stream: support importing under sub-interpreters#342
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Python 3.12+ won't load single-phase C extensions inside a sub-interpreter. Convert _stream to multi-phase init so it imports there, and declare it safe to run with a per-interpreter GIL. LZ4StreamError moves from a global into per-module state, so every interpreter gets its own. Also drop a redundant error raise in a stream helper; its caller already raises the same error. No API change, and older Python versions are unaffected.
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What
Python 3.12+ won't import single-phase C extensions inside a sub-interpreter.
This converts
_streamto multi-phase init so it imports there, and declares itsafe to run with a per-interpreter GIL.
Why it's safe
LZ4StreamErrormoves from a module global into per-module state, so eachinterpreter gets its own copy. There is no other shared mutable state, and the
bundled liblz4 is reentrant.
One raise site lived in a state-less helper (
store_block_length); its onlycaller already raises the same error, so the redundant raise was removed.
Compatibility
No API change. The new declaration is guarded for Python 3.12+, so builds on
older Python are unaffected.
Note
lz4.streamis experimental — built only withPYLZ4_EXPERIMENTAL=1andexcluded from the default package. This change keeps it consistent with
blockand
framefor when it graduates.Testing
tests/streampasses (5,441 passed, 2,700 skipped)._streamimports and works in isolated, own-GIL sub-interpreters,and that
LZ4StreamErroris a distinct object per interpreter.Refs: PEP 489, Isolating Extension Modules