Re: [boost] [interprocess] [bimap] Using raw pointers

Subject: Re: [boost] [interprocess] [bimap] Using raw pointers
From: Matias Capeletto (matias.capeletto_at_[hidden])
Date: 2013-01-26 01:32:49

On Fri, Jan 25, 2013 at 11:49 PM, Ion Gaztañaga <igaztanaga_at_[hidden]> wrote:
> El 25/01/2013 21:47, Matias Capeletto escribió:
>> But still when users will select an interprocess allocator they will
>> be paying for every call to the views:
>>
>>    left_type& left = bm.left;
>>    left.size(); // needs to use offset_ptr
>
> Have this problem also with iterators. Containers with interprocess
> allocators will return an iterator that can be placed in shared memory
> (contains offset_ptr) but when you use it to iterate in your process, you
> pay the price of offset_ptr. I think multiindex also pays this price.

Ok, that is interesting. Maybe I should just use offset_ptr then, if
every time I iterate over the container I am using them anyways.

>> What MultiIndex is doing is creating the index views with a pointer to
>> (this) every time the user ask them. I could do the same if I
>> deprecate .left and .right and include get_left() and get_right()
>> functions. But as I said I will like to keep the current interface...
>> is something like the rewire extension impossible? (I am afraid it is
>> if you are pointing to read only memory).
>
> I don't fully understand what do you achieve with "rewire", can you
> elaborate, please?

Maybe you do not understand this because is a crazy idea in the
context of Interprocess. I looked at your code and in the
segment_manager, before you return the user the found Bimap* I wanted
a user extension point to be called on the pointer:

    if( t_ret ) rewire_after_loading_from_shared_memory( t_ret );
      return std::pair<T*, size_type>(t_ret ,sz);

And I will do something like (this function being a friend of the views):

template<class L, class R>
void rewire_after_loading_from_shared_memory(bimap<L,R>* t) {
  t->left.rewire(t); t->right.rewire(t);
}

In left_type and right_type private section:
void rewire(Core* c) { if(core!=c) core=c; }

Event if this could work, the question will be if we want to allow
users to place views in shared memory. For Bimap, I think it doesn't
make sense... you should always stored the bimap and then get the
views.

But now I looked better at MultiIndex implementation and it is
actually pushing the index as part of the main container hierarchy
using CRTP to access the core, something I thought about yesterday
also. I think I will end up doing the same for Bimap then.

Thanks,
Best
Matias