## sắp xếp trộn song song

-mình chưa hiểu rõ về phần mergesort trong đoạn code sau bạn nào có thể giải thích giúp mình với
Code:
```#include <stdio.h>
#include <stdlib.h>

/*
NOTE:
The mergesort boils downs to this..
Given two sorted array's how do we merge this?
We need a new array to hold the result of merging
otherwise it is not possible to do it using array,
so we may need a linked list
*/

int a[] = {10, 8, 5, 2, 3, 6, 7, 1, 4, 9};

typedef struct node {
int i;
int j;
} NODE;

void merge(int i, int j)
{
int mid = (i+j)/2;
int ai = i;
int bi = mid+1;

int newa[j-i+1], newai = 0;

while(ai <= mid && bi <= j) {
if (a[ai] > a[bi])
newa[newai++] = a[bi++];
else
newa[newai++] = a[ai++];
}

while(ai <= mid) {
newa[newai++] = a[ai++];
}

while(bi <= j) {
newa[newai++] = a[bi++];
}

for (ai = 0; ai < (j-i+1) ; ai++)
a[i+ai] = newa[ai];

}

void * mergesort(void *a)
{
NODE *p = (NODE *)a;
NODE n1, n2;
int mid = (p->i+p->j)/2;
int ret;

n1.i = p->i;
n1.j = mid;

n2.i = mid+1;
n2.j = p->j;

if (p->i >= p->j) return;

ret = pthread_create(&tid1, NULL, mergesort, &n1);
if (ret) {
printf("%d %s - unable to create thread - ret - %d\n", __LINE__, __FUNCTION__, ret);
exit(1);
}

ret = pthread_create(&tid2, NULL, mergesort, &n2);
if (ret) {
printf("%d %s - unable to create thread - ret - %d\n", __LINE__, __FUNCTION__, ret);
exit(1);
}

merge(p->i, p->j);
}

int main()
{
int i;
NODE m;
m.i = 0;
m.j = 9;

int ret;

if (ret) {
printf("%d %s - unable to create thread - ret - %d\n", __LINE__, __FUNCTION__, ret);
exit(1);
}