线程池都准备好了，我们需要利用起来了。我们一客户端的connect为例讲述这个过程。下面是我们触发了链接这个动作
ChannelFuture f = b.connect(host, port).sync();
他里面是怎样的逻辑呢？
private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
//利用反射创建channel类，并且初始化它
final ChannelFuture regFuture = initAndRegister();
...
//真正的链接服务端
return doResolveAndConnect0(channel, remoteAddress, localAddress, channel.newPromise());
}
}
中间省略了好多代码，只留下关键的代码。首先我们回忆一下NIO的经典操作。首先创建一个channel，然后在selector上注册，并指明感兴趣的事件，随后selector就select了，等待感兴趣的事件到来，事件到达，处理请求。这是原生的NIO的处理过程，既然netty是基于nio的，顶多是帮助我们封装了这些操作而已，让我们可以更加舒服的利用netty的api处理网络的请求。看看上面的注释，基本上和我们的了解一致，至于是不是真的一致，那么久得继续往下看了。
final ChannelFuture initAndRegister() {
Channel channel = null;
channel = channelFactory.newChannel(); //利用反射创建对象
init(channel); //初始化，添加逻辑处理器，设置channel的Option与属性Attribute
...
ChannelFuture regFuture = config().group().register(channel);
...
return regFuture;
}
利用反射创建了代码中我们指定的channel，init初始化，添加逻辑处理器，设置channel的Option与属性Attribute。我们更为关键的是看一下如果进行注册上篇文章也介绍了groupMultithreadEventLoopGroup的实例。
### io.netty.channel.MultithreadEventLoopGroup#register(io.netty.channel.Channel)
@Override
public ChannelFuture register(Channel channel) {
return next().register(channel);
}
这个next方法就是我们的选择器发挥作用了，选择一个孩子来进行处理（负载均衡的考虑）。具体的是NioEventLoop的事例进行的register操作，他没有复写父类的方法，所以由父类SingleThreadEventLoop来具体处理
### io.netty.channel.SingleThreadEventLoop#register(io.netty.channel.Channel)
@Override
public ChannelFuture register(Channel channel) {
return register(new DefaultChannelPromise(channel, this));
}
将channel包装成了DefaultChannelPromise的对象进行操作。
### io.netty.channel.AbstractChannel.AbstractUnsafe#register
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
...
AbstractChannel.this.eventLoop = eventLoop;
...
eventLoop.execute(new Runnable() { //有具体的线程池进行处理，参数传递过来的
@Override
public void run() {
register0(promise);
}
});
...
}
}
老样子，省略好多代码，只留下重点。eventLoop是NioEnevtLoop的实例，所以看一下他的execute,同样的他没有复写这个方法，所以还是由父类提供
### io.netty.util.concurrent.SingleThreadEventExecutor#execute
@Override
public void execute(Runnable task) {
...
startThread(); //开启线程
addTask(task); //处理请求
...
}
### io.netty.util.concurrent.SingleThreadEventExecutor#startThread
private void startThread() {
...
doStartThread();
...
}
private void doStartThread() {
assert thread == null;
executor.execute(new Runnable() { //重点关注这个executor
@Override
public void run() {
thread = Thread.currentThread();
if (interrupted) {
thread.interrupt();
}
boolean success = false;
updateLastExecutionTime();
try {
SingleThreadEventExecutor.this.run(); //SingleThreadEventExecutor.this是NioEventLoop的事例
success = true;
} catch (Throwable t) {
logger.warn("Unexpected exception from an event executor: ", t);
} finally {
for (;;) {
int oldState = state;
if (oldState >= ST_SHUTTING_DOWN || STATE_UPDATER.compareAndSet(
SingleThreadEventExecutor.this, oldState, ST_SHUTTING_DOWN)) {
break;
}
}
// Check if confirmShutdown() was called at the end of the loop.
if (success && gracefulShutdownStartTime == 0) {
logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +
SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called " +
"before run() implementation terminates.");
}
try {
// Run all remaining tasks and shutdown hooks.
for (;;) {
if (confirmShutdown()) {
break;
}
}
} finally {
try {
cleanup();
} finally {
STATE_UPDATER.set(SingleThreadEventExecutor.this, ST_TERMINATED);
threadLock.release();
if (!taskQueue.isEmpty()) {
logger.warn(
"An event executor terminated with " +
"non-empty task queue (" + taskQueue.size() + ')');
}
terminationFuture.setSuccess(null);
}
}
}
}
});
}
这里有一个细节点不能忽略就是executor.execute，我们要知道这个executor是啥，再创建NioEventLoopGroup时，有这样的逻辑
### io.netty.util.concurrent.MultithreadEventExecutorGroup#MultithreadEventExecutorGroup(int, java.util.concurrent.Executor, io.netty.util.concurrent.EventExecutorChooserFactory, java.lang.Object...)
if (executor == null) {
executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
}
protected ThreadFactory newDefaultThreadFactory() {
return new DefaultThreadFactory(getClass());
}
### io.netty.util.concurrent.DefaultThreadFactory
@Override
public Thread newThread(Runnable r) {
Thread t = newThread(new DefaultRunnableDecorator(r), prefix + nextId.incrementAndGet());
try {
if (t.isDaemon() != daemon) {
t.setDaemon(daemon);
}
if (t.getPriority() != priority) {
t.setPriority(priority);
}
} catch (Exception ignored) {
// Doesn't matter even if failed to set.
}
return t;
}
private static final class DefaultRunnableDecorator implements Runnable {
private final Runnable r;
DefaultRunnableDecorator(Runnable r) {
this.r = r;
}
@Override
public void run() {
try {
r.run();
} finally {
FastThreadLocal.removeAll();
}
}
}
线程工厂创建线程的逻辑，线程池里面设置了线程工厂，那么线程池运行多线程任务的时候，其实是利用线程工厂创建线程来运行
### io.netty.util.concurrent.ThreadPerTaskExecutor
public final class ThreadPerTaskExecutor implements Executor {
private final ThreadFactory threadFactory;
public ThreadPerTaskExecutor(ThreadFactory threadFactory) {
if (threadFactory == null) {
throw new NullPointerException("threadFactory");
}
this.threadFactory = threadFactory;
}
@Override
public void execute(Runnable command) {
threadFactory.newThread(command).start();
}
}
当线程池有任务过来时，会调用线程工厂创建线程，并且启动该线程来处理,我们看一下NioEventLoop的run方法
@Override
protected void run() {
for (;;) {
...
processSelectedKeys(); //处理Nio中的SelectedKeys
...
}
}
###
private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe();
if (!k.isValid()) {
final EventLoop eventLoop;
try {
eventLoop = ch.eventLoop();
} catch (Throwable ignored) {
// If the channel implementation throws an exception because there is no event loop, we ignore this
// because we are only trying to determine if ch is registered to this event loop and thus has authority
// to close ch.
return;
}
// Only close ch if ch is still registered to this EventLoop. ch could have deregistered from the event loop
// and thus the SelectionKey could be cancelled as part of the deregistration process, but the channel is
// still healthy and should not be closed.
// See https://github.com/netty/netty/issues/5125
if (eventLoop != this || eventLoop == null) {
return;
}
// close the channel if the key is not valid anymore
unsafe.close(unsafe.voidPromise());
return;
}
try {
int readyOps = k.readyOps();
// We first need to call finishConnect() before try to trigger a read(...) or write(...) as otherwise
// the NIO JDK channel implementation may throw a NotYetConnectedException.
if ((readyOps & SelectionKey.OP_CONNECT) != 0) { //如何是链接的请求，调用unsafe的finishConnect
// 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();
}
// Process OP_WRITE first as we may be able to write some queued buffers and so free memory.
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();
}
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
unsafe.read(); //读取数据
}
} catch (CancelledKeyException ignored) {
unsafe.close(unsafe.voidPromise());
}
}
好像终于和我们的NIO有点联系了。无非也就是等感兴趣的事件来了就处理，调用unsafe来处理，首先我们说一下unsafe,他是NioSocketChannelUnsafe的事例，而这个类继承了NioByteUnsafe，并且大部分的方法都是在NioByteUnSafe,我们比较关心她的读取数据的过程
@Override
public final void read() {
final ChannelConfig config = config();
final ChannelPipeline pipeline = pipeline();
final ByteBufAllocator allocator = config.getAllocator();
final RecvByteBufAllocator.Handle allocHandle = recvBufAllocHandle();
allocHandle.reset(config);
ByteBuf byteBuf = null;
boolean close = false;
try {
do {
byteBuf = allocHandle.allocate(allocator);
allocHandle.lastBytesRead(doReadBytes(byteBuf));
if (allocHandle.lastBytesRead() <= 0) {
// nothing was read. release the buffer.
byteBuf.release();
byteBuf = null;
close = allocHandle.lastBytesRead() < 0;
break;
}
allocHandle.incMessagesRead(1);
readPending = false;
pipeline.fireChannelRead(byteBuf); //触发pipeline的生命周期方法，接收消息，处理消息
byteBuf = null;
} while (allocHandle.continueReading());
allocHandle.readComplete();
pipeline.fireChannelReadComplete();
if (close) {
closeOnRead(pipeline);
}
} catch (Throwable t) {
handleReadException(pipeline, byteBuf, t, close, allocHandle);
} finally {
// Check if there is a readPending which was not processed yet.
// This could be for two reasons:
// * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
// * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
//
// See https://github.com/netty/netty/issues/2254
if (!readPending && !config.isAutoRead()) {
removeReadOp();
}
}
}
}
调用pipeline的生命周期方，同时将数据传递过去，handler开始处理了。以上皆是处理了SelectionKey的过程。注册搞好了，我们就可以开始连接。在我们追踪下来，connect核心的代码
doConnect(remoteAddress, localAddress)
### io.netty.channel.socket.nio.NioSocketChannel#doConnect
@Override
protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
if (localAddress != null) {
doBind0(localAddress);
}
boolean success = false;
try {
boolean connected = SocketUtils.connect(javaChannel(), remoteAddress);
if (!connected) {
selectionKey().interestOps(SelectionKey.OP_CONNECT);
}
success = true;
return connected;
} finally {
if (!success) {
doClose();
}
}
}
socket 链接远程服务器，因为是异步链接，所以connected为false,那么就注册了OP_CONNECT事件，这样，当连接事件做好之后，在线程组中会有无限循环，查询准备好的事件，连接事件好了，就会进行处理，同时触发声明周期的方法，进行流程的流转。
以上。
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