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

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

       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

       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.

       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

       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

       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.

	   use Thread qw(:DEFAULT async yield);

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

	   $result = $t->join;

	   if ($t->done) {

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


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


	   my @list = Thread->list;

       The "Thread" module provides multithreading support for Perl.

       $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->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

	       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...

	       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->new", "async" returns a thread object.

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

	       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

       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 "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.

       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.

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

	       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

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

       threads, threads::shared, Thread::Queue, Thread::Semaphore

perl v5.16.3				    2013-02-26				      Thread(3pm)
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