Re: [Boost-users] mpi/serialization: broadcast function and the value argument

Subject: Re: [Boost-users] mpi/serialization: broadcast function and the value argument
From: Hicham Mouline (hicham_at_[hidden])
Date: 2010-12-13 15:31:24

>-----Original Message----- 
>From: "Matthias Troyer" [troyer_at_[hidden]] 
>Date: 09/12/2010 02:39 PM 
>To: boost-users_at_[hidden] 
>Subject: Re: [Boost-users] mpi/serialization: broadcast function and the value argument 
>>On Dec 8, 2010, at 5:50 PM, Hicham Mouline wrote: 
>>> Following a suggestion from another thread, I have tried broadcasting in a polymorphic way. 
>>> 
>>> I have a hierarchy of polymorphic struct (they have 2 virtual functions). I was wondering if it was possible/allowed to 
>>> 
>>> root process: 
>>> base* b; /// b points to an actual derived struct but may also point the base struct (not abstract) 
>>> broadcast( ..., b, ...); 
>>> 
>>> slave processes: 
>>> base* b; 
>>> broadcast( ..., b, ...); /// broadcast constructs the appropriate struct and makes b point to where it did that 
>>> 
>>> assuming all the conditions for pointer to class conditions are satisfied for the serialization library. 
>>> 
>>If serialization works on your polymorphic class then this should work as well. 
>>Matthias 

>It appears the implementation of mpi::broadcast(), according to this post, 
>http://lists.boost.org/boost-users/2010/12/64802.php 
>and I confirm that expects an already built object to call the 
>(de)serialization procedure on. 
>Therefore, this seems a specific issue that mpi::broadcast() may want to handle differently, 
>could you confirm/correct? 
>thanks, 

I would very much appreciate extra opinions about this issue and the route I have taken to solve it.
Let me sum up:

mpi::broadcast() appears to be incapable of sending the argument "value" in a polymorphic way, ie:

sender-------------------
Base* base;
If I call      boost::mpi::broadcast(..., base, ...)

receiver-----------------
Base* base;
boost::mpi::broadcast(..., base, ...)
This does not construct the most derived type of base on the heap and make base point there, as serialization would do.

I therefore used a variant made of all the classes of the hierarchy and broadcast it instead.

sender-------------------
variant<...> v;
boost::mpi::broadcast(..., v, ...)

receiver-----------------
variant<...> v;
boost::mpi::broadcast(..., v, ...)

This works but before I replicate it in other parts of the code, I would appreciate your opinions about this solution provided by Riccardo.

Regards,