8253750: use build-stable default seed for Utils.RANDOM_GENERATOR

Reviewed-by: rriggs

Author: iignatev

test/lib-test/jdk/test/lib/RandomGeneratorTest.java

@@ -46,9 +46,10 @@
 /**
  * The test verifies correctness of work {@link jdk.test.lib.Utils#getRandomInstance()}.
  * Test works in three modes: same seed provided, no seed provided and
- * different seed provided. In the first case the test expects that all random numbers
- * will be repeated in all next iterations. For other two modes test expects that
- * randomly generated numbers differ from original.
+ * different seed provided.
+ * In the first case, the test expects that all random numbers will be repeated in all next iterations.
+ * In the second case, the numbers are expected to be the same for promotable builds and different for other builds.
+ * In the last case, the test expects the randomly generated numbers differ from original.
  */
 public class RandomGeneratorTest {
     private static final String SEED_VM_OPTION = "-D" + Utils.SEED_PROPERTY_NAME + "=";
@@ -102,12 +103,22 @@ public void verify(String orig, String[] cmdLine) {
                 cmdLine[0] = getSeedOption();
                 super.verify(orig, cmdLine);
             }
+
+            @Override
+            protected boolean isOutputExpected(String orig, String output) {
+                return !output.equals(orig);
+            }
         },
         NO_SEED {
             @Override
             public String getSeedOption() {
                 return null;
             }
+
+            @Override
+            protected boolean isOutputExpected(String orig, String output) {
+                return Runtime.version().build().orElse(0) > 0 ^ !output.equals(orig);
+            }
         };
 
         /**
@@ -118,9 +129,7 @@ public String getSeedOption() {
          */
         public abstract String getSeedOption();
 
-        protected boolean isOutputExpected(String orig, String output) {
-            return !output.equals(orig);
-        }
+        protected abstract boolean isOutputExpected(String orig, String output);
 
         /**
          * Verifies that the original output meets expectations

test/lib/jdk/test/lib/Utils.java

@@ -25,8 +25,6 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.lang.annotation.Annotation;
-import java.lang.reflect.Method;
 import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
@@ -35,11 +33,15 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.attribute.FileAttribute;
 import java.nio.channels.SocketChannel;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -127,9 +129,8 @@ public final class Utils {
      */
     public static final String SEED_PROPERTY_NAME = "jdk.test.lib.random.seed";
 
-    /* (non-javadoc)
-     * Random generator with (or without) predefined seed. Depends on
-     * "jdk.test.lib.random.seed" property value.
+    /**
+     * Random generator with predefined seed.
      */
     private static volatile Random RANDOM_GENERATOR;
 
@@ -141,7 +142,32 @@ public final class Utils {
     /**
      * Contains the seed value used for {@link java.util.Random} creation.
      */
-    public static final long SEED = Long.getLong(SEED_PROPERTY_NAME, new Random().nextLong());
+    public static final long SEED;
+    static {
+       var seed = Long.getLong(SEED_PROPERTY_NAME);
+       if (seed != null) {
+           // use explicitly set seed
+           SEED = seed;
+       } else {
+           var v = Runtime.version();
+           // promotable builds have build number, and it's greater than 0
+           if (v.build().orElse(0) > 0) {
+               // promotable build -> use 1st 8 bytes of md5($version)
+               try {
+                   var md = MessageDigest.getInstance("MD5");
+                   var bytes = v.toString()
+                                .getBytes(StandardCharsets.UTF_8);
+                   bytes = md.digest(bytes);
+                   SEED = ByteBuffer.wrap(bytes).getLong();
+               } catch (NoSuchAlgorithmException e) {
+                   throw new Error(e);
+               }
+           } else {
+               // "personal" build -> use random seed
+               SEED = new Random().nextLong();
+           }
+       }
+    }
     /**
      * Returns the value of 'test.timeout.factor' system property
      * converted to {@code double}.
@@ -531,9 +557,13 @@ public static byte[] toByteArray(String hex) {
 
     /**
      * Returns {@link java.util.Random} generator initialized with particular seed.
-     * The seed could be provided via system property {@link Utils#SEED_PROPERTY_NAME}
-     * In case no seed is provided, the method uses a random number.
+     * The seed could be provided via system property {@link Utils#SEED_PROPERTY_NAME}.
+     * In case no seed is provided and the build under test is "promotable"
+     * (its build number ({@code $BUILD} in {@link Runtime.Version}) is greater than 0,
+     * the seed based on string representation of {@link Runtime#version()} is used.
+     * Otherwise, the seed is randomly generated.
      * The used seed printed to stdout.
+     *
      * @return {@link java.util.Random} generator with particular seed.
      */
     public static Random getRandomInstance() {