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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.21 by root, Sat Apr 6 03:40:31 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 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 can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head2 COMPARISON TO OTHER MODULES
		46
		47	There is an abundance of modules on CPAN that do "something fork", such as
		48	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		49	or L<AnyEvent::Subprocess>. There are modules that implement their own
		50	process management, such as L<AnyEvent::DBI>.
		51
		52	The problems that all these modules try to solve are real, however, none
		53	of them (from what I have seen) tackle the very real problems of unwanted
		54	memory sharing, efficiency, not being able to use event processing or
		55	similar modules in the processes they create.
		56
		57	This module doesn't try to replace any of them - instead it tries to solve
		58	the problem of creating processes with a minimum of fuss and overhead (and
		59	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		60	except they were written before AnyEvent:Fork was available, so obviously
		61	had to roll their own.
		62
		63	=head2 PROBLEM STATEMENT
		64
		65	There are two traditional ways to implement parallel processing on UNIX
		66	like operating systems - fork and process, and fork+exec and process. They
		67	have different advantages and disadvantages that I describe below,
		68	together with how this module tries to mitigate the disadvantages.
		69
		70	=over 4
		71
		72	=item Forking from a big process can be very slow.
		73
		74	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		75	overhead is often shared with exec (because you have to fork first), but
		76	in some circumstances (e.g. when vfork is used), fork+exec can be much
		77	faster.
		78
		79	This module can help here by telling a small(er) helper process to fork,
		80	which is faster then forking the main process, and also uses vfork where
		81	possible. This gives the speed of vfork, with the flexibility of fork.
		82
		83	=item Forking usually creates a copy-on-write copy of the parent
		84	process.
		85
		86	For example, modules or data files that are loaded will not use additional
		87	memory after a fork. When exec'ing a new process, modules and data files
		88	might need to be loaded again, at extra CPU and memory cost. But when
		89	forking, literally all data structures are copied - if the program frees
		90	them and replaces them by new data, the child processes will retain the
		91	old version even if it isn't used, which can suddenly and unexpectedly
		92	increase memory usage when freeing memory.
		93
		94	The trade-off is between more sharing with fork (which can be good or
		95	bad), and no sharing with exec.
		96
		97	This module allows the main program to do a controlled fork, and allows
		98	modules to exec processes safely at any time. When creating a custom
		99	process pool you can take advantage of data sharing via fork without
		100	risking to share large dynamic data structures that will blow up child
		101	memory usage.
		102
		103	In other words, this module puts you into control over what is being
		104	shared and what isn't, at all times.
		105
		106	=item Exec'ing a new perl process might be difficult.
		107
		108	For example, it is not easy to find the correct path to the perl
		109	interpreter - C<$^X> might not be a perl interpreter at all.
		110
		111	This module tries hard to identify the correct path to the perl
		112	interpreter. With a cooperative main program, exec'ing the interpreter
		113	might not even be necessary, but even without help from the main program,
		114	it will still work when used from a module.
		115
		116	=item Exec'ing a new perl process might be slow, as all necessary modules
		117	have to be loaded from disk again, with no guarantees of success.
		118
		119	Long running processes might run into problems when perl is upgraded
		120	and modules are no longer loadable because they refer to a different
		121	perl version, or parts of a distribution are newer than the ones already
		122	loaded.
		123
		124	This module supports creating pre-initialised perl processes to be used as
		125	a template for new processes.
		126
		127	=item Forking might be impossible when a program is running.
		128
		129	For example, POSIX makes it almost impossible to fork from a
		130	multi-threaded program while doing anything useful in the child - in
		131	fact, if your perl program uses POSIX threads (even indirectly via
		132	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		133	anymore without risking corruption issues on a number of operating
		134	systems.
		135
		136	This module can safely fork helper processes at any time, by calling
		137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		138
		139	=item Parallel processing with fork might be inconvenient or difficult
		140	to implement. Modules might not work in both parent and child.
		141
		142	For example, when a program uses an event loop and creates watchers it
		143	becomes very hard to use the event loop from a child program, as the
		144	watchers already exist but are only meaningful in the parent. Worse, a
		145	module might want to use such a module, not knowing whether another module
		146	or the main program also does, leading to problems.
		147
		148	Apart from event loops, graphical toolkits also commonly fall into the
		149	"unsafe module" category, or just about anything that communicates with
		150	the external world, such as network libraries and file I/O modules, which
		151	usually don't like being copied and then allowed to continue in two
		152	processes.
		153
		154	With this module only the main program is allowed to create new processes
		155	by forking (because only the main program can know when it is still safe
		156	to do so) - all other processes are created via fork+exec, which makes it
		157	possible to use modules such as event loops or window interfaces safely.
		158
		159	=back
		160
		161	=head1 EXAMPLES
		162
10	# create a single new process, tell it to run your worker function	163	=head2 Create a single new process, tell it to run your worker function.
11		164
12	AnyEvent::Fork	165	AnyEvent::Fork
13	->new	166	->new
14	->require ("MyModule")	167	->require ("MyModule")
15	->run ("MyModule::worker, sub {	168	->run ("MyModule::worker, sub {
…		…
17		170
18	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
20	});	173	});
21		174
22	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
23	sub MyModule::worker {	179	sub worker {
24	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
25		181
26	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
28	}	184	}
29		185
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	186	=head2 Create a pool of server processes all accepting on the same socket.
32		187
33	# create listener socket	188	# create listener socket
34	my $listener = ...;	189	my $listener = ...;
35		190
36	# create a pool template, initialise it and give it the socket	191	# create a pool template, initialise it and give it the socket
…		…
48	}	203	}
49		204
50	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
52		207
53	# My::Server::run might look like this	208	C<My::Server> might look like this:
54	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
55	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
56		214
57	close $slave; # we do not use the socket, so close it to save resources	215	close $slave; # we do not use the socket, so close it to save resources
58		216
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	217	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	219	while (my $socket = $listener->accept) {
62	# do sth. with new socket	220	# do sth. with new socket
63	}	221	}
64	}	222	}
65		223
66	=head1 DESCRIPTION	224	=head2 use AnyEvent::Fork as a faster fork+exec
67		225
68	This module allows you to create new processes, without actually forking	226	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
69	them from your current process (avoiding the problems of forking), but	227	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	228	faster than fork+exec, but still lets you prepare the environment.
71		229
72	It can be used to create new worker processes or new independent	230	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		231
78	Special care has been taken to make this module useful from other modules,	232	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	233	->new
80	or L<PAR::Packer>.	234	->eval ('
		235	# compile a helper function for later use
		236	sub run {
		237	my ($fh, $output, @cmd) = @_;
81		238
82	=head1 WHAT THIS MODULE IS NOT	239	# perl will clear close-on-exec on STDOUT/STDERR
		240	open STDOUT, ">&", $output or die;
		241	open STDERR, ">&", $fh or die;
83		242
84	This module only creates processes and lets you pass file handles and	243	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	244	}
86	there is no back channel from the process back to you, and there is no RPC	245	')
87	or message passing going on.	246	->send_fh ($output)
		247	->send_arg ("/bin/echo", "hi")
		248	->run ("run", my $cv = AE::cv);
88		249
89	If you need some form of RPC, you can either implement it yourself	250	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		251
159	=head1 CONCEPTS	252	=head1 CONCEPTS
160		253
161	This module can create new processes either by executing a new perl	254	This module can create new processes either by executing a new perl
162	process, or by forking from an existing "template" process.	255	process, or by forking from an existing "template" process.
…		…
241	my ($fork_fh) = @_;	334	my ($fork_fh) = @_;
242	});	335	});
243		336
244	=back	337	=back
245		338
246	=head1 FUNCTIONS	339	=head1 THE C<AnyEvent::Fork> CLASS
		340
		341	This module exports nothing, and only implements a single class -
		342	C<AnyEvent::Fork>.
		343
		344	There are two class constructors that both create new processes - C<new>
		345	and C<new_exec>. The C<fork> method creates a new process by forking an
		346	existing one and could be considered a third constructor.
		347
		348	Most of the remaining methods deal with preparing the new process, by
		349	loading code, evaluating code and sending data to the new process. They
		350	usually return the process object, so you can chain method calls.
		351
		352	If a process object is destroyed before calling its C<run> method, then
		353	the process simply exits. After C<run> is called, all responsibility is
		354	passed to the specified function.
		355
		356	As long as there is any outstanding work to be done, process objects
		357	resist being destroyed, so there is no reason to store them unless you
		358	need them later - configure and forget works just fine.
247		359
248	=over 4	360	=over 4
249		361
250	=cut	362	=cut
251		363
…		…
258	use AnyEvent;	370	use AnyEvent;
259	use AnyEvent::Util ();	371	use AnyEvent::Util ();
260		372
261	use IO::FDPass;	373	use IO::FDPass;
262		374
263	our $VERSION = 0.5;	375	our $VERSION = 0.6;
264
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267	=item my $pool = new AnyEvent::Fork key => value...
268
269	Create a new process pool. The following named parameters are supported:
270		376
271	=over 4	377	=over 4
272		378
273	=back	379	=back
274		380
…		…
353	if ($pid eq 0) {	459	if ($pid eq 0) {
354	require AnyEvent::Fork::Serve;	460	require AnyEvent::Fork::Serve;
355	$AnyEvent::Fork::Serve::OWNER = $parent;	461	$AnyEvent::Fork::Serve::OWNER = $parent;
356	close $fh;	462	close $fh;
357	$0 = "$_[1] of $parent";	463	$0 = "$_[1] of $parent";
358	$SIG{CHLD} = 'IGNORE';
359	AnyEvent::Fork::Serve::serve ($slave);	464	AnyEvent::Fork::Serve::serve ($slave);
360	exit 0;	465	exit 0;
361	} elsif (!$pid) {	466	} elsif (!$pid) {
362	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	467	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
363	}	468	}
…		…
370	Create a new "empty" perl interpreter process and returns its process	475	Create a new "empty" perl interpreter process and returns its process
371	object for further manipulation.	476	object for further manipulation.
372		477
373	The new process is forked from a template process that is kept around	478	The new process is forked from a template process that is kept around
374	for this purpose. When it doesn't exist yet, it is created by a call to	479	for this purpose. When it doesn't exist yet, it is created by a call to
375	C<new_exec> and kept around for future calls.	480	C<new_exec> first and then stays around for future calls.
376
377	When the process object is destroyed, it will release the file handle
378	that connects it with the new process. When the new process has not yet
379	called C<run>, then the process will exit. Otherwise, what happens depends
380	entirely on the code that is executed.
381		481
382	=cut	482	=cut
383		483
384	sub new {	484	sub new {
385	my $class = shift;	485	my $class = shift;
…		…
475	}	575	}
476		576
477	=item $pid = $proc->pid	577	=item $pid = $proc->pid
478		578
479	Returns the process id of the process I<iff it is a direct child of the	579	Returns the process id of the process I<iff it is a direct child of the
480	process> running AnyEvent::Fork, and C<undef> otherwise.	580	process running AnyEvent::Fork>, and C<undef> otherwise.
481		581
482	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	582	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
483	L<AnyEvent::Fork::Template> are direct children, and you are responsible	583	L<AnyEvent::Fork::Template> are direct children, and you are responsible
484	to clean up their zombies when they die.	584	to clean up their zombies when they die.
485		585
486	All other processes are not direct children, and will be cleaned up by	586	All other processes are not direct children, and will be cleaned up by
487	AnyEvent::Fork.	587	AnyEvent::Fork itself.
488		588
489	=cut	589	=cut
490		590
491	sub pid {	591	sub pid {
492	$_[0][0]	592	$_[0][0]
493	}	593	}
494		594
495	=item $proc = $proc->eval ($perlcode, @args)	595	=item $proc = $proc->eval ($perlcode, @args)
496		596
497	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	597	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
498	the strings specified by C<@args>.	598	the strings specified by C<@args>, in the "main" package.
499		599
500	This call is meant to do any custom initialisation that might be required	600	This call is meant to do any custom initialisation that might be required
501	(for example, the C<require> method uses it). It's not supposed to be used	601	(for example, the C<require> method uses it). It's not supposed to be used
502	to completely take over the process, use C<run> for that.	602	to completely take over the process, use C<run> for that.
503		603
504	The code will usually be executed after this call returns, and there is no	604	The code will usually be executed after this call returns, and there is no
505	way to pass anything back to the calling process. Any evaluation errors	605	way to pass anything back to the calling process. Any evaluation errors
506	will be reported to stderr and cause the process to exit.	606	will be reported to stderr and cause the process to exit.
507		607
		608	If you want to execute some code (that isn't in a module) to take over the
		609	process, you should compile a function via C<eval> first, and then call
		610	it via C<run>. This also gives you access to any arguments passed via the
		611	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		612	a faster fork+exec> example to see it in action.
		613
508	Returns the process object for easy chaining of method calls.	614	Returns the process object for easy chaining of method calls.
509		615
510	=cut	616	=cut
511		617
512	sub eval {	618	sub eval {
…		…
537	=item $proc = $proc->send_fh ($handle, ...)	643	=item $proc = $proc->send_fh ($handle, ...)
538		644
539	Send one or more file handles (I<not> file descriptors) to the process,	645	Send one or more file handles (I<not> file descriptors) to the process,
540	to prepare a call to C<run>.	646	to prepare a call to C<run>.
541		647
542	The process object keeps a reference to the handles until this is done,	648	The process object keeps a reference to the handles until they have
543	so you must not explicitly close the handles. This is most easily	649	been passed over to the process, so you must not explicitly close the
544	accomplished by simply not storing the file handles anywhere after passing	650	handles. This is most easily accomplished by simply not storing the file
545	them to this method.	651	handles anywhere after passing them to this method - when AnyEvent::Fork
		652	is finished using them, perl will automatically close them.
546		653
547	Returns the process object for easy chaining of method calls.	654	Returns the process object for easy chaining of method calls.
548		655
549	Example: pass a file handle to a process, and release it without	656	Example: pass a file handle to a process, and release it without
550	closing. It will be closed automatically when it is no longer used.	657	closing. It will be closed automatically when it is no longer used.
…		…
566	}	673	}
567		674
568	=item $proc = $proc->send_arg ($string, ...)	675	=item $proc = $proc->send_arg ($string, ...)
569		676
570	Send one or more argument strings to the process, to prepare a call to	677	Send one or more argument strings to the process, to prepare a call to
571	C<run>. The strings can be any octet string.	678	C<run>. The strings can be any octet strings.
572		679
573	The protocol is optimised to pass a moderate number of relatively short	680	The protocol is optimised to pass a moderate number of relatively short
574	strings - while you can pass up to 4GB of data in one go, this is more	681	strings - while you can pass up to 4GB of data in one go, this is more
575	meant to pass some ID information or other startup info, not big chunks of	682	meant to pass some ID information or other startup info, not big chunks of
576	data.	683	data.
…		…
587	$self	694	$self
588	}	695	}
589		696
590	=item $proc->run ($func, $cb->($fh))	697	=item $proc->run ($func, $cb->($fh))
591		698
592	Enter the function specified by the fully qualified name in C<$func> in	699	Enter the function specified by the function name in C<$func> in the
593	the process. The function is called with the communication socket as first	700	process. The function is called with the communication socket as first
594	argument, followed by all file handles and string arguments sent earlier	701	argument, followed by all file handles and string arguments sent earlier
595	via C<send_fh> and C<send_arg> methods, in the order they were called.	702	via C<send_fh> and C<send_arg> methods, in the order they were called.
596		703
597	If the called function returns, the process exits.
598
599	Preparing the process can take time - when the process is ready, the
600	callback is invoked with the local communications socket as argument.
601
602	The process object becomes unusable on return from this function.	704	The process object becomes unusable on return from this function - any
		705	further method calls result in undefined behaviour.
		706
		707	The function name should be fully qualified, but if it isn't, it will be
		708	looked up in the C<main> package.
		709
		710	If the called function returns, doesn't exist, or any error occurs, the
		711	process exits.
		712
		713	Preparing the process is done in the background - when all commands have
		714	been sent, the callback is invoked with the local communications socket
		715	as argument. At this point you can start using the socket in any way you
		716	like.
603		717
604	If the communication socket isn't used, it should be closed on both sides,	718	If the communication socket isn't used, it should be closed on both sides,
605	to save on kernel memory.	719	to save on kernel memory.
606		720
607	The socket is non-blocking in the parent, and blocking in the newly	721	The socket is non-blocking in the parent, and blocking in the newly
608	created process. The close-on-exec flag is set on both. Even if not used	722	created process. The close-on-exec flag is set in both.
		723
609	otherwise, the socket can be a good indicator for the existence of the	724	Even if not used otherwise, the socket can be a good indicator for the
610	process - if the other process exits, you get a readable event on it,	725	existence of the process - if the other process exits, you get a readable
611	because exiting the process closes the socket (if it didn't create any	726	event on it, because exiting the process closes the socket (if it didn't
612	children using fork).	727	create any children using fork).
613		728
614	Example: create a template for a process pool, pass a few strings, some	729	Example: create a template for a process pool, pass a few strings, some
615	file handles, then fork, pass one more string, and run some code.	730	file handles, then fork, pass one more string, and run some code.
616		731
617	my $pool = AnyEvent::Fork	732	my $pool = AnyEvent::Fork
…		…
625	->send_arg ("str3")	740	->send_arg ("str3")
626	->run ("Some::function", sub {	741	->run ("Some::function", sub {
627	my ($fh) = @_;	742	my ($fh) = @_;
628		743
629	# fh is nonblocking, but we trust that the OS can accept these	744	# fh is nonblocking, but we trust that the OS can accept these
630	# extra 3 octets anyway.	745	# few octets anyway.
631	syswrite $fh, "hi #$_\n";	746	syswrite $fh, "hi #$_\n";
632		747
633	# $fh is being closed here, as we don't store it anywhere	748	# $fh is being closed here, as we don't store it anywhere
634	});	749	});
635	}	750	}
…		…
637	# Some::function might look like this - all parameters passed before fork	752	# Some::function might look like this - all parameters passed before fork
638	# and after will be passed, in order, after the communications socket.	753	# and after will be passed, in order, after the communications socket.
639	sub Some::function {	754	sub Some::function {
640	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	755	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
641		756
642	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	757	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
643	}	758	}
644		759
645	=cut	760	=cut
646		761
647	sub run {	762	sub run {
…		…
681	479 vfork+execs per second, using AnyEvent::Fork->new_exec	796	479 vfork+execs per second, using AnyEvent::Fork->new_exec
682		797
683	So how can C<< AnyEvent->new >> be faster than a standard fork, even	798	So how can C<< AnyEvent->new >> be faster than a standard fork, even
684	though it uses the same operations, but adds a lot of overhead?	799	though it uses the same operations, but adds a lot of overhead?
685		800
686	The difference is simply the process size: forking the 6MB process takes	801	The difference is simply the process size: forking the 5MB process takes
687	so much longer than forking the 2.5MB template process that the overhead	802	so much longer than forking the 2.5MB template process that the extra
688	introduced is canceled out.	803	overhead introduced is canceled out.
689		804
690	If the benchmark process grows, the normal fork becomes even slower:	805	If the benchmark process grows, the normal fork becomes even slower:
691		806
692	1340 new processes, manual fork in a 20MB process	807	1340 new processes, manual fork of a 20MB process
693	731 new processes, manual fork in a 200MB process	808	731 new processes, manual fork of a 200MB process
694	235 new processes, manual fork in a 2000MB process	809	235 new processes, manual fork of a 2000MB process
695		810
696	What that means (to me) is that I can use this module without having a	811	What that means (to me) is that I can use this module without having a bad
697	very bad conscience because of the extra overhead required to start new	812	conscience because of the extra overhead required to start new processes.
698	processes.
699		813
700	=head1 TYPICAL PROBLEMS	814	=head1 TYPICAL PROBLEMS
701		815
702	This section lists typical problems that remain. I hope by recognising	816	This section lists typical problems that remain. I hope by recognising
703	them, most can be avoided.	817	them, most can be avoided.
704		818
705	=over 4	819	=over 4
706		820
707	=item "leaked" file descriptors for exec'ed processes	821	=item leaked file descriptors for exec'ed processes
708		822
709	POSIX systems inherit file descriptors by default when exec'ing a new	823	POSIX systems inherit file descriptors by default when exec'ing a new
710	process. While perl itself laudably sets the close-on-exec flags on new	824	process. While perl itself laudably sets the close-on-exec flags on new
711	file handles, most C libraries don't care, and even if all cared, it's	825	file handles, most C libraries don't care, and even if all cared, it's
712	often not possible to set the flag in a race-free manner.	826	often not possible to set the flag in a race-free manner.
…		…
732	libraries or the code that leaks those file descriptors.	846	libraries or the code that leaks those file descriptors.
733		847
734	Fortunately, most of these leaked descriptors do no harm, other than	848	Fortunately, most of these leaked descriptors do no harm, other than
735	sitting on some resources.	849	sitting on some resources.
736		850
737	=item "leaked" file descriptors for fork'ed processes	851	=item leaked file descriptors for fork'ed processes
738		852
739	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	853	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
740	which closes file descriptors not marked for being inherited.	854	which closes file descriptors not marked for being inherited.
741		855
742	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	856	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
751		865
752	The solution is to either not load these modules before use'ing	866	The solution is to either not load these modules before use'ing
753	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	867	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
754	initialising them, for example, by calling C<init Gtk2> manually.	868	initialising them, for example, by calling C<init Gtk2> manually.
755		869
756	=item exit runs destructors	870	=item exiting calls object destructors
757		871
758	This only applies to users of Lc<AnyEvent::Fork:Early> and	872	This only applies to users of L<AnyEvent::Fork:Early> and
759	L<AnyEvent::Fork::Template>.	873	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		874	that reference external resources.
760		875
761	When a process created by AnyEvent::Fork exits, it might do so by calling	876	When a process created by AnyEvent::Fork exits, it might do so by calling
762	exit, or simply letting perl reach the end of the program. At which point	877	exit, or simply letting perl reach the end of the program. At which point
763	Perl runs all destructors.	878	Perl runs all destructors.
764		879
…		…
783	to make it so, mostly due to the bloody broken perl that nobody seems to	898	to make it so, mostly due to the bloody broken perl that nobody seems to
784	care about. The fork emulation is a bad joke - I have yet to see something	899	care about. The fork emulation is a bad joke - I have yet to see something
785	useful that you can do with it without running into memory corruption	900	useful that you can do with it without running into memory corruption
786	issues or other braindamage. Hrrrr.	901	issues or other braindamage. Hrrrr.
787		902
788	Cygwin perl is not supported at the moment, as it should implement fd	903	Cygwin perl is not supported at the moment due to some hilarious
789	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	904	shortcomings of its API - see L<IO::FDPoll> for more details.
790	support enough functionality to do it.
791		905
792	=head1 SEE ALSO	906	=head1 SEE ALSO
793		907
794	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	908	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
795	L<AnyEvent::Fork::Template> (to create a process by forking the main	909	L<AnyEvent::Fork::Template> (to create a process by forking the main

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.21 by root, Sat Apr 6 03:40:31 2013 UTC vs. Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.21 by root, Sat Apr 6 03:40:31 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC