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())); }
