Java Monitor

public abstract class Cache<From,To> {
    private Map<From,To> cache;
 
    protected abstract To createItem(From f);
 
    public final To get(From f) {
        To t = inspectValue(f);
        if (t != null) {
            return t;
        }
        To newT = createItem(f);
        return registerValue(f, newT);
    }
 
 
    private synchronized To inspectValue(From f) {
        if (cache == null) {
            cache = new HashMap<From, To>();
        }
        return cache.get(f);
    }
 
    private synchronized To registerValue(From f, To newT) {
        To t = cache.get(f);
        if (t == null) {
            cache.put(f, newT);
            return newT;
        } else {
            return t;
        }
    }
}
 

int value =  cache.get("123");
assertEquals("3*10=30", 30, value);
 

Thread Test Watch Dog: testDeadlockViaAPI
 org.apidesign.javamonitorflaws.Cache.inspectValue:32
 org.apidesign.javamonitorflaws.Cache.get:22
 org.apidesign.javamonitorflaws.CacheTest.testDeadlockViaAPI:134

public class MultiplyCache extends Cache<String,Integer>
implements CacheTest.CacheToTest {
    private PropertyChangeSupport pcs;
    private int multiply;
    public static final String PROP_MULTIPLY = "multiply";
 
    public synchronized int getMultiply() {
        return multiply;
    }
    public synchronized void setMultiply(int multiply) {
        int oldMultiply = this.multiply;
        this.multiply = multiply;
        pcs.firePropertyChange(PROP_MULTIPLY, oldMultiply, multiply);
    }
 
    public synchronized void addPropertyChangeListener(
        PropertyChangeListener listener
    ) {
        if (pcs == null) {
            pcs = new PropertyChangeSupport(this);
        }
        pcs.addPropertyChangeListener(listener);
    }
    public synchronized void removePropertyChangeListener(
        PropertyChangeListener listener
    ) {
        if (pcs != null) {
            pcs.removePropertyChangeListener(listener);
        }
    }
 
    @Override
    protected Integer createItem(String f) {
        return f.length() * multiply;
    }
}
 

private static void testDeadlockViaAPI(final CacheToTest cache)
throws Exception {
    class ToDeadlock implements Runnable, PropertyChangeListener {
        int lastMultiply;
 
        public void run() {
            cache.setMultiply(10);
        }
        public void propertyChange(PropertyChangeEvent evt) {
            try {
                storeMultiply();
            } catch (InterruptedException ex) {
                // ok
            }
        }
 
        private synchronized void storeMultiply()
        throws InterruptedException {
            lastMultiply = cache.getMultiply();
            // simulates "starvation"
            wait();
        }
 
        public void assertMultiplyByTen() {
        }
    }
    ToDeadlock toDeadlock = new ToDeadlock();
    cache.addPropertyChangeListener(toDeadlock);
    Thread t = new Thread(toDeadlock, "Deadlock using API");
    t.start();
 
    Thread.sleep(100);
 
    int value =  cache.get("123");
    assertEquals("3*10=30", 30, value);
}