This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Integrate mainline
[perl5.git] / lib / Thread.pm
CommitLineData
43d3ddbe
JH
1package Thread;
2
4038bebf
JH
3use strict;
4
4cf4ea45 5our($VERSION, $ithreads, $othreads);
4038bebf 6
43d3ddbe 7BEGIN {
4cf4ea45 8 $VERSION = '2.00';
43d3ddbe 9 use Config;
4038bebf
JH
10 $ithreads = $Config{useithreads};
11 $othreads = $Config{use5005threads};
43d3ddbe
JH
12}
13
14require Exporter;
15use XSLoader ();
4cf4ea45 16our(@ISA, @EXPORT, @EXPORT_OK);
43d3ddbe
JH
17
18@ISA = qw(Exporter);
19
20BEGIN {
21 if ($ithreads) {
91c54917 22 @EXPORT = qw(cond_wait cond_broadcast cond_signal)
43d3ddbe
JH
23 } elsif ($othreads) {
24 @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait);
25 }
26 push @EXPORT_OK, qw(async yield);
27}
28
29=head1 NAME
30
31Thread - manipulate threads in Perl
32
33=head1 CAVEAT
34
35Perl has two thread models.
36
37In Perl 5.005 the thread model was that all data is implicitly shared
38and shared access to data has to be explicitly synchronized.
39This model is called "5005threads".
40
41In Perl 5.6 a new model was introduced in which all is was thread
42local and shared access to data has to be explicitly declared.
43This model is called "ithreads", for "interpreter threads".
44
45In Perl 5.6 the ithreads model was not available as a public API,
46only as an internal API that was available for extension writers,
47and to implement fork() emulation on Win32 platforms.
48
49In Perl 5.8 the ithreads model became available through the C<threads>
50module.
51
52Neither model is configured by default into Perl (except, as mentioned
8a20485c
JH
53above, in Win32 ithreads are always available.) You can see your
54Perl's threading configuration by running C<perl -V> and looking for
55the I<use...threads> variables, or inside script by C<use Config;>
56and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>.
57
58For old code and interim backwards compatibility, the Thread module
59has been reworked to function as a frontend for both 5005threads and
60ithreads.
43d3ddbe 61
43d3ddbe
JH
62Note that the compatibility is not complete: because the data sharing
63models are directly opposed, anything to do with data sharing has to
64be thought differently. With the ithreads you must explicitly share()
65variables between the threads.
66
8a20485c
JH
67For new code the use of the C<Thread> module is discouraged and
68the direct use use of the C<threads> and C<threads::shared> modules
69is encouraged instead.
70
43d3ddbe
JH
71Finally, note that there are many known serious problems with the
725005threads, one of the least of which is that regular expression
73match variables like $1 are not threadsafe, that is, they easily get
74corrupted by competing threads. Other problems include more insidious
75data corruption and mysterious crashes. You are seriously urged to
76use ithreads instead.
77
78=head1 SYNOPSIS
79
80 use Thread;
81
82 my $t = Thread->new(\&start_sub, @start_args);
83
84 $result = $t->join;
85 $result = $t->eval;
86 $t->detach;
87
88 if ($t->done) {
89 $t->join;
90 }
91
92 if($t->equal($another_thread)) {
93 # ...
94 }
95
96 yield();
97
98 my $tid = Thread->self->tid;
99
100 lock($scalar);
101 lock(@array);
102 lock(%hash);
103
104 lock(\&sub); # not available with ithreads
105
106 $flags = $t->flags; # not available with ithreads
107
108 my @list = Thread->list; # not available with ithreads
109
43d3ddbe
JH
110 use Thread 'async';
111
112=head1 DESCRIPTION
113
114The C<Thread> module provides multithreading support for perl.
115
116=head1 FUNCTIONS
117
118=over 8
119
120=item $thread = Thread->new(\&start_sub)
121
122=item $thread = Thread->new(\&start_sub, LIST)
123
124C<new> starts a new thread of execution in the referenced subroutine. The
125optional list is passed as parameters to the subroutine. Execution
126continues in both the subroutine and the code after the C<new> call.
127
128C<Thread-&gt;new> returns a thread object representing the newly created
129thread.
130
131=item lock VARIABLE
132
91c54917 133C<lock> places a lock on a variable until the lock goes out of scope.
43d3ddbe
JH
134
135If the variable is locked by another thread, the C<lock> call will
136block until it's available. C<lock> is recursive, so multiple calls
137to C<lock> are safe--the variable will remain locked until the
138outermost lock on the variable goes out of scope.
139
140Locks on variables only affect C<lock> calls--they do I<not> affect normal
141access to a variable. (Locks on subs are different, and covered in a bit.)
142If you really, I<really> want locks to block access, then go ahead and tie
143them to something and manage this yourself. This is done on purpose.
144While managing access to variables is a good thing, Perl doesn't force
145you out of its living room...
146
147If a container object, such as a hash or array, is locked, all the
148elements of that container are not locked. For example, if a thread
149does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
150block.
151
152With 5005threads you may also C<lock> a sub, using C<lock &sub>.
153Any calls to that sub from another thread will block until the lock
154is released. This behaviour is not equivalent to declaring the sub
155with the C<locked> attribute. The C<locked> attribute serializes
156access to a subroutine, but allows different threads non-simultaneous
157access. C<lock &sub>, on the other hand, will not allow I<any> other
158thread access for the duration of the lock.
159
160Finally, C<lock> will traverse up references exactly I<one> level.
161C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
162
163=item async BLOCK;
164
165C<async> creates a thread to execute the block immediately following
166it. This block is treated as an anonymous sub, and so must have a
167semi-colon after the closing brace. Like C<Thread-&gt;new>, C<async>
168returns a thread object.
169
170=item Thread->self
171
172The C<Thread-E<gt>self> function returns a thread object that represents
173the thread making the C<Thread-E<gt>self> call.
174
175=item cond_wait VARIABLE
176
177The C<cond_wait> function takes a B<locked> variable as
178a parameter, unlocks the variable, and blocks until another thread
179does a C<cond_signal> or C<cond_broadcast> for that same locked
180variable. The variable that C<cond_wait> blocked on is relocked
181after the C<cond_wait> is satisfied. If there are multiple threads
182C<cond_wait>ing on the same variable, all but one will reblock waiting
183to reaquire the lock on the variable. (So if you're only using
184C<cond_wait> for synchronization, give up the lock as soon as
185possible.)
186
187=item cond_signal VARIABLE
188
189The C<cond_signal> function takes a locked variable as a parameter and
190unblocks one thread that's C<cond_wait>ing on that variable. If more than
191one thread is blocked in a C<cond_wait> on that variable, only one (and
192which one is indeterminate) will be unblocked.
193
194If there are no threads blocked in a C<cond_wait> on the variable,
195the signal is discarded.
196
197=item cond_broadcast VARIABLE
198
199The C<cond_broadcast> function works similarly to C<cond_signal>.
200C<cond_broadcast>, though, will unblock B<all> the threads that are
201blocked in a C<cond_wait> on the locked variable, rather than only
202one.
203
204=item yield
205
206The C<yield> function allows another thread to take control of the
207CPU. The exact results are implementation-dependent.
208
209=back
210
211=head1 METHODS
212
213=over 8
214
215=item join
216
217C<join> waits for a thread to end and returns any values the thread
218exited with. C<join> will block until the thread has ended, though
219it won't block if the thread has already terminated.
220
221If the thread being C<join>ed C<die>d, the error it died with will
222be returned at this time. If you don't want the thread performing
223the C<join> to die as well, you should either wrap the C<join> in
224an C<eval> or use the C<eval> thread method instead of C<join>.
225
226=item eval
227
228The C<eval> method wraps an C<eval> around a C<join>, and so waits for
229a thread to exit, passing along any values the thread might have returned.
230Errors, of course, get placed into C<$@>. (Not available with ithreads.)
231
232=item detach
233
234C<detach> tells a thread that it is never going to be joined i.e.
235that all traces of its existence can be removed once it stops running.
236Errors in detached threads will not be visible anywhere - if you want
237to catch them, you should use $SIG{__DIE__} or something like that.
238
239=item equal
240
241C<equal> tests whether two thread objects represent the same thread and
242returns true if they do.
243
244=item tid
245
246The C<tid> method returns the tid of a thread. The tid is
247a monotonically increasing integer assigned when a thread is
248created. The main thread of a program will have a tid of zero,
249while subsequent threads will have tids assigned starting with one.
250
251=item flags
252
253The C<flags> method returns the flags for the thread. This is the
254integer value corresponding to the internal flags for the thread,
255and the value may not be all that meaningful to you.
256(Not available with ithreads.)
257
258=item done
259
260The C<done> method returns true if the thread you're checking has
261finished, and false otherwise. (Not available with ithreads.)
262
263=back
264
265=head1 LIMITATIONS
266
267The sequence number used to assign tids is a simple integer, and no
268checking is done to make sure the tid isn't currently in use. If a
269program creates more than 2**32 - 1 threads in a single run, threads
270may be assigned duplicate tids. This limitation may be lifted in
271a future version of Perl.
272
273=head1 SEE ALSO
274
275L<threads::shared> (not available with 5005threads)
276
277L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>,
278L<Thread::Specific> (not available with ithreads)
279
280=cut
281
282#
283# Methods
284#
285
286#
287# Exported functions
288#
289
290sub async (&) {
291 return Thread->new($_[0]);
292}
293
294sub eval {
295 return eval { shift->join; };
296}
297
298sub unimplemented {
299 print $_[0], " unimplemented with ",
300 $Config{useithreads} ? "ithreads" : "5005threads", "\n";
301
302}
303
304sub unimplement {
305 for my $m (@_) {
4038bebf 306 no strict 'refs';
43d3ddbe
JH
307 *{"Thread::$m"} = sub { unimplemented $m };
308 }
309}
310
311BEGIN {
312 if ($ithreads) {
733129fe
JH
313 if ($othreads) {
314 require Carp;
315 Carp::croak("This Perl has both ithreads and 5005threads (serious malconfiguration)");
316 }
43d3ddbe 317 XSLoader::load 'threads';
e7b4e24c 318 for my $m (qw(new join detach yield self tid equal list)) {
4038bebf 319 no strict 'refs';
43d3ddbe
JH
320 *{"Thread::$m"} = \&{"threads::$m"};
321 }
e7b4e24c 322 require 'threads/shared.pm';
91c54917 323 for my $m (qw(cond_signal cond_broadcast cond_wait)) {
4038bebf 324 no strict 'refs';
43d3ddbe
JH
325 *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"};
326 }
d7ceb7fc 327 # trying to unimplement eval gives redefined warning
e7b4e24c 328 unimplement(qw(done flags));
43d3ddbe
JH
329 } elsif ($othreads) {
330 XSLoader::load 'Thread';
43d3ddbe
JH
331 } else {
332 require Carp;
733129fe 333 Carp::croak("This Perl has neither ithreads nor 5005threads");
43d3ddbe
JH
334 }
335}
336
3371;