Java Concurrency Uncovered-Part 16: Parallel Processing

From ThreadPoolExecutor and ForkJoinPool to Parallel Streams and Work-Stealing

In previous articles, we explored how concurrent collections help manage shared state safely and how choosing the right data structure depends on the application’s access pattern. But when an application has multiple independent tasks that can execute at the same time, we also need to decide how that work should be executed in parallel.

This is where parallel processing comes in.

In this part, we’ll explore different approaches to executing work in parallel, including ThreadPoolExecutor, ForkJoinPool, and parallel streams. We'll see how they work, where work-stealing fits in, and how to choose the right strategy for a given workload.

Concurrency vs Parallelism

Concurrency is about structuring a program so multiple tasks can make progress independently, even when they share the same underlying resources. A single CPU core, for example, can switch between multiple I/O-bound tasks while they wait for external operations to complete.

Parallelism, by contrast, means multiple tasks actually execute at the same time, typically across multiple CPU cores. It is most useful for…