ThreadLocal 中的 UUID.randomUUID

Question

I am looking at the following method and I am wondering if putting UUID.randomUUID() within ThreadLocal makes any sense or will not introduce an unintentional overhead:

class UUIDUtil {

// TODO: why putting randomUUID into ThreadLocal? Will this avoid contentions?
public static final ThreadLocal<UUID> generator = 
                    ThreadLocal.withInitial(UUID::randomUUID);

}

Should I leave randomUUID within a ThreadLocal ? And if so, why?

Does putting UUID in ThreadLocal avoids contention if multiple threads want to generate a UUID at the same time?

Answer 1

When you have a look to the JavaDoc for ThreadLocal, you will find there some sample code that can be used to give each Thread a unique number (the original thread id will be reused!!).

With your code here, you will give each thread a unique id in the form of a UUID. And that has to be stored inside a ThreadLocal instance …

If that makes sense is a different story, but it can be useful for logging purposes, as it allows you to distinguish the threads more clearly as with the thread id only.