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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Single-Phase Init Extension Module Init Functions Still Run in Isolated Interpreters","articleBody":"# Bug report\n\n### Bug description:\n\nWhen an extension module is imported the first time, we load the shared-object file and get the module's init function from it.  We then run that init function and use the returned object to decide if the module is single-phase init or multi-phase init.\n\nFor isolated subinterpreters, where `PyInterpreterConfig.check_multi_interp_extensions` (AKA `Py_RTFLAGS_MULTI_INTERP_EXTENSIONS`) is True, we immediately fail single-phase init modules.  The problem is that at that point the init function has already run, which all sorts of potential side effects and process-global state (including registered callbacks) that we mostly can't clean up.\n\nThis has come up before, for example with the readline module.  It's potentially a bigger problem than I thought at first, so I'd like to get it sorted out for 3.13.\n\n----\n\nFWIW, the simplest solution I can think of is to always call the module init func from the main interpreter (without necessarily doing all the other import steps there).  That would look something like this:\n\n1. start a normal import in an isolated subinterpreter\n2. get the init function\n3. switch to the main interpreter\n4. call the init function\n5. switch back\n6. fail if it is single-phase init (and remember that fact)\n\nFor the main interpreter and non-isolated subinterpreters, nothing different would happen from now; there would be no switching.  Also, if the first attempt was in an isolated interpreter (which would fail), a subsequent import of that module in the main interpreter (or a non-isolated one) would succeed.\n\nThe only tricky part is, when the init function raises an exception, how to an propagate it from the main interpreter to the subinterpreter.  For multi-phase init (if known) we would just call the init func again after switching back.  For single-phase init (or unknown) we'd have preserve the exception somehow.  This is something I had to deal with for `_interpreters.exec()`, but I'm not sure the same thing will work here.\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-117487\n* gh-118116\n* gh-118156\n* gh-118157\n* gh-118167\n* gh-118192\n* gh-118193\n* gh-118194\n* gh-118203\n* gh-118204\n* gh-118205\n* gh-118206\n* gh-118250\n* gh-118532\n* gh-118684\n* gh-120689\n* gh-120707\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/ericsnowcurrently","@type":"Person","name":"ericsnowcurrently"},"datePublished":"2024-04-16T23:47:11.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/117953/cpython/issues/117953"}