python的并发异步问题答案

【问题标题】：Concurrency async issue with pythonpython的并发异步问题
【发布时间】：2020-04-09 19:29:23
【问题描述】：

我是 python 新手，我试图解决一个简单的问题：我有两个操作块（块 A 和块 B），每个块执行不同的 shell 命令，这些命令应该在块内异步执行（在同一个块中我可以执行一个新操作，而不必等待第一个操作的结果)。

只有在“Block A”的所有操作都完成后，我才能开始运行“Block B”的操作。

import asyncio
import subprocess
import sys
import threading


async def run_command(number, timeSleep):
    cmd = "(echo '"+ number +" Start -->' $(date) ;sleep "+timeSleep +" ;echo '"+ number +" End -->' $(date) ) >> /tmp/log.txt"

    p = subprocess.Popen(cmd, stderr=subprocess.PIPE, shell=True)

async def block_a():
    await asyncio.gather(
        run_command("Block A: Operation 1","8"),
        run_command("Block A: Operation 2","4"),
        run_command("Block A: Operation 3","2"))

async def block_b():
    await asyncio.gather(
        run_command("Block B Operation 1","5"),
        run_command("Block B Operation 2","4"),
        run_command("Block B Operation 3","1"))


async def main():
    await asyncio.gather(
        block_a(),
        block_b())

if __name__ == '__main__':
    # Create the asyncio event loop
    loop = asyncio.get_event_loop()
    try:
        loop.run_until_complete(main())
    finally:
        # Shutdown the loop even if there is an exception
        loop.close()

我得到以下输出：

Block A: Operation 2 Start --> Thu Apr 9 21:21:27 CEST 2020
Block A: Operation 3 Start --> Thu Apr 9 21:21:27 CEST 2020
Block A: Operation 1 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 1 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 2 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 3 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 3 End --> Thu Apr 9 21:21:28 CEST 2020
Block A: Operation 3 End --> Thu Apr 9 21:21:29 CEST 2020
Block A: Operation 2 End --> Thu Apr 9 21:21:31 CEST 2020
Block B Operation 2 End --> Thu Apr 9 21:21:31 CEST 2020
Block B Operation 1 End --> Thu Apr 9 21:21:32 CEST 2020
Block A: Operation 1 End --> Thu Apr 9 21:21:35 CEST 2020

我希望在 Block A 的操作完成后开始 Block B 的操作。
我期待的输出是这样的：

Block A: Operation 2 Start --> Thu Apr 9 21:21:27 CEST 2020
Block A: Operation 3 Start --> Thu Apr 9 21:21:27 CEST 2020
Block A: Operation 1 Start --> Thu Apr 9 21:21:27 CEST 2020
Block A: Operation 3 End --> Thu Apr 9 21:21:29 CEST 2020
Block A: Operation 2 End --> Thu Apr 9 21:21:31 CEST 2020
Block A: Operation 1 End --> Thu Apr 9 21:21:35 CEST 2020
Block B Operation 1 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 2 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 3 Start --> Thu Apr 9 21:21:27 CEST 2020
Block B Operation 3 End --> Thu Apr 9 21:21:28 CEST 2020
Block B Operation 2 End --> Thu Apr 9 21:21:31 CEST 2020
Block B Operation 1 End --> Thu Apr 9 21:21:32 CEST 2020

【问题讨论】：

标签： python concurrency python-asyncio

【解决方案1】：

您必须使用asyncio 模块来创建子进程，而不是直接使用subprocess 模块。
来自docs：

import asyncio

async def run(cmd):
    proc = await asyncio.create_subprocess_shell(
        cmd,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE)

    stdout, stderr = await proc.communicate()

    print(f'[{cmd!r} exited with {proc.returncode}]')
    if stdout:
        print(f'[stdout]\n{stdout.decode()}')
    if stderr:
        print(f'[stderr]\n{stderr.decode()}')

asyncio.run(run('ls /zzz'))

【讨论】：