[3.5] bpo-30814: Add a test for concurrent relative import. (GH-2580).

[serhiy-storchaka]

(cherry picked from commit b4baace)

[vstinner]

Hum, the test fails on my Windows VM:

AttributeError: module 'package' has no attribute 'submodule'

If I modify the test to only run 1 loop iteration, the test pass, but fail if run again... It fails randomly.

Please don't add such test to 3.5 yet :-)

[vstinner]

Hum, I forgot to explain how I tested: I downloaded this PR in my 3.5 checkout of CPython on Windows, and ran the test using "python -m test -m test_concurrency -v test_import".

[serhiy-storchaka]

Thanks for testing on Windows @Haypo. Now we know that the bug exposed in bpo-30891 exists on 3.5.

[larryhastings]

Just a reminder: I expect to tag 3.5.4rc1 in eleven or twelve hours. If this is a bugfix (not a security fix), and it isn't merged by then, it will probably never be merged into 3.5.

[serhiy-storchaka]

Since Victor's fix was not backported, the test can't be added.

[vstinner]

Yeah, I agree that it's too late in the 3.5 cycle (moving to security-only fixes) for work on such old importlib bug.