如何在django视图中使用asyncio（协程）和ThreadPoolExecutor(多线程)

Django视图函数执行，不在主线程中，直接

loop = asyncio.new_event_loop()  # 更不能loop = asyncio.get_event_loop()

会触发

RuntimeError: There is no current event loop in thread 

因为asyncio程序中的每个线程都有自己的事件循环，但它只会在主线程中为你自动创建一个事件循环。所以如果你asyncio.get_event_loop在主线程中调用一次，它将自动创建一个循环对象并将其设置为默认值，但是如果你在一个子线程中再次调用它，你会得到这个错误。相反，您需要在线程启动时显式创建/设置事件循环：

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)


在Django单个视图中使用asyncio实例代码如下（有多个IO任务时）

　　

from django.views import View
import asyncio
import time
from django.http import JsonResponse

class TestAsyncioView(View):
    def get(self, request, *args, **kwargs):
        """
        利用asyncio和async await关键字（python3.5之前使用yield）实现协程
        """
        start_time = time.time()
        loop = asyncio.new_event_loop()  # 或 loop = asyncio.SelectorEventLoop()
        asyncio.set_event_loop(loop)
        self.loop = loop
        try:
            results = loop.run_until_complete(self.gather_tasks())
        finally:
            loop.close()
        end_time = time.time()
        return JsonResponse({'results': results, 'cost_time': (end_time - start_time)})

    async def gather_tasks(self):
        """
         也可以用回调函数处理results
        task1 = self.loop.run_in_executor(None, self.io_task1, 2)
        future1 = asyncio.ensure_future(task1)
        future1.add_done_callback(callback)

        def callback(self, future):
            print("callback:",future.result())
        """
        tasks = (
            self.make_future(self.io_task1, 2),
            self.make_future(self.io_task2, 2)
        )
        results = await asyncio.gather(*tasks)
        return results

    async def make_future(self, func, *args):
        future = self.loop.run_in_executor(None, func, *args)
        response = await future
        return response

    """
    # python3.5之前无async await写法
    import types
    @types.coroutine
    # @asyncio.coroutine  # 这个也行
    def make_future(self, func, *args):
        future = self.loop.run_in_executor(None, func, *args)
        response = yield from future
        return response
    """

    def io_task1(self, sleep_time):
        time.sleep(sleep_time)
        return 66

    def io_task2(self, sleep_time):
        time.sleep(sleep_time)
        return 77

　　

在Django单个视图中使用ThreadPoolExecutor实例代码如下（有多个IO任务时）

from django.views import View
import time
from concurrent.futures import ThreadPoolExecutor, as_completed


class TestThreadView(View):
    def get(self, request, *args, **kargs):
        start_time = time.time()
        future_set = set()
        tasks = (self.io_task1, self.io_task2)
        with ThreadPoolExecutor(len(tasks)) as executor:
            for task in tasks:
                future = executor.submit(task, 2)
                future_set.add(future)
        for future in as_completed(future_set):
            error = future.exception()
            if error is not None:
                raise error
        results = self.get_results(future_set)
        end_time = time.time()
        return JsonResponse({'results': results, 'cost_time': (end_time - start_time)})

    def get_results(self, future_set):
        """
        处理io任务执行结果，也可以用future.add_done_callback(self.get_result)
        def get(self, request, *args, **kargs):
            start_time = time.time()
            future_set = set()
            tasks = (self.io_task1, self.io_task2)
            with ThreadPoolExecutor(len(tasks)) as executor:
                for task in tasks:
                    future = executor.submit(task, 2).add_done_callback(self.get_result)
                    future_set.add(future)
            for future in as_completed(future_set):
                error = future.exception()
                print(dir(future))
                if error is not None:
                    raise error
            self.results = results = []
            end_time = time.time()
            return JsonResponse({'results': results, 'cost_time': (end_time - start_time)})

        def get_result(self, future):
            self.results.append(future.result())
        """
        results = []
        for future in future_set:
            results.append(future.result())
        return results

    def io_task1(self, sleep_time):
        time.sleep(sleep_time)
        return 10

    def io_task2(self, sleep_time):
        time.sleep(sleep_time)
        return 66

 
附tornado中不依赖异步库实现异步非阻塞

from tornado.web import RequestHandler
from concurrent.futures import ThreadPoolExecutor
class NonBlockingHandler(RequestHandler):
    """
    不依赖tornado的异步库实现异步非阻塞
    使用 gen.coroutine 装饰器编写异步函数，如果库本身不支持异步，那么响应任然是阻塞的。
    在 Tornado 中有个装饰器能使用 ThreadPoolExecutor 来让阻塞过程编程非阻塞，
    其原理是在 Tornado 本身这个线程之外另外启动一个线程来执行阻塞的程序，从而让 Tornado 变得非阻塞
    """
    executor = ThreadPoolExecutor(max_workers=2)

    # executor默认需为这个名字，否则@run_on_executor(executor='_thread_pool')自定义名字，经测试max_workers也可以等于1

    @coroutine  # 使用@coroutine这个装饰器加yield关键字，或者使用async加await关键字
    def get(self, *args, **kwargs):
        second = yield self.blocking_task(20)
        self.write('noBlocking Request: {}'.format(second))

    """
    async def get(self, *args, **kwargs):
        second = await self.blocking_task(5)
        self.write('noBlocking Request: {}'.format(second))
        """

    @run_on_executor
    def blocking_task(self, second):
        """
        阻塞任务
        """
        time.sleep(second)
        return second

参考 https://blog.csdn.net/qq_34367804/article/details/75046718

　　https://www.cnblogs.com/zhaof/p/8490045.html

　　https://stackoverflow.com/questions/41594266/asyncio-with-django