Laid groundwork for displaying avatar images

avcache.py

@@ -0,0 +1,40 @@
+from threading import RLock
+
+
+class AvCache:
+    """
+    Store a cache of avatar images we've already downloaded.
+    This cache will be accessed by a number of threads, so it includes
+    a lock as well.
+    """
+
+    class __impl:
+        """ Implementation of the singleton interface """
+
+        def __init__(self):
+            self.lock = RLock()
+            self.map = {}
+
+
+    # storage for the instance reference
+    __instance = None
+
+    def __init__(self):
+        """ Create singleton instance """
+        # Check whether we already have an instance
+        if AvCache.__instance is None:
+            # Create and remember instance
+            AvCache.__instance = AvCache.__impl()
+
+        # Store instance reference as the only member in the handle
+        self.__dict__['_AvCache__instance'] = AvCache.__instance
+
+    def __getattr__(self, attr):
+        """ Delegate access to implementation """
+        return getattr(self.__instance, attr)
+
+    def __setattr__(self, attr, value):
+        """ Delegate access to implementation """
+        return setattr(self.__instance, attr, value)
+
+# end class AvCache