LoadError: unkown opcode '\x00'

I get this weird issue on Windows/PyPy5.7.1:

pypy-30-43 inst-nodeps: f:\projects\pytest-cov\.tox\dist\pytest-cov-2.5.0.zip
pypy-30-43 installed: apipkg==1.4,appdirs==1.4.3,cffi==1.10.0,colorama==0.3.9,coverage==4.3.4,execnet==1.4.1,fields==5.0.0,greenlet==0.4.12,packaging==16.8,process-tests==1.2.1,py
=1.4.33,pyparsing==2.2.0,pytest==3.0.7,pytest-capturelog==0.7,pytest-cov==2.5.0,pytest-xdist==1.16.0,readline==6.2.4.1,six==1.10.0,virtualenv==15.1.0
pypy-30-43 runtests: PYTHONHASHSEED='103'
pypy-30-43 runtests: commands[0] | pytest test_things.py -n 2 --cov --cov-report=term --max-slave-restart=0
============================= test session starts =============================
platform win32 -- Python 2.7.13[pypy-5.7.1-final], pytest-3.0.7, py-1.4.33, pluggy-0.4.0
rootdir: f:\projects\pytest-cov, inifile: setup.cfg
plugins: xdist-1.16.0, cov-2.5.0, capturelog-0.7
gw0 C / gw1 C[gw0] node down: Traceback (most recent call last):
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 841, in _local_receive
    data = loads_internal(data, channel, strconfig)
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 1350, in loads_internal
    return Unserializer(io, channelfactory, strconfig).load()
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 1160, in load
    "wire protocol corruption?" % (opcode,))
LoadError: unkown opcode '\x00' - wire protocol corruption?

Slave restarting disabled
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\main.py", line 98, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\main.py", line 132, in _main
INTERNALERROR>     config.hook.pytest_collection(session=session)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 745, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 339, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 334, in <lambda>
INTERNALERROR>     _MultiCall(methods, kwargs, hook.spec_opts).execute()
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 614, in execute
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "<remote exec>", line 43, in pytest_collection
INTERNALERROR>   File "<remote exec>", line 25, in sendevent
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 716, in send
INTERNALERROR>     raise IOError("cannot send to %r" % (self,))
INTERNALERROR> IOError: cannot send to <Channel id=1 closed>
[gw1] node down: Traceback (most recent call last):
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 841, in _local_receive
    data = loads_internal(data, channel, strconfig)
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 1350, in loads_internal
    return Unserializer(io, channelfactory, strconfig).load()
  File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 1160, in load
    "wire protocol corruption?" % (opcode,))
LoadError: unkown opcode '\x00' - wire protocol corruption?

Slave restarting disabled
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\main.py", line 98, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\main.py", line 132, in _main
INTERNALERROR>     config.hook.pytest_collection(session=session)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 745, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 339, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 334, in <lambda>
INTERNALERROR>     _MultiCall(methods, kwargs, hook.spec_opts).execute()
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\_pytest\vendored_packages\pluggy.py", line 614, in execute
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "<remote exec>", line 43, in pytest_collection
INTERNALERROR>   File "<remote exec>", line 25, in sendevent
INTERNALERROR>   File "f:\projects\pytest-cov\.tox\pypy-30-43\site-packages\execnet\gateway_base.py", line 716, in send
INTERNALERROR>     raise IOError("cannot send to %r" % (self,))
INTERNALERROR> IOError: cannot send to <Channel id=1 closed>

Any clues as to what is wrong?

Reproduce the reported command from test_things.py on Windows with PyPy 5.7.1, then start at execnet/gateway_base.py where loads_internal and Unserializer.load report the protocol error. Compare the worker and controller behavior around the pytest-xdist distributed run; done means identifying the cause of the corrupted wire protocol and confirming a fix with the same scenario.