COSC 4330                      QUIZ #2         Thursday, April 8, 1999

CLOSED BOOK.  You can have one sheet of notes. Each question is worth
20 points.

1.   Consider the function

               doubledouble(int *pa, int *pb){
               *pa = 2*(*pa); *pb = 2*(*pb);
          } //doubledouble

          and assume the following calling sequence:
 
          int alpha = 10;
          doubledouble(&alpha, &alpha)
     What will be the value of alpha after the call assuming:

     (a)  The call was a regular procedure call:  ____40_______

     (b)  The call was a remote procedure call?   ____20_______
          

2.   What is very wrong with the following monitor statement?

     condition notfull = 0;

     YOU CANNOT INITIALIZE MONITOR CONDITIONS AS THEY HAVE NO VALUE.
     
3.   What is very wrong with this piece of code?  You can assume that
     mutex is a mutual exclusion semaphore.  (Hint: you do not need to
     understand the problem to find the error.)

     producer() {
          struct xyz item;
          for(;;) {
               produce(&item);
               P(&mutex);
               if (nfreeslots == 0) continue; //buffer full
               put(item);
               V(&mutex);
          } // for
     } // producer */
     
     WHEN THE PRODUCER ENCOUNTERS A FULL BUFFER, IT DOES A BUSY
     WAIT *INSIDE* THE MONITOR< WHICH GUARANTEES A DEADLOCK.

4.   What is the major use of the UNIX semctl() system call?

     DESTROYING SEMAPHORE ARRAYS.

5.   How could you prevent deadlocks by denying the hold and wait
     condition in the dining philosophers problem?

     FORCING ALL PHILOSOPHERS TO GET EITHER BOTH LEFT OR RIGHT FORKS
     OR NEITHER OF THEM.

--IMPORTANT----IMPORTANT----IMPORTANT----IMPORTANT----IMPORTANT--
Please do not try to answer these questions by yourself BEFORE
having a clear idea of what's on the test for which you are
studying.

Materials covered in each test DO VARY from semester to semester
because the pace of the course can change, some materials are be
added and other deleted almost every semester.
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