channel的註冊主要在AbstractBootstrap類下的
<code>ChannelFuture regFuture = config().group().register(channel);/<code>
config方法返回的是ServerBootstrapConfig對象
然後調用下面這個方法：
MultithreadEventLoopGroup
<code>@Override
public ChannelFuture register(Channel channel) {
return next().register(channel);
}/<code>接下來就是next()方法了：
MultithreadEventExecutorGroup#next
<code>private final EventExecutorChooserFactory.EventExecutorChooser chooser;
@Override
public EventExecutor next() {
return chooser.next();
}/<code>EventExecutorChooserFactory
<code>@UnstableApi
public interface EventExecutorChooserFactory {
/**
* Returns a new {@link EventExecutorChooser}.
*/
EventExecutorChooser newChooser(EventExecutor[] executors);
/**
* Chooses the next {@link EventExecutor} to use.
*/
@UnstableApi
interface EventExecutorChooser {
/**
* Returns the new {@link EventExecutor} to use.
*/
EventExecutor next();
}
}/<code>EventExecutorChooserFactory的實現只有一個，跟進去發現其實這個簡單的算法，也就是說會以round-robin的方式（可以看作隨機選一個）選一個executor。
這裡總結一下，也就是說EventLoopGroup可以看作一個獨立的線程池，這個線程池中有很多的executor，現在這個裡面還有一個叫EventExecutorChooserFactory，它的作用僅僅是從線程池中的executor中隨機返回一個出來。
回到MultithreadEventLoopGroup，調用完next之後得到了executor選擇器。
通過debug，可知，返回的這個executor是SingleThreadEventLoop中的register方法，這個loop會講所有的event放到一個線程去執行。
SingleThreadEventLoop#register
<code>@Override
public ChannelFuture register(Channel channel) {
return register(new DefaultChannelPromise(channel, this));
}
@Override
public ChannelFuture register(final ChannelPromise promise) {
ObjectUtil.checkNotNull(promise, "promise");
promise.channel().unsafe().register(this, promise);
return promise;
}/<code>unsafe不是sun提供的，而是netty在AbstractNioChannel中定義的unsafe
<code>@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
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;
if (eventLoop.inEventLoop()) {
register0(promise);
} 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);
}
}
}/<code>判斷一下當前正在執行方法調用線程和eventLoop所維護的線程是否為同一個線程對象（singleThreadEventExecutor中只有一個線程）。
<code>@Override
protected void doRegister() throws Exception {
boolean selected = false;
for (;;) {
try {
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;
}
}
}
}/<code>到這裡，就真正調用了底層的註冊方式，就到了NIO的領域了。
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