Python垃圾回收机制:gc模块

import gc
import sys

class CGcLeak(object):
    def __init__(self):
        self._text = '#' * 10

    def __del__(self):
        pass

def make_circle_ref():
    _gcleak = CGcLeak()
    print "_gcleak ref count0: %d" %(sys.getrefcount(_gcleak))
    del _gcleak
    try:
        print "_gcleak ref count1 :%d" %(sys.getrefcount(_gcleak))
    except UnboundLocalError:           # 本地变量xxx引用前没定义
        print "_gcleak is invalid!"
def test_gcleak():
    gc.enable()                         #设置垃圾回收器调试标志
    gc.set_debug(gc.DEBUG_COLLECTABLE | gc.DEBUG_UNCOLLECTABLE | gc.DEBUG_INSTANCES | gc.DEBUG_OBJECTS)

    print "begin leak test..."
    make_circle_ref()

    print "\nbegin collect..."
    _unreachable = gc.collect()
    print "unreachable object num:%d" %(_unreachable)
    print "garbage object num:%d" %(len(gc.garbage))   #gc.garbage是一个list对象，列表项是垃圾收集器发现的不可达（即垃圾对象）、但又不能释放(不可回收)的对象，通常gc.garbage中的对象是引用对象还中的对象。因Python不知用什么顺序来调用对象的__del__函数，导致对象始终存活在gc.garbage中，造成内存泄露 if __name__ == "__main__": test_gcleak()。如果知道一个安全次序，那么就可以打破引用焕，再执行del gc.garbage[:]从而清空垃圾对象列表
if __name__ == "__main__":
    test_gcleak()

begin leak test...
_gcleak ref count0: 2         #对象_gcleak的引用计数为2
_gcleak is invalid!           #因为执行了del函数，_gcleak变为了不可达的对象

begin collect...              #开始垃圾回收
unreachable object num:0      #本次垃圾回收发现的不可达的对象个数为0
garbage object num:0          #整个解释器中垃圾对象的个数为0

import gc
import sys

class CGcLeak(object):
    def __init__(self):
        self._text = '#' * 10

    def __del__(self):
        pass

def make_circle_ref():
    _gcleak = CGcLeak()
    _gcleak._self = _gcleak     #自己循环引用自己
    print "_gcleak ref count0: %d" %(sys.getrefcount(_gcleak))
    del _gcleak
    try:
        print "_gcleak ref count1 :%d" %(sys.getrefcount(_gcleak))
    except UnboundLocalError:
        print "_gcleak is invalid!"

def test_gcleak():
    gc.enable()
    gc.set_debug(gc.DEBUG_COLLECTABLE | gc.DEBUG_UNCOLLECTABLE | gc.DEBUG_INSTANCES | gc.DEBUG_OBJECTS)

    print "begin leak test..."
    make_circle_ref()

    print "\nbegin collect..."
    _unreachable = gc.collect()
    print "unreachable object num:%d" %(_unreachable)
    print "garbage object num:%d" %(len(gc.garbage))

if __name__ == "__main__":
    test_gcleak()

begin leak test...
gc: uncollectable <CGcLeak 00000000026366A0>
_gcleak ref count0: 3
_gcleak is invalid!
gc: uncollectable <dict 0000000002667BD8>

begin collect...
unreachable object num:2       #本次回收不可达的对象个数为2
garbage object num:1           #整个解释器中垃圾个数为1

import gc
import sys

class CGcLeakA(object):
    def __init__(self):
        self._text = '$' * 10

    def __del__(self):
        pass

class CGcLeakB(object):
    def __init__(self):
        self._text = '$' * 10

    def __del__(self):
        pass

def make_circle_ref():
    _a = CGcLeakA()
    _b = CGcLeakB()
    _a.s = _b
    _b.d = _a
    print "ref count0:a=%d b=%d" %(sys.getrefcount(_a), sys.getrefcount(_b))
    del _a
    del _b
    try:
        print "ref count1:a%d" %(sys.getrefcount(_a))
    except UnboundLocalError:
        print "_a is invalid!"

def test_gcleak():
    gc.enable()
    gc.set_debug(gc.DEBUG_COLLECTABLE | gc.DEBUG_UNCOLLECTABLE | gc.DEBUG_INSTANCES | gc.DEBUG_OBJECTS)

    print "begin leak test..."
    make_circle_ref()

    print "\nbegin collect..."
    _unreachable = gc.collect()
    print "unreachable object num:%d" %(_unreachable)
    print "garbage object num:%d" %(len(gc.garbage))

if __name__ == "__main__":
    test_gcleak()