4 our($VERSION, @ISA, @EXPORT);
9 @EXPORT_OK = qw(yield cond_signal cond_broadcast cond_wait async);
13 Thread - manipulate threads in Perl (EXPERIMENTAL, subject to change)
17 The Thread extension requires Perl to be built in a particular way to
18 enable the older 5.005 threading model. Just to confuse matters, there
19 is an alternate threading model known as "ithreads" that does NOT
20 support this extension. If you are using a binary distribution such
21 as ActivePerl that is built with ithreads support, this extension CANNOT
28 my $t = new Thread \&start_sub, @start_args;
39 if($t->equal($another_thread)) {
43 my $tid = Thread->self->tid;
44 my $tlist = Thread->list;
53 WARNING: Threading is an experimental feature. Both the interface
54 and implementation are subject to change drastically. In fact, this
55 documentation describes the flavor of threads that was in version
56 5.005. Perl 5.6.0 and later have the beginnings of support for
57 interpreter threads, which (when finished) is expected to be
58 significantly different from what is described here. The information
59 contained here may therefore soon be obsolete. Use at your own risk!
61 The C<Thread> module provides multithreading support for perl.
69 =item new \&start_sub, LIST
71 C<new> starts a new thread of execution in the referenced subroutine. The
72 optional list is passed as parameters to the subroutine. Execution
73 continues in both the subroutine and the code after the C<new> call.
75 C<new Thread> returns a thread object representing the newly created
80 C<lock> places a lock on a variable until the lock goes out of scope. If
81 the variable is locked by another thread, the C<lock> call will block until
82 it's available. C<lock> is recursive, so multiple calls to C<lock> are
83 safe--the variable will remain locked until the outermost lock on the
84 variable goes out of scope.
86 Locks on variables only affect C<lock> calls--they do I<not> affect normal
87 access to a variable. (Locks on subs are different, and covered in a bit)
88 If you really, I<really> want locks to block access, then go ahead and tie
89 them to something and manage this yourself. This is done on purpose. While
90 managing access to variables is a good thing, perl doesn't force you out of
93 If a container object, such as a hash or array, is locked, all the elements
94 of that container are not locked. For example, if a thread does a C<lock
95 @a>, any other thread doing a C<lock($a[12])> won't block.
97 You may also C<lock> a sub, using C<lock &sub>. Any calls to that sub from
98 another thread will block until the lock is released. This behaviour is not
99 equivalent to declaring the sub with the C<locked> attribute. The C<locked>
100 attribute serializes access to a subroutine, but allows different threads
101 non-simultaneous access. C<lock &sub>, on the other hand, will not allow
102 I<any> other thread access for the duration of the lock.
104 Finally, C<lock> will traverse up references exactly I<one> level.
105 C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
109 C<async> creates a thread to execute the block immediately following
110 it. This block is treated as an anonymous sub, and so must have a
111 semi-colon after the closing brace. Like C<new Thread>, C<async> returns a
116 The C<Thread-E<gt>self> function returns a thread object that represents
117 the thread making the C<Thread-E<gt>self> call.
121 C<Thread-E<gt>list> returns a list of thread objects for all running and
122 finished but un-C<join>ed threads.
124 =item cond_wait VARIABLE
126 The C<cond_wait> function takes a B<locked> variable as a parameter,
127 unlocks the variable, and blocks until another thread does a C<cond_signal>
128 or C<cond_broadcast> for that same locked variable. The variable that
129 C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied.
130 If there are multiple threads C<cond_wait>ing on the same variable, all but
131 one will reblock waiting to reaquire the lock on the variable. (So if
132 you're only using C<cond_wait> for synchronization, give up the lock as
135 =item cond_signal VARIABLE
137 The C<cond_signal> function takes a locked variable as a parameter and
138 unblocks one thread that's C<cond_wait>ing on that variable. If more than
139 one thread is blocked in a C<cond_wait> on that variable, only one (and
140 which one is indeterminate) will be unblocked.
142 If there are no threads blocked in a C<cond_wait> on the variable, the
145 =item cond_broadcast VARIABLE
147 The C<cond_broadcast> function works similarly to C<cond_signal>.
148 C<cond_broadcast>, though, will unblock B<all> the threads that are blocked
149 in a C<cond_wait> on the locked variable, rather than only one.
153 The C<yield> function allows another thread to take control of the
154 CPU. The exact results are implementation-dependent.
164 C<join> waits for a thread to end and returns any values the thread exited
165 with. C<join> will block until the thread has ended, though it won't block
166 if the thread has already terminated.
168 If the thread being C<join>ed C<die>d, the error it died with will be
169 returned at this time. If you don't want the thread performing the C<join>
170 to die as well, you should either wrap the C<join> in an C<eval> or use the
171 C<eval> thread method instead of C<join>.
175 The C<eval> method wraps an C<eval> around a C<join>, and so waits for a
176 thread to exit, passing along any values the thread might have returned.
177 Errors, of course, get placed into C<$@>.
181 C<detach> tells a thread that it is never going to be joined i.e.
182 that all traces of its existence can be removed once it stops running.
183 Errors in detached threads will not be visible anywhere - if you want
184 to catch them, you should use $SIG{__DIE__} or something like that.
188 C<equal> tests whether two thread objects represent the same thread and
189 returns true if they do.
193 The C<tid> method returns the tid of a thread. The tid is a monotonically
194 increasing integer assigned when a thread is created. The main thread of a
195 program will have a tid of zero, while subsequent threads will have tids
196 assigned starting with one.
200 The C<flags> method returns the flags for the thread. This is the
201 integer value corresponding to the internal flags for the thread, and
202 the value may not be all that meaningful to you.
206 The C<done> method returns true if the thread you're checking has
207 finished, and false otherwise.
213 The sequence number used to assign tids is a simple integer, and no
214 checking is done to make sure the tid isn't currently in use. If a program
215 creates more than 2^32 - 1 threads in a single run, threads may be assigned
216 duplicate tids. This limitation may be lifted in a future version of Perl.
220 L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, L<Thread::Specific>.
232 return new Thread $_[0];
236 return eval { shift->join; };
239 XSLoader::load 'Thread';