Thread join 有点困惑

import logging
import threading
import time

def thread_function(name):
    logging.info("Thread %s: starting", name)
    time.sleep(name)
    logging.info("Thread %s: finishing", name)

if __name__ == "__main__":
    format = "%(asctime)s: %(message)s"
    logging.basicConfig(format=format, level=logging.INFO,
                        datefmt="%H:%M:%S")

    logging.info("Main    : before creating thread")
    t1 = threading.Thread(target=thread_function, args=(1,))
    t5 = threading.Thread(target=thread_function, args=(5,))
    logging.info("Main    : before running thread")
    t1.start()
    t5.start()
    logging.info("Main    : wait for the thread to finish")
    t5.join()
    print('between 5 & 1')
    t1.join()
    logging.info("Main    : all done")

14:44:51: Main    : before creating thread
14:44:51: Main    : before running thread
14:44:51: Thread 1: starting
14:44:51: Thread 5: starting
14:44:51: Main    : wait for the thread to finish
14:44:52: Thread 1: finishing
14:44:56: Thread 5: finishing
between 5 & 1
14:44:56: Main    : all done

显然 t1 比 t5 先结束，t5.join()只能 block main thread，那 t1.join()还有任何意义吗？会不会出现 thread 在 join 之前就结束的情况？

timeline

main -----------------------*
t1    |---*
t5    |---------------------*