Can pwrite in C be used to write file in parallel?

Question

I am wondering when we are going to use pwrite to write a data to different locations with multiple threads. (I.e., Each thread writes a data to the single file but in different offset.)

Here is the sample code.

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>

char buf[50000000];

void *p_function(void * arg)
{
        int s,e;
        s = clock();
        int* arr = (int*)arg;
        int ret = pwrite(arr[0], buf, sizeof(buf), 100000000*arr[1]);
        e = clock();
        printf("Elapsed time : %d\n", e-s);
}

int main(void)
{
        for(int i = 0; i < 50000000; i++) {
                buf[i] = 5;
        }

        pthread_t pthread[3];
        int thr_id;
        int status;

        int fd = open("File", O_RDWR);

        int arg[3][2];

        int thread_num = 3;

        int s,e;
        s = clock();
        for(int i = 0; i < thread_num; i++) {
                arg[i][1] = i;
                arg[i][0] = fd;
            pthread_create(&pthread[i], NULL, p_function, (void*)arg[i]);
        }

        for(int i = 0; i < thread_num; i++) {
                pthread_join(pthread[i], (void **)&status);
        }
        e = clock();
        printf("Elapsed time : %d", e-s);

        return 0;
}

File
 ------------------------------------------------
|   Location 1   |   Location 2  |   Location 3  |
 ------------------------------------------------
     ㄴthread 1        ㄴthread 2      ㄴthread 3

With this code, I see there is no benefit of multithreading. (I expected that elapsed time is much faster than that of single thread, which is writing 150000000 bytes with one thread.)

Do I miss something?

Thank you in advance.