NAME

       Coro::SemaphoreSet - efficient set of counting semaphores

SYNOPSIS

        use Coro;

        $sig = new Coro::SemaphoreSet [initial value];

        $sig->down ("semaphoreid"); # wait for signal

        # ... some other "thread"

        $sig->up ("semaphoreid");

DESCRIPTION

       This module implements sets of counting semaphores (see Coro::Semaphore). It is nothing
       more than a hash with normal semaphores as members, but is more efficiently managed.

       This is useful if you want to allow parallel tasks to run in parallel but not on the same
       problem. Just use a SemaphoreSet and lock on the problem identifier.

       You don't have to load "Coro::SemaphoreSet" manually, it will be loaded automatically when
       you "use Coro" and call the "new" constructor.

       new [inital count]
           Creates a new semaphore set with the given initial lock count for each individual
           semaphore. See Coro::Semaphore.

       $semset->down ($id)
           Decrement the counter, therefore "locking" the named semaphore. This method waits
           until the semaphore is available if the counter is zero.

       $semset->up ($id)
           Unlock the semaphore again. If the semaphore reaches the default count for this set
           and has no waiters, the space allocated for it will be freed.

       $semset->try ($id)
           Try to "down" the semaphore. Returns true when this was possible, otherwise return
           false and leave the semaphore unchanged.

       $semset->count ($id)
           Return the current semaphore count for the specified semaphore.

       $semset->waiters ($id)
           Returns the number (in scalar context) or list (in list context) of waiters waiting on
           the specified semaphore.

       $semset->wait ($id)
           Same as Coro::Semaphore::wait on the specified semaphore.

       $guard = $semset->guard ($id)
           This method calls "down" and then creates a guard object. When the guard object is
           destroyed it automatically calls "up".

       $semaphore = $semset->sem ($id)
           This SemaphoreSet version is based on Coro::Semaphore's. This function creates (if
           necessary) the underlying Coro::Semaphore object and returns it. You may legally call
           any Coro::Semaphore method on it, but note that calling "$semset->up" can invalidate
           the returned semaphore.

AUTHOR

        Marc Lehmann <schmorp@schmorp.de>
        http://home.schmorp.de/