当前位置: 首页 > news >正文

python可以用del释放资源_Python 中带有显式 __del__ 方法的对象需要手动释放循环引用...

Python中有自动gc,这个gc在一般情况下也可以清除循环引用的对象。

不过有个例外的情况:一个对象显式定义了__del__方法。

例如如下的代码:

#!/usr/bin/env python

class Foo:

def __init__(self):

self._bar = {"test": self.test}

print "construct"

def test(self):

print "test"

def __del__(self):

print "del"

f = Foo()

del f

运行结果是不会打印”del”的。

gc.garbage

A list of objects which the collector found to be unreachable but could not be freed (uncollectable objects). By default, this list contains only objects with __del__() methods. [1] Objects that have __del__() methods and are part of a reference cycle cause the entire reference cycle to be uncollectable, including objects not necessarily in the cycle but reachable only from it. Python doesn’t collect such cycles automatically because, in general, it isn’t possible for Python to guess a safe order in which to run the __del__() methods. If you know a safe order, you can force the issue by examining the garbage list, and explicitly breaking cycles due to your objects within the list. Note that these objects are kept alive even so by virtue of being in the garbage list, so they should be removed from garbage too. For example, after breaking cycles, do del gc.garbage[:] to empty the list. It’s generally better to avoid the issue by not creating cycles containing objects with __del__() methods, and garbage can be examined in that case to verify that no such cycles are being created.

当一个对象显式定义了__del__方法,而且里面有循环引用,Python不会自动回收这个对象。如果这种情况没有正确处理,会造成内存泄漏。

解决的办法是在__del__中手动解除循环引用,或者干脆避免这种有循环引用的写法。

这个问题导致数据库连接不能释放,终于在周末晚上数据库连接爆了,丢脸啊。

PS: 这次事件也再一次显示“分层架构互不信任防雪崩策略”的重要性。这个出事的DB是一个slave,它的max_connection和max_user_connection是一样的,而且连接超时竟然是8小时……如果max_user_connection设小点,顶多是使用这个用户的系统挂掉,而不会是所有使用这个DB的系统都挂掉,把影响隔离起来。

相关文章:

  • mybatis mysql自增主键_mybatis 自增主键配置
  • mysql groupby rullup_group by后加rollup子句的用法
  • Mysql历史事务_mysql事务
  • python读取多列csv文件_多列上的csvjoin
  • sql 孩子兄弟表示法 所有子节点_sunxiaohang
  • mysql redis集群 同步_redis集群和redis主从同步的区别
  • java逆向_Java逆向武器库_反编译工具
  • java加速_java写入加速
  • java部门树_java部门树的递归
  • mysql为什么创建不了表_求教,,为什么创建不了表
  • java目前主流框架_java的三大主流框架介绍
  • java elasticsearch_Java操作ElasticSearch
  • java 拆分xml_使用Java分割1GB Xml文件
  • a与a的共轭转置相乘_线性代数A矩阵乘以A的转置的含义或者几何意义
  • java 会话管理_java会话管理