Parallel and Concurrent Programming in Haskell

Chapter 1. Introduction

For a long time, the programming community has known that programming with threads and locks is hard. It often requires an inordinate degree of expertise even for simple problems and leads to programs that have faults that are hard to diagnose. Still, threads and locks are general enough to express everything we might need to write, from parallel image processors to concurrent web servers, and there is an undeniable benefit in having a single general API. However, if we want to make programming concurrent and parallel software easier, we need to embrace the idea that different problems require different tools; a single tool just doesn’t cut it. Image processing is naturally expressed in terms of parallel array operations, whereas threads are a good fit in the case of a concurrent web server.

So in Haskell, we aim to provide the right tool for the job, for as many jobs as possible. If a job is found for which Haskell doesn’t have the right tool, then we try to find a way to build it. The inevitable downside of this diversity is that there is a lot to learn, and that is what this book is all about. In this book, I’ll discuss how to write parallel and concurrent programs in Haskell, ranging from the simple uses of parallelism to speed up computation-heavy programs to the use of lightweight threads for writing high-speed concurrent network servers. Along the way, we’ll see how to use Haskell to write programs that run on the powerful processor in a modern graphics ...