在 Java 1.4 中获取线程的唯一标识符

Question

In Java 1.4, is there any better way of getting a Thread's ID than using Thread.getName() ?

I mean, getName() in unit tests returns something like "Thread-1" , but in WebLogic 10 I get "[ACTIVE] ExecuteThread: '1' for queue: 'weblogic.kernel.Default (self-tuning)'.xml" .

Answer 1

Thread.getId (it can theoretically overflow , but it is defined not to and in practice will not).

1.5 is going through its End of Service Life period now, but if you are using old dusty-decks 1.4, then you can implement your own with ThreadLocal . (Note, don't follow the Java SE 6 API docs too closely!)

Answer 2

Why do you need this? Because depending on your answer, there are several approaches.

First, understand that a thread's name is not guaranteed to be unique. Nor is identity hashcode.

If you truly want to associate a unique ID to a thread, you're going to need to do it yourself. Probably using an IdentityHashMap. However, that will introduce a strong reference that you don't want to have hanging around in a production app.

Edit: TofuBeer has solution that's probably better, although the docs note that thread IDs can be reused.

Answer 3

As mentioned in " Thread.getId() global uniqueness question " SO question, and confirmed by the source code of Thread.java :

/* For generating thread ID */
private static long threadSeqNumber;

/* Set thread ID */
tid = nextThreadID();

private static synchronized long nextThreadID() {
    return ++threadSeqNumber;
}

The thread id is very simple to implement yourself if your are still in java1.4.
However this implementation means a given thread will not have the same id when you are running your program several times.
So depending on what you need, you may have to implement a naming policy which is both:

• unique for a given runtime session
• reused from session to session
• still linked to the internal original naming policy managed by the 1.4 JVM ("Thread-1", "Thread-2", ...)

Answer 4

You can use getID if you are on JDK 1.5 or higher.

Is it the case that you need a consistent value for each time you run the unit tests, or is just a unique value good enough?