Redesign cleanupSites() and all the related stuff and rename it to periodic maintenance.

src/util/CircularIterator.py

@@ -0,0 +1,34 @@
+import random
+
+class CircularIterator:
+    def __init__(self):
+        self.successive_count = 0
+        self.last_size = 0
+        self.index = -1
+
+    def next(self, items):
+        self.last_size = len(items)
+
+        if self.last_size == 0:
+            return None
+
+        if self.index < 0:
+            self.index = random.randint(0, self.last_size)
+        else:
+            self.index += 1
+
+        self.index = self.index % self.last_size
+
+        self.successive_count += 1
+
+        return items[self.index]
+
+    def resetSuccessiveCount(self):
+        self.successive_count = 0
+
+    def getSuccessiveCount(self):
+        return self.successive_count
+
+    def isWrapped(self):
+        return self.successive_count >= self.last_size
+

src/util/__init__.py

@@ -1,4 +1,5 @@
 from .Cached import Cached
+from .CircularIterator import CircularIterator
 from .Event import Event
 from .Noparallel import Noparallel
 from .Pooled import Pooled