block: support importing under sub-interpreters - #341
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Python 3.12+ won't load single-phase C extensions inside a sub-interpreter. Convert _block to multi-phase init so it imports there, and declare it safe to run with a per-interpreter GIL. LZ4BlockError moves from a global into per-module state, so every interpreter gets its own. 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
_blockto multi-phase init so it imports there, and declares itsafe to run with a per-interpreter GIL.
Part of #345 - multi-phase init for the
_blockmodule (see also #340_frame, #342_stream, #343_version).Why it's safe
LZ4BlockErrormoves 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. So the module is safe even in fully isolated
interpreters.
Compatibility
No API change. The new declaration is guarded for Python 3.12+, so builds on
older Python are unaffected. (Uses
PyModule_AddObjectrather thanPyModule_AddObjectRefto keep the 3.9 minimum.)Testing
tests/blockpasses (7,217 tests)._blockimports and round-trips in isolated, own-GILsub-interpreters, and that
LZ4BlockErroris a distinct object perinterpreter.
Refs: PEP 489, Isolating Extension Modules