22 General utilities library [utilities]

22.12 Execution policies [execpol]

22.12.7 Unsequenced execution policy [execpol.unseq]

class execution::unsequenced_policy { unspecified };
The class 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 vectorized, e.g., executed on a single thread using instructions that operate on multiple data items.
During the execution of a parallel algorithm with the execution​::​unsequenced_policy policy, if the invocation of an element access function exits via an exception, terminate is invoked ([except.terminate]).