The P and V operations on counting semaphores, where s is a counting semaphore, are defined as follows: P(s) : s = s - 1; if (s < 0) then wait; V(s) : s = s + 1; if (s <= 0) then wakeup a process waiting on s; Assume that Pb and Vb the wait and signal operations on binary semaphores are provided. Two binary semaphores Xb and Yb are used to implement the semaphore operations P(s) and V(s) as follows: P(s) : Pb(Xb); s = s - 1; if (s < 0) { Vb(Xb) ; Pb(Yb) ; } else Vb(Xb); V(s) : Pb(Xb) ; s = s + 1; if (s <= 0) Vb(Yb) ; Vb(Xb) ; The initial values of Xb and Yb are respectively
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The P and V operations on counting semaphores, where s is a counting semaphore, are defined as follows: P(s) : s = s - 1; if (s < 0) then wait; V(s) : s = s + 1; if (s <= 0) then wakeup a process waiting on s; Assume that Pb and Vb the wait and signal operations on binary semaphores are provided. Two binary semaphores Xb and Yb are used to implement the semaphore operations P(s) and V(s) as follows: P(s) : Pb(Xb); s = s - 1; if (s < 0) { Vb(Xb) ; Pb(Yb) ; } else Vb(Xb); V(s) : Pb(Xb) ; s = s + 1; if (s <= 0) Vb(Yb) ; Vb(Xb) ; The initial values of Xb and Yb are respectively
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Both P(s) and V(s) operations are perform Pb(xb) as first step. If Xb is 0, then all processes executing these operations will be blocked. Therefore, Xb must be 1.
If Yb is 1, it may become possible that two processes can execute P(s) one after other (implying 2 processes in critical section). Consider the case when s = 1, y = 1. So Yb must be 0.
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* השאלה נוספה בתאריך: 20-07-2020