c ++服务器-共享内存中的客户端boost ::进程间数组访问

Question

I am developing a Server/Client program that makes use of the boost::interprocess shared memory library. I would like my Sever to create a shared memory object, which will be filled with a vector of int. Once this object is constructed, before its destruction, I would like, my Client to have access to the shared memory object and read this vector. The problem I have now is that my Server creates the shared memory object, stores the vector, and fills it whit 100 numbers int. On the Client side, I open the shared memory object and read this, but the results are different. What I realized, after printing the shared memory object address created by server and client, is that they are different, ie The Client is looking at the wrong memory address (I guess this is likely to be the main issue), however, I cannot explain why this happens and where is the mistake in my code.

The output I get is:

*Server.cpp:*

 managed_shared_memory created

 ADDRESS: 0000023B68A10000

 Vector constructed

 Vector filled

Now launch Client and wait for analysis...

*Client.cpp:*

 managed_shared_memory opened

 ADDRESS: 000002EE6BD90000

 Vector Found

 2.122e-314 6.36599e-314 1.061e-313 1.4854e-313 1.9098e-313                                 

Server and Client codes are below. Thanks.

Server.cpp

#include <cstdlib>
#include <string>
#include <iostream>

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/allocators/allocator.hpp>

using namespace boost::interprocess;

//Define an STL compatible allocator of ints that allocates from the managed_shared_memory.
//This allocator will allow placing containers in the segment
typedef allocator<int, managed_shared_memory::segment_manager>  ShmemAllocator;

//Alias a vector that uses the previous STL-like allocator so that allocates
//its values from the segment
typedef vector<int, ShmemAllocator> MyVector;

//Main function. For parent process argc == 1, for child process argc == 2
int main()
{
     //Remove shared memory on construction and destruction
    struct shm_remove
    {
      shm_remove() { shared_memory_object::remove("MySharedMemoryNew"); }
      ~shm_remove() { shared_memory_object::remove("MySharedMemoryNew"); }
    } remover;

    //Create a new segment with given name and size
    managed_shared_memory segment(create_only, "MySharedMemoryNew", 65536);
    std::cout << " managed_shared_memory created" << std::endl;

    //Initialize shared memory STL-compatible allocator
    const ShmemAllocator alloc_inst(segment.get_segment_manager());
    std::cout << " ADDRESS: " <<segment.get_address() << std::endl;

    //Construct a vector named "MyVector" in shared memory with argument alloc_inst
    MyVector* myvector = segment.construct<MyVector>("MySharedVector")(alloc_inst);
    std::cout << " Vector constructed" << std::endl;

    for (int i = 0; i < 5; ++i)  //Insert data in the vector
      myvector->push_back(i);
    std::cout << " Vector filled" << std::endl;
    
    std::cout << " Now launch Client and wait for analysis... " << std::endl;
    int carryon;
    //only after client has been launched
    std::cin >> carryon;

  return 0;
}

Client.cpp

#include <cstdlib>
#include <string>
#include <iostream>

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/allocators/allocator.hpp>

using namespace boost::interprocess;

//Define an STL compatible allocator of ints that allocates from the managed_shared_memory.
//This allocator will allow placing containers in the segment
typedef allocator<double, managed_shared_memory::segment_manager>  ShmemAllocator;

//Alias a vector that uses the previous STL-like allocator so that allocates
//its values from the segment
typedef vector<double, ShmemAllocator> MyVector;

int main()
{

  //Open a segment with given name
  managed_shared_memory segment(open_only, "MySharedMemoryNew");
  std::cout << " managed_shared_memory opened" << std::endl;
  std::cout << " ADDRESS: " << segment.get_address() << std::endl;

  // access to the vector
  MyVector* myvector = segment.find<MyVector>("MySharedVector").first;
  std::cout << " Vector Found" << std::endl;

  for (unsigned int k = 0; k < 5; k++) {
    std::cout << (*myvector)[k] << " ";
  }

  return 0;
}

Answer 1

The code looks essentially correct, however the problem might be some conflict generated by the fact that in server.cpp Vector and Allocator are defined as int whilst in client.cpp they are double . Check this.

Answer 2

The answer is that vector has a data member that is a pointer to the elements in the vector. That is not translated to client.

On the server the data might point to 0000023B68A11000

On the client it will still point to 0000023B68A11000 but the correct address might be 000002EE6BD91000