[Dynamic Selection] Customization of Backends and Policies

[danhoeflinger]

Dynamic Selection API: Backend and Policy Customization & Removal of Selection API

This PR refactors the Dynamic Selection API to introduce a flexible backend architecture and simplify the user-facing API by removing the select() function. It provides better tools for customization of backend and policies to allow for easier customization and more flexibility for users.

Implements RFCs #2220.

Key Changes

Backend Architecture

• Added policy_base.h and default_backend.h to provide common base classes for policies and backends respectively
• Backends now accept ResourceAdapter function to support different flavors of resource with the same backend (e.g. sycl::queue vs sycl::queue*)

API Simplification

• Removed select() function - selections are now internal implementation details
• Addition of try_submit- always returns a std::optional quickly, returns empty if unable to obtain a resource
• Users now exclusively use try_submit, submit() and submit_and_wait() functions
• Policies expose try_select_impl() (returns std::optional) instead of public select()

Execution Info & Reporting

• Backends validate reporting requirements at construction and filter incompatible resources
• Clear runtime errors when no compatible resources remain after filtering

---

Summary of changes to look out for from individual components:

• Documentation:
  • Removal of public select API
• Examples:
  • Policy template argument adjustment (by resource first rather than backend)
• Policies:
  • Adjustment to use policy_base, remove repetative code
  • Implement try_select_impl instead of select
  • Implement initialize_impl instead of initialize
• Sycl Backend:
  • Conversion to partial specialization of default backend, use of backend_base
  • Addition of ResourceAdapter to support different flavors from a single base resource / backend
  • Improve system of reporting requirements for better filtering and error messages
  • Adjust support for profiling to require sycl extension for profiling (only reliable way to time)
    • Filter devices accordingly
• Tests:
  • Removal of testing of select before submit
  • Addition of default universe initialization testing
  • Addition of testing of use of resource adapter to support sycl::queue* in addition to sycl::queue

[vossmjp]

Does this return a std::optional now?

[danhoeflinger]

good catch, fixed.

[akukanov]

I wonder if we should name it "on-demand reporting" or similarly - at least in the documentation (while the API naming can be discussed / addressed later).

[danhoeflinger]

@vossmjp Do you have an opinion here? This is not something new in the design, but just something we've documented. I have no strong opinions here, but there are a few places we would have to change it if we choose to.

[akukanov]

To be clear, my comment is primarily about the documentation. And it's also minor and can be postponed.

[vossmjp]

I don't have a strong objection to the change itself, but I'd prefer to defer all but essential changes at this point so we can get things merged.

[akukanov]

This approval is for the public documentation update in the PR. I have not reviewed anything else.

[vossmjp]

LGTM

[SergeyKopienko]

LGTM