40

在创建我需要的实际应用程序之前，我试图对此有一个基本的了解。我最近从 2.7 转到 3.3。

从 python 文档直接复制粘贴此代码失败，这里的一个稍微简单的示例也是如此。

这是我的代码，源自第二个示例：

import concurrent.futures

nums = [1,2,3,4,5,6,7,8,9,10]

def f(x):
    return x * x

# Make sure the map and function are working
print([val for val in map(f, nums)])

# Test to make sure concurrent map is working
with concurrent.futures.ProcessPoolExecutor() as executor:
    for item in executor.map(f, nums):
        print(item)

这是输出：

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
Traceback (most recent call last):
  File "<string>", line 420, in run_nodebug
  File "<module1>", line 13, in <module>
  File "C:\Python33\lib\concurrent\futures\_base.py", line 546, in result_iterator
    yield future.result()
  File "C:\Python33\lib\concurrent\futures\_base.py", line 399, in result
    return self.__get_result()
  File "C:\Python33\lib\concurrent\futures\_base.py", line 351, in __get_result
    raise self._exception
concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending.

我怎样才能让这个代码按预期工作？我希望这些例子能开箱即用。

4

2 回答 2

50

这是我的错，有两个原因：

  1. 代码是无人看守的，即没有if __name__
  2. 看起来奇怪的 Traceback 是因为文件没有保存。以前从未给我造成过问题，但在这种情况下确实如此。

更正这两个修复了错误。

最终测试代码：

import concurrent.futures

nums = [1,2,3,4,5,6,7,8,9,10]

def f(x):
    return x * x
def main():
    # Make sure the map and function are working
    print([val for val in map(f, nums)])

    # Test to make sure concurrent map is working
    with concurrent.futures.ProcessPoolExecutor() as executor:
        print([val for val in executor.map(f, nums)])

if __name__ == '__main__':
    main()

输出，如预期：

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
于 2013-04-10T06:42:12.663 回答
25

在 Windows 下，当使用 processpoolexecutor 或任何其他生成新进程的并行代码时，保护代码的主循环以避免递归生成子进程非常重要。

基本上，所有创建新进程的代码都必须在 下if __name__ == '__main__':，出于同样的原因，您不能在解释器中执行它。

于 2017-07-25T11:57:35.237 回答