def stop_expr(self, expr_id):
        self.log.debug("begin to stop %s" % str(expr_id))
        expr = Experiment.objects(id=expr_id, status=EStatus.RUNNING).first()
        if expr is not None:
            starter = self.get_starter(expr.hackathon, expr.template)
            if starter:
                starter.stop_expr(Context(experiment_id=expr.id, experiment=expr))
            self.log.debug("experiment %s ended success" % expr_id)
            return ok('OK')
        else:
            return ok()
cameraStopPreview()
dataset/ETHPy150Open msopentechcn/open-hackathon/open-hackathon-server/src/hackathon/expr/expr_mgr.py/ExprManager.stop_expr--crossover with--dataset/ETHPy150Open brousch/sl4a_pydroid_mock_api/src/android/utils/androidhelper_r6.py/Android.cameraStopPreview