对Cocos2dX的内存管理不了解的人会有这样的疑惑，Cocos2dX的自动内存池是干什么的？当调用一个对象的autorelease后，该对象就被加入到自动内存池中。那是否意味着我们可以不用再去对该对象进行retain，release了呢？
答案是错的。自动内存池只作用于那些”创建期“的对象，也就是说对于那些用create函数创建出来的对象，实际上是调用了autorelease，而autorelease会把该对象加入到自动内存池中，而在用create函数创建了对象后的那一帧，当前自动内存池中的所有对象都会被release一次，然后清空该自动内存池。下面是分析过程：
一.create函数的内幕
使用create函数创建对象实际上会调用autorelease，而autorelease又会将该对象加入到当前自动内存池中：
#define CREATE_FUNC(__TYPE__) \
static __TYPE__* create() \
{ \
__TYPE__ *pRet = new(std::nothrow) __TYPE__(); \
if (pRet && pRet->init()) \
{ \
pRet->autorelease(); \
return pRet; \
} \
else \
{ \
delete pRet; \
pRet = NULL; \
return NULL; \
} \
}
Ref* Ref::autorelease()
{
PoolManager::getInstance()->getCurrentPool()->addObject(this);
return this;
}
二.为什么会有自动内存池
我们来看下每帧中自动内存池会执行什么：
int APIENTRY _tWinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPTSTR lpCmdLine,int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
// create the application instance
AppDelegate app;
return Application::getInstance()->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 1;
}
auto director = Director::getInstance();
auto glview = director->getOpenGLView();
// Retain glview to avoid glview being released in the while loop
glview->retain();
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 0;
}
run函数中有这么一句，director->mainLoop()，跟踪进去：
void DisplayLinkDirector::mainLoop()
{
if (_purgeDirectorInNextLoop)
{
_purgeDirectorInNextLoop = false;
purgeDirector();
}
else if (_restartDirectorInNextLoop)
{
_restartDirectorInNextLoop = false;
restartDirector();
}
else if (! _invalid)
{
drawScene();
// release the objects
PoolManager::getInstance()->getCurrentPool()->clear();
}
}
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
}
调用releasings.swap(_managedObjectArray)后当前自动内存池中就被清空了。
for (const auto &obj : releasings)
{
obj->release();
}
创建一个对象时，该对象的引用计数被初始化为1，如果我们没有对该对象进行retain操作，或者没有使用它（也就是没有其它对象引用它），那么该对象的引用计数则为1，调用上面的代码后，该对象的引用计数变为0，之后便不复存在。
