CS33211 "Operating Systems"

            HOMEWORK #2

        Due in class  11/02/2004

The numbers in parenthesis refer to exercises in "Operating System
Concepts" (OSC) textbook. 

Unless otherwise specified, each question is worth 3 points.


1. Modify the solution for barrier synchronization as follows. There
   are three processes and each process can depart from the barrier
   only when the other two are at the barrier.

2. Modify the solution to the semaphore-based producer/consumer problem
   to allow multiple producers and consumers. Note that you have
   to allow multiple producers as well as multiple consumers
   to proceed concurrently if possible. 

3. Solve OSC 7.8 using locks and condition variables

4. The locks and CVs solution to producer/consumer that we studied in
   class assumes an unbounded buffer. Provide a bounded buffer solution
   to producers/consumer problem using locks and CVs

5. Consider a system of processes P1,P2,...,PN. Each process has
   unique identifier 1 through N. The processes may concurrently
   access a certain file by invoking procedure READ_FILE(). The
   constraint is that the processes can read the file as long as
   the sum of the identifiers of the processes is less than a number
   S > N.

   Write a locks and CV-s based implementation of READ_FILE().

6. [each sub-question is worth 1 point]

   The below real-world problem require the application of one of the
   classic problems of concurrency that we studied. Identify
   the problem and explain your choice. Suggest (but do not supply)
   a solution out of the ones we studied.

       a) A scheduler function of the OS manipulates the ready-queue
          of PCBs. The scheduler can be run by any process in the
          system when this process is in kernel mode. However, only
          one process running the scheduler code is allowed to
          manipulate the ready-queue at a time.

       b) multiple processes iteratively process an array of elements
          Every process concurrently works on a single array elements,
	  however, the work depends on the result of the previous iteration
	  of all elements

       c) the network stack consists of TCP and IP layer programs.
          the TCP layer passes the messages to IP layer to send over
	  the network. The layers work concurrently and vary in speed.
	  To increase concurrency the messages are stored in an array.

       d) There are parallel processes competing for limited
          memory. The process memory requirements differ. Each process
          cannot proceed until its memory requirements are satisfied,
	  however, more than one process can proceed simultaneously
	  if their memory requirements are met.

       e) The files on the web-server are updated concurrently with the
          requests from the web to download the files. The update process
	  can update one file at a time and the downloads also
	  require one file at a time. Multiple downloads can overlap
	  but they cannot overlap with the file update. Multiple
	  file updates of the same file cannot overlap either.