Exchanger

Exchanger class simplifies the exchange of data between two threads. Exchanger waits until two separate threads call its exchange( ) method. When that occurs, it exchanges the data supplied by the threads.

Exchanger is a generic class that is declared as shown here:

 
Exchanger<V>

V specifies the type of the data being exchanged.

The only method defined by Exchanger is exchange( ), which has the two forms shown here:


V exchange(V buffer) throws InterruptedException 
V exchange(V buffer, long wait, TimeUnit tu) throws InterruptedException, TimeoutException

buffer is a reference to the data to exchange. The data received from the other thread is returned.

The second form of exchange( ) allows a time-out period to be specified.

exchange( ) won't succeed until it has been called on the same Exchanger object by two separate threads. exchange( ) synchronizes the exchange of the data.

 
// An example of Exchanger. 
import java.util.Date;
import java.util.concurrent.Exchanger;

public class Main {
  public static void main(String args[]) {
    Exchanger<String> exgr = new Exchanger<String>();
    new Consumer(exgr);
    new Producer(exgr);
  }
}

class Producer implements Runnable {
  Exchanger<String> ex;
  Producer(Exchanger<String> c) {
    ex = c;
    new Thread(this).start();
  }

  public void run() {
    for (int i = 0; i < 5; i++) {
      try {
        System.out.println("giving:"+ new Date());
        String str = ex.exchange(new Date()+"");
        System.out.println("Producer got:"+ str);
      } catch (Exception exc) {
        System.out.println(exc);
      }
    }
  }
}
class Consumer implements Runnable {
  Exchanger<String> ex;
  Consumer(Exchanger<String> c) {
    ex = c;
    new Thread(this).start();
  }

  public void run() {
    for (int i = 0; i < 5; i++) {
      try {
        String str = ex.exchange("Consumer Success");
        System.out.println("Consumer Got: " + str);
      } catch (Exception exc) {
        System.out.println(exc);
      }
    }
  }
}