Cant pass different strings to multiple threads - multithreading

Question

I have a function that will generate multiple threads and i pass to them a different string every time, but it seems that the threads have the same string. The strings are coming from a socket. Here is the code:
pthread_t *MirrorManager;
MirrorManager = malloc(sizeof(pthread_t)*th_size);
if( MirrorManager == NULL ) { perror("malloc"); exit(1); }
/* -------------------------------------- */
int th_num = 0;
while( true )
{
received = 0;
/* Read the desired readable size */
if( read(newsock, &size, sizeof(size)) < 0 )
{ perror("Read"); exit(1); }
/* Read all data */
while( received < size )
{
if( (nread = read(newsock, buffer + received, size - received)) < 0 )
{ perror("Read"); exit(1); }
received += nread;
}
if( strcmp(buffer, "end") == 0 ) { break; }
printf("Received string: %s\n",buffer);
/* Create thread */
strcpy(th_str, buffer);
if( (err = pthread_create(&MirrorManager[th_num], NULL, thread_start, (void*) th_str)) == true )
{ show_error("pthread_create", err); }
/* Take next thread */
th_num++;
}
Here i generate two threads. The two threads have the same string, actually this string is the last string that will come out of the socket. Why this is happening and how can i prevent this? Please help i have stuck here for a few days now.

Answer 1

You should post the complete code.
Given what you have posted, it looks like your issue is that all of your threads share the same parameter th_str:
pthread_create(&MirrorManager[th_num], NULL, thread_start, (void*) th_str))
Instead you should be allocating a separate th_str for each thread, as you're passing a pointer to it for each thread, rather than the string itself.
th_str = malloc(strlen(buffer));
strcpy(th_str, buffer);
And then be sure to have each thread free the pointer that was passed into it.
PS: I'd strongly recommend using strncmp and strncpy on all data from your socket.