Asynchronous multiprocessing.Pipe reads throw when using uvloop #686
Description
Summary
When using an asyncio.Event() with loop.add_reader() to asynchronously read from a multiprocessing.Pipe, the call to recv_bytes() throws:
Process reader: Traceback (most recent call last): File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/multiprocessing/process.py", line 313, in _bootstrap self.run() ~~~~~~~~^^ File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/multiprocessing/process.py", line 108, in run self._target(*self._args, **self._kwargs) ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/james/code/connection_test.py", line 25, in reader_wrapper uvloop.run(async_reader(read_pipe)) ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/james/code/.venv/lib/python3.13/site-packages/uvloop/__init__.py", line 109, in run return __asyncio.run( ~~~~~~~~~~~~~^ wrapper(), ^^^^^^^^^^ ...<2 lines>... **run_kwargs ^^^^^^^^^^^^ ) ^ File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/asyncio/runners.py", line 195, in run return runner.run(main) ~~~~~~~~~~^^^^^^ File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/asyncio/runners.py", line 118, in run return self._loop.run_until_complete(task) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^ File "uvloop/loop.pyx", line 1518, in uvloop.loop.Loop.run_until_complete File "/home/james/code/.venv/lib/python3.13/site-packages/uvloop/__init__.py", line 61, in wrapper return await main ^^^^^^^^^^ File "/home/james/code/connection_test.py", line 20, in async_reader message = read_pipe.recv_bytes() File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/multiprocessing/connection.py", line 216, in recv_bytes buf = self._recv_bytes(maxlength) File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/multiprocessing/connection.py", line 437, in _recv_bytes return self._recv(size) ~~~~~~~~~~^^^^^^ File "/home/james/.pyenv/versions/3.13.5/lib/python3.13/multiprocessing/connection.py", line 395, in _recv chunk = read(handle, remaining) BlockingIOError: [Errno 11] Resource temporarily unavailable This does not occur when running with asyncio
Environment
Python: 3.13.5 uvloop: 0.21.0 Reproduction
import asyncio import uvloop from multiprocessing import Process from multiprocessing.connection import Connection, Pipe, wait def writer(write_pipe: Connection): message = b'!' * 65536 while True: write_pipe.send_bytes(message) async def async_reader(read_pipe: Connection): message_available = asyncio.Event() asyncio.get_running_loop().add_reader( read_pipe.fileno(), message_available.set ) while True: await message_available.wait() while read_pipe.poll(): message = read_pipe.recv_bytes() print('Got message') message_available.clear() def reader_wrapper(read_pipe: Connection): uvloop.run(async_reader(read_pipe)) if __name__ == '__main__': read_pipe, write_pipe = Pipe(duplex=False) reader_process = Process( name="reader", target=reader_wrapper, args=(read_pipe,) ) reader_process.start() writer_process = Process( name="writer", target=writer, args=(write_pipe,) ) writer_process.start() wait([reader_process.sentinel, writer_process.sentinel])