// Copyright 2007 Christian d'Heureuse, www.source-code.biz
//
// This module is multi-licensed and may be used under the terms
// of any of the following licenses:
//
// EPL, Eclipse Public License, http://www.eclipse.org/legal
// LGPL, GNU Lesser General Public License, http://www.gnu.org/licenses/lgpl.html
// MPL, Mozilla Public License 1.1, http://www.mozilla.org/MPL
//
// This module is provided "as is", without warranties of any kind.
package net.jxta.impl.cm.sql;
import java.util.concurrent.Semaphore;
import java.util.Stack;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.concurrent.TimeUnit;
import javax.sql.ConnectionPoolDataSource;
import javax.sql.ConnectionEvent;
import javax.sql.ConnectionEventListener;
import javax.sql.PooledConnection;
/**
* A simple standalone JDBC connection pool manager.
* <p>
* The public methods of this class are thread-safe.
* <p>
* Author: Christian d'Heureuse (<a href="http://www.source-code.biz">www.source-code.biz</a>)<br>
* Multi-licensed: EPL/LGPL/MPL.
* <p>
* 2007-06-21: Constructor with a timeout parameter added.<br>
* 2008-05-03: Additional licenses added (EPL/MPL).
*/
public class MiniConnectionPoolManager {
private ConnectionPoolDataSource dataSource;
private int maxConnections;
private int timeout;
private PrintWriter logWriter;
private Semaphore semaphore;
private Stack<PooledConnection> recycledConnections;
private int activeConnections;
private PoolConnectionEventListener poolConnectionEventListener;
private boolean isDisposed;
/**
* Thrown in {@link #getConnection()} when no free connection becomes available within <code>timeout</code> seconds.
*/
public static class TimeoutException extends RuntimeException {
private static final long serialVersionUID = 1;
public TimeoutException () {
super ("Timeout while waiting for a free database connection."); }}
/**
* Constructs a MiniConnectionPoolManager object with a timeout of 60 seconds.
* @param dataSource the data source for the connections.
* @param maxConnections the maximum number of connections.
*/
public MiniConnectionPoolManager (ConnectionPoolDataSource dataSource, int maxConnections) {
this (dataSource, maxConnections, 60); }
/**
* Constructs a MiniConnectionPoolManager object.
* @param dataSource the data source for the connections.
* @param maxConnections the maximum number of connections.
* @param timeout the maximum time in seconds to wait for a free connection.
*/
public MiniConnectionPoolManager (ConnectionPoolDataSource dataSource, int maxConnections, int timeout) {
this.dataSource = dataSource;
this.maxConnections = maxConnections;
this.timeout = timeout;
try {
logWriter = dataSource.getLogWriter(); }
catch (SQLException e) {}
if (maxConnections < 1) throw new IllegalArgumentException("Invalid maxConnections value.");
semaphore = new Semaphore(maxConnections,true);
recycledConnections = new Stack<PooledConnection>();
poolConnectionEventListener = new PoolConnectionEventListener(); }
/**
* Closes all unused pooled connections.
*/
public synchronized void dispose() throws SQLException {
if (isDisposed) return;
isDisposed = true;
SQLException e = null;
while (!recycledConnections.isEmpty()) {
PooledConnection pconn = recycledConnections.pop();
try {
pconn.close(); }
catch (SQLException e2) {
if (e == null) e = e2; }}
if (e != null) throw e; }
/**
* Retrieves a connection from the connection pool.
* If <code>maxConnections</code> connections are already in use, the method
* waits until a connection becomes available or <code>timeout</code> seconds elapsed.
* When the application is finished using the connection, it must close it
* in order to return it to the pool.
* @return a new Connection object.
* @throws TimeoutException when no connection becomes available within <code>timeout</code> seconds.
*/
public Connection getConnection() throws SQLException {
// This routine is unsynchronized, because semaphore.tryAcquire() may block.
synchronized (this) {
if (isDisposed) throw new IllegalStateException("Connection pool has been disposed."); }
try {
if (!semaphore.tryAcquire(timeout,TimeUnit.SECONDS))
throw new TimeoutException(); }
catch (InterruptedException e) {
throw new RuntimeException("Interrupted while waiting for a database connection.",e); }
boolean ok = false;
try {
Connection conn = getConnection2();
ok = true;
return conn; }
finally {
if (!ok) semaphore.release(); }}
private synchronized Connection getConnection2() throws SQLException {
if (isDisposed) throw new IllegalStateException("Connection pool has been disposed."); // test again with lock
PooledConnection pconn;
if (!recycledConnections.empty()) {
pconn = recycledConnections.pop(); }
else {
pconn = dataSource.getPooledConnection(); }
Connection conn = pconn.getConnection();
activeConnections++;
pconn.addConnectionEventListener (poolConnectionEventListener);
assertInnerState();
return conn; }
private synchronized void recycleConnection (PooledConnection pconn) {
if (isDisposed) { disposeConnection (pconn); return; }
if (activeConnections <= 0) throw new AssertionError();
activeConnections--;
semaphore.release();
recycledConnections.push (pconn);
assertInnerState(); }
private synchronized void disposeConnection (PooledConnection pconn) {
if (activeConnections <= 0) throw new AssertionError();
activeConnections--;
semaphore.release();
closeConnectionNoEx (pconn);
assertInnerState(); }
private void closeConnectionNoEx (PooledConnection pconn) {
try {
pconn.close(); }
catch (SQLException e) {
log ("Error while closing database connection: "+e.toString()); }}
private void log (String msg) {
String s = "MiniConnectionPoolManager: "+msg;
try {
if (logWriter == null)
System.err.println (s);
else
logWriter.println (s); }
catch (Exception e) {}}
private void assertInnerState() {
if (activeConnections < 0) throw new AssertionError();
if (activeConnections+recycledConnections.size() > maxConnections) throw new AssertionError();
if (activeConnections+semaphore.availablePermits() > maxConnections) throw new AssertionError(); }
private class PoolConnectionEventListener implements ConnectionEventListener {
public void connectionClosed (ConnectionEvent event) {
PooledConnection pconn = (PooledConnection)event.getSource();
pconn.removeConnectionEventListener (this);
recycleConnection (pconn); }
public void connectionErrorOccurred (ConnectionEvent event) {
PooledConnection pconn = (PooledConnection)event.getSource();
pconn.removeConnectionEventListener (this);
disposeConnection (pconn); }}
/**
* Returns the number of active (open) connections of this pool.
* This is the number of <code>Connection</code> objects that have been
* issued by {@link #getConnection()} for which <code>Connection.close()</code>
* has not yet been called.
* @return the number of active connections.
**/
public synchronized int getActiveConnections() {
return activeConnections; }
} // end class MiniConnectionPoolManager