Promise factories (#26990)
* Poll type for promises library * Library to talk about things that look like promises if you squint * Library to talk about things that make promises * build * Changes to sync required for promise activities * sanitized * remove bad comment * possible windows fix? * fix * ugh * comment fix * fix build * Automated change: Fix sanity tests Co-authored-by: ctiller <ctiller@users.noreply.github.com>pull/27005/head
Craig Tiller
4 years ago
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8 changed files with 383 additions and 1 deletions
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// Copyright 2021 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef GRPC_CORE_LIB_PROMISE_DETAIL_PROMISE_FACTORY_H |
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#define GRPC_CORE_LIB_PROMISE_DETAIL_PROMISE_FACTORY_H |
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#include <grpc/impl/codegen/port_platform.h> |
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#include "src/core/lib/promise/detail/promise_like.h" |
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#include "src/core/lib/promise/poll.h" |
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#include "absl/meta/type_traits.h" |
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// PromiseFactory is an adaptor class.
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//
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// Where a Promise is a thing that's polled periodically, a PromiseFactory
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// creates a Promise. Within this Promise/Activity framework, PromiseFactory's
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// then provide the edges for computation -- invoked at state transition
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// boundaries to provide the new steady state.
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//
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// A PromiseFactory formally is f(A) -> Promise<T> for some types A & T.
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// This get a bit awkward and inapproprate to write however, and so the type
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// contained herein can adapt various kinds of callable into the correct form.
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// Of course a callable of a single argument returning a Promise will see an
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// identity translation. One taking no arguments and returning a Promise
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// similarly.
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//
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// A Promise passed to a PromiseFactory will yield a PromiseFactory that
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// returns just that Promise.
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//
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// Generalizing slightly, a callable taking a single argument A and returning a
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// Poll<T> will yield a PromiseFactory that captures it's argument A and
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// returns a Poll<T>.
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//
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// Since various consumers of PromiseFactory run either repeatedly through an
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// overarching Promises lifetime, or just once, and we can optimize just once
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// by moving the contents of the PromiseFactory, two factory methods are
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// provided: Once, that can be called just once, and Repeated, that can (wait
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// for it) be called Repeatedly.
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namespace grpc_core { |
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namespace promise_detail { |
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// Helper trait: given a T, and T x, is calling x() legal?
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template <typename T, typename Ignored = void> |
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struct IsVoidCallableT { |
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static constexpr bool value = false; |
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}; |
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template <typename F> |
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struct IsVoidCallableT<F, absl::void_t<decltype(std::declval<F>()())>> { |
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static constexpr bool value = true; |
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}; |
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// Wrap that trait in some nice syntax.
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template <typename T> |
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constexpr bool IsVoidCallable() { |
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return IsVoidCallableT<T>::value; |
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} |
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// T -> T, const T& -> T
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template <typename T> |
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using RemoveCVRef = absl::remove_cv_t<absl::remove_reference_t<T>>; |
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// Given F(A,B,C,...), what's the return type?
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template <typename T, typename Ignored = void> |
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struct ResultOfTInner; |
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template <typename F, typename... Args> |
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struct ResultOfTInner<F(Args...), absl::void_t<decltype(std::declval<F>()( |
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std::declval<Args>()...))>> { |
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using T = decltype(std::declval<F>()(std::declval<Args>()...)); |
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}; |
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template <typename T> |
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struct ResultOfT; |
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template <typename F, typename... Args> |
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struct ResultOfT<F(Args...)> { |
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using FP = RemoveCVRef<F>; |
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using T = typename ResultOfTInner<FP(Args...)>::T; |
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}; |
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template <typename T> |
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using ResultOf = typename ResultOfT<T>::T; |
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// Captures the promise functor and the argument passed.
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// Provides the interface of a promise.
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template <typename F, typename Arg> |
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class Curried { |
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public: |
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Curried(F&& f, Arg&& arg) |
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: f_(std::forward<F>(f)), arg_(std::forward<Arg>(arg)) {} |
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using Result = decltype(std::declval<F>()(std::declval<Arg>())); |
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Result operator()() { return f_(arg_); } |
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private: |
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GPR_NO_UNIQUE_ADDRESS F f_; |
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GPR_NO_UNIQUE_ADDRESS Arg arg_; |
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}; |
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// Promote a callable(A) -> T | Poll<T> to a PromiseFactory(A) -> Promise<T> by
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// capturing A.
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template <typename A, typename F> |
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absl::enable_if_t<!IsVoidCallable<ResultOf<F(A)>>(), PromiseLike<Curried<A, F>>> |
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PromiseFactoryImpl(F&& f, A&& arg) { |
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return Curried<A, F>(std::forward<F>(f), std::forward<A>(arg)); |
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} |
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// Promote a callable() -> T|Poll<T> to a PromiseFactory(A) -> Promise<T>
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// by dropping the argument passed to the factory.
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template <typename A, typename F> |
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absl::enable_if_t<!IsVoidCallable<ResultOf<F()>>(), PromiseLike<RemoveCVRef<F>>> |
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PromiseFactoryImpl(F f, A&&) { |
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return PromiseLike<F>(std::move(f)); |
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} |
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// Promote a callable() -> T|Poll<T> to a PromiseFactory() -> Promise<T>
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template <typename F> |
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absl::enable_if_t<!IsVoidCallable<ResultOf<F()>>(), PromiseLike<RemoveCVRef<F>>> |
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PromiseFactoryImpl(F f) { |
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return PromiseLike<F>(std::move(f)); |
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} |
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// Given a callable(A) -> Promise<T>, name it a PromiseFactory and use it.
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template <typename A, typename F> |
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absl::enable_if_t<IsVoidCallable<ResultOf<F(A)>>(), |
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PromiseLike<decltype(std::declval<F>()(std::declval<A>()))>> |
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PromiseFactoryImpl(F&& f, A&& arg) { |
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return f(std::forward<A>(arg)); |
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} |
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// Given a callable() -> Promise<T>, promote it to a
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// PromiseFactory(A) -> Promise<T> by dropping the first argument.
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template <typename A, typename F> |
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absl::enable_if_t<IsVoidCallable<ResultOf<F()>>(), |
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PromiseLike<decltype(std::declval<F>()())>> |
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PromiseFactoryImpl(F&& f, A&&) { |
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return f(); |
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} |
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// Given a callable() -> Promise<T>, name it a PromiseFactory and use it.
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template <typename F> |
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absl::enable_if_t<IsVoidCallable<ResultOf<F()>>(), |
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PromiseLike<decltype(std::declval<F>()())>> |
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PromiseFactoryImpl(F&& f) { |
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return f(); |
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}; |
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template <typename A, typename F> |
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class PromiseFactory { |
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private: |
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GPR_NO_UNIQUE_ADDRESS F f_; |
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public: |
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using Arg = A; |
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explicit PromiseFactory(F f) : f_(std::move(f)) {} |
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auto Once(Arg&& a) |
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-> decltype(PromiseFactoryImpl(std::move(f_), std::forward<Arg>(a))) { |
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return PromiseFactoryImpl(std::move(f_), std::forward<Arg>(a)); |
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} |
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auto Repeated(Arg&& a) const |
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-> decltype(PromiseFactoryImpl(f_, std::forward<Arg>(a))) { |
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return PromiseFactoryImpl(f_, std::forward<Arg>(a)); |
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} |
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}; |
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template <typename F> |
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class PromiseFactory<void, F> { |
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private: |
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GPR_NO_UNIQUE_ADDRESS F f_; |
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public: |
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using Arg = void; |
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explicit PromiseFactory(F f) : f_(std::move(f)) {} |
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auto Once() -> decltype(PromiseFactoryImpl(std::move(f_))) { |
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return PromiseFactoryImpl(std::move(f_)); |
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} |
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auto Repeated() const -> decltype(PromiseFactoryImpl(f_)) { |
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return PromiseFactoryImpl(f_); |
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} |
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}; |
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} // namespace promise_detail
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} // namespace grpc_core
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#endif // GRPC_CORE_LIB_PROMISE_DETAIL_PROMISE_FACTORY_H
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@ -0,0 +1,69 @@ |
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// Copyright 2021 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "src/core/lib/promise/detail/promise_factory.h" |
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#include <gtest/gtest.h> |
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#include "absl/functional/bind_front.h" |
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#include "src/core/lib/gprpp/capture.h" |
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#include "src/core/lib/promise/promise.h" |
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namespace grpc_core { |
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namespace promise_detail { |
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namespace testing { |
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template <typename Arg, typename F> |
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PromiseFactory<Arg, F> MakeFactory(F f) { |
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return PromiseFactory<Arg, F>(std::move(f)); |
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} |
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TEST(AdaptorTest, FactoryFromPromise) { |
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EXPECT_EQ( |
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MakeFactory<void>([]() { return Poll<int>(Poll<int>(42)); }).Once()(), |
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Poll<int>(42)); |
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EXPECT_EQ( |
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MakeFactory<void>([]() { return Poll<int>(Poll<int>(42)); }).Repeated()(), |
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Poll<int>(42)); |
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EXPECT_EQ(MakeFactory<void>(Promise<int>([]() { |
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return Poll<int>(Poll<int>(42)); |
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})).Once()(), |
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Poll<int>(42)); |
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EXPECT_EQ(MakeFactory<void>(Promise<int>([]() { |
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return Poll<int>(Poll<int>(42)); |
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})).Repeated()(), |
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Poll<int>(42)); |
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} |
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TEST(AdaptorTest, FactoryFromBindFrontPromise) { |
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EXPECT_EQ(MakeFactory<void>( |
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absl::bind_front([](int i) { return Poll<int>(i); }, 42)) |
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.Once()(), |
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Poll<int>(42)); |
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} |
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TEST(AdaptorTest, FactoryFromCapturePromise) { |
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EXPECT_EQ(MakeFactory<void>( |
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grpc_core::Capture([](int* i) { return Poll<int>(*i); }, 42)) |
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.Once()(), |
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Poll<int>(42)); |
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} |
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} // namespace testing
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} // namespace promise_detail
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} // namespace grpc_core
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int main(int argc, char** argv) { |
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::testing::InitGoogleTest(&argc, argv); |
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return RUN_ALL_TESTS(); |
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} |
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