9 my $XS_VERSION = $VERSION;
10 $VERSION = eval $VERSION;
14 # Verify this Perl supports threads
16 if (! $Config{useithreads}) {
17 die("This Perl not built to support threads\n");
20 # Declare that we have been loaded
21 $threads::threads = 1;
23 # Complain if 'threads' is loaded after 'threads::shared'
24 if ($threads::shared::threads_shared) {
26 Warning, threads::shared has already been loaded. To
27 enable shared variables, 'use threads' must be called
28 before threads::shared or any module that uses it.
36 XSLoader::load('threads', $XS_VERSION);
43 my $class = shift; # Not used
45 # Exported subroutines
46 my @EXPORT = qw(async);
49 while (my $sym = shift) {
50 if ($sym =~ /^stack/) {
51 threads->set_stack_size(shift);
53 } elsif ($sym =~ /all/) {
54 push(@EXPORT, qw(yield));
61 # Export subroutine names
62 my $caller = caller();
63 foreach my $sym (@EXPORT) {
65 *{$caller.'::'.$sym} = \&{$sym};
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'});
77 # 'new' is an alias for 'create'
80 # 'async' is a function alias for the 'threads->create()' method
83 unshift(@_, 'threads');
84 # Use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
88 # Thread object equality checking
91 '!=' => sub { ! equal(@_) },
101 threads - Perl interpreter-based threads
105 This document describes threads version 1.29
109 use threads ('yield', 'stack_size' => 64*4096);
113 print "Thread started: @args\n";
115 my $thread = threads->create('start_thread', 'argument');
118 threads->create(sub { print("I am a thread\n"); })->join();
120 my $thread3 = async { foreach (@files) { ... } };
123 # Invoke thread in list context so it can return a list
124 my ($thr) = threads->create(sub { return (qw/a b c/); });
125 my @results = $thr->join();
129 $thread = threads->self();
130 $thread = threads->object($tid);
132 $tid = threads->tid();
133 $tid = threads->self->tid();
134 $tid = $thread->tid();
139 my @threads = threads->list();
140 my $thread_count = threads->list();
142 if ($thr1 == $thr2) {
146 $stack_size = threads->get_stack_size();
147 $old_size = threads->set_stack_size(32*4096);
149 $thr->kill('SIGUSR1');
153 Perl 5.6 introduced something called interpreter threads. Interpreter threads
154 are different from I<5005threads> (the thread model of Perl 5.005) by creating
155 a new Perl interpreter per thread, and not sharing any data or state between
158 Prior to Perl 5.8, this has only been available to people embedding Perl, and
159 for emulating fork() on Windows.
161 The I<threads> API is loosely based on the old Thread.pm API. It is very
162 important to note that variables are not shared between threads, all variables
163 are by default thread local. To use shared variables one must use
166 It is also important to note that you must enable threads by doing C<use
167 threads> as early as possible in the script itself, and that it is not
168 possible to enable threading inside an C<eval "">, C<do>, C<require>, or
169 C<use>. In particular, if you are intending to share variables with
170 L<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.)
175 =item $thr = threads->create(FUNCTION, ARGS)
177 This will create a new thread that will begin execution with the specified
178 entry point function, and give it the I<ARGS> list as parameters. It will
179 return the corresponding threads object, or C<undef> if thread creation failed.
181 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
184 my $thr = threads->create('func_name', ...);
186 my $thr = threads->create(sub { ... }, ...);
188 my $thr = threads->create(\&func, ...);
190 The thread may be created in I<list> context, or I<scalar> context as follows:
192 # Create thread in list context
193 my ($thr) = threads->create(...);
195 # Create thread in scalar context
196 my $thr = threads->create(...);
198 This has consequences for the C<-E<gt>join()> method describe below.
200 Although a thread may be created in I<void> context, to do so you must
201 I<chain> either the C<-E<gt>join()> or C<-E<gt>detach()> method to the
202 C<-E<gt>create()> call:
204 threads->create(...)->join();
206 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
210 This will wait for the corresponding thread to complete its execution. When
211 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
212 entry point function.
214 The context (void, scalar or list) of the thread creation is also the
215 context for C<-E<gt>join()>. This means that if you intend to return an array
216 from a thread, you must use C<my ($thr) = threads->create(...)>, and that
217 if you intend to return a scalar, you must use C<my $thr = ...>:
219 # Create thread in list context
220 my ($thr1) = threads->create(sub {
221 my @results = qw(a b c);
224 # Retrieve list results from thread
225 my @res1 = $thr1->join();
227 # Create thread in scalar context
228 my $thr2 = threads->create(sub {
232 # Retrieve scalar result from thread
233 my $res2 = $thr2->join();
235 If the program exits without all other threads having been either joined or
236 detached, then a warning will be issued. (A program exits either because one
237 of its threads explicitly calls L<exit()|perlfunc/"exit EXPR">, or in the case
238 of the main thread, reaches the end of the main program file.)
240 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
241 cause an error to be thrown.
245 Makes the thread unjoinable, and causes any eventual return value to be
248 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
249 will cause an error to be thrown.
251 =item threads->detach()
253 Class method that allows a thread to detach itself.
255 =item threads->self()
257 Class method that allows a thread to obtain its own I<threads> object.
261 Returns the ID of the thread. Thread IDs are unique integers with the main
262 thread in a program being 0, and incrementing by 1 for every thread created.
266 Class method that allows a thread to obtain its own ID.
268 =item threads->object($tid)
270 This will return the I<threads> object for the I<active> thread associated
271 with the specified thread ID. Returns C<undef> if there is no thread
272 associated with the TID, if the thread is joined or detached, if no TID is
273 specified or if the specified TID is undef.
275 =item threads->yield()
277 This is a suggestion to the OS to let this thread yield CPU time to other
278 threads. What actually happens is highly dependent upon the underlying
279 thread implementation.
281 You may do C<use threads qw(yield)>, and then just use C<yield()> in your
284 =item threads->list()
286 In a list context, returns a list of all non-joined, non-detached I<threads>
287 objects. In a scalar context, returns a count of the same.
289 =item $thr1->equal($thr2)
291 Tests if two threads objects are the same thread or not. This is overloaded
292 to the more natural forms:
294 if ($thr1 == $thr2) {
295 print("Threads are the same\n");
298 if ($thr1 != $thr2) {
299 print("Threads differ\n");
302 (Thread comparison is based on thread IDs.)
306 C<async> creates a thread to execute the block immediately following
307 it. This block is treated as an anonymous subroutine, and so must have a
308 semi-colon after the closing brace. Like C<threads->create()>, C<async>
309 returns a I<threads> object.
311 =item $thr->_handle()
313 This I<private> method returns the memory location of the internal thread
314 structure associated with a threads object. For Win32, this is a pointer to
315 the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
316 platforms, it is a pointer to the C<pthread_t> structure used in the
317 C<pthread_create> call (i.e., C<pthread_t *>).
319 This method is of no use for general Perl threads programming. Its intent is
320 to provide other (XS-based) thread modules with the capability to access, and
321 possibly manipulate, the underlying thread structure associated with a Perl
324 =item threads->_handle()
326 Class method that allows a thread to obtain its own I<handle>.
330 =head1 THREAD STACK SIZE
332 The default per-thread stack size for different platforms varies
333 significantly, and is almost always far more than is needed for most
334 applications. On Win32, Perl's makefile explicitly sets the default stack to
335 16 MB; on most other platforms, the system default is used, which again may be
336 much larger than is needed.
338 By tuning the stack size to more accurately reflect your application's needs,
339 you may significantly reduce your application's memory usage, and increase the
340 number of simultaneously running threads.
342 N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
343 setting the stack smaller than that on Win32 Perl will not save any more
348 =item threads->get_stack_size();
350 Returns the current default per-thread stack size. The default is zero, which
351 means the system default stack size is currently in use.
353 =item $size = $thr->get_stack_size();
355 Returns the stack size for a particular thread. A return value of zero
356 indicates the system default stack size was used for the thread.
358 =item $old_size = threads->set_stack_size($new_size);
360 Sets a new default per-thread stack size, and returns the previous setting.
362 Some platforms have a minimum thread stack size. Trying to set the stack size
363 below this value will result in a warning, and the minimum stack size will be
366 Some Linux platforms have a maximum stack size. Setting too large of a stack
367 size will cause thread creation to fail.
369 If needed, C<$new_size> will be rounded up to the next multiple of the memory
370 page size (usually 4096 or 8192).
372 Threads created after the stack size is set will then either call
373 C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
374 stack size to C<CreateThread()> I<(for Win32 Perl)>.
376 (Obviously, this call does not affect any currently extant threads.)
378 =item use threads ('stack_size' => VALUE);
380 This sets the default per-thread stack size at the start of the application.
382 =item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
384 The default per-thread stack size may be set at the start of the application
385 through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
387 PERL5_ITHREADS_STACK_SIZE=1048576
388 export PERL5_ITHREADS_STACK_SIZE
389 perl -e'use threads; print(threads->get_stack_size(), "\n")'
391 This value overrides any C<stack_size> parameter given to C<use threads>. Its
392 primary purpose is to permit setting the per-thread stack size for legacy
393 threaded applications.
395 =item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
397 This change to the thread creation method permits specifying the stack size
398 for an individual thread.
400 =item $thr2 = $thr1->create(FUNCTION, ARGS)
402 This creates a new thread (C<$thr2>) that inherits the stack size from an
403 existing thread (C<$thr1>). This is shorthand for the following:
405 my $stack_size = $thr1->get_stack_size();
406 my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
410 =head1 THREAD SIGNALLING
412 When safe signals is in effect (the default behavior - see L<Unsafe signals>
413 for more details), then signals may be sent and acted upon by individual
418 =item $thr->kill('SIG...');
420 Sends the specified signal to the thread. Signal names and (positive) signal
421 numbers are the same as those supported by
422 L<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()>.
425 Returns the thread object to allow for method chaining:
427 $thr->kill('SIG...')->join();
431 Signal handlers need to be set up in the threads for the signals they are
432 expected to act upon. Here's an example for I<cancelling> a thread:
436 # Suppress warning message when thread is 'killed'
437 no warnings 'threads';
441 # Thread 'cancellation' signal handler
442 $SIG{'KILL'} = sub { die("Thread killed\n"); };
448 my $thr = threads->create('thr_func');
452 # Signal the thread to terminate, and then detach
453 # it so that it will get cleaned up automatically
454 $thr->kill('KILL')->detach();
456 Here's another simplistic example that illustrates the use of thread
457 signalling in conjunction with a semaphore to provide rudimentary I<suspend>
458 and I<resume> capabilities:
461 use Thread::Semaphore;
467 # Thread 'suspend/resume' signal handler
469 $sema->down(); # Thread suspended
470 $sema->up(); # Thread resumes
476 # Create a semaphore and send it to a thread
477 my $sema = Thread::Semaphore->new();
478 my $thr = threads->create('thr_func', $sema);
486 # Allow the thread to continue
489 CAVEAT: The thread signalling capability provided by this module does not
490 actually send signals via the OS. It I<emulates> signals at the Perl-level
491 such that signal handlers are called in the appropriate thread. For example,
492 sending C<$thr-E<gt>kill('STOP')> does not actually suspend a thread (or the
493 whole process), but does cause a C<$SIG{'STOP'}> handler to be called in that
494 thread (as illustrated above).
496 As such, signals that would normally not be appropriate to use in the
497 C<kill()> command (e.g., C<kill('KILL', $$)>) are okay to use with the
498 C<-E<gt>kill()> method (again, as illustrated above).
500 Correspondingly, sending a signal to a thread does not disrupt the operation
501 the thread is currently working on: The signal will be acted upon after the
502 current operation has completed. For instance, if the thread is I<stuck> on
503 an I/O call, sending it a signal will not cause the I/O call to be interrupted
504 such that the signal is acted up immediately.
510 =item A thread exited while # other threads were still running
512 A thread (not necessarily the main thread) exited while there were still other
513 threads running. Usually, it's a good idea to first collect the return values
514 of the created threads by joining them, and only then exit from the main
517 =item Thread creation failed: pthread_create returned #
519 See the appropriate I<man> page for C<pthread_create> to determine the actual
520 cause for the failure.
522 =item Thread # terminated abnormally: ...
524 A thread terminated in some manner other than just returning from its entry
525 point function. For example, the thread may have exited via C<die>.
527 =item Using minimum thread stack size of #
529 Some platforms have a minimum thread stack size. Trying to set the stack size
530 below this value will result in the above warning, and the stack size will be
533 =item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
535 The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
536 value for the stack size.
540 If needed, thread warnings can be suppressed by using:
542 no warnings 'threads';
544 in the appropriate scope.
550 =item This Perl not built to support threads
552 The particular copy of Perl that you're trying to use was not built using the
553 C<useithreads> configuration option.
555 Having threads support requires all of Perl and all of the XS modules in the
556 Perl installation to be rebuilt; it is not just a question of adding the
557 L<threads> module (i.e., threaded and non-threaded Perls are binary
560 =item Cannot change stack size of an existing thread
562 The stack size of currently extant threads cannot be changed, therefore, the
563 following results in the above error:
565 $thr->set_stack_size($size);
567 =item Cannot signal other threads without safe signals
569 Safe signals must be in effect to use the C<-E<gt>kill()> signalling method.
570 See L<Unsafe signals> for more details.
572 =item Unrecognized signal name: ...
574 The particular copy of Perl that you're trying to use does not support the
575 specified signal being used in a C<-E<gt>kill()> call.
583 =item Parent-child threads
585 On some platforms, it might not be possible to destroy I<parent> threads while
586 there are still existing I<child> threads.
588 =item Creating threads inside special blocks
590 Creating threads inside C<BEGIN>, C<CHECK> or C<INIT> blocks should not be
591 relied upon. Depending on the Perl version and the application code, results
592 may range from success, to (apparently harmless) warnings of leaked scalar,
593 all the way up to crashing of the Perl interpreter.
597 Since Perl 5.8.0, signals have been made safer in Perl by postponing their
598 handling until the interpreter is in a I<safe> state. See
599 L<perl58delta/"Safe Signals"> and L<perlipc/"Deferred Signals (Safe Signals)">
602 Safe signals is the default behavior, and the old, immediate, unsafe
603 signalling behavior is only in effect in the following situations:
607 =item * Perl was been built with C<PERL_OLD_SIGNALS> (see C<perl -V>).
609 =item * The environment variable C<PERL_SIGNALS> is set to C<unsafe> (see L<perlrun/"PERL_SIGNALS">).
611 =item * The module L<Perl::Unsafe::Signals> is used.
615 If unsafe signals is in effect, then signal handling is not thread-safe, and
616 the C<-E<gt>kill()> signalling method cannot be used.
618 =item Returning closures from threads
620 Returning closures from threads should not be relied upon. Depending of the
621 Perl version and the application code, results may range from success, to
622 (apparently harmless) warnings of leaked scalar, all the way up to crashing of
623 the Perl interpreter.
625 =item Perl Bugs and the CPAN Version of L<threads>
627 Support for threads extents beyond the code in this module (i.e.,
628 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
629 versions of Perl contain bugs that may manifest themselves despite using the
630 latest version of L<threads> from CPAN. There is no workaround for this other
631 than upgrading to the lastest version of Perl.
633 (Before you consider posting a bug report, please consult, and possibly post a
634 message to the discussion forum to see if what you've encountered is a known
645 L<threads> Discussion Forum on CPAN:
646 L<http://www.cpanforum.com/dist/threads>
648 Annotated POD for L<threads>:
649 L<http://annocpan.org/~JDHEDDEN/threads-1.29/shared.pm>
651 L<threads::shared>, L<perlthrtut>
653 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
654 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
656 Perl threads mailing list:
657 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
659 Stack size discussion:
660 L<http://www.perlmonks.org/?node_id=532956>
664 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
666 threads is released under the same license as Perl.
668 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
670 =head1 ACKNOWLEDGEMENTS
672 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
673 Helping me out tons, trying to find reasons for races and other weird bugs!
675 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
676 Being there to answer zillions of annoying questions
678 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
680 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
681 Helping with debugging
683 Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -