public Object call() throws Exception {
   _barrier.await(); // barrier, to force racing start
   for (long j = 0; j < _count; j++)
     _map.put(
         j + _offset,
         new TestKey(_rand.nextLong(), _rand.nextInt(), (short) _rand.nextInt(Short.MAX_VALUE)));
   return null;
 }
 @Override
 public void run() {
   try {
     LongValue value = new LongValueNative();
     barrier.await();
     for (int i = 0; i < iterations; i++) {
       map.acquireUsing(key, value);
       value.addAtomicValue(1);
     }
   } catch (Exception e) {
     e.printStackTrace();
   }
 }
 public Integer call() throws Exception {
   _barrier.await();
   int count = 0;
   for (TestKey item : _items) {
     if (_map.contains(item._id)) {
       System.err.printf("COLLISION DETECTED: %s exists\n", item.toString());
     }
     final TestKey exists = _map.putIfAbsent(item._id, item);
     if (exists == null) {
       count++;
     } else {
       System.err.printf(
           "COLLISION DETECTED: %s exists as %s\n", item.toString(), exists.toString());
     }
   }
   return count;
 }