Suppose we want to synchronize two concurrent processes P and Q using binary semaphores S and T. The code for the processes P and Q is shown below.

Process P:

while(1){
  W:
  Print '0';
  Print '0';
  X:
}

Process Q:

while(1){
  Y:
  Print '1';
  Print '1';
  Z:
}

Synchronization statements can be inserted only at points W, X, Y, and Z.

Which of the following will ensure that the output string never contains a substring of the form 01ⁿ0 or 10ⁿ1 where n is odd?

Consider Peterson’s algorithm for mutual exclusion between two concurrent processes i and j. The program executed by process is shown below.

 Repeat 
     flag[i]=true; 
     turn=j; 
     while (P) do no-op; 
     Enter critical section, perform actions, then 
     exit critical section 
     Flag[i]=false; 
     Perform other non-critical section actions. 
 Until false;

For the program to guarantee mutual exclusion, the predicate P in the while loop should be

Each process P_i,i=1.....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) in place of P(mutex). What is the largest number of processes that can be inside the critical section at any moment?

A solution to the Dining Philosophers Problem which avoids deadlock is