r=redis.StrictRedis(host=xxxx, port=xxxx, db=xxxx)
 r.xxxx()

pool = redis.ConnectionPool(host=xxx, port=xxx, db=xxxx)
r = redis.Redis(connection_pool=pool)

class StrictRedis(object):
........
  def __init__(self, host='localhost', port=6379,
         db=0, password=None, socket_timeout=None,
         socket_connect_timeout=None,
         socket_keepalive=None, socket_keepalive_options=None,
         connection_pool=None, unix_socket_path=None,
         encoding='utf-8', encoding_errors='strict',
         charset=None, errors=None,
         decode_responses=False, retry_on_timeout=False,
         ssl=False, ssl_keyfile=None, ssl_certfile=None,
         ssl_cert_reqs=None, ssl_ca_certs=None):
     if not connection_pool:
       ..........
       connection_pool = ConnectionPool(**kwargs)
     self.connection_pool = connection_pool

  # COMMAND EXECUTION AND PROTOCOL PARSING
  def execute_command(self, *args, **options):
    "Execute a command and return a parsed response"
    pool = self.connection_pool
    command_name = args[0]
    connection = pool.get_connection(command_name, **options) #調(diào)用ConnectionPool.get_connection方法獲取一個連接
    try:
      connection.send_command(*args) #命令執(zhí)行，這里為Connection.send_command
      return self.parse_response(connection, command_name, **options)
    except (ConnectionError, TimeoutError) as e:
      connection.disconnect()
      if not connection.retry_on_timeout and isinstance(e, TimeoutError):
        raise
      connection.send_command(*args) 
      return self.parse_response(connection, command_name, **options)
    finally:
      pool.release(connection) #調(diào)用ConnectionPool.release釋放連接

class ConnectionPool(object): 
    ...........
  def __init__(self, connection_class=Connection, max_connections=None,
         **connection_kwargs):  #類初始化時調(diào)用構(gòu)造函數(shù)
    max_connections = max_connections or 2 ** 31
    if not isinstance(max_connections, (int, long)) or max_connections < 0: #判斷輸入的max_connections是否合法
      raise ValueError('"max_connections" must be a positive integer')
    self.connection_class = connection_class #設(shè)置對應(yīng)的參數(shù)
    self.connection_kwargs = connection_kwargs
    self.max_connections = max_connections
    self.reset() #初始化ConnectionPool 時的reset操作
  def reset(self):
    self.pid = os.getpid()
    self._created_connections = 0 #已經(jīng)創(chuàng)建的連接的計數(shù)器
    self._available_connections = []  #聲明一個空的數(shù)組，用來存放可用的連接
    self._in_use_connections = set() #聲明一個空的集合，用來存放已經(jīng)在用的連接
    self._check_lock = threading.Lock()
.......
  def get_connection(self, command_name, *keys, **options): #在連接池中獲取連接的方法
    "Get a connection from the pool"
    self._checkpid()
    try:
      connection = self._available_connections.pop() #獲取并刪除代表連接的元素，在第一次獲取connectiong時，因為_available_connections是一個空的數(shù)組，
      會直接調(diào)用make_connection方法
    except IndexError:
      connection = self.make_connection()
    self._in_use_connections.add(connection)  #向代表正在使用的連接的集合中添加元素
    return connection  
  def make_connection(self): #在_available_connections數(shù)組為空時獲取連接調(diào)用的方法
    "Create a new connection"
    if self._created_connections >= self.max_connections:  #判斷創(chuàng)建的連接是否已經(jīng)達到最大限制，max_connections可以通過參數(shù)初始化
      raise ConnectionError("Too many connections")
    self._created_connections += 1  #把代表已經(jīng)創(chuàng)建的連接的數(shù)值+1
    return self.connection_class(**self.connection_kwargs)   #返回有效的連接，默認(rèn)為Connection(**self.connection_kwargs)
  def release(self, connection): #釋放連接，鏈接并沒有斷開，只是存在鏈接池中
    "Releases the connection back to the pool"
    self._checkpid()
    if connection.pid != self.pid:
      return
    self._in_use_connections.remove(connection)  #從集合中刪除元素
    self._available_connections.append(connection) #并添加到_available_connections 的數(shù)組中
  def disconnect(self): #斷開所有連接池中的鏈接
    "Disconnects all connections in the pool"
    all_conns = chain(self._available_connections,
             self._in_use_connections)
    for connection in all_conns:
      connection.disconnect()

class Connection(object):
  "Manages TCP communication to and from a Redis server"
  def __del__(self):  #對象刪除時的操作，調(diào)用disconnect釋放連接
    try:
      self.disconnect()
    except Exception:
      pass

 def _connect(self):
    err = None
    for res in socket.getaddrinfo(self.host, self.port, 0,
                   socket.SOCK_STREAM):
      family, socktype, proto, canonname, socket_address = res
      sock = None
      try:
        sock = socket.socket(family, socktype, proto)
        # TCP_NODELAY
        sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
        # TCP_KEEPALIVE
        if self.socket_keepalive:  #構(gòu)造函數(shù)中默認(rèn) socket_keepalive=False，因此這里默認(rèn)為短連接
          sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
          for k, v in iteritems(self.socket_keepalive_options):
            sock.setsockopt(socket.SOL_TCP, k, v)
        # set the socket_connect_timeout before we connect
        sock.settimeout(self.socket_connect_timeout) #構(gòu)造函數(shù)中默認(rèn)socket_connect_timeout=None，即連接為blocking的模式
        # connect
        sock.connect(socket_address)
        # set the socket_timeout now that we're connected
        sock.settimeout(self.socket_timeout) #構(gòu)造函數(shù)中默認(rèn)socket_timeout=None
        return sock
      except socket.error as _:
        err = _
        if sock is not None:
          sock.close()
.....

  def disconnect(self):
    "Disconnects from the Redis server"
    self._parser.on_disconnect()
    if self._sock is None:
      return
    try:
      self._sock.shutdown(socket.SHUT_RDWR) #先shutdown再close
      self._sock.close()
    except socket.error:
      pass
    self._sock = None