Understanding the IO model

BIO

Synchronize and block （ Traditional obstructive type ）, The server implements a pattern of one thread per connection , That is, when the client has a connection request, the server needs to start a thread for processing , If the connection does nothing, it will cause unnecessary thread overhead .

NIO

Synchronous nonblocking , The server implementation mode deals with multiple requests for one thread ( Connect ), That is, the connection request sent by the client will be registered on the multiplexer , Multiplexer polled for I/O The request will be processed .

Selector

Selector The multiplexer is right linux Under the select/poll/epoll encapsulate ,selector There can be multiple implementations ,linux By default, the system uses epoll How to implement .

1. Java Of NIO Non blocking I/O The way . You can handle several client connections with one thread , Will be used to Selector（ Selectors ）.
2. Selector It can detect whether events occur on multiple registration channels ( Multiple Channel Register to the same as an event selector), If something happens , Then we get the events and deal with them accordingly .
3. Only when there is a real read-write event in the connection , To read and write , Reduced system overhead , And you don't have to create a thread for each connection , No need to maintain multiple threads .
4. Avoid the overhead caused by context switching between multiple threads .

AIO

Asynchronous non-blocking ,AIO The concept of asynchronous channel is introduced , Adopted Proactor Pattern , Simplified programming , Valid request to start thread , Its characteristic is to inform the server program to start the thread to process after the operating system completes , Generally, it is suitable for applications with more connections and longer connection time .