在 Python 中使用 multiprocessing.Array 时出现 OSError (Errno 9)

Question

我正在尝试在 Python 3.7.4 (macOS 10.14.6) 的两个独立进程中使用multiprocessing.Array 。 我首先使用spawn上下文创建一个新进程，并将一个Array对象作为参数传递给它：

import multiprocessing, time, ctypes


def fn(c):
    time.sleep(1)
    print("value:", c.value)


def main():
    ctx = multiprocessing.get_context("spawn")
    arr = multiprocessing.Array(ctypes.c_char, 32)

    p = ctx.Process(target=fn, args=(arr,))
    p.start()

    arr.value = b"hello"
    p.join()


if __name__ == "__main__":
    main()

但是，当我尝试阅读它时，出现以下错误：

Process SpawnProcess-1:
Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/multiprocessing/process.py", line 297, in _bootstrap
    self.run()
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/multiprocessing/process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/federico/Workspace/test/test.py", line 6, in fn
    print("value:", c.value)
  File "<string>", line 3, in getvalue
OSError: [Errno 9] Bad file descriptor

然而，预期的输出是value: hello 。 有谁知道这里可能出了什么问题？ 谢谢。

Answer 1

该数组还应在您为多处理定义的上下文中定义，如下所示：

import multiprocessing, time
import ctypes
from multiprocessing import Process


def fn(arr):
    time.sleep(1)
    print("value:", arr.value)


def main():
    ctx = multiprocessing.get_context("spawn")
    arr = ctx.Array(ctypes.c_char, 32)
    p = ctx.Process(target=fn, args=(arr,))
    p.start()
    arr.value = b'hello'
    p.join()


if __name__ == "__main__":
    main()