What is Multithreading

Multithreading is a programming paradigm that allows multiple threads of execution to run concurrently within a single application. A thread is the smallest unit of execution that can be scheduled by the operating system. Unlike processes, which have separate memory spaces, threads within the same process share the same memory space, making inter-thread communication fast and efficient.

Table of Contents

Table of Contents.......................................................................... 1

1. Introduction to Multithreading.................................................... 1

1.1 What is Multithreading?......................................................... 1

1.2 Process vs Thread................................................................. 1

2. Thread Lifecycle & States........................................................... 1

2.1 Thread States Diagram.......................................................... 1

2.2 Detailed State Descriptions................................................... 1

2.2.1 State Transition Methods................................................. 1

3. Creating Threads in Java............................................................. 1

3.1 Method 1: Extending Thread Class......................................... 1

3.2 Method 2: Implementing Runnable Interface (Preferred)......... 1

3.3 Comparison: Thread vs Runnable.......................................... 1

4. Thread Synchronization.............................................................. 1

4.1 The Need for Synchronization................................................ 1

4.2 Race Condition Example........................................................ 1

4.3 Synchronization Mechanisms................................................ 1

4.3.1 Synchronized Method...................................................... 1

4.3.2 Synchronized Block.......................................................... 1

5. Volatile & Atomic Variables........................................................ 1

5.1 The Volatile Keyword............................................................. 1

5.2 Atomic Variables................................................................... 1

5.3 Comparison Table................................................................. 1

6. Deadlock & Concurrency Issues................................................. 1

6.1 What is Deadlock?................................................................. 1

6.2 Deadlock Example................................................................. 1

6.3 Preventing Deadlocks............................................................ 1

6.3.1 Fixed Deadlock Example.................................................. 1

7. Executor Framework & Thread Pools.......................................... 1

7.1 Why Use Executors?.............................................................. 1

7.2 Thread Pool Architecture....................................................... 1

7.3 Types of Thread Pools............................................................ 1

7.3.1 Fixed Thread Pool Example............................................... 1

7.3.2 Callable and Future......................................................... 1

8. CompletableFuture & Async Programming................................. 1

8.1 Introduction to CompletableFuture........................................ 1

8.2 Basic Operations................................................................... 1

8.3 CompletableFuture Methods................................................. 1

8.3.1 Combining Multiple Futures............................................. 1

8.3.2 Error Handling.................................................................. 1

9. Virtual Threads (Java 21+)........................................................... 1

9.1 What are Virtual Threads?...................................................... 1

9.2 Platform Threads vs Virtual Threads....................................... 1

9.3 Creating Virtual Threads........................................................ 1

9.4 When to Use Virtual Threads.................................................. 1

10. Advanced Concurrency Utilities............................................... 1

10.1 CountDownLatch................................................................ 1

10.2 CyclicBarrier....................................................................... 1

10.3 Semaphore.......................................................................... 1

10.4 Phaser................................................................................. 1

10.5 Comparison of Coordination Utilities................................... 1

11. Best Practices & Design Patterns.............................................. 1

11.1 Thread Safety Best Practices................................................ 1

11.2 Common Pitfalls to Avoid..................................................... 1

11.3 Thread Pool Sizing............................................................... 1

11.4 Thread-Safe Singleton Pattern.............................................. 1

12. Performance Optimization....................................................... 1

12.1 Lock-Free Programming....................................................... 1

12.2 ForkJoin Framework............................................................. 1

12.3 Reducing Contention........................................................... 1

13. Testing Multithreaded Code...................................................... 1

13.1 Challenges in Testing........................................................... 1

13.2 Testing Strategies................................................................ 1

14. Summary & Quick Reference.................................................... 1