Illustrate the volatile variables : Volatile « Threads « Java

1. Java
2. Threads
3. Volatile

Illustrate the volatile variables

public class Volatile extends Object implements Runnable {
  // not marked as 'volatile', but it should be!
  private int value;

  private volatile boolean missedIt;

  // doesn't need to be volatile-doesn't change
  private long creationTime;

  public Volatile() {
    value = 10;
    missedIt = false;
    creationTime = System.currentTimeMillis();
  }

  public void run() {
    print("entering run()");

    // each time, check to see if 'value' is different
    while (value < 20) {
      // Used to break out of the loop if change to
      // value is missed.
      if (missedIt) {
        int currValue = value;

        // Simply execute a synchronized statement on an
        // arbitrary object to see the effect.
        Object lock = new Object();
        synchronized (lock) {
          // do nothing!
        }

        int valueAfterSync = value;

        print("in run() - see value=" + currValue
            + ", but rumor has it that it changed!");
        print("in run() - valueAfterSync=" + valueAfterSync);

        break;
      }
    }

    print("leaving run()");
  }

  public void workMethod() throws InterruptedException {
    print("entering workMethod()");

    print("about to sleep for 2 seconds");
    Thread.sleep(2000);

    value = 50;
    print("just set value=" + value);

    print("about to sleep for 5 seconds");
    Thread.sleep(5000);

    missedIt = true;
    print("just set missedIt=" + missedIt);

    print("about to sleep for 3 seconds");
    Thread.sleep(3000);

    print("leaving workMethod()");
  }

  private void print(String msg) {
    long interval = System.currentTimeMillis() - creationTime;

    String tmpStr = (interval / 1000.0) + "000";

    int pos = tmpStr.indexOf(".");
    String secStr = tmpStr.substring(pos - 2, pos + 4);

    String nameStr = Thread.currentThread().getName();

    nameStr = nameStr.substring(nameStr.length() - 8, nameStr.length());

    System.out.println(secStr + " " + nameStr + ": " + msg);
  }

  public static void main(String[] args) {
    try {
      Volatile vol = new Volatile();

      // slight pause to let some time elapse
      Thread.sleep(100);

      Thread t = new Thread(vol);
      t.start();

      // slight pause to allow run() to go first
      Thread.sleep(100);

      vol.workMethod();
    } catch (InterruptedException x) {
      System.err.println("one of the sleeps was interrupted");
    }
  }
}

           
       

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