Question

(b) Consider the following two programs. They both access a shared variable count and increment it. One is lock-based using spin-lock, and the other is lock-free. They both use C11 CAS(compare and swap) function and eventually get the sane result, ie., cunt 10.000.000. Please fill in the blanks to complete the lock-free version. Each blank contains at most one statement. (5 marks) lock-based #include 2 #include 3 | # include 5 int count 0; 6 int lock 0; 8 voidadding (void input) int expected0 for (int i-0; i

Answer 1

#include<stdio.h>
#include<stdatomic.h>
#include<pthread.h>

int count=0;

void * adding(void * input)
{
   int val;
   for(int i=0;i<3;i++)
   {
       do {
           val=count; //store count value in val variable...
       }while(!atomic_compare_exchange_weak(&val,&count,++val));   
   }
}

int main()
{
   pthread_t tid[10];
  
   for(int i=0;i<10;i++)
   {
       pthread_create (&tid[i],NULL,adding,NULL);
   }
   for(int i=0;i<1;i++)
   {
       pthread_join (tid[i],NULL);
   }
   printf("The value of count is %d\n",count);
}

//code explanation:
/*
if(*(&val)==*(&count))
{
   *(&count)=++val;
   return true;
}
else
{
   *(&val)=*(&count);
   return false;
}
*/