Cursor-rules-java 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, scoped values, backpressure, cancellation discipline, and observability for concurrent systems. Part of the skills-for-java project

install

source · Clone the upstream repo

git clone https://github.com/jabrena/cursor-rules-java

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/jabrena/cursor-rules-java "$T" && mkdir -p ~/.claude/skills && cp -r "$T/skills/125-java-concurrency" ~/.claude/skills/jabrena-cursor-rules-java-125-java-concurrency && rm -rf "$T"

manifest: skills/125-java-concurrency/SKILL.md

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
```
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

Reference

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