In _DummyThread objects the lock stored in __block (allocated thanks to

_Thread.__init__) was never used.  This is a waste since locks use OS
primitives that are in limited supply.  So the lock is deleted in
_DummyThread.__init__ .

Closes bug #1089632.

Lib/threading.py

@@ -653,6 +653,7 @@ class _DummyThread(Thread):
 
     def __init__(self):
         Thread.__init__(self, name=_newname("Dummy-%d"))
+        del self._Thread__block
         self._Thread__started = True
         _active_limbo_lock.acquire()
         _active[_get_ident()] = self

Misc/NEWS

@@ -33,6 +33,11 @@ Extension Modules
 Library
 -------
 
+- _DummyThread objects in the threading module now delete self.__block that is
+  inherited from _Thread since it uses up a lock allocated by 'thread'.  The
+  lock primitives tend to be limited in number and thus should not be wasted on
+  a _DummyThread object.  Fixes bug #1089632.
+
 - The imghdr module now detects Exif files.
 
 - StringIO.truncate() now correctly adjusts the size attribute.