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f8c075f2b1
We already had head(), so let's also have tail().
95 lines
2.2 KiB
C++
95 lines
2.2 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/IntrusiveList.h>
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#include <AK/OwnPtr.h>
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#include <AK/SinglyLinkedList.h>
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#include <AK/Vector.h>
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namespace AK {
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template<typename T, int segment_size = 1000>
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class Queue {
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public:
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Queue() = default;
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~Queue()
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{
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clear();
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}
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size_t size() const { return m_size; }
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bool is_empty() const { return m_size == 0; }
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template<typename U = T>
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void enqueue(U&& value)
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{
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if (m_segments.is_empty() || m_segments.last()->data.size() >= segment_size) {
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auto segment = new QueueSegment;
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m_segments.append(*segment);
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}
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m_segments.last()->data.append(forward<U>(value));
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++m_size;
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}
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T dequeue()
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{
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VERIFY(!is_empty());
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auto value = move(m_segments.first()->data[m_index_into_first++]);
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if (m_index_into_first == segment_size) {
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delete m_segments.take_first();
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m_index_into_first = 0;
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}
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--m_size;
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if (m_size == 0 && !m_segments.is_empty()) {
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// This is not necessary for correctness but avoids faulting in
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// all the pages for the underlying Vector in the case where
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// the caller repeatedly enqueues and then dequeues a single item.
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m_index_into_first = 0;
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m_segments.last()->data.clear_with_capacity();
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}
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return value;
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}
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T const& head() const
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{
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VERIFY(!is_empty());
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return m_segments.first()->data[m_index_into_first];
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}
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T& tail()
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{
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VERIFY(!is_empty());
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return m_segments.last()->data.last();
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}
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void clear()
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{
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while (auto* segment = m_segments.take_first())
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delete segment;
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m_index_into_first = 0;
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m_size = 0;
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}
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private:
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struct QueueSegment {
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Vector<T, segment_size> data;
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IntrusiveListNode<QueueSegment> node;
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};
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IntrusiveList<&QueueSegment::node> m_segments;
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size_t m_index_into_first { 0 };
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size_t m_size { 0 };
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};
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}
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#if USING_AK_GLOBALLY
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using AK::Queue;
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#endif
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