Linked tables that point to the same database now share the connection.

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

+/*
+ * Copyright 2004-2008 H2 Group. Multiple-Licensed under the H2 License, 
+ * Version 1.0, and under the Eclipse Public License, Version 1.0
+ * (http://h2database.com/html/license.html).
+ * Initial Developer: H2 Group
+ */
+package org.h2.table;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.HashMap;
+
+import org.h2.util.JdbcUtils;
+import org.h2.util.ObjectUtils;
+import org.h2.util.StringUtils;
+
+/**
+ * A connection for a linked table. The same connection may be used for multiple
+ * tables, that means a connection may be shared.
+ */
+public class TableLinkConnection {
+
+    /**
+     * The map where the link is kept.
+     */
+    private HashMap map;
+    
+    /**
+     * The connection information.
+     */
+    private final String driver, url, user, password;
+    
+    /**
+     * The database connection.
+     */
+    private Connection conn;
+    
+    /**
+     * How many times the connection is used.
+     */
+    private int useCounter;
+    
+    public static TableLinkConnection open(HashMap map, String driver, String url, String user, String password) throws SQLException {
+        TableLinkConnection t = new TableLinkConnection(map, driver, url, user, password);
+        synchronized (map) {
+            TableLinkConnection result = (TableLinkConnection) map.get(t);
+            if (result == null) {
+                synchronized (t) {
+                    t.open();
+                }
+                // put the connection in the map after is has been opened,
+                // so we know it works
+                map.put(t, t);
+                result = t;
+            }
+            synchronized (result) {
+                result.useCounter++;
+            }
+            return result;
+        }
+    }
+    
+    private TableLinkConnection(HashMap map, String driver, String url, String user, String password) {
+        this.map = map;
+        this.driver = driver;
+        this.url = url;
+        this.user = user;
+        this.password = password;
+    }
+    
+    private void open() throws SQLException {
+        conn = JdbcUtils.getConnection(driver, url, user, password);
+    }
+    
+    public int hashCode() {
+        return ObjectUtils.hashCode(driver) 
+                ^ ObjectUtils.hashCode(url) 
+                ^ ObjectUtils.hashCode(user)
+                ^ ObjectUtils.hashCode(password);
+    }
+    
+    public boolean equals(Object o) {
+        if (o instanceof TableLinkConnection) {
+            TableLinkConnection other = (TableLinkConnection) o;
+            return StringUtils.equals(driver, other.driver) 
+                    && StringUtils.equals(url, other.url)
+                    && StringUtils.equals(user, other.user) 
+                    && StringUtils.equals(password, other.password);
+        }
+        return false;
+    }
+    
+    /**
+     * Get the connection. 
+     * This method and methods on the statement must be
+     * synchronized on this object.
+     * 
+     * @return the connection
+     */
+    Connection getConnection() {
+        return conn;
+    }
+
+    /**
+     * Closes the connection if this is the last link to it.
+     */
+    synchronized void close() throws SQLException {
+        if (--useCounter == 0) {
+            conn.close();
+            conn = null;
+            synchronized (map) {
+                map.remove(this);
+            }
+        }        
+    }
+
+}