!7

sclass ORef {
  S globalID = aGlobalID();
  WeakReference ref;
  new Set<S> forMachines;
  long created = now(), lastAccessed;
}

module ObjectReferences > DynObjectTable<ORef> {
  transient Map<S, ORef> byGlobalID = synchroMap();
  transient Map<O, ORef> byObject = weakIdentityHashMap();
  
  // API
  
  // returns global ID
  S addReferencedObject(O object, S forMachine) {
    lock lock;
    ORef r = byObject.get(object);
    if (r == null) {
      new ORef r;
      r.ref = weakRef(object);
      byGlobalID.put(r.globalID, r);
      byObject.put(object, r);
    }
    r.lastAccessed = now();
    r.forMachines.add(forMachine);
    ret r.globalID;
  }
  
  O getReferencedObject(S globalID) {
    ORef r = byGlobalID.get(r);
    ret r == null ? null : r.ref!;
  }
}