[SPARK-54456][PYTHON] Import worker module after fork to avoid deadlock #53166
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HyukjinKwon
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ueshin
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Nov 24, 2025
| if len(sys.argv) > 1 and sys.argv[1].startswith("pyspark"): | ||
| import importlib | ||
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| worker_module = importlib.import_module(sys.argv[1]) |
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Just a QQ: Is it ok to call this multiple times? This worker function will be called every UDF execution.
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Yes, the imported module will be cached, just like the normal import keyword.
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Merged to master. |
huangxiaopingRD
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Nov 25, 2025
### 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 `multiprocessing` start method to "spawn" since 3.14. It would be a huge effort for us to give up `fork` entirely, 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_read` for 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 Closes apache#53166 from gaogaotiantian/move-worker-module-import. Authored-by: Tian Gao <gaogaotiantian@hotmail.com> Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>
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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