Index: src/main/java/org/apache/hadoop/hbase/client/HTable.java =================================================================== --- src/main/java/org/apache/hadoop/hbase/client/HTable.java (revision 17131) +++ src/main/java/org/apache/hadoop/hbase/client/HTable.java (working copy) @@ -28,6 +28,7 @@ import java.util.Arrays; import java.util.List; import java.util.Map; +import java.util.Collections; import java.util.NavigableMap; import java.util.TreeMap; import java.util.concurrent.ExecutorService; @@ -1267,8 +1268,8 @@ Batch.Call callable) throws IOException, Throwable { - final Map results = new TreeMap( - Bytes.BYTES_COMPARATOR); + final Map results = Collections.synchronizedMap(new TreeMap( + Bytes.BYTES_COMPARATOR)); coprocessorExec(protocol, startKey, endKey, callable, new Batch.Callback(){ public void update(byte[] region, byte[] row, R value) {