unordered_map 与 managed_shared_memory 中的字符串失败

Question

这是我的代码：

int main (int argc, char *argv[])
{
    typedef int KeyType;
    typedef string MappedType;

    typedef std::pair<KeyType, MappedType> ValueType;
    typedef boost::interprocess::allocator<ValueType, boost::interprocess::managed_shared_memory::segment_manager> ShmAlloc;
    typedef boost::unordered_map<KeyType, MappedType, boost::hash<KeyType>, std::equal_to<KeyType>, ShmAlloc> ShmHashMap;

    boost::interprocess::managed_shared_memory segment(boost::interprocess::open_or_create, "ContainerSharedMemory", 65536);

    if(argc == 2 && string(argv[1]) == "clear")
    {
        boost::interprocess::shared_memory_object::remove("ContainerSharedMemory");
        return 0;
    }

    ShmHashMap *hash_map = segment.find_or_construct<ShmHashMap>(boost::interprocess::unique_instance)(segment.get_segment_manager());

    if(hash_map == NULL)
    {
        cout << "find_or_construct error" << endl;
        return 0;
    }

    for(int i = 0; i < 5; ++i) {
        ShmHashMap::iterator iter = hash_map->find(i);
        if (iter == hash_map->end()) {
            hash_map->insert(ValueType(i, "test"));
        }
    }

    cout << "all..." << endl;
    for(ShmHashMap::iterator iter = hash_map->begin(); iter != hash_map->end(); ++iter)
    {
        cout << iter->first << "|" << iter->second << endl;
    }
    cout << "end..." << endl;

    return 0;
}

当 MappedType 为 int 时一切正常，但出现如下代码的段错误：

重新运行此程序以访问共享内存中的哈希映射将核心转储

----------------------------再次编辑---------------- ------------------

关于字符串的问题sehe解决了，谢谢如果我设计一个模板 class 想隐藏那个细节，我该怎么办？如果有什么完美的方法

template<typename MappedType>
struct ComplexMappedType
{
    ComplexMappedType(): t_access(0), t_expire(0) {}
    ComplexMappedType(const MappedType& v, uint32_t a, uint32_t e): value(v), t_access(a), t_expire(e) {}
    MappedType value;
     uint32_t t_access;
     uint32_t t_expire;
 };

 template <typename KeyType, typename MappedType>
 class MMSHashMap
 {
 private:
    typedef ComplexMappedType<MappedType> DataType;
    typedef std::pair<KeyType, DataType> ValueType;
    typedef boost::interprocess::allocator<ValueType, boost::interprocess::managed_shared_memory::segment_manager> ShmAlloc;
    typedef boost::unordered_map<KeyType, DataType, boost::hash<KeyType>, std::equal_to<KeyType>, ShmAlloc> ShmHashMap;

public:
    MMSHashMap(const std::string& name, size_t size, float e_thr, float e_scale);
    ~MMSHashMap() {delete pMemorySegment;}

    size_t getMEMSize() { return pMemorySegment->get_size(); }
    size_t getMEMFreeSize() { return pMemorySegment->get_free_memory(); }

    bool get(const KeyType& key, MappedType& value, uint32_t& expire);
    bool set(const KeyType& key, const MappedType& value, uint32_t expire);
    bool del(const KeyType& key);

private:
    void doCapacityElimination();

    std::string _name;
    boost::interprocess::managed_shared_memory* pMemorySegment;
    boost::shared_mutex mutex, mutex_eliminate;
    float fEliminateThreshold, fEliminateScale;
};

Answer 1

当然可以。 std::string 从堆中分配。

堆位于您的进程地址 space 中，因此读取同一共享内存的任何其他进程都将在那里获得错误的原始指针并调用 UB。

您也需要对字符串使用共享内存分配器。

Live On Coliru（为 Coliru 使用映射文件）

共享内存：

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/container/scoped_allocator.hpp>
#include <boost/container/string.hpp>
#include <boost/unordered_map.hpp>
#include <iostream>

namespace bip = boost::interprocess;

int main (int argc, char *argv[])
{
    typedef int KeyType;

    typedef boost::container::basic_string<char, std::char_traits<char>, bip::allocator<char, bip::managed_shared_memory::segment_manager> > MappedType;

    typedef std::pair<KeyType, MappedType> ValueType;
    typedef boost::interprocess::allocator<ValueType, boost::interprocess::managed_shared_memory::segment_manager> ShmAlloc;
    typedef boost::unordered_map<KeyType, MappedType, boost::hash<KeyType>, std::equal_to<KeyType>, boost::container::scoped_allocator_adaptor<ShmAlloc> > ShmHashMap;

    boost::interprocess::managed_shared_memory segment(boost::interprocess::open_or_create, "ContainerSharedMemory", 65536);

    if(argc == 2 && std::string(argv[1]) == "clear")
    {
        boost::interprocess::shared_memory_object::remove("ContainerSharedMemory");
        return 0;
    }

    ShmHashMap *hash_map = segment.find_or_construct<ShmHashMap>(boost::interprocess::unique_instance)(segment.get_segment_manager());

    if(hash_map == NULL)
    {
        std::cout << "find_or_construct error" << std::endl;
        return 0;
    }

    for(int i = 0; i < 5; ++i) {
        ShmHashMap::iterator iter = hash_map->find(i);
        if (iter == hash_map->end()) {
            hash_map->insert(ValueType(i, MappedType { "hello", segment.get_segment_manager() }));
        }
    }

    std::cout << "all..." << std::endl;
    for(ShmHashMap::iterator iter = hash_map->begin(); iter != hash_map->end(); ++iter)
    {
        std::cout << iter->first << "|" << iter->second << std::endl;
    }
    std::cout << "end..." << std::endl;
}

版画

all...
4|hello
3|hello
2|hello
1|hello
0|hello
end...

unordered_map 与 managed_shared_memory 中的字符串失败

unordered_map with string in managed_shared_memory fails

boost

unordered-map

interprocess