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Java Concurrency

  • 419 installs
  • 40 repo stars
  • Updated January 5, 2026
  • pluginagentmarketplace/custom-plugin-java

java-concurrency is an agent skill that designs thread-safe Java services using executors, locks, concurrent collections, and structured async patterns for developers who need scalable, correct backends under load.

About

java-concurrency is an agent skill in pluginagentmarketplace/custom-plugin-java focused on designing thread-safe Java services for production backends. The skill covers executors, locks, concurrent collections, and structured async patterns so concurrent code stays correct under load. Developers reach for java-concurrency when building or refactoring Java services where race conditions, pool sizing, or shared mutable state threaten reliability. The skill emphasizes scalable backend patterns rather than single-threaded prototypes. Use it during service implementation when concurrency primitives and async structure must be chosen deliberately before traffic hits the system.

  • Executor and thread-pool sizing patterns
  • Lock-free versus synchronized tradeoffs
  • Concurrent collection selection guidance
  • Race and deadlock diagnostic tactics
  • CompletableFuture and structured task flows

Java Concurrency by the numbers

  • 419 all-time installs (skills.sh)
  • +7 installs in the week ending Aug 4, 2026 (Skillselion tracking)
  • Ranked #14 of 89 Java & JVM skills by installs in the Skillselion catalog
  • Data as of Aug 4, 2026 (Skillselion catalog sync)
npx skills add https://github.com/pluginagentmarketplace/custom-plugin-java --skill java-concurrency

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Listed on Skillselion
Installs419
repo stars40
Last updatedJanuary 5, 2026
Repositorypluginagentmarketplace/custom-plugin-java

How do you design thread-safe Java services under load?

Design thread-safe Java services using executors, locks, concurrent collections, and structured async patterns for scalable, correct backends under load.

Who is it for?

Java backend developers implementing or refactoring services that must stay correct under concurrent requests and shared state.

Skip if: Developers working on single-threaded scripts, frontend code, or JVM performance tuning without concurrency design needs.

When should I use this skill?

A Java backend task involves executors, locks, concurrent collections, race conditions, or structured async under load.

What you get

Concurrency-safe service designs with executor configs, lock strategies, concurrent collection choices, and structured async patterns.

  • Thread-safe service design
  • Executor and lock strategy recommendations

Files

SKILL.mdMarkdownGitHub ↗

Java Concurrency Skill

Master Java concurrency patterns for thread-safe applications.

Overview

This skill covers concurrency from basic threads to virtual threads (Java 21+), including thread pools, synchronization, and CompletableFuture.

When to Use This Skill

Use when you need to:

  • Write thread-safe code
  • Implement parallel processing
  • Use async programming patterns
  • Tune thread pools
  • Debug concurrency issues

Topics Covered

Thread Management

  • Thread lifecycle and states
  • Daemon vs user threads
  • Interrupt handling

Synchronization

  • synchronized, volatile
  • Lock interfaces (ReentrantLock)
  • Atomic operations

Executors

  • ThreadPoolExecutor configuration
  • ForkJoinPool
  • Virtual Threads (Java 21+)

CompletableFuture

  • Async execution
  • Chaining and composition
  • Exception handling

Quick Reference

// Virtual Threads (Java 21+)
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 10_000).forEach(i ->
        executor.submit(() -> processRequest(i)));
}

// CompletableFuture composition
CompletableFuture<Result> result = fetchUser(id)
    .thenCompose(user -> fetchOrders(user.id()))
    .thenApply(orders -> processOrders(orders))
    .exceptionally(ex -> handleError(ex))
    .orTimeout(5, TimeUnit.SECONDS);

// Thread pool configuration
ThreadPoolExecutor executor = new ThreadPoolExecutor(
    10, 50, 60L, TimeUnit.SECONDS,
    new ArrayBlockingQueue<>(1000),
    new ThreadPoolExecutor.CallerRunsPolicy()
);

// Lock with timeout
ReentrantLock lock = new ReentrantLock();
if (lock.tryLock(1, TimeUnit.SECONDS)) {
    try {
        // critical section
    } finally {
        lock.unlock();
    }
}

Thread Pool Sizing

WorkloadFormulaExample
CPU-boundcores8 threads
I/O-boundcores * (1 + wait/compute)80 threads

Troubleshooting

ProblemCauseSolution
DeadlockCircular lockLock ordering, tryLock
Race conditionMissing syncAdd locks/atomics
Thread starvationUnfair schedulingFair locks

Debug Commands

jstack -l <pid> > threaddump.txt
jcmd <pid> Thread.print

Usage

Skill("java-concurrency")

Related skills

FAQ

What Java concurrency primitives does java-concurrency cover?

java-concurrency covers executors, locks, concurrent collections, and structured async patterns for thread-safe Java services. The skill targets scalable backend correctness when multiple threads access shared state under load.

When should a developer invoke java-concurrency?

java-concurrency should be invoked while building or refactoring Java backend services where concurrent requests, shared mutable state, or executor configuration affect correctness. The skill focuses on design patterns rather than JVM profiling.

Java & JVMbackend

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