为什么 UVICORN/Starlette/FastAPI 在不使用“ASYNC”时会产生更多线程，而在使用“ASYNC”时却不会？

Question

好的，所以我正在对 进行比较研究using ASYNC vs without using ASYNC in FastAPI。然而，我得到了一些意想不到的结果，并且不明白为什么。

这是设置 1：

不使用异步的 API

import uvicorn
from fastapi import FastAPI
import PIL.Image as Image
import requests
from loguru import logger
import sys

log_format = "{level} {process}-{thread} {time} {name}:{line} - {message}"
logger.remove()
logger.add(sys.stderr, format=log_format, backtrace=True, diagnose=True)
logger.add("logs/" + "t_{time}.log", format=log_format, colorize=True, backtrace=True, diagnose=True)

Image.MAX_IMAGE_PIXELS = None

def get_the_image_from_net():
    a = requests.get("https://eoimages.gsfc.nasa.gov/images/imagerecords/73000/73751/world.topo.bathy.200407.3x21600x21600.A1.jpg")
    return True


app = FastAPI()

@app.get("/expectoPatronum")
def get_image_of_the_new_world():
    """
    Gets Image of the World
    """
    logger.info("Received request for getting Image of the world")
    image_bytes: bytes = get_the_image_from_net()
    logger.info("Image has been downloaded and processed as bytes array")
    return True

uvicorn.run(app, host="0.0.0.0", port=10009)

我如何调用 ABOVE API（通过使用多处理池）

import time
from multiprocessing import Pool, Manager
import requests


def test_function(index_iterator: int):
    start_time = time.time()
    response = requests.get("http://localhost:10009/expectoPatronum")
    print(f"response.content: {str(response.content)}")
    if response.status_code != 200:
        print("----------------------NOT 200")
        print(f"response.content: {str(response.content)}")
    end_time = time.time()
    elapsed_time = end_time - start_time


pool = Pool(5)
pool.map(test_function, [i for i in range(1,6)])
pool.close

这是调用 API 时从我的 API 端读取的日志：

INFO 9408-140671786272512 2022-07-13T01:32:37.498465+0530 __main__:27 - Received request for getting Image of the world
INFO 9408-140671777879808 2022-07-13T01:32:37.501623+0530 __main__:27 - Received request for getting Image of the world
INFO 9408-140671769487104 2022-07-13T01:32:37.504744+0530 __main__:27 - Received request for getting Image of the world
INFO 9408-140671760897792 2022-07-13T01:32:37.504929+0530 __main__:27 - Received request for getting Image of the world
INFO 9408-140671752242944 2022-07-13T01:32:37.505638+0530 __main__:27 - Received request for getting Image of the world
INFO 9408-140671786272512 2022-07-13T01:33:04.845982+0530 __main__:29 - Image has been downloaded and processed as bytes array
INFO 9408-140671777879808 2022-07-13T01:33:16.167435+0530 __main__:29 - Image has been downloaded and processed as bytes array
INFO 9408-140671769487104 2022-07-13T01:33:17.284000+0530 __main__:29 - Image has been downloaded and processed as bytes array
INFO 9408-140671752242944 2022-07-13T01:33:37.771086+0530 __main__:29 - Image has been downloaded and processed as bytes array
INFO 9408-140671760897792 2022-07-13T01:33:38.016435+0530 __main__:29 - Image has been downloaded and processed as bytes array

请注意：创建了多个线程（140671786272512、140671777879808 ..等等）

这是设置2：

使用异步的 API

import uvicorn
from fastapi import FastAPI, Response, APIRouter
import httpx
from loguru import logger
import sys

log_format = "{level} {process}-{thread} {time} {name}:{line} - {message}"
logger.remove()
logger.add(sys.stderr, format=log_format, backtrace=True, diagnose=True)
logger.add("logs/" + "t_{time}.log", format=log_format, colorize=True, backtrace=True, diagnose=True)

Image.MAX_IMAGE_PIXELS = None

async def get_the_image_from_net():
    async with httpx.AsyncClient() as client:
        a = await client.get('https://eoimages.gsfc.nasa.gov/images/imagerecords/73000/73751/world.topo.bathy.200407.3x21600x21600.A1.jpg')

    return True


app = FastAPI()

@app.get("/expectoPatronum")
async def get_image_of_the_new_world():
    """
    Gets Image of the World
    """
    logger.info("Received request for getting Image of the world")
    image_bytes = await get_the_image_from_net()
    logger.info("Image has been downloaded and processed as bytes array")
    return True

uvicorn.run(app, host="0.0.0.0", port=10008)

我如何调用 ABOVE API（通过使用多处理池（与上面的调用方法相同，但端口号不同）

import time
from multiprocessing import Pool, Manager
import requests


def test_function(index_iterator: int):
    start_time = time.time()
    response = requests.get("http://localhost:10008/expectoPatronum")
    print(f"response.content: {str(response.content)}")
    if response.status_code != 200:
        print("----------------------NOT 200")
        print(f"response.content: {str(response.content)}")
    end_time = time.time()
    elapsed_time = end_time - start_time


pool = Pool(5)
pool.map(test_function, [i for i in range(1,6)])
pool.close

这是调用 API 时从我的 API 端读取的日志：

INFO 9442-140295303571264 2022-07-13T01:36:26.762525+0530 __main__:43 - Received request for getting Image of the world
INFO 9442-140295303571264 2022-07-13T01:36:26.776561+0530 __main__:43 - Received request for getting Image of the world
INFO 9442-140295303571264 2022-07-13T01:36:26.783669+0530 __main__:43 - Received request for getting Image of the world
INFO 9442-140295303571264 2022-07-13T01:36:26.790367+0530 __main__:43 - Received request for getting Image of the world
INFO 9442-140295303571264 2022-07-13T01:36:26.796934+0530 __main__:43 - Received request for getting Image of the world
INFO 9442-140295303571264 2022-07-13T01:37:38.086156+0530 __main__:45 - Image has been downloaded and processed as bytes array
INFO 9442-140295303571264 2022-07-13T01:37:43.709798+0530 __main__:45 - Image has been downloaded and processed as bytes array
INFO 9442-140295303571264 2022-07-13T01:37:43.827959+0530 __main__:45 - Image has been downloaded and processed as bytes array
INFO 9442-140295303571264 2022-07-13T01:37:47.218717+0530 __main__:45 - Image has been downloaded and processed as bytes array
INFO 9442-140295303571264 2022-07-13T01:37:51.712889+0530 __main__:45 - Image has been downloaded and processed as bytes array

请注意：只有 1 个线程 (140295303571264)

现在我无法弄清楚：为什么在 SETUP-1 中，uvicorn 会产生超过 1 个线程？我认为它是一个单线程服务器，如何限制它在进程内仅生成 1 个线程？

这两种设置的时间结果确实令人沮丧。对于不使用异步的 SETUP-1，时间为：27.36284899711609,38.68544268608093,39.79848337173462,60.28416633605957,60.529775857925415

对于使用异步的 SETUP-2，时间为：71.32960891723633,76.95274710655212,77.07157778739929,80.4650149345398,84.95978450775146

Answer 1

当您使用普通def而不是声明路径操作函数时，它会在等待的async def外部运行，而不是直接调用（因为它会阻塞服务器）。threadpool您可以在 FastAPI 文档中阅读更多内容