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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.3 by root, Tue Apr 2 18:00:04 2013 UTC vs.
Revision 1.48 by root, Fri Apr 19 10:51:41 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::ProcessPool - manage pools of perl worker processes, exec'ed or fork'ed	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::ProcessPool;	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 single worker processes but also worker	18	This module allows you to create new processes, without actually forking
12	pool that share memory, by forking from the main program, or exec'ing new	19	them from your current process (avoiding the problems of forking), but
13	perl interpreters from a module.	20	preserving most of the advantages of fork.
14		21
15	You create a new processes in a pool by specifying a function to call	22	It can be used to create new worker processes or new independent
16	with any combination of string values and file handles.	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.
17		27
18	A pool can have initialisation code which is executed before forking. The	28	Special care has been taken to make this module useful from other modules,
19	initialisation code is only executed once and the resulting process is	29	while still supporting specialised environments such as L<App::Staticperl>
20	cached, to be used as a template.	30	or L<PAR::Packer>.
21		31
22	Pools without such initialisation code don't cache an extra process.	32	=head2 WHAT THIS MODULE IS NOT
23		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
24	=head1 PROBLEM STATEMENT	66	=head2 PROBLEM STATEMENT
25		67
26	There are two ways to implement parallel processing on UNIX like operating	68	There are two traditional ways to implement parallel processing on UNIX
27	systems - fork and process, and fork+exec and process. They have different	69	like operating systems - fork and process, and fork+exec and process. They
28	advantages and disadvantages that I describe below, together with how this	70	have different advantages and disadvantages that I describe below,
29	module tries to mitigate the disadvantages.	71	together with how this module tries to mitigate the disadvantages.
30		72
31	=over 4	73	=over 4
32		74
33	=item Forking from a big process can be very slow (a 5GB process needs	75	=item Forking from a big process can be very slow.
34	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead	76
		77	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
35	is often shared with exec (because you have to fork first), but in some	78	overhead is often shared with exec (because you have to fork first), but
36	circumstances (e.g. when vfork is used), fork+exec can be much faster.	79	in some circumstances (e.g. when vfork is used), fork+exec can be much
		80	faster.
37		81
38	This module can help here by telling a small(er) helper process to fork,	82	This module can help here by telling a small(er) helper process to fork,
39	or fork+exec instead.	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.
40		85
41	=item Forking usually creates a copy-on-write copy of the parent	86	=item Forking usually creates a copy-on-write copy of the parent
42	process. Memory (for example, modules or data files that have been	87	process.
43	will not take additional memory). When exec'ing a new process, modules	88
44	and data files might need to be loaded again, at extra cpu and memory	89	For example, modules or data files that are loaded will not use additional
45	cost. Likewise when forking, all data structures are copied as well - if	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
46	the program frees them and replaces them by new data, the child processes	93	them and replaces them by new data, the child processes will retain the
47	will retain the memory even if it isn't used.	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.
48		99
49	This module allows the main program to do a controlled fork, and allows	100	This module allows the main program to do a controlled fork, and allows
50	modules to exec processes safely at any time. When creating a custom	101	modules to exec processes safely at any time. When creating a custom
51	process pool you can take advantage of data sharing via fork without	102	process pool you can take advantage of data sharing via fork without
52	risking to share large dynamic data structures that will blow up child	103	risking to share large dynamic data structures that will blow up child
53	memory usage.	104	memory usage.
54		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
55	=item Exec'ing a new perl process might be difficult and slow. For	109	=item Exec'ing a new perl process might be difficult.
		110
56	example, it is not easy to find the correct path to the perl interpreter,	111	For example, it is not easy to find the correct path to the perl
57	and all modules have to be loaded from disk again. Long running processes	112	interpreter - C<$^X> might not be a perl interpreter at all.
58	might run into problems when perl is upgraded for example.
59		113
60	This module supports creating pre-initialised perl processes to be used
61	as template, and also tries hard to identify the correct path to the perl	114	This module tries hard to identify the correct path to the perl
62	interpreter. With a cooperative main program, exec'ing the interpreter	115	interpreter. With a cooperative main program, exec'ing the interpreter
63	might not even be necessary.	116	might not even be necessary, but even without help from the main program,
		117	it will still work when used from a module.
64		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
65	=item Forking might be impossible when a program is running. For example,	130	=item Forking might be impossible when a program is running.
66	POSIX makes it almost impossible to fork from a multithreaded program and
67	do anything useful in the child - strictly speaking, if your perl program
68	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
69	you cannot call fork on the perl level anymore, at all.
70		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
71	This module can safely fork helper processes at any time, by caling	139	This module can safely fork helper processes at any time, by calling
72	fork+exec in C, in a POSIX-compatible way.	140	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
73		141
74	=item Parallel processing with fork might be inconvenient or difficult	142	=item Parallel processing with fork might be inconvenient or difficult
		143	to implement. Modules might not work in both parent and child.
		144
75	to implement. For example, when a program uses an event loop and creates	145	For example, when a program uses an event loop and creates watchers it
76	watchers it becomes very hard to use the event loop from a child	146	becomes very hard to use the event loop from a child program, as the
77	program, as the watchers already exist but are only meaningful in the	147	watchers already exist but are only meaningful in the parent. Worse, a
78	parent. Worse, a module might want to use such a system, not knowing	148	module might want to use such a module, not knowing whether another module
79	whether another module or the main program also does, leading to problems.	149	or the main program also does, leading to problems.
80		150
81	This module only lets the main program create pools by forking (because	151	Apart from event loops, graphical toolkits also commonly fall into the
82	only the main program can know when it is still safe to do so) - all other	152	"unsafe module" category, or just about anything that communicates with
83	pools are created by fork+exec, after which such modules can again be	153	the external world, such as network libraries and file I/O modules, which
84	loaded.	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.
85		161
86	=back	162	=back
		163
		164	=head1 EXAMPLES
		165
		166	=head2 Create a single new process, tell it to run your worker function.
		167
		168	AnyEvent::Fork
		169	->new
		170	->require ("MyModule")
		171	->run ("MyModule::worker, sub {
		172	my ($master_filehandle) = @_;
		173
		174	# now $master_filehandle is connected to the
		175	# $slave_filehandle in the new process.
		176	});
		177
		178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
		182	sub worker {
		183	my ($slave_filehandle) = @_;
		184
		185	# now $slave_filehandle is connected to the $master_filehandle
		186	# in the original prorcess. have fun!
		187	}
		188
		189	=head2 Create a pool of server processes all accepting on the same socket.
		190
		191	# create listener socket
		192	my $listener = ...;
		193
		194	# create a pool template, initialise it and give it the socket
		195	my $pool = AnyEvent::Fork
		196	->new
		197	->require ("Some::Stuff", "My::Server")
		198	->send_fh ($listener);
		199
		200	# now create 10 identical workers
		201	for my $id (1..10) {
		202	$pool
		203	->fork
		204	->send_arg ($id)
		205	->run ("My::Server::run");
		206	}
		207
		208	# now do other things - maybe use the filehandle provided by run
		209	# to wait for the processes to die. or whatever.
		210
		211	C<My::Server> might look like this:
		212
		213	package My::Server;
		214
		215	sub run {
		216	my ($slave, $listener, $id) = @_;
		217
		218	close $slave; # we do not use the socket, so close it to save resources
		219
		220	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
		221	# or anything we usually couldn't do in a process forked normally.
		222	while (my $socket = $listener->accept) {
		223	# do sth. with new socket
		224	}
		225	}
		226
		227	=head2 use AnyEvent::Fork as a faster fork+exec
		228
		229	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
		230	and standard error redirected to the communications socket. It is usually
		231	faster than fork+exec, but still lets you prepare the environment.
		232
		233	open my $output, ">/tmp/log" or die "$!";
		234
		235	AnyEvent::Fork
		236	->new
		237	->eval ('
		238	# compile a helper function for later use
		239	sub run {
		240	my ($fh, $output, @cmd) = @_;
		241
		242	# perl will clear close-on-exec on STDOUT/STDERR
		243	open STDOUT, ">&", $output or die;
		244	open STDERR, ">&", $fh or die;
		245
		246	exec @cmd;
		247	}
		248	')
		249	->send_fh ($output)
		250	->send_arg ("/bin/echo", "hi")
		251	->run ("run", my $cv = AE::cv);
		252
		253	my $stderr = $cv->recv;
87		254
88	=head1 CONCEPTS	255	=head1 CONCEPTS
89		256
90	This module can create new processes either by executing a new perl	257	This module can create new processes either by executing a new perl
91	process, or by forking from an existing "template" process.	258	process, or by forking from an existing "template" process.
		259
		260	All these processes are called "child processes" (whether they are direct
		261	children or not), while the process that manages them is called the
		262	"parent process".
92		263
93	Each such process comes with its own file handle that can be used to	264	Each such process comes with its own file handle that can be used to
94	communicate with it (it's actually a socket - one end in the new process,	265	communicate with it (it's actually a socket - one end in the new process,
95	one end in the main process), and among the things you can do in it are	266	one end in the main process), and among the things you can do in it are
96	load modules, fork new processes, send file handles to it, and execute	267	load modules, fork new processes, send file handles to it, and execute
108	needed the first time. Forking from this process shares the memory used	279	needed the first time. Forking from this process shares the memory used
109	for the perl interpreter with the new process, but loading modules takes	280	for the perl interpreter with the new process, but loading modules takes
110	time, and the memory is not shared with anything else.	281	time, and the memory is not shared with anything else.
111		282
112	This is ideal for when you only need one extra process of a kind, with the	283	This is ideal for when you only need one extra process of a kind, with the
113	option of starting and stipping it on demand.	284	option of starting and stopping it on demand.
		285
		286	Example:
		287
		288	AnyEvent::Fork
		289	->new
		290	->require ("Some::Module")
		291	->run ("Some::Module::run", sub {
		292	my ($fork_fh) = @_;
		293	});
114		294
115	=item fork a new template process, load code, then fork processes off of	295	=item fork a new template process, load code, then fork processes off of
116	it and run the code	296	it and run the code
117		297
118	When you need to have a bunch of processes that all execute the same (or	298	When you need to have a bunch of processes that all execute the same (or
…		…
124	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
125	consumes relatively little memory of its own.	305	consumes relatively little memory of its own.
126		306
127	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
128	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
129	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
130	the template process.	310	the template process.
		311
		312	Example:
		313
		314	my $template = AnyEvent::Fork->new->require ("Some::Module");
		315
		316	for (1..10) {
		317	$template->fork->run ("Some::Module::run", sub {
		318	my ($fork_fh) = @_;
		319	});
		320	}
		321
		322	# at this point, you can keep $template around to fork new processes
		323	# later, or you can destroy it, which causes it to vanish.
131		324
132	=item execute a new perl interpreter, load some code, run it	325	=item execute a new perl interpreter, load some code, run it
133		326
134	This is relatively slow, and doesn't allow you to share memory between	327	This is relatively slow, and doesn't allow you to share memory between
135	multiple processes.	328	multiple processes.
…		…
137	The only advantage is that you don't have to have a template process	330	The only advantage is that you don't have to have a template process
138	hanging around all the time to fork off some new processes, which might be	331	hanging around all the time to fork off some new processes, which might be
139	an advantage when there are long time spans where no extra processes are	332	an advantage when there are long time spans where no extra processes are
140	needed.	333	needed.
141		334
		335	Example:
		336
		337	AnyEvent::Fork
		338	->new_exec
		339	->require ("Some::Module")
		340	->run ("Some::Module::run", sub {
		341	my ($fork_fh) = @_;
		342	});
		343
142	=back	344	=back
143		345
144	=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.
145		366
146	=over 4	367	=over 4
147		368
148	=cut	369	=cut
149		370
150	package AnyEvent::ProcessPool;	371	package AnyEvent::Fork;
151		372
152	use common::sense;	373	use common::sense;
153		374
154	use Socket ();	375	use Errno ();
155		376
156	use Proc::FastSpawn;
157	use AnyEvent;	377	use AnyEvent;
158	use AnyEvent::ProcessPool::Util;
159	use AnyEvent::Util ();	378	use AnyEvent::Util ();
160		379
161	BEGIN {	380	use IO::FDPass;
162	# require Exporter;
163	}
164		381
165	=item my $pool = new AnyEvent::ProcessPool key => value...	382	our $VERSION = 0.7;
166		383
167	Create a new process pool. The following named parameters are supported:	384	# the early fork template process
		385	our $EARLY;
168		386
169	=over 4
170
171	=back
172
173	=cut
174
175	# the template process	387	# the empty template process
176	our $template;	388	our $TEMPLATE;
177		389
178	sub _queue {	390	sub QUEUE() { 0 }
179	my ($pid, $fh) = @_;	391	sub FH() { 1 }
		392	sub WW() { 2 }
		393	sub PID() { 3 }
		394	sub CB() { 4 }
180		395
181	[	396	sub _new {
		397	my ($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
182	$pid,	405	$pid,
183	$fh,	406	], $self;
184	[],
185	undef
186	]
187	}
188		407
		408	$self
		409	}
		410
189	sub queue_cmd {	411	sub _cmd {
190	my $queue = shift;	412	my $self = shift;
191		413
192	push @{ $queue->[2] }, pack "N/a", pack "a (w/a)*", @_;	414	# ideally, we would want to use "a (w/a)*" as format string, but perl
		415	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
		416	# it.
		417	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
193		418
194	$queue->[3] \|\|= AE::io $queue->[1], 1, sub {	419	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		420	do {
		421	# send the next "thing" in the queue - either a reference to an fh,
		422	# or a plain string.
		423
195	if (ref $queue->[2][0]) {	424	if (ref $self->[QUEUE][0]) {
196	AnyEvent::ProcessPool::Util::fd_send fileno $queue->[1], fileno ${ $queue->[2][0] }	425	# send fh
		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
197	and shift @{ $queue->[2] };	432	shift @{ $self->[QUEUE] };
		433
198	} else {	434	} else {
		435	# send string
199	my $len = syswrite $queue->[1], $queue->[2][0]	436	my $len = syswrite $self->[FH], $self->[QUEUE][0];
200	or do { undef $queue->[3]; die "AnyEvent::ProcessPool::queue write failure: $!" };	437
		438	unless ($len) {
		439	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		440	undef $self->[3];
		441	die "AnyEvent::Fork: command write failure: $!";
		442	}
		443
201	substr $queue->[2][0], 0, $len, "";	444	substr $self->[QUEUE][0], 0, $len, "";
202	shift @{ $queue->[2] } unless length $queue->[2][0];	445	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
		446	}
		447	} while @{ $self->[QUEUE] };
		448
		449	# everything written
		450	undef $self->[WW];
		451
		452	# invoke run callback, if any
		453	if ($self->[CB]) {
		454	$self->[CB]->($self->[FH]);
		455	@$self = ();
203	}	456	}
204
205	undef $queue->[3] unless @{ $queue->[2] };
206	};	457	};
207	}
208		458
209	sub run_template {	459	() # make sure we don't leak the watcher
210	return if $template;	460	}
211		461
		462	# fork template from current process, used by AnyEvent::Fork::Early/Template
		463	sub _new_fork {
212	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	464	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
213	AnyEvent::Util::fh_nonblocking $fh, 1;	465	my $parent = $$;
214	fd_inherit fileno $slave;
215		466
216	my %env = %ENV;	467	my $pid = fork;
217	$env{PERL5LIB} = join ":", grep !ref, @INC;
218		468
219	my $pid = spawn	469	if ($pid eq 0) {
220	$^X,	470	require AnyEvent::Fork::Serve;
221	["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave],	471	$AnyEvent::Fork::Serve::OWNER = $parent;
222	[map "$_=$env{$_}", keys %env],	472	close $fh;
223	or die "unable to spawn AnyEvent::ProcessPool server: $!";	473	$0 = "$_[1] of $parent";
		474	AnyEvent::Fork::Serve::serve ($slave);
		475	exit 0;
		476	} elsif (!$pid) {
		477	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
		478	}
224		479
225	close $slave;	480	AnyEvent::Fork->_new ($fh, $pid)
226
227	$template = _queue $pid, $fh;
228
229	my ($a, $b) = AnyEvent::Util::portable_socketpair;
230
231	queue_cmd $template, "Iabc";
232	push @{ $template->[2] }, \$b;
233
234	use Coro::AnyEvent; Coro::AnyEvent::sleep 1;
235	undef $b;
236	die "x" . <$a>;
237	}	481	}
		482
		483	=item my $proc = new AnyEvent::Fork
		484
		485	Create a new "empty" perl interpreter process and returns its process
		486	object for further manipulation.
		487
		488	The new process is forked from a template process that is kept around
		489	for this purpose. When it doesn't exist yet, it is created by a call to
		490	C<new_exec> first and then stays around for future calls.
		491
		492	=cut
238		493
239	sub new {	494	sub new {
240	my $class = shift;	495	my $class = shift;
241		496
242	my $self = bless {	497	$TEMPLATE \|\|= $class->new_exec;
243	@_	498	$TEMPLATE->fork
244	}, $class;	499	}
245		500
246	run_template;	501	=item $new_proc = $proc->fork
		502
		503	Forks C<$proc>, creating a new process, and returns the process object
		504	of the new process.
		505
		506	If any of the C<send_> functions have been called before fork, then they
		507	will be cloned in the child. For example, in a pre-forked server, you
		508	might C<send_fh> the listening socket into the template process, and then
		509	keep calling C<fork> and C<run>.
		510
		511	=cut
		512
		513	sub fork {
		514	my ($self) = @_;
		515
		516	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		517
		518	$self->send_fh ($slave);
		519	$self->_cmd ("f");
		520
		521	AnyEvent::Fork->_new ($fh)
		522	}
		523
		524	=item my $proc = new_exec AnyEvent::Fork
		525
		526	Create a new "empty" perl interpreter process and returns its process
		527	object for further manipulation.
		528
		529	Unlike the C<new> method, this method I<always> spawns a new perl process
		530	(except in some cases, see L<AnyEvent::Fork::Early> for details). This
		531	reduces the amount of memory sharing that is possible, and is also slower.
		532
		533	You should use C<new> whenever possible, except when having a template
		534	process around is unacceptable.
		535
		536	The path to the perl interpreter is divined using various methods - first
		537	C<$^X> is investigated to see if the path ends with something that sounds
		538	as if it were the perl interpreter. Failing this, the module falls back to
		539	using C<$Config::Config{perlpath}>.
		540
		541	=cut
		542
		543	sub new_exec {
		544	my ($self) = @_;
		545
		546	return $EARLY->fork
		547	if $EARLY;
		548
		549	# first find path of perl
		550	my $perl = $;
		551
		552	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
		553	# that looks like perl. this obviously only works for posix and win32
		554	unless (
		555	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
		556	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
		557	) {
		558	# if it doesn't look perlish enough, try Config
		559	require Config;
		560	$perl = $Config::Config{perlpath};
		561	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		562	}
		563
		564	require Proc::FastSpawn;
		565
		566	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
		567	Proc::FastSpawn::fd_inherit (fileno $slave);
		568
		569	# new fh's should always be set cloexec (due to $^F),
		570	# but hey, not on win32, so we always clear the inherit flag.
		571	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
		572
		573	# quick. also doesn't work in win32. of course. what did you expect
		574	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
		575	my %env = %ENV;
		576	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
		577
		578	my $pid = Proc::FastSpawn::spawn (
		579	$perl,
		580	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
		581	[map "$_=$env{$_}", keys %env],
		582	) or die "unable to spawn AnyEvent::Fork server: $!";
		583
		584	$self->_new ($fh, $pid)
		585	}
		586
		587	=item $pid = $proc->pid
		588
		589	Returns the process id of the process I<iff it is a direct child of the
		590	process running AnyEvent::Fork>, and C<undef> otherwise.
		591
		592	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		593	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		594	to clean up their zombies when they die.
		595
		596	All other processes are not direct children, and will be cleaned up by
		597	AnyEvent::Fork itself.
		598
		599	=cut
		600
		601	sub pid {
		602	$_[0][PID]
		603	}
		604
		605	=item $proc = $proc->eval ($perlcode, @args)
		606
		607	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
		608	the strings specified by C<@args>, in the "main" package.
		609
		610	This call is meant to do any custom initialisation that might be required
		611	(for example, the C<require> method uses it). It's not supposed to be used
		612	to completely take over the process, use C<run> for that.
		613
		614	The code will usually be executed after this call returns, and there is no
		615	way to pass anything back to the calling process. Any evaluation errors
		616	will be reported to stderr and cause the process to exit.
		617
		618	If you want to execute some code (that isn't in a module) to take over the
		619	process, you should compile a function via C<eval> first, and then call
		620	it via C<run>. This also gives you access to any arguments passed via the
		621	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		622	a faster fork+exec> example to see it in action.
		623
		624	Returns the process object for easy chaining of method calls.
		625
		626	=cut
		627
		628	sub eval {
		629	my ($self, $code, @args) = @_;
		630
		631	$self->_cmd (e => pack "(w/a)", $code, @args);
247		632
248	$self	633	$self
249	}	634	}
250		635
		636	=item $proc = $proc->require ($module, ...)
		637
		638	Tries to load the given module(s) into the process
		639
		640	Returns the process object for easy chaining of method calls.
		641
		642	=cut
		643
		644	sub require {
		645	my ($self, @modules) = @_;
		646
		647	s%::%/%g for @modules;
		648	$self->eval ('require "$_.pm" for @_', @modules);
		649
		650	$self
		651	}
		652
		653	=item $proc = $proc->send_fh ($handle, ...)
		654
		655	Send one or more file handles (I<not> file descriptors) to the process,
		656	to prepare a call to C<run>.
		657
		658	The process object keeps a reference to the handles until they have
		659	been passed over to the process, so you must not explicitly close the
		660	handles. This is most easily accomplished by simply not storing the file
		661	handles anywhere after passing them to this method - when AnyEvent::Fork
		662	is finished using them, perl will automatically close them.
		663
		664	Returns the process object for easy chaining of method calls.
		665
		666	Example: pass a file handle to a process, and release it without
		667	closing. It will be closed automatically when it is no longer used.
		668
		669	$proc->send_fh ($my_fh);
		670	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
		671
		672	=cut
		673
		674	sub send_fh {
		675	my ($self, @fh) = @_;
		676
		677	for my $fh (@fh) {
		678	$self->_cmd ("h");
		679	push @{ $self->[QUEUE] }, \$fh;
		680	}
		681
		682	$self
		683	}
		684
		685	=item $proc = $proc->send_arg ($string, ...)
		686
		687	Send one or more argument strings to the process, to prepare a call to
		688	C<run>. The strings can be any octet strings.
		689
		690	The protocol is optimised to pass a moderate number of relatively short
		691	strings - while you can pass up to 4GB of data in one go, this is more
		692	meant to pass some ID information or other startup info, not big chunks of
		693	data.
		694
		695	Returns the process object for easy chaining of method calls.
		696
		697	=cut
		698
		699	sub send_arg {
		700	my ($self, @arg) = @_;
		701
		702	$self->_cmd (a => pack "(w/a)", @arg);
		703
		704	$self
		705	}
		706
		707	=item $proc->run ($func, $cb->($fh))
		708
		709	Enter the function specified by the function name in C<$func> in the
		710	process. The function is called with the communication socket as first
		711	argument, followed by all file handles and string arguments sent earlier
		712	via C<send_fh> and C<send_arg> methods, in the order they were called.
		713
		714	The process object becomes unusable on return from this function - any
		715	further method calls result in undefined behaviour.
		716
		717	The function name should be fully qualified, but if it isn't, it will be
		718	looked up in the C<main> package.
		719
		720	If the called function returns, doesn't exist, or any error occurs, the
		721	process exits.
		722
		723	Preparing the process is done in the background - when all commands have
		724	been sent, the callback is invoked with the local communications socket
		725	as argument. At this point you can start using the socket in any way you
		726	like.
		727
		728	If the communication socket isn't used, it should be closed on both sides,
		729	to save on kernel memory.
		730
		731	The socket is non-blocking in the parent, and blocking in the newly
		732	created process. The close-on-exec flag is set in both.
		733
		734	Even if not used otherwise, the socket can be a good indicator for the
		735	existence of the process - if the other process exits, you get a readable
		736	event on it, because exiting the process closes the socket (if it didn't
		737	create any children using fork).
		738
		739	Example: create a template for a process pool, pass a few strings, some
		740	file handles, then fork, pass one more string, and run some code.
		741
		742	my $pool = AnyEvent::Fork
		743	->new
		744	->send_arg ("str1", "str2")
		745	->send_fh ($fh1, $fh2);
		746
		747	for (1..2) {
		748	$pool
		749	->fork
		750	->send_arg ("str3")
		751	->run ("Some::function", sub {
		752	my ($fh) = @_;
		753
		754	# fh is nonblocking, but we trust that the OS can accept these
		755	# few octets anyway.
		756	syswrite $fh, "hi #$_\n";
		757
		758	# $fh is being closed here, as we don't store it anywhere
		759	});
		760	}
		761
		762	# Some::function might look like this - all parameters passed before fork
		763	# and after will be passed, in order, after the communications socket.
		764	sub Some::function {
		765	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
		766
		767	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
		768	}
		769
		770	=cut
		771
		772	sub run {
		773	my ($self, $func, $cb) = @_;
		774
		775	$self->[CB] = $cb;
		776	$self->_cmd (r => $func);
		777	}
		778
		779	=item $proc->to_fh ($cb->($fh))
		780
		781	Flushes all commands out to the process and then calls the callback with
		782	the communications socket.
		783
		784	The process object becomes unusable on return from this function - any
		785	further method calls result in undefined behaviour.
		786
		787	The point of this method is to give you a file handle thta you cna pass
		788	to another process. In that other process, you can call C<new_from_fh
		789	AnyEvent::Fork::RPC> to create a new C<AnyEvent::Fork> object from it,
		790	thereby effectively passing a fork object to another process.
		791
		792	=cut
		793
		794	sub to_fh {
		795	my ($self, $cb) = @_;
		796
		797	$self->[CB] = $cb;
		798
		799	unless ($self->[WW]) {
		800	$self->[CB]->($self->[FH]);
		801	@$self = ();
		802	}
		803	}
		804
		805	=item new_from_fh AnyEvent::Fork $fh
		806
		807	Takes a file handle originally rceeived by the C<to_fh> method and creates
		808	a new C<AnyEvent:Fork> object. The child process itself will not change in
		809	any way, i.e. it will keep all the modifications done to it before calling
		810	C<to_fh>.
		811
		812	The new object is very much like the original object, except that the
		813	C<pid> method will return C<undef> even if the process is a direct child.
		814
		815	=cut
		816
		817	sub new_from_fh {
		818	my ($class, $fh) = @_;
		819
		820	$class->_new ($fh)
		821	}
		822
251	=back	823	=back
252		824
253	=head1 AUTHOR	825	=head1 PERFORMANCE
		826
		827	Now for some unscientific benchmark numbers (all done on an amd64
		828	GNU/Linux box). These are intended to give you an idea of the relative
		829	performance you can expect, they are not meant to be absolute performance
		830	numbers.
		831
		832	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		833	exit in the child and waits for the socket to close in the parent. I did
		834	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		835
		836	2079 new processes per second, using manual socketpair + fork
		837
		838	Then I did the same thing, but instead of calling fork, I called
		839	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		840	socket from the child to close on exit. This does the same thing as manual
		841	socket pair + fork, except that what is forked is the template process
		842	(2440kB), and the socket needs to be passed to the server at the other end
		843	of the socket first.
		844
		845	2307 new processes per second, using AnyEvent::Fork->new
		846
		847	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		848	a new perl interpreter and compile the small server each time, I get:
		849
		850	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		851
		852	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		853	though it uses the same operations, but adds a lot of overhead?
		854
		855	The difference is simply the process size: forking the 5MB process takes
		856	so much longer than forking the 2.5MB template process that the extra
		857	overhead is canceled out.
		858
		859	If the benchmark process grows, the normal fork becomes even slower:
		860
		861	1340 new processes, manual fork of a 20MB process
		862	731 new processes, manual fork of a 200MB process
		863	235 new processes, manual fork of a 2000MB process
		864
		865	What that means (to me) is that I can use this module without having a bad
		866	conscience because of the extra overhead required to start new processes.
		867
		868	=head1 TYPICAL PROBLEMS
		869
		870	This section lists typical problems that remain. I hope by recognising
		871	them, most can be avoided.
		872
		873	=over 4
		874
		875	=item leaked file descriptors for exec'ed processes
		876
		877	POSIX systems inherit file descriptors by default when exec'ing a new
		878	process. While perl itself laudably sets the close-on-exec flags on new
		879	file handles, most C libraries don't care, and even if all cared, it's
		880	often not possible to set the flag in a race-free manner.
		881
		882	That means some file descriptors can leak through. And since it isn't
		883	possible to know which file descriptors are "good" and "necessary" (or
		884	even to know which file descriptors are open), there is no good way to
		885	close the ones that might harm.
		886
		887	As an example of what "harm" can be done consider a web server that
		888	accepts connections and afterwards some module uses AnyEvent::Fork for the
		889	first time, causing it to fork and exec a new process, which might inherit
		890	the network socket. When the server closes the socket, it is still open
		891	in the child (which doesn't even know that) and the client might conclude
		892	that the connection is still fine.
		893
		894	For the main program, there are multiple remedies available -
		895	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		896	C<new_exec> is another, as in both cases, the first process can be exec'ed
		897	well before many random file descriptors are open.
		898
		899	In general, the solution for these kind of problems is to fix the
		900	libraries or the code that leaks those file descriptors.
		901
		902	Fortunately, most of these leaked descriptors do no harm, other than
		903	sitting on some resources.
		904
		905	=item leaked file descriptors for fork'ed processes
		906
		907	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		908	which closes file descriptors not marked for being inherited.
		909
		910	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		911	a way to create these processes by forking, and this leaks more file
		912	descriptors than exec'ing them, as there is no way to mark descriptors as
		913	"close on fork".
		914
		915	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		916	pipes for internal uses, and L<Gtk2> might open a connection to the X
		917	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		918	trouble with a fork.
		919
		920	The solution is to either not load these modules before use'ing
		921	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		922	initialising them, for example, by calling C<init Gtk2> manually.
		923
		924	=item exiting calls object destructors
		925
		926	This only applies to users of L<AnyEvent::Fork:Early> and
		927	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		928	that reference external resources.
		929
		930	When a process created by AnyEvent::Fork exits, it might do so by calling
		931	exit, or simply letting perl reach the end of the program. At which point
		932	Perl runs all destructors.
		933
		934	Not all destructors are fork-safe - for example, an object that represents
		935	the connection to an X display might tell the X server to free resources,
		936	which is inconvenient when the "real" object in the parent still needs to
		937	use them.
		938
		939	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		940	it as the very first thing, right?
		941
		942	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		943	is to not create objects with nontrivial destructors that might have an
		944	effect outside of Perl.
		945
		946	=back
		947
		948	=head1 PORTABILITY NOTES
		949
		950	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
		951	and ::Template is not going to work), and it cost a lot of blood and sweat
		952	to make it so, mostly due to the bloody broken perl that nobody seems to
		953	care about. The fork emulation is a bad joke - I have yet to see something
		954	useful that you can do with it without running into memory corruption
		955	issues or other braindamage. Hrrrr.
		956
		957	Cygwin perl is not supported at the moment due to some hilarious
		958	shortcomings of its API - see L<IO::FDPoll> for more details.
		959
		960	=head1 SEE ALSO
		961
		962	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		963	(part of this distribution).
		964
		965	L<AnyEvent::Fork::Template>, to create a process by forking the main
		966	program at a convenient time (part of this distribution).
		967
		968	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		969
		970	=head1 AUTHOR AND CONTACT INFORMATION
254		971
255	Marc Lehmann <schmorp@schmorp.de>	972	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	973	http://software.schmorp.de/pkg/AnyEvent-Fork
257		974
258	=cut	975	=cut
259		976
260	1	977	1
261		978

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Revision 1.48 by root, Fri Apr 19 10:51:41 2013 UTC