Thread(3perl) | Perl Programmers Reference Guide | Thread(3perl) |
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 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.
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.
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;
The "Thread" module provides multithreading support for Perl.
"Thread->new" returns a thread object representing the newly created thread.
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.
If there are no threads blocked in a "cond_wait" on the variable, the signal is discarded.
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".
The following were implemented with 5005threads, but are no longer available with ithreads.
Also, subroutines could be declared with the ":locked" attribute which would serialize access to the subroutine, but allowed different threads non-simultaneous access.
threads, threads::shared, Thread::Queue, Thread::Semaphore
2023-11-25 | perl v5.32.1 |