added singleton and thread safe queue classes

src/python/dm/common/utility/singleton.py

+#!/usr/bin/env python
+
+class Singleton(object):
+
+    __instance = None
+
+    def __new__(cls, *args, **kwargs):
+        # Allow subclasses to create their own instances.
+        if cls.__instance is None or cls != type(cls.__instance):
+            instance = object.__new__(cls, *args, **kwargs)
+            cls.__instance = instance
+            instance.__init__(*args, **kwargs)
+        return cls.__instance
+
+    @classmethod
+    def getInstance(cls, *args, **kwargs):
+        return cls.__new__(cls, *args, **kwargs)
+
+    def __init__(self, *args, **kwargs):
+        # Only initialize once.
+        if Singleton.__instance is not None:
+            return
+
+####################################################################
+# Testing
+if __name__ == '__main__':
+    s1 = Singleton.getInstance()
+    s2 = Singleton()
+    s3 = Singleton.getInstance()
+    s4 = Singleton()
+    print 'S1: ', s1
+    print 'S2: ', s2
+    print 'S3: ', s3
+    print 'S4: ', s4
+    class A(Singleton):
+        def __init__(self, x):
+            self.x = x
+    class B(Singleton):
+        def __init__(self, x):
+            self.x = x
+    class C(Singleton):
+        def __init__(self):
+            self.x = 14
+
+    a1 = A(3)
+    a2 = A(4)
+    print a1
+    print a2
+    print a2.x, a1.x
+
+    b1 = B(6)
+    b2 = B(5)
+    print b1
+    print b2
+    print b2.x, b1.x
+
+    c1 = C()
+    c2 = C()
+    print c1
+    print c2
+    print c2.x, c1.x

src/python/dm/common/utility/threadSafeQueue.py

+#!/usr/bin/env python
+
+import threading
+
+class ThreadSafeQueue:
+
+    def __init__(self):
+        self.lock = threading.RLock()
+        self.queue = []
+
+    def push(self, item):
+        self.lock.acquire()
+        try:
+            self.queue.insert(0,item)
+        finally:
+            self.lock.release()
+
+    def pop(self):
+        # Return None if work queue is empty.
+        self.lock.acquire()
+        try:
+            item = None
+            if len(self.queue):
+                item = self.queue.pop()
+            return item
+        finally:
+            self.lock.release()
+
+    def getLength(self):
+        return len(self.queue)
+
+    def isEmpty(self):
+        return len(self.queue) == 0
+
+####################################################################
+# Testing
+
+if __name__ == '__main__':
+    q = ThreadSafeQueue()
+    for i in range(0,10):
+        q.push(i)
+        print 'Added: ', i
+
+    while not q.isEmpty():
+        i = q.pop() 
+        print 'Got: ', i
+
+
+