Coro-Multicore/Multicore.pm

=head1 NAME

Coro::Multicore - make coro threads on multiple cores with specially supported modules

=head1 SYNOPSIS

 use Coro::Multicore;

 # or, if you want it disabled by default (e.g. to use it from a module)
 use Coro::Multicore ();

=head1 DESCRIPTION

EXPERIMENTAL WARNING: This module is in its early stages of
development. It's fine to try out, but it didn't receive the normal amount
of testing and real-world usage that my other modules have gone through.

While L<Coro> threads (unlike ithreads) provide real threads similar to
pthreads, python threads and so on, they do not run in parallel to each
other even on machines with multiple CPUs or multiple CPU cores.

This module lifts this restriction under two very specific but useful
conditions: firstly, the coro thread executes in XS code and does not
touch any perl data structures, and secondly, the XS code is specially
prepared to allow this.

This means that, when you call an XS function of a module prepared for it,
this XS function can execute in parallel to any other Coro threads.

The mechanism to support this is easily added to existing modules
and is independent of L<Coro> or L<Coro::Multicore>, and therefore
could be used, without changes, with other, similar, modules, or even
the perl core, should it gain real thread support anytime soon. See
L<http://perlmulticore.schmorp.de/> for more info on how to prepare a
module to allow parallel execution. Preparing an existing module is easy,
doesn't add much overhead and no dependencies.

This module is an L<AnyEvent> user (and also, if not obvious, uses
L<Coro>).

=head1 HOW TO USE IT

It could hardly be simpler - if you use coro threads, and before you call
a supported lengthy operation implemented in XS, use this module and other
coro threads can run in parallel:

   use Coro::Multicore;

This module has no important API functions to learn or remember. All you
need to do is I<load> it before you can take advantage of it.

=head2 EXPORTS

This module does not (at the moment) export any symbols. It does, however,
export "behaviour" - if you use the default import, then Coro::Multicore
will be enabled for all threads and all callers in the whole program:

   use Coro::Multicore;

In a module where you don't control what else might be loaded and run, you
might want to be more conservative, and not import anything. This has the
effect of not enabling the functionality by default, so you have to enable
it per scope:

   use Coro::Multicore ();

   sub myfunc {
      Coro::Multicore::scoped_enable;

      # from here to the end of this function, and in any functions
      # called from this function, tasks will be executed asynchronously.
   }

=head1 API FUNCTIONS

=over 4

=item $previous = Coro::Multicore::enable [$enable]

This function enables (if C<$enable> is true) or disables (if C<$enable>
is false) the multicore functionality globally. By default, it is enabled.

This can be used to effectively disable this module's functionality by
default, and enable it only for selected threads or scopes, by calling
C<Coro::Multicore::scope_enable>.

The function returns the previous value of the enable flag.

=item Coro::Multicore::scoped_enable

This function instructs Coro::Multicore to handle all requests executed
in the current coro thread, from the call to the end of the current scope.

Calls to C<scoped_enable> and C<scoped_disable> don't nest very well at
the moment, so don't nest them.

=item Coro::Multicore::scoped_disable

The opposite of C<Coro::Multicore::scope_disable>: instructs Coro::Multicore to
I<not> handle the next multicore-enabled request.

=back

=cut

package Coro::Multicore;

use Coro ();
use AnyEvent ();

BEGIN {
   our $VERSION = 0.02;

   use XSLoader;
   XSLoader::load __PACKAGE__, $VERSION;
}


sub import {
   if (@_ > 1) {
      require Carp;
      Carp::croak ("Coro::Multicore does not export any symbols");
   }

   enable 1;
}

our $WATCHER = AE::io fd, 0, \&poll;

=head1 INTERACTION WITH OTHER SOFTWARE

This module is very similar to other environments where perl interpreters
are moved between threads, such as mod_perl2, and the same caveats apply.

I want to spell out the most important ones:

=over 4

=item pthreads usage

Any creation of pthreads make it impossible to fork portably from a
perl program, as forking from within a threaded program will leave the
program in a state similar to a signal handler. While it might work on
some platforms (as an extension), this might also result in silent data
corruption. It also seems to work most of the time, so it's hard to test
for this.

I recommend using something like L<AnyEvent::Fork>, which can create
subprocesses safely (via L<Proc::FastSpawn>).

Similar issues exist for signal handlers, although this module works hard
to keep safe perl signals safe.

=item module support

This module moves the same perl interpreter between different
threads. Some modules might get confused by that (although this can
usually be considered a bug). This is a rare case though.

=item event loop reliance

To be able to wake up programs waiting for results, this module relies on
an active event loop (via L<AnyEvent>). This is used to notify the perl
interpreter when the asynchronous task is done.

Since event loops typically fail to work properly after a fork, this means
that some operations that were formerly working will now hang after fork.

A workaround is to call C<Coro::Multicore::enable 0> after a fork to
disable the module.

Future versions of this module might do this automatically.

=back

=head1 BUGS

=over 4

=item (OS-) threads are never released

At the moment, threads that were created once will never be freed. They
will be reused for asynchronous requests, though, so as long as you limit
the maximum number of concurrent asynchronous tasks, this will also limit
the maximum number of threads created.

The idle threads are not necessarily using a lot of resources: on
GNU/Linux + glibc, each thread takes about 8KiB of userspace memory +
whatever the kernel needs (probably less than 8KiB).

Future versions will likely lift this limitation.

=item AnyEvent is initalised at module load time

AnyEvent is initialised on module load, as opposed to at a later time.

Future versions will likely change this.

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/AnyEvent-XSThreadPool.html

Additional thanks to Zsbán Ambrus, who gave considerable desing input for
this module and the perl multicore specification.

=cut

1

Revision:	1.8
Committed:	Fri Jul 3 02:55:03 2015 UTC (8 years, 11 months ago) by root
Branch:	MAIN
Changes since 1.7:	+5 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Coro::Multicore - make coro threads on multiple cores with specially supported modules
4
5			=head1 SYNOPSIS
6
7			use Coro::Multicore;
8
9	root	1.5	# or, if you want it disabled by default (e.g. to use it from a module)
10			use Coro::Multicore ();
11
12	root	1.1	=head1 DESCRIPTION
13
14	root	1.7	EXPERIMENTAL WARNING: This module is in its early stages of
15			development. It's fine to try out, but it didn't receive the normal amount
16			of testing and real-world usage that my other modules have gone through.
17
18	root	1.2	While L<Coro> threads (unlike ithreads) provide real threads similar to
19	root	1.3	pthreads, python threads and so on, they do not run in parallel to each
20	root	1.2	other even on machines with multiple CPUs or multiple CPU cores.
21
22			This module lifts this restriction under two very specific but useful
23			conditions: firstly, the coro thread executes in XS code and does not
24			touch any perl data structures, and secondly, the XS code is specially
25			prepared to allow this.
26
27			This means that, when you call an XS function of a module prepared for it,
28			this XS function can execute in parallel to any other Coro threads.
29
30	root	1.3	The mechanism to support this is easily added to existing modules
31			and is independent of L<Coro> or L<Coro::Multicore>, and therefore
32			could be used, without changes, with other, similar, modules, or even
33			the perl core, should it gain real thread support anytime soon. See
34	root	1.5	L<http://perlmulticore.schmorp.de/> for more info on how to prepare a
35			module to allow parallel execution. Preparing an existing module is easy,
36			doesn't add much overhead and no dependencies.
37	root	1.3
38			This module is an L<AnyEvent> user (and also, if not obvious, uses
39			L<Coro>).
40
41			=head1 HOW TO USE IT
42
43			It could hardly be simpler - if you use coro threads, and before you call
44			a supported lengthy operation implemented in XS, use this module and other
45			coro threads can run in parallel:
46
47			use Coro::Multicore;
48
49			This module has no important API functions to learn or remember. All you
50			need to do is I<load> it before you can take advantage of it.
51
52	root	1.5	=head2 EXPORTS
53
54			This module does not (at the moment) export any symbols. It does, however,
55			export "behaviour" - if you use the default import, then Coro::Multicore
56			will be enabled for all threads and all callers in the whole program:
57
58			use Coro::Multicore;
59
60			In a module where you don't control what else might be loaded and run, you
61			might want to be more conservative, and not import anything. This has the
62			effect of not enabling the functionality by default, so you have to enable
63			it per scope:
64
65			use Coro::Multicore ();
66
67			sub myfunc {
68			Coro::Multicore::scoped_enable;
69
70			# from here to the end of this function, and in any functions
71	root	1.6	# called from this function, tasks will be executed asynchronously.
72	root	1.5	}
73
74	root	1.4	=head1 API FUNCTIONS
75	root	1.3
76	root	1.4	=over 4
77
78			=item $previous = Coro::Multicore::enable [$enable]
79
80			This function enables (if C<$enable> is true) or disables (if C<$enable>
81			is false) the multicore functionality globally. By default, it is enabled.
82
83			This can be used to effectively disable this module's functionality by
84			default, and enable it only for selected threads or scopes, by calling
85			C<Coro::Multicore::scope_enable>.
86
87			The function returns the previous value of the enable flag.
88	root	1.2
89	root	1.4	=item Coro::Multicore::scoped_enable
90
91			This function instructs Coro::Multicore to handle all requests executed
92			in the current coro thread, from the call to the end of the current scope.
93
94			Calls to C<scoped_enable> and C<scoped_disable> don't nest very well at
95			the moment, so don't nest them.
96
97			=item Coro::Multicore::scoped_disable
98
99			The opposite of C<Coro::Multicore::scope_disable>: instructs Coro::Multicore to
100			I<not> handle the next multicore-enabled request.
101	root	1.1
102	root	1.3	=back
103
104	root	1.1	=cut
105
106			package Coro::Multicore;
107
108			use Coro ();
109			use AnyEvent ();
110
111			BEGIN {
112			our $VERSION = 0.02;
113
114			use XSLoader;
115			XSLoader::load __PACKAGE__, $VERSION;
116			}
117
118	root	1.5
119			sub import {
120			if (@_ > 1) {
121			require Carp;
122			Carp::croak ("Coro::Multicore does not export any symbols");
123			}
124
125			enable 1;
126			}
127
128	root	1.1	our $WATCHER = AE::io fd, 0, \&poll;
129
130	root	1.5	=head1 INTERACTION WITH OTHER SOFTWARE
131
132	root	1.7	This module is very similar to other environments where perl interpreters
133			are moved between threads, such as mod_perl2, and the same caveats apply.
134
135			I want to spell out the most important ones:
136
137			=over 4
138
139			=item pthreads usage
140
141			Any creation of pthreads make it impossible to fork portably from a
142			perl program, as forking from within a threaded program will leave the
143			program in a state similar to a signal handler. While it might work on
144			some platforms (as an extension), this might also result in silent data
145			corruption. It also seems to work most of the time, so it's hard to test
146			for this.
147
148			I recommend using something like L<AnyEvent::Fork>, which can create
149			subprocesses safely (via L<Proc::FastSpawn>).
150
151			Similar issues exist for signal handlers, although this module works hard
152			to keep safe perl signals safe.
153
154			=item module support
155
156			This module moves the same perl interpreter between different
157			threads. Some modules might get confused by that (although this can
158			usually be considered a bug). This is a rare case though.
159
160			=item event loop reliance
161
162			To be able to wake up programs waiting for results, this module relies on
163			an active event loop (via L<AnyEvent>). This is used to notify the perl
164			interpreter when the asynchronous task is done.
165
166			Since event loops typically fail to work properly after a fork, this means
167			that some operations that were formerly working will now hang after fork.
168
169			A workaround is to call C<Coro::Multicore::enable 0> after a fork to
170			disable the module.
171
172			Future versions of this module might do this automatically.
173
174			=back
175	root	1.5
176			=head1 BUGS
177
178	root	1.6	=over 4
179
180			=item (OS-) threads are never released
181
182	root	1.5	At the moment, threads that were created once will never be freed. They
183	root	1.8	will be reused for asynchronous requests, though, so as long as you limit
184	root	1.5	the maximum number of concurrent asynchronous tasks, this will also limit
185			the maximum number of threads created.
186
187	root	1.8	The idle threads are not necessarily using a lot of resources: on
188			GNU/Linux + glibc, each thread takes about 8KiB of userspace memory +
189			whatever the kernel needs (probably less than 8KiB).
190
191	root	1.5	Future versions will likely lift this limitation.
192
193	root	1.7	=item AnyEvent is initalised at module load time
194	root	1.6
195			AnyEvent is initialised on module load, as opposed to at a later time.
196
197			Future versions will likely change this.
198
199			=back
200
201	root	1.1	=head1 AUTHOR
202
203			Marc Lehmann <schmorp@schmorp.de>
204			http://software.schmorp.de/pkg/AnyEvent-XSThreadPool.html
205
206	root	1.6	Additional thanks to Zsbán Ambrus, who gave considerable desing input for
207			this module and the perl multicore specification.
208
209	root	1.1	=cut
210
211			1
212