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99 lines
2.9 KiB
99 lines
2.9 KiB
/* Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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#pragma once
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#include <memory>
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#include <thread>
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namespace paddle {
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namespace framework {
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namespace details {
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// Change it to thread safe flags if needed.
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class ThreadUnsafeOwnershipFlags {
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public:
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ThreadUnsafeOwnershipFlags(bool flag) : flag_(flag) {}
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ThreadUnsafeOwnershipFlags(const ThreadUnsafeOwnershipFlags& other) = delete;
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ThreadUnsafeOwnershipFlags& operator=(
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const ThreadUnsafeOwnershipFlags& other) = delete;
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ThreadUnsafeOwnershipFlags(ThreadUnsafeOwnershipFlags&& other) = default;
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void SetOwnership(bool flag) { flag_ = flag; }
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// Invoke the callback if it is not owned.
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template <typename Callback>
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void AcquireOwnershipOnce(Callback acquire) {
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if (!flag_) {
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acquire();
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flag_ = true;
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}
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}
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private:
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bool flag_;
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};
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// Copy-On-Write pointer.
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// It will hold a T* pointer, and only copy once when `MutableData` is invoked.
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//
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// The template parameter OwnershipFlags should have:
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// * a constructor takes a bool. True if own.
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// * SetOwnership(bool flag).
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// * AcquireOwnershipOnce(Callback). It will invoke the callback if it is not
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// owned.
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//
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// https://en.wikipedia.org/wiki/Copy-on-write
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template <typename T, typename OwnershipFlags = ThreadUnsafeOwnershipFlags>
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class COWPtr {
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public:
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// Ctor from raw pointer.
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explicit COWPtr(T* ptr) : payload_(ptr), ownership_{true} {}
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// Move methods. Steal ownership from origin
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COWPtr(COWPtr&& other)
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: payload_(other.payload_), ownership_{std::move(other.ownership_)} {}
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COWPtr& operator=(COWPtr&& origin) = default;
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// Copy methods. Not own payload
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COWPtr(const COWPtr& other) : payload_(other.payload_), ownership_{false} {}
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COWPtr& operator=(const COWPtr& other) {
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payload_ = other.payload_;
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ownership_.SetOwnership(false);
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return *this;
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}
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// Access read only data.
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const T& Data() const { return *payload_; }
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// Access mutable data. If the data is not owned, the data will be copied
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// before.
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T* MutableData() {
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ownership_.AcquireOwnershipOnce(
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[this] { payload_.reset(new T(*payload_)); });
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return payload_.get();
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}
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private:
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// Actual data pointer.
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std::shared_ptr<T> payload_;
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// Ownership flag.
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OwnershipFlags ownership_;
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};
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} // namespace details
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} // namespace framework
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} // namespace paddle
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