33 Execution control library [exec]

33.5 Queries [exec.queries]

33.5.8 execution​::​get_forward_progress_guarantee [exec.get.fwd.progress]

namespace std::execution { enum class forward_progress_guarantee { concurrent, parallel, weakly_parallel }; }
1
#
get_forward_progress_guarantee asks a scheduler about the forward progress guarantee of execution agents created by that scheduler's associated execution resource ([intro.progress]).
2
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The name get_forward_progress_guarantee denotes a query object.
For a subexpression sch, let Sch be decltype((sch)).
If Sch does not satisfy scheduler, get_forward_progress_guarantee is ill-formed.
Otherwise, get_forward_progress_guarantee(sch) is expression-equivalent to:
  • (2.1)
    MANDATE-NOTHROW(as_const(sch).query(get_forward_progress_guarantee)), if that expression is well-formed.
    Mandates: The type of the expression above is forward_progress_guarantee.
  • (2.2)
    Otherwise, forward_progress_guarantee​::​weakly_parallel.
3
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If get_forward_progress_guarantee(sch) for some scheduler sch returns forward_progress_guarantee​::​concurrent, all execution agents created by that scheduler's associated execution resource shall provide the concurrent forward progress guarantee.
If it returns forward_progress_guarantee​::​parallel, all such execution agents shall provide at least the parallel forward progress guarantee.