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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 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	And if you need some automatic process pool management on top of
		44	L<AnyEvent::Fork::RPC>, you can look at the L<AnyEvent::Fork::Pool>
		45	companion module.
		46
		47	Or you can implement it yourself in whatever way you like: use some
		48	message-passing module such as L<AnyEvent::MP>, some pipe such as
		49	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		50	e.g. JSON or Storable messages, and so on.
		51
		52	=head2 COMPARISON TO OTHER MODULES
		53
		54	There is an abundance of modules on CPAN that do "something fork", such as
		55	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		56	or L<AnyEvent::Subprocess>. There are modules that implement their own
		57	process management, such as L<AnyEvent::DBI>.
		58
		59	The problems that all these modules try to solve are real, however, none
		60	of them (from what I have seen) tackle the very real problems of unwanted
		61	memory sharing, efficiency, not being able to use event processing or
		62	similar modules in the processes they create.
		63
		64	This module doesn't try to replace any of them - instead it tries to solve
		65	the problem of creating processes with a minimum of fuss and overhead (and
		66	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		67	except they were written before AnyEvent:Fork was available, so obviously
		68	had to roll their own.
		69
		70	=head2 PROBLEM STATEMENT
		71
		72	There are two traditional ways to implement parallel processing on UNIX
		73	like operating systems - fork and process, and fork+exec and process. They
		74	have different advantages and disadvantages that I describe below,
		75	together with how this module tries to mitigate the disadvantages.
		76
		77	=over 4
		78
		79	=item Forking from a big process can be very slow.
		80
		81	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		82	overhead is often shared with exec (because you have to fork first), but
		83	in some circumstances (e.g. when vfork is used), fork+exec can be much
		84	faster.
		85
		86	This module can help here by telling a small(er) helper process to fork,
		87	which is faster then forking the main process, and also uses vfork where
		88	possible. This gives the speed of vfork, with the flexibility of fork.
		89
		90	=item Forking usually creates a copy-on-write copy of the parent
		91	process.
		92
		93	For example, modules or data files that are loaded will not use additional
		94	memory after a fork. When exec'ing a new process, modules and data files
		95	might need to be loaded again, at extra CPU and memory cost. But when
		96	forking, literally all data structures are copied - if the program frees
		97	them and replaces them by new data, the child processes will retain the
		98	old version even if it isn't used, which can suddenly and unexpectedly
		99	increase memory usage when freeing memory.
		100
		101	The trade-off is between more sharing with fork (which can be good or
		102	bad), and no sharing with exec.
		103
		104	This module allows the main program to do a controlled fork, and allows
		105	modules to exec processes safely at any time. When creating a custom
		106	process pool you can take advantage of data sharing via fork without
		107	risking to share large dynamic data structures that will blow up child
		108	memory usage.
		109
		110	In other words, this module puts you into control over what is being
		111	shared and what isn't, at all times.
		112
		113	=item Exec'ing a new perl process might be difficult.
		114
		115	For example, it is not easy to find the correct path to the perl
		116	interpreter - C<$^X> might not be a perl interpreter at all.
		117
		118	This module tries hard to identify the correct path to the perl
		119	interpreter. With a cooperative main program, exec'ing the interpreter
		120	might not even be necessary, but even without help from the main program,
		121	it will still work when used from a module.
		122
		123	=item Exec'ing a new perl process might be slow, as all necessary modules
		124	have to be loaded from disk again, with no guarantees of success.
		125
		126	Long running processes might run into problems when perl is upgraded
		127	and modules are no longer loadable because they refer to a different
		128	perl version, or parts of a distribution are newer than the ones already
		129	loaded.
		130
		131	This module supports creating pre-initialised perl processes to be used as
		132	a template for new processes.
		133
		134	=item Forking might be impossible when a program is running.
		135
		136	For example, POSIX makes it almost impossible to fork from a
		137	multi-threaded program while doing anything useful in the child - in
		138	fact, if your perl program uses POSIX threads (even indirectly via
		139	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		140	anymore without risking corruption issues on a number of operating
		141	systems.
		142
		143	This module can safely fork helper processes at any time, by calling
		144	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		145
		146	=item Parallel processing with fork might be inconvenient or difficult
		147	to implement. Modules might not work in both parent and child.
		148
		149	For example, when a program uses an event loop and creates watchers it
		150	becomes very hard to use the event loop from a child program, as the
		151	watchers already exist but are only meaningful in the parent. Worse, a
		152	module might want to use such a module, not knowing whether another module
		153	or the main program also does, leading to problems.
		154
		155	Apart from event loops, graphical toolkits also commonly fall into the
		156	"unsafe module" category, or just about anything that communicates with
		157	the external world, such as network libraries and file I/O modules, which
		158	usually don't like being copied and then allowed to continue in two
		159	processes.
		160
		161	With this module only the main program is allowed to create new processes
		162	by forking (because only the main program can know when it is still safe
		163	to do so) - all other processes are created via fork+exec, which makes it
		164	possible to use modules such as event loops or window interfaces safely.
		165
		166	=back
		167
		168	=head1 EXAMPLES
		169
10	# create a single new process, tell it to run your worker function	170	=head2 Create a single new process, tell it to run your worker function.
11		171
12	AnyEvent::Fork	172	AnyEvent::Fork
13	->new	173	->new
14	->require ("MyModule")	174	->require ("MyModule")
15	->run ("MyModule::worker, sub {	175	->run ("MyModule::worker, sub {
…		…
17		177
18	# now $master_filehandle is connected to the	178	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	179	# $slave_filehandle in the new process.
20	});	180	});
21		181
22	# MyModule::worker might look like this	182	C<MyModule> might look like this:
		183
		184	package MyModule;
		185
23	sub MyModule::worker {	186	sub worker {
24	my ($slave_filehandle) = @_;	187	my ($slave_filehandle) = @_;
25		188
26	# now $slave_filehandle is connected to the $master_filehandle	189	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	190	# in the original prorcess. have fun!
28	}	191	}
29		192
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	193	=head2 Create a pool of server processes all accepting on the same socket.
32		194
33	# create listener socket	195	# create listener socket
34	my $listener = ...;	196	my $listener = ...;
35		197
36	# create a pool template, initialise it and give it the socket	198	# create a pool template, initialise it and give it the socket
…		…
48	}	210	}
49		211
50	# now do other things - maybe use the filehandle provided by run	212	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	213	# to wait for the processes to die. or whatever.
52		214
53	# My::Server::run might look like this	215	C<My::Server> might look like this:
54	sub My::Server::run {	216
		217	package My::Server;
		218
		219	sub run {
55	my ($slave, $listener, $id) = @_;	220	my ($slave, $listener, $id) = @_;
56		221
57	close $slave; # we do not use the socket, so close it to save resources	222	close $slave; # we do not use the socket, so close it to save resources
58		223
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	224	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	226	while (my $socket = $listener->accept) {
62	# do sth. with new socket	227	# do sth. with new socket
63	}	228	}
64	}	229	}
65		230
66	##################################################################
67	# use AnyEvent::Fork as a faster fork+exec	231	=head2 use AnyEvent::Fork as a faster fork+exec
68		232
69	# this runs /bin/echo hi, with stdout redirected to /tmp/log	233	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
70	# and stderr to the communications socket. it is usually faster	234	and standard error redirected to the communications socket. It is usually
71	# than fork+exec, but still let's you prepare the environment.	235	faster than fork+exec, but still lets you prepare the environment.
72		236
73	open my $output, ">/tmp/log" or die "$!";	237	open my $output, ">/tmp/log" or die "$!";
74		238
75	AnyEvent::Fork	239	AnyEvent::Fork
76	->new	240	->new
77	->eval ('	241	->eval ('
		242	# compile a helper function for later use
78	sub run {	243	sub run {
79	my ($fh, $output, @cmd) = @_;	244	my ($fh, $output, @cmd) = @_;
80		245
81	# perl will clear close-on-exec on STDOUT/STDERR	246	# perl will clear close-on-exec on STDOUT/STDERR
82	open STDOUT, ">&", $output or die;	247	open STDOUT, ">&", $output or die;
…		…
89	->send_arg ("/bin/echo", "hi")	254	->send_arg ("/bin/echo", "hi")
90	->run ("run", my $cv = AE::cv);	255	->run ("run", my $cv = AE::cv);
91		256
92	my $stderr = $cv->recv;	257	my $stderr = $cv->recv;
93		258
94	=head1 DESCRIPTION	259	=head2 For stingy users: put the worker code into a C<DATA> section.
95		260
96	This module allows you to create new processes, without actually forking	261	When you want to be stingy with files, you cna put your code into the
97	them from your current process (avoiding the problems of forking), but	262	C<DATA> section of your module (or program):
98	preserving most of the advantages of fork.
99		263
100	It can be used to create new worker processes or new independent	264	use AnyEvent::Fork;
101	subprocesses for short- and long-running jobs, process pools (e.g. for use
102	in pre-forked servers) but also to spawn new external processes (such as
103	CGI scripts from a web server), which can be faster (and more well behaved)
104	than using fork+exec in big processes.
105		265
106	Special care has been taken to make this module useful from other modules,	266	AnyEvent::Fork
107	while still supporting specialised environments such as L<App::Staticperl>	267	->new
108	or L<PAR::Packer>.	268	->eval (do { local $/; <DATA> })
		269	->run ("doit", sub { ... });
109		270
110	=head1 WHAT THIS MODULE IS NOT	271	__DATA__
111		272
112	This module only creates processes and lets you pass file handles and	273	sub doit {
113	strings to it, and run perl code. It does not implement any kind of RPC -	274	... do something!
114	there is no back channel from the process back to you, and there is no RPC	275	}
115	or message passing going on.
116		276
117	If you need some form of RPC, you can either implement it yourself	277	=head2 For stingy standalone programs: do not rely on external files at
118	in whatever way you like, use some message-passing module such	278	all.
119	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
120	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
121	and so on.
122		279
123	=head1 PROBLEM STATEMENT	280	For single-file scripts it can be inconvenient to rely on external
		281	files - even when using < C<DATA> section, you still need to C<exec>
		282	an external perl interpreter, which might not be available when using
		283	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
124		284
125	There are two ways to implement parallel processing on UNIX like operating	285	Two modules help here - L<AnyEvent::Fork::Early> forks a template process
126	systems - fork and process, and fork+exec and process. They have different	286	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
127	advantages and disadvantages that I describe below, together with how this	287	forks the main program as a template process.
128	module tries to mitigate the disadvantages.
129		288
130	=over 4	289	Here is how your main program should look like:
131		290
132	=item Forking from a big process can be very slow (a 5GB process needs	291	#! perl
133	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
134	is often shared with exec (because you have to fork first), but in some
135	circumstances (e.g. when vfork is used), fork+exec can be much faster.
136		292
137	This module can help here by telling a small(er) helper process to fork,	293	# optional, as the very first thing.
138	or fork+exec instead.	294	# in case modules want to create their own processes.
		295	use AnyEvent::Fork::Early;
139		296
140	=item Forking usually creates a copy-on-write copy of the parent	297	# next, load all modules you need in your template process
141	process. Memory (for example, modules or data files that have been	298	use Example::My::Module
142	will not take additional memory). When exec'ing a new process, modules	299	use Example::Whatever;
143	and data files might need to be loaded again, at extra CPU and memory
144	cost. Likewise when forking, all data structures are copied as well - if
145	the program frees them and replaces them by new data, the child processes
146	will retain the memory even if it isn't used.
147		300
148	This module allows the main program to do a controlled fork, and allows	301	# next, put your run function definition and anything else you
149	modules to exec processes safely at any time. When creating a custom	302	# need, but do not use code outside of BEGIN blocks.
150	process pool you can take advantage of data sharing via fork without	303	sub worker_run {
151	risking to share large dynamic data structures that will blow up child	304	my ($fh, @args) = @_;
152	memory usage.	305	...
		306	}
153		307
154	=item Exec'ing a new perl process might be difficult and slow. For	308	# now preserve everything so far as AnyEvent::Fork object
155	example, it is not easy to find the correct path to the perl interpreter,	309	# in §TEMPLATE.
156	and all modules have to be loaded from disk again. Long running processes	310	use AnyEvent::Fork::Template;
157	might run into problems when perl is upgraded for example.
158		311
159	This module supports creating pre-initialised perl processes to be used	312	# do not put code outside of BEGIN blocks until here
160	as template, and also tries hard to identify the correct path to the perl
161	interpreter. With a cooperative main program, exec'ing the interpreter
162	might not even be necessary.
163		313
164	=item Forking might be impossible when a program is running. For example,	314	# now use the $TEMPLATE process in any way you like
165	POSIX makes it almost impossible to fork from a multi-threaded program and
166	do anything useful in the child - strictly speaking, if your perl program
167	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
168	you cannot call fork on the perl level anymore, at all.
169		315
170	This module can safely fork helper processes at any time, by calling	316	# for example: create 10 worker processes
171	fork+exec in C, in a POSIX-compatible way.	317	my @worker;
172		318	my $cv = AE::cv;
173	=item Parallel processing with fork might be inconvenient or difficult	319	for (1..10) {
174	to implement. For example, when a program uses an event loop and creates	320	$cv->begin;
175	watchers it becomes very hard to use the event loop from a child	321	$TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub {
176	program, as the watchers already exist but are only meaningful in the	322	push @worker, shift;
177	parent. Worse, a module might want to use such a system, not knowing	323	$cv->end;
178	whether another module or the main program also does, leading to problems.	324	});
179		325	}
180	This module only lets the main program create pools by forking (because	326	$cv->recv;
181	only the main program can know when it is still safe to do so) - all other
182	pools are created by fork+exec, after which such modules can again be
183	loaded.
184
185	=back
186		327
187	=head1 CONCEPTS	328	=head1 CONCEPTS
188		329
189	This module can create new processes either by executing a new perl	330	This module can create new processes either by executing a new perl
190	process, or by forking from an existing "template" process.	331	process, or by forking from an existing "template" process.
		332
		333	All these processes are called "child processes" (whether they are direct
		334	children or not), while the process that manages them is called the
		335	"parent process".
191		336
192	Each such process comes with its own file handle that can be used to	337	Each such process comes with its own file handle that can be used to
193	communicate with it (it's actually a socket - one end in the new process,	338	communicate with it (it's actually a socket - one end in the new process,
194	one end in the main process), and among the things you can do in it are	339	one end in the main process), and among the things you can do in it are
195	load modules, fork new processes, send file handles to it, and execute	340	load modules, fork new processes, send file handles to it, and execute
…		…
269	my ($fork_fh) = @_;	414	my ($fork_fh) = @_;
270	});	415	});
271		416
272	=back	417	=back
273		418
274	=head1 FUNCTIONS	419	=head1 THE C<AnyEvent::Fork> CLASS
		420
		421	This module exports nothing, and only implements a single class -
		422	C<AnyEvent::Fork>.
		423
		424	There are two class constructors that both create new processes - C<new>
		425	and C<new_exec>. The C<fork> method creates a new process by forking an
		426	existing one and could be considered a third constructor.
		427
		428	Most of the remaining methods deal with preparing the new process, by
		429	loading code, evaluating code and sending data to the new process. They
		430	usually return the process object, so you can chain method calls.
		431
		432	If a process object is destroyed before calling its C<run> method, then
		433	the process simply exits. After C<run> is called, all responsibility is
		434	passed to the specified function.
		435
		436	As long as there is any outstanding work to be done, process objects
		437	resist being destroyed, so there is no reason to store them unless you
		438	need them later - configure and forget works just fine.
275		439
276	=over 4	440	=over 4
277		441
278	=cut	442	=cut
279		443
…		…
286	use AnyEvent;	450	use AnyEvent;
287	use AnyEvent::Util ();	451	use AnyEvent::Util ();
288		452
289	use IO::FDPass;	453	use IO::FDPass;
290		454
291	our $VERSION = 0.5;	455	our $VERSION = '1.0';
292
293	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
294
295	=item my $pool = new AnyEvent::Fork key => value...
296
297	Create a new process pool. The following named parameters are supported:
298
299	=over 4
300
301	=back
302
303	=cut
304		456
305	# the early fork template process	457	# the early fork template process
306	our $EARLY;	458	our $EARLY;
307		459
308	# the empty template process	460	# the empty template process
309	our $TEMPLATE;	461	our $TEMPLATE;
		462
		463	sub QUEUE() { 0 }
		464	sub FH() { 1 }
		465	sub WW() { 2 }
		466	sub PID() { 3 }
		467	sub CB() { 4 }
		468
		469	sub _new {
		470	my ($self, $fh, $pid) = @_;
		471
		472	AnyEvent::Util::fh_nonblocking $fh, 1;
		473
		474	$self = bless [
		475	[], # write queue - strings or fd's
		476	$fh,
		477	undef, # AE watcher
		478	$pid,
		479	], $self;
		480
		481	$self
		482	}
310		483
311	sub _cmd {	484	sub _cmd {
312	my $self = shift;	485	my $self = shift;
313		486
314	# ideally, we would want to use "a (w/a)*" as format string, but perl	487	# ideally, we would want to use "a (w/a)*" as format string, but perl
315	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack	488	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
316	# it.	489	# it.
317	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	490	push @{ $self->[QUEUE] }, pack "a N/a*", $_[0], $_[1];
318		491
319	$self->[3] \|\|= AE::io $self->[1], 1, sub {	492	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
320	do {	493	do {
321	# send the next "thing" in the queue - either a reference to an fh,	494	# send the next "thing" in the queue - either a reference to an fh,
322	# or a plain string.	495	# or a plain string.
323		496
324	if (ref $self->[2][0]) {	497	if (ref $self->[QUEUE][0]) {
325	# send fh	498	# send fh
326	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	499	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
327	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	500	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
328	undef $self->[3];	501	undef $self->[WW];
329	die "AnyEvent::Fork: file descriptor send failure: $!";	502	die "AnyEvent::Fork: file descriptor send failure: $!";
330	}	503	}
331		504
332	shift @{ $self->[2] };	505	shift @{ $self->[QUEUE] };
333		506
334	} else {	507	} else {
335	# send string	508	# send string
336	my $len = syswrite $self->[1], $self->[2][0];	509	my $len = syswrite $self->[FH], $self->[QUEUE][0];
337		510
338	unless ($len) {	511	unless ($len) {
339	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	512	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
340	undef $self->[3];	513	undef $self->[WW];
341	die "AnyEvent::Fork: command write failure: $!";	514	die "AnyEvent::Fork: command write failure: $!";
342	}	515	}
343		516
344	substr $self->[2][0], 0, $len, "";	517	substr $self->[QUEUE][0], 0, $len, "";
345	shift @{ $self->[2] } unless length $self->[2][0];	518	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
346	}	519	}
347	} while @{ $self->[2] };	520	} while @{ $self->[QUEUE] };
348		521
349	# everything written	522	# everything written
350	undef $self->[3];	523	undef $self->[WW];
351		524
352	# invoke run callback, if any	525	# invoke run callback, if any
353	$self->[4]->($self->[1]) if $self->[4];	526	if ($self->[CB]) {
		527	$self->[CB]->($self->[FH]);
		528	@$self = ();
		529	}
354	};	530	};
355		531
356	() # make sure we don't leak the watcher	532	() # make sure we don't leak the watcher
357	}
358
359	sub _new {
360	my ($self, $fh, $pid) = @_;
361
362	AnyEvent::Util::fh_nonblocking $fh, 1;
363
364	$self = bless [
365	$pid,
366	$fh,
367	[], # write queue - strings or fd's
368	undef, # AE watcher
369	], $self;
370
371	$self
372	}	533	}
373		534
374	# fork template from current process, used by AnyEvent::Fork::Early/Template	535	# fork template from current process, used by AnyEvent::Fork::Early/Template
375	sub _new_fork {	536	sub _new_fork {
376	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	537	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
381	if ($pid eq 0) {	542	if ($pid eq 0) {
382	require AnyEvent::Fork::Serve;	543	require AnyEvent::Fork::Serve;
383	$AnyEvent::Fork::Serve::OWNER = $parent;	544	$AnyEvent::Fork::Serve::OWNER = $parent;
384	close $fh;	545	close $fh;
385	$0 = "$_[1] of $parent";	546	$0 = "$_[1] of $parent";
386	$SIG{CHLD} = 'IGNORE';
387	AnyEvent::Fork::Serve::serve ($slave);	547	AnyEvent::Fork::Serve::serve ($slave);
388	exit 0;	548	exit 0;
389	} elsif (!$pid) {	549	} elsif (!$pid) {
390	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	550	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
391	}	551	}
…		…
398	Create a new "empty" perl interpreter process and returns its process	558	Create a new "empty" perl interpreter process and returns its process
399	object for further manipulation.	559	object for further manipulation.
400		560
401	The new process is forked from a template process that is kept around	561	The new process is forked from a template process that is kept around
402	for this purpose. When it doesn't exist yet, it is created by a call to	562	for this purpose. When it doesn't exist yet, it is created by a call to
403	C<new_exec> and kept around for future calls.	563	C<new_exec> first and then stays around for future calls.
404
405	When the process object is destroyed, it will release the file handle
406	that connects it with the new process. When the new process has not yet
407	called C<run>, then the process will exit. Otherwise, what happens depends
408	entirely on the code that is executed.
409		564
410	=cut	565	=cut
411		566
412	sub new {	567	sub new {
413	my $class = shift;	568	my $class = shift;
…		…
503	}	658	}
504		659
505	=item $pid = $proc->pid	660	=item $pid = $proc->pid
506		661
507	Returns the process id of the process I<iff it is a direct child of the	662	Returns the process id of the process I<iff it is a direct child of the
508	process> running AnyEvent::Fork, and C<undef> otherwise.	663	process running AnyEvent::Fork>, and C<undef> otherwise.
509		664
510	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	665	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
511	L<AnyEvent::Fork::Template> are direct children, and you are responsible	666	L<AnyEvent::Fork::Template> are direct children, and you are responsible
512	to clean up their zombies when they die.	667	to clean up their zombies when they die.
513		668
514	All other processes are not direct children, and will be cleaned up by	669	All other processes are not direct children, and will be cleaned up by
515	AnyEvent::Fork.	670	AnyEvent::Fork itself.
516		671
517	=cut	672	=cut
518		673
519	sub pid {	674	sub pid {
520	$_[0][0]	675	$_[0][PID]
521	}	676	}
522		677
523	=item $proc = $proc->eval ($perlcode, @args)	678	=item $proc = $proc->eval ($perlcode, @args)
524		679
525	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	680	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
526	the strings specified by C<@args>, in the "main" package.	681	the strings specified by C<@args>, in the "main" package.
527		682
528	This call is meant to do any custom initialisation that might be required	683	This call is meant to do any custom initialisation that might be required
529	(for example, the C<require> method uses it). It's not supposed to be used	684	(for example, the C<require> method uses it). It's not supposed to be used
530	to completely take over the process, use C<run> for that.	685	to completely take over the process, use C<run> for that.
531		686
532	The code will usually be executed after this call returns, and there is no	687	The code will usually be executed after this call returns, and there is no
533	way to pass anything back to the calling process. Any evaluation errors	688	way to pass anything back to the calling process. Any evaluation errors
534	will be reported to stderr and cause the process to exit.	689	will be reported to stderr and cause the process to exit.
535		690
536	If you want to execute some code to take over the process (see the	691	If you want to execute some code (that isn't in a module) to take over the
537	"fork+exec" example in the SYNOPSIS), you should compile a function via	692	process, you should compile a function via C<eval> first, and then call
538	C<eval> first, and then call it via C<run>. This also gives you access to	693	it via C<run>. This also gives you access to any arguments passed via the
539	any arguments passed via the C<send_xxx> methods, such as file handles.	694	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		695	a faster fork+exec> example to see it in action.
540		696
541	Returns the process object for easy chaining of method calls.	697	Returns the process object for easy chaining of method calls.
542		698
543	=cut	699	=cut
544		700
…		…
570	=item $proc = $proc->send_fh ($handle, ...)	726	=item $proc = $proc->send_fh ($handle, ...)
571		727
572	Send one or more file handles (I<not> file descriptors) to the process,	728	Send one or more file handles (I<not> file descriptors) to the process,
573	to prepare a call to C<run>.	729	to prepare a call to C<run>.
574		730
575	The process object keeps a reference to the handles until this is done,	731	The process object keeps a reference to the handles until they have
576	so you must not explicitly close the handles. This is most easily	732	been passed over to the process, so you must not explicitly close the
577	accomplished by simply not storing the file handles anywhere after passing	733	handles. This is most easily accomplished by simply not storing the file
578	them to this method.	734	handles anywhere after passing them to this method - when AnyEvent::Fork
		735	is finished using them, perl will automatically close them.
579		736
580	Returns the process object for easy chaining of method calls.	737	Returns the process object for easy chaining of method calls.
581		738
582	Example: pass a file handle to a process, and release it without	739	Example: pass a file handle to a process, and release it without
583	closing. It will be closed automatically when it is no longer used.	740	closing. It will be closed automatically when it is no longer used.
…		…
590	sub send_fh {	747	sub send_fh {
591	my ($self, @fh) = @_;	748	my ($self, @fh) = @_;
592		749
593	for my $fh (@fh) {	750	for my $fh (@fh) {
594	$self->_cmd ("h");	751	$self->_cmd ("h");
595	push @{ $self->[2] }, \$fh;	752	push @{ $self->[QUEUE] }, \$fh;
596	}	753	}
597		754
598	$self	755	$self
599	}	756	}
600		757
601	=item $proc = $proc->send_arg ($string, ...)	758	=item $proc = $proc->send_arg ($string, ...)
602		759
603	Send one or more argument strings to the process, to prepare a call to	760	Send one or more argument strings to the process, to prepare a call to
604	C<run>. The strings can be any octet string.	761	C<run>. The strings can be any octet strings.
605		762
606	The protocol is optimised to pass a moderate number of relatively short	763	The protocol is optimised to pass a moderate number of relatively short
607	strings - while you can pass up to 4GB of data in one go, this is more	764	strings - while you can pass up to 4GB of data in one go, this is more
608	meant to pass some ID information or other startup info, not big chunks of	765	meant to pass some ID information or other startup info, not big chunks of
609	data.	766	data.
…		…
625	Enter the function specified by the function name in C<$func> in the	782	Enter the function specified by the function name in C<$func> in the
626	process. The function is called with the communication socket as first	783	process. The function is called with the communication socket as first
627	argument, followed by all file handles and string arguments sent earlier	784	argument, followed by all file handles and string arguments sent earlier
628	via C<send_fh> and C<send_arg> methods, in the order they were called.	785	via C<send_fh> and C<send_arg> methods, in the order they were called.
629		786
		787	The process object becomes unusable on return from this function - any
		788	further method calls result in undefined behaviour.
		789
630	The function name should be fully qualified, but if it isn't, it will be	790	The function name should be fully qualified, but if it isn't, it will be
631	looked up in the main package.	791	looked up in the C<main> package.
632		792
633	If the called function returns, doesn't exist, or any error occurs, the	793	If the called function returns, doesn't exist, or any error occurs, the
634	process exits.	794	process exits.
635		795
636	Preparing the process is done in the background - when all commands have	796	Preparing the process is done in the background - when all commands have
637	been sent, the callback is invoked with the local communications socket	797	been sent, the callback is invoked with the local communications socket
638	as argument. At this point you can start using the socket in any way you	798	as argument. At this point you can start using the socket in any way you
639	like.	799	like.
640
641	The process object becomes unusable on return from this function - any
642	further method calls result in undefined behaviour.
643		800
644	If the communication socket isn't used, it should be closed on both sides,	801	If the communication socket isn't used, it should be closed on both sides,
645	to save on kernel memory.	802	to save on kernel memory.
646		803
647	The socket is non-blocking in the parent, and blocking in the newly	804	The socket is non-blocking in the parent, and blocking in the newly
…		…
686	=cut	843	=cut
687		844
688	sub run {	845	sub run {
689	my ($self, $func, $cb) = @_;	846	my ($self, $func, $cb) = @_;
690		847
691	$self->[4] = $cb;	848	$self->[CB] = $cb;
692	$self->_cmd (r => $func);	849	$self->_cmd (r => $func);
		850	}
		851
		852	=back
		853
		854	=head2 ADVANCED METHODS
		855
		856	=over 4
		857
		858	=item new_from_stdio AnyEvent::Fork $fh
		859
		860	Assume that you have a perl interpreter running (without any special
		861	options or a program) somewhere and it has it's STDIN and STDOUT connected
		862	to the C<$fh> somehow. I.e. exactly the state perl is in when you start it
		863	without any arguments:
		864
		865	perl
		866
		867	Then you can create an C<AnyEvent::Fork> object out of this perl
		868	interpreter with this constructor.
		869
		870	When the usefulness of this isn't immediately clear, imagine you manage to
		871	run a perl interpreter remotely (F<ssh remotemachine perl>), then you can
		872	manage it mostly like a local C<AnyEvent::Fork> child.
		873
		874	This works without any module support, i.e. the remote F<perl> does not
		875	need to have any special modules installed.
		876
		877	There are a number of limitations though: C<send_fh> will only work if the
		878	L<IO::FDPass> module is loadable by the remote perl and the two processes
		879	are connected in a way that let's L<IO::FDPass> do it's work.
		880
		881	This will therefore not work over a network connection. From this follows
		882	that C<fork> will also not work under these circumstances, as it relies on
		883	C<send_fh> internally.
		884
		885	Although not a limitation of this module, keep in mind that the
		886	"communications socket" is simply C<STDIN>, and depending on how you
		887	started F<perl> (e.g. via F<ssh>), it might only be half-duplex. This is
		888	fine for C<AnyEvent::Fork>, but your C<run> function might want to use
		889	C<STDIN> (or the "communications socket") for input and C<STDOUT> for
		890	output.
		891
		892	You can support both cases by checking the C<fileno> of the handle passed
		893	to your run function:
		894
		895	sub run {
		896	my ($rfh) = @_;
		897
		898	my $wfh = fileno $rfh ? $rfh : *STDOUT;
		899
		900	# now use $rfh for reading and $wfh for writing
		901	}
		902
		903	=cut
		904
		905	sub new_from_stdio {
		906	my ($class, $fh) = @_;
		907
		908	my $self = $class->_new ($fh);
		909
		910	# send startup code
		911	push @{ $self->[QUEUE] },
		912	(do "AnyEvent/Fork/serve.pl")
		913	. <<'EOF';
		914
		915	$OWNER = "another process";
		916	$0 = "AnyEvent::Fork/stdio of $OWNER";
		917
		918	serve *STDIN;
		919	__END__
		920	EOF
		921
		922	# the data is only sent when the user requests additional things, which
		923	# is likely early enough for our purposes.
		924
		925	$self
		926	}
		927
		928	=back
		929
		930	=head2 EXPERIMENTAL METHODS
		931
		932	These methods might go away completely or change behaviour, a any time.
		933
		934	=over 4
		935
		936	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		937
		938	Flushes all commands out to the process and then calls the callback with
		939	the communications socket.
		940
		941	The process object becomes unusable on return from this function - any
		942	further method calls result in undefined behaviour.
		943
		944	The point of this method is to give you a file handle thta you cna pass
		945	to another process. In that other process, you can call C<new_from_fh
		946	AnyEvent::Fork> to create a new C<AnyEvent::Fork> object from it, thereby
		947	effectively passing a fork object to another process.
		948
		949	=cut
		950
		951	sub to_fh {
		952	my ($self, $cb) = @_;
		953
		954	$self->[CB] = $cb;
		955
		956	unless ($self->[WW]) {
		957	$self->[CB]->($self->[FH]);
		958	@$self = ();
		959	}
		960	}
		961
		962	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		963
		964	Takes a file handle originally rceeived by the C<to_fh> method and creates
		965	a new C<AnyEvent:Fork> object. The child process itself will not change in
		966	any way, i.e. it will keep all the modifications done to it before calling
		967	C<to_fh>.
		968
		969	The new object is very much like the original object, except that the
		970	C<pid> method will return C<undef> even if the process is a direct child.
		971
		972	=cut
		973
		974	sub new_from_fh {
		975	my ($class, $fh) = @_;
		976
		977	$class->_new ($fh)
693	}	978	}
694		979
695	=back	980	=back
696		981
697	=head1 PERFORMANCE	982	=head1 PERFORMANCE
…		…
707		992
708	2079 new processes per second, using manual socketpair + fork	993	2079 new processes per second, using manual socketpair + fork
709		994
710	Then I did the same thing, but instead of calling fork, I called	995	Then I did the same thing, but instead of calling fork, I called
711	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the	996	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
712	socket form the child to close on exit. This does the same thing as manual	997	socket from the child to close on exit. This does the same thing as manual
713	socket pair + fork, except that what is forked is the template process	998	socket pair + fork, except that what is forked is the template process
714	(2440kB), and the socket needs to be passed to the server at the other end	999	(2440kB), and the socket needs to be passed to the server at the other end
715	of the socket first.	1000	of the socket first.
716		1001
717	2307 new processes per second, using AnyEvent::Fork->new	1002	2307 new processes per second, using AnyEvent::Fork->new
…		…
722	479 vfork+execs per second, using AnyEvent::Fork->new_exec	1007	479 vfork+execs per second, using AnyEvent::Fork->new_exec
723		1008
724	So how can C<< AnyEvent->new >> be faster than a standard fork, even	1009	So how can C<< AnyEvent->new >> be faster than a standard fork, even
725	though it uses the same operations, but adds a lot of overhead?	1010	though it uses the same operations, but adds a lot of overhead?
726		1011
727	The difference is simply the process size: forking the 6MB process takes	1012	The difference is simply the process size: forking the 5MB process takes
728	so much longer than forking the 2.5MB template process that the overhead	1013	so much longer than forking the 2.5MB template process that the extra
729	introduced is canceled out.	1014	overhead is canceled out.
730		1015
731	If the benchmark process grows, the normal fork becomes even slower:	1016	If the benchmark process grows, the normal fork becomes even slower:
732		1017
733	1340 new processes, manual fork in a 20MB process	1018	1340 new processes, manual fork of a 20MB process
734	731 new processes, manual fork in a 200MB process	1019	731 new processes, manual fork of a 200MB process
735	235 new processes, manual fork in a 2000MB process	1020	235 new processes, manual fork of a 2000MB process
736		1021
737	What that means (to me) is that I can use this module without having a	1022	What that means (to me) is that I can use this module without having a bad
738	very bad conscience because of the extra overhead required to start new	1023	conscience because of the extra overhead required to start new processes.
739	processes.
740		1024
741	=head1 TYPICAL PROBLEMS	1025	=head1 TYPICAL PROBLEMS
742		1026
743	This section lists typical problems that remain. I hope by recognising	1027	This section lists typical problems that remain. I hope by recognising
744	them, most can be avoided.	1028	them, most can be avoided.
745		1029
746	=over 4	1030	=over 4
747		1031
748	=item "leaked" file descriptors for exec'ed processes	1032	=item leaked file descriptors for exec'ed processes
749		1033
750	POSIX systems inherit file descriptors by default when exec'ing a new	1034	POSIX systems inherit file descriptors by default when exec'ing a new
751	process. While perl itself laudably sets the close-on-exec flags on new	1035	process. While perl itself laudably sets the close-on-exec flags on new
752	file handles, most C libraries don't care, and even if all cared, it's	1036	file handles, most C libraries don't care, and even if all cared, it's
753	often not possible to set the flag in a race-free manner.	1037	often not possible to set the flag in a race-free manner.
…		…
773	libraries or the code that leaks those file descriptors.	1057	libraries or the code that leaks those file descriptors.
774		1058
775	Fortunately, most of these leaked descriptors do no harm, other than	1059	Fortunately, most of these leaked descriptors do no harm, other than
776	sitting on some resources.	1060	sitting on some resources.
777		1061
778	=item "leaked" file descriptors for fork'ed processes	1062	=item leaked file descriptors for fork'ed processes
779		1063
780	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	1064	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
781	which closes file descriptors not marked for being inherited.	1065	which closes file descriptors not marked for being inherited.
782		1066
783	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	1067	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
792		1076
793	The solution is to either not load these modules before use'ing	1077	The solution is to either not load these modules before use'ing
794	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	1078	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
795	initialising them, for example, by calling C<init Gtk2> manually.	1079	initialising them, for example, by calling C<init Gtk2> manually.
796		1080
797	=item exit runs destructors	1081	=item exiting calls object destructors
798		1082
799	This only applies to users of Lc<AnyEvent::Fork:Early> and	1083	This only applies to users of L<AnyEvent::Fork:Early> and
800	L<AnyEvent::Fork::Template>.	1084	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1085	that reference external resources.
801		1086
802	When a process created by AnyEvent::Fork exits, it might do so by calling	1087	When a process created by AnyEvent::Fork exits, it might do so by calling
803	exit, or simply letting perl reach the end of the program. At which point	1088	exit, or simply letting perl reach the end of the program. At which point
804	Perl runs all destructors.	1089	Perl runs all destructors.
805		1090
…		…
824	to make it so, mostly due to the bloody broken perl that nobody seems to	1109	to make it so, mostly due to the bloody broken perl that nobody seems to
825	care about. The fork emulation is a bad joke - I have yet to see something	1110	care about. The fork emulation is a bad joke - I have yet to see something
826	useful that you can do with it without running into memory corruption	1111	useful that you can do with it without running into memory corruption
827	issues or other braindamage. Hrrrr.	1112	issues or other braindamage. Hrrrr.
828		1113
829	Cygwin perl is not supported at the moment, as it should implement fd	1114	Since fork is endlessly broken on win32 perls (it doesn't even remotely
830	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	1115	work within it's documented limits) and quite obviously it's not getting
831	support enough functionality to do it.	1116	improved any time soon, the best way to proceed on windows would be to
		1117	always use C<new_exec> and thus never rely on perl's fork "emulation".
		1118
		1119	Cygwin perl is not supported at the moment due to some hilarious
		1120	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1121	use C<send_fh> and always use C<new_exec> to create processes, it should
		1122	work though.
832		1123
833	=head1 SEE ALSO	1124	=head1 SEE ALSO
834		1125
835	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	1126	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1127	(part of this distribution).
		1128
836	L<AnyEvent::Fork::Template> (to create a process by forking the main	1129	L<AnyEvent::Fork::Template>, to create a process by forking the main
837	program at a convenient time).	1130	program at a convenient time (part of this distribution).
838		1131
839	=head1 AUTHOR	1132	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1133
		1134	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1135
		1136	=head1 AUTHOR AND CONTACT INFORMATION
840		1137
841	Marc Lehmann <schmorp@schmorp.de>	1138	Marc Lehmann <schmorp@schmorp.de>
842	http://home.schmorp.de/	1139	http://software.schmorp.de/pkg/AnyEvent-Fork
843		1140
844	=cut	1141	=cut
845		1142
846	1	1143	1
847		1144

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs. Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC