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()  
# 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
        """
        self.id = 5
        start_time = time.time()

        '''
        # 同步执行
        # results = [self.io_task1(self.id),
        # self.io_task2(self.id),
        # self.io_task2(self.id)]
        '''


        loop = asyncio.new_event_loop()  # 或 loop = asyncio.SelectorEventLoop()
        asyncio.set_event_loop(loop)
        self.loop = loop

        works = [
            asyncio.ensure_future(self.io_task3(5)),
            asyncio.ensure_future(self.io_task3(5)),
            asyncio.ensure_future(self.io_task3(5)),
            asyncio.ensure_future(self.io_task3(5)),
            asyncio.ensure_future(self.io_task3(5)),

        ]

        try:

            results = loop.run_until_complete(asyncio.gather(*works)) # 两种写法
            # 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):

        tasks = (
            self.make_future(self.io_task1, self.id),
            self.make_future(self.io_task2, self.id),
            self.make_future(self.io_task2, self.id),
            self.make_future(self.io_task1, self.id),
            self.make_future(self.io_task2, self.id),
            self.make_future(self.io_task2, self.id),
        )
        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

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

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

    async def io_task3(self, sleep_time):
        # await asyncio.sleep(sleep_time)
        s = await self.do(sleep_time)
        return s

    async def do(self, sleep_time):
        await asyncio.sleep(sleep_time)
        return 66

　

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, self.io_task2, self.io_task1, self.io_task2, self.io_task2)
        with ThreadPoolExecutor(len(tasks)) as executor:
            for task in tasks:
                future = executor.submit(task, 5)
                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):

        results = []
        for future in future_set:
            results.append(future.result())
        return results

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

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