You shouldn't need the call to cond_signal(...) unless you are trying to deliberately meter the flow of your threads (a bad idea in most cases), or possible if you are going to need to re-access the same variable later at the same scope, Otherwise, and in most cases, you only need to let the lock go out of scope for the shared variable to become unlocked.

Also, you (probably) shouldn't be locking the whole array, just the element that you want to access.

sub run {
    my $self          = Foo->new(@_);
    my $id            = $self->{id};
    ...

    print "Hello from thread $id.\n";
    lock($aryItems[$id]);
    print "Item $aryItems[$id]\n";
    delete $aryItems[$id];

    # The lock is removed once when the function returns
    return 1; 
}
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There is a caveat of using delete, unlike with splice the array element is not removed, it is effectively just undefed.

It is difficult to be more specific without understanding more about what it is that your code is trying to achieve. I realise that you probably just exploring the possibilities at the moment, but there are different ways of using threads depending upon your ultimate goal.