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