| // Copyright 2021 The Abseil Authors. | |
| // | |
| // Licensed under the Apache License, Version 2.0 (the "License"); | |
| // you may not use this file except in compliance with the License. | |
| // You may obtain a copy of the License at | |
| // | |
| // https://www.apache.org/licenses/LICENSE-2.0 | |
| // | |
| // Unless required by applicable law or agreed to in writing, software | |
| // distributed under the License is distributed on an "AS IS" BASIS, | |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| // See the License for the specific language governing permissions and | |
| // limitations under the License. | |
| // | |
| // ----------------------------------------------------------------------------- | |
| // File: cleanup.h | |
| // ----------------------------------------------------------------------------- | |
| // | |
| // `absl::Cleanup` implements the scope guard idiom, invoking the contained | |
| // callback's `operator()() &&` on scope exit. | |
| // | |
| // Example: | |
| // | |
| // ``` | |
| // absl::Status CopyGoodData(const char* source_path, const char* sink_path) { | |
| // FILE* source_file = fopen(source_path, "r"); | |
| // if (source_file == nullptr) { | |
| // return absl::NotFoundError("No source file"); // No cleanups execute | |
| // } | |
| // | |
| // // C++17 style cleanup using class template argument deduction | |
| // absl::Cleanup source_closer = [source_file] { fclose(source_file); }; | |
| // | |
| // FILE* sink_file = fopen(sink_path, "w"); | |
| // if (sink_file == nullptr) { | |
| // return absl::NotFoundError("No sink file"); // First cleanup executes | |
| // } | |
| // | |
| // // C++11 style cleanup using the factory function | |
| // auto sink_closer = absl::MakeCleanup([sink_file] { fclose(sink_file); }); | |
| // | |
| // Data data; | |
| // while (ReadData(source_file, &data)) { | |
| // if (!data.IsGood()) { | |
| // absl::Status result = absl::FailedPreconditionError("Read bad data"); | |
| // return result; // Both cleanups execute | |
| // } | |
| // SaveData(sink_file, &data); | |
| // } | |
| // | |
| // return absl::OkStatus(); // Both cleanups execute | |
| // } | |
| // ``` | |
| // | |
| // Methods: | |
| // | |
| // `std::move(cleanup).Cancel()` will prevent the callback from executing. | |
| // | |
| // `std::move(cleanup).Invoke()` will execute the callback early, before | |
| // destruction, and prevent the callback from executing in the destructor. | |
| // | |
| // Usage: | |
| // | |
| // `absl::Cleanup` is not an interface type. It is only intended to be used | |
| // within the body of a function. It is not a value type and instead models a | |
| // control flow construct. Check out `defer` in Golang for something similar. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| template <typename Arg, typename Callback = void()> | |
| class ABSL_MUST_USE_RESULT Cleanup final { | |
| static_assert(cleanup_internal::WasDeduced<Arg>(), | |
| "Explicit template parameters are not supported."); | |
| static_assert(cleanup_internal::ReturnsVoid<Callback>(), | |
| "Callbacks that return values are not supported."); | |
| public: | |
| Cleanup(Callback callback) : storage_(std::move(callback)) {} // NOLINT | |
| Cleanup(Cleanup&& other) = default; | |
| void Cancel() && { | |
| ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged()); | |
| storage_.DestroyCallback(); | |
| } | |
| void Invoke() && { | |
| ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged()); | |
| storage_.InvokeCallback(); | |
| storage_.DestroyCallback(); | |
| } | |
| ~Cleanup() { | |
| if (storage_.IsCallbackEngaged()) { | |
| storage_.InvokeCallback(); | |
| storage_.DestroyCallback(); | |
| } | |
| } | |
| private: | |
| cleanup_internal::Storage<Callback> storage_; | |
| }; | |
| // `absl::Cleanup c = /* callback */;` | |
| // | |
| // C++17 type deduction API for creating an instance of `absl::Cleanup` | |
| template <typename Callback> | |
| Cleanup(Callback callback) -> Cleanup<cleanup_internal::Tag, Callback>; | |
| // `auto c = absl::MakeCleanup(/* callback */);` | |
| // | |
| // C++11 type deduction API for creating an instance of `absl::Cleanup` | |
| template <typename... Args, typename Callback> | |
| absl::Cleanup<cleanup_internal::Tag, Callback> MakeCleanup(Callback callback) { | |
| static_assert(cleanup_internal::WasDeduced<cleanup_internal::Tag, Args...>(), | |
| "Explicit template parameters are not supported."); | |
| static_assert(cleanup_internal::ReturnsVoid<Callback>(), | |
| "Callbacks that return values are not supported."); | |
| return {std::move(callback)}; | |
| } | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |