cdm/src/main/java/ucar/nc2/dt/grid/GridDataset.java
@Override
  public synchronized void close() throws java.io.IOException {
    if (fileCache != null) {
      if (fileCache.release(this)) return;
    }

    try {
      if (ncd != null) ncd.close();
    } finally {
      ncd = null;
      }
  }
@Override
  public synchronized void close() throws java.io.IOException {
    if (fileCache != null) {
      if (fileCache.release(this)) return;
    }

    try {
      if (ncd != null) ncd.close();
    } finally {
      ncd = null;
      }
  }
FileCacheable