Use a collections.deque which has thread safe pop/append

Incase of multithreading deques are inherently safe to do
pop/appends on while arrays may not be (but are likely). To
ensure this use the deque which is specified to be thread
safe for these operations.

osprofiler/profiler.py

@@ -13,7 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-
+import collections
 import threading
 import uuid
 
@@ -66,7 +66,7 @@ class Profiler(object):
         self.notifier = notifier.get_notifier()
         if not base_id:
             base_id = str(uuid.uuid4())
-        self._trace_stack = [base_id, parent_id or base_id]
+        self._trace_stack = collections.deque([base_id, parent_id or base_id])
         self._name = []
 
     def __call__(self, name, info=None):