ExperimentalAtomicApi  
    @Target(allowedTargets = [AnnotationTarget.CLASS, AnnotationTarget.ANNOTATION_CLASS, AnnotationTarget.PROPERTY, AnnotationTarget.FIELD, AnnotationTarget.LOCAL_VARIABLE, AnnotationTarget.VALUE_PARAMETER, AnnotationTarget.CONSTRUCTOR, AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY_GETTER, AnnotationTarget.PROPERTY_SETTER, AnnotationTarget.TYPEALIAS]           ) 
This annotation marks the experimental Kotlin Atomics API.
Beware using the annotated API especially if you're developing a library, since your library might become binary incompatible with the future versions of the standard library.
Any usage of a declaration annotated with @ExperimentalAtomicApi must be accepted either by annotating that usage with the OptIn annotation, e.g. @OptIn(ExperimentalAtomicApi::class), or by using the compiler argument -opt-in=kotlin.concurrent.atomics.ExperimentalAtomicApi.