为什么我在 Windows 上使用 async 和 wait 时会收到 NotImplementedError 错误？

我有这段代码：

import os
import time
import asyncio


async def run_command(*args):
    """
    Example from:
        http://asyncio.readthedocs.io/en/latest/subprocess.html
    """
    # Create subprocess
    process = await asyncio.create_subprocess_exec(
        *args,
        # stdout must a pipe to be accessible as process.stdout
        stdout=asyncio.subprocess.PIPE)

    # Wait for the subprocess to finish
    stdout, stderr = await process.communicate()

    # Result
    result = stdout.decode().strip()

    # Return stdout
    return result


def run_asyncio_commands(tasks):
    """Run tasks using asyncio and return results"""
    loop = asyncio.get_event_loop()
    commands = asyncio.gather(*tasks)  # Unpack list using *
    results = loop.run_until_complete(commands)
    loop.close()
    return results


if __name__ == '__main__':

    start = time.time()

    cmds = [
        ['du', '-sh', '/Users/fredrik/Desktop'],
        ['du', '-sh', '/Users/fredrik'],
        ['du', '-sh', '/Users/fredrik/Pictures']
    ]

    tasks = []
    for cmd in cmds:
        tasks.append(run_command(*cmd))
    results = run_asyncio_commands(tasks)
    print(results)

    end = time.time()
    print('Script ran in', str(end - start), 'seconds')

当我在 Mac 上的 Python 3.6.1 中运行该代码时，我得到：

['780K\t/Users/fredrik/Desktop', '46G\t/Users/fredrik', '52M\t/Users/fredrik/Pictures']
Script ran in 6.405519008636475 seconds

但是当我在 Windows 上运行相同的脚本时（但将 du 命令替换为某些内容）它适用于 Windows），也适用于 Python 3.6.1，我得到这个：

Traceback (most recent call last):
  File "C:\Users\iruser\Desktop\asynciotest.py", line 66, in <module>
    results = run_asyncio_commands(tasks)
  File "C:\Users\iruser\Desktop\asynciotest.py", line 41, in run_asyncio_commands
    results = loop.run_until_complete(commands)
  File "C:\Users\fredrik\condaenvs\dev_py36\lib\asyncio\base_events.py", line 466, in run_until_complete
    return future.result()
  File "C:\Users\iruser\Desktop\asynciotest.py", line 16, in run_command
    stdout=asyncio.subprocess.PIPE)
  File "C:\Users\fredrik\condaenvs\dev_py36\lib\asyncio\subprocess.py", line 225, in create_subprocess_exec
    stderr=stderr, **kwds)
  File "C:\Users\fredrik\condaenvs\dev_py36\lib\asyncio\base_events.py", line 1190, in subprocess_exec
    bufsize, **kwargs)
  File "C:\Users\fredrik\condaenvs\dev_py36\lib\asyncio\coroutines.py", line 210, in coro
    res = func(*args, **kw)
  File "C:\Users\fredrik\condaenvs\dev_py36\lib\asyncio\base_events.py", line 340, in _make_subprocess_transp
ort
    raise NotImplementedError
NotImplementedError

这是我在 Windows 上替换 Unix 命令的内容：

cmds = [['C:/Windows/system32/HOSTNAME.EXE']]

Python 和 Windows 版本信息：

Python 3.6.1 | packaged by conda-forge | (default, May 23 2017, 14:21:39) [MSC v.1900 64 bit (AMD64)] on win32
Windows 10 Pro, version 1703, OS build 15063.413

这个错误信息 “NotImplementedError: ” 在 Windows 上使用 asyncio 时通常意味着你正尝试使用一个尚未在 Windows 上实现的 asyncio 的特性。具体来说，你在代码中遇到的问题在于使用 asyncio.create_subprocess_exec 时将 stdout 或 stderr 设置为 asyncio.subprocess.PIPE 。

在 Windows 上， asyncio 的子进程管道处理方式与 Unix 系统不同。在 Windows 上，你需要使用线程来处理来自子进程的标准输出和标准错误流。

以下是如何在 Windows 上修改你的代码以使其正常工作的示例：

import os
import time
import asyncio

async def run_command(*args):
    """Runs a command asynchronously."""

    # Launch the subprocess
    process = await asyncio.create_subprocess_exec(
        *args,
        # Do not redirect stdout or stderr
        stdout=None,
        stderr=None,
    )

    # Wait for the subprocess to finish
    await process.wait()

    # Return the return code
    return process.returncode


async def run_asyncio_commands(tasks):
    """Runs tasks using asyncio and returns results."""

    results = await asyncio.gather(*tasks)
    return results


if __name__ == "__main__":
    start = time.time()

    cmds = [['C:/Windows/system32/HOSTNAME.EXE']]

    tasks = [run_command(*cmd) for cmd in cmds]
    results = asyncio.run(run_asyncio_commands(tasks))
    print(f"Return codes: {results}")

    end = time.time()
    print(f"Script ran in {end - start:.4f} seconds")

这个修改后的代码中，我们不再尝试使用管道来读取子进程的输出。我们只是启动子进程，等待它完成，然后返回它的返回码。

如果你需要从子进程中捕获输出，你需要使用一个不同的方法，比如使用一个线程来读取子进程的输出流。