docs: public void close()
                      throws IOException {
          //
          // The disk is kept permanently consistent, and the application now
          // controls the filemgr, so we have nothing to do any more.
          //        
          iterationLock.p();
          try {
              synchronized (this) {
                  header.write();
                  filemgr = null;
              }
          } finally {
              releaseMemoryToPool();
              iterationLock.v();
          }
      }