How to write program to run Only one executable in Unix

The following program to make sure that we are running only one instance of a program in Unix :-) 

The concept is based on the named key Creation when creating any IPC mechanism. 

int main()
{   
    sem_t *mysem;
    mysem = sem_open("MyUniqueName", O_CREAT|O_EXCL);
    if ( mysem == NULL )
    {      
        fprintf(stderr, "I am already running!\n");
        exit(1);
    }  
 
    /* the app code here*/    

    /* end of the app */   

    sem_unlink("MyUniqueName"); 
    sem_close(mysem);
}