Netty代码下载和编译参考前一篇Netty文章
https://blog.51cto.com/483181/2112163
一般Netty服务器端这样编写
EventLoopGroup bossGroup = new NioEventLoopGroup(); //1. 实例化NioEventLoopGroup对象
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap(); //2.
b.group(bossGroup, workerGroup) //3.
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 100)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new FixedLengthFrameDecoder(20));
}
});
ChannelFuture f = b.bind(port).sync(); //4.
f.channel().closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
一步步来看，首先看第一个注释，初始化NioEventLoopGroup对象
EventLoopGroup bossGroup = new NioEventLoopGroup(); //1. 实例化NioEventLoopGroup对象下图是NioEventLoopGroup的类继承图，包含类成员和方法，比较详细。 这个功能是IntelliJ 自带的。
右击NioEventLoopGroup类名，选择Diagrams->Show Diagram->上面有f，m的按钮，分别对应field和method。
如下：
public NioEventLoopGroup() {
this(0);
}
public NioEventLoopGroup(int nThreads) {
this(nThreads, (Executor) null);
}
public NioEventLoopGroup(int nThreads, Executor executor) {
this(nThreads, executor, SelectorProvider.provider());
}
public NioEventLoopGroup(
int nThreads, Executor executor, final SelectorProvider selectorProvider) {
this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
}
public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
final SelectStrategyFactory selectStrategyFactory) {
super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
}
我们可以看到几点
private static SelectorProvider provider = null;
public static SelectorProvider provider() {
synchronized (lock) {
if (provider != null)
return provider;
return AccessController.doPrivileged(
new PrivilegedAction<SelectorProvider>() {
public SelectorProvider run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = sun.nio.ch.DefaultSelectorProvider.create();
return provider;
}
});
}
}
public class DefaultSelectorProvider {
private DefaultSelectorProvider() {
}
public static SelectorProvider create() {
return new KQueueSelectorProvider();
}
}
public class KQueueSelectorProvider extends SelectorProviderImpl {
public KQueueSelectorProvider() {
}
public AbstractSelector openSelector() throws IOException {
return new KQueueSelectorImpl(this);
}
}
这段代码我们也可以看到几点:
这个先记下来，也许后面分析会有用，继续分析MultithreadEventLoopGroup的构造函数。
protected MultithreadEventLoopGroup(int nThreads, ThreadFactory threadFactory, Object... args) {
super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, threadFactory, args);
}
private static final int DEFAULT_EVENT_LOOP_THREADS;
static {
DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
"io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));
} 上面这段代码我们可以看到这几点：
继续父类MultithreadEventExecutorGroup
protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
EventExecutorChooserFactory chooserFactory, Object... args) {
...
children = new EventExecutor[nThreads]; //1. 实例化children数组
for (int i = 0; i < nThreads; i ++) { //2. 循环初始化children
boolean success = false;
try {
children[i] = newChild(executor, args);
success = true;
} catch (Exception e) {
throw new IllegalStateException("failed to create a child event loop", e);
} finally {
...
}
}
chooser = chooserFactory.newChooser(children); //3. 实例化chooser
final FutureListener<Object> terminationListener = new FutureListener<Object>() {
@Override
public void operationComplete(Future<Object> future) throws Exception {
if (terminatedChildren.incrementAndGet() == children.length) {
terminationFuture.setSuccess(null);
}
}
};
for (EventExecutor e: children) {
e.terminationFuture().addListener(terminationListener);
}
Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
Collections.addAll(childrenSet, children);
readonlyChildren = Collections.unmodifiableSet(childrenSet);
}上面这段代码可以从下面几个点分析：
private final EventExecutor[] children;protected EventLoop newChild(Executor executor, Object... args) throws Exception {
return new NioEventLoop(this, executor, (SelectorProvider) args[0],
((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
}NioEventLoop的继承关系是这样的，继承于SingleThreadEventLoop，别忘了上面我们看到NioEventLoopGroup继承自MultithreadEventLoopGroup.(看名字是单线程和多线程的区别？)
继续看NioEventLoop的构造函数
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
provider = selectorProvider;
final SelectorTuple selectorTuple = openSelector();
selector = selectorTuple.selector;
unwrappedSelector = selectorTuple.unwrappedSelector;
selectStrategy = strategy;
}
private SelectorTuple openSelector() {
final Selector unwrappedSelector;
try {
unwrappedSelector = provider.openSelector();
} catch (IOException e) {
throw new ChannelException("failed to open a new selector", e);
}
if (DISABLE_KEYSET_OPTIMIZATION) {
return new SelectorTuple(unwrappedSelector);
}
...
}
从上面这段代码我们可以看出这几点
selector, unwrappedSelector是通过provider.openSelector()打开的.
根据2.3段的介绍，provider之前介绍的类型是KQueueSelectorProvider，然后它的openSelector会生成一个KQueueSelectorImpl
所以provider.openSelector()得到是KQueueSelectorImpl，KQueueSelectorImpl的继承关系如下：
继续往回看，看MultithreadEventExecutorGroup的构造函数。
EventExecutorChooserFactory.EventExecutorChooser chooser;
protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
}
chooser = chooserFactory.newChooser(children);上面代码我们可以看到：
public EventExecutorChooser newChooser(EventExecutor[] executors) {
if (isPowerOfTwo(executors.length)) {
return new PowerOfTwoEventExecutorChooser(executors);
} else {
return new GenericEventExecutorChooser(executors);
}
}public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();
继续看newChooser的实现
newChooser的代码就不贴了，上面就有，从上面代码可以看到：
private static boolean isPowerOfTwo(int val) {
return (val & -val) == val;
}
private static final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
private final AtomicInteger idx = new AtomicInteger();
private final EventExecutor[] executors;
PowerOfTwoEventExecutorChooser(EventExecutor[] executors) {
this.executors = executors;
}
@Override
public EventExecutor next() {
return executors[idx.getAndIncrement() & executors.length - 1];
}
}
private static final class GenericEventExecutorChooser implements EventExecutorChooser {
private final AtomicInteger idx = new AtomicInteger();
private final EventExecutor[] executors;
GenericEventExecutorChooser(EventExecutor[] executors) {
this.executors = executors;
}
@Override
public EventExecutor next() {
return executors[Math.abs(idx.getAndIncrement() % executors.length)];
}
} 这种实现方法感觉比较优雅和高效，首先拿到-val，也就是val的二进制倒转，然后+1。再做&运算。
大家自己可以拿到数字举个例子，比较巧妙。后续自己写代码可以借鉴，这是读源码的一个好处，可以学习到别人很多优秀的写法。
但是说实话，我没有想到这两种算法有什么区别，如果谁知道，请告诉我，谢谢。
return executors[idx.getAndIncrement() & executors.length - 1];
return executors[Math.abs(idx.getAndIncrement() % executors.length)];继续往回走，MultithreadEventExecutorGroup的构造函数就基本看完了。
我们来总结下NioEventLoopGroup的实例化过程，可以得到以下几点。
1. NioEventLoopGroup的父类MultithreadEventExecutorGroup包含一个NioEventLoop数组children，数组的大小等于nThreads线程数目。如果没有指定，默认一般是cpu核数 x 2
2. NioEventLoopGroup和NioEventLoop一样都是继承自Executor，但是NioEventLoopGroup又包含多个NioEventLoop(children数组)，这种关系有点像android里面ViewGroup和View的关系。或者装饰者模式？
3. NioEventLoopGroup继承自MultithreadEventLoopGroup，而NioEventLoop继承自SingleThreadEventLoop，从名字看，不知道和多线程，单线程有没有关系。
4. MultithreadEventLoopGroup有个chooser，执行next方法的时候，会选择下一个NioEventLoop对象，虽然并不知道两个chooser算法有何区别。
5. NioEventLoopGroup里面重写了newChild方法，里面实例化NioEventLoop。
6. NioEventLoop里面包含了Selector，类型是KQueueSelectorImpl
SelectorProvider provider
SelectStrategy selectStrategy
SelectStrategy这个我们上面我们没有关注，其实它是NioEventLoopGroup构造函数传进去的，如下：
public NioEventLoopGroup(
int nThreads, Executor executor, final SelectorProvider selectorProvider) {
this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
}
public final class DefaultSelectStrategyFactory implements SelectStrategyFactory {
public static final SelectStrategyFactory INSTANCE = new DefaultSelectStrategyFactory();
private DefaultSelectStrategyFactory() { }
@Override
public SelectStrategy newSelectStrategy() {
return DefaultSelectStrategy.INSTANCE;
}
}
final class DefaultSelectStrategy implements SelectStrategy {
static final SelectStrategy INSTANCE = new DefaultSelectStrategy();
private DefaultSelectStrategy() { }
@Override
public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
return hasTasks ? selectSupplier.get() : SelectStrategy.SELECT;
}
}所以SelectStrategy的实现类是DefaultSelectStrategy.
在理清楚NioEventLoopGroup实例化的过程之后，我们下一篇继续按照源代码分析Netty服务器端的源代码。
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