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[oneDPL] Add special predefined policy templates #654

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[oneDPL] Add special predefined policy templates #654

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5d0c3c0
Add synopsis and a short description for new policy instance templates
akukanov Oct 6, 2025
682aced
Improve the wording. Add a note about exceptions.
akukanov Oct 6, 2025
13afe49
Fix the RST syntax for inlined code
akukanov Oct 6, 2025
502ae26
Require non-throwing construction of predefined policies
akukanov Oct 7, 2025
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23 changes: 21 additions & 2 deletions source/elements/oneDPL/source/parallel_api/execution_policies.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,15 @@ A device execution policy represents a `SYCL`_ device and queue to run oneDPL al
class device_policy;

inline const device_policy<> dpcpp_default;

template <typename KernelName = /*unspecified*/>
const device_policy<KernelName> dpdefault;

template <typename KernelName = /*unspecified*/>
const device_policy<KernelName> dpgpu;

template <typename KernelName = /*unspecified*/>
const device_policy<KernelName> dpcpu;

template <typename KernelName = /*unspecified*/>
device_policy<KernelName>
Expand Down Expand Up @@ -151,13 +160,23 @@ Return the queue the policy is associated with.

Allow implicit conversion of the policy to a ``sycl::queue`` object.

Predefined Device Policy
^^^^^^^^^^^^^^^^^^^^^^^^
Predefined Device Policies
^^^^^^^^^^^^^^^^^^^^^^^^^^

``dpcpp_default`` is a predefined execution policy object to run algorithms on the default SYCL device.
It is a global immutable (``const``) instance of type ``device_policy<>``.
[*Note*: ``dpcpp_default`` can be copied but cannot be moved. -- *end note*]
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Would we want to deprecate this policy object as well to convince people to switch to the new ones, or leave it as is?

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@timmiesmith timmiesmith Oct 6, 2025 •
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@danhoeflinger isn't the question whether to redefine dpcpp_default to be an instance of dpdefault instead of deprecating it?

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If I understand correctly, beyond just the name shortening, I think the other advantage here is that the new policy templates are on-demand usage and cannot cause problems for broken SYCL environments on startup with eager global queue creation. If we allow an easy path for users to continue using dpcpp_default as a instance of the new template, then we perpetuate both of the things we are aiming to improve.

I don't think we can just remove it, but we can deprecate it for eventual removal of the requirement to have some lazy queue creation system in oneDPL implementations. (uxlfoundation/oneDPL#1652)


``dpdefault``, ``dpgpu``, and ``dpcpu`` are variable templates for creating ``device_policy`` objects,
possibly with explicit kernel names, to run algorithms on the default SYCL device, a GPU device,
and a CPU device, respectively. An object instantiated from one of these templates is a global
immutable ``device_policy`` object. It is associated with a SYCL queue constructed with
the SYCL device selector that corresponds to the used variable template.
[*Example*: ``dpgpu<>`` is associated with a queue created by ``sycl::gpu_selector_v``. -- *end example*]

Creation or use of a ``dpgpu`` or a ``dpcpu`` policy object can throw ``sycl::exception``
if no appropriate device is found.

make_device_policy Function
^^^^^^^^^^^^^^^^^^^^^^^^^^^

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