Programming Clojure, 3rd Edition

Concurrency, Parallelism, and Locking

A concurrent program models more than one thing happening simultaneously. A parallel program takes an operation that could be sequential and chooses to break it into separate pieces that can execute concurrently to speed overall execution.

There are many reasons to write concurrent or parallel programs:

• For decades, performance improvements have come from packing more power into cores. Now, and for the near future, performance improvements will come from using more cores. Our hardware is itself more concurrent than ever, and systems must be concurrent to take advantage of this power.

• Expensive computations may need to execute in parallel on multiple cores (or multiple boxes) to complete in a timely ...