@Override
  public Set<DistributedMember> getGroupMembers(String group) {
    HashSet<DistributedMember> result = null;
    for (DistributedMember m : getDistributionManagerIdsIncludingAdmin()) {
      if (m.getGroups().contains(group)) {
        if (result == null) {
          result = new HashSet<>();
        }
        result.add(m);
      }
    }
    if (result == null) {
      return Collections.emptySet();
    } else {
      return result;
    }
  }
this causes the given InternalDistributedMembers to log thread dumps. If useNative is true we
attempt to use OSProcess native code for the dumps. This goes to stdout instead of the
system.log files.
geode-core/src/main/java/org/apache/geode/distributed/internal/ClusterDistributionManager.java