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#include <AK/StringView.h>
8#include <Kernel/DoubleBuffer.h>
9#include <Kernel/InterruptDisabler.h>
10
11namespace Kernel {
12
13inline void DoubleBuffer::compute_lockfree_metadata()
14{
15 InterruptDisabler disabler;
16 m_empty = m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size == 0;
17 m_space_for_writing = m_capacity - m_write_buffer->size;
18}
19
20ErrorOr<NonnullOwnPtr<DoubleBuffer>> DoubleBuffer::try_create(StringView name, size_t capacity)
21{
22 auto storage = TRY(KBuffer::try_create_with_size(name, capacity * 2, Memory::Region::Access::ReadWrite));
23 return adopt_nonnull_own_or_enomem(new (nothrow) DoubleBuffer(capacity, move(storage)));
24}
25
26DoubleBuffer::DoubleBuffer(size_t capacity, NonnullOwnPtr<KBuffer> storage)
27 : m_write_buffer(&m_buffer1)
28 , m_read_buffer(&m_buffer2)
29 , m_storage(move(storage))
30 , m_capacity(capacity)
31{
32 m_buffer1.data = m_storage->data();
33 m_buffer1.size = 0;
34 m_buffer2.data = m_storage->data() + capacity;
35 m_buffer2.size = 0;
36 m_space_for_writing = capacity;
37}
38
39void DoubleBuffer::flip()
40{
41 VERIFY(m_read_buffer_index == m_read_buffer->size);
42 swap(m_read_buffer, m_write_buffer);
43 m_write_buffer->size = 0;
44 m_read_buffer_index = 0;
45 compute_lockfree_metadata();
46}
47
48ErrorOr<size_t> DoubleBuffer::write(UserOrKernelBuffer const& data, size_t size)
49{
50 if (!size)
51 return 0;
52 MutexLocker locker(m_lock);
53 size_t bytes_to_write = min(size, m_space_for_writing);
54 u8* write_ptr = m_write_buffer->data + m_write_buffer->size;
55 TRY(data.read(write_ptr, bytes_to_write));
56 m_write_buffer->size += bytes_to_write;
57 compute_lockfree_metadata();
58 if (m_unblock_callback && !m_empty)
59 m_unblock_callback();
60 return bytes_to_write;
61}
62
63ErrorOr<size_t> DoubleBuffer::read_impl(UserOrKernelBuffer& data, size_t size, MutexLocker&, bool advance_buffer_index)
64{
65 if (size == 0)
66 return 0;
67 if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0)
68 flip();
69 if (m_read_buffer_index >= m_read_buffer->size)
70 return 0;
71 size_t nread = min(m_read_buffer->size - m_read_buffer_index, size);
72 TRY(data.write(m_read_buffer->data + m_read_buffer_index, nread));
73 if (advance_buffer_index)
74 m_read_buffer_index += nread;
75 compute_lockfree_metadata();
76 if (m_unblock_callback && m_space_for_writing > 0)
77 m_unblock_callback();
78 return nread;
79}
80
81ErrorOr<size_t> DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
82{
83 MutexLocker locker(m_lock);
84 return read_impl(data, size, locker, true);
85}
86
87ErrorOr<size_t> DoubleBuffer::peek(UserOrKernelBuffer& data, size_t size)
88{
89 MutexLocker locker(m_lock);
90 return read_impl(data, size, locker, false);
91}
92
93}