Re: 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()));
    }