标签：
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 {
//得到当前的key关注的事件
int readyOps = k.readyOps();
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
//一个刚刚创建的NioServersocketChannel感兴趣的事件是0。
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {//可以读取操作 --对于serverSocket来说就是acceptor事件、对于socketChannel来说就是read事件
//INFO: channel类型为io.netty.channel.socket.nio.NioSocketChannel unsafe类型为io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe
Object obj = k.attachment();//得到NioServerSocketChannel或者NioSocketChannel
if(obj instanceof NioServerSocketChannel){
System.out.println(obj.getClass().getName()+ " 开始接收连接");
}else{
System.out.println(obj.getClass().getName()+ " 开始接收字节");
}
//不同的socketChannel对于那个的unsafe是不同的。例如Server端的是messageUnsafe 而 clinet端是byteUnsafe
unsafe.read();//对于接受链接或者read兴趣都会添加进入read操作调用serverSocket->NioMessageUnsafe
if (!ch.isOpen()) {
// Connection already closed - no need to handle write.
return;
}
}
if ((readyOps & SelectionKey.OP_WRITE) != 0) {//对于半包消息进行输出操作
// 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/924
int ops = k.interestOps();
ops &= ~SelectionKey.OP_CONNECT;
k.interestOps(ops);
unsafe.finishConnect();
}
} catch (CancelledKeyException e) {
unsafe.close(unsafe.voidPromise());
}
}
这里我们以连接的建立(NioMessageUnsafe)为线索进行讲解。后续会有基于byte的unsafe进行讲解的(Unsafe不知道为啥要这么叫，本人也感到挺费解的，不过现在看来感觉就是一个工具对象。不要从名称上惧怕它)。下面来看NioMessageUnsafe的read方法进行讲解。直接讲代码(后面也会有图形讲解，方便大家理解):
@Override
public void read() {
assert eventLoop().inEventLoop();
if (!config().isAutoRead()) {
removeReadOp();
}
final ChannelConfig config = config();
//得到本次方法调用可以接收的连接数目
final int maxMessagesPerRead = config.getMaxMessagesPerRead();
final boolean autoRead = config.isAutoRead();
final ChannelPipeline pipeline = pipeline();
boolean closed = false;
Throwable exception = null;
try {
for (;;) {
//将msg从读取出来(SocketChannel-(common msg); serverSocketChannel(socketChannel msg))
int localRead = doReadMessages(readBuf);//readBuf仅仅是在本方法中起到缓冲统计的作用。不要多想哦！！
if (localRead == 0) {
break;
}
if (localRead < 0) {
closed = true;
break;
}
//每次读取的message的个数---
if (readBuf.size() >= maxMessagesPerRead | !autoRead) {
break;//避免一次性创建过多的连接个数
}
}
} catch (Throwable t) {
exception = t;
}
int size = readBuf.size();
for (int i = 0; i < size; i ++) {
//对于server端来说，第一个handler为io.netty.bootstrap.ServerBootstrap$ServerBootstrapAcceptor
////针对所有的channel都会执行一个read操作;对于ServerSocketChannel ServerSocketChannel对应的pipeline的fireChannelRead方法
//因为ServerSocketChannel的pipeline的第一个handler
pipeline.fireChannelRead(readBuf.get(i));
}
readBuf.clear();//清空到的连接缓存
pipeline.fireChannelReadComplete();
if (exception != null) {
if (exception instanceof IOException) {
// ServerChannel should not be closed even on IOException because it can often continue
// accepting incoming connections. (e.g. too many open files)
closed = !(AbstractNioMessageChannel.this instanceof ServerChannel);
}
pipeline.fireExceptionCaught(exception);
}
if (closed) {
if (isOpen()) {
close(voidPromise());
}
}
}
}
下面让我们来看看上面这段代码中提到的
int localRead = doReadMessages(readBuf);//doReadMessages是个抽象方法
上代码：
@Override
protected int doReadMessages(List<Object> buf) throws Exception {//对于NioServerSocketChannel，它的读取操作，就是接受客户端的链接和创建NioSocketChannel
SocketChannel ch = javaChannel().accept();//得到java远程的socketChannel对象。不要认为此处会阻塞，不会的因为connec事件发生了。所以会立即返回
try {
if (ch != null) {
//进行包装，包装成netty的NioSocketChannel对象-将所有绑定socketChannel的处理线程
buf.add(new NioSocketChannel(this, childEventLoopGroup().next(), ch));
return 1;//每次仅仅处理一个，并且将得到连接对象放入到buf列表对象中进行保存
}
} 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;
}
标签：
原文地址：http://my.oschina.net/hotbain/blog/420941
