将分配器添加到C类模板以创建共享内存对象

简而言之,我的问题是：如果您有类,MyClass< T>,您如何更改类定义以支持您拥有MyClass< T,Alloc>的情况,类似于STL vector提供的方式.

我需要此功能来支持共享内存的分配器.具体来说,我试图在共享内存中实现一个环形缓冲区.目前它有以下ctor：

template<typename ItemType>
SharedMemoryBuffer<ItemType>::SharedMemoryBuffer( unsigned long capacity, std::string name )

其中ItemType是要放在缓冲区的每个槽中的数据的类型.

现在,当我从主程序创建缓冲区时,这种方法非常出色

SharedMemoryBuffer<int>* sb;
sb = new SharedMemoryBuffer<int>(BUFFER_CAPACITY + 1, sharedMemoryName);

但是,在这种情况下,缓冲区本身不会在共享内存中创建,因此其他进程无法访问.我想做的是能够做类似的事情

typedef allocator<int, managed_shared_memory::segment_manager>  ShmemAllocator;
typedef SharedMemoryBuffer<int, ShmemAllocator> MyBuffer;

managed_shared_memory segment(create_only, "MySharedMemory", 65536);
const ShmemAllocator alloc_inst (segment.get_segment_manager());
MyBuffer *mybuf = segment.construct<MyBuffer>("MyBuffer")(alloc_inst);

但是,我不知道如何在类模板中添加显式分配器.

令我困惑的是,为什么你需要在SharedMemory(SHM)中分配或创建一个对象,例如,如果你保留大小为65536字节的共享内存,那么假设你在地址0x1ABC0000获得共享内存,如果预订成功,你将在0x1ABC0000到0x1ABCFFFF处有可自由且可直接访问的存储空间.

然后当你的应用程序需要在大小sizeof(SHMObject)的SHM中“分配”对象,并且你的内存管理器看到0x1ABC0000 0x1A的地址是空闲时,你的内存管理器应该只返回0x1ABC001A值,并标记(0x1ABC001A到0x1ABC001A sizeof(SHMObject) ))被占用,你只需要转换：SHMObject * shmObjectPtr =(SHMObject *)(0x1ABC001A);

当然,假设你有自己的自定义内存分配器,它可以在指定的内存地址范围内工作.

至于模板,我真的不明白你的SHM环缓冲区是怎么样的,但是在使用SHM之前我已经这样做了,我的实现是这样的：
`

//memory SHM allocator
template<typename T> class ShmRingAllocator
{
    protected:
        void* baseAddress;
    public:
        ShmRingAllocator(void* baseAddress,int memSize);
        void* allocate(); //this function do what I described earlier, or you can use placement new: new (baseAddress+offset)T;
}

//some kind of shared_ptr<> that handle object in SHM, this provides mechanishm to check is the pointer still valid in shm or not
template<typname T> ShmRingObjectPtr 
{
    protected:
         T* object; //mapped address of object at current process
         ShmBuffer* shm; //every object has pointer to which SHM does this pointer pointing at
    public:
         virtual T* operator->(); //operator overload to access T object
}

class ShmBuffer //base class for all kind of SHM buffer
{
    protected:
         std::string shmName;
         void* shmBasePtr;
}

template<typename T,class A=ShmRingAllocator<T>> ShmRingBuffer : public ShmBuffer
{
    protected:
         A allocator;
    public:
         ShmRingObjectPtr<T> insert() //push one element to ring buffer
         {
              return ShmRingObjectPtr<T>((T*)this->allocator.allocate(),this);
         }
}

`