Java Tries a New Way to Use Multithreading: Structured Concurrency

'Structured concurrency is a new way to use multithreading in Java,' reports InfoWorld.

'It allows developers to think about work in logical groups while taking advantage of both traditional and virtual threads.'

Available in preview in Java 21, structured concurrency is a key aspect of Java's future, so now is a good time to start working with it... Java's thread model makes it a strong contender among concurrent languages, but multithreading has always been inherently tricky. Structured concurrency allows you to use multiple threads with structured programming syntax. In essence, it provides a way to write concurrent software using familiar program flows and constructs. This lets developers focus on the business at hand, instead of the orchestration of threading.

As the JEP for structured concurrency says, 'If a task splits into concurrent subtasks then they all return to the same place, namely the task's code block.' Virtual threads, now an official feature of Java, create the possibility of cheaply spawning threads to gain concurrent performance. Structured concurrency provides the simple syntax to do so. As a result, Java now has a unique and highly-optimized threading system that is also easy to understand...

Between virtual threads and structured concurrency, Java developers have a compelling new mechanism for breaking up almost any code into concurrent tasks without much overhead... Any time you encounter a bottleneck where many tasks are occurring, you can easily hand them all off to the virtual thread engine, which will find the best way to orchestrate them. The new thread model with structured concurrency also makes it easy to customize and fine-tune this behavior. It will be very interesting to see how developers use these new concurrency capabilities in our applications, frameworks, and servers going forward.
It involves a new class StructuredTaskScope located in the java.util.concurrent library. (InfoWorld points out that 'you'll need to use --enable-preview and --source 21 or --source 22 to enable structured concurrency.')

Their reporter shared an example on GitHub, and there's more examples in the Java 21 documentation. 'The structured concurrency documentation includes an example of collecting subtask results as they succeed or fail and then returning the results.'

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