(Silberschatz et al, 6/e, Sec. 7.7)
Each philosopher must observe the protocol to eat:
dp.pickup(i);
// eat
dp.putdown(i);
But it impossible to enforce the protocol. (Limitation of monitors)
The book solution (Fig. 7.22) guarantees deadlock-free, since only one process is allowed active in the monitor, and a philosopher picks up chopsticks only when both are available.
The solution, however, is not starvation-free.
Let’s […]
(Silberschatz et al, 6/e, p. 220)
There are three design option for signaling process P and waiting process Q.
(Hoare)
P: waits until Q either a) leaves monitor (line 4), or b) waits for another condition (line 3).
(easier to prove)
(Brinch-Hansen)
Q: waits until P either a) leaves monitor (line 4), or b) waits for another condition (line 3).
(more reasonable, […]
(Silberschatz et al., 6/e, p. 214)
region v when B do S; // S: critical section
Each such conditional critical region (or critical region) statement is mapped to the following code.
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wait(mutex);
while (!B) {
first_count++;
if (second_count > 0) signal(second_delay);
else signal(mutex);
wait(first_delay);
first_count–;
second_count++;
if (first_count > 0) signal(first_delay);
else signal(second_delay);
wait(second_delay);
second_count–;
}
S; // critical section accessing V
if (first_count > 0) signal(first_delay);
else if (second_count > 0) signal(second_delay);
else signal(mutex);
first_delay: queues processes that fail evaluation of B
second_delay: […]