Adaptive Software Solutions

I read this article by Bill Pugh on why the double checked locking idiom does not guarantee thread safety in Java Singletons. That article taught me a lot of new things, and to be honest, I had to re-read that article at least a couple of times to partially understand it :-) I recently created a presentation to make at DevCamp on this topic. What follows are my slides and an explanation of each slide. I hope you enjoy this presentation and find it useful. Double checkedlockingjavasingletons View more presentations from parag . slide 1: In this presentation I will discuss the double checked locking idiom, and explain why it does not work to provide thread safety to Java Singletons. I will also talk about how using volatile fields will fix the problem in JDK 1.5 onwards. slide 2 (Singleton): Many of you might already have used the Singleton design pattern . In case you have not, here is a brief description of what Singletons are. The Singleton pattern is used when we want to ensure...

In the previous post I had said that it may not be a good idea to have static attributes in your class. The Singleton design pattern also uses a static attribute to hold the Singleton instance. Even though there are valid uses of Singletons, lately this pattern has come under considerable attack . Here is another page on the Portland Pattern Repository Wiki , that outlines a practical problem someone faced while using Singletons. Google has an open source tool to detect Singletons. They call it the Google Singleton Detector . They have identified 4 types of Singletons, namely: Singletons, Hingletons, Mingletons, and Fingletons. You can find definitions for all the funny _ingletons on their wiki , but for those of you too lazy to visit the wiki, I will quote them here: Singleton: A class for which there should only be one instance in the entire system at any given time. This program detects singletons which enforce their own singularity, which means they keep one static instance of the...