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\markright{\footnotesize CS 481 Operating Systems Principles, Fall 2000}

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\section*{Homework 2 --- due in class on Thursday 14 September}

Total number of points available on this homework is 110. Full credit
is equivalent to 100 points.


 1. (20 pts) If we wanted to use a file to communicate between
  two processes, what issues would the programmer need explicitly to
  address?  

 2. (20 pts) What are the states that a process can be in and what causes it
	to change state?

 3. (20 pts) With most operating systems, the PCB for a process is
	maintained in operating system memory, which can only be accessed and
	modified in kernel mode.  Suppose the PCB for a process was
	maintained in the address space of the process and could therefore be
	accessed and modified by the process itself.  What problems might this
	cause?

 4. (20 pts) Compare the performance of the following program when it is
	compiled with the \\
-DFAKESYSTEMCALLS=1 flag and when it is compiled with
	the -DFAKESYSTEMCALLS=0  flag.  How long does it take to execute in each case?  What causes the difference? 

\begin{verbatim}
#include <stdlib.h>

#if FAKESYSTEMCALLS
int getpid() { return 55; }
#else
#include <unistd.h>
#endif

int main ( ) {
  int a;
  int limit = 10000000;
  int i;
  for (i = 0; i < limit; i++ ) {
    a = getpid ();
  }
}
\end{verbatim}

 5. (20 pts) Write a program under Unix with the following
	characteristics.  A parent process
        creates two children.  The parent then waits for the 
	first child to complete, and kills the second when the first
	completes.  After that, the parent exits. 

 6. (10 pts) In Unix,  what is a zombie process?

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