public void emergencyClose() {
    if (dm != null) {
      Distribution mm = dm.getDistribution();
      if (mm != null) {
        mm.emergencyClose();
      }
    }

    // Garbage collection
    // Leave dm alone; its CancelCriterion will help people die
    isConnected = false;
    if (dm != null) {
      dm.setRootCause(SystemFailure.getFailure());
    }
    isDisconnecting = true;
    disconnectListeners.clear();
  }
Closes the membership manager

@see SystemFailure#emergencyClose()
geode-core/src/main/java/org/apache/geode/distributed/internal/InternalDistributedSystem.java