Defined in header <execution> | ||
inlineconstexpr std::execution::sequenced_policy seq{/* unspecified */}; | (since C++17) | |
inlineconstexpr std::execution::parallel_policy par{/* unspecified */}; | (since C++17) | |
inlineconstexpr std::execution::parallel_unsequenced_policy par_unseq{/* unspecified */}; | (since C++17) | |
inlineconstexpr std::execution::unsequenced_policy unseq{/* unspecified */}; | (since C++20) | |
The execution policy types
have the following respective instances:
std::execution::seq,std::execution::par,std::execution::par_unseq, andstd::execution::unseq.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 includestd::parallel::cuda andstd::parallel::opencl).
#include <algorithm>#include <chrono>#include <cstdint>#include <iostream>#include <random>#include <vector> #ifdef PARALLEL#include <execution>namespace execution= std::execution;#elseenumclass execution{ seq, unseq, par_unseq, par};#endif void measure([[maybe_unused]]auto policy,std::vector<std::uint64_t> v){constauto start=std::chrono::steady_clock::now();#ifdef PARALLELstd::sort(policy, v.begin(), v.end());#elsestd::sort(v.begin(), v.end());#endifconstauto 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)81ms80ms79ms78ms // with g++ -std=c++23 -O3 ./test.cpp -ltbb -DPARALLEL165ms163ms30ms27ms
(C++17)(C++17)(C++17)(C++20) | execution policy types (class)[edit] |
