Computer Science 322
                              Quiz 6           Name__________________________-

1. When a new thread is created it begins execution at:

   a. The start of the main()      b. the line of code following the
      procedure in the program        call to create_thread()
      in which it was created.

   c. The start of the function
      specified in the call to
      create_thread().

2. Consider the following code segment:

   int a = 0;            |--->   for (c = 0; c < 100000; c++)
   void xthread(         |           a = a + 1;
   int x,                |
   int y)                |       }
   {                     |
      int c, d;  ---------

   Suppose two threads are created and both run the function xthread
   which of the following BEST characterizes the sharing of data.

   a. The variable 'a' is shared      b. 'a' and 'x' are shared but
      but both threads have private      'c' is private.
      copies of 'x' and 'c'.

   c. All five variables are shared   d. all five variables are private.
      (i.e. if either thread changes
      one of them, the change is seen
      by the other thread.

3. Suppose the above function is run concurrently as 4 separate
   threads.  After all threads complete the value of "a" will be:

   a. somewhat less than 400000       b. somewhat greater than 400000
      or possibly even equal to          or possibly even equal to
      400000                             400000

   c. exactly 100000                  d. exactly 400000

4. Describe how the following  approach to providing mutual exclusion
   works or fails to work:
   Both processes have a "Process using Critical Section" flag.
   Before entering, a process sets its own flag and then loops until
   the other processes flag is clear.

   a. Not safe.                  b. Could cause starvation (livelock).

   c. Could cause deadlock.      d. Causes strictly alternating access
                                    to critical section.
   e. Works correctly

5. In the unsafe version of the mutual exclusion algorithm the failure
   will occur:

   a. Every time a process is          b. Regardless of whether or not
      preempted while trying to           a process is preempted while
      enter the CS.                       trying to enter the CS.

   c. Only when a process has been
      preempted while trying to enter
      the CS.. but not necessarily
      every time this happens.