为什么在另一个线程中启动异步事件循环会与我的 pipe 混淆？

Question

I have 2 processes. I would like write.py to write a message to read.py through a Linux pipe.

### write.py
import subprocess
import asyncio
from threading import Thread

# !-- Offending code here. --!
# loop = asyncio.new_event_loop()
# def side_thread(loop):
#     asyncio.set_event_loop(loop)
#     loop.run_forever()
# thread = Thread(target=side_thread, args=(loop,))
# thread.start()

notify_proc = subprocess.Popen("python read.py".split(), stdin=subprocess.PIPE)

notify_proc.stdin.write("hello\n".encode("utf-8"))

### read.py
import sys

for line in sys.stdin:
  print("Got something!")
  print(line)

As given, when I run python write.py , I get the expected output:

Got something!
hello

But when I uncomment the offending code, I don't get any output. Why?

• Python 3.9.7
• Linux 5.4.72-microsoft-standard-WSL2 x86_64

Answer 1

Your buffer won't get sent over until the buffer is flushed or the process ends, and the process will not end as long as a non-daemon thread is running. In the short term, you can add notify_proc.stdin.flush() , but your mixing of multiprocessing, threading and asyncio is going to lead to tears. What on earth are you trying to do here?