inconsistent file descriptor blocking state when running in asyncio vs uvloop

Bắt đầu bằng cách chạy bản tái hiện asyncio so với uvloop được cung cấp và kiểm tra các điểm vào của uvloop cho loop.add_reader() và loop.add_writer(). So sánh cách chúng xử lý bộ mô tả tệp với selector loop asyncio tiêu chuẩn; hoàn tất khi việc đăng ký stdin, stdout và stderr vẫn giữ nguyên trạng thái chặn của chúng trên uvloop.

When running under uvloop, registering stdin, stdout, or stderr with loop.add_reader() / loop.add_writer() implicitly changes their blocking mode from blocking to non-blocking. This behaviour does not occur under the standard asyncio selector event loop.

This is causing some issues when running with rich/promptkit in fast-agent

Under the following test code

import anyio
import sys
import os
import asyncio

async def main():

    loop = asyncio.get_running_loop()
    print(f"Using event loop: {type(loop)}")

    stdin = sys.stdin.fileno()
    stdout = sys.stdout.fileno()
    stderr = sys.stderr.fileno()

    print(f"initial:\tstdin fd: {stdin}, stdout fd: {stdout}, stderr fd: {stderr}")
    print(f"blocking:\tstdin fd: {os.get_blocking(stdin)}, stdout fd: {os.get_blocking(stdout)}, stderr fd: {os.get_blocking(stderr)}")

    loop.add_writer(stdin, lambda: None)
    loop.add_writer(stdout, lambda: None)
    loop.add_writer(stderr, lambda: None)

    print(f"writer: \tstdin fd: {stdin}, stdout fd: {stdout}, stderr fd: {stderr}")
    print(f"blocking:\tstdin fd: {os.get_blocking(stdin)}, stdout fd: {os.get_blocking(stdout)}, stderr fd: {os.get_blocking(stderr)}")

    loop.add_reader(stdin, lambda: None)
    loop.add_reader(stdout, lambda: None)
    loop.add_reader(stderr, lambda: None)

    print(f"reader: \tstdin fd: {stdin}, stdout fd: {stdout}, stderr fd: {stderr}")
    print(f"blocking:\tstdin fd: {os.get_blocking(stdin)}, stdout fd: {os.get_blocking(stdout)}, stderr fd: {os.get_blocking(stderr)}")

anyio.run(main, backend="asyncio", backend_options={"use_uvloop": False})
print("-" * 40)
anyio.run(main, backend="asyncio", backend_options={"use_uvloop": True})

I see the following output, where the blocking status of the stdio file descriptors are changed from blocking to non blocking when running under uvloop but not asyncio.

Using event loop: <class 'asyncio.unix_events._UnixSelectorEventLoop'>
initial:        stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: True, stdout fd: True, stderr fd: True
writer:         stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: True, stdout fd: True, stderr fd: True
reader:         stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: True, stdout fd: True, stderr fd: True
----------------------------------------
Using event loop: <class 'uvloop.Loop'>
initial:        stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: True, stdout fd: True, stderr fd: True
writer:         stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: False, stdout fd: False, stderr fd: False
reader:         stdin fd: 0, stdout fd: 1, stderr fd: 2
blocking:       stdin fd: False, stdout fd: False, stderr fd: False