819	the network socket. When the server closes the socket, it is still open
		820	in the child (which doesn't even know that) and the client might conclude
		821	that the connection is still fine.
		822
		823	For the main program, there are multiple remedies available -
		824	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		825	C<new_exec> is another, as in both cases, the first process can be exec'ed
		826	well before many random file descriptors are open.
		827
		828	In general, the solution for these kind of problems is to fix the
		829	libraries or the code that leaks those file descriptors.
		830
		831	Fortunately, most of these leaked descriptors do no harm, other than
		832	sitting on some resources.
		833
		834	=item "leaked" file descriptors for fork'ed processes
		835
		836	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		837	which closes file descriptors not marked for being inherited.
		838
		839	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		840	a way to create these processes by forking, and this leaks more file
		841	descriptors than exec'ing them, as there is no way to mark descriptors as
		842	"close on fork".
		843
		844	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		845	pipes for internal uses, and L<Gtk2> might open a connection to the X
		846	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		847	trouble with a fork.
		848
		849	The solution is to either not load these modules before use'ing
		850	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		851	initialising them, for example, by calling C<init Gtk2> manually.
		852
		853	=item exit runs destructors
		854
		855	This only applies to users of Lc<AnyEvent::Fork:Early> and
		856	L<AnyEvent::Fork::Template>.
		857
		858	When a process created by AnyEvent::Fork exits, it might do so by calling
		859	exit, or simply letting perl reach the end of the program. At which point
		860	Perl runs all destructors.
		861
		862	Not all destructors are fork-safe - for example, an object that represents
		863	the connection to an X display might tell the X server to free resources,
		864	which is inconvenient when the "real" object in the parent still needs to
		865	use them.
		866
		867	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		868	it as the very first thing, right?
		869
		870	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		871	is to not create objects with nontrivial destructors that might have an
		872	effect outside of Perl.
		873
		874	=back
		875
		876	=head1 PORTABILITY NOTES
		877
		878	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		879	and ::Template is not going to work), and it cost a lot of blood and sweat
		880	to make it so, mostly due to the bloody broken perl that nobody seems to
		881	care about. The fork emulation is a bad joke - I have yet to see something
		882	useful that you can do with it without running into memory corruption
		883	issues or other braindamage. Hrrrr.
		884
		885	Cygwin perl is not supported at the moment, as it should implement fd
		886	passing, but doesn't, and rolling my own is hard, as cygwin doesn't
		887	support enough functionality to do it.
		888
		889	=head1 SEE ALSO
		890
		891	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
		892	L<AnyEvent::Fork::Template> (to create a process by forking the main
		893	program at a convenient time).
413		894
414	=head1 AUTHOR	895	=head1 AUTHOR
415		896
416	Marc Lehmann <schmorp@schmorp.de>	897	Marc Lehmann <schmorp@schmorp.de>
417	http://home.schmorp.de/	898	http://home.schmorp.de/

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Revision 1.31 by root, Sat Apr 6 09:29:26 2013 UTC