Aspect Storage_Model_Type (GNAT Reference Manual) (original) (raw)

17.3.2.1 Aspect Storage_Model_Type ¶

A Storage model is a type with a specified Storage_Model_Typeaspect, e.g.:

type A_Model is null record with Storage_Model_Type (...);

Storage_Model_Type itself accepts six parameters:

• Address_Type, the type of the address managed by this model. This has to be a scalar type or derived from System.Address.
• Allocate, a procedure used for allocating memory in this model
• Deallocate, a procedure used for deallocating memory in this model
• Copy_To, a procedure used to copy memory from native memory to this model
• Copy_From, a procedure used to copy memory from this model to native memory
• Storage_Size, a function returning the amount of memory left
• Null_Address, a value for the null address value

By default, Address_Type is System.Address, and the five subprograms perform native operations (e.g. the allocator is the native new allocator). Users can decide to specify one or more of these. When an Address_Type is specified to be other than System.Address, all of the subprograms have to be specified.

The prototypes of these procedures are as follows:

procedure Allocate (Model : in out A_Model; Storage_Address : out Address_Type; Size : Storage_Count; Alignment : Storage_Count);

procedure Deallocate (Model : in out A_Model; Storage_Address : out Address_Type; Size : Storage_Count; Alignment : Storage_Count);

procedure Copy_To (Model : in out A_Model; Target : Address_Type; Source : System.Address; Size : Storage_Count);

procedure Copy_From (Model : in out A_Model; Target : System.Address; Source : Address_Type; Size : Storage_Count);

function Storage_Size (Pool : A_Model) return Storage_Count;

Here’s an example of how this could be instantiated in the context of CUDA:

package CUDA_Memory is

type CUDA_Storage_Model is null record with Storage_Model_Type => ( Address_Type => CUDA_Address, Allocate => CUDA_Allocate, Deallocate => CUDA_Deallocate, Copy_To => CUDA_Copy_To, Copy_From => CUDA_Copy_From, Storage_Size => CUDA_Storage_Size, Null_Address => CUDA_Null_Address );

type CUDA_Address is new System.Address; -- We're assuming for now same address size on host and device

procedure CUDA_Allocate (Model : in out CUDA_Storage_Model; Storage_Address : out CUDA_Address; Size : Storage_Count; Alignment : Storage_Count);

procedure CUDA_Deallocate (Model : in out CUDA_Storage_Model; Storage_Address : out CUDA_Address; Size : Storage_Count; Alignment : Storage_Count);

procedure CUDA_Copy_To (Model : in out CUDA_Storage_Model; Target : CUDA_Address; Source : System.Address; Size : Storage_Count);

procedure CUDA_Copy_From (Model : in out CUDA_Storage_Model; Target : System.Address; Source : CUDA_Address; Size : Storage_Count);

function CUDA_Storage_Size (Pool : CUDA_Storage_Model) return Storage_Count return Storage_Count'Last;

CUDA_Null_Address : constant CUDA_Address := CUDA_Address (System.Null_Address);

CUDA_Memory : CUDA_Storage_Model;

end CUDA_Memory;