mutex

lock.c

function lock(boolean *lock) { 
       while (test_and_set(lock) == 1); 
}

test_and_set.c

/* set the lock to true and send its previous value. lock=true means it is locked.
Notice that the test_and_lock always locks the lock (set lock == true) and returns the previous value before the locking*/
boolean_ref test_and_set(boolean_ref lock) {
    boolean initial = lock;
    lock = true;
    return initial;
}