Flask App 不能用一个浏览器处理超过 6 个请求

Question

I'm trying to make a camera server that shows multiple video process streaming results through Chrome browser using Flask, OpenCV.

Problem

It can handle 6 request at most with a single browser, but I need to process more than 60 camera requests.

Things I've tried.

At first I thought CPU couldn't handle more than 6 inputs but when I request it from another browser(chrome,Firefox,Edge etc), it can handle more simultaneously. So hardware seems not to be a problem. It's somehow limiting the requests per browser. So every single browser could handle only 6 at most.

If I request more than 6 it starts processing the first 6 request and wait till one of them finishes then starts next requests. I think it's because Flask app handles process synchronously.

I've tried with thread=True options with Flask, and with gunicorn for async process. but there is no difference.

gunicorn video:app -w 81 --threads 81 -k gevent --worker-connections 1000

I have no idea why it's limited to 6 requests only. is it possible to solve this?

Here is a sample code for the project.

video.py

import cv2
from flask import Flask,request, Response


def loadVideo(video):
    cap = cv2.VideoCapture(video)

    if cap.isOpened(): # try to get the first frame
        rval, frame = cap.read()
    else:
        rval = False


    IMG_SIZE = 640
    while(1):
        rval, image = cap.read()
        image = cv2.resize(image, (IMG_SIZE, IMG_SIZE))  

        if rval==True:
            orig = image.copy()
            frame = cv2.blur(image, (3,3))

            yield (b'--frame\r\n' b'Content-Type: image/jpeg\r\n\r\n'+ cv2.imencode('.jpg', frame)[1].tostring() + b'\r\n')

        elif rval==False:
                break
    end = time.time()
    cap.release()

app = Flask(__name__)

@app.route('/')
def hello():
    return "Server Established!"

@app.route('/detect',methods = ['GET'])
def detect():
    try:
        if request.method == 'GET':
            src = request.args.get('src')
            return Response(loadVideo(src),
        mimetype = "multipart/x-mixed-replace; boundary=frame")
    except Exception as e:
        return e


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0', port=3999, threaded=True)

Answer 1

It's browser's TCP connection is limited to 6 only.

reference

How to solve this

Firefox can be configured from within about:config, filter on network.http for various settings; network.http.max-persistent-connections-per-server is the one to change.

ref

But as it's browser's problem I may use different approach like creating same server with different port.

Answer 2

我建议使用uwsgi并根据工作人员/流程进行扩展。

uwsgi --http :9090 --wsgi-file foobar.py --master --processes 4 --threads 2