34 Execution control library [exec]

forwarding_query asks a query object whether it should be forwarded through queryable adaptors.

The name forwarding_query denotes a query object.

For some query object q of type Q, forwarding_query(q) is expression-equivalent to:

• (2.1)
  MANDATE-NOTHROW(q.query(forwarding_query)) if that expression is well-formed.
  Mandates: The expression above has type bool and is a core constant expression if q is a core constant expression.
• (2.2)
  Otherwise, true if derived_from<Q, forwarding_query_t> is true.
• (2.3)
  Otherwise, false.

get_allocator asks a queryable object for its associated allocator.

The name get_allocator denotes a query object.

For a subexpression env, get_allocator(env) is expression-equivalent to MANDATE-NOTHROW(as_const(env).query(get_allocator)).

Mandates: If the expression above is well-formed, its type satisfies simple-allocator ([allocator.requirements.general]).

forwarding_query(get_allocator) is a core constant expression and has value true.

get_stop_token asks a queryable object for an associated stop token.

The name get_stop_token denotes a query object.

For a subexpression env, get_stop_token(env) is expression-equivalent to:

• (2.1)
  MANDATE-NOTHROW(as_const(env).query(get_stop_token)) if that expression is well-formed.
  Mandates: The type of the expression above satisfies stoppable_token.
• (2.2)
  Otherwise, never_stop_token{}.

forwarding_query(get_stop_token) is a core constant expression and has value true.

execution​::​get_env is a customization point object.

For a subexpression o, execution​::​get_env(o) is expression-equivalent to:

• (1.1)
  MANDATE-NOTHROW(as_const(o).get_env()) if that expression is well-formed.
  Mandates: The type of the expression above satisfies queryable ([exec.queryable]).
• (1.2)
  Otherwise, empty_env{}.

The value of get_env(o) shall be valid while o is valid.

get_domain asks a queryable object for its associated execution domain tag.

The name get_domain denotes a query object.

For a subexpression env, get_domain(env) is expression-equivalent to MANDATE-NOTHROW(as_const(env).query(get_domain)).

forwarding_query(execution​::​get_domain) is a core constant expression and has value true.

get_scheduler asks a queryable object for its associated scheduler.

The name get_scheduler denotes a query object.

For a subexpression env, get_scheduler(env) is expression-equivalent to MANDATE-NOTHROW(as_const(env).query(get_scheduler)).

Mandates: If the expression above is well-formed, its type satisfies scheduler.

forwarding_query(execution​::​get_scheduler) is a core constant expression and has value true.

get_delegation_scheduler asks a queryable object for a scheduler that can be used to delegate work to for the purpose of forward progress delegation ([intro.progress]).

The name get_delegation_scheduler denotes a query object.

For a subexpression env, get_delegation_scheduler(env) is expression-equivalent to MANDATE-NOTHROW(as_const(env).query(get_delegation_scheduler)).

Mandates: If the expression above is well-formed, its type satisfies scheduler.

forwarding_query(execution​::​get_delegation_scheduler) is a core constant expression and has value true.

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]).

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.

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.

get_completion_scheduler<completion-tag> obtains the completion scheduler associated with a completion tag from a sender's attributes.

The name get_completion_scheduler denotes a query object template.

For a subexpression q, the expression get_completion_scheduler<completion-tag>(q) is ill-formed if completion-tag is not one of set_value_t, set_error_t, or set_stopped_t.

Otherwise, get_completion_scheduler<completion-tag>(q) is expression-equivalent to MANDATE-NOTHROW(as_const(q).query(get_completion_scheduler<completion-tag>)) Mandates: If the expression above is well-formed, its type satisfies scheduler.

Let completion-fn be a completion function ([exec.async.ops]); let completion-tag be the associated completion tag of completion-fn; let args be a pack of subexpressions; and let sndr be a subexpression such that sender<decltype((sndr))> is true and get_completion_scheduler<completion-tag>(get_env(sndr)) is well-formed and denotes a scheduler sch.

If an asynchronous operation created by connecting sndr with a receiver rcvr causes the evaluation of completion-fn(rcvr, args...), the behavior is undefined unless the evaluation happens on an execution agent that belongs to sch's associated execution resource.

The expression forwarding_query(get_completion_scheduler<completion-tag>) is a core constant expression and has value true.