Non-Blocking IO (NIO)

NIO is about not constantly blocking a thread by waiting for any IO to happen.

NIO is the default

NIO is the default way of processing HTTP requests in Apache Tomcat. This is exactly why we see the thread with name http-nio- in Spring Boot

Blocking IO (BIO)

1. JVM listens on the server port. Eg., 8080. This is the acceptor/main thread.
2. When a request arrives at the this port, then main thread then calls the run method of the new thread with the socket object to a thread.
3. The Socket Processor then converts the socket object to an HTTP request object and then calls the servlet.
4. This thread remains blocked until the complete connection is closed.
5. If all threads are used up, then no new sockets can be accepted and the client requests hangs.

TCP is Persistent

There is always one TCP session used to exchange multiple HTTP messages between clients. So the thread in the BIO case is blocked by one connection until it's fully closed.

Non-Blocking IO (NIO)

1. JVM listens on the server port. Eg., 8080. This is the acceptor/main thread.
2. The acceptor thread forwards the socket object to poller queue.
3. Poller then checks/polls the socket for messages.
4. Forwards it to thread pool whenever a message is available.

Information Sources

• https://www.cnblogs.com/kukuxjx/p/18013373
• https://velog.io/@hyunjong96/Spring-NIO-Connector-BIO-Connector
• https://blog.liu-kevin.com/2022/07/26/tomcatwang-luo-mo-xing/