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

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	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 can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head2 COMPARISON TO OTHER MODULES
		46
		47	There is an abundance of modules on CPAN that do "something fork", such as
		48	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		49	or L<AnyEvent::Subprocess>. There are modules that implement their own
		50	process management, such as L<AnyEvent::DBI>.
		51
		52	The problems that all these modules try to solve are real, however, none
		53	of them (from what I have seen) tackle the very real problems of unwanted
		54	memory sharing, efficiency, not being able to use event processing or
		55	similar modules in the processes they create.
		56
		57	This module doesn't try to replace any of them - instead it tries to solve
		58	the problem of creating processes with a minimum of fuss and overhead (and
		59	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		60	except they were written before AnyEvent:Fork was available, so obviously
		61	had to roll their own.
		62
		63	=head2 PROBLEM STATEMENT
		64
		65	There are two traditional ways to implement parallel processing on UNIX
		66	like operating systems - fork and process, and fork+exec and process. They
		67	have different advantages and disadvantages that I describe below,
		68	together with how this module tries to mitigate the disadvantages.
		69
		70	=over 4
		71
		72	=item Forking from a big process can be very slow.
		73
		74	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		75	overhead is often shared with exec (because you have to fork first), but
		76	in some circumstances (e.g. when vfork is used), fork+exec can be much
		77	faster.
		78
		79	This module can help here by telling a small(er) helper process to fork,
		80	which is faster then forking the main process, and also uses vfork where
		81	possible. This gives the speed of vfork, with the flexibility of fork.
		82
		83	=item Forking usually creates a copy-on-write copy of the parent
		84	process.
		85
		86	For example, modules or data files that are loaded will not use additional
		87	memory after a fork. When exec'ing a new process, modules and data files
		88	might need to be loaded again, at extra CPU and memory cost. But when
		89	forking, literally all data structures are copied - if the program frees
		90	them and replaces them by new data, the child processes will retain the
		91	old version even if it isn't used, which can suddenly and unexpectedly
		92	increase memory usage when freeing memory.
		93
		94	The trade-off is between more sharing with fork (which can be good or
		95	bad), and no sharing with exec.
		96
		97	This module allows the main program to do a controlled fork, and allows
		98	modules to exec processes safely at any time. When creating a custom
		99	process pool you can take advantage of data sharing via fork without
		100	risking to share large dynamic data structures that will blow up child
		101	memory usage.
		102
		103	In other words, this module puts you into control over what is being
		104	shared and what isn't, at all times.
		105
		106	=item Exec'ing a new perl process might be difficult.
		107
		108	For example, it is not easy to find the correct path to the perl
		109	interpreter - C<$^X> might not be a perl interpreter at all.
		110
		111	This module tries hard to identify the correct path to the perl
		112	interpreter. With a cooperative main program, exec'ing the interpreter
		113	might not even be necessary, but even without help from the main program,
		114	it will still work when used from a module.
		115
		116	=item Exec'ing a new perl process might be slow, as all necessary modules
		117	have to be loaded from disk again, with no guarantees of success.
		118
		119	Long running processes might run into problems when perl is upgraded
		120	and modules are no longer loadable because they refer to a different
		121	perl version, or parts of a distribution are newer than the ones already
		122	loaded.
		123
		124	This module supports creating pre-initialised perl processes to be used as
		125	a template for new processes.
		126
		127	=item Forking might be impossible when a program is running.
		128
		129	For example, POSIX makes it almost impossible to fork from a
		130	multi-threaded program while doing anything useful in the child - in
		131	fact, if your perl program uses POSIX threads (even indirectly via
		132	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		133	anymore without risking corruption issues on a number of operating
		134	systems.
		135
		136	This module can safely fork helper processes at any time, by calling
		137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		138
		139	=item Parallel processing with fork might be inconvenient or difficult
		140	to implement. Modules might not work in both parent and child.
		141
		142	For example, when a program uses an event loop and creates watchers it
		143	becomes very hard to use the event loop from a child program, as the
		144	watchers already exist but are only meaningful in the parent. Worse, a
		145	module might want to use such a module, not knowing whether another module
		146	or the main program also does, leading to problems.
		147
		148	Apart from event loops, graphical toolkits also commonly fall into the
		149	"unsafe module" category, or just about anything that communicates with
		150	the external world, such as network libraries and file I/O modules, which
		151	usually don't like being copied and then allowed to continue in two
		152	processes.
		153
		154	With this module only the main program is allowed to create new processes
		155	by forking (because only the main program can know when it is still safe
		156	to do so) - all other processes are created via fork+exec, which makes it
		157	possible to use modules such as event loops or window interfaces safely.
		158
		159	=back
		160
		161	=head1 EXAMPLES
		162
10	# create a single new process, tell it to run your worker function	163	=head2 Create a single new process, tell it to run your worker function.
11		164
12	AnyEvent::Fork	165	AnyEvent::Fork
13	->new	166	->new
14	->require ("MyModule")	167	->require ("MyModule")
15	->run ("MyModule::worker, sub {	168	->run ("MyModule::worker, sub {
…		…
17		170
18	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
20	});	173	});
21		174
22	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
23	sub MyModule::worker {	179	sub worker {
24	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
25		181
26	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
28	}	184	}
29		185
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	186	=head2 Create a pool of server processes all accepting on the same socket.
32		187
33	# create listener socket	188	# create listener socket
34	my $listener = ...;	189	my $listener = ...;
35		190
36	# create a pool template, initialise it and give it the socket	191	# create a pool template, initialise it and give it the socket
…		…
48	}	203	}
49		204
50	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
52		207
53	# My::Server::run might look like this	208	C<My::Server> might look like this:
54	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
55	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
56		214
57	close $slave; # we do not use the socket, so close it to save resources	215	close $slave; # we do not use the socket, so close it to save resources
58		216
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	217	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	219	while (my $socket = $listener->accept) {
62	# do sth. with new socket	220	# do sth. with new socket
63	}	221	}
64	}	222	}
65		223
66	##################################################################
67	# use AnyEvent::Fork as a faster fork+exec	224	=head2 use AnyEvent::Fork as a faster fork+exec
68		225
69	# this runs /bin/echo hi, with stdout redirected to /tmp/log	226	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
70	# and stderr to the communications socket. it is usually faster	227	and standard error redirected to the communications socket. It is usually
71	# than fork+exec, but still let's you prepare the environment.	228	faster than fork+exec, but still lets you prepare the environment.
72		229
73	open my $output, ">/tmp/log" or die "$!";	230	open my $output, ">/tmp/log" or die "$!";
74		231
75	AnyEvent::Fork	232	AnyEvent::Fork
76	->new	233	->new
77	->eval ('	234	->eval ('
		235	# compile a helper function for later use
78	sub run {	236	sub run {
79	my ($fh, $output, @cmd) = @_;	237	my ($fh, $output, @cmd) = @_;
80		238
81	# perl will clear close-on-exec on STDOUT/STDERR	239	# perl will clear close-on-exec on STDOUT/STDERR
82	open STDOUT, ">&", $output or die;	240	open STDOUT, ">&", $output or die;
…		…
88	->send_fh ($output)	246	->send_fh ($output)
89	->send_arg ("/bin/echo", "hi")	247	->send_arg ("/bin/echo", "hi")
90	->run ("run", my $cv = AE::cv);	248	->run ("run", my $cv = AE::cv);
91		249
92	my $stderr = $cv->recv;	250	my $stderr = $cv->recv;
93
94	=head1 DESCRIPTION
95
96	This module allows you to create new processes, without actually forking
97	them from your current process (avoiding the problems of forking), but
98	preserving most of the advantages of fork.
99
100	It can be used to create new worker processes or new independent
101	subprocesses for short- and long-running jobs, process pools (e.g. for use
102	in pre-forked servers) but also to spawn new external processes (such as
103	CGI scripts from a web server), which can be faster (and more well behaved)
104	than using fork+exec in big processes.
105
106	Special care has been taken to make this module useful from other modules,
107	while still supporting specialised environments such as L<App::Staticperl>
108	or L<PAR::Packer>.
109
110	=head1 WHAT THIS MODULE IS NOT
111
112	This module only creates processes and lets you pass file handles and
113	strings to it, and run perl code. It does not implement any kind of RPC -
114	there is no back channel from the process back to you, and there is no RPC
115	or message passing going on.
116
117	If you need some form of RPC, you can either implement it yourself
118	in whatever way you like, use some message-passing module such
119	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
120	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
121	and so on.
122
123	=head1 PROBLEM STATEMENT
124
125	There are two ways to implement parallel processing on UNIX like operating
126	systems - fork and process, and fork+exec and process. They have different
127	advantages and disadvantages that I describe below, together with how this
128	module tries to mitigate the disadvantages.
129
130	=over 4
131
132	=item Forking from a big process can be very slow (a 5GB process needs
133	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
134	is often shared with exec (because you have to fork first), but in some
135	circumstances (e.g. when vfork is used), fork+exec can be much faster.
136
137	This module can help here by telling a small(er) helper process to fork,
138	or fork+exec instead.
139
140	=item Forking usually creates a copy-on-write copy of the parent
141	process. Memory (for example, modules or data files that have been
142	will not take additional memory). When exec'ing a new process, modules
143	and data files might need to be loaded again, at extra CPU and memory
144	cost. Likewise when forking, all data structures are copied as well - if
145	the program frees them and replaces them by new data, the child processes
146	will retain the memory even if it isn't used.
147
148	This module allows the main program to do a controlled fork, and allows
149	modules to exec processes safely at any time. When creating a custom
150	process pool you can take advantage of data sharing via fork without
151	risking to share large dynamic data structures that will blow up child
152	memory usage.
153
154	=item Exec'ing a new perl process might be difficult and slow. For
155	example, it is not easy to find the correct path to the perl interpreter,
156	and all modules have to be loaded from disk again. Long running processes
157	might run into problems when perl is upgraded for example.
158
159	This module supports creating pre-initialised perl processes to be used
160	as template, and also tries hard to identify the correct path to the perl
161	interpreter. With a cooperative main program, exec'ing the interpreter
162	might not even be necessary.
163
164	=item Forking might be impossible when a program is running. For example,
165	POSIX makes it almost impossible to fork from a multi-threaded program and
166	do anything useful in the child - strictly speaking, if your perl program
167	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
168	you cannot call fork on the perl level anymore, at all.
169
170	This module can safely fork helper processes at any time, by calling
171	fork+exec in C, in a POSIX-compatible way.
172
173	=item Parallel processing with fork might be inconvenient or difficult
174	to implement. For example, when a program uses an event loop and creates
175	watchers it becomes very hard to use the event loop from a child
176	program, as the watchers already exist but are only meaningful in the
177	parent. Worse, a module might want to use such a system, not knowing
178	whether another module or the main program also does, leading to problems.
179
180	This module only lets the main program create pools by forking (because
181	only the main program can know when it is still safe to do so) - all other
182	pools are created by fork+exec, after which such modules can again be
183	loaded.
184
185	=back
186		251
187	=head1 CONCEPTS	252	=head1 CONCEPTS
188		253
189	This module can create new processes either by executing a new perl	254	This module can create new processes either by executing a new perl
190	process, or by forking from an existing "template" process.	255	process, or by forking from an existing "template" process.
…		…
269	my ($fork_fh) = @_;	334	my ($fork_fh) = @_;
270	});	335	});
271		336
272	=back	337	=back
273		338
274	=head1 FUNCTIONS	339	=head1 THE C<AnyEvent::Fork> CLASS
		340
		341	This module exports nothing, and only implements a single class -
		342	C<AnyEvent::Fork>.
		343
		344	There are two class constructors that both create new processes - C<new>
		345	and C<new_exec>. The C<fork> method creates a new process by forking an
		346	existing one and could be considered a third constructor.
		347
		348	Most of the remaining methods deal with preparing the new process, by
		349	loading code, evaluating code and sending data to the new process. They
		350	usually return the process object, so you can chain method calls.
		351
		352	If a process object is destroyed before calling its C<run> method, then
		353	the process simply exits. After C<run> is called, all responsibility is
		354	passed to the specified function.
		355
		356	As long as there is any outstanding work to be done, process objects
		357	resist being destroyed, so there is no reason to store them unless you
		358	need them later - configure and forget works just fine.
275		359
276	=over 4	360	=over 4
277		361
278	=cut	362	=cut
279		363
…		…
286	use AnyEvent;	370	use AnyEvent;
287	use AnyEvent::Util ();	371	use AnyEvent::Util ();
288		372
289	use IO::FDPass;	373	use IO::FDPass;
290		374
291	our $VERSION = 0.5;	375	our $VERSION = 0.6;
292
293	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
294
295	=item my $pool = new AnyEvent::Fork key => value...
296
297	Create a new process pool. The following named parameters are supported:
298		376
299	=over 4	377	=over 4
300		378
301	=back	379	=back
302		380
…		…
381	if ($pid eq 0) {	459	if ($pid eq 0) {
382	require AnyEvent::Fork::Serve;	460	require AnyEvent::Fork::Serve;
383	$AnyEvent::Fork::Serve::OWNER = $parent;	461	$AnyEvent::Fork::Serve::OWNER = $parent;
384	close $fh;	462	close $fh;
385	$0 = "$_[1] of $parent";	463	$0 = "$_[1] of $parent";
386	$SIG{CHLD} = 'IGNORE';
387	AnyEvent::Fork::Serve::serve ($slave);	464	AnyEvent::Fork::Serve::serve ($slave);
388	exit 0;	465	exit 0;
389	} elsif (!$pid) {	466	} elsif (!$pid) {
390	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	467	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
391	}	468	}
…		…
398	Create a new "empty" perl interpreter process and returns its process	475	Create a new "empty" perl interpreter process and returns its process
399	object for further manipulation.	476	object for further manipulation.
400		477
401	The new process is forked from a template process that is kept around	478	The new process is forked from a template process that is kept around
402	for this purpose. When it doesn't exist yet, it is created by a call to	479	for this purpose. When it doesn't exist yet, it is created by a call to
403	C<new_exec> and kept around for future calls.	480	C<new_exec> first and then stays around for future calls.
404
405	When the process object is destroyed, it will release the file handle
406	that connects it with the new process. When the new process has not yet
407	called C<run>, then the process will exit. Otherwise, what happens depends
408	entirely on the code that is executed.
409		481
410	=cut	482	=cut
411		483
412	sub new {	484	sub new {
413	my $class = shift;	485	my $class = shift;
…		…
503	}	575	}
504		576
505	=item $pid = $proc->pid	577	=item $pid = $proc->pid
506		578
507	Returns the process id of the process I<iff it is a direct child of the	579	Returns the process id of the process I<iff it is a direct child of the
508	process> running AnyEvent::Fork, and C<undef> otherwise.	580	process running AnyEvent::Fork>, and C<undef> otherwise.
509		581
510	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and	582	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
511	L<AnyEvent::Fork::Template> are direct children, and you are responsible	583	L<AnyEvent::Fork::Template> are direct children, and you are responsible
512	to clean up their zombies when they die.	584	to clean up their zombies when they die.
513		585
514	All other processes are not direct children, and will be cleaned up by	586	All other processes are not direct children, and will be cleaned up by
515	AnyEvent::Fork.	587	AnyEvent::Fork itself.
516		588
517	=cut	589	=cut
518		590
519	sub pid {	591	sub pid {
520	$_[0][0]	592	$_[0][0]
…		…
531		603
532	The code will usually be executed after this call returns, and there is no	604	The code will usually be executed after this call returns, and there is no
533	way to pass anything back to the calling process. Any evaluation errors	605	way to pass anything back to the calling process. Any evaluation errors
534	will be reported to stderr and cause the process to exit.	606	will be reported to stderr and cause the process to exit.
535		607
536	If you want to execute some code to take over the process (see the	608	If you want to execute some code (that isn't in a module) to take over the
537	"fork+exec" example in the SYNOPSIS), you should compile a function via	609	process, you should compile a function via C<eval> first, and then call
538	C<eval> first, and then call it via C<run>. This also gives you access to	610	it via C<run>. This also gives you access to any arguments passed via the
539	any arguments passed via the C<send_xxx> methods, such as file handles.	611	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		612	a faster fork+exec> example to see it in action.
540		613
541	Returns the process object for easy chaining of method calls.	614	Returns the process object for easy chaining of method calls.
542		615
543	=cut	616	=cut
544		617
…		…
570	=item $proc = $proc->send_fh ($handle, ...)	643	=item $proc = $proc->send_fh ($handle, ...)
571		644
572	Send one or more file handles (I<not> file descriptors) to the process,	645	Send one or more file handles (I<not> file descriptors) to the process,
573	to prepare a call to C<run>.	646	to prepare a call to C<run>.
574		647
575	The process object keeps a reference to the handles until this is done,	648	The process object keeps a reference to the handles until they have
576	so you must not explicitly close the handles. This is most easily	649	been passed over to the process, so you must not explicitly close the
577	accomplished by simply not storing the file handles anywhere after passing	650	handles. This is most easily accomplished by simply not storing the file
578	them to this method.	651	handles anywhere after passing them to this method - when AnyEvent::Fork
		652	is finished using them, perl will automatically close them.
579		653
580	Returns the process object for easy chaining of method calls.	654	Returns the process object for easy chaining of method calls.
581		655
582	Example: pass a file handle to a process, and release it without	656	Example: pass a file handle to a process, and release it without
583	closing. It will be closed automatically when it is no longer used.	657	closing. It will be closed automatically when it is no longer used.
…		…
599	}	673	}
600		674
601	=item $proc = $proc->send_arg ($string, ...)	675	=item $proc = $proc->send_arg ($string, ...)
602		676
603	Send one or more argument strings to the process, to prepare a call to	677	Send one or more argument strings to the process, to prepare a call to
604	C<run>. The strings can be any octet string.	678	C<run>. The strings can be any octet strings.
605		679
606	The protocol is optimised to pass a moderate number of relatively short	680	The protocol is optimised to pass a moderate number of relatively short
607	strings - while you can pass up to 4GB of data in one go, this is more	681	strings - while you can pass up to 4GB of data in one go, this is more
608	meant to pass some ID information or other startup info, not big chunks of	682	meant to pass some ID information or other startup info, not big chunks of
609	data.	683	data.
…		…
625	Enter the function specified by the function name in C<$func> in the	699	Enter the function specified by the function name in C<$func> in the
626	process. The function is called with the communication socket as first	700	process. The function is called with the communication socket as first
627	argument, followed by all file handles and string arguments sent earlier	701	argument, followed by all file handles and string arguments sent earlier
628	via C<send_fh> and C<send_arg> methods, in the order they were called.	702	via C<send_fh> and C<send_arg> methods, in the order they were called.
629		703
		704	The process object becomes unusable on return from this function - any
		705	further method calls result in undefined behaviour.
		706
630	The function name should be fully qualified, but if it isn't, it will be	707	The function name should be fully qualified, but if it isn't, it will be
631	looked up in the main package.	708	looked up in the C<main> package.
632		709
633	If the called function returns, doesn't exist, or any error occurs, the	710	If the called function returns, doesn't exist, or any error occurs, the
634	process exits.	711	process exits.
635		712
636	Preparing the process is done in the background - when all commands have	713	Preparing the process is done in the background - when all commands have
637	been sent, the callback is invoked with the local communications socket	714	been sent, the callback is invoked with the local communications socket
638	as argument. At this point you can start using the socket in any way you	715	as argument. At this point you can start using the socket in any way you
639	like.	716	like.
640
641	The process object becomes unusable on return from this function - any
642	further method calls result in undefined behaviour.
643		717
644	If the communication socket isn't used, it should be closed on both sides,	718	If the communication socket isn't used, it should be closed on both sides,
645	to save on kernel memory.	719	to save on kernel memory.
646		720
647	The socket is non-blocking in the parent, and blocking in the newly	721	The socket is non-blocking in the parent, and blocking in the newly
…		…
722	479 vfork+execs per second, using AnyEvent::Fork->new_exec	796	479 vfork+execs per second, using AnyEvent::Fork->new_exec
723		797
724	So how can C<< AnyEvent->new >> be faster than a standard fork, even	798	So how can C<< AnyEvent->new >> be faster than a standard fork, even
725	though it uses the same operations, but adds a lot of overhead?	799	though it uses the same operations, but adds a lot of overhead?
726		800
727	The difference is simply the process size: forking the 6MB process takes	801	The difference is simply the process size: forking the 5MB process takes
728	so much longer than forking the 2.5MB template process that the overhead	802	so much longer than forking the 2.5MB template process that the extra
729	introduced is canceled out.	803	overhead introduced is canceled out.
730		804
731	If the benchmark process grows, the normal fork becomes even slower:	805	If the benchmark process grows, the normal fork becomes even slower:
732		806
733	1340 new processes, manual fork in a 20MB process	807	1340 new processes, manual fork of a 20MB process
734	731 new processes, manual fork in a 200MB process	808	731 new processes, manual fork of a 200MB process
735	235 new processes, manual fork in a 2000MB process	809	235 new processes, manual fork of a 2000MB process
736		810
737	What that means (to me) is that I can use this module without having a	811	What that means (to me) is that I can use this module without having a bad
738	very bad conscience because of the extra overhead required to start new	812	conscience because of the extra overhead required to start new processes.
739	processes.
740		813
741	=head1 TYPICAL PROBLEMS	814	=head1 TYPICAL PROBLEMS
742		815
743	This section lists typical problems that remain. I hope by recognising	816	This section lists typical problems that remain. I hope by recognising
744	them, most can be avoided.	817	them, most can be avoided.
745		818
746	=over 4	819	=over 4
747		820
748	=item "leaked" file descriptors for exec'ed processes	821	=item leaked file descriptors for exec'ed processes
749		822
750	POSIX systems inherit file descriptors by default when exec'ing a new	823	POSIX systems inherit file descriptors by default when exec'ing a new
751	process. While perl itself laudably sets the close-on-exec flags on new	824	process. While perl itself laudably sets the close-on-exec flags on new
752	file handles, most C libraries don't care, and even if all cared, it's	825	file handles, most C libraries don't care, and even if all cared, it's
753	often not possible to set the flag in a race-free manner.	826	often not possible to set the flag in a race-free manner.
…		…
773	libraries or the code that leaks those file descriptors.	846	libraries or the code that leaks those file descriptors.
774		847
775	Fortunately, most of these leaked descriptors do no harm, other than	848	Fortunately, most of these leaked descriptors do no harm, other than
776	sitting on some resources.	849	sitting on some resources.
777		850
778	=item "leaked" file descriptors for fork'ed processes	851	=item leaked file descriptors for fork'ed processes
779		852
780	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	853	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
781	which closes file descriptors not marked for being inherited.	854	which closes file descriptors not marked for being inherited.
782		855
783	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	856	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
792		865
793	The solution is to either not load these modules before use'ing	866	The solution is to either not load these modules before use'ing
794	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	867	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
795	initialising them, for example, by calling C<init Gtk2> manually.	868	initialising them, for example, by calling C<init Gtk2> manually.
796		869
797	=item exit runs destructors	870	=item exiting calls object destructors
798		871
799	This only applies to users of Lc<AnyEvent::Fork:Early> and	872	This only applies to users of L<AnyEvent::Fork:Early> and
800	L<AnyEvent::Fork::Template>.	873	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		874	that reference external resources.
801		875
802	When a process created by AnyEvent::Fork exits, it might do so by calling	876	When a process created by AnyEvent::Fork exits, it might do so by calling
803	exit, or simply letting perl reach the end of the program. At which point	877	exit, or simply letting perl reach the end of the program. At which point
804	Perl runs all destructors.	878	Perl runs all destructors.
805		879
…		…
824	to make it so, mostly due to the bloody broken perl that nobody seems to	898	to make it so, mostly due to the bloody broken perl that nobody seems to
825	care about. The fork emulation is a bad joke - I have yet to see something	899	care about. The fork emulation is a bad joke - I have yet to see something
826	useful that you can do with it without running into memory corruption	900	useful that you can do with it without running into memory corruption
827	issues or other braindamage. Hrrrr.	901	issues or other braindamage. Hrrrr.
828		902
829	Cygwin perl is not supported at the moment, as it should implement fd	903	Cygwin perl is not supported at the moment due to some hilarious
830	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	904	shortcomings of its API - see L<IO::FDPoll> for more details.
831	support enough functionality to do it.
832		905
833	=head1 SEE ALSO	906	=head1 SEE ALSO
834		907
835	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	908	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
836	L<AnyEvent::Fork::Template> (to create a process by forking the main	909	L<AnyEvent::Fork::Template> (to create a process by forking the main

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs. Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.23 by root, Sat Apr 6 08:29:43 2013 UTC vs.
Revision 1.41 by root, Mon Apr 8 03:20:53 2013 UTC