First of all, let's review the previous work , stay netty Server startup in , Detailed netty The four steps of the initialization process ：

• Create server channel, call jdk At the bottom api establish jdk Of channel, after netty Pack it into your own channel, And create some basic components bound to the channel On .
• Initialize the server channel, After the creation is completed, the channel Do some initialization work , For example, initialize some basic properties , Add some logical processors .
• register selector,netty take jdk At the bottom channel Register to event poller selector above .
• Port binding , call jdk Bottom api Monitor the port .

The first two steps are Create server channel and Initialize the server channel In detail , This section introduces the third step ： register selector, Its main function is to jdk At the bottom channel Register with the event poller .

1. register selector Overall process

Similarly, first according to the overall process given by flash , Register for selector Part has a whole cognition ：

The source code part goes on channel Registration and initialization of , As shown in the figure below , After initialization, there is a registered part , The code here corresponds to AbstractChannel Class register Method , That is, the first step in the overall process .

2. register(channel) Method

The source code of this method is as follows ：

The first few lines are if Judge , There are two main places ：AbstractChannel.this.eventLoop = eventLoop Be responsible for binding eventLoop Threads are used to process requests that have only ;register0(promise) Is the part of the actual registration , The source code is as follows ：

register0 The method mainly analyzes the three places marked in the figure .

2.1 doRegister() Method

The method is located in AbstractNioChannel Class , The source code is as follows ：

among javaChannel() Method returns through jdk Bottom api Create a new server channel, After that register Part is the specific registration , take this Sign up to eventLoop().selector above , there this It's a AbstractNioChannel object , I understand that you are right java Bottom channel An encapsulation of . Another parameter is ops Indicates that registration is a time of concern ,0 I don't care about anything . such netty By calling java Bottom channel Your registration method is complete selector Registration of .

2.2 invokeHandlerAddedIfNeeded() And fireChannelRegistered()

stay register0() In the method , Let's focus on three steps , except doRegister The other part is the part that needs to be expanded in this section .

among 2 and 3 Part corresponds to... Of the user code handler part , Here we introduce a ServerHandler, It rewrites three methods , These three methods are related to invokeHandlerAddedIfNeeded()、fireChannelRegistered() Corresponding .

Run the program , Change can see that we are ServerHandler Output in ：

3. Summary

• register selector when , With register(channel) The method is the entrance

  • First bind the thread
  • After that by regiter0 Complete the actual registration , The registration part is mainly divided into three steps

    • call jdk Bottom channel Your registration method is complete selector Registration of
    • invokeHandlerAddedIfNeeded()
    • fireChannelRegistered()