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``fence()`` | ||
=========== | ||
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.. role::cpp(code) | ||
:language: cpp | ||
Header File: ``<Kokkos_Core.hpp>`` | ||
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Usage: | ||
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.. code-block:: cpp | ||
Kokkos::fence(); | ||
Blocks on completion of all outstanding asynchronous Kokkos operations. | ||
That includes parallel dispatch (e.g. `parallel_for() <parallel_for.html#kokkosparallel_for>`_, `parallel_reduce() <parallel_reduce.html#kokkosparallel_reduce>`_ | ||
and `parallel_scan() <parallel_scan.html#kokkosparallel_scan>`_) as well as asynchronous data operations such as three-argument `deep_copy <../view/deep_copy.html>`_. | ||
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Note: there is a execution space instance specific ``fence`` too: `ExecutionSpaceConcept <../execution_spaces.html#executionspaceconcept>`_ | ||
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Interface | ||
--------- | ||
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.. code-block:: cpp | ||
void Kokkos::fence(); | ||
.. code-block:: cpp | ||
void Kokkos::fence(const std::string& label); | ||
Parameters | ||
~~~~~~~~~~ | ||
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- ``label``: A label to identify a specific fence in fence profiling operations. ``label`` does not have to be unique. | ||
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Requirements | ||
~~~~~~~~~~~~ | ||
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- ``Kokkos::fence()`` cannot be called inside an existing parallel region (i.e. inside the ``operator()`` of a functor or lambda). | ||
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Semantics | ||
--------- | ||
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- 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. | ||
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Examples | ||
-------- | ||
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Timing kernels | ||
~~~~~~~~~~~~~~ | ||
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.. code-block:: cpp | ||
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 | ||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | ||
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.. code-block:: cpp | ||
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 |