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Serenity Operating System
1/*
2 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 *
8 * 1. Redistributions of source code must retain the above copyright notice, this
9 * list of conditions and the following disclaimer.
10 *
11 * 2. Redistributions in binary form must reproduce the above copyright notice,
12 * this list of conditions and the following disclaimer in the documentation
13 * and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
23 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
24 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#pragma once
28
29#include <AK/Types.h>
30#include <Kernel/KBuffer.h>
31#include <Kernel/Lock.h>
32
33namespace Kernel {
34
35class DoubleBuffer {
36public:
37 explicit DoubleBuffer(size_t capacity = 65536);
38
39 ssize_t write(const u8*, ssize_t);
40 ssize_t read(u8*, ssize_t);
41
42 bool is_empty() const { return m_empty; }
43
44 size_t space_for_writing() const { return m_space_for_writing; }
45
46private:
47 void flip();
48 void compute_lockfree_metadata();
49
50 struct InnerBuffer {
51 u8* data { nullptr };
52 size_t size;
53 };
54
55 InnerBuffer* m_write_buffer { nullptr };
56 InnerBuffer* m_read_buffer { nullptr };
57 InnerBuffer m_buffer1;
58 InnerBuffer m_buffer2;
59
60 KBuffer m_storage;
61 size_t m_capacity { 0 };
62 size_t m_read_buffer_index { 0 };
63 size_t m_space_for_writing { 0 };
64 bool m_empty { true };
65 mutable Lock m_lock { "DoubleBuffer" };
66};
67
68}