# 125 Java Concurrency

> Use when you need to apply Java concurrency best practices — including thread safety fundamentals, ExecutorService thread pool management, concurrent design patterns like Producer-Consumer, asynchronous programming with CompletableFuture, immutability and safe publication, deadlock avoidance, virtual threads, structured concurrency, scoped values, backpressure, cancellation discipline, and observ…

- **Type:** Skill
- **Install:** `agentstack add skill-jabrena-cursor-rules-java-125-java-concurrency`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [jabrena](https://agentstack.voostack.com/s/jabrena)
- **Installs:** 0
- **Category:** [Developer Tools](https://agentstack.voostack.com/c/developer-tools)
- **Latest version:** 0.1.0
- **License:** Apache-2.0
- **Upstream author:** [jabrena](https://github.com/jabrena)
- **Source:** https://github.com/jabrena/cursor-rules-java/tree/main/skills/125-java-concurrency
- **Website:** https://jabrena.github.io/cursor-rules-java/

## Install

```sh
agentstack add skill-jabrena-cursor-rules-java-125-java-concurrency
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# 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 and virtual threads.

**What is covered in this Skill?**

- 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 patterns with `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
- Structured Concurrency (`StructuredTaskScope`) for related subtasks in Java 27 preview
- `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
- Fit-for-purpose primitives: `LongAdder`, `CopyOnWriteArrayList`, `StampedLock`, `Semaphore`, `CountDownLatch`, `Phaser`

**Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

## Constraints

Before applying any concurrency changes, ensure the project compiles. If compilation fails, stop immediately — compilation failure is a blocking condition. After applying improvements, run full verification.

- **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change
- **SAFETY**: If compilation fails, stop immediately — compilation failure is a blocking condition that prevents any further processing
- **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements
- **BEFORE APPLYING**: Read the reference for detailed good/bad examples, constraints, and safeguards for each concurrency pattern

## When to use this skill

- Review Java code for concurrency

## Workflow

1. **Compile project before concurrency changes**

Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.

2. **Read concurrency reference and analyze hotspots**

Read `references/125-java-concurrency.md` and identify thread-safety, coordination, and throughput issues to address.

3. **Apply concurrency improvements**

Implement suitable concurrency patterns, structured task scopes where they fit related subtasks, cancellation discipline, and fit-for-purpose primitives.

4. **Verify with full build**

Run `./mvnw clean verify` or `mvn clean verify` after applying improvements.

## Reference

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

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [jabrena](https://github.com/jabrena)
- **Source:** [jabrena/cursor-rules-java](https://github.com/jabrena/cursor-rules-java)
- **License:** Apache-2.0
- **Homepage:** https://jabrena.github.io/cursor-rules-java/

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-jabrena-cursor-rules-java-125-java-concurrency
- Seller: https://agentstack.voostack.com/s/jabrena
- Browse the marketplace: https://agentstack.voostack.com/browse

---
Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.