Channel
功能说明
io.netty.channel.Channel 是 Netty 的网络操作抽象类,聚合了一组功能,包括但不限于网络读写、客户端发起连接、主动关闭连接,同时也包含了 Netty 框架相关的一些功能,包括获取 Channel 的 EventLoop,获取缓冲区分配器 ByteBufAllocator 和 pipeline 等。
为了 Netty 不使用 NIO 的原生 Channel,而是要另起炉灶呢?主要原因如下:
- JDK 的 SocketChannel 和 ServerSocketChannel 没有统一的 Channel 接口供业务开发者使用。对用户而言,
没有统一的操作视图,使用起来不方便
。 - JDK 的 SocketChannel 和 ServerSocketChannel 是
SPI 类接口,通过继承来扩展很不方便
,不如开发一个新的。 - Netty 的 Channel 需要能跟 Netty 架构融合在一起。
- 自定义 Channel 功能实现会更灵活。
基于以上原因,Netty 重新设计了 Channel,其主要设计理念如下:
- 在 Channel 接口层,
采用 Facade 模式统一封装
,将网络 I/O 操作、网络 I/O 相关联的其他操作封装起来,统一对外提供。 -
Channel 接口定义尽量大而全
,为 SocketChannel 和 ServerSocketChannel 提供统一的视图,由不同子类实现不同的功能,公共功能在抽象父类中实现,最大程度上实现功能和接口的重用。 -
具体实现采用聚合而非包含的方式,Channel 负责统一分配和调度,更加灵活
。
Netty 的 Channel 都有哪些功能呢?
- 常见的网络 IO 操作:读、写、绑定端口、连接、关闭连接等。
- 获取 EventLoop。
- 获取 parent Channel,对于服务端 SocketChannel 来说,parent 就是创建它的 ServerSocketChannel。
- 唯一标志 id。
- 元数据 metadata,获取 TCP 参数配置等。
常用接口
- eventLoop(),Channel需要注册到EventLoop的多路复用器上,用于处理IO事件,通过eventLoop方法可以获取到Channel注册的EventLoop。EventLoop本质上就是处理网络读写事件的Reactor线程。在Netty中,它不仅仅用来处理网络事件,也可以用来执行定时任务和用户自定义NioTask等任务。
- metadata(),熟悉TCP协议的同学可能知道,当创建Socket的时候需要指定TCP参数,例如接收和发送的TCP缓冲区大小,TCP的超时时间,是否重用地址等等。在Netty中,每个Channel对应一个物理连接,每个连接都有自己的TCP参数配置。所以,Channel会聚合一个ChannelMetadata用来对TCP参数提供元数据描述信息,通过metadata方法就可以获取当前Channel的TCP参数配置。
- parent(),对于服务端Channel而言,它的父Channel为空,对于客户端Channel,它的父Channel就是创建它的ServerSocketChannel。
用户获取Channel标识的id,它返回ChannelId对象,ChannelId是Channel的唯一标识,它的可能生成策略如下:
- 机器的MAC地址(EUI-48或者EUI-64)等可以代表全局唯一的信息。
- 当前进程的ID。
- 当前系统时间的毫秒——System.currentTimeMillis
- 当前系统时间的纳秒——System.nanoTime
- 32位的随机整型数
- 32位自增的序列数
Channel 源码分析
继承关系类图
NioServerSocketChannel、NioSocketChannel 两者都继承了 Channel、AbstractChannel、AbstractNioChannel。
AbstractChannel
主要成员变量如下所示:
// 父 Channel
private final Channel parent;
// 全局唯一 id。
private final ChannelId id;
// Unsafe 实例
private final Unsafe unsafe;
// 当前 Channel 对应的 DefaultChannelPipeline。
private final DefaultChannelPipeline pipeline;
private final VoidChannelPromise unsafeVoidPromise = new VoidChannelPromise(this, false);
private final CloseFuture closeFuture = new CloseFuture(this);
private volatile SocketAddress localAddress;
private volatile SocketAddress remoteAddress;
// EventLoop
private volatile EventLoop eventLoop;
private volatile boolean registered;
private boolean closeInitiated;
private Throwable initialCloseCause;
AbstractChannel 中的网络 I/O 操作都是调用 pipeline 中的对应方法,继而由 pipeline 调用 ChannelHandler 进行处理。
@Override
public ChannelFuture bind(SocketAddress localAddress) {
return pipeline.bind(localAddress);
}
@Override
public ChannelFuture connect(SocketAddress remoteAddress) {
return pipeline.connect(remoteAddress);
}
@Override
public ChannelFuture write(Object msg) {
return pipeline.write(msg);
}
AbstractNioChannel
- SelectableChannel:这是一个 Java NIO SocketChannel 和 ServerSocketChannel 的公共父类,放在这里是因为 AbstractNioChannel 也是 NioSocketChannel 和 NioServerSocketChannel 的公共父类。
- readInterestOp:代表 JDK SelectionKey 的 OP_READ。
- SelectionKey:Channel 注册到 EventLoop(Selector)时返回的 key,修改它可以改变感兴趣的事件。
- connectPromise:代表连接操作结果。
- connectTimeoutFuture:连接超时定时器。
- requestedRemoteAddress:connect 时的远程地址。
AbstractNioChannel 类里比较重要的方法是 doRegister,该方法负责将 Channel 注册到多路复用器 Selector。
@Override
protected void doRegister() throws Exception {
boolean selected = false;
for (;;) {
try {
selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
return;
} catch (CancelledKeyException e) {
if (!selected) {
// Force the Selector to select now as the "canceled" SelectionKey may still be
// cached and not removed because no Select.select(..) operation was called yet.
eventLoop().selectNow();
selected = true;
} else {
// We forced a select operation on the selector before but the SelectionKey is still cached
// for whatever reason. JDK bug ?
throw e;
}
}
}
}
在 doRegister 方法中,对 ops 字段设置为 0,也就是对任何事件都不感兴趣。真正的设置读操作位是在 doBeginRead 方法中,那么写操作位在何时设置呢?当然是有数据要写,而缓冲区满(或其他不能立即写)的情况。
@Override
protected void doBeginRead() throws Exception {
// Channel.read() or ChannelHandlerContext.read() was called
final SelectionKey selectionKey = this.selectionKey;
if (!selectionKey.isValid()) {
return;
}
readPending = true;
final int interestOps = selectionKey.interestOps();
if ((interestOps & readInterestOp) == 0) {
selectionKey.interestOps(interestOps | readInterestOp);
}
}
AbstractNioByteChannel
AbstractNioByteChannel 是 NioSocketChannel 的父类,只有一个成员变量 flushTask,负责写半包消息。
private Runnable flushTask;
最主要的方法是 doWrite:
@Override
protected void doWrite(ChannelOutboundBuffer in) throws Exception {
int writeSpinCount = -1;
boolean setOpWrite = false;
for (;;) {
Object msg = in.current();
// 如果没有要写的数据,就清除写标志位,并返回
if (msg == null) {
// Wrote all messages.
clearOpWrite();
// Directly return here so incompleteWrite(...) is not called.
return;
}
// 对于 ByteBuf 类型、FileRegion 类型分开处理,其他未知类型抛异常
if (msg instanceof ByteBuf) {
ByteBuf buf = (ByteBuf) msg;
int readableBytes = buf.readableBytes();
if (readableBytes == 0) {
in.remove();
continue;
}
boolean done = false;
long flushedAmount = 0;
if (writeSpinCount == -1) {
writeSpinCount = config().getWriteSpinCount();
}
// 只循环写 writeSpinCount 次,为了避免写大块儿数据时,阻塞其他线程过长时间
for (int i = writeSpinCount - 1; i >= 0; i --) {
int localFlushedAmount = doWriteBytes(buf);
// 返回 0 表示写缓冲区满,setOpWrite 为 true 会设置 SelectionKey 的写标志位,在可写时会得到通知。
if (localFlushedAmount == 0) {
setOpWrite = true;
break;
}
flushedAmount += localFlushedAmount;
if (!buf.isReadable()) {
done = true;
break;
}
}
in.progress(flushedAmount);
if (done) {
in.remove();
} else {
// Break the loop and so incompleteWrite(...) is called.
break;
}
} else if (msg instanceof FileRegion) {
FileRegion region = (FileRegion) msg;
boolean done = region.transferred() >= region.count();
if (!done) {
long flushedAmount = 0;
if (writeSpinCount == -1) {
writeSpinCount = config().getWriteSpinCount();
}
for (int i = writeSpinCount - 1; i >= 0; i--) {
long localFlushedAmount = doWriteFileRegion(region);
if (localFlushedAmount == 0) {
setOpWrite = true;
break;
}
flushedAmount += localFlushedAmount;
if (region.transferred() >= region.count()) {
done = true;
break;
}
}
in.progress(flushedAmount);
}
if (done) {
in.remove();
} else {
// Break the loop and so incompleteWrite(...) is called.
break;
}
} else {
// Should not reach here.
throw new Error();
}
}
incompleteWrite(setOpWrite);
}
// 走到这里,说明还有数据没有发送完毕,需要进一步处理
protected final void incompleteWrite(boolean setOpWrite) {
// setOpWrite 为 true,设置 SelectionKey 写标志位
if (setOpWrite) {
setOpWrite();
} else {
// 否则,启动 flushTask 继续写半包消息
Runnable flushTask = this.flushTask;
if (flushTask == null) {
flushTask = this.flushTask = new Runnable() {
@Override
public void run() {
flush();
}
};
}
eventLoop().execute(flushTask);
}
}
AbstractNioMessageChannel
AbstractNioMessageChannel 是 NioServerSocketChannel、NioDatagramChannel 的父类。其主要方法也是 doWrite,功能和 AbstractNioByteChannel 的 doWrite 也类似,区别只是后者只处理 ByteBuf 和 FileRegion,前者无此限制,处理所有 Object。
protected void doWrite(ChannelOutboundBuffer in) throws Exception {
final SelectionKey key = selectionKey();
final int interestOps = key.interestOps();
for (;;) {
Object msg = in.current();
if (msg == null) {
// Wrote all messages.
if ((interestOps & SelectionKey.OP_WRITE) != 0) {
key.interestOps(interestOps & ~SelectionKey.OP_WRITE);
}
break;
}
try {
boolean done = false;
for (int i = config().getWriteSpinCount() - 1; i >= 0; i--) {
if (doWriteMessage(msg, in)) {
done = true;
break;
}
}
if (done) {
in.remove();
} else {
// Did not write all messages.
if ((interestOps & SelectionKey.OP_WRITE) == 0) {
key.interestOps(interestOps | SelectionKey.OP_WRITE);
}
break;
}
} catch (Exception e) {
if (continueOnWriteError()) {
in.remove(e);
} else {
throw e;
}
}
}
}
// 处理 msg,由子类实现
protected abstract boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception;
doWriteMessage 方法在 NioServerSocketChannel 中实现如下所示,是因为 NioServerSocketChannel 只是用来监听端口,接收客户端请求,不负责传输实际数据。
protected boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception {
throw new UnsupportedOperationException();
}
doWriteMessage 方法在 NioSctpChannel 中是由具体实现的,从代码中可以看出来,它处理的只是 SctpMessage 类型的数据。
protected boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception {
SctpMessage packet = (SctpMessage) msg;
ByteBuf data = packet.content();
int dataLen = data.readableBytes();
if (dataLen == 0) {
return true;
}
ByteBufAllocator alloc = alloc();
boolean needsCopy = data.nioBufferCount() != 1;
if (!needsCopy) {
if (!data.isDirect() && alloc.isDirectBufferPooled()) {
needsCopy = true;
}
}
ByteBuffer nioData;
if (!needsCopy) {
nioData = data.nioBuffer();
} else {
data = alloc.directBuffer(dataLen).writeBytes(data);
nioData = data.nioBuffer();
}
final MessageInfo mi = MessageInfo.createOutgoing(association(), null, packet.streamIdentifier());
mi.payloadProtocolID(packet.protocolIdentifier());
mi.streamNumber(packet.streamIdentifier());
mi.unordered(packet.isUnordered());
// 写数据
final int writtenBytes = javaChannel().send(nioData, mi);
return writtenBytes > 0;
}
NioServerSocketChannel
NioServerSocketChannel 是服务端 Channel 的实现类,有一个用于配置 TCP 参数的 ServerSocketChannelConfig。
private final ServerSocketChannelConfig config;
作为服务端 Channel,其核心方法是端口绑定 doBind 方法、创建 SocketChannel 的 doReadMessages 方法。
protected void doBind(SocketAddress localAddress) throws Exception {
if (PlatformDependent.javaVersion() >= 7) {
javaChannel().bind(localAddress, config.getBacklog());
} else {
javaChannel().socket().bind(localAddress, config.getBacklog());
}
}
protected int doReadMessages(List<Object> buf) throws Exception {
SocketChannel ch = SocketUtils.accept(javaChannel());
try {
if (ch != null) {
buf.add(new NioSocketChannel(this, ch));
return 1;
}
} catch (Throwable t) {
logger.warn("Failed to create a new channel from an accepted socket.", t);
try {
ch.close();
} catch (Throwable t2) {
logger.warn("Failed to close a socket.", t2);
}
}
return 0;
}
对于和服务端 Channel 无关的方法,要果断抛出 UnsupportedOperationException 异常。
@Override
protected void doDisconnect() throws Exception {
throw new UnsupportedOperationException();
}
@Override
protected boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception {
throw new UnsupportedOperationException();
}
@Override
protected final Object filterOutboundMessage(Object msg) throws Exception {
throw new UnsupportedOperationException();
}
NioSocketChannel
NioSocketChannel 是客户端 Channel 的实现类,也是只有一个用于配置参数的变量 SocketChannelConfig。
private final SocketChannelConfig config;
客户端 Channel 的核心方法有连接 doConnect、写半包 doWrite、读操作 doReadBytes,下面我们挨个分析。
连接操作 doConnect 具体实现如下:
- 如果 localAddress 为空,则进行绑定操作。
- 调用 socketChannel.connect 进行连接。
- 如果连接尚未完成,则注册 OP_CONNECT 事件。
- 如果连接失败抛出异常,也要调用 doClose 关闭连接。
protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
if (localAddress != null) {
doBind0(localAddress);
}
boolean success = false;
try {
// 实际上是调用了 socketChannel.connect 方法。
boolean connected = SocketUtils.connect(javaChannel(), remoteAddress);
if (!connected) {
selectionKey().interestOps(SelectionKey.OP_CONNECT);
}
success = true;
return connected;
} finally {
if (!success) {
doClose();
}
}
}
写操作 doWrite 具体实现如下:
- 判断待写数据大小,若为 0 则清除写标志位,并返回。
- 从 ChannelOutboundBuffer 里获取待写 ByteBuffer 数组,和待写 ByteBuffer 数量 nioBufferCnt。
- 针对 nioBufferCnt 的不同大小进行了区别处理。
- 如果 nioBufferCnt 为 0,则调用父类的方法处理,以防有除了 ByteBuffer 之外的数据需要写。
- nioBufferCnt 为 1 和大于 1 的处理类似,都是循环写 getWriteSpinCount 次,若写完则结束,未写完则设置后续写半包的方式。这一点和父类 AbstractNioByteChannel 中的处理方法类似。
protected void doWrite(ChannelOutboundBuffer in) throws Exception {
for (;;) {
int size = in.size();
if (size == 0) {
// All written so clear OP_WRITE
clearOpWrite();
break;
}
long writtenBytes = 0;
boolean done = false;
boolean setOpWrite = false;
// Ensure the pending writes are made of ByteBufs only.
ByteBuffer[] nioBuffers = in.nioBuffers();
int nioBufferCnt = in.nioBufferCount();
long expectedWrittenBytes = in.nioBufferSize();
SocketChannel ch = javaChannel();
// Always us nioBuffers() to workaround data-corruption.
switch (nioBufferCnt) {
case 0:
// We have something else beside ByteBuffers to write so fallback to normal writes.
super.doWrite(in);
return;
case 1:
// 和 default 的区别只是传给 ch.write 的是数组还是单个 ByteBuffer
ByteBuffer nioBuffer = nioBuffers[0];
for (int i = config().getWriteSpinCount() - 1; i >= 0; i --) {
final int localWrittenBytes = ch.write(nioBuffer);
if (localWrittenBytes == 0) {
setOpWrite = true;
break;
}
expectedWrittenBytes -= localWrittenBytes;
writtenBytes += localWrittenBytes;
if (expectedWrittenBytes == 0) {
done = true;
break;
}
}
break;
default:
for (int i = config().getWriteSpinCount() - 1; i >= 0; i --) {
final long localWrittenBytes = ch.write(nioBuffers, 0, nioBufferCnt);
if (localWrittenBytes == 0) {
setOpWrite = true;
break;
}
expectedWrittenBytes -= localWrittenBytes;
writtenBytes += localWrittenBytes;
// expectedWrittenBytes 为 0 表示数据发送完毕
if (expectedWrittenBytes == 0) {
done = true;
break;
}
}
break;
}
// Release the fully written buffers, and update the indexes of the partially written buffer.
in.removeBytes(writtenBytes);
if (!done) {
// 设置后续写半包方式
incompleteWrite(setOpWrite);
break;
}
}
}
读操作比较简单,主要是通过 ByteBuf 来从 Channel 中读取数据。
protected int doReadBytes(ByteBuf byteBuf) throws Exception {
final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
allocHandle.attemptedBytesRead(byteBuf.writableBytes());
return byteBuf.writeBytes(javaChannel(), allocHandle.attemptedBytesRead());
}
总结
Channel 类体系的设计与其实现功能密不可分,父类中实现的是子类共同的功能。在多层次的抽象类中,每一个层次的抽象类负责实现一种功能。
当父类提供大而全的接口时,父类可以根据需要去实现,不需要的可以抛出 UnsupportedOperationException 异常。
Unsafe
功能说明
Unsafe接口实际上是Channel 接口的辅助接口,它不应被用户代码 直接调用,实际的I/O 读写操作者是由Unsafe接口负责完成的。
在netty中一个很核心的组件,封装了java底层的socket操作,作为连接netty和java 底层nio的重要桥梁。
方法名 | 返回值 | 功能说明 |
invoker() | ChannelHandlerInvoker | 返回默认使用的ChannelHandlerlnvoker |
localAddress() | SocketAddress | 返回本地绑定的Socket地址 |
remoteAddress() | SocketAddress | 返回通信对端Socket地址 |
register(ChannelPromise promise) | void | 注册Channel 到多路复用器上,一旦完成,通知channelFuture |
bind(SocketAddress localAddress,ChannelPromise promise) | void | 绑定指定的本地地址 localAddress到当前的Channel 上,一旦完成,通知channelFuture |
connect(SocketAddress remoteAddress,SocketAddress localAddress,ChannelPromise promise) | void | 绑定本地的 localAddress之后,连接服务端,一旦完成,通知channelFuture |
disconnect(ChannelPromise promise) | void | 断天Channel的连接。一旦完成,通知channelFuture |
close(ChannelPromise promise) | void | 关闭Channel的连接,一旦完成,通知channelFuture |
closcForcibly() | void | 强制立即关闭连接 |
beginRead() | void | 设置网络操作位为读用于读取信息 |
write(Object msg,ChannelPromise promise) | void | 发送消息,一但完成,通知ChannelFuture |
flush() | void | 将发送缓冲数组中的消息写入到Channel中 |
voidPromise() | ChannelPromise | 返回一个特殊的可重用和传递的ChannelPromise,它不用于操作成功或者失败的通知器,仅仅作为一容器被使用 |
outboundBuffer() | ChannelOutboundBuffer | 返回消息发送缓冲区 |
Unsafe继承关系类图:
AbstractUnsafe 源码分析
- register方法:主要用于将当前Unsafe对应的Channel注册到EventLoop的多路复用器上,然后调用DefaultChannelPipeline的fireChannelRegisted方法,如果Channel被激活,则调用fireChannelActive方法。
- bind方法:主要用于绑定指定端口。对于服务端,用于绑定监听端口,并设置backlog参数;对于客户端,用于指定客户端Channel的本地绑定Socket地址
- disconnect方法: 该方法用于客户端或服务端主动关闭连接
- close方法:确保在多线程环境下,多次调用close和一次调用的影响一致,并且可以通过promis得到同样的结果。
- 保证在执行close的过程中,不能向channel写数据。
- 调用doClose0执行执真正的close操作。
- 调用deregister对channel做最后的清理工作,并触发channelInactive, channelUnregistered事件。
- write方法:实际上是将消息添加到环形发送数组上,并不真正的写Channel(真正的写Channel是flush方法)。如果Channel 没有处于激活状态,说明TCP链路还有真正建立成功,当前Channel存在以下两种状态
- Channel 打开,但是TCP链路尚未建立成功
- Channel 已经关闭
- flush方法:前面提到,write方法负责将消息放进发送缓冲区,并没有真正的发送,而flush方法就负责将发送缓冲区中待发送的消息全部写进Channel中并发送。
部分源码如下:
protected abstract class AbstractUnsafe implements Unsafe {
//下面是绑定方法的逻辑 传入的是SocketAddress
@Override
public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
// 确认当前channel已经注册
assertEventLoop();
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
//验证传入的参数
// See: https://github.com/netty/netty/issues/576
if (Boolean.TRUE.equals(config().getOption(ChannelOption.SO_BROADCAST)) &&
localAddress instanceof InetSocketAddress &&
!((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress() &&
!PlatformDependent.isWindows() && !PlatformDependent.maybeSuperUser()) {
// Warn a user about the fact that a non-root user can't receive a
// broadcast packet on *nix if the socket is bound on non-wildcard address.
logger.warn(
"A non-root user can't receive a broadcast packet if the socket " +
"is not bound to a wildcard address; binding to a non-wildcard " +
"address (" + localAddress + ") anyway as requested.");
}
boolean wasActive = isActive();
try {
//具体的绑定操作在doBind方法里执行 这个方法是channel的方法,也就是我们在上面NioServerSocketChannel 里分析的逻辑
doBind(localAddress);
} catch (Throwable t) {
safeSetFailure(promise, t);
closeIfClosed();
return;
}
//触发 active事件,在pipline链里传播
if (!wasActive && isActive()) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireChannelActive();
}
});
}
safeSetSuccess(promise);
}
//往外写数据的操作(这里只往缓存里写数据)
@Override
public final void write(Object msg, ChannelPromise promise) {
//验证是否已经注册并且react线程是否已经准备好
assertEventLoop();
//ChannelOutboundBuffer 表示要往外写数据的缓存
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, WRITE_CLOSED_CHANNEL_EXCEPTION);
// release message now to prevent resource-leak
ReferenceCountUtil.release(msg);
return;
}
int size;
try {
//对需要写的数据进行过滤
msg = filterOutboundMessage(msg);
//对需要写的数据进行大小的预估
size = pipeline.estimatorHandle().size(msg);
if (size < 0) {
size = 0;
}
} catch (Throwable t) {
safeSetFailure(promise, t);
ReferenceCountUtil.release(msg);
return;
}
//将数据增加到缓存中
outboundBuffer.addMessage(msg, size, promise);
}
// flush方法用于将数据写入到网络中
@Override
public final void flush() {
assertEventLoop();
//往外发送的缓存对象不能为空
ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
if (outboundBuffer == null) {
return;
}
outboundBuffer.addFlush();
flush0();
}
//最终会调用到这个方法
@SuppressWarnings("deprecation")
protected void flush0() {
if (inFlush0) {
// Avoid re-entrance
return;
}
final ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
if (outboundBuffer == null || outboundBuffer.isEmpty()) {
return;
}
inFlush0 = true;
//对channel的状态进行验证
// Mark all pending write requests as failure if the channel is inactive.
if (!isActive()) {
try {
if (isOpen()) {
outboundBuffer.failFlushed(FLUSH0_NOT_YET_CONNECTED_EXCEPTION, true);
} else {
// Do not trigger channelWritabilityChanged because the channel is closed already.
outboundBuffer.failFlushed(FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
}
} finally {
inFlush0 = false;
}
return;
}
try {
//会调用到Channel的doWrite方法,具体实现的源码可以看NioSocketChannel
doWrite(outboundBuffer);
} catch (Throwable t) {
if (t instanceof IOException && config().isAutoClose()) {
/**
* Just call {@link #close(ChannelPromise, Throwable, boolean)} here which will take care of
* failing all flushed messages and also ensure the actual close of the underlying transport
* will happen before the promises are notified.
*
* This is needed as otherwise {@link #isActive()} , {@link #isOpen()} and {@link #isWritable()}
* may still return {@code true} even if the channel should be closed as result of the exception.
*/
close(voidPromise(), t, FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
} else {
try {
shutdownOutput(voidPromise(), t);
} catch (Throwable t2) {
close(voidPromise(), t2, FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
}
}
} finally {
inFlush0 = false;
}
}
//开始读方法的逻辑
@Override
public final void beginRead() {
assertEventLoop();
if (!isActive()) {
return;
}
try {
//会调用channel的doBeginRead方法 可以看上面AbstractNioChannel方法里的注释
doBeginRead();
} catch (final Exception e) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireExceptionCaught(e);
}
});
close(voidPromise());
}
}
//注册方法,channel会往selector里注册关注的事件
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
//验证数据
if (eventLoop == null) {
throw new NullPointerException("eventLoop");
}
if (isRegistered()) {
promise.setFailure(new IllegalStateException("registered to an event loop already"));
return;
}
if (!isCompatible(eventLoop)) {
promise.setFailure(
new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
return;
}
AbstractChannel.this.eventLoop = eventLoop;
if (eventLoop.inEventLoop()) {
//调用下面的方法
register0(promise);
} else {
try {
eventLoop.execute(new Runnable() {
@Override
public void run() {
register0(promise);
}
});
} catch (Throwable t) {
logger.warn(
"Force-closing a channel whose registration task was not accepted by an event loop: {}",
AbstractChannel.this, t);
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
}
private void register0(ChannelPromise promise) {
try {
// check if the channel is still open as it could be closed in the mean time when the register
// call was outside of the eventLoop
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
boolean firstRegistration = neverRegistered;
//会调用到channel里的方法 可以参考上面的AbstractNioChannel类
doRegister();
neverRegistered = false;
registered = true;
// Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
// user may already fire events through the pipeline in the ChannelFutureListener.
pipeline.invokeHandlerAddedIfNeeded();
safeSetSuccess(promise);
pipeline.fireChannelRegistered();
// Only fire a channelActive if the channel has never been registered. This prevents firing
// multiple channel actives if the channel is deregistered and re-registered.
if (isActive()) {
if (firstRegistration) {
pipeline.fireChannelActive();
} else if (config().isAutoRead()) {
// This channel was registered before and autoRead() is set. This means we need to begin read
// again so that we process inbound data.
//
// See https://github.com/netty/netty/issues/4805
beginRead();
}
}
} catch (Throwable t) {
// Close the channel directly to avoid FD leak.
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
}
Netty服务端接收客户端数据的调用流程
读数据的调用流程
NioEventLoop的run方法会监控SelectionKey对象
,当有读事件时,会调用unsafe对象的read()方法
,在read方法的逻辑里会触发pipeline对象链的调用
,最终调用到设置的各种ChannelHandler
写数据的调用流程
通过Channel的writeAndFlush会调用到pipeline的writeAndFlush方法里
,在pipeline的调用链里会调用链中的各种ChannelHandler(各以对需要写入的数据进行格式转换)最终通过HeadContext的write方法调用到unsafe里的write逻辑
。这里只是把数据写入到ByteBuffer里。通过调用unsafe的flash方法才能最终将数据写入到网络中,也就是上面的分析过程。