public Set<K> getUnmatchedKeys() {
        stateLock.readLock().lock();
        try {
            return new HashSet<K>(this.actualIndices.keySet());
        } finally {
            stateLock.readLock().unlock();
        }
    }
public Set < K > getUnmatchedKeys ( ) { stateLock . readLock ( ) . lock ( ) ; try { return new HashSet < K > ( this . actualIndices . keySet ( ) ) ; } finally { stateLock . readLock ( ) . unlock ( ) ; } }
Get a point-in-time view of the unmatched keys.
This may be immediately out of date unless additional
synchronization is performed to prevent concurrent updates.