Creating immutable data and sharing it

[Simen kjaeraas]

Lutger <lutger.blijdestijn at gmail.com> wrote:

> Aha, thanks. I have made a conceptual diagram to help understand this,  
> would you
> care to take a look and confirm whether this is correct or not?
>
> http://picasaweb.google.com/Lutger.blijdestijn/Illustration#5519337139518828386
>
> I hope it explains itself, the edges reflect the types and the nodes the  
> memory
> storage.

That looks very much correct. I'm somewhat confused by the 'static data'
part, as it connected only to one thread, and static data is in TLS, as far
as I know.


>> Immutable global state may be instantiated from non-immutable data in
>> module constructors. I believe that is the canonical way.
>>
>
> Sometimes this is not possible. For example if you want to create a data
> structure from user input once, then use it read-only for the rest of the
> program.

Indeed. In that case, would a shared pointer/array to immutable data work  
for
you? In such a case, you are free to have local (non-shared) pointers to  
the
very same data, and thus have no need for locking (which might be needed to
dereference the shared pointer).


-- 
Simen