jcs.org
Serenity Operating System
1/*
2 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
3 *
4 * SPDX-License-Identifier: BSD-2-Clause
5 */
6
7#pragma once
8
9#include <AK/Assertions.h>
10#include <AK/Forward.h>
11#include <AK/StdLibExtras.h>
12
13namespace AK {
14
15template<typename T, size_t Capacity>
16class CircularQueue {
17public:
18 CircularQueue() = default;
19
20 ~CircularQueue()
21 {
22 clear();
23 }
24
25 void clear()
26 {
27 for (size_t i = 0; i < m_size; ++i)
28 elements()[(m_head + i) % Capacity].~T();
29
30 m_head = 0;
31 m_size = 0;
32 }
33
34 bool is_empty() const { return m_size == 0; }
35 size_t size() const { return m_size; }
36
37 size_t capacity() const { return Capacity; }
38
39 template<typename U = T>
40 void enqueue(U&& value)
41 {
42 auto& slot = elements()[(m_head + m_size) % Capacity];
43 if (m_size == Capacity)
44 slot.~T();
45
46 new (&slot) T(forward<U>(value));
47 if (m_size == Capacity)
48 m_head = (m_head + 1) % Capacity;
49 else
50 ++m_size;
51 }
52
53 T dequeue()
54 {
55 VERIFY(!is_empty());
56 auto& slot = elements()[m_head];
57 T value = move(slot);
58 slot.~T();
59 m_head = (m_head + 1) % Capacity;
60 --m_size;
61 return value;
62 }
63
64 T const& at(size_t index) const { return elements()[(m_head + index) % Capacity]; }
65 T& at(size_t index) { return elements()[(m_head + index) % Capacity]; }
66
67 T const& first() const { return at(0); }
68 T const& last() const { return at(size() - 1); }
69
70 class ConstIterator {
71 public:
72 bool operator!=(ConstIterator const& other) { return m_index != other.m_index; }
73 ConstIterator& operator++()
74 {
75 ++m_index;
76 return *this;
77 }
78
79 T const& operator*() const { return m_queue.at(m_index); }
80
81 private:
82 friend class CircularQueue;
83 ConstIterator(CircularQueue const& queue, const size_t index)
84 : m_queue(queue)
85 , m_index(index)
86 {
87 }
88 CircularQueue const& m_queue;
89 size_t m_index { 0 };
90 };
91
92 class Iterator {
93 public:
94 bool operator!=(Iterator const& other) { return m_index != other.m_index; }
95 Iterator& operator++()
96 {
97 ++m_index;
98 return *this;
99 }
100
101 T& operator*() const { return m_queue.at(m_index); }
102
103 private:
104 friend class CircularQueue;
105 Iterator(CircularQueue& queue, size_t const index)
106 : m_queue(queue)
107 , m_index(index)
108 {
109 }
110 CircularQueue& m_queue;
111 size_t m_index { 0 };
112 };
113
114 ConstIterator begin() const { return ConstIterator(*this, 0); }
115 ConstIterator end() const { return ConstIterator(*this, size()); }
116
117 Iterator begin() { return Iterator(*this, 0); }
118 Iterator end() { return Iterator(*this, size()); }
119
120 size_t head_index() const { return m_head; }
121
122protected:
123 T* elements() { return reinterpret_cast<T*>(m_storage); }
124 T const* elements() const { return reinterpret_cast<T const*>(m_storage); }
125
126 friend class ConstIterator;
127 alignas(T) u8 m_storage[sizeof(T) * Capacity];
128 size_t m_size { 0 };
129 size_t m_head { 0 };
130};
131
132}
133
134#if USING_AK_GLOBALLY
135using AK::CircularQueue;
136#endif