求助 Python 多线程下的一个诡异问题,求解惑(20 行代码) - V2EX
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JL1990
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求助 Python 多线程下的一个诡异问题,求解惑(20 行代码)

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  •   JL1990 Feb 25, 2020 1857 views
    This topic created in 2257 days ago, the information mentioned may be changed or developed.
    from concurrent.futures import ThreadPoolExecutor insert_executor = ThreadPoolExecutor(max_workers=20) _TOTAL_TEST_DATA_NUMBERS = 5000000 _INSERT_DATA_BLOCK_SIZE = 500 def data_generator(): ret_data = [] for i in range(1, _TOTAL_TEST_DATA_NUMBERS + 1): data = {"id": i} ret_data.append(data) if len(ret_data) >= _INSERT_DATA_BLOCK_SIZE: yield ret_data ret_data.clear() yield ret_data def data_process(data): value = max(data, key=lambda item: item["id"]) print("max id {}".format(value["id"])) if __name__ == '__main__': dg = data_generator() for d in dg: insert_executor.submit(data_process, d) 

    data_generator,生成一个大小是 500 的数组,最大 id 是 5000000,理论上每次生成的最大 id 是能被 500 整除的。

    实际上,data_process 打印出来的 id,总是会出现类似 4855854 这样的不规则数字,和 data_generator 函数生成的数据理论上不一致,请问是什么原因?有大哥指导一下吗?

    4 replies    2020-02-25 17:11:39 +08:00
    ccpp132
        1
    ccpp132  
       Feb 25, 2020   1
    ret_data.clear() 改成 ret_data = []
    理解一下引用
    JL1990
        2
    JL1990  
    OP
       Feb 25, 2020
    @ccpp132 #1 大哥,你说的好像是对的,不过这里只有一个 ret_data,怎么又和引用扯上关系了呢?
    sessionreckon
        3
    sessionreckon  
       Feb 25, 2020
    @JL1990
    线程池里还没有算完 max,对应的 ret_data 已经被修改了
    所以有问题,你不用线程池,或者 new 一个新的 list 都可以解决问题
    再说了,一个计算密集型的 max 计算用什么线程池
    JL1990
        4
    JL1990  
    OP
       Feb 25, 2020
    @sessionreckon #3 感谢,明白原因了。
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