Fix Python 3.12 deprecation warning about os.fork()#1070
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mhucka merged 2 commits intoquantumlib:masterfrom Jun 5, 2025
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Fix Python 3.12 deprecation warning about os.fork()#1070mhucka merged 2 commits intoquantumlib:masterfrom
mhucka merged 2 commits intoquantumlib:masterfrom
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I've adjusted the multiprocessing start method to 'forkserver' within the `ParallelLinearQubitOperator` class. This should resolve warnings concerning `os.fork()` in multithreaded environments (specifically with JAX in Python 3.12) that could potentially lead to deadlocks.
This change ensures that `multiprocessing.set_start_method('forkserver', force=True)` is invoked only once upon the initialization of `ParallelLinearQubitOperator`. The tests in `performance_benchmarks_test.py` are now passing without any warnings.
mhucka
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Seems like the default behaviour will change in python 3.14 (away from fork), maybe worth opening an issue and adding it as a link in the code to revisit in the future. |
fdmalone
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Jun 5, 2025
mhucka
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Sep 25, 2025
In Python 3.12, on Linux at least, `src/openfermion/testing/performance_benchmarks_test.py` produces the following warnings: ``` ~/.pyenv/versions/3.12.5/lib/python3.12/multiprocessing/popen_fork.py:66: RuntimeWarning: os.fork() was called. os.fork() is incompatible with multithreaded code, and JAX is multithreaded, so this will likely lead to a deadlock. self.pid = os.fork() src/openfermion/testing/performance_benchmarks_test.py::test_run_linear_qop src/openfermion/testing/performance_benchmarks_test.py::test_run_linear_qop src/openfermion/testing/performance_benchmarks_test.py::test_run_linear_qop src/openfermion/testing/performance_benchmarks_test.py::test_run_linear_qop src/openfermion/testing/performance_benchmarks_test.py::test_run_linear_qop ~/.pyenv/versions/3.12.5/lib/python3.12/multiprocessing/popen_fork.py:66: DeprecationWarning: This process (pid=3069778) is multi-threaded, use of fork() may lead to deadlocks in the child. self.pid = os.fork() ``` This can be resolved by calling `multiprocessing.set_start_method()` in `__init__` of the `ParallelLinearQuibitOperator` class. Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
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In Python 3.12, on Linux at least,
src/openfermion/testing/performance_benchmarks_test.pyproduces the following warnings:This can be resolved by calling
multiprocessing.set_start_method()in__init__of theParallelLinearQuibitOperatorclass.