04 flask源码剖析之LocalStack和Local对象实现栈的管理

04 LocalStack和Local对象实现栈的管理

1.源码入口

from flask import globals
# 从globals进入可以看见此源码

1. flask源码关于local的实现

1. local与localstack关系

   • flask中是localstack结合local使用
   • local为localstack提供基本结构

2. 源码实现

   try:
       # 协程
       from greenlet import getcurrent as get_ident
   except ImportError:
       try:
           from thread import get_ident
       except ImportError:
           from _thread import get_ident
   """
   __storage__ = {
       1111:{"stack":[张三] }
   }
   """
   class Local(object):
   
       def __init__(self):
           # self.__storage__ = {}
           # self.__ident_func__ = get_ident
           object.__setattr__(self, "__storage__", {})
           object.__setattr__(self, "__ident_func__", get_ident)
   
       def __iter__(self):
           return iter(self.__storage__.items())
   
       def __release_local__(self):
           self.__storage__.pop(self.__ident_func__(), None)
   
       def __getattr__(self, name):
           try:
               return self.__storage__[self.__ident_func__()][name]
           except KeyError:
               raise AttributeError(name)
   
       def __setattr__(self, name, value):
           ident = self.__ident_func__() # 1111
           storage = self.__storage__
           try:
               storage[ident][name] = value
           except KeyError:
               storage[ident] = {name: value}
   
       def __delattr__(self, name):
           try:
               del self.__storage__[self.__ident_func__()][name]
           except KeyError:
               raise AttributeError(name)

2. flask源码关于localstack的实现

1. 两个localstack对象

   • 存储RequestContext相关，包括reqeust、session
   • 存储AppContenxt相关，包括app、g（所有app对象都包括在里边）

   _request_ctx_stack = LocalStack()
   __storage__ = {
    1111:{'stack':[RequestContext(reqeust,session),]},
       1123:{'stack':[RequestContext(reqeust,session),]},
   }
   
   _app_ctx_stack = LocalStack()
   __storage__ = {
    1111:{'stack':[AppContenxt(app,g),]}
       1123:{'stack':[AppContenxt(app,g),]},
   }

2. localstack源码实现

   class LocalStack(object):
       def __init__(self):
           self._local = Local()
       def push(self, obj):
           """Pushes a new item to the stack"""
           # self._local.stack == getattr
           # rv = None
           rv = getattr(self._local, "stack", None)
           if rv is None:
               self._local.stack = rv = []
           rv.append(obj)
           return rv
   
       def pop(self):
           stack = getattr(self._local, "stack", None)
           if stack is None:
               return None
           elif len(stack) == 1:
               # release_local(self._local)
               # del __storage__[1111]
               return stack[-1]
           else:
               return stack.pop()
   
       @property
       def top(self):
           try:
               return self._local.stack[-1]
           except (AttributeError, IndexError):
               return None
   
   obj = LocalStack()
   obj.push('张三')
   obj.push('李四')
   
   print(obj.top)
   
   obj.pop()
   obj.pop()

3. 总结

• 在flask中有个local类，他和threading.local的功能一样，为每个线程开辟空间进行存取数据，他们两个的内部实现机制，内部维护一个字典，以线程(协程)ID为key，进行数据隔离，如：

  __storage__ = {
      1211:{'k1':123}
  }
  
  obj = Local()
  obj.k1 = 123

• 在flask中还有一个LocalStack的类，他内部会依赖local对象，local对象负责存储数据，localstack对象用于将local中的值维护成一个栈。

  __storage__ = {
  1211:{'stack':['k1',]}
  }
  
  obj= LocalStack()
  obj.push('k1')
  obj.top
  obj.pop()

• flask上下文管理也是基于此

  • 请求上下文管理
  • 应用上下文管理

原文：https://www.cnblogs.com/liubing8/p/11930180.html