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

       threads - Perl extension allowing use of interpreter based threads from perl

	   use threads;

	   sub start_thread {
	       print "Thread started\n";

	   my $thread  = threads->create("start_thread","argument");
	   my $thread2 = $thread->create(sub { print "I am a thread"},"argument");
	   my $thread3 = async { foreach (@files) { ... } };


	   $thread = threads->self();
	   $thread = threads->object( $tid );




       Perl 5.6 introduced something called interpreter threads.  Interpreter threads are differ-
       ent from "5005threads" (the thread model of Perl 5.005) by creating a new perl interpreter
       per thread and not sharing any data or state between threads by default.

       Prior to perl 5.8 this has only been available to people embedding perl and for emulating
       fork() on windows.

       The threads API is loosely based on the old Thread.pm API. It is very important to note
       that variables are not shared between threads, all variables are per default thread local.
       To use shared variables one must use threads::shared.

       It is also important to note that you must enable threads by doing "use threads" as early
       as possible in the script itself and that it is not possible to enable threading inside an
       "eval """, "do", "require", or "use".  In particular, if you are intending to share vari-
       ables with threads::shared, you must "use threads" before you "use threads::shared" and
       "threads" will emit a warning if you do it the other way around.

       $thread = threads->create(function, LIST)
	   This will create a new thread with the entry point function and give it LIST as param-
	   eters.  It will return the corresponding threads object. The new() method is an alias
	   for create().

	   This will wait for the corresponding thread to join. When the thread finishes, join()
	   will return the return values of the entry point function. If the thread has been
	   detached, an error will be thrown.  If the program exits without all other threads
	   having been either joined or detached, then a warning will be issued. (A program exits
	   either because one of its threads explicitly calls exit(), or in the case of the main
	   thread, reaches the end of the main program file.)

	   Will make the thread unjoinable, and cause any eventual return value to be discarded.

	   This will return the thread object for the current thread.

	   This will return the id of the thread.  Thread IDs are integers, with the main thread
	   in a program being 0.  Currently Perl assigns a unique tid to every thread ever cre-
	   ated in your program, assigning the first thread to be created a tid of 1, and
	   increasing the tid by 1 for each new thread that's created.

	   NB the class method "threads->tid()" is a quick way to get the current thread id if
	   you don't have your thread object handy.

       threads->object( tid )
	   This will return the thread object for the thread associated with the specified tid.
	   Returns undef if there is no thread associated with the tid or no tid is specified or
	   the specified tid is undef.

	   This is a suggestion to the OS to let this thread yield CPU time to other threads.
	   What actually happens is highly dependent upon the underlying thread implementation.

	   You may do "use threads qw(yield)" then use just a bare "yield" in your code.

	   This will return a list of all non joined, non detached threads.

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

       A thread exited while %d other threads were still running
	   A thread (not necessarily the main thread) exited while there were still other threads
	   running.  Usually it's a good idea to first collect the return values of the created
	   threads by joining them, and only then exit from the main thread.

       The current implementation of threads has been an attempt to get a correct threading sys-
       tem working that could be built on, and optimized, in newer versions of perl.

       Currently the overhead of creating a thread is rather large, also the cost of returning
       values can be large. These are areas were there most likely will be work done to optimize
       what data that needs to be cloned.

       Parent-Child threads.
	   On some platforms it might not be possible to destroy "parent" threads while there are
	   still existing child "threads".

	   This will possibly be fixed in later versions of perl.

       tid is I32
	   The thread id is a 32 bit integer, it can potentially overflow.  This might be fixed
	   in a later version of perl.

       Returning objects
	   When you return an object the entire stash that the object is blessed as well.  This
	   will lead to a large memory usage.  The ideal situation would be to detect the origi-
	   nal stash if it existed.

       Creating threads inside BEGIN blocks
	   Creating threads inside BEGIN blocks (or during the compilation phase in general) does
	   not work.  (In Windows, trying to use fork() inside BEGIN blocks is an equally losing
	   proposition, since it has been implemented in very much the same way as threads.)

       PERL_OLD_SIGNALS are not threadsafe, will not be.
	   If your Perl has been built with PERL_OLD_SIGNALS (one has to explicitly add that sym-
	   bol to ccflags, see "perl -V"), signal handling is not threadsafe.

       Arthur Bergman <arthur at contiller.se>

       threads is released under the same license as Perl.

       Thanks to

       Richard Soderberg <rs at crystalflame.net> Helping me out tons, trying to find reasons for
       races and other weird bugs!

       Simon Cozens <simon at brecon.co.uk> Being there to answer zillions of annoying questions

       Rocco Caputo <troc at netrus.net>

       Vipul Ved Prakash <mail at vipul.net> Helping with debugging.

       please join perl-ithreads@perl.org for more information

       threads::shared, perlthrtut, <http://www.perl.com/pub/a/2002/06/11/threads.html>, perl-
       call, perlembed, perlguts

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