连接池的实现 redis例子

# -*- encoding:utf-8 -*-
# import pymysql
#
# conn = pymysql.connect(host="127.0.0.1", port=3306, user="py",passwd="", db="codeline",client_flag=5)
# #conn2 = pymysql.connect(host="127.0.0.1", port=3306, user="py",
#            #            passwd="", db="codeline")
# conn.ping(True)
# #conn2.ping(True)
# while True:
#     print (1)
# cursor = conn.cursor()
# SQL = ("SELECT username FROM logint WHERE username='%s'" % username)
# print(username)
# cursor.execute(SQL)
# user = cursor.fetchone()
# conn.commit()

# Redis是StrictRedis的子类
class Redis(StrictRedis):
    """
    Provides backwards compatibility with older versions of redis-py that
    changed arguments to some commands to be more Pythonic, sane, or by
    accident.
    """
# StrictRedis基类
class StrictRedis(object):
    """
    Implementation of the Redis protocol.

    This abstract class provides a Python interface to all Redis commands
    and an implementation of the Redis protocol.

    Connection and Pipeline derive from this, implementing how
    the commands are sent and received to the Redis server
    """

    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):
        # 如果connection_pool没有定义的话就尝试获取其它设置后并重新创建连接池
        if not connection_pool:
            if charset is not None:
                warnings.warn(DeprecationWarning(
                    '"charset" is deprecated. Use "encoding" instead'))
                encoding = charset
            if errors is not None:
                warnings.warn(DeprecationWarning(
                    '"errors" is deprecated. Use "encoding_errors" instead'))
                encoding_errors = errors

            kwargs = {
                'db': db,
                'password': password,
                'socket_timeout': socket_timeout,
                'encoding': encoding,
                'encoding_errors': encoding_errors,
                'decode_responses': decode_responses,
                'retry_on_timeout': retry_on_timeout
            }
            # based on input, setup appropriate connection args
            if unix_socket_path is not None:
                kwargs.update({
                    'path': unix_socket_path,
                    'connection_class': UnixDomainSocketConnection
                })
            else:
                # TCP specific options
                kwargs.update({
                    'host': host,
                    'port': port,
                    'socket_connect_timeout': socket_connect_timeout,
                    'socket_keepalive': socket_keepalive,
                    'socket_keepalive_options': socket_keepalive_options,
                })

                if ssl:
                    kwargs.update({
                        'connection_class': SSLConnection,
                        'ssl_keyfile': ssl_keyfile,
                        'ssl_certfile': ssl_certfile,
                        'ssl_cert_reqs': ssl_cert_reqs,
                        'ssl_ca_certs': ssl_ca_certs,
                    })
            connection_pool = ConnectionPool(**kwargs)
        # 如果没有已经创建连接池则使用已经创建的连接池如果没有连接池则默认也会创建连接池
        self.connection_pool = connection_pool
        self._use_lua_lock = None

        self.response_callbacks = self.__class__.RESPONSE_CALLBACKS.copy()

    # 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]
        # 从连接池中获取连接执行command_name
        connection = pool.get_connection(command_name, **options)
        try:
            connection.send_command(*args)
            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)

# 创建连接池类
class ConnectionPool(object):
    "Generic connection pool"
    @classmethod
    def from_url(cls, url, db=None, **kwargs):
        """
        Return a connection pool configured from the given URL.

        For example::

            redis://[:password]@localhost:6379/0
            rediss://[:password]@localhost:6379/0
            unix://[:password]@/path/to/socket.sock?db=0

        Three URL schemes are supported:
            redis:// creates a normal TCP socket connection
            rediss:// creates a SSL wrapped TCP socket connection
            unix:// creates a Unix Domain Socket connection

        There are several ways to specify a database number. The parse function
        will return the first specified option:
            1. A ``db`` querystring option, e.g. redis://localhost?db=0
            2. If using the redis:// scheme, the path argument of the url, e.g.
               redis://localhost/0
            3. The ``db`` argument to this function.

        If none of these options are specified, db=0 is used.

        Any additional querystring arguments and keyword arguments will be
        passed along to the ConnectionPool class's initializer. In the case
        of conflicting arguments, querystring arguments always win.
        """

    def __init__(self, connection_class=Connection, max_connections=None,
                 **connection_kwargs):
        """
        Create a connection pool. If max_connections is set, then this
        object raises redis.ConnectionError when the pool's limit is reached.

        By default, TCP connections are created connection_class is specified.
        Use redis.UnixDomainSocketConnection for unix sockets.

        Any additional keyword arguments are passed to the constructor of
        connection_class.
        """
        # 最大连接数默认为62
        max_connections = max_connections or 2 ** 31
        if not isinstance(max_connections, (int, long)) or max_connections < 0:
            raise ValueError('"max_connections" must be a positive integer')

        self.connection_class = connection_class
        self.connection_kwargs = connection_kwargs
        self.max_connections = max_connections
        # 初始化线程池
        self.reset()

    def __repr__(self):
        return "%s<%s>" % (
            type(self).__name__,
            self.connection_class.description_format % self.connection_kwargs,
        )
    # 初始化线程池
    def reset(self):
        # 获取当前的进程号,后面判断进程是否挂掉
        self.pid = os.getpid()
        # 存放已经创建的连接(计数)
        self._created_connections = 0
        # 存放可用的连接对象(列表)
        self._available_connections = []
        # 存放正在使用的连接对象(集合)
        self._in_use_connections = set()
        # 创建线程锁
        self._check_lock = threading.Lock()

    def _checkpid(self):
        if self.pid != os.getpid():
            with self._check_lock:
                if self.pid == os.getpid():
                    # another thread already did the work while we waited
                    # on the lock.
                    return
                self.disconnect()
                self.reset()
    # 从连接池中获取连接
    def get_connection(self, command_name, *keys, **options):
        "Get a connection from the pool"
        self._checkpid()
        try:
            # 从连接池中pop出一个连接对象
            connection = self._available_connections.pop()
        except IndexError:
            # 如果连接池中已经没有连接的话重新创建连接
            connection = self.make_connection()
        # 当前正在使用的连接集合中添加此连接
        self._in_use_connections.add(connection)
        # 并返回此连接对象
        return connection
    # 创建连接
    def make_connection(self):
        "Create a new connection"
        # 如果大于最大连接数则抛出异常
        if self._created_connections >= self.max_connections:
            raise ConnectionError("Too many connections")
        # 否则创建的连接数++
        self._created_connections += 1
        # 利用创建连接类实例化一个连接
        return self.connection_class(**self.connection_kwargs)
    # 释放连接
    def release(self, connection):
        "Releases the connection back to the pool"
        self._checkpid()
        if connection.pid != self.pid:
            return
        # 并没有关闭连接而是从在使用的连接列表中删除此连接,回收连接对象
        self._in_use_connections.remove(connection)
        # 可用连接就回收了一个连接对象
        self._available_connections.append(connection)
    # 关闭连接
    def disconnect(self):
        "Disconnects all connections in the pool"
        # 关联获取所有可迭代对象获取所有连接对象
        all_conns = chain(self._available_connections,
                          self._in_use_connections)
        # 便历关闭所有连接
        for connection in all_conns:
            connection.disconnect()

# 创建连接类
class Connection(object):
    "Manages TCP communication to and from a Redis server"
    description_format = "Connection<host=%(host)s,port=%(port)s,db=%(db)s>"

    def __init__(self, host='localhost', port=6379, db=0, password=None,
                 socket_timeout=None, socket_connect_timeout=None,
                 socket_keepalive=False, socket_keepalive_options=None,
                 retry_on_timeout=False, encoding='utf-8',
                 encoding_errors='strict', decode_responses=False,
                 parser_class=DefaultParser, socket_read_size=65536):
        self.pid = os.getpid()
        self.host = host
        self.port = int(port)
        self.db = db
        self.password = password
        self.socket_timeout = socket_timeout
        self.socket_connect_timeout = socket_connect_timeout or socket_timeout
        self.socket_keepalive = socket_keepalive
        self.socket_keepalive_options = socket_keepalive_options or {}
        self.retry_on_timeout = retry_on_timeout
        self.encoding = encoding
        self.encoding_errors = encoding_errors
        self.decode_responses = decode_responses
        self._sock = None
        self._parser = parser_class(socket_read_size=socket_read_size)
        self._description_args = {
            'host': self.host,
            'port': self.port,
            'db': self.db,
        }
        self._connect_callbacks = []

    def __repr__(self):
        return self.description_format % self._description_args
    # 对象删除时调用disconnect方法关闭对象
    def __del__(self):
        try:
            self.disconnect()
        except Exception:
            pass

    def register_connect_callback(self, callback):
        self._connect_callbacks.append(callback)

    def clear_connect_callbacks(self):
        self._connect_callbacks = []
    # 核心的连接方法还是通过socket模块儿实现
    def connect(self):
        "Connects to the Redis server if not already connected"
        if self._sock:
            return
        try:
            # 私有方法创建连接
            sock = self._connect()
        except socket.error:
            e = sys.exc_info()[1]
            raise ConnectionError(self._error_message(e))

        self._sock = sock
        try:
            self.on_connect()
        except RedisError:
            # clean up after any error in on_connect
            self.disconnect()
            raise

        # run any user callbacks. right now the only internal callback
        # is for pubsub channel/pattern resubscription
        for callback in self._connect_callbacks:
            callback(self)
    # 创建tcp socket
    def _connect(self):
        "Create a TCP socket connection"
        # we want to mimic what socket.create_connection does to support
        # ipv4/ipv6, but we want to set options prior to calling
        # socket.connect()
        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
                # 默认使用的是短连接,设置socket_keepalive=True保持长连接
                if self.socket_keepalive:
                    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)
                # 设置超市时间,默认不设置为阻塞模式
                # set the socket_connect_timeout before we connect
                sock.settimeout(self.socket_connect_timeout)

                # connect
                sock.connect(socket_address)

                # set the socket_timeout now that we're connected
                sock.settimeout(self.socket_timeout)
                return sock

            except socket.error as _:
                err = _
                if sock is not None:
                    sock.close()

        if err is not None:
            raise err
        raise socket.error("socket.getaddrinfo returned an empty list")

    def _error_message(self, exception):
        # args for socket.error can either be (errno, "message")
        # or just "message"
        if len(exception.args) == 1:
            return "Error connecting to %s:%s. %s." % \
                (self.host, self.port, exception.args[0])
        else:
            return "Error %s connecting to %s:%s. %s." % \
                (exception.args[0], self.host, self.port, exception.args[1])

    def on_connect(self):
        "Initialize the connection, authenticate and select a database"
        self._parser.on_connect(self)

        # if a password is specified, authenticate
        if self.password:
            self.send_command('AUTH', self.password)
            if nativestr(self.read_response()) != 'OK':
                raise AuthenticationError('Invalid Password')

        # if a database is specified, switch to it
        if self.db:
            self.send_command('SELECT', self.db)
            if nativestr(self.read_response()) != 'OK':
                raise ConnectionError('Invalid Database')
    # 关闭连接
    def disconnect(self):
        "Disconnects from the Redis server"
        self._parser.on_disconnect()
        if self._sock is None:
            return
        try:
            # 先shutdown然后再close
            self._sock.shutdown(socket.SHUT_RDWR)
            self._sock.close()
        except socket.error:
            pass
        self._sock = None

    def send_packed_command(self, command):
        "Send an already packed command to the Redis server"
        if not self._sock:
            self.connect()
        try:
            if isinstance(command, str):
                command = [command]
            for item in command:
                self._sock.sendall(item)
        except socket.timeout:
            self.disconnect()
            raise TimeoutError("Timeout writing to socket")
        except socket.error:
            e = sys.exc_info()[1]
            self.disconnect()
            if len(e.args) == 1:
                _errno, errmsg = 'UNKNOWN', e.args[0]
            else:
                _errno, errmsg = e.args
            raise ConnectionError("Error %s while writing to socket. %s." %
                                  (_errno, errmsg))
        except:
            self.disconnect()
            raise

    def send_command(self, *args):
        "Pack and send a command to the Redis server"
        self.send_packed_command(self.pack_command(*args))

    def can_read(self):
        "Poll the socket to see if there's data that can be read."
        sock = self._sock
        if not sock:
            self.connect()
            sock = self._sock
        return bool(select([sock], [], [], 0)[0]) or self._parser.can_read()

    def read_response(self):
        "Read the response from a previously sent command"
        try:
            response = self._parser.read_response()
        except:
            self.disconnect()
            raise
        if isinstance(response, ResponseError):
            raise response
        return response

    def encode(self, value):
        "Return a bytestring representation of the value"
        if isinstance(value, Token):
            return b(value.value)
        elif isinstance(value, bytes):
            return value
        elif isinstance(value, (int, long)):
            value = b(str(value))
        elif isinstance(value, float):
            value = b(repr(value))
        elif not isinstance(value, basestring):
            value = str(value)
        if isinstance(value, unicode):
            value = value.encode(self.encoding, self.encoding_errors)
        return value

    def pack_command(self, *args):
        "Pack a series of arguments into the Redis protocol"
        output = []
        # the client might have included 1 or more literal arguments in
        # the command name, e.g., 'CONFIG GET'. The Redis server expects these
        # arguments to be sent separately, so split the first argument
        # manually. All of these arguements get wrapped in the Token class
        # to prevent them from being encoded.
        command = args[0]
        if ' ' in command:
            args = tuple([Token(s) for s in command.split(' ')]) + args[1:]
        else:
            args = (Token(command),) + args[1:]

        buff = SYM_EMPTY.join(
            (SYM_STAR, b(str(len(args))), SYM_CRLF))

        for arg in imap(self.encode, args):
            # to avoid large string mallocs, chunk the command into the
            # output list if we're sending large values
            if len(buff) > 6000 or len(arg) > 6000:
                buff = SYM_EMPTY.join(
                    (buff, SYM_DOLLAR, b(str(len(arg))), SYM_CRLF))
                output.append(buff)
                output.append(arg)
                buff = SYM_CRLF
            else:
                buff = SYM_EMPTY.join((buff, SYM_DOLLAR, b(str(len(arg))),
                                       SYM_CRLF, arg, SYM_CRLF))
        output.append(buff)
        return output

    def pack_commands(self, commands):
        "Pack multiple commands into the Redis protocol"
        output = []
        pieces = []
        buffer_length = 0

        for cmd in commands:
            for chunk in self.pack_command(*cmd):
                pieces.append(chunk)
                buffer_length += len(chunk)

            if buffer_length > 6000:
                output.append(SYM_EMPTY.join(pieces))
                buffer_length = 0
                pieces = []

        if pieces:
            output.append(SYM_EMPTY.join(pieces))
        return output