/**
* Uses random numbers to sample the entire map.
*
* @return an array of sampled elements
*/
private LfuPolicy.Metadata[] sampleElements(Map map) {
int[] offsets = LfuPolicy.generateRandomSample(map.size());
DiskElement[] elements = new DiskElement[offsets.length];
Iterator iterator = map.values().iterator();
for (int i = 0; i < offsets.length; i++) {
for (int j = 0; j < offsets[i]; j++) {
iterator.next();
}
elements[i] = (DiskElement) iterator.next();
}
return elements;
}
/**
* Uses random numbers to sample the entire map.
*
* <p>This implemenation uses a key array.
*
* @return a random sample of elements
*/
protected Element[] sampleElementsViaKeyArray() {
int[] indices = LfuPolicy.generateRandomSampleIndices(maximumSize);
Element[] elements = new Element[indices.length];
for (int i = 0; i < indices.length; i++) {
Object key = keyArray.get(indices[i]);
if (key == null) {
continue;
}
elements[i] = (Element) map.get(key);
}
return elements;
}
/**
* Uses random numbers to sample the entire map.
*
* <p>This implemenation uses the {@link ConcurrentHashMap} iterator.
*
* @return a random sample of elements
*/
protected Element[] sampleElements(int size) {
int[] offsets = LfuPolicy.generateRandomSample(size);
Element[] elements = new Element[offsets.length];
Iterator iterator = map.values().iterator();
for (int i = 0; i < offsets.length; i++) {
for (int j = 0; j < offsets[i]; j++) {
// fast forward
try {
iterator.next();
} catch (NoSuchElementException e) {
// e.printStackTrace();
}
}
try {
elements[i] = ((Element) iterator.next());
} catch (NoSuchElementException e) {
// e.printStackTrace();
}
}
return elements;
}
/** Find a "relatively" unused disk element, but not the element just added. */
private DiskElement findRelativelyUnused() {
LfuPolicy.Metadata[] elements = sampleElements(diskElements);
LfuPolicy.Metadata metadata = LfuPolicy.leastHit(elements, null);
return (DiskElement) metadata;
}
