// Configure the server. EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workerGroup = new NioEventLoopGroup(); final EchoServerHandler serverHandler = new EchoServerHandler(); try { //初始化一个服务端引导类 ServerBootstrap b = new ServerBootstrap(); b.group(bossGroup, workerGroup) //设置线程组 .channel(NioServerSocketChannel.class)//设置ServerSocketChannel的IO模型 分为epoll与Nio .option(ChannelOption.SO_BACKLOG, 100)//设置option参数，保存成一个LinkedHashMap, Object>() .handler(new LoggingHandler(LogLevel.INFO))//这个hanlder 只专属于 ServerSocketChannel 而不是 SocketChannel。 .childHandler(new ChannelInitializer() { //这个handler 将会在每个客户端连接的时候调用。供 SocketChannel 使用。@Override br/>@Override ChannelPipeline p = ch.pipeline(); if (sslCtx != null) { p.addLast(sslCtx.newHandler(ch.alloc())); } //p.addLast(new LoggingHandler(LogLevel.INFO)); p.addLast(serverHandler); } });
// Start the server. 启动服务
ChannelFuture f = b.bind(PORT).sync();
// Wait until the server socket is closed.
f.channel().closeFuture().sync();
} finally {
// Shut down all event loops to terminate all threads.
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
接下来我们主要从服务端的socket在哪里初始化与哪里accept连接这两个问题入手对netty服务端启动的流程进行分析；
@Override public T newChannel() { try { return clazz.getConstructor().newInstance();//反射创建 } catch (Throwable t) { throw new ChannelException("Unable to create Channel from class " + clazz, t); } }
public B channel(Class channelClass) { if (channelClass == null) { throw new NullPointerException("channelClass"); } return channelFactory(new ReflectiveChannelFactory(channelClass)); }
Create a new instance */ public NioServerSocketChannel() { this(newSocket(DEFAULT_SELECTOR_PROVIDER));//传入默认的SelectorProvider }
private static ServerSocketChannel newSocket(SelectorProvider provider) {
try {
/**
* Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
* {@link SelectorProvider#provider()} which is called by each ServerSocketChannel.open() otherwise.
*
* See #2308.
*/
return provider.openServerSocketChannel();//可以看到创建的是jdk底层的ServerSocketChannel
} catch (IOException e) {
throw new ChannelException(
"Failed to open a server socket.", e);
}
}
第二步是通过NioServerSocketChannelConfig配置服务端Channel的构造函数，在代码中我们可以看到我们把NioServerSocketChannel这个类传入到了NioServerSocketChannelConfig的构造函数中进行配置
/**
Create a new instance using the given {@link ServerSocketChannel}. */ public NioServerSocketChannel(ServerSocketChannel channel) { super(null, channel, SelectionKey.OP_ACCEPT);//调用父类构造函数,传入创建的channel config = new NioServerSocketChannelConfig(this, javaChannel().socket()); }
@param parent the parent {@link Channel} by which this instance was created. May be {@code null}
@param ch the underlying {@link SelectableChannel} on which it operates
@param readInterestOp the ops to set to receive data from the {@link SelectableChannel} */ protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) { super(parent); this.ch = ch;//这个ch就是传入的通过jdk创建的Channel this.readInterestOp = readInterestOp; try { ch.configureBlocking(false);//设置为非阻塞 } catch (IOException e) { try { ch.close(); } catch (IOException e2) { if (logger.isWarnEnabled()) { logger.warn( "Failed to close a partially initialized socket.", e2); } }
throw new ChannelException("Failed to enter non-blocking mode.", e);
}
}
第四步调用AbstractChannel这个抽象类的构造函数设置Channel的id（每个Channel都有一个id，唯一标识）,unsafe（tcp相关底层操作），pipeline（逻辑链）等，而不管是服务的Channel还是客户端的Channel都继承自这个抽象类，他们也都会有上述相应的属性。我们看下AbstractChannel的构造函数
/**
Creates a new instance.
@param parent
the parent of this channel. {@code null} if there's no parent. */ protected AbstractChannel(Channel parent) { this.parent = parent; id = newId();//创建Channel唯一标识 unsafe = newUnsafe();//netty封装的TCP 相关操作类 pipeline = newChannelPipeline();//逻辑链 }
3、异步（因为我们这里直到现在还是 main 线程在执行，不属于当前线程）的执行 register0 方法。*/ @Override br/>*/ @Override 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;//绑定线程
if (eventLoop.inEventLoop()) {
register0(promise);//实际的注册过程
} 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);
}
}
}
首先我们对整个注册的流程做一个梳理 接下来我们进入register0()方法看下注册过程的具体实现
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; doRegister();//jdk channel的底层注册 neverRegistered = false; registered = true;
// 触发绑定的handler事件
// 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);
}
}
AbstractNioChannel中doRegister()的具体实现就是把jdk底层的channel绑定到eventLoop的selecor上
@Override protected void doRegister() throws Exception { boolean selected = false; for (;;) { try { //把channel注册到eventLoop上的selector上 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; } } } }
@Override public final void bind(final SocketAddress localAddress, final ChannelPromise promise) { assertEventLoop();
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
// 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();//判断绑定是否完成
try {
doBind(localAddress);//底层jdk绑定端口
} catch (Throwable t) {
safeSetFailure(promise, t);
closeIfClosed();
return;
}
if (!wasActive && isActive()) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireChannelActive();//触发ChannelActive事件
}
});
}
safeSetSuccess(promise);
}
在doBind(localAddress)中netty实现了jdk底层端口的绑定
@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);//readInterestOp为 SelectionKey.OP_ACCEPT
}
}
