tornado.gen.engine v/s tornado.gen.coroutine的区别

Question

通过tornado.gen 文档,有人可以帮助我理解tornado.gen.coroutine和tornado.gen.engine之间的确切区别

Answer 1

正如龙卷风文档中gen.engine所说：

此装饰器与协程类似，不同的是它不返回Future且未对callback参数进行特殊处理。

正如gen.coroutine文档所说

从调用者的角度来看，@ gen.coroutine类似于@return_future和@ gen.engine的组合。

gen.engine基本上是协程所做的较旧的，精简的版本。如果要编写新代码，则应遵循文档的建议并始终使用tornado.gen.coroutine。

如果您查看这两个函数的代码（除去文档），这是很明显的。

发动机：

def engine(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        runner = None

        def handle_exception(typ, value, tb):
            if runner is not None:
                return runner.handle_exception(typ, value, tb)
            return False
        with ExceptionStackContext(handle_exception) as deactivate:
            try:
                result = func(*args, **kwargs)
            except (Return, StopIteration) as e:
                result = getattr(e, 'value', None)
            else:
                if isinstance(result, types.GeneratorType):
                    def final_callback(value):
                        if value is not None:
                            raise ReturnValueIgnoredError(
                                "@gen.engine functions cannot return values: "
                                "%r" % (value,))
                        assert value is None
                        deactivate()
                    runner = Runner(result, final_callback)
                    runner.run()
                    return
            if result is not None:
                raise ReturnValueIgnoredError(
                    "@gen.engine functions cannot return values: %r" %
                    (result,))
            deactivate()
            # no yield, so we're done
    return wrapper

协程：

def coroutine(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        runner = None
        future = TracebackFuture()

        if 'callback' in kwargs:
            callback = kwargs.pop('callback')
            IOLoop.current().add_future(
                future, lambda future: callback(future.result()))

        def handle_exception(typ, value, tb):
            try:
                if runner is not None and runner.handle_exception(typ, value, tb):
                    return True
            except Exception:
                typ, value, tb = sys.exc_info()
            future.set_exc_info((typ, value, tb))
            return True
        with ExceptionStackContext(handle_exception) as deactivate:
            try:
                result = func(*args, **kwargs)
            except (Return, StopIteration) as e:
                result = getattr(e, 'value', None)
            except Exception:
                deactivate()
                future.set_exc_info(sys.exc_info())
                return future
            else:
                if isinstance(result, types.GeneratorType):
                    def final_callback(value):
                        deactivate()
                        future.set_result(value)
                    runner = Runner(result, final_callback)
                    runner.run()
                    return future
            deactivate()
            future.set_result(result)
        return future
    return wrapper

乍一看，这两个都可能很难理解。但是，很明显，代码非常相似，除了@gen.coroutine对callbackkwarg 进行了一些特殊处理外，它还会生成/返回a Future。@gen.engine如果您尝试从中返回某些内容而不是将其放入，则其中的某些代码专门抛出了错误Future。