In the multi-threaded mode, database metadata operations did sometimes not work…

In the multi-threaded mode, database metadata operations did sometimes not work if the schema was changed at the same time (for example, if tables were dropped).

h2/src/main/org/h2/mvstore/db/MVTable.java

@@ -50,7 +50,8 @@ public class MVTable extends TableBase {
     private final ArrayList<Index> indexes = New.arrayList();
     private long lastModificationId;
     private volatile Session lockExclusiveSession;
-    /** using a ConcurrentHashMap as a Set */
+    
+    // using a ConcurrentHashMap as a set
     private final ConcurrentHashMap<Session, Session> lockSharedSessions = new ConcurrentHashMap<Session, Session>();
 
     /**
@@ -750,7 +751,6 @@ public class MVTable extends TableBase {
         }
         primaryIndex.remove(session);
         database.removeMeta(session, getId());
-        primaryIndex = null;
         close(session);
         invalidate();
     }

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

@@ -8,6 +8,7 @@ package org.h2.table;
 import java.util.ArrayList;
 import java.util.List;
 import org.h2.command.ddl.CreateTableData;
+import org.h2.engine.Database;
 import org.h2.engine.DbSettings;
 import org.h2.mvstore.db.MVTableEngine;
 import org.h2.util.StatementBuilder;
@@ -51,6 +52,11 @@ public abstract class TableBase extends Table {
 
     @Override
     public String getCreateSQL() {
+        Database db = getDatabase();
+        if (db == null) {
+            // closed
+            return null;
+        }
         StatementBuilder buff = new StatementBuilder("CREATE ");
         if (isTemporary()) {
             if (isGlobalTemporary()) {
@@ -79,7 +85,7 @@ public abstract class TableBase extends Table {
         }
         buff.append("\n)");
         if (tableEngine != null) {
-            DbSettings s = getDatabase().getSettings();
+            DbSettings s = db.getSettings();
             String d = s.defaultTableEngine;
             if (d == null && s.mvStore) {
                 d = MVTableEngine.class.getName();