Python与Redis的连接教程

class ConnectionPool(object): 
    ...........
  def __init__(self, connection_class=Connection, max_connections=None,
         **connection_kwargs):  #类初始化时调用构造函数
    max_connections = max_connections or 2 ** 31
    if not isinstance(max_connections, (int, long)) or max_connections < 0: #判断输入的max_connections是否合法
      raise ValueError('"max_connections" must be a positive integer')
    self.connection_class = connection_class #设置对应的参数
    self.connection_kwargs = connection_kwargs
    self.max_connections = max_connections
    self.reset() #初始化ConnectionPool 时的reset操作
  def reset(self):
    self.pid = os.getpid()
    self._created_connections = 0 #已经创建的连接的计数器
    self._available_connections = []  #声明一个空的数组，用来存放可用的连接
    self._in_use_connections = set() #声明一个空的集合，用来存放已经在用的连接
    self._check_lock = threading.Lock()
.......
  def get_connection(self, command_name, *keys, **options): #在连接池中获取连接的方法
    "Get a connection from the pool"
    self._checkpid()
    try:
      connection = self._available_connections.pop() #获取并删除代表连接的元素，在第一次获取connectiong时，因为_available_connections是一个空的数组，
      会直接调用make_connection方法
    except IndexError:
      connection = self.make_connection()
    self._in_use_connections.add(connection)  #向代表正在使用的连接的集合中添加元素
    return connection  
  def make_connection(self): #在_available_connections数组为空时获取连接调用的方法
    "Create a new connection"
    if self._created_connections >= self.max_connections:  #判断创建的连接是否已经达到最大限制，max_connections可以通过参数初始化
      raise ConnectionError("Too many connections")
    self._created_connections += 1  #把代表已经创建的连接的数值+1
    return self.connection_class(**self.connection_kwargs)   #返回有效的连接，默认为Connection(**self.connection_kwargs)
  def release(self, connection): #释放连接，链接并没有断开，只是存在链接池中
    "Releases the connection back to the pool"
    self._checkpid()
    if connection.pid != self.pid:
      return
    self._in_use_connections.remove(connection)  #从集合中删除元素
    self._available_connections.append(connection) #并添加到_available_connections 的数组中
  def disconnect(self): #断开所有连接池中的链接
    "Disconnects all connections in the pool"
    all_conns = chain(self._available_connections,
             self._in_use_connections)
    for connection in all_conns:
      connection.disconnect()

execute_command最终调用的是Connection.send_command方法，关闭链接为 Connection.disconnect方法，而Connection类的实现：

class Connection(object):
  "Manages TCP communication to and from a Redis server"
  def __del__(self):  #对象删除时的操作，调用disconnect释放连接
    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:  #构造函数中默认 socket_keepalive=False，因此这里默认为短连接
          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) #构造函数中默认socket_connect_timeout=None，即连接为blocking的模式
        # connect
        sock.connect(socket_address)
        # set the socket_timeout now that we're connected
        sock.settimeout(self.socket_timeout) #构造函数中默认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