在Python中如果對(duì)象定義了__del__方法的話，在對(duì)象的引用記數(shù)為0時(shí)會(huì)自動(dòng)調(diào)用__del__方法(很象c++中的析構(gòu)函數(shù))，但如果A對(duì)象引用B對(duì)象，B對(duì)象又引用A對(duì)象，就形成循環(huán)引用，此時(shí)A，B對(duì)象引用次數(shù)都為1。python就無(wú)法正常調(diào)用__del__方法，原計(jì)劃在__del__方法里釋放的資源自然也就無(wú)法釋放。

一個(gè)連接池?fù)碛卸鄠€(gè)連接，而每個(gè)連接又擁有這個(gè)連接池的實(shí)例(一個(gè)叫pool的屬性)。這樣就產(chǎn)生了剛剛說(shuō)的哪個(gè)問(wèn)題。我想到的辦法就是在每次從池中獲取連接的時(shí)候?qū)⑦B接的pool設(shè)置為當(dāng)前實(shí)例，然后在歸還這個(gè)連接的時(shí)候再將其設(shè)置為None，并且要在這個(gè)連接對(duì)象的__del__方法中將pool屬性設(shè)置為None。具體看代碼吧。(目前只實(shí)現(xiàn)了SQLite3的)

'''

Created on 2009-4-17

@author: phyeas

'''

import time

from queue import Queue

class PoolException(Exception):

pass

class Pool(object):

'''一個(gè)數(shù)據(jù)庫(kù)連接池'''

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):

'''釋放資源，關(guān)閉池中的所有連接'''

print("release Pool..")

while self.__freeConns and not self.__freeConns.empty():

con = self.get()

con.release()

self.__freeConns = None

def _create_conn(self):

'''創(chuàng)建連接 '''

if self.db_type in dbcs:

return dbcs[self.db_type](**self.config);

def get(self, timeout=None):

'''獲取一個(gè)連接

@param timeout:超時(shí)時(shí)間

'''

if timeout is None:

timeout = self.maxWait

conn = None

if self.__freeConns.empty():#如果容器是空的，直接創(chuàng)建一個(gè)連接

conn = self._create_conn()

else:

conn = self.__freeConns.get(timeout=timeout)

conn.pool = self

return conn

def free(self, conn):

'''將一個(gè)連接放回池中

@param conn: 連接對(duì)象

'''

conn.pool = None

if(self.__freeConns.full()):#如果當(dāng)前連接池已滿(mǎn)，直接關(guān)閉連接

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("連接已關(guān)閉")

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("無(wú)法創(chuàng)建數(shù)據(jù)庫(kù)連接 或連接已關(guān)閉")

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()

以上代碼在python3.0中測(cè)試通過(guò)……

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