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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.27 by root, Sat Apr 6 09:05:50 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

…		…
27		27
28	Special care has been taken to make this module useful from other modules,	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>	29	while still supporting specialised environments such as L<App::Staticperl>
30	or L<PAR::Packer>.	30	or L<PAR::Packer>.
31		31
32	=head1 WHAT THIS MODULE IS NOT	32	=head2 WHAT THIS MODULE IS NOT
33		33
34	This module only creates processes and lets you pass file handles and	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 -	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	36	there is no back channel from the process back to you, and there is no RPC
37	or message passing going on.	37	or message passing going on.
…		…
40	in whatever way you like, use some message-passing module such	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	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,	42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
43	and so on.	43	and so on.
44		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
45	=head1 PROBLEM STATEMENT	63	=head2 PROBLEM STATEMENT
46		64
47	There are two traditional ways to implement parallel processing on UNIX	65	There are two traditional ways to implement parallel processing on UNIX
48	like operating systems - fork and process, and fork+exec and process. They	66	like operating systems - fork and process, and fork+exec and process. They
49	have different advantages and disadvantages that I describe below,	67	have different advantages and disadvantages that I describe below,
50	together with how this module tries to mitigate the disadvantages.	68	together with how this module tries to mitigate the disadvantages.
…		…
152		170
153	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
154	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
155	});	173	});
156		174
157	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
158	sub MyModule::worker {	179	sub worker {
159	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
160		181
161	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
162	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
163	}	184	}
…		…
182	}	203	}
183		204
184	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
185	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
186		207
187	# My::Server::run might look like this	208	C<My::Server> might look like this:
188	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
189	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
190		214
191	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
192		216
193	# 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,
…		…
197	}	221	}
198	}	222	}
199		223
200	=head2 use AnyEvent::Fork as a faster fork+exec	224	=head2 use AnyEvent::Fork as a faster fork+exec
201		225
202	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to	226	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
203	the communications socket. It is usually faster than fork+exec, but still	227	and standard error redirected to the communications socket. It is usually
204	let's you prepare the environment.	228	faster than fork+exec, but still lets you prepare the environment.
205		229
206	open my $output, ">/tmp/log" or die "$!";	230	open my $output, ">/tmp/log" or die "$!";
207		231
208	AnyEvent::Fork	232	AnyEvent::Fork
209	->new	233	->new
210	->eval ('	234	->eval ('
		235	# compile a helper function for later use
211	sub run {	236	sub run {
212	my ($fh, $output, @cmd) = @_;	237	my ($fh, $output, @cmd) = @_;
213		238
214	# perl will clear close-on-exec on STDOUT/STDERR	239	# perl will clear close-on-exec on STDOUT/STDERR
215	open STDOUT, ">&", $output or die;	240	open STDOUT, ">&", $output or die;
…		…
314	=head1 THE C<AnyEvent::Fork> CLASS	339	=head1 THE C<AnyEvent::Fork> CLASS
315		340
316	This module exports nothing, and only implements a single class -	341	This module exports nothing, and only implements a single class -
317	C<AnyEvent::Fork>.	342	C<AnyEvent::Fork>.
318		343
319	There are two constructors that both create new processes - C<new> and	344	There are two class constructors that both create new processes - C<new>
320	C<new_exec>. The C<fork> method creates a new process by forking an	345	and C<new_exec>. The C<fork> method creates a new process by forking an
321	existing one and could be considered a third constructor.	346	existing one and could be considered a third constructor.
322		347
323	Most of the remaining methods deal with preparing the new process, by	348	Most of the remaining methods deal with preparing the new process, by
324	loading code, evaluating code and sending data to the new process. They	349	loading code, evaluating code and sending data to the new process. They
325	usually return the process object, so you can chain method calls.	350	usually return the process object, so you can chain method calls.
326		351
327	If a process object is destroyed before calling its C<run> method, then	352	If a process object is destroyed before calling its C<run> method, then
328	the process simply exits. After C<run> is called, all responsibility is	353	the process simply exits. After C<run> is called, all responsibility is
329	passed to the specified function.	354	passed to the specified function.
330		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.
		359
331	=over 4	360	=over 4
332		361
333	=cut	362	=cut
334		363
335	package AnyEvent::Fork;	364	package AnyEvent::Fork;
…		…
341	use AnyEvent;	370	use AnyEvent;
342	use AnyEvent::Util ();	371	use AnyEvent::Util ();
343		372
344	use IO::FDPass;	373	use IO::FDPass;
345		374
346	our $VERSION = 0.5;	375	our $VERSION = 0.6;
347
348	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
349
350	=item my $pool = new AnyEvent::Fork key => value...
351
352	Create a new process pool. The following named parameters are supported:
353		376
354	=over 4	377	=over 4
355		378
356	=back	379	=back
357		380
…		…
436	if ($pid eq 0) {	459	if ($pid eq 0) {
437	require AnyEvent::Fork::Serve;	460	require AnyEvent::Fork::Serve;
438	$AnyEvent::Fork::Serve::OWNER = $parent;	461	$AnyEvent::Fork::Serve::OWNER = $parent;
439	close $fh;	462	close $fh;
440	$0 = "$_[1] of $parent";	463	$0 = "$_[1] of $parent";
441	$SIG{CHLD} = 'IGNORE';
442	AnyEvent::Fork::Serve::serve ($slave);	464	AnyEvent::Fork::Serve::serve ($slave);
443	exit 0;	465	exit 0;
444	} elsif (!$pid) {	466	} elsif (!$pid) {
445	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	467	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
446	}	468	}
…		…
453	Create a new "empty" perl interpreter process and returns its process	475	Create a new "empty" perl interpreter process and returns its process
454	object for further manipulation.	476	object for further manipulation.
455		477
456	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
457	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
458	C<new_exec> and kept around for future calls.	480	C<new_exec> first and then stays around for future calls.
459
460	When the process object is destroyed, it will release the file handle
461	that connects it with the new process. When the new process has not yet
462	called C<run>, then the process will exit. Otherwise, what happens depends
463	entirely on the code that is executed.
464		481
465	=cut	482	=cut
466		483
467	sub new {	484	sub new {
468	my $class = shift;	485	my $class = shift;
…		…
558	}	575	}
559		576
560	=item $pid = $proc->pid	577	=item $pid = $proc->pid
561		578
562	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
563	process> running AnyEvent::Fork, and C<undef> otherwise.	580	process running AnyEvent::Fork>, and C<undef> otherwise.
564		581
565	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	582	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
566	L<AnyEvent::Fork::Template> are direct children, and you are responsible	583	L<AnyEvent::Fork::Template> are direct children, and you are responsible
567	to clean up their zombies when they die.	584	to clean up their zombies when they die.
568		585
569	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
570	AnyEvent::Fork.	587	AnyEvent::Fork itself.
571		588
572	=cut	589	=cut
573		590
574	sub pid {	591	sub pid {
575	$_[0][0]	592	$_[0][0]
…		…
586		603
587	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
588	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
589	will be reported to stderr and cause the process to exit.	606	will be reported to stderr and cause the process to exit.
590		607
591	If you want to execute some code to take over the process (see the	608	If you want to execute some code (that isn't in a module) to take over the
592	"fork+exec" example in the SYNOPSIS), you should compile a function via	609	process, you should compile a function via C<eval> first, and then call
593	C<eval> first, and then call it via C<run>. This also gives you access to	610	it via C<run>. This also gives you access to any arguments passed via the
594	any arguments passed via the C<send_xxx> methods, such as file handles.	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.
595		613
596	Returns the process object for easy chaining of method calls.	614	Returns the process object for easy chaining of method calls.
597		615
598	=cut	616	=cut
599		617
…		…
625	=item $proc = $proc->send_fh ($handle, ...)	643	=item $proc = $proc->send_fh ($handle, ...)
626		644
627	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,
628	to prepare a call to C<run>.	646	to prepare a call to C<run>.
629		647
630	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
631	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
632	accomplished by simply not storing the file handles anywhere after passing	650	handles. This is most easily accomplished by simply not storing the file
633	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.
634		653
635	Returns the process object for easy chaining of method calls.	654	Returns the process object for easy chaining of method calls.
636		655
637	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
638	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.
…		…
654	}	673	}
655		674
656	=item $proc = $proc->send_arg ($string, ...)	675	=item $proc = $proc->send_arg ($string, ...)
657		676
658	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
659	C<run>. The strings can be any octet string.	678	C<run>. The strings can be any octet strings.
660		679
661	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
662	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
663	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
664	data.	683	data.
…		…
680	Enter the function specified by the function name in C<$func> in the	699	Enter the function specified by the function name in C<$func> in the
681	process. The function is called with the communication socket as first	700	process. The function is called with the communication socket as first
682	argument, followed by all file handles and string arguments sent earlier	701	argument, followed by all file handles and string arguments sent earlier
683	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.
684		703
		704	The process object becomes unusable on return from this function - any
		705	further method calls result in undefined behaviour.
		706
685	The function name should be fully qualified, but if it isn't, it will be	707	The function name should be fully qualified, but if it isn't, it will be
686	looked up in the main package.	708	looked up in the C<main> package.
687		709
688	If the called function returns, doesn't exist, or any error occurs, the	710	If the called function returns, doesn't exist, or any error occurs, the
689	process exits.	711	process exits.
690		712
691	Preparing the process is done in the background - when all commands have	713	Preparing the process is done in the background - when all commands have
692	been sent, the callback is invoked with the local communications socket	714	been sent, the callback is invoked with the local communications socket
693	as argument. At this point you can start using the socket in any way you	715	as argument. At this point you can start using the socket in any way you
694	like.	716	like.
695
696	The process object becomes unusable on return from this function - any
697	further method calls result in undefined behaviour.
698		717
699	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,
700	to save on kernel memory.	719	to save on kernel memory.
701		720
702	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
…		…
777	479 vfork+execs per second, using AnyEvent::Fork->new_exec	796	479 vfork+execs per second, using AnyEvent::Fork->new_exec
778		797
779	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
780	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?
781		800
782	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
783	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
784	introduced is canceled out.	803	overhead introduced is canceled out.
785		804
786	If the benchmark process grows, the normal fork becomes even slower:	805	If the benchmark process grows, the normal fork becomes even slower:
787		806
788	1340 new processes, manual fork in a 20MB process	807	1340 new processes, manual fork of a 20MB process
789	731 new processes, manual fork in a 200MB process	808	731 new processes, manual fork of a 200MB process
790	235 new processes, manual fork in a 2000MB process	809	235 new processes, manual fork of a 2000MB process
791		810
792	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
793	very bad conscience because of the extra overhead required to start new	812	conscience because of the extra overhead required to start new processes.
794	processes.
795		813
796	=head1 TYPICAL PROBLEMS	814	=head1 TYPICAL PROBLEMS
797		815
798	This section lists typical problems that remain. I hope by recognising	816	This section lists typical problems that remain. I hope by recognising
799	them, most can be avoided.	817	them, most can be avoided.
800		818
801	=over 4	819	=over 4
802		820
803	=item "leaked" file descriptors for exec'ed processes	821	=item leaked file descriptors for exec'ed processes
804		822
805	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
806	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
807	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
808	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.
…		…
828	libraries or the code that leaks those file descriptors.	846	libraries or the code that leaks those file descriptors.
829		847
830	Fortunately, most of these leaked descriptors do no harm, other than	848	Fortunately, most of these leaked descriptors do no harm, other than
831	sitting on some resources.	849	sitting on some resources.
832		850
833	=item "leaked" file descriptors for fork'ed processes	851	=item leaked file descriptors for fork'ed processes
834		852
835	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,
836	which closes file descriptors not marked for being inherited.	854	which closes file descriptors not marked for being inherited.
837		855
838	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	856	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
847		865
848	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
849	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
850	initialising them, for example, by calling C<init Gtk2> manually.	868	initialising them, for example, by calling C<init Gtk2> manually.
851		869
852	=item exit runs destructors	870	=item exiting calls object destructors
853		871
854	This only applies to users of Lc<AnyEvent::Fork:Early> and	872	This only applies to users of L<AnyEvent::Fork:Early> and
855	L<AnyEvent::Fork::Template>.	873	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		874	that reference external resources.
856		875
857	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
858	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
859	Perl runs all destructors.	878	Perl runs all destructors.
860		879
…		…
879	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
880	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
881	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
882	issues or other braindamage. Hrrrr.	901	issues or other braindamage. Hrrrr.
883		902
884	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
885	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.
886	support enough functionality to do it.
887		905
888	=head1 SEE ALSO	906	=head1 SEE ALSO
889		907
890	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	908	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
891	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 1.27 by root, Sat Apr 6 09:05:50 2013 UTC vs. Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.27 by root, Sat Apr 6 09:05:50 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC