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[perl5.git] / ext / threads / threads.pm
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1package threads;
2
32419a4c 3use 5.008;
fcea4b7c 4
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5use strict;
6use warnings;
73e09c8f 7
c0003851 8our $VERSION = '1.27';
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9my $XS_VERSION = $VERSION;
10$VERSION = eval $VERSION;
73e09c8f 11
73e09c8f 12
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13BEGIN {
14 # Verify this Perl supports threads
15 use Config;
16 if (! $Config{useithreads}) {
17 die("This Perl not built to support threads\n");
73e09c8f 18 }
47ba8780 19
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20 # Declare that we have been loaded
21 $threads::threads = 1;
22
23 # Complain if 'threads' is loaded after 'threads::shared'
24 if ($threads::shared::threads_shared) {
25 warn <<'_MSG_';
26Warning, threads::shared has already been loaded. To
27enable shared variables, 'use threads' must be called
28before threads::shared or any module that uses it.
29_MSG_
30 }
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31}
32
fc04eb16 33
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34# Load the XS code
35require XSLoader;
fcea4b7c 36XSLoader::load('threads', $XS_VERSION);
47ba8780 37
47ba8780 38
0f1612a7 39### Export ###
47ba8780 40
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41sub import
42{
43 my $class = shift; # Not used
44
45 # Exported subroutines
46 my @EXPORT = qw(async);
47
48 # Handle args
49 while (my $sym = shift) {
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50 if ($sym =~ /^stack/) {
51 threads->set_stack_size(shift);
52
53 } elsif ($sym =~ /all/) {
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54 push(@EXPORT, qw(yield));
55
56 } else {
57 push(@EXPORT, $sym);
58 }
59 }
60
61 # Export subroutine names
62 my $caller = caller();
63 foreach my $sym (@EXPORT) {
64 no strict 'refs';
65 *{$caller.'::'.$sym} = \&{$sym};
66 }
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67
68 # Set stack size via environment variable
69 if (exists($ENV{'PERL5_ITHREADS_STACK_SIZE'})) {
70 threads->set_stack_size($ENV{'PERL5_ITHREADS_STACK_SIZE'});
71 }
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72}
73
74
75### Methods, etc. ###
47ba8780 76
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77# 'new' is an alias for 'create'
78*new = \&create;
68795e93 79
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80# 'async' is a function alias for the 'threads->create()' method
81sub async (&;@)
82{
83 unshift(@_, 'threads');
84 # Use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
85 goto &create;
86}
87
88# Thread object equality checking
89use overload (
90 '==' => \&equal,
91 '!=' => sub { ! equal(@_) },
92 'fallback' => 1
93);
94
47ba8780 951;
0f1612a7 96
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97__END__
98
99=head1 NAME
100
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101threads - Perl interpreter-based threads
102
103=head1 VERSION
104
c0003851 105This document describes threads version 1.27
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106
107=head1 SYNOPSIS
108
514612b7 109 use threads ('yield', 'stack_size' => 64*4096);
47ba8780 110
38875929 111 sub start_thread {
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112 my @args = @_;
113 print "Thread started: @args\n";
38875929 114 }
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115 my $thread = threads->create('start_thread', 'argument');
116 $thread->join();
117
118 threads->create(sub { print("I am a thread\n"); })->join();
47ba8780 119
38875929 120 my $thread3 = async { foreach (@files) { ... } };
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121 $thread3->join();
122
123 # Invoke thread in list context so it can return a list
124 my ($thr) = threads->create(sub { return (qw/a b c/); });
125 my @results = $thr->join();
47ba8780 126
38875929 127 $thread->detach();
47ba8780 128
38875929 129 $thread = threads->self();
0f1612a7 130 $thread = threads->object($tid);
11c51ed3 131
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132 $tid = threads->tid();
133 $tid = threads->self->tid();
134 $tid = $thread->tid();
47ba8780 135
38875929 136 threads->yield();
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137 yield();
138
139 my @threads = threads->list();
fcea4b7c 140 my $thread_count = threads->list();
f9dff5f5 141
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142 if ($thr1 == $thr2) {
143 ...
144 }
678a9b6c 145
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146 $stack_size = threads->get_stack_size();
147 $old_size = threads->set_stack_size(32*4096);
148
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149 $thr->kill('SIGUSR1');
150
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151=head1 DESCRIPTION
152
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153Perl 5.6 introduced something called interpreter threads. Interpreter threads
154are different from I<5005threads> (the thread model of Perl 5.005) by creating
155a new Perl interpreter per thread, and not sharing any data or state between
156threads by default.
11c51ed3 157
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158Prior to Perl 5.8, this has only been available to people embedding Perl, and
159for emulating fork() on Windows.
11c51ed3 160
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161The I<threads> API is loosely based on the old Thread.pm API. It is very
162important to note that variables are not shared between threads, all variables
163are by default thread local. To use shared variables one must use
164L<threads::shared>.
11c51ed3 165
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166It is also important to note that you must enable threads by doing C<use
167threads> as early as possible in the script itself, and that it is not
168possible to enable threading inside an C<eval "">, C<do>, C<require>, or
169C<use>. In particular, if you are intending to share variables with
170L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
171(C<threads> will emit a warning if you do it the other way around.)
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172
173=over
174
0f1612a7 175=item $thr = threads->create(FUNCTION, ARGS)
47ba8780 176
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177This will create a new thread that will begin execution with the specified
178entry point function, and give it the I<ARGS> list as parameters. It will
179return the corresponding threads object, or C<undef> if thread creation failed.
47ba8780 180
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181I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
182a code ref.
47ba8780 183
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184 my $thr = threads->create('func_name', ...);
185 # or
186 my $thr = threads->create(sub { ... }, ...);
187 # or
188 my $thr = threads->create(\&func, ...);
93512b4d 189
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190The thread may be created in I<list> context, or I<scalar> context as follows:
191
192 # Create thread in list context
193 my ($thr) = threads->create(...);
194
195 # Create thread in scalar context
196 my $thr = threads->create(...);
197
198This has consequences for the C<-E<gt>join()> method describe below.
199
200Although a thread may be created in I<void> context, to do so you must
201I<chain> either the C<-E<gt>join()> or C<-E<gt>detach()> method to the
202C<-E<gt>create()> call:
93512b4d 203
0f1612a7 204 threads->create(...)->join();
47ba8780 205
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206The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
207
208=item $thr->join()
209
210This will wait for the corresponding thread to complete its execution. When
211the thread finishes, C<-E<gt>join()> will return the return value(s) of the
212entry point function.
213
214The context (void, scalar or list) of the thread creation is also the
215context for C<-E<gt>join()>. This means that if you intend to return an array
216from a thread, you must use C<my ($thr) = threads->create(...)>, and that
217if you intend to return a scalar, you must use C<my $thr = ...>:
218
219 # Create thread in list context
220 my ($thr1) = threads->create(sub {
221 my @results = qw(a b c);
222 return (@results);
223 };
224 # Retrieve list results from thread
225 my @res1 = $thr1->join();
226
227 # Create thread in scalar context
228 my $thr2 = threads->create(sub {
229 my $result = 42;
230 return ($result);
231 };
232 # Retrieve scalar result from thread
233 my $res2 = $thr2->join();
234
235If the program exits without all other threads having been either joined or
236detached, then a warning will be issued. (A program exits either because one
237of its threads explicitly calls L<exit()|perlfunc/"exit EXPR">, or in the case
238of the main thread, reaches the end of the main program file.)
93512b4d 239
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240Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
241cause an error to be thrown.
47ba8780 242
fcea4b7c 243=item $thr->detach()
47ba8780 244
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245Makes the thread unjoinable, and causes any eventual return value to be
246discarded.
247
248Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
249will cause an error to be thrown.
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250
251=item threads->detach()
252
253Class method that allows a thread to detach itself.
254
fcea4b7c 255=item threads->self()
47ba8780 256
fcea4b7c 257Class method that allows a thread to obtain its own I<threads> object.
47ba8780 258
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259=item $thr->tid()
260
261Returns the ID of the thread. Thread IDs are unique integers with the main
262thread in a program being 0, and incrementing by 1 for every thread created.
47ba8780 263
0f1612a7 264=item threads->tid()
38875929 265
0f1612a7 266Class method that allows a thread to obtain its own ID.
47ba8780 267
0f1612a7 268=item threads->object($tid)
8c9849ff 269
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270This will return the I<threads> object for the I<active> thread associated
271with the specified thread ID. Returns C<undef> if there is no thread
272associated with the TID, if the thread is joined or detached, if no TID is
273specified or if the specified TID is undef.
8c9849ff 274
fcea4b7c 275=item threads->yield()
f9dff5f5 276
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277This is a suggestion to the OS to let this thread yield CPU time to other
278threads. What actually happens is highly dependent upon the underlying
279thread implementation.
f9dff5f5 280
fcea4b7c 281You may do C<use threads qw(yield)>, and then just use C<yield()> in your
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282code.
283
f4cc38af 284=item threads->list()
678a9b6c 285
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286In a list context, returns a list of all non-joined, non-detached I<threads>
287objects. In a scalar context, returns a count of the same.
678a9b6c 288
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289=item $thr1->equal($thr2)
290
291Tests if two threads objects are the same thread or not. This is overloaded
fcea4b7c 292to the more natural forms:
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293
294 if ($thr1 == $thr2) {
295 print("Threads are the same\n");
296 }
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297 # or
298 if ($thr1 != $thr2) {
299 print("Threads differ\n");
300 }
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301
302(Thread comparison is based on thread IDs.)
303
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304=item async BLOCK;
305
306C<async> creates a thread to execute the block immediately following
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307it. This block is treated as an anonymous subroutine, and so must have a
308semi-colon after the closing brace. Like C<threads->create()>, C<async>
309returns a I<threads> object.
386c44e5 310
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311=item $thr->_handle()
312
313This I<private> method returns the memory location of the internal thread
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314structure associated with a threads object. For Win32, this is a pointer to
315the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
316platforms, it is a pointer to the C<pthread_t> structure used in the
317C<pthread_create> call (i.e., C<pthread_t *>.
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318
319This method is of no use for general Perl threads programming. Its intent is
320to provide other (XS-based) thread modules with the capability to access, and
321possibly manipulate, the underlying thread structure associated with a Perl
322thread.
323
324=item threads->_handle()
325
326Class method that allows a thread to obtain its own I<handle>.
327
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328=back
329
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330=head1 THREAD STACK SIZE
331
332The default per-thread stack size for different platforms varies
333significantly, and is almost always far more than is needed for most
334applications. On Win32, Perl's makefile explicitly sets the default stack to
33516 MB; on most other platforms, the system default is used, which again may be
336much larger than is needed.
337
338By tuning the stack size to more accurately reflect your application's needs,
339you may significantly reduce your application's memory usage, and increase the
340number of simultaneously running threads.
341
342N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
343setting the stack smaller than that on Win32 Perl will not save any more
344memory.
345
346=over
347
348=item threads->get_stack_size();
349
350Returns the current default per-thread stack size. The default is zero, which
351means the system default stack size is currently in use.
352
353=item $size = $thr->get_stack_size();
354
355Returns the stack size for a particular thread. A return value of zero
356indicates the system default stack size was used for the thread.
357
358=item $old_size = threads->set_stack_size($new_size);
359
360Sets a new default per-thread stack size, and returns the previous setting.
361
362Some platforms have a minimum thread stack size. Trying to set the stack size
363below this value will result in a warning, and the minimum stack size will be
364used.
365
366Some Linux platforms have a maximum stack size. Setting too large of a stack
367size will cause thread creation to fail.
368
369If needed, C<$new_size> will be rounded up to the next multiple of the memory
370page size (usually 4096 or 8192).
371
372Threads created after the stack size is set will then either call
373C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
374stack size to C<CreateThread()> I<(for Win32 Perl)>.
375
376(Obviously, this call does not affect any currently extant threads.)
377
378=item use threads ('stack_size' => VALUE);
379
380This sets the default per-thread stack size at the start of the application.
381
382=item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
383
384The default per-thread stack size may be set at the start of the application
385through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
386
387 PERL5_ITHREADS_STACK_SIZE=1048576
388 export PERL5_ITHREADS_STACK_SIZE
389 perl -e'use threads; print(threads->get_stack_size(), "\n")'
390
391This value overrides any C<stack_size> parameter given to C<use threads>. Its
392primary purpose is to permit setting the per-thread stack size for legacy
393threaded applications.
394
395=item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
396
397This change to the thread creation method permits specifying the stack size
398for an individual thread.
399
400=item $thr2 = $thr1->create(FUNCTION, ARGS)
401
402This creates a new thread (C<$thr2>) that inherits the stack size from an
403existing thread (C<$thr1>). This is shorthand for the following:
404
405 my $stack_size = $thr1->get_stack_size();
406 my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
407
408=back
409
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410=head1 THREAD SIGNALLING
411
412If Perl has been compiled to use safe signals (i.e., was not built with
413C<PERL_OLD_SIGNALS> - see C<perl -V>), then signals may be sent and acted upon
414by individual threads.
415
416=over 4
417
418=item $thr->kill('SIG...');
419
420Sends the specified signal to the thread. Signal names and (positive) signal
421numbers are the same as those supported by
422L<kill()|perlfunc/"kill SIGNAL, LIST">. For example, 'SIGTERM', 'TERM' and
423(depending on the OS) 15 are all valid arguments to C<-E<gt>kill()>.
424
425Returns the thread object to allow for method chaining:
426
427 $thr->kill('SIG...')->join();
428
429=back
430
431Signal handlers need to be set up in the threads for the signals they are
432expected to act upon. Here's an example for I<cancelling> a thread:
433
434 use threads;
435
436 # Suppress warning message when thread is 'killed'
437 no warnings 'threads';
438
439 sub thr_func
440 {
441 # Thread 'cancellation' signal handler
442 $SIG{'KILL'} = sub { die("Thread killed\n"); };
443
444 ...
445 }
446
447 # Create a thread
448 my $thr = threads->create('thr_func');
449
450 ...
451
452 # Signal the thread to terminate, and then detach
453 # it so that it will get cleaned up automatically
454 $thr->kill('KILL')->detach();
455
456Here's another example that uses a semaphore to provide I<suspend> and
457I<resume> capabilities:
458
459 use threads;
460 use Thread::Semaphore;
461
462 sub thr_func
463 {
464 my $sema = shift;
465
466 # Thread 'suspend/resume' signal handler
467 $SIG{'STOP'} = sub {
468 $sema->down(); # Thread suspended
469 $sema->up(); # Thread resumes
470 };
471
472 ...
473 }
474
475 # Create a semaphore and send it to a thread
476 my $sema = Thread::Semaphore->new();
477 my $thr = threads->create('thr_func', $sema);
478
479 # Suspend the thread
480 $sema->down();
481 $thr->kill('STOP');
482
483 ...
484
485 # Allow the thread to continue
486 $sema->up();
487
488CAVEAT: Sending a signal to a thread does not disrupt the operation the
489thread is currently working on: The signal will be acted upon after the
490current operation has completed. For instance, if the thread is I<stuck> on
491an I/O call, sending it a signal will not cause the I/O call to be interrupted
492such that the signal is acted up immediately.
493
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494=head1 WARNINGS
495
496=over 4
497
fcea4b7c 498=item A thread exited while # other threads were still running
e4f9f4fe 499
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500A thread (not necessarily the main thread) exited while there were still other
501threads running. Usually, it's a good idea to first collect the return values
502of the created threads by joining them, and only then exit from the main
503thread.
e4f9f4fe 504
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505=item Thread creation failed: pthread_create returned #
506
507See the appropriate I<man> page for C<pthread_create> to determine the actual
508cause for the failure.
509
510=item Thread # terminated abnormally: ...
511
512A thread terminated in some manner other than just returning from its entry
513point function. For example, the thread may have exited via C<die>.
514
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515=item Using minimum thread stack size of #
516
517Some platforms have a minimum thread stack size. Trying to set the stack size
518below this value will result in the above warning, and the stack size will be
519set to the minimum.
520
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521=item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
522
523The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
524value for the stack size.
525
e4f9f4fe 526=back
47ba8780 527
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528If needed, thread warnings can be suppressed by using:
529
530 no warnings 'threads';
531
532in the appropriate scope.
533
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534=head1 ERRORS
535
536=over 4
537
fcea4b7c 538=item This Perl not built to support threads
678a9b6c 539
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540The particular copy of Perl that you're trying to use was not built using the
541C<useithreads> configuration option.
678a9b6c 542
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543Having threads support requires all of Perl and all of the XS modules in the
544Perl installation to be rebuilt; it is not just a question of adding the
545L<threads> module (i.e., threaded and non-threaded Perls are binary
546incompatible.)
547
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548=item Cannot change stack size of an existing thread
549
550The stack size of currently extant threads cannot be changed, therefore, the
551following results in the above error:
552
553 $thr->set_stack_size($size);
554
c0003851 555=item Cannot signal other threads without safe signals
514612b7 556
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557The particular copy of Perl that you're trying to use was built using
558C<PERL_OLD_SIGNALS>. As a result, the C<-E<gt>kill()> signalling method
559cannot be used.
560
561=item Unrecognized signal name: ...
562
563The particular copy of Perl that you're trying to use does not support the
564specified signal being used in a C<-E<gt>kill()> call.
514612b7 565
0f1612a7 566=back
47ba8780 567
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568=head1 BUGS
569
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570=over
571
fcea4b7c 572=item Parent-child threads
678a9b6c 573
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574On some platforms, it might not be possible to destroy I<parent> threads while
575there are still existing I<child> threads.
678a9b6c 576
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577=item Creating threads inside BEGIN blocks
578
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579Creating threads inside BEGIN blocks (or during the compilation phase in
580general) does not work. (In Windows, trying to use fork() inside BEGIN blocks
581is an equally losing proposition, since it has been implemented in very much
582the same way as threads.)
88f8c1df 583
678a9b6c 584=item PERL_OLD_SIGNALS are not threadsafe, will not be.
47ba8780 585
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586If your Perl has been built with PERL_OLD_SIGNALS (one has to explicitly add
587that symbol to I<ccflags>, see C<perl -V>), signal handling is not threadsafe.
88f8c1df 588
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589=item Returning closures from threads
590
591Returning a closure from a thread does not work, usually crashing Perl in the
592process.
593
594=item Perl Bugs and the CPAN Version of L<threads>
595
596Support for threads extents beyond the code in this module (i.e.,
597F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
598versions of Perl contain bugs that may manifest themselves despite using the
599latest version of L<threads> from CPAN. There is no workaround for this other
600than upgrading to the lastest version of Perl.
601
602(Before you consider posting a bug report, please consult, and possibly post a
603message to the discussion forum to see if what you've encountered is a known
604problem.)
605
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606=back
607
0f1612a7 608=head1 REQUIREMENTS
47ba8780 609
0f1612a7 610Perl 5.8.0 or later
47ba8780 611
0f1612a7 612=head1 SEE ALSO
47ba8780 613
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614L<threads> Discussion Forum on CPAN:
615L<http://www.cpanforum.com/dist/threads>
47ba8780 616
0f1612a7 617Annotated POD for L<threads>:
c0003851 618L<http://annocpan.org/~JDHEDDEN/threads-1.27/shared.pm>
47ba8780 619
0f1612a7 620L<threads::shared>, L<perlthrtut>
47ba8780 621
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622L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
623L<http://www.perl.com/pub/a/2002/09/04/threads.html>
47ba8780 624
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625Perl threads mailing list:
626L<http://lists.cpan.org/showlist.cgi?name=iThreads>
47ba8780 627
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628Stack size discussion:
629L<http://www.perlmonks.org/?node_id=532956>
630
0f1612a7 631=head1 AUTHOR
47ba8780 632
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633Artur Bergman E<lt>sky AT crucially DOT netE<gt>
634
635threads is released under the same license as Perl.
636
637CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
638
639=head1 ACKNOWLEDGEMENTS
640
641Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
642Helping me out tons, trying to find reasons for races and other weird bugs!
643
644Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
645Being there to answer zillions of annoying questions
646
647Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
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649Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
650Helping with debugging
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652Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -
653Stack size API
654
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