mina高并发短连接导致java.io.IOException: Too many open files解决方案

   这几天在解决一个用mina开发的高并发通信过程中产生的一个bug。

   模拟场景为：

   通过定时触发启动线程模拟高并发短连接测试，测试的服务端有2个，一个是服务有起，一个没起，客户端和服务端均在同一服务器上。执行一段时间后linux主机上通过lsof命令查看，发现有递增的文件句柄，pipe和eventpoll。

   抛出的异常如下：

  

2012-10-13 10:09:48 -org.apache.mina.core.service.SimpleIoProcessorPool.<init>(SimpleIoProcessorPool.java:197)
 Failed to create a new instance of org.apache.mina.transport.socket.nio.NioProcessor:null
java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedConstructorAccessor110.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at org.apache.mina.core.service.SimpleIoProcessorPool.<init>(SimpleIoProcessorPool.java:180)
        at org.apache.mina.core.service.SimpleIoProcessorPool.<init>(SimpleIoProcessorPool.java:112)
        at org.apache.mina.core.polling.AbstractPollingIoConnector.<init>(AbstractPollingIoConnector.java:93)
        at org.apache.mina.transport.socket.nio.NioSocketConnector.<init>(NioSocketConnector.java:56)
        at com.develop.webplatform.funnel.client.JobClient.sendMessage(JobClient.java:39)
        at com.develop.webplatform.funnel.client.JobClient.sendJob(JobClient.java:126)
        at com.develop.webplatform.funnel.extend.JobExecRemotelyBySocket.execJobByTask(JobExecRemotelyBySocket.java:66)
        at com.develop.webplatform.funnel.JobManager.execJobByTask(JobManager.java:27)
        at com.develop.webplatform.quartz.job.TaskJob.executeInternal(TaskJob.java:38)
        at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
        at org.quartz.core.JobRunShell.run(JobRunShell.java:223)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:549)
Caused by: org.apache.mina.core.RuntimeIoException: Failed to open a selector.
        at org.apache.mina.transport.socket.nio.NioProcessor.<init>(NioProcessor.java:61)
        ... 15 more
Caused by: java.io.IOException: Too many open files
        at sun.nio.ch.IOUtil.initPipe(Native Method)
        at sun.nio.ch.EPollSelectorImpl.<init>(EPollSelectorImpl.java:49)
        at sun.nio.ch.EPollSelectorProvider.openSelector(EPollSelectorProvider.java:18)
        at java.nio.channels.Selector.open(Selector.java:209)
        at org.apache.mina.transport.socket.nio.NioProcessor.<init>(NioProcessor.java:59)
        ... 15 more

    

    原代码中，关于客户端连接的代码如下：

   

final NioSocketConnector connector = new NioSocketConnector();
		final String[] result = new String[1];
		connector.getFilterChain().addLast("codec",
				new ProtocolCodecFilter(new ObjectSerializationCodecFactory()));
		connector.setHandler(handler);

		//设置超时
		connector.setConnectTimeoutMillis(defaultConnectTimeOut);
		ConnectFuture connectFuture = connector.connect(address);
		connectFuture.awaitUninterruptibly();	//同步，等待，直到连接完成
		if (connectFuture.isDone()) {
			if (!connectFuture.isConnected()) {	//若在指定时间内没连接成功，则抛出异常
				logger.info("fail to connect " + logInfo);

				throw new Exception();
			}
		}

       

         经过分析，导致主机文件句柄泄露的原因为，客户端发起服务端连接时，会请求系统分配相关的文件句柄，在原代码中，仅仅判断是否连接成功，而未对连接失败进行资源释放，从而造成文件句柄泄露。当总的文件句柄数超过系统设置值（ulimit -n 查看同一个进程允许的最大文件句柄数），则抛出异常“java.io.IOException: Too many open files",导致无法创建新的连接，服务器挂掉。

      更改后的代码如下：

  

final NioSocketConnector connector = new NioSocketConnector();
		final String[] result = new String[1];
		connector.getFilterChain().addLast("codec",
				new ProtocolCodecFilter(new ObjectSerializationCodecFactory()));
		connector.setHandler(handler);

		//设置超时
		connector.setConnectTimeoutMillis(defaultConnectTimeOut);
		ConnectFuture connectFuture = connector.connect(address);
		connectFuture.awaitUninterruptibly();	//同步，等待，直到连接完成
		if (connectFuture.isDone()) {
			if (!connectFuture.isConnected()) {	//若在指定时间内没连接成功，则抛出异常
				logger.info("fail to connect " + logInfo);
				connector.dispose();	//不关闭的话会运行一段时间后抛出，too many open files异常，导致无法连接

				throw new Exception();
			}
		}