CS 3733 Operating Systems, Spring 2008 Exam 2 Comments

Grade distribution:

• 90-99: 1
• 80-89: 3
• 70-79: 3
• 60-69: 6
• 50-59: 2
• below 50: 4
• Average: 63

• Problem 1: Part b: Both processes are on the same machine so the child can write a raw double value (sizeof(double) bytes) to the pipe and the parent can read that number of bytes. You need to make sure the correct number of bytes have been read.
  Part c is already handled in Part b. When a process reads from a pipe, the process blocks while the pipe is empty.
• Problem 2: The problem does not say anything about B making a request to A for the value. The two processes need to decide on a protocol for sending the value since if sent raw, the byte ordering may be different as well as the floating point format or even the number of bytes.
• Problem 3b: You cannot use a mutex lock to wait until the value is ready unless the created thread locks the mutex during the entire calculation process. Even so, you would need to make sure the created thread locked the mutex before the original thread tried to get at x. You need to use a semaphore (or condition variable) here. You cannot send a signal to a thread, you send it to a process. You do not know how to make sure that a particular thread will receive the value (although it can be done).
• Problem 4b: Read the problems carefully and answer the questions that are asked. This is about the process signal mask, not about any data structures the program has defined.
• Problem 5c: Semaphores can be used to do things other than protecting critical sections. See part d) for an example. This question does not ask about how semaphores are used.
• Problems 6a and 6b: These are general questions, not related to a particular implementation such as paging or partitions.
• Problem 6c: This is specifically about partitions.