Stop a the optimistic GC thread

def gc_stop():
    """
    Stop a the optimistic GC thread
    """
    global gc_thread
    
    if gc_thread:
        log.info("Shutting down GC thread")
        gc_thread.signal_stop()
        gc_thread.join()
        log.info("GC thread joined")
        gc_thread = None
    else:
        log.info("GC thread already joined")