CODEWITHSUNDEEP
pythonasync-awaitpython-asyncio
d.golov
d.golov

Reputation: 61

Run blocking and unblocking tasks together with asyncio

I want to run blocking and unblocking tasks together asynchronously. Obviously that it is necessary to use run_in_executor method for blocking tasks from asyncio. Here is my sample code:

import asyncio
import concurrent.futures
import datetime
import time


def blocking():
    print("Enter to blocking()", datetime.datetime.now().time())
    time.sleep(2)
    print("Exited from blocking()", datetime.datetime.now().time())


async def waiter():
    print("Enter to waiter()", datetime.datetime.now().time())
    await asyncio.sleep(3)
    print("Exit from waiter()", datetime.datetime.now().time())


async def asynchronous(loop):
    print("Create tasks", datetime.datetime.now().time())
    task_1 = asyncio.create_task(waiter())

    executor = concurrent.futures.ThreadPoolExecutor(max_workers=3)
    task_2 = loop.run_in_executor(executor, blocking)

    tasks = [task_1, task_2]
    print("Tasks are created", datetime.datetime.now().time())
    await asyncio.wait(tasks)


if __name__ == "__main__":
    try:
        loop = asyncio.get_event_loop()
        loop.run_until_complete(asynchronous(loop))
    except (OSError) as exc:
        sys.exit('Exception: ' + str(exc))

Should I use the same event loop for blocking task in run_in_executor, or it is necessary to use another one? What should I change in my code to make it work asynchronously? Thanks

Upvotes: 3

Views: 3996

Answers (1)

Dunes
Dunes

Reputation: 40703

You must use the same loop. The loop delegates to the executor, which runs tasks is separate threads to the event loop. So you don't have to worry about your blocking tasks blocking the event loop. If you use a separate loop, your async functions from the event loop will not be able to await the results of blocking the functions run in the new loop.

The event loop manages this by creating a future to represent the executor task. It then runs the blocking task in one of the executors threads, and when the executor task returns the result of the future is set and control returned to awaiting function in the event loop (if any).

Upvotes: 4

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