Thread - multithreading
use Thread; my $t = new Thread \&start_sub, @start_args; $t->join; my $tid = Thread->self->tid; my $tlist = Thread->list; lock($scalar); use Thread 'async'; use Thread 'eval';
Thread module provides multithreading support for perl.
- new \&start_sub
- new \&start_sub, LIST
newstarts 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 Threadreturns a thread object representing the newly created thread.
- lock VARIABLE
lockplaces a lock on a variable until the lock goes out of scope. If the variable is locked by another thread, the
lockcall will block until it's available.
lockis recursive, so multiple calls to
lockare safe--the variable will remain locked until the outermost lock on the variable goes out of scope.
Locks on variables only affect
lockcalls--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
You may also
locka sub, using
lock &sub. Any calls to that sub from another thread will block until the lock is released. This behaviour is not equvalent to
use attrs qw(locked)in the sub.
use attrs qw(locked)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.
lockwill traverse up references exactly one level.
lock(\$a)is equivalent to
- async BLOCK;
asynccreates 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
asyncreturns a thread object.
Thread->selffunction returns a thread object that represents the thread making the
Thread->listreturns a list of thread objects for all running and finished but un-
- cond_wait VARIABLE
cond_waitfunction takes a locked variable as a parameter, unlocks the variable, and blocks until another thread does a
cond_broadcastfor that same locked variable. The variable that
cond_waitblocked on is relocked after the
cond_waitis 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_waitfor synchronization, give up the lock as soon as possible)
- cond_signal VARIABLE
cond_signalfunction 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_waiton that variable, only one (and which one is indeterminate) will be unblocked.
If there are no threads blocked in a
cond_waiton the variable, the signal is discarded.
- cond_broadcast VARIABLE
cond_broadcastfunction works similarly to
cond_broadcast, though, will unblock all the threads that are blocked in a
cond_waiton the locked variable, rather than only one.
joinwaits for a thread to end and returns any values the thread exited with.
joinwill block until the thread has ended, though it won't block if the thread has already terminated.
If the thread being
died, the error it died with will be returned at this time. If you don't want the thread performing the
jointo die as well, you should either wrap the
evalor use the
evalthread method instead of
evalmethod wraps an
join, and so waits for a thread to exit, passing along any values the thread might have returned. Errors, of course, get placed into
tidmethod 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.
1 POD Error
The following errors were encountered while parsing the POD:
- Around line 155:
You forgot a '=back' before '=head1'