[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 1.35 by root, Sat Apr 6 09:39:12 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	# $slave_filehandle in the new process.
20	});	155	});
21		156
22	# MyModule::worker might look like this	157	C<MyModule> might look like this:
		158
		159	package MyModule;
		160
23	sub MyModule::worker {	161	sub worker {
24	my ($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 $listener = ...;
35		172
36	# create a pool template, initialise it and give it the socket	173	# create a pool template, initialise it and give it the socket
…		…
48	}	185	}
49		186
50	# now do other things - maybe use the filehandle provided by run	187	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	188	# to wait for the processes to die. or whatever.
52		189
53	# My::Server::run might look like this	190	C<My::Server> might look like this:
54	sub My::Server::run {	191
		192	package My::Server;
		193
		194	sub run {
55	my ($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	##################################################################
67	# use AnyEvent::Fork as a faster fork+exec	206	=head2 use AnyEvent::Fork as a faster fork+exec
68		207
69	# this runs /bin/echo hi, with stdout redirected to /tmp/log	208	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
70	# and stderr to the communications socket. it is usually faster	209	and standard error redirected to the communications socket. It is usually
71	# than fork+exec, but still let's you prepare the environment.	210	faster than fork+exec, but still lets you prepare the environment.
72		211
73	open my $output, ">/tmp/log" or die "$!";	212	open my $output, ">/tmp/log" or die "$!";
74		213
75	AnyEvent::Fork	214	AnyEvent::Fork
76	->new	215	->new
…		…
88	->send_fh ($output)	227	->send_fh ($output)
89	->send_arg ("/bin/echo", "hi")	228	->send_arg ("/bin/echo", "hi")
90	->run ("run", my $cv = AE::cv);	229	->run ("run", my $cv = AE::cv);
91		230
92	my $stderr = $cv->recv;	231	my $stderr = $cv->recv;
93
94	=head1 DESCRIPTION
95
96	This module allows you to create new processes, without actually forking
97	them from your current process (avoiding the problems of forking), but
98	preserving most of the advantages of fork.
99
100	It can be used to create new worker processes or new independent
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
106	Special care has been taken to make this module useful from other modules,
107	while still supporting specialised environments such as L<App::Staticperl>
108	or L<PAR::Packer>.
109
110	=head1 WHAT THIS MODULE IS NOT
111
112	This module only creates processes and lets you pass file handles and
113	strings to it, and run perl code. It does not implement any kind of RPC -
114	there is no back channel from the process back to you, and there is no RPC
115	or message passing going on.
116
117	If you need some form of RPC, you can either implement it yourself
118	in whatever way you like, use some message-passing module such
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
123	=head1 PROBLEM STATEMENT
124
125	There are two ways to implement parallel processing on UNIX like operating
126	systems - fork and process, and fork+exec and process. They have different
127	advantages and disadvantages that I describe below, together with how this
128	module tries to mitigate the disadvantages.
129
130	=over 4
131
132	=item Forking from a big process can be very slow (a 5GB process needs
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
137	This module can help here by telling a small(er) helper process to fork,
138	or fork+exec instead.
139
140	=item Forking usually creates a copy-on-write copy of the parent
141	process. Memory (for example, modules or data files that have been
142	will not take additional memory). When exec'ing a new process, modules
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
148	This module allows the main program to do a controlled fork, and allows
149	modules to exec processes safely at any time. When creating a custom
150	process pool you can take advantage of data sharing via fork without
151	risking to share large dynamic data structures that will blow up child
152	memory usage.
153
154	=item Exec'ing a new perl process might be difficult and slow. For
155	example, it is not easy to find the correct path to the perl interpreter,
156	and all modules have to be loaded from disk again. Long running processes
157	might run into problems when perl is upgraded for example.
158
159	This module supports creating pre-initialised perl processes to be used
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
164	=item Forking might be impossible when a program is running. For example,
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
170	This module can safely fork helper processes at any time, by calling
171	fork+exec in C, in a POSIX-compatible way.
172
173	=item Parallel processing with fork might be inconvenient or difficult
174	to implement. For example, when a program uses an event loop and creates
175	watchers it becomes very hard to use the event loop from a child
176	program, as the watchers already exist but are only meaningful in the
177	parent. Worse, a module might want to use such a system, not knowing
178	whether another module or the main program also does, leading to problems.
179
180	This module only lets the main program create pools by forking (because
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		232
187	=head1 CONCEPTS	233	=head1 CONCEPTS
188		234
189	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
190	process, or by forking from an existing "template" process.	236	process, or by forking from an existing "template" process.
…		…
269	my ($fork_fh) = @_;	315	my ($fork_fh) = @_;
270	});	316	});
271		317
272	=back	318	=back
273		319
274	=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.
275		340
276	=over 4	341	=over 4
277		342
278	=cut	343	=cut
279		344
…		…
289	use IO::FDPass;	354	use IO::FDPass;
290		355
291	our $VERSION = 0.5;	356	our $VERSION = 0.5;
292		357
293	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
294
295	=item my $pool = new AnyEvent::Fork key => value...
296
297	Create a new process pool. The following named parameters are supported:
298		359
299	=over 4	360	=over 4
300		361
301	=back	362	=back
302		363
…		…
398	Create a new "empty" perl interpreter process and returns its process	459	Create a new "empty" perl interpreter process and returns its process
399	object for further manipulation.	460	object for further manipulation.
400		461
401	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
402	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
403	C<new_exec> and kept around for future calls.	464	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		465
410	=cut	466	=cut
411		467
412	sub new {	468	sub new {
413	my $class = shift;	469	my $class = shift;
…		…
503	}	559	}
504		560
505	=item $pid = $proc->pid	561	=item $pid = $proc->pid
506		562
507	Returns the process id of the process I<iff it is a direct child of the	563	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.	564	process running AnyEvent::Fork>, and C<undef> otherwise.
509		565
510	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	566	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
511	L<AnyEvent::Fork::Template> are direct children, and you are responsible	567	L<AnyEvent::Fork::Template> are direct children, and you are responsible
512	to clean up their zombies when they die.	568	to clean up their zombies when they die.
513		569
514	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
515	AnyEvent::Fork.	571	AnyEvent::Fork itself.
516		572
517	=cut	573	=cut
518		574
519	sub pid {	575	sub pid {
520	$_[0][0]	576	$_[0][0]
…		…
531		587
532	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
533	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
534	will be reported to stderr and cause the process to exit.	590	will be reported to stderr and cause the process to exit.
535		591
536	If you want to execute some code to take over the process (see the	592	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	593	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	594	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.	595	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		596	a faster fork+exec> example to see it in action.
540		597
541	Returns the process object for easy chaining of method calls.	598	Returns the process object for easy chaining of method calls.
542		599
543	=cut	600	=cut
544		601
…		…
570	=item $proc = $proc->send_fh ($handle, ...)	627	=item $proc = $proc->send_fh ($handle, ...)
571		628
572	Send one or more file handles (I<not> file descriptors) to the process,	629	Send one or more file handles (I<not> file descriptors) to the process,
573	to prepare a call to C<run>.	630	to prepare a call to C<run>.
574		631
575	The process object keeps a reference to the handles until this is done,	632	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	633	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	634	handles. This is most easily accomplished by simply not storing the file
578	them to this method.	635	handles anywhere after passing them to this method - when AnyEvent::Fork
		636	is finished using them, perl will automatically close them.
579		637
580	Returns the process object for easy chaining of method calls.	638	Returns the process object for easy chaining of method calls.
581		639
582	Example: pass a file handle to a process, and release it without	640	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.	641	closing. It will be closed automatically when it is no longer used.
…		…
599	}	657	}
600		658
601	=item $proc = $proc->send_arg ($string, ...)	659	=item $proc = $proc->send_arg ($string, ...)
602		660
603	Send one or more argument strings to the process, to prepare a call to	661	Send one or more argument strings to the process, to prepare a call to
604	C<run>. The strings can be any octet string.	662	C<run>. The strings can be any octet strings.
605		663
606	The protocol is optimised to pass a moderate number of relatively short	664	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	665	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	666	meant to pass some ID information or other startup info, not big chunks of
609	data.	667	data.
…		…
625	Enter the function specified by the function name in C<$func> in the	683	Enter the function specified by the function name in C<$func> in the
626	process. The function is called with the communication socket as first	684	process. The function is called with the communication socket as first
627	argument, followed by all file handles and string arguments sent earlier	685	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.	686	via C<send_fh> and C<send_arg> methods, in the order they were called.
629		687
		688	The process object becomes unusable on return from this function - any
		689	further method calls result in undefined behaviour.
		690
630	The function name should be fully qualified, but if it isn't, it will be	691	The function name should be fully qualified, but if it isn't, it will be
631	looked up in the main package.	692	looked up in the C<main> package.
632		693
633	If the called function returns, doesn't exist, or any error occurs, the	694	If the called function returns, doesn't exist, or any error occurs, the
634	process exits.	695	process exits.
635		696
636	Preparing the process is done in the background - when all commands have	697	Preparing the process is done in the background - when all commands have
637	been sent, the callback is invoked with the local communications socket	698	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	699	as argument. At this point you can start using the socket in any way you
639	like.	700	like.
640
641	The process object becomes unusable on return from this function - any
642	further method calls result in undefined behaviour.
643		701
644	If the communication socket isn't used, it should be closed on both sides,	702	If the communication socket isn't used, it should be closed on both sides,
645	to save on kernel memory.	703	to save on kernel memory.
646		704
647	The socket is non-blocking in the parent, and blocking in the newly	705	The socket is non-blocking in the parent, and blocking in the newly

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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 1.35 by root, Sat Apr 6 09:39:12 2013 UTC

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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 1.35 by root, Sat Apr 6 09:39:12 2013 UTC