asyncio重构Flask接口，QPS从120飙到850的完整记录

# before.py - 同步版本（Flask 2.2.5, Gunicorn 20.1.0, 4 workers）
import requests
from flask import Flask, jsonify

app = Flask(__name__)

def fetch_stock(product_id):
    resp = requests.get(f'http://stock-svc:8001/stock/{product_id}', timeout=2)
    return resp.json()

def fetch_price(product_id):
    resp = requests.get(f'http://price-svc:8002/price/{product_id}', timeout=2)
    return resp.json()

def fetch_reviews(product_id):
    resp = requests.get(f'http://review-svc:8003/reviews/{product_id}', timeout=2)
    return resp.json()

@app.route('/api/v1/product/detail/')
def product_detail(product_id):
    stock = fetch_stock(product_id)
    price = fetch_price(product_id)
    reviews = fetch_reviews(product_id)
    return jsonify({"product_id": product_id, "stock": stock, "price": price, "reviews": reviews})

# after.py - 异步版本（核心代码）
import asyncio
import aiohttp
from flask import Flask, jsonify

app = Flask(__name__)

# 全局连接池：每worker最多100个连接，并发请求上限50
CONNECTOR = aiohttp.TCPConnector(
    limit=50,          # 每worker最大并发连接数
    limit_per_host=20, # 每个host最多20连接
    ttl_dns_cache=300, # DNS缓存5分钟
    enable_cleanup_closed=True  # 自动清理废弃连接
)
SESSION = aiohttp.ClientSession(
    connector=CONNECTOR,
    timeout=aiohttp.ClientTimeout(total=30, connect=2)
)

# 并发信号量：限制同时打向上游的请求数
SEMAPHORE = asyncio.Semaphore(10)

async def fetch_json(session, url, semaphore, timeout=2.5):
    """带信号量限流 + 独立超时的异步GET"""
    async with semaphore:
        try:
            async with session.get(url, timeout=aiohttp.ClientTimeout(total=timeout)) as resp:
                if resp.status == 200:
                    return await resp.json()
                else:
                    # 非200返回空dict，由调用方兜底
                    return {"error": f"HTTP {resp.status}"}
        except asyncio.TimeoutError:
            return {"error": "timeout"}
        except aiohttp.ClientError as e:
            return {"error": str(e)}

async def fetch_all(product_id):
    """并发获取三个上游数据"""
    base = "http://"
    tasks = [
        fetch_json(SESSION, f"{base}stock-svc:8001/stock/{product_id}"),
        fetch_json(SESSION, f"{base}price-svc:8002/price/{product_id}"),
        fetch_json(SESSION, f"{base}review-svc:8003/reviews/{product_id}")
    ]
    # gather返回顺序与tasks顺序一致，不是完成顺序
    return await asyncio.gather(*tasks, return_exceptions=False)

@app.route('/api/v1/product/detail/')
def product_detail(product_id):
    # Flask同步视图内部启动一次性事件循环
    stock, price, reviews = asyncio.run(fetch_all(product_id))
    return jsonify({
        "product_id": product_id,
        "stock": stock,
        "price": price,
        "reviews": reviews
    })

# gunicorn.conf.py
workers = 4          # 进程数，不宜超过CPU核数
worker_class = 'sync' # 保持同步worker，内部用asyncio.run
timeout = 30         # 请求超时30秒
keepalive = 5        # 长连接5秒
max_requests = 1000  # 每worker处理1000个请求后重启（防内存泄漏）