mirror of https://github.com/grpc/grpc.git
Generic promise facilities (#26916)
* Poll type for promises library * Library to talk about things that look like promises if you squint * Promise helpers, and basic type erasure * build * Changes to sync required for promise activities * sanitized * Automated change: Fix sanity tests * suppressions * try to fix windows failure * Automated change: Fix sanity tests Co-authored-by: ctiller <ctiller@users.noreply.github.com>reviewable/pr26954/r4
Craig Tiller
3 years ago
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GitHub
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2e56b42ada
8 changed files with 246 additions and 16 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_PROMISE_H |
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#define GRPC_CORE_LIB_PROMISE_PROMISE_H |
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#include <grpc/impl/codegen/port_platform.h> |
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#include <functional> |
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#include "absl/types/optional.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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namespace grpc_core { |
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// A Promise is any functor that takes no arguments and returns Poll<T>.
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// Most of the time we just pass around the functor, but occasionally
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// it pays to have a type erased variant, which we define here.
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template <typename T> |
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using Promise = std::function<Poll<T>()>; |
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// Helper to execute a promise immediately and return either the result or
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// nothing.
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template <typename Promise> |
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auto NowOrNever(Promise promise) |
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-> absl::optional<typename promise_detail::PromiseLike<Promise>::Result> { |
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auto r = promise_detail::PromiseLike<Promise>(std::move(promise))(); |
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if (auto* p = absl::get_if<kPollReadyIdx>(&r)) { |
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return std::move(*p); |
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} |
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return {}; |
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} |
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// A promise that never completes.
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template <typename T> |
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struct Never { |
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Poll<T> operator()() { return Pending(); } |
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}; |
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namespace promise_detail { |
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// A promise that immediately completes.
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template <typename T> |
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class Immediate { |
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public: |
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explicit Immediate(T value) : value_(std::move(value)) {} |
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Poll<T> operator()() { return std::move(value_); } |
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private: |
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T value_; |
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}; |
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} // namespace promise_detail
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// Return \a value immediately
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template <typename T> |
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promise_detail::Immediate<T> Immediate(T value) { |
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return promise_detail::Immediate<T>(std::move(value)); |
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} |
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// Typecheck that a promise returns the expected return type.
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// usage: auto promise = WithResult<int>([]() { return 3; });
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// NOTE: there are tests in promise_test.cc that are commented out because they
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// should fail to compile. When modifying this code these should be uncommented
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// and their miscompilation verified.
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template <typename T, typename F> |
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auto WithResult(F f) -> |
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typename std::enable_if<std::is_same<decltype(f()), Poll<T>>::value, |
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F>::type { |
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return f; |
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} |
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} // namespace grpc_core
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#endif // GRPC_CORE_LIB_PROMISE_PROMISE_H
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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/promise.h" |
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#include <gtest/gtest.h> |
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namespace grpc_core { |
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TEST(PromiseTest, Works) { |
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Promise<int> x = []() { return 42; }; |
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EXPECT_EQ(x(), Poll<int>(42)); |
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} |
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TEST(PromiseTest, Immediate) { EXPECT_EQ(Immediate(42)(), Poll<int>(42)); } |
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TEST(PromiseTest, WithResult) { |
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EXPECT_EQ(WithResult<int>(Immediate(42))(), Poll<int>(42)); |
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// Fails to compile: WithResult<int>(Immediate(std::string("hello")));
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// Fails to compile: WithResult<int>(Immediate(42.9));
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} |
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TEST(PromiseTest, NowOrNever) { |
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EXPECT_EQ(NowOrNever(Immediate(42)), absl::optional<int>(42)); |
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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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