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  • tornado--SESSION框架，一致性hash，分布式存储


    预备知识

    1. tornado框架session要自己写

    2. cookie存储在客户端浏览器上，session数据放在服务器上

    3. session依赖cookie

    4. 扩展tornado，返回请求前自定义session

    5. 面向对象的知识，obj['xxx']==>_getitems__,obj['xxx']=xxx ==> __setitems__, del obj['xxx'] ==> __delitems__

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    class Foo(object):
       
        def __getitem__(self, key):
            print  '__getitem__',key
       
        def __setitem__(self, key, value):
            print '__setitem__',key,value
       
        def __delitem__(self, key):
            print '__delitem__',key
       
       
       
    obj = Foo()
    result = obj['k1']
    #obj['k2'] = 'wupeiqi'
    #del obj['k1']




    session实现机制

    1. tornado框架中，通过application的url映射到MainHandler类处理请求，根据请求的方式，通过反射执行对应的get或post等方法

    2. tornado源码中有很多扩展点（钩子）供开发者使用，如在执行get或post方法之前先执行initialiaze方法，即使没有调用也执行

    3. 扩展initialiaze，用户请求进来，读一下用户的cookie，如果有的话，能够拿到，没有可以创建一个

    4. 为避免重复在每个映射的类里都写一遍initialiaze，可以在他们的共同的基类BaseHandler（自定义的类）里写initialiaze方法

    5. 其实这些类应该继承tornado.web.RequestHandler类，让BaseHandler继承这个类，其他类也就继承了

    6. initialiaze中定义了self.my_session字段，它是一个session类的对象，init中获取或创建session

    7. 用户登录，通过__setitem__设置session中的内容，session保存在服务器中

    8. session_container是用来保存session的字典

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    import tornado.ioloop
    import tornado.web
    from hashlib import sha1
    import os, time
       
    session_container = {}
       
    create_session_id = lambda: sha1('%s%s' % (os.urandom(16), time.time())).hexdigest()
       
       
    class Session(object):
       
        session_id = "__sessionId__"
       
        def __init__(self, request):
            session_value = request.get_cookie(Session.session_id)
            if not session_value:
                self._id = create_session_id()
            else:
                self._id = session_value
            request.set_cookie(Session.session_id, self._id)
       
        def __getitem__(self, key):
            return session_container[self._id][key]
       
        def __setitem__(self, key, value):
            if session_container.has_key(self._id):
                session_container[self._id][key] = value
            else:
                session_container[self._id] = {key: value}
       
        def __delitem__(self, key):
            del session_container[self._id][key]
       
       
    class BaseHandler(tornado.web.RequestHandler):
       
        def initialize(self):
            # my_session['k1']访问 __getitem__ 方法
            self.my_session = Session(self)
       
       
    class MainHandler(BaseHandler):
       
        def get(self):
            print self.my_session['c_user']
            print self.my_session['c_card']
            self.write('index')
       
    class LoginHandler(BaseHandler):
       
        def get(self):
            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.my_session['c_user'] = 'wupeiqi'
                self.my_session['c_card'] = '12312312309823012'
       
                self.redirect('/index')
            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()



    session分布式

    1. session可以存在其它地方，如redis，数据库，mongo等等

    2. 当session规模达到很大数量级，就采用多台分布式存储，经过一致性hash算法，分配到对应的机器上

    3. 根据cookie字符串转换成一串数字，每台机器分管的数字段区域不同，权重大的管的大

    一致性哈希​
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    #!/usr/bin/env python
    #coding:utf-8
     
    import sys
    import math
    from bisect import bisect
     
     
    if sys.version_info >= (2, 5):
        import hashlib
        md5_constructor = hashlib.md5
    else:
        import md5
        md5_constructor = md5.new
     
     
    class HashRing(object):
        """一致性哈希"""
         
        def __init__(self,nodes):
            '''初始化
            nodes : 初始化的节点，其中包含节点已经节点对应的权重
                    默认每一个节点有32个虚拟节点
                    对于权重，通过多创建虚拟节点来实现
                    如：nodes = [
                            {'host':'127.0.0.1:8000','weight':1},
                            {'host':'127.0.0.1:8001','weight':2},
                            {'host':'127.0.0.1:8002','weight':1},
                        ]
            '''
             
            self.ring = dict()
            self._sorted_keys = []
     
            self.total_weight = 0
             
            self.__generate_circle(nodes)
             
                 
                 
        def __generate_circle(self,nodes):
            for node_info in nodes:
                self.total_weight += node_info.get('weight',1)
                 
            for node_info in nodes:
                weight = node_info.get('weight',1)
                node = node_info.get('host',None)
                     
                virtual_node_count = math.floor((32*len(nodes)*weight) / self.total_weight)
                for i in xrange(0,int(virtual_node_count)):
                    key = self.gen_key_thirty_two( '%s-%s' % (node, i) )
                    if self._sorted_keys.__contains__(key):
                        raise Exception('该节点已经存在.')
                    self.ring[key] = node
                    self._sorted_keys.append(key)
                 
        def add_node(self,node):
            ''' 新建节点
            node : 要添加的节点，格式为：{'host':'127.0.0.1:8002','weight':1}，其中第一个元素表示节点，第二个元素表示该节点的权重。
            '''
            node = node.get('host',None)
            if not node:
                    raise Exception('节点的地址不能为空.')
                     
            weight = node.get('weight',1)
             
            self.total_weight += weight
            nodes_count = len(self._sorted_keys) + 1
             
            virtual_node_count = math.floor((32 * nodes_count * weight) / self.total_weight)
            for i in xrange(0,int(virtual_node_count)):
                key = self.gen_key_thirty_two( '%s-%s' % (node, i) )
                if self._sorted_keys.__contains__(key):
                    raise Exception('该节点已经存在.')
                self.ring[key] = node
                self._sorted_keys.append(key)
             
        def remove_node(self,node):
            ''' 移除节点
            node : 要移除的节点 '127.0.0.1:8000'
            '''
            for key,value in self.ring.items():
                if value == node:
                    del self.ring[key]
                    self._sorted_keys.remove(key)
         
        def get_node(self,string_key):
            '''获取 string_key 所在的节点'''
            pos = self.get_node_pos(string_key)
            if pos is None:
                return None
            return self.ring[ self._sorted_keys[pos]].split(':')
         
        def get_node_pos(self,string_key):
            '''获取 string_key 所在的节点的索引'''
            if not self.ring:
                return None
                 
            key = self.gen_key_thirty_two(string_key)
            nodes = self._sorted_keys
            pos = bisect(nodes, key)
            return pos
         
        def gen_key_thirty_two(self, key):
             
            m = md5_constructor()
            m.update(key)
            return long(m.hexdigest(), 16)
             
        def gen_key_sixteen(self,key):
             
            b_key = self.__hash_digest(key)
            return self.__hash_val(b_key, lambda x: x)
     
        def __hash_val(self, b_key, entry_fn):
            return (( b_key[entry_fn(3)] << 24)|(b_key[entry_fn(2)] << 16)|(b_key[entry_fn(1)] << 8)| b_key[entry_fn(0)] )
     
        def __hash_digest(self, key):
            m = md5_constructor()
            m.update(key)
            return map(ord, m.digest())
     
     
    """
    nodes = [
        {'host':'127.0.0.1:8000','weight':1},
        {'host':'127.0.0.1:8001','weight':2},
        {'host':'127.0.0.1:8002','weight':1},
    ]
     
    ring = HashRing(nodes)
    result = ring.get_node('98708798709870987098709879087')
    print result
     
    """
     
    一致性哈希


    session

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    from hashlib import sha1
    import os, time
     
     
    create_session_id = lambda: sha1('%s%s' % (os.urandom(16), time.time())).hexdigest()
     
     
    class Session(object):
     
        session_id = "__sessionId__"
     
        def __init__(self, request):
            session_value = request.get_cookie(Session.session_id)
            if not session_value:
                self._id = create_session_id()
            else:
                self._id = session_value
            request.set_cookie(Session.session_id, self._id)
     
        def __getitem__(self, key):
            # 根据 self._id ，在一致性哈西中找到其对应的服务器IP
            # 找到相对应的redis服务器，如： r = redis.StrictRedis(host='localhost', port=6379, db=0)
            # 使用python redis api 链接
            # 获取数据，即：
            # return self._redis.hget(self._id, name)
     
        def __setitem__(self, key, value):
            # 根据 self._id ，在一致性哈西中找到其对应的服务器IP
            # 使用python redis api 链接
            # 设置session
            # self._redis.hset(self._id, name, value)
     
     
        def __delitem__(self, key):
            # 根据 self._id 找到相对应的redis服务器
            # 使用python redis api 链接
            # 删除，即：
            return self._redis.hdel(self._id, name)
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  • 原文地址：https://www.cnblogs.com/daliangtou/p/5481577.html
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