CyclicBarrier Pattern

Imagine you're building a parallel sorting algorithm. You divide the data among four threads. Each thread sorts its portion.

But here's the problem: before you can merge the results, all four threads must finish sorting. If one thread merges before the others finish sorting, the result is garbage.

This isn't unique to sorting. Parallel simulations, game loops, image processing pipelines, and iterative algorithms all face the same challenge: multiple threads must complete their current phase before any can proceed to the next.

How do you make N threads wait for each other at a specific point, then all proceed together?

The CyclicBarrier Pattern solves exactly this problem. It creates a synchronization point where threads wait until all participants arrive, then releases them simultaneously. And unlike one-time synchronization primitives, it can be reused across multiple rounds.

In this chapter, we'll explore: