Thread safe Timed Set

Question

Hello,
I'm trying to create a thread safe set that also contains a time when it was updated last. It's a cache of a table from the db. I am using CopyOnWriteArraySet as the set is going to be modified rarely, items from set are never modified or removed individually.
There are couple of questions, is the an existing collection that I can use to achieve the same in JDK 6 (not external libraries)? Is there a better choice over CopyOnWriteArraySet? I tried searching but couldn't find anything.
If not, would the following implementation suffice my requirements?
Any suggestions greatly appreciated.
Thanks in advance,
-t
public class CacheSet<T> extends CopyOnWriteArraySet<T> {
private static final long serialVersionUID = 1L;
private long lastSyncTime = 0;
* @param lastSyncTime
*          the lastSyncTime to set
public synchronized void setLastSyncTime(long lastSyncTime) {
this.lastSyncTime = lastSyncTime;
* @return the lastSyncTime
public synchronized long getLastSyncTime() {
return lastSyncTime;
}

Answer 1

if you are caching the contents of a table, i assume you are only ever replacing the set. i would suggest something like this:
public class TableData<T>
  private final Set<T> _tableData;
  private final long _timestamp;
  public TableData(Set<T> data, long timestamp) {
    _tableData = Collections.unmodifiableSet(data);
    _timestamp = timestamp;
  // normal accessors here
public class TableCache<T>
  private volatile TableData<T> _curTable;
  public void update(TableData<T> newTable)
    _curTable = newTable;
  public TableData<T> get()
    return _curTable;
}the basic idea is that the TableData class is immutable (e.g. when you update the cache, you create a new set and new TableData instance), so you don't need to worry about concurrency issues (you can pass it a normal HashSet or whatever). thread visibility issues are resolved by using volatile on the TableCache class.
Edited by: jtahlborn on Apr 17, 2010 10:47 AM