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 1.41
136 use threads ('yield', 'stack_size' => 64*4096, 'exit' => 'threads_only');
140 print('Thread started: ', join(' ', @args), "\n");
142 my $thr = threads->create('start_thread', 'argument');
145 threads->create(sub { print("I am a thread\n"); })->join();
147 my $thr2 = async { foreach (@files) { ... } };
150 # Invoke thread in list context (implicit) so it can return a list
151 my ($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 $thr = threads->self();
161 $thr = threads->object($tid);
164 $tid = threads->tid();
167 # Give other threads a chance to run
171 # Lists of non-detached threads
172 my @threads = threads->list();
173 my $thread_count = threads->list();
175 my @running = threads->list(threads::running);
176 my @joinable = threads->list(threads::joinable);
178 # Test thread objects
179 if ($thr1 == $thr2) {
183 # Manage thread stack size
184 $stack_size = threads->get_stack_size();
185 $old_size = threads->set_stack_size(32*4096);
187 # Create a thread with a specific context and stack size
188 my $thr = threads->create({ 'context' => 'list',
189 'stack_size' => 32*4096,
190 'exit' => 'thread_only' },
193 # Get thread's context
194 my $wantarray = $thr->wantarray();
196 # Check thread's state
197 if ($thr->is_running()) {
200 if ($thr->is_joinable()) {
204 # Send a signal to a thread
205 $thr->kill('SIGUSR1');
212 Perl 5.6 introduced something called interpreter threads. Interpreter threads
213 are different from I<5005threads> (the thread model of Perl 5.005) by creating
214 a new Perl interpreter per thread, and not sharing any data or state between
217 Prior to Perl 5.8, this has only been available to people embedding Perl, and
218 for emulating fork() on Windows.
220 The I<threads> API is loosely based on the old Thread.pm API. It is very
221 important to note that variables are not shared between threads, all variables
222 are by default thread local. To use shared variables one must use
225 It is also important to note that you must enable threads by doing C<use
226 threads> as early as possible in the script itself, and that it is not
227 possible to enable threading inside an C<eval "">, C<do>, C<require>, or
228 C<use>. In particular, if you are intending to share variables with
229 L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
230 (C<threads> will emit a warning if you do it the other way around.)
234 =item $thr = threads->create(FUNCTION, ARGS)
236 This will create a new thread that will begin execution with the specified
237 entry point function, and give it the I<ARGS> list as parameters. It will
238 return the corresponding threads object, or C<undef> if thread creation failed.
240 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
243 my $thr = threads->create('func_name', ...);
245 my $thr = threads->create(sub { ... }, ...);
247 my $thr = threads->create(\&func, ...);
249 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
253 This will wait for the corresponding thread to complete its execution. When
254 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
255 entry point function.
257 The context (void, scalar or list) for the return value(s) for C<-E<gt>join()>
258 is determined at the time of thread creation.
260 # Create thread in list context (implicit)
261 my ($thr1) = threads->create(sub {
262 my @results = qw(a b c);
266 my $thr1 = threads->create({'context' => 'list'},
268 my @results = qw(a b c);
271 # Retrieve list results from thread
272 my @res1 = $thr1->join();
274 # Create thread in scalar context (implicit)
275 my $thr2 = threads->create(sub {
279 # Retrieve scalar result from thread
280 my $res2 = $thr2->join();
282 # Create a thread in void context (explicit)
283 my $thr3 = threads->create({'void' => 1},
284 sub { print("Hello, world\n"); });
285 # Join the thread in void context (i.e., no return value)
288 See L</"THREAD CONTEXT"> for more details.
290 If the program exits without all threads having either been joined or
291 detached, then a warning will be issued.
293 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
294 cause an error to be thrown.
298 Makes the thread unjoinable, and causes any eventual return value to be
299 discarded. When the program exits, any detached threads that are still
300 running are silently terminated.
302 If the program exits without all threads having either been joined or
303 detached, then a warning will be issued.
305 Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
306 will cause an error to be thrown.
308 =item threads->detach()
310 Class method that allows a thread to detach itself.
312 =item threads->self()
314 Class method that allows a thread to obtain its own I<threads> object.
318 Returns the ID of the thread. Thread IDs are unique integers with the main
319 thread in a program being 0, and incrementing by 1 for every thread created.
323 Class method that allows a thread to obtain its own ID.
325 =item threads->object($tid)
327 This will return the I<threads> object for the I<active> thread associated
328 with the specified thread ID. Returns C<undef> if there is no thread
329 associated with the TID, if the thread is joined or detached, if no TID is
330 specified or if the specified TID is undef.
332 =item threads->yield()
334 This is a suggestion to the OS to let this thread yield CPU time to other
335 threads. What actually happens is highly dependent upon the underlying
336 thread implementation.
338 You may do C<use threads qw(yield)>, and then just use C<yield()> in your
341 =item threads->list()
343 =item threads->list(threads::all)
345 =item threads->list(threads::running)
347 =item threads->list(threads::joinable)
349 With no arguments (or using C<threads::all>) and in a list context, returns a
350 list of all non-joined, non-detached I<threads> objects. In a scalar context,
351 returns a count of the same.
353 With a I<true> argument (using C<threads::running>), returns a list of all
354 non-detached I<threads> objects that are still running.
356 With a I<false> argument (using C<threads::joinable>), returns a list of all
357 non-joined, non-detached I<threads> objects that have finished running (i.e.,
358 for which C<-E<gt>join()> will not I<block>).
360 =item $thr1->equal($thr2)
362 Tests if two threads objects are the same thread or not. This is overloaded
363 to the more natural forms:
365 if ($thr1 == $thr2) {
366 print("Threads are the same\n");
369 if ($thr1 != $thr2) {
370 print("Threads differ\n");
373 (Thread comparison is based on thread IDs.)
377 C<async> creates a thread to execute the block immediately following
378 it. This block is treated as an anonymous subroutine, and so must have a
379 semi-colon after the closing brace. Like C<threads->create()>, C<async>
380 returns a I<threads> object.
382 =item $thr->_handle()
384 This I<private> method returns the memory location of the internal thread
385 structure associated with a threads object. For Win32, this is a pointer to
386 the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
387 platforms, it is a pointer to the C<pthread_t> structure used in the
388 C<pthread_create> call (i.e., C<pthread_t *>).
390 This method is of no use for general Perl threads programming. Its intent is
391 to provide other (XS-based) thread modules with the capability to access, and
392 possibly manipulate, the underlying thread structure associated with a Perl
395 =item threads->_handle()
397 Class method that allows a thread to obtain its own I<handle>.
401 =head1 EXITING A THREAD
403 The usual method for terminating a thread is to
404 L<return()|perlfunc/"return EXPR"> from the entry point function with the
405 appropriate return value(s).
409 =item threads->exit()
411 If needed, a thread can be exited at any time by calling
412 C<threads-E<gt>exit()>. This will cause the thread to return C<undef> in a
413 scalar context, or the empty list in a list context.
415 When called from the I<main> thread, this behaves the same as C<exit(0)>.
417 =item threads->exit(status)
419 When called from a thread, this behaves like C<threads-E<gt>exit()> (i.e., the
420 exit status code is ignored).
422 When called from the I<main> thread, this behaves the same as C<exit(status)>.
426 Calling C<die()> in a thread indicates an abnormal exit for the thread. Any
427 C<$SIG{__DIE__}> handler in the thread will be called first, and then the
428 thread will exit with a warning message that will contain any arguments passed
429 in the C<die()> call.
433 Calling L<exit()|perlfunc/"exit EXPR"> inside a thread causes the whole
434 application to terminate. Because of this, the use of C<exit()> inside
435 threaded code, or in modules that might be used in threaded applications, is
436 strongly discouraged.
438 If C<exit()> really is needed, then consider using the following:
440 threads->exit() if threads->can('exit'); # Thread friendly
443 =item use threads 'exit' => 'thread_only'
445 This globally overrides the default behavior of calling C<exit()> inside a
446 thread, and effectively causes such calls to behave the same as
447 C<threads-E<gt>exit()>. In other words, with this setting, calling C<exit()>
448 causes only the thread to terminate.
450 Because of its global effect, this setting should not be used inside modules
453 The I<main> thread is unaffected by this setting.
455 =item threads->create({'exit' => 'thread_only'}, ...)
457 This overrides the default behavior of C<exit()> inside the newly created
460 =item $thr->set_thread_exit_only(boolean)
462 This can be used to change the I<exit thread only> behavior for a thread after
463 it has been created. With a I<true> argument, C<exit()> will cause the only
464 the thread to exit. With a I<false> argument, C<exit()> will terminate the
467 The I<main> thread is unaffected by this call.
469 =item threads->set_thread_exit_only(boolean)
471 Class method for use inside a thread to changes its own behavior for
474 The I<main> thread is unaffected by this call.
480 The following boolean methods are useful in determining the I<state> of a
485 =item $thr->is_running()
487 Returns true if a thread is still running (i.e., if its entry point function
488 has not yet finished/exited).
490 =item $thr->is_joinable()
492 Returns true if the thread has finished running, is not detached and has not
493 yet been joined. In other works, the thread is ready to be joined and will
496 =item $thr->is_detached()
498 Returns true if the thread has been detached.
500 =item threads->is_detached()
502 Class method that allows a thread to determine whether or not it is detached.
506 =head1 THREAD CONTEXT
508 As with subroutines, the type of value returned from a thread's entry point
509 function may be determined by the thread's I<context>: list, scalar or void.
510 The thread's context is determined at thread creation. This is necessary so
511 that the context is available to the entry point function via
512 L<wantarray()|perlfunc/"wantarray">. The thread may then specify a value of
513 the appropriate type to be returned from C<-E<gt>join()>.
515 =head2 Explicit context
517 Because thread creation and thread joining may occur in different contexts, it
518 may be desirable to state the context explicitly to the thread's entry point
519 function. This may be done by calling C<-E<gt>create()> with a parameter hash
520 as the first argument:
522 my $thr = threads->create({'context' => 'list'}, \&foo);
524 my @results = $thr->join();
526 In the above, the threads object is returned to the parent thread in scalar
527 context, and the thread's entry point function C<foo> will be called in list
528 context such that the parent thread can receive a list from the C<-E<gt>join()>
529 call. Similarly, if you need the threads object, but your thread will not be
530 returning a value (i.e., I<void> context), you would do the following:
532 my $thr = threads->create({'context' => 'void'}, \&foo);
536 The context type may also be used as the I<key> in the parameter hash followed
539 threads->create({'scalar' => 1}, \&foo);
541 my ($thr) = threads->list();
542 my $result = $thr->join();
544 =head2 Implicit context
546 If not explicitly stated, the thread's context is implied from the context
547 of the C<-E<gt>create()> call:
549 # Create thread in list context
550 my ($thr) = threads->create(...);
552 # Create thread in scalar context
553 my $thr = threads->create(...);
555 # Create thread in void context
556 threads->create(...);
558 =head2 $thr->wantarray()
560 This returns the thread's context in the same manner as
561 L<wantarray()|perlfunc/"wantarray">.
563 =head2 threads->wantarray()
565 Class method to return the current thread's context. This is the same as
566 running L<wantarray()|perlfunc/"wantarray"> in the current thread.
568 =head1 THREAD STACK SIZE
570 The default per-thread stack size for different platforms varies
571 significantly, and is almost always far more than is needed for most
572 applications. On Win32, Perl's makefile explicitly sets the default stack to
573 16 MB; on most other platforms, the system default is used, which again may be
574 much larger than is needed.
576 By tuning the stack size to more accurately reflect your application's needs,
577 you may significantly reduce your application's memory usage, and increase the
578 number of simultaneously running threads.
580 N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
581 setting the stack smaller than that on Win32 Perl will not save any more
586 =item threads->get_stack_size();
588 Returns the current default per-thread stack size. The default is zero, which
589 means the system default stack size is currently in use.
591 =item $size = $thr->get_stack_size();
593 Returns the stack size for a particular thread. A return value of zero
594 indicates the system default stack size was used for the thread.
596 =item $old_size = threads->set_stack_size($new_size);
598 Sets a new default per-thread stack size, and returns the previous setting.
600 Some platforms have a minimum thread stack size. Trying to set the stack size
601 below this value will result in a warning, and the minimum stack size will be
604 Some Linux platforms have a maximum stack size. Setting too large of a stack
605 size will cause thread creation to fail.
607 If needed, C<$new_size> will be rounded up to the next multiple of the memory
608 page size (usually 4096 or 8192).
610 Threads created after the stack size is set will then either call
611 C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
612 stack size to C<CreateThread()> I<(for Win32 Perl)>.
614 (Obviously, this call does not affect any currently extant threads.)
616 =item use threads ('stack_size' => VALUE);
618 This sets the default per-thread stack size at the start of the application.
620 =item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
622 The default per-thread stack size may be set at the start of the application
623 through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
625 PERL5_ITHREADS_STACK_SIZE=1048576
626 export PERL5_ITHREADS_STACK_SIZE
627 perl -e'use threads; print(threads->get_stack_size(), "\n")'
629 This value overrides any C<stack_size> parameter given to C<use threads>. Its
630 primary purpose is to permit setting the per-thread stack size for legacy
631 threaded applications.
633 =item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
635 The stack size an individual threads may also be specified. This may be done
636 by calling C<-E<gt>create()> with a parameter hash as the first argument:
638 my $thr = threads->create({'stack_size' => 32*4096}, \&foo, @args);
640 =item $thr2 = $thr1->create(FUNCTION, ARGS)
642 This creates a new thread (C<$thr2>) that inherits the stack size from an
643 existing thread (C<$thr1>). This is shorthand for the following:
645 my $stack_size = $thr1->get_stack_size();
646 my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
650 =head1 THREAD SIGNALLING
652 When safe signals is in effect (the default behavior - see L</"Unsafe signals">
653 for more details), then signals may be sent and acted upon by individual
658 =item $thr->kill('SIG...');
660 Sends the specified signal to the thread. Signal names and (positive) signal
661 numbers are the same as those supported by
662 L<kill()|perlfunc/"kill SIGNAL, LIST">. For example, 'SIGTERM', 'TERM' and
663 (depending on the OS) 15 are all valid arguments to C<-E<gt>kill()>.
665 Returns the thread object to allow for method chaining:
667 $thr->kill('SIG...')->join();
671 Signal handlers need to be set up in the threads for the signals they are
672 expected to act upon. Here's an example for I<cancelling> a thread:
678 # Thread 'cancellation' signal handler
679 $SIG{'KILL'} = sub { threads->exit(); };
685 my $thr = threads->create('thr_func');
689 # Signal the thread to terminate, and then detach
690 # it so that it will get cleaned up automatically
691 $thr->kill('KILL')->detach();
693 Here's another simplistic example that illustrates the use of thread
694 signalling in conjunction with a semaphore to provide rudimentary I<suspend>
695 and I<resume> capabilities:
698 use Thread::Semaphore;
704 # Thread 'suspend/resume' signal handler
706 $sema->down(); # Thread suspended
707 $sema->up(); # Thread resumes
713 # Create a semaphore and send it to a thread
714 my $sema = Thread::Semaphore->new();
715 my $thr = threads->create('thr_func', $sema);
723 # Allow the thread to continue
726 CAVEAT: The thread signalling capability provided by this module does not
727 actually send signals via the OS. It I<emulates> signals at the Perl-level
728 such that signal handlers are called in the appropriate thread. For example,
729 sending C<$thr-E<gt>kill('STOP')> does not actually suspend a thread (or the
730 whole process), but does cause a C<$SIG{'STOP'}> handler to be called in that
731 thread (as illustrated above).
733 As such, signals that would normally not be appropriate to use in the
734 C<kill()> command (e.g., C<kill('KILL', $$)>) are okay to use with the
735 C<-E<gt>kill()> method (again, as illustrated above).
737 Correspondingly, sending a signal to a thread does not disrupt the operation
738 the thread is currently working on: The signal will be acted upon after the
739 current operation has completed. For instance, if the thread is I<stuck> on
740 an I/O call, sending it a signal will not cause the I/O call to be interrupted
741 such that the signal is acted up immediately.
743 Sending a signal to a terminated thread is ignored.
749 =item Perl exited with active threads:
751 If the program exits without all threads having either been joined or
752 detached, then this warning will be issued.
754 NOTE: If the I<main> thread exits, then this warning cannot be suppressed
755 using C<no warnings 'threads';> as suggested below.
757 =item Thread creation failed: pthread_create returned #
759 See the appropriate I<man> page for C<pthread_create> to determine the actual
760 cause for the failure.
762 =item Thread # terminated abnormally: ...
764 A thread terminated in some manner other than just returning from its entry
765 point function. For example, the thread may have terminated using C<die>.
767 =item Using minimum thread stack size of #
769 Some platforms have a minimum thread stack size. Trying to set the stack size
770 below this value will result in the above warning, and the stack size will be
773 =item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
775 The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
776 value for the stack size.
780 If needed, thread warnings can be suppressed by using:
782 no warnings 'threads';
784 in the appropriate scope.
790 =item This Perl not built to support threads
792 The particular copy of Perl that you're trying to use was not built using the
793 C<useithreads> configuration option.
795 Having threads support requires all of Perl and all of the XS modules in the
796 Perl installation to be rebuilt; it is not just a question of adding the
797 L<threads> module (i.e., threaded and non-threaded Perls are binary
800 =item Cannot change stack size of an existing thread
802 The stack size of currently extant threads cannot be changed, therefore, the
803 following results in the above error:
805 $thr->set_stack_size($size);
807 =item Cannot signal threads without safe signals
809 Safe signals must be in effect to use the C<-E<gt>kill()> signalling method.
810 See L</"Unsafe signals"> for more details.
812 =item Unrecognized signal name: ...
814 The particular copy of Perl that you're trying to use does not support the
815 specified signal being used in a C<-E<gt>kill()> call.
823 =item Parent-child threads
825 On some platforms, it might not be possible to destroy I<parent> threads while
826 there are still existing I<child> threads.
828 =item Creating threads inside special blocks
830 Creating threads inside C<BEGIN>, C<CHECK> or C<INIT> blocks should not be
831 relied upon. Depending on the Perl version and the application code, results
832 may range from success, to (apparently harmless) warnings of leaked scalar, or
833 all the way up to crashing of the Perl interpreter.
837 Since Perl 5.8.0, signals have been made safer in Perl by postponing their
838 handling until the interpreter is in a I<safe> state. See
839 L<perl58delta/"Safe Signals"> and L<perlipc/"Deferred Signals (Safe Signals)">
842 Safe signals is the default behavior, and the old, immediate, unsafe
843 signalling behavior is only in effect in the following situations:
847 =item * Perl was been built with C<PERL_OLD_SIGNALS> (see C<perl -V>).
849 =item * The environment variable C<PERL_SIGNALS> is set to C<unsafe> (see L<perlrun/"PERL_SIGNALS">).
851 =item * The module L<Perl::Unsafe::Signals> is used.
855 If unsafe signals is in effect, then signal handling is not thread-safe, and
856 the C<-E<gt>kill()> signalling method cannot be used.
858 =item Returning closures from threads
860 Returning closures from threads should not be relied upon. Depending of the
861 Perl version and the application code, results may range from success, to
862 (apparently harmless) warnings of leaked scalar, or all the way up to crashing
863 of the Perl interpreter.
865 =item Perl Bugs and the CPAN Version of L<threads>
867 Support for threads extents beyond the code in this module (i.e.,
868 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
869 versions of Perl contain bugs that may manifest themselves despite using the
870 latest version of L<threads> from CPAN. There is no workaround for this other
871 than upgrading to the lastest version of Perl.
873 (Before you consider posting a bug report, please consult, and possibly post a
874 message to the discussion forum to see if what you've encountered is a known
885 L<threads> Discussion Forum on CPAN:
886 L<http://www.cpanforum.com/dist/threads>
888 Annotated POD for L<threads>:
889 L<http://annocpan.org/~JDHEDDEN/threads-1.41/threads.pm>
891 L<threads::shared>, L<perlthrtut>
893 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
894 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
896 Perl threads mailing list:
897 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
899 Stack size discussion:
900 L<http://www.perlmonks.org/?node_id=532956>
904 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
906 threads is released under the same license as Perl.
908 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
910 =head1 ACKNOWLEDGEMENTS
912 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
913 Helping me out tons, trying to find reasons for races and other weird bugs!
915 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
916 Being there to answer zillions of annoying questions
918 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
920 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
921 Helping with debugging
923 Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -