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）

　　

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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）

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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

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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