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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add a Module Def Slot for Supporting Multiple Interpreters","articleBody":"PEP 489 is clear that extension modules implementing multi-phase init are expected to support use in multiple interpreters.  However, there are two situations where that mandate isn't sufficient:\r\n\r\n1. PEP 684 introduces a per-interpreter GIL, where there is an additional thread-safety constraint beyond support for multiple interpreters\r\n2. the HPy project implies modules with multi-phase init but not necessarily supporting multiple interpreters\r\n\r\nIn both cases a new module def slot (the same one, in fact) is a correct solution.\r\n\r\nFor per-interpreter GIL, [PEP 684 specifies](https://peps.python.org/pep-0684/#extension-module-thread-safety) that we must add a module def slot for opting in to supporting per-interpreter GIL.\r\n\r\nFor HPy, the situation was pointed out to me by @hodgestar during a conversation at PyCon.\r\n\r\nCC @encukou\r\n\r\n----\r\n\r\nI propose the following solution:\r\n\r\n1. add a new `Py_mod_multiple_interpreters` module def slot\r\n2. interpret the value to indicate support for multiple interpreters and for per-interpreter GIL\r\n3. call `_PyImport_CheckSubinterpIncompatibleExtensionAllowed()` when appropriate in `PyModule_FromDefAndSpec2()`\r\n\r\nThe slot value may be one of the following:\r\n\r\n* `0` - does not support multiple interpreters (for HPy)\r\n* `1` - supports multiple interpreters (the default)\r\n* `2` - supports per-interpreter GIL\r\n\r\nIt would probably make sense to define a constant (macro) for each of those.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-104148\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/ericsnowcurrently","@type":"Person","name":"ericsnowcurrently"},"datePublished":"2023-05-02T23:37:33.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":12},"url":"https://github.com/104108/cpython/issues/104108"}