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设计Python数据库连接池1-对象的循环引用问题

Python中如果对象定义了__del__方法的话,在对象的引用记数为0时会自动调用__del__方法 (很象c++中的析构函数),但如果A对象引用B对象,B对象又引用A对象,就形成循环引用,此时A,B对象 引用次数都为1。python就无法正常调用__del__方法,原计划在__del__方法里释放的资源自然也就无 法释放。

一个连接池拥有多个连接,而每个连接又拥有这个连接池的实例(一个叫pool的属性)。这样就产生了刚刚 说的哪个问题。我想到的办法就是在每次从池中获取连接的时候将连接的pool设置为当前实例,然后在归 还这个连接的时候再将其设置为None,并且要在这个连接对象的__del__方法中将pool属性设置为 None。具体看代码吧。(目前只实现了SQLite3的)

'''
Created on 2009-4-17
@author: phyeas
'''
import time
from queue import Queue
class PoolException(Exception):
pass
class Pool(object):
'''一个数据库连接池'''
def __init__(self, maxActive=5, maxWait=None, init_size=0, db_type="SQLite3", **config):
self.__freeConns = Queue(maxActive)
self.maxWait = maxWait
self.db_type = db_type
self.config = config
if init_size > maxActive:
init_size = maxActive
for i in range(init_size):
self.free(self._create_conn())
def __del__(self):
print("__del__ Pool..")
self.release()
def release(self):
'''释放资源,关闭池中的所有连接'''
print("release Pool..")
while self.__freeConns and not self.__freeConns.empty():
con = self.get()
con.release()
self.__freeConns = None
def _create_conn(self):
'''创建连接 '''
if self.db_type in dbcs:
return dbcs[self.db_type](**self.config);
def get(self, timeout=None):
'''获取一个连接
@param timeout:超时时间
'''
if timeout is None:
timeout = self.maxWait
conn = None
if self.__freeConns.empty():#如果容器是空的,直接创建一个连接
conn = self._create_conn()
else:
conn = self.__freeConns.get(timeout=timeout)
conn.pool = self
return conn
def free(self, conn):
'''将一个连接放回池中
@param conn: 连接对象
'''
conn.pool = None
if(self.__freeConns.full()):#如果当前连接池已满,直接关闭连接
conn.release()
return
self.__freeConns.put_nowait(conn)
from abc import ABCMeta, abstractmethod
class PoolingConnection(object, metaclass=ABCMeta):
def __init__(self, **config):
self.conn = None
self.config = config
self.pool = None
def __del__(self):
self.release()
def __enter__(self):
pass
def __exit__(self, exc_type, exc_value, traceback):
self.close()
def release(self):
print("release PoolingConnection..")
if(self.conn is not None):
self.conn.close()
self.conn = None
self.pool = None
def close(self):
if self.pool is None:
raise PoolException("连接已关闭")
self.pool.free(self)
def __getattr__(self, val):
if self.conn is None and self.pool is not None:
self.conn = self._create_conn(**self.config)
if self.conn is None:
raise PoolException("无法创建数据库连接 或连接已关闭")
return getattr(self.conn, val)
@abstractmethod
def _create_conn(self, **config):
pass
class SQLit3PoolConnection(PoolingConnection):
def _create_conn(self, **config):
import sqlite3
return sqlite3.connect(**config)
dbcs = {"SQLite3":SQLit3PoolConnection}
pool = Pool(database="F:\\test\\a")
def test():
conn = pool.get()
with conn:
for a in conn.execute("SELECT * FROM A"):
print(a)
if __name__ == "__main__":
test()
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