# std::execution::seq, std::execution::par, std::execution::par_unseq, std::execution::unseq

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< cpp‎ | algorithm

Defined in header `<execution>` |  |
inline constexpr std::execution::sequenced_policy seq { /* unspecified */ }; |  | (since C++17)
inline constexpr std::execution::parallel_policy par { /* unspecified */ }; |  | (since C++17)
inline constexpr std::execution::parallel_unsequenced_policy par_unseq { /* unspecified */ }; |  | (since C++17)
inline constexpr std::execution::unsequenced_policy unseq { /* unspecified */ }; |  | (since C++20)

`std::execution::seq`, `std::execution::par`, `std::execution::par_unseq`, and `std::execution::unseq` are instances of the execution policy types std::execution::sequenced_policy, std::execution::parallel_policy, std::execution::parallel_unsequenced_policy, and std::execution::unsequenced_policy respectively. They are used to specify the execution policy of parallel algorithms - i.e., the kinds of parallelism allowed.

Additional execution policies may be provided by a standard library implementation (possible future additions may include `std::parallel::cuda` and `std::parallel::opencl`)

### See also

sequenced_policy parallel_policy parallel_unsequenced_policy unsequenced_policy (C++17)(C++17)(C++17)(C++20) | execution policy types (class)

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