code: public void stop() throws Exception {
  		synchronized (this.lock) {
  			if (this.nephele != null) {
  				this.nephele.stop();
  				this.nephele = null;
  			} else {
  				throw new IllegalStateException("The local executor was not started.");
  			}
  		}
  	}
docs: Stop the local executor instance. You should not call executePlan after this.