The Joy of Clojure, Second Edition

Chapter 11. Parallelism

This chapter covers

• When to use futures
• When to use promises
• Parallel operations
• Introduction to reducer/fold

Typically, parallel tasks work toward an aggregate goal; and the result of one task doesn’t affect the behavior of any other parallel task, thus maintaining determinacy. Whereas in the previous chapter we stated that concurrency was about the design of a system, parallelism is about the execution model. Although concurrency and parallelism aren’t quite the same thing, some concurrent designs are parallelizable. Recall that in the previous chapter we showed an illustration of a concurrent work queue design featuring a producer and two consumer threads (see figure 11.1).

Figure 11.1. The concurrent design ...