MAPREDUCE-7156. NullPointerException when reaching max shuffle connections. Contributed by Peter Bacsko

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/ShuffleHandler.java

@@ -910,6 +910,8 @@ public class ShuffleHandler extends AuxiliaryService {
     @Override
     public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent evt) 
         throws Exception {
+      super.channelOpen(ctx, evt);
+
       if ((maxShuffleConnections > 0) && (accepted.size() >= maxShuffleConnections)) {
         LOG.info(String.format("Current number of shuffle connections (%d) is " + 
             "greater than or equal to the max allowed shuffle connections (%d)", 
@@ -925,8 +927,6 @@ public class ShuffleHandler extends AuxiliaryService {
         return;
       }
       accepted.add(evt.getChannel());
-      super.channelOpen(ctx, evt);
-     
     }
 
     @Override