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




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;

           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->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...

               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.

       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 re-acquire 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 "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 "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(3), threads::shared(3), Thread::Queu(3)e, Thread::Semaphore(3)



perl v5.24.0                      2016-02-05                       Thread(3pm)

perl 5.24 - Generated Sat Nov 26 06:36:57 CST 2016
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