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The following program consists of 3 concurrent processes and 3 binary semaphores. The semaphores are initialized as S0 = 1, S1 = 0, S2 = 0. How many times will P0 print ‘0’? Process P0 while(true) { wait(S0); print '0'; release(S1); release(S2); } Process P1 wait(S1); release(S0); Process P2 wait(S2); release(S0);
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מיין לפי
Each process Pi, i = 0,1,2,3,……,9 is coded as follows. repeat P(mutex) {Critical Section} V(mutex) forever The code for P10 is identical except that it uses V(mutex) instead of P(mutex). What is the largest number of processes that can be inside the critical section at any moment (the mutex being initialized to 1)?
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Explanation: Any one of the 9 processes can get into critical section after executing P(mutex) which decrements the mutex value to 0. At this time P10 can enter critical section by incrementing the value to 1. Now any of the 9 processes can enter the critical section by again decrementing the mutex value to 0. None of the remaining processes can get into their critical sections.
מיין לפי
Two processes, P1 and P2, need to access a critical section of code. Consider the following synchronization construct used by the processes. Process P1 : while(true) { w1 = true; while(w2 == true); Critical section w1 = false; } Remainder Section Process P2 : while(true) { w2 = true; while(w1 == true); Critical section w2 = false; } Remainder Section Here, w1 and w2 have shared variables, which are initialized to false. Which one of the following statements is TRUE about the above construct?
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מיין לפי
What will happen if a non-recursive mutex is locked more than once?
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Explanation: If a thread which had already locked a mutex, tries to lock the mutex again, it will enter into the waiting list of that mutex, which results in a deadlock. It is because no other thread can unlock the mutex.
מיין לפי
At a particular time of computation the value of a counting semaphore is 7.Then 20 P operations and 15 V operations were completed on this semaphore. The resulting value of the semaphore is?
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Explanation: P represents Wait and V represents Signal. P operation will decrease the value by 1 every time and V operation will increase the value by 1 every time.
מיין לפי
The following pair of processes share a common variable X. Process A int Y; A1: Y = X*2; A2: X = Y; Process B int Z; B1: Z = X+1; B2: X = Z; X is set to 5 before either process begins execution. As usual, statements within a process are executed sequentially, but statements in process A may execute in any order with respect to statements in process B. How many different values of X are possible after both processes finish executing?
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A1 A2 B1 B2: X = 11
A1 B1 A2 B2: X = 6
A1 B1 B2 A2: X = 10
B1 A1 B2 A2: X = 10
B1 A1 A2 B2: X = 6
B1 B2 A1 A2: X = 12.
מיין לפי
The program follows to use a shared binary semaphore T. Process A int Y; A1: Y = X*2; A2: X = Y; signal(T); Process B int Z; B1: wait(T); B2: Z = X+1; X = Z; T is set to 0 before either process begins execution and, as before, X is set to 5. Now, how many different values of X are possible after both processes finish executing?
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Explanation: The semaphore T ensures that all the statements from A finish execution before B begins. So now there is only one way in which statements from A and B can be interleaved:
A1 A2 B1 B2: X = 11.
מיין לפי