From Jason Turner

[exec.sysctxrepl]

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tmp/tmpkghp6stk/{from.md → to.md} RENAMED
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+ ## Namespace `system_context_replaceability` <a id="exec.sysctxrepl">[[exec.sysctxrepl]]</a>
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+
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+ ### General <a id="exec.sysctxrepl.general">[[exec.sysctxrepl.general]]</a>
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+
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+ Facilities in the `system_context_replaceability` namespace allow users
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+ to replace the default implementation of `parallel_scheduler`.
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+
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+ ### Receiver proxies <a id="exec.sysctxrepl.recvproxy">[[exec.sysctxrepl.recvproxy]]</a>
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+
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+ ``` cpp
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+ namespace std::execution::system_context_replaceability {
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+ struct receiver_proxy {
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+ virtual ~receiver_proxy() = default;
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+
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+ protected:
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+ virtual bool query-env(unspecified) noexcept = 0; // exposition only
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+
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+ public:
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+ virtual void set_value() noexcept = 0;
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+ virtual void set_error(exception_ptr) noexcept = 0;
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+ virtual void set_stopped() noexcept = 0;
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+
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+ template<class P, class-type Query>
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+ optional<P> try_query(Query q) noexcept;
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+ };
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+
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+ struct bulk_item_receiver_proxy : receiver_proxy {
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+ virtual void execute(size_t, size_t) noexcept = 0;
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+ };
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+ }
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+ ```
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+
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+ `receiver_proxy` represents a receiver that will be notified by the
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+ implementations of `parallel_scheduler_backend` to trigger the
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+ completion operations. `bulk_item_receiver_proxy` is derived from
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+ `receiver_proxy` and is used for `bulk_chunked` and `bulk_unchunked`
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+ customizations that will also receive notifications from implementations
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+ of `parallel_scheduler_backend` corresponding to different iterations.
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+
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+ ``` cpp
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+ template<class P, class-type Query>
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+ optional<P> try_query(Query q) noexcept;
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+ ```
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+
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+ *Mandates:* `P` is a cv-unqualified non-array object type.
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+
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+ *Returns:* Let `env` be the environment of the receiver represented by
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+ `*this`. If
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+
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+ - `Query` is not a member of an implementation-defined set of supported
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+ queries; or
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+ - `P` is not a member of an implementation-defined set of supported
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+ result types for `Query`; or
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+ - the expression `q(env)` is not well-formed or does not have type cv
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+ `P`,
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+
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+ then returns `nullopt`. Otherwise, returns `q(env)`.
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+
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+ *Remarks:* `get_stop_token_t` is in the implementation-defined set of
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+ supported queries, and `inplace_stop_token` is a member of the
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+ implementation-defined set of supported result types for
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+ `get_stop_token_t`.
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+
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+ ### `query_parallel_scheduler_backend` <a id="exec.sysctxrepl.query">[[exec.sysctxrepl.query]]</a>
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+
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+ ``` cpp
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+ shared_ptr<parallel_scheduler_backend> query_parallel_scheduler_backend();
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+ ```
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+
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+ `query_parallel_scheduler_backend()` returns the implementation object
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+ for a parallel scheduler.
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+
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+ *Returns:* A non-null shared pointer to an object that implements the
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+ `parallel_scheduler_backend` interface.
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+
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+ *Remarks:* This function is replaceable [[term.replaceable.function]].
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+
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+ ### Class `parallel_scheduler_backend` <a id="exec.sysctxrepl.psb">[[exec.sysctxrepl.psb]]</a>
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+
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+ ``` cpp
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+ namespace std::execution::system_context_replaceability {
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+ struct parallel_scheduler_backend {
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+ virtual ~parallel_scheduler_backend() = default;
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+
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+ virtual void schedule(receiver_proxy&, span<byte>) noexcept = 0;
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+ virtual void schedule_bulk_chunked(size_t, bulk_item_receiver_proxy&,
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+ span<byte>) noexcept = 0;
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+ virtual void schedule_bulk_unchunked(size_t, bulk_item_receiver_proxy&,
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+ span<byte>) noexcept = 0;
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+ };
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+ }
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+ ```
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+
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+ ``` cpp
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+ virtual void schedule(receiver_proxy& r, span<byte> s) noexcept = 0;
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+ ```
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+
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+ *Preconditions:* The ends of the lifetimes of `*this`, the object
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+ referred to by `r`, and any storage referenced by `s` all happen after
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+ the beginning of the evaluation of the call to `set_value`, `set_error`,
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+ or `set_done` on `r` (see below).
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+
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+ *Effects:* A derived class shall implement this function such that:
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+
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+ - One of the following expressions is evaluated:
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+ - `r.set_value()`, if no error occurs, and the work is successful;
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+ - `r.set_error(eptr)`, if an error occurs, where `eptr` is an object
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+ of type `exception_ptr`;
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+ - `r.set_stopped()`, if the work is canceled.
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+ - Any call to `r.set_value()` happens on an execution agent of the
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+ execution context represented by `*this`.
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+
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+ *Remarks:* The storage referenced by `s` may be used by `*this` as
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+ temporary storage for the duration of the operation launched by this
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+ call.
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+
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+ ``` cpp
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+ virtual void schedule_bulk_chunked(size_t n, bulk_item_receiver_proxy& r,
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+ span<byte> s) noexcept = 0;
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+ ```
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+
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+ *Preconditions:* The ends of the lifetimes of `*this`, the object
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+ referred to by `r`, and any storage referenced by `s` all happen after
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+ the beginning of the evaluation of one of the expressions below.
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+
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+ *Effects:* A derived class shall implement this function such that:
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+
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+ - Eventually, one of the following expressions is evaluated:
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+ - `r.set_value()`, if no error occurs, and the work is successful;
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+ - `r.set_error(eptr)`, if an error occurs, where `eptr` is an object
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+ of type `exception_ptr`;
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+ - `r.set_stopped()`, if the work is canceled.
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+ - If `r.execute(b, e)` is called, then `b` and `e` are in the range
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+ \[`0`, `n`\] and `b` < `e`.
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+ - For each i in \[`0`, `n`), there is at most one call to
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+ `r.execute(b, e)` such that i is in the range \[`b`, `e`).
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+ - If `r.set_value()` is called, then for each i in \[`0`, `n`), there is
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+ exactly one call to `r.execute(b, e)` such that i is in the range
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+ \[`b`, `e`).
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+ - All calls to `execute` on `r` happen before the call to either
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+ `set_value`, `set_error`, or `set_stopped` on `r`.
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+ - All calls to `execute` and `set_value` on `r` are made on execution
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+ agents of the execution context represented by `*this`.
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+
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+ *Remarks:* The storage referenced by `s` may be used by `*this` as
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+ temporary storage for the duration of the operation launched by this
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+ call.
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+
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+ ``` cpp
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+ virtual void schedule_bulk_unchunked(size_t n, bulk_item_receiver_proxy& r,
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+ span<byte> s) noexcept = 0;
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+ ```
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+
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+ *Preconditions:* The ends of the lifetimes of `*this`, the object
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+ referred to by `r`, and any storage referenced by `s` all happen after
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+ the beginning of the evaluation of one of the expressions below.
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+
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+ *Effects:* A derived class shall implement this function such that:
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+
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+ - Eventually, one of the following expressions is evaluated:
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+ - `r.set_value()`, if no error occurs, and the work is successful;
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+ - `r.set_error(eptr)`, if an error occurs, where `eptr` is an object
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+ of type `exception_ptr`;
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+ - `r.set_stopped()`, if the work is canceled.
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+ - If `r.execute(b, e)` is called, then `b` is in the range \[`0`, `n`)
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+ and `e` is equal to `b + 1`. For each i in \[`0`, `n`), there is at
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+ most one call to `r.execute(`i`, `i` + 1)`.
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+ - If `r.set_value()` is called, then for each i in \[`0`, `n`), there is
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+ exactly one call to `r.execute(`i`, `i` + 1)`.
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+ - All calls to `execute` on `r` happen before the call to either
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+ `set_value`, `set_error`, or `set_stopped` on `r`.
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+ - All calls to `execute` and `set_value` on `r` are made on execution
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+ agents of the execution context represented by `*this`.
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+
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+ *Remarks:* The storage referenced by `s` may be used by `*this` as
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+ temporary storage for the duration of the operation launched by this
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+ call.
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+
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+ <!-- Link reference definitions -->
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+ [algorithms.parallel.exec]: algorithms.md#algorithms.parallel.exec
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+ [allocator.requirements.general]: library.md#allocator.requirements.general
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+ [basic.def.odr]: basic.md#basic.def.odr
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+ [concepts.equality]: concepts.md#concepts.equality
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+ [customization.point.object]: library.md#customization.point.object
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+ [dcl.init]: dcl.md#dcl.init
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+ [dcl.struct.bind]: dcl.md#dcl.struct.bind
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+ [defns.block]: intro.md#defns.block
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+ [except.terminate]: except.md#except.terminate
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+ [exec]: #exec
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+ [exec.adapt]: #exec.adapt
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+ [exec.adapt.general]: #exec.adapt.general
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+ [exec.adapt.obj]: #exec.adapt.obj
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+ [exec.affine.on]: #exec.affine.on
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+ [exec.as.awaitable]: #exec.as.awaitable
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+ [exec.associate]: #exec.associate
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+ [exec.async.ops]: #exec.async.ops
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+ [exec.awaitable]: #exec.awaitable
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+ [exec.bulk]: #exec.bulk
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+ [exec.cmplsig]: #exec.cmplsig
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+ [exec.connect]: #exec.connect
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+ [exec.consumers]: #exec.consumers
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+ [exec.continues.on]: #exec.continues.on
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+ [exec.coro.util]: #exec.coro.util
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+ [exec.counting.scopes]: #exec.counting.scopes
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+ [exec.counting.scopes.general]: #exec.counting.scopes.general
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+ [exec.ctx]: #exec.ctx
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+ [exec.domain.default]: #exec.domain.default
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+ [exec.env]: #exec.env
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+ [exec.envs]: #exec.envs
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+ [exec.factories]: #exec.factories
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+ [exec.fwd.env]: #exec.fwd.env
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+ [exec.general]: #exec.general
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+ [exec.get.allocator]: #exec.get.allocator
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+ [exec.get.await.adapt]: #exec.get.await.adapt
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+ [exec.get.compl.sched]: #exec.get.compl.sched
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+ [exec.get.delegation.scheduler]: #exec.get.delegation.scheduler
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+ [exec.get.domain]: #exec.get.domain
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+ [exec.get.env]: #exec.get.env
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+ [exec.get.fwd.progress]: #exec.get.fwd.progress
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+ [exec.get.scheduler]: #exec.get.scheduler
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+ [exec.get.stop.token]: #exec.get.stop.token
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+ [exec.getcomplsigs]: #exec.getcomplsigs
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+ [exec.inline.scheduler]: #exec.inline.scheduler
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+ [exec.into.variant]: #exec.into.variant
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+ [exec.just]: #exec.just
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+ [exec.let]: #exec.let
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+ [exec.on]: #exec.on
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+ [exec.opstate]: #exec.opstate
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+ [exec.opstate.general]: #exec.opstate.general
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+ [exec.opstate.start]: #exec.opstate.start
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+ [exec.par.scheduler]: #exec.par.scheduler
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+ [exec.pos]: #exec.pos
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+ [exec.prop]: #exec.prop
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+ [exec.queries]: #exec.queries
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+ [exec.queryable]: #exec.queryable
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+ [exec.queryable.concept]: #exec.queryable.concept
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+ [exec.queryable.general]: #exec.queryable.general
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+ [exec.read.env]: #exec.read.env
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+ [exec.recv]: #exec.recv
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+ [exec.recv.concepts]: #exec.recv.concepts
241
+ [exec.run.loop]: #exec.run.loop
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+ [exec.run.loop.ctor]: #exec.run.loop.ctor
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+ [exec.run.loop.general]: #exec.run.loop.general
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+ [exec.run.loop.members]: #exec.run.loop.members
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+ [exec.run.loop.types]: #exec.run.loop.types
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+ [exec.sched]: #exec.sched
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+ [exec.schedule]: #exec.schedule
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+ [exec.schedule.from]: #exec.schedule.from
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+ [exec.scope]: #exec.scope
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+ [exec.scope.concepts]: #exec.scope.concepts
251
+ [exec.scope.counting]: #exec.scope.counting
252
+ [exec.scope.simple.counting]: #exec.scope.simple.counting
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+ [exec.scope.simple.counting.general]: #exec.scope.simple.counting.general
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+ [exec.set.error]: #exec.set.error
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+ [exec.set.stopped]: #exec.set.stopped
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+ [exec.set.value]: #exec.set.value
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+ [exec.simple.counting.ctor]: #exec.simple.counting.ctor
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+ [exec.simple.counting.mem]: #exec.simple.counting.mem
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+ [exec.simple.counting.token]: #exec.simple.counting.token
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+ [exec.snd]: #exec.snd
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+ [exec.snd.apply]: #exec.snd.apply
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+ [exec.snd.concepts]: #exec.snd.concepts
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+ [exec.snd.expos]: #exec.snd.expos
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+ [exec.snd.general]: #exec.snd.general
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+ [exec.snd.transform]: #exec.snd.transform
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+ [exec.snd.transform.env]: #exec.snd.transform.env
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+ [exec.spawn]: #exec.spawn
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+ [exec.spawn.future]: #exec.spawn.future
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+ [exec.starts.on]: #exec.starts.on
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+ [exec.stop.when]: #exec.stop.when
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+ [exec.stopped.err]: #exec.stopped.err
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+ [exec.stopped.opt]: #exec.stopped.opt
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+ [exec.summary]: #exec.summary
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+ [exec.sync.wait]: #exec.sync.wait
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+ [exec.sync.wait.var]: #exec.sync.wait.var
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+ [exec.sysctxrepl]: #exec.sysctxrepl
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+ [exec.sysctxrepl.general]: #exec.sysctxrepl.general
278
+ [exec.sysctxrepl.psb]: #exec.sysctxrepl.psb
279
+ [exec.sysctxrepl.query]: #exec.sysctxrepl.query
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+ [exec.sysctxrepl.recvproxy]: #exec.sysctxrepl.recvproxy
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+ [exec.task]: #exec.task
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+ [exec.task.scheduler]: #exec.task.scheduler
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+ [exec.then]: #exec.then
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+ [exec.unstoppable]: #exec.unstoppable
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+ [exec.when.all]: #exec.when.all
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+ [exec.with.awaitable.senders]: #exec.with.awaitable.senders
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+ [exec.write.env]: #exec.write.env
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+ [execution.syn]: #execution.syn
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+ [expr.await]: expr.md#expr.await
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+ [expr.const]: expr.md#expr.const
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+ [func.def]: utilities.md#func.def
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+ [func.require]: utilities.md#func.require
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+ [function.objects]: utilities.md#function.objects
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+ [intro.multithread]: basic.md#intro.multithread
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+ [intro.progress]: basic.md#intro.progress
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+ [intro.races]: basic.md#intro.races
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+ [meta.trans.other]: meta.md#meta.trans.other
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+ [namespace.std]: library.md#namespace.std
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+ [task.class]: #task.class
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+ [task.members]: #task.members
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+ [task.overview]: #task.overview
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+ [task.promise]: #task.promise
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+ [task.state]: #task.state
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+ [term.replaceable.function]: dcl.md#term.replaceable.function
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+ [thread.req.lockable.general]: thread.md#thread.req.lockable.general