Thread: pthread hanging

hi all
i am doing a gui application using pthread
if i do like this my application is not hanging.

Code:

      pthread_t thread;
      gint  iret1;
      iret1=pthread_create( &thread, NULL, write_data, NULL);

and if i do like this my application is hanging

Code:

      pthread_t thread;
      gint  iret1;
      iret1=pthread_create( &thread, NULL, write_data, NULL);
      pthread_join( thread, NULL );

and also what is the deference b/w
pthread_exit(NULL) and
pthread_exit(0);

but i need to join the thread.
can you help me

how can i solve this problem

thank you in advance