MAPREDUCE-4464. Reduce tasks failing with NullPointerException in ConcurrentHashMap.get(). Contributed by Clint Heath. (harsh)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1391089 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -78,6 +78,9 @@ Release 1.2.0 - unreleased
     MAPREDUCE-2770. Improve hadoop.job.history.location doc in
     mapred-default.xml. (Sandy Ryza via tomwhite)
 
+    MAPREDUCE-4464. Reduce tasks failing with NullPointerException in
+    ConcurrentHashMap.get(). (Clint Heath via harsh)
+
   OPTIMIZATIONS
 
     HDFS-2533. Backport: Remove needless synchronization on some FSDataSet

src/mapred/org/apache/hadoop/mapred/ReduceTask.java

@@ -2916,6 +2916,12 @@ class ReduceTask extends Task {
             {
               URI u = URI.create(event.getTaskTrackerHttp());
               String host = u.getHost();
+              if (host == null) {
+                throw new IOException("Invalid hostname found in tracker" +
+                   " location: '" +
+                   event.getTaskTrackerHttp() +
+                   "'");
+              }
               TaskAttemptID taskId = event.getTaskAttemptId();
               URL mapOutputLocation = new URL(event.getTaskTrackerHttp() + 
                                       "/mapOutput?job=" + taskId.getJobID() +