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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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")