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项目中需要使用定时器，每次都使用构造器函数调用：

timer = threading.Timer(timerFlag, upload_position)
timer.start()   

打印线程后发现，每次都会创建一个新的子线程，虽然活跃的线程只有一个，但是也是种资源浪费：

print("threading active = {} \n   \n".format(threading.enumerate()))

#打印
threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145498161152)>]
threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145498161152)>]
threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145498161152)>]

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-2, started 123145503416320)>]
threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-2, started 123145503416320)>]

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-3, started 123145498161152)>]
threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-3, started 123145498161152)>]

阅读源码和文档

class Timer(Thread):
    """Call a function after a specified number of seconds:

            t = Timer(30.0, f, args=None, kwargs=None)
            t.start()
            t.cancel()     # stop the timer's action if it's still waiting

    """

    def __init__(self, interval, function, args=None, kwargs=None):
        Thread.__init__(self)
        self.interval = interval
        self.function = function
        self.args = args if args is not None else []
        self.kwargs = kwargs if kwargs is not None else {}
        self.finished = Event()

    def cancel(self):
        """Stop the timer if it hasn't finished yet."""
        self.finished.set()

    def run(self):
        self.finished.wait(self.interval)
        if not self.finished.is_set():
            self.function(*self.args, **self.kwargs)
        self.finished.set()

# Special thread class to represent the main thread
# This is garbage collected through an exit handler

发现，其实Timer是threading的子类，用wait实现了定时效果，绑定了入参function，于是修改代码如下

def startTimer():
    global timer
    if timer != None:
        timer.finished.wait(timerFlag)
        timer.function()   
    else:
        timer = threading.Timer(timerFlag, upload_position)
        timer.start()

打印结果：

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]



threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]


threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]

threading active = [<_MainThread(MainThread, stopped 140735596835712)>, <Timer(Thread-1, started 123145516048384)>]

始终只有一个线程且重复调用函数方法~End~