COSC 4330                SECOND MIDTERM   NAME:_______________________
              
CLosed Book.   You can have one sheet of notes.

1.   For  each  of  the  statements below, indicate  in  one  sentence
     whether the statement is true or false (2 points), and why
     (3 points).
     
     (a)  Monitor conditions can only have positive values. 

     (b)  Most programmers like to  put all their signal operations at
          the end of their monitor procedures.

     (c)  Critical sections are consumable resources.

     (d)  Peterson's algorithm assumes the existence of shared 
	  variables.

     (e)  One cannot prevent deadlocks in client/server systems.

     (f)  One cannot initialize binary semaphores.

2.   Complete the following sentences: (4X×5 points)

     In some implementations of monitors the signal operation is
     replaced by a _______________________________ operation.

     In Java, a monitor procedure must start with the two keywords
     public and  ___________________________________.

     You should use streams rather than datagrams when you have to
     transmit ______________ quantities of data.

     The main disadvantage of atomic transactions is that they are

     ____________________________________________________________

3.   Consider the function

          double_trouble(int *pa, int *pb){
               (*pa) += 5; (*pb) += 5;
          } //double_trouble

     and assume the following calling sequence:

          int alpha = 10;
          double_trouble(&alpha, &alpha);

    What will be the value of alpha after the call assuming that:

    (a)  the call was a regular procedure call:  __________ (5 points)

    (b)  the call was a remote procedure call?   __________ (5 points)
     
4.  Write one short idempotent procedure in any reasonable
    approximation of C and explain in a single sentence why it is
    idempotent. (2×5 points)

5.  Fill the blanks in the following solution to the mutual exclusion
    problem.  (4X5 points)

    void enter_region(int *plock) {
       
            int private = ______;
       
            while(private == ______)
       
                 swap(__________, &private); // single instruction
       } // leave_region
       
       void leave_region(int *plock) {
       
            ____________ = 1;
       } // leave_region
       
6. Consider the following solution to the mutual exclusion  problem
   and explain when it fails and what will be the result of such failure.
   (2X×5 points:  I do not care about how you could fix it.)

       int must_wait; // process that must wait
       int enter[2] = {0, 0};
       
       void enter_region(int pid) {
            enter[pid] = 1;
            must_wait = pid;
            while (enter[1 - pid] || must_wait==pid);
            } // enter_region
       
       void leave_region(int pid){
            enter[pid] = 0;
       } // leave_region