Expose multiprocessing_context for dataloading

[maciej-sypetkowski]

Changelogs

• Expose multiprocessing_context argument for DataModule classes (constructor & config).

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Checklist:

• Was this PR discussed in an issue? It is recommended to first discuss a new feature into a GitHub issue before opening a PR.
• Add tests to cover the fixed bug(s) or the new introduced feature(s) (if appropriate).
• Update the API documentation is a new function is added, or an existing one is deleted.
• Write concise and explanatory changelogs above.
• If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

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discussion related to that PR

Changing multiprocessing_context to spawn can sometimes give a significant data loading speedup.

[codecov]

Codecov Report

Merging #446 (5d316bd) into main (95ece97) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #446      +/-   ##
==========================================
+ Coverage   65.37%   65.38%   +0.01%     
==========================================
  Files          92       92              
  Lines        8253     8256       +3     
==========================================
+ Hits         5395     5398       +3     
  Misses       2858     2858              

Flag	Coverage Δ
unittests	65.38% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
ipu	49.14% <ø> (ø)

[DomInvivo]

Perhaps grouping everything into a dataloader_kwargs that takes any dict of options, so that we don't need to expose new options every time we need something new.

[maciej-sypetkowski]

Perhaps grouping everything into a dataloader_kwargs that takes any dict of options, so that we don't need to expose new options every time we need something new.

I agree, but let's tackle it in another PR in the future.