thread_merge_sort.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <time.h>
int* a;
int* b; //sorted array
int n;
void reader(char* filename){
	FILE* f = fopen(filename,"r");
	fscanf(f,"%d",&n);
	a = (int*) malloc(sizeof(int)*n);
	int i;
	for (i = 0; i < n; ++i)
		fscanf(f,"%d",&a[i]);
	fclose(f);
}

void print(int* a){
	int i;
	for (i = 0; i < n; ++i)
		printf("%d ",a[i]);
	printf("\n");
}

void writer(char* filename){
	FILE* f = fopen(filename,"w");
	fprintf(f,"sorted array of size %d :\n",n);
	int i;
	for (i = 0; i < n; ++i)
		fprintf(f,"%d ",b[i]);
	fprintf(f,"\n");
	fclose(f);
}

struct index{int p,r;};

void* merge_sort(void* param){
	struct index* pr = (struct index*) param;
	int p = pr->p,  r = pr->r , ret1,ret2;
	if (p==r)
		pthread_exit(0);

	pthread_t thread1,thread2;
	struct index pr1,pr2;
	int q = (p+r)/2;
	pr1.p = p;    pr1.r = q;
	pr2.p = q+1;  pr2.r = r;

	ret1 = pthread_create(&thread1,NULL,merge_sort,(void*) &pr1);
	if (ret1>0)
		printf("failed to create new thread 1\n");

	ret2 = pthread_create(&thread2,NULL,merge_sort,(void*) &pr2);
	if (ret2>0)
		printf("failed to create new thread 2\n");

	pthread_join(thread1,NULL);
	pthread_join(thread2,NULL);

	int k = p ,i = p ,j = q+1;

	while (i<=q && j<=r){
		if (a[i] < a[j])
			b[k++] = a[i++];
		else
			b[k++] = a[j++];
	}
	for (; i<=q ; i++)
		b[k++] = a[i];
	for (; j<=r ; j++)
		b[k++] = a[j];

	for (i= p ; i <= r ;i++)
		a[i] = b[i];

	pthread_exit(0);
	return NULL;
}

void printingFunc(int len)
{
 
    printf("\nSorted Array:\n");
    for(int i=0;i<len;i++)
    {
        printf("%d ",a[i]);
    }
    printf("\n");

    
    return;
}

void scan_function(int len)
{
 
    printf("Enter the elements\n");
    for(int i=0;i<len;i++)
    {
        scanf("%d",&a[i]);
    }

}

int main(void) {
	//reader("input.txt");
	int length;
	printf("Enter the number of elements \n");
	scanf("%d",&length); 
	scan_function(length);

	b = (int*)malloc(sizeof(int)*n);
	struct index start;
	start.p = 0;    start.r = n-1;
	pthread_t start_thread;

	struct timeval tv;
	gettimeofday(&tv,NULL);
	long long t1 = tv.tv_usec;

	pthread_create(&start_thread,NULL,merge_sort,&start);
	pthread_join(start_thread,NULL);

	gettimeofday(&tv,NULL);
	long long t2 = tv.tv_usec;

	//print(a);
	printingFunc(length);
	return 0;
}