When concurrently preparing many statements with a subquery, in some cases the query didn't run.

h2/src/main/org/h2/command/dml/Query.java

@@ -427,20 +427,9 @@ public abstract class Query extends Prepared {
     }
 
     public final long getMaxDataModificationId() {
-        ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.SET_MAX_DATA_MODIFICATION_ID);
+        ExpressionVisitor visitor = ExpressionVisitor.getMaxModificationIdVisitor();
         isEverything(visitor);
         return visitor.getMaxDataModificationId();
     }
 
-    /**
-     * Visit all expressions and subqueries in this query using the visitor pattern.
-     *
-     * @param expressionVisitorType the visitor type
-     * @return true if no component returned false
-     */
-    public final boolean isEverything(int expressionVisitorType) {
-        ExpressionVisitor visitor = ExpressionVisitor.get(expressionVisitorType);
-        return isEverything(visitor);
-    }
-
 }

h2/src/main/org/h2/command/dml/Select.java

@@ -789,8 +789,8 @@ public class Select extends Query {
         }
         if (isGroupQuery && groupIndex == null && havingIndex < 0 && filters.size() == 1) {
             if (condition == null) {
-                ExpressionVisitor optimizable = ExpressionVisitor.get(ExpressionVisitor.OPTIMIZABLE_MIN_MAX_COUNT_ALL);
-                optimizable.setTable((filters.get(0)).getTable());
+                Table t = filters.get(0).getTable();
+                ExpressionVisitor optimizable = ExpressionVisitor.getOptimizableVisitor(t);
                 isQuickAggregateQuery = isEverything(optimizable);
             }
         }
@@ -1193,22 +1193,21 @@ public class Select extends Query {
         }
         default:
         }
-        visitor.incrementQueryLevel(1);
+        ExpressionVisitor v2 = visitor.incrementQueryLevel(1);
         boolean result = true;
         for (int i = 0, size = expressions.size(); i < size; i++) {
             Expression e = expressions.get(i);
-            if (!e.isEverything(visitor)) {
+            if (!e.isEverything(v2)) {
                 result = false;
                 break;
             }
         }
-        if (result && condition != null && !condition.isEverything(visitor)) {
+        if (result && condition != null && !condition.isEverything(v2)) {
             result = false;
         }
-        if (result && having != null && !having.isEverything(visitor)) {
+        if (result && having != null && !having.isEverything(v2)) {
             result = false;
         }
-        visitor.incrementQueryLevel(-1);
         return result;
     }
 

h2/src/main/org/h2/expression/Comparison.java

@@ -356,14 +356,12 @@ public class Comparison extends Condition {
             return;
         }
         if (l == null) {
-            ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.NOT_FROM_RESOLVER);
-            visitor.setResolver(filter);
+            ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
             if (!left.isEverything(visitor)) {
                 return;
             }
         } else if (r == null) {
-            ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.NOT_FROM_RESOLVER);
-            visitor.setResolver(filter);
+            ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
             if (!right.isEverything(visitor)) {
                 return;
             }

h2/src/main/org/h2/expression/ConditionIn.java

@@ -110,8 +110,7 @@ public class ConditionIn extends Condition {
             return;
         }
         if (session.getDatabase().getSettings().optimizeInList) {
-            ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.NOT_FROM_RESOLVER);
-            visitor.setResolver(filter);
+            ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
             for (Expression e : valueList) {
                 if (!e.isEverything(visitor)) {
                     return;

h2/src/main/org/h2/expression/ConditionInSelect.java

@@ -130,8 +130,7 @@ public class ConditionInSelect extends Condition {
         if (filter != l.getTableFilter()) {
             return;
         }
-        ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.NOT_FROM_RESOLVER);
-        visitor.setResolver(filter);
+        ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
         if (!query.isEverything(visitor)) {
             return;
         }

h2/src/main/org/h2/expression/Expression.java

@@ -128,18 +128,6 @@ public abstract class Expression {
      */
     public abstract int getCost();
 
-    /**
-     * Check if this expression and all sub-expressions can fulfill a criteria.
-     * This is a convenience function.
-     *
-     * @param expressionVisitorType the visitor type
-     * @return if the criteria can be fulfilled
-     */
-    public final boolean isEverything(int expressionVisitorType) {
-        ExpressionVisitor visitor = ExpressionVisitor.get(expressionVisitorType);
-        return isEverything(visitor);
-    }
-
     /**
      * If it is possible, return the negated expression. This is used
      * to optimize NOT expressions: NOT ID>10 can be converted to

h2/src/main/org/h2/expression/ExpressionColumn.java

@@ -165,6 +165,7 @@ public class ExpressionColumn extends Expression {
         }
         Value value = columnResolver.getValue(column);
         if (value == null) {
+            columnResolver.getValue(column);
             throw DbException.get(ErrorCode.MUST_GROUP_BY_COLUMN_1, getSQL());
         }
         return value;

h2/src/main/org/h2/expression/ExpressionVisitor.java

@@ -7,10 +7,7 @@
 package org.h2.expression;
 
 import java.util.HashSet;
-
-import org.h2.constant.SysProperties;
 import org.h2.engine.DbObject;
-import org.h2.message.DbException;
 import org.h2.table.ColumnResolver;
 import org.h2.table.Table;
 
@@ -98,15 +95,29 @@ public class ExpressionVisitor {
      */
     public static final ExpressionVisitor QUERY_COMPARABLE_VISITOR = new ExpressionVisitor(QUERY_COMPARABLE);
 
-    private int queryLevel;
-    private Table table;
-    private int type;
-    private long maxDataModificationId;
-    private ColumnResolver resolver;
-    private HashSet<DbObject> dependencies;
+    private final int type;
+    private final int queryLevel;
+    private final HashSet<DbObject> dependencies;
+    private final Table table;
+    private final long[] maxDataModificationId;
+    private final ColumnResolver resolver;
+
+    private ExpressionVisitor(int type, int queryLevel, HashSet<DbObject> dependencies, Table table, ColumnResolver resolver, long[] maxDataModificationId) {
+        this.type = type;
+        this.queryLevel = queryLevel;
+        this.dependencies = dependencies;
+        this.table = table;
+        this.resolver = resolver;
+        this.maxDataModificationId = maxDataModificationId;
+    }
 
     private ExpressionVisitor(int type) {
         this.type = type;
+        this.queryLevel = 0;
+        this.dependencies = null;
+        this.table = null;
+        this.resolver = null;
+        this.maxDataModificationId = null;
     }
 
     /**
@@ -115,18 +126,22 @@ public class ExpressionVisitor {
      * @param type the visitor type
      * @return the new visitor
      */
-    public static ExpressionVisitor get(int type) {
-        if (SysProperties.CHECK) {
-            switch (type) {
-            case INDEPENDENT:
-            case DETERMINISTIC:
-            case EVALUATABLE:
-            case READONLY:
-            case QUERY_COMPARABLE:
-                throw DbException.throwInternalError("Singleton not used");
-            }
-        }
-        return new ExpressionVisitor(type);
+
+
+    public static ExpressionVisitor getDependenciesVisitor(HashSet<DbObject> dependencies) {
+        return new ExpressionVisitor(GET_DEPENDENCIES, 0, dependencies, null, null, null);
+    }
+
+    public static ExpressionVisitor getOptimizableVisitor(Table table) {
+        return new ExpressionVisitor(OPTIMIZABLE_MIN_MAX_COUNT_ALL, 0, null, table, null, null);
+    }
+
+    public static ExpressionVisitor getNotFromResolverVisitor(ColumnResolver resolver) {
+        return new ExpressionVisitor(NOT_FROM_RESOLVER, 0, null, null, resolver, null);
+    }
+
+    public static ExpressionVisitor getMaxModificationIdVisitor() {
+        return new ExpressionVisitor(SET_MAX_DATA_MODIFICATION_ID, 0, null, null, null, new long[1]);
     }
 
     /**
@@ -149,23 +164,14 @@ public class ExpressionVisitor {
         return dependencies;
     }
 
-    /**
-     * Set all dependencies.
-     * This is used for GET_DEPENDENCIES visitors.
-     *
-     * @param dependencies the dependency set
-     */
-    public void setDependencies(HashSet<DbObject> dependencies) {
-        this.dependencies = dependencies;
-    }
-
     /**
      * Increment or decrement the query level.
      *
      * @param offset 1 to increment, -1 to decrement
+     * @return a clone of this expression visitor, with the changed query level
      */
-    public void incrementQueryLevel(int offset) {
-        queryLevel += offset;
+    public ExpressionVisitor incrementQueryLevel(int offset) {
+        return new ExpressionVisitor(type, queryLevel + offset, dependencies, table, resolver, maxDataModificationId);
     }
 
     /**
@@ -178,16 +184,6 @@ public class ExpressionVisitor {
         return resolver;
     }
 
-    /**
-     * Set the column resolver.
-     * This is used for NOT_FROM_RESOLVER visitors.
-     *
-     * @param resolver the column resolver
-     */
-    public void setResolver(ColumnResolver resolver) {
-        this.resolver = resolver;
-    }
-
     /**
      * Update the field maxDataModificationId if this value is higher
      * than the current value.
@@ -196,7 +192,10 @@ public class ExpressionVisitor {
      * @param value the data modification id
      */
     public void addDataModificationId(long value) {
-        maxDataModificationId = Math.max(maxDataModificationId, value);
+        long m = maxDataModificationId[0];
+        if (value > m) {
+            maxDataModificationId[0] = value;
+        }
     }
 
     /**
@@ -206,27 +205,13 @@ public class ExpressionVisitor {
      * @return the maximum modification id
      */
     public long getMaxDataModificationId() {
-        return maxDataModificationId;
+        return maxDataModificationId[0];
     }
 
     int getQueryLevel() {
         return queryLevel;
     }
 
-    void setQueryLevel(int queryLevel) {
-        this.queryLevel = queryLevel;
-    }
-
-    /**
-     * Set the table.
-     * This is used for OPTIMIZABLE_MIN_MAX_COUNT_ALL visitors.
-     *
-     * @param table the table
-     */
-    public void setTable(Table table) {
-        this.table = table;
-    }
-
     /**
      * Get the table.
      * This is used for OPTIMIZABLE_MIN_MAX_COUNT_ALL visitors.

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

@@ -297,8 +297,7 @@ public abstract class Table extends SchemaObjectBase {
                 dependencies.add(s);
             }
         }
-        ExpressionVisitor visitor = ExpressionVisitor.get(ExpressionVisitor.GET_DEPENDENCIES);
-        visitor.setDependencies(dependencies);
+        ExpressionVisitor visitor = ExpressionVisitor.getDependenciesVisitor(dependencies);
         for (Column col : columns) {
             col.isEverything(visitor);
         }

h2/src/test/org/h2/test/db/TestMultiConn.java

@@ -62,7 +62,11 @@ public class TestMultiConn extends TestBase implements DatabaseEventListener {
         } catch (SQLException e) {
             // ignore
         }
-        t.get();
+        try {
+            t.get();
+        } catch (Exception e) {
+            // ignore
+        }
     }
 
     private void testThreeThreads() throws Exception {