private static final int hash() {
    int h = System.identityHashCode(Thread.currentThread());
    // You would think that System.identityHashCode on the current thread
    // would be a good hash fcn, but actually on SunOS 5.8 it is pretty lousy
    // in the low bits.
    h ^= (h>>>20) ^ (h>>>12);   // Bit spreader, borrowed from Doug Lea
    h ^= (h>>> 7) ^ (h>>> 4);
    return h<<2;                // Pad out cache lines.  The goal is to avoid cache-line contention
  }