Class 15: Homework

You must print this sheet out and write/type answers on it!
Consider the program collatz.c

    given below:
 1 #include <unistd.h>
 2 #include <stdio.h>
 3 #include <pthread.h>
 4 
 5 unsigned int volatile next = 2; // Ignore the "volatile" keyword here!
 6 int maxes[4] = {0,0,0,0}, N[4] = {0,0,0,0};
 7 
 8 int collatz(unsigned int n, int k) { return n == 1 ? k : collatz((n%2 ? 3*n+1 : n/2),k+1); }
 9 
10 void* checkerThread(void * p)
11 { 
12   int id = pthread_self();
13   while(1)
14   {
15     int mp = collatz(next,1);
16     if (mp > maxes[id]) { maxes[id] = mp; N[id] = next; }
17     ++next;
18   }
19 }
20 
21 int main()
22 {
23   pthread_t ltA, ltB;
24   pthread_create(&ltA,NULL,checkerThread,NULL);
25   pthread_create(&ltB,NULL,checkerThread,NULL);  
26   do {
27     sleep(1);
28     printf("next = %i: A -> %i,%i: B -> %i,%i\n",next,maxes[ltA],N[ltA],maxes[ltB],N[ltB]);
29   } while(next < 100000000);
30   return 0;
31 }

    
    

      
	How many threads total are there for this program?
	


	
      


      
	What are the "shared resources" for this program?
	


	
      


      
	What is the "critical section" for this program? (Give the
	line numbers!)
	


	
      


      
	Show how to rewrite checkerThread to reduce the
	time spent in the "critical section"?  Be sure to point out
	which lines in the new code actually constitute the critical section!