内存分配管理（一）

看jrtplib源码时，对其中的内存管理不理解，遂向高手请教，把所得记于此：

主要的两个类：

class RTPMemoryManager{public:RTPMemoryManager(){ }virtual ~RTPMemoryManager(){ }virtual void *AllocateBuffer(size_t numbytes, int memtype) = 0;virtual void FreeBuffer(void *buffer) = 0;};

class RTPMemoryObject{protected:#ifdef RTP_SUPPORT_MEMORYMANAGEMENTRTPMemoryObject(RTPMemoryManager *memmgr) : mgr(memmgr){ }#elseRTPMemoryObject(RTPMemoryManager *memmgr){ }#endif // RTP_SUPPORT_MEMORYMANAGEMENTvirtual ~RTPMemoryObject(){ }#ifdef RTP_SUPPORT_MEMORYMANAGEMENTRTPMemoryManager *GetMemoryManager() const{ return mgr; }void SetMemoryManager(RTPMemoryManager *m){ mgr = m; }#elseRTPMemoryManager *GetMemoryManager() const{ return 0; }void SetMemoryManager(RTPMemoryManager *m){ }#endif // RTP_SUPPORT_MEMORYMANAGEMENT#ifdef RTP_SUPPORT_MEMORYMANAGEMENTprivate:RTPMemoryManager *mgr;#endif // RTP_SUPPORT_MEMORYMANAGEMENT};

据说下面这个类RTPMemoryObkect的作用是为了把具体工作的类与RTPMemoryManager分离（设计模式->适配器模式）

首先，它有自己的new：

inline void *operator new[](size_t numbytes, RTPMemoryManager *mgr, int memtype){if (mgr == 0)return operator new[](numbytes);return mgr->AllocateBuffer(numbytes,memtype);}

重载 operator new 的参数个数是可以任意的 , 只需要保证第一个参数为 size_t, 返回类型为 void * 即可 , 而且其重载的参数类型也不必包含自定义类型 。

然后这样使用：

#define RTPNew(a,b) new(a,b)uint8_t *localhostname = RTPNew(GetMemoryManager(),RTPMEM_TYPE_OTHER) uint8_t [localhostnamelength+1];

真正的内存分配需要用户来完成，也就是上面的纯虚函数AllocateBuffer，jrtplib中有个example5，给出了示例：

class MyMemoryManager : public RTPMemoryManager{public:MyMemoryManager() { mutex.Init();alloccount = 0; freecount = 0; }~MyMemoryManager() { std::cout << "alloc: " << alloccount << " free: " << freecount << std::endl; }void *AllocateBuffer(size_t numbytes, int memtype){mutex.Lock();void *buf = malloc(numbytes);std::cout << "Allocated " << numbytes << " bytes at location " << buf << " (memtype = " << memtype << ")" << std::endl;alloccount++;mutex.Unlock();return buf;}void FreeBuffer(void *p){mutex.Lock();std::cout << "Freeing block " << p << std::endl;freecount++;free(p);mutex.Unlock();}private:int alloccount,freecount;JMutex mutex;};

最后这样使用：

MyMemoryManager mgr;RTPSession sess(0, &mgr);

这种方法很巧妙，也很难看懂，example里面的内存分配方式简易了点，自己实现时可以考虑内存池，因为RTP数据发送时申请和释放内存还是挺频繁的。