Module mutex
Mutual exclusion -- for use with module sched
A mutex has two pieces of state -- a 'locked' bit and a queue. When
the mutex is not locked, the queue is empty. Otherwise, the queue
contains 0 or more (function, argument) pairs representing functions (or
methods) waiting to acquire the lock. When the mutex is unlocked while
the queue is not empty, the first queue entry is removed and its
function(argument) pair called, implying it now has the lock.
Of course, no multi-threading is implied -- hence the funny interface
for lock, where a function is called once the lock is aquired.
Imports:
deque