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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.24 by root, Sat Apr 6 08:32:23 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,	42
43	and so on.	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
		70	=head2 PROBLEM STATEMENT
		71
		72	There are two traditional ways to implement parallel processing on UNIX
		73	like operating systems - fork and process, and fork+exec and process. They
		74	have different advantages and disadvantages that I describe below,
		75	together with how this module tries to mitigate the disadvantages.
		76
		77	=over 4
		78
		79	=item Forking from a big process can be very slow.
		80
		81	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		82	overhead is often shared with exec (because you have to fork first), but
		83	in some circumstances (e.g. when vfork is used), fork+exec can be much
		84	faster.
		85
		86	This module can help here by telling a small(er) helper process to fork,
		87	which is faster then forking the main process, and also uses vfork where
		88	possible. This gives the speed of vfork, with the flexibility of fork.
		89
		90	=item Forking usually creates a copy-on-write copy of the parent
		91	process.
		92
		93	For example, modules or data files that are loaded will not use additional
		94	memory after a fork. When exec'ing a new process, modules and data files
		95	might need to be loaded again, at extra CPU and memory cost. But when
		96	forking, literally all data structures are copied - if the program frees
		97	them and replaces them by new data, the child processes will retain the
		98	old version even if it isn't used, which can suddenly and unexpectedly
		99	increase memory usage when freeing memory.
		100
		101	The trade-off is between more sharing with fork (which can be good or
		102	bad), and no sharing with exec.
		103
		104	This module allows the main program to do a controlled fork, and allows
		105	modules to exec processes safely at any time. When creating a custom
		106	process pool you can take advantage of data sharing via fork without
		107	risking to share large dynamic data structures that will blow up child
		108	memory usage.
		109
		110	In other words, this module puts you into control over what is being
		111	shared and what isn't, at all times.
		112
		113	=item Exec'ing a new perl process might be difficult.
		114
		115	For example, it is not easy to find the correct path to the perl
		116	interpreter - C<$^X> might not be a perl interpreter at all.
		117
		118	This module tries hard to identify the correct path to the perl
		119	interpreter. With a cooperative main program, exec'ing the interpreter
		120	might not even be necessary, but even without help from the main program,
		121	it will still work when used from a module.
		122
		123	=item Exec'ing a new perl process might be slow, as all necessary modules
		124	have to be loaded from disk again, with no guarantees of success.
		125
		126	Long running processes might run into problems when perl is upgraded
		127	and modules are no longer loadable because they refer to a different
		128	perl version, or parts of a distribution are newer than the ones already
		129	loaded.
		130
		131	This module supports creating pre-initialised perl processes to be used as
		132	a template for new processes.
		133
		134	=item Forking might be impossible when a program is running.
		135
		136	For example, POSIX makes it almost impossible to fork from a
		137	multi-threaded program while doing anything useful in the child - in
		138	fact, if your perl program uses POSIX threads (even indirectly via
		139	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		140	anymore without risking corruption issues on a number of operating
		141	systems.
		142
		143	This module can safely fork helper processes at any time, by calling
		144	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		145
		146	=item Parallel processing with fork might be inconvenient or difficult
		147	to implement. Modules might not work in both parent and child.
		148
		149	For example, when a program uses an event loop and creates watchers it
		150	becomes very hard to use the event loop from a child program, as the
		151	watchers already exist but are only meaningful in the parent. Worse, a
		152	module might want to use such a module, not knowing whether another module
		153	or the main program also does, leading to problems.
		154
		155	Apart from event loops, graphical toolkits also commonly fall into the
		156	"unsafe module" category, or just about anything that communicates with
		157	the external world, such as network libraries and file I/O modules, which
		158	usually don't like being copied and then allowed to continue in two
		159	processes.
		160
		161	With this module only the main program is allowed to create new processes
		162	by forking (because only the main program can know when it is still safe
		163	to do so) - all other processes are created via fork+exec, which makes it
		164	possible to use modules such as event loops or window interfaces safely.
		165
		166	=back
44		167
45	=head1 EXAMPLES	168	=head1 EXAMPLES
46		169
47	=head2 Create a single new process, tell it to run your worker function.	170	=head2 Create a single new process, tell it to run your worker function.
48		171
…		…
54		177
55	# now $master_filehandle is connected to the	178	# now $master_filehandle is connected to the
56	# $slave_filehandle in the new process.	179	# $slave_filehandle in the new process.
57	});	180	});
58		181
59	# MyModule::worker might look like this	182	C<MyModule> might look like this:
		183
		184	package MyModule;
		185
60	sub MyModule::worker {	186	sub worker {
61	my ($slave_filehandle) = @_;	187	my ($slave_filehandle) = @_;
62		188
63	# now $slave_filehandle is connected to the $master_filehandle	189	# now $slave_filehandle is connected to the $master_filehandle
64	# in the original prorcess. have fun!	190	# in the original prorcess. have fun!
65	}	191	}
…		…
84	}	210	}
85		211
86	# now do other things - maybe use the filehandle provided by run	212	# now do other things - maybe use the filehandle provided by run
87	# to wait for the processes to die. or whatever.	213	# to wait for the processes to die. or whatever.
88		214
89	# My::Server::run might look like this	215	C<My::Server> might look like this:
90	sub My::Server::run {	216
		217	package My::Server;
		218
		219	sub run {
91	my ($slave, $listener, $id) = @_;	220	my ($slave, $listener, $id) = @_;
92		221
93	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
94		223
95	# 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,
…		…
99	}	228	}
100	}	229	}
101		230
102	=head2 use AnyEvent::Fork as a faster fork+exec	231	=head2 use AnyEvent::Fork as a faster fork+exec
103		232
104	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>
105	the communications socket. It is usually faster than fork+exec, but still	234	and standard error redirected to the communications socket. It is usually
106	let's you prepare the environment.	235	faster than fork+exec, but still lets you prepare the environment.
107		236
108	open my $output, ">/tmp/log" or die "$!";	237	open my $output, ">/tmp/log" or die "$!";
109		238
110	AnyEvent::Fork	239	AnyEvent::Fork
111	->new	240	->new
112	->eval ('	241	->eval ('
		242	# compile a helper function for later use
113	sub run {	243	sub run {
114	my ($fh, $output, @cmd) = @_;	244	my ($fh, $output, @cmd) = @_;
115		245
116	# perl will clear close-on-exec on STDOUT/STDERR	246	# perl will clear close-on-exec on STDOUT/STDERR
117	open STDOUT, ">&", $output or die;	247	open STDOUT, ">&", $output or die;
…		…
124	->send_arg ("/bin/echo", "hi")	254	->send_arg ("/bin/echo", "hi")
125	->run ("run", my $cv = AE::cv);	255	->run ("run", my $cv = AE::cv);
126		256
127	my $stderr = $cv->recv;	257	my $stderr = $cv->recv;
128		258
129	=head1 PROBLEM STATEMENT	259	=head2 For stingy users: put the worker code into a C<DATA> section.
130		260
131	There are two ways to implement parallel processing on UNIX like operating	261	When you want to be stingy with files, you cna put your code into the
132	systems - fork and process, and fork+exec and process. They have different	262	C<DATA> section of your module (or program):
133	advantages and disadvantages that I describe below, together with how this
134	module tries to mitigate the disadvantages.
135		263
136	=over 4	264	use AnyEvent::Fork;
137		265
138	=item Forking from a big process can be very slow (a 5GB process needs	266	AnyEvent::Fork
139	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead	267	->new
140	is often shared with exec (because you have to fork first), but in some	268	->eval (do { local $/; <DATA> })
141	circumstances (e.g. when vfork is used), fork+exec can be much faster.	269	->run ("doit", sub { ... });
142		270
143	This module can help here by telling a small(er) helper process to fork,	271	__DATA__
144	or fork+exec instead.
145		272
146	=item Forking usually creates a copy-on-write copy of the parent	273	sub doit {
147	process. Memory (for example, modules or data files that have been	274	... do something!
148	will not take additional memory). When exec'ing a new process, modules	275	}
149	and data files might need to be loaded again, at extra CPU and memory
150	cost. Likewise when forking, all data structures are copied as well - if
151	the program frees them and replaces them by new data, the child processes
152	will retain the memory even if it isn't used.
153		276
154	This module allows the main program to do a controlled fork, and allows	277	=head2 For stingy standalone programs: do not rely on external files at
155	modules to exec processes safely at any time. When creating a custom	278	all.
156	process pool you can take advantage of data sharing via fork without
157	risking to share large dynamic data structures that will blow up child
158	memory usage.
159		279
160	=item Exec'ing a new perl process might be difficult and slow. For	280	For single-file scripts it can be inconvenient to rely on external
161	example, it is not easy to find the correct path to the perl interpreter,	281	files - even when using < C<DATA> section, you still need to C<exec>
162	and all modules have to be loaded from disk again. Long running processes	282	an external perl interpreter, which might not be available when using
163	might run into problems when perl is upgraded for example.	283	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
164		284
165	This module supports creating pre-initialised perl processes to be used	285	Two modules help here - L<AnyEvent::Fork::Early> forks a template process
166	as template, and also tries hard to identify the correct path to the perl	286	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
167	interpreter. With a cooperative main program, exec'ing the interpreter	287	forks the main program as a template process.
168	might not even be necessary.
169		288
170	=item Forking might be impossible when a program is running. For example,	289	Here is how your main program should look like:
171	POSIX makes it almost impossible to fork from a multi-threaded program and
172	do anything useful in the child - strictly speaking, if your perl program
173	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
174	you cannot call fork on the perl level anymore, at all.
175		290
176	This module can safely fork helper processes at any time, by calling	291	#! perl
177	fork+exec in C, in a POSIX-compatible way.
178		292
179	=item Parallel processing with fork might be inconvenient or difficult	293	# optional, as the very first thing.
180	to implement. For example, when a program uses an event loop and creates	294	# in case modules want to create their own processes.
181	watchers it becomes very hard to use the event loop from a child	295	use AnyEvent::Fork::Early;
182	program, as the watchers already exist but are only meaningful in the
183	parent. Worse, a module might want to use such a system, not knowing
184	whether another module or the main program also does, leading to problems.
185		296
186	This module only lets the main program create pools by forking (because	297	# next, load all modules you need in your template process
187	only the main program can know when it is still safe to do so) - all other	298	use Example::My::Module
188	pools are created by fork+exec, after which such modules can again be	299	use Example::Whatever;
189	loaded.
190		300
191	=back	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	$cv->recv;
192		327
193	=head1 CONCEPTS	328	=head1 CONCEPTS
194		329
195	This module can create new processes either by executing a new perl	330	This module can create new processes either by executing a new perl
196	process, or by forking from an existing "template" process.	331	process, or by forking from an existing "template" process.
		332
		333	All these processes are called "child processes" (whether they are direct
		334	children or not), while the process that manages them is called the
		335	"parent process".
197		336
198	Each such process comes with its own file handle that can be used to	337	Each such process comes with its own file handle that can be used to
199	communicate with it (it's actually a socket - one end in the new process,	338	communicate with it (it's actually a socket - one end in the new process,
200	one end in the main process), and among the things you can do in it are	339	one end in the main process), and among the things you can do in it are
201	load modules, fork new processes, send file handles to it, and execute	340	load modules, fork new processes, send file handles to it, and execute
…		…
275	my ($fork_fh) = @_;	414	my ($fork_fh) = @_;
276	});	415	});
277		416
278	=back	417	=back
279		418
280	=head1 FUNCTIONS	419	=head1 THE C<AnyEvent::Fork> CLASS
		420
		421	This module exports nothing, and only implements a single class -
		422	C<AnyEvent::Fork>.
		423
		424	There are two class constructors that both create new processes - C<new>
		425	and C<new_exec>. The C<fork> method creates a new process by forking an
		426	existing one and could be considered a third constructor.
		427
		428	Most of the remaining methods deal with preparing the new process, by
		429	loading code, evaluating code and sending data to the new process. They
		430	usually return the process object, so you can chain method calls.
		431
		432	If a process object is destroyed before calling its C<run> method, then
		433	the process simply exits. After C<run> is called, all responsibility is
		434	passed to the specified function.
		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.
281		439
282	=over 4	440	=over 4
283		441
284	=cut	442	=cut
285		443
…		…
292	use AnyEvent;	450	use AnyEvent;
293	use AnyEvent::Util ();	451	use AnyEvent::Util ();
294		452
295	use IO::FDPass;	453	use IO::FDPass;
296		454
297	our $VERSION = 0.5;	455	our $VERSION = '1.0';
298
299	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
300
301	=item my $pool = new AnyEvent::Fork key => value...
302
303	Create a new process pool. The following named parameters are supported:
304
305	=over 4
306
307	=back
308
309	=cut
310		456
311	# the early fork template process	457	# the early fork template process
312	our $EARLY;	458	our $EARLY;
313		459
314	# the empty template process	460	# the empty template process
315	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	}
316		483
317	sub _cmd {	484	sub _cmd {
318	my $self = shift;	485	my $self = shift;
319		486
320	# 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
321	# 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
322	# it.	489	# it.
323	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	490	push @{ $self->[QUEUE] }, pack "a N/a*", $_[0], $_[1];
324		491
325	$self->[3] \|\|= AE::io $self->[1], 1, sub {	492	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
326	do {	493	do {
327	# 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,
328	# or a plain string.	495	# or a plain string.
329		496
330	if (ref $self->[2][0]) {	497	if (ref $self->[QUEUE][0]) {
331	# send fh	498	# send fh
332	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	499	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
333	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	500	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
334	undef $self->[3];	501	undef $self->[WW];
335	die "AnyEvent::Fork: file descriptor send failure: $!";	502	die "AnyEvent::Fork: file descriptor send failure: $!";
336	}	503	}
337		504
338	shift @{ $self->[2] };	505	shift @{ $self->[QUEUE] };
339		506
340	} else {	507	} else {
341	# send string	508	# send string
342	my $len = syswrite $self->[1], $self->[2][0];	509	my $len = syswrite $self->[FH], $self->[QUEUE][0];
343		510
344	unless ($len) {	511	unless ($len) {
345	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	512	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
346	undef $self->[3];	513	undef $self->[WW];
347	die "AnyEvent::Fork: command write failure: $!";	514	die "AnyEvent::Fork: command write failure: $!";
348	}	515	}
349		516
350	substr $self->[2][0], 0, $len, "";	517	substr $self->[QUEUE][0], 0, $len, "";
351	shift @{ $self->[2] } unless length $self->[2][0];	518	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
352	}	519	}
353	} while @{ $self->[2] };	520	} while @{ $self->[QUEUE] };
354		521
355	# everything written	522	# everything written
356	undef $self->[3];	523	undef $self->[WW];
357		524
358	# invoke run callback, if any	525	# invoke run callback, if any
359	$self->[4]->($self->[1]) if $self->[4];	526	if ($self->[CB]) {
		527	$self->[CB]->($self->[FH]);
		528	@$self = ();
		529	}
360	};	530	};
361		531
362	() # make sure we don't leak the watcher	532	() # make sure we don't leak the watcher
363	}
364
365	sub _new {
366	my ($self, $fh, $pid) = @_;
367
368	AnyEvent::Util::fh_nonblocking $fh, 1;
369
370	$self = bless [
371	$pid,
372	$fh,
373	[], # write queue - strings or fd's
374	undef, # AE watcher
375	], $self;
376
377	$self
378	}	533	}
379		534
380	# fork template from current process, used by AnyEvent::Fork::Early/Template	535	# fork template from current process, used by AnyEvent::Fork::Early/Template
381	sub _new_fork {	536	sub _new_fork {
382	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	537	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
387	if ($pid eq 0) {	542	if ($pid eq 0) {
388	require AnyEvent::Fork::Serve;	543	require AnyEvent::Fork::Serve;
389	$AnyEvent::Fork::Serve::OWNER = $parent;	544	$AnyEvent::Fork::Serve::OWNER = $parent;
390	close $fh;	545	close $fh;
391	$0 = "$_[1] of $parent";	546	$0 = "$_[1] of $parent";
392	$SIG{CHLD} = 'IGNORE';
393	AnyEvent::Fork::Serve::serve ($slave);	547	AnyEvent::Fork::Serve::serve ($slave);
394	exit 0;	548	exit 0;
395	} elsif (!$pid) {	549	} elsif (!$pid) {
396	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	550	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
397	}	551	}
…		…
404	Create a new "empty" perl interpreter process and returns its process	558	Create a new "empty" perl interpreter process and returns its process
405	object for further manipulation.	559	object for further manipulation.
406		560
407	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
408	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
409	C<new_exec> and kept around for future calls.	563	C<new_exec> first and then stays around for future calls.
410
411	When the process object is destroyed, it will release the file handle
412	that connects it with the new process. When the new process has not yet
413	called C<run>, then the process will exit. Otherwise, what happens depends
414	entirely on the code that is executed.
415		564
416	=cut	565	=cut
417		566
418	sub new {	567	sub new {
419	my $class = shift;	568	my $class = shift;
…		…
509	}	658	}
510		659
511	=item $pid = $proc->pid	660	=item $pid = $proc->pid
512		661
513	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
514	process> running AnyEvent::Fork, and C<undef> otherwise.	663	process running AnyEvent::Fork>, and C<undef> otherwise.
515		664
516	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	665	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
517	L<AnyEvent::Fork::Template> are direct children, and you are responsible	666	L<AnyEvent::Fork::Template> are direct children, and you are responsible
518	to clean up their zombies when they die.	667	to clean up their zombies when they die.
519		668
520	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
521	AnyEvent::Fork.	670	AnyEvent::Fork itself.
522		671
523	=cut	672	=cut
524		673
525	sub pid {	674	sub pid {
526	$_[0][0]	675	$_[0][PID]
527	}	676	}
528		677
529	=item $proc = $proc->eval ($perlcode, @args)	678	=item $proc = $proc->eval ($perlcode, @args)
530		679
531	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
532	the strings specified by C<@args>, in the "main" package.	681	the strings specified by C<@args>, in the "main" package.
533		682
534	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
535	(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
536	to completely take over the process, use C<run> for that.	685	to completely take over the process, use C<run> for that.
537		686
538	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
539	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
540	will be reported to stderr and cause the process to exit.	689	will be reported to stderr and cause the process to exit.
541		690
542	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
543	"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
544	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
545	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.
546		696
547	Returns the process object for easy chaining of method calls.	697	Returns the process object for easy chaining of method calls.
548		698
549	=cut	699	=cut
550		700
…		…
576	=item $proc = $proc->send_fh ($handle, ...)	726	=item $proc = $proc->send_fh ($handle, ...)
577		727
578	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,
579	to prepare a call to C<run>.	729	to prepare a call to C<run>.
580		730
581	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
582	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
583	accomplished by simply not storing the file handles anywhere after passing	733	handles. This is most easily accomplished by simply not storing the file
584	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.
585		736
586	Returns the process object for easy chaining of method calls.	737	Returns the process object for easy chaining of method calls.
587		738
588	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
589	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.
…		…
596	sub send_fh {	747	sub send_fh {
597	my ($self, @fh) = @_;	748	my ($self, @fh) = @_;
598		749
599	for my $fh (@fh) {	750	for my $fh (@fh) {
600	$self->_cmd ("h");	751	$self->_cmd ("h");
601	push @{ $self->[2] }, \$fh;	752	push @{ $self->[QUEUE] }, \$fh;
602	}	753	}
603		754
604	$self	755	$self
605	}	756	}
606		757
607	=item $proc = $proc->send_arg ($string, ...)	758	=item $proc = $proc->send_arg ($string, ...)
608		759
609	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
610	C<run>. The strings can be any octet string.	761	C<run>. The strings can be any octet strings.
611		762
612	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
613	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
614	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
615	data.	766	data.
…		…
631	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
632	process. The function is called with the communication socket as first	783	process. The function is called with the communication socket as first
633	argument, followed by all file handles and string arguments sent earlier	784	argument, followed by all file handles and string arguments sent earlier
634	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.
635		786
		787	The process object becomes unusable on return from this function - any
		788	further method calls result in undefined behaviour.
		789
636	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
637	looked up in the main package.	791	looked up in the C<main> package.
638		792
639	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
640	process exits.	794	process exits.
641		795
642	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
643	been sent, the callback is invoked with the local communications socket	797	been sent, the callback is invoked with the local communications socket
644	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
645	like.	799	like.
646
647	The process object becomes unusable on return from this function - any
648	further method calls result in undefined behaviour.
649		800
650	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,
651	to save on kernel memory.	802	to save on kernel memory.
652		803
653	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
…		…
692	=cut	843	=cut
693		844
694	sub run {	845	sub run {
695	my ($self, $func, $cb) = @_;	846	my ($self, $func, $cb) = @_;
696		847
697	$self->[4] = $cb;	848	$self->[CB] = $cb;
698	$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)
699	}	978	}
700		979
701	=back	980	=back
702		981
703	=head1 PERFORMANCE	982	=head1 PERFORMANCE
…		…
713		992
714	2079 new processes per second, using manual socketpair + fork	993	2079 new processes per second, using manual socketpair + fork
715		994
716	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
717	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
718	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
719	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
720	(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
721	of the socket first.	1000	of the socket first.
722		1001
723	2307 new processes per second, using AnyEvent::Fork->new	1002	2307 new processes per second, using AnyEvent::Fork->new
…		…
728	479 vfork+execs per second, using AnyEvent::Fork->new_exec	1007	479 vfork+execs per second, using AnyEvent::Fork->new_exec
729		1008
730	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
731	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?
732		1011
733	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
734	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
735	introduced is canceled out.	1014	overhead is canceled out.
736		1015
737	If the benchmark process grows, the normal fork becomes even slower:	1016	If the benchmark process grows, the normal fork becomes even slower:
738		1017
739	1340 new processes, manual fork in a 20MB process	1018	1340 new processes, manual fork of a 20MB process
740	731 new processes, manual fork in a 200MB process	1019	731 new processes, manual fork of a 200MB process
741	235 new processes, manual fork in a 2000MB process	1020	235 new processes, manual fork of a 2000MB process
742		1021
743	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
744	very bad conscience because of the extra overhead required to start new	1023	conscience because of the extra overhead required to start new processes.
745	processes.
746		1024
747	=head1 TYPICAL PROBLEMS	1025	=head1 TYPICAL PROBLEMS
748		1026
749	This section lists typical problems that remain. I hope by recognising	1027	This section lists typical problems that remain. I hope by recognising
750	them, most can be avoided.	1028	them, most can be avoided.
751		1029
752	=over 4	1030	=over 4
753		1031
754	=item "leaked" file descriptors for exec'ed processes	1032	=item leaked file descriptors for exec'ed processes
755		1033
756	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
757	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
758	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
759	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.
…		…
779	libraries or the code that leaks those file descriptors.	1057	libraries or the code that leaks those file descriptors.
780		1058
781	Fortunately, most of these leaked descriptors do no harm, other than	1059	Fortunately, most of these leaked descriptors do no harm, other than
782	sitting on some resources.	1060	sitting on some resources.
783		1061
784	=item "leaked" file descriptors for fork'ed processes	1062	=item leaked file descriptors for fork'ed processes
785		1063
786	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,
787	which closes file descriptors not marked for being inherited.	1065	which closes file descriptors not marked for being inherited.
788		1066
789	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	1067	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
798		1076
799	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
800	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
801	initialising them, for example, by calling C<init Gtk2> manually.	1079	initialising them, for example, by calling C<init Gtk2> manually.
802		1080
803	=item exit runs destructors	1081	=item exiting calls object destructors
804		1082
805	This only applies to users of Lc<AnyEvent::Fork:Early> and	1083	This only applies to users of L<AnyEvent::Fork:Early> and
806	L<AnyEvent::Fork::Template>.	1084	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1085	that reference external resources.
807		1086
808	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
809	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
810	Perl runs all destructors.	1089	Perl runs all destructors.
811		1090
…		…
830	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
831	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
832	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
833	issues or other braindamage. Hrrrr.	1112	issues or other braindamage. Hrrrr.
834		1113
835	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
836	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
837	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.
838		1123
839	=head1 SEE ALSO	1124	=head1 SEE ALSO
840		1125
841	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
842	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
843	program at a convenient time).	1130	program at a convenient time (part of this distribution).
844		1131
845	=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
846		1137
847	Marc Lehmann <schmorp@schmorp.de>	1138	Marc Lehmann <schmorp@schmorp.de>
848	http://home.schmorp.de/	1139	http://software.schmorp.de/pkg/AnyEvent-Fork
849		1140
850	=cut	1141	=cut
851		1142
852	1	1143	1
853		1144

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.24 by root, Sat Apr 6 08:32:23 2013 UTC vs. Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC

Diff Legend

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.24 by root, Sat Apr 6 08:32:23 2013 UTC vs.
Revision 1.54 by root, Fri Apr 26 17:24:05 2013 UTC