最近發現系統中出現了很多 IOException: Connection reset by peer 與 ClosedChannelException: null

深入看了看代碼, 做了些測試, 發現 Connection reset 會在客戶端不知道 channel 被關閉的情況下, 觸發了 eventloop 的 unsafe.read() 操作拋出

而 ClosedChannelException 一般是由 Netty 主動拋出的, 在 AbstractChannel 以及 SSLHandler 里都可以看到 ClosedChannel 相關的代碼

AbstractChannel?

static final ClosedChannelException CLOSED_CHANNEL_EXCEPTION = new ClosedChannelException();...static {CLOSED_CHANNEL_EXCEPTION.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);NOT_YET_CONNECTED_EXCEPTION.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);}...@Overridepublic void write(Object msg, ChannelPromise promise) {ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;if (outboundBuffer == null) {// If the outboundBuffer is null we know the channel was closed and so// need to fail the future right away. If it is not null the handling of the rest// will be done in flush0()// See https://github.com/netty/netty/issues/2362 safeSetFailure(promise, CLOSED_CHANNEL_EXCEPTION);// release message now to prevent resource-leak ReferenceCountUtil.release(msg);return;}outboundBuffer.addMessage(msg, promise);}

在代碼的許多部分, 都會有這個 ClosedChannelException, 大概的意思是說在 channel close 以后, 如果還調用了 write 方法, 則會將 write 的 future 設置為 failure, 并將 cause 設置為 ClosedChannelException, 同樣 SSLHandler 中也類似

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回到 Connection reset by peer, 要模擬這個情況比較簡單, 就是在 server 端設置一個在 channelActive 的時候就 close channel 的 handler. 而在 client 端則寫一個 Connect 成功后立即發送請求數據的 listener. 如下

client

public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});b.connect("localhost", 8090).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (future.isSuccess()) {future.channel().write(Unpooled.buffer().writeBytes("123".getBytes()));future.channel().flush();}}});

server

public class SimpleServer {public static void main(String[] args) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_REUSEADDR, true).childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {ch.pipeline().addLast(new SimpleServerHandler());}});b.bind(8090).sync().channel().closeFuture().sync();} }public class SimpleServerHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.channel().close().sync();}@Overridepublic void channelRead(ChannelHandlerContext ctx, final Object msg) throws Exception {System.out.println(123);}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {System.out.println("inactive");} }

?

這種情況之所以能觸發 connection reset by peer 異常, 是因為 connect 成功以后, client 段先會觸發 connect 成功的 listener, 這個時候 server 段雖然斷開了 channel, 也觸發 channel 斷開的事件 (它會觸發一個客戶端 read 事件, 但是這個 read 會返回 -1, -1 代表 channel 關閉, client 的 channelInactive 跟 channel ?active 狀態的改變都是在這時發生的), 但是這個事件是在 connect 成功的 listener 之后執行, 所以這個時候 listener 里的 channel 并不知道自己已經斷開, 它還是會繼續進行 write 跟 flush 操作, 在調用 flush 后, eventloop 會進入 OP_READ 事件里, 這時候 unsafe.read() 就會拋出 connection reset 異常. eventloop 代碼如下

NioEventLoop

private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {final NioUnsafe unsafe = ch.unsafe();if (!k.isValid()) {// close the channel if the key is not valid anymore unsafe.close(unsafe.voidPromise());return;}try {int readyOps = k.readyOps();// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead// to a spin loopif ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {unsafe.read();if (!ch.isOpen()) {// Connection already closed - no need to handle write. return;}}if ((readyOps & SelectionKey.OP_WRITE) != 0) {// Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write ch.unsafe().forceFlush();}if ((readyOps & SelectionKey.OP_CONNECT) != 0) {// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking// See https://github.com/netty/netty/issues/924int ops = k.interestOps();ops &= ~SelectionKey.OP_CONNECT;k.interestOps(ops);unsafe.finishConnect();}} catch (CancelledKeyException e) {unsafe.close(unsafe.voidPromise());}}

這就是 connection reset by peer 產生的原因

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再來看 ClosedChannelException 如何產生, 要復現他也很簡單. 首先要明確, 并沒有客戶端主動關閉才會出現 ClosedChannelException 這么一說. 下面來看兩種出現 ClosedChannelException 的客戶端寫法

client 1, 主動關閉 channel

public class SimpleClient {private static final Logger logger = LoggerFactory.getLogger(SimpleClient.class);public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});b.connect("localhost", 8090).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (future.isSuccess()) { future.channel().close();future.channel().write(Unpooled.buffer().writeBytes("123".getBytes())).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (!future.isSuccess()) {logger.error("Error", future.cause());}}});future.channel().flush();}}});} }

?

只要在 write 之前主動調用了 close, 那么 write 必然會知道 close 是 close 狀態, 最后 write 就會失敗, 并且 future 里的 cause 就是 ClosedChannelException

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client 2. 由服務端造成的 ClosedChannelException

public class SimpleClient {private static final Logger logger = LoggerFactory.getLogger(SimpleClient.class);public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});Channel channel = b.connect("localhost", 8090).sync().channel();Thread.sleep(3000);channel.writeAndFlush(Unpooled.buffer().writeBytes("123".getBytes())).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (!future.isSuccess()) {logger.error("error", future.cause());}}});} }

服務端

public class SimpleServer {public static void main(String[] args) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_REUSEADDR, true).childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {ch.pipeline().addLast(new SimpleServerHandler());}});b.bind(8090).sync().channel().closeFuture().sync();} }

這種情況下, ?服務端將 channel 關閉, 客戶端先 sleep, 這期間 client 的 eventLoop 會處理客戶端關閉的時間, 也就是 eventLoop 的 processKey 方法會進入 OP_READ, 然后 read 出來一個 -1, 最后觸發 client channelInactive 事件, 當 sleep 醒來以后, 客戶端調用 writeAndFlush, 這時候客戶端 channel 的狀態已經變為了 inactive, 所以 write 失敗, cause 為 ClosedChannelException

轉載于:https://www.cnblogs.com/zemliu/p/3864131.html

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