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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.26 by root, Sat Apr 6 08:58:51 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 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
…		…
309	my ($fork_fh) = @_;	333	my ($fork_fh) = @_;
310	});	334	});
311		335
312	=back	336	=back
313		337
314	=head1 FUNCTIONS	338	=head1 THE C<AnyEvent::Fork> CLASS
		339
		340	This module exports nothing, and only implements a single class -
		341	C<AnyEvent::Fork>.
		342
		343	There are two class constructors that both create new processes - C<new>
		344	and C<new_exec>. The C<fork> method creates a new process by forking an
		345	existing one and could be considered a third constructor.
		346
		347	Most of the remaining methods deal with preparing the new process, by
		348	loading code, evaluating code and sending data to the new process. They
		349	usually return the process object, so you can chain method calls.
		350
		351	If a process object is destroyed before calling its C<run> method, then
		352	the process simply exits. After C<run> is called, all responsibility is
		353	passed to the specified function.
		354
		355	As long as there is any outstanding work to be done, process objects
		356	resist being destroyed, so there is no reason to store them unless you
		357	need them later - configure and forget works just fine.
315		358
316	=over 4	359	=over 4
317		360
318	=cut	361	=cut
319		362
…		…
329	use IO::FDPass;	372	use IO::FDPass;
330		373
331	our $VERSION = 0.5;	374	our $VERSION = 0.5;
332		375
333	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	376	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
334
335	=item my $pool = new AnyEvent::Fork key => value...
336
337	Create a new process pool. The following named parameters are supported:
338		377
339	=over 4	378	=over 4
340		379
341	=back	380	=back
342		381
…		…
438	Create a new "empty" perl interpreter process and returns its process	477	Create a new "empty" perl interpreter process and returns its process
439	object for further manipulation.	478	object for further manipulation.
440		479
441	The new process is forked from a template process that is kept around	480	The new process is forked from a template process that is kept around
442	for this purpose. When it doesn't exist yet, it is created by a call to	481	for this purpose. When it doesn't exist yet, it is created by a call to
443	C<new_exec> and kept around for future calls.	482	C<new_exec> first and then stays around for future calls.
444
445	When the process object is destroyed, it will release the file handle
446	that connects it with the new process. When the new process has not yet
447	called C<run>, then the process will exit. Otherwise, what happens depends
448	entirely on the code that is executed.
449		483
450	=cut	484	=cut
451		485
452	sub new {	486	sub new {
453	my $class = shift;	487	my $class = shift;
…		…
543	}	577	}
544		578
545	=item $pid = $proc->pid	579	=item $pid = $proc->pid
546		580
547	Returns the process id of the process I<iff it is a direct child of the	581	Returns the process id of the process I<iff it is a direct child of the
548	process> running AnyEvent::Fork, and C<undef> otherwise.	582	process running AnyEvent::Fork>, and C<undef> otherwise.
549		583
550	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	584	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
551	L<AnyEvent::Fork::Template> are direct children, and you are responsible	585	L<AnyEvent::Fork::Template> are direct children, and you are responsible
552	to clean up their zombies when they die.	586	to clean up their zombies when they die.
553		587
554	All other processes are not direct children, and will be cleaned up by	588	All other processes are not direct children, and will be cleaned up by
555	AnyEvent::Fork.	589	AnyEvent::Fork itself.
556		590
557	=cut	591	=cut
558		592
559	sub pid {	593	sub pid {
560	$_[0][0]	594	$_[0][0]
…		…
571		605
572	The code will usually be executed after this call returns, and there is no	606	The code will usually be executed after this call returns, and there is no
573	way to pass anything back to the calling process. Any evaluation errors	607	way to pass anything back to the calling process. Any evaluation errors
574	will be reported to stderr and cause the process to exit.	608	will be reported to stderr and cause the process to exit.
575		609
576	If you want to execute some code to take over the process (see the	610	If you want to execute some code (that isn't in a module) to take over the
577	"fork+exec" example in the SYNOPSIS), you should compile a function via	611	process, you should compile a function via C<eval> first, and then call
578	C<eval> first, and then call it via C<run>. This also gives you access to	612	it via C<run>. This also gives you access to any arguments passed via the
579	any arguments passed via the C<send_xxx> methods, such as file handles.	613	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		614	a faster fork+exec> example to see it in action.
580		615
581	Returns the process object for easy chaining of method calls.	616	Returns the process object for easy chaining of method calls.
582		617
583	=cut	618	=cut
584		619
…		…
610	=item $proc = $proc->send_fh ($handle, ...)	645	=item $proc = $proc->send_fh ($handle, ...)
611		646
612	Send one or more file handles (I<not> file descriptors) to the process,	647	Send one or more file handles (I<not> file descriptors) to the process,
613	to prepare a call to C<run>.	648	to prepare a call to C<run>.
614		649
615	The process object keeps a reference to the handles until this is done,	650	The process object keeps a reference to the handles until they have
616	so you must not explicitly close the handles. This is most easily	651	been passed over to the process, so you must not explicitly close the
617	accomplished by simply not storing the file handles anywhere after passing	652	handles. This is most easily accomplished by simply not storing the file
618	them to this method.	653	handles anywhere after passing them to this method - when AnyEvent::Fork
		654	is finished using them, perl will automatically close them.
619		655
620	Returns the process object for easy chaining of method calls.	656	Returns the process object for easy chaining of method calls.
621		657
622	Example: pass a file handle to a process, and release it without	658	Example: pass a file handle to a process, and release it without
623	closing. It will be closed automatically when it is no longer used.	659	closing. It will be closed automatically when it is no longer used.
…		…
639	}	675	}
640		676
641	=item $proc = $proc->send_arg ($string, ...)	677	=item $proc = $proc->send_arg ($string, ...)
642		678
643	Send one or more argument strings to the process, to prepare a call to	679	Send one or more argument strings to the process, to prepare a call to
644	C<run>. The strings can be any octet string.	680	C<run>. The strings can be any octet strings.
645		681
646	The protocol is optimised to pass a moderate number of relatively short	682	The protocol is optimised to pass a moderate number of relatively short
647	strings - while you can pass up to 4GB of data in one go, this is more	683	strings - while you can pass up to 4GB of data in one go, this is more
648	meant to pass some ID information or other startup info, not big chunks of	684	meant to pass some ID information or other startup info, not big chunks of
649	data.	685	data.
…		…
665	Enter the function specified by the function name in C<$func> in the	701	Enter the function specified by the function name in C<$func> in the
666	process. The function is called with the communication socket as first	702	process. The function is called with the communication socket as first
667	argument, followed by all file handles and string arguments sent earlier	703	argument, followed by all file handles and string arguments sent earlier
668	via C<send_fh> and C<send_arg> methods, in the order they were called.	704	via C<send_fh> and C<send_arg> methods, in the order they were called.
669		705
		706	The process object becomes unusable on return from this function - any
		707	further method calls result in undefined behaviour.
		708
670	The function name should be fully qualified, but if it isn't, it will be	709	The function name should be fully qualified, but if it isn't, it will be
671	looked up in the main package.	710	looked up in the C<main> package.
672		711
673	If the called function returns, doesn't exist, or any error occurs, the	712	If the called function returns, doesn't exist, or any error occurs, the
674	process exits.	713	process exits.
675		714
676	Preparing the process is done in the background - when all commands have	715	Preparing the process is done in the background - when all commands have
677	been sent, the callback is invoked with the local communications socket	716	been sent, the callback is invoked with the local communications socket
678	as argument. At this point you can start using the socket in any way you	717	as argument. At this point you can start using the socket in any way you
679	like.	718	like.
680
681	The process object becomes unusable on return from this function - any
682	further method calls result in undefined behaviour.
683		719
684	If the communication socket isn't used, it should be closed on both sides,	720	If the communication socket isn't used, it should be closed on both sides,
685	to save on kernel memory.	721	to save on kernel memory.
686		722
687	The socket is non-blocking in the parent, and blocking in the newly	723	The socket is non-blocking in the parent, and blocking in the newly
…		…
762	479 vfork+execs per second, using AnyEvent::Fork->new_exec	798	479 vfork+execs per second, using AnyEvent::Fork->new_exec
763		799
764	So how can C<< AnyEvent->new >> be faster than a standard fork, even	800	So how can C<< AnyEvent->new >> be faster than a standard fork, even
765	though it uses the same operations, but adds a lot of overhead?	801	though it uses the same operations, but adds a lot of overhead?
766		802
767	The difference is simply the process size: forking the 6MB process takes	803	The difference is simply the process size: forking the 5MB process takes
768	so much longer than forking the 2.5MB template process that the overhead	804	so much longer than forking the 2.5MB template process that the extra
769	introduced is canceled out.	805	overhead introduced is canceled out.
770		806
771	If the benchmark process grows, the normal fork becomes even slower:	807	If the benchmark process grows, the normal fork becomes even slower:
772		808
773	1340 new processes, manual fork in a 20MB process	809	1340 new processes, manual fork of a 20MB process
774	731 new processes, manual fork in a 200MB process	810	731 new processes, manual fork of a 200MB process
775	235 new processes, manual fork in a 2000MB process	811	235 new processes, manual fork of a 2000MB process
776		812
777	What that means (to me) is that I can use this module without having a	813	What that means (to me) is that I can use this module without having a bad
778	very bad conscience because of the extra overhead required to start new	814	conscience because of the extra overhead required to start new processes.
779	processes.
780		815
781	=head1 TYPICAL PROBLEMS	816	=head1 TYPICAL PROBLEMS
782		817
783	This section lists typical problems that remain. I hope by recognising	818	This section lists typical problems that remain. I hope by recognising
784	them, most can be avoided.	819	them, most can be avoided.
785		820
786	=over 4	821	=over 4
787		822
788	=item "leaked" file descriptors for exec'ed processes	823	=item leaked file descriptors for exec'ed processes
789		824
790	POSIX systems inherit file descriptors by default when exec'ing a new	825	POSIX systems inherit file descriptors by default when exec'ing a new
791	process. While perl itself laudably sets the close-on-exec flags on new	826	process. While perl itself laudably sets the close-on-exec flags on new
792	file handles, most C libraries don't care, and even if all cared, it's	827	file handles, most C libraries don't care, and even if all cared, it's
793	often not possible to set the flag in a race-free manner.	828	often not possible to set the flag in a race-free manner.
…		…
813	libraries or the code that leaks those file descriptors.	848	libraries or the code that leaks those file descriptors.
814		849
815	Fortunately, most of these leaked descriptors do no harm, other than	850	Fortunately, most of these leaked descriptors do no harm, other than
816	sitting on some resources.	851	sitting on some resources.
817		852
818	=item "leaked" file descriptors for fork'ed processes	853	=item leaked file descriptors for fork'ed processes
819		854
820	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	855	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
821	which closes file descriptors not marked for being inherited.	856	which closes file descriptors not marked for being inherited.
822		857
823	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	858	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
832		867
833	The solution is to either not load these modules before use'ing	868	The solution is to either not load these modules before use'ing
834	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	869	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
835	initialising them, for example, by calling C<init Gtk2> manually.	870	initialising them, for example, by calling C<init Gtk2> manually.
836		871
837	=item exit runs destructors	872	=item exiting calls object destructors
838		873
839	This only applies to users of Lc<AnyEvent::Fork:Early> and	874	This only applies to users of L<AnyEvent::Fork:Early> and
840	L<AnyEvent::Fork::Template>.	875	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		876	that reference external resources.
841		877
842	When a process created by AnyEvent::Fork exits, it might do so by calling	878	When a process created by AnyEvent::Fork exits, it might do so by calling
843	exit, or simply letting perl reach the end of the program. At which point	879	exit, or simply letting perl reach the end of the program. At which point
844	Perl runs all destructors.	880	Perl runs all destructors.
845		881
…		…
864	to make it so, mostly due to the bloody broken perl that nobody seems to	900	to make it so, mostly due to the bloody broken perl that nobody seems to
865	care about. The fork emulation is a bad joke - I have yet to see something	901	care about. The fork emulation is a bad joke - I have yet to see something
866	useful that you can do with it without running into memory corruption	902	useful that you can do with it without running into memory corruption
867	issues or other braindamage. Hrrrr.	903	issues or other braindamage. Hrrrr.
868		904
869	Cygwin perl is not supported at the moment, as it should implement fd	905	Cygwin perl is not supported at the moment due to some hilarious
870	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	906	shortcomings of its API - see L<IO::FDPoll> for more details.
871	support enough functionality to do it.
872		907
873	=head1 SEE ALSO	908	=head1 SEE ALSO
874		909
875	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	910	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
876	L<AnyEvent::Fork::Template> (to create a process by forking the main	911	L<AnyEvent::Fork::Template> (to create a process by forking the main

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.26 by root, Sat Apr 6 08:58:51 2013 UTC vs. Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.26 by root, Sat Apr 6 08:58:51 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC