


Thread(3p)       Perl Programmers Reference Guide      Thread(3p)


NAME
       Thread - Manipulate threads in Perl (for old code only)

DEPRECATED
       The "Thread" module served as the frontend to the old-
       style thread model, called 5005threads, that was
       introduced in release 5.005.  That model was deprecated,
       and has been removed in version 5.10.

       For old code and interim backwards compatibility, the
       "Thread" module has been reworked to function as a
       frontend for the new interpreter threads (ithreads) model.
       However, some previous functionality is not available.
       Further, the data sharing models between the two thread
       models are completely different, and anything to do with
       data sharing has to be thought differently.  With
       ithreads, you must explicitly "share()" variables between
       the threads.

       You are strongly encouraged to migrate any existing
       threaded code to the new model (i.e., use the "threads"
       and "threads::shared" modules) as soon as possible.

HISTORY
       In Perl 5.005, the thread model was that all data is
       implicitly shared, and shared access to data has to be
       explicitly synchronized.  This model is called
       5005threads.

       In Perl 5.6, a new model was introduced in which all is
       was thread local and shared access to data has to be
       explicitly declared.  This model is called ithreads, for
       "interpreter threads".

       In Perl 5.6, the ithreads model was not available as a
       public API; only as an internal API that was available for
       extension writers, and to implement fork() emulation on
       Win32 platforms.

       In Perl 5.8, the ithreads model became available through
       the "threads" module, and the 5005threads model was
       deprecated.

       In Perl 5.10, the 5005threads model was removed from the
       Perl interpreter.

SYNOPSIS
           use Thread qw(:DEFAULT async yield);

           my $t = Thread->new(\&start_sub, @start_args);

           $result = $t->join;
           $t->detach;




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Thread(3p)       Perl Programmers Reference Guide      Thread(3p)


           if ($t->done) {
               $t->join;
           }

           if($t->equal($another_thread)) {
               # ...
           }

           yield();

           my $tid = Thread->self->tid;

           lock($scalar);
           lock(@array);
           lock(%hash);

           my @list = Thread->list;

DESCRIPTION
       The "Thread" module provides multithreading support for
       Perl.

FUNCTIONS
       $thread = Thread->new(\&start_sub)
       $thread = Thread->new(\&start_sub, LIST)
               "new" starts a new thread of execution in the
               referenced subroutine. The optional list is passed
               as parameters to the subroutine. Execution
               continues in both the subroutine and the code
               after the "new" call.

               "Thread-&gt;new" returns a thread object
               representing the newly created thread.

       lock VARIABLE
               "lock" places a lock on a variable until the lock
               goes out of scope.

               If the variable is locked by another thread, the
               "lock" call will block until it's available.
               "lock" is recursive, so multiple calls to "lock"
               are safe--the variable will remain locked until
               the outermost lock on the variable goes out of
               scope.

               Locks on variables only affect "lock" calls--they
               do not affect normal access to a variable. (Locks
               on subs are different, and covered in a bit.)  If
               you really, really want locks to block access,
               then go ahead and tie them to something and manage
               this yourself.  This is done on purpose.  While
               managing access to variables is a good thing, Perl
               doesn't force you out of its living room...




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Thread(3p)       Perl Programmers Reference Guide      Thread(3p)


               If a container object, such as a hash or array, is
               locked, all the elements of that container are not
               locked. For example, if a thread does a "lock @a",
               any other thread doing a "lock($a[12])" won't
               block.

               Finally, "lock" will traverse up references
               exactly one level.  "lock(\$a)" is equivalent to
               "lock($a)", while "lock(\\$a)" is not.

       async BLOCK;
               "async" creates a thread to execute the block
               immediately following it.  This block is treated
               as an anonymous sub, and so must have a semi-colon
               after the closing brace. Like "Thread-&gt;new",
               "async" returns a thread object.

       Thread->self
               The "Thread->self" function returns a thread
               object that represents the thread making the
               "Thread->self" call.

       Thread->list
               Returns a list of all non-joined, non-detached
               Thread objects.

       cond_wait VARIABLE
               The "cond_wait" function takes a locked variable
               as a parameter, unlocks the variable, and blocks
               until another thread does a "cond_signal" or
               "cond_broadcast" for that same locked variable.
               The variable that "cond_wait" blocked on is
               relocked after the "cond_wait" is satisfied.  If
               there are multiple threads "cond_wait"ing on the
               same variable, all but one will reblock waiting to
               reaquire the lock on the variable.  (So if you're
               only using "cond_wait" for synchronization, give
               up the lock as soon as possible.)

       cond_signal VARIABLE
               The "cond_signal" function takes a locked variable
               as a parameter and unblocks one thread that's
               "cond_wait"ing on that variable. If more than one
               thread is blocked in a "cond_wait" on that
               variable, only one (and which one is
               indeterminate) will be unblocked.

               If there are no threads blocked in a "cond_wait"
               on the variable, the signal is discarded.

       cond_broadcast VARIABLE
               The "cond_broadcast" function works similarly to
               "cond_signal".  "cond_broadcast", though, will
               unblock all the threads that are blocked in a



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Thread(3p)       Perl Programmers Reference Guide      Thread(3p)


               "cond_wait" on the locked variable, rather than
               only one.

       yield   The "yield" function allows another thread to take
               control of the CPU. The exact results are
               implementation-dependent.

METHODS
       join    "join" waits for a thread to end and returns any
               values the thread exited with.  "join" will block
               until the thread has ended, though it won't block
               if the thread has already terminated.

               If the thread being "join"ed "die"d, the error it
               died with will be returned at this time. If you
               don't want the thread performing the "join" to die
               as well, you should either wrap the "join" in an
               "eval" or use the "eval" thread method instead of
               "join".

       detach  "detach" tells a thread that it is never going to
               be joined i.e.  that all traces of its existence
               can be removed once it stops running.  Errors in
               detached threads will not be visible anywhere - if
               you want to catch them, you should use
               $SIG{__DIE__} or something like that.

       equal   "equal" tests whether two thread objects represent
               the same thread and returns true if they do.

       tid     The "tid" method returns the tid of a thread. The
               tid is a monotonically increasing integer assigned
               when a thread is created. The main thread of a
               program will have a tid of zero, while subsequent
               threads will have tids assigned starting with one.

       done    The "done" method returns true if the thread
               you're checking has finished, and false otherwise.

DEFUNCT
       The following were implemented with 5005threads, but are
       no longer available with ithreads.

       lock(\&sub)
               With 5005threads, you could also "lock" a sub such
               that any calls to that sub from another thread
               would block until the lock was released.

               Also, subroutines could be declared with the
               ":locked" attribute which would serialize access
               to the subroutine, but allowed different threads
               non-simultaneous access.

       eval    The "eval" method wrapped an "eval" around a



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Thread(3p)       Perl Programmers Reference Guide      Thread(3p)


               "join", and so waited for a thread to exit,
               passing along any values the thread might have
               returned and placing any errors into $@.

       flags   The "flags" method returned the flags for the
               thread - an integer value corresponding to the
               internal flags for the thread.

SEE ALSO
       threads, threads::shared, Thread::Queue, Thread::Semaphore















































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