5

（注意：这个问题的背景很冗长，但是底部有一个SSCCE可以跳过）

背景

我正在尝试开发一个基于 Python 的 CLI 来与 Web 服务交互。在我的代码库中，我有一个CommunicationService类可以处理与 Web 服务的所有直接通信。它公开了一个received_response属性，该属性返回一个Observable（来自 RxPY），其他对象可以订阅该属性，以便在从 Web 服务接收到响应时得到通知。

我的 CLI 逻辑基于click库，其中我的子命令之一实现如下：

async def enabled(self, request: str, response_handler: Callable[[str], Tuple[bool, str]]) -> None:
    self._generate_request(request)
    if response_handler is None:
        return None

    while True:
        response = await self.on_response
        success, value = response_handler(response)
        print(success, value)
        if success:
            return value

这里发生的事情（在response_handler不是的情况下None）是子命令表现得像一个协程，它等待来自 Web 服务 ( self.on_response == CommunicationService.received_response) 的响应并从它可以处理的第一个响应中返回一些处理后的值。

CommunicationService我试图通过创建完全模拟的测试用例来测试我的 CLI 的行为；一个假Subject的被创建（它可以作为一个Observable）并被CommunicationService.received_response模拟返回它。作为测试的一部分，on_next调用主体的方法将模拟 Web 服务响应传回生产代码：

@when('the communications service receives a response from TestCube Web Service')
def step_impl(context):
    context.mock_received_response_subject.on_next(context.text)

我使用了一个 click 'result callback' 函数，该函数在 CLI 调用结束时被调用并阻塞，直到协程（子命令）完成：

@cli.resultcallback()
def _handle_command_task(task: Coroutine, **_) -> None:
    if task:
        loop = asyncio.get_event_loop()
        result = loop.run_until_complete(task)
        loop.close()
        print('RESULT:', result)

问题

在测试开始时，我跑去CliRunner.invoke发射整个shebang。问题是这是一个阻塞调用，并且会阻塞线程，直到 CLI 完成并返回结果，如果我需要我的测试线程继续运行以便它可以同时产生模拟 Web 服务响应，这将没有帮助。

我想我需要做的是CliRunner.invoke使用ThreadPoolExecutor. 这允许测试逻辑在原始线程上继续并执行@when上面发布的步骤。但是，发布的通知 mock_received_response_subject.on_next 似乎不会触发在子命令中继续执行。

我相信解决方案将涉及使用 RxPY's AsyncIOScheduler，但我发现这方面的文档有点稀疏且无益。

SSCCE

下面的片段抓住了我希望是问题的本质。如果可以对其进行修改以使其工作，我应该能够将相同的解决方案应用于我的实际代码，以使其按我想要的方式运行。

import asyncio
import logging
import sys
import time

import click
from click.testing import CliRunner
from rx.subjects import Subject

web_response_subject = Subject()
web_response_observable = web_response_subject.as_observable()

thread_loop = asyncio.new_event_loop()


@click.group()
def cli():
    asyncio.set_event_loop(thread_loop)


@cli.resultcallback()
def result_handler(task, **_):
    loop = asyncio.get_event_loop()
    result = loop.run_until_complete(task) # Should block until subject publishes value
    loop.close()

    print(result)


@cli.command()
async def get_web_response():
    return await web_response_observable


def test():
    runner = CliRunner()
    future = thread_loop.run_in_executor(None, runner.invoke, cli, ['get_web_response'])
    time.sleep(1)
    web_response_subject.on_next('foo') # Simulate reception of web response.
    time.sleep(1)
    result = future.result()
    print(result.output)

logging.basicConfig(
    level=logging.DEBUG,
    format='%(threadName)10s %(name)18s: %(message)s',
    stream=sys.stderr,
)

test()

当前行为

程序在运行时挂起，在result = loop.run_until_complete(task).

验收标准

程序终止并foo在stdout.

更新 1

根据文森特的帮助，我对我的代码进行了一些更改。

Relay.enabled（等待来自 Web 服务的响应以处理它们的子命令）现在实现如下：

async def enabled(self, request: str, response_handler: Callable[[str], Tuple[bool, str]]) -> None:
    self._generate_request(request)

    if response_handler is None:
        return None

    return await self.on_response \
        .select(response_handler) \
        .where(lambda result, i: result[0]) \
        .select(lambda result, index: result[1]) \
        .first()

我不太确定observable 的await行为如何RxPY——它们会在生成的每个元素上将执行返回给调用者，还是仅在 observable 完成（或出错？）时返回执行。我现在知道是后者，老实说，这感觉像是更自然的选择，并且让我让这个函数的实现感觉更加优雅和反应灵敏。

我还修改了生成模拟 Web 服务响应的测试步骤：

@when('the communications service receives a response from TestCube Web Service')
def step_impl(context):
    loop = asyncio.get_event_loop()
    loop.call_soon_threadsafe(context.mock_received_response_subject.on_next, context.text)

不幸的是，这将无法正常工作，因为 CLI 正在其自己的线程中被调用...

@when('the CLI is run with "{arguments}"')
def step_impl(context, arguments):
    loop = asyncio.get_event_loop()
    if 'async.cli' in context.tags:
        context.async_result = loop.run_in_executor(None, context.cli_runner.invoke, testcube.cli, arguments.split())
    else:
        ...

并且 CLI 在调用时会创建自己的线程私有事件循环......

def cli(context, hostname, port):
    _initialize_logging(context.meta['click_log.core.logger']['level'])

    # Create a new event loop for processing commands asynchronously on.
    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)
    ...

我认为我需要一种方法来允许我的测试步骤在新线程上调用 CLI ，然后获取它正在使用的事件循环：

@when('the communications service receives a response from TestCube Web Service')
def step_impl(context):
    loop = _get_cli_event_loop() # Needs to be implemented.
    loop.call_soon_threadsafe(context.mock_received_response_subject.on_next, context.text)

更新 2

似乎没有一种简单的方法来获取特定线程为其自身创建和使用的事件循环，因此我接受了 Victor 的建议并模拟asyncio.new_event_loop返回一个我的测试代码创建和存储的事件循环：

def _apply_mock_event_loop_patch(context):
    # Close any already-existing exit stacks.
    if hasattr(context, 'mock_event_loop_exit_stack'):
        context.mock_event_loop_exit_stack.close()

    context.test_loop = asyncio.new_event_loop()
    print(context.test_loop)
    context.mock_event_loop_exit_stack = ExitStack()
    context.mock_event_loop_exit_stack.enter_context(
        patch.object(asyncio, 'new_event_loop', spec=True, return_value=context.test_loop))

我将“收到的模拟网络响应”测试步骤更改为执行以下操作：

@when('the communications service receives a response from TestCube Web Service')
def step_impl(context):
    loop = context.test_loop
    loop.call_soon_threadsafe(context.mock_received_response_subject.on_next, context.text)

好消息是，当执行此步骤时，我实际上正在Relay.enabled触发协程！

现在唯一的问题是最后的测试步骤，我等待在自己的线程中执行 CLI 并验证 CLI 是否正在发送它的未来stdout：

@then('the CLI should print "{output}"')
def step_impl(context, output):
    if 'async.cli' in context.tags:
        loop = asyncio.get_event_loop() # main loop, not test loop
        result = loop.run_until_complete(context.async_result)
    else:
        result = context.result
    assert_that(result.output, equal_to(output))

我已经尝试过解决这个问题，但我似乎无法context.async_result（从 存储未来loop.run_in_executor）很好地过渡到done并返回结果。在当前的实现中，第一个测试（ ）出现错误，第二个测试（1.1）出现无限期挂起1.2：

 @mock.comms @async.cli @wip
  Scenario Outline: Querying relay enable state -- @1.1                           # testcube/tests/features/relay.feature:45
    When the user queries the enable state of relay 0                             # testcube/tests/features/steps/relay.py:17 0.003s
    Then the CLI should query the web service about the enable state of relay 0   # testcube/tests/features/steps/relay.py:48 0.000s
    When the communications service receives a response from TestCube Web Service # testcube/tests/features/steps/core.py:58 0.000s
      """
      {'module':'relays','path':'relays[0].enabled','data':[True]}'
      """
    Then the CLI should print "True"                                              # testcube/tests/features/steps/core.py:94 0.003s
      Traceback (most recent call last):
        File "/Users/davidfallah/testcube_env/lib/python3.5/site-packages/behave/model.py", line 1456, in run
          match.run(runner.context)
        File "/Users/davidfallah/testcube_env/lib/python3.5/site-packages/behave/model.py", line 1903, in run
          self.func(context, *args, **kwargs)
        File "testcube/tests/features/steps/core.py", line 99, in step_impl
          result = loop.run_until_complete(context.async_result)
        File "/usr/local/Cellar/python3/3.5.2_1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 387, in run_until_complete
          return future.result()
        File "/usr/local/Cellar/python3/3.5.2_1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 274, in result
          raise self._exception
        File "/usr/local/Cellar/python3/3.5.2_1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/concurrent/futures/thread.py", line 55, in run
          result = self.fn(*self.args, **self.kwargs)
        File "/Users/davidfallah/testcube_env/lib/python3.5/site-packages/click/testing.py", line 299, in invoke
          output = out.getvalue()
      ValueError: I/O operation on closed file.

      Captured stdout:
      RECEIVED WEB RESPONSE: {'module':'relays','path':'relays[0].enabled','data':[True]}'
      <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /usr/local/Cellar/python3/3.5.2_1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py:431]>

  @mock.comms @async.cli @wip
  Scenario Outline: Querying relay enable state -- @1.2                           # testcube/tests/features/relay.feature:46
    When the user queries the enable state of relay 1                             # testcube/tests/features/steps/relay.py:17 0.005s
    Then the CLI should query the web service about the enable state of relay 1   # testcube/tests/features/steps/relay.py:48 0.001s
    When the communications service receives a response from TestCube Web Service # testcube/tests/features/steps/core.py:58 0.000s
      """
      {'module':'relays','path':'relays[1].enabled','data':[False]}'
      """
RECEIVED WEB RESPONSE: {'module':'relays','path':'relays[1].enabled','data':[False]}'
    Then the CLI should print "False"                                             # testcube/tests/features/steps/core.py:94

第 3 章：结局

搞砸所有这些异步多线程的东西，我太笨了。

首先，不要像这样描述场景......

When the user queries the enable state of relay <relay_id>
Then the CLI should query the web service about the enable state of relay <relay_id>
When the communications service receives a response from TestCube Web Service:
  """
  {"module":"relays","path":"relays[<relay_id>].enabled","data":[<relay_enabled>]}
  """
Then the CLI should print "<relay_enabled>"

我们是这样描述的：

Given the communications service will respond to requests:
  """
  {"module":"relays","path":"relays[<relay_id>].enabled","data":[<relay_enabled>]}
  """
When the user queries the enable state of relay <relay_id>
Then the CLI should query the web service about the enable state of relay <relay_id>
And the CLI should print "<relay_enabled>"

实施新的给定步骤：

@given('the communications service will respond to requests')
def step_impl(context):
    response = context.text

    def publish_mock_response(_):
        loop = context.test_loop
        loop.call_soon_threadsafe(context.mock_received_response_subject.on_next, response)

    # Configure the mock comms service to publish a mock response when a request is made.
    instance = context.mock_comms.return_value
    instance.send_request.on_next.side_effect = publish_mock_response

繁荣

2 features passed, 0 failed, 0 skipped
22 scenarios passed, 0 failed, 0 skipped
58 steps passed, 0 failed, 0 skipped, 0 undefined
Took 0m0.111s
4

1 回答 1

4

我可以看到您的代码存在两个问题：

  • asyncio 不是线程安全的，除非您使用call_soon_threadsafe或run_coroutine_threadsafe。RxPy不使用Observable.to_future中的任何一个，因此您必须访问RxPy运行 asyncio 事件循环的同一线程中的对象。
  • RxPy在调用时设置未来的结果on_completed，以便等待可观察对象返回最后一个发出的对象。这意味着您必须同时调用两者on_next并on_completed返回await。

这是一个工作示例：

import click
import asyncio
from rx.subjects import Subject
from click.testing import CliRunner

web_response_subject = Subject()
web_response_observable = web_response_subject.as_observable()
main_loop = asyncio.get_event_loop()

@click.group()
def cli():
    pass

@cli.resultcallback()
def result_handler(task, **_):
    future = asyncio.run_coroutine_threadsafe(task, main_loop)
    print(future.result())

@cli.command()
async def get_web_response():
    return await web_response_observable

def test():
    runner = CliRunner()
    future = main_loop.run_in_executor(
        None, runner.invoke, cli, ['get_web_response'])
    main_loop.call_later(1, web_response_subject.on_next, 'foo')
    main_loop.call_later(2, web_response_subject.on_completed)
    result = main_loop.run_until_complete(future)
    print(result.output, end='')

if __name__ == '__main__':
    test()
于 2016-09-05T11:00:20.110 回答