Exchanger in Java's Concurrent API

The Exchanger class in Java's java.util.concurrent package offers a unique synchronization mechanism for concurrent programming. It facilitates exchange of objects between two threads in a pair, acting as a rendezvous point where both threads must arrive with their respective objects before any actual exchange occurs.

Key Concepts:

• Object Exchange: Each thread presents an object upon calling exchange(). When both threads arrive, they exchange their objects and proceed.
• Synchronization: exchange() blocks the calling thread until its partner arrives, ensuring data consistency and preventing race conditions.
• Bidirectional Queue: Consider Exchanger as a two-slot circular buffer where threads take and put items alternatively.
• Generic Type: Accommodates exchange of objects of any type (T).

Methods:

• exchange(T object): Exchanges the given object with another thread's and returns the received object. Blocks until another thread arrives.
• exchange(T object, long timeout, TimeUnit unit): Similar to exchange(), but with a timeout. Throws TimeoutException if the wait exceeds the specified duration.

Common Use Cases:

• Producer-Consumer: Efficient data transfer between producing and consuming threads, avoiding busy waiting.
• Pipeline Processing: Implement stages in a processing pipeline where data is passed between stages.
• Buffer Management: Allocate buffers shared between threads, one waiting for an empty buffer while the other fills it.

Example:

Java

import java.util.concurrent.Exchanger;

public class ExchangerExample {

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<>();

        Thread producer = new Thread(() -> {
            try {
                String message = "Hello from producer!";
                String received = exchanger.exchange(message);
                System.out.println("Producer received: " + received);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });

        Thread consumer = new Thread(() -> {
            try {
                String received = exchanger.exchange(null);
                System.out.println("Consumer received: " + received);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });

        producer.start();
        consumer.start();
    }
}

Use code with caution. Learn more

Additional Notes:

• Exchanger is generally not suitable for frequent exchanges due to its blocking nature. Consider less disruptive mechanisms for high-performance scenarios.
• For more complex data sharing patterns, alternative synchronization constructs like BlockingQueue or concurrent data structures might be more appropriate.