execution

execution#

This library implements executors and execution policies for use with parallel algorithms and other facilities related to managing the execution of tasks.

See the API reference of the module for more details.

Describing execution policies with policy_traits#

hpx::execution::policy_traits<Policy> reports the properties of an execution policy: is_policy, is_rebound, is_parallel, is_sequenced, is_unsequenced, is_async and is_vectorpack. With datapar enabled it also reports num_lanes. The is_*_execution_policy traits are defined in terms of it.

A policy can provide these properties in either of two ways.

  • Declare static constexpr bool members with these names on the policy type. Declare only the true ones; missing members are false.

  • Specialize policy_traits<Policy> for a type you cannot modify, deriving from hpx::execution::detail::policy_traits_default.

struct my_policy
{
    static constexpr bool is_policy = true;
    static constexpr bool is_parallel = true;
};

static_assert(hpx::execution::policy_traits<my_policy>::is_parallel);
static_assert(!hpx::execution::policy_traits<my_policy>::is_async);

Fixed-size SIMD policies (for example simd_fixed_size<N>) set num_lanes = N. A value of 0 selects the native pack width.

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