#现代异步IO编程指南

# 同步IO典型场景：卡死式文件处理
def process_file():
    # 1. CPU飞速跑预处理（几毫秒）
    do_some_preprocessing()
    
    # 2. 线程直接「挂起摆烂」等文件读完（可能几秒甚至更久！）
    with open('/path/to/user/data.txt', 'r') as f:
        data = f.read()
    
    # 3. 终于等到数据了，继续用CPU处理
    process_data(data)

# 伪代码示例：三层回调的地狱场景
def async_user_workflow():
    # 第一层：读用户ID文件
    start_async_read('/user/id.txt', 
        lambda user_id: 
            # 第二层：用ID查数据库
            start_async_db_query(user_id,
                lambda user_info:
                    # 第三层：发激活邮件
                    start_async_send_email(user_info['email'],
                        lambda status: print(f"邮件发送{status}!")
                    )
            )
    )

# Python asyncio协程写法（自然！清晰！）
import asyncio
import aiofiles  # 异步文件库，别用内置open

async def process_file():
    do_some_preprocessing()
    
    # await关键字：暂停当前协程，把控制权交还给事件循环，去做别的事
    async with aiofiles.open('/path/to/user/data.txt', 'r') as f:
        data = await f.read()
    
    process_data(data)

# 启动事件循环运行协程
asyncio.run(process_file())

import asyncio
import aiohttp

# 异步抓取网页的协程
async def fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.text()

async def main():
    # 批量创建异步任务（一次性取多个咖啡号！）
    tasks = [
        fetch('https://example.com'),
        fetch('https://example.org'),
        fetch('https://python.org')
    ]
    # 等待所有任务完成并收集结果
    results = await asyncio.gather(*tasks)
    print([len(res) for res in results])  # 输出每个网页的长度

asyncio.run(main())

import asyncio
import concurrent.futures

# 假设有个CPU密集型的图片压缩函数
def compress_big_image(img_path):
    # 假设这里有10秒的纯CPU计算
    ...

async def async_compress(img_path):
    loop = asyncio.get_running_loop()
    # 用默认线程池跑压缩，await不阻塞事件循环
    with concurrent.futures.ThreadPoolExecutor() as pool:
        await loop.run_in_executor(pool, compress_big_image, img_path)

import asyncio
import aiohttp

# 最多同时跑10个抓取任务
semaphore = asyncio.Semaphore(10)

async def limited_fetch(url):
    async with semaphore:  # 拿到信号量才能跑
        async with aiohttp.ClientSession() as session:
            async with session.get(url) as response:
                return await response.text()

import asyncio
import aiohttp

async def safe_fetch(url):
    try:
        # 超时时间设为3秒
        return await asyncio.wait_for(
            aiohttp.ClientSession().get(url).text(),
            timeout=3.0
        )
    except asyncio.TimeoutError:
        print(f"请求{url}超时！")
        return None
    except aiohttp.ClientError as e:
        print(f"请求{url}出错：{e}")
        return None