Issue #7282: Fix a memory leak when an RLock was used in a thread other

than those started through `threading.Thread` (for example, using
`thread.start_new_thread()`.

Lib/test/lock_tests.py

@@ -130,6 +130,19 @@ class BaseLockTests(BaseTestCase):
         # Check the lock is unacquired
         Bunch(f, 1).wait_for_finished()
 
+    def test_thread_leak(self):
+        # The lock shouldn't leak a Thread instance when used from a foreign
+        # (non-threading) thread.
+        lock = self.locktype()
+        def f():
+            lock.acquire()
+            lock.release()
+        n = len(threading.enumerate())
+        # We run many threads in the hope that existing threads ids won't
+        # be recycled.
+        Bunch(f, 15).wait_for_finished()
+        self.assertEqual(n, len(threading.enumerate()))
+
 
 class LockTests(BaseLockTests):
     """

Lib/test/test_threading.py

@@ -143,11 +143,9 @@ class ThreadTests(BaseTestCase):
     def test_foreign_thread(self):
         # Check that a "foreign" thread can use the threading module.
         def f(mutex):
-            # Acquiring an RLock forces an entry for the foreign
+            # Calling current_thread() forces an entry for the foreign
             # thread to get made in the threading._active map.
-            r = threading.RLock()
-            r.acquire()
-            r.release()
+            threading.current_thread()
             mutex.release()
 
         mutex = threading.Lock()

Lib/threading.py

@@ -106,14 +106,16 @@ class _RLock(_Verbose):
 
     def __repr__(self):
         owner = self.__owner
-        return "<%s(%s, %d)>" % (
-                self.__class__.__name__,
-                owner and owner.name,
-                self.__count)
+        try:
+            owner = _active[owner].name
+        except KeyError:
+            pass
+        return "<%s owner=%r count=%d>" % (
+                self.__class__.__name__, owner, self.__count)
 
     def acquire(self, blocking=1):
-        me = current_thread()
-        if self.__owner is me:
+        me = _get_ident()
+        if self.__owner == me:
             self.__count = self.__count + 1
             if __debug__:
                 self._note("%s.acquire(%s): recursive success", self, blocking)
@@ -132,7 +134,7 @@ class _RLock(_Verbose):
     __enter__ = acquire
 
     def release(self):
-        if self.__owner is not current_thread():
+        if self.__owner != _get_ident():
             raise RuntimeError("cannot release un-acquired lock")
         self.__count = count = self.__count - 1
         if not count:
@@ -168,7 +170,7 @@ class _RLock(_Verbose):
         return (count, owner)
 
     def _is_owned(self):
-        return self.__owner is current_thread()
+        return self.__owner == _get_ident()
 
 
 def Condition(*args, **kwargs):

Misc/NEWS

@@ -426,6 +426,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #7282: Fix a memory leak when an RLock was used in a thread other
+  than those started through `threading.Thread` (for example, using
+  `thread.start_new_thread()`.
+
 - Issue #7264: Fix a possible deadlock when deallocating thread-local objects
   which are part of a reference cycle.