Tornado异步

星哥玩云

发布于 2022-09-14 19:14:03

7480

发布于 2022-09-14 19:14:03

文章被收录于专栏：开源部署开源部署

一、说明

因为epoll主要是用来解决网络IO的并发问题，所以Tornado的异步编程也主要体现在网络IO的异步上，即异步Web请求

二、Tornado异步处理方法与类

tornado.httpclient.AsyncHTTPClient Tornado提供了一个异步Web请求客户端tornado.httpclient.AsyncHTTPClient用来进行异步Web请求
fetch(request, callback=None) 用于执行一个web请求request，并异步返回一个tornado.httpclient.HTTPResponse响应 request可以是一个url，也可以是一个tornado.httpclient.HTTPRequest对象。如果是url，fetch会自己构造一个HTTPRequest对象
HTTPRequest HTTP请求类，HTTPRequest的构造函数可以接收众多构造参数，最常用的如下
- url(string) – 要访问的url，此参数必传，除此之外均为可选参数
- method (string) – HTTP访问方式，如“GET”或“POST”，默认为GET方式
- headers (HTTPHeaders or dict) – 附加的HTTP协议头
- body – HTTP请求的请求体
HTTPResponse HTTP响应类，其常用属性如下：
- code: HTTP状态码，如 200 或 404
- reason: 状态码描述信息
- body: 响应体字符串
- error: 异常（可有可无）

三、tornado.web.asynchronous 回调异步

说明

此装饰器用于回调形式的异步方法，并且应该仅用于HTTP的方法上（如get、post等）

此装饰器不会让被装饰的方法变为异步，而只是告诉框架被装饰的方法是异步的，当方法返回时响应尚未完成。只有在request handler调用了finish方法后，才会结束本次请求处理，发送响应

不带此装饰器的请求在get、post等方法返回时自动完成结束请求处理

协程异步

<span class="hljs-keyword">import</span> tornado.web
<span class="hljs-keyword">import</span> tornado.httpclient


<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IndexHandler</span><span class="hljs-params">(tornado.web.RequestHandler)</span>:</span>
<span class="hljs-meta">    @tornado.gen.coroutine</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get</span><span class="hljs-params">(self)</span>:</span>
        http = tornado.httpclient.AsyncHTTPClient()
        response = <span class="hljs-keyword">yield</span> http.fetch(<span class="hljs-string">"http://www.baidu.com"</span>)
        <span class="hljs-keyword">if</span> response.error:
            self.send_error(<span class="hljs-number">500</span>)
        <span class="hljs-keyword">else</span>:
            print(response.body.decode(<span class="hljs-string">'utf-8'</span>))
            f = open(<span class="hljs-string">'baidu.html'</span>, <span class="hljs-string">'wb'</span>)
            f.write(response.body)
            f.close()
            self.write(<span class="hljs-string">"操作成功"</span>)

也可以将异步Web请求单独出来

<span class="hljs-keyword">import</span> tornado.web
<span class="hljs-keyword">import</span> tornado.httpclient


<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IndexHandler</span><span class="hljs-params">(tornado.web.RequestHandler)</span>:</span>
<span class="hljs-meta">    @tornado.gen.coroutine</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get</span><span class="hljs-params">(self)</span>:</span>
        rep = <span class="hljs-keyword">yield</span> self.get_body_info(<span class="hljs-string">"http://www.baidu.com"</span>)
        <span class="hljs-keyword">if</span> rep[<span class="hljs-string">'ret'</span>] == <span class="hljs-number">1</span>:
            print(rep[<span class="hljs-string">'body'</span>])
        self.write(<span class="hljs-string">"成功"</span>)

<span class="hljs-meta">    @tornado.gen.coroutine</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_body_info</span><span class="hljs-params">(self, url)</span>:</span>
        rep = {<span class="hljs-string">"ret"</span>:<span class="hljs-number">1</span>}
        http = tornado.httpclient.AsyncHTTPClient()
        response = <span class="hljs-keyword">yield</span> http.fetch(url)
        <span class="hljs-keyword">if</span> response.error:
            rep = {<span class="hljs-string">"ret"</span>:<span class="hljs-number">0</span>}
        <span class="hljs-keyword">else</span>:
            rep[<span class="hljs-string">'body'</span>] = response.body.decode(<span class="hljs-string">'utf-8'</span>)
            f = open(<span class="hljs-string">'baidu.html'</span>, <span class="hljs-string">'wb'</span>)
            f.write(response.body)
            f.close()
            self.write(<span class="hljs-string">"操作成功"</span>)
        <span class="hljs-keyword">raise</span> tornado.gen.Return(rep)  <span class="hljs-comment"># 此处需要注意</span>

代码中我们需要注意的地方是get_body_info返回值的方式，在python 2中，使用了yield的生成器可以使用不返回任何值的return，但不能return value，因此Tornado为我们封装了用于在生成器中返回值的特殊异常tornado.gen.Return，并用raise来返回此返回值

并行协程

Tornado可以同时执行多个异步，并发的异步可以使用列表或字典

<span class="hljs-keyword">import</span> tornado.web
<span class="hljs-keyword">import</span> tornado.httpclient


<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IndexHandler</span><span class="hljs-params">(tornado.web.RequestHandler)</span>:</span>
<span class="hljs-meta">    @tornado.gen.coroutine</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get</span><span class="hljs-params">(self)</span>:</span>
        self.urls = [<span class="hljs-string">"http://www.baidu.com"</span>,<span class="hljs-string">"http://www.webometrics.info/en/Asia"</span>]
        rep1, rep2 = <span class="hljs-keyword">yield</span> [self.get_url_info(self.urls[<span class="hljs-number">0</span>]), self.get_url_info(self.urls[<span class="hljs-number">1</span>])]
        self.write_response(self.urls[<span class="hljs-number">0</span>], rep1, <span class="hljs-string">'baidu.html'</span>)
        self.write_response(self.urls[<span class="hljs-number">1</span>], rep2, <span class="hljs-string">'Asia.html'</span>)

    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_response</span><span class="hljs-params">(self, url, response, name)</span>:</span>
        self.write(url)
        self.write(<span class="hljs-string">":&lt;br/&gt;"</span>)
        <span class="hljs-keyword">if</span> <span class="hljs-number">1</span> == response[<span class="hljs-string">"ret"</span>]:
            f = open(name, <span class="hljs-string">'wb'</span>)
            f.write(response[<span class="hljs-string">'body'</span>])
            f.close()
            self.write(<span class="hljs-string">"操作成功"</span>)
        <span class="hljs-keyword">else</span>:
            self.write(<span class="hljs-string">"获取数据失败&lt;br/&gt;"</span>)

<span class="hljs-meta">    @tornado.gen.coroutine</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_url_info</span><span class="hljs-params">(self, url)</span>:</span>
        rep = {<span class="hljs-string">"ret"</span>: <span class="hljs-number">1</span>}
        http = tornado.httpclient.AsyncHTTPClient()
        response = <span class="hljs-keyword">yield</span> http.fetch(url)
        <span class="hljs-keyword">if</span> response.error:
            rep = {<span class="hljs-string">"ret"</span>: <span class="hljs-number">0</span>}
        <span class="hljs-keyword">else</span>:
            rep[<span class="hljs-string">'body'</span>] = response.body
        <span class="hljs-keyword">raise</span> tornado.gen.Return(rep)  <span class="hljs-comment"># 此处需要注意</span>