Java Concurrency (&c)

I was asked a question about benign data races in Java this week, so I thought I would take the opportunity to discuss one of the (only) approved patterns for benign races. So, at the risk of encouraging bad behavior (don't use data races in your code!), I will discuss the canonical example of "benign races for performance improvement". Also, I'll put in another plug for Josh Bloch's new revision of Effective Java (lgt amazon) , which I continue to recommend. As a reminder, basically, a data race is when you have one (or more) writes, and potentially some reads; they are all to the same memory location; they can happen at the same time; and that there is nothing in the program to prevent it. This is different from a race condition , which is when you just don't know the order in which two actions are going to occur. I've put more discussion of what a data race actually is at the bottom of this post. A lot of people think that it is okay to have a data