Revert "bpo-40521: Remove freelist from collections.deque() (GH-21073)" by rhettinger · Pull Request #24944

Revert "bpo-40521: Remove freelist from collections.deque() (GH-21073)" by rhettinger · Pull Request #24944 · python/cpython

…-21073)"

This reverts commit 32f2eda.
It can be re-applied if the subinterpreter PEP is approved.
Otherwise, the commit degraded performance with no offsetting
benefit.

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It can be re-applied if the subinterpreters PEP is approved.

subinterpreters exist for years and are used by multiple projects. The recent work is to make more code compatible with subinterpreters (make the code "correct"), only a small part of the work is really specific to preparing CPython code base for running multiple interpreters in parallel.


		#define MAXFREEBLOCKS 16
		static Py_ssize_t numfreeblocks = 0;
		static block *freeblocks[MAXFREEBLOCKS];

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Can you define the freelist in PyInterpreterState to make it per-interpreter, and so compatible with subinterpreters?

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The subinterpreters PEP is not approved a likely won't be for Python 3.10, so I don't want to pay that cost now. These macros are used heavily throughout the rest of the module and are performance sensitive. For Python 3.11 and later, this can be reapplied. Even then, it would probably be better to remove the freelists entirely than to add fenced logic to get the current interpreter.