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Thread(3perl) | Perl Programmers Reference Guide | Thread(3perl) |
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.
- lock VARIABLE
- "lock" places a lock on a variable until the lock
goes out of scope.
- 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 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.
- 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.
- 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.
- 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, threads::shared, Thread::Queue, Thread::Semaphore2010-12-30 | perl v5.14.2 |