Issue #11915: threading.RLock()._release_save() raises a RuntimeError if the

lock was not acquired.

Lib/test/lock_tests.py

@@ -247,6 +247,7 @@ class RLockTests(BaseLockTests):
         # Cannot release an unacquired lock
         lock = self.locktype()
         self.assertRaises(RuntimeError, lock.release)
+        self.assertRaises(RuntimeError, lock._release_save)
         lock.acquire()
         lock.acquire()
         lock.release()
@@ -254,6 +255,7 @@ class RLockTests(BaseLockTests):
         lock.release()
         lock.release()
         self.assertRaises(RuntimeError, lock.release)
+        self.assertRaises(RuntimeError, lock._release_save)
 
     def test_different_thread(self):
         # Cannot release from a different thread

Lib/threading.py

@@ -157,6 +157,8 @@ class _RLock(_Verbose):
     def _release_save(self):
         if __debug__:
             self._note("%s._release_save()", self)
+        if self._count == 0:
+            raise RuntimeError("cannot release un-acquired lock")
         count = self._count
         self._count = 0
         owner = self._owner

Misc/NEWS

@@ -113,6 +113,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #11915: threading.RLock()._release_save() raises a RuntimeError if the
+  lock was not acquired.
+
 - Issue #11258: Speed up ctypes.util.find_library() under Linux by a factor
   of 5 to 10.  Initial patch by Jonas H.
 

Modules/_threadmodule.c

@@ -414,6 +414,12 @@ rlock_release_save(rlockobject *self)
     long owner;
     unsigned long count;
 
+    if (self->rlock_count == 0) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "cannot release un-acquired lock");
+        return NULL;
+    }
+
     owner = self->rlock_owner;
     count = self->rlock_count;
     self->rlock_count = 0;