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';
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($a[12]) won't block.
You may also lock a sub, using lock &sub. Any calls to that sub from another thread will block until the lock is
released. This behaviour is not equvalent to use attrs qw(locked) in the sub. use attrs qw(locked)
serializes access to a subroutine, but allows different threads
non-simultaneous access. lock &sub, on the other hand, will not allow
any other thread access for the duration of the lock.
Finally, lock will traverse up references exactly one level.
lock(\$a) is equivalent to lock($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_wait.
cond_broadcast, though, will unblock all the threads that are blocked in a cond_wait on 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.
$@.
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 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.