NioEventLoop.run select处理IO事件（boss/worker）流程：
processSelectedKeys
processSelectedKeysOptimized
processSelectedKey
以read为例:
unsafe.read()
NioServerSocketChannel（boss)
//读取accept connect
AbstractNioMessageChannel.NioMessageUnsafe.read
fireChannelRead
invokeChannelRead
//将connnected channel注册到worker
ServerBootstrapAcceptor.channelRead
NioSocketChannel(worker)
//worker从注册的channels读取数据
AbstractNioByteChannel.NioByteUnsafe.read
fireChannelRead
invokeChannelRead
调用用户的childHandler。
runAllTasks运行添加的task。