Thread - multithreading
my $t = new Thread \&start_sub, @start_args;
my $tid = Thread->self->tid;
my $tlist = Thread->list;
use Thread 'async';
use Thread 'eval';
Thread module provides multithreading support for perl.
newstarts a new thread of execution in the referenced subroutine. The optional list is passed as parameters to the subroutine. Execution continues in both the subroutine and the code after the
new Thread returns a thread object representing the newly created thread.
lockplaces a lock on a variable until the lock goes out of scope. If the variable is locked by another thread, the
lockcall will block until it's available.
lockis recursive, so multiple calls to
lockare safe--the variable will remain locked until the outermost lock on the variable goes out of scope.
Locks on variables only affect
lock calls--they do not affect normal access to a variable. (Locks on subs are different, and
covered in a bit) If you really, really want locks to block access, then go ahead and tie them to something and
manage this yourself. This is done on purpose. While managing access to
variables is a good thing, perl doesn't force you out of its living room...
If a container object, such as a hash or array, is locked, all the elements
of that container are not locked. For example, if a thread does a
@a, any other thread doing a
lock($a) 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 equvalent to
use attrs qw(locked) in the sub.
use attrs qw(locked)
serializes access to a subroutine, but allows different threads
lock &sub, on the other hand, will not allow
any other thread access for the duration of the lock.
lock will traverse up references exactly one level.
lock(\$a) is equivalent to
lock(\\$a) is not.
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-joined threads.
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_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_wait on the variable, the signal is discarded.
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.
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.
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.
the attrs manpage, Thread::Queue, Thread::Semaphore, Thread::Specific.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.