RFR 8024253: ThreadLocal random can use SecureRandom for the initial seed

[Doug Lea]

On 09/16/2013 10:39 AM, Peter Levart wrote:

> So perhaps the right strategy would be to get the hardware address of the 1st
> interface that has it, but don't bother to search more than N interfaces

Where N==2 seems to be the best policy, since at most loopback is
legitimately null. Putting the suggestions together:

     private static long initialSeed() {
         String pp = java.security.AccessController.doPrivileged(
                 new sun.security.action.GetPropertyAction(
                         "java.util.secureRandomSeed"));
         if (pp != null && pp.equalsIgnoreCase("true")) {
             byte[] seedBytes = java.security.SecureRandom.getSeed(8);
             long s = (long)(seedBytes[0]) & 0xffL;
             for (int i = 1; i < 8; ++i)
                 s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
             return s;
         }
         long h = 0L;
         try {
             Enumeration<NetworkInterface> ifcs =
                 NetworkInterface.getNetworkInterfaces();
             boolean retry = false; // retry once if getHardwareAddress is null
             while (ifcs.hasMoreElements()) {
                 NetworkInterface ifc = ifcs.nextElement();
                 byte[] bs = ifc.getHardwareAddress();
                 if (bs != null) {
                     for (int i = 0; i < 8 && i < bs.length; ++i)
                         h = (h << 8) ^ bs[i];
                     break;
                 }
                 else if (!retry)
                     retry = true;
                 else
                     break;
             }
         } catch (Exception ignore) {
         }
         return (mix64(h ^ System.currentTimeMillis()) ^
                 mix64(System.nanoTime()));
     }