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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs.
Revision 1.48 by root, Fri Apr 19 10:51:41 2013 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	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
10	# 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.
11		167
12	AnyEvent::Fork	168	AnyEvent::Fork
13	->new	169	->new
14	->require ("MyModule")	170	->require ("MyModule")
15	->run ("MyModule::worker, sub {	171	->run ("MyModule::worker, sub {
…		…
17		173
18	# now $master_filehandle is connected to the	174	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	175	# $slave_filehandle in the new process.
20	});	176	});
21		177
22	# MyModule::worker might look like this	178	C<MyModule> might look like this:
		179
		180	package MyModule;
		181
23	sub MyModule::worker {	182	sub worker {
24	my ($slave_filehandle) = @_;	183	my ($slave_filehandle) = @_;
25		184
26	# now $slave_filehandle is connected to the $master_filehandle	185	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	186	# in the original prorcess. have fun!
28	}	187	}
29		188
30	##################################################################
31	# 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.
32		190
33	# create listener socket	191	# create listener socket
34	my $listener = ...;	192	my $listener = ...;
35		193
36	# create a pool template, initialise it and give it the socket	194	# create a pool template, initialise it and give it the socket
…		…
48	}	206	}
49		207
50	# now do other things - maybe use the filehandle provided by run	208	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	209	# to wait for the processes to die. or whatever.
52		210
53	# My::Server::run might look like this	211	C<My::Server> might look like this:
54	sub My::Server::run {	212
		213	package My::Server;
		214
		215	sub run {
55	my ($slave, $listener, $id) = @_;	216	my ($slave, $listener, $id) = @_;
56		217
57	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
58		219
59	# 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,
…		…
61	while (my $socket = $listener->accept) {	222	while (my $socket = $listener->accept) {
62	# do sth. with new socket	223	# do sth. with new socket
63	}	224	}
64	}	225	}
65		226
66	=head1 DESCRIPTION	227	=head2 use AnyEvent::Fork as a faster fork+exec
67		228
68	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>
69	them from your current process (avoiding the problems of forking), but	230	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	231	faster than fork+exec, but still lets you prepare the environment.
71		232
72	It can be used to create new worker processes or new independent	233	open my $output, ">/tmp/log" or die "$!";
73	subprocesses for short- and long-running jobs, process pools (e.g. for use
74	in pre-forked servers) but also to spawn new external processes (such as
75	CGI scripts from a web server), which can be faster (and more well behaved)
76	than using fork+exec in big processes.
77		234
78	Special care has been taken to make this module useful from other modules,	235	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	236	->new
80	or L<PAR::Packer>.	237	->eval ('
		238	# compile a helper function for later use
		239	sub run {
		240	my ($fh, $output, @cmd) = @_;
81		241
82	=head1 WHAT THIS MODULE IS NOT	242	# perl will clear close-on-exec on STDOUT/STDERR
		243	open STDOUT, ">&", $output or die;
		244	open STDERR, ">&", $fh or die;
83		245
84	This module only creates processes and lets you pass file handles and	246	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	247	}
86	there is no back channel from the process back to you, and there is no RPC	248	')
87	or message passing going on.	249	->send_fh ($output)
		250	->send_arg ("/bin/echo", "hi")
		251	->run ("run", my $cv = AE::cv);
88		252
89	If you need some form of RPC, you can either implement it yourself	253	my $stderr = $cv->recv;
90	in whatever way you like, use some message-passing module such
91	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
92	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
93	and so on.
94
95	=head1 PROBLEM STATEMENT
96
97	There are two ways to implement parallel processing on UNIX like operating
98	systems - fork and process, and fork+exec and process. They have different
99	advantages and disadvantages that I describe below, together with how this
100	module tries to mitigate the disadvantages.
101
102	=over 4
103
104	=item Forking from a big process can be very slow (a 5GB process needs
105	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
106	is often shared with exec (because you have to fork first), but in some
107	circumstances (e.g. when vfork is used), fork+exec can be much faster.
108
109	This module can help here by telling a small(er) helper process to fork,
110	or fork+exec instead.
111
112	=item Forking usually creates a copy-on-write copy of the parent
113	process. Memory (for example, modules or data files that have been
114	will not take additional memory). When exec'ing a new process, modules
115	and data files might need to be loaded again, at extra CPU and memory
116	cost. Likewise when forking, all data structures are copied as well - if
117	the program frees them and replaces them by new data, the child processes
118	will retain the memory even if it isn't used.
119
120	This module allows the main program to do a controlled fork, and allows
121	modules to exec processes safely at any time. When creating a custom
122	process pool you can take advantage of data sharing via fork without
123	risking to share large dynamic data structures that will blow up child
124	memory usage.
125
126	=item Exec'ing a new perl process might be difficult and slow. For
127	example, it is not easy to find the correct path to the perl interpreter,
128	and all modules have to be loaded from disk again. Long running processes
129	might run into problems when perl is upgraded for example.
130
131	This module supports creating pre-initialised perl processes to be used
132	as template, and also tries hard to identify the correct path to the perl
133	interpreter. With a cooperative main program, exec'ing the interpreter
134	might not even be necessary.
135
136	=item Forking might be impossible when a program is running. For example,
137	POSIX makes it almost impossible to fork from a multi-threaded program and
138	do anything useful in the child - strictly speaking, if your perl program
139	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
140	you cannot call fork on the perl level anymore, at all.
141
142	This module can safely fork helper processes at any time, by calling
143	fork+exec in C, in a POSIX-compatible way.
144
145	=item Parallel processing with fork might be inconvenient or difficult
146	to implement. For example, when a program uses an event loop and creates
147	watchers it becomes very hard to use the event loop from a child
148	program, as the watchers already exist but are only meaningful in the
149	parent. Worse, a module might want to use such a system, not knowing
150	whether another module or the main program also does, leading to problems.
151
152	This module only lets the main program create pools by forking (because
153	only the main program can know when it is still safe to do so) - all other
154	pools are created by fork+exec, after which such modules can again be
155	loaded.
156
157	=back
158		254
159	=head1 CONCEPTS	255	=head1 CONCEPTS
160		256
161	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
162	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".
163		263
164	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
165	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,
166	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
167	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
…		…
241	my ($fork_fh) = @_;	341	my ($fork_fh) = @_;
242	});	342	});
243		343
244	=back	344	=back
245		345
246	=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.
247		366
248	=over 4	367	=over 4
249		368
250	=cut	369	=cut
251		370
…		…
258	use AnyEvent;	377	use AnyEvent;
259	use AnyEvent::Util ();	378	use AnyEvent::Util ();
260		379
261	use IO::FDPass;	380	use IO::FDPass;
262		381
263	our $VERSION = 0.2;	382	our $VERSION = 0.7;
264
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267	=item my $pool = new AnyEvent::Fork key => value...
268
269	Create a new process pool. The following named parameters are supported:
270
271	=over 4
272
273	=back
274
275	=cut
276		383
277	# the early fork template process	384	# the early fork template process
278	our $EARLY;	385	our $EARLY;
279		386
280	# the empty template process	387	# the empty template process
281	our $TEMPLATE;	388	our $TEMPLATE;
		389
		390	sub QUEUE() { 0 }
		391	sub FH() { 1 }
		392	sub WW() { 2 }
		393	sub PID() { 3 }
		394	sub CB() { 4 }
		395
		396	sub _new {
		397	my ($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	}
282		410
283	sub _cmd {	411	sub _cmd {
284	my $self = shift;	412	my $self = shift;
285		413
286	# ideally, we would want to use "a (w/a)*" as format string, but perl	414	# ideally, we would want to use "a (w/a)*" as format string, but perl
287	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack	415	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
288	# it.	416	# it.
289	push @{ $self->[2] }, pack "L/a", pack "(w/a)*", @_;	417	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
290		418
291	unless ($self->[3]) {	419	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
292	my $wcb = sub {
293	do {	420	do {
294	# 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,
295	# or a plain string.	422	# or a plain string.
296		423
297	if (ref $self->[2][0]) {	424	if (ref $self->[QUEUE][0]) {
298	# send fh	425	# send fh
299	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	426	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
300	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	427	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
301	undef $self->[3];	428	undef $self->[WW];
302	die "AnyEvent::Fork: file descriptor send failure: $!";	429	die "AnyEvent::Fork: file descriptor send failure: $!";
303	}
304
305	shift @{ $self->[2] };
306
307	} else {
308	# send string
309	my $len = syswrite $self->[1], $self->[2][0];
310
311	unless ($len) {
312	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
313	undef $self->[3];
314	die "AnyEvent::Fork: command write failure: $!";
315	}
316
317	substr $self->[2][0], 0, $len, "";
318	shift @{ $self->[2] } unless length $self->[2][0];
319	}	430	}
		431
		432	shift @{ $self->[QUEUE] };
		433
		434	} else {
		435	# send string
		436	my $len = syswrite $self->[FH], $self->[QUEUE][0];
		437
		438	unless ($len) {
		439	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		440	undef $self->[3];
		441	die "AnyEvent::Fork: command write failure: $!";
		442	}
		443
		444	substr $self->[QUEUE][0], 0, $len, "";
		445	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
		446	}
320	} while @{ $self->[2] };	447	} while @{ $self->[QUEUE] };
321		448
322	# everything written	449	# everything written
323	undef $self->[3];	450	undef $self->[WW];
		451
324	# invoke run callback	452	# invoke run callback, if any
		453	if ($self->[CB]) {
325	$self->[0]->($self->[1]) if $self->[0];	454	$self->[CB]->($self->[FH]);
		455	@$self = ();
326	};	456	}
327
328	$wcb->();
329
330	$self->[3] \|\|= AE::io $self->[1], 1, $wcb
331	if @{ $self->[2] };
332	}	457	};
333		458
334	() # make sure we don't leak the watcher	459	() # make sure we don't leak the watcher
335	}
336
337	sub _new {
338	my ($self, $fh) = @_;
339
340	AnyEvent::Util::fh_nonblocking $fh, 1;
341
342	$self = bless [
343	undef, # run callback
344	$fh,
345	[], # write queue - strings or fd's
346	undef, # AE watcher
347	], $self;
348
349	$self
350	}	460	}
351		461
352	# fork template from current process, used by AnyEvent::Fork::Early/Template	462	# fork template from current process, used by AnyEvent::Fork::Early/Template
353	sub _new_fork {	463	sub _new_fork {
354	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	464	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
359	if ($pid eq 0) {	469	if ($pid eq 0) {
360	require AnyEvent::Fork::Serve;	470	require AnyEvent::Fork::Serve;
361	$AnyEvent::Fork::Serve::OWNER = $parent;	471	$AnyEvent::Fork::Serve::OWNER = $parent;
362	close $fh;	472	close $fh;
363	$0 = "$_[1] of $parent";	473	$0 = "$_[1] of $parent";
364	$SIG{CHLD} = 'IGNORE';
365	AnyEvent::Fork::Serve::serve ($slave);	474	AnyEvent::Fork::Serve::serve ($slave);
366	exit 0;	475	exit 0;
367	} elsif (!$pid) {	476	} elsif (!$pid) {
368	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	477	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
369	}	478	}
370		479
371	AnyEvent::Fork->_new ($fh)	480	AnyEvent::Fork->_new ($fh, $pid)
372	}	481	}
373		482
374	=item my $proc = new AnyEvent::Fork	483	=item my $proc = new AnyEvent::Fork
375		484
376	Create a new "empty" perl interpreter process and returns its process	485	Create a new "empty" perl interpreter process and returns its process
377	object for further manipulation.	486	object for further manipulation.
378		487
379	The new process is forked from a template process that is kept around	488	The new process is forked from a template process that is kept around
380	for this purpose. When it doesn't exist yet, it is created by a call to	489	for this purpose. When it doesn't exist yet, it is created by a call to
381	C<new_exec> and kept around for future calls.	490	C<new_exec> first and then stays around for future calls.
382
383	When the process object is destroyed, it will release the file handle
384	that connects it with the new process. When the new process has not yet
385	called C<run>, then the process will exit. Otherwise, what happens depends
386	entirely on the code that is executed.
387		491
388	=cut	492	=cut
389		493
390	sub new {	494	sub new {
391	my $class = shift;	495	my $class = shift;
…		…
469	# quick. also doesn't work in win32. of course. what did you expect	573	# quick. also doesn't work in win32. of course. what did you expect
470	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	574	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
471	my %env = %ENV;	575	my %env = %ENV;
472	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	576	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
473		577
474	Proc::FastSpawn::spawn (	578	my $pid = Proc::FastSpawn::spawn (
475	$perl,	579	$perl,
476	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	580	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
477	[map "$_=$env{$_}", keys %env],	581	[map "$_=$env{$_}", keys %env],
478	) or die "unable to spawn AnyEvent::Fork server: $!";	582	) or die "unable to spawn AnyEvent::Fork server: $!";
479		583
480	$self->_new ($fh)	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]
481	}	603	}
482		604
483	=item $proc = $proc->eval ($perlcode, @args)	605	=item $proc = $proc->eval ($perlcode, @args)
484		606
485	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	607	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
486	the strings specified by C<@args>.	608	the strings specified by C<@args>, in the "main" package.
487		609
488	This call is meant to do any custom initialisation that might be required	610	This call is meant to do any custom initialisation that might be required
489	(for example, the C<require> method uses it). It's not supposed to be used	611	(for example, the C<require> method uses it). It's not supposed to be used
490	to completely take over the process, use C<run> for that.	612	to completely take over the process, use C<run> for that.
491		613
492	The code will usually be executed after this call returns, and there is no	614	The code will usually be executed after this call returns, and there is no
493	way to pass anything back to the calling process. Any evaluation errors	615	way to pass anything back to the calling process. Any evaluation errors
494	will be reported to stderr and cause the process to exit.	616	will be reported to stderr and cause the process to exit.
495		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
496	Returns the process object for easy chaining of method calls.	624	Returns the process object for easy chaining of method calls.
497		625
498	=cut	626	=cut
499		627
500	sub eval {	628	sub eval {
501	my ($self, $code, @args) = @_;	629	my ($self, $code, @args) = @_;
502		630
503	$self->_cmd (e => $code, @args);	631	$self->_cmd (e => pack "(w/a)", $code, @args);
504		632
505	$self	633	$self
506	}	634	}
507		635
508	=item $proc = $proc->require ($module, ...)	636	=item $proc = $proc->require ($module, ...)
…		…
525	=item $proc = $proc->send_fh ($handle, ...)	653	=item $proc = $proc->send_fh ($handle, ...)
526		654
527	Send one or more file handles (I<not> file descriptors) to the process,	655	Send one or more file handles (I<not> file descriptors) to the process,
528	to prepare a call to C<run>.	656	to prepare a call to C<run>.
529		657
530	The process object keeps a reference to the handles until this is done,	658	The process object keeps a reference to the handles until they have
531	so you must not explicitly close the handles. This is most easily	659	been passed over to the process, so you must not explicitly close the
532	accomplished by simply not storing the file handles anywhere after passing	660	handles. This is most easily accomplished by simply not storing the file
533	them to this method.	661	handles anywhere after passing them to this method - when AnyEvent::Fork
		662	is finished using them, perl will automatically close them.
534		663
535	Returns the process object for easy chaining of method calls.	664	Returns the process object for easy chaining of method calls.
536		665
537	Example: pass a file handle to a process, and release it without	666	Example: pass a file handle to a process, and release it without
538	closing. It will be closed automatically when it is no longer used.	667	closing. It will be closed automatically when it is no longer used.
…		…
545	sub send_fh {	674	sub send_fh {
546	my ($self, @fh) = @_;	675	my ($self, @fh) = @_;
547		676
548	for my $fh (@fh) {	677	for my $fh (@fh) {
549	$self->_cmd ("h");	678	$self->_cmd ("h");
550	push @{ $self->[2] }, \$fh;	679	push @{ $self->[QUEUE] }, \$fh;
551	}	680	}
552		681
553	$self	682	$self
554	}	683	}
555		684
556	=item $proc = $proc->send_arg ($string, ...)	685	=item $proc = $proc->send_arg ($string, ...)
557		686
558	Send one or more argument strings to the process, to prepare a call to	687	Send one or more argument strings to the process, to prepare a call to
559	C<run>. The strings can be any octet string.	688	C<run>. The strings can be any octet strings.
560		689
561	The protocol is optimised to pass a moderate number of relatively short	690	The protocol is optimised to pass a moderate number of relatively short
562	strings - while you can pass up to 4GB of data in one go, this is more	691	strings - while you can pass up to 4GB of data in one go, this is more
563	meant to pass some ID information or other startup info, not big chunks of	692	meant to pass some ID information or other startup info, not big chunks of
564	data.	693	data.
…		…
568	=cut	697	=cut
569		698
570	sub send_arg {	699	sub send_arg {
571	my ($self, @arg) = @_;	700	my ($self, @arg) = @_;
572		701
573	$self->_cmd (a => @arg);	702	$self->_cmd (a => pack "(w/a)", @arg);
574		703
575	$self	704	$self
576	}	705	}
577		706
578	=item $proc->run ($func, $cb->($fh))	707	=item $proc->run ($func, $cb->($fh))
579		708
580	Enter the function specified by the fully qualified name in C<$func> in	709	Enter the function specified by the function name in C<$func> in the
581	the process. The function is called with the communication socket as first	710	process. The function is called with the communication socket as first
582	argument, followed by all file handles and string arguments sent earlier	711	argument, followed by all file handles and string arguments sent earlier
583	via C<send_fh> and C<send_arg> methods, in the order they were called.	712	via C<send_fh> and C<send_arg> methods, in the order they were called.
584		713
585	If the called function returns, the process exits.
586
587	Preparing the process can take time - when the process is ready, the
588	callback is invoked with the local communications socket as argument.
589
590	The process object becomes unusable on return from this function.	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.
591		727
592	If the communication socket isn't used, it should be closed on both sides,	728	If the communication socket isn't used, it should be closed on both sides,
593	to save on kernel memory.	729	to save on kernel memory.
594		730
595	The socket is non-blocking in the parent, and blocking in the newly	731	The socket is non-blocking in the parent, and blocking in the newly
596	created process. The close-on-exec flag is set on both. Even if not used	732	created process. The close-on-exec flag is set in both.
		733
597	otherwise, the socket can be a good indicator for the existence of the	734	Even if not used otherwise, the socket can be a good indicator for the
598	process - if the other process exits, you get a readable event on it,	735	existence of the process - if the other process exits, you get a readable
599	because exiting the process closes the socket (if it didn't create any	736	event on it, because exiting the process closes the socket (if it didn't
600	children using fork).	737	create any children using fork).
601		738
602	Example: create a template for a process pool, pass a few strings, some	739	Example: create a template for a process pool, pass a few strings, some
603	file handles, then fork, pass one more string, and run some code.	740	file handles, then fork, pass one more string, and run some code.
604		741
605	my $pool = AnyEvent::Fork	742	my $pool = AnyEvent::Fork
…		…
613	->send_arg ("str3")	750	->send_arg ("str3")
614	->run ("Some::function", sub {	751	->run ("Some::function", sub {
615	my ($fh) = @_;	752	my ($fh) = @_;
616		753
617	# fh is nonblocking, but we trust that the OS can accept these	754	# fh is nonblocking, but we trust that the OS can accept these
618	# extra 3 octets anyway.	755	# few octets anyway.
619	syswrite $fh, "hi #$_\n";	756	syswrite $fh, "hi #$_\n";
620		757
621	# $fh is being closed here, as we don't store it anywhere	758	# $fh is being closed here, as we don't store it anywhere
622	});	759	});
623	}	760	}
…		…
625	# Some::function might look like this - all parameters passed before fork	762	# Some::function might look like this - all parameters passed before fork
626	# and after will be passed, in order, after the communications socket.	763	# and after will be passed, in order, after the communications socket.
627	sub Some::function {	764	sub Some::function {
628	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	765	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
629		766
630	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	767	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
631	}	768	}
632		769
633	=cut	770	=cut
634		771
635	sub run {	772	sub run {
636	my ($self, $func, $cb) = @_;	773	my ($self, $func, $cb) = @_;
637		774
638	$self->[0] = $cb;	775	$self->[CB] = $cb;
639	$self->_cmd (r => $func);	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)
640	}	821	}
641		822
642	=back	823	=back
643		824
644	=head1 PERFORMANCE	825	=head1 PERFORMANCE
…		…
654		835
655	2079 new processes per second, using manual socketpair + fork	836	2079 new processes per second, using manual socketpair + fork
656		837
657	Then I did the same thing, but instead of calling fork, I called	838	Then I did the same thing, but instead of calling fork, I called
658	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the	839	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
659	socket form the child to close on exit. This does the same thing as manual	840	socket from the child to close on exit. This does the same thing as manual
660	socket pair + fork, except that what is forked is the template process	841	socket pair + fork, except that what is forked is the template process
661	(2440kB), and the socket needs to be passed to the server at the other end	842	(2440kB), and the socket needs to be passed to the server at the other end
662	of the socket first.	843	of the socket first.
663		844
664	2307 new processes per second, using AnyEvent::Fork->new	845	2307 new processes per second, using AnyEvent::Fork->new
…		…
669	479 vfork+execs per second, using AnyEvent::Fork->new_exec	850	479 vfork+execs per second, using AnyEvent::Fork->new_exec
670		851
671	So how can C<< AnyEvent->new >> be faster than a standard fork, even	852	So how can C<< AnyEvent->new >> be faster than a standard fork, even
672	though it uses the same operations, but adds a lot of overhead?	853	though it uses the same operations, but adds a lot of overhead?
673		854
674	The difference is simply the process size: forking the 6MB process takes	855	The difference is simply the process size: forking the 5MB process takes
675	so much longer than forking the 2.5MB template process that the overhead	856	so much longer than forking the 2.5MB template process that the extra
676	introduced is canceled out.	857	overhead is canceled out.
677		858
678	If the benchmark process grows, the normal fork becomes even slower:	859	If the benchmark process grows, the normal fork becomes even slower:
679		860
680	1340 new processes, manual fork in a 20MB process	861	1340 new processes, manual fork of a 20MB process
681	731 new processes, manual fork in a 200MB process	862	731 new processes, manual fork of a 200MB process
682	235 new processes, manual fork in a 2000MB process	863	235 new processes, manual fork of a 2000MB process
683		864
684	What that means (to me) is that I can use this module without having a	865	What that means (to me) is that I can use this module without having a bad
685	very bad conscience because of the extra overhead required to start new	866	conscience because of the extra overhead required to start new processes.
686	processes.
687		867
688	=head1 TYPICAL PROBLEMS	868	=head1 TYPICAL PROBLEMS
689		869
690	This section lists typical problems that remain. I hope by recognising	870	This section lists typical problems that remain. I hope by recognising
691	them, most can be avoided.	871	them, most can be avoided.
692		872
693	=over 4	873	=over 4
694		874
695	=item exit runs destructors
696
697	=item "leaked" file descriptors for exec'ed processes	875	=item leaked file descriptors for exec'ed processes
698		876
699	POSIX systems inherit file descriptors by default when exec'ing a new	877	POSIX systems inherit file descriptors by default when exec'ing a new
700	process. While perl itself laudably sets the close-on-exec flags on new	878	process. While perl itself laudably sets the close-on-exec flags on new
701	file handles, most C libraries don't care, and even if all cared, it's	879	file handles, most C libraries don't care, and even if all cared, it's
702	often not possible to set the flag in a race-free manner.	880	often not possible to set the flag in a race-free manner.
…		…
722	libraries or the code that leaks those file descriptors.	900	libraries or the code that leaks those file descriptors.
723		901
724	Fortunately, most of these leaked descriptors do no harm, other than	902	Fortunately, most of these leaked descriptors do no harm, other than
725	sitting on some resources.	903	sitting on some resources.
726		904
727	=item "leaked" file descriptors for fork'ed processes	905	=item leaked file descriptors for fork'ed processes
728		906
729	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	907	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
730	which closes file descriptors not marked for being inherited.	908	which closes file descriptors not marked for being inherited.
731		909
732	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	910	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
740	trouble with a fork.	918	trouble with a fork.
741		919
742	The solution is to either not load these modules before use'ing	920	The solution is to either not load these modules before use'ing
743	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	921	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
744	initialising them, for example, by calling C<init Gtk2> manually.	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.
745		945
746	=back	946	=back
747		947
748	=head1 PORTABILITY NOTES	948	=head1 PORTABILITY NOTES
749		949
…		…
752	to make it so, mostly due to the bloody broken perl that nobody seems to	952	to make it so, mostly due to the bloody broken perl that nobody seems to
753	care about. The fork emulation is a bad joke - I have yet to see something	953	care about. The fork emulation is a bad joke - I have yet to see something
754	useful that you can do with it without running into memory corruption	954	useful that you can do with it without running into memory corruption
755	issues or other braindamage. Hrrrr.	955	issues or other braindamage. Hrrrr.
756		956
757	Cygwin perl is not supported at the moment, as it should implement fd	957	Cygwin perl is not supported at the moment due to some hilarious
758	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	958	shortcomings of its API - see L<IO::FDPoll> for more details.
759	support enough functionality to do it.
760		959
761	=head1 SEE ALSO	960	=head1 SEE ALSO
762		961
763	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	962	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		963	(part of this distribution).
		964
764	L<AnyEvent::Fork::Template> (to create a process by forking the main	965	L<AnyEvent::Fork::Template>, to create a process by forking the main
765	program at a convenient time).	966	program at a convenient time (part of this distribution).
766		967
767	=head1 AUTHOR	968	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		969
		970	=head1 AUTHOR AND CONTACT INFORMATION
768		971
769	Marc Lehmann <schmorp@schmorp.de>	972	Marc Lehmann <schmorp@schmorp.de>
770	http://home.schmorp.de/	973	http://software.schmorp.de/pkg/AnyEvent-Fork
771		974
772	=cut	975	=cut
773		976
774	1	977	1
775		978

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs. Revision 1.48 by root, Fri Apr 19 10:51:41 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.18 by root, Sat Apr 6 01:33:56 2013 UTC vs.
Revision 1.48 by root, Fri Apr 19 10:51:41 2013 UTC