标签：代理类 art 应用 wrap cti class 为什么 port reason
为什么使用自定义 Local，而不是 threading.local。这是由内核决定的
1. web 应用在启动之后，是一单线+协成程启动的话，会污染全局变量，无法区分，
2. 使用多线程+协成无法保证，派发请求的工作协程，无法保证同时工作时且分别位于多个线程内，彼此互不影响
所以： werkzeug 给出了自己的解决方案：Local 和 LocalStack
那么问题来了：请求的上下文的私有变量存储在 Local 和 LocalStack 中，那在多任务时，每次调用 from flask import request, g, session ， 如何保证获取正确的上下文，而不发生混乱？
在 flask.globals.py 中
def _lookup_req_object(name): top = _request_ctx_stack.top if top is None: raise RuntimeError(‘working outside of request context‘) return getattr(top, name) _request_ctx_stack = LocalStack() request = LocalProxy(partial(_lookup_req_object, ‘request‘)) session = LocalProxy(partial(_lookup_req_object, ‘session‘))
在 werkzeug.local.py 中, LocalProxy是一个 Local or LocalStack 的一个代理
@implements_bool class LocalProxy(object): """""" __slots__ = ("__local", "__dict__", "__name__", "__wrapped__") def __init__(self, local, name=None): object.__setattr__(self, "_LocalProxy__local", local) object.__setattr__(self, "__name__", name) if callable(local) and not hasattr(local, "__release_local__"): # "local" is a callable that is not an instance of Local or # LocalManager: mark it as a wrapped function. object.__setattr__(self, "__wrapped__", local) def _get_current_object(self): """Return the current object. This is useful if you want the real object behind the proxy at a time for performance reasons or because you want to pass the object into a different context. """ if not hasattr(self.__local, "__release_local__"): return self.__local() try: return getattr(self.__local, self.__name__) except AttributeError: raise RuntimeError("no object bound to %s" % self.__name__) def __getattr__(self, name): if name == "__members__": return dir(self._get_current_object()) return getattr(self._get_current_object(), name)
调用 reqeust：动态 request <= 动态的 _request_ctx_stack.top <= LocalStack() 每次调用产生使用新的实例与方法结合（request）<= LoaclStack.call?
是的，每次调用 request，就会新产生一个proxy实例，每次pop, push, top 均是针对 Local 的操作，而 Local 的属性赋值与获取均是针对 get_ident 获取的！
class Local(object): __slots__ = ("__storage__", "__ident_func__") def __init__(self): object.__setattr__(self, "__storage__", {}) object.__setattr__(self, "__ident_func__", get_ident) """""" 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__() storage = self.__storage__ try: storage[ident][name] = value except KeyError: storage[ident] = {name: value}
perfect！每次新请求来临时，flask 会把上下文存储在 werkzeug Local 中，使用时根据线程或者协程id获取
flask 中的 werkzeug Local，LocalStack 和 LocalProxy 技术应用
标签：代理类 art 应用 wrap cti class 为什么 port reason
原文地址：https://www.cnblogs.com/spaceapp/p/12157940.html
