Instead of adding a lock_frame to the list when mp_dispatch_lock() is
called, just set a simple flag. This uses the fact that the lock is not
recursive, and can happen once per mp_dispatch_queue_process(). It
avoids the dynamic allocation, and makes error checking slightly
stricter.
Again, this is actually redundant and exists only for error-checking.
It'd actually need only a counter, because the actual locking is done by
"parking" the target thread in mp_dispatch_queue_process() and then
setting queue->idling=false. Only when mp_dispatch_unlock() sets it to
true again other work can proceed again. Document this too.
wm4
6cd80e972e