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Last lesson, we had a preliminary understanding of Netty. In this lesson, we will overlook the whole context of Netty, so as to have a general understanding of the architecture principle of Netty! The diagram below is the main framework of Netty: (welcome to pay attention to wX public number: [source code apprentice] explore all kinds of open source code implementation!)
Basic knowledge of EventLoopGroup
Netty has implemented a number of extensions to the EventLoopGroup.
Our lesson use case, use NioEventLoopGroup, he is the realization of the NIO, can see he is a subclass of MultithreadEventLoopGroup, can be seen from the name, NioEventLoopGroup is a multi-threaded event loop group, Here you can think of it as a thread pool with multiple threads (NioEventLoop) inside, one thread for each SocketChannel to which the client connects (NioEventLoop)!
NioEventLoop (SingleThreadEventLoop) NioEventLoop (SingleThreadEventLoop) NioEventLoop (SingleThreadEventLoop) As you can see, the parent interface of NIoEventLoop is actually inherited from the EventLoopGroup, which means that although NIoEventLoop is a single-threaded event loop, we can also think of it as a thread pool based on the interface, except that there is only one thread in the thread pool!
## Netty communication channel
What we need to know about the types of pipes in Netty, here we focus on NIO implementation:
We can see that there are two main implementations of Netty’s Socket communication channel, NioServerSocketChannel and NioSocketChannel. These two implementations are different implementations of Netty’s server channel and client channel. We specify the type of pipe to use when developing the Netty server and client! There are one of the more important point, namely NioServerSocketChannel superclass implementation is AbstractNioMessageChannel, NioSocketChannel superclass implementation is AbstractNioByteChannel, These two implementations are important for determining whether to process connections or data during subsequent NIO event loops, so keep an eye on them and we’ll get into more about them later!
Netty pipe flow
What we need to know about Netty’s business execution chain, also called the ChannelPipeline:
Our Netty code will consist of code that looks like this:
It is the main implementation of Netty that allows us to focus on the business. Its main implementation is a two-way linked list, where a business Handler is appendedto the end of the list. There are roughly two types of handlers:
As shown in the above, he has two implementations, one is ChannelInboundHandlerAdapter ChannelOutboundHandlerAdapter, they call in a business flow of execution order as follows, we use a chart to illustrate:
When we call the Socket’s API to read data from the Socket pipe, the Pipeline will execute the Inbound Handler in the order you added it. When we finish reading the event, we call the write method to write data into the channel. The pipe flow starts calling the Outbound Handler method, in reverse order! This reverse order call may not be easy to understand, but let’s use the diagram to illustrate:
When the read method is called, the Inbound nodes are called sequentially! When calling the write method, call the outbount method in reverse order!
Netty Handler event callback type
1. ChannelInboundHandler
| Method names | Methods effect |
|---|---|
| handlerAdded | The channel is added by 1 |
| channelRegistered | Method 2 to call back all handlers after successful JDK registration |
| channelActive | Callback 3 after jdkChannel is activated |
| channelRead | There is data readable in the channel 4 |
| channelReadComplete | Data is read. 5 |
| channelInactive | Call back to method 6 after the channel is closed |
| channelUnregistered | The channel is unregistered back to call this method 7 |
| handlerRemoved | The channel is deleted 8 |
| userEventTriggered | This method is called if a user event is fired. |
| channelWritabilityChanged | Writable state changes |
| exceptionCaught | Something abnormal happened |
2. ChannelOutboundHandler
| Method names | Methods effect |
|---|---|
| bind | Called after a binding operation. |
| connect | Called after a connection operation. |
| disconnect | Called after a disconnection operation. |
| close | Called after a close operation. |
| deregister | Called after an unlogout operation from a currently registered EventLoop. |
| read | Read the data |
| write | Write the data |
| flush | Flush to pipe |
conclusion
Through this article, we can learn some important concepts in Netty, including the basic concept of EventLoopGroup, the concept of channel in Netty, and the concept of pipe flow in Netty.