Concurrency versus parallelism

Right off the bat, we’ll dive into this subject by defining what concurrency is. Since it is quite easy to confuse concurrent with parallel, we will try to make a clear distinction between the two from the get-go.

Important

Concurrency is about dealing with a lot of things at the same time.

Parallelism is about doing a lot of things at the same time.

We call the concept of progressing multiple tasks at the same time multitasking. There are two ways to multitask. One is by progressing tasks concurrently, but not at the same time. Another is to progress tasks at the exact same time in parallel. Figure 1.1 depicts the difference between the two scenarios:

Figure 1.1 – Multitasking two tasks

First, we need to agree on some definitions:

• Resource: This is something we need to be able to progress a task. Our resources are limited. This could be CPU time or memory.
• Task: This is a set of operations...