The core concept in Netty isEvent loop (EventLoop), Which is actually Reactor in Reactor mode,Responsible for monitoring network events and calling event handlers for processing.In the 4.x version of Netty, the network connection and EventLoop have a stable many-to-one relationship, while EventLoop and the Java thread have a one-to-one relationship. The stability here means that once the relationship is determined, it will not change. In other words, a network connection will only correspond to a single EventLoop, and an EventLoop will only correspond to a Java thread, soA network connection will only correspond to a Java thread.

A network connection corresponds to a Java thread. What are the benefits? The biggest advantage is that the event processing for a network connection is single-threaded, which avoids various concurrency problems.

Another core concept in Netty isEventLoopGroupAs the name implies, an EventLoopGroup is composed of a set of EventLoops. In actual use, two EventLoopGroups are generally created, one is called bossGroup and the other is called workerGroup. Why are there two EventLoopGroups?

This is related to the mechanism by which socket handles network requests. The socket handles TCP network connection requests. It is in an independent socket. Whenever a TCP connection is successfully established, a new socket is created, and then the TCP connection is read and written. Completed by the newly created socket. In other wordsProcessing TCP connection requests and read and write requests is done through two different sockets.When we discussed network requests above, in order to simplify the model, we only discussed read and write requests, but did not discuss connection requests.

In Netty, bossGroup is used to handle connection requests, and workerGroup is used to handle read and write requests.After bossGroup has processed the connection request, it will submit the connection to workerGroup for processing. There are multiple EventLoops in workerGroup. Which EventLoop will be handed over to the new connection for processing? This requires a load balancing algorithm, the one currently used in Netty isPolling algorithm.