Homework 2

22C:116, Fall 1998

Due Wednesday Sept 9, 1998, in class

1. Why, in the example thread manager, was it necessary to have two distinct functions, thread_manager_init and thread_manager_start?

2. Inspect the thread data structure thread and the implementation of the thread_relinquish operation, and compare these to the suggested process table fields given in Figure 2-4 of the text and the context switching operation given in Figure 2-5 of the text. Explain the major differences!

3. Propose a set of data structures that would allow implementation of semaphores under the example thread manager; these should make maximal use of the types already declared in the source code for the thread manager.

4. Consider the following little UNIX program using parallel processes:

   main()
   {
      int i;
      i = 0;
      if (fork()) {
          int j;
          for (j = 0;j < 1000; j++) { i++; }
          wait();
      } else {
          int j;
          for (j = 0;j < 1000; j++) { i--; }
          exit();
      }
      printf( "%d\n", i );
   }
   

   What output did this program produce? Explain why the output is not zero!