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RedHat 9 (Linux i386) - man page for thread (redhat section 3pm)

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

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

CAVEAT
       Perl has two thread models.

       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 plat-
       forms.

       In Perl 5.8 the ithreads model became available through the "threads" module.

       Neither model is configured by default into Perl (except, as mentioned above, in Win32
       ithreads are always available.)	You can see your Perl's threading configuration by run-
       ning "perl -V" and looking for the use...threads variables, or inside script by "use Con-
       fig;" and testing for $Config{use5005threads} and $Config{useithreads}.

       For old code and interim backwards compatibility, the Thread module has been reworked to
       function as a frontend for both 5005threads and ithreads.

       Note that the compatibility is not complete: because the data sharing models are directly
       opposed, anything to do with data sharing has to be thought differently.  With the
       ithreads you must explicitly share() variables between the threads.

       For new code the use of the "Thread" module is discouraged and the direct use of the
       "threads" and "threads::shared" modules is encouraged instead.

       Finally, note that there are many known serious problems with the 5005threads, one of the
       least of which is that regular expression match variables like $1 are not threadsafe, that
       is, they easily get corrupted by competing threads.  Other problems include more insidious
       data corruption and mysterious crashes.	You are seriously urged to use ithreads instead.

SYNOPSIS
	   use Thread;

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

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

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

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

	   yield();

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

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

	   lock(\&sub);        # not available with ithreads

	   $flags = $t->flags; # not available with ithreads

	   my @list = Thread->list;    # not available with ithreads

	   use Thread 'async';

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 vari-
	       able 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 vari-
	       ables 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.

	       With 5005threads you may also "lock" a sub, using "lock &sub".  Any calls to that
	       sub from another thread will block until the lock is released. This behaviour is
	       not equivalent to declaring the sub with the "locked" attribute.  The "locked"
	       attribute serializes access to a subroutine, but allows different threads non-
	       simultaneous access. "lock &sub", on the other hand, will not allow any other
	       thread access for the duration of the lock.

	       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.

       cond_wait VARIABLE
	       The "cond_wait" function takes a locked variable as a parameter, unlocks the vari-
	       able, 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 "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".

       eval    The "eval" method wraps an "eval" around a "join", and so waits for a thread to
	       exit, passing along any values the thread might have returned.  Errors, of course,
	       get placed into $@.  (Not available with ithreads.)

       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 increas-
	       ing 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.

       flags   The "flags" method returns the flags for the thread. This is the integer value
	       corresponding to the internal flags for the thread, and the value may not be all
	       that meaningful to you.	(Not available with ithreads.)

       done    The "done" method returns true if the thread you're checking has finished, and
	       false otherwise.  (Not available with ithreads.)

LIMITATIONS
       The sequence number used to assign tids is a simple integer, and no checking is done to
       make sure the tid isn't currently in use.  If a program creates more than 2**32 - 1
       threads in a single run, threads may be assigned duplicate tids.  This limitation may be
       lifted in a future version of Perl.

SEE ALSO
       threads::shared (not available with 5005threads)

       attributes, Thread::Queue, Thread::Semaphore, Thread::Specific (not available with
       ithreads)

perl v5.8.0				    2002-06-01				      Thread(3pm)


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