fence#

Header File: <Kokkos_Core.hpp>

Usage:

Kokkos::fence();

Blocks on completion of all outstanding asynchronous Kokkos operations. That includes parallel dispatch (e.g. parallel_for(), parallel_reduce() and parallel_scan()) as well as asynchronous data operations such as three-argument deep_copy.

Note: there is a execution space instance specific fence too: ExecutionSpaceConcept

Interface#

void Kokkos::fence();

void Kokkos::fence(const std::string& label);

Parameters#

  • label: A label to identify a specific fence in fence profiling operations. label does not have to be unique.

Requirements#

  • Kokkos::fence() cannot be called inside an existing parallel region (i.e. inside the operator() of a functor or lambda).

Semantics#

  • Blocks on completion of all outstanding asynchronous works. Side effects of outstanding work will be observable upon completion of the fence call - that means Kokkos::fence() implies a memory fence.

Examples#

Timing kernels#

Kokkos::Timer timer;
// This operation is asynchronous, without a fence
// one would time only the launch overhead
Kokkos::parallel_for("Test", N, functor);
Kokkos::fence();
double time = timer.seconds();

Use with asynchronous deep copy#

Kokkos::deep_copy(exec1, a,b);
Kokkos::deep_copy(exec2, a,b);
// do some stuff which doesn't touch a or b
Kokkos::parallel_for("Test", N, functor);

// wait for all three operations to finish
Kokkos::fence();

// do something with a and b