22 General utilities library [utilities]

22.12 Execution policies [execpol]

22.12.6 Parallel and unsequenced execution policy [execpol.parunseq]

class execution::parallel_unsequenced_policy { unspecified };
The class execution​::​parallel_unsequenced_policy is an execution policy type used as a unique type to disambiguate parallel algorithm overloading and indicate that a parallel algorithm's execution may be parallelized and vectorized.
During the execution of a parallel algorithm with the execution​::​parallel_unsequenced_policy policy, if the invocation of an element access function exits via an exception, terminate is invoked ([except.terminate]).