CS 439: HW 3

Due: 7:45 AM. Fr. Sep. 21

Turn-in Instructions

1. When executing system or library calls from multi-threaded code, it is important to know which calls are re-entrant and which are not.
   1. What is the meaning of re-entrant?
   2. How does a re-entrant call behave differently from a call that is not re-entrant?
   3. Why is this an important consideration for multi-threaded code?
      
   4. What's the difference between a thread-safe implementation and one that's re-entrant?
2. For the program given below, do the following twice
   Once without optimization level (No -O flag)
   Again using optimization level -O3
    
   1. Compile the program to assembler source (gcc -S)
   2. Copy/paste the assembler listing for the code in main
   3. Analyze the assembler code and determine whether or not it will load/store x each time through the loop (or not.)
      Show your answer.

   // volatile
   int x=0;
   
   int main() {
     while (x==0) {}
     return 0;
   }

3. Repeat #2, but this time, uncomment the line:
   //volatile
4. For each of these architectures:
   • X86-64
   • PowerPC
   1. List all their atomic instructions.
   2. List all their memory barrier instructions.
   3. Give an example of how to use one atomic instruction.