A little while ago, I got asked a question about when an object is allowed to be collected. It turns out that objects can be collected sooner than you think. In this entry, I'll talk a little about that. When we were formulating the memory model, this question came up with finalizers. Finalizers run in separate threads (usually they run in a dedicated finalizer thread). As a result, we had to worry about memory model effects. The basic question we had to answer was, what writes are the finalizers guaranteed to see? (If that doesn't sound like an interesting question, you should either go read my blog entry on volatiles or admit to yourself that this is not a blog in which you have much interest). Let's start with a mini-puzzler. A brief digression: I'm calling it a mini-puzzler because in general, for puzzlers, if you actually run them, you will get weird behavior. In this case, you probably won't see the weird behavior. But the weird behavior is perfectly legal Java behavior. That's the problem with multithreading and the memory model — you really never know what the results of a program will be from doing something as distasteful as actually running it.
Read more: Java Concurrency
Read more: Java Concurrency