Thread.getId() global uniqueness question

Question

If multiple Java applications are running on a system, is each Thread ID unique relative to all other Java threads, regardless of what application they are running in?

J

Answer 1

According to the JDK source, a thread ID is unique in a given JVM - in fact, it's simply implemented as a running sequence.

Here's the nextThreadID() method from 1.6.0_10:

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

(there's probably actually a long overflow bug in there, presumably it's never actually happened)