From: Joseph Tibbertsma <josephtibbertsma@gmail.com>
Date: Wed, 25 Jun 2025 16:41:36 +0000 (-0700)
Subject: Fix needless spinning in `_PyMutex_LockTimed` with zero timeout (gh-135872)
X-Git-Tag: v3.15.0a1~1184
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=cbfaf41caf135b8598a560854cd59e992a2ccfed;p=thirdparty%2FPython%2Fcpython.git

Fix needless spinning in `_PyMutex_LockTimed` with zero timeout (gh-135872)

The free threading build could spin unnecessarily on `_Py_yield()` if the initial
compare and swap failed.
---

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-06-23-18-08-32.gh-issue-135871.50C528.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-23-18-08-32.gh-issue-135871.50C528.rst
new file mode 100644
index 000000000000..ce29ddecefe1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-23-18-08-32.gh-issue-135871.50C528.rst
@@ -0,0 +1,2 @@
+Non-blocking mutex lock attempts now return immediately when the lock is busy
+instead of briefly spinning in the :term:`free threading` build.
diff --git a/Python/lock.c b/Python/lock.c
index b125ad0c9e35..ea6ac00bfecc 100644
--- a/Python/lock.c
+++ b/Python/lock.c
@@ -58,7 +58,7 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags)
             return PY_LOCK_ACQUIRED;
         }
     }
-    else if (timeout == 0) {
+    if (timeout == 0) {
         return PY_LOCK_FAILURE;
     }