Running repetitive coroutines (Providing a list of arguments for the coroutine) in limited number of coroutines running at a time.

asyncio_dispatching_works.py

import asyncio
import random
from uuid import uuid4

MAX_WORKERS = 20

# The semaphore for synchronization
sema = asyncio.Semaphore(MAX_WORKERS)
# Storing currently running tasks
tasks = set()
# Gathering results
results = list()


async def gather(id, coro, args):
    """Await the coroutine and gather the result."""
    result = await coro(args)
    results.append(result)
    tasks.remove(id)
    sema.release()


async def dispatching(coro, args_list):
    """Dispatching list of arguments to a coroutine."""
    for args in args_list:
        print('Wait for semaphore...')
        await sema.acquire()
        id = uuid4()
        print('Got it! Dispatching job. ID: {}'.format(id))
        tasks.add(id)
        asyncio.ensure_future(gather(id, coro, args))
    while tasks:
        await asyncio.sleep(1)


async def work(args):
    """A fake working function mimicking a function that requires some time to run."""
    # Randomly sleep between 1 to 3 seconds
    await asyncio.sleep(1 + (random.random() * 2))
    return args


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(dispatching(work, range(100)))
    print('All tasks done.')
    results.sort()
    print(results)
    assert results == list(range(100))