Codecov Report

Base: 93.96% // Head: 93.73% // Decreases project coverage by -0.23% ⚠️

Coverage data is based on head (0568c24) compared to base (796e7aa).
Patch coverage: 100.00% of modified lines in pull request are covered.

@@            Coverage Diff             @@
##           master    #1356      +/-   ##
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- Coverage   93.96%   93.73%   -0.24%     
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  Files          52       52              
  Lines        7291     7291              
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- Hits         6851     6834      -17     
- Misses        440      457      +17     

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The things I am wondering about:

• right now the JOBLIB_DEFAULT_PARALLEL_BACKEND is only checked when joblib.parallel is imported and setting it to another value after joblib.parallel is imported will not have any effect. Is this OK or do we want to check the environment variable when a Parallel object is created?
• do we need to add a CI build for running the tests with threading as the default backend?

do we need to add a CI build for running the tests with threading as the default backend?

I think so, otherwise the test suite will become loky specific again without us realizing it.

right now the JOBLIB_DEFAULT_PARALLEL_BACKEND is only checked when joblib.parallel is imported and setting it to another value after joblib.parallel is imported will not have any effect. Is this OK or do we want to check the environment variable when a Parallel object is created?

I think it's fine to only check it at joblib import time.

The windows error does not seem related, maybe similar to #1275

@GaelVaroquaux raised the concern that the environment variable could be set for other purposes than testing and that users in some environments would not realize that system administrator might change the joblib behaviors without the users being aware causing hard to debug and support situations.

Maybe we would instead change the default backend via a environment variable that would only impact a dedicated pytest configuration (e.g. module level setup function in a top level conftest.py file) instead of inspecting the environment variable in joblib/parallel.py directly.

Thanks for the improvement @lesteve!

We now need something similar to run the scikit-learn tests with nogil CPython and the threading backend.

Yep this is on the list, as an intermediary step I tried a while ago to run the joblib tests with nogil and the threading backend as default, and there were some failures which I did not investigate.