Issue 29704: Can't read data from Transport after asyncio.SubprocessStreamProtocol closes (original) (raw)

Copied from https://github.com/python/asyncio/issues/484

""" From https://bugs.python.org/issue23242#msg284930

The following script is used to reproduce the bug:

import asyncio

async def execute(): process = await asyncio.create_subprocess_exec( "timeout", "0.1", "cat", "/dev/urandom", stdout=asyncio.subprocess.PIPE)

while True:
    data = await process.stdout.read(65536)
    print('read %d bytes' % len(data))
    if data:
        await asyncio.sleep(0.3)
    else:
        break

asyncio.get_event_loop().run_until_complete(execute())

will produce following output and terminate with exception:

read 65536 bytes read 65536 bytes Traceback (most recent call last): File "read_subprocess.py", line 18, in asyncio.get_event_loop().run_until_complete(execute()) File "/usr/lib/python3.6/asyncio/base_events.py", line 466, in run_until_complete return future.result() File "read_subprocess.py", line 9, in execute data = await process.stdout.read(65536) File "/usr/lib/python3.6/asyncio/streams.py", line 634, in read self._maybe_resume_transport() File "/usr/lib/python3.6/asyncio/streams.py", line 402, in _maybe_resume_transport self._transport.resume_reading() File "/usr/lib/python3.6/asyncio/unix_events.py", line 401, in resume_reading self._loop._add_reader(self._fileno, self._read_ready) AttributeError: 'NoneType' object has no attribute '_add_reader'

When the process exits https://github.com/python/asyncio/blob/master/asyncio/unix_events.py#L444 is called which sets this._loop = None Next time read() is called on the pipe the above exception is thrown. I have tried to fix this issue myself but would sometimes have read terminate too early and miss the last chunks of data. """

• BotoX