Multi-threading using Merge sort

Question

I am newly starting using Linux in Ubuntu and am trying to code a multi-threading merge sort but some kind of errors are showing on Windows terminal.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <pthread.h>
struct Params
{
    int *start;
    size_t len;
    int depth;
};
pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
void *merge_sort_thread(void *pv);
void merge(int *start, int *mid, int *end)
{
    int *res = malloc((end -start)*sizeof(*res));
    int *lhs = start, *rhs = mid, *dst = res;
    while (lhs != mid && rhs != end)*dst++ = (*lhs <= *rhs) ? *lhs++ : *rhs++;
    while (lhs != mid)*dst++ = *lhs++;
    while (rhs != end)*dst++ = *rhs++;
    memcpy(start, res, (end -start)*sizeof(*res));free(res);
}
void merge_sort_mt(int *start, size_t len, int depth)
{
    if (len < 2)return;
    if (depth <= 0 || len < 4)
    {
        merge_sort_mt(start, len/2, 0);
        merge_sort_mt(start+len/2, len-len/2, 0);
    }
    else{
        struct Params params = { start, len/2, depth/2 };
        pthread_t thrd;pthread_mutex_lock(&mtx);
        printf("Starting subthread...\n");
        pthread_mutex_unlock(&mtx);
        pthread_create(&thrd, NULL, merge_sort_thread, &params);
        merge_sort_mt(start+len/2, len-len/2, depth/2);
        pthread_join(thrd, NULL);
        pthread_mutex_lock(&mtx);
        printf("Finished subthread.\n");
        pthread_mutex_unlock(&mtx);
    }
    merge(start, start+len/2, start+len);
}
void *merge_sort_thread(void *pv)
{
    struct Params *params = pv;
    merge_sort_mt(params->start, params->len, params->depth);
    return pv;
}
void merge_sort(int *start, size_t len)
{
    merge_sort_mt(start, len, 4);
}
int main()
{
    static const unsigned int N = 2048;
    int *data = malloc(N * sizeof(*data));
    unsigned int i;
    srand((unsigned)time(0));
    for (i=0; i<N; ++i)
    {
        data[i] = rand() % 1024;
        printf("%4d ", data[i]);
        if ((i+1)%8 == 0)
            printf("\n");
    }
    printf("\n");
    merge_sort(data, N);
    for (i=0; i<N; ++i)
    {
        printf("%4d ", data[i]);
        if ((i+1)%8 == 0)
            printf("\n");
    }
    printf("\n");
    free(data);
    return 0;
}

Here, is the .c code of multithreadind but not complete the program due to errors. Here below, is the errors..

/tmp/ccTNp3Yz.o: In function `merge_sort_mt':
OS.c:(.text+0x213): undefined reference to `pthread_create'
OS.c:(.text+0x269): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status

If any library or any correction in code please tell and please add some important libraries which is usually used in terminal like sudo

Answer 1

As was stated at the comment above, you need to link your program with pthread library.

add -lpthread to your link command.