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Thread - manipulate threads in Perl |
Thread - manipulate threads in Perl (EXPERIMENTAL, subject to change)
none
The Thread extension requires Perl to be built in a particular way to enable the older 5.005 threading model. Just to confuse matters, there is an alternate threading model known as ``ithreads'' that does NOT support this extension. If you are using a binary distribution such as ActivePerl that is built with ithreads support, this extension CANNOT be used.
use Thread;
my $t = new Thread \&start_sub, @start_args;
$result = $t->join;
$result = $t->eval;
$t->detach;
if($t->equal($another_thread)) {
# ...
}
my $tid = Thread->self->tid;
my $tlist = Thread->list;
lock($scalar);
yield();
use Thread 'async';
WARNING: Threading is an experimental feature. Both the interface
and implementation are subject to change drastically. In fact, this
documentation describes the flavor of threads that was in version
5.005. Perl 5.6.0 and later have the beginnings of support for
interpreter threads, which (when finished) is expected to be
significantly different from what is described here. The information
contained here may therefore soon be obsolete. Use at your own risk!
The Thread module provides multithreading support for perl.
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.
new Thread returns a thread object representing the newly created
thread.
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($a[12]) won't block.
You may also lock a sub, using lock &sub. Any calls to that sub from
another thread will block until the lock is released. This behaviour is not
equivalent to declaring the sub with the locked attribute. The locked
attribute serializes access to a subroutine, but allows different threads
non-simultaneous access. lock &sub, on the other hand, will not allow
any other thread access for the duration of the lock.
Finally, lock will traverse up references exactly one level.
lock(\$a) is equivalent to lock($a), while lock(\\$a) is not.
async 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 new Thread, async returns a
thread object.
Thread->self function returns a thread object that represents
the thread making the Thread->self call.
Thread->list returns a list of thread objects for all running and
finished but un-joined threads.
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_waiting 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 function takes a locked variable as a parameter and
unblocks one thread that's cond_waiting 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 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 function allows another thread to take control of the
CPU. The exact results are implementation-dependent.
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 joined died, 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 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 $@.
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 tests whether two thread objects represent the same thread and
returns true if they do.
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.
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.
the attributes manpage, the Thread::Queue manpage, the Thread::Semaphore manpage, the Thread::Specific manpage.
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Thread - manipulate threads in Perl |