Modern Concurrency in Java

In this GOTO Book Club episode, Java Champion A N M Bazlur Rahman joins host and fellow Java Champion Michael Redlich to discuss Modern Concurrency in Java — the first comprehensive update to Java concurrency literature in 20 years. Bazlur traces his motivation to the arrival of virtual threads in JDK 21, which he describes as a fundamental shift in Java's concurrency cost model: platform threads were expensive and scarce, demanding careful pooling; virtual threads are cheap, plentiful, and behave like ordinary threads from the developer's perspective, without requiring a new programming model. The book covers this evolution end-to-end, from the history of threads through to structured concurrency, scope values, and the modern frameworks that have already adopted virtual threads — most with a single config change.

The conversation also takes a nuanced look at reactive programming's future. Bazlur's conclusion is that reactive remains compelling in specific contexts — event-driven streaming systems, architectures needing end-to-end back-pressure — but it's no longer the default answer to scalability. For most microservices doing blocking I/O, virtual threads are now the stronger default, and reactive becomes a deliberate architectural choice rather than an automatic one. The book's goal is to give developers both the conceptual grounding and the practical guidance to make that choice confidently — understanding the tool one level deep, so they can design better systems, not just configure their way through a framework.