private void checkClosed() {
    parent.getCancelCriterion().checkCancelInProgress(null);
    if (!closed) {
      return;
    }
    throw new OplogCancelledException("This Oplog has been closed.");
  }
A check to confirm that the oplog has been closed because of the cache being closed
geode-core/src/main/java/org/apache/geode/internal/cache/OverflowOplog.java