Java Concurrency & Multithreading Examples

A hands-on collection of Java concurrency, multithreading, and performance-tuning examples. This repository demonstrates core concurrency concepts, thread signaling patterns, high-concurrency bottlenecks, deadlock mitigation strategies, and modern features like Virtual Threads.

---

📌 Topics & Examples Covered

1. Modern Java Concurrency

• Java Virtual Thread Example
  • Demonstrates lightweight, high-throughput concurrency using Project Loom / Virtual Threads (Executors.newVirtualThreadPerTaskExecutor()) vs. platform threads.

2. Deadlocks & Mitigation

• Java Deadlock
  • Demonstrates how circular waiting and mismatched lock ordering lead to thread deadlocks.
• Java Deadlock Prevention - Timeout Backoff
  • Shows how to prevent permanent deadlocks using ReentrantLock.tryLock() with time-outs and exponential backoff.

3. Memory & Hardware Performance

• Java False Sharing Example
  • Demonstrates how multiple threads modifying adjacent variables on the same CPU cache line cause cache invalidation thrashing, and how to resolve it using @Contended padding.

4. Thread Congestion & Queue Architectures

• Java Thread Congestion - Shared BlockingQueue Example
  • Illustrates performance bottlenecks when multiple producer and consumer threads contend for a single, shared BlockingQueue.
• Java Thread Congestion - Separate BlockingQueue Example
  • Resolves queue contention by partitioning workloads across distinct queues (e.g., actor model or single-producer/single-consumer lanes).

5. Thread Signaling Patterns

• Java Thread Signaling Example 1 (Basic wait() / notify())
  • Low-level signaling using intrinsic monitors and Object.wait() / Object.notify().
• Java Thread Signaling Example 2 (Condition Variables)
  • Modern signaling using ReentrantLock and explicit Condition instances (await() / signal()).
• Java Thread Signaling Example 3 (CountDownLatch)
  • One-shot barrier signaling allowing one or more threads to wait until a set of operations completes.
• Java Thread Signaling Example 4 (Phaser / CyclicBarrier)
  • Reusable, phased barrier signaling for multi-stage concurrent task coordination.

6. Parallel Computing with ForkJoinPool

• Java ForkJoinPool Example 1 (Divide and Conquer with RecursiveTask)
  • Parallelizing computational workloads using work-stealing algorithms to compute results.
• Java ForkJoinPool Example 2 (RecursiveAction & Custom Thread Pools)
  • Side-effect, result-less parallel processing and executing tasks on isolated ForkJoinPool instances.

---

🛠️ Prerequisites

• JDK 21+ (Required for Virtual Threads)