Java Inter-thread Comm

Inter-thread communication in Java refers to the mechanism by which threads can exchange information, coordinate their activities, and synchronize their operations in a multithreaded environment. Proper inter-thread communication is essential for avoiding race conditions, ensuring thread safety, and creating efficient and coordinated multithreaded applications.

Java provides several mechanisms for inter-thread communication, including:

1. Object Locks (Synchronized Blocks): Java provides the synchronized keyword to create synchronized blocks or methods. By synchronizing on an object, a thread can acquire the object’s monitor lock, allowing it to access shared resources in a thread-safe manner. Other threads attempting to access the synchronized block will be blocked until the lock is released.
2. Wait and Notify (NotifyAll): Threads can use the wait(), notify(), and notifyAll() methods from the Object class to communicate and coordinate with each other. When a thread calls wait(), it releases the lock on the object and enters a waiting state. Other threads can notify the waiting thread using notify() or notifyAll() to wake it up when certain conditions are met.
3. Java Concurrency Utilities: The java.util.concurrent package provides higher-level abstractions and utilities for inter-thread communication. For example, CountDownLatch, Semaphore, CyclicBarrier, and BlockingQueue can be used to synchronize threads and control their execution.
4. Thread Joining: The join() method allows one thread to wait for the completion of another thread. When a thread calls join() on another thread, it waits until that thread finishes its execution before continuing its own execution.
5. Thread Signaling: Developers can use custom signaling mechanisms, such as flags or signals shared between threads, to communicate and coordinate their activities.

Here’s a simple example of using inter-thread communication with wait and notify:

public class InterThreadCommunicationExample {
    public static void main(String[] args) {
        final Message message = new Message();

        // Create and start the producer thread
        Thread producerThread = new Thread(() -> {
            String[] messages = { "Hello", "World", "Bye" };
            for (String msg : messages) {
                message.putMessage(msg);
            }
            message.putMessage("exit"); // Signal to terminate the consumer thread
        });

        // Create and start the consumer thread
        Thread consumerThread = new Thread(() -> {
            while (true) {
                String msg = message.getMessage();
                if (msg.equals("exit")) {
                    break; // Terminate the loop when the exit signal is received
                }
                System.out.println("Received: " + msg);
            }
        });

        // Start both threads
        producerThread.start();
        consumerThread.start();
    }
}

class Message {
    private String message;
    private boolean empty = true;

    public synchronized void putMessage(String msg) {
        while (!empty) {
            try {
                wait(); // Wait until the consumer consumes the previous message
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        this.message = msg;
        empty = false;
        notify(); // Notify the consumer that a message is available
    }

    public synchronized String getMessage() {
        while (empty) {
            try {
                wait(); // Wait until a message is produced
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        empty = true;
        notify(); // Notify the producer that the message has been consumed
        return message;
    }
}

In this example, we have a simple Message class that allows a producer thread to put a message, and a consumer thread to retrieve and print the message. The producer and consumer threads communicate and coordinate with each other using the wait() and notify() methods.

Inter-thread communication is crucial for designing efficient, coordinated, and thread-safe multithreaded applications in Java. Proper synchronization and communication mechanisms help avoid race conditions and ensure that threads work together harmoniously.