EOFError when executiong pytest with --looponfail

Exception raised while running pytest -f with EXECNET_DEBUG=2

[2064] gw0 [receiver-thread] received <Message CHANNEL_DATA channel=2 lendata=73>
[2068] gw0-worker sent <Message CHANNEL_DATA channel=2 lendata=73>
[2064] gw0 [receiver-thread] received <Message CHANNEL_DATA channel=2 lendata=73>
[2068] gw0-worker sent <Message CHANNEL_DATA channel=2 lendata=73>
[2064] gw0 [receiver-thread] EOF without prior gateway termination message
[2064] gw0 [receiver-thread] finishing receiving thread
[2064] gw0 [receiver-thread] terminating execution
[2064] gw0 [receiver-thread] closing read
[2064] gw0 gateway.exit() called
[2064] gw0 --> sending GATEWAY_TERMINATE
[2064] gw0 [receiver-thread] closing write
[2064] gw0 failed to send <Message GATEWAY_TERMINATE channel=0 lendata=0> [Errno 32] Broken pipe
[2064] gw0 io-error: could not send termination sequence
[2064] gw0  exception: OSError('cannot send (already closed?)')
Traceback (most recent call last):
  File "/code/.venv/lib/python3.8/site-packages/execnet/gateway_base.py", line 432, in from_io
    header = io.read(9)  # type 1, channel 4, payload 4
  File "/code/.venv/lib/python3.8/site-packages/execnet/gateway_base.py", line 402, in read
    raise EOFError("expected %d bytes, got %d" % (numbytes, len(buf)))
EOFError: expected 9 bytes, got 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/code/.venv/bin/pytest", line 8, in <module>
    sys.exit(console_main())
  File "/code/.venv/lib/python3.8/site-packages/_pytest/config/__init__.py", line 185, in console_main
    code = main()
  File "/code/.venv/lib/python3.8/site-packages/_pytest/config/__init__.py", line 162, in main
    ret: Union[ExitCode, int] = config.hook.pytest_cmdline_main(
  File "/code/.venv/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/code/.venv/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/code/.venv/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
    self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
  File "/code/.venv/lib/python3.8/site-packages/pluggy/callers.py", line 208, in _multicall
    return outcome.get_result()
  File "/code/.venv/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/code/.venv/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/code/.venv/lib/python3.8/site-packages/xdist/looponfail.py", line 35, in pytest_cmdline_main
    looponfail_main(config)
  File "/code/.venv/lib/python3.8/site-packages/xdist/looponfail.py", line 45, in looponfail_main
    remotecontrol.loop_once()
  File "/code/.venv/lib/python3.8/site-packages/xdist/looponfail.py", line 117, in loop_once
    result = self.runsession()
  File "/code/.venv/lib/python3.8/site-packages/xdist/looponfail.py", line 106, in runsession
    return self.channel.receive()
  File "/code/.venv/lib/python3.8/site-packages/execnet/gateway_base.py", line 749, in receive
    raise self._getremoteerror() or EOFError()
  File "/code/.venv/lib/python3.8/site-packages/execnet/gateway_base.py", line 967, in _thread_receiver
    msg = Message.from_io(io)
  File "/code/.venv/lib/python3.8/site-packages/execnet/gateway_base.py", line 437, in from_io
    raise EOFError("couldnt load message header, " + e.args[0])
EOFError: couldnt load message header, expected 9 bytes, got 0
[2064] === atexit cleanup <Group []> ===

Dependency tree

pytest-xdist==2.2.0
  - execnet [required: >=1.1, installed: 1.8.0]
    - apipkg [required: >=1.4, installed: 1.5]
  - pytest [required: >=6.0.0, installed: 6.2.2]
    - attrs [required: >=19.2.0, installed: 20.3.0]
    - iniconfig [required: Any, installed: 1.1.1]
    - packaging [required: Any, installed: 20.9]
      - pyparsing [required: >=2.0.2, installed: 2.4.7]
    - pluggy [required: <1.0.0a1,>=0.12, installed: 0.13.1]
    - py [required: >=1.8.2, installed: 1.10.0]
    - toml [required: Any, installed: 0.10.2]
  - pytest-forked [required: Any, installed: 1.3.0]
    - py [required: Any, installed: 1.10.0]
    - pytest [required: >=3.10, installed: 6.2.2]
      - attrs [required: >=19.2.0, installed: 20.3.0]
      - iniconfig [required: Any, installed: 1.1.1]
      - packaging [required: Any, installed: 20.9]
        - pyparsing [required: >=2.0.2, installed: 2.4.7]
      - pluggy [required: <1.0.0a1,>=0.12, installed: 0.13.1]
      - py [required: >=1.8.2, installed: 1.10.0]
      - toml [required: Any, installed: 0.10.2]

Project is fairly basic. Running in a ubuntu:focal container using a pipenv managed virtualenv.

Start by reproducing pytest -f with EXECNET_DEBUG=2 in the Ubuntu Focal/Pipenv setup described. Read xdist/looponfail.py around looponfail_main, loop_once, and runsession, then inspect the reported execnet/gateway_base.py receiver path; done means the EOFError and broken-pipe failure are resolved or clearly diagnosed with a regression test.