Issue#550: double buffer pattern (#1024)

* Basic implementation

* implement double buffer

* add unit test

* add unit test

* Add Readme

* Change local value declaration to var

* Remove unused fields

pom.xml

@@ -183,6 +183,7 @@
         <module>data-locality</module>
         <module>subclass-sandbox</module>
         <module>circuit-breaker</module>
+        <module>double-buffer</module>
     </modules>
 
     <repositories>