booleanlock.java

Java Thread Programming (Source

public class BooleanLock extends Object {
	private boolean value;

	public BooleanLock(boolean initialValue) {
		value = initialValue;
	}

	public BooleanLock() {
		this(false);
	}

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

	public synchronized boolean waitToSetTrue(long msTimeout) 
			throws InterruptedException {

		boolean success = waitUntilFalse(msTimeout);
		if ( success ) {
			setValue(true);
		}

		return success;
	}

	public synchronized boolean waitToSetFalse(long msTimeout) 
			throws InterruptedException {

		boolean success = waitUntilTrue(msTimeout);
		if ( success ) {
			setValue(false);
		}

		return success;
	}

	public synchronized boolean isTrue() {
		return value;
	}

	public synchronized boolean isFalse() {
		return !value;
	}

	public synchronized boolean waitUntilTrue(long msTimeout) 
			throws InterruptedException {

		return waitUntilStateIs(true, msTimeout);
	}

	public synchronized boolean waitUntilFalse(long msTimeout) 
			throws InterruptedException {

		return waitUntilStateIs(false, msTimeout);
	}

	public synchronized boolean waitUntilStateIs(
				boolean state, 
				long msTimeout
			) throws InterruptedException {

		if ( msTimeout == 0L ) {
			while ( value != state ) {
				wait();  // wait indefinitely until notified
			}

			// condition has finally been met
			return true;
		} 

		// only wait for the specified amount of time
		long endTime = System.currentTimeMillis() + msTimeout;
		long msRemaining = msTimeout;

		while ( ( value != state ) && ( msRemaining > 0L ) ) {
			wait(msRemaining);
			msRemaining = endTime - System.currentTimeMillis();
		}

		// May have timed out, or may have met value, 
		// calculate return value.
		return ( value == state );
	}
}