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Single -threaded model (single Reactor single thread)
Multi -threaded model (single Reactor multi -threaded)
Mainly and secondary multi -threaded model (multi -Reactor multi -thread)

1. Single Reactor single thread

All operations are processed in the same NIO thread. In this single thread, it is necessary to take responsibility for receiving requests, processing IO, and encoding all operations, which is equivalent to only one person in a restaurant. At the same time, it is responsible for the front desk and background services.

1. A NIO thread processing hundreds of thousands of connections at the same time, the performance cannot be supported. Even if the CPU load of the NIO thread reaches 100%, it cannot meet the encoding, decoding, reading and sending of massive information.
   2. When the NIO thread load is too heavy, the processing speed will slow down, which will cause a large number of clients to connect the timeout. After the overtime, it will often be re -issued. Timeout becomes the performance bottleneck of the system.
   3. Reliability issues: Once the NIO thread runs unexpectedly, or enter the dead cycle, it will cause the entire system communication module to be unavailable and cannot receive and process external messages, causing node failures.

Use scenario: The number of connections on the client is limited, and the business thread processing time can be used to maintain multiple different connections with a single thread, which means that there are Redis.

Netty related code

EventLoopGroup bossGroup = new NioEventLoopGroup(1);
ServerBootstrap bootstrap = new ServerBootstrap();

advantage:
No context switching, no thread security problem

shortcoming:
1. There is only one thread processing, and the efficiency of the CPU multi -core cannot be used
2. If there are more requests, it is easy to encounter bottlenecks
3. Some accidents are terminated, resulting in the entire system module cannot be used.

There are certain restrictions on the number of client connections, and the business processing time is very fast.

2. Single Reactor Multi -thread

It is equivalent to a restaurant with a front desk responsible for reception, and many waiters to do the latter work, so that the efficiency is much higher than the single -threaded model.

1. The Reactor thread-ACCEPTOR thread is used to monitor the server, receiving the client connection request;
2. Network I/O operation reading, writing, etc. are handled by the Reactor thread pool;
3. One Reactor thread can handle multiple links at the same time, but a link can only correspond to a reactor thread, which can avoid concurrent operation problems;
4. In most scenarios, the Reactor multi -threaded model can meet performance needs. However, in extremely special special scenarios, a Reactor thread is responsible for monitoring and processing all client connections may have performance problems. For example, a million client connection, or the server requires a security certification of the client handshake, but the certification itself is very losing to performance. Therefore, the third thread model was born;

Netty settings related code

EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup(2);
ServerBootstrap bootstrap = new ServerBootstrap();

Create 1 thread Bossground thread group. This thread is responsible for handling the client's connection request, and WorkerGroup uses the number of threads of the processor to handle the number of threads to handle I/O operations by default. This is equivalent to the multi -threaded model of Reactor.

advantage：
You can make full use of multi -threaded multi -core processing capabilities, and the processing efficiency is faster than single -threaded

shortcoming:
Access data between threads may encounter thread security issues.

3. Reactor Main Strike Model

The disadvantage of the multi -threaded model is that when the amount of concurrency is high, there is only one Reactor single thread to deal with it. It is not enough to have only one front desk reception at the restaurant. To this end, the main and slab model needs to be used.
Mainly -consisting model: A set of thread pools receive requests, and a set of thread pools handle IO.

1. The server uses an independent Reactor thread pool to handle the client connection. When the server receives a connection request, a Reactor thread is randomly selected from the main thread pool as the accessor thread processing connection;
2. After the link was successfully established, register the newly created SocketChannel to a reactor thread at the Sub Reactor thread pool, and it will process the subsequent I/O operation.

1. MainReactor is responsible for listening to the Server Socket to handle the establishment of new connections. The SocketChannel is specified to the SocketChannel to SubremeActor.
2.SubReactor maintains its selector, and the SocketChannel multi -road separation IO reading and writing event is separated based on the SocketChannel registered, read and write network data, and the functions of business processing are thrown to the worker thread pool to complete.

It is easy to understand as: MainReactor is the boss, only responsible for the interface, and the SubremeActor is responsible for the front desk reception, that is, multiple front desk receptions.

Compared to multi -threaded single RECTOR models, it is divided into two parts. MainReactor is responsible for monitoring and accepting new connections, and then the established socket is assigned to Subjector through the ACCEPTOR. SUBREACTOR is responsible for multi -way separation socket, read and write network data; business processing function, it is handed over to the Worker thread pool to complete. Usually, the number of Subreactor can be equal to the number of CPUs.