在 managed_shared_memory 中带有字符串的 unordered_map 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 是 int 时一切正常，但是这段代码出现了段错误，如下所示：

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string的问题sehe解决了，谢谢 如果我设计一个模板类想要隐藏那个细节，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。 std::string 从堆中分配。

堆在您的进程地址空间中，因此读取同一共享内存的任何其他进程都会在此处获得错误的原始指针并调用 UB。

您还需要对字符串使用共享内存分配器。

Live On Coliru（使用 Coliru 的映射文件）

使用共享内存：

#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;
}

打印

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