Re: [Boost-users] Boost.Interprocess: Can I share the multi_index array between processes?

Subject: Re: [Boost-users] Boost.Interprocess: Can I share the multi_index array between processes?
From: Arman Khalatyan (arm2arm_at_[hidden])
Date: 2010-04-06 17:31:26

Hi,
Thanks for your detailed explanations.
I was paying with your nice example.
Currently my structure is keeping only several floats, ints and unsigned
ints. Following the Interprocess documentation, as you  wrote, I can put
them directly into shared memory:

 server_side:
   P.insert(particleID(0,0));
   P.insert(particleID(-1,1));
   P.insert(particleID(-2,2));
   P.insert(particleID(-3,3));
   try{
      //Erase previous shared memory
      shared_memory_object::remove("shared_memory");

      //Create a shared memory object.
      shared_memory_object shm (create_only, "shared_memory", read_write);

      //Set size
  size_t P_len=P.size()*sizeof(particleID);
      shm.truncate(P_len);

      //Map the whole shared memory in this process
      mapped_region region(shm, read_write);

      //Write all the memory to 1
      std::memset(region.get_address(), 1, region.get_size());
  print_out_by<ID>(P);
  boost::xtime xt;
  boost::xtime_get(&xt, boost::TIME_UTC);
  xt.sec += 100;
  for(;;)boost::thread::sleep(xt);
   }
   catch(interprocess_exception &ex){
      shared_memory_object::remove("shared_memory");
      std::cout << ex.what() << std::endl;
      return 1;
   }

Now I am trying to access the memory from client:
  shared_memory_object shm (open_only, "shared_memory", read_only);

      //Map the whole shared memory in this process
      mapped_region region(shm, read_only);

      //Check that memory was initialized to 1
      const particlesID_set *P =
static_cast<particlesID_set*>(region.get_address());

  //const particlesID_set::nth_index<1>::type L1_ID_index = (*P).get<1>();//
This does not compile, Why?

  print_out_by<ID>((*P));  //This cannot access the memory...

In Client I cannot get the index, it claims that cannot access to protected
member.

Maybe I am missing something?Could you please advice me?

kind regards Arman.
On Tue, Apr 6, 2010 at 8:59 PM, Joaquin M Lopez Munoz <joaquin_at_[hidden]>wrote:

> arm2arm <arm2arm <at> gmail.com> writes:
> >
> >
> > Hello,
> > I would like to load multiindex container by one process lets say
> > serverside_loader. And access that array by another clientside_analyser
> > process? How to do that?
>
> Hi Arman,
>
> Yes, this can be done. There's an example that shows you how
> to do it:
>
> http://www.boost.org/libs/multi_index/doc/examples.html#example12
>
> Basically, you've got to take care of three things:
>
> * The element type (particleID in this case) must be placeable
> in shared memory, see
>
> http://tinyurl.com/ygau74j
>
> for info on the limitations imposed on such objects. particleID
> is a simple class and can be directly put in shared memory.
> * You must use a special Boost.Interprocess allocator for
> the multi-index container. Use the aforementioned example as
> a guide.
> * Access to the container must be properly synchronized, just
> as you'd do for instance in a multi-threaded program.
>
> Good luck with your project, come back if you have some
> difficulty.
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>