bonecp回缩功能实现

原由

bonecp不具有回缩功能，即链接池持有链接以后，不会主动去释放这些链接（即便这些链接始终处于空闲状态），所以在使用一段时间以后，链接池会达到配置的最大值。

这种方式必定程度上形成了资源的浪费。

改造

参考tomcat-jdbc的策略，每隔一段时间（可配置）会启动定时任务扫描partition中的idle队列，判断idle链接数是否大于partition可持有的最小链接数，若是是，则启动清理方法，将链接释放掉。

为了达到这个目的，实现了ConnectionCleanThread类：

package com.jolbox.bonecp;

import java.sql.SQLException;
import java.util.concurrent.BlockingQueue;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ConnectionCleanThread implements Runnable {

    private static final Logger logger = LoggerFactory.getLogger(ConnectionCleanThread.class);
    
    private ConnectionPartition partition;
    
    private BoneCP pool;
    
    protected ConnectionCleanThread(ConnectionPartition connectionPartition, BoneCP pool) {
        this.partition = connectionPartition;
        this.pool = pool;
    }
    
    @Override
    public void run() {
        BlockingQueue freeQueue = null;
        ConnectionHandle connection = null;
        //得到partition的大小
        int partitionSize = this.partition.getAvailableConnections();
        for (int i = 0; i < partitionSize; i++) {
            //获得free链接的queue
            freeQueue = this.partition.getFreeConnections();
            //若是空闲链接大于partition的最小容许链接数,回缩到最小容许链接数
            while (freeQueue.size() > this.partition.getMinConnections()) {
                connection = freeQueue.poll();
                connection.lock();
                closeConnection(connection);
                connection.unlock();
            }
        }
    }
    
    /** Closes off this connection
     * @param connection to close
     */
    private void closeConnection(ConnectionHandle connection) {

        if (connection != null && !connection.isClosed()) {
            try {
                connection.internalClose();
            } catch (SQLException e) {
                logger.error("Destroy connection exception", e);
            } finally {
                this.pool.postDestroyConnection(connection);
                connection.getOriginatingPartition().getPoolWatchThreadSignalQueue().offer(new Object()); // item being pushed is not important.
            }
        }
    }

}

同时须要对核心类ConnectionHandle进行改造，加上链接的上锁方法：

protected void lock() {
    lock.writeLock().lock();
}
    
protected void unlock() {
    lock.writeLock().unlock();
}

在BoneCP类的构造器内加上该线程的定时任务：

/**
 * 空闲链接清理任务
*/
private ScheduledExecutorService connectionCleanScheduler;

...

this.connectionCleanScheduler = Executors.newScheduledThreadPool(this.config.getPartitionCount(), new CustomThreadFactory("BoneCP-connection-clean-thread"+suffix, true));

...

//按期启动一个线程清理空闲链接
//add 2017-2-10
final Runnable connectionCleaner = new ConnectionCleanThread(connectionPartition, this);
this.connectionCleanScheduler.scheduleAtFixedRate(connectionCleaner, this.config.getConnectionCleanTimeInSeconds(), this.config.getConnectionCleanTimeInSeconds(), TimeUnit.SECONDS);

效果

通过实际测试，能够在后台自动的回收idle链接。

如今只是实现了功能，各类状况暂时没有加入考虑，好比没有判断该链接是否应该被释放。

GitHub地址

bonecp