mirror of https://github.com/grpc/grpc.git
[promises] Add a promise-based match operator (#37981)
Closes #37981
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37981 from ctiller:match-promise 8341b09901
PiperOrigin-RevId: 689223259
pull/37996/head
Craig Tiller
3 months ago
committed by
Copybara-Service
parent
53c7d45dd0
commit
8b7496172d
7 changed files with 292 additions and 0 deletions
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// Copyright 2024 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_SRC_CORE_LIB_PROMISE_MATCH_PROMISE_H |
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#define GRPC_SRC_CORE_LIB_PROMISE_MATCH_PROMISE_H |
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#include "absl/types/variant.h" |
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#include "src/core/lib/promise/detail/promise_factory.h" |
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#include "src/core/lib/promise/detail/promise_like.h" |
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#include "src/core/util/overload.h" |
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namespace grpc_core { |
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namespace promise_detail { |
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// This types job is to visit a supplied variant, and apply a mapping
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// Constructor from input types to promises, returning a variant full of
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// promises.
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template <typename Constructor, typename... Ts> |
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struct ConstructPromiseVariantVisitor { |
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// Factory functions supplied to the top level `Match` object, wrapped by
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// OverloadType to become overloaded members.
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Constructor constructor; |
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// Helper function... only callable once.
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// Given a value, construct a Promise Factory that accepts that value type,
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// and uses the constructor type above to map from that type to a promise
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// returned by the factory.
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// We use the Promise Factory infrastructure to deal with all the common
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// variants of factory signatures that we've found to be convenient.
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template <typename T> |
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auto CallConstructorThenFactory(T x) { |
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OncePromiseFactory<T, Constructor> factory(std::move(constructor)); |
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return factory.Make(std::move(x)); |
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} |
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// Polling operator.
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// Given a visited type T, construct a Promise Factory, use it, and then cast
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// the result into a variant type that covers ALL of the possible return types
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// given the input types listed in Ts...
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template <typename T> |
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auto operator()(T x) |
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-> absl::variant<promise_detail::PromiseLike< |
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decltype(CallConstructorThenFactory(std::declval<Ts>()))>...> { |
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return CallConstructorThenFactory(x); |
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} |
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}; |
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// Visitor function for PromiseVariant - calls the poll operator on the inner
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// type
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class PollVisitor { |
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public: |
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template <typename T> |
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auto operator()(T& x) { |
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return x(); |
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} |
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}; |
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// Helper type - given a variant V, provides the poll operator (which simply
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// visits the inner type on the variant with PollVisitor)
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template <typename V> |
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class PromiseVariant { |
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public: |
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explicit PromiseVariant(V variant) : variant_(std::move(variant)) {} |
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auto operator()() { return absl::visit(PollVisitor(), variant_); } |
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private: |
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V variant_; |
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}; |
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} // namespace promise_detail
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// Match for promises
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// Like the Match function takes a variant of some set of types,
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// and a set of functions - one per variant type.
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// We use these functions as Promise Factories, and return a Promise that can be
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// polled selected by the type that was in the variant.
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template <typename... Fs, typename... Ts> |
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auto MatchPromise(absl::variant<Ts...> value, Fs... fs) { |
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// Construct a variant of promises using the factory functions fs, selected by
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// the type held by value.
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auto body = absl::visit( |
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promise_detail::ConstructPromiseVariantVisitor<OverloadType<Fs...>, |
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Ts...>{ |
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OverloadType<Fs...>(std::move(fs)...)}, |
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std::move(value)); |
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// Wrap that in a PromiseVariant that provides the promise API on the wrapped
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// variant.
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return promise_detail::PromiseVariant<decltype(body)>(std::move(body)); |
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} |
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} // namespace grpc_core
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#endif // GRPC_SRC_CORE_LIB_PROMISE_MATCH_PROMISE_H
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@ -0,0 +1,66 @@ |
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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/match_promise.h" |
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#include <memory> |
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#include "absl/strings/str_cat.h" |
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#include "gtest/gtest.h" |
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#include "src/core/lib/promise/promise.h" |
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#include "test/core/promise/poll_matcher.h" |
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namespace grpc_core { |
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TEST(MatchPromiseTest, Works) { |
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struct Int { |
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int x; |
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}; |
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struct Float { |
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float x; |
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}; |
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using V = absl::variant<Int, Float, std::string>; |
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auto make_promise = [](V v) -> Promise<std::string> { |
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return MatchPromise( |
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std::move(v), |
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[](Float x) mutable { |
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return [n = 3, x]() mutable -> Poll<std::string> { |
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--n; |
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if (n > 0) return Pending{}; |
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return absl::StrCat(x.x); |
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}; |
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}, |
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[](Int x) { |
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return []() mutable -> Poll<std::string> { return Pending{}; }; |
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}, |
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[](std::string x) { return x; }); |
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}; |
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auto promise = make_promise(V(Float{3.0f})); |
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EXPECT_THAT(promise(), IsPending()); |
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EXPECT_THAT(promise(), IsPending()); |
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EXPECT_THAT(promise(), IsReady("3")); |
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promise = make_promise(V(Int{42})); |
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for (int i = 0; i < 10000; i++) { |
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EXPECT_THAT(promise(), IsPending()); |
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} |
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promise = make_promise(V("hello")); |
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EXPECT_THAT(promise(), IsReady("hello")); |
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} |
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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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