[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 1.31 by root, Sat Apr 6 09:29:26 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	=head1 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head1 PROBLEM STATEMENT
		46
		47	There are two traditional ways to implement parallel processing on UNIX
		48	like operating systems - fork and process, and fork+exec and process. They
		49	have different advantages and disadvantages that I describe below,
		50	together with how this module tries to mitigate the disadvantages.
		51
		52	=over 4
		53
		54	=item Forking from a big process can be very slow.
		55
		56	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		57	overhead is often shared with exec (because you have to fork first), but
		58	in some circumstances (e.g. when vfork is used), fork+exec can be much
		59	faster.
		60
		61	This module can help here by telling a small(er) helper process to fork,
		62	which is faster then forking the main process, and also uses vfork where
		63	possible. This gives the speed of vfork, with the flexibility of fork.
		64
		65	=item Forking usually creates a copy-on-write copy of the parent
		66	process.
		67
		68	For example, modules or data files that are loaded will not use additional
		69	memory after a fork. When exec'ing a new process, modules and data files
		70	might need to be loaded again, at extra CPU and memory cost. But when
		71	forking, literally all data structures are copied - if the program frees
		72	them and replaces them by new data, the child processes will retain the
		73	old version even if it isn't used, which can suddenly and unexpectedly
		74	increase memory usage when freeing memory.
		75
		76	The trade-off is between more sharing with fork (which can be good or
		77	bad), and no sharing with exec.
		78
		79	This module allows the main program to do a controlled fork, and allows
		80	modules to exec processes safely at any time. When creating a custom
		81	process pool you can take advantage of data sharing via fork without
		82	risking to share large dynamic data structures that will blow up child
		83	memory usage.
		84
		85	In other words, this module puts you into control over what is being
		86	shared and what isn't, at all times.
		87
		88	=item Exec'ing a new perl process might be difficult.
		89
		90	For example, it is not easy to find the correct path to the perl
		91	interpreter - C<$^X> might not be a perl interpreter at all.
		92
		93	This module tries hard to identify the correct path to the perl
		94	interpreter. With a cooperative main program, exec'ing the interpreter
		95	might not even be necessary, but even without help from the main program,
		96	it will still work when used from a module.
		97
		98	=item Exec'ing a new perl process might be slow, as all necessary modules
		99	have to be loaded from disk again, with no guarantees of success.
		100
		101	Long running processes might run into problems when perl is upgraded
		102	and modules are no longer loadable because they refer to a different
		103	perl version, or parts of a distribution are newer than the ones already
		104	loaded.
		105
		106	This module supports creating pre-initialised perl processes to be used as
		107	a template for new processes.
		108
		109	=item Forking might be impossible when a program is running.
		110
		111	For example, POSIX makes it almost impossible to fork from a
		112	multi-threaded program while doing anything useful in the child - in
		113	fact, if your perl program uses POSIX threads (even indirectly via
		114	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		115	anymore without risking corruption issues on a number of operating
		116	systems.
		117
		118	This module can safely fork helper processes at any time, by calling
		119	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		120
		121	=item Parallel processing with fork might be inconvenient or difficult
		122	to implement. Modules might not work in both parent and child.
		123
		124	For example, when a program uses an event loop and creates watchers it
		125	becomes very hard to use the event loop from a child program, as the
		126	watchers already exist but are only meaningful in the parent. Worse, a
		127	module might want to use such a module, not knowing whether another module
		128	or the main program also does, leading to problems.
		129
		130	Apart from event loops, graphical toolkits also commonly fall into the
		131	"unsafe module" category, or just about anything that communicates with
		132	the external world, such as network libraries and file I/O modules, which
		133	usually don't like being copied and then allowed to continue in two
		134	processes.
		135
		136	With this module only the main program is allowed to create new processes
		137	by forking (because only the main program can know when it is still safe
		138	to do so) - all other processes are created via fork+exec, which makes it
		139	possible to use modules such as event loops or window interfaces safely.
		140
		141	=back
		142
		143	=head1 EXAMPLES
		144
10	# create a single new process, tell it to run your worker function	145	=head2 Create a single new process, tell it to run your worker function.
11		146
12	AnyEvent::Fork	147	AnyEvent::Fork
13	->new	148	->new
14	->require ("MyModule")	149	->require ("MyModule")
15	->run ("MyModule::worker, sub {	150	->run ("MyModule::worker, sub {
…		…
17		152
18	# now $master_filehandle is connected to the	153	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	154	# $slave_filehandle in the new process.
20	});	155	});
21		156
22	# MyModule::worker might look like this	157	MyModule might look like this:
		158
		159	package MyModule;
		160
23	sub MyModule::worker {	161	sub worker {
24	my ($slave_filehandle) = @_;	162	my ($slave_filehandle) = @_;
25		163
26	# now $slave_filehandle is connected to the $master_filehandle	164	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	165	# in the original prorcess. have fun!
28	}	166	}
29		167
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	168	=head2 Create a pool of server processes all accepting on the same socket.
32		169
33	# create listener socket	170	# create listener socket
34	my $listener = ...;	171	my $listener = ...;
35		172
36	# create a pool template, initialise it and give it the socket	173	# create a pool template, initialise it and give it the socket
…		…
48	}	185	}
49		186
50	# now do other things - maybe use the filehandle provided by run	187	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	188	# to wait for the processes to die. or whatever.
52		189
53	# My::Server::run might look like this	190	My::Server might look like this:
54	sub My::Server::run {	191
		192	package My::Server;
		193
		194	sub run {
55	my ($slave, $listener, $id) = @_;	195	my ($slave, $listener, $id) = @_;
56		196
57	close $slave; # we do not use the socket, so close it to save resources	197	close $slave; # we do not use the socket, so close it to save resources
58		198
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	199	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	201	while (my $socket = $listener->accept) {
62	# do sth. with new socket	202	# do sth. with new socket
63	}	203	}
64	}	204	}
65		205
66	=head1 DESCRIPTION	206	=head2 use AnyEvent::Fork as a faster fork+exec
67		207
68	This module allows you to create new processes, without actually forking	208	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to
69	them from your current process (avoiding the problems of forking), but	209	the communications socket. It is usually faster than fork+exec, but still
70	preserving most of the advantages of fork.	210	let's you prepare the environment.
71		211
72	It can be used to create new worker processes or new independent	212	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		213
78	Special care has been taken to make this module useful from other modules,	214	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	215	->new
80	or L<PAR::Packer>.	216	->eval ('
		217	sub run {
		218	my ($fh, $output, @cmd) = @_;
81		219
82	=head1 WHAT THIS MODULE IS NOT	220	# perl will clear close-on-exec on STDOUT/STDERR
		221	open STDOUT, ">&", $output or die;
		222	open STDERR, ">&", $fh or die;
83		223
84	This module only creates processes and lets you pass file handles and	224	exec @cmd;
85	strings to it, and run perl code. It does not implement any kind of RPC -	225	}
86	there is no back channel from the process back to you, and there is no RPC	226	')
87	or message passing going on.	227	->send_fh ($output)
		228	->send_arg ("/bin/echo", "hi")
		229	->run ("run", my $cv = AE::cv);
88		230
89	If you need some form of RPC, you can either implement it yourself	231	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		232
159	=head1 CONCEPTS	233	=head1 CONCEPTS
160		234
161	This module can create new processes either by executing a new perl	235	This module can create new processes either by executing a new perl
162	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
241	my ($fork_fh) = @_;	315	my ($fork_fh) = @_;
242	});	316	});
243		317
244	=back	318	=back
245		319
246	=head1 FUNCTIONS	320	=head1 THE C<AnyEvent::Fork> CLASS
		321
		322	This module exports nothing, and only implements a single class -
		323	C<AnyEvent::Fork>.
		324
		325	There are two class constructors that both create new processes - C<new>
		326	and C<new_exec>. The C<fork> method creates a new process by forking an
		327	existing one and could be considered a third constructor.
		328
		329	Most of the remaining methods deal with preparing the new process, by
		330	loading code, evaluating code and sending data to the new process. They
		331	usually return the process object, so you can chain method calls.
		332
		333	If a process object is destroyed before calling its C<run> method, then
		334	the process simply exits. After C<run> is called, all responsibility is
		335	passed to the specified function.
		336
		337	As long as there is any outstanding work to be done, process objects
		338	resist being destroyed, so there is no reason to store them unless you
		339	need them later - configure and forget works just fine.
247		340
248	=over 4	341	=over 4
249		342
250	=cut	343	=cut
251		344
…		…
261	use IO::FDPass;	354	use IO::FDPass;
262		355
263	our $VERSION = 0.5;	356	our $VERSION = 0.5;
264		357
265	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	358	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267	=item my $pool = new AnyEvent::Fork key => value...
268
269	Create a new process pool. The following named parameters are supported:
270		359
271	=over 4	360	=over 4
272		361
273	=back	362	=back
274		363
…		…
370	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
371	object for further manipulation.	460	object for further manipulation.
372		461
373	The new process is forked from a template process that is kept around	462	The new process is forked from a template process that is kept around
374	for this purpose. When it doesn't exist yet, it is created by a call to	463	for this purpose. When it doesn't exist yet, it is created by a call to
375	C<new_exec> and kept around for future calls.	464	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		465
382	=cut	466	=cut
383		467
384	sub new {	468	sub new {
385	my $class = shift;	469	my $class = shift;
…		…
482	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
483	L<AnyEvent::Fork::Template> are direct children, and you are responsible	567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
484	to clean up their zombies when they die.	568	to clean up their zombies when they die.
485		569
486	All other processes are not direct children, and will be cleaned up by	570	All other processes are not direct children, and will be cleaned up by
487	AnyEvent::Fork.	571	AnyEvent::Fork itself.
488		572
489	=cut	573	=cut
490		574
491	sub pid {	575	sub pid {
492	$_[0][0]	576	$_[0][0]
493	}	577	}
494		578
495	=item $proc = $proc->eval ($perlcode, @args)	579	=item $proc = $proc->eval ($perlcode, @args)
496		580
497	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	581	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
498	the strings specified by C<@args>.	582	the strings specified by C<@args>, in the "main" package.
499		583
500	This call is meant to do any custom initialisation that might be required	584	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	585	(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.	586	to completely take over the process, use C<run> for that.
503		587
504	The code will usually be executed after this call returns, and there is no	588	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	589	way to pass anything back to the calling process. Any evaluation errors
506	will be reported to stderr and cause the process to exit.	590	will be reported to stderr and cause the process to exit.
		591
		592	If you want to execute some code to take over the process (see the
		593	"fork+exec" example in the SYNOPSIS), you should compile a function via
		594	C<eval> first, and then call it via C<run>. This also gives you access to
		595	any arguments passed via the C<send_xxx> methods, such as file handles.
507		596
508	Returns the process object for easy chaining of method calls.	597	Returns the process object for easy chaining of method calls.
509		598
510	=cut	599	=cut
511		600
…		…
587	$self	676	$self
588	}	677	}
589		678
590	=item $proc->run ($func, $cb->($fh))	679	=item $proc->run ($func, $cb->($fh))
591		680
592	Enter the function specified by the fully qualified name in C<$func> in	681	Enter the function specified by the function name in C<$func> in the
593	the process. The function is called with the communication socket as first	682	process. The function is called with the communication socket as first
594	argument, followed by all file handles and string arguments sent earlier	683	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.	684	via C<send_fh> and C<send_arg> methods, in the order they were called.
596		685
597	If the called function returns, the process exits.	686	The function name should be fully qualified, but if it isn't, it will be
		687	looked up in the main package.
598		688
599	Preparing the process can take time - when the process is ready, the	689	If the called function returns, doesn't exist, or any error occurs, the
		690	process exits.
		691
		692	Preparing the process is done in the background - when all commands have
600	callback is invoked with the local communications socket as argument.	693	been sent, the callback is invoked with the local communications socket
		694	as argument. At this point you can start using the socket in any way you
		695	like.
601		696
602	The process object becomes unusable on return from this function.	697	The process object becomes unusable on return from this function - any
		698	further method calls result in undefined behaviour.
603		699
604	If the communication socket isn't used, it should be closed on both sides,	700	If the communication socket isn't used, it should be closed on both sides,
605	to save on kernel memory.	701	to save on kernel memory.
606		702
607	The socket is non-blocking in the parent, and blocking in the newly	703	The socket is non-blocking in the parent, and blocking in the newly
608	created process. The close-on-exec flag is set on both. Even if not used	704	created process. The close-on-exec flag is set in both.
		705
609	otherwise, the socket can be a good indicator for the existence of the	706	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,	707	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	708	event on it, because exiting the process closes the socket (if it didn't
612	children using fork).	709	create any children using fork).
613		710
614	Example: create a template for a process pool, pass a few strings, some	711	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.	712	file handles, then fork, pass one more string, and run some code.
616		713
617	my $pool = AnyEvent::Fork	714	my $pool = AnyEvent::Fork
…		…
625	->send_arg ("str3")	722	->send_arg ("str3")
626	->run ("Some::function", sub {	723	->run ("Some::function", sub {
627	my ($fh) = @_;	724	my ($fh) = @_;
628		725
629	# fh is nonblocking, but we trust that the OS can accept these	726	# fh is nonblocking, but we trust that the OS can accept these
630	# extra 3 octets anyway.	727	# few octets anyway.
631	syswrite $fh, "hi #$_\n";	728	syswrite $fh, "hi #$_\n";
632		729
633	# $fh is being closed here, as we don't store it anywhere	730	# $fh is being closed here, as we don't store it anywhere
634	});	731	});
635	}	732	}
…		…
637	# Some::function might look like this - all parameters passed before fork	734	# Some::function might look like this - all parameters passed before fork
638	# and after will be passed, in order, after the communications socket.	735	# and after will be passed, in order, after the communications socket.
639	sub Some::function {	736	sub Some::function {
640	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	737	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
641		738
642	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	739	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
643	}	740	}
644		741
645	=cut	742	=cut
646		743
647	sub run {	744	sub run {

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