[SPARK-54456][PYTHON] Import worker module after fork to avoid deadlock #53166
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HyukjinKwon
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What changes were proposed in this pull request?
We lazy-import the worker module after fork to avoid potential deadlock caused by importing some modules that spawns multiple threads.
Why are the changes needed?
https://discuss.python.org/t/switching-default-multiprocessing-context-to-spawn-on-posix-as-well/21868
It's impossible to do a thread-safe fork in CPython. CPython started issuing warnings from 3.12 and switched the default
multiprocessingstart method to "spawn" since 3.14.It would be a huge effort for us to give up
forkentirely, but we can try out best to not import random modules before fork by lazy-importing worker module after fork.We already have some workers that import dangerous libraries like
pyarrow-plan_data_source_readfor example.Does this PR introduce any user-facing change?
No
How was this patch tested?
CI should pass.
Was this patch authored or co-authored using generative AI tooling?
No