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pw_bluetooth: Specify the Deleter when using std::unique_ptr
In several cases we use std::unique_ptr<T> to return an object with RAII semantics, meaning that some action is needed by the backend to release the resource when the object goes out of scope. However, using using std::unique_ptr<T> with the default deleter forces the pw_bluetooth backend to use new/delete to allocate the T interface implementation. This patch introduces a RaiiPtr<Api, void (Api::*OnDestroy)()> template class as an alias of std::unique_ptr with a custom deleter that calls the Api::OnDestroy parametric method instead of calling "delete". This template class is used instead of the plain std::unique_ptr when returning objects from the pw_bluetooth API for the all the "Api" classes with only pure virtual methods. In all 5 cases where this pattern was used the abstract class has one more private pure virtual method (the one used as Api::OnDestroy parameter) which must be implemented by the backend. This allows a backend to manage the memory for the returned objects with something other than new/delete, for example it can return a RaiiPtr to a std::optional instance or to one of the existing pre-allocated objects and re-use them when needed. This is particularly useful in cases where there can only be a fixed small number of objects for the given type, like in the Scan or AdvertisingParameters case where there is only one object at a time. Bug: 250930246 Change-Id: I724ff5135e0f73f5fb74c7fc92abdffa6a9e2d2d Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/113210 Reviewed-by: Wyatt Hepler <hepler@google.com> Commit-Queue: Alex Deymo <deymo@google.com> Reviewed-by: Ben Lawson <benlawson@google.com>
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| // Copyright 2022 The Pigweed 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. | ||
| #pragma once | ||
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|
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| #include <memory> | ||
| #include <type_traits> | ||
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| namespace pw::bluetooth::internal { | ||
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| // Helper deleter struct to call the OnDestroy template parameter method when | ||
| // RaiiPtr<Api, OnDestroy> is destroyed. | ||
| template <class Api, void (Api::*OnDestroy)()> | ||
| struct RaiiPtrDeleter { | ||
| void operator()(Api* api) { (api->*OnDestroy)(); } | ||
| }; | ||
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| // Smart pointer class to expose an API with RAII semantics that calls a | ||
| // specific method of the API implementation when it is destroyed, instead of | ||
| // calling delete on the API object like the default std::unique_ptr deleter | ||
| // behavior. This allows to be used like if it was a std::unique_ptr<API> but | ||
| // leaving the memory management implementation details up to the backend | ||
| // implementing the API. | ||
| // | ||
| // Example usage: | ||
| // class SomeApi { | ||
| // public: | ||
| // virtual ~SomeApi() = default; | ||
| // | ||
| // virtual void MethodOne() = 0; | ||
| // virtual void MethodTwo(int) = 0; | ||
| // | ||
| // private: | ||
| // // Method used to release the resource in the backend. | ||
| // virtual void DeleteResource() = 0; | ||
| // | ||
| // public: | ||
| // using Ptr = RaiiPtr<SomeApi, &SomeApi::DeleteResource>; | ||
| // }; | ||
| // | ||
| // // The concrete backend implementation. | ||
| // class BackendImplementation final : public SomeApi { | ||
| // public: | ||
| // void MethodOne() override { ... } | ||
| // void MethodTwo(int) override { ... } | ||
| // void DeleteResource() override { ... } | ||
| // }; | ||
| // | ||
| // // Example using a static global resource object. GetResource should check | ||
| // // whether the global resource is in use. | ||
| // BackendImplementation backend_impl; | ||
| // SomeApi::Ptr GetResource() { ...; return &backend_impl; } | ||
| // | ||
| template <class Api, void (Api::*OnDestroy)()> | ||
| using RaiiPtr = std::unique_ptr<Api, RaiiPtrDeleter<Api, OnDestroy>>; | ||
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| } // namespace pw::bluetooth::internal |
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