Java Concurrency Guide

A practical guide to Java multithreading and concurrency concepts with production-ready examples.

📌 Contents

• Core Concepts

  • Thread lifecycle and states
  • Daemon vs Non-daemon threads
  • Thread priority and scheduling

• Synchronization

  • synchronized methods/blocks
  • volatile keyword
  • Atomic classes (AtomicInteger, etc.)
  • Reentrant locks

• Concurrency Utilities

  • Executor Framework (ThreadPools)
  • Future and CompletableFuture
  • CountDownLatch/CyclicBarrier
  • BlockingQueue implementations

• Advanced Patterns

  • Producer-Consumer problem
  • Read-Write locks
  • ForkJoinPool
  • ThreadLocal usage

🚀 Quick Start

// Basic Thread Example
public class Main {
    public static void main(String[] args) {
        Thread thread = new Thread(() -> {
            System.out.println("Running in: " + Thread.currentThread().getName());
        });
        thread.start();
    }
}

🔧 Common Pitfalls

• Race conditions - When threads access shared data without proper synchronization
• Deadlocks - When threads block each other waiting for resources
• Thread starvation - When threads don't get CPU time due to priority issues
• False sharing - Performance degradation when unrelated data shares cache lines

📚 Resources

• Java Concurrency in Practice - The definitive book on Java concurrency
• Oracle Concurrency Tutorial - Official Java tutorials
• Java Atomic Classes - Documentation for atomic operations

🛡️ Best Practices

1. Prefer java.util.concurrent over raw threads for better maintainability
2. Use immutable objects where possible to avoid synchronization
3. Document thread-safety clearly in your code documentation
4. Avoid excessive synchronization as it can hurt performance
5. Test under load conditions to uncover concurrency issues

💡 Interview Questions

• How does synchronized work under the hood? (Monitor locks, JVM implementation)
• Difference between wait() and sleep()? (Object monitor vs thread timing)
• Explain the Java Memory Model (Happens-before relationship, visibility guarantees)
• How would you implement a thread-safe cache? (ConcurrentHashMap, read-write locks)

📜 License

MIT © [Ravik5]