Demo of yield-dependent behavior when a coroutine blocks the event loop.

block_event_loop.py

# Demo of yield-dependent behavior when a coroutine blocks the event loop.
#
# Vary the number of calls to asyncio.sleep(0.0) in either block, and behavior will change greatly.
#
# (4 in top block, 9 in bottom block)
# 0 3.0027458667755127
# 1 2.0022785663604736
# 2 8.320808410644531e-05
# 3 4.38690185546875e-05
# 4 3.838539123535156e-05
#
# (4 in top block, 18 in bottom block)
# 0 5.005687952041626
# 1 0.00013685226440429688
# 2 7.081031799316406e-05
# 3 7.128715515136719e-05
# 4 6.723403930664062e-05
#
# (4 in top block, 2 in bottom block)
# 0 1.0011606216430664
# 1 1.0011751651763916
# 2 1.0011844635009766
# 3 1.0011827945709229
# 4 1.0010712146759033

import asyncio
import time


async def f():
    for i in range(5):
        yield i
        time.sleep(1)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)


async def main():
    pre = time.time()

    q = asyncio.Queue()

    async def drive_generator():
        async for x in f():
            await q.put(x)

    asyncio.create_task(drive_generator())

    for _ in range(5):
        x = await q.get()
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        await asyncio.sleep(0.0)
        cur = time.time()
        print(x, cur - pre)
        pre = cur


asyncio.run(main())