实现一个内存池管理的类

模拟STL中的freelist,有这个思想在内。

    union obj        {          union obj* next;          char p[1];             };                class MemoryPool        {              public:                    MemoryPool()                    {                       union obj* temp;                       m_memory.assign(5,(union obj*)NULL);                                for(int i=0;i<m_memory.size();i++)                       {                           for(int j=0;j<m_memory.size();j++)                           {                             temp = (obj*)malloc(sizeof(char)*(1<<(i+3)));                                  temp->next = m_memory[i];                             m_memory[i] = temp;                            }                       }                    }                    char* mem_get(int size)                    {                       int j;                       if( size > 128)                       {                          char* start = (char*)malloc(sizeof(char)*size);                          return start;                        }                       int index = freelist_index(size);                       obj* temp = m_memory[index];                       if(temp == NULL)  //                       {                          for(j = index+1;j<m_memory.size();j++)                          {                             temp = m_memory[j];                             if(temp != NULL)                             {                               m_memory[j] = temp->next;                               break;                                    }                               }                          if(j>= m_memory.size())                          {                             for(int j=0;j<m_memory.size();j++)                            {                              temp = (obj*)malloc(sizeof(char)*(1<<(index+3)));                                   temp->next = m_memory[index];                              m_memory[index] = temp;                             }                              temp = m_memory[index];                            m_memory[index] = temp->next;                            return (char*)temp;                          }                          else                          {                             obj* cur;                                                         int up_size = round_up(size);                             for(int i=0;i<(1<<(j-index));i++)                             {                                cur =  temp;                                cur->next = m_memory[index];                                m_memory[index] = cur;                                temp = cur+up_size;                                                       }                              temp = m_memory[index];                             m_memory[index] = temp->next;                             return (char*)temp;                          }                            }                       else                       {                           m_memory[index] = temp->next;                          return (char*)temp;                        }                    }                    void mem_free(void* p,int size)                    {                      if(size > 128)                      {                        free(p);                        return ;                         }                         obj* temp = (obj*)p;                      int index = freelist_index(size);                      temp->next = m_memory[index];                      m_memory[index]  = temp;                    }             private:                     enum {_ALIGN = 8};//                     int freelist_index(int __bytes)                      {                         return (((__bytes) + (int)_ALIGN-1)/(size_t)_ALIGN - 1);                     }                     int round_up(int __bytes)                      {                        return (((__bytes) + (int) _ALIGN-1) & ~((int) _ALIGN - 1));                      }                     vector<union obj*> m_memory;               };