I am using FastApi and have one endpoint.
I have two long running functions which I want to run concurrently using asyncio
Therefore, I have created two functions:
async def get_data_one():
return 'done_one'
async def get_data_two():
return 'done_two'
These functions get data from external webservices.
I want to execute them concurrently so I have created a another function that does it:
async def get_data():
loop = asyncio.get_event_loop()
asyncio.set_event_loop(loop)
task_1 = loop.create_task(get_data_one)
task_2 = loop.create_task(get_data_two)
tasks = (task_1, task_2)
first, second = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()
# I will then perform cpu intensive computation on the results
# for now - assume i am just concatenating the results
return first + second
Finally, I have my endpoint:
@app.post("/result")
async def get_result_async():
r = await get_data()
return r
Even this simple example breaks and I get the following exception when I hit the endpoint:
RuntimeError: This event loop is already running ERROR: _GatheringFuture exception was never retrieved future: <_GatheringFuture finished exception=AttributeError("'function' object has no attribute 'send'",)> AttributeError: 'function' object has no attribute 'send'
This is a simplified code but I would really appreciate how to do it the right way.
When in FastAPI context, you never need to run an asyncio loop; it's always running for as long as your server process lives.
Therefore, all you need is
import asyncio
async def get_data_one():
return "done_one"
async def get_data_two():
return "done_two"
async def get_data():
a, b = await asyncio.gather(get_data_one(), get_data_two())
return a + b
#@route decorator here...
async def get_result_async():
r = await get_data()
print("Get_data said:", r)
return r
# (this is approximately what is done under the hood,
# presented here to make this a self-contained example)
asyncio.run(get_result_async())
It's as simple as:
async def get_data():
first, second = await asyncio.gather(
get_data_one(),
get_data_two(),
)
return first + second