Ada Reference Manual (Ada 2022)

C.6.5 The Package System.Atomic_Operations.Modular_Arithmetic

The language-defined generic package System.Atomic_Operations.Modular_Arithmetic provides operations to perform arithmetic atomically on objects of modular types.

Static Semantics

The generic library package System.Atomic_Operations.Modular_Arithmetic has the following declaration:

generic
type Atomic_Type is mod <> with Atomic;
package System.Atomic_Operations.Modular_Arithmetic
with Pure, Nonblocking is

procedure Atomic_Add (Item : aliased in out Atomic_Type;
Value : Atomic_Type)
with Convention => Intrinsic;

procedure Atomic_Subtract (Item : aliased in out Atomic_Type;
Value : Atomic_Type)
with Convention => Intrinsic;

function Atomic_Fetch_And_Add
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
with Convention => Intrinsic;

function Atomic_Fetch_And_Subtract
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
with Convention => Intrinsic;

function Is_Lock_Free (Item : aliased Atomic_Type) return Boolean
with Convention => Intrinsic;

end System.Atomic_Operations.Modular_Arithmetic;

The operations of this package are defined as follows:

procedure Atomic_Add (Item : aliased in out Atomic_Type;
Value : Atomic_Type)
with Convention => Intrinsic;

Atomically performs: Item := Item + Value;

procedure Atomic_Subtract (Item : aliased in out Atomic_Type;
Value : Atomic_Type)
with Convention => Intrinsic;

Atomically performs: Item := Item - Value;

function Atomic_Fetch_And_Add
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
with Convention => Intrinsic;

Atomically performs: Tmp := Item; Item := Item + Value; return Tmp;

function Atomic_Fetch_And_Subtract
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
with Convention => Intrinsic;

Atomically performs: Tmp := Item; Item := Item - Value; return Tmp;