C.6.1 The Package System.Atomic_Operations

The language-defined package System.Atomic_Operations is the parent of a set of child units that provide facilities for manipulating objects of atomic types and for supporting lock-free synchronization. The subprograms of this subsystem are Intrinsic subprograms (see 6.3.1) in order to provide convenient access to machine operations that can provide these capabilities if they are available in the target environment.

The library package System.Atomic_Operations has the following declaration:

System.Atomic_Operations serves as the parent of other language-defined library units that manipulate atomic objects; its declaration is empty.

A call to a subprogram is said to be lock-free if the subprogram is guaranteed to return from the call while keeping the processor of the logical thread of control busy for the duration of the call.

In each child package, a function Is_Lock_Free(...) is provided to check whether the operations of the child package can all be provided lock-free for a given object. Is_Lock_Free returns True if operations defined in the child package are lock-free when applied to the object denoted by Item, and Is_Lock_Free returns False otherwise.