/* This class is thread-safe, and optimized for more parallelism. E.g.,
  we can run incUpper and decLower at the same time. */

public class RangeOpt {
    private int lower;
    private Object lowerLock = new Object(); // guards lower
    private int upper;
    private Object upperLock = new Object(); // guards upper
    // INVARIANT: lowerLock acquired before upperLock to avoid deadlock
    // INVARIANT: lower <= upper
    private boolean invariantOK(int l, int u) {
	return l <= u;
    }
    public RangeOpt(int lower, int upper) throws IllegalArgumentException {
	if (!invariantOK(lower,upper)) 
	    throw new IllegalArgumentException();
	this.lower = lower;
	this.upper = upper;
    }
    public boolean inRange(int v) {
	synchronized (lowerLock) {
	    synchronized (upperLock) {
		if (v >= lower && v <= upper) return true;
		return false;
	    }
	}
    }
    public void incUpper() {
	synchronized (upperLock) {
	    upper ++;
	}
    }
    public void incLower() throws IllegalArgumentException {
	synchronized (lowerLock) {
	    synchronized (upperLock) {
		if (!invariantOK(lower+1,upper)) 
		    throw new IllegalArgumentException();
		lower ++;
	    }
	}
    }
    public void decLower() {
	synchronized (lowerLock) {
	    lower-- ;
	}
    }
    public void decUpper() throws IllegalArgumentException {
	synchronized (lowerLock) {
	    synchronized (upperLock) {
		if (!invariantOK(lower,upper-1)) 
		    throw new IllegalArgumentException();
		upper --;
	    }
	}
    }
}