Programming Interviews Exposed: Secrets to Landing Your Next Job, 3rd Edition

Chapter 9

Concurrency

Not that long ago, it was common for programs to have a single thread of execution, even if they were running on a multithreading system. Even today, code you write for an application or web server is often single-threaded, even if the server itself is multithreaded. Why? Because multithreaded programming (often referred to as concurrency) is hard to do correctly, even when the programming language directly supports it. Incorrect use of threads can easily halt your program’s execution or corrupt its data; worse yet, it can lead to intermittent, difficult to reproduce bugs.

However, if you write an application that has a graphical user interface that may perform lengthy operations, you probably need to use threads to maintain a responsive interface. Even non-interactive applications use threads: Increases in processing power these days come mostly in the form of additional cores, which a single-threaded application can’t take advantage of. Thread-related issues can appear even in environments that don’t explicitly support threads, such as JavaScript programmers doing AJAX-style programming, because the web server responses are processed asynchronously, and hence the JavaScript that runs to process the response may access data used by other parts of the application. That’s why good programmers take the time to learn how to write multithreaded programs correctly.