启动
一个典型的nettyserver拥有两个EventLoopGroup(parent负责连接，childGroup负责具体IO）.前者也一般被称为bossGroup，后者则被称为workerGroup。
EventLoopGroup 是一组 EventLoop 的抽象，一个 EventLoopGroup 当中会包含一个或多个 EventLoop，EventLoopGroup 提供 next 接口，可以从一组 EventLoop 里面按照一定规则获取其中一个 EventLoop 来处理任务。
启动时，bossGroup会完成
ChannelFuture regFuture = group().register(channel);
BossEventLoopGroup 通常是一个单线程的 EventLoop，EventLoop 维护着一个注册了 ServerSocketChannel 的 Selector 实例。
既然注册上去了，意味着就能被select到。同时在channel的pipeline中加入aceeptor
p.addLast(new ChannelInitializer<Channel>() {
@Override
public void initChannel(Channel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
ChannelHandler handler = handler();
if (handler != null) {
pipeline.addLast(handler);
}
pipeline.addLast(new ServerBootstrapAcceptor(
currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
其acceptor的代码如下
public void channelRead(ChannelHandlerContext ctx, Object msg) {
final Channel child = (Channel) msg;
child.pipeline().addLast(childHandler);
try {
childGroup.register(child)
channel被转给childGroup。childGroup将提供一个EventLoop来处理这个channel的后续情况的处理。每个EventLoop相当于拥有一个selector。其中epollEventpoll调用
selectedKeys = Native.epollWait(this.epollFd.intValue(), this.events, 0);
if (selectedKeys > 0) {
return selectedKeys;
}
来获取已经就绪的事件
核心循环代码如下
@Override
protected void run() {
for (;;) {
try {
int strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks());
switch (strategy) {
case SelectStrategy.CONTINUE:
continue;
case SelectStrategy.SELECT:
//epollWait相当于select。返回的就绪事件在对象的events字段中
strategy = epollWait(WAKEN_UP_UPDATER.getAndSet(this, 0) == 1);
// 'wakenUp.compareAndSet(false, true)' is always evaluated
// before calling 'selector.wakeup()' to reduce the wake-up
// overhead. (Selector.wakeup() is an expensive operation.)
//
// However, there is a race condition in this approach.
// The race condition is triggered when 'wakenUp' is set to
// true too early.
//
// 'wakenUp' is set to true too early if:
// 1) Selector is waken up between 'wakenUp.set(false)' and
// 'selector.select(...)'. (BAD)
// 2) Selector is waken up between 'selector.select(...)' and
// 'if (wakenUp.get()) { ... }'. (OK)
//
// In the first case, 'wakenUp' is set to true and the
// following 'selector.select(...)' will wake up immediately.
// Until 'wakenUp' is set to false again in the next round,
// 'wakenUp.compareAndSet(false, true)' will fail, and therefore
// any attempt to wake up the Selector will fail, too, causing
// the following 'selector.select(...)' call to block
// unnecessarily.
//
// To fix this problem, we wake up the selector again if wakenUp
// is true immediately after selector.select(...).
// It is inefficient in that it wakes up the selector for both
// the first case (BAD - wake-up required) and the second case
// (OK - no wake-up required).
if (wakenUp == 1) {
Native.eventFdWrite(eventFd.intValue(), 1L);
}
default:
// fallthrough
}
final int ioRatio = this.ioRatio;
if (ioRatio == 100) {
if (strategy > 0) {
//处理就绪事件
processReady(events, strategy);
}
runAllTasks();
} else {
final long ioStartTime = System.nanoTime();
if (strategy > 0) {
processReady(events, strategy);
}
final long ioTime = System.nanoTime() - ioStartTime;
runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
}
if (allowGrowing && strategy == events.length()) {
//increase the size of the array as we needed the whole space for the events
events.increase();
}
if (isShuttingDown()) {
closeAll();
if (confirmShutdown()) {
break;
}
}
} catch (Throwable t) {
logger.warn("Unexpected exception in the selector loop.", t);
// Prevent possible consecutive immediate failures that lead to
// excessive CPU consumption.
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// Ignore.
}
}
}
}
淘宝Remoting框架中的代码实现（dubbo）
dubbo底层的rpc代码如下。可以看到使用 pipeline.addLast(“handler”, rpcHandler);来规定了后续的使用步骤
@Override
protected void doInit() {
if (this.addressParser == null) {
this.addressParser = new RpcAddressParser();
}
if (this.switches().isOn(GlobalSwitch.SERVER_MANAGE_CONNECTION_SWITCH)) {
this.connectionEventHandler = new RpcConnectionEventHandler(switches());
this.connectionManager = new DefaultConnectionManager(new RandomSelectStrategy());
this.connectionEventHandler.setConnectionManager(this.connectionManager);
this.connectionEventHandler.setConnectionEventListener(this.connectionEventListener);
} else {
this.connectionEventHandler = new ConnectionEventHandler(switches());
this.connectionEventHandler.setConnectionEventListener(this.connectionEventListener);
}
initRpcRemoting();
this.bootstrap = new ServerBootstrap();
this.bootstrap.group(bossGroup, workerGroup)
.channel(NettyEventLoopUtil.getServerSocketChannelClass())
.option(ChannelOption.SO_BACKLOG, ConfigManager.tcp_so_backlog())
.option(ChannelOption.SO_REUSEADDR, ConfigManager.tcp_so_reuseaddr())
.childOption(ChannelOption.TCP_NODELAY, ConfigManager.tcp_nodelay())
.childOption(ChannelOption.SO_KEEPALIVE, ConfigManager.tcp_so_keepalive());
// set write buffer water mark
initWriteBufferWaterMark();
// init byte buf allocator
if (ConfigManager.netty_buffer_pooled()) {
this.bootstrap.option(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);
} else {
this.bootstrap.option(ChannelOption.ALLOCATOR, UnpooledByteBufAllocator.DEFAULT)
.childOption(ChannelOption.ALLOCATOR, UnpooledByteBufAllocator.DEFAULT);
}
// enable trigger mode for epoll if need
NettyEventLoopUtil.enableTriggeredMode(bootstrap);
final boolean idleSwitch = ConfigManager.tcp_idle_switch();
final int idleTime = ConfigManager.tcp_server_idle();
final ChannelHandler serverIdleHandler = new ServerIdleHandler();
final RpcHandler rpcHandler = new RpcHandler(true, this.userProcessors);
this.bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel channel) {
ChannelPipeline pipeline = channel.pipeline();
pipeline.addLast("decoder", codec.newDecoder());
pipeline.addLast("encoder", codec.newEncoder());
if (idleSwitch) {
pipeline.addLast("idleStateHandler", new IdleStateHandler(0, 0, idleTime,
TimeUnit.MILLISECONDS));
pipeline.addLast("serverIdleHandler", serverIdleHandler);
}
pipeline.addLast("connectionEventHandler", connectionEventHandler);
pipeline.addLast("handler", rpcHandler);
createConnection(channel);
}
/**
* create connection operation<br>
* <ul>
* <li>If flag manageConnection be true, use {@link DefaultConnectionManager} to add a new connection, meanwhile bind it with the channel.</li>
* <li>If flag manageConnection be false, just create a new connection and bind it with the channel.</li>
* </ul>
*/
private void createConnection(SocketChannel channel) {
Url url = addressParser.parse(RemotingUtil.parseRemoteAddress(channel));
if (switches().isOn(GlobalSwitch.SERVER_MANAGE_CONNECTION_SWITCH)) {
connectionManager.add(new Connection(channel, url), url.getUniqueKey());
} else {
new Connection(channel, url);
}
channel.pipeline().fireUserEventTriggered(ConnectionEventType.CONNECT);
}
});
}