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
java
// 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
| Workload | Formula | Example |
|---|---|---|
| CPU-bound | cores | 8 threads |
| I/O-bound | cores * (1 + wait/compute) | 80 threads |
Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| Deadlock | Circular lock | Lock ordering, tryLock |
| Race condition | Missing sync | Add locks/atomics |
| Thread starvation | Unfair scheduling | Fair locks |
Debug Commands
bash
jstack -l <pid> > threaddump.txt jcmd <pid> Thread.print
Usage
code
Skill("java-concurrency")