protected void addCriticalMember(final DistributedMember idm) {
    synchronized (memoryThresholdReachedMembers) {
      if (memoryThresholdReachedMembers.isEmpty()) {
        setMemoryThresholdReached(true);
      }
      memoryThresholdReachedMembers.add(idm);
    }
  }
@param idm member whose threshold has been exceeded
geode-core/src/main/java/org/apache/geode/internal/cache/DistributedRegion.java