The pillars of Concurrency

Concurrency and asynchrony are the techniques that most programming languages use to enhance response time and scalability, and Java is no exception. Asynchronous method calls is a technique by which the caller of a potentially time-consuming computation does not wait for a response, but rather continues to proceed with other code while the computation is ongoing. The caller will be notified once running has completed, receiving notification of either a successful result or a failure message.

The traditional way to deal with asynchronous code in Java has mostly been through the registration of callbacks, that is, placeholders that are called upon completion. Complexity tends to increase when working with asynchronous code as the sequence of execution is not deterministic, that is, the order of execution is not guaranteed. Executing code concurrently is, therefore, more difficult to test since it may not produce the same result on successive invocations. Furthermore...