Merged revisions 76117 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r76117 | antoine.pitrou | 2009-11-05 14:42:29 +0100 (jeu., 05 nov. 2009) | 5 lines

  Issue #7264: Fix a possible deadlock when deallocating thread-local objects
  which are part of a reference cycle.
........

Lib/_threading_local.py

@@ -218,10 +218,12 @@ def __del__(self):
         key = object.__getattribute__(self, '_local__key')
 
         try:
-            threads = list(threading.enumerate())
+            # We use the non-locking API since we might already hold the lock
+            # (__del__ can be called at any point by the cyclic GC).
+            threads = threading._enumerate()
         except:
-            # If enumerate fails, as it seems to do during
+            # If enumerating the current threads fails, as it seems to do
-            # shutdown, we'll skip cleanup under the assumption
+            # during shutdown, we'll skip cleanup under the assumption
             # that there is nothing to clean up.
             return
 

Lib/threading.py

@@ -815,6 +815,10 @@ def activeCount():
 
 active_count = activeCount
 
+def _enumerate():
+    # Same as enumerate(), but without the lock. Internal use only.
+    return _active.values() + _limbo.values()
+
 def enumerate():
     _active_limbo_lock.acquire()
     active = _active.values() + _limbo.values()

Misc/NEWS

@@ -24,6 +24,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #7264: Fix a possible deadlock when deallocating thread-local objects
+  which are part of a reference cycle.
+
 - Issue #7249: Methods of io.BytesIO now allow `long` as well as `int`
   arguments.