tornado框架学习
tornado是一个非阻塞的web服务器框架，每秒可以处理上千个客户端连接（都是在一个线程中，不需要为每个客户端创建线程，资源消耗少），适合用来开发web长连接应用，如long polling（轮询），WebSocket协议等（http协议为短连接）。
1，简单使用
#coding:utf-8 import tornado.ioloop import tornado.web from controllers.login import LoginHandler class HomeHandler(tornado.web.RequestHandler): #处理'/index'的请求，若是get请求，即调用get方法 def get(self, *args, **kwargs): self.write('home page') settings = { 'template_path':'views' #配置html文件的目录，即html文件存储在views文件夹路径下
'static_path':'statics', # 配置静态url路径，用来存放css，js文件等
} app = tornado.web.Application([ (r'/index',HomeHandler), # 路由分发器，HomeHandler为该路由的处理类 (r'/login',LoginHandler), ],**settings) #加入配置文件 if __name__ == '__main__': app.listen(8080) #监听端口号 tornado.ioloop.IOLoop.instance().start() #开启服务器
上面代码即建立起一个web服务器，在浏览器输入127.0.0.1:8080/index， 就会得到包含‘home page’字符的网页。另外，上面将所有代码写在了有个代码文件中，也可以利用MVC的设计方式分开来写，如下面的的架构和代码：将处理‘/login’请求的类LoginHandler放在controllers文件夹下，将视图文件login.html放在views文件夹下（需要配置‘template_path’）,而models文件夹下可以存放和数据库处理相关的代码，statics中存放静态文件，如css，js等，需要配置路径：'static_path':'statics'。
#coding:utf-8 import tornado.ioloop import tornado.web from controllers.login import LoginHandler class HomeHandler(tornado.web.RequestHandler): #处理'/index'的请求，若是get请求，即调用get方法 def get(self, *args, **kwargs): self.write('home page') settings = { 'template_path':'views' #配置html文件的目录，即html文件存储在views文件夹路径下 } app = tornado.web.Application([ (r'/index',HomeHandler), # 路由分发器，HomeHandler为该路由的处理类 (r'/login',LoginHandler), ],**settings) #加入配置文件 if __name__ == '__main__': app.listen(8080) #监听端口号 tornado.ioloop.IOLoop.instance().start() #开启服务器
#coding:utf-8 import tornado class LoginHandler(tornado.web.RequestHandler): def get(self): self.render('login.html')
2.模板
tornado也支持和django类似的模板引擎语言，表达语句用{{ item[0] }}，控制语句{% if %}。。。。 {% end %}，tornado支持if，while，for，try等，但都是以{% end %}结束，不同于django。tornado也支持模板继承，{% extends 'index.html' %} 和 {% block body%}。。。。{% end %}（也是以{% end %}结尾）。
http://www.tornadoweb.org/en/stable/template.html
https://github.com/tornadoweb/tornado/blob/master/tornado/template.py
Tornado默认提供的这些功能其实本质上就是 UIMethod 和 UIModule，我们也可以自定义从而实现类似于Django的simple_tag的功能：
定义：
#coding:utf-8 from tornado import escape def mytag(request,value): #默认会传递一个参数（HomeHandler object），前端需要传值时需要再加一个参数value #print request return '<h3>我是tag%s</h3>'%value # 前端默认会对和h3进行转义，需要不转义时前端使用raw 关键字
#coding:utf-8 from tornado import escape from tornado.web import UIModule class CustomUIModule(UIModule): def embedded_javascript(self): # render执行时，会在html文件中加入javascript return "console.log(123);" def javascript_files(self): ## render执行时，会在html文件中引入javascript文件 return 'commons.js' def embedded_css(self): return '.but{color:red}' def css_files(self): return 'commons.css' def render(self, value): v = '<h3>我是一个UIModule tag%s</h3>'%value #默认不转义</h3>，前端显示我是一个UIModule tag3 #v = escape.xhtml_escape(v) # 转义</h3>，前端显示<h3>我是一个UIModule tag3</h3> return v
设置：
#coding:utf-8 import tornado.ioloop import tornado.web from controllers.login import LoginHandler import uimethods import uimodules class HomeHandler(tornado.web.RequestHandler): #处理'/index'的请求，若是get请求，即调用get方法 def get(self, *args, **kwargs): #self.write('home page') self.render('home.html') settings = { 'template_path':'views', #配置html文件的目录，即html文件存储在views文件夹路径下 'static_path':'statics', # 配置静态url路径，用来存放css，js文件等 'ui_methods':uimethods, 'ui_modules':uimodules, } app = tornado.web.Application([ (r'/index',HomeHandler), # 路由分发器，HomeHandler为该路由的处理类 (r'/login',LoginHandler), ],**settings) #加入配置文件 if __name__ == '__main__': app.listen(8080) #监听端口号 tornado.ioloop.IOLoop.instance().start() #开启服务器
使用
<!DOCTYPE html> <html lang="zh-CN"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>主页</title> </head> <body> {{ mytag(1)}} {% raw mytag(2) %} {% module CustomUIModule(3) %} <p class="but">验证css代码</p> <p class="but2">验证css文件</p> </body> </html>
网页效果：
注意的是在UIModule中可以向html文件中加入css，js代码及文件。
3，静态文件设置
app配置
settings = { 'static_path':'statics', # 配置静态url路径，用来存放css，js文件等 'static_url_prefix':'/statics/', #href中的起始路径 }
html
<link rel="stylesheet" href="/statics/commons.css"> #statics目录下的commons.css
4. 跨站请求伪造（cross site request forgery）
https://www.tornadoweb.org/en/stable/guide/security.html?highlight=ajax
app设置
settings = { "xsrf_cookies": True, }
表单使用
<form action="/new_message" method="post"> {% module xsrf_form_html() %} <input type="text" name="message"/> <input type="submit" value="Post"/> </form>
ajax使用:
本质上去cookie中获取_xsrf，再携带_xsrf值提交数据（document.cookie：）
function getCookie(name) { var r = document.cookie.match("\\b" + name + "=([^;]*)\\b"); return r ? r[1] : undefined; } jQuery.postJSON = function(url, args, callback) { args._xsrf = getCookie("_xsrf"); $.ajax({url: url, data: $.param(args), dataType: "text", type: "POST", success: function(response) { callback(eval("(" + response + ")")); }}); };
function getCookie(name) { var r = document.cookie.match("\\b" + name + "=([^;]*)\\b"); return r ? r[1] : undefined; } $('#send').click(function () { var _xsrf = getCookie('_xsrf') var msg = $('#msg').val(); $.ajax({ url:'/login', data:{ '_xsrf':_xsrf, 'msg':msg, }, type:"POST", success:function (callback) { console.log(callback); } }); });
5，ajax上传文件
不用ajax前端
<!DOCTYPE html> <html lang="zh-CN"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>Title</title> </head> <body> <div> <input type="file" id="img"/> <button onclick="upload();">上传</button> </div> </body> <script src="/statics/jquery-3.3.1.min.js"></script> <script> function upload() { var file = document.getElementById('img').files[0]; var form = new FormData(); //form.append('k1','v1'); form.append('fileobj',file); var request = new XMLHttpRequest(); request.open('post','/index',true); request.send(form); } </script> </html>
ajax前端
<!DOCTYPE html> <html lang="zh-CN"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>Title</title> </head> <body> <div> <input type="file" id="img"/> <button onclick="upload();">上传</button> </div> </body> <script src="/statics/jquery-3.3.1.min.js"></script> <script> function upload() { var file = document.getElementById('img').files[0]; var form = new FormData(); //form.append('k1','v1'); form.append('fileobj',file); //var request = new XMLHttpRequest(); //request.open('post','/index',true); //request.send(form); $.ajax({ url:'/index', type:'POST', data:form, processData:false, //让jquery不处理数据 contentType:false, // 让jquery不设置contentType success:function (callback) { console.log(callback); } }); } </script> </html>
后端
#coding:utf-8 import tornado.web class HomeHandler(tornado.web.RequestHandler): def get(self): self.render('LoadFile.html') def post(self): fileobjs = self.request.files['fileobj'] #fileobjs为一个列表 for file in fileobjs: file_name = file['filename'] #fileobjs[0]['filename'] print type(file_name) with open(file_name,'wb') as f: f.write(file['body']) settings={ 'template_path':'views', 'static_path':'statics', 'static_url_prefix':'/statics/', } application = tornado.web.Application([ (r'/index', HomeHandler) ],**settings) if __name__ == '__main__': application.listen(8888) tornado.ioloop.IOLoop.instance().start()
6，cookie
获取和设置cookie(不加密)：
get_cookie(self, name, default=None): 未取到时返回默认值
def set_cookie(self, name, value, domain=None, expires=None, path="/",expires_days=None, **kwargs):
class HomeHandler(tornado.web.RequestHandler): #处理'/index'的请求，若是get请求，即调用get方法 def get(self, *args, **kwargs): #self.write('home page') if self.get_cookie(name='id'): print self.get_cookie(name='id') else: self.set_cookie(name='id',value='asdfg') self.render('home.html')
获取和设置cookie(加密)：需要在配置中设置秘钥：'cookie_secret'
get_secure_cookie(self, name, value=None, max_age_days=31, min_version=None): 对于加密后的cookie，get_secure_cookie拿到的为解密后的cookie值，get_cookie拿到的为加密的值
set_secure_cookie(self, name, value, expires_days=30, version=None, **kwargs):
class HomeHandler(tornado.web.RequestHandler): #处理'/index'的请求，若是get请求，即调用get方法 def get(self, *args, **kwargs): if self.get_secure_cookie(name='secret_id'): print self.get_secure_cookie(name='secret_id') ##前端显示的为加密后，拿到的为明文 else: self.set_secure_cookie(name='secret_id',value='message') self.render('home.html') settings = { 'template_path':'views', #配置html文件的目录，即html文件存储在views文件夹路径下 'static_path':'statics', # 配置静态url路径，用来存放css，js文件等 'static_url_prefix':'/statics/', 'ui_methods':uimethods, 'ui_modules':uimodules, 'xsrf_cookies':True, 'cookie_secret':'asdfghhj', }
cookie两个版本的加密算法：
def _create_signature_v1(secret, *parts): hash = hmac.new(utf8(secret), digestmod=hashlib.sha1) for part in parts: hash.update(utf8(part)) return utf8(hash.hexdigest()) def _create_signature_v2(secret, s): hash = hmac.new(utf8(secret), digestmod=hashlib.sha256) hash.update(utf8(s)) return utf8(hash.hexdigest())
#加密 def create_signed_value(secret, name, value, version=None, clock=None, key_version=None): if version is None: version = DEFAULT_SIGNED_VALUE_VERSION if clock is None: clock = time.time timestamp = utf8(str(int(clock()))) value = base64.b64encode(utf8(value)) if version == 1: signature = _create_signature_v1(secret, name, value, timestamp) value = b"|".join([value, timestamp, signature]) return value elif version == 2: # The v2 format consists of a version number and a series of # length-prefixed fields "%d:%s", the last of which is a # signature, all separated by pipes. All numbers are in # decimal format with no leading zeros. The signature is an # HMAC-SHA256 of the whole string up to that point, including # the final pipe. # # The fields are: # - format version (i.e. 2; no length prefix) # - key version (integer, default is 0) # - timestamp (integer seconds since epoch) # - name (not encoded; assumed to be ~alphanumeric) # - value (base64-encoded) # - signature (hex-encoded; no length prefix) def format_field(s): return utf8("%d:" % len(s)) + utf8(s) to_sign = b"|".join([ b"2", format_field(str(key_version or 0)), format_field(timestamp), format_field(name), format_field(value), b'']) if isinstance(secret, dict): assert key_version is not None, 'Key version must be set when sign key dict is used' assert version >= 2, 'Version must be at least 2 for key version support' secret = secret[key_version] signature = _create_signature_v2(secret, to_sign) return to_sign + signature else: raise ValueError("Unsupported version %d" % version) #解密： def _decode_signed_value_v1(secret, name, value, max_age_days, clock): parts = utf8(value).split(b"|") if len(parts) != 3: return None signature = _create_signature_v1(secret, name, parts[0], parts[1]) if not _time_independent_equals(parts[2], signature): gen_log.warning("Invalid cookie signature %r", value) return None timestamp = int(parts[1]) if timestamp < clock() - max_age_days * 86400: gen_log.warning("Expired cookie %r", value) return None if timestamp > clock() + 31 * 86400: # _cookie_signature does not hash a delimiter between the # parts of the cookie, so an attacker could transfer trailing # digits from the payload to the timestamp without altering the # signature. For backwards compatibility, sanity-check timestamp # here instead of modifying _cookie_signature. gen_log.warning("Cookie timestamp in future; possible tampering %r", value) return None if parts[1].startswith(b"0"): gen_log.warning("Tampered cookie %r", value) return None try: return base64.b64decode(parts[0]) except Exception: return None def _decode_fields_v2(value): def _consume_field(s): length, _, rest = s.partition(b':') n = int(length) field_value = rest[:n] # In python 3, indexing bytes returns small integers; we must # use a slice to get a byte string as in python 2. if rest[n:n + 1] != b'|': raise ValueError("malformed v2 signed value field") rest = rest[n + 1:] return field_value, rest rest = value[2:] # remove version number key_version, rest = _consume_field(rest) timestamp, rest = _consume_field(rest) name_field, rest = _consume_field(rest) value_field, passed_sig = _consume_field(rest) return int(key_version), timestamp, name_field, value_field, passed_sig def _decode_signed_value_v2(secret, name, value, max_age_days, clock): try: key_version, timestamp, name_field, value_field, passed_sig = _decode_fields_v2(value) except ValueError: return None signed_string = value[:-len(passed_sig)] if isinstance(secret, dict): try: secret = secret[key_version] except KeyError: return None expected_sig = _create_signature_v2(secret, signed_string) if not _time_independent_equals(passed_sig, expected_sig): return None if name_field != utf8(name): return None timestamp = int(timestamp) if timestamp < clock() - max_age_days * 86400: # The signature has expired. return None try: return base64.b64decode(value_field) except Exception: return None def get_signature_key_version(value): value = utf8(value) version = _get_version(value) if version < 2: return None try: key_version, _, _, _, _ = _decode_fields_v2(value) except ValueError: return None return key_version
tornado自带的基于cookie的验证机制：
必须重写方法get_current_user(self):，self.current_user()会调用该方法，拿到当前用户
@tornado.web.authenticated，装饰器修饰的请求会要求验证，self.current_user()中拿到值时，能进行访问，无值时跳转到登录页面（必须进行配置：'login_url':'/login'）
#!/usr/bin/env python # -*- coding:utf-8 -*- import tornado.ioloop import tornado.web class BaseHandler(tornado.web.RequestHandler): def get_current_user(self): return self.get_secure_cookie("login_user") class MainHandler(BaseHandler): @tornado.web.authenticated #需要登录后才能访问（self.current_user()拿到当前用户），否则跳转到登录页面 def get(self): login_user = self.current_user self.write(login_user) class LoginHandler(tornado.web.RequestHandler): def get(self): self.current_user() self.render('login.html', **{'status': ''}) def post(self, *args, **kwargs): username = self.get_argument('name') password = self.get_argument('pwd') if username == 'wupeiqi' and password == '123': self.set_secure_cookie('login_user', 'zack') self.redirect('/') else: self.render('login.html', **{'status': '用户名或密码错误'}) settings = { 'template_path': 'template', 'static_path': 'static', 'static_url_prefix': '/static/', 'cookie_secret': 'aiuasdhflashjdfoiuashdfiuh', 'login_url': '/login' } application = tornado.web.Application([ (r"/index", MainHandler), (r"/login", LoginHandler), ], **settings) if __name__ == "__main__": application.listen(8888) tornado.ioloop.IOLoop.instance().start()
7, 自定义session框架
预备知识一：字典
任何类实现了__getitem__(), __setitem__(), __delitem__()方法，就能向字典一样存取，删除数据
class Adict(object): def __init__(self): self.container = {} def __getitem__(self, key): print 'get' if key in self.container: return self.container[key] else: return None def __setitem__(self, key, value): print 'set' self.container[key]=value def __delitem__(self, key): print 'del' del self.container[key] D = Adict() D['user']='zack' #调用 __setitem__方法 D['user'] #调用 __getitem__方法 del D['user'] # 调用 __delitem__方法
预备知识二：类继承
#coding:utf-8 #C实例化时，先调用A的实例化方法，而其会调用self.initialize()时会只执行B的initialize()方法 class A(object): def __init__(self): print 'A' self.initialize() def initialize(self): print 'A初始化' class B(A): def initialize(self): print 'B初始化' class C(B): pass c = C()
#coding:utf-8 #C实例化时，先调用A的实例化方法，而其会调用self.initialize()时会只调用B的initialize()方法，而B的initialize()方法又调用了A的initialize方法 class A(object): def __init__(self): print 'A' self.initialize() def initialize(self): print 'A初始化' class B(object): def initialize(self): print 'B初始化' super(B,self).initialize() #此处super先寻找其父类，没找到，再找A的initialize方法，（先深度，后广度） class C(B,A): pass c = C()
预备知识三：在RequestHandler的源码中，__init__()函数调用了self.initialize()函数
class RequestHandler(object): """Base class for HTTP request handlers. Subclasses must define at least one of the methods defined in the "Entry points" section below. """ SUPPORTED_METHODS = ("GET", "HEAD", "POST", "DELETE", "PATCH", "PUT", "OPTIONS") _template_loaders = {} # type: typing.Dict[str, template.BaseLoader] _template_loader_lock = threading.Lock() _remove_control_chars_regex = re.compile(r"[\x00-\x08\x0e-\x1f]") def __init__(self, application, request, **kwargs): super(RequestHandler, self).__init__() self.application = application self.request = request self._headers_written = False self._finished = False self._auto_finish = True self._transforms = None # will be set in _execute self._prepared_future = None self._headers = None # type: httputil.HTTPHeaders self.path_args = None self.path_kwargs = None self.ui = ObjectDict((n, self._ui_method(m)) for n, m in application.ui_methods.items()) # UIModules are available as both `modules` and `_tt_modules` in the # template namespace. Historically only `modules` was available # but could be clobbered by user additions to the namespace. # The template {% module %} directive looks in `_tt_modules` to avoid # possible conflicts. self.ui["_tt_modules"] = _UIModuleNamespace(self, application.ui_modules) self.ui["modules"] = self.ui["_tt_modules"] self.clear() self.request.connection.set_close_callback(self.on_connection_close) self.initialize(**kwargs) def initialize(self): """Hook for subclass initialization. Called for each request. A dictionary passed as the third argument of a url spec will be supplied as keyword arguments to initialize(). Example:: class ProfileHandler(RequestHandler): def initialize(self, database): self.database = database def get(self, username): ... app = Application([ (r'/user/(.*)', ProfileHandler, dict(database=database)), ]) """ pass
自定义session框架
#coding:utf-8 import tornado.ioloop import tornado.web from hashlib import sha1 import time import os container={} create_session_id = lambda: sha1('%s%s' % (os.urandom(16), time.time())).hexdigest() class Session(object): #一个类实现了__setitem__，__getitem__就可以向字典一样读取和存取数据 session_id='session_id' def __init__(self,request): session_value = request.get_cookie(Session.session_id,None) if not session_value: self._id = create_session_id() else: if session_value in container: self._id=session_value else: self._id = create_session_id() request.set_cookie(Session.session_id,self._id) if self._id not in container: container[self._id]={} def __setitem__(self, key, value): container[self._id][key]=value print container def __getitem__(self, key): if key in container[self._id]: return container[self._id][key] else: return None def __delitem__(self, key): del container[self._id][key] def clear(self): del container[self._id] # class BaseHandler(object): # def initialize(self): # self.session = Session(self) # super(BaseHandler,self).initialize() #不会覆盖tornado.web.RequestHandler的initialiaze方法 # # class HomeHandler(BaseHandler,tornado.web.RequestHandler): # class BaseHandler(tornado.web.RequestHandler): def initialize(self): # 覆盖tornado.web.RequestHandler的initialiaze方法，初始化时父类中会调用该方法 self.session = Session(self) class HomeHandler(BaseHandler): def get(self): user = self.session['user'] if user: self.write(user) else: self.redirect('/login') class LoginHandler(BaseHandler): def get(self): self.render('login.html') def post(self): username = self.get_body_argument('username') password = self.get_body_argument('password') if username=='zack' and password=='1234': self.session['user']='zack' self.session['pwd']='1234' self.redirect('/index') else: self.render('login.html') settings={ 'template_path':'views' } application = tornado.web.Application([ (r'/index', HomeHandler), (r'/login', LoginHandler), ],**settings) if __name__ == '__main__': application.listen(9999) tornado.ioloop.IOLoop.instance().start()
8，异步非阻塞
http://www.tornadoweb.org/en/stable/guide/async.html
上面都是利用tornado的同步访问请求，当一个请求被阻塞时，下一个请求访问时不能被处理。如下面代码，当先访问‘/mani’时，由于MainHandler中，get方法sleep会阻塞在此处，此时若访问‘/page’，也会阻塞，等待MainHandler中get方法执行完成后，才会执行PageHandler中的get方法。
#coding:utf-8 import tornado.web import tornado.ioloop from tornado.concurrent import Future import time class MainHandler(tornado.web.RequestHandler): def get(self): time.sleep(10) self.write('main') class PageHandler(tornado.web.RequestHandler): def get(self): self.write('page') application = tornado.web.Application([ (r'/main',MainHandler), (r'/page',PageHandler) ]) if __name__ == '__main__': application.listen(8888) tornado.ioloop.IOLoop.instance().start()
tornado中，利用装饰器@gen.coroutine +yield Future对象，来支持异步非阻塞。如下面代码，当给MainHandler中get方法加上装饰器@gen.coroutine，并返回Future对象时，就变成了异步非阻塞，也就是说，当我们先访问‘/mani’时，MainHandler中get方法会阻塞在这里，但当我们此时去访问访问‘/page’，PageHandler中的get方法会立即执行，而不会阻塞。
#coding:utf-8 import tornado.web import tornado.ioloop from tornado import gen from tornado.concurrent import Future import time class MainHandler(tornado.web.RequestHandler): @gen.coroutine def get(self): future = Future() yield future self.write('main') class PageHandler(tornado.web.RequestHandler): def get(self): self.write('page') application = tornado.web.Application([ (r'/main',MainHandler), (r'/page',PageHandler) ]) if __name__ == '__main__': application.listen(8888) tornado.ioloop.IOLoop.instance().start()
上面写的异步非阻塞并没实际用途，下面是它的一个应用场景，在代码中，MainHandler的get方法中，fetch()比较耗时，但其返回一Future对象，当我们先访问‘/mani’时，MainHandler中get方法会阻塞在这里，但当我们此时去访问访问‘/page’，PageHandler中的get方法会立即执行
#coding:utf-8 import tornado.web import tornado.ioloop from tornado import gen, httpclient from tornado.concurrent import Future class MainHandler(tornado.web.RequestHandler): @gen.coroutine def get(self): http = httpclient.AsyncHTTPClient() #发送异步请求 data = yield http.fetch('https://www.youtube.com/',raise_error=False) #其源码中可以看到return future，即返回future对象 print 'done',data self.write('main') self.finish('dd') # 加入回调函数处理 # @gen.coroutine # def get(self): # http = httpclient.AsyncHTTPClient() #发送异步请求 # yield http.fetch('https://www.youtube.com/',callback=self.done,raise_error=False) #其源码中可以看到return future，即返回future对象 # # def done(self,response): # print 'done',response # self.write('main') # self.finish('dd') class PageHandler(tornado.web.RequestHandler): def get(self): self.write('page') application = tornado.web.Application([ (r'/main',MainHandler), (r'/page',PageHandler) ]) if __name__ == '__main__': application.listen(8888) tornado.ioloop.IOLoop.instance().start()
从python 3.5 开始，关键字async 和 await可以用来代替@gen.coroutine +yield，代码如下：
http://www.tornadoweb.org/en/stable/guide/coroutines.html
async def fetch_coroutine(url): http_client = AsyncHTTPClient() response = await http_client.fetch(url) return response.body ''' # Decorated: # Native: # Normal function declaration # with decorator # "async def" keywords @gen.coroutine def a(): async def a(): # "yield" all async funcs # "await" all async funcs b = yield c() b = await c() # "return" and "yield" # cannot be mixed in # Python 2, so raise a # special exception. # Return normally raise gen.Return(b) return b '''
其实现异步阻塞的关键在于Future对象，下面是其部分源码，可以看到其_result属性初始化没有值，tornado内部会监听每一个Future对象的_result属性值，若没有值时，继续阻塞，若有值时，若某个Future对象的_result属性值有值了，处理该请求，结束阻塞，继续监听其他Future对象。
关于Future类可以参考：https://www.cnblogs.com/silence-cho/p/9867499.html
class Future(object): """Represents the result of an asynchronous computation.""" def __init__(self): """Initializes the future. Should not be called by clients.""" self._condition = threading.Condition() self._state = PENDING self._result = None self._exception = None self._traceback = None self._waiters = [] self._done_callbacks = []
参考文章：
官方文档：http://www.tornadoweb.org/en/stable/index.html
http://www.cnblogs.com/wupeiqi/articles/5341480.html
http://www.cnblogs.com/wupeiqi/articles/5702910.html
http://www.cnblogs.com/wupeiqi/p/6536518.html
