原文地址：http://www.cnblogs.com/yu-chao/p/3697459.html
今天想探索一下cocos2dx的内存管理，我们就先从CCObject开始吧
class CC_DLL CCObject : public CCcopying { public: // object id,ccScriptSupport need public m_uID unsigned int m_uID; Lua reference id int m_nLuaID; protected: count of references unsigned int m_uReference; count of autorelease unsigned int m_uAutoReleaseCount; public: CCObject(void); virtual ~CCObject(void); void release(void retain(void); CCObject* autorelease(void); CCObject* copy(bool isSingleReference(void); unsigned int retainCount(virtual bool isEqual(const CCObject* pObject); void update(float dt) {CC_UNUSED_ParaM(dt);}; friend class CCAutoreleasePool; unsigned int getAutoReleaseCount(); };
以上是CCObject的定义，可以看出CCObject主要有两个保护成员：m_uReference和m_uAutoReleaseCount，这个两个成员到底有什么用呢？让我们一探究竟，首先我们来看一下CCObject的构造函数：
CCObject::CCObject(void) : m_nLuaID(0),m_uReference(1) when the object is created,the reference count of it is 1,m_uAutoReleaseCount(0) { static unsigned int uObjectCount = 0; m_uID = ++uObjectCount; }
从构造函数我么可以看出m_uReference初始化为1，m_uAutoReleaseCount初始化为0，另外CCObject维护了一个静态无符号整型变量：uObjectCount来记录CCObject实例的总数目。然后我们来看一下release()和retain()函数：
void CCObject::release(void)
{
if (m_uReference == 0) {modify by yangm
CCLOG("CCObject::release reference count should greater than 0");
return;
}
CCAssert(m_uReference > 0,reference count should greater than 0");
--m_uReference;
0)
{
delete this;
}
}
由release()函数可以看到每执行一次release()，m_uReference自减一，只有当m_uReference为零时CCObject对象才会被释放；
void CCObject::retain(CCObject::retain reference count should greater than 0,m_uReference=%d",m_uReference);
");
++m_uReference;
}
retain()函数和release()函数功能正好相反，每调用一次retain()，m_uReference会自增一；接下来我们再来看看autorelease()函数：
CCObject* CCObject::autorelease(void) { CCPoolManager::sharedPoolManager()->addobject(this); return this; } void CCPoolManager::addobject(CCObject* pObject) { getCurReleasePool()->addobject(pObject); 获取栈顶得CCAutoreleasePool实例，并将CCObject加入到CCAutoreleasePool中 }
此处涉及到一个CCPoolManager类，该类内部有一个CCAutoreleasePool类型的栈，而CCPoolManager又是什么呢？其实CCPoolManager就是一个CCArray一个可增长的数组，我们来看看他得addobject(CCObject* pObject)函数：
void
CCAutoreleasePool::addobject(CCObject* pObject) { m_pManagedobjectArray->addobject(pObject); 向CCArray中添加CCObject实例 CCAssert(pObject->m_uReference > 1,0);line-height:1.5 !important;">reference count should be greater than 1"); ++(pObject->m_uAutoReleaseCount); CCObject的m_uAutoReleaseCount自增一 pObject->release(); no ref count,in this case autorelease pool added. }
在调试的时候我们会发现CCObject在release()时他的m_uReference为2，也就避免了被释放，其实该对象实例在添加到自动释放池（CCAutoreleasePool）的时候retain了一下；我们来验证一下，来看看下面的几个函数：
void CCArray::addobject(CCObject* object)
{
ccArrayAppendobjectWithResize(data,object);
}
/** Appends an object. Capacity of arr is increased if needed. */
void ccArrayAppendobjectWithResize(ccArray *arr,CCObject* object)
{
ccArrayEnsureExtraCapacity(arr,1);
ccArrayAppendobject(arr,255);line-height:1.5 !important;">object);
}
* Appends an object. Behavior undefined if array doesn't have enough capacity. void ccArrayAppendobject(ccArray *arr,255);line-height:1.5 !important;">object)
{
CCAssert(object != NULL,0);line-height:1.5 !important;">Invalid parameter!");
object->retain(); 此处果然retain了一下
arr->arr[arr->num] = object;
arr->num++;
}
接下来我们来看一下cocos2dx如何销毁那些无效的对象实例，以下是整个程序的主循环：
void
CCdisplayLinkDirector::mainLoop(if (m_bPurgeDirecotorInNextLoop) { m_bPurgeDirecotorInNextLoop = false; purgeDirector(); } else if (! m_bInvalid) { drawScene(); release the objects CCPoolManager::sharedPoolManager()->pop(); } }
由上面函数可知coco2dx在每一帧的帧尾会调用自动释放内存池的管理者—CCPoolManager的pop()函数，我们来看看该函数主要做了哪些工作？
void
CCPoolManager::pop() { if (! m_pCurReleasePool) { return; } int nCount = m_pReleasePoolStack->count(); m_pCurReleasePool->clear(); if(nCount > 1) { m_pReleasePoolStack->removeObjectAtIndex(nCount-1); if(nCount > 1) { m_pCurReleasePool = m_pReleasePoolStack->objectAtIndex(nCount - 2); return; } m_pCurReleasePool = (CCAutoreleasePool*)m_pReleasePoolStack->objectAtIndex(nCount - 2); } m_pCurReleasePool = NULL;*/ }
主要做的就两点：1、清除当前的自动释放池，2、更新当前自动释放池指针；我们来看看他是如何clear？
void
CCAutoreleasePool::clear() { if(m_pManagedobjectArray->count() > 0) { CCAutoreleasePool* pReleasePool; #ifdef _DEBUG int nIndex = m_pManagedobjectArray->count() - 1; #endif CCObject* pObj = NULL; CCARRAY_FOREACH_REVERSE(m_pManagedobjectArray,pObj) { if(!pObj) break; --(pObj->m_uAutoReleaseCount); if( (int)(pObj->m_uAutoReleaseCount)<0 ){ pObj->m_uAutoReleaseCount = 0; } (*it)->release(); delete (*it); #ifdef _DEBUG nIndex--; #endif } m_pManagedobjectArray->removeAllObjects(); } }
以上函数主要做的工作是：1、将内部的所有元素的自动释放引用m_uAutoReleaseCount减一。2、清除内部的所有元素。看到这里我很诧异：为什么要清除所有的元素呢？难道不是清除那些无效的对象实例吗？紧接着看下面的函数看他如何removeAllObjects。
void
CCArray::removeAllObjects() { ccArrayRemoveAllObjects(data); } void ccArrayRemoveAllObjects(ccArray *arr) { while( arr->num > 0 ) { (arr->arr[—arr->num])->release(); 注意此处的—arr->num } }