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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.28 by root, Sat Apr 6 09:06:43 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 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.
38		38
39	If you need some form of RPC, you can either implement it yourself	39	If you need some form of RPC, you could use the L<AnyEvent::Fork::RPC>
40	in whatever way you like, use some message-passing module such	40	companion module, which adds simple RPC/job queueing to a process created
41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use	41	by this module.
42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
43	and so on.
44		42
		43	And if you need some automatic process pool management on top of
		44	L<AnyEvent::Fork::RPC>, you can look at the L<AnyEvent::Fork::Pool>
		45	companion module.
		46
		47	Or you can implement it yourself in whatever way you like: use some
		48	message-passing module such as L<AnyEvent::MP>, some pipe such as
		49	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		50	e.g. JSON or Storable messages, and so on.
		51
		52	=head2 COMPARISON TO OTHER MODULES
		53
		54	There is an abundance of modules on CPAN that do "something fork", such as
		55	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		56	or L<AnyEvent::Subprocess>. There are modules that implement their own
		57	process management, such as L<AnyEvent::DBI>.
		58
		59	The problems that all these modules try to solve are real, however, none
		60	of them (from what I have seen) tackle the very real problems of unwanted
		61	memory sharing, efficiency, not being able to use event processing or
		62	similar modules in the processes they create.
		63
		64	This module doesn't try to replace any of them - instead it tries to solve
		65	the problem of creating processes with a minimum of fuss and overhead (and
		66	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		67	except they were written before AnyEvent:Fork was available, so obviously
		68	had to roll their own.
		69
45	=head1 PROBLEM STATEMENT	70	=head2 PROBLEM STATEMENT
46		71
47	There are two traditional ways to implement parallel processing on UNIX	72	There are two traditional ways to implement parallel processing on UNIX
48	like operating systems - fork and process, and fork+exec and process. They	73	like operating systems - fork and process, and fork+exec and process. They
49	have different advantages and disadvantages that I describe below,	74	have different advantages and disadvantages that I describe below,
50	together with how this module tries to mitigate the disadvantages.	75	together with how this module tries to mitigate the disadvantages.
…		…
152		177
153	# now $master_filehandle is connected to the	178	# now $master_filehandle is connected to the
154	# $slave_filehandle in the new process.	179	# $slave_filehandle in the new process.
155	});	180	});
156		181
157	# MyModule::worker might look like this	182	C<MyModule> might look like this:
		183
		184	package MyModule;
		185
158	sub MyModule::worker {	186	sub worker {
159	my ($slave_filehandle) = @_;	187	my ($slave_filehandle) = @_;
160		188
161	# now $slave_filehandle is connected to the $master_filehandle	189	# now $slave_filehandle is connected to the $master_filehandle
162	# in the original prorcess. have fun!	190	# in the original prorcess. have fun!
163	}	191	}
…		…
182	}	210	}
183		211
184	# now do other things - maybe use the filehandle provided by run	212	# now do other things - maybe use the filehandle provided by run
185	# to wait for the processes to die. or whatever.	213	# to wait for the processes to die. or whatever.
186		214
187	# My::Server::run might look like this	215	C<My::Server> might look like this:
188	sub My::Server::run {	216
		217	package My::Server;
		218
		219	sub run {
189	my ($slave, $listener, $id) = @_;	220	my ($slave, $listener, $id) = @_;
190		221
191	close $slave; # we do not use the socket, so close it to save resources	222	close $slave; # we do not use the socket, so close it to save resources
192		223
193	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	224	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
197	}	228	}
198	}	229	}
199		230
200	=head2 use AnyEvent::Fork as a faster fork+exec	231	=head2 use AnyEvent::Fork as a faster fork+exec
201		232
202	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to	233	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
203	the communications socket. It is usually faster than fork+exec, but still	234	and standard error redirected to the communications socket. It is usually
204	let's you prepare the environment.	235	faster than fork+exec, but still lets you prepare the environment.
205		236
206	open my $output, ">/tmp/log" or die "$!";	237	open my $output, ">/tmp/log" or die "$!";
207		238
208	AnyEvent::Fork	239	AnyEvent::Fork
209	->new	240	->new
210	->eval ('	241	->eval ('
		242	# compile a helper function for later use
211	sub run {	243	sub run {
212	my ($fh, $output, @cmd) = @_;	244	my ($fh, $output, @cmd) = @_;
213		245
214	# perl will clear close-on-exec on STDOUT/STDERR	246	# perl will clear close-on-exec on STDOUT/STDERR
215	open STDOUT, ">&", $output or die;	247	open STDOUT, ">&", $output or die;
…		…
222	->send_arg ("/bin/echo", "hi")	254	->send_arg ("/bin/echo", "hi")
223	->run ("run", my $cv = AE::cv);	255	->run ("run", my $cv = AE::cv);
224		256
225	my $stderr = $cv->recv;	257	my $stderr = $cv->recv;
226		258
		259	=head2 For stingy users: put the worker code into a C<DATA> section.
		260
		261	When you want to be stingy with files, you cna put your code into the
		262	C<DATA> section of your module (or program):
		263
		264	use AnyEvent::Fork;
		265
		266	AnyEvent::Fork
		267	->new
		268	->eval (do { local $/; <DATA> })
		269	->run ("doit", sub { ... });
		270
		271	__DATA__
		272
		273	sub doit {
		274	... do something!
		275	}
		276
		277	=head2 For stingy standalone programs: do not rely on external files at
		278	all.
		279
		280	For single-file scripts it can be inconvenient to rely on external
		281	files - even when using < C<DATA> section, you still need to C<exec>
		282	an external perl interpreter, which might not be available when using
		283	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
		284
		285	Two modules help here - L<AnyEvent::Fork::Early> forks a template process
		286	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
		287	forks the main program as a template process.
		288
		289	Here is how your main program should look like:
		290
		291	#! perl
		292
		293	# optional, as the very first thing.
		294	# in case modules want to create their own processes.
		295	use AnyEvent::Fork::Early;
		296
		297	# next, load all modules you need in your template process
		298	use Example::My::Module
		299	use Example::Whatever;
		300
		301	# next, put your run function definition and anything else you
		302	# need, but do not use code outside of BEGIN blocks.
		303	sub worker_run {
		304	my ($fh, @args) = @_;
		305	...
		306	}
		307
		308	# now preserve everything so far as AnyEvent::Fork object
		309	# in §TEMPLATE.
		310	use AnyEvent::Fork::Template;
		311
		312	# do not put code outside of BEGIN blocks until here
		313
		314	# now use the $TEMPLATE process in any way you like
		315
		316	# for example: create 10 worker processes
		317	my @worker;
		318	my $cv = AE::cv;
		319	for (1..10) {
		320	$cv->begin;
		321	$TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub {
		322	push @worker, shift;
		323	$cv->end;
		324	});
		325	}
		326	$cv->recv;
		327
227	=head1 CONCEPTS	328	=head1 CONCEPTS
228		329
229	This module can create new processes either by executing a new perl	330	This module can create new processes either by executing a new perl
230	process, or by forking from an existing "template" process.	331	process, or by forking from an existing "template" process.
		332
		333	All these processes are called "child processes" (whether they are direct
		334	children or not), while the process that manages them is called the
		335	"parent process".
231		336
232	Each such process comes with its own file handle that can be used to	337	Each such process comes with its own file handle that can be used to
233	communicate with it (it's actually a socket - one end in the new process,	338	communicate with it (it's actually a socket - one end in the new process,
234	one end in the main process), and among the things you can do in it are	339	one end in the main process), and among the things you can do in it are
235	load modules, fork new processes, send file handles to it, and execute	340	load modules, fork new processes, send file handles to it, and execute
…		…
326		431
327	If a process object is destroyed before calling its C<run> method, then	432	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	433	the process simply exits. After C<run> is called, all responsibility is
329	passed to the specified function.	434	passed to the specified function.
330		435
		436	As long as there is any outstanding work to be done, process objects
		437	resist being destroyed, so there is no reason to store them unless you
		438	need them later - configure and forget works just fine.
		439
331	=over 4	440	=over 4
332		441
333	=cut	442	=cut
334		443
335	package AnyEvent::Fork;	444	package AnyEvent::Fork;
…		…
341	use AnyEvent;	450	use AnyEvent;
342	use AnyEvent::Util ();	451	use AnyEvent::Util ();
343		452
344	use IO::FDPass;	453	use IO::FDPass;
345		454
346	our $VERSION = 0.5;	455	our $VERSION = '1.0';
347
348	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
349
350	=over 4
351
352	=back
353
354	=cut
355		456
356	# the early fork template process	457	# the early fork template process
357	our $EARLY;	458	our $EARLY;
358		459
359	# the empty template process	460	# the empty template process
360	our $TEMPLATE;	461	our $TEMPLATE;
		462
		463	sub QUEUE() { 0 }
		464	sub FH() { 1 }
		465	sub WW() { 2 }
		466	sub PID() { 3 }
		467	sub CB() { 4 }
		468
		469	sub _new {
		470	my ($self, $fh, $pid) = @_;
		471
		472	AnyEvent::Util::fh_nonblocking $fh, 1;
		473
		474	$self = bless [
		475	[], # write queue - strings or fd's
		476	$fh,
		477	undef, # AE watcher
		478	$pid,
		479	], $self;
		480
		481	$self
		482	}
361		483
362	sub _cmd {	484	sub _cmd {
363	my $self = shift;	485	my $self = shift;
364		486
365	# ideally, we would want to use "a (w/a)*" as format string, but perl	487	# ideally, we would want to use "a (w/a)*" as format string, but perl
366	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack	488	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
367	# it.	489	# it.
368	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	490	push @{ $self->[QUEUE] }, pack "a N/a*", $_[0], $_[1];
369		491
370	$self->[3] \|\|= AE::io $self->[1], 1, sub {	492	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
371	do {	493	do {
372	# send the next "thing" in the queue - either a reference to an fh,	494	# send the next "thing" in the queue - either a reference to an fh,
373	# or a plain string.	495	# or a plain string.
374		496
375	if (ref $self->[2][0]) {	497	if (ref $self->[QUEUE][0]) {
376	# send fh	498	# send fh
377	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	499	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
378	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	500	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
379	undef $self->[3];	501	undef $self->[WW];
380	die "AnyEvent::Fork: file descriptor send failure: $!";	502	die "AnyEvent::Fork: file descriptor send failure: $!";
381	}	503	}
382		504
383	shift @{ $self->[2] };	505	shift @{ $self->[QUEUE] };
384		506
385	} else {	507	} else {
386	# send string	508	# send string
387	my $len = syswrite $self->[1], $self->[2][0];	509	my $len = syswrite $self->[FH], $self->[QUEUE][0];
388		510
389	unless ($len) {	511	unless ($len) {
390	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	512	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
391	undef $self->[3];	513	undef $self->[WW];
392	die "AnyEvent::Fork: command write failure: $!";	514	die "AnyEvent::Fork: command write failure: $!";
393	}	515	}
394		516
395	substr $self->[2][0], 0, $len, "";	517	substr $self->[QUEUE][0], 0, $len, "";
396	shift @{ $self->[2] } unless length $self->[2][0];	518	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
397	}	519	}
398	} while @{ $self->[2] };	520	} while @{ $self->[QUEUE] };
399		521
400	# everything written	522	# everything written
401	undef $self->[3];	523	undef $self->[WW];
402		524
403	# invoke run callback, if any	525	# invoke run callback, if any
404	$self->[4]->($self->[1]) if $self->[4];	526	if ($self->[CB]) {
		527	$self->[CB]->($self->[FH]);
		528	@$self = ();
		529	}
405	};	530	};
406		531
407	() # make sure we don't leak the watcher	532	() # make sure we don't leak the watcher
408	}
409
410	sub _new {
411	my ($self, $fh, $pid) = @_;
412
413	AnyEvent::Util::fh_nonblocking $fh, 1;
414
415	$self = bless [
416	$pid,
417	$fh,
418	[], # write queue - strings or fd's
419	undef, # AE watcher
420	], $self;
421
422	$self
423	}	533	}
424		534
425	# fork template from current process, used by AnyEvent::Fork::Early/Template	535	# fork template from current process, used by AnyEvent::Fork::Early/Template
426	sub _new_fork {	536	sub _new_fork {
427	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	537	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
432	if ($pid eq 0) {	542	if ($pid eq 0) {
433	require AnyEvent::Fork::Serve;	543	require AnyEvent::Fork::Serve;
434	$AnyEvent::Fork::Serve::OWNER = $parent;	544	$AnyEvent::Fork::Serve::OWNER = $parent;
435	close $fh;	545	close $fh;
436	$0 = "$_[1] of $parent";	546	$0 = "$_[1] of $parent";
437	$SIG{CHLD} = 'IGNORE';
438	AnyEvent::Fork::Serve::serve ($slave);	547	AnyEvent::Fork::Serve::serve ($slave);
439	exit 0;	548	exit 0;
440	} elsif (!$pid) {	549	} elsif (!$pid) {
441	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	550	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
442	}	551	}
…		…
449	Create a new "empty" perl interpreter process and returns its process	558	Create a new "empty" perl interpreter process and returns its process
450	object for further manipulation.	559	object for further manipulation.
451		560
452	The new process is forked from a template process that is kept around	561	The new process is forked from a template process that is kept around
453	for this purpose. When it doesn't exist yet, it is created by a call to	562	for this purpose. When it doesn't exist yet, it is created by a call to
454	C<new_exec> and kept around for future calls.	563	C<new_exec> first and then stays around for future calls.
455
456	When the process object is destroyed, it will release the file handle
457	that connects it with the new process. When the new process has not yet
458	called C<run>, then the process will exit. Otherwise, what happens depends
459	entirely on the code that is executed.
460		564
461	=cut	565	=cut
462		566
463	sub new {	567	sub new {
464	my $class = shift;	568	my $class = shift;
…		…
554	}	658	}
555		659
556	=item $pid = $proc->pid	660	=item $pid = $proc->pid
557		661
558	Returns the process id of the process I<iff it is a direct child of the	662	Returns the process id of the process I<iff it is a direct child of the
559	process> running AnyEvent::Fork, and C<undef> otherwise.	663	process running AnyEvent::Fork>, and C<undef> otherwise.
560		664
561	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	665	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
562	L<AnyEvent::Fork::Template> are direct children, and you are responsible	666	L<AnyEvent::Fork::Template> are direct children, and you are responsible
563	to clean up their zombies when they die.	667	to clean up their zombies when they die.
564		668
565	All other processes are not direct children, and will be cleaned up by	669	All other processes are not direct children, and will be cleaned up by
566	AnyEvent::Fork.	670	AnyEvent::Fork itself.
567		671
568	=cut	672	=cut
569		673
570	sub pid {	674	sub pid {
571	$_[0][0]	675	$_[0][PID]
572	}	676	}
573		677
574	=item $proc = $proc->eval ($perlcode, @args)	678	=item $proc = $proc->eval ($perlcode, @args)
575		679
576	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	680	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
577	the strings specified by C<@args>, in the "main" package.	681	the strings specified by C<@args>, in the "main" package.
578		682
579	This call is meant to do any custom initialisation that might be required	683	This call is meant to do any custom initialisation that might be required
580	(for example, the C<require> method uses it). It's not supposed to be used	684	(for example, the C<require> method uses it). It's not supposed to be used
581	to completely take over the process, use C<run> for that.	685	to completely take over the process, use C<run> for that.
582		686
583	The code will usually be executed after this call returns, and there is no	687	The code will usually be executed after this call returns, and there is no
584	way to pass anything back to the calling process. Any evaluation errors	688	way to pass anything back to the calling process. Any evaluation errors
585	will be reported to stderr and cause the process to exit.	689	will be reported to stderr and cause the process to exit.
586		690
587	If you want to execute some code to take over the process (see the	691	If you want to execute some code (that isn't in a module) to take over the
588	"fork+exec" example in the SYNOPSIS), you should compile a function via	692	process, you should compile a function via C<eval> first, and then call
589	C<eval> first, and then call it via C<run>. This also gives you access to	693	it via C<run>. This also gives you access to any arguments passed via the
590	any arguments passed via the C<send_xxx> methods, such as file handles.	694	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		695	a faster fork+exec> example to see it in action.
591		696
592	Returns the process object for easy chaining of method calls.	697	Returns the process object for easy chaining of method calls.
593		698
594	=cut	699	=cut
595		700
…		…
621	=item $proc = $proc->send_fh ($handle, ...)	726	=item $proc = $proc->send_fh ($handle, ...)
622		727
623	Send one or more file handles (I<not> file descriptors) to the process,	728	Send one or more file handles (I<not> file descriptors) to the process,
624	to prepare a call to C<run>.	729	to prepare a call to C<run>.
625		730
626	The process object keeps a reference to the handles until this is done,	731	The process object keeps a reference to the handles until they have
627	so you must not explicitly close the handles. This is most easily	732	been passed over to the process, so you must not explicitly close the
628	accomplished by simply not storing the file handles anywhere after passing	733	handles. This is most easily accomplished by simply not storing the file
629	them to this method.	734	handles anywhere after passing them to this method - when AnyEvent::Fork
		735	is finished using them, perl will automatically close them.
630		736
631	Returns the process object for easy chaining of method calls.	737	Returns the process object for easy chaining of method calls.
632		738
633	Example: pass a file handle to a process, and release it without	739	Example: pass a file handle to a process, and release it without
634	closing. It will be closed automatically when it is no longer used.	740	closing. It will be closed automatically when it is no longer used.
…		…
641	sub send_fh {	747	sub send_fh {
642	my ($self, @fh) = @_;	748	my ($self, @fh) = @_;
643		749
644	for my $fh (@fh) {	750	for my $fh (@fh) {
645	$self->_cmd ("h");	751	$self->_cmd ("h");
646	push @{ $self->[2] }, \$fh;	752	push @{ $self->[QUEUE] }, \$fh;
647	}	753	}
648		754
649	$self	755	$self
650	}	756	}
651		757
652	=item $proc = $proc->send_arg ($string, ...)	758	=item $proc = $proc->send_arg ($string, ...)
653		759
654	Send one or more argument strings to the process, to prepare a call to	760	Send one or more argument strings to the process, to prepare a call to
655	C<run>. The strings can be any octet string.	761	C<run>. The strings can be any octet strings.
656		762
657	The protocol is optimised to pass a moderate number of relatively short	763	The protocol is optimised to pass a moderate number of relatively short
658	strings - while you can pass up to 4GB of data in one go, this is more	764	strings - while you can pass up to 4GB of data in one go, this is more
659	meant to pass some ID information or other startup info, not big chunks of	765	meant to pass some ID information or other startup info, not big chunks of
660	data.	766	data.
…		…
676	Enter the function specified by the function name in C<$func> in the	782	Enter the function specified by the function name in C<$func> in the
677	process. The function is called with the communication socket as first	783	process. The function is called with the communication socket as first
678	argument, followed by all file handles and string arguments sent earlier	784	argument, followed by all file handles and string arguments sent earlier
679	via C<send_fh> and C<send_arg> methods, in the order they were called.	785	via C<send_fh> and C<send_arg> methods, in the order they were called.
680		786
		787	The process object becomes unusable on return from this function - any
		788	further method calls result in undefined behaviour.
		789
681	The function name should be fully qualified, but if it isn't, it will be	790	The function name should be fully qualified, but if it isn't, it will be
682	looked up in the main package.	791	looked up in the C<main> package.
683		792
684	If the called function returns, doesn't exist, or any error occurs, the	793	If the called function returns, doesn't exist, or any error occurs, the
685	process exits.	794	process exits.
686		795
687	Preparing the process is done in the background - when all commands have	796	Preparing the process is done in the background - when all commands have
688	been sent, the callback is invoked with the local communications socket	797	been sent, the callback is invoked with the local communications socket
689	as argument. At this point you can start using the socket in any way you	798	as argument. At this point you can start using the socket in any way you
690	like.	799	like.
691
692	The process object becomes unusable on return from this function - any
693	further method calls result in undefined behaviour.
694		800
695	If the communication socket isn't used, it should be closed on both sides,	801	If the communication socket isn't used, it should be closed on both sides,
696	to save on kernel memory.	802	to save on kernel memory.
697		803
698	The socket is non-blocking in the parent, and blocking in the newly	804	The socket is non-blocking in the parent, and blocking in the newly
…		…
737	=cut	843	=cut
738		844
739	sub run {	845	sub run {
740	my ($self, $func, $cb) = @_;	846	my ($self, $func, $cb) = @_;
741		847
742	$self->[4] = $cb;	848	$self->[CB] = $cb;
743	$self->_cmd (r => $func);	849	$self->_cmd (r => $func);
		850	}
		851
		852	=back
		853
		854	=head2 ADVANCED METHODS
		855
		856	=over 4
		857
		858	=item new_from_stdio AnyEvent::Fork $fh
		859
		860	Assume that you have a perl interpreter running (without any special
		861	options or a program) somewhere and it has it's STDIN and STDOUT connected
		862	to the C<$fh> somehow. I.e. exactly the state perl is in when you start it
		863	without any arguments:
		864
		865	perl
		866
		867	Then you can create an C<AnyEvent::Fork> object out of this perl
		868	interpreter with this constructor.
		869
		870	When the usefulness of this isn't immediately clear, imagine you manage to
		871	run a perl interpreter remotely (F<ssh remotemachine perl>), then you can
		872	manage it mostly like a local C<AnyEvent::Fork> child.
		873
		874	This works without any module support, i.e. the remote F<perl> does not
		875	need to have any special modules installed.
		876
		877	There are a number of limitations though: C<send_fh> will only work if the
		878	L<IO::FDPass> module is loadable by the remote perl and the two processes
		879	are connected in a way that let's L<IO::FDPass> do it's work.
		880
		881	This will therefore not work over a network connection. From this follows
		882	that C<fork> will also not work under these circumstances, as it relies on
		883	C<send_fh> internally.
		884
		885	Although not a limitation of this module, keep in mind that the
		886	"communications socket" is simply C<STDIN>, and depending on how you
		887	started F<perl> (e.g. via F<ssh>), it might only be half-duplex. This is
		888	fine for C<AnyEvent::Fork>, but your C<run> function might want to use
		889	C<STDIN> (or the "communications socket") for input and C<STDOUT> for
		890	output.
		891
		892	You can support both cases by checking the C<fileno> of the handle passed
		893	to your run function:
		894
		895	sub run {
		896	my ($rfh) = @_;
		897
		898	my $wfh = fileno $rfh ? $rfh : *STDOUT;
		899
		900	# now use $rfh for reading and $wfh for writing
		901	}
		902
		903	=cut
		904
		905	sub new_from_stdio {
		906	my ($class, $fh) = @_;
		907
		908	my $self = $class->_new ($fh);
		909
		910	# send startup code
		911	push @{ $self->[QUEUE] },
		912	(do "AnyEvent/Fork/serve.pl")
		913	. <<'EOF';
		914
		915	$OWNER = "another process";
		916	$0 = "AnyEvent::Fork/stdio of $OWNER";
		917
		918	serve *STDIN;
		919	__END__
		920	EOF
		921
		922	# the data is only sent when the user requests additional things, which
		923	# is likely early enough for our purposes.
		924
		925	$self
		926	}
		927
		928	=back
		929
		930	=head2 EXPERIMENTAL METHODS
		931
		932	These methods might go away completely or change behaviour, a any time.
		933
		934	=over 4
		935
		936	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		937
		938	Flushes all commands out to the process and then calls the callback with
		939	the communications socket.
		940
		941	The process object becomes unusable on return from this function - any
		942	further method calls result in undefined behaviour.
		943
		944	The point of this method is to give you a file handle thta you cna pass
		945	to another process. In that other process, you can call C<new_from_fh
		946	AnyEvent::Fork> to create a new C<AnyEvent::Fork> object from it, thereby
		947	effectively passing a fork object to another process.
		948
		949	=cut
		950
		951	sub to_fh {
		952	my ($self, $cb) = @_;
		953
		954	$self->[CB] = $cb;
		955
		956	unless ($self->[WW]) {
		957	$self->[CB]->($self->[FH]);
		958	@$self = ();
		959	}
		960	}
		961
		962	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		963
		964	Takes a file handle originally rceeived by the C<to_fh> method and creates
		965	a new C<AnyEvent:Fork> object. The child process itself will not change in
		966	any way, i.e. it will keep all the modifications done to it before calling
		967	C<to_fh>.
		968
		969	The new object is very much like the original object, except that the
		970	C<pid> method will return C<undef> even if the process is a direct child.
		971
		972	=cut
		973
		974	sub new_from_fh {
		975	my ($class, $fh) = @_;
		976
		977	$class->_new ($fh)
744	}	978	}
745		979
746	=back	980	=back
747		981
748	=head1 PERFORMANCE	982	=head1 PERFORMANCE
…		…
758		992
759	2079 new processes per second, using manual socketpair + fork	993	2079 new processes per second, using manual socketpair + fork
760		994
761	Then I did the same thing, but instead of calling fork, I called	995	Then I did the same thing, but instead of calling fork, I called
762	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the	996	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
763	socket form the child to close on exit. This does the same thing as manual	997	socket from the child to close on exit. This does the same thing as manual
764	socket pair + fork, except that what is forked is the template process	998	socket pair + fork, except that what is forked is the template process
765	(2440kB), and the socket needs to be passed to the server at the other end	999	(2440kB), and the socket needs to be passed to the server at the other end
766	of the socket first.	1000	of the socket first.
767		1001
768	2307 new processes per second, using AnyEvent::Fork->new	1002	2307 new processes per second, using AnyEvent::Fork->new
…		…
773	479 vfork+execs per second, using AnyEvent::Fork->new_exec	1007	479 vfork+execs per second, using AnyEvent::Fork->new_exec
774		1008
775	So how can C<< AnyEvent->new >> be faster than a standard fork, even	1009	So how can C<< AnyEvent->new >> be faster than a standard fork, even
776	though it uses the same operations, but adds a lot of overhead?	1010	though it uses the same operations, but adds a lot of overhead?
777		1011
778	The difference is simply the process size: forking the 6MB process takes	1012	The difference is simply the process size: forking the 5MB process takes
779	so much longer than forking the 2.5MB template process that the overhead	1013	so much longer than forking the 2.5MB template process that the extra
780	introduced is canceled out.	1014	overhead is canceled out.
781		1015
782	If the benchmark process grows, the normal fork becomes even slower:	1016	If the benchmark process grows, the normal fork becomes even slower:
783		1017
784	1340 new processes, manual fork in a 20MB process	1018	1340 new processes, manual fork of a 20MB process
785	731 new processes, manual fork in a 200MB process	1019	731 new processes, manual fork of a 200MB process
786	235 new processes, manual fork in a 2000MB process	1020	235 new processes, manual fork of a 2000MB process
787		1021
788	What that means (to me) is that I can use this module without having a	1022	What that means (to me) is that I can use this module without having a bad
789	very bad conscience because of the extra overhead required to start new	1023	conscience because of the extra overhead required to start new processes.
790	processes.
791		1024
792	=head1 TYPICAL PROBLEMS	1025	=head1 TYPICAL PROBLEMS
793		1026
794	This section lists typical problems that remain. I hope by recognising	1027	This section lists typical problems that remain. I hope by recognising
795	them, most can be avoided.	1028	them, most can be avoided.
796		1029
797	=over 4	1030	=over 4
798		1031
799	=item "leaked" file descriptors for exec'ed processes	1032	=item leaked file descriptors for exec'ed processes
800		1033
801	POSIX systems inherit file descriptors by default when exec'ing a new	1034	POSIX systems inherit file descriptors by default when exec'ing a new
802	process. While perl itself laudably sets the close-on-exec flags on new	1035	process. While perl itself laudably sets the close-on-exec flags on new
803	file handles, most C libraries don't care, and even if all cared, it's	1036	file handles, most C libraries don't care, and even if all cared, it's
804	often not possible to set the flag in a race-free manner.	1037	often not possible to set the flag in a race-free manner.
…		…
824	libraries or the code that leaks those file descriptors.	1057	libraries or the code that leaks those file descriptors.
825		1058
826	Fortunately, most of these leaked descriptors do no harm, other than	1059	Fortunately, most of these leaked descriptors do no harm, other than
827	sitting on some resources.	1060	sitting on some resources.
828		1061
829	=item "leaked" file descriptors for fork'ed processes	1062	=item leaked file descriptors for fork'ed processes
830		1063
831	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	1064	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
832	which closes file descriptors not marked for being inherited.	1065	which closes file descriptors not marked for being inherited.
833		1066
834	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	1067	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
843		1076
844	The solution is to either not load these modules before use'ing	1077	The solution is to either not load these modules before use'ing
845	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	1078	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
846	initialising them, for example, by calling C<init Gtk2> manually.	1079	initialising them, for example, by calling C<init Gtk2> manually.
847		1080
848	=item exit runs destructors	1081	=item exiting calls object destructors
849		1082
850	This only applies to users of Lc<AnyEvent::Fork:Early> and	1083	This only applies to users of L<AnyEvent::Fork:Early> and
851	L<AnyEvent::Fork::Template>.	1084	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1085	that reference external resources.
852		1086
853	When a process created by AnyEvent::Fork exits, it might do so by calling	1087	When a process created by AnyEvent::Fork exits, it might do so by calling
854	exit, or simply letting perl reach the end of the program. At which point	1088	exit, or simply letting perl reach the end of the program. At which point
855	Perl runs all destructors.	1089	Perl runs all destructors.
856		1090
…		…
875	to make it so, mostly due to the bloody broken perl that nobody seems to	1109	to make it so, mostly due to the bloody broken perl that nobody seems to
876	care about. The fork emulation is a bad joke - I have yet to see something	1110	care about. The fork emulation is a bad joke - I have yet to see something
877	useful that you can do with it without running into memory corruption	1111	useful that you can do with it without running into memory corruption
878	issues or other braindamage. Hrrrr.	1112	issues or other braindamage. Hrrrr.
879		1113
880	Cygwin perl is not supported at the moment, as it should implement fd	1114	Since fork is endlessly broken on win32 perls (it doesn't even remotely
881	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	1115	work within it's documented limits) and quite obviously it's not getting
882	support enough functionality to do it.	1116	improved any time soon, the best way to proceed on windows would be to
		1117	always use C<new_exec> and thus never rely on perl's fork "emulation".
		1118
		1119	Cygwin perl is not supported at the moment due to some hilarious
		1120	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1121	use C<send_fh> and always use C<new_exec> to create processes, it should
		1122	work though.
883		1123
884	=head1 SEE ALSO	1124	=head1 SEE ALSO
885		1125
886	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	1126	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1127	(part of this distribution).
		1128
887	L<AnyEvent::Fork::Template> (to create a process by forking the main	1129	L<AnyEvent::Fork::Template>, to create a process by forking the main
888	program at a convenient time).	1130	program at a convenient time (part of this distribution).
889		1131
890	=head1 AUTHOR	1132	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1133
		1134	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1135
		1136	=head1 AUTHOR AND CONTACT INFORMATION
891		1137
892	Marc Lehmann <schmorp@schmorp.de>	1138	Marc Lehmann <schmorp@schmorp.de>
893	http://home.schmorp.de/	1139	http://software.schmorp.de/pkg/AnyEvent-Fork
894		1140
895	=cut	1141	=cut
896		1142
897	1	1143	1
898		1144

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.28 by root, Sat Apr 6 09:06:43 2013 UTC vs. Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.28 by root, Sat Apr 6 09:06:43 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC