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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Deadlock when calling PyGILState_Ensure() from a fresh C thread","articleBody":"# Bug report\r\n\r\nThis used to work with py 3.8, 3.9 and 3.10 but now fails. The failure is due to a deadlock condition due to the move of an alloc from before a HEAD_LOCK() to after causing a recursive call to PyGILState_Ensure() which eventually deadlocks on the HEAD_LOCK().\r\n\r\nThe following is a trace of calls from the initial call to PyGILState_Ensure() to the eventual deadlock:\r\n\r\n```\r\npystate:PyGILState_Ensure()\r\npystate:PyThreadState_New()\r\npystate:new_threadstate()\r\n  HEAD_LOCK()  \u003c-- Initial head locked, the alloc_threadstate() call below used to happen before this in previous versions of Python.\r\npystate:alloc_threadstate()\r\nobmalloc:PyMem_RawCalloc()\r\n_tracemalloc:_PyMem_Raw.calloc()\r\n_tracemalloc:tracemalloc_raw_calloc()\r\n  get_reentrant() = 0\r\n  set_reenterant(1)\r\npystate:PyGILState_Ensure()\r\npystate:PyThreadState_New()\r\npystate:new_threadstate()\r\n  HEAD_LOCK()  \u003c--   DEADLOCK HERE!\r\n```\r\n\r\nSteps to reproduce: In a Python C extension module, create a C thread then try to call PyGILState_Ensure() in that thread with no previous existing Python threadstate.\r\n\r\n# Your environment\r\n\r\nPython 3.11.0rc1\r\nLinux tom-VirtualBox 5.15.0-46-generic #49~20.04.1-Ubuntu SMP Thu Aug 4 19:15:44 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux\r\n","author":{"url":"https://github.com/tom-pytel","@type":"Person","name":"tom-pytel"},"datePublished":"2022-08-18T12:29:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":17},"url":"https://github.com/96071/cpython/issues/96071"}