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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.10 by root, Thu Apr 4 06:09:15 2013 UTC vs.
Revision 1.73 by root, Wed Jan 26 16:44:16 2022 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't	3	AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
4		4
5	ATTENTION, this is a very early release, and very untested. Consider it a
6	technology preview.
7
8	=head1 SYNOPSIS	5	=head1 SYNOPSIS
9		6
10	use AnyEvent::Fork;	7	use AnyEvent::Fork;
11		8
12	##################################################################	9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
		15
		16	=head1 DESCRIPTION
		17
		18	This module allows you to create new processes, without actually forking
		19	them from your current process (avoiding the problems of forking), but
		20	preserving most of the advantages of fork.
		21
		22	It can be used to create new worker processes or new independent
		23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
		27
		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>
		30	or L<PAR::Packer>.
		31
		32	=head2 WHAT THIS MODULE IS NOT
		33
		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 -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you could use the L<AnyEvent::Fork::RPC>
		40	companion module, which adds simple RPC/job queueing to a process created
		41	by this module.
		42
		43	And if you need some automatic process pool management on top of
		44	L<AnyEvent::Fork::RPC>, you can look at the L<AnyEvent::Fork::Pool>
		45	companion module.
		46
		47	Or you can implement it yourself in whatever way you like: use some
		48	message-passing module such as L<AnyEvent::MP>, some pipe such as
		49	L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send
		50	e.g. JSON or Storable messages, and so on.
		51
		52	=head2 COMPARISON TO OTHER MODULES
		53
		54	There is an abundance of modules on CPAN that do "something fork", such as
		55	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		56	or L<AnyEvent::Subprocess>. There are modules that implement their own
		57	process management, such as L<AnyEvent::DBI>.
		58
		59	The problems that all these modules try to solve are real, however, none
		60	of them (from what I have seen) tackle the very real problems of unwanted
		61	memory sharing, efficiency 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
		180
		181	=head1 EXAMPLES
		182
		183	This is where the wall of text ends and code speaks.
		184
13	# create a single new process, tell it to run your worker function	185	=head2 Create a single new process, tell it to run your worker function.
14		186
15	AnyEvent::Fork	187	AnyEvent::Fork
16	->new	188	->new
17	->require ("MyModule")	189	->require ("MyModule")
18	->run ("MyModule::worker, sub {	190	->run ("MyModule::worker, sub {
20		192
21	# now $master_filehandle is connected to the	193	# now $master_filehandle is connected to the
22	# $slave_filehandle in the new process.	194	# $slave_filehandle in the new process.
23	});	195	});
24		196
25	# MyModule::worker might look like this	197	C<MyModule> might look like this:
		198
		199	package MyModule;
		200
26	sub MyModule::worker {	201	sub worker {
27	my ($slave_filehandle) = @_;	202	my ($slave_filehandle) = @_;
28		203
29	# now $slave_filehandle is connected to the $master_filehandle	204	# now $slave_filehandle is connected to the $master_filehandle
30	# in the original prorcess. have fun!	205	# in the original process. have fun!
31	}	206	}
32		207
33	##################################################################
34	# create a pool of server processes all accepting on the same socket	208	=head2 Create a pool of server processes all accepting on the same socket.
35		209
36	# create listener socket	210	# create listener socket
37	my $listener = ...;	211	my $listener = ...;
38		212
39	# create a pool template, initialise it and give it the socket	213	# create a pool template, initialise it and give it the socket
…		…
51	}	225	}
52		226
53	# now do other things - maybe use the filehandle provided by run	227	# now do other things - maybe use the filehandle provided by run
54	# to wait for the processes to die. or whatever.	228	# to wait for the processes to die. or whatever.
55		229
56	# My::Server::run might look like this	230	C<My::Server> might look like this:
57	sub My::Server::run {	231
		232	package My::Server;
		233
		234	sub run {
58	my ($slave, $listener, $id) = @_;	235	my ($slave, $listener, $id) = @_;
59		236
60	close $slave; # we do not use the socket, so close it to save resources	237	close $slave; # we do not use the socket, so close it to save resources
61		238
62	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	239	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
64	while (my $socket = $listener->accept) {	241	while (my $socket = $listener->accept) {
65	# do sth. with new socket	242	# do sth. with new socket
66	}	243	}
67	}	244	}
68		245
69	=head1 DESCRIPTION	246	=head2 use AnyEvent::Fork as a faster fork+exec
70		247
71	This module allows you to create new processes, without actually forking	248	This runs C</bin/echo hi>, with standard output redirected to F</tmp/log>
72	them from your current process (avoiding the problems of forking), but	249	and standard error redirected to the communications socket. It is usually
73	preserving most of the advantages of fork.	250	faster than fork+exec, but still lets you prepare the environment.
74		251
75	It can be used to create new worker processes or new independent	252	open my $output, ">/tmp/log" or die "$!";
76	subprocesses for short- and long-running jobs, process pools (e.g. for use
77	in pre-forked servers) but also to spawn new external processes (such as
78	CGI scripts from a webserver), which can be faster (and more well behaved)
79	than using fork+exec in big processes.
80		253
81	Special care has been taken to make this module useful from other modules,	254	AnyEvent::Fork
82	while still supporting specialised environments such as L<App::Staticperl>	255	->new
83	or L<PAR::Packer>.	256	->eval ('
		257	# compile a helper function for later use
		258	sub run {
		259	my ($fh, $output, @cmd) = @_;
84		260
85	=head1 PROBLEM STATEMENT	261	# perl will clear close-on-exec on STDOUT/STDERR
		262	open STDOUT, ">&", $output or die;
		263	open STDERR, ">&", $fh or die;
86		264
87	There are two ways to implement parallel processing on UNIX like operating	265	exec @cmd;
88	systems - fork and process, and fork+exec and process. They have different	266	}
89	advantages and disadvantages that I describe below, together with how this	267	')
90	module tries to mitigate the disadvantages.	268	->send_fh ($output)
		269	->send_arg ("/bin/echo", "hi")
		270	->run ("run", my $cv = AE::cv);
91		271
92	=over 4	272	my $stderr = $cv->recv;
93		273
94	=item Forking from a big process can be very slow (a 5GB process needs	274	=head2 For stingy users: put the worker code into a C<DATA> section.
95	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
96	is often shared with exec (because you have to fork first), but in some
97	circumstances (e.g. when vfork is used), fork+exec can be much faster.
98		275
99	This module can help here by telling a small(er) helper process to fork,	276	When you want to be stingy with files, you can put your code into the
100	or fork+exec instead.	277	C<DATA> section of your module (or program):
101		278
102	=item Forking usually creates a copy-on-write copy of the parent	279	use AnyEvent::Fork;
103	process. Memory (for example, modules or data files that have been
104	will not take additional memory). When exec'ing a new process, modules
105	and data files might need to be loaded again, at extra cpu and memory
106	cost. Likewise when forking, all data structures are copied as well - if
107	the program frees them and replaces them by new data, the child processes
108	will retain the memory even if it isn't used.
109		280
110	This module allows the main program to do a controlled fork, and allows	281	AnyEvent::Fork
111	modules to exec processes safely at any time. When creating a custom	282	->new
112	process pool you can take advantage of data sharing via fork without	283	->eval (do { local $/; <DATA> })
113	risking to share large dynamic data structures that will blow up child	284	->run ("doit", sub { ... });
114	memory usage.
115		285
116	=item Exec'ing a new perl process might be difficult and slow. For	286	__DATA__
117	example, it is not easy to find the correct path to the perl interpreter,
118	and all modules have to be loaded from disk again. Long running processes
119	might run into problems when perl is upgraded for example.
120		287
121	This module supports creating pre-initialised perl processes to be used	288	sub doit {
122	as template, and also tries hard to identify the correct path to the perl	289	... do something!
123	interpreter. With a cooperative main program, exec'ing the interpreter	290	}
124	might not even be necessary.
125		291
126	=item Forking might be impossible when a program is running. For example,	292	=head2 For stingy standalone programs: do not rely on external files at
127	POSIX makes it almost impossible to fork from a multithreaded program and	293	all.
128	do anything useful in the child - strictly speaking, if your perl program
129	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
130	you cannot call fork on the perl level anymore, at all.
131		294
132	This module can safely fork helper processes at any time, by caling	295	For single-file scripts it can be inconvenient to rely on external
133	fork+exec in C, in a POSIX-compatible way.	296	files - even when using a C<DATA> section, you still need to C<exec> an
		297	external perl interpreter, which might not be available when using
		298	L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example.
134		299
135	=item Parallel processing with fork might be inconvenient or difficult	300	Two modules help here - L<AnyEvent::Fork::Early> forks a template process
136	to implement. For example, when a program uses an event loop and creates	301	for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template>
137	watchers it becomes very hard to use the event loop from a child	302	forks the main program as a template process.
138	program, as the watchers already exist but are only meaningful in the
139	parent. Worse, a module might want to use such a system, not knowing
140	whether another module or the main program also does, leading to problems.
141		303
142	This module only lets the main program create pools by forking (because	304	Here is how your main program should look like:
143	only the main program can know when it is still safe to do so) - all other
144	pools are created by fork+exec, after which such modules can again be
145	loaded.
146		305
147	=back	306	#! perl
		307
		308	# optional, as the very first thing.
		309	# in case modules want to create their own processes.
		310	use AnyEvent::Fork::Early;
		311
		312	# next, load all modules you need in your template process
		313	use Example::My::Module
		314	use Example::Whatever;
		315
		316	# next, put your run function definition and anything else you
		317	# need, but do not use code outside of BEGIN blocks.
		318	sub worker_run {
		319	my ($fh, @args) = @_;
		320	...
		321	}
		322
		323	# now preserve everything so far as AnyEvent::Fork object
		324	# in $TEMPLATE.
		325	use AnyEvent::Fork::Template;
		326
		327	# do not put code outside of BEGIN blocks until here
		328
		329	# now use the $TEMPLATE process in any way you like
		330
		331	# for example: create 10 worker processes
		332	my @worker;
		333	my $cv = AE::cv;
		334	for (1..10) {
		335	$cv->begin;
		336	$TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub {
		337	push @worker, shift;
		338	$cv->end;
		339	});
		340	}
		341	$cv->recv;
148		342
149	=head1 CONCEPTS	343	=head1 CONCEPTS
150		344
151	This module can create new processes either by executing a new perl	345	This module can create new processes either by executing a new perl
152	process, or by forking from an existing "template" process.	346	process, or by forking from an existing "template" process.
		347
		348	All these processes are called "child processes" (whether they are direct
		349	children or not), while the process that manages them is called the
		350	"parent process".
153		351
154	Each such process comes with its own file handle that can be used to	352	Each such process comes with its own file handle that can be used to
155	communicate with it (it's actually a socket - one end in the new process,	353	communicate with it (it's actually a socket - one end in the new process,
156	one end in the main process), and among the things you can do in it are	354	one end in the main process), and among the things you can do in it are
157	load modules, fork new processes, send file handles to it, and execute	355	load modules, fork new processes, send file handles to it, and execute
…		…
169	needed the first time. Forking from this process shares the memory used	367	needed the first time. Forking from this process shares the memory used
170	for the perl interpreter with the new process, but loading modules takes	368	for the perl interpreter with the new process, but loading modules takes
171	time, and the memory is not shared with anything else.	369	time, and the memory is not shared with anything else.
172		370
173	This is ideal for when you only need one extra process of a kind, with the	371	This is ideal for when you only need one extra process of a kind, with the
174	option of starting and stipping it on demand.	372	option of starting and stopping it on demand.
175		373
176	Example:	374	Example:
177		375
178	AnyEvent::Fork	376	AnyEvent::Fork
179	->new	377	->new
…		…
194	modules you loaded) is shared between the processes, and each new process	392	modules you loaded) is shared between the processes, and each new process
195	consumes relatively little memory of its own.	393	consumes relatively little memory of its own.
196		394
197	The disadvantage of this approach is that you need to create a template	395	The disadvantage of this approach is that you need to create a template
198	process for the sole purpose of forking new processes from it, but if you	396	process for the sole purpose of forking new processes from it, but if you
199	only need a fixed number of proceses you can create them, and then destroy	397	only need a fixed number of processes you can create them, and then destroy
200	the template process.	398	the template process.
201		399
202	Example:	400	Example:
203		401
204	my $template = AnyEvent::Fork->new->require ("Some::Module");	402	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
231	my ($fork_fh) = @_;	429	my ($fork_fh) = @_;
232	});	430	});
233		431
234	=back	432	=back
235		433
236	=head1 FUNCTIONS	434	=head1 THE C<AnyEvent::Fork> CLASS
		435
		436	This module exports nothing, and only implements a single class -
		437	C<AnyEvent::Fork>.
		438
		439	There are two class constructors that both create new processes - C<new>
		440	and C<new_exec>. The C<fork> method creates a new process by forking an
		441	existing one and could be considered a third constructor.
		442
		443	Most of the remaining methods deal with preparing the new process, by
		444	loading code, evaluating code and sending data to the new process. They
		445	usually return the process object, so you can chain method calls.
		446
		447	If a process object is destroyed before calling its C<run> method, then
		448	the process simply exits. After C<run> is called, all responsibility is
		449	passed to the specified function.
		450
		451	As long as there is any outstanding work to be done, process objects
		452	resist being destroyed, so there is no reason to store them unless you
		453	need them later - configure and forget works just fine.
237		454
238	=over 4	455	=over 4
239		456
240	=cut	457	=cut
241		458
242	package AnyEvent::Fork;	459	package AnyEvent::Fork;
243		460
244	use common::sense;	461	use common::sense;
245		462
246	use Socket ();	463	use Errno ();
247		464
248	use AnyEvent;	465	use AnyEvent;
249	use AnyEvent::Fork::Util;
250	use AnyEvent::Util ();	466	use AnyEvent::Util ();
251		467
252	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	468	use IO::FDPass;
253		469
254	=item my $pool = new AnyEvent::Fork key => value...	470	our $VERSION = 1.32;
255
256	Create a new process pool. The following named parameters are supported:
257
258	=over 4
259
260	=back
261
262	=cut
263		471
264	# the early fork template process	472	# the early fork template process
265	our $EARLY;	473	our $EARLY;
266		474
267	# the empty template process	475	# the empty template process
268	our $TEMPLATE;	476	our $TEMPLATE;
269		477
		478	sub QUEUE() { 0 }
		479	sub FH() { 1 }
		480	sub WW() { 2 }
		481	sub PID() { 3 }
		482	sub CB() { 4 }
		483
		484	sub _new {
		485	my ($self, $fh, $pid) = @_;
		486
		487	AnyEvent::Util::fh_nonblocking $fh, 1;
		488
		489	$self = bless [
		490	[], # write queue - strings or fd's
		491	$fh,
		492	undef, # AE watcher
		493	$pid,
		494	], $self;
		495
		496	$self
		497	}
		498
270	sub _cmd {	499	sub _cmd {
271	my $self = shift;	500	my $self = shift;
272		501
273	#TODO: maybe append the packet to any existing string command already in the queue
274
275	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	502	# ideally, we would want to use "a (w/a)*" as format string, but perl
276	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	503	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
277	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	504	# it.
		505	push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1];
278		506
279	$self->[3] \|\|= AE::io $self->[1], 1, sub {	507	$self->[WW] \|\|= AE::io $self->[FH], 1, sub {
		508	do {
280	# send the next "thing" in the queue - either a reference to an fh,	509	# send the next "thing" in the queue - either a reference to an fh,
281	# or a plain string.	510	# or a plain string.
282		511
283	if (ref $self->[2][0]) {	512	if (ref $self->[QUEUE][0]) {
284	# send fh	513	# send fh
285	AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] }	514	unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) {
		515	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		516	undef $self->[WW];
		517	die "AnyEvent::Fork: file descriptor send failure: $!";
		518	}
		519
286	and shift @{ $self->[2] };	520	shift @{ $self->[QUEUE] };
287		521
288	} else {	522	} else {
289	# send string	523	# send string
290	my $len = syswrite $self->[1], $self->[2][0]	524	my $len = syswrite $self->[FH], $self->[QUEUE][0];
		525
		526	unless ($len) {
		527	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		528	undef $self->[WW];
291	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	529	die "AnyEvent::Fork: command write failure: $!";
		530	}
292		531
293	substr $self->[2][0], 0, $len, "";	532	substr $self->[QUEUE][0], 0, $len, "";
294	shift @{ $self->[2] } unless length $self->[2][0];	533	shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0];
295	}	534	}
		535	} while @{ $self->[QUEUE] };
296		536
297	unless (@{ $self->[2] }) {	537	# everything written
298	undef $self->[3];	538	undef $self->[WW];
		539
299	# invoke run callback	540	# invoke run callback, if any
		541	if ($self->[CB]) {
300	$self->[0]->($self->[1]) if $self->[0];	542	$self->[CB]->($self->[FH]);
		543	@$self = ();
301	}	544	}
302	};	545	};
303	}
304		546
305	sub _new {	547	() # make sure we don't leak the watcher
306	my ($self, $fh) = @_;
307
308	AnyEvent::Util::fh_nonblocking $fh, 1;
309
310	$self = bless [
311	undef, # run callback
312	$fh,
313	[], # write queue - strings or fd's
314	undef, # AE watcher
315	], $self;
316
317	$self
318	}	548	}
319		549
320	# fork template from current process, used by AnyEvent::Fork::Early/Template	550	# fork template from current process, used by AnyEvent::Fork::Early/Template
321	sub _new_fork {	551	sub _new_fork {
322	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	552	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
326		556
327	if ($pid eq 0) {	557	if ($pid eq 0) {
328	require AnyEvent::Fork::Serve;	558	require AnyEvent::Fork::Serve;
329	$AnyEvent::Fork::Serve::OWNER = $parent;	559	$AnyEvent::Fork::Serve::OWNER = $parent;
330	close $fh;	560	close $fh;
331	$0 = "$_[1] of $parent";	561	$0 = "$parent AnyEvent::Fork/exec";
332	AnyEvent::Fork::Serve::serve ($slave);	562	AnyEvent::Fork::Serve::serve ($slave);
333	AnyEvent::Fork::Util::_exit 0;	563	exit 0;
334	} elsif (!$pid) {	564	} elsif (!$pid) {
335	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	565	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
336	}	566	}
337		567
338	AnyEvent::Fork->_new ($fh)	568	AnyEvent::Fork->_new ($fh, $pid)
339	}	569	}
340		570
341	=item my $proc = new AnyEvent::Fork	571	=item my $proc = new AnyEvent::Fork
342		572
343	Create a new "empty" perl interpreter process and returns its process	573	Create a new "empty" perl interpreter process and returns its process
344	object for further manipulation.	574	object for further manipulation.
345		575
346	The new process is forked from a template process that is kept around	576	The new process is forked from a template process that is kept around
347	for this purpose. When it doesn't exist yet, it is created by a call to	577	for this purpose. When it doesn't exist yet, it is created by a call to
348	C<new_exec> and kept around for future calls.	578	C<new_exec> first and then stays around for future calls.
349
350	When the process object is destroyed, it will release the file handle
351	that connects it with the new process. When the new process has not yet
352	called C<run>, then the process will exit. Otherwise, what happens depends
353	entirely on the code that is executed.
354		579
355	=cut	580	=cut
356		581
357	sub new {	582	sub new {
358	my $class = shift;	583	my $class = shift;
…		…
394	reduces the amount of memory sharing that is possible, and is also slower.	619	reduces the amount of memory sharing that is possible, and is also slower.
395		620
396	You should use C<new> whenever possible, except when having a template	621	You should use C<new> whenever possible, except when having a template
397	process around is unacceptable.	622	process around is unacceptable.
398		623
399	The path to the perl interpreter is divined usign various methods - first	624	The path to the perl interpreter is divined using various methods - first
400	C<$^X> is investigated to see if the path ends with something that sounds	625	C<$^X> is investigated to see if the path ends with something that looks
401	as if it were the perl interpreter. Failing this, the module falls back to	626	as if it were the perl interpreter. Failing this, the module falls back to
402	using C<$Config::Config{perlpath}>.	627	using C<$Config::Config{perlpath}>.
403		628
		629	The path to perl can also be overridden by setting the global variable
		630	C<$AnyEvent::Fork::PERL> - it's value will be used for all subsequent
		631	invocations.
		632
404	=cut	633	=cut
		634
		635	our $PERL;
405		636
406	sub new_exec {	637	sub new_exec {
407	my ($self) = @_;	638	my ($self) = @_;
408		639
409	return $EARLY->fork	640	return $EARLY->fork
410	if $EARLY;	641	if $EARLY;
411		642
		643	unless (defined $PERL) {
412	# first find path of perl	644	# first find path of perl
413	my $perl = $;	645	my $perl = $^X;
414		646
415	# first we try $^X, but the path must be absolute (always on win32), and end in sth.	647	# first we try $^X, but the path must be absolute (always on win32), and end in sth.
416	# that looks like perl. this obviously only works for posix and win32	648	# that looks like perl. this obviously only works for posix and win32
417	unless (	649	unless (
418	(AnyEvent::Fork::Util::WIN32 \|\| $perl =~ m%^/%)	650	($^O eq "MSWin32" \|\| $perl =~ m%^/%)
419	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i	651	&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i
420	) {	652	) {
421	# if it doesn't look perlish enough, try Config	653	# if it doesn't look perlish enough, try Config
422	require Config;	654	require Config;
423	$perl = $Config::Config{perlpath};	655	$perl = $Config::Config{perlpath};
424	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;	656	$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/;
		657	}
		658
		659	$PERL = $perl;
425	}	660	}
426		661
427	require Proc::FastSpawn;	662	require Proc::FastSpawn;
428		663
429	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;	664	my ($fh, $slave) = AnyEvent::Util::portable_socketpair;
…		…
434	Proc::FastSpawn::fd_inherit (fileno $fh, 0);	669	Proc::FastSpawn::fd_inherit (fileno $fh, 0);
435		670
436	# quick. also doesn't work in win32. of course. what did you expect	671	# quick. also doesn't work in win32. of course. what did you expect
437	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	672	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
438	my %env = %ENV;	673	my %env = %ENV;
439	$env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC;	674	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
440		675
441	Proc::FastSpawn::spawn (	676	my $pid = Proc::FastSpawn::spawn (
442	$perl,	677	$PERL,
443	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	678	[$PERL, "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
444	[map "$_=$env{$_}", keys %env],	679	[map "$_=$env{$_}", keys %env],
445	) or die "unable to spawn AnyEvent::Fork server: $!";	680	) or die "unable to spawn AnyEvent::Fork server: $!";
446		681
447	$self->_new ($fh)	682	$self->_new ($fh, $pid)
		683	}
		684
		685	=item $pid = $proc->pid
		686
		687	Returns the process id of the process I<iff it is a direct child of the
		688	process running AnyEvent::Fork>, and C<undef> otherwise. As a general
		689	rule (that you cannot rely upon), processes created via C<new_exec>,
		690	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template> are direct
		691	children, while all other processes are not.
		692
		693	Or in other words, you do not normally have to take care of zombies for
		694	processes created via C<new>, but when in doubt, or zombies are a problem,
		695	you need to check whether a process is a diretc child by calling this
		696	method, and possibly creating a child watcher or reap it manually.
		697
		698	=cut
		699
		700	sub pid {
		701	$_[0][PID]
448	}	702	}
449		703
450	=item $proc = $proc->eval ($perlcode, @args)	704	=item $proc = $proc->eval ($perlcode, @args)
451		705
452	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	706	Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_>
453	the strings specified by C<@args>.	707	to the strings specified by C<@args>, in the "main" package (so you can
		708	access the args using C<$_[0]> and so on, but not using implicit C<shit>
		709	as the latter works on C<@ARGV>).
454		710
455	This call is meant to do any custom initialisation that might be required	711	This call is meant to do any custom initialisation that might be required
456	(for example, the C<require> method uses it). It's not supposed to be used	712	(for example, the C<require> method uses it). It's not supposed to be used
457	to completely take over the process, use C<run> for that.	713	to completely take over the process, use C<run> for that.
458		714
459	The code will usually be executed after this call returns, and there is no	715	The code will usually be executed after this call returns, and there is no
460	way to pass anything back to the calling process. Any evaluation errors	716	way to pass anything back to the calling process. Any evaluation errors
461	will be reported to stderr and cause the process to exit.	717	will be reported to stderr and cause the process to exit.
462		718
		719	If you want to execute some code (that isn't in a module) to take over the
		720	process, you should compile a function via C<eval> first, and then call
		721	it via C<run>. This also gives you access to any arguments passed via the
		722	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		723	a faster fork+exec> example to see it in action.
		724
463	Returns the process object for easy chaining of method calls.	725	Returns the process object for easy chaining of method calls.
		726
		727	It's common to want to call an iniitalisation function with some
		728	arguments. Make sure you actually pass C<@_> to that function (for example
		729	by using C<&name> syntax), and do not just specify a function name:
		730
		731	$proc->eval ('&MyModule::init', $string1, $string2);
464		732
465	=cut	733	=cut
466		734
467	sub eval {	735	sub eval {
468	my ($self, $code, @args) = @_;	736	my ($self, $code, @args) = @_;
469		737
470	$self->_cmd (e => $code, @args);	738	$self->_cmd (e => pack "(w/a)", $code, @args);
471		739
472	$self	740	$self
473	}	741	}
474		742
475	=item $proc = $proc->require ($module, ...)	743	=item $proc = $proc->require ($module, ...)
…		…
492	=item $proc = $proc->send_fh ($handle, ...)	760	=item $proc = $proc->send_fh ($handle, ...)
493		761
494	Send one or more file handles (I<not> file descriptors) to the process,	762	Send one or more file handles (I<not> file descriptors) to the process,
495	to prepare a call to C<run>.	763	to prepare a call to C<run>.
496		764
497	The process object keeps a reference to the handles until this is done,	765	The process object keeps a reference to the handles until they have
498	so you must not explicitly close the handles. This is most easily	766	been passed over to the process, so you must not explicitly close the
499	accomplished by simply not storing the file handles anywhere after passing	767	handles. This is most easily accomplished by simply not storing the file
500	them to this method.	768	handles anywhere after passing them to this method - when AnyEvent::Fork
		769	is finished using them, perl will automatically close them.
501		770
502	Returns the process object for easy chaining of method calls.	771	Returns the process object for easy chaining of method calls.
503		772
504	Example: pass an fh to a process, and release it without closing. it will	773	Example: pass a file handle to a process, and release it without
505	be closed automatically when it is no longer used.	774	closing. It will be closed automatically when it is no longer used.
506		775
507	$proc->send_fh ($my_fh);	776	$proc->send_fh ($my_fh);
508	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	777	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
509		778
510	=cut	779	=cut
…		…
512	sub send_fh {	781	sub send_fh {
513	my ($self, @fh) = @_;	782	my ($self, @fh) = @_;
514		783
515	for my $fh (@fh) {	784	for my $fh (@fh) {
516	$self->_cmd ("h");	785	$self->_cmd ("h");
517	push @{ $self->[2] }, \$fh;	786	push @{ $self->[QUEUE] }, \$fh;
518	}	787	}
519		788
520	$self	789	$self
521	}	790	}
522		791
523	=item $proc = $proc->send_arg ($string, ...)	792	=item $proc = $proc->send_arg ($string, ...)
524		793
525	Send one or more argument strings to the process, to prepare a call to	794	Send one or more argument strings to the process, to prepare a call to
526	C<run>. The strings can be any octet string.	795	C<run>. The strings can be any octet strings.
527		796
		797	The protocol is optimised to pass a moderate number of relatively short
		798	strings - while you can pass up to 4GB of data in one go, this is more
		799	meant to pass some ID information or other startup info, not big chunks of
		800	data.
		801
528	Returns the process object for easy chaining of emthod calls.	802	Returns the process object for easy chaining of method calls.
529		803
530	=cut	804	=cut
531		805
532	sub send_arg {	806	sub send_arg {
533	my ($self, @arg) = @_;	807	my ($self, @arg) = @_;
534		808
535	$self->_cmd (a => @arg);	809	$self->_cmd (a => pack "(w/a)", @arg);
536		810
537	$self	811	$self
538	}	812	}
539		813
540	=item $proc->run ($func, $cb->($fh))	814	=item $proc->run ($func, $cb->($fh))
541		815
542	Enter the function specified by the fully qualified name in C<$func> in	816	Enter the function specified by the function name in C<$func> in the
543	the process. The function is called with the communication socket as first	817	process. The function is called with the communication socket as first
544	argument, followed by all file handles and string arguments sent earlier	818	argument, followed by all file handles and string arguments sent earlier
545	via C<send_fh> and C<send_arg> methods, in the order they were called.	819	via C<send_fh> and C<send_arg> methods, in the order they were called.
546		820
547	If the called function returns, the process exits.
548
549	Preparing the process can take time - when the process is ready, the
550	callback is invoked with the local communications socket as argument.
551
552	The process object becomes unusable on return from this function.	821	The process object becomes unusable on return from this function - any
		822	further method calls result in undefined behaviour.
		823
		824	The function name should be fully qualified, but if it isn't, it will be
		825	looked up in the C<main> package.
		826
		827	If the called function returns, doesn't exist, or any error occurs, the
		828	process exits.
		829
		830	Preparing the process is done in the background - when all commands have
		831	been sent, the callback is invoked with the local communications socket
		832	as argument. At this point you can start using the socket in any way you
		833	like.
553		834
554	If the communication socket isn't used, it should be closed on both sides,	835	If the communication socket isn't used, it should be closed on both sides,
555	to save on kernel memory.	836	to save on kernel memory.
556		837
557	The socket is non-blocking in the parent, and blocking in the newly	838	The socket is non-blocking in the parent, and blocking in the newly
558	created process. The close-on-exec flag is set on both. Even if not used	839	created process. The close-on-exec flag is set in both.
		840
559	otherwise, the socket can be a good indicator for the existance of the	841	Even if not used otherwise, the socket can be a good indicator for the
560	process - if the other process exits, you get a readable event on it,	842	existence of the process - if the other process exits, you get a readable
561	because exiting the process closes the socket (if it didn't create any	843	event on it, because exiting the process closes the socket (if it didn't
562	children using fork).	844	create any children using fork).
		845
		846	=over 4
		847
		848	=item Compatibility to L<AnyEvent::Fork::Remote>
		849
		850	If you want to write code that works with both this module and
		851	L<AnyEvent::Fork::Remote>, you need to write your code so that it assumes
		852	there are two file handles for communications, which might not be unix
		853	domain sockets. The C<run> function should start like this:
		854
		855	sub run {
		856	my ($rfh, @args) = @_; # @args is your normal arguments
		857	my $wfh = fileno $rfh ? $rfh : *STDOUT;
		858
		859	# now use $rfh for reading and $wfh for writing
		860	}
		861
		862	This checks whether the passed file handle is, in fact, the process
		863	C<STDIN> handle. If it is, then the function was invoked visa
		864	L<AnyEvent::Fork::Remote>, so STDIN should be used for reading and
		865	C<STDOUT> should be used for writing.
		866
		867	In all other cases, the function was called via this module, and there is
		868	only one file handle that should be sued for reading and writing.
		869
		870	=back
563		871
564	Example: create a template for a process pool, pass a few strings, some	872	Example: create a template for a process pool, pass a few strings, some
565	file handles, then fork, pass one more string, and run some code.	873	file handles, then fork, pass one more string, and run some code.
566		874
567	my $pool = AnyEvent::Fork	875	my $pool = AnyEvent::Fork
…		…
575	->send_arg ("str3")	883	->send_arg ("str3")
576	->run ("Some::function", sub {	884	->run ("Some::function", sub {
577	my ($fh) = @_;	885	my ($fh) = @_;
578		886
579	# fh is nonblocking, but we trust that the OS can accept these	887	# fh is nonblocking, but we trust that the OS can accept these
580	# extra 3 octets anyway.	888	# few octets anyway.
581	syswrite $fh, "hi #$_\n";	889	syswrite $fh, "hi #$_\n";
582		890
583	# $fh is being closed here, as we don't store it anywhere	891	# $fh is being closed here, as we don't store it anywhere
584	});	892	});
585	}	893	}
…		…
587	# Some::function might look like this - all parameters passed before fork	895	# Some::function might look like this - all parameters passed before fork
588	# and after will be passed, in order, after the communications socket.	896	# and after will be passed, in order, after the communications socket.
589	sub Some::function {	897	sub Some::function {
590	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	898	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
591		899
592	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	900	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
593	}	901	}
594		902
595	=cut	903	=cut
596		904
597	sub run {	905	sub run {
598	my ($self, $func, $cb) = @_;	906	my ($self, $func, $cb) = @_;
599		907
600	$self->[0] = $cb;	908	$self->[CB] = $cb;
601	$self->_cmd (r => $func);	909	$self->_cmd (r => $func);
602	}	910	}
		911
		912	=back
		913
		914
		915	=head2 CHILD PROCESS INTERFACE
		916
		917	This module has a limited API for use in child processes.
		918
		919	=over 4
		920
		921	=item @args = AnyEvent::Fork::Serve::run_args
		922
		923	This function, which only exists before the C<run> method is called,
		924	returns the arguments that would be passed to the run function, and clears
		925	them.
		926
		927	This is mainly useful to get any file handles passed via C<send_fh>, but
		928	works for any arguments passed via C<< send_I<xxx> >> methods.
		929
		930	=back
		931
		932
		933	=head2 EXPERIMENTAL METHODS
		934
		935	These methods might go away completely or change behaviour, at any time.
		936
		937	=over 4
		938
		939	=item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED
		940
		941	Flushes all commands out to the process and then calls the callback with
		942	the communications socket.
		943
		944	The process object becomes unusable on return from this function - any
		945	further method calls result in undefined behaviour.
		946
		947	The point of this method is to give you a file handle that you can pass
		948	to another process. In that other process, you can call C<new_from_fh
		949	AnyEvent::Fork $fh> to create a new C<AnyEvent::Fork> object from it,
		950	thereby effectively passing a fork object to another process.
		951
		952	=cut
		953
		954	sub to_fh {
		955	my ($self, $cb) = @_;
		956
		957	$self->[CB] = $cb;
		958
		959	unless ($self->[WW]) {
		960	$self->[CB]->($self->[FH]);
		961	@$self = ();
		962	}
		963	}
		964
		965	=item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED
		966
		967	Takes a file handle originally rceeived by the C<to_fh> method and creates
		968	a new C<AnyEvent:Fork> object. The child process itself will not change in
		969	any way, i.e. it will keep all the modifications done to it before calling
		970	C<to_fh>.
		971
		972	The new object is very much like the original object, except that the
		973	C<pid> method will return C<undef> even if the process is a direct child.
		974
		975	=cut
		976
		977	sub new_from_fh {
		978	my ($class, $fh) = @_;
		979
		980	$class->_new ($fh)
		981	}
		982
		983	=back
		984
		985	=head1 PERFORMANCE
		986
		987	Now for some unscientific benchmark numbers (all done on an amd64
		988	GNU/Linux box). These are intended to give you an idea of the relative
		989	performance you can expect, they are not meant to be absolute performance
		990	numbers.
		991
		992	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		993	exit in the child and waits for the socket to close in the parent. I did
		994	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		995
		996	2079 new processes per second, using manual socketpair + fork
		997
		998	Then I did the same thing, but instead of calling fork, I called
		999	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		1000	socket from the child to close on exit. This does the same thing as manual
		1001	socket pair + fork, except that what is forked is the template process
		1002	(2440kB), and the socket needs to be passed to the server at the other end
		1003	of the socket first.
		1004
		1005	2307 new processes per second, using AnyEvent::Fork->new
		1006
		1007	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		1008	a new perl interpreter and compile the small server each time, I get:
		1009
		1010	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		1011
		1012	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		1013	though it uses the same operations, but adds a lot of overhead?
		1014
		1015	The difference is simply the process size: forking the 5MB process takes
		1016	so much longer than forking the 2.5MB template process that the extra
		1017	overhead is canceled out.
		1018
		1019	If the benchmark process grows, the normal fork becomes even slower:
		1020
		1021	1340 new processes, manual fork of a 20MB process
		1022	731 new processes, manual fork of a 200MB process
		1023	235 new processes, manual fork of a 2000MB process
		1024
		1025	What that means (to me) is that I can use this module without having a bad
		1026	conscience because of the extra overhead required to start new processes.
		1027
		1028	=head1 TYPICAL PROBLEMS
		1029
		1030	This section lists typical problems that remain. I hope by recognising
		1031	them, most can be avoided.
		1032
		1033	=over 4
		1034
		1035	=item leaked file descriptors for exec'ed processes
		1036
		1037	POSIX systems inherit file descriptors by default when exec'ing a new
		1038	process. While perl itself laudably sets the close-on-exec flags on new
		1039	file handles, most C libraries don't care, and even if all cared, it's
		1040	often not possible to set the flag in a race-free manner.
		1041
		1042	That means some file descriptors can leak through. And since it isn't
		1043	possible to know which file descriptors are "good" and "necessary" (or
		1044	even to know which file descriptors are open), there is no good way to
		1045	close the ones that might harm.
		1046
		1047	As an example of what "harm" can be done consider a web server that
		1048	accepts connections and afterwards some module uses AnyEvent::Fork for the
		1049	first time, causing it to fork and exec a new process, which might inherit
		1050	the network socket. When the server closes the socket, it is still open
		1051	in the child (which doesn't even know that) and the client might conclude
		1052	that the connection is still fine.
		1053
		1054	For the main program, there are multiple remedies available -
		1055	L<AnyEvent::Fork::Early> is one, creating a process early and not using
		1056	C<new_exec> is another, as in both cases, the first process can be exec'ed
		1057	well before many random file descriptors are open.
		1058
		1059	In general, the solution for these kind of problems is to fix the
		1060	libraries or the code that leaks those file descriptors.
		1061
		1062	Fortunately, most of these leaked descriptors do no harm, other than
		1063	sitting on some resources.
		1064
		1065	=item leaked file descriptors for fork'ed processes
		1066
		1067	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
		1068	which closes file descriptors not marked for being inherited.
		1069
		1070	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
		1071	a way to create these processes by forking, and this leaks more file
		1072	descriptors than exec'ing them, as there is no way to mark descriptors as
		1073	"close on fork".
		1074
		1075	An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create
		1076	pipes for internal uses, and L<Gtk2> might open a connection to the X
		1077	server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have
		1078	trouble with a fork.
		1079
		1080	The solution is to either not load these modules before use'ing
		1081	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
		1082	initialising them, for example, by calling C<init Gtk2> manually.
		1083
		1084	=item exiting calls object destructors
		1085
		1086	This only applies to users of L<AnyEvent::Fork:Early> and
		1087	L<AnyEvent::Fork::Template>, or when initialising code creates objects
		1088	that reference external resources.
		1089
		1090	When a process created by AnyEvent::Fork exits, it might do so by calling
		1091	exit, or simply letting perl reach the end of the program. At which point
		1092	Perl runs all destructors.
		1093
		1094	Not all destructors are fork-safe - for example, an object that represents
		1095	the connection to an X display might tell the X server to free resources,
		1096	which is inconvenient when the "real" object in the parent still needs to
		1097	use them.
		1098
		1099	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		1100	it as the very first thing, right?
		1101
		1102	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		1103	is to not create objects with nontrivial destructors that might have an
		1104	effect outside of Perl.
603		1105
604	=back	1106	=back
605		1107
606	=head1 PORTABILITY NOTES	1108	=head1 PORTABILITY NOTES
607		1109
608	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	1110	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
609	and ::Template is not going to work), and it cost a lot of blood and sweat	1111	and ::Template is not going to work), and it cost a lot of blood and sweat
610	to make it so, mostly due to the bloody broken perl that nobody seems to	1112	to make it so, mostly due to the bloody broken perl that nobody seems to
611	care about. The fork emulation is a bad joke - I have yet to see something	1113	care about. The fork emulation is a bad joke - I have yet to see something
612	useful that you cna do with it without running into memory corruption	1114	useful that you can do with it without running into memory corruption
613	issues or other braindamage. Hrrrr.	1115	issues or other braindamage. Hrrrr.
614		1116
615	Cygwin perl is not supported at the moment, as it should implement fd	1117	Since fork is endlessly broken on win32 perls (it doesn't even remotely
616	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	1118	work within it's documented limits) and quite obviously it's not getting
617	support enough functionality to do it.	1119	improved any time soon, the best way to proceed on windows would be to
		1120	always use C<new_exec> and thus never rely on perl's fork "emulation".
618		1121
619	=head1 AUTHOR	1122	Cygwin perl is not supported at the moment due to some hilarious
		1123	shortcomings of its API - see L<IO::FDPoll> for more details. If you never
		1124	use C<send_fh> and always use C<new_exec> to create processes, it should
		1125	work though.
		1126
		1127	=head1 USING AnyEvent::Fork IN SUBPROCESSES
		1128
		1129	AnyEvent::Fork itself cannot generally be used in subprocesses. As long as
		1130	only one process ever forks new processes, sharing the template processes
		1131	is possible (you could use a pipe as a lock by writing a byte into it to
		1132	unlock, and reading the byte to lock for example)
		1133
		1134	To make concurrent calls possible after fork, you should get rid of the
		1135	template and early fork processes. AnyEvent::Fork will create a new
		1136	template process as needed.
		1137
		1138	undef $AnyEvent::Fork::EARLY;
		1139	undef $AnyEvent::Fork::TEMPLATE;
		1140
		1141	It doesn't matter whether you get rid of them in the parent or child after
		1142	a fork.
		1143
		1144	=head1 SEE ALSO
		1145
		1146	L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all
		1147	(part of this distribution).
		1148
		1149	L<AnyEvent::Fork::Template>, to create a process by forking the main
		1150	program at a convenient time (part of this distribution).
		1151
		1152	L<AnyEvent::Fork::Remote>, for another way to create processes that is
		1153	mostly compatible to this module and modules building on top of it, but
		1154	works better with remote processes.
		1155
		1156	L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN).
		1157
		1158	L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN).
		1159
		1160	=head1 AUTHOR AND CONTACT INFORMATION
620		1161
621	Marc Lehmann <schmorp@schmorp.de>	1162	Marc Lehmann <schmorp@schmorp.de>
622	http://home.schmorp.de/	1163	http://software.schmorp.de/pkg/AnyEvent-Fork
623		1164
624	=cut	1165	=cut
625		1166
626	1	1167	1
627		1168

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.10 by root, Thu Apr 4 06:09:15 2013 UTC vs. Revision 1.73 by root, Wed Jan 26 16:44:16 2022 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
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Revision 1.73 by root, Wed Jan 26 16:44:16 2022 UTC