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Que. The following two functions P1 and P2 that share a variable B with an initial value of 2 execute concurrently.

P1()
{
C = B – 1;
B = 2*C;
}

P2()
{
D = 2 * B;
B = D - 1;
}

The number of distinct values that B can possibly take after the execution is
a. 3
b. 2
c. 5
d. 4
Answer:3
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void barrier (void) {
1: P(S);
2: process_arrived++;
3. V(S);
4: while (process_arrived !=3);
5: P(S);
6: process_left++;
7: if (process_left==3) {
8: process_arrived = 0;
9: process_left = 0;
10: }
11: V(S);
}

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P1 :
While true do {
L1 : ................
L2 : ................
X = X + 1;
Y = Y - 1;
V(SX);
V(SY);
}

P2 :
While true do {
L3 : ................
L4 : ................
Y = Y + 1;
X = Y - 1;
V(SY);
V(SX);
}

In order to avoid deadlock, the correct operators at L1, L2, L3 and L4 are respectively
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