RFR 8066397 Remove network-related seed initialization code in ThreadLocal/SplittableRandom

[Chris Hegarty]

Thanks for doing this Paul. Looks good ( with Alan and Doug’s comments ).

-Chris.

On 2 Dec 2014, at 10:02, Paul Sandoz <paul.sandoz at oracle.com> wrote:

> Hi,
> 
> Please find below a patch to remove the networking code computing a seed in ThreadLocal/SplittableRandom.
> 
> We thought it a good idea at the time :-) but subsequently on certain platforms this results in very high initalization costs that can propagate to other classes such as ConcurrentSkipList*.
> 
> The short-term solution is to remove this code and fallback just using current system time. This needs to be back-ported to 8u40.
> 
> A longer term solution is to provide a simple public API to get access to some seed bytes that is optimal for the underlying platform, for example, based on Peter's investigations. For linux /dev/urandom is sufficient as a source of bytes. The main problem seems to be Windows. It would also be nice to back-port to say 8u60 using a private API and update TLR/SR.
> 
> Paul.
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8060435
> 
> diff -r 1b599b4755bd src/java.base/share/classes/java/util/SplittableRandom.java
> --- a/src/java.base/share/classes/java/util/SplittableRandom.java	Mon Dec 01 17:59:39 2014 -0800
> +++ b/src/java.base/share/classes/java/util/SplittableRandom.java	Tue Dec 02 10:53:47 2014 +0100
> @@ -237,34 +237,7 @@
>                 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();
> -                if (!ifc.isVirtual()) { // skip fake addresses
> -                    byte[] bs = ifc.getHardwareAddress();
> -                    if (bs != null) {
> -                        int n = bs.length;
> -                        int m = Math.min(n >>> 1, 4);
> -                        for (int i = 0; i < m; ++i)
> -                            h = (h << 16) ^ (bs[i] << 8) ^ bs[n-1-i];
> -                        if (m < 4)
> -                            h = (h << 8) ^ bs[n-1-m];
> -                        h = mix64(h);
> -                        break;
> -                    }
> -                    else if (!retry)
> -                        retry = true;
> -                    else
> -                        break;
> -                }
> -            }
> -        } catch (Exception ignore) {
> -        }
> -        return (h ^ mix64(System.currentTimeMillis()) ^
> +        return (mix64(System.currentTimeMillis()) ^
>                 mix64(System.nanoTime()));
>     }
> 
> diff -r 1b599b4755bd src/java.base/share/classes/java/util/concurrent/ThreadLocalRandom.java
> --- a/src/java.base/share/classes/java/util/concurrent/ThreadLocalRandom.java	Mon Dec 01 17:59:39 2014 -0800
> +++ b/src/java.base/share/classes/java/util/concurrent/ThreadLocalRandom.java	Tue Dec 02 10:53:47 2014 +0100
> @@ -147,34 +147,7 @@
>                 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();
> -                if (!ifc.isVirtual()) { // skip fake addresses
> -                    byte[] bs = ifc.getHardwareAddress();
> -                    if (bs != null) {
> -                        int n = bs.length;
> -                        int m = Math.min(n >>> 1, 4);
> -                        for (int i = 0; i < m; ++i)
> -                            h = (h << 16) ^ (bs[i] << 8) ^ bs[n-1-i];
> -                        if (m < 4)
> -                            h = (h << 8) ^ bs[n-1-m];
> -                        h = mix64(h);
> -                        break;
> -                    }
> -                    else if (!retry)
> -                        retry = true;
> -                    else
> -                        break;
> -                }
> -            }
> -        } catch (Exception ignore) {
> -        }
> -        return (h ^ mix64(System.currentTimeMillis()) ^
> +        return (mix64(System.currentTimeMillis()) ^
>                 mix64(System.nanoTime()));
>     }