CS 3733 Operating Systems, Fall 1998 Assignment 3 Comments

General Comments

If I have written a small circled number to refer to something on your assignment, it refers to the following:
  1. A lint warning that a system function is implicitly declared to return int means that the appropriate header file was not included.
  2. A lint warning that one of your functions is implicitly declared to return int means that you did not include a prototype of that function
  3. Do not hard code in the size of an int as 4.
  4. drand48 is a poor random number generator in that when the seeds are close the values generated will be related.
  5. When linting the rings, lint with myrandom.c also.

Part 1

How close is close? What do you expect the range of counts to be? One way to tell is to look at the standard deviation. Theoretically, the standard deviation should be sqrt(99/12) which is about 2.87.

Part 2

Running for the same number of processes on the same machine will usually produce the same order, but there is nothing that guarantees a particular order or that the order will always be the same.

The prompt appears when the original process terminates. If a process's parent terminates before the process gets its parent id, the parent id will be displayed as 1, the init process which inherits all processes whose parent no longer exists.

Part 3

All processes should generate the same random number since the initialization is done before the fork and so each process has a copy of the same initialization. The initialization should be before the start of the loop or it will be called several times, including after the first fork.

Part 4

Now the processes generate independent random numbers. You should get different results each time it is run. The order of the messages should reflect the order of the random numbers generated.

Part 5

Each process should print out the value corresponding to the pid of its original parent (usually one less than its pid) except for the first process which should print the pid of the last process. Because the print is after the write, it is possible for a process to print before its predecessor. Note that you are supposed to read and write integers as 4-byte quantities. Do not use fprintf and fscanf to send information around the ring. These send character strings.

Part 6

Since all processes are blocked on the read, no process will do any I/O after the fork.

Part 7

Now the processes will usually print out in order with the first process coming last. It is possible for the output to be different if a process loses the CPU between the read and the fprintf. Often, the first process will terminate when it does its second write to the ring if process 2 has already exited due to the SIGPIPE signal it receives.