6.11. Summary

We’ve covered some heavy material in this chapter! We began with a look at the new reality of an increasing number of cores inside CPUs and the need for increasingly multithreaded software. We then looked at the problems that are encountered when programs have more than one thread of execution, specifically when these threads need to make changes to shared data. We looked at the traditional way of solving these problems—using locks—and then briefly looked at the new problems that they introduce.

Finally, we looked at Clojure’s approach to these issues. It has a different approach to state, one that involves immutability. Changes to state are modeled by carefully changing managed references so that they point to different immutable values over time. And because the Clojure runtime itself manages these references, it’s able to offer the programmer a great deal of automated support in their use.