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源码剖析:TheManaWorld_资源管理系统
TheManaWorld是一个开源2D MMORPGhttps://www.themanaworld.org/ 以下简称TMW，它的资源管理比较典型：
1 基于引用计数使资源自动归还
2 各种资源在加载时根据类型做分派
先从Resouce与ResouceManager这两个类开始,Resouce主要提供了引用计数的功能，ResouceManager基于Resouce提供的抽象接口编写资源管理的方法。
class Resource{ friend class ResourceManager; public: enum OrphanPolicy { DeleteLater, DeleteImmediately }; Resource(): mRefCount(0) {} /** * Increments the internal reference count. */ void incRef() { ++mRefCount; } /** * Decrements the reference count. When no references are left, either * schedules the object for deletion or deletes it immediately, * depending on the \a orphanPolicy. */ void decRef(OrphanPolicy orphanPolicy = DeleteLater); /** * Return the path identifying this resource. */ const std::string &getIdPath() const { return mIdPath; } protected: virtual ~Resource() {} private: std::string mIdPath; /**< Path identifying this resource. */ time_t mTimeStamp; /**< Time at which the resource was orphaned. */ unsigned mRefCount; /**< Reference count. */};
OrphanPolicy指明了在引用计数降为0时资源回收的策略,马上回收与延后回收。延后回收的策略非常有用，比如游戏中常有同造型的怪删除后又马上创建出来。
void Resource::decRef(OrphanPolicy orphanPolicy){ // Reference may not already have reached zero if (mRefCount == 0) { logger->log("Warning: mRefCount already zero for %s", mIdPath.c_str()); assert(false); } --mRefCount; if (mRefCount == 0) { ResourceManager *resman = ResourceManager::getInstance(); switch (orphanPolicy) { case DeleteLater: default: resman->release(this); break; case DeleteImmediately: resman->remove(this); delete this; break; } }}
ResouceManager::getInstance()说明资源管理器采用的是单例模式，比较直观。因为游戏只需要一个资源管理器，且为其他地方的代码直接访问资源管理器提供了方便。
然后跟踪Reslese和remove两种方法有何不同
class ResouceManager{ ... typedef std::map<std::string, Resource*> Resources; typedef Resources::iterator ResourceIterator; Resources mOrphanedResources; Resources mResources; }void ResourceManager::release(Resource *res){ ResourceIterator resIter = mResources.find(res->mIdPath); // The resource has to exist assert(resIter != mResources.end() && resIter->second == res); timeval tv; gettimeofday(&tv, NULL); time_t timestamp = tv.tv_sec; res->mTimeStamp = timestamp; if (mOrphanedResources.empty()) mOldestOrphan = timestamp; mOrphanedResources.insert(*resIter); mResources.erase(resIter);}void ResourceManager::remove(Resource *res){ mResources.erase(res->mIdPath);}
ResouceManager维护了两个列表mOrphanedResources和mResources,
延后删除的资源从mResources中移除后放到mOrphanedResources中时时保存起来,并且记录下时间戳.时间戳主要作用就是判断mOrphanedResources中的资源是否长期不引用到了应该彻底回收的时候
void ResourceManager::cleanOrphans(){ timeval tv; gettimeofday(&tv, NULL); // Delete orphaned resources after 30 seconds. time_t oldest = tv.tv_sec; time_t threshold = oldest - 30; if (mOrphanedResources.empty() || mOldestOrphan >= threshold) return; ResourceIterator iter = mOrphanedResources.begin(); while (iter != mOrphanedResources.end()) { Resource *res = iter->second; time_t t = res->mTimeStamp; if (t >= threshold) { if (t < oldest) oldest = t; ++iter; } else { logger->log("ResourceManager::release(%s)", res->mIdPath.c_str()); ResourceIterator toErase = iter; ++iter; mOrphanedResources.erase(toErase); delete res; // delete only after removal from list, to avoid issues in recursion } } mOldestOrphan = oldest;}
从当前时间点往前推30秒threshold，如果在这个时间之前release的则应该回收，之后的保留，并且统计出保留的资源里最老的时间戳mOldestOrphan，如果下次清理资源的时候发现mOldestOrphan还在threshold之后，那说明没有资源需要回收，可以避免不必要的遍历.那么cleanOrphans()何时调用呢？这个因各个游戏的资源管理策略而定，TMW是在每次请求资源的时候调用一次.
那外部如何从资源管理器请求资源，请求的资源又如何从硬盘加载?我们从上层逻辑代码往下跟.
怪物,NPC,玩家都是类Being,Being的构造函数调用setSubtype()->setupSpriteDisplay
void ActorSprite::setupSpriteDisplay(const SpriteDisplay &display, bool forceDisplay){ clear(); SpriteRefs it, it_end; for (it = display.sprites.begin(), it_end = display.sprites.end(); it != it_end; it++) { std::string file = paths.getStringValue("sprites") + it->sprite; int variant = it->variant; addSprite(AnimatedSprite::load(file, variant)); }
…
setupSpriteDisplay会遍历所需要加载的sprite信息,调用addSprite,addSprite是CompoundSprite类的成员函数，Being继承于CompoundSprite,是Sprite的组合。跟进AnimatedSprite::load(file, variant)看sprite是如何加载的
AnimatedSpritre::load
ResourceManager *resman = ResourceManager::getInstance();
SpriteDef *s = resman->getSprite(filename, variant);
SpriteDef *ResourceManager::getSprite(const std::string &path, int variant){ SpriteDefLoader l = { path, variant }; std::stringstream ss; ss << path << "[" << variant << "]"; return static_cast<SpriteDef*>(get(ss.str(), SpriteDefLoader::load, &l));}Resource *ResourceManager::get(const std::string &idPath, generator fun, void *data){ // Check if the id exists, and return the value if it does. ResourceIterator resIter = mResources.find(idPath); if (resIter != mResources.end()) { resIter->second->incRef(); return resIter->second; } resIter = mOrphanedResources.find(idPath); if (resIter != mOrphanedResources.end()) { Resource *res = resIter->second; mResources.insert(*resIter); mOrphanedResources.erase(resIter); res->incRef(); return res; } Resource *resource = fun(data); if (resource) { resource->incRef(); resource->mIdPath = idPath; mResources[idPath] = resource; cleanOrphans(); } // Returns NULL if the object could not be created. return resource;}
struct SpriteDefLoader
{
std::string path;
int variant;
static Resource *load(void *v)
{
SpriteDefLoader *l = static_cast< SpriteDefLoader * >(v);
return SpriteDef::load(l->path, l->variant);
}
};
注意get资源的第二个参数SpriteDefLoader::load ,参数类型在ResouceManager中有定义typedef Resource *(*generator)(void *) 是一个函数指针,函数指针为完成各种类型资源加载提供了间接层
而SpriteDef继承于Resouce，其成员函数load完成读取xml配置加载动画的任务.加载动画时又会进一步分解为加载帧图片的任务
void SpriteDef::loadImageSet(xmlNodePtr node, const std::string &palettes){ const std::string name = XML::getProperty(node, "name", ""); // We don‘t allow redefining image sets. This way, an included sprite // definition will use the already loaded image set with the same name. if (mImageSets.find(name) != mImageSets.end()) return; const int width = XML::getProperty(node, "width", 0); const int height = XML::getProperty(node, "height", 0); std::string imageSrc = http://www.mamicode.com/XML::getProperty(node, "src", ""); Dye::instantiate(imageSrc, palettes); ResourceManager *resman = ResourceManager::getInstance(); ImageSet *imageSet = resman->getImageSet(imageSrc, width, height); if (!imageSet) { logger->error(strprintf("Couldn‘t load imageset (%s)!", imageSrc.c_str()).c_str()); } imageSet->setOffsetX(XML::getProperty(node, "offsetX", 0)); imageSet->setOffsetY(XML::getProperty(node, "offsetY", 0)); mImageSets[name] = imageSet;}
ImageSet是调用一连串的帧图片，也会通过ResourceManager的getImage接口
struct DyedImageLoader{ ResourceManager *manager; std::string path; static Resource *load(void *v) { DyedImageLoader *l = static_cast< DyedImageLoader * >(v); std::string path = l->path; std::string::size_type p = path.find(‘|‘); Dye *d = NULL; if (p != std::string::npos) { d = new Dye(path.substr(p + 1)); path = path.substr(0, p); } SDL_RWops *rw = PHYSFSRWOPS_openRead(path.c_str()); if (!rw) { delete d; return NULL; } Resource *res = d ? Image::load(rw, *d) : Image::load(rw); delete d; return res; }};Image *ResourceManager::getImage(const std::string &idPath){ DyedImageLoader l = { this, idPath }; return static_cast<Image*>(get(idPath, DyedImageLoader::load, &l));}
image的load非常简单，PHYSFSRWOPS_openRead是PHYSFS与SDL_RWops的封装函数.PHYSFS好像是一个提供了挂接解压等功能的跨平台文件库，开源游戏里经常见到，有时间研究下…
致此TMW的资源管理思路就大致摸清了，其他如粒子和音效的资源也是这么管理的,跟踪resourceManager的get就能看到脉络。
TMW的资源管理比较简单，功能也比较单一，只是使用引用计数来跟踪回收。游戏中的资源管理器有着各种各样的策略，因需求而定。有的游戏会分别拟定每种类型的资源占用内存的上限，如果超过上限会单独回收这种资源,还有的会结合内存池的使用，减少堆的碎片。游戏的资源管理总是跟内存管理息息相关，而C++在内存管理方面天生的定制能力提供了优势。页游中的资源管理方式则与此大相径庭的，如AS依赖于垃圾回收又苦于垃圾回收对稳定速度的干扰，带宽的紧张使得资源的释放也不能这么随意等等，思路又是截然不同。
总之，这个资源管理器对于2D小游戏来说足够简单实用，想在上面加功能也是比较容易的。