Merge pull request #192 from svladykin/nullRow

Table.getNullRow() improved concurrency

h2/src/main/org/h2/table/Table.java

@@ -6,6 +6,7 @@
 package org.h2.table;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Set;
@@ -104,7 +105,7 @@ public abstract class Table extends SchemaObjectBase {
     private ArrayList<TableView> views;
     private boolean checkForeignKeyConstraints = true;
     private boolean onCommitDrop, onCommitTruncate;
-    private Row nullRow;
+    private volatile Row nullRow;
 
     public Table(Schema schema, int id, String name, boolean persistIndexes,
             boolean persistData) {
@@ -616,14 +617,15 @@ public abstract class Table extends SchemaObjectBase {
         return new SimpleRow(new Value[columns.length]);
     }
 
-    synchronized Row getNullRow() {
-        if (nullRow == null) {
-            nullRow = new Row(new Value[columns.length], 1);
-            for (int i = 0; i < columns.length; i++) {
-                nullRow.setValue(i, ValueNull.INSTANCE);
-            }
+    Row getNullRow() {
+        Row row = nullRow;
+        if (row == null) {
+            // Here can be concurrently produced more than one row, but it must be ok.
+            Value[] values = new Value[columns.length];
+            Arrays.fill(values, ValueNull.INSTANCE);
+            nullRow = row = new Row(values, 1);
         }
-        return nullRow;
+        return row;
     }
 
     public Column[] getColumns() {