crash using concurrency multiprocessing

Originally reported by Lorenzo Boffelli (Bitbucket: lboff, GitHub: lboff)

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Hello, I am using pytest with pytest-cov and coverage. I wrote some tests where I run a process (multiprocessing.Process) The process uses gunicorn and start three worker. the test call a API server by one of the three worker.

1. If I do not add the option concurrency=multiprocessing I get always the same coverage. I think only the process startup is measured but the code executed after the process receive the API request is not reported as executed.

2. If I add the concurrency=multiprocessing it seems the code executed after the process receive the API request is reported as executed but coverage crash like reported below.

I can not add here the code at the moment but I can eventually exec other tests you could suggest and try to troubleshoot together

Thanks Lorenzo

Traceback (most recent call last):
  File ".tox/dev/bin/py.test", line 11, in <module>
    sys.exit(main())
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/config.py", line 49, in main
    return config.hook.pytest_cmdline_main(config=config)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 724, in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 338, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 333, in <lambda>
    _MultiCall(methods, kwargs, hook.spec_opts).execute()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 596, in execute
    res = hook_impl.function(*args)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/main.py", line 119, in pytest_cmdline_main
    return wrap_session(config, _main)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/main.py", line 114, in wrap_session
    exitstatus=session.exitstatus)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 724, in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 338, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 333, in <lambda>
    _MultiCall(methods, kwargs, hook.spec_opts).execute()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 595, in execute
    return _wrapped_call(hook_impl.function(*args), self.execute)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 249, in _wrapped_call
    wrap_controller.send(call_outcome)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/terminal.py", line 363, in pytest_sessionfinish
    outcome.get_result()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 279, in get_result
    _reraise(*ex)  # noqa
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 264, in __init__
    self.result = func()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 596, in execute
    res = hook_impl.function(*args)
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/pytest_cov/plugin.py", line 160, in pytest_sessionfinish
    self.cov_controller.finish()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/pytest_cov/engine.py", line 141, in finish
    self.cov.stop()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/coverage/control.py", line 692, in stop
    self.collector.stop()
  File "/home/vnapi/vnapi/.tox/dev/local/lib/python2.7/site-packages/coverage/collector.py", line 277, in stop
  **  "Expected current collector to be %r, but it's %r" % (self, self._collectors[-1])
_pytest.assertion.reinterpret.AssertionError: Expected current collector to be <Collector at 0x7fc71b219a90: CTracer>, but it's <Collector at 0x7fc712037650: CTracer>**

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• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/488

[nedbat]

@mathfac Can you give me a way to reproduce the issue?

[mathfac]

@nedbat, thank you for the question. Issue was that we had the unit test (link) that was testing jupyter noebook using nbval plugin and gc.collect() was called in the end:

        pytest.main(
            [
                "--nbval-lax",
                "notebooks/relative_camera_views_transform_and_warping_demo.ipynb",
            ]
        )

        # NB: Force a gc collect run as it can take a little bit for
        # the cleanup to happen after the notebook and we get
        # a double context crash!
        gc.collect()

I didn’t debug further, as the test was already deprecated, I deleted it and the issue was fixed.