模板元编程如何专注于集合

Question

我有以下UtlSharedIPCWrapper我创建的模板类访问放置在进程间内存中的用户定义类型。

通常这个类是使用一个简单的类型，例如：

// construct a FaultReport - default to no faults 
auto faultWrapper = managed_shm.construct< 
    UtlSharedIPCWrapper<uint64_t>>("FaultReport")(0); 

，这工作得很好，但是我最近有需要使用升压共享存储器映射集合（boost::interprocess::map）作为模板参数）如：

using char_allocator = boost::interprocess::managed_shared_memory::allocator<char>::type; 
using shm_string = boost::interprocess::basic_string<char, std::char_traits<char>, char_allocator>; 
using KeyType = shm_string; 
using ValueType = std::pair<const KeyType, shm_string>; 
using ShmemAllocator = boost::interprocess::allocator<ValueType, boost::interprocess::managed_shared_memory::segment_manager>; 
using SharedMemoryMap = boost::interprocess::map<shm_string, shm_string, std::less<KeyType>, ShmemAllocator>; 

... 

// create a new shared memory segment 2K size 
managed_shared_memory managed_shm(open_only, "sharedmemname"); 

//Initialize the shared memory STL-compatible allocator 
ShmemAllocator alloc(managed_shm.get_segment_manager()); 

auto pSharedNVPairs = managed_shm.find<UtlSharedIPCWrapper< 
    SharedMemoryMap>>("NameValuePairs").first; 

我的问题是如何改变下面的模板类定义通过收集::值类型的作为参数，而不是单独地读取整个地图作为一个操作通过pSharedNVPairs->getSharedData()更新的T并通过pSharedNVPairs->setSharedData(*pSharedNVPairs)再次将其写回共享内存。我知道这对于不是集合的类型会有所不同，因此一些模板元编程魔术将不得不被执行，如果选择性启用等，但我想有一种方法添加到我的类，沿着

// I don't know the correct signature here 
void setSharedDataValue(const T::value_type& rSharedDataValue) { 
    boost::interprocess::scoped_lock<upgradable_mutex_type> lock(mMutex); 
    ... not sure what to do here to update the collection 
} 

template<typename T> 
struct UtlSharedIPCWrapper { 
private: 
    using upgradable_mutex_type = boost::interprocess::interprocess_upgradable_mutex; 

    mutable upgradable_mutex_type mMutex; 
    /*volatile*/ T mSharedData; 
public: 
    // explicit constructor used to initialize directly from existing memory 
    explicit UtlSharedIPCWrapper(const T& rInitialValue) 
     : mSharedData(rInitialValue) 
    {} 

    T getSharedData() const { 
     boost::interprocess::sharable_lock<upgradable_mutex_type> lock(mMutex); 
     return mSharedData; 
    } 

    void setSharedData(const T& rSharedData) { 
     boost::interprocess::scoped_lock<upgradable_mutex_type> lock(mMutex); 
     // update the shared data copy mapped - scoped locked used if exception thrown 
     // a bit like the lock guard we normally use 
     this->mSharedData = rSharedData; 
    } 
}; 

Answer 1

为什么不

// I don't know the correct signature here 
void setSharedDataValue(const typename T::value_type& rSharedDataValue)  { 
    boost::interprocess::scoped_lock<upgradable_mutex_type> lock(mMutex); 
    mSharedData.insert(rSharedDataValue); 
}