Consider the following program:
Boolean blocked [2];
Int turn;
Void P (int id)
{
While (true) {
Blocked [id] = true;
While (turn! = id) {
While (blocked [1-id])
/* do nothing */;
Turn = id;
}
/* critical section */
Blocked [id] = false;
/* remainder */
}
}
Void main ()
{
Blocked [0] = false;
Blocked [1] = false;
Turn = 0;
Par begin (P (0), P (1));
}
This software solution to the mutual exclusion problem for two processes is proposed in [HYMA66]. Find a counterexample that demonstrates that this solution is incorrect. It is interesting to note that even the Communications of the ACM was fooled on this one