自己动手写cocos2dx游戏引擎(七)——自动释放池

上一节说到的Ref的引用计数时，没有说自动释放。

自动释放功能相对来说比较复杂。

首先有一个自动释放池。

#ifndef __AUTORELEASEPOOL_H__
#define __AUTORELEASEPOOL_H__

#include <string>
#include <vector>
#include "Ref.h"

class AutoreleasePool {
public:
AutoreleasePool();
AutoreleasePool(const std::string &name);
~AutoreleasePool();
void addObject(Ref *object);
void clear();
bool contains(Ref* object) const;
private:
std::vector<Ref*> _managedObjectArray;// 对象数组，存放自动释放的对象
std::string _name;// 释放池名字
};

class PoolManager {
public:
static PoolManager* getInstance();
static void destroyInstance();

AutoreleasePool *getCurrentPool() const;
bool isObjectInPools(Ref* obj) const;

friend class AutoreleasePool;
private:
PoolManager();
~PoolManager();

void push(AutoreleasePool *pool);
void pop();

static PoolManager* s_singleInstance;
std::vector<AutoreleasePool*> _releasePoolStack;
};

AutoreleasePool::AutoreleasePool(): _name("") {
_managedObjectArray.reserve(150);
PoolManager::getInstance()->push(this);
}

AutoreleasePool::AutoreleasePool(const std::string &name): _name(name) {
_managedObjectArray.reserve(150);
PoolManager::getInstance()->push(this);
}

AutoreleasePool::~AutoreleasePool() {
clear();
PoolManager::getInstance()->pop();
}

void AutoreleasePool::clear() {
// 与一个默认大小的vector交换，使其恢复到默认大小
// 再释放临时vector中的对象，以达到释放内存，恢复到默认大小的目的
std::vector<Ref*> releasings;
releasings.swap(_managedObjectArray);
std::vector<Ref*>::iterator it = releasings.begin();
for (; it != releasings.end(); it++) {
(*it)->release();
}
}

bool AutoreleasePool::contains(Ref* object) const {
std::vector<Ref*>::const_iterator it = _managedObjectArray.begin();
for (; it != _managedObjectArray.end(); it++) {
if(object == (*it)) {
return true;
}
}
return false;
}

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

/*
* PoolManager
* */
PoolManager* PoolManager::s_singleInstance = NULL;

PoolManager* PoolManager::getInstance() {
if (NULL == s_singleInstance) {
s_singleInstance = new PoolManager();
// 创建单例的后悔初始化自动释放池
new AutoreleasePool("cocos2d autorelease pool");
}
return s_singleInstance;
}

void PoolManager::destroyInstance() {
delete s_singleInstance;
s_singleInstance = NULL;
}

PoolManager::PoolManager() {
_releasePoolStack.reserve(10);
}

PoolManager::~PoolManager() {
while (!_releasePoolStack.empty()) {
AutoreleasePool* pool = _releasePoolStack.back();
delete pool;
}
}

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

bool PoolManager::isObjectInPools(Ref* obj) const {
std::vector<AutoreleasePool*>::const_iterator it =  _releasePoolStack.begin();
for (;it != _releasePoolStack.end(); ++it) {
if ((*it)->contains(obj)) {
return true;
}
}
return false;
}

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

void PoolManager::pop() {
if (!_releasePoolStack.empty()) {
_releasePoolStack.pop_back();
}
}

#endif

当我们调用Ref对象的autorelease方法时，就会当该对象加入到自动释放池中。

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

另外，还有一个自动释放池对象PoolManager，专门来管理自动释放池。

自动释放管理对象是一个单例，但我们第一次获取这个单例的时候，就会创建一个自动释放池。

PoolManager* PoolManager::getInstance() {
if (NULL == s_singleInstance) {
s_singleInstance = new PoolManager();
// 创建单例的后初始化自动释放池
new AutoreleasePool("cocos2d autorelease pool");
}
return s_singleInstance;
}

然后在Director的mainLoop中，每一帧都会检测自动释放池，release对象，释放引用计数为0的对象。

void DisplayLinkDirector::mainLoop() {
drawScene();
// 每一帧都会检测自动释放池
PoolManager::getInstance()->getCurrentPool()->clear();
}

代码