HDFS-2541. svn merge -c 1204114 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1204115 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -31,6 +31,9 @@ Release 0.23.1 - UNRELEASED
 
   BUG FIXES
 
+    HDFS-2541. For a sufficiently large value of blocks, the DN Scanner 
+    may request a random number with a negative seed value. (harsh)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockPoolSliceScanner.java

@@ -34,7 +34,6 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
-import java.util.Random;
 import java.util.TreeSet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -252,8 +251,9 @@ class BlockPoolSliceScanner {
      */
     long period = Math.min(scanPeriod, 
                            Math.max(blockMap.size(),1) * 600 * 1000L);
+    int periodInt = Math.abs((int)period);
     return System.currentTimeMillis() - scanPeriod + 
-        DFSUtil.getRandom().nextInt((int)period);    
+        DFSUtil.getRandom().nextInt(periodInt);
   }
 
   /** Adds block to list of blocks */