boost :: interprocess不在共享内存中的容器容器

Question

我有一个boost::interprocess Containers of containers类型的示例演示程序。 但我喜欢在我的进程内存中使用这个类也是一个普通的类。 有人可以帮我写一个构造函数，它不需要任何参数就可以在当前进程内存中初始化类。

#include <boost/interprocess/containers/vector.hpp> 
#include <boost/interprocess/allocators/allocator.hpp> 
#include <boost/interprocess/managed_shared_memory.hpp> 
#include <boost/archive/xml_oarchive.hpp> 
#include <boost/archive/xml_iarchive.hpp> 
#include <shmfw/serialization/interprocess_vector.hpp> 
#include <stdlib.h>  /* srand, rand */ 
#include <time.h>  /* time */ 


using namespace boost::interprocess; 
//Alias an STL-like allocator of ints that allocates ints from the segment 
typedef allocator<int, managed_shared_memory::segment_manager> ShmemAllocator; 

//Alias a vector that uses the previous STL-like allocator 
typedef vector<int, ShmemAllocator> MyVector; 

typedef allocator<void, managed_shared_memory::segment_manager >       void_allocator; 

class MyStruct { 
public: 
    MyVector myVector; 
    //Since void_allocator is convertible to any other allocator<T>, we can simplify 
    //the initialization taking just one allocator for all inner containers. 
    MyStruct (const void_allocator &void_alloc) 
     : myVector (void_alloc) 
    {} 
    // Thats what I like to have  
    //MyStruct() 
    // : myVector (??) 
    //{} 
}; 

int main() { 

    // I would like to have something like that working and also the shm stuff below 
    // MyStruct x; 


    managed_shared_memory segment; 
    //A managed shared memory where we can construct objects 
    //associated with a c-string 
    try { 
     segment = managed_shared_memory(create_only, "MySharedMemory", 65536); 
    } catch (...){ 
     segment = managed_shared_memory(open_only, "MySharedMemory"); 
    } 

    //Initialize the STL-like allocator 
    const ShmemAllocator alloc_inst (segment.get_segment_manager()); 

    MyStruct *myStruct_src = segment.find_or_construct<MyStruct> ("MyStruct") (alloc_inst); 
    srand (time(NULL)); 
    myStruct_src->myVector.push_back (rand()); 

    MyStruct *myStruct_des = segment.find_or_construct<MyStruct> ("MyStruct") (alloc_inst); 

    for (size_t i = 0; i < myStruct_src->myVector.size(); i++) { 
     std::cout << i << ": " << myStruct_src->myVector[i] << " = " << myStruct_des->myVector[i] << std::endl; 
    if(myStruct_src->myVector[i] != myStruct_des->myVector[i]) { 
     std::cout << "Something went wrong!" << std::endl; 
    } 
    } 


    //segment.destroy<MyVector> ("MyVector"); 
    return 0; 
} 

Answer 1

如果更改分配器类型，则更改容器（例如编译时模板实例化的本质）。从技术上讲，你可以设计一个类型删除的分配器（àla std::function或boost::any_iterator），但这可能会导致糟糕的性能。而且，它仍然会要求所有的分配器在所有静态已知的属性中对应，从而降低了灵活性。

在现实中，我建议只在Allocator类型上使用MyStruct作为任何嵌入容器的模板。那么具体采取这种分配器在构造函数中：

// Variant to use on the heap: 
using HeapStruct = MyStruct<std::allocator>; 
// Variant to use in shared memory: 
using ShmemStruct = MyStruct<BoundShmemAllocator>; 

演示程序：

#include <boost/interprocess/containers/vector.hpp> 
#include <boost/interprocess/allocators/allocator.hpp> 
#include <boost/interprocess/managed_shared_memory.hpp> 
#include <boost/range/algorithm.hpp> 
#include <iostream> 
#include <cassert> 

namespace bip = boost::interprocess; 
template <typename T> 
    using BoundShmemAllocator = bip::allocator<T, bip::managed_shared_memory::segment_manager>; 

/////////////////////////////////////////////////////////////// 
// Your MyStruct, templatized for an Allocator class template 

template <template<typename...> class Allocator> 
class MyStruct { 
public: 
    bip::vector<int, Allocator<int> > ints; 
    bip::vector<double, Allocator<double> > doubles; 

    MyStruct(const Allocator<void>& void_alloc = {}) 
     : ints(void_alloc), 
      doubles(void_alloc) 
    {} 
}; 

// Variant to use on the heap: 
using HeapStruct = MyStruct<std::allocator>; 
// Variant to use in shared memory: 
using ShmemStruct = MyStruct<BoundShmemAllocator>; 

// 
/////////////////////////////////////////////////////////////// 

int main() { 
    srand(time(NULL)); 

    // You can have something like this working: 
    HeapStruct x; // and also the shm stuff below 
    std::generate_n(std::back_inserter(x.ints), 20, &std::rand); 
    std::generate_n(std::back_inserter(x.doubles), 20, &std::rand); 

    // A managed shared memory where we can construct objects 
    bip::managed_shared_memory segment = bip::managed_shared_memory(bip::open_or_create, "MySharedMemory", 65536); 
    BoundShmemAllocator<int> const shmem_alloc(segment.get_segment_manager()); 

    auto src = segment.find_or_construct<ShmemStruct>("MyStruct")(shmem_alloc); 
    src->ints.insert(src->ints.end(),  x.ints.begin(), x.ints.end()); 
    src->doubles.insert(src->doubles.end(), x.doubles.begin(), x.doubles.end()); 

    auto des = segment.find_or_construct<ShmemStruct>("MyStruct")(shmem_alloc); 

    std::cout << "-------------------------"; 
    boost::copy(src->ints, std::ostream_iterator<int>(std::cout << "\nsrc ints: ", "; ")); 
    boost::copy(des->ints, std::ostream_iterator<int>(std::cout << "\ndes ints: ", "; ")); 
    std::cout << "\n-------------------------"; 
    boost::copy(src->doubles, std::ostream_iterator<double>(std::cout << "\nsrc doubles: ", "; ")); 
    boost::copy(des->doubles, std::ostream_iterator<double>(std::cout << "\ndes doubles: ", "; ")); 

    assert(src->ints.size() == des->ints.size()); 
    assert(src->doubles.size() == des->doubles.size()); 
    assert(boost::mismatch(src->ints, des->ints) == std::make_pair(src->ints.end(), des->ints.end())); 
    assert(boost::mismatch(src->doubles, des->doubles) == std::make_pair(src->doubles.end(), des->doubles.end())); 

    segment.destroy<ShmemStruct>("MyStruct"); 
}