Flask+gevent 异步 WEB 架构

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异步 WEB 架构的特点：

gevent 为 Python 提供了比较完善的协程支持，其基于 greenlet 实现协程。

当 greenlet 遇到如网络访问、磁盘 IO 等操作时，就将自动切换至其他的 greenlet，待操作完成后，在适合的时间点回切 greenlet 继续执行。由于网络访问、磁盘 IO 等操作耗时较长，且实际 CPU 使用率较低（大部分工作由 DMA 等设备完成）。所以倘若非异步，涉及以上操作并发将以顺序执行， CPU 长期处于空闲状态。而异步模式将能实现并发程序间的切换，从而保证 CPU 有较高的利用率，而不是等待如网络访问、磁盘 IO 等操作。 

注意：gevent 的使用并不能减少实际 CPU 的使用量，所以若程序的执行过程消耗的全为 CPU 资源，则其异步也是毫无意义的。

 

Flask+gevent 的最小程序实例：

最小程序实例如下。

from gevent import monkey

monkey.patch_all()

from flask import Flask

from gevent import pywsgi

                                       

app = Flask(__name__)

                                       

@app.route('/')

def index():

    return 'Hello World'

                                   

server = pywsgi.WSGIServer(('127.0.0.1', 5000), app)

server.serve_forever()

注意：为实现 Flask 与 gevent 的结合，需在程序开头引入 monkey patch。monkey patch 将以闭包的形式修改可以实现异步的标准库，从而实现异步。

注意：需使用支持 gevent 的 WSGI，例如：gevent.pywsgi、gunicorn 等。