I want to run a slow blocking method (actually from a 3rd-party library) in tornado's async GET request handler. Let the method be just:
def blocking_method(uid):
print("slow method started: ", uid)
time.sleep(10)
print("slow method done: ", uid)
return "slow method ({}) result".format(uid)
Moreover, I prefer running the tornado server in asyncio's event loop:
if __name__ == '__main__':
tornado.platform.asyncio.AsyncIOMainLoop().install()
loop = asyncio.get_event_loop()
loop.run_until_complete(make_app())
loop.run_forever()
I knew about @run_in_executor decorator but it's not suitable for me, since I use asyncio. To run a blocking method in async coroutine I should use run_in_executor method of asyncio.get_event_loop(). Here is an example how to do it, from this answer:
import asyncio
async def main():
loop = asyncio.get_event_loop()
executor = concurrent.futures.ThreadPoolExecutor(max_workers=4)
future1 = loop.run_in_executor(executor, blocking_method, 1)
future2 = loop.run_in_executor(executor, blocking_method, 2)
response1 = await future1
response2 = await future2
print(response1)
print(response2)
if __name__ == '__main__':
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
And it works perfectly, here is output from the previous script:
slow method started: 1
slow method started: 2
slow method done: 2
slow method done: 1
slow method (1) result
slow method (2) result
But if I use the very same technique in async def get method of tornado's RequestHandler:
class AsyncHandler(tornado.web.RequestHandler):
async def get(self):
# simple counter to distinguish requests
self.application.counter += 1
in_msg = "Registered request #{}, working...".format(self.application.counter)
print(in_msg)
loop = asyncio.get_event_loop()
future = loop.run_in_executor(self.application.executor,
blocking_method,
self.application.counter)
result = await future
out_msg = "Request processed, result: {}".format(result)
print(out_msg)
self.write(out_msg)
it blocks the method of the handler. In other words, If I open http://localhost:8888/ in several browser tabs (let it be two), then I expect two requests working in parallel, with the following output:
Registered request #1, working...
slow method started: 1
Registered request #2, working...
slow method started: 2
slow method done: 1
Request processed, result: slow method (1) result
slow method done: 2
Request processed, result: slow method (2) result
But the requests are executed consequently:
Registered request #1, working...
slow method started: 1
slow method done: 1
Request processed, result: slow method (1) result
Registered request #2, working...
slow method started: 2
slow method done: 2
Request processed, result: slow method (2) result
So, where am I wrong? What should I do to allow execution the request handler in parallel?
Here is full script that describes my problem:
import asyncio
import concurrent.futures
import time
import tornado.web
import tornado.platform
def blocking_method(uid):
print("slow method started: ", uid)
time.sleep(10)
print("slow method done: ", uid)
return "slow method ({}) result".format(uid)
class AsyncHandler(tornado.web.RequestHandler):
async def get(self):
# simple counter to distinguish requests
self.application.counter += 1
in_msg = "Registered request #{}, working...".format(self.application.counter)
print(in_msg)
loop = asyncio.get_event_loop()
future = loop.run_in_executor(self.application.executor,
blocking_method,
self.application.counter)
result = await future
out_msg = "Request processed, result: {}".format(result)
print(out_msg)
self.write(out_msg)
async def make_app():
handlers = [(r"/", AsyncHandler)]
app = tornado.web.Application(handlers, debug=True)
app.executor = concurrent.futures.ThreadPoolExecutor(max_workers=4)
app.counter = 0
app.listen(8888)
if __name__ == '__main__':
tornado.platform.asyncio.AsyncIOMainLoop().install()
loop = asyncio.get_event_loop()
loop.run_until_complete(make_app())
loop.run_forever()
