摘要：對背后運行機制感興趣，參考網上資料，結合源碼分析函數運行時的機制，主要整理出函數調用棧。以分析首先官方文檔經典示例現在來分析啟動時發生了什么代碼只列出用到的函數，去掉注釋等函數導入運行函數主要運行調用返回類，然后調用返回類的。

對flask背后運行機制感興趣，參考網上資料，結合源碼分析run函數運行時的機制，主要整理出函數調用棧。以flask0.1分析

首先
Flask官方文檔經典示例 hello.py

from flask import Flask
app = Flask(__name__)

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

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

現在來分析app.run()啟動時發生了什么？ # 代碼只列出用到的函數，去掉注釋等
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函數導入from werkzeug import run_simple 運行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函數主要運行inner(),inner調用make_server（）返回類，然后調用返回類的serve_forever()。先來看看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) 傳入的都是默認參數，起作用的代碼是

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) ,其實就是srv = WSGIServer((host, port), BaseRequestHandler)，返回類就是WSGIServer ，綁定BaseRequestHandler。先看WSGIServer

wsgiref/simple_server.py

class WSGIServer(HTTPServer):
  def __init__=  標準庫 BaseHTTPServer.py  class HTTPServer(SocketServer.TCPServer) : #WSGIServer繼承HTTPServer的__init__函數，它自己沒有 ，這句是我加的方便理解 ，下同

  def set_app(self,application):    #這個就是make_server函數中調用的 set_app
        self.application = application
  def get_app(self):            #
        return self.application

標準庫 BaseHTTPServer.py  
class HTTPServer(SocketServer.TCPServer) 
  def __init__=  標準庫 SocketServer.py class TCPServer(BaseServer):


標準庫 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:         # 這里調用socket.socket綁定端口
            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):    #這個就是run_simple中調用的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()   #調用serve_forever時調用_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)  #繼續
            except:
                self.handle_error(request, client_address)
                self.shutdown_request(request)

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

    def finish_request(self, request, client_address):
        self.RequestHandlerClass(request, client_address, self)    # #繼續 并參見 werkzeug/serving.py  make_server()    

調用serve_forever后到了self.RequestHandlerClass(request, client_address, self) ，根據前面的代碼可知RequestHandlerClass 就是werkzeug/serving.py中的BaseRequestHandler，繼續

class BaseRequestHandler(WSGIRequestHandler):
    def __init__=  標準庫 wsgiref/simple_server.py class WSGIRequestHandler(BaseHTTPRequestHandler): #這句跟前面一樣繼承父類   
    

wsgiref/simple_server.py

class WSGIRequestHandler(BaseHTTPRequestHandler):
    def __init__=  標準庫 BaseHTTPServer.py class BaseHTTPRequestHandler(SocketServer.StreamRequestHandler): #繼續父類

BaseHTTPServer.py
class BaseHTTPRequestHandler(SocketServer.StreamRequestHandler):
    def __init__=  標準庫 SocketServer.py  class StreamRequestHandler(BaseRequestHandler):  #繼續父類


SocketServer.py

class StreamRequestHandler(BaseRequestHandler):
 #繼續父類

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()   # 運行  參見 werkzeug/serving.py  class BaseRequestHandler.handle
        finally:
            self.finish()

最后運行了self.handle() 參見 werkzeug/serving.py class BaseRequestHandler.handle
前面有，再貼下看看

class BaseRequestHandler(WSGIRequestHandler):
   def handle(self):     #1、調用的就是這個handle，覆蓋了父類的handle 
        self.raw_requestline = self.rfile.readline()
        if self.parse_request():
            self.get_handler().run(self.server.get_app())  #2、調用 get_handler()后，還繼續調用 run（） ，get_app就是wsgiref/simple_server.py中WSGIServer類定義的函數   

    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、新建一個類 返回的就是這個類 ，繼承ServerHandler
              """   
                  5、直接從其他文件copy出所需代碼，也就是handler的父類
                   wsgiref/simple_server.py  class ServerHandler(SimpleHandler): 繼續父類 
                   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、調用的就是這個類的run函數
                                  def run(self, application):
                                    try:
                                        self.setup_environ()
                                        self.result = application(self.environ, self.start_response)   #7、調用app，也就是app=Flask() Flask類的 __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

 

可以看出最后調用的是application(self.environ, self.start_response) 這個application就是開始的app = Flask(__name__)，調用類就是調用類的__call__ 函數 ，繼續貼一下源碼

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，最后調用wsgi_app(self, environ, start_response)函數，這個就是返回響應的主函數了！！

從整個流程中，flask利用WSGIServer類啟動監聽端口并綁定，BaseRequestHandler類接收、返回相應的信息！完全符合WSGI要求。
剩余的工作就太過于底層，不好深入分析了。也畫了調用流程圖，不過太大不好傳，如果有需要可以繼續交流！