Concurrency and parallelism are two terms that are sometimes used interchangeably. However, they are not the same and it is important to understand the difference. A program is said to run concurrently if it has multiple individual control flows running during overlapping time periods. In C++, each individual control flow is represented by a thread. The threads may or may not execute at the exact same time, though. If they do, they are said to execute in parallel. For a concurrent program to run in parallel, it needs to be executed on a machine that has support for parallel execution of instructions: that is, machines with multiple CPU cores.
At first glance, it might seem obvious that we always want concurrent ...
