From 77aabda51a00356240a1dc74a06aad8ca7d550be Mon Sep 17 00:00:00 2001 From: Peter Hawkins Date: Tue, 14 Jul 2026 20:08:50 +0000 Subject: [PATCH] gh-152075: Avoid lock contention in _Py_Specialize_LoadGlobal under free threading Under high thread concurrency in free-threaded builds, `_Py_Specialize_LoadGlobal` suffers from lock contention when acquiring the critical section mutexes for the `globals` and `builtins` dictionaries during bytecode specialization. This PR skips LOAD_GLOBAL bytecode specialization if acquiring the two object mutexes would block. --- .../2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst | 2 ++ Python/specialize.c | 8 ++++++++ 2 files changed, 10 insertions(+) create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst new file mode 100644 index 000000000000000..84c7d36b97acba0 --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst @@ -0,0 +1,2 @@ +Reduced lock contention during LOAD_GLOBAL bytecode specialization under +free threading. diff --git a/Python/specialize.c b/Python/specialize.c index 773b55c329c7720..05cb76ff015ff40 100644 --- a/Python/specialize.c +++ b/Python/specialize.c @@ -1457,6 +1457,14 @@ _Py_Specialize_LoadGlobal( PyObject *globals, PyObject *builtins, _Py_CODEUNIT *instr, PyObject *name) { +#ifdef Py_GIL_DISABLED + if (PyMutex_IsLocked(&globals->ob_mutex) || PyMutex_IsLocked(&builtins->ob_mutex)) { + // Skip specialization if either dictionary is locked to avoid lock + // contention. + unspecialize(instr); + return; + } +#endif Py_BEGIN_CRITICAL_SECTION2(globals, builtins); specialize_load_global_lock_held(globals, builtins, instr, name); Py_END_CRITICAL_SECTION2();