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P3396R1 std::execution wording fixes #7464

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Dec 17, 2024
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P3396R1 std::execution wording fixes #7464

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113 changes: 79 additions & 34 deletions source/exec.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -91,8 +91,8 @@
\item
\tcode{err} if \tcode{decay_t<Err>} denotes the type \tcode{exception_ptr}.

\mandates
\tcode{err != exception_ptr()} is \tcode{true}.
\expects
\tcode{!err} is \tcode{false}.
\item
Otherwise,
\tcode{make_exception_ptr(system_error(err))}
Expand Down Expand Up @@ -229,7 +229,6 @@
representing the execution-time properties of the operation's caller.
The caller of an asynchronous operation is
its parent operation or the function that created it.
An asynchronous operation's operation state owns the operation's environment.

\pnum
An asynchronous operation has an associated receiver.
Expand Down Expand Up @@ -1012,7 +1011,7 @@
-> @\libconcept{same_as}@<remove_cvref_t<Sch>>;
} &&
@\libconcept{equality_comparable}@<remove_cvref_t<Sch>> &&
@\libconcept{copy_constructible}@<remove_cvref_t<Sch>>;
@\libconcept{copyable}@<remove_cvref_t<Sch>>;
}
\end{codeblock}

Expand All @@ -1025,17 +1024,15 @@
shall be modeled.

\pnum
None of a scheduler's
copy constructor,
destructor,
equality comparison, or
\tcode{swap} member functions
No operation required by
\tcode{\libconcept{copyable}<remove_cvref_t<Sch>>} and
\tcode{\libconcept{equality_comparable}<remove_cvref_t<Sch>>}
shall exit via an exception.
None of these member functions,
None of these operations,
nor a scheduler type's \tcode{schedule} function,
shall introduce data races
as a result of potentially concurrent\iref{intro.races} invocations
of those functions from different threads.
of those operations from different threads.

\pnum
For any two values \tcode{sch1} and \tcode{sch2}
Expand Down Expand Up @@ -1727,10 +1724,16 @@

\pnum
The expression in the \tcode{noexcept} clause of
the constructor of \exposid{basic-state} is:
the constructor of \exposid{basic-state} is
\begin{codeblock}
is_nothrow_move_constructible_v<Rcvr> &&
@\exposconcept{nothrow-callable}@<decltype(@\exposid{impls-for}@<tag_of_t<Sndr>>::@\exposid{get-state}@), Sndr, Rcvr&>
@\exposconcept{nothrow-callable}@<decltype(@\exposid{impls-for}@<tag_of_t<Sndr>>::@\exposid{get-state}@), Sndr, Rcvr&> &&
(same_as<@\exposid{state-type}@<Sndr, Rcvr>, @\exposid{get-state-result}@> ||
is_nothrow_constructible_v<@\exposid{state-type}@<Sndr, Rcvr>, @\exposid{get-state-result}@>)
\end{codeblock}
where \exposid{get-state-result} is
\begin{codeblock}
@\exposid{call-result-t}@<decltype(@\exposid{impls-for}@<tag_of_t<Sndr>>::@\exposid{get-state}@), Sndr, Rcvr&>.
\end{codeblock}

\pnum
Expand Down Expand Up @@ -1879,11 +1882,24 @@
struct @\exposid{impls-for}@<@\exposid{write-env-t}@> : @\exposid{default-impls}@ {
static constexpr auto @\exposid{get-env}@ =
[](auto, const auto& state, const auto& rcvr) noexcept {
return @\exposid{JOIN-ENV}@(state, get_env(rcvr));
return @\seebelow@;
};
};
\end{codeblock}
\end{itemdescr}
Invocation of
\tcode{\exposid{impls-for}<\exposid{write-env-t}>::\exposid{get-env}}
returns an object \tcode{e} such that
\begin{itemize}
\item
\tcode{decltype(e)} models \exposconcept{queryable} and
\item
given a query object \tcode{q},
the expression \tcode{e.query(q)} is expression-equivalent
to \tcode{state.query(q)} if that expression is valid,
otherwise, \tcode{e.query(q)} is expression-equivalent
to \tcode{get_env(rcvr).query(q)}.
\end{itemize}

\rSec2[exec.snd.concepts]{Sender concepts}

Expand Down Expand Up @@ -2455,14 +2471,13 @@
Let \exposid{operation-state-task} be the following exposition-only class:
\begin{codeblock}
namespace std::execution {
struct @\exposid{operation-state-task}@ {
struct @\exposid{operation-state-task}@ { // \expos
using operation_state_concept = operation_state_t;
using promise_type = @\exposid{connect-awaitable-promise}@;

explicit @\exposid{operation-state-task}@(coroutine_handle<> h) noexcept : coro(h) {}
@\exposid{operation-state-task}@(@\exposid{operation-state-task}@&& o) noexcept
: @\exposid{coro}@(exchange(o.@\exposid{coro}@, {})) {}
~@\exposid{operation-state-task}@() { if (@\exposid{coro}@) @\exposid{coro}@.destroy(); }
@\exposid{operation-state-task}@(@\exposid{operation-state-task}@&&) = delete;
~@\exposid{operation-state-task}@() { @\exposid{coro}@.destroy(); }

void start() & noexcept {
@\exposid{coro}@.resume();
Expand Down Expand Up @@ -3053,15 +3068,14 @@
using result_t = @\exposid{decayed-tuple}@<Tag, Args...>;
constexpr bool nothrow = is_nothrow_constructible_v<result_t, Tag, Args...>;

@\exposid{TRY-EVAL}@(rcvr, [&]() noexcept(nothrow) {
try {
state.@\exposid{async-result}@.template emplace<result_t>(Tag(), std::forward<Args>(args)...);
}());

if (state.@\exposid{async-result}@.valueless_by_exception())
return;
if (state.@\exposid{async-result}@.index() == 0)
return;

} catch (...) {
if constexpr (!nothrow) {
set_error(std::move(rcvr), current_exception());
return;
}
}
start(state.@\exposid{op-state}@);
};
\end{codeblock}
Expand Down Expand Up @@ -3448,14 +3462,26 @@
}

decltype(auto) get_env() const noexcept {
return @\exposid{JOIN-ENV}@(@\exposid{env}@, @\exposid{FWD-ENV}@(execution::get_env(@\exposid{rcvr}@)));
return @\seebelow@;
}

Rcvr& @\exposid{rcvr}@; // \expos
Env @\exposid{env}@; // \expos
};
}
\end{codeblock}
Invocation of the function \tcode{\exposid{receiver2}::get_env}
returns an object \tcode{e} such that
\begin{itemize}
\item
\tcode{decltype(e)} models \exposconcept{queryable} and
\item
given a query object \tcode{q},
the expression \tcode{e.query(q)} is expression-equivalent
to \tcode{\exposid{env}.query(q)} if that expression is valid,
otherwise \tcode{e.query(q)} is expression-equivalent
to \tcode{get_env(\exposid{rcvr}).query(q)}.
\end{itemize}

\pnum
\tcode{\exposid{impls-for}<\exposid{decayed-typeof}<\exposid{let-cpo}>>::\exposid{get-state}}
Expand Down Expand Up @@ -3647,7 +3673,7 @@
\item
on a value completion operation,
invokes \tcode{f(i, args...)}
for every \tcode{i} of type \tcode{Shape} from \tcode{0} to \tcode{shape},
for every \tcode{i} of type \tcode{Shape} in \range{\tcode{0}}{\tcode{shape}},
where \tcode{args} is a pack of lvalue subexpressions
referring to the value completion result datums of the input sender, and
\item
Expand Down Expand Up @@ -4101,10 +4127,20 @@
equivalent to the following lambda expression:
\begin{codeblock}
[]<class State, class Rcvr>(auto&&, State& state, const Receiver& rcvr) noexcept {
return @\exposid{JOIN-ENV}@(
@\exposid{MAKE-ENV}@(get_stop_token, state.@\exposid{stop_src}@.get_token()), get_env(rcvr));
return @\seebelow@;
}
\end{codeblock}
Returns an object \tcode{e} such that
\begin{itemize}
\item
\tcode{decltype(e)} models \exposconcept{queryable}, and
\item
\tcode{e.query(get_stop_token)} is expression-equivalent to
\tcode{state.\exposid{stop-src}.get_token()}, and
\item
given a query object \tcode{q} with type other than \cv{} \tcode{stop_token_t},
\tcode{e.query(q)} is expression-equivalent to \tcode{get_env(rcvr).query(q)}.
\end{itemize}

\pnum
The member \tcode{\exposid{impls-for}<when_all_t>::\exposid{get-state}}
Expand Down Expand Up @@ -4957,7 +4993,8 @@
A \tcode{run_loop} instance has an associated \defn{count}
that corresponds to the number of work items that are in its queue.
Additionally, a \tcode{run_loop} instance has an associated state
that can be one of \defn{starting}, \defn{running}, or \defn{finishing}.
that can be one of
\defn{starting}, \defn{running}, \defn{finishing}, or \defn{finished}.

\pnum
Concurrent invocations of the member functions of \tcode{run_loop}
Expand Down Expand Up @@ -5146,7 +5183,8 @@
\begin{itemize}
\item
\exposid{count} is \tcode{0} and \exposid{state} is \exposid{finishing},
in which case \exposid{pop-front} returns \tcode{nullptr}; or
in which case \exposid{pop-front} sets \exposid{state} to \exposid{finished}
and returns \tcode{nullptr}; or
\item
\exposid{count} is greater than \tcode{0},
in which case an item is removed from the front of the queue,
Expand Down Expand Up @@ -5191,11 +5229,14 @@
\begin{itemdescr}
\pnum
\expects
\exposid{state} is \exposid{starting}.
\exposid{state} is either \exposid{starting} or \exposid{finishing}.

\pnum
\effects
Sets the \exposid{state} to \exposid{running}. Then, equivalent to:
If \exposid{state} is \exposid{starting},
sets the \exposid{state} to \exposid{running},
otherwise leaves \exposid{state} unchanged.
Then, equivalent to:
\begin{codeblock}
while (auto* op = @\exposid{pop-front}@()) {
op->@\exposid{execute}@();
Expand All @@ -5213,6 +5254,10 @@
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\exposid{state} is either \exposid{starting} or \exposid{running}.

\pnum
\effects
Changes \exposid{state} to \exposid{finishing}.
Expand Down
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