Synchronize

• A producer and a consumer each runs in its own thread.
• The producer calls put while the consumer calls get. We want every item to be consumed exactly once.

public class CubbyHole {
  private int contents;
  private boolean available = false;

  public synchronized int get() {
    while (available == false) {
      try {
        wait();
      } catch (InterruptedException e) { }
    }
    available = false;
    notifyAll();
    return contents;
  }

  public synchronized void put(int value) {
    while (available == true) {
      try {
        wait();
      } catch (InterruptedException e) { }
    }
    contents = value;
    available = true;
    notifyAll();
  }
}

public class ProducerConsumerTest {
  public static void main(String[] args) {
    CubbyHole c = new CubbyHole();
    Producer p1 = new Producer(c, 1);
    Consumer c1 = new Consumer(c, 1);

    p1.start();
    c1.start();
  }
}

• The synchronized keyword means that only one thread can be accessing that function at a time.
• The wait method will block until that object (CubbyHole) calls notifyAll. Since it blocks it means that some other thread must make that call.