Michal Kleczek wrote:

[ciach]
>
> Nie trzeba watku skanujacego - wystarczy usuwajacy. Od skanowania jest
> java.lang.ref.ReferenceQueue
>

Sprobuj moze jakos tak:

class IdMap<ID, ITEM> {

private final Map<Reference<?>, ID> refToIdMap = new HashMap();
private final Map<ID, Reference<ITEM>> idToRefMap = new HashMap();

private final ReferenceQueue<ITEM> referenceQueue = new ReferenceQueue();

//needs to be static so that we do not keep
//reference to the parent IdMap
private static class Remover<S, T> implements Runnable {

//keep just a (weak) reference to parent map
//so that we know when to finish removal
private final Reference<IdMap<S, T>> idMapRef;

private ReferenceQueue<T> getRefQueue() {
IdMap<S, T> idMap = idMapRef.get();
return idMap != null ? idMap.referenceQueue : null;
}

public Remover(IdMap<S, T> idMap) {
this.idMapRef = new WeakReference<IdMap<S, T>>(idMap);
}

@Override
public void run() {
try {
ReferenceQueue<T> referenceQueue = getRefQueue();
while (referenceQueue != null) {
//wait for next reference to remove
final Reference<? extends T> itemRef = referenceQueue.remove();
final IdMap<S, T> idMap = idMapRef.get();
if (idMap != null) {
idMap.remove(itemRef);
}

referenceQueue = getRefQueue();
}
}
catch (InterruptedException e) {
//ignore and return
}
}

}

private synchronized void remove(Reference<?> ref) {
final ID id = refToIdMap.remove(ref);
idToRefMap.remove(id);
}

public IdMap() {
new Thread(new Remover(this)).start();
}

public ITEM get(ID id) {
final Reference<ITEM> itemRef = idToRefMap.get(id);
return itemRef != null ? itemRef.get() : null;
}

public synchronized void put(ID id, ITEM item) {
final Reference<ITEM> itemRef = new WeakReference<ITEM>(item);
idToRefMap.put(id, itemRef);
refToIdMap.put(itemRef, id);
}

}


--
Michal