unordered_map在managed_shared_memory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; 
} 

一切正常时MappedType是int，但是段故障丝毫这这样的代码：

重新运行该程序访问在共享内存中哈希表将再次核心转储

----------------------------编辑--------- -------------------------

关于字符串的问题是通过sehe解决的，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从堆分配。

堆在你的进程地址空间，所以任何其他进程读取相同的共享内存是会得到一个错误的原始指针有和调用UB。

您需要使用共享内存分配器与琴弦太。

Live On Coliru（使用Coliru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; 
} 

打印

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