使用的方法：
r=redis.StrictRedis(host=xxxx, port=xxxx, db=xxxx) r.xxxx()
有了ConnectionPool这个类之后，可以使用如下方法
pool = redis.ConnectionPool(host=xxx, port=xxx, db=xxxx) r = redis.Redis(connection_pool=pool)
这里Redis是StrictRedis的子类
简单分析如下：
在StrictRedis类的__init__方法中，可以初始化connection_pool这个参数，其对应的是一个ConnectionPool的对象：
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
在StrictRedis的实例执行具体的命令时会调用execute_command方法，这里可以看到具体实现是从连接池中获取一个具体的连接，然后执行命令，完成后释放连接：
# 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) #调用ConnectionPool.get_connection方法获取一个连接 try: connection.send_command(*args) #命令执行，这里为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) #调用ConnectionPool.release释放连接
在来看看ConnectionPool类：
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，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
核心的链接建立方法是通过socket模块实现：
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() .....
关闭链接的方法：
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
可以小结如下
1）默认情况下每创建一个Redis实例都会构造出一个ConnectionPool实例，每一次访问redis都会从这个连接池得到一个连接，操作完成后会把该连接放回连接池（连接并没有释放）,可以构造一个统一的ConnectionPool，在创建Redis实例时，可以将该ConnectionPool传入，那么后续的操作会从给定的ConnectionPool获得连接，不会再重复创建ConnectionPool。
2）默认情况下没有设置keepalive和timeout，建立的连接是blocking模式的短连接。
3）不考虑底层tcp的情况下，连接池中的连接会在ConnectionPool.disconnect中统一销毁。