mergesort using 2 thread ID's - c

Question

hi i want to use mergesort to an array using threads i need to use two thread id in order to sort recursionly
here is my code
void Recursive_Divition(int a[], int l, int h,int Degree_of_parallelism,int count)//this function divdis recursivly the array
{//and sends it to merge sort
struct thread_data thread_data_array[Degree_of_parallelism];
int i, len=(h-l+1);
// Using insertion sort for small sized array
if (len==2*Degree_of_parallelism)//a stoping condition if the array size is equal to the degree of parallisim then send the array to be sortrd
{
pthread_t * thread = (pthread_t *)malloc(Degree_of_parallelism*sizeof(pthread_t ));//creating a pointer to thread array
thread_data_array[count].low=l;//the arguments for the merge sort
thread_data_array[count].high=h/2;
pthread_create(&thread[count],NULL,threaded_merge_sort,(void *) &thread_data_array[count]);//create a thread and send it to the function
count++;
thread_data_array[count].low=h/2+1;//the argument for the other thread
thread_data_array[count].high=h;
pthread_create(&thread[count],NULL,threaded_merge_sort,(void *) &thread_data_array[count]);
pthread_join(thread[count-1],NULL);
pthread_join(thread[count],NULL);
free(thread);
}
if(len>Degree_of_parallelism){
Recursive_Divition(a,l,l+len/2-1,Degree_of_parallelism,count);//for the first half
Recursive_Divition(a,l+len/2,h,Degree_of_parallelism,count);//for the secound half
merge(a, l, l+len/2-1, h);
}
}
and here is the threaded merge sort
void *threaded_merge_sort(void *param)
{
printf("Create a thread %u\n", (unsigned int)pthread_self());//this function calls the merge sort function
struct thread_data *my_data;
my_data = (struct thread_data *) param;
int l=my_data->low;
int h=my_data->high;
printf("low is : %d high is : %d\n",l,h);
mergeSort(array,l,h);
pthread_exit(NULL);
and i got the following output the problem appears to be in the index and i didn't know how to fix it
Amount of numbers that sort: 16
Degree of parallelism: 8
Array Before Sort: 1,5,6,33,77,12,90,87,0,10,34,2,741,453,19,132
Create a thread 3158492928
low is : 0 high is : 1
Create a thread 3150100224
low is : 2 high is : 3
Create a thread 3141707520
low is : 4 high is : 3
Create a thread 3133314816
low is : 4 high is : 7
Create a thread 3122734848
low is : 8 high is : 5
Create a thread 3114342144
low is : 6 high is : 11
Create a thread 3105949440
Create a thread 3097556736
low is : 8 high is : 15
low is : 12 high is : 7
Array After Sort: 1,5,6,10,19,33,12,34,0,2,77,87,90,132,453,741

Answer 1

The indexing problem is here:
thread_data_array[count].low=l;//the arguments for the merge sort
thread_data_array[count].high=h/2;
[...]
thread_data_array[count].low=h/2+1;//the argument for the other thread
thread_data_array[count].high=h;
That does not correctly split the (sub)array into halves unless l is 0. For example, if h is 16 then your array break is always at 8, even if that's less than l.
Instead, you appear to want
thread_data_array[count].low = l;
thread_data_array[count].high= (l + h) / 2;
and
thread_data_array[count].low = (l + h) / 2 + 1;
thread_data_array[count].high=h;
Also, I suspect you want an else before the second if in Recursive_Divition(), and you may also need to add final else block.