Mini Connection Pool Manager
// Test program for the MiniConnectionPoolManager class.
import java.io.PrintWriter;
import java.lang.Thread;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Random;
import javax.sql.ConnectionPoolDataSource;
import biz.source_code.miniConnectionPoolManager.MiniConnectionPoolManager;
public class TestMiniConnectionPoolManager {
private static final int maxConnections = 8; // number of connections
private static final int noOfThreads = 50; // number of worker threads
private static final int processingTime = 30; // total processing time of the test program in seconds
private static final int threadPauseTime1 = 100; // max. thread pause time in microseconds, without a connection
private static final int threadPauseTime2 = 100; // max. thread pause time in microseconds, with a connection
private static MiniConnectionPoolManager poolMgr;
private static WorkerThread[] threads;
private static boolean shutdownFlag;
private static Object shutdownObj = new Object();
private static Random random = new Random();
private static class WorkerThread extends Thread {
public int threadNo;
public void run() {threadMain (threadNo); }};
private static ConnectionPoolDataSource createDataSource() throws Exception {
// Version for H2:
org.h2.jdbcx.JdbcDataSource dataSource = new org.h2.jdbcx.JdbcDataSource();
dataSource.setURL ("jdbc:h2:file:c:/temp/temp_TestMiniConnectionPoolManagerDB;DB_CLOSE_DELAY=-1");
// Version for Apache Derby:
/*
org.apache.derby.jdbc.EmbeddedConnectionPoolDataSource dataSource = new org.apache.derby.jdbc.EmbeddedConnectionPoolDataSource();
dataSource.setDatabaseName ("c:/temp/temp_TestMiniConnectionPoolManagerDB");
dataSource.setCreateDatabase ("create");
dataSource.setLogWriter (new PrintWriter(System.out));
*/
// Versioo for JTDS:
/*
net.sourceforge.jtds.jdbcx.JtdsDataSource dataSource = new net.sourceforge.jtds.jdbcx.JtdsDataSource();
dataSource.setAppName ("TestMiniConnectionPoolManager");
dataSource.setDatabaseName ("Northwind");
dataSource.setServerName ("localhost");
dataSource.setUser ("sa");
dataSource.setPassword (System.getProperty("saPassword"));
*/
// Version for the Microsoft SQL Server driver (sqljdbc.jar):
/*
// The sqljdbc 1.1 documentation, chapter "Using Connection Pooling", recommends to use
// SQLServerXADataSource instead of SQLServerConnectionPoolDataSource, even when no
// distributed transactions are used.
com.microsoft.sqlserver.jdbc.SQLServerXADataSource dataSource = new com.microsoft.sqlserver.jdbc.SQLServerXADataSource();
dataSource.setApplicationName ("TestMiniConnectionPoolManager");
dataSource.setDatabaseName ("Northwind");
dataSource.setServerName ("localhost");
dataSource.setUser ("sa");
dataSource.setPassword (System.getProperty("saPassword"));
dataSource.setLogWriter (new PrintWriter(System.out));
*/
return dataSource; }
public static void main (String[] args) throws Exception {
System.out.println ("Program started.");
ConnectionPoolDataSource dataSource = createDataSource();
poolMgr = new MiniConnectionPoolManager(dataSource,maxConnections);
initDb();
startWorkerThreads();
pause (processingTime*1000000);
System.out.println ("\nStopping threads.");
stopWorkerThreads();
System.out.println ("\nAll threads stopped.");
poolMgr.dispose();
System.out.println ("Program completed."); }
private static void startWorkerThreads() {
threads = new WorkerThread[noOfThreads];
for (int threadNo=0; threadNo<noOfThreads; threadNo++) {
WorkerThread thread = new WorkerThread();
threads[threadNo] = thread;
thread.threadNo = threadNo;
thread.start(); }}
private static void stopWorkerThreads() throws Exception {
setShutdownFlag();
for (int threadNo=0; threadNo<noOfThreads; threadNo++) {
threads[threadNo].join(); }}
private static void setShutdownFlag() {
synchronized (shutdownObj) {
shutdownFlag = true;
shutdownObj.notifyAll(); }}
private static void threadMain (int threadNo) {
try {
threadMain2 (threadNo); }
catch (Throwable e) {
System.out.println ("\nException in thread "+threadNo+": "+e);
e.printStackTrace (System.out);
setShutdownFlag(); }}
private static void threadMain2 (int threadNo) throws Exception {
// System.out.println ("Thread "+threadNo+" started.");
while (true) {
if (!pauseRandom(threadPauseTime1)) return;
threadTask (threadNo); }}
private static void threadTask (int threadNo) throws Exception {
Connection conn = null;
try {
conn = poolMgr.getConnection();
if (shutdownFlag) return;
System.out.print (threadNo+" ");
incrementThreadCounter (conn,threadNo);
pauseRandom (threadPauseTime2); }
finally {
if (conn != null) conn.close(); }}
private static boolean pauseRandom (int maxPauseTime) throws Exception {
return pause (random.nextInt(maxPauseTime)); }
private static boolean pause (int pauseTime) throws Exception {
synchronized (shutdownObj) {
if (shutdownFlag) return false;
if (pauseTime <= 0) return true;
int ms = pauseTime / 1000;
int ns = (pauseTime % 1000) * 1000;
shutdownObj.wait (ms,ns); }
return true; }
private static void initDb() throws SQLException {
Connection conn = null;
try {
conn = poolMgr.getConnection();
System.out.println ("initDb connected");
initDb2 (conn); }
finally {
if (conn != null) conn.close(); }
System.out.println ("initDb done"); }
private static void initDb2 (Connection conn) throws SQLException {
execSqlNoErr (conn,"drop table temp");
execSql (conn,"create table temp (threadNo integer, ctr integer)");
for (int i=0; i<noOfThreads; i++)
execSql (conn,"insert into temp values("+i+",0)"); }
private static void incrementThreadCounter (Connection conn, int threadNo) throws SQLException {
execSql (conn,"update temp set ctr = ctr + 1 where threadNo="+threadNo); }
private static void execSqlNoErr (Connection conn, String sql) {
try {
execSql (conn,sql); }
catch (SQLException e) {}}
private static void execSql (Connection conn, String sql) throws SQLException {
Statement st = null;
try {
st = conn.createStatement();
st.executeUpdate(sql); }
finally {
if (st != null) st.close(); }}
} // end class TestMiniConnectionPoolManager
// Copyright 2007 Christian d'Heureuse, www.source-code.biz
//
// This module is free software: you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version. See http://www.gnu.org/licenses/lgpl.html.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
package biz.source_code.miniConnectionPoolManager;
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>
* License: <a href="http://www.gnu.org/licenses/lgpl.html">LGPL</a>
* <p>
* 2007-06-21: Constructor with a timeout parameter added.
*/
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
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