java-concurrency

name	java-concurrency
description	Implement modern concurrency with Virtual Threads and Structured Concurrency in Java. Use when implementing Java Virtual Threads (Java 21), Structured Concurrency with StructuredTaskScope, CompletableFuture pipelines, or debugging race conditions.
metadata	{"triggers":{"files":["**/*.java"],"keywords":["Thread","Executor","synchronized","lock","CompletableFuture","StructuredTaskScope","VirtualThread","AtomicInteger","async","race condition"]}}

Java Concurrency

Priority: P1 (HIGH)

Implementation Guidelines

• Virtual Threads (Java 21): Use for high-throughput I/O. Executors.newVirtualThreadPerTaskExecutor().
• Structured Concurrency: Use StructuredTaskScope to treat related tasks as single unit (Scope, Fork, Join).
• Immutability: Share immutable data between threads to avoid race conditions.
• CompletableFuture: Use for composing async pipelines (if not using Virtual Threads).
• Atomic Variables: Use AtomicInteger, LongAdder for simple counters.
• Locks: Prefer ReentrantLock / ReadWriteLock over synchronized for fine-grained control.
• Thread Safety: Document @ThreadSafe or @NotThreadSafe.

Anti-Patterns

• No new Thread(): Use Executors or virtual threads; never create threads manually.
• No Pooling Virtual Threads: Virtual threads cheap; never pool them.
• No Blocking in synchronized: Pins carrier thread (Loom pitfall); use ReentrantLock instead.
• No Shared Mutable State: Share only immutable data between threads.
• No Thread.stop/suspend: Deprecated; use interruption or cancellation instead.

References

• StructuredTaskScope & VirtualThread Examples