/* Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved. 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 http://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 #include #include // NOLINT namespace paddle { namespace framework { namespace details { // Change it to thread safe flags if needed. class ThreadUnsafeOwnershipFlags { public: explicit ThreadUnsafeOwnershipFlags(bool flag) : flag_(flag) {} ThreadUnsafeOwnershipFlags(const ThreadUnsafeOwnershipFlags& other) = delete; ThreadUnsafeOwnershipFlags& operator=( const ThreadUnsafeOwnershipFlags& other) = delete; ThreadUnsafeOwnershipFlags(ThreadUnsafeOwnershipFlags&& other) = default; void SetOwnership(bool flag) { flag_ = flag; } // Invoke the callback if it is not owned. template void AcquireOwnershipOnce(Callback acquire) { if (!flag_) { acquire(); flag_ = true; } } private: bool flag_; }; // Copy-On-Write pointer. // It will hold a T* pointer, and only copy once when `MutableData` is invoked. // // The template parameter OwnershipFlags should have: // * a constructor takes a bool. True if own. // * SetOwnership(bool flag). // * AcquireOwnershipOnce(Callback). It will invoke the callback if it is not // owned. // // https://en.wikipedia.org/wiki/Copy-on-write template class COWPtr { public: // Ctor from raw pointer. explicit COWPtr(T* ptr) : payload_(ptr), ownership_{true} {} // Move methods. Steal ownership from origin COWPtr(COWPtr&& other) : payload_(other.payload_), ownership_{std::move(other.ownership_)} {} COWPtr& operator=(COWPtr&& origin) = default; // Copy methods. Not own payload COWPtr(const COWPtr& other) : payload_(other.payload_), ownership_{false} {} COWPtr& operator=(const COWPtr& other) { payload_ = other.payload_; ownership_.SetOwnership(false); return *this; } // Access read only data. const T& Data() const { return *payload_; } // Access mutable data. If the data is not owned, the data will be copied // before. T* MutableData() { ownership_.AcquireOwnershipOnce( [this] { payload_.reset(new T(*payload_)); }); return payload_.get(); } private: // Actual data pointer. std::shared_ptr payload_; // Ownership flag. OwnershipFlags ownership_; }; } // namespace details } // namespace framework } // namespace paddle