C - Singleton Pattern Implementation with double-checked locking

as you know the singleton pattern ensures a class has only one instance, and provides a global point of access to it.

We are going to implement getInstance method respect to the double checked locking using with C programming language (POSIX library) in to the given template code below. Also, we should use semaphore.

Here is my code

#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#define NO_OF_THREADS 10

struct Singleton {
   char *Data;  
};


struct Singleton *singletonObjectPointer;


int addresses[NO_OF_THREADS];
sem_t sem;

void *runner(void *params); /* the thread */
struct Singleton *getInstance();

int main()
{
    int i;
    sem_init(&sem,0,1);
    pthread_t threadIds[NO_OF_THREADS];


    for (i=0; i < NO_OF_THREADS; i++){
        pthread_create(&threadIds[i], NULL, &runner, (void *)(i));
    } 

    /* Wait until all threads are done */
    for (i=0; i < NO_OF_THREADS; i++){
        pthread_join(threadIds[i], NULL);
    } 

    /* Control addresses. All of them should be same */
    int prevAddr=addresses[0];
    for (i=1; i < NO_OF_THREADS; i++){
        if(addresses[i]!=prevAddr){
            printf("Object is created more than once\n");
            return -1;
        }
        prevAddr=addresses[i];
    }
    for (i=0; i < NO_OF_THREADS; i++){
        printf("Singleton Addresses for each thread %x\n",addresses[i]);
    }
    printf("Successful\n");
    return 1;
}

/**
 * The thread will begin control in this function
 */
void *runner(void *params) 
{
    int i = (int)params;
    printf("Thread %d\n",i);
    struct Singleton *s = getInstance();
    addresses[i]=s;
    pthread_exit(0);
}

//Fill this method
struct Singleton *getInstance(){

        singletonObjectPointer = (struct Singleton *)malloc(sizeof(struct Singleton));
        printf("---Address of singletonObjectPointer is %x\n",singletonObjectPointer);
        singletonObjectPointer->Data="This is object data"; 

    return singletonObjectPointer;
}