# 项目文件：demos/semaphore_limit.py
# 三个任务只允许两个同时进入等待操作；退出 async with 自动归还名额。
import asyncio


async def main():
    semaphore = asyncio.Semaphore(2)
    active = peak = 0

    async def work(value):
        nonlocal active, peak
        async with semaphore:
            active += 1
            peak = max(peak, active)
            try:
                await asyncio.sleep(0)
                return value * 2
            finally:
                active -= 1

    async with asyncio.TaskGroup() as group:
        tasks = [group.create_task(work(value)) for value in [20, 35, 45]]
    print([task.result() for task in tasks], "最多同时进入", peak)


if __name__ == "__main__":
    asyncio.run(main())

# 项目文件：demos/async_queue.py
# 两个工作任务处理五项输入，队列至多保存两项尚未取出的数据。
import asyncio


async def consume(queue, results):
    while True:
        item = await queue.get()
        try:
            if item is None:
                return
            await asyncio.sleep(0)
            results.append((item, item * item))
        finally:
            queue.task_done()


async def main():
    queue, results = asyncio.Queue(maxsize=2), []
    async with asyncio.TaskGroup() as group:
        workers = [group.create_task(consume(queue, results)) for _ in range(2)]
        for value in range(5):
            await queue.put(value)
        for _ in workers:
            await queue.put(None)
        await queue.join()
    print([result for value, result in sorted(results)])


if __name__ == "__main__":
    asyncio.run(main())