從SocketServer 講起

    +------------+
    | BaseServer |
    +------------+
          |
          v
    +-----------+        +------------------+
    | TCPServer |------->| UnixStreamServer |
    +-----------+        +------------------+
          |
          v
    +-----------+        +--------------------+
    | UDPServer |------->| UnixDatagramServer |
    +-----------+        +--------------------+

整個(gè)模塊的結(jié)構(gòu)大概是這樣的熄攘，由BaseServer衍生出TCPServer补鼻，UDPServer胀葱，然后以此為基類，后續(xù)還有HTTPServer(SocketServer.TCPServer)唇牧，class WSGIServer(HTTPServer)罕扎，但入口都是接下去要說的SockerServer中的一些類。

BaseServer 有以下的一些方法

Methods for the caller:

    - __init__(server_address, RequestHandlerClass)
    - serve_forever(poll_interval=0.5)
    - shutdown()
    - handle_request()  # if you do not use serve_forever()
    - fileno() -> int   # for select()

    Methods that may be overridden:

    - server_bind()
    - server_activate()
    - get_request() -> request, client_address
    - handle_timeout()
    - verify_request(request, client_address)
    - server_close()
    - process_request(request, client_address)
    - shutdown_request(request)
    - close_request(request)
    - handle_error()

    Methods for derived classes:

    - finish_request(request, client_address)

    Class variables that may be overridden by derived classes or
    instances:

    - timeout
    - address_family
    - socket_type
    - allow_reuse_address

    Instance variables:

    - RequestHandlerClass
    - socket

這其中有一系列鉤子方法留著給子類復(fù)寫以實(shí)現(xiàn)其特有的功能丐重。其中實(shí)現(xiàn)具體處理邏輯的為_handle_request_noblock方法

def _handle_request_noblock(self):
    """Handle one request, without blocking.

    I assume that select.select has returned that the socket is
    readable before this function was called, so there should be
    no risk of blocking in get_request().
    """
    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)
        except:
            self.handle_error(request, client_address)
            self.shutdown_request(request)

get_request 需要子類來實(shí)現(xiàn)腔召，獲取request和address，而后由process_request 來處理扮惦，process_request 會依次調(diào)用finish_request 和shutdown_request,finish_request會調(diào)用RequestHandlerClass（需要傳入臀蛛，為具體處理的handler）。

def serve_forever(self, poll_interval=0.5):
    self.__is_shut_down.clear()
    try:
        while not self.__shutdown_request:
            # XXX: Consider using another file descriptor or
            # connecting to the socket to wake this up instead of
            # polling. Polling reduces our responsiveness to a
            # shutdown request and wastes cpu at all other times.
            r, w, e = _eintr_retry(select.select, [self], [], [],
                                   poll_interval)
            if self in r:
                self._handle_request_noblock()
    finally:
        self.__shutdown_request = False
        self.__is_shut_down.set()

在serve_forever 中崖蜜，會使用select 獲取需要處理的內(nèi)容浊仆，再調(diào)用上邊的_handle_request_noblock。

簡單的流程是這樣的豫领，BaseServer中定義了一些處理流程方面的東西抡柿，并沒有任何具體的處理，所有的處理流程等恐，都留給了子類洲劣。另外還有些上述沒提到的留給TCP 和UDPserver的方法，比如TCP的server_bind等不一一說了课蔬，具體看代碼囱稽。

Threading , Forking

這個(gè)模塊非常巧妙的使用mix-in class實(shí)現(xiàn)了Threading和Forking。

通過上面的分析我們知道二跋，核心的處理邏輯是process_request方法战惊，以多線程為例，如果我們要實(shí)現(xiàn)多線程扎即，其實(shí)只需要對這個(gè)方法做些改動即可吞获。

def process_request_thread(self, request, client_address):
    """Same as in BaseServer but as a thread.
    In addition, exception handling is done here.
    """
    try:
        self.finish_request(request, client_address)
        self.shutdown_request(request)
    except:
        self.handle_error(request, client_address)
        self.shutdown_request(request)

def process_request(self, request, client_address):
    """Start a new thread to process the request."""
    t = threading.Thread(target = self.process_request_thread,
                         args = (request, client_address))
    t.daemon = self.daemon_threads
    t.start()

class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass

就是這么簡單的實(shí)現(xiàn)，同樣的還有ForkingMixIn 铺遂， 這兩個(gè)mix-in class在后續(xù)很多地方都還會使用到衫哥，簡直是mix-in使用的完美范例茎刚。

handler

handler的基類是BaseRequestHandler,非常的短襟锐。

def __init__(self, request, client_address, server):
    self.request = request
    self.client_address = client_address
    self.server = server
    self.setup()
    try:
        self.handle()
    finally:
        self.finish()

def setup(self):
    pass

def handle(self):
    pass

def finish(self):
    pass

而后還有兩個(gè)具體的實(shí)現(xiàn)，StreamRequestHandler 和DatagramRequestHandler膛锭，分別用于TCP 和UDPServer中粮坞，也只是簡單實(shí)現(xiàn)了setup和finish蚊荣，核心handle方法留給子類實(shí)現(xiàn)。

入BaseHttpServer中莫杈，有一個(gè)BaseHTTPRequestHandler互例，針對http協(xié)議做了一系列處理，當(dāng)然筝闹，既然以base開頭媳叨，也只是為后續(xù)實(shí)現(xiàn)提供方便。如werkzeug.serving中的WSGIRequestHandler关顷，在繼承BaseHTTPRequestHandler的基礎(chǔ)上糊秆，做了一些修改，用于適配wsgi標(biāo)準(zhǔn)议双。如需要傳入application痘番，用于處理具體業(yè)務(wù)。