Fixed assertion "Someone released me too many times: too many tokens!"

nova/process.py

@@ -205,13 +205,13 @@ class ProcessPool(object):
         self._pool.release()
         return rv
 
-class SharedPool(ProcessPool):
+class SharedPool(object):
     _instance = None
-    def __new__(cls, *args, **kwargs):
-        if not cls._instance:
-            cls._instance = super(SharedPool, cls).__new__(
-                    cls, *args, **kwargs)
-        return cls._instance
+    def __init__(self):
+        if SharedPool._instance is None:
+            self.__class__._instance = ProcessPool()
+    def __getattr__(self, key):
+        return getattr(self._instance, key)
 
 def simple_execute(cmd, **kwargs):
     return SharedPool().simple_execute(cmd, **kwargs)

nova/tests/process_unittest.py

@@ -118,5 +118,12 @@ class ProcessTestCase(test.TrialTestCase):
     def test_shared_pool_is_singleton(self):
         pool1 = process.SharedPool()
         pool2 = process.SharedPool()
-        self.assert_(id(pool1) == id(pool2))
+        self.assertEqual(id(pool1._instance), id(pool2._instance))
 
+    def test_shared_pool_works_as_singleton(self):
+        d1 = process.simple_execute('sleep 1')
+        d2 = process.simple_execute('sleep 0.005')
+        # lp609749: would have failed with
+        # exceptions.AssertionError: Someone released me too many times:
+        # too many tokens!
+        return d1