Don't deadlock on a reentrant call.
diff --git a/Lib/functools.py b/Lib/functools.py
index 226a46e..71022e5 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -14,9 +14,9 @@
 from _functools import partial, reduce
 from collections import namedtuple
 try:
-    from _thread import allocate_lock as Lock
+    from _thread import RLock
 except:
-    from _dummy_thread import allocate_lock as Lock
+    from dummy_threading import RLock
 
 
 ################################################################################
@@ -207,7 +207,7 @@
         hits = misses = currsize = 0
         full = False
         cache_get = cache.get    # bound method to lookup a key or return None
-        lock = Lock()            # because linkedlist updates aren't threadsafe
+        lock = RLock()           # because linkedlist updates aren't threadsafe
         root = []                # root of the circular doubly linked list
         root[:] = [root, root, None, None]     # initialize by pointing to self