FastApi - 为什么服务器可以在同步模式下同时处理多个请求

Question

我运行以下程序：

import time
from datetime import datetime
from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def root():
    print(f"Started at {datetime.now()}")
    time.sleep(30)
    print(f"Executed at {datetime.now()}")
    return {"message": "Hello World"}

与独角兽。 然后我在短时间内在两个不同的选项卡中打开浏览器http://127.0.0.1:8000/。输出是这样的：

Started at 2023-04-01 23:40:53.668811
Started at 2023-04-01 23:41:16.992891
Executed at 2023-04-01 23:41:23.779460
INFO:     127.0.0.1:54310 - "GET / HTTP/1.1" 200 OK
Executed at 2023-04-01 23:41:47.248950
INFO:     127.0.0.1:54311 - "GET / HTTP/1.1" 200 OK

即使

root

不是异步的，为什么第二个 Start 在第一个 Executed 之前进行？