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 1.32
109 use threads ('yield', 'stack_size' => 64*4096);
113 print('Thread started: ', join(' ', @args), "\n");
115 my $thread = threads->create('start_thread', 'argument');
118 threads->create(sub { print("I am a thread\n"); })->join();
120 my $thread3 = async { foreach (@files) { ... } };
123 # Invoke thread in list context (implicit) so it can return a list
124 my ($thr) = threads->create(sub { return (qw/a b c/); });
125 # or specify list context explicitly
126 my $thr = threads->create({'context' => 'list'},
127 sub { return (qw/a b c/); });
128 my @results = $thr->join();
132 $thread = threads->self();
133 $thread = threads->object($tid);
135 $tid = threads->tid();
136 $tid = threads->self->tid();
137 $tid = $thread->tid();
142 my @threads = threads->list();
143 my $thread_count = threads->list();
145 if ($thr1 == $thr2) {
149 $stack_size = threads->get_stack_size();
150 $old_size = threads->set_stack_size(32*4096);
152 # Create a thread with a specific context and stack size
153 my $thr = threads->create({ 'context' => 'list',
154 'stack_size' => 32*4096 },
156 my @results = $thr->join();
158 $thr->kill('SIGUSR1');
162 Perl 5.6 introduced something called interpreter threads. Interpreter threads
163 are different from I<5005threads> (the thread model of Perl 5.005) by creating
164 a new Perl interpreter per thread, and not sharing any data or state between
167 Prior to Perl 5.8, this has only been available to people embedding Perl, and
168 for emulating fork() on Windows.
170 The I<threads> API is loosely based on the old Thread.pm API. It is very
171 important to note that variables are not shared between threads, all variables
172 are by default thread local. To use shared variables one must use
175 It is also important to note that you must enable threads by doing C<use
176 threads> as early as possible in the script itself, and that it is not
177 possible to enable threading inside an C<eval "">, C<do>, C<require>, or
178 C<use>. In particular, if you are intending to share variables with
179 L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
180 (C<threads> will emit a warning if you do it the other way around.)
184 =item $thr = threads->create(FUNCTION, ARGS)
186 This will create a new thread that will begin execution with the specified
187 entry point function, and give it the I<ARGS> list as parameters. It will
188 return the corresponding threads object, or C<undef> if thread creation failed.
190 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
193 my $thr = threads->create('func_name', ...);
195 my $thr = threads->create(sub { ... }, ...);
197 my $thr = threads->create(\&func, ...);
199 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
203 This will wait for the corresponding thread to complete its execution. When
204 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
205 entry point function.
207 The context (void, scalar or list) for the return value(s) for C<-E<gt>join()>
208 is determined at the time of thread creation.
210 # Create thread in list context (implicit)
211 my ($thr1) = threads->create(sub {
212 my @results = qw(a b c);
216 my $thr1 = threads->create({'context' => 'list'},
218 my @results = qw(a b c);
221 # Retrieve list results from thread
222 my @res1 = $thr1->join();
224 # Create thread in scalar context (implicit)
225 my $thr2 = threads->create(sub {
229 # Retrieve scalar result from thread
230 my $res2 = $thr2->join();
232 # Create a thread in void context (explicit)
233 my $thr3 = threads->create({'void' => 1},
234 sub { print("Hello, world\n"); });
235 # Join the thread in void context (i.e., no return value)
238 See L</"THREAD CONTEXT"> for more details.
240 If the program exits without all other threads having been either joined or
241 detached, then a warning will be issued. (A program exits either because one
242 of its threads explicitly calls L<exit()|perlfunc/"exit EXPR">, or in the case
243 of the main thread, reaches the end of the main program file.)
245 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
246 cause an error to be thrown.
250 Makes the thread unjoinable, and causes any eventual return value to be
253 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
254 will cause an error to be thrown.
256 =item threads->detach()
258 Class method that allows a thread to detach itself.
260 =item threads->self()
262 Class method that allows a thread to obtain its own I<threads> object.
266 Returns the ID of the thread. Thread IDs are unique integers with the main
267 thread in a program being 0, and incrementing by 1 for every thread created.
271 Class method that allows a thread to obtain its own ID.
273 =item threads->object($tid)
275 This will return the I<threads> object for the I<active> thread associated
276 with the specified thread ID. Returns C<undef> if there is no thread
277 associated with the TID, if the thread is joined or detached, if no TID is
278 specified or if the specified TID is undef.
280 =item threads->yield()
282 This is a suggestion to the OS to let this thread yield CPU time to other
283 threads. What actually happens is highly dependent upon the underlying
284 thread implementation.
286 You may do C<use threads qw(yield)>, and then just use C<yield()> in your
289 =item threads->list()
291 In a list context, returns a list of all non-joined, non-detached I<threads>
292 objects. In a scalar context, returns a count of the same.
294 =item $thr1->equal($thr2)
296 Tests if two threads objects are the same thread or not. This is overloaded
297 to the more natural forms:
299 if ($thr1 == $thr2) {
300 print("Threads are the same\n");
303 if ($thr1 != $thr2) {
304 print("Threads differ\n");
307 (Thread comparison is based on thread IDs.)
311 C<async> creates a thread to execute the block immediately following
312 it. This block is treated as an anonymous subroutine, and so must have a
313 semi-colon after the closing brace. Like C<threads->create()>, C<async>
314 returns a I<threads> object.
316 =item $thr->_handle()
318 This I<private> method returns the memory location of the internal thread
319 structure associated with a threads object. For Win32, this is a pointer to
320 the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
321 platforms, it is a pointer to the C<pthread_t> structure used in the
322 C<pthread_create> call (i.e., C<pthread_t *>).
324 This method is of no use for general Perl threads programming. Its intent is
325 to provide other (XS-based) thread modules with the capability to access, and
326 possibly manipulate, the underlying thread structure associated with a Perl
329 =item threads->_handle()
331 Class method that allows a thread to obtain its own I<handle>.
335 =head1 THREAD CONTEXT
337 As with subroutines, the type of value returned from a thread's entry point
338 function may be determined by the thread's I<context>: list, scalar or void.
339 The thread's context is determined at thread creation. This is necessary so
340 that the context is available to the entry point function via
341 L<wantarray()|perlfunc/"wantarray">. The thread may then specify a value of
342 the appropriate type to be returned from C<-E<gt>join()>.
344 =head2 Explicit context
346 Because thread creation and thread joining may occur in different contexts, it
347 may be desirable to state the context explicitly to the thread's entry point
348 function. This may be done by calling C<-E<gt>create()> with a parameter hash
349 as the first argument:
351 my $thr = threads->create({'context' => 'list'}, \&foo);
353 my @results = $thr->join();
355 In the above, the threads object is returned to the parent thread in scalar
356 context, and the thread's entry point function C<foo> will be called in list
357 context such that the parent thread can receive a list from the C<-E<gt>join()>
358 call. Similarly, if you need the threads object, but your thread will not be
359 returning a value (i.e., I<void> context), you would do the following:
361 my $thr = threads->create({'context' => 'void'}, \&foo);
365 The context type may also be used as the I<key> in the parameter hash followed
368 threads->create({'scalar' => 1}, \&foo);
370 my ($thr) = threads->list();
371 my $result = $thr->join();
373 =head2 Implicit context
375 If not explicitly stated, the thread's context is implied from the context
376 of the C<-E<gt>create()> call:
378 # Create thread in list context
379 my ($thr) = threads->create(...);
381 # Create thread in scalar context
382 my $thr = threads->create(...);
384 # Create thread in void context
385 threads->create(...);
387 =head1 THREAD STACK SIZE
389 The default per-thread stack size for different platforms varies
390 significantly, and is almost always far more than is needed for most
391 applications. On Win32, Perl's makefile explicitly sets the default stack to
392 16 MB; on most other platforms, the system default is used, which again may be
393 much larger than is needed.
395 By tuning the stack size to more accurately reflect your application's needs,
396 you may significantly reduce your application's memory usage, and increase the
397 number of simultaneously running threads.
399 N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
400 setting the stack smaller than that on Win32 Perl will not save any more
405 =item threads->get_stack_size();
407 Returns the current default per-thread stack size. The default is zero, which
408 means the system default stack size is currently in use.
410 =item $size = $thr->get_stack_size();
412 Returns the stack size for a particular thread. A return value of zero
413 indicates the system default stack size was used for the thread.
415 =item $old_size = threads->set_stack_size($new_size);
417 Sets a new default per-thread stack size, and returns the previous setting.
419 Some platforms have a minimum thread stack size. Trying to set the stack size
420 below this value will result in a warning, and the minimum stack size will be
423 Some Linux platforms have a maximum stack size. Setting too large of a stack
424 size will cause thread creation to fail.
426 If needed, C<$new_size> will be rounded up to the next multiple of the memory
427 page size (usually 4096 or 8192).
429 Threads created after the stack size is set will then either call
430 C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
431 stack size to C<CreateThread()> I<(for Win32 Perl)>.
433 (Obviously, this call does not affect any currently extant threads.)
435 =item use threads ('stack_size' => VALUE);
437 This sets the default per-thread stack size at the start of the application.
439 =item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
441 The default per-thread stack size may be set at the start of the application
442 through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
444 PERL5_ITHREADS_STACK_SIZE=1048576
445 export PERL5_ITHREADS_STACK_SIZE
446 perl -e'use threads; print(threads->get_stack_size(), "\n")'
448 This value overrides any C<stack_size> parameter given to C<use threads>. Its
449 primary purpose is to permit setting the per-thread stack size for legacy
450 threaded applications.
452 =item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
454 The stack size an individual threads may also be specified. This may be done
455 by calling C<-E<gt>create()> with a parameter hash as the first argument:
457 my $thr = threads->create({'stack_size' => 32*4096}, \&foo, @args);
459 =item $thr2 = $thr1->create(FUNCTION, ARGS)
461 This creates a new thread (C<$thr2>) that inherits the stack size from an
462 existing thread (C<$thr1>). This is shorthand for the following:
464 my $stack_size = $thr1->get_stack_size();
465 my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
469 =head1 THREAD SIGNALLING
471 When safe signals is in effect (the default behavior - see L</"Unsafe signals">
472 for more details), then signals may be sent and acted upon by individual
477 =item $thr->kill('SIG...');
479 Sends the specified signal to the thread. Signal names and (positive) signal
480 numbers are the same as those supported by
481 L<kill()|perlfunc/"kill SIGNAL, LIST">. For example, 'SIGTERM', 'TERM' and
482 (depending on the OS) 15 are all valid arguments to C<-E<gt>kill()>.
484 Returns the thread object to allow for method chaining:
486 $thr->kill('SIG...')->join();
490 Signal handlers need to be set up in the threads for the signals they are
491 expected to act upon. Here's an example for I<cancelling> a thread:
495 # Suppress warning message when thread is 'killed'
496 no warnings 'threads';
500 # Thread 'cancellation' signal handler
501 $SIG{'KILL'} = sub { die("Thread killed\n"); };
507 my $thr = threads->create('thr_func');
511 # Signal the thread to terminate, and then detach
512 # it so that it will get cleaned up automatically
513 $thr->kill('KILL')->detach();
515 Here's another simplistic example that illustrates the use of thread
516 signalling in conjunction with a semaphore to provide rudimentary I<suspend>
517 and I<resume> capabilities:
520 use Thread::Semaphore;
526 # Thread 'suspend/resume' signal handler
528 $sema->down(); # Thread suspended
529 $sema->up(); # Thread resumes
535 # Create a semaphore and send it to a thread
536 my $sema = Thread::Semaphore->new();
537 my $thr = threads->create('thr_func', $sema);
545 # Allow the thread to continue
548 CAVEAT: The thread signalling capability provided by this module does not
549 actually send signals via the OS. It I<emulates> signals at the Perl-level
550 such that signal handlers are called in the appropriate thread. For example,
551 sending C<$thr-E<gt>kill('STOP')> does not actually suspend a thread (or the
552 whole process), but does cause a C<$SIG{'STOP'}> handler to be called in that
553 thread (as illustrated above).
555 As such, signals that would normally not be appropriate to use in the
556 C<kill()> command (e.g., C<kill('KILL', $$)>) are okay to use with the
557 C<-E<gt>kill()> method (again, as illustrated above).
559 Correspondingly, sending a signal to a thread does not disrupt the operation
560 the thread is currently working on: The signal will be acted upon after the
561 current operation has completed. For instance, if the thread is I<stuck> on
562 an I/O call, sending it a signal will not cause the I/O call to be interrupted
563 such that the signal is acted up immediately.
569 =item A thread exited while # other threads were still running
571 A thread (not necessarily the main thread) exited while there were still other
572 threads running. Usually, it's a good idea to first collect the return values
573 of the created threads by joining them, and only then exit from the main
576 =item Thread creation failed: pthread_create returned #
578 See the appropriate I<man> page for C<pthread_create> to determine the actual
579 cause for the failure.
581 =item Thread # terminated abnormally: ...
583 A thread terminated in some manner other than just returning from its entry
584 point function. For example, the thread may have exited via C<die>.
586 =item Using minimum thread stack size of #
588 Some platforms have a minimum thread stack size. Trying to set the stack size
589 below this value will result in the above warning, and the stack size will be
592 =item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
594 The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
595 value for the stack size.
599 If needed, thread warnings can be suppressed by using:
601 no warnings 'threads';
603 in the appropriate scope.
609 =item This Perl not built to support threads
611 The particular copy of Perl that you're trying to use was not built using the
612 C<useithreads> configuration option.
614 Having threads support requires all of Perl and all of the XS modules in the
615 Perl installation to be rebuilt; it is not just a question of adding the
616 L<threads> module (i.e., threaded and non-threaded Perls are binary
619 =item Cannot change stack size of an existing thread
621 The stack size of currently extant threads cannot be changed, therefore, the
622 following results in the above error:
624 $thr->set_stack_size($size);
626 =item Cannot signal other threads without safe signals
628 Safe signals must be in effect to use the C<-E<gt>kill()> signalling method.
629 See L</"Unsafe signals"> for more details.
631 =item Unrecognized signal name: ...
633 The particular copy of Perl that you're trying to use does not support the
634 specified signal being used in a C<-E<gt>kill()> call.
642 =item Parent-child threads
644 On some platforms, it might not be possible to destroy I<parent> threads while
645 there are still existing I<child> threads.
647 =item Creating threads inside special blocks
649 Creating threads inside C<BEGIN>, C<CHECK> or C<INIT> blocks should not be
650 relied upon. Depending on the Perl version and the application code, results
651 may range from success, to (apparently harmless) warnings of leaked scalar, or
652 all the way up to crashing of the Perl interpreter.
656 Since Perl 5.8.0, signals have been made safer in Perl by postponing their
657 handling until the interpreter is in a I<safe> state. See
658 L<perl58delta/"Safe Signals"> and L<perlipc/"Deferred Signals (Safe Signals)">
661 Safe signals is the default behavior, and the old, immediate, unsafe
662 signalling behavior is only in effect in the following situations:
666 =item * Perl was been built with C<PERL_OLD_SIGNALS> (see C<perl -V>).
668 =item * The environment variable C<PERL_SIGNALS> is set to C<unsafe> (see L<perlrun/"PERL_SIGNALS">).
670 =item * The module L<Perl::Unsafe::Signals> is used.
674 If unsafe signals is in effect, then signal handling is not thread-safe, and
675 the C<-E<gt>kill()> signalling method cannot be used.
677 =item Returning closures from threads
679 Returning closures from threads should not be relied upon. Depending of the
680 Perl version and the application code, results may range from success, to
681 (apparently harmless) warnings of leaked scalar, or all the way up to crashing
682 of the Perl interpreter.
684 =item Perl Bugs and the CPAN Version of L<threads>
686 Support for threads extents beyond the code in this module (i.e.,
687 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
688 versions of Perl contain bugs that may manifest themselves despite using the
689 latest version of L<threads> from CPAN. There is no workaround for this other
690 than upgrading to the lastest version of Perl.
692 (Before you consider posting a bug report, please consult, and possibly post a
693 message to the discussion forum to see if what you've encountered is a known
704 L<threads> Discussion Forum on CPAN:
705 L<http://www.cpanforum.com/dist/threads>
707 Annotated POD for L<threads>:
708 L<http://annocpan.org/~JDHEDDEN/threads-1.32/shared.pm>
710 L<threads::shared>, L<perlthrtut>
712 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
713 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
715 Perl threads mailing list:
716 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
718 Stack size discussion:
719 L<http://www.perlmonks.org/?node_id=532956>
723 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
725 threads is released under the same license as Perl.
727 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
729 =head1 ACKNOWLEDGEMENTS
731 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
732 Helping me out tons, trying to find reasons for races and other weird bugs!
734 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
735 Being there to answer zillions of annoying questions
737 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
739 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
740 Helping with debugging
742 Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -