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 = '1.17';
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 # || 0 to ensure compatibility with previous versions
80 sub equal { ($_[0]->tid == $_[1]->tid) || 0 }
82 # use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
83 # should also be faster
84 sub async (&;@) { unshift @_,'threads'; goto &new }
87 return undef unless @_ > 1;
88 foreach (threads->list) {
89 return $_ if $_->tid == $_[1];
94 $threads::threads = 1;
96 # why document 'new' then use 'create' in the tests!
105 threads - Perl interpreter-based threads
109 This document describes threads version 1.17
113 use threads ('yield');
117 print "Thread started: @args\n";
119 my $thread = threads->create('start_thread', 'argument');
122 threads->create(sub { print("I am a thread\n"); })->join();
124 my $thread3 = async { foreach (@files) { ... } };
127 # Invoke thread in list context so it can return a list
128 my ($thr) = threads->create(sub { return (qw/a b c/); });
129 my @results = $thr->join();
133 $thread = threads->self();
134 $thread = threads->object($tid);
136 $tid = threads->tid();
137 $tid = threads->self->tid();
138 $tid = $thread->tid();
143 my @threads = threads->list();
145 if ($thr1 == $thr2) {
151 Perl 5.6 introduced something called interpreter threads. Interpreter
152 threads are different from "5005threads" (the thread model of Perl
153 5.005) by creating a new perl interpreter per thread and not sharing
154 any data or state between threads by default.
156 Prior to perl 5.8 this has only been available to people embedding
157 perl and for emulating fork() on windows.
159 The threads API is loosely based on the old Thread.pm API. It is very
160 important to note that variables are not shared between threads, all
161 variables are per default thread local. To use shared variables one
162 must use threads::shared.
164 It is also important to note that you must enable threads by doing
165 C<use threads> as early as possible in the script itself and that it
166 is not possible to enable threading inside an C<eval "">, C<do>,
167 C<require>, or C<use>. In particular, if you are intending to share
168 variables with threads::shared, you must C<use threads> before you
169 C<use threads::shared> and C<threads> will emit a warning if you do
170 it the other way around.
174 =item $thr = threads->create(FUNCTION, ARGS)
176 This will create a new thread that will begin execution with the specified
177 entry point function, and give it the I<ARGS> list as parameters. It will
178 return the corresponding threads object, or C<undef> if thread creation failed.
180 I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
183 my $thr = threads->create('func_name', ...);
185 my $thr = threads->create(sub { ... }, ...);
187 my $thr = threads->create(\&func, ...);
189 The thread may be created in I<list> context, or I<scalar> context as follows:
191 # Create thread in list context
192 my ($thr) = threads->create(...);
194 # Create thread in scalar context
195 my $thr = threads->create(...);
197 This has consequences for the C<-E<gt>join()> method describe below.
199 Although a thread may be created in I<void> context, to do so you must
200 I<chain> either the C<-E<gt>join()> or C<-E<gt>detach()> method to the
201 C<-E<gt>create()> call:
203 threads->create(...)->join();
205 The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
209 This will wait for the corresponding thread to complete its execution. When
210 the thread finishes, C<-E<gt>join()> will return the return value(s) of the
211 entry point function.
213 The context (void, scalar or list) of the thread creation is also the
214 context for C<-E<gt>join()>. This means that if you intend to return an array
215 from a thread, you must use C<my ($thr) = threads->create(...)>, and that
216 if you intend to return a scalar, you must use C<my $thr = ...>:
218 # Create thread in list context
219 my ($thr1) = threads->create(sub {
220 my @results = qw(a b c);
223 # Retrieve list results from thread
224 my @res1 = $thr1->join();
226 # Create thread in scalar context
227 my $thr2 = threads->create(sub {
231 # Retrieve scalar result from thread
232 my $res2 = $thr2->join();
234 If the program exits without all other threads having been either joined or
235 detached, then a warning will be issued. (A program exits either because one
236 of its threads explicitly calls L<exit()|perlfunc/"exit EXPR">, or in the case
237 of the main thread, reaches the end of the main program file.)
239 =item $thread->detach
241 Will make the thread unjoinable, and cause any eventual return value
244 Calling C<-E<gt>join()> on a detached thread will cause an error to be thrown.
246 =item threads->detach()
248 Class method that allows a thread to detach itself.
252 This will return the thread object for the current thread.
256 Returns the ID of the thread. Thread IDs are unique integers with the main
257 thread in a program being 0, and incrementing by 1 for every thread created.
261 Class method that allows a thread to obtain its own ID.
263 =item threads->object($tid)
265 This will return the I<threads> object for the I<active> thread associated
266 with the specified thread ID. Returns C<undef> if there is no thread
267 associated with the TID, if the thread is joined or detached, if no TID is
268 specified or if the specified TID is undef.
270 =item threads->yield();
272 This is a suggestion to the OS to let this thread yield CPU time to other
273 threads. What actually happens is highly dependent upon the underlying
274 thread implementation.
276 You may do C<use threads qw(yield)> then use just a bare C<yield> in your
279 =item threads->list();
281 This will return a list of all non joined, non detached threads.
283 =item $thr1->equal($thr2)
285 Tests if two threads objects are the same thread or not. This is overloaded
286 to the more natural form:
288 if ($thr1 == $thr2) {
289 print("Threads are the same\n");
292 (Thread comparison is based on thread IDs.)
296 C<async> creates a thread to execute the block immediately following
297 it. This block is treated as an anonymous sub, and so must have a
298 semi-colon after the closing brace. Like C<< threads->new >>, C<async>
299 returns a thread object.
307 =item A thread exited while %d other threads were still running
309 A thread (not necessarily the main thread) exited while there were
310 still other threads running. Usually it's a good idea to first collect
311 the return values of the created threads by joining them, and only then
312 exit from the main thread.
320 =item This Perl hasn't been configured and built properly for the threads...
322 The particular copy of Perl that you're trying to use was not built using the
323 C<useithreads> configuration option.
325 Having threads support requires all of Perl and all of the XS modules in the
326 Perl installation to be rebuilt; it is not just a question of adding the
327 L<threads> module (i.e., threaded and non-threaded Perls are binary
336 =item Parent-Child threads.
338 On some platforms it might not be possible to destroy "parent"
339 threads while there are still existing child "threads".
343 The thread id is a 32 bit integer, it can potentially overflow.
344 This might be fixed in a later version of perl.
346 =item Creating threads inside BEGIN blocks
348 Creating threads inside BEGIN blocks (or during the compilation phase
349 in general) does not work. (In Windows, trying to use fork() inside
350 BEGIN blocks is an equally losing proposition, since it has been
351 implemented in very much the same way as threads.)
353 =item PERL_OLD_SIGNALS are not threadsafe, will not be.
355 If your Perl has been built with PERL_OLD_SIGNALS (one has
356 to explicitly add that symbol to ccflags, see C<perl -V>),
357 signal handling is not threadsafe.
359 =item Returning closures from threads
361 Returning a closure from a thread does not work, usually crashing Perl in the
364 =item Perl Bugs and the CPAN Version of L<threads>
366 Support for threads extents beyond the code in this module (i.e.,
367 F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
368 versions of Perl contain bugs that may manifest themselves despite using the
369 latest version of L<threads> from CPAN. There is no workaround for this other
370 than upgrading to the lastest version of Perl.
372 (Before you consider posting a bug report, please consult, and possibly post a
373 message to the discussion forum to see if what you've encountered is a known
384 L<threads> Discussion Forum on CPAN:
385 L<http://www.cpanforum.com/dist/threads>
387 Annotated POD for L<threads>:
388 L<http://annocpan.org/~JDHEDDEN/threads-1.17/shared.pm>
390 L<threads::shared>, L<perlthrtut>
392 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
393 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
395 Perl threads mailing list:
396 L<http://lists.cpan.org/showlist.cgi?name=iThreads>
400 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
402 threads is released under the same license as Perl.
404 CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
406 =head1 ACKNOWLEDGEMENTS
408 Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
409 Helping me out tons, trying to find reasons for races and other weird bugs!
411 Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
412 Being there to answer zillions of annoying questions
414 Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
416 Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
417 Helping with debugging