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异步Web服务（二）

真正的 Tornado 异步非阻塞

前言：

　　其中 Tornado 的定义是 Web 框架和异步网络库，其中他具备有异步非阻塞能力，能解决他两个框架请求阻塞的问题，在需要并发能力时候就应该使用 Tornado。

　　但是在实际使用过程中很容易把 Tornado 使用成异步阻塞框架，这样对比其他两大框架没有任何优势而言，本文就如何实现真正的异步非阻塞记录。

笔记：

默认情况下tornado是单线程阻塞模式，如果阻塞所有请求都需要等待
tornado.web.asynchronous可以异步使用，得益于AsyncHTTPClient模块的配合使用，两者缺一不可
tornado.gen.coroutine严重依赖第三方库的使用，如果没有第三方库的支持则依然是阻塞模式
Tornado 提供了多种的异步编写形式：回调、Future、协程等，其中以协程模式最是简单和用的最多
Tornado 实现异步的多种方式：coroutine配合第三方库、启用多线程、使用celery等

1、使用 gen.coroutine 异步编程

在 Tornado 中两个装饰器：

tornado.web.asynchronous
tornado.gen.coroutine

① asynchronous 装饰器是让请求变成长连接的方式，必须手动调用 self.finish() 才会响应

class MainHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        # bad 
        self.write("Hello, world")

asynchronous 装饰器不会自动调用self.finish() ，如果没有没有指定结束，该长连接会一直保持直到 pending 状态

所以正确是使用方式是使用了 asynchronous 需要手动 finish

class MainHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        self.write("Hello, world")
        self.finish()

② coroutine 装饰器是指定改请求为协程模式，说明白点就是能使用 yield 配合 Tornado 编写异步程序。

Tronado 为协程实现了一套自己的协议，不能使用 Python 普通的生成器。

在使用协程模式编程之前要知道如何编写 Tornado 中的异步函数，Tornado 提供了多种的异步编写形式：回调、Future、协程等，其中以协程模式最是简单和用的最多。

编写一个基于协程的异步函数同样需要 coroutine 装饰器

@gen.coroutine
def sleep(self):
    yield gen.sleep(10)
    raise gen.Return([1, 2, 3, 4, 5])

这就是一个异步函数，Tornado 的协程异步函数有两个特点：

需要使用 coroutine 装饰器
返回值需要使用 raise gen.Return() 当做异常抛出

返回值作为异常抛出是因为在 Python 3.2 之前生成器是不允许有返回值的。

使用过 Python 生成器应该知道，想要启动生成器的话必须手动执行 next() 方法才行，所以这里的 coroutine 装饰器的其中一个作用就是在调用这个异步函数时候自动执行生成器。

使用 coroutine 方式有个很明显是缺点就是严重依赖第三方库的实现，如果库本身不支持 Tornado 的异步操作再怎么使用协程也是白搭依然会是阻塞的，放个例子感受一下

import time
import logging
import tornado.ioloop
import tornado.web
import tornado.options
from tornado import gen

tornado.options.parse_command_line()

class MainHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        self.write("Hello, world")
        self.finish()

class NoBlockingHnadler(tornado.web.RequestHandler):
    @gen.coroutine
    def get(self):
        yield gen.sleep(2)
        self.write('Blocking Request')


class BlockingHnadler(tornado.web.RequestHandler):
    @gen.coroutine
    def get(self):
        time.sleep(2)
        self.write('Blocking Request')

def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
        (r"/block", BlockingHnadler),
        (r"/noblock", NoBlockingHnadler),
    ], autoreload=True)

if __name__ == "__main__":
    app = make_app()
    app.listen(8001)
    tornado.ioloop.IOLoop.current().start()

当我们使用 yield gen.sleep(10) 这个异步的 sleep 时候，请求是不阻塞的。　　

[root@localhost ~]# siege http://192.168.0.2:8001/noblock -c100 -t10s
** SIEGE 3.0.8
** Preparing 100 concurrent users for battle.
The server is now under siege...
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.88 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.88 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.88 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.87 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.85 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.86 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.83 secs:      16 bytes ==> GET  /noblock
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /noblock

Lifting the server siege...      done.

Transactions:                 337 hits
Availability:              100.00 %
Elapsed time:                9.35 secs
Data transferred:            0.01 MB
Response time:                1.85 secs
Transaction rate:           36.04 trans/sec
Throughput:                0.00 MB/sec
Concurrency:               66.55
Successful transactions:         337
Failed transactions:               0
Longest transaction:            1.88
Shortest transaction:            1.83
 
FILE: /root/siege.log
You can disable this annoying message by editing
the .siegerc file in your home directory; change
the directive 'show-logfile' to false.

基准测试输出

测试结果：100并发，请求10s，共发送337次请求，平均每秒处理36.04次请求，很明显程序是非阻塞的

当使用 time.sleep(10) 时候请求时阻塞的。

[root@localhost ~]# siege http://192.168.0.2:8001/block -c100 -t10s
** SIEGE 3.0.8
** Preparing 100 concurrent users for battle.
The server is now under siege...
HTTP/1.1 200   1.84 secs:      16 bytes ==> GET  /block
HTTP/1.1 200   3.68 secs:      16 bytes ==> GET  /block
HTTP/1.1 200   5.51 secs:      16 bytes ==> GET  /block
HTTP/1.1 200   7.34 secs:      16 bytes ==> GET  /block
HTTP/1.1 200   9.17 secs:      16 bytes ==> GET  /block

Lifting the server siege...      done.

Transactions:                   5 hits
Availability:              100.00 %
Elapsed time:                9.23 secs
Data transferred:            0.00 MB
Response time:                5.51 secs
Transaction rate:            0.54 trans/sec
Throughput:                0.00 MB/sec
Concurrency:                2.98
Successful transactions:           5
Failed transactions:               0
Longest transaction:            9.17
Shortest transaction:            0.00
 
FILE: /root/siege.log
You can disable this annoying message by editing
the .siegerc file in your home directory; change
the directive 'show-logfile' to false.

基准测试输出

测试结果：100并发，请求10s，共发送5次请求，平均每秒处理0.5次请求，和time.sleep 2秒钟预先的效果是一致的。

gen.coroutine 在 Tornado 3.1 后会自动调用 self.finish() 结束请求，可以不使用 asynchronous 装饰器。

所以这种实现异步非阻塞的方式需要依赖大量的基于 Tornado 协议的异步库，使用上比较局限，好在还是有一些可以用的异步库

2、启用线程的处理异步编程

注：使用 gen.coroutine 装饰器编写异步函数，如果库本身不支持异步，那么响应任然是阻塞的。

在 Tornado 中有个装饰器能使用 ThreadPoolExecutor 来让阻塞过程编程非阻塞，其原理是在 Tornado 本身这个线程之外另外启动一个线程来执行阻塞的程序，从而让 Tornado 变得非阻塞，根本原理就是启用多个线程处理，处理后的线程并不会自动关闭

import time
import logging
import tornado.ioloop
import tornado.web
import tornado.options
from tornado import gen
from tornado.concurrent import run_on_executor
from concurrent.futures import ThreadPoolExecutor

tornado.options.parse_command_line()

class MainHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        self.write("Hello, world")
        self.finish()


class NoBlockingHnadler(tornado.web.RequestHandler):
    executor = ThreadPoolExecutor(4)              # 启动4个线程处理阻塞请求

    def sleep(self, second):
        time.sleep(second)
        return second

    @run_on_executor
    def get(self):
        second = yield self.sleep(5)
        self.write('noBlocking Request: {}'.format(second))

def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
        (r"/noblock", NoBlockingHnadler),
    ], autoreload=True)

if __name__ == "__main__":
    app = make_app()
    app.listen(8000)
    tornado.ioloop.IOLoop.current().start()

hreadPoolExecutor 是对标准库中的 threading 的高度封装，利用线程的方式让阻塞函数异步化，解决了很多库是不支持异步的问题。

但是与之而来的问题是，如果大量使用线程化的异步函数做一些高负载的活动，会导致该 Tornado 进程性能低下响应缓慢，这只是从一个问题到了另一个问题而已。

所以在处理一些小负载的工作，是能起到很好的效果，让 Tornado 异步非阻塞的跑起来。

但是明明知道这个函数中做的是高负载的工作，那么你应该采用另一种方式，使用 Tornado 结合 Celery 来实现异步非阻塞。

[root@localhost ~]# siege http://192.168.0.2:8001/noblock -c10 -t10s
** SIEGE 3.0.8
** Preparing 10 concurrent users for battle.
The server is now under siege...
HTTP/1.1 200   4.59 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   4.59 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   4.60 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   4.60 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   9.18 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   8.18 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   8.18 secs:      21 bytes ==> GET  /noblock
HTTP/1.1 200   8.18 secs:      21 bytes ==> GET  /noblock

Lifting the server siege...      done.

Transactions:                   8 hits
Availability:              100.00 %
Elapsed time:                9.42 secs
Data transferred:            0.00 MB
Response time:                6.51 secs
Transaction rate:            0.85 trans/sec
Throughput:                0.00 MB/sec
Concurrency:                5.53
Successful transactions:           8
Failed transactions:               0
Longest transaction:            9.18
Shortest transaction:            0.00
 
FILE: /root/siege.log
You can disable this annoying message by editing
the .siegerc file in your home directory; change
the directive 'show-logfile' to false.

基准测试输出

3、基于 Celery 的异步编程

Celery 是一个简单、灵活且可靠的，处理大量消息的分布式系统，专注于实时处理的任务队列，同时也支持任务调度。

Celery 并不是唯一选择，你可选择其他的任务队列来实现，但是 Celery 是 Python 所编写，能很快的上手，同时 Celery 提供了优雅的接口，易于与 Python Web 框架集成等特点。

与 Tornado 的配合可以使用 tornado-celery ，该包已经把 Celery 封装到 Tornado 中，可以直接使用（本节暂未测试，文章转载）

实际测试中，由于 tornado-celery 很久没有更新，导致请求会一直阻塞，不会返回

解决办法是：

把 celery 降级到 3.1 pip install celery==3.1
把 pika 降级到 0.9.14 pip install pika==0.9.14

Tornado服务端：

import time
import logging
import tornado.ioloop
import tornado.web
import tornado.options
from tornado import gen

import tcelery, tasks

tornado.options.parse_command_line()
tcelery.setup_nonblocking_producer()


class MainHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        self.write("Hello, world")
        self.finish()


class CeleryHandler(tornado.web.RequestHandler):
    @gen.coroutine
    def get(self):
        response = yield gen.Task(tasks.sleep.apply_async, args=[5])
        self.write('CeleryBlocking Request: {}'.format(response.result))


def make_app(): 
    return tornado.web.Application([
        (r"/", MainHandler),
        (r"/celery-block", CeleryHandler),
    ], autoreload=True)

if __name__ == "__main__":
    app = make_app()
    app.listen(8000)
    tornado.ioloop.IOLoop.current().start()

celery调度端：

import os
import time
from celery import Celery
from tornado import gen

celery = Celery("tasks", broker="amqp://")
celery.conf.CELERY_RESULT_BACKEND = os.environ.get('CELERY_RESULT_BACKEND', 'amqp')

@celery.task
def sleep(seconds):
    time.sleep(float(seconds))
    return seconds

if __name__ == "__main__":
    celery.start()

Celery 的 Worker 运行在另一个进程中，独立于 Tornado 进程，不会影响 Tornado 运行效率，在处理复杂任务时候比进程模式更有效率。

总结

推荐使用线程和 Celery 的模式进行异步编程，轻量级的放在线程中执行，复杂的放在 Celery 中执行。当然如果有异步库使用那最好不过了。目前没有找到最佳的异步非阻塞的编程模式，可用的异步库比较局限，只有经常用的，个人编写异步库比较困难。

Python 3 中可以把 Tornado 设置为 asyncio 的模式，这样就使用兼容 asyncio 模式的库，这应该是日后的方向。

Reference

《Tornado异步一》------跳转

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原文地址：https://www.cnblogs.com/lianzhilei/p/7821889.html