python之socket編程

本章內容

　　1、socket

　　2、IO多路復用

　　3、socketserver

Socket

socket起源於Unix，而Unix/Linux基本哲學之一就是“一切皆文件”，對於文件用【打開】【讀寫】【關閉】模式來操作。socket就是該模式的一個實現，socket即是一種特殊的文件，一些socket函數就是對其進行的操作（讀/寫IO、打開、關閉）

基本上，Socket 是任何一種計算機網絡通訊中最基礎的內容。例如當你在瀏覽器地址欄中輸入 http://www.cnblogs.com/ 時，你會打開一個套接字，然后連接到 http://www.cnblogs.com/ 並讀取響應的頁面然后然后顯示出來。而其他一些聊天客戶端如 gtalk 和 skype 也是類似。任何網絡通訊都是通過 Socket 來完成的。

Python 官方關於 Socket 的函數請看 http://docs.python.org/library/socket.html

socket和file的區別：

　　1、file模塊是針對某個指定文件進行【打開】【讀寫】【關閉】

　　2、socket模塊是針對 服務器端 和 客戶端Socket 進行【打開】【讀寫】【關閉】

那我們就先來創建一個socket服務端吧

import socket

sk = socket.socket()
sk.bind(("127.0.0.1",8080))
sk.listen(5)

conn,address = sk.accept()
sk.sendall(bytes("Hello world",encoding="utf-8"))

import socket

obj = socket.socket()
obj.connect(("127.0.0.1",8080))

ret = str(obj.recv(1024),encoding="utf-8")
print(ret)

 

socket更多功能

    def bind(self, address): # real signature unknown; restored from __doc__
        """
        bind(address)
        
        Bind the socket to a local address.  For IP sockets, the address is a
        pair (host, port); the host must refer to the local host. For raw packet
        sockets the address is a tuple (ifname, proto [,pkttype [,hatype]])
        """
'''將套接字綁定到本地地址。是一個IP套接字的地址對(主機、端口),主機必須參考本地主機。'''
        pass

    def close(self): # real signature unknown; restored from __doc__
        """
        close()
        
        Close the socket.  It cannot be used after this call.
        """
        '''關閉socket'''
        pass

    def connect(self, address): # real signature unknown; restored from __doc__
        """
        connect(address)
        
        Connect the socket to a remote address.  For IP sockets, the address
        is a pair (host, port).
        """
        '''將套接字連接到遠程地址。IP套接字的地址'''
        pass

    def connect_ex(self, address): # real signature unknown; restored from __doc__
        """
        connect_ex(address) -> errno
        
        This is like connect(address), but returns an error code (the errno value)
        instead of raising an exception when an error occurs.
        """
        pass

    def detach(self): # real signature unknown; restored from __doc__
        """
        detach()
        
        Close the socket object without closing the underlying file descriptor.
        The object cannot be used after this call, but the file descriptor
        can be reused for other purposes.  The file descriptor is returned.
        """
'''關閉套接字對象沒有關閉底層的文件描述符。'''
        pass

    def fileno(self): # real signature unknown; restored from __doc__
        """
        fileno() -> integer
        
        Return the integer file descriptor of the socket.
        """
        '''返回整數的套接字的文件描述符。'''
        return 0

    def getpeername(self): # real signature unknown; restored from __doc__
        """
        getpeername() -> address info
        
        Return the address of the remote endpoint.  For IP sockets, the address
        info is a pair (hostaddr, port).
            """
        '''返回遠程端點的地址。IP套接字的地址'''
        pass

    def getsockname(self): # real signature unknown; restored from __doc__
        """
        getsockname() -> address info
        
        Return the address of the local endpoint.  For IP sockets, the address
        info is a pair (hostaddr, port).
        """
        '''返回遠程端點的地址。IP套接字的地址'''
        pass

    def getsockopt(self, level, option, buffersize=None): # real signature unknown; restored from __doc__
        """
        getsockopt(level, option[, buffersize]) -> value
        
        Get a socket option.  See the Unix manual for level and option.
        If a nonzero buffersize argument is given, the return value is a
        string of that length; otherwise it is an integer.
        """
        '''得到一個套接字選項'''
        pass

    def gettimeout(self): # real signature unknown; restored from __doc__
        """
        gettimeout() -> timeout
        
        Returns the timeout in seconds (float) associated with socket 
        operations. A timeout of None indicates that timeouts on socket 
        operations are disabled.
        """
        '''返回的超時秒數(浮動)與套接字相關聯'''
        return timeout

    def ioctl(self, cmd, option): # real signature unknown; restored from __doc__
        """
        ioctl(cmd, option) -> long
        
        Control the socket with WSAIoctl syscall. Currently supported 'cmd' values are
        SIO_RCVALL:  'option' must be one of the socket.RCVALL_* constants.
        SIO_KEEPALIVE_VALS:  'option' is a tuple of (onoff, timeout, interval).
        """
        return 0

    def listen(self, backlog=None): # real signature unknown; restored from __doc__
        """
        listen([backlog])
        
        Enable a server to accept connections.  If backlog is specified, it must be
        at least 0 (if it is lower, it is set to 0); it specifies the number of
        unaccepted connections that the system will allow before refusing new
        connections. If not specified, a default reasonable value is chosen.
        """
        '''使服務器能夠接受連接。'''
        pass

    def recv(self, buffersize, flags=None): # real signature unknown; restored from __doc__
        """
        recv(buffersize[, flags]) -> data
        
        Receive up to buffersize bytes from the socket.  For the optional flags
        argument, see the Unix manual.  When no data is available, block until
        at least one byte is available or until the remote end is closed.  When
        the remote end is closed and all data is read, return the empty string.
        """
'''當沒有數據可用,阻塞,直到至少一個字節是可用的或遠程結束之前關閉。'''
        pass

    def recvfrom(self, buffersize, flags=None): # real signature unknown; restored from __doc__
        """
        recvfrom(buffersize[, flags]) -> (data, address info)
        
        Like recv(buffersize, flags) but also return the sender's address info.
        """
        pass

    def recvfrom_into(self, buffer, nbytes=None, flags=None): # real signature unknown; restored from __doc__
        """
        recvfrom_into(buffer[, nbytes[, flags]]) -> (nbytes, address info)
        
        Like recv_into(buffer[, nbytes[, flags]]) but also return the sender's address info.
        """
        pass

    def recv_into(self, buffer, nbytes=None, flags=None): # real signature unknown; restored from __doc__
        """
        recv_into(buffer, [nbytes[, flags]]) -> nbytes_read
        
        A version of recv() that stores its data into a buffer rather than creating 
        a new string.  Receive up to buffersize bytes from the socket.  If buffersize 
        is not specified (or 0), receive up to the size available in the given buffer.
        
        See recv() for documentation about the flags.
        """
        pass

    def send(self, data, flags=None): # real signature unknown; restored from __doc__
        """
        send(data[, flags]) -> count
        
        Send a data string to the socket.  For the optional flags
        argument, see the Unix manual.  Return the number of bytes
        sent; this may be less than len(data) if the network is busy.
        """
        '''發送一個數據字符串到套接字。'''
        pass

    def sendall(self, data, flags=None): # real signature unknown; restored from __doc__
        """
        sendall(data[, flags])
        
        Send a data string to the socket.  For the optional flags
        argument, see the Unix manual.  This calls send() repeatedly
        until all data is sent.  If an error occurs, it's impossible
        to tell how much data has been sent.
        """
        '''發送一個數據字符串到套接字，直到所有數據發送完成'''
        pass

    def sendto(self, data, flags=None, *args, **kwargs): # real signature unknown; NOTE: unreliably restored from __doc__ 
        """
        sendto(data[, flags], address) -> count
        
        Like send(data, flags) but allows specifying the destination address.
        For IP sockets, the address is a pair (hostaddr, port).
        """
        pass

    def setblocking(self, flag): # real signature unknown; restored from __doc__
        """
        setblocking(flag)
        
        Set the socket to blocking (flag is true) or non-blocking (false).
        setblocking(True) is equivalent to settimeout(None);
        setblocking(False) is equivalent to settimeout(0.0).
        """
'''是否阻塞（默認True），如果設置False，那么accept和recv時一旦無數據，則報錯。'''
        pass

    def setsockopt(self, level, option, value): # real signature unknown; restored from __doc__
        """
        setsockopt(level, option, value)
        
        Set a socket option.  See the Unix manual for level and option.
        The value argument can either be an integer or a string.
        """
        pass

    def settimeout(self, timeout): # real signature unknown; restored from __doc__
        """
        settimeout(timeout)
        
        Set a timeout on socket operations.  'timeout' can be a float,
        giving in seconds, or None.  Setting a timeout of None disables
        the timeout feature and is equivalent to setblocking(1).
        Setting a timeout of zero is the same as setblocking(0).
        """
        pass

    def share(self, process_id): # real signature unknown; restored from __doc__
        """
        share(process_id) -> bytes
        
        Share the socket with another process.  The target process id
        must be provided and the resulting bytes object passed to the target
        process.  There the shared socket can be instantiated by calling
        socket.fromshare().
        """
        return b""

    def shutdown(self, flag): # real signature unknown; restored from __doc__
        """
        shutdown(flag)
        
        Shut down the reading side of the socket (flag == SHUT_RD), the writing side
        of the socket (flag == SHUT_WR), or both ends (flag == SHUT_RDWR).
        """
        pass

    def _accept(self): # real signature unknown; restored from __doc__
        """
        _accept() -> (integer, address info)
        
        Wait for an incoming connection.  Return a new socket file descriptor
        representing the connection, and the address of the client.
        For IP sockets, the address info is a pair (hostaddr, port).
        """
        pass
    

注：擼主知道大家懶，所以把全部功能的中文標記在每個功能的下面啦。下面擼主列一些經常用到的吧

sk.bind(address)

　　s.bind(address) 將套接字綁定到地址。address地址的格式取決於地址族。在AF_INET下，以元組（host,port）的形式表示地址。

sk.listen(backlog)

　　開始監聽傳入連接。backlog指定在拒絕連接之前，可以掛起的最大連接數量。

      backlog等於5，表示內核已經接到了連接請求，但服務器還沒有調用accept進行處理的連接個數最大為5
      這個值不能無限大，因為要在內核中維護連接隊列

sk.setblocking(bool)

　　是否阻塞（默認True），如果設置False，那么accept和recv時一旦無數據，則報錯。

sk.accept()

　　接受連接並返回（conn,address）,其中conn是新的套接字對象，可以用來接收和發送數據。address是連接客戶端的地址。

　　接收TCP 客戶的連接（阻塞式）等待連接的到來

sk.connect(address)

　　連接到address處的套接字。一般，address的格式為元組（hostname,port）,如果連接出錯，返回socket.error錯誤。

sk.connect_ex(address)

　　同上，只不過會有返回值，連接成功時返回 0 ，連接失敗時候返回編碼，例如：10061

sk.close()

　　關閉套接字

sk.recv(bufsize[,flag])

　　接受套接字的數據。數據以字符串形式返回，bufsize指定最多可以接收的數量。flag提供有關消息的其他信息，通常可以忽略。

sk.recvfrom(bufsize[.flag])

　　與recv()類似，但返回值是（data,address）。其中data是包含接收數據的字符串，address是發送數據的套接字地址。

sk.send(string[,flag])

　　將string中的數據發送到連接的套接字。返回值是要發送的字節數量，該數量可能小於string的字節大小。即：可能未將指定內容全部發送。

sk.sendall(string[,flag])

　　將string中的數據發送到連接的套接字，但在返回之前會嘗試發送所有數據。成功返回None，失敗則拋出異常。

      內部通過遞歸調用send，將所有內容發送出去。

sk.sendto(string[,flag],address)

　　將數據發送到套接字，address是形式為（ipaddr，port）的元組，指定遠程地址。返回值是發送的字節數。該函數主要用於UDP協議。

sk.settimeout(timeout)

　　設置套接字操作的超時期，timeout是一個浮點數，單位是秒。值為None表示沒有超時期。一般，超時期應該在剛創建套接字時設置，因為它們可能用於連接的操作（如 client 連接最多等待5s ）

sk.getpeername()

　　返回連接套接字的遠程地址。返回值通常是元組（ipaddr,port）。

sk.getsockname()

　　返回套接字自己的地址。通常是一個元組(ipaddr,port)

sk.fileno()

　　套接字的文件描述符

TCP：

 

import  socketserver
服務端

class Myserver(socketserver.BaseRequestHandler):

    def handle(self):

        conn = self.request
        conn.sendall(bytes("你好，我是機器人",encoding="utf-8"))
        while True:
            ret_bytes = conn.recv(1024)
            ret_str = str(ret_bytes,encoding="utf-8")
            if ret_str == "q":
                break
            conn.sendall(bytes(ret_str+"你好我好大家好",encoding="utf-8"))

if __name__ == "__main__":
    server = socketserver.ThreadingTCPServer(("127.0.0.1",8080),Myserver)
    server.serve_forever()

客戶端

import socket

obj = socket.socket()

obj.connect(("127.0.0.1",8080))

ret_bytes = obj.recv(1024)
ret_str = str(ret_bytes,encoding="utf-8")
print(ret_str)

while True:
    inp = input("你好請問您有什么問題？ \n >>>")
    if inp == "q":
        obj.sendall(bytes(inp,encoding="utf-8"))
        break
    else:
        obj.sendall(bytes(inp, encoding="utf-8"))
        ret_bytes = obj.recv(1024)
        ret_str = str(ret_bytes,encoding="utf-8")
        print(ret_str)

服務端

import socket

sk = socket.socket()

sk.bind(("127.0.0.1",8080))
sk.listen(5)

while True:
    conn,address = sk.accept()
    conn.sendall(bytes("歡迎光臨我愛我家",encoding="utf-8"))

    size = conn.recv(1024)
    size_str = str(size,encoding="utf-8")
    file_size = int(size_str)

    conn.sendall(bytes("開始傳送", encoding="utf-8"))

    has_size = 0
    f = open("db_new.jpg","wb")
    while True:
        if file_size == has_size:
            break
        date = conn.recv(1024)
        f.write(date)
        has_size += len(date)

    f.close()

客戶端

import socket
import os

obj = socket.socket()

obj.connect(("127.0.0.1",8080))

ret_bytes = obj.recv(1024)
ret_str = str(ret_bytes,encoding="utf-8")
print(ret_str)

size = os.stat("yan.jpg").st_size
obj.sendall(bytes(str(size),encoding="utf-8"))

obj.recv(1024)

with open("yan.jpg","rb") as f:
    for line in f:
        obj.sendall(line)

UdP

import socket
ip_port = ('127.0.0.1',9999)
sk = socket.socket(socket.AF_INET,socket.SOCK_DGRAM,0)
sk.bind(ip_port)

while True:
    data = sk.recv(1024)
    print data




import socket
ip_port = ('127.0.0.1',9999)

sk = socket.socket(socket.AF_INET,socket.SOCK_DGRAM,0)
while True:
    inp = input('數據：').strip()
    if inp == 'exit':
        break
    sk.sendto(bytes(inp,encoding = "utf-8"),ip_port)

sk.close()

WEB服務應用：

#!/usr/bin/env python
#coding:utf-8
import socket
 
def handle_request(client):
    buf = client.recv(1024)
    client.send("HTTP/1.1 200 OK\r\n\r\n")
    client.send("Hello, World")
 
def main():
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.bind(('localhost',8080))
    sock.listen(5)
 
    while True:
        connection, address = sock.accept()
        handle_request(connection)
        connection.close()
 
if __name__ == '__main__':
  main()

 

IO多路復用 

I/O（input/output），即輸入/輸出端口。每個設備都會有一個專用的I/O地址，用來處理自己的輸入輸出信息首先什么是I/O：

I/O分為磁盤io和網絡io，這里說的是網絡io

IO多路復用:

I/O多路復用指：通過一種機制，可以監視多個描述符(socket)，一旦某個描述符就緒（一般是讀就緒或者寫就緒），能夠通知程序進行相應的讀寫操作。

Linux

Linux中的 select，poll，epoll 都是IO多路復用的機制。

Linux下網絡I/O使用socket套接字來通信，普通I/O模型只能監聽一個socket，而I/O多路復用可同時監聽多個socket.

I/O多路復用避免阻塞在io上，原本為多進程或多線程來接收多個連接的消息變為單進程或單線程保存多個socket的狀態后輪詢處理.

Python  

Python中有一個select模塊，其中提供了：select、poll、epoll三個方法，分別調用系統的 select，poll，epoll 從而實現IO多路復用。

Windows Python：

    提供： select

Mac Python：

    提供： select

Linux Python：

    提供： select、poll、epoll

對於select模塊操作的方法：

句柄列表11, 句柄列表22, 句柄列表33 = select.select(句柄序列1, 句柄序列2, 句柄序列3, 超時時間)
 
參數： 可接受四個參數（前三個必須）
返回值：三個列表
 
select方法用來監視文件句柄，如果句柄發生變化，則獲取該句柄。
1、當 參數1 序列中的句柄發生可讀時（accetp和read），則獲取發生變化的句柄並添加到 返回值1 序列中
2、當 參數2 序列中含有句柄時，則將該序列中所有的句柄添加到 返回值2 序列中
3、當 參數3 序列中的句柄發生錯誤時，則將該發生錯誤的句柄添加到 返回值3 序列中
4、當 超時時間 未設置，則select會一直阻塞，直到監聽的句柄發生變化
5、當 超時時間 ＝ 1時，那么如果監聽的句柄均無任何變化，則select會阻塞 1 秒，之后返回三個空列表，如果監聽的句柄有變化，則直接執行。

import socket
import select


sk1 = socket.socket()
sk1.bind(("127.0.0.1",8001))
sk1.listen()

sk2 = socket.socket()
sk2.bind(("127.0.0.1",8002))
sk2.listen()

sk3 = socket.socket()
sk3.bind(("127.0.0.1",8003))
sk3.listen()

li = [sk1,sk2,sk3]

while True:
    r_list,w_list,e_list = select.select(li,[],[],1) # r_list可變化的
    for line in r_list: 
        conn,address = line.accept()
        conn.sendall(bytes("Hello World !",encoding="utf-8"))

服務端：
sk1 = socket.socket()
sk1.bind(("127.0.0.1",8001))
sk1.listen()

inpu = [sk1,]

while True:
    r_list,w_list,e_list = select.select(inpu,[],[],1)
    for sk in r_list:
        if sk == sk1:
            conn,address = sk.accept()
            inpu.append(conn)
        else:
            try:
                ret = str(sk.recv(1024),encoding="utf-8")
                sk.sendall(bytes(ret+"hao",encoding="utf-8"))
            except Exception as ex:
                inpu.remove(sk)

客戶端
import socket

obj = socket.socket()

obj.connect(('127.0.0.1',8001))

while True:
    inp = input("Please(q\退出):\n>>>")
    obj.sendall(bytes(inp,encoding="utf-8"))
    if inp == "q":
        break
    ret = str(obj.recv(1024),encoding="utf-8")
    print(ret)

服務端：
import socket
sk1 = socket.socket()
sk1.bind(("127.0.0.1",8001))
sk1.listen()
inputs = [sk1]
import select
message_dic = {}
outputs = []
while True:

    r_list, w_list, e_list = select.select(inputs,[],inputs,1)
    print("正在監聽的socket對象%d" % len(inputs))
    print(r_list)
    for sk1_or_conn in r_list:
        if sk1_or_conn == sk1:
            conn,address = sk1_or_conn.accept()
            inputs.append(conn)
            message_dic[conn] = []
        else:
            try:
                data_bytes = sk1_or_conn.recv(1024)
                data_str = str(data_bytes,encoding="utf-8")
                sk1_or_conn.sendall(bytes(data_str+"好",encoding="utf-8"))
            except Exception as ex:
                inputs.remove(sk1_or_conn)
            else:
                data_str = str(data_bytes,encoding="utf-8")
                message_dic[sk1_or_conn].append(data_str)
                outputs.append(sk1_or_conn)
        for conn in w_list:
            recv_str = message_dic[conn][0]
            del message_dic[conn][0]
            conn.sendall(bytes(recv_str+"好",encoding="utf-8"))
        for sk in e_list:
            inputs.remove(sk)

客戶端：
import socket

obj = socket.socket()

obj.connect(('127.0.0.1',8001))

while True:
    inp = input("Please(q\退出):\n>>>")
    obj.sendall(bytes(inp,encoding="utf-8"))
    if inp == "q":
        break
    ret = str(obj.recv(1024),encoding="utf-8")
    print(ret)

 

socketserver

SocketServer內部使用 IO多路復用 以及 “多線程” 和 “多進程” ，從而實現並發處理多個客戶端請求的Socket服務端。即：每個客戶端請求連接到服務器時，Socket服務端都會在服務器是創建一個“線程”或者“進程” 專門負責處理當前客戶端的所有請求。

ThreadingTCPServer

ThreadingTCPServer實現的Soket服務器內部會為每個client創建一個 “線程”，該線程用來和客戶端進行交互。

1、ThreadingTCPServer基礎

使用ThreadingTCPServer:

• 創建一個繼承自 SocketServer.BaseRequestHandler 的類
• 類中必須定義一個名稱為 handle 的方法
• 啟動ThreadingTCPServer

import  socketserver

class Myserver(socketserver.BaseRequestHandler):

    def handle(self):

        conn = self.request
        conn.sendall(bytes("你好，我是機器人",encoding="utf-8"))
        while True:
            ret_bytes = conn.recv(1024)
            ret_str = str(ret_bytes,encoding="utf-8")
            if ret_str == "q":
                break
            conn.sendall(bytes(ret_str+"你好我好大家好",encoding="utf-8"))

if __name__ == "__main__":
    server = socketserver.ThreadingTCPServer(("127.0.0.1",8080),Myserver)
    server.serve_forever()

import socket

obj = socket.socket()

obj.connect(("127.0.0.1",8080))

ret_bytes = obj.recv(1024)
ret_str = str(ret_bytes,encoding="utf-8")
print(ret_str)

while True:
    inp = input("你好請問您有什么問題？ \n >>>")
    if inp == "q":
        obj.sendall(bytes(inp,encoding="utf-8"))
        break
    else:
        obj.sendall(bytes(inp, encoding="utf-8"))
        ret_bytes = obj.recv(1024)
        ret_str = str(ret_bytes,encoding="utf-8")
        print(ret_str)

2、ThreadingTCPServer源碼剖析

ThreadingTCPServer的類圖關系如下：

內部調用流程為：

• 啟動服務端程序
• 執行 TCPServer.__init__ 方法，創建服務端Socket對象並綁定 IP 和 端口
• 執行 BaseServer.__init__ 方法，將自定義的繼承自SocketServer.BaseRequestHandler 的類 MyRequestHandle賦值給 self.RequestHandlerClass
• 執行 BaseServer.server_forever 方法，While 循環一直監聽是否有客戶端請求到達 ...
• 當客戶端連接到達服務器
• 執行 ThreadingMixIn.process_request 方法，創建一個 “線程” 用來處理請求
• 執行 ThreadingMixIn.process_request_thread 方法
• 執行 BaseServer.finish_request 方法，執行 self.RequestHandlerClass()  即：執行 自定義 MyRequestHandler 的構造方法（自動調用基類BaseRequestHandler的構造方法，在該構造方法中又會調用 MyRequestHandler的handle方法）

 

相對應的源碼如下：

class BaseServer:

    """Base class for server classes.

    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

    """

    timeout = None

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor.  May be extended, do not override."""
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def server_activate(self):
        """Called by constructor to activate the server.

        May be overridden.

        """
        pass

    def serve_forever(self, poll_interval=0.5):
        """Handle one request at a time until shutdown.

        Polls for shutdown every poll_interval seconds. Ignores
        self.timeout. If you need to do periodic tasks, do them in
        another thread.
        """
        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()

    def shutdown(self):
        """Stops the serve_forever loop.

        Blocks until the loop has finished. This must be called while
        serve_forever() is running in another thread, or it will
        deadlock.
        """
        self.__shutdown_request = True
        self.__is_shut_down.wait()

    # The distinction between handling, getting, processing and
    # finishing a request is fairly arbitrary.  Remember:
    #
    # - handle_request() is the top-level call.  It calls
    #   select, get_request(), verify_request() and process_request()
    # - get_request() is different for stream or datagram sockets
    # - process_request() is the place that may fork a new process
    #   or create a new thread to finish the request
    # - finish_request() instantiates the request handler class;
    #   this constructor will handle the request all by itself

    def handle_request(self):
        """Handle one request, possibly blocking.

        Respects self.timeout.
        """
        # Support people who used socket.settimeout() to escape
        # handle_request before self.timeout was available.
        timeout = self.socket.gettimeout()
        if timeout is None:
            timeout = self.timeout
        elif self.timeout is not None:
            timeout = min(timeout, self.timeout)
        fd_sets = _eintr_retry(select.select, [self], [], [], timeout)
        if not fd_sets[0]:
            self.handle_timeout()
            return
        self._handle_request_noblock()

    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)

    def handle_timeout(self):
        """Called if no new request arrives within self.timeout.

        Overridden by ForkingMixIn.
        """
        pass

    def verify_request(self, request, client_address):
        """Verify the request.  May be overridden.

        Return True if we should proceed with this request.

        """
        return True

    def process_request(self, request, client_address):
        """Call finish_request.

        Overridden by ForkingMixIn and ThreadingMixIn.

        """
        self.finish_request(request, client_address)
        self.shutdown_request(request)

    def server_close(self):
        """Called to clean-up the server.

        May be overridden.

        """
        pass

    def finish_request(self, request, client_address):
        """Finish one request by instantiating RequestHandlerClass."""
        self.RequestHandlerClass(request, client_address, self)

    def shutdown_request(self, request):
        """Called to shutdown and close an individual request."""
        self.close_request(request)

    def close_request(self, request):
        """Called to clean up an individual request."""
        pass

    def handle_error(self, request, client_address):
        """Handle an error gracefully.  May be overridden.

        The default is to print a traceback and continue.

        """
        print '-'*40
        print 'Exception happened during processing of request from',
        print client_address
        import traceback
        traceback.print_exc() # XXX But this goes to stderr!
        print '-'*40

class TCPServer(BaseServer):

    """Base class for various socket-based server classes.

    Defaults to synchronous IP stream (i.e., TCP).

    Methods for the caller:

    - __init__(server_address, RequestHandlerClass, bind_and_activate=True)
    - serve_forever(poll_interval=0.5)
    - shutdown()
    - handle_request()  # if you don't 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)
    - 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
    - request_queue_size (only for stream sockets)
    - allow_reuse_address

    Instance variables:

    - server_address
    - RequestHandlerClass
    - socket

    """

    address_family = socket.AF_INET

    socket_type = socket.SOCK_STREAM

    request_queue_size = 5

    allow_reuse_address = False

    def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
        """Constructor.  May be extended, do not override."""
        BaseServer.__init__(self, server_address, RequestHandlerClass)
        self.socket = socket.socket(self.address_family,
                                    self.socket_type)
        if bind_and_activate:
            try:
                self.server_bind()
                self.server_activate()
            except:
                self.server_close()
                raise

    def server_bind(self):
        """Called by constructor to bind the socket.

        May be overridden.

        """
        if self.allow_reuse_address:
            self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.socket.bind(self.server_address)
        self.server_address = self.socket.getsockname()

    def server_activate(self):
        """Called by constructor to activate the server.

        May be overridden.

        """
        self.socket.listen(self.request_queue_size)

    def server_close(self):
        """Called to clean-up the server.

        May be overridden.

        """
        self.socket.close()

    def fileno(self):
        """Return socket file number.

        Interface required by select().

        """
        return self.socket.fileno()

    def get_request(self):
        """Get the request and client address from the socket.

        May be overridden.

        """
        return self.socket.accept()

    def shutdown_request(self, request):
        """Called to shutdown and close an individual request."""
        try:
            #explicitly shutdown.  socket.close() merely releases
            #the socket and waits for GC to perform the actual close.
            request.shutdown(socket.SHUT_WR)
        except socket.error:
            pass #some platforms may raise ENOTCONN here
        self.close_request(request)

    def close_request(self, request):
        """Called to clean up an individual request."""
        request.close()

class ThreadingMixIn:
    """Mix-in class to handle each request in a new thread."""

    # Decides how threads will act upon termination of the
    # main process
    daemon_threads = False

    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 BaseRequestHandler:

    """Base class for request handler classes.

    This class is instantiated for each request to be handled.  The
    constructor sets the instance variables request, client_address
    and server, and then calls the handle() method.  To implement a
    specific service, all you need to do is to derive a class which
    defines a handle() method.

    The handle() method can find the request as self.request, the
    client address as self.client_address, and the server (in case it
    needs access to per-server information) as self.server.  Since a
    separate instance is created for each request, the handle() method
    can define arbitrary other instance variariables.

    """

    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

SocketServer的ThreadingTCPServer之所以可以同時處理請求得益於 select 和 Threading 兩個東西，其實本質上就是在服務器端為每一個客戶端創建一個線程，當前線程用來處理對應客戶端的請求，所以，可以支持同時n個客戶端鏈接（長連接）。