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

[Paul Sandoz]

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()));
     }