Is Java Thread getId() thread-safe?

As the question title says, is Thread.getId() thread-safe? I recently had a problem whilst multithreading and the solution was to remove the getId() call as it was making the thread hang.

Yes, it’s entirely thread-safe. The full implementation in JDK8 is:

public long getId() {
    return tid;
}

tid is initialized once during construction of the Thread object and never changed afterward.

If there was a problem in your code that removing it solved, it was what you were doing with the ID once you had it, not getting the ID.

short answer: yes,

long answer: thread safe means protecting against race condition

/**
 * Returns the identifier of this Thread.  The thread ID is a positive
 * <tt>long</tt> number generated when this thread was created.
 * The thread ID is unique and remains unchanged during its lifetime.
 * When a thread is terminated, this thread ID may be reused.
 *
 * @return this thread's ID.
 * @since 1.5
 */
public long getId() {
    return tid;
}

as you see the method is not synchronized, and the tid is private and not final declared, but the tid is set in the private method init and is never changing after that, that makes the value of tid immutable making it as well thread-safe