Project Loom in IntelliJ IDEA: Virtual Threads, Scoped Values, and Structured Concurrency

Summary

Project Loom in IntelliJ IDEA introduces Java developers to three cohesive concurrency features: Virtual Threads (JEP 444, stable since Java 21), Scoped Values (JEP 506, stable since Java 25), and Structured Concurrency (JEP 533, seventh preview in Java 27). The post identifies pain points such as CompletableFuture ignoring interrupt flags, manual ExecutionException unwrapping chains, duplicated cancel() calls across catch blocks, mutable ThreadLocal pitfalls, and flat thread dumps lacking request hierarchy. A CustomerProfileService example is refactored from CompletableFuture.allOf to StructuredTaskScope.ShutdownOnFailure, where sibling tasks are cancelled automatically and a single timeout covers the whole scope. IntelliJ IDEA debugger support from version 2026.1 groups virtual threads forked within a StructuredTaskScope into containers representing their scopes, and the post walks through downloading JDK 27 (EA) and enabling the experimental language level.

Takeaways

1. 1

   Project Loom combines three JEPs: Virtual Threads (JEP 444, stable since Java 21), Scoped Values (JEP 506, stable since Java 25), and Structured Concurrency (JEP 533, seventh preview in Java 27).

2. 2

   CompletableFuture.supplyAsync with cancel(true) ignores the interrupt flag for already-running tasks, so cancellation logic must be duplicated across both TimeoutException and ExecutionException catch blocks and manually extended whenever a new parallel call is added.

3. 3

   IntelliJ IDEA 2026.1 debugger groups virtual threads forked within a StructuredTaskScope into containers representing their scopes, exposing the parent-child hierarchy that was missing from traditional pool thread dumps.