earlyreturnfix.java

Java Thread Programming (Source

public class EarlyReturnFix extends Object {
	private volatile int value;

	public EarlyReturnFix(int initialValue) {
		value = initialValue;
	}

	public synchronized void setValue(int newValue) {
		if ( value != newValue ) {
			value = newValue;
			notifyAll();
		}
	}

	public synchronized boolean waitUntilAtLeast(
				int minValue,
				long msTimeout
			) throws InterruptedException {

		System.out.println("entering waitUntilAtLeast() - " + 
				"value=" + value + ",minValue=" + minValue);

		long endTime = System.currentTimeMillis() + msTimeout;
		long msRemaining = msTimeout;

		while ( ( value < minValue ) && ( msRemaining > 0L ) ) {
			System.out.println("in waitUntilAtLeast() - " + 
					"about to: wait(" + msRemaining + ")");
			wait(msRemaining);
			msRemaining = endTime - System.currentTimeMillis();
			System.out.println("in waitUntilAtLeast() - " +
					"back from wait(), new msRemaining=" +
					msRemaining);
		}

		System.out.println("leaving waitUntilAtLeast() - " +
				"value=" + value + ",minValue=" + minValue);

		// May have timed out, or may have met value, 
		// calc return value.
		return ( value >= minValue );
	}

	public static void main(String[] args) {
		try {
			final EarlyReturnFix er = new EarlyReturnFix(0);

			Runnable r = new Runnable() {
					public void run() {
						try {
							Thread.sleep(1500);
							er.setValue(2);
							Thread.sleep(500);
							er.setValue(3);
							Thread.sleep(500);
							er.setValue(4);
						} catch ( Exception x ) {
							x.printStackTrace();
						}
					}
				};

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

			System.out.println(
					"about to: waitUntilAtLeast(5, 3000)");
			long startTime = System.currentTimeMillis();
			boolean retVal = er.waitUntilAtLeast(5, 3000);
			long elapsedTime = 
					System.currentTimeMillis() - startTime;

			System.out.println("after " + elapsedTime + 
					" ms, retVal=" + retVal);
		} catch ( InterruptedException ix ) {
			ix.printStackTrace();
		}
	}
}