连接池

Question

 BlockingQueue<Connection> connections = new LinkedBlockingQueue<Connection>(maxConnection);

AtomicInteger numberOfDrewedConnectionFromPool

In my ConnectionPool i use LinkedBlockingQueue. I have some doubt whether multiply "if statement" will be thread-safe. maxConnection is constant. numberOfDrewedConnectionFromPool changes also in method releaseConection without lock()..

 public Connection getConnection() throws ConnectionPoolException {
    Connection connection = null;

    if ((connections.poll() == null) && (maxConnection > numberOfDrewedConnectionFromPool.get())) {
        return newConnection();
    } else {
        return connections.poll();
    }
}


private Connection newConnection() throws ConnectionPoolException {
    lock.lock();
    Connection connection = null;
    try {
        try {
            connection = DriverManager.getConnection(url, user, password);
            numberOfDrewedConnectionFromPool.incrementAndGet();
        } catch (SQLException exception) {
            throw new ConnectionPoolException();
        }
    } finally {
        lock.unlock();
        return connection;
    }

}

Answer 1

No, your code is not thread-safe.

Between the time where connections.poll() is called and the time where the number of connections is compared to the max, some other thread might have released or taken a connection, and the number of connections might have changed. Moreover, you're polling the queue twice to get a single connection.

Side note: why are you reinventing the wheel? There are plenty of free connection pools available.