public DistributionManager getDistributionManager() {
    try {
      DistributionManager result = system.getDistributionManager();
      if (result == null) {
        result = dmgr;
        Assert.assertTrue(result != null, "null DistributionManager");
      }
      return result;
    } catch (IllegalStateException ex) {
      // fix for bug 35000
      system.getCancelCriterion().checkCancelInProgress(null);
      throw new DistributedSystemDisconnectedException(ex.getMessage());
    }
  }
get the distribution manager for this processor. If the distributed system has a distribution
manager, it is used. Otherwise, we expect a distribution manager has been set with
setDistributionManager and we'll use that
geode-core/src/main/java/org/apache/geode/distributed/internal/ReplyProcessor21.java