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Higher Study | Operating Systems | Concurrency and Synchronization

What is the name of the technique in which the operating system of a computer executes several programs concurrently by switching back and forth between them?
Consider the methods used by processes P1 and P2 for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S1 and S2 are randomly assigned. Method used by PI Method used by P2 While (S1 == S2); Critical Section S1 = S2; While (S1 != S2); Critical Section S2 = not (S1);   Which one of the following statements describes the properties achieved?
A certain computation generates two arrays a and b such that a[i]=f(i) for 0 ≤ i < n and b[i] = g (a[i] ) for 0 ≤ i < n. Suppose this computation is decomposed into two concurrent processes X and Y such that X computes the array a and Y computes the array b. The processes employ two binary semaphores R and S, both initialized to zero. The array a is shared by the two processes. The structures of the processes are shown below. Process X: private i; for (i=0; i<n; i++) {      a[i] = f(i);      ExitX(R, S); } Process Y: private i; for (i=0; i<n; i++) {       EntryY(R, S);       b[i] = g(a[i]); } Which one of the following represents the CORRECT implementations of ExitX and EntryY?
A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?
Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P. CODE SECTION P wait (a); count=count+1 ; if (count==n) signal (b) ; signal (a) ; wait (b) ; signal (b) ; CODE SECTION Q What does the code achieve?
What problem is solved by Dijkstra banker’s algorithm?
Which of the following is not among the properties of child processes created by most of the Operating Systems? A. Computation speed­up B. Priority for critical functions C. Protecting parent processes from errors
Three concurrent processes X, Y, and Z execute three different code segments that access and update certain shared variables. Process X executes the P operation (i.e., wait) on semaphores a, b and c; process Y executes the P operation on semaphores b, c and d; process Z executes the P operation on semaphores c, d, and a before entering the respective code segments. After completing the execution of its code segment, each process invokes the V operation (i.e., signal) on its three semaphores. All semaphores are binary semaphores initialized to one. Which one of the following represents a deadlock-free order of invoking the P operations by the processes?
Which of the following is not an optimization criterion in the design of a CPU scheduling algorithm?
Which of the following is/are the common services provided by an operating system?
Which of the following is not related to synchronization in Operating System?
Processes P1 and P2 have a producer-consumer relationship, communicating by the use of a set of shared buffers. P1: repeat                 Obtain a full buffer                 Empty it                 Return an empty buffer forever P2 P2P2: repeat             Obtain a full buffer             Empty it             Return an empty buffer          forever Increasing the number of buffers is likely to do which of the following? I. Increase the rate at which requests are satisfied (throughput) II. Decrease the likelihood of deadlock III. Increase the ease of achieving a correct implementation 
The hardware implementation which provides mutual exclusion is
Consider the following policies for preventing deadlock in a system with mutually exclusive resources. I. Processes should acquire all their resources at the beginning of execution. If any resource is not available, all resources acquired so far are released II. The resources are numbered uniquely, and processes are allowed to request for resources only in increasing resource numbers III. The resources are numbered uniquely, and processes are allowed to request for resources only in decreasing resource numbers IV. The resources are numbered uniquely. A process is allowed to request only for a resource with resource number larger than its currently held resources Which of the above policies can be used for preventing deadlock?
Consider the following proposed solution for the critical section problem. There are n processes: P0…Pn – 1. In the code, function pmax returns an integer not smaller than any of its arguments. For all i, t[i] is initialized to zero. Code for Pi: do {                 c [i]=1; t[i] = pmax (t [0],…, t[n-1]) +1; c[i]=0;                 for every j ≠ I in {0,…,n-1} {                                 while (c[j]);                                 while (t[j] != 0 && t[j]<=t[i]) ;                 ]                 Critical section;                 t[i] =0;                 Remainder Section; } While (true); Which one of the following is TRUE about the above solution?
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