Topic 08: Multithreaded Programming

Goal

To introduce students to multithreading concepts in Java, including thread creation, thread lifecycle management, synchronization, and thread coordination for developing concurrent and efficient applications.

🎯 Learning Objectives

Students should be able to:

1. Explain the concepts of processes, threads, and concurrency.
2. Differentiate between single-threaded and multithreaded applications.
3. Define and create threads using:
   • Thread class
   • Runnable interface
   • Lambda expressions
4. Start and manage multiple threads in a Java application.
5. Describe the thread lifecycle and thread states.
6. Apply methods that influence thread execution such as:
   • sleep()
   • yield()
   • join()
7. Explain race conditions and critical sections in concurrent programming.
8. Implement thread synchronization using:
   • synchronized methods
   • synchronized blocks
9. Coordinate communication between threads using:
   • wait()
   • notify()
   • notifyAll()
10. Develop simple multithreaded Java applications involving shared resources.

📌 Topics to Cover

1. Introduction to Processes and Threads
   • Process vs thread
   • Concurrency and multitasking
   • Context switching
   • Lightweight processes
2. Single-thread vs Multi-thread Applications
   • Advantages of multithreading
   • Resource sharing
   • Improved responsiveness
3. Java Threads
   • JVM main thread
   • Thread call stack
   • Thread execution flow
4. Defining Threads Extending the Thread class

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread running");
    }
}

Implementing the Runnable interface

class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Runnable thread");
    }
}

Lambda Expression with Runnable

Runnable r = () -> System.out.println("Lambda Thread");

5. Creating and Starting Threads
   • Thread constructors
   • start() vs run()
   • Multiple thread execution
6. Thread Lifecycle and States
   • NEW
   • RUNNABLE
   • BLOCKED
   • WAITING
   • TIMED_WAITING
   • TERMINATED
7. Influencing Thread Execution
   • sleep(milliseconds)
   • yield()
   • join()
   • Thread scheduling
8. Race Conditions and Critical Sections
   • Shared resources
   • Data inconsistency problems
   • Mutual exclusion
9. Thread Synchronization Synchronized Methods

public synchronized void withdraw(int amt) {
    // critical section
}

Synchronized Blocks

synchronized(this) {
    // critical section
}

10. Thread Communication
    • wait()
    • notify()
    • notifyAll()
    • Monitor locks
11. Exception Handling in Threads
    • InterruptedException
    • Illegal monitor state issues

🛠️ Hands-on Activity

Activity 1: Creating a Simple Thread

Students create a Java program that:

• Extends the Thread class
• Displays thread messages using the run() method

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Activity 2: Runnable Interface

Students develop a program using:

• Runnable
• Multiple thread objects
• Different thread names

Example Output:

Run by Ali
Run by Bob
Run by Jim

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Activity 3: Thread Sleep Demonstration

Students create a program that:

• Uses Thread.sleep()
• Displays delayed execution

Example:

Thread.sleep(1000);

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Activity 4: Joining Threads

Students implement:

• Parent thread waiting for child thread completion
• join() method usage

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Activity 5: Simulating Race Condition

Students develop a banking withdrawal simulation:

• Shared bank account
• Multiple withdrawal threads
• Observe inconsistent results without synchronization

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Activity 6: Synchronization

Students improve the banking simulation by:

• Adding synchronized methods
• Preventing race conditions

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Activity 7: Producer-Consumer Communication

Students create two threads:

• Producer thread
• Consumer thread

Using:

• wait()
• notify()

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Activity 8: Thread Lifecycle Observation

Students develop a program that:

• Displays thread states during execution
• Observes transitions between:
  • NEW
  • RUNNABLE
  • BLOCKED
  • WAITING
  • TIMED_WAITING
  • TERMINATED

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📚 Suggested Readings

1. https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html
2. https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.State.html
3. https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Thread.State.html
4. https://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html
5. https://en.wikipedia.org/wiki/Java_concurrency
6. https://medium.com/@syed.fawzul.azim/how-java-threads-work-jvm-internals-cpu-level-execution-and-multi-threading-in-java-89d8d343677f
7. https://www.w3schools.com/java/java_threads.asp