code: @Override
      public void checkIn(ServiceHandle<S> handle) throws Exception {
          checkNotNull(handle);
  
          S service = handle.getService();
          ServiceEndPoint endPoint = handle.getEndPoint();
  
          // Figure out if we should check this revision in.  If it was created before the last known invalid revision
          // for this particular end point, or the cache is closed, then we shouldn't check it in.
          Long invalidRevision = _invalidRevisions.get(endPoint);
          Long serviceRevision = _checkedOutRevisions.remove(handle);
  
          if (_isClosed || (invalidRevision != null && serviceRevision < invalidRevision)) {
              _pool.invalidateObject(endPoint, service);
          } else {
              _pool.returnObject(endPoint, service);
          }
      }
docs: Returns a service instance for an end point to the cache so that it may be used by other users.
  
  @param handle The service handle that is being checked in.
  @throws Exception Never.