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/i) {
51 threads->set_stack_size(shift);
53 } elsif ($sym =~ /^exit/i) {
55 $threads::thread_exit_only = $flag =~ /^thread/i;
57 } elsif ($sym =~ /all/) {
58 push(@EXPORT, qw(yield));
65 # Export subroutine names
66 my $caller = caller();
67 foreach my $sym (@EXPORT) {
69 *{$caller.'::'.$sym} = \&{$sym};
72 # Set stack size via environment variable
73 if (exists($ENV{'PERL5_ITHREADS_STACK_SIZE'})) {
74 threads->set_stack_size($ENV{'PERL5_ITHREADS_STACK_SIZE'});
81 # Exit from a thread (only)
84 my ($class, $status) = @_;
85 if (! defined($status)) {
92 Carp::croak("Usage: threads->exit(status)");
95 $class->set_thread_exit_only(1);
99 # 'Constant' args for threads->list()
101 sub threads::running { 1 }
102 sub threads::joinable { 0 }
104 # 'new' is an alias for 'create'
107 # 'async' is a function alias for the 'threads->create()' method
110 unshift(@_, 'threads');
111 # Use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
115 # Thread object equality checking
118 '!=' => sub { ! equal(@_) },
128 threads - Perl interpreter-based threads
132 This document describes threads version 1.37
136 use threads ('yield', 'stack_size' => 64*4096, 'exit' => 'threads_only');
140 print('Thread started: ', join(' ', @args), "\n");
142 my $thread = threads->create('start_thread', 'argument');
145 threads->create(sub { print("I am a thread\n"); })->join();
147 my $thread3 = async { foreach (@files) { ... } };
150 # Invoke thread in list context (implicit) so it can return a list
151 my ($thr) = threads->create(sub { return (qw/a b c/); });
152 # or specify list context explicitly
153 my $thr = threads->create({'context' => 'list'},
154 sub { return (qw/a b c/); });
155 my @results = $thr->join();
159 # Get a thread's object
160 $thread = threads->self();
161 $thread = threads->object($tid);
164 $tid = threads->tid();
165 $tid = threads->self->tid();
166 $tid = $thread->tid();
168 # Give other threads a chance to run
172 # Lists of non-detached threads
173 my @threads = threads->list();
174 my $thread_count = threads->list();
176 my @running = threads->list(threads::running);
177 my @joinable = threads->list(threads::joinable);
179 # Test thread objects
180 if ($thr1 == $thr2) {
184 # Manage thread stack size
185 $stack_size = threads->get_stack_size();
186 $old_size = threads->set_stack_size(32*4096);
188 # Create a thread with a specific context and stack size
189 my $thr = threads->create({ 'context' => 'list',
190 'stack_size' => 32*4096,
191 'exit' => 'thread_only' },
194 # Get thread's context
195 my $wantarray = $thr->wantarray();
197 # Check thread's state
198 if ($thr->is_running()) {
201 if ($thr->is_joinable()) {
205 # Send a signal to a thread
206 $thr->kill('SIGUSR1');
213 Perl 5.6 introduced something called interpreter threads. Interpreter threads
214 are different from I<5005threads> (the thread model of Perl 5.005) by creating
215 a new Perl interpreter per thread, and not sharing any data or state between
218 Prior to Perl 5.8, this has only been available to people embedding Perl, and
219 for emulating fork() on Windows.
221 The I<threads> API is loosely based on the old Thread.pm API. It is very
222 important to note that variables are not shared between threads, all variables
223 are by default thread local. To use shared variables one must use
226 It is also important to note that you must enable threads by doing C<use
227 threads> as early as possible in the script itself, and that it is not
228 possible to enable threading inside an C<eval "">, C<do>, C<require>, or
229 C<use>. In particular, if you are intending to share variables with
230 L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
231 (C<threads> will emit a warning if you do it the other way around.)
235 =item $thr = threads->create(FUNCTION, ARGS)
237 This will create a new thread that will begin execution with the specified
238 entry point function, and give it the I<ARGS> list as parameters. It will
239 return the corresponding threads object, or C<undef> if thread creation failed.
241 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
244 my $thr = threads->create('func_name', ...);
246 my $thr = threads->create(sub { ... }, ...);
248 my $thr = threads->create(\&func, ...);
250 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
254 This will wait for the corresponding thread to complete its execution. When
255 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
256 entry point function.
258 The context (void, scalar or list) for the return value(s) for C<-E<gt>join()>
259 is determined at the time of thread creation.
261 # Create thread in list context (implicit)
262 my ($thr1) = threads->create(sub {
263 my @results = qw(a b c);
267 my $thr1 = threads->create({'context' => 'list'},
269 my @results = qw(a b c);
272 # Retrieve list results from thread
273 my @res1 = $thr1->join();
275 # Create thread in scalar context (implicit)
276 my $thr2 = threads->create(sub {
280 # Retrieve scalar result from thread
281 my $res2 = $thr2->join();
283 # Create a thread in void context (explicit)
284 my $thr3 = threads->create({'void' => 1},
285 sub { print("Hello, world\n"); });
286 # Join the thread in void context (i.e., no return value)
289 See L</"THREAD CONTEXT"> for more details.
291 If the program exits without all threads having either been joined or
292 detached, then a warning will be issued.
294 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
295 cause an error to be thrown.
299 Makes the thread unjoinable, and causes any eventual return value to be
300 discarded. When the program exits, any detached threads that are still
301 running are silently terminated.
303 If the program exits without all threads having either been joined or
304 detached, then a warning will be issued.
306 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
307 will cause an error to be thrown.
309 =item threads->detach()
311 Class method that allows a thread to detach itself.
313 =item threads->self()
315 Class method that allows a thread to obtain its own I<threads> object.
319 Returns the ID of the thread. Thread IDs are unique integers with the main
320 thread in a program being 0, and incrementing by 1 for every thread created.
324 Class method that allows a thread to obtain its own ID.
326 =item threads->object($tid)
328 This will return the I<threads> object for the I<active> thread associated
329 with the specified thread ID. Returns C<undef> if there is no thread
330 associated with the TID, if the thread is joined or detached, if no TID is
331 specified or if the specified TID is undef.
333 =item threads->yield()
335 This is a suggestion to the OS to let this thread yield CPU time to other
336 threads. What actually happens is highly dependent upon the underlying
337 thread implementation.
339 You may do C<use threads qw(yield)>, and then just use C<yield()> in your
342 =item threads->list()
344 =item threads->list(threads::all)
346 =item threads->list(threads::running)
348 =item threads->list(threads::joinable)
350 With no arguments (or using C<threads::all>) and in a list context, returns a
351 list of all non-joined, non-detached I<threads> objects. In a scalar context,
352 returns a count of the same.
354 With a I<true> argument (using C<threads::running>), returns a list of all
355 non-detached I<threads> objects that are still running.
357 With a I<false> argument (using C<threads::joinable>), returns a list of all
358 non-joined, non-detached I<threads> objects that have finished running (i.e.,
359 for which C<-E<gt>join()> will not I<block>).
361 =item $thr1->equal($thr2)
363 Tests if two threads objects are the same thread or not. This is overloaded
364 to the more natural forms:
366 if ($thr1 == $thr2) {
367 print("Threads are the same\n");
370 if ($thr1 != $thr2) {
371 print("Threads differ\n");
374 (Thread comparison is based on thread IDs.)
378 C<async> creates a thread to execute the block immediately following
379 it. This block is treated as an anonymous subroutine, and so must have a
380 semi-colon after the closing brace. Like C<threads->create()>, C<async>
381 returns a I<threads> object.
383 =item $thr->_handle()
385 This I<private> method returns the memory location of the internal thread
386 structure associated with a threads object. For Win32, this is a pointer to
387 the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
388 platforms, it is a pointer to the C<pthread_t> structure used in the
389 C<pthread_create> call (i.e., C<pthread_t *>).
391 This method is of no use for general Perl threads programming. Its intent is
392 to provide other (XS-based) thread modules with the capability to access, and
393 possibly manipulate, the underlying thread structure associated with a Perl
396 =item threads->_handle()
398 Class method that allows a thread to obtain its own I<handle>.
402 =head1 EXITING A THREAD
404 The usual method for terminating a thread is to
405 L<return()|perlfunc/"return EXPR"> from the entry point function with the
406 appropriate return value(s).
410 =item threads->exit()
412 If needed, a thread can be exited at any time by calling
413 C<threads-E<gt>exit()>. This will cause the thread to return C<undef> in a
414 scalar context, or the empty list in a list context.
416 When called from the I<main> thread, this behaves the same as C<exit(0)>.
418 =item threads->exit(status)
420 When called from a thread, this behaves like C<threads-E<gt>exit()> (i.e., the
421 exit status code is ignored).
423 When called from the I<main> thread, this behaves the same as C<exit(status)>.
427 Calling C<die()> in a thread indicates an abnormal exit for the thread. Any
428 C<$SIG{__DIE__}> handler in the thread will be called first, and then the
429 thread will exit with a warning message that will contain any arguments passed
430 in the C<die()> call.
434 Calling L<exit()|perlfunc/"exit EXPR"> inside a thread causes the whole
435 application to terminate. Because of this, the use of C<exit()> inside
436 threaded code, or in modules that might be used in threaded applications, is
437 strongly discouraged.
439 If C<exit()> really is needed, then consider using the following:
441 threads->exit() if $threads::threads; # Thread friendly
444 =item use threads 'exit' => 'thread_only'
446 This globally overrides the default behavior of calling C<exit()> inside a
447 thread, and effectively causes such calls to behave the same as
448 C<threads-E<gt>exit()>. In other words, with this setting, calling C<exit()>
449 causes only the thread to terminate.
451 Because of its global effect, this setting should not be used inside modules
454 The I<main> thread is unaffected by this setting.
456 =item threads->create({'exit' => 'thread_only'}, ...)
458 This overrides the default behavior of C<exit()> inside the newly created
461 =item $thr->set_thread_exit_only(boolean)
463 This can be used to change the I<exit thread only> behavior for a thread after
464 it has been created. With a I<true> argument, C<exit()> will cause the only
465 the thread to exit. With a I<false> argument, C<exit()> will terminate the
468 The I<main> thread is unaffected by this call.
470 =item threads->set_thread_exit_only(boolean)
472 Class method for use inside a thread to changes its own behavior for
475 The I<main> thread is unaffected by this call.
481 The following boolean methods are useful in determining the I<state> of a
486 =item $thr->is_running()
488 Returns true if a thread is still running (i.e., if its entry point function
489 has not yet finished/exited).
491 =item $thr->is_joinable()
493 Returns true if the thread has finished running, is not detached and has not
494 yet been joined. In other works, the thread is ready to be joined and will
497 =item $thr->is_detached()
499 Returns true if the thread has been detached.
501 =item threads->is_detached()
503 Class method that allows a thread to determine whether or not it is detached.
507 =head1 THREAD CONTEXT
509 As with subroutines, the type of value returned from a thread's entry point
510 function may be determined by the thread's I<context>: list, scalar or void.
511 The thread's context is determined at thread creation. This is necessary so
512 that the context is available to the entry point function via
513 L<wantarray()|perlfunc/"wantarray">. The thread may then specify a value of
514 the appropriate type to be returned from C<-E<gt>join()>.
516 =head2 Explicit context
518 Because thread creation and thread joining may occur in different contexts, it
519 may be desirable to state the context explicitly to the thread's entry point
520 function. This may be done by calling C<-E<gt>create()> with a parameter hash
521 as the first argument:
523 my $thr = threads->create({'context' => 'list'}, \&foo);
525 my @results = $thr->join();
527 In the above, the threads object is returned to the parent thread in scalar
528 context, and the thread's entry point function C<foo> will be called in list
529 context such that the parent thread can receive a list from the C<-E<gt>join()>
530 call. Similarly, if you need the threads object, but your thread will not be
531 returning a value (i.e., I<void> context), you would do the following:
533 my $thr = threads->create({'context' => 'void'}, \&foo);
537 The context type may also be used as the I<key> in the parameter hash followed
540 threads->create({'scalar' => 1}, \&foo);
542 my ($thr) = threads->list();
543 my $result = $thr->join();
545 =head2 Implicit context
547 If not explicitly stated, the thread's context is implied from the context
548 of the C<-E<gt>create()> call:
550 # Create thread in list context
551 my ($thr) = threads->create(...);
553 # Create thread in scalar context
554 my $thr = threads->create(...);
556 # Create thread in void context
557 threads->create(...);
559 =head2 $thr->wantarray()
561 This returns the thread's context in the same manner as
562 L<wantarray()|perlfunc/"wantarray">.
564 =head2 threads->wantarray()
566 Class method to return the current thread's context. This is the same as
567 running L<wantarray()|perlfunc/"wantarray"> in the current thread.
569 =head1 THREAD STACK SIZE
571 The default per-thread stack size for different platforms varies
572 significantly, and is almost always far more than is needed for most
573 applications. On Win32, Perl's makefile explicitly sets the default stack to
574 16 MB; on most other platforms, the system default is used, which again may be
575 much larger than is needed.
577 By tuning the stack size to more accurately reflect your application's needs,
578 you may significantly reduce your application's memory usage, and increase the
579 number of simultaneously running threads.
581 N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
582 setting the stack smaller than that on Win32 Perl will not save any more
587 =item threads->get_stack_size();
589 Returns the current default per-thread stack size. The default is zero, which
590 means the system default stack size is currently in use.
592 =item $size = $thr->get_stack_size();
594 Returns the stack size for a particular thread. A return value of zero
595 indicates the system default stack size was used for the thread.
597 =item $old_size = threads->set_stack_size($new_size);
599 Sets a new default per-thread stack size, and returns the previous setting.
601 Some platforms have a minimum thread stack size. Trying to set the stack size
602 below this value will result in a warning, and the minimum stack size will be
605 Some Linux platforms have a maximum stack size. Setting too large of a stack
606 size will cause thread creation to fail.
608 If needed, C<$new_size> will be rounded up to the next multiple of the memory
609 page size (usually 4096 or 8192).
611 Threads created after the stack size is set will then either call
612 C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
613 stack size to C<CreateThread()> I<(for Win32 Perl)>.
615 (Obviously, this call does not affect any currently extant threads.)
617 =item use threads ('stack_size' => VALUE);
619 This sets the default per-thread stack size at the start of the application.
621 =item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
623 The default per-thread stack size may be set at the start of the application
624 through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
626 PERL5_ITHREADS_STACK_SIZE=1048576
627 export PERL5_ITHREADS_STACK_SIZE
628 perl -e'use threads; print(threads->get_stack_size(), "\n")'
630 This value overrides any C<stack_size> parameter given to C<use threads>. Its
631 primary purpose is to permit setting the per-thread stack size for legacy
632 threaded applications.
634 =item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
636 The stack size an individual threads may also be specified. This may be done
637 by calling C<-E<gt>create()> with a parameter hash as the first argument:
639 my $thr = threads->create({'stack_size' => 32*4096}, \&foo, @args);
641 =item $thr2 = $thr1->create(FUNCTION, ARGS)
643 This creates a new thread (C<$thr2>) that inherits the stack size from an
644 existing thread (C<$thr1>). This is shorthand for the following:
646 my $stack_size = $thr1->get_stack_size();
647 my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
651 =head1 THREAD SIGNALLING
653 When safe signals is in effect (the default behavior - see L</"Unsafe signals">
654 for more details), then signals may be sent and acted upon by individual
659 =item $thr->kill('SIG...');
661 Sends the specified signal to the thread. Signal names and (positive) signal
662 numbers are the same as those supported by
663 L<kill()|perlfunc/"kill SIGNAL, LIST">. For example, 'SIGTERM', 'TERM' and
664 (depending on the OS) 15 are all valid arguments to C<-E<gt>kill()>.
666 Returns the thread object to allow for method chaining:
668 $thr->kill('SIG...')->join();
672 Signal handlers need to be set up in the threads for the signals they are
673 expected to act upon. Here's an example for I<cancelling> a thread:
679 # Thread 'cancellation' signal handler
680 $SIG{'KILL'} = sub { threads->exit(); };
686 my $thr = threads->create('thr_func');
690 # Signal the thread to terminate, and then detach
691 # it so that it will get cleaned up automatically
692 $thr->kill('KILL')->detach();
694 Here's another simplistic example that illustrates the use of thread
695 signalling in conjunction with a semaphore to provide rudimentary I<suspend>
696 and I<resume> capabilities:
699 use Thread::Semaphore;
705 # Thread 'suspend/resume' signal handler
707 $sema->down(); # Thread suspended
708 $sema->up(); # Thread resumes
714 # Create a semaphore and send it to a thread
715 my $sema = Thread::Semaphore->new();
716 my $thr = threads->create('thr_func', $sema);
724 # Allow the thread to continue
727 CAVEAT: The thread signalling capability provided by this module does not
728 actually send signals via the OS. It I<emulates> signals at the Perl-level
729 such that signal handlers are called in the appropriate thread. For example,
730 sending C<$thr-E<gt>kill('STOP')> does not actually suspend a thread (or the
731 whole process), but does cause a C<$SIG{'STOP'}> handler to be called in that
732 thread (as illustrated above).
734 As such, signals that would normally not be appropriate to use in the
735 C<kill()> command (e.g., C<kill('KILL', $$)>) are okay to use with the
736 C<-E<gt>kill()> method (again, as illustrated above).
738 Correspondingly, sending a signal to a thread does not disrupt the operation
739 the thread is currently working on: The signal will be acted upon after the
740 current operation has completed. For instance, if the thread is I<stuck> on
741 an I/O call, sending it a signal will not cause the I/O call to be interrupted
742 such that the signal is acted up immediately.
744 Sending a signal to a terminated thread is ignored.
750 =item Perl exited with active threads:
752 If the program exits without all threads having either been joined or
753 detached, then this warning will be issued.
755 NOTE: If the I<main> thread exits, then this warning cannot be suppressed
756 using C<no warnings 'threads';> as suggested below.
758 =item Thread creation failed: pthread_create returned #
760 See the appropriate I<man> page for C<pthread_create> to determine the actual
761 cause for the failure.
763 =item Thread # terminated abnormally: ...
765 A thread terminated in some manner other than just returning from its entry
766 point function. For example, the thread may have terminated using C<die>.
768 =item Using minimum thread stack size of #
770 Some platforms have a minimum thread stack size. Trying to set the stack size
771 below this value will result in the above warning, and the stack size will be
774 =item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
776 The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
777 value for the stack size.
781 If needed, thread warnings can be suppressed by using:
783 no warnings 'threads';
785 in the appropriate scope.
791 =item This Perl not built to support threads
793 The particular copy of Perl that you're trying to use was not built using the
794 C<useithreads> configuration option.
796 Having threads support requires all of Perl and all of the XS modules in the
797 Perl installation to be rebuilt; it is not just a question of adding the
798 L<threads> module (i.e., threaded and non-threaded Perls are binary
801 =item Cannot change stack size of an existing thread
803 The stack size of currently extant threads cannot be changed, therefore, the
804 following results in the above error:
806 $thr->set_stack_size($size);
808 =item Cannot signal threads without safe signals
810 Safe signals must be in effect to use the C<-E<gt>kill()> signalling method.
811 See L</"Unsafe signals"> for more details.
813 =item Unrecognized signal name: ...
815 The particular copy of Perl that you're trying to use does not support the
816 specified signal being used in a C<-E<gt>kill()> call.
824 =item Parent-child threads
826 On some platforms, it might not be possible to destroy I<parent> threads while
827 there are still existing I<child> threads.
829 =item Creating threads inside special blocks
831 Creating threads inside C<BEGIN>, C<CHECK> or C<INIT> blocks should not be
832 relied upon. Depending on the Perl version and the application code, results
833 may range from success, to (apparently harmless) warnings of leaked scalar, or
834 all the way up to crashing of the Perl interpreter.
838 Since Perl 5.8.0, signals have been made safer in Perl by postponing their
839 handling until the interpreter is in a I<safe> state. See
840 L<perl58delta/"Safe Signals"> and L<perlipc/"Deferred Signals (Safe Signals)">
843 Safe signals is the default behavior, and the old, immediate, unsafe
844 signalling behavior is only in effect in the following situations:
848 =item * Perl was been built with C<PERL_OLD_SIGNALS> (see C<perl -V>).
850 =item * The environment variable C<PERL_SIGNALS> is set to C<unsafe> (see L<perlrun/"PERL_SIGNALS">).
852 =item * The module L<Perl::Unsafe::Signals> is used.
856 If unsafe signals is in effect, then signal handling is not thread-safe, and
857 the C<-E<gt>kill()> signalling method cannot be used.
859 =item Returning closures from threads
861 Returning closures from threads should not be relied upon. Depending of the
862 Perl version and the application code, results may range from success, to
863 (apparently harmless) warnings of leaked scalar, or all the way up to crashing
864 of the Perl interpreter.
866 =item Perl Bugs and the CPAN Version of L<threads>
868 Support for threads extents beyond the code in this module (i.e.,
869 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
870 versions of Perl contain bugs that may manifest themselves despite using the
871 latest version of L<threads> from CPAN. There is no workaround for this other
872 than upgrading to the lastest version of Perl.
874 (Before you consider posting a bug report, please consult, and possibly post a
875 message to the discussion forum to see if what you've encountered is a known
886 L<threads> Discussion Forum on CPAN:
887 L<http://www.cpanforum.com/dist/threads>
889 Annotated POD for L<threads>:
890 L<http://annocpan.org/~JDHEDDEN/threads-1.37/threads.pm>
892 L<threads::shared>, L<perlthrtut>
894 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
895 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
897 Perl threads mailing list:
898 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
900 Stack size discussion:
901 L<http://www.perlmonks.org/?node_id=532956>
905 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
907 threads is released under the same license as Perl.
909 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
911 =head1 ACKNOWLEDGEMENTS
913 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
914 Helping me out tons, trying to find reasons for races and other weird bugs!
916 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
917 Being there to answer zillions of annoying questions
919 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
921 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
922 Helping with debugging
924 Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -