Exchanger

Exchanger

The 

java.util.concurrent.Exchanger

 class represents a kind of rendezvous point where two threads can exchange objects. Here is an illustration of this mechanism:

Two threads exchanging objects via an Exchanger.

Exchanging objects is done via one of the two 

exchange()

 methods. Here is an example:

Exchanger exchanger = new Exchanger();

ExchangerRunnable exchangerRunnable1 =
new ExchangerRunnable(exchanger, "A");

ExchangerRunnable exchangerRunnable2 =
new ExchangerRunnable(exchanger, "B");

new Thread(exchangerRunnable1).start();
new Thread(exchangerRunnable2).start();

Here is the 

ExchangerRunnable

 code:

public class ExchangerRunnable implements Runnable{

Exchanger exchanger = null;
Object    object    = null;

public ExchangerRunnable(Exchanger exchanger, Object object) {
this.exchanger = exchanger;
this.object = object;
}

public void run() {
try {
Object previous = this.object;

this.object = this.exchanger.exchange(this.object);

System.out.println(
Thread.currentThread().getName() +
" exchanged " + previous + " for " + this.object
);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

This example prints out this:

Thread-0 exchanged A for B
Thread-1 exchanged B for A