9 unless ($Config{useithreads}) {
10 my @caller = caller(2);
12 $caller[1] line $caller[2]:
14 This Perl hasn't been configured and built properly for the threads
15 module to work. (The 'useithreads' configuration option hasn't been used.)
17 Having threads support requires all of Perl and all of the XS modules in
18 the Perl installation to be rebuilt, it is not just a question of adding
19 the threads module. (In other words, threaded and non-threaded Perls
20 are binary incompatible.)
22 If you want to the use the threads module, please contact the people
25 Cannot continue, aborting.
35 warn "Warning, threads::shared has already been loaded. ".
36 "To enable shared variables for these modules 'use threads' ".
37 "must be called before any of those modules are loaded\n"
38 if($threads::shared::threads_shared);
41 our $VERSION = '1.18';
46 XSLoader::load('threads', $VERSION);
53 my $class = shift; # Not used
55 # Exported subroutines
56 my @EXPORT = qw(async);
59 while (my $sym = shift) {
61 push(@EXPORT, qw(yield));
68 # Export subroutine names
69 my $caller = caller();
70 foreach my $sym (@EXPORT) {
72 *{$caller.'::'.$sym} = \&{$sym};
79 # use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
80 # should also be faster
81 sub async (&;@) { unshift @_,'threads'; goto &new }
83 $threads::threads = 1;
85 # 'new' is an alias for 'create'
94 threads - Perl interpreter-based threads
98 This document describes threads version 1.18
102 use threads ('yield');
106 print "Thread started: @args\n";
108 my $thread = threads->create('start_thread', 'argument');
111 threads->create(sub { print("I am a thread\n"); })->join();
113 my $thread3 = async { foreach (@files) { ... } };
116 # Invoke thread in list context so it can return a list
117 my ($thr) = threads->create(sub { return (qw/a b c/); });
118 my @results = $thr->join();
122 $thread = threads->self();
123 $thread = threads->object($tid);
125 $tid = threads->tid();
126 $tid = threads->self->tid();
127 $tid = $thread->tid();
132 my @threads = threads->list();
134 if ($thr1 == $thr2) {
140 Perl 5.6 introduced something called interpreter threads. Interpreter
141 threads are different from "5005threads" (the thread model of Perl
142 5.005) by creating a new perl interpreter per thread and not sharing
143 any data or state between threads by default.
145 Prior to perl 5.8 this has only been available to people embedding
146 perl and for emulating fork() on windows.
148 The threads API is loosely based on the old Thread.pm API. It is very
149 important to note that variables are not shared between threads, all
150 variables are per default thread local. To use shared variables one
151 must use threads::shared.
153 It is also important to note that you must enable threads by doing
154 C<use threads> as early as possible in the script itself and that it
155 is not possible to enable threading inside an C<eval "">, C<do>,
156 C<require>, or C<use>. In particular, if you are intending to share
157 variables with threads::shared, you must C<use threads> before you
158 C<use threads::shared> and C<threads> will emit a warning if you do
159 it the other way around.
163 =item $thr = threads->create(FUNCTION, ARGS)
165 This will create a new thread that will begin execution with the specified
166 entry point function, and give it the I<ARGS> list as parameters. It will
167 return the corresponding threads object, or C<undef> if thread creation failed.
169 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
172 my $thr = threads->create('func_name', ...);
174 my $thr = threads->create(sub { ... }, ...);
176 my $thr = threads->create(\&func, ...);
178 The thread may be created in I<list> context, or I<scalar> context as follows:
180 # Create thread in list context
181 my ($thr) = threads->create(...);
183 # Create thread in scalar context
184 my $thr = threads->create(...);
186 This has consequences for the C<-E<gt>join()> method describe below.
188 Although a thread may be created in I<void> context, to do so you must
189 I<chain> either the C<-E<gt>join()> or C<-E<gt>detach()> method to the
190 C<-E<gt>create()> call:
192 threads->create(...)->join();
194 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
198 This will wait for the corresponding thread to complete its execution. When
199 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
200 entry point function.
202 The context (void, scalar or list) of the thread creation is also the
203 context for C<-E<gt>join()>. This means that if you intend to return an array
204 from a thread, you must use C<my ($thr) = threads->create(...)>, and that
205 if you intend to return a scalar, you must use C<my $thr = ...>:
207 # Create thread in list context
208 my ($thr1) = threads->create(sub {
209 my @results = qw(a b c);
212 # Retrieve list results from thread
213 my @res1 = $thr1->join();
215 # Create thread in scalar context
216 my $thr2 = threads->create(sub {
220 # Retrieve scalar result from thread
221 my $res2 = $thr2->join();
223 If the program exits without all other threads having been either joined or
224 detached, then a warning will be issued. (A program exits either because one
225 of its threads explicitly calls L<exit()|perlfunc/"exit EXPR">, or in the case
226 of the main thread, reaches the end of the main program file.)
228 =item $thread->detach
230 Will make the thread unjoinable, and cause any eventual return value
233 Calling C<-E<gt>join()> on a detached thread will cause an error to be thrown.
235 =item threads->detach()
237 Class method that allows a thread to detach itself.
241 This will return the thread object for the current thread.
245 Returns the ID of the thread. Thread IDs are unique integers with the main
246 thread in a program being 0, and incrementing by 1 for every thread created.
250 Class method that allows a thread to obtain its own ID.
252 =item threads->object($tid)
254 This will return the I<threads> object for the I<active> thread associated
255 with the specified thread ID. Returns C<undef> if there is no thread
256 associated with the TID, if the thread is joined or detached, if no TID is
257 specified or if the specified TID is undef.
259 =item threads->yield();
261 This is a suggestion to the OS to let this thread yield CPU time to other
262 threads. What actually happens is highly dependent upon the underlying
263 thread implementation.
265 You may do C<use threads qw(yield)> then use just a bare C<yield> in your
268 =item threads->list()
270 In a list context, returns a list of all non-joined, non-detached I<threads>
271 objects. In a scalar context, returns a count of the same.
273 =item $thr1->equal($thr2)
275 Tests if two threads objects are the same thread or not. This is overloaded
276 to the more natural form:
278 if ($thr1 == $thr2) {
279 print("Threads are the same\n");
282 (Thread comparison is based on thread IDs.)
286 C<async> creates a thread to execute the block immediately following
287 it. This block is treated as an anonymous sub, and so must have a
288 semi-colon after the closing brace. Like C<< threads->new >>, C<async>
289 returns a thread object.
291 =item $thr->_handle()
293 This I<private> method returns the memory location of the internal thread
294 structure associated with a threads object. For Win32, this is the handle
295 returned by C<CreateThread>; for other platforms, it is the pointer returned
296 by C<pthread_create>.
298 This method is of no use for general Perl threads programming. Its intent is
299 to provide other (XS-based) thread modules with the capability to access, and
300 possibly manipulate, the underlying thread structure associated with a Perl
303 =item threads->_handle()
305 Class method that allows a thread to obtain its own I<handle>.
313 =item A thread exited while %d other threads were still running
315 A thread (not necessarily the main thread) exited while there were
316 still other threads running. Usually it's a good idea to first collect
317 the return values of the created threads by joining them, and only then
318 exit from the main thread.
326 =item This Perl hasn't been configured and built properly for the threads...
328 The particular copy of Perl that you're trying to use was not built using the
329 C<useithreads> configuration option.
331 Having threads support requires all of Perl and all of the XS modules in the
332 Perl installation to be rebuilt; it is not just a question of adding the
333 L<threads> module (i.e., threaded and non-threaded Perls are binary
342 =item Parent-Child threads.
344 On some platforms it might not be possible to destroy "parent"
345 threads while there are still existing child "threads".
347 =item Creating threads inside BEGIN blocks
349 Creating threads inside BEGIN blocks (or during the compilation phase
350 in general) does not work. (In Windows, trying to use fork() inside
351 BEGIN blocks is an equally losing proposition, since it has been
352 implemented in very much the same way as threads.)
354 =item PERL_OLD_SIGNALS are not threadsafe, will not be.
356 If your Perl has been built with PERL_OLD_SIGNALS (one has
357 to explicitly add that symbol to ccflags, see C<perl -V>),
358 signal handling is not threadsafe.
360 =item Returning closures from threads
362 Returning a closure from a thread does not work, usually crashing Perl in the
365 =item Perl Bugs and the CPAN Version of L<threads>
367 Support for threads extents beyond the code in this module (i.e.,
368 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
369 versions of Perl contain bugs that may manifest themselves despite using the
370 latest version of L<threads> from CPAN. There is no workaround for this other
371 than upgrading to the lastest version of Perl.
373 (Before you consider posting a bug report, please consult, and possibly post a
374 message to the discussion forum to see if what you've encountered is a known
385 L<threads> Discussion Forum on CPAN:
386 L<http://www.cpanforum.com/dist/threads>
388 Annotated POD for L<threads>:
389 L<http://annocpan.org/~JDHEDDEN/threads-1.18/shared.pm>
391 L<threads::shared>, L<perlthrtut>
393 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
394 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
396 Perl threads mailing list:
397 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
401 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
403 threads is released under the same license as Perl.
405 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
407 =head1 ACKNOWLEDGEMENTS
409 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
410 Helping me out tons, trying to find reasons for races and other weird bugs!
412 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
413 Being there to answer zillions of annoying questions
415 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
417 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
418 Helping with debugging