public void start() {
    if (stopRequested) {
      throw new RuntimeException(
          "A health monitor can not be started once it has been stopped");
    }
    if (t.isAlive()) {
      // it is already running
      return;
    }
    t.start();
  }
Starts the monitor so that it will periodically do health checks.
geode-core/src/main/java/org/apache/geode/distributed/internal/HealthMonitorImpl.java