Re: Custom Storage Pool questions

["J-P. Rosen" <rosen@adalog.fr>]

Le 14/09/2021 à 02:48, Jere a écrit :
>>> In particular, the blog there advocates for separately counting for
>>> things like unconstrained array First/Last indices or the Prev/Next
>>> pointers used for Controlled objects. Normally I would have assumed
>>> that the Size_In_Storage_Elements parameter in Allocate would account
>>> for that, but the blog clearly shows that it doesn't
>> [...]
>>
>> That blog shows a special use for Storage_Pools, where you allocate
>> /user/ data on top of the requested memory. When called by the compiler,
>> it is up to the compiler to compute how much memory is needed, and your
>> duty is to just allocate that.
>>
> Yes, but if you look at that blog, they are allocating space for the /user/ data
> and for the Next/Prev for controlled types and First/Last for unconstrained
> arrays in addition to the size specified by allocate.
> 
> I agree I feel it is up to the compiler to provide the correct size to Allocate,
> but the blog would indicate that GNAT does not (or did not..old blog..so
> who knows?).  Does the RM require that an implementation pass the full
> amount of memory needed to Allocate when new is called?
> 

The RM says that an allocator allocates storage from the storage pool. 
You could argue that it does not say "allocates all needed storage...", 
but that would be a bit far fetched.

Anyway, a blog is not the proper place to get information from for that 
kind of issue. Look at the Gnat documentation.

-- 
J-P. Rosen
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