Java rules for Concurrency objects

Identify and apply Java concurrency best practices to improve thread safety, scalability, and maintainability by using modern java.util.concurrent utilities, virtual threads, and structured concurrency.

Prerequisites: Run ./mvnw compile or mvn compile before applying any change. If compilation fails, stop immediately — compilation failure is a blocking condition that prevents any further processing.

Core areas: Thread safety fundamentals (ConcurrentHashMap, AtomicInteger, ReentrantLock, ReadWriteLock, Java Memory Model), ExecutorService thread pool configuration (sizing, keep-alive, bounded queues, rejection policies, graceful shutdown), Producer-Consumer and Publish-Subscribe concurrent design patterns (BlockingQueue), CompletableFuture for non-blocking async composition (thenApply/thenCompose/exceptionally/orTimeout), immutability and safe publication (volatile, static initializers), lock contention and false-sharing performance optimization, virtual threads (Executors.newVirtualThreadPerTaskExecutor()) for I/O-bound scalability, StructuredTaskScope for lifecycle-scoped task management, ScopedValue over ThreadLocal for immutable cross-task data, cooperative cancellation and InterruptedException discipline, backpressure with bounded queues and CallerRunsPolicy, deadlock avoidance via global lock ordering and tryLock with timeouts, ForkJoin/parallel-stream discipline for CPU-bound work, virtual-thread pinning detection (JFR VirtualThreadPinned), thread naming and UncaughtExceptionHandler observability, and fit-for-purpose primitives (LongAdder, CopyOnWriteArrayList, StampedLock, Semaphore, CountDownLatch, Phaser).

Scope: The reference is organized by examples (with good/bad code patterns) for each core area. Apply recommendations based on applicable examples; validate compilation before changes and run ./mvnw clean verify or mvn clean verify after applying improvements.

Before applying changes: Read the reference for detailed good/bad examples, constraints, and safeguards for each concurrency pattern.

Reference

For detailed guidance, examples, and constraints, see references/125-java-concurrency.md.