Concurrency Review

Concurrency Review Skill

Review Java concurrent code for correctness, safety, and modern best practices.

Why This Matters

Nearly 60% of multithreaded applications encounter issues due to improper management of shared resources. - ACM Study

Concurrency bugs are:

• Hard to reproduce - timing-dependent
• Hard to test - may only appear under load
• Hard to debug - non-deterministic behavior

This skill helps catch issues before they reach production.

When to Use

• Reviewing code with synchronized, volatile, Lock
• Checking @Async, CompletableFuture, ExecutorService
• Validating thread safety of shared state
• Reviewing Virtual Threads / Structured Concurrency code
• Any code accessed by multiple threads

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Modern Java (21/25): Virtual Threads

When to Use Virtual Threads

// ✅ Perfect for I/O-bound tasks (HTTP, DB, file I/O)
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (Request request : requests) {
        executor.submit(() -> callExternalApi(request));
    }
}

// ❌ Not beneficial for CPU-bound tasks
// Use platform threads / ForkJoinPool instead