[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 1.63 by root, Wed Nov 26 13:36:18 2014 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 or not being able to use event processing, GUI
		62	toolkits or 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. Exec'ing a new process, in contrast, means modules
		95	and data files might need to be loaded again, at extra CPU and memory
		96	cost.
		97
		98	But when forking, you still create a copy of your data structures - if
		99	the program frees them and replaces them by new data, the child processes
		100	will retain the old version even if it isn't used, which can suddenly and
		101	unexpectedly increase memory usage when freeing memory.
		102
		103	For example, L<Gtk2::CV> is an image viewer optimised for large
		104	directories (millions of pictures). It also forks subprocesses for
		105	thumbnail generation, which inherit the data structure that stores all
		106	file information. If the user changes the directory, it gets freed in
		107	the main process, leaving a copy in the thumbnailer processes. This can
		108	lead to many times the memory usage that would actually be required. The
		109	solution is to fork early (and being unable to dynamically generate more
		110	subprocesses or do this from a module)... or to use L<AnyEvent:Fork>.
		111
		112	There is a trade-off between more sharing with fork (which can be good or
		113	bad), and no sharing with exec.
		114
		115	This module allows the main program to do a controlled fork, and allows
		116	modules to exec processes safely at any time. When creating a custom
		117	process pool you can take advantage of data sharing via fork without
		118	risking to share large dynamic data structures that will blow up child
		119	memory usage.
		120
		121	In other words, this module puts you into control over what is being
		122	shared and what isn't, at all times.
		123
		124	=item Exec'ing a new perl process might be difficult.
		125
		126	For example, it is not easy to find the correct path to the perl
		127	interpreter - C<$^X> might not be a perl interpreter at all. Worse, there
		128	might not even be a perl binary installed on the system.
		129
		130	This module tries hard to identify the correct path to the perl
		131	interpreter. With a cooperative main program, exec'ing the interpreter
		132	might not even be necessary, but even without help from the main program,
		133	it will still work when used from a module.
		134
		135	=item Exec'ing a new perl process might be slow, as all necessary modules
		136	have to be loaded from disk again, with no guarantees of success.
		137
		138	Long running processes might run into problems when perl is upgraded
		139	and modules are no longer loadable because they refer to a different
		140	perl version, or parts of a distribution are newer than the ones already
		141	loaded.
		142
		143	This module supports creating pre-initialised perl processes to be used as
		144	a template for new processes at a later time, e.g. for use in a process
		145	pool.
		146
		147	=item Forking might be impossible when a program is running.
		148
		149	For example, POSIX makes it almost impossible to fork from a
		150	multi-threaded program while doing anything useful in the child - in
		151	fact, if your perl program uses POSIX threads (even indirectly via
		152	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		153	anymore without risking memory corruption or worse on a number of
		154	operating systems.
		155
		156	This module can safely fork helper processes at any time, by calling
		157	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		158
		159	=item Parallel processing with fork might be inconvenient or difficult
		160	to implement. Modules might not work in both parent and child.
		161
		162	For example, when a program uses an event loop and creates watchers it
		163	becomes very hard to use the event loop from a child program, as the
		164	watchers already exist but are only meaningful in the parent. Worse, a
		165	module might want to use such a module, not knowing whether another module
		166	or the main program also does, leading to problems.
		167
		168	Apart from event loops, graphical toolkits also commonly fall into the
		169	"unsafe module" category, or just about anything that communicates with
		170	the external world, such as network libraries and file I/O modules, which
		171	usually don't like being copied and then allowed to continue in two
		172	processes.
		173
		174	With this module only the main program is allowed to create new processes
		175	by forking (because only the main program can know when it is still safe
		176	to do so) - all other processes are created via fork+exec, which makes it
		177	possible to use modules such as event loops or window interfaces safely.
		178
		179	=back
44		180
45	=head1 EXAMPLES	181	=head1 EXAMPLES
46		182
47	=head2 Create a single new process, tell it to run your worker function.	183	=head2 Create a single new process, tell it to run your worker function.
48		184
…		…
54		190
55	# now $master_filehandle is connected to the	191	# now $master_filehandle is connected to the
56	# $slave_filehandle in the new process.	192	# $slave_filehandle in the new process.
57	});	193	});
58		194
59	# MyModule::worker might look like this	195	C<MyModule> might look like this:
		196
		197	package MyModule;
		198
60	sub MyModule::worker {	199	sub worker {
61	my ($slave_filehandle) = @_;	200	my ($slave_filehandle) = @_;
62		201
63	# now $slave_filehandle is connected to the $master_filehandle	202	# now $slave_filehandle is connected to the $master_filehandle
64	# in the original prorcess. have fun!	203	# in the original prorcess. have fun!
65	}	204	}
…		…
84	}	223	}
85		224
86	# now do other things - maybe use the filehandle provided by run	225	# now do other things - maybe use the filehandle provided by run
87	# to wait for the processes to die. or whatever.	226	# to wait for the processes to die. or whatever.
88		227
89	# My::Server::run might look like this	228	C<My::Server> might look like this:
90	sub My::Server::run {	229
		230	package My::Server;
		231
		232	sub run {
91	my ($slave, $listener, $id) = @_;	233	my ($slave, $listener, $id) = @_;
92		234
93	close $slave; # we do not use the socket, so close it to save resources	235	close $slave; # we do not use the socket, so close it to save resources
94		236
95	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	237	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
99	}	241	}
100	}	242	}
101		243
102	=head2 use AnyEvent::Fork as a faster fork+exec	244	=head2 use AnyEvent::Fork as a faster fork+exec
103		245
104	This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to	246	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	247	and standard error redirected to the communications socket. It is usually
106	let's you prepare the environment.	248	faster than fork+exec, but still lets you prepare the environment.
107		249
108	open my $output, ">/tmp/log" or die "$!";	250	open my $output, ">/tmp/log" or die "$!";
109		251
110	AnyEvent::Fork	252	AnyEvent::Fork
111	->new	253	->new
112	->eval ('	254	->eval ('
		255	# compile a helper function for later use
113	sub run {	256	sub run {
114	my ($fh, $output, @cmd) = @_;	257	my ($fh, $output, @cmd) = @_;
115		258
116	# perl will clear close-on-exec on STDOUT/STDERR	259	# perl will clear close-on-exec on STDOUT/STDERR
117	open STDOUT, ">&", $output or die;	260	open STDOUT, ">&", $output or die;
…		…
124	->send_arg ("/bin/echo", "hi")	267	->send_arg ("/bin/echo", "hi")
125	->run ("run", my $cv = AE::cv);	268	->run ("run", my $cv = AE::cv);
126		269
127	my $stderr = $cv->recv;	270	my $stderr = $cv->recv;
128		271
129	=head1 PROBLEM STATEMENT	272	=head2 For stingy users: put the worker code into a C<DATA> section.
130		273
131	There are two ways to implement parallel processing on UNIX like operating	274	When you want to be stingy with files, you can put your code into the
132	systems - fork and process, and fork+exec and process. They have different	275	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		276
136	=over 4	277	use AnyEvent::Fork;
137		278
138	=item Forking from a big process can be very slow (a 5GB process needs	279	AnyEvent::Fork
139	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead	280	->new
140	is often shared with exec (because you have to fork first), but in some	281	->eval (do { local $/; <DATA> })
141	circumstances (e.g. when vfork is used), fork+exec can be much faster.	282	->run ("doit", sub { ... });
142		283
143	This module can help here by telling a small(er) helper process to fork,	284	__DATA__
144	or fork+exec instead.
145		285
146	=item Forking usually creates a copy-on-write copy of the parent	286	sub doit {
147	process. Memory (for example, modules or data files that have been	287	... do something!
148	will not take additional memory). When exec'ing a new process, modules	288	}
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		289
154	This module allows the main program to do a controlled fork, and allows	290	=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	291	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		292
160	=item Exec'ing a new perl process might be difficult and slow. For	293	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,	294	files - even when using a C<DATA> section, you still need to C<exec> an
162	and all modules have to be loaded from disk again. Long running processes	295	external perl interpreter, which might not be available when using
163	might run into problems when perl is upgraded for example.	296	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
164		297
165	This module supports creating pre-initialised perl processes to be used	298	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	299	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
167	interpreter. With a cooperative main program, exec'ing the interpreter	300	forks the main program as a template process.
168	might not even be necessary.
169		301
170	=item Forking might be impossible when a program is running. For example,	302	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		303
176	This module can safely fork helper processes at any time, by calling	304	#! perl
177	fork+exec in C, in a POSIX-compatible way.
178		305
179	=item Parallel processing with fork might be inconvenient or difficult	306	# optional, as the very first thing.
180	to implement. For example, when a program uses an event loop and creates	307	# in case modules want to create their own processes.
181	watchers it becomes very hard to use the event loop from a child	308	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		309
186	This module only lets the main program create pools by forking (because	310	# 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	311	use Example::My::Module
188	pools are created by fork+exec, after which such modules can again be	312	use Example::Whatever;
189	loaded.
190		313
191	=back	314	# next, put your run function definition and anything else you
		315	# need, but do not use code outside of BEGIN blocks.
		316	sub worker_run {
		317	my ($fh, @args) = @_;
		318	...
		319	}
		320
		321	# now preserve everything so far as AnyEvent::Fork object
		322	# in $TEMPLATE.
		323	use AnyEvent::Fork::Template;
		324
		325	# do not put code outside of BEGIN blocks until here
		326
		327	# now use the $TEMPLATE process in any way you like
		328
		329	# for example: create 10 worker processes
		330	my @worker;
		331	my $cv = AE::cv;
		332	for (1..10) {
		333	$cv->begin;
		334	$TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub {
		335	push @worker, shift;
		336	$cv->end;
		337	});
		338	}
		339	$cv->recv;
192		340
193	=head1 CONCEPTS	341	=head1 CONCEPTS
194		342
195	This module can create new processes either by executing a new perl	343	This module can create new processes either by executing a new perl
196	process, or by forking from an existing "template" process.	344	process, or by forking from an existing "template" process.
		345
		346	All these processes are called "child processes" (whether they are direct
		347	children or not), while the process that manages them is called the
		348	"parent process".
197		349
198	Each such process comes with its own file handle that can be used to	350	Each such process comes with its own file handle that can be used to
199	communicate with it (it's actually a socket - one end in the new process,	351	communicate with it (it's actually a socket - one end in the new process,
200	one end in the main process), and among the things you can do in it are	352	one end in the main process), and among the things you can do in it are
201	load modules, fork new processes, send file handles to it, and execute	353	load modules, fork new processes, send file handles to it, and execute
…		…
275	my ($fork_fh) = @_;	427	my ($fork_fh) = @_;
276	});	428	});
277		429
278	=back	430	=back
279		431
280	=head1 FUNCTIONS	432	=head1 THE C<AnyEvent::Fork> CLASS
		433
		434	This module exports nothing, and only implements a single class -
		435	C<AnyEvent::Fork>.
		436
		437	There are two class constructors that both create new processes - C<new>
		438	and C<new_exec>. The C<fork> method creates a new process by forking an
		439	existing one and could be considered a third constructor.
		440
		441	Most of the remaining methods deal with preparing the new process, by
		442	loading code, evaluating code and sending data to the new process. They
		443	usually return the process object, so you can chain method calls.
		444
		445	If a process object is destroyed before calling its C<run> method, then
		446	the process simply exits. After C<run> is called, all responsibility is
		447	passed to the specified function.
		448
		449	As long as there is any outstanding work to be done, process objects
		450	resist being destroyed, so there is no reason to store them unless you
		451	need them later - configure and forget works just fine.
281		452
282	=over 4	453	=over 4
283		454
284	=cut	455	=cut
285		456
…		…
292	use AnyEvent;	463	use AnyEvent;
293	use AnyEvent::Util ();	464	use AnyEvent::Util ();
294		465
295	use IO::FDPass;	466	use IO::FDPass;
296		467
297	our $VERSION = 0.5;	468	our $VERSION = 1.2;
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		469
311	# the early fork template process	470	# the early fork template process
312	our $EARLY;	471	our $EARLY;
313		472
314	# the empty template process	473	# the empty template process
315	our $TEMPLATE;	474	our $TEMPLATE;
		475
		476	sub QUEUE() { 0 }
		477	sub FH() { 1 }
		478	sub WW() { 2 }
		479	sub PID() { 3 }
		480	sub CB() { 4 }
		481
		482	sub _new {
		483	my ($self, $fh, $pid) = @_;
		484
		485	AnyEvent::Util::fh_nonblocking $fh, 1;
		486
		487	$self = bless [
		488	[], # write queue - strings or fd's
		489	$fh,
		490	undef, # AE watcher
		491	$pid,
		492	], $self;
		493
		494	$self
		495	}
316		496
317	sub _cmd {	497	sub _cmd {
318	my $self = shift;	498	my $self = shift;
319		499
320	# ideally, we would want to use "a (w/a)*" as format string, but perl	500	# 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	501	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
322	# it.	502	# it.
323	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];	503	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
324		504
325	$self->[3] \|\|= AE::io $self->[1], 1, sub {	505	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
326	do {	506	do {
327	# send the next "thing" in the queue - either a reference to an fh,	507	# send the next "thing" in the queue - either a reference to an fh,
328	# or a plain string.	508	# or a plain string.
329		509
330	if (ref $self->[2][0]) {	510	if (ref $self->[QUEUE][0]) {
331	# send fh	511	# send fh
332	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {	512	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
333	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	513	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
334	undef $self->[3];	514	undef $self->[WW];
335	die "AnyEvent::Fork: file descriptor send failure: $!";	515	die "AnyEvent::Fork: file descriptor send failure: $!";
336	}	516	}
337		517
338	shift @{ $self->[2] };	518	shift @{ $self->[QUEUE] };
339		519
340	} else {	520	} else {
341	# send string	521	# send string
342	my $len = syswrite $self->[1], $self->[2][0];	522	my $len = syswrite $self->[FH], $self->[QUEUE][0];
343		523
344	unless ($len) {	524	unless ($len) {
345	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;	525	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
346	undef $self->[3];	526	undef $self->[WW];
347	die "AnyEvent::Fork: command write failure: $!";	527	die "AnyEvent::Fork: command write failure: $!";
348	}	528	}
349		529
350	substr $self->[2][0], 0, $len, "";	530	substr $self->[QUEUE][0], 0, $len, "";
351	shift @{ $self->[2] } unless length $self->[2][0];	531	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
352	}	532	}
353	} while @{ $self->[2] };	533	} while @{ $self->[QUEUE] };
354		534
355	# everything written	535	# everything written
356	undef $self->[3];	536	undef $self->[WW];
357		537
358	# invoke run callback, if any	538	# invoke run callback, if any
359	$self->[4]->($self->[1]) if $self->[4];	539	if ($self->[CB]) {
		540	$self->[CB]->($self->[FH]);
		541	@$self = ();
		542	}
360	};	543	};
361		544
362	() # make sure we don't leak the watcher	545	() # make sure we don't leak the watcher
363	}
364
365	sub _new {
366	my ($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	$self
378	}	546	}
379		547
380	# fork template from current process, used by AnyEvent::Fork::Early/Template	548	# fork template from current process, used by AnyEvent::Fork::Early/Template
381	sub _new_fork {	549	sub _new_fork {
382	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	550	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
387	if ($pid eq 0) {	555	if ($pid eq 0) {
388	require AnyEvent::Fork::Serve;	556	require AnyEvent::Fork::Serve;
389	$AnyEvent::Fork::Serve::OWNER = $parent;	557	$AnyEvent::Fork::Serve::OWNER = $parent;
390	close $fh;	558	close $fh;
391	$0 = "$_[1] of $parent";	559	$0 = "$_[1] of $parent";
392	$SIG{CHLD} = 'IGNORE';
393	AnyEvent::Fork::Serve::serve ($slave);	560	AnyEvent::Fork::Serve::serve ($slave);
394	exit 0;	561	exit 0;
395	} elsif (!$pid) {	562	} elsif (!$pid) {
396	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	563	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
397	}	564	}
…		…
404	Create a new "empty" perl interpreter process and returns its process	571	Create a new "empty" perl interpreter process and returns its process
405	object for further manipulation.	572	object for further manipulation.
406		573
407	The new process is forked from a template process that is kept around	574	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	575	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.	576	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		577
416	=cut	578	=cut
417		579
418	sub new {	580	sub new {
419	my $class = shift;	581	my $class = shift;
…		…
456		618
457	You should use C<new> whenever possible, except when having a template	619	You should use C<new> whenever possible, except when having a template
458	process around is unacceptable.	620	process around is unacceptable.
459		621
460	The path to the perl interpreter is divined using various methods - first	622	The path to the perl interpreter is divined using various methods - first
461	C<$^X> is investigated to see if the path ends with something that sounds	623	C<$^X> is investigated to see if the path ends with something that looks
462	as if it were the perl interpreter. Failing this, the module falls back to	624	as if it were the perl interpreter. Failing this, the module falls back to
463	using C<$Config::Config{perlpath}>.	625	using C<$Config::Config{perlpath}>.
464		626
		627	The path to perl can also be overriden by setting the global variable
		628	C<$AnyEvent::Fork::PERL> - it's value will be used for all subsequent
		629	invocations.
		630
465	=cut	631	=cut
		632
		633	our $PERL;
466		634
467	sub new_exec {	635	sub new_exec {
468	my ($self) = @_;	636	my ($self) = @_;
469		637
470	return $EARLY->fork	638	return $EARLY->fork
471	if $EARLY;	639	if $EARLY;
472		640
		641	unless (defined $PERL) {
473	# first find path of perl	642	# first find path of perl
474	my $perl = $;	643	my $perl = $^X;
475		644
476	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	645	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
477	# that looks like perl. this obviously only works for posix and win32	646	# that looks like perl. this obviously only works for posix and win32
478	unless (	647	unless (
479	($^O eq "MSWin32" \|\| $perl =~ m%^/%)	648	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
480	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	649	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
481	) {	650	) {
482	# if it doesn't look perlish enough, try Config	651	# if it doesn't look perlish enough, try Config
483	require Config;	652	require Config;
484	$perl = $Config::Config{perlpath};	653	$perl = $Config::Config{perlpath};
485	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;	654	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		655	}
		656
		657	$PERL = $perl;
486	}	658	}
487		659
488	require Proc::FastSpawn;	660	require Proc::FastSpawn;
489		661
490	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	662	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
498	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	670	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
499	my %env = %ENV;	671	my %env = %ENV;
500	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	672	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
501		673
502	my $pid = Proc::FastSpawn::spawn (	674	my $pid = Proc::FastSpawn::spawn (
503	$perl,	675	$PERL,
504	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	676	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
505	[map "$_=$env{$_}", keys %env],	677	[map "$_=$env{$_}", keys %env],
506	) or die "unable to spawn AnyEvent::Fork server: $!";	678	) or die "unable to spawn AnyEvent::Fork server: $!";
507		679
508	$self->_new ($fh, $pid)	680	$self->_new ($fh, $pid)
509	}	681	}
510		682
511	=item $pid = $proc->pid	683	=item $pid = $proc->pid
512		684
513	Returns the process id of the process I<iff it is a direct child of the	685	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.	686	process running AnyEvent::Fork>, and C<undef> otherwise. As a general
		687	rule (that you cannot rely upon), processes created via C<new_exec>,
		688	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template> are direct
		689	children, while all other processes are not.
515		690
516	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	691	Or in other words, you do not normally have to take care of zombies for
517	L<AnyEvent::Fork::Template> are direct children, and you are responsible	692	processes created via C<new>, but when in doubt, or zombies are a problem,
518	to clean up their zombies when they die.	693	you need to check whether a process is a diretc child by calling this
519		694	method, and possibly creating a child watcher or reap it manually.
520	All other processes are not direct children, and will be cleaned up by
521	AnyEvent::Fork.
522		695
523	=cut	696	=cut
524		697
525	sub pid {	698	sub pid {
526	$_[0][0]	699	$_[0][PID]
527	}	700	}
528		701
529	=item $proc = $proc->eval ($perlcode, @args)	702	=item $proc = $proc->eval ($perlcode, @args)
530		703
531	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	704	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to
532	the strings specified by C<@args>, in the "main" package.	705	the strings specified by C<@args>, in the "main" package.
533		706
534	This call is meant to do any custom initialisation that might be required	707	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	708	(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.	709	to completely take over the process, use C<run> for that.
537		710
538	The code will usually be executed after this call returns, and there is no	711	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	712	way to pass anything back to the calling process. Any evaluation errors
540	will be reported to stderr and cause the process to exit.	713	will be reported to stderr and cause the process to exit.
541		714
542	If you want to execute some code to take over the process (see the	715	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	716	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	717	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.	718	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		719	a faster fork+exec> example to see it in action.
546		720
547	Returns the process object for easy chaining of method calls.	721	Returns the process object for easy chaining of method calls.
548		722
549	=cut	723	=cut
550		724
…		…
576	=item $proc = $proc->send_fh ($handle, ...)	750	=item $proc = $proc->send_fh ($handle, ...)
577		751
578	Send one or more file handles (I<not> file descriptors) to the process,	752	Send one or more file handles (I<not> file descriptors) to the process,
579	to prepare a call to C<run>.	753	to prepare a call to C<run>.
580		754
581	The process object keeps a reference to the handles until this is done,	755	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	756	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	757	handles. This is most easily accomplished by simply not storing the file
584	them to this method.	758	handles anywhere after passing them to this method - when AnyEvent::Fork
		759	is finished using them, perl will automatically close them.
585		760
586	Returns the process object for easy chaining of method calls.	761	Returns the process object for easy chaining of method calls.
587		762
588	Example: pass a file handle to a process, and release it without	763	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.	764	closing. It will be closed automatically when it is no longer used.
…		…
596	sub send_fh {	771	sub send_fh {
597	my ($self, @fh) = @_;	772	my ($self, @fh) = @_;
598		773
599	for my $fh (@fh) {	774	for my $fh (@fh) {
600	$self->_cmd ("h");	775	$self->_cmd ("h");
601	push @{ $self->[2] }, \$fh;	776	push @{ $self->[QUEUE] }, \$fh;
602	}	777	}
603		778
604	$self	779	$self
605	}	780	}
606		781
607	=item $proc = $proc->send_arg ($string, ...)	782	=item $proc = $proc->send_arg ($string, ...)
608		783
609	Send one or more argument strings to the process, to prepare a call to	784	Send one or more argument strings to the process, to prepare a call to
610	C<run>. The strings can be any octet string.	785	C<run>. The strings can be any octet strings.
611		786
612	The protocol is optimised to pass a moderate number of relatively short	787	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	788	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	789	meant to pass some ID information or other startup info, not big chunks of
615	data.	790	data.
…		…
631	Enter the function specified by the function name in C<$func> in the	806	Enter the function specified by the function name in C<$func> in the
632	process. The function is called with the communication socket as first	807	process. The function is called with the communication socket as first
633	argument, followed by all file handles and string arguments sent earlier	808	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.	809	via C<send_fh> and C<send_arg> methods, in the order they were called.
635		810
		811	The process object becomes unusable on return from this function - any
		812	further method calls result in undefined behaviour.
		813
636	The function name should be fully qualified, but if it isn't, it will be	814	The function name should be fully qualified, but if it isn't, it will be
637	looked up in the main package.	815	looked up in the C<main> package.
638		816
639	If the called function returns, doesn't exist, or any error occurs, the	817	If the called function returns, doesn't exist, or any error occurs, the
640	process exits.	818	process exits.
641		819
642	Preparing the process is done in the background - when all commands have	820	Preparing the process is done in the background - when all commands have
643	been sent, the callback is invoked with the local communications socket	821	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	822	as argument. At this point you can start using the socket in any way you
645	like.	823	like.
646		824
647	The process object becomes unusable on return from this function - any
648	further method calls result in undefined behaviour.
649
650	If the communication socket isn't used, it should be closed on both sides,	825	If the communication socket isn't used, it should be closed on both sides,
651	to save on kernel memory.	826	to save on kernel memory.
652		827
653	The socket is non-blocking in the parent, and blocking in the newly	828	The socket is non-blocking in the parent, and blocking in the newly
654	created process. The close-on-exec flag is set in both.	829	created process. The close-on-exec flag is set in both.
655		830
656	Even if not used otherwise, the socket can be a good indicator for the	831	Even if not used otherwise, the socket can be a good indicator for the
657	existence of the process - if the other process exits, you get a readable	832	existence of the process - if the other process exits, you get a readable
658	event on it, because exiting the process closes the socket (if it didn't	833	event on it, because exiting the process closes the socket (if it didn't
659	create any children using fork).	834	create any children using fork).
		835
		836	=over 4
		837
		838	=item Compatibility to L<AnyEvent::Fork::Remote>
		839
		840	If you want to write code that works with both this module and
		841	L<AnyEvent::Fork::Remote>, you need to write your code so that it assumes
		842	there are two file handles for communications, which might not be unix
		843	domain sockets. The C<run> function should start like this:
		844
		845	sub run {
		846	my ($rfh, @args) = @_; # @args is your normal arguments
		847	my $wfh = fileno $rfh ? $rfh : *STDOUT;
		848
		849	# now use $rfh for reading and $wfh for writing
		850	}
		851
		852	This checks whether the passed file handle is, in fact, the process
		853	C<STDIN> handle. If it is, then the function was invoked visa
		854	L<AnyEvent::Fork::Remote>, so STDIN should be used for reading and
		855	C<STDOUT> should be used for writing.
		856
		857	In all other cases, the function was called via this module, and there is
		858	only one file handle that should be sued for reading and writing.
		859
		860	=back
660		861
661	Example: create a template for a process pool, pass a few strings, some	862	Example: create a template for a process pool, pass a few strings, some
662	file handles, then fork, pass one more string, and run some code.	863	file handles, then fork, pass one more string, and run some code.
663		864
664	my $pool = AnyEvent::Fork	865	my $pool = AnyEvent::Fork
…		…
692	=cut	893	=cut
693		894
694	sub run {	895	sub run {
695	my ($self, $func, $cb) = @_;	896	my ($self, $func, $cb) = @_;
696		897
697	$self->[4] = $cb;	898	$self->[CB] = $cb;
698	$self->_cmd (r => $func);	899	$self->_cmd (r => $func);
		900	}
		901
		902	=back
		903
		904	=head2 EXPERIMENTAL METHODS
		905
		906	These methods might go away completely or change behaviour, at any time.
		907
		908	=over 4
		909
		910	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		911
		912	Flushes all commands out to the process and then calls the callback with
		913	the communications socket.
		914
		915	The process object becomes unusable on return from this function - any
		916	further method calls result in undefined behaviour.
		917
		918	The point of this method is to give you a file handle that you can pass
		919	to another process. In that other process, you can call C<new_from_fh
		920	AnyEvent::Fork $fh> to create a new C<AnyEvent::Fork> object from it,
		921	thereby effectively passing a fork object to another process.
		922
		923	=cut
		924
		925	sub to_fh {
		926	my ($self, $cb) = @_;
		927
		928	$self->[CB] = $cb;
		929
		930	unless ($self->[WW]) {
		931	$self->[CB]->($self->[FH]);
		932	@$self = ();
		933	}
		934	}
		935
		936	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		937
		938	Takes a file handle originally rceeived by the C<to_fh> method and creates
		939	a new C<AnyEvent:Fork> object. The child process itself will not change in
		940	any way, i.e. it will keep all the modifications done to it before calling
		941	C<to_fh>.
		942
		943	The new object is very much like the original object, except that the
		944	C<pid> method will return C<undef> even if the process is a direct child.
		945
		946	=cut
		947
		948	sub new_from_fh {
		949	my ($class, $fh) = @_;
		950
		951	$class->_new ($fh)
699	}	952	}
700		953
701	=back	954	=back
702		955
703	=head1 PERFORMANCE	956	=head1 PERFORMANCE
…		…
713		966
714	2079 new processes per second, using manual socketpair + fork	967	2079 new processes per second, using manual socketpair + fork
715		968
716	Then I did the same thing, but instead of calling fork, I called	969	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	970	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	971	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	972	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	973	(2440kB), and the socket needs to be passed to the server at the other end
721	of the socket first.	974	of the socket first.
722		975
723	2307 new processes per second, using AnyEvent::Fork->new	976	2307 new processes per second, using AnyEvent::Fork->new
…		…
728	479 vfork+execs per second, using AnyEvent::Fork->new_exec	981	479 vfork+execs per second, using AnyEvent::Fork->new_exec
729		982
730	So how can C<< AnyEvent->new >> be faster than a standard fork, even	983	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?	984	though it uses the same operations, but adds a lot of overhead?
732		985
733	The difference is simply the process size: forking the 6MB process takes	986	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	987	so much longer than forking the 2.5MB template process that the extra
735	introduced is canceled out.	988	overhead is canceled out.
736		989
737	If the benchmark process grows, the normal fork becomes even slower:	990	If the benchmark process grows, the normal fork becomes even slower:
738		991
739	1340 new processes, manual fork in a 20MB process	992	1340 new processes, manual fork of a 20MB process
740	731 new processes, manual fork in a 200MB process	993	731 new processes, manual fork of a 200MB process
741	235 new processes, manual fork in a 2000MB process	994	235 new processes, manual fork of a 2000MB process
742		995
743	What that means (to me) is that I can use this module without having a	996	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	997	conscience because of the extra overhead required to start new processes.
745	processes.
746		998
747	=head1 TYPICAL PROBLEMS	999	=head1 TYPICAL PROBLEMS
748		1000
749	This section lists typical problems that remain. I hope by recognising	1001	This section lists typical problems that remain. I hope by recognising
750	them, most can be avoided.	1002	them, most can be avoided.
751		1003
752	=over 4	1004	=over 4
753		1005
754	=item "leaked" file descriptors for exec'ed processes	1006	=item leaked file descriptors for exec'ed processes
755		1007
756	POSIX systems inherit file descriptors by default when exec'ing a new	1008	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	1009	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	1010	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.	1011	often not possible to set the flag in a race-free manner.
…		…
779	libraries or the code that leaks those file descriptors.	1031	libraries or the code that leaks those file descriptors.
780		1032
781	Fortunately, most of these leaked descriptors do no harm, other than	1033	Fortunately, most of these leaked descriptors do no harm, other than
782	sitting on some resources.	1034	sitting on some resources.
783		1035
784	=item "leaked" file descriptors for fork'ed processes	1036	=item leaked file descriptors for fork'ed processes
785		1037
786	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	1038	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
787	which closes file descriptors not marked for being inherited.	1039	which closes file descriptors not marked for being inherited.
788		1040
789	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	1041	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
798		1050
799	The solution is to either not load these modules before use'ing	1051	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	1052	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
801	initialising them, for example, by calling C<init Gtk2> manually.	1053	initialising them, for example, by calling C<init Gtk2> manually.
802		1054
803	=item exit runs destructors	1055	=item exiting calls object destructors
804		1056
805	This only applies to users of Lc<AnyEvent::Fork:Early> and	1057	This only applies to users of L<AnyEvent::Fork:Early> and
806	L<AnyEvent::Fork::Template>.	1058	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1059	that reference external resources.
807		1060
808	When a process created by AnyEvent::Fork exits, it might do so by calling	1061	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	1062	exit, or simply letting perl reach the end of the program. At which point
810	Perl runs all destructors.	1063	Perl runs all destructors.
811		1064
…		…
830	to make it so, mostly due to the bloody broken perl that nobody seems to	1083	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	1084	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	1085	useful that you can do with it without running into memory corruption
833	issues or other braindamage. Hrrrr.	1086	issues or other braindamage. Hrrrr.
834		1087
835	Cygwin perl is not supported at the moment, as it should implement fd	1088	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	1089	work within it's documented limits) and quite obviously it's not getting
837	support enough functionality to do it.	1090	improved any time soon, the best way to proceed on windows would be to
		1091	always use C<new_exec> and thus never rely on perl's fork "emulation".
		1092
		1093	Cygwin perl is not supported at the moment due to some hilarious
		1094	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1095	use C<send_fh> and always use C<new_exec> to create processes, it should
		1096	work though.
		1097
		1098	=head1 USING AnyEvent::Fork IN SUBPROCESSES
		1099
		1100	AnyEvent::Fork itself cannot generally be used in subprocesses. As long as
		1101	only one process ever forks new processes, sharing the template processes
		1102	is possible (you could use a pipe as a lock by writing a byte into it to
		1103	unlock, and reading the byte to lock for example)
		1104
		1105	To make concurrent calls possible after fork, you should get rid of the
		1106	template and early fork processes. AnyEvent::Fork will create a new
		1107	template process as needed.
		1108
		1109	undef $AnyEvent::Fork::EARLY;
		1110	undef $AnyEvent::Fork::TEMPLATE;
		1111
		1112	It doesn't matter whether you get rid of them in the parent or child after
		1113	a fork.
838		1114
839	=head1 SEE ALSO	1115	=head1 SEE ALSO
840		1116
841	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	1117	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1118	(part of this distribution).
		1119
842	L<AnyEvent::Fork::Template> (to create a process by forking the main	1120	L<AnyEvent::Fork::Template>, to create a process by forking the main
843	program at a convenient time).	1121	program at a convenient time (part of this distribution).
844		1122
845	=head1 AUTHOR	1123	L<AnyEvent::Fork::Remote>, for another way to create processes that is
		1124	mostly compatible to this module and modules building on top of it, but
		1125	works better with remote processes.
		1126
		1127	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1128
		1129	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1130
		1131	=head1 AUTHOR AND CONTACT INFORMATION
846		1132
847	Marc Lehmann <schmorp@schmorp.de>	1133	Marc Lehmann <schmorp@schmorp.de>
848	http://home.schmorp.de/	1134	http://software.schmorp.de/pkg/AnyEvent-Fork
849		1135
850	=cut	1136	=cut
851		1137
852	1	1138	1
853		1139

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.24 by root, Sat Apr 6 08:32:23 2013 UTC vs. Revision 1.63 by root, Wed Nov 26 13:36:18 2014 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.24 by root, Sat Apr 6 08:32:23 2013 UTC vs.
Revision 1.63 by root, Wed Nov 26 13:36:18 2014 UTC