Flask上下文管理
主要内容
- 1. Flask 请求上下文管理
- 2. Flask 应用上下文管理
1. Flask请求上下文管理
1.1 Flask请求上文
- 当请求进来时,app(), Flask实例化对象app执行__call__
def __call__(self, environ, start_response): """The WSGI server calls the Flask application object as the WSGI application. This calls :meth:`wsgi_app` which can be wrapped to applying middleware.""" return self.wsgi_app(environ, start_response)
- 执行wsgi_app 得到 一个 RequestContext的对象 ctx (封装了request以及session)
ctx = self.request_context(environ)
class RequestContext(object): #此时的self是RequestContext对象 -->ctx 中封装了request/session def __init__(self, app, environ, request=None): self.app = app #app = Flask对象 if request is None: #请求的原始信息通过request_class后此时request已经存在,request.methods等 request = app.request_class(environ) self.request = request self.url_adapter = app.create_url_adapter(self.request) self.flashes = None self.session = None
- ctx 执行 ctx.push():
ctx = self.request_context(environ) error = None try: try: ctx.push() response = self.full_dispatch_request() except Exception as e: error = e response = self.handle_exception(e)
- RequestContext对象的push方法
def push(self): # _request_ctx_stack = LocalStack()一个LocalStack对象 # _request_ctx_stack._local = LocalStack()._loacl = {"__storage__":{},"__ident_func__":get_ident} top = _request_ctx_stack.top #top =None if top is not None and top.preserved: top.pop(top._preserved_exc)
_request_ctx_stack是一个LocalStack对象 ,LocalStack()._local是一个Local对象 即Local()
class LocalStack(object): def __init__(self): self._local = Local() #self._loacl = {"__storage__":{},"__ident_func__":get_ident}
Local对象经过初始化得到的字典值
class Local(object): #限定当前只能由两个属性值 __slots__ = ('__storage__', '__ident_func__') def __init__(self): object.__setattr__(self, '__storage__', {}) object.__setattr__(self, '__ident_func__', get_ident) # {"__storage__":{},"__ident_func__":get_ident} #此时get_dient 是个没有执行的函数,内存地址
_request_ctx_stack中top方法,返回None
@property def top(self): """The topmost item on the stack. If the stack is empty, `None` is returned. """ try: # self._local 即Local对象调用__getattr__方法 #在下文时候Local对象{"__storage__":{8080:{stack:rv=[ctx->request/session]}},"__ident_func__":get_ident} # [ctx->request/session] return self._local.stack[-1] #得到ctx对象 except (AttributeError, IndexError): return None
_request_ctx_stack 对象执行push方法
#当前的self为ctx _request_ctx_stack.push(self)
def push(self, obj): #此时的self是LocalStack对象, obj为ctx """Pushes a new item to the stack""" # self._local = {"__storage__":{},"__ident_func__":get_ident} #找不到返回值是None rv = getattr(self._local, 'stack', None) if rv is None: #由于.stack后面有等号,执行的时候Local()对象的__setattr__方法 #实际上是地址的赋值,此时stack和rv都指向空列表 self._local.stack = rv = [] #{"__storage__":{8080:{stack:rv=[]}},"__ident_func__":get_ident} rv.append(obj) # {"__storage__":{8080:{stack:rv=[ctx->request/session]}},"__ident_func__":get_ident} # 应用上下文时候{"__storage__":{8080:{stack:rv=[app_ctx->(app/g)]}},"__ident_func__":get_ident} return rv #rv=[ctx->request/session]
def __setattr__(self, name, value): #name=stack value=rv=[] #self是Local对象 {"__storage__":{},"__ident_func__":get_ident} ident = self.__ident_func__() #执行get_ident函数获取当前线程id 8080 storage = self.__storage__ #storge ={8080:{stack:rv=[]}} try: storage[ident][name] = value except KeyError: storage[ident] = {name: value} #storage={} # {"__storage__":{8080:{stack:rv=[]}},"__ident_func__":get_ident}
- 执行完push方法 请求上文结束:
#当请求进来,第一件事就是要把当前这个请求在我服务器上的线程开辟一个空间(线程对应的空间,必须含有stack对应一个列表存放ctx(request/session) # {"__storage__":{8080:{stack:rv=[ctx->request/session]}},"__ident_func__":get_ident}
1.2 Flask请求下文
- 导入request开始使用,在request中
#此时request是一个函数包裹一个偏函数 LocalProxy()是一个代理 #当前的request是一个LocalProxy() request.method 执行__getattr__方法 request = LocalProxy( partial(_lookup_req_object, 'request') #return request对象 )
- 在偏函数中 将request传入到 _lookup_req_object中: 此时得到一个request对象
def _lookup_req_object(name): # _request_ctx_stack是LocalStack对象 top = _request_ctx_stack.top #下文[ctx->request/session] if top is None: raise RuntimeError(_request_ctx_err_msg) #此时的name是request,从ctx对象中找出request对象 return getattr(top, name)
@property def top(self): """The topmost item on the stack. If the stack is empty, `None` is returned. """ try: # self._local 即Local对象调用__getattr__方法 #在下文时候Local对象{"__storage__":{8080:{stack:rv=[ctx->request/session]}},"__ident_func__":get_ident} # [ctx->request/session] return self._local.stack[-1] #得到ctx对象 except (AttributeError, IndexError): return None
此时的top不是None已经存在值
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partial(_lookup_req_object, 'request') 这一层执行完得到一个reauest对象,将偏函数传入到LocalProxy中
@implements_bool class LocalProxy(object): __slots__ = ('__local', '__dict__', '__name__', '__wrapped__') def __init__(self, local, name=None): #local是request偏函数 object.__setattr__(self, '_LocalProxy__local', local) #__local = request偏函数 object.__setattr__(self, '__name__', name) #当前偏函数可以执行而且判断loacl中是否有 __release_local__ ==>这句话成立 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) #__warpped__还是local偏函数
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当前的request是一个LocalProxy() request.method 执行LocalProxy中的__getattr__方法
def __getattr__(self, name): # name是method(举例) if name == '__members__': return dir(self._get_current_object()) #此时self._get_current_object()是经过_local 执行后得到的request对象,从request对象中去取出method return getattr(self._get_current_object(), name)
def _get_current_object(self): #self._local是偏函数 if not hasattr(self.__local, '__release_local__'): #执行偏函数,返回request对象 return self.__local() try: return getattr(self.__local, self.__name__) except AttributeError: raise RuntimeError('no object bound to %s' % self.__name__)
2. Flask 应用上下文管理
- 执行wsgi_app方法
#ctx为一个RequestContext的对象,参数为environ ctx = self.request_context(environ) error = None try: try: ctx.push() response = self.full_dispatch_request() except Exception as e: error = e response = self.handle_exception(e)
- 执行push方法,_app_ctx_stack 同样是LocalStck对象,初始化时候top为None
def push(self): app_ctx = _app_ctx_stack.top #app_ctx = None if app_ctx is None or app_ctx.app != self.app: app_ctx = self.app.app_context() #app_context是AppContext对象 与RequestContenx一样,知识序列化出app和g app_ctx.push() # 应用上文时候{"__storage__":{8080:{stack:rv=[app_ctx->(app/g)]}},"__ident_func__":get_ident} self._implicit_app_ctx_stack.append(app_ctx) else: self._implicit_app_ctx_stack.append(None)
执行app_ctx.push 进而 _app_ctx_stack.push
def push(self): """Binds the app context to the current context.""" self._refcnt += 1 if hasattr(sys, 'exc_clear'): sys.exc_clear() #将AppContext存在LocalStack对象中 _app_ctx_stack.push(self) appcontext_pushed.send(self.app)
def push(self, obj): #此时的self是LocalStack对象, obj为ctx """Pushes a new item to the stack""" # self._local = {"__storage__":{},"__ident_func__":get_ident} #找不到返回值是None rv = getattr(self._local, 'stack', None) if rv is None: #由于.stack后面有等号,执行的时候Local()对象的__setattr__方法 #实际上是地址的赋值,此时stack和rv都指向改空列表 self._local.stack = rv = [] #{"__storage__":{8080:{stack:rv=[]}},"__ident_func__":get_ident} rv.append(obj) # {"__storage__":{8080:{stack:rv=[ctx->request/session]}},"__ident_func__":get_ident} # 应用上下文时候{"__storage__":{8080:{stack:rv=[app_ctx->(app/g)]}},"__ident_func__":get_ident} return rv #rv=[ctx->request/session]
到此,push完毕,应用上文结束,应用下文在离线脚本时候使用
另外:在global.py中
def _find_app(): top = _app_ctx_stack.top #得到app_ctx(app / g) if top is None: raise RuntimeError(_app_ctx_err_msg) return top.app #返回一个app即flask对象 只不过此时的flask对象 是公共的,与初始化的相同 # 但是是独立出来已经被配置好的Flask对象 # LocalStack是 针对当前这个线程对独立的Flask_app进行修改, 不影响现在运行的app =>离线脚本 #但是这个app 在请求结束后会从LocalStack中通过 __delattr__ 删除 # context locals _request_ctx_stack = LocalStack() #LocalStark = self._loacl = {"__storage__":{},"__ident_func__":get_ident} _app_ctx_stack = LocalStack() current_app = LocalProxy(_find_app) # current_app可以点 .run | .route 等
