Coroutine

Before learning coroutine, let see the history of Process and Thread. Coroutine is better than them in most cases.

Coroutine uses event loop, controls the timing of each tasks.

To learn more about event loop, check nginx.

Coroutine needs async I/O.

import time
import asyncio

async def worker_1():
    print('worker_1 start')
    await asyncio.sleep(1)
    print('worker_1 done')

async def worker_2():
    print('worker_2 start')
    await asyncio.sleep(2)
    print('worker_2 done')

async def main():
    print('before await')
    await worker_1()
    print('awaited worker_1')
    await worker_2()
    print('awaited worker_2')

%time asyncio.run(main())

########## output ##########

before await
worker_1 start
worker_1 done
awaited worker_1
worker_2 start
worker_2 done
awaited worker_2
Wall time: 3 s

In this example, all the function are async. However, we use async / await to make them run sync.

To run them in coroutine, we need to create task using asyncio.create_task.


import asyncio

async def worker_1():
    print('worker_1 start')
    await asyncio.sleep(1)
    print('worker_1 done')

async def worker_2():
    print('worker_2 start')
    await asyncio.sleep(2)
    print('worker_2 done')

async def main():
    task1 = asyncio.create_task(worker_1())
    task2 = asyncio.create_task(worker_2())
    print('before await')
    await task1
    print('awaited worker_1')
    await task2
    print('awaited worker_2')

%time asyncio.run(main())

########## output ##########

before await
worker_1 start
worker_2 start
worker_1 done
awaited worker_1
worker_2 done
awaited worker_2
Wall time: 2.01 s

In this exemple, we did following thing:

run asyncio.run(main()): start event loop
create 2 tasks
run await task1: leave the main, enter worker_1
run await asyncio.sleep(1) in worker_1: leave worker_1, enter worker_2
run await asyncio.sleep(2) in worker_2: leave worker_2, enter worker_1 6.work_1 finished: leave worker_1, enter main
run print('awaited worker_1'): leave main, enter worker_2
worker_2 finished: leave worker_2, enter main

As we can see, main, worker_1, worker_2 works together. One of them sleeps, we run one of the rest.

There is another way to run tasks:

await asyncio.gather(task_1, task_2)

It's simpler.