@Override
    public String cancelInProgress() {
      checkFailure();

      // remove call to validateDM() to fix bug 38356

      if (dm.shutdownMsgSent) {
        return String.format("%s: Message distribution has terminated",
            dm);
      }
      if (dm.rootCause != null) {
        return dm + ": " + dm.rootCause.getMessage();
      }

      // Nope.
      return null;
    }
test method to get the member IDs of all locators in the distributed system
geode-core/src/main/java/org/apache/geode/distributed/internal/ClusterDistributionManager.java