https://github.com/python/cpython/commit/ac8ba0ca5a04cd7b27b44822d31df640e817fd78
commit: ac8ba0ca5a04cd7b27b44822d31df640e817fd78
branch: main
author: Peter Hawkins <[email protected]>
committer: colesbury <[email protected]>
date: 2026-07-31T01:28:20Z
summary:
gh-152075: Avoid lock contention in _Py_Specialize_LoadGlobal under free
threading (gh-153720)
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.
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-07-14-20-19-48.gh-issue-152075.V9Rwhp.rst
M Python/specialize.c
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();
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