Overview
This module provides comprehensive coverage of multithreading and concurrency in Java. Learn thread creation, synchronization, inter-thread communication, concurrent collections, and modern concurrency utilities.
Learning Objectives
- Understand threads and concurrency concepts
- Master thread creation and lifecycle
- Learn synchronization mechanisms
- Work with concurrent collections
- Use Executor framework
- Understand thread safety issues
- Apply concurrent programming patterns
Topics Covered
14.1 Introduction to Multithreading
14.1.1 Understanding Threads
- What is a Thread?
- Process vs Thread
- Multitasking vs Multithreading
- Benefits of Multithreading
- Challenges
14.1.2 Thread Lifecycle
- New State
- Runnable State
- Running State
- Blocked/Waiting State
- Terminated State
- State Transitions
14.1.3 Main Thread
- Default Thread
- main() Method Thread
- Thread Priority
- Daemon vs User Threads
14.2 Creating Threads
14.2.1 Extending Thread Class
- Thread Class Overview
- Overriding run() Method
- start() vs run()
- Limitations
14.2.2 Implementing Runnable Interface
- Runnable Interface
- Separation of Task and Thread
- Preferred Approach
- Multiple Inheritance Support
14.2.3 Anonymous Classes
- Anonymous Thread Creation
- Anonymous Runnable
- Inline Implementation
14.2.4 Lambda Expressions (Java 8+)
- Functional Interface
- Concise Syntax
- Modern Approach
14.2.5 Callable and Future
- Callable Interface
- Returning Values
- Throwing Exceptions
- Future Interface
14.3 Thread Class Methods
14.3.1 Essential Methods
- start()
- run()
- sleep()
- join()
- yield()
- interrupt()
- isAlive()
14.3.2 Thread Properties
- getName(), setName()
- getPriority(), setPriority()
- isDaemon(), setDaemon()
- getId()
- getState()
14.3.3 Static Methods
- currentThread()
- sleep()
- yield()
- interrupted()
- activeCount()
14.4 Thread Synchronization
14.4.1 Understanding Synchronization
- Race Condition
- Critical Section
- Mutual Exclusion
- Thread Safety
- Data Consistency
14.4.2 synchronized Keyword
- Synchronized Methods
- Synchronized Blocks
- Intrinsic Locks (Monitors)
- Lock Acquisition
14.4.3 Synchronized Methods
- Instance Method Synchronization
- Static Method Synchronization
- Lock Objects
- Limitations
14.4.4 Synchronized Blocks
- Fine-Grained Locking
- Lock Objects
- Reducing Contention
- Best Practices
14.4.5 Class Level Synchronization
- Static Synchronization
- Class Object Lock
- Use Cases
14.5 Inter-Thread Communication
14.5.1 wait(), notify(), notifyAll()
- Object Class Methods
- Waiting for Conditions
- Notifying Threads
- Monitor Methods
14.5.2 Producer-Consumer Pattern
- Wait and Notify Usage
- Queue Implementation
- Coordination
- Classic Example
14.5.3 Wait/Notify Best Practices
- Always Use in Loop
- Synchronized Context
- Spurious Wakeups
- Lost Notification
14.6 Thread Deadlock
14.6.1 Understanding Deadlock
- Circular Wait
- Necessary Conditions
- Detection
- Prevention
14.6.2 Deadlock Example
- Multiple Resource Locking
- Lock Ordering Issues
- Demonstration
14.6.3 Deadlock Prevention
- Lock Ordering
- Timeout
- Try-Lock
- Design Strategies
14.6.4 Deadlock Detection
- Thread Dumps
- JConsole/VisualVM
- Monitoring Tools
14.7 volatile Keyword
14.7.1 Understanding volatile
- Memory Visibility
- Happens-Before Relationship
- Cache Coherence
- When to Use
14.7.2 volatile vs synchronized
- Visibility Only
- No Atomicity
- Performance
- Use Cases
14.7.3 Double-Checked Locking
- Singleton Pattern
- volatile Variable
- Lazy Initialization
- Correct Implementation
14.8 Thread Safety
14.8.1 Thread-Safe Code
- Immutability
- Statelessness
- Synchronization
- Atomic Operations
14.8.2 Immutable Objects
- Final Fields
- No Setters
- Thread Safety
- Performance Benefits
14.8.3 Thread Local
- ThreadLocal Class
- Thread-Specific Data
- Use Cases
- Memory Leaks
14.9 Locks and Reentrant Locks
14.9.1 Lock Interface
- java.util.concurrent.locks
- Explicit Locking
- lock(), unlock()
- tryLock()
14.9.2 ReentrantLock
- Flexible Locking
- Try-Lock with Timeout
- Interruptible Locks
- Fair vs Unfair
14.9.3 ReadWriteLock
- ReentrantReadWriteLock
- Multiple Readers
- Single Writer
- Performance Benefits
14.9.4 Condition Variables
- Await and Signal
- Multiple Conditions
- await(), signal(), signalAll()
- Better than wait/notify
14.10 Atomic Variables
14.10.1 Atomic Classes
- java.util.concurrent.atomic
- AtomicInteger
- AtomicLong
- AtomicBoolean
- AtomicReference
14.10.2 Atomic Operations
- compareAndSet()
- getAndIncrement()
- incrementAndGet()
- Lock-Free Algorithms
14.10.3 Performance Benefits
- No Locks Required
- CAS Operations
- Scalability
- Use Cases
14.11 Concurrent Collections
14.11.1 ConcurrentHashMap
- Thread-Safe Map
- Lock Striping
- High Concurrency
- Atomic Operations
14.11.2 CopyOnWriteArrayList
- Thread-Safe List
- Copy on Modification
- Iterator Consistency
- Use Cases
14.11.3 ConcurrentLinkedQueue
- Non-Blocking Queue
- Lock-Free
- High Performance
- FIFO Order
14.11.4 BlockingQueue
- Producer-Consumer
- put() and take()
- Implementations
- ArrayBlockingQueue
- LinkedBlockingQueue
- PriorityBlockingQueue
14.12 Executor Framework
14.12.1 Understanding Executors
- Thread Pool Management
- Task Submission
- Resource Management
- Decoupling
14.12.2 Executor Interface
- execute() Method
- Task Execution
- Fire and Forget
14.12.3 ExecutorService
- Lifecycle Management
- submit() Method
- shutdown()
- shutdownNow()
- Future Results
14.12.4 Thread Pools
- FixedThreadPool
- CachedThreadPool
- SingleThreadExecutor
- ScheduledThreadPool
- Executors Factory Methods
14.12.5 ThreadPoolExecutor
- Custom Thread Pools
- Core vs Maximum Pool Size
- Keep-Alive Time
- Work Queues
- Rejection Policies
14.12.6 ScheduledExecutorService
- Scheduled Tasks
- schedule()
- scheduleAtFixedRate()
- scheduleWithFixedDelay()
- Timer Alternative
14.13 Future and Callable
14.13.1 Future Interface
- get()
- cancel()
- isDone()
- isCancelled()
- Timeout Support
14.13.2 CompletableFuture (Java 8+)
- Asynchronous Programming
- Chaining Operations
- Combining Futures
- Exception Handling
- Non-Blocking
14.13.3 Future Patterns
- Future Chaining
- Future Composition
- Error Handling
- Timeout Management
14.14 Fork/Join Framework
14.14.1 Understanding Fork/Join
- Divide and Conquer
- Work Stealing
- RecursiveTask
- RecursiveAction
14.14.2 ForkJoinPool
- Parallel Processing
- fork() and join()
- compute()
- Use Cases
14.14.3 Parallel Streams
- Stream API Integration
- parallelStream()
- Automatic Parallelization
- Performance Considerations
14.15 Semaphore and CountDownLatch
14.15.1 Semaphore
- Permit Management
- acquire() and release()
- Resource Pooling
- Rate Limiting
14.15.2 CountDownLatch
- Thread Coordination
- countDown()
- await()
- One-Time Barrier
14.15.3 CyclicBarrier
- Reusable Barrier
- await()
- Parties
- Barrier Action
14.15.4 Phaser
- Flexible Synchronization
- Dynamic Parties
- Multiple Phases
- Advanced Scenarios
14.16 Concurrency Best Practices
14.16.1 Design Principles
- Minimize Shared State
- Immutability
- Thread Confinement
- Synchronization Policy
14.16.2 Performance Optimization
- Reduce Lock Contention
- Lock-Free Algorithms
- Read-Write Locks
- Thread Local Storage
14.16.3 Testing Concurrent Code
- Race Condition Detection
- Stress Testing
- Thread Safety Analysis
- Tools and Techniques
14.16.4 Common Pitfalls
- Deadlocks
- Race Conditions
- Memory Visibility
- Thread Leaks
- Resource Exhaustion
14.17 Modern Concurrency (Java 9+)
14.17.1 Reactive Streams
- Flow API
- Publisher/Subscriber
- Backpressure
- Asynchronous Processing
14.17.2 CompletableFuture Enhancements
- Timeout Support
- Executor Selection
- New Methods
- Better Composition
14.18 Virtual Threads (Java 19+)
14.18.1 Project Loom
- Lightweight Threads
- High Concurrency
- Simple Threading Model
- Performance Benefits
Hands-on Exercises
- Create threads using different methods
- Implement synchronized methods and blocks
- Build producer-consumer pattern
- Create thread pool applications
- Implement concurrent collections usage
- Build task scheduling system
- Create parallel processing algorithms
- Implement fork/join tasks
- Build thread-safe cache
- Create web crawler with executors
- Implement rate limiter
- Build concurrent download manager
Key Takeaways
- Multithreading enables parallelism
- Synchronization prevents race conditions
- Executors manage thread pools efficiently
- Concurrent collections are thread-safe
- Lock-free algorithms improve performance
- CompletableFuture enables async programming
- Proper design prevents concurrency issues
Common Mistakes to Avoid
- Not synchronizing shared data
- Deadlock scenarios
- Ignoring thread safety
- Overusing synchronization
- Memory visibility issues
- Thread leaks
- Not shutting down executors
Real-World Applications
- Web servers
- Database connection pools
- Parallel data processing
- Real-time systems
- Game engines
- File processors
- Network applications
Additional Resources
- Java Concurrency in Practice
- Effective Java - Concurrency
- Java Concurrent API Documentation
- Doug Lea's Concurrent Programming
Assessment
- Quiz on concurrency concepts
- Practical: Implement thread-safe applications
- Synchronization exercises
- Executor framework challenges
- Debug concurrent code issues