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

#define AS 100000
#define DT 1000
struct shared
{
  int * A;
  int * sum;
  pthread_mutex_t * pmutex;
};
/*
void boring(void * S)
{ struct shared * dat;
  int i;  int ax;  int j;
  ax = 0;
  dat = (struct shared *) S;
  for(i=0;i<AS;i++)
   { ax = ax + dat->A[i]; 
     for(j=0;j<DT;j++) {ax--; ax++;} // dummy delay loop    
   }
  dat->sum = ax;
}
*/

void * fsum(void * S)
{ struct shared * dat;
  int i;  int j, ax;   ax = 0;
  dat = (struct shared *) S;
  for(i=0;i<AS/2;i++)
   {
     pthread_mutex_lock(dat->pmutex);
       *(dat->sum) += dat->A[i]; 
     pthread_mutex_unlock(dat->pmutex);     
       for(j=0;j<DT;j++) {ax--; ax++;} // dummy delay

   }
}//fsum

void * bsum(void * S)
{ 
 struct shared * dat;
 int i;  int j, ax;   ax = 0;
  dat = (struct shared *) S;
  for(i=AS-1;i>=AS/2;i--)
   { 
     pthread_mutex_lock(dat->pmutex);
       *(dat->sum) +=  dat->A[i]; 
     pthread_mutex_unlock(dat->pmutex);
       for(j=0;j<DT;j++) {ax--; ax++;} // dummy delay
   }
}//bsum

int main()
{ 
  struct shared S1;  struct shared S2;
  pthread_t tid1, tid2;
  pthread_mutex_t mutex;
  int* sum1, *sum2;  int i;  
  int ssum;  // shared sumation variable
  int A[AS];
  for(i=0;i<AS;i++) A[i] = i;
  
  pthread_mutex_init(&mutex,NULL);
  ssum = 0;
  S1.A = A;   S2.A = A;
  S1.sum = &ssum;  S2.sum = &ssum;
  S1.pmutex = &mutex; S2.pmutex = &mutex; 

  pthread_create(&tid1,NULL,fsum,&S1);
  pthread_create(&tid2,NULL,bsum,&S2);

  pthread_join(tid1,NULL);
  pthread_join(tid2,NULL);
  i = ssum;

  /*
  boring(&S1);
  i = S1.sum;
  */
  printf("sum == %d\n",i);
  exit(0);
}