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，但这段代码出现段错误，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coredump

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

关于字符串的问题由sehe解决，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？如果有一些完美的方式

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。

堆位于进程地址空间中，因此读取相同共享内存的任何其他进程将在那里获取错误的原始指针并调用UB。

您还需要在字符串中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...

managed_shared_memory中带有字符串的unordered_map失败

1 个答案: