flask源码分析，run函数启动分析

摘要：对背后运行机制感兴趣，参考网上资料，结合源码分析函数运行时的机制，主要整理出函数调用栈。以分析首先官方文档经典示例现在来分析启动时发生了什么代码只列出用到的函数，去掉注释等函数导入运行函数主要运行调用返回类，然后调用返回类的。

对flask背后运行机制感兴趣，参考网上资料，结合源码分析run函数运行时的机制，主要整理出函数调用栈。以flask0.1分析

首先
Flask官方文档经典示例 hello.py

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == "__main__":
    app.run() 

现在来分析app.run()启动时发生了什么？ # 代码只列出用到的函数，去掉注释等
flask.py

class Flask(object):

  def run(self, host="localhost", port=5000, **options):
       
        from werkzeug import run_simple
        if "debug" in options:
            self.debug = options.pop("debug")
        options.setdefault("use_reloader", self.debug)
        options.setdefault("use_debugger", self.debug)
        return run_simple(host, port, self, **options)

   

run函数导入from werkzeug import run_simple 运行run_simple(host, port, self, **options)

werkzeug/serving.py

def run_simple(hostname, port, application, use_reloader=False, extra_files=None, threaded=False, processes=1):
    
    def inner():
        srv = make_server(hostname, port, application, threaded,
                          processes)
        try:
            srv.serve_forever()
        except KeyboardInterrupt:
            pass
    inner()

run_simple函数主要运行inner(),inner调用make_server（）返回类，然后调用返回类的serve_forever()。先来看看make_server（）

werkzeug/serving.py

ddef make_server(host, port, app=None, threaded=False, processes=1):
    
    if threaded and processes > 1:
        raise ValueError("cannot have a multithreaded and "
                         "multi process server.")
    elif threaded:
        class handler(BaseRequestHandler):
            multithreaded = True
        class server(ThreadingMixIn, WSGIServer):
            pass
    elif processes > 1:
        class handler(BaseRequestHandler):
            multiprocess = True
            max_children = processes - 1
        class server(ForkingMixIn, WSGIServer):
            pass
    else:
        handler = BaseRequestHandler
        server = WSGIServer
    srv = server((host, port), handler)
    srv.set_app(app)
    return srv

make_server(hostname, port, application, threaded, processes) 传入的都是默认参数，起作用的代码是

else:
        handler = BaseRequestHandler
        server = WSGIServer
    srv = server((host, port), handler)
    srv.set_app(app)
    return srv

可以看出srv = server((host, port), handler) ,其实就是srv = WSGIServer((host, port), BaseRequestHandler)，返回类就是WSGIServer ，绑定BaseRequestHandler。先看WSGIServer

wsgiref/simple_server.py

class WSGIServer(HTTPServer):
  def __init__=  标准库 BaseHTTPServer.py  class HTTPServer(SocketServer.TCPServer) : #WSGIServer继承HTTPServer的__init__函数，它自己没有 ，这句是我加的方便理解 ，下同

  def set_app(self,application):    #这个就是make_server函数中调用的 set_app
        self.application = application
  def get_app(self):            #
        return self.application

标准库 BaseHTTPServer.py  
class HTTPServer(SocketServer.TCPServer) 
  def __init__=  标准库 SocketServer.py class TCPServer(BaseServer):


标准库 SocketServer.py 
class TCPServer(BaseServer):
   def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
        BaseServer.__init__(self, server_address, RequestHandlerClass)
        self.socket = socket.socket(self.address_family,
                                    self.socket_type)
        if bind_and_activate:         # 这里调用socket.socket绑定端口
            try:
                self.server_bind()
                self.server_activate()
            except:
                self.server_close()
                raise

class BaseServer:
    def __init__(self, server_address, RequestHandlerClass):
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def serve_forever(self, poll_interval=0.5):    #这个就是run_simple中调用的serve_forever
        
        self.__is_shut_down.clear()
        try:
            while not self.__shutdown_request:
                
                r, w, e = _eintr_retry(select.select, [self], [], [],
                                       poll_interval)
                if self in r:
                    self._handle_request_noblock()   #调用serve_forever时调用_handle_request_noblock
        finally:
            self.__shutdown_request = False

            self.__is_shut_down.set()
    def _handle_request_noblock(self):   
       
        try:
            request, client_address = self.get_request()
        except socket.error:
            return
        if self.verify_request(request, client_address):
            try:
                self.process_request(request, client_address)  #继续
            except:
                self.handle_error(request, client_address)
                self.shutdown_request(request)

    def process_request(self, request, client_address):
        
        self.finish_request(request, client_address)   #继续
        self.shutdown_request(request)

    def finish_request(self, request, client_address):
        self.RequestHandlerClass(request, client_address, self)    # #继续 并参见 werkzeug/serving.py  make_server()    

调用serve_forever后到了self.RequestHandlerClass(request, client_address, self) ，根据前面的代码可知RequestHandlerClass 就是werkzeug/serving.py中的BaseRequestHandler，继续

class BaseRequestHandler(WSGIRequestHandler):
    def __init__=  标准库 wsgiref/simple_server.py class WSGIRequestHandler(BaseHTTPRequestHandler): #这句跟前面一样继承父类   
    

wsgiref/simple_server.py

class WSGIRequestHandler(BaseHTTPRequestHandler):
    def __init__=  标准库 BaseHTTPServer.py class BaseHTTPRequestHandler(SocketServer.StreamRequestHandler): #继续父类

BaseHTTPServer.py
class BaseHTTPRequestHandler(SocketServer.StreamRequestHandler):
    def __init__=  标准库 SocketServer.py  class StreamRequestHandler(BaseRequestHandler):  #继续父类


SocketServer.py

class StreamRequestHandler(BaseRequestHandler):
 #继续父类

class BaseRequestHandler:

    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        self.setup()
        try:
            self.handle()   # 运行  参见 werkzeug/serving.py  class BaseRequestHandler.handle
        finally:
            self.finish()

最后运行了self.handle() 参见 werkzeug/serving.py class BaseRequestHandler.handle
前面有，再贴下看看

class BaseRequestHandler(WSGIRequestHandler):
   def handle(self):     #1、调用的就是这个handle，覆盖了父类的handle 
        self.raw_requestline = self.rfile.readline()
        if self.parse_request():
            self.get_handler().run(self.server.get_app())  #2、调用 get_handler()后，还继续调用 run（） ，get_app就是wsgiref/simple_server.py中WSGIServer类定义的函数   

    def get_handler(self):  # 3、看看它返回了什么
        handler = self._handler_class
        if handler is None:
            class handler(ServerHandler):  #4、新建一个类 返回的就是这个类 ，继承ServerHandler
              """   
                  5、直接从其他文件copy出所需代码，也就是handler的父类
                   wsgiref/simple_server.py  class ServerHandler(SimpleHandler): 继续父类 
                   wsgiref/handlers.py  
                       class SimpleHandler(BaseHandler):
                          def __init__(self,stdin,stdout,stderr,environ,multithread=True, multiprocess=False ):
                              self.stdin = stdin
                              self.stdout = stdout
                              self.stderr = stderr
                              self.base_env = environ
                              self.wsgi_multithread = multithread
                              self.wsgi_multiprocess = multiprocess
                       class BaseHandler:  #6、调用的就是这个类的run函数
                                  def run(self, application):
                                    try:
                                        self.setup_environ()
                                        self.result = application(self.environ, self.start_response)   #7、调用app，也就是app=Flask() Flask类的 __call__
                                        self.finish_response()
                                    except:
                                          try:
                                               self.handle_error()
                                          except:
                                             # If we get an error handling an error, just give up already!
                                             self.close()
                                             raise   # ...and let the actual server figure it out.


                 """
                wsgi_multithread = self.multithreaded                      
                wsgi_multiprocess = self.multiprocess
            self._handler_class = handler

        rv = handler(self.rfile, self.wfile, self.get_stderr(),
                     self.get_environ())
        rv.request_handler = self
        return rv

 

可以看出最后调用的是application(self.environ, self.start_response) 这个application就是开始的app = Flask(__name__)，调用类就是调用类的__call__ 函数 ，继续贴一下源码

class Flask(object):

   def __call__(self, environ, start_response):
        return self.wsgi_app(environ, start_response)

   def wsgi_app(self, environ, start_response):
        
        with self.request_context(environ):
            rv = self.preprocess_request()
            if rv is None:
                rv = self.dispatch_request()
            response = self.make_response(rv)
            response = self.process_response(response)
            return response(environ, start_response)

OK，大功告成，最后调用wsgi_app(self, environ, start_response)函数，这个就是返回响应的主函数了！！

从整个流程中，flask利用WSGIServer类启动监听端口并绑定，BaseRequestHandler类接收、返回相应的信息！完全符合WSGI要求。
剩余的工作就太过于底层，不好深入分析了。也画了调用流程图，不过太大不好传，如果有需要可以继续交流！