std::execution::seq, std::execution::par, std::execution::par_unseq, std::execution::unseq - cppreference.com (original) (raw)

| Defined in header | | | | --------------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | 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) |

The execution policy types

have the following respective instances:

These instances 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).

[edit] Example

#include #include #include #include #include #include   #ifdef PARALLEL #include namespace execution = std::execution; #else enum class execution { seq, unseq, par_unseq, par }; #endif   void measure([[maybe_unused]] auto policy, std::vector<std::uint64_t> v) { const auto start = std::chrono::steady_clock::now(); #ifdef PARALLEL std::sort(policy, v.begin(), v.end()); #else std::sort(v.begin(), v.end()); #endif const auto finish = std::chrono::steady_clock::now(); std::cout << std::chrono::duration_cast<std::chrono::milliseconds>(finish - start) << '\n'; };   int main() { std::vector<std::uint64_t> v(1'000'000); std::mt19937 gen {std::random_device{}()}; std::ranges::generate(v, gen);   measure(execution::seq, v); measure(execution::unseq, v); measure(execution::par_unseq, v); measure(execution::par, v); }

Possible output:

// online GNU/gcc compiler (PARALLEL macro is not defined) 81ms 80ms 79ms 78ms   // with g++ -std=c++23 -O3 ./test.cpp -ltbb -DPARALLEL 165ms 163ms 30ms 27ms

[edit] See also