name: java-concurrency
description: Master Java concurrency - threads, executors, locks, CompletableFuture, virtual threads
sasmp_version: "1.3.0"
version: "3.0.0"
bonded_agent: 02-java-advanced
bond_type: PRIMARY_BOND
allowed-tools: Read, Write, Bash, Glob, Grep

Parameter Validation

parameters:
concurrency_model:
type: string
enum: [threads, executors, virtual_threads, reactive]
java_version:
type: string
default: "21"

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

Troubleshooting

Debug Commands

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

Usage

Skill("java-concurrency")