cocos2dx 3.x内存管理源代码追踪

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cocos2dx的内存管理,我有空追踪一下源代码 理解一下。
我们都知道 cocos2dx是靠引用计数实现的,顺便加入了对象池的管理。

涉及到一下几个类,AutorealsePool,PoolManager,Ref,DisplayLinkDirector.
函数
mainLoop,retain,release,autoRealse.

1.首先跳转到Application::run()

,
int Application::run()
{
PVRFrameEnableControlWindow(false);

// Main message loop:
LARGE_INTEGER nLast;
LARGE_INTEGER nNow;

QueryPerformanceCounter(&nLast);
initGLContextAttrs();

// Initialize instance and cocos2d.
if (!applicationDidFinishLaunching())
{
    return 0;
}

auto director = Director::getInstance();
auto glview = director->getOpenGLView();

// Retain glview to avoid glview being released in the while loop
glview->retain();
//如果窗口未关闭  就是一个while死循环
while(!glview->windowShouldClose())
{
    QueryPerformanceCounter(&nNow);
    if (nNow.QuadPart - nLast.QuadPart > _animationInterval.QuadPart)
    {
        nLast.QuadPart = nNow.QuadPart - (nNow.QuadPart % _animationInterval.QuadPart);

        director->mainLoop();
        glview->pollEvents();
    }
    else
    {
        Sleep(1);
    }
}

// Director should still do a cleanup if the window was closed manually.
if (glview->isOpenGLReady())
{
    director->end();
    director->mainLoop();
    director = nullptr;
}
glview->release();
return true;

}
,

2.跳转到mainLoop函数

void DisplayLinkDirector::mainLoop()
{
    if (_purgeDirectorInNextLoop)
    {
        _purgeDirectorInNextLoop = false;
        purgeDirector();
    }
    else if (_restartDirectorInNextLoop)
    {
        _restartDirectorInNextLoop = false;
        restartDirector();
    }
    else if (! _invalid)
    {
        drawScene();

        // release the objects
        auto count = PoolManager::getInstance()->getPoolCount();//这个函数我自己加的,方便打印
        CCLOG("$$$$$$$$$$=========== %d",count);
        CCLOG("&&&&&&&&&&=========== %s",PoolManager::getInstance()->getCurrentPool()->getName());//这个函数我自己加的,方便打印 auto pool = PoolManager::getInstance()->getCurrentPool();
        CCLOG("前面pool count is %d",pool->getCount());

        PoolManager::getInstance()->getCurrentPool()->clear();
        CCLOG("后面pool count is %d",pool->getCount());
    }
}

其他的先不管 ,就看PoolManager::getInstance()->getCurrentPool()->clear();这行代码

PoolManager这个类,从字面上的意思它是个管理类,所以它被写成单例模式。单例的代码

PoolManager* PoolManager::getInstance()
{
    if (s_singleInstance == nullptr)
    {
        s_singleInstance = new (std::nothrow) PoolManager();
        // Add the first auto release pool
        new AutoreleasePool("cocos2d autorelease pool");
    }
    return s_singleInstance;
}

以上代码是个典型的单例模式写法,但是有行代码
new AutoreleasePool(“cocos2d autorelease pool”);我从没看过生成一个对象 却不用其他的引用或者指针指向它,写的好奇怪。

3.查看AutoreleasePool这个类

查看他的构造函数

AutoreleasePool::AutoreleasePool(const std::string &name)
: _name(name)
#if defined(COCOS2D_DEBUG) && (COCOS2D_DEBUG > 0),_isClearing(false)
#endif
{
    _managedObjectArray.reserve(150);
    PoolManager::getInstance()->push(this);
}

原来AutoreleasePool类生成对象的时候,在构造函数调用
PoolManager::getInstance()->push(this)。

void PoolManager::push(AutoreleasePool *pool)
{
    _releasePoolStack.push_back(pool);
}

看懂了吧,原来push函数原来在这里调用了,但是这种写法很奇怪,可能是我c++功力太浅了,要是我直接在单例getInstance函数中push了。

PoolManager类成员变量:
std::vector 《AutoreleasePool*》 _releasePoolStack
其实这个_releasePoolStack断点的时候,只有在生成单例模式的push了一个AutoreleasePool对象,_releasePoolStack的size() = 1。
所以在mainLoop中:

auto count = PoolManager::getInstance()->getPoolCount();
CCLOG("$$$$$$$$$$=========== %d",count);

定义如下
int PoolManager::getPoolCount()
{
    return _releasePoolStack.size();
}

打印始终都是size等于1

AutoreleasePool* PoolManager::getCurrentPool() const
{
    return _releasePoolStack.back();
}

这个函数返回的是_releasePoolStack的末尾引用
而_releasePoolStack的数据size其实只有一条,既然是一条,那干嘛用vector呢?这点没弄明白 难道是因为喜欢用vector存贮数据?

接下来看AutoreleasePool::clear()函数

void AutoreleasePool::clear()
{
#if defined(COCOS2D_DEBUG) && (COCOS2D_DEBUG > 0)
    _isClearing = true;
#endif
    std::vector<Ref*> releasings;
    releasings.swap(_managedObjectArray);
    for (const auto &obj : releasings)
    {
        obj->release();
    }
#if defined(COCOS2D_DEBUG) && (COCOS2D_DEBUG > 0)
    _isClearing = false;
#endif
}

_managedObjectArray数据被清空,这个函数中有个重要的知识点 那就是vector的swap的用法,swap可以清空vector申请的内存,而clear却不一定。详情可参照:

简单的程序诠释C++ STL算法系列之十五:swap

追踪release代码

void Ref::release()
{
    CCASSERT(_referenceCount > 0,"reference count should be greater than 0");
    --_referenceCount;

    if (_referenceCount == 0)
    {
#if defined(COCOS2D_DEBUG) && (COCOS2D_DEBUG > 0)
        auto poolManager = PoolManager::getInstance();
        if (!poolManager->getCurrentPool()->isClearing() && poolManager->isObjectInPools(this)) { CCASSERT(false,"The reference shouldn't be 0 because it is still in autorelease pool."); } #endif #if CC_REF_LEAK_DETECTION untrackRef(this); #endif delete this; } }

release函数 就是将计数自减一,将0的Ref析构掉。

每个集成了Ref的对象 都有属性_referenceCount,那它在哪里自增呢?

举个例子,去看看Sprite的create函数

Sprite* Sprite::create(const std::string& filename)
{
    Sprite *sprite = new (std::nothrow) Sprite();
    if (sprite && sprite->initWithFile(filename))
    {
        sprite->autorelease();
        return sprite;
    }
    CC_SAFE_DELETE(sprite);
    return nullptr;
}

autorelease函数的定义

Ref* Ref::autorelease()
{
    PoolManager::getInstance()->getCurrentPool()->addObject(this);
    return this;
}

再追踪addObject函数

void AutoreleasePool::addObject(Ref* object)
{
    _managedObjectArray.push_back(object);
}

奇怪 不是说好 一个精灵创建的时候 引用计数就加1吗?但是我们找了半天没发现,原来是Ref构造的时候就默认设置成1了,如下代码

Ref::Ref()
: _referenceCount(1) // when the Ref is created,the reference count of it is 1
{
#if CC_ENABLE_SCRIPT_BINDING
    static unsigned int uObjectCount = 0;
    _luaID = 0;
    _ID = ++uObjectCount;
    _scriptObject = nullptr;
#endif

#if CC_REF_LEAK_DETECTION
    trackRef(this);
#endif
}

我们知道 cocos2dx 中node sprite都是继承Ref,C++中对象生成的时候,先调用父类的构造函数 ,再调用自己的构造函数

4.引用计数 自增和自减 在哪些地方出现?

  1. addChild()函数
    Node下面好几个addChild函数,都是函数重载,最终都用到这个函数
    addChildHelper()
void Node::addChildHelper(Node* child,int localZOrder,int tag,const std::string &name,bool setTag)
{
    if (_children.empty())
    {
        this->childrenAlloc();
    }

    this->insertChild(child,localZOrder);

    if (setTag)
        child->setTag(tag);
    else
        child->setName(name);

    child->setParent(this);
    child->setOrderOfArrival(s_globalOrderOfArrival++);

#if CC_USE_PHYSICS
    // Recursive add children with which have physics body.
    auto scene = this->getScene();
    if (scene && scene->getPhysicsWorld())
    {
        scene->addChildToPhysicsWorld(child);
    }
#endif

    if( _running )
    {
        child->onEnter();
        // prevent onEnterTransitionDidFinish to be called twice when a node is added in onEnter
        if (_isTransitionFinished)
        {
            child->onEnterTransitionDidFinish();
        }
    }

    if (_cascadeColorEnabled)
    {
        updateCascadeColor();
    }

    if (_cascadeOpacityEnabled)
    {
        updateCascadeOpacity();
    }
}

找到insertChild函数

void Node::insertChild(Node* child,int z)
{
    _transformUpdated = true;
    _reorderChildDirty = true;
    _children.pushBack(child);
    child->_localZOrder = z;
}

接着找到pushBack函数,开始以为就是vector中的函数呢,其实不然:

void pushBack(T object)
    {
        CCASSERT(object != nullptr,"The object should not be nullptr");
        _data.push_back( object );
        object->retain();
    }

终于找到retain函数了啊!

  1. setParent函数
void Node::setParent(Node * parent)
{
    _parent = parent;
    _transformUpdated = _transformDirty = _inverseDirty = true;
}

发现这个函数根本没有使引用计数增加,而我在项目中使用setParent的时候 根本一个节点没有显示出来,所以这个函数只是一个指向关系,并未将孩子真正加入到父节点中,所以我基本不使用它,我都是使用addChild函数

所以当你生成一个Sprite并把它加入到layer之后,他的引用计数是2。

  1. removeFromParent函数
void Node::removeFromParent()
{
    this->removeFromParentAndCleanup(true);
}

void Node::removeFromParentAndCleanup(bool cleanup)
{
    if (_parent != nullptr)
    {
        _parent->removeChild(this,cleanup);
    } 
}

我们可以看到这两个函数几乎等同,接着removeChild:

void Node::removeChild(Node* child,bool cleanup /* = true */)
{
    // explicit nil handling
    if (_children.empty())
    {
        return;
    }

    ssize_t index = _children.getIndex(child);
    if( index != CC_INVALID_INDEX )
        this->detachChild( child,index,cleanup );
}

接着detachChild:

void Node::detachChild(Node *child,ssize_t childIndex,bool doCleanup)
{
    // IMPORTANT:
    // -1st do onExit
    // -2nd cleanup
    if (_running)
    {
        child->onExitTransitionDidStart();
        child->onExit();
    }

#if CC_USE_PHYSICS
    child->removeFromPhysicsWorld();
#endif

    // If you don't do cleanup,the child's actions will not get removed and the
    // its scheduledSelectors_ dict will not get released!
    if (doCleanup)
    {
        child->cleanup();
    }

    // set parent nil at the end
    child->setParent(nullptr);

    _children.erase(childIndex);
}

接着cleanup函数

void Node::cleanup()
{
    // actions
    this->stopAllActions();
    this->unscheduleAllCallbacks();

#if CC_ENABLE_SCRIPT_BINDING
    if ( _scriptType != kScriptTypeNone)
    {
        int action = kNodeOnCleanup;
        BasicScriptData data(this,(void*)&action);
        ScriptEvent scriptEvent(kNodeEvent,(void*)&data);
        ScriptEngineManager::getInstance()->getScriptEngine()->sendEvent(&scriptEvent);
    }
#endif // #if CC_ENABLE_SCRIPT_BINDING

    // timers
    for( const auto &child: _children)
        child->cleanup();
}

可以看到 递归调用了cleanup函数 子节点都是处理一些事情,detachChild函数最后将子节点的父节点设置为空,最后看erase函数

iterator erase(ssize_t index)
    {
        CCASSERT(!_data.empty() && index >=0 && index < size(),"Invalid index!");
        auto it = std::next( begin(),index );
        (*it)->release();
        return _data.erase(it);
    }

终于找到了release函数了。

有时候我容易将 std::vector和cocos2dx封装的Vector搞混淆,真是眼睛不好啊!现在内存管理的基本思路搞清楚了。

原文链接:https://www.f2er.com/cocos2dx/339239.html

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