package net.jcip.examples;

import java.util.concurrent.atomic.*;

import net.jcip.annotations.*;

/**

* CasNumberRange

* <p/>

* Preserving multivariable invariants using CAS

*

* @author Brian Goetz and Tim Peierls

*/

@ThreadSafe

public class CasNumberRange {

@Immutable

private static class IntPair {

// INVARIANT: lower <= upper

final int lower;

final int upper;

public IntPair(int lower, int upper) {

this.lower = lower;

this.upper = upper;

}

}

private final AtomicReference<IntPair> values =

new AtomicReference<IntPair>(new IntPair(0, 0));

public int getLower() {

return values.get().lower;

}

public int getUpper() {

return values.get().upper;

}

public void setLower(int i) {

while (true) {

IntPair oldv = values.get();

if (i > oldv.upper)

throw new IllegalArgumentException("Can't set lower to " + i + " > upper");

IntPair newv = new IntPair(i, oldv.upper);

if (values.compareAndSet(oldv, newv))

return;

}

}

public void setUpper(int i) {

while (true) {

IntPair oldv = values.get();

if (i < oldv.lower)

throw new IllegalArgumentException("Can't set upper to " + i + " < lower");

IntPair newv = new IntPair(oldv.lower, i);

if (values.compareAndSet(oldv, newv))

return;

}

}

}