JUG.CY Meetup with Dr Heinz Kabutz: The Hidden Art of Thread-Safe Programming

Join us on Wednesday, 21 October 2026, for the next JUG.CY meetup with Dr Heinz Kabutz, Java Champion and creator of The Java Specialists’ Newsletter.

Concurrency bugs are among the most challenging defects to find. Code may appear correct in testing and run successfully in production for years before a rare combination of timing, load, and thread interleaving finally exposes a race condition or deadlock.
Even `Vector`, one of Java’s original thread-safe collections, contained a race condition for approximately five years. The attempt to fix it introduced a potential deadlock that remained in the JDK for roughly another nine years. It is a powerful reminder that thread safety is not achieved simply by adding `synchronized`.

This session will be particularly valuable for:

• Java developers working with multithreaded or asynchronous systems;
• architects designing concurrent services and data-processing pipelines;
• engineers investigating race conditions, deadlocks, or contention;
• developers interested in JDK internals and the Java Memory Model;
• anyone who uses `java.util.concurrent` and wants to understand what happens beneath its API.

No previous knowledge of the internal implementations is required, but familiarity with basic Java concurrency concepts will help you get the most from the session.

Participation is completely free, but places are limited. Please check in if you plan to attend the meeting; we can't let you into the office if you are not on the list.

Agenda for this evening:

- Doors open at 18:30
- Talks will start at 19:00
- We will have a short break after the first part
- We will have discussions regarding the talks with networking opportunities after.
- We will finish before 22:00 at the office, but nothing can stop us from continuing somewhere in the cozy bar.

Talk:

**The Hidden Art of Thread-Safe Programming: Exploring java.util.concurrent**

The classes in `java.util.concurrent` sit beneath a vast amount of production Java software. We use them directly in application code and indirectly through frameworks, libraries, executors, queues, synchronizers, and other infrastructure.
But how are these classes themselves made thread-safe, scalable, and sufficiently predictable under contention?
In this session, Heinz will take us inside several familiar concurrency utilities and examine the implementation techniques behind them. Rather than treating these classes as black boxes, we will explore the design decisions, trade-offs, and subtle correctness requirements that make them work.

The talk will cover:

• striping and contention reduction in `LongAdder` and `Striped64`;
• lock splitting between producers and consumers in `LinkedBlockingQueue`;
• weakly consistent iteration in `ArrayBlockingQueue`;
• double-checked and check-then-act patterns in `CopyOnWriteArrayList`;
• why concurrency defects can survive testing and remain hidden for years;
• how studying JDK implementations can help us design safer concurrent code.

We will also look at why commonly used concurrency utilities are often the safest foundation for new designs, where their limits lie, and what developers should consider before creating custom synchronizers or concurrent collections.

This is not an introductory session about starting threads. It is a technical exploration of the mechanisms used inside the JDK and the lessons they offer for building robust, high-performance Java systems.

About the speakers:

Dr Heinz M. Kabutz (javaspecialists.eu) is a Java Champion and the creator of The Java Specialists’ Newsletter, one of the longest-running publications dedicated to advanced Java programming.
With a PhD in Computer Science and decades of practical Java experience, Heinz is widely known for his work on concurrency, performance optimisation, data structures, and advanced programming techniques. He is an international speaker, trainer, consultant, and contributor to the evolution and quality of the Java platform.
In 2025, Heinz received the Java Community Lifetime Achievement Award at Devoxx UK.