Thinking about this further, a pragmatic enhancement to Thread::yield might look like this:

    enum Hint {
      ALWAYS,
      FREQUENT,
      SOMETIMES,
      INFREQUENT,
      NEVER
    }

    Thread::yield(Hint);

The method could be intrinsic to the compiler+runtime to provide runtime optimization (loop unrolling, tuning, etc.) of the 2nd - 4th cases. This would neatly avoid the need to:

    long n = 0;
    while (true) {
        // stuff
        if (++n > SOME_LIMIT) {
            n = 0;
            // yield here
        }
    }

... or similar.