91 lines
4.1 KiB
Plaintext
91 lines
4.1 KiB
Plaintext
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/ Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:Scheduler Scheduler concept]
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template<class S>
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concept scheduler =
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copy_constructible<remove_cvref_t<S>> &&
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equality_comparable<remove_cvref_t<S>> &&
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requires(E&& e) {
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execution::schedule((E&&)e);
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};
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None of a scheduler's copy constructor, destructor, equality comparison, or
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`swap` operation shall exit via an exception.
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None of these operations, nor a scheduler type's `schedule` function, or
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associated query functions shall introduce data races as a result of concurrent
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invocations of those functions from different threads.
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For any two (possibly const) values `x1` and `x2` of some scheduler type `X`,
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`x1 == x2` shall return `true` only if `boost::asio::query(x1, p) == boost::asio::query(x2,
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p)` for every property `p` where both `boost::asio::query(x1, p)` and `boost::asio::query(x2,
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p)` are well-formed and result in a non-void type that is `EqualityComparable`
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(C++Std [equalitycomparable]). [inline_note The above requirements imply that
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`x1 == x2` returns `true` if `x1` and `x2` can be interchanged with identical
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effects. A scheduler may conceptually contain additional properties which are
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not exposed by a named property type that can be observed via `boost::asio::query`; in
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this case, it is up to the concrete scheduler implementation to decide if these
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properties affect equality. Returning `false` does not necessarily imply that
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the effects are not identical.]
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A scheduler type's destructor shall not block pending completion of any
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receivers submitted to the sender objects returned from `schedule`.
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[inline_note The ability to wait for completion of submitted function objects
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may be provided by the execution context that produced the scheduler.]
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In addition to the above requirements, type `S` models `scheduler` only if it
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satisfies the requirements in the Table below.
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In the Table below,
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* `s` denotes a (possibly const) scheduler object of type `S`,
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* `N` denotes a type that models `sender`, and
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* `n` denotes a sender object of type `N`
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[table Scheduler requirements
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[[expression] [return type] [operation semantics]]
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[
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[`execution::schedule(s)`]
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[`N`]
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[Evaluates `execution::schedule(s)` on the calling thread to create `N`.]
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]
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]
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`execution::start(o)`, where `o` is the result of a call to
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`execution::connect(N, r)` for some receiver object `r`, is required to eagerly
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submit `r` for execution on an execution agent that `s` creates for it. Let
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`rc` be `r` or an object created by copy or move construction from `r`. The
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semantic constraints on the `sender` `N` returned from a scheduler `s`'s
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`schedule` function are as follows:
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* If `rc`'s `set_error` function is called in response to a submission error,
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scheduling error, or other internal error, let `E` be an expression that
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refers to that error if `set_error(rc, E)` is well-formed; otherwise, let `E`
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be an `exception_ptr` that refers to that error. [Note: `E` could be the
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result of calling `current_exception` or `make_exception_ptr`.]
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The scheduler calls `set_error(rc, E)` on an unspecified weakly-parallel
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execution agent ([Note: An invocation of `set_error` on a receiver is
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required to be `noexcept`]), and
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* If `rc`'s `set_error` function is called in response to an exception that
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propagates out of the invocation of `set_value` on `rc`, let `E` be
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`make_exception_ptr(receiver_invocation_error{})` invoked from within a catch
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clause that has caught the exception. The executor calls `set_error(rc, E)`
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on an unspecified weakly-parallel execution agent, and
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* A call to `set_done(rc)` is made on an unspecified weakly-parallel execution
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agent ([Note: An invocation of a receiver's `set_done` function is required
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to be `noexcept`]).
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[inline_note The senders returned from a scheduler's `schedule` function have
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wide discretion when deciding which of the three receiver functions to call
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upon submission.]
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[endsect]
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