Java Multithreading for Senior Engineering Interviews (Notes from an Educative course)

Photo by Michiel Leunens on Unsplash

The Basics

The simplest example to think of a concurrent system is a single-processor machine running your favourite IDE. Say you edit one of your code files and click save, that clicking of the button will initiate a workflow which will cause bytes to be written out to the underlying physical disk. However, IO is an expensive operation, and the CPU will be idle while bytes are being written out to the disk.

Whilst IO takes place, the idle CPU could work on something useful and here is where threads come in — the IO thread is switched out and the UI thread gets scheduled on the CPU so that if you click elsewhere on the screen, your IDE is still responsive and does not appear hung or frozen.