109 lines
3.0 KiB
C++
109 lines
3.0 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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*/
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#pragma once
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#include <folly/AtomicIntrusiveLinkedList.h>
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#include <folly/Memory.h>
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namespace folly {
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/**
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* A very simple atomic single-linked list primitive.
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*
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* Usage:
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*
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* AtomicLinkedList<MyClass> list;
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* list.insert(a);
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* list.sweep([] (MyClass& c) { doSomething(c); }
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*/
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template <class T>
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class AtomicLinkedList {
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public:
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AtomicLinkedList() {}
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AtomicLinkedList(const AtomicLinkedList&) = delete;
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AtomicLinkedList& operator=(const AtomicLinkedList&) = delete;
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AtomicLinkedList(AtomicLinkedList&& other) noexcept = default;
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AtomicLinkedList& operator=(AtomicLinkedList&& other) = default;
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~AtomicLinkedList() {
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sweep([](T&&) {});
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}
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bool empty() const {
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return list_.empty();
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}
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/**
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* Atomically insert t at the head of the list.
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* @return True if the inserted element is the only one in the list
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* after the call.
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*/
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bool insertHead(T t) {
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auto wrapper = std::make_unique<Wrapper>(std::move(t));
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return list_.insertHead(wrapper.release());
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}
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/**
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* Repeatedly pops element from head,
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* and calls func() on the removed elements in the order from tail to head.
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* Stops when the list is empty.
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*/
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template <typename F>
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void sweep(F&& func) {
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list_.sweep([&](Wrapper* wrapperPtr) mutable {
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std::unique_ptr<Wrapper> wrapper(wrapperPtr);
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func(std::move(wrapper->data));
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});
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}
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/**
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* Similar to sweep() but calls func() on elements in LIFO order.
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*
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* func() is called for all elements in the list at the moment
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* reverseSweep() is called. Unlike sweep() it does not loop to ensure the
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* list is empty at some point after the last invocation. This way callers
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* can reason about the ordering: elements inserted since the last call to
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* reverseSweep() will be provided in LIFO order.
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*
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* Example: if elements are inserted in the order 1-2-3, the callback is
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* invoked 3-2-1. If the callback moves elements onto a stack, popping off
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* the stack will produce the original insertion order 1-2-3.
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*/
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template <typename F>
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void reverseSweep(F&& func) {
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list_.reverseSweep([&](Wrapper* wrapperPtr) mutable {
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std::unique_ptr<Wrapper> wrapper(wrapperPtr);
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func(std::move(wrapper->data));
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});
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}
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private:
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struct Wrapper {
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explicit Wrapper(T&& t) : data(std::move(t)) {}
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AtomicIntrusiveLinkedListHook<Wrapper> hook;
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T data;
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};
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AtomicIntrusiveLinkedList<Wrapper, &Wrapper::hook> list_;
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};
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} // namespace folly
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