Promise if construct (#26914)
* 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 * Promises if construct * build * Automated change: Fix sanity tests Co-authored-by: ctiller <ctiller@users.noreply.github.com>reviewable/pr27031/r1
Craig Tiller
4 years ago
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GitHub
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8 changed files with 296 additions and 10 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_IF_H |
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#define GRPC_CORE_LIB_PROMISE_IF_H |
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#include <grpc/impl/codegen/port_platform.h> |
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#include "absl/status/statusor.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/poll.h" |
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namespace grpc_core { |
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namespace promise_detail { |
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template <typename CallPoll, typename T, typename F> |
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typename CallPoll::PollResult ChooseIf(CallPoll call_poll, bool result, |
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T* if_true, F* if_false) { |
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if (result) { |
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auto promise = if_true->Once(); |
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return call_poll(promise); |
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} else { |
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auto promise = if_false->Once(); |
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return call_poll(promise); |
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} |
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} |
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template <typename CallPoll, typename T, typename F> |
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typename CallPoll::PollResult ChooseIf(CallPoll call_poll, |
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absl::StatusOr<bool> result, T* if_true, |
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F* if_false) { |
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if (!result.ok()) { |
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return typename CallPoll::PollResult(result.status()); |
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} else if (*result) { |
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auto promise = if_true->Once(); |
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return call_poll(promise); |
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} else { |
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auto promise = if_false->Once(); |
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return call_poll(promise); |
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} |
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} |
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template <typename C, typename T, typename F> |
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class If { |
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private: |
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using TrueFactory = promise_detail::PromiseFactory<void, T>; |
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using FalseFactory = promise_detail::PromiseFactory<void, F>; |
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using ConditionPromise = PromiseLike<C>; |
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using TruePromise = typename TrueFactory::Promise; |
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using FalsePromise = typename FalseFactory::Promise; |
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using Result = |
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typename PollTraits<decltype(std::declval<TruePromise>()())>::Type; |
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public: |
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If(C condition, T if_true, F if_false) |
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: state_(Evaluating{ConditionPromise(std::move(condition)), |
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TrueFactory(std::move(if_true)), |
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FalseFactory(std::move(if_false))}) {} |
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Poll<Result> operator()() { |
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return absl::visit(CallPoll<false>{this}, state_); |
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} |
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private: |
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struct Evaluating { |
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ConditionPromise condition; |
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TrueFactory if_true; |
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FalseFactory if_false; |
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}; |
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using State = absl::variant<Evaluating, TruePromise, FalsePromise>; |
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State state_; |
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template <bool kSetState> |
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struct CallPoll { |
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using PollResult = Poll<Result>; |
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If* const self; |
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PollResult operator()(Evaluating& evaluating) const { |
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static_assert( |
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!kSetState, |
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"shouldn't need to set state coming through the initial branch"); |
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auto r = evaluating.condition(); |
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if (auto* p = absl::get_if<kPollReadyIdx>(&r)) { |
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return ChooseIf(CallPoll<true>{self}, std::move(*p), |
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&evaluating.if_true, &evaluating.if_false); |
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} |
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return Pending(); |
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} |
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template <class Promise> |
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PollResult operator()(Promise& promise) const { |
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auto r = promise(); |
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if (kSetState && absl::holds_alternative<Pending>(r)) { |
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self->state_.template emplace<Promise>(std::move(promise)); |
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} |
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return r; |
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} |
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}; |
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}; |
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} // namespace promise_detail
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// If promise combinator.
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// Takes 3 promise factories, and evaluates the first.
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// If it returns failure, returns failure for the entire combinator.
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// If it returns true, evaluates the second promise.
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// If it returns false, evaluates the third promise.
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template <typename C, typename T, typename F> |
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promise_detail::If<C, T, F> If(C condition, T if_true, F if_false) { |
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return promise_detail::If<C, T, F>(std::move(condition), std::move(if_true), |
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std::move(if_false)); |
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} |
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} // namespace grpc_core
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#endif // GRPC_CORE_LIB_PROMISE_IF_H
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@ -0,0 +1,57 @@ |
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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/if.h" |
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#include <gtest/gtest.h> |
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namespace grpc_core { |
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TEST(IfTest, ChooseTrue) { |
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EXPECT_EQ(If([]() { return true; }, []() { return 1; }, []() { return 2; })(), |
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Poll<int>(1)); |
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} |
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TEST(IfTest, ChooseFalse) { |
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EXPECT_EQ( |
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If([]() { return false; }, []() { return 1; }, []() { return 2; })(), |
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Poll<int>(2)); |
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} |
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TEST(IfTest, ChooseSuccesfulTrue) { |
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EXPECT_EQ(If([]() { return absl::StatusOr<bool>(true); }, |
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[]() { return absl::StatusOr<int>(1); }, |
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[]() { return absl::StatusOr<int>(2); })(), |
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Poll<absl::StatusOr<int>>(absl::StatusOr<int>(1))); |
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} |
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TEST(IfTest, ChooseSuccesfulFalse) { |
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EXPECT_EQ(If([]() { return absl::StatusOr<bool>(false); }, |
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[]() { return absl::StatusOr<int>(1); }, |
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[]() { return absl::StatusOr<int>(2); })(), |
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Poll<absl::StatusOr<int>>(absl::StatusOr<int>(2))); |
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} |
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TEST(IfTest, ChooseFailure) { |
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EXPECT_EQ(If([]() { return absl::StatusOr<bool>(); }, |
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[]() { return absl::StatusOr<int>(1); }, |
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[]() { return absl::StatusOr<int>(2); })(), |
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Poll<absl::StatusOr<int>>(absl::StatusOr<int>())); |
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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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