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improve thread linking options on VMS
[perl5.git] / ext / threads / threads.pm
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1package threads;
2
32419a4c 3use 5.008;
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4use strict;
5use warnings;
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6use Config;
7
8BEGIN {
9 unless ($Config{useithreads}) {
10 my @caller = caller(2);
11 die <<EOF;
12$caller[1] line $caller[2]:
13
14This Perl hasn't been configured and built properly for the threads
15module to work. (The 'useithreads' configuration option hasn't been used.)
16
5e549d84 17Having threads support requires all of Perl and all of the XS modules in
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18the Perl installation to be rebuilt, it is not just a question of adding
19the threads module. (In other words, threaded and non-threaded Perls
20are binary incompatible.)
21
22If you want to the use the threads module, please contact the people
23who built your Perl.
24
25Cannot continue, aborting.
26EOF
27 }
28}
47ba8780 29
68795e93 30use overload
43d3ddbe 31 '==' => \&equal,
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32 'fallback' => 1;
33
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34BEGIN {
35 warn "Warning, threads::shared has already been loaded. ".
36 "To enable shared variables for these modules 'use threads' ".
37 "must be called before any of those modules are loaded\n"
38 if($threads::shared::threads_shared);
39}
40
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41require Exporter;
42require DynaLoader;
43
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44our @ISA = qw(Exporter DynaLoader);
45
70f2e746 46our %EXPORT_TAGS = ( all => [qw(yield)]);
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47
48our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
49
50our @EXPORT = qw(
dcb6ccbc 51async
47ba8780 52);
cad5770b 53our $VERSION = '1.07_01';
47ba8780 54
47ba8780 55
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56# || 0 to ensure compatibility with previous versions
57sub equal { ($_[0]->tid == $_[1]->tid) || 0 }
47ba8780 58
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59# use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
60# should also be faster
abec23e7 61sub async (&;@) { unshift @_,'threads'; goto &new }
dcb6ccbc 62
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63sub object {
64 return undef unless @_ > 1;
65 foreach (threads->list) {
66 return $_ if $_->tid == $_[1];
67 }
68 return undef;
69}
70
8222d950 71$threads::threads = 1;
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72
73bootstrap threads $VERSION;
74
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75# why document 'new' then use 'create' in the tests!
76*create = \&new;
77
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78# Preloaded methods go here.
79
801;
81__END__
82
83=head1 NAME
84
85threads - Perl extension allowing use of interpreter based threads from perl
86
87=head1 SYNOPSIS
88
38875929 89 use threads;
47ba8780 90
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91 sub start_thread {
92 print "Thread started\n";
93 }
47ba8780 94
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95 my $thread = threads->create("start_thread","argument");
96 my $thread2 = $thread->create(sub { print "I am a thread"},"argument");
97 my $thread3 = async { foreach (@files) { ... } };
47ba8780 98
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99 $thread->join();
100 $thread->detach();
47ba8780 101
38875929 102 $thread = threads->self();
8c9849ff 103 $thread = threads->object( $tid );
11c51ed3 104
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105 $thread->tid();
106 threads->tid();
107 threads->self->tid();
47ba8780 108
38875929 109 threads->yield();
f9dff5f5 110
38875929 111 threads->list();
678a9b6c 112
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113=head1 DESCRIPTION
114
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115Perl 5.6 introduced something called interpreter threads. Interpreter
116threads are different from "5005threads" (the thread model of Perl
1175.005) by creating a new perl interpreter per thread and not sharing
32419a4c 118any data or state between threads by default.
11c51ed3 119
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120Prior to perl 5.8 this has only been available to people embedding
121perl and for emulating fork() on windows.
11c51ed3 122
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123The threads API is loosely based on the old Thread.pm API. It is very
124important to note that variables are not shared between threads, all
125variables are per default thread local. To use shared variables one
126must use threads::shared.
11c51ed3 127
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128It is also important to note that you must enable threads by doing
129C<use threads> as early as possible in the script itself and that it
130is not possible to enable threading inside an C<eval "">, C<do>,
131C<require>, or C<use>. In particular, if you are intending to share
132variables with threads::shared, you must C<use threads> before you
133C<use threads::shared> and C<threads> will emit a warning if you do
134it the other way around.
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135
136=over
137
9c4972d9 138=item $thread = threads->create(function, LIST)
47ba8780 139
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140This will create a new thread with the entry point function and give
141it LIST as parameters. It will return the corresponding threads
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142object, or C<undef> if thread creation failed. The new() method is an
143alias for create().
47ba8780 144
11c51ed3 145=item $thread->join
47ba8780 146
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147This will wait for the corresponding thread to join. When the thread
148finishes, join() will return the return values of the entry point
149function. If the thread has been detached, an error will be thrown.
93512b4d 150
16c6ee18 151The context (void, scalar or list) of the thread creation is also the
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152context for join(). This means that if you intend to return an array
153from a thread, you must use C<my ($thread) = threads->new(...)>, and
154that if you intend to return a scalar, you must use C<my $thread = ...>.
155
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156If the program exits without all other threads having been either
157joined or detached, then a warning will be issued. (A program exits
158either because one of its threads explicitly calls exit(), or in the
159case of the main thread, reaches the end of the main program file.)
47ba8780 160
93512b4d 161
11c51ed3 162=item $thread->detach
47ba8780 163
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164Will make the thread unjoinable, and cause any eventual return value
165to be discarded.
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166
167=item threads->self
168
38875929 169This will return the thread object for the current thread.
47ba8780 170
11c51ed3 171=item $thread->tid
47ba8780 172
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173This will return the id of the thread. Thread IDs are integers, with
174the main thread in a program being 0. Currently Perl assigns a unique
175tid to every thread ever created in your program, assigning the first
176thread to be created a tid of 1, and increasing the tid by 1 for each
177new thread that's created.
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178
179NB the class method C<< threads->tid() >> is a quick way to get the
180current thread id if you don't have your thread object handy.
47ba8780 181
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182=item threads->object( tid )
183
184This will return the thread object for the thread associated with the
185specified tid. Returns undef if there is no thread associated with the tid
186or no tid is specified or the specified tid is undef.
187
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188=item threads->yield();
189
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190This is a suggestion to the OS to let this thread yield CPU time to other
191threads. What actually happens is highly dependent upon the underlying
192thread implementation.
f9dff5f5 193
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194You may do C<use threads qw(yield)> then use just a bare C<yield> in your
195code.
196
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197=item threads->list();
198
199This will return a list of all non joined, non detached threads.
200
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201=item async BLOCK;
202
203C<async> creates a thread to execute the block immediately following
204it. This block is treated as an anonymous sub, and so must have a
38875929 205semi-colon after the closing brace. Like C<< threads->new >>, C<async>
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206returns a thread object.
207
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208=back
209
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210=head1 WARNINGS
211
212=over 4
213
c133c03f 214=item A thread exited while %d other threads were still running
e4f9f4fe 215
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216A thread (not necessarily the main thread) exited while there were
217still other threads running. Usually it's a good idea to first collect
218the return values of the created threads by joining them, and only then
32419a4c 219exit from the main thread.
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220
221=back
47ba8780 222
ab80e3f2 223=head1 TODO
678a9b6c 224
38875929 225The current implementation of threads has been an attempt to get
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226a correct threading system working that could be built on,
227and optimized, in newer versions of perl.
228
38875929 229Currently the overhead of creating a thread is rather large,
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230also the cost of returning values can be large. These are areas
231were there most likely will be work done to optimize what data
232that needs to be cloned.
47ba8780 233
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234=head1 BUGS
235
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236=over
237
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238=item Parent-Child threads.
239
240On some platforms it might not be possible to destroy "parent"
241threads while there are still existing child "threads".
242
ab80e3f2 243This will possibly be fixed in later versions of perl.
16c6ee18 244
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245=item tid is I32
246
32419a4c 247The thread id is a 32 bit integer, it can potentially overflow.
678a9b6c 248This might be fixed in a later version of perl.
47ba8780 249
678a9b6c 250=item Returning objects
47ba8780 251
678a9b6c 252When you return an object the entire stash that the object is blessed
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253as well. This will lead to a large memory usage. The ideal situation
254would be to detect the original stash if it existed.
678a9b6c 255
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256=item Creating threads inside BEGIN blocks
257
258Creating threads inside BEGIN blocks (or during the compilation phase
259in general) does not work. (In Windows, trying to use fork() inside
260BEGIN blocks is an equally losing proposition, since it has been
261implemented in very much the same way as threads.)
262
678a9b6c 263=item PERL_OLD_SIGNALS are not threadsafe, will not be.
47ba8780 264
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265If your Perl has been built with PERL_OLD_SIGNALS (one has
266to explicitly add that symbol to ccflags, see C<perl -V>),
267signal handling is not threadsafe.
268
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269=back
270
271=head1 AUTHOR and COPYRIGHT
272
35bc0dc8 273Arthur Bergman E<lt>sky at nanisky.comE<gt>
47ba8780 274
43d3ddbe 275threads is released under the same license as Perl.
47ba8780 276
68795e93 277Thanks to
47ba8780 278
ca9279ba 279Richard Soderberg E<lt>perl at crystalflame.netE<gt>
ad91d581 280Helping me out tons, trying to find reasons for races and other weird bugs!
47ba8780 281
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282Simon Cozens E<lt>simon at brecon.co.ukE<gt>
283Being there to answer zillions of annoying questions
47ba8780 284
ad91d581 285Rocco Caputo E<lt>troc at netrus.netE<gt>
47ba8780 286
ad91d581 287Vipul Ved Prakash E<lt>mail at vipul.netE<gt>
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288Helping with debugging.
289
290please join perl-ithreads@perl.org for more information
291
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292=head1 SEE ALSO
293
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294L<threads::shared>, L<perlthrtut>,
295L<http://www.perl.com/pub/a/2002/06/11/threads.html>,
296L<perlcall>, L<perlembed>, L<perlguts>
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297
298=cut