Ada Conformity Assessment Authority      Home Conformity Assessment   Test Suite ARGAda Standard
 
Ada Reference Manual (Ada 2022 with Amendment 1) — Legal Information
Contents   Index   References   Search   Previous   Next 

C.6.4 The Package System.Atomic_Operations.Integer_Arithmetic

1/5
The language-defined generic package System.Atomic_Operations.Integer_Arithmetic provides operations to perform arithmetic atomically on objects of integer types. 

Static Semantics

2/5
The generic library package System.Atomic_Operations.Integer_Arithmetic has the following declaration:
3/5
generic
   type Atomic_Type is range <> with Atomic;
package System.Atomic_Operations.Integer_Arithmetic
   with Pure, Nonblocking is
4/5
   procedure Atomic_Add (Item  : aliased in out Atomic_Type;
                         Value : Atomic_Type)
      with Convention => Intrinsic;
5/5
   procedure Atomic_Subtract (Item  : aliased in out Atomic_Type;
                              Value : Atomic_Type)
      with Convention => Intrinsic;
6/5
   function Atomic_Fetch_And_Add
     (Item  : aliased in out Atomic_Type;
      Value : Atomic_Type) return Atomic_Type
      with Convention => Intrinsic;
7/5
   function Atomic_Fetch_And_Subtract
     (Item  : aliased in out Atomic_Type;
      Value : Atomic_Type) return Atomic_Type
      with Convention => Intrinsic;
8/5
   function Is_Lock_Free (Item : aliased Atomic_Type) return Boolean
      with Convention => Intrinsic;
9/5
end System.Atomic_Operations.Integer_Arithmetic;
10/5
The operations of this package are defined as follows:
11/5
procedure Atomic_Add (Item  : aliased in out Atomic_Type;
                      Value : Atomic_Type)
   with Convention => Intrinsic;
12/5
Atomically performs: Item := Item + Value;
13/5
procedure Atomic_Subtract (Item  : aliased in out Atomic_Type;
                           Value : Atomic_Type)
   with Convention => Intrinsic;
14/5
Atomically performs: Item := Item - Value;
15/5
function Atomic_Fetch_And_Add
  (Item  : aliased in out Atomic_Type;
   Value : Atomic_Type) return Atomic_Type
   with Convention => Intrinsic;
16/5
Atomically performs: Tmp := Item; Item := Item + Value; return Tmp;
17/5
function Atomic_Fetch_And_Subtract
  (Item  : aliased in out Atomic_Type;
   Value : Atomic_Type) return Atomic_Type
   with Convention => Intrinsic;
18/5
Atomically performs: Tmp := Item; Item := Item - Value; return Tmp;

Implementation Permissions

19/6
An implementation may allow Item to be modified if the operation defined in an instance of System.Atomic_Operations.Integer_Arithmetic fails a language-defined check. Additionally, an implementation may check that predicates are satisfied after the atomic operation.

Usage

20/6
The subtype used to instantiate System.Atomic_Operations.Integer_Arithmetic should not have predicates, as those probably will not be checked atomically, potentially causing incorrect check failures if another task has modified the value between the operation and the check. For the best performance, the subtype should be a base subtype so that no range check need be performed.
Contents   Index   References   Search   Previous   Next 
Ada-Europe Ada 2005 and 2012 Editions sponsored in part by Ada-Europe