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)
19 my $t = new Thread \&start_sub, @start_args;
25 if($t->equal($another_thread)) {
29 my $tid = Thread->self->tid;
30 my $tlist = Thread->list;
39 WARNING: Threading is an experimental feature. Both the interface
40 and implementation are subject to change drastically. In fact, this
41 documentation describes the flavor of threads that was in version
42 5.005. Perl 5.6.0 and later have the beginnings of support for
43 interpreter threads, which (when finished) is expected to be
44 significantly different from what is described here. The information
45 contained here may therefore soon be obsolete. Use at your own risk!
47 The C<Thread> module provides multithreading support for perl.
55 =item new \&start_sub, LIST
57 C<new> starts a new thread of execution in the referenced subroutine. The
58 optional list is passed as parameters to the subroutine. Execution
59 continues in both the subroutine and the code after the C<new> call.
61 C<new Thread> returns a thread object representing the newly created
66 C<lock> places a lock on a variable until the lock goes out of scope. If
67 the variable is locked by another thread, the C<lock> call will block until
68 it's available. C<lock> is recursive, so multiple calls to C<lock> are
69 safe--the variable will remain locked until the outermost lock on the
70 variable goes out of scope.
72 Locks on variables only affect C<lock> calls--they do I<not> affect normal
73 access to a variable. (Locks on subs are different, and covered in a bit)
74 If you really, I<really> want locks to block access, then go ahead and tie
75 them to something and manage this yourself. This is done on purpose. While
76 managing access to variables is a good thing, perl doesn't force you out of
79 If a container object, such as a hash or array, is locked, all the elements
80 of that container are not locked. For example, if a thread does a C<lock
81 @a>, any other thread doing a C<lock($a[12])> won't block.
83 You may also C<lock> a sub, using C<lock &sub>. Any calls to that sub from
84 another thread will block until the lock is released. This behaviour is not
85 equivalent to declaring the sub with the C<locked> attribute. The C<locked>
86 attribute serializes access to a subroutine, but allows different threads
87 non-simultaneous access. C<lock &sub>, on the other hand, will not allow
88 I<any> other thread access for the duration of the lock.
90 Finally, C<lock> will traverse up references exactly I<one> level.
91 C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
95 C<async> creates a thread to execute the block immediately following
96 it. This block is treated as an anonymous sub, and so must have a
97 semi-colon after the closing brace. Like C<new Thread>, C<async> returns a
102 The C<Thread-E<gt>self> function returns a thread object that represents
103 the thread making the C<Thread-E<gt>self> call.
107 C<Thread-E<gt>list> returns a list of thread objects for all running and
108 finished but un-C<join>ed threads.
110 =item cond_wait VARIABLE
112 The C<cond_wait> function takes a B<locked> variable as a parameter,
113 unlocks the variable, and blocks until another thread does a C<cond_signal>
114 or C<cond_broadcast> for that same locked variable. The variable that
115 C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied.
116 If there are multiple threads C<cond_wait>ing on the same variable, all but
117 one will reblock waiting to reaquire the lock on the variable. (So if
118 you're only using C<cond_wait> for synchronization, give up the lock as
121 =item cond_signal VARIABLE
123 The C<cond_signal> function takes a locked variable as a parameter and
124 unblocks one thread that's C<cond_wait>ing on that variable. If more than
125 one thread is blocked in a C<cond_wait> on that variable, only one (and
126 which one is indeterminate) will be unblocked.
128 If there are no threads blocked in a C<cond_wait> on the variable, the
131 =item cond_broadcast VARIABLE
133 The C<cond_broadcast> function works similarly to C<cond_signal>.
134 C<cond_broadcast>, though, will unblock B<all> the threads that are blocked
135 in a C<cond_wait> on the locked variable, rather than only one.
139 The C<yield> function allows another thread to take control of the
140 CPU. The exact results are implementation-dependent.
150 C<join> waits for a thread to end and returns any values the thread exited
151 with. C<join> will block until the thread has ended, though it won't block
152 if the thread has already terminated.
154 If the thread being C<join>ed C<die>d, the error it died with will be
155 returned at this time. If you don't want the thread performing the C<join>
156 to die as well, you should either wrap the C<join> in an C<eval> or use the
157 C<eval> thread method instead of C<join>.
161 The C<eval> method wraps an C<eval> around a C<join>, and so waits for a
162 thread to exit, passing along any values the thread might have returned.
163 Errors, of course, get placed into C<$@>.
167 C<detach> tells a thread that it is never going to be joined i.e.
168 that all traces of its existence can be removed once it stops running.
169 Errors in detached threads will not be visible anywhere - if you want
170 to catch them, you should use $SIG{__DIE__} or something like that.
174 C<equal> tests whether two thread objects represent the same thread and
175 returns true if they do.
179 The C<tid> method returns the tid of a thread. The tid is a monotonically
180 increasing integer assigned when a thread is created. The main thread of a
181 program will have a tid of zero, while subsequent threads will have tids
182 assigned starting with one.
188 The sequence number used to assign tids is a simple integer, and no
189 checking is done to make sure the tid isn't currently in use. If a program
190 creates more than 2^32 - 1 threads in a single run, threads may be assigned
191 duplicate tids. This limitation may be lifted in a future version of Perl.
195 L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, L<Thread::Specific>.
207 return new Thread $_[0];
211 return eval { shift->join; };
214 XSLoader::load 'Thread';