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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <AK/StringView.h>
#include <Kernel/DoubleBuffer.h>
namespace Kernel {
inline void DoubleBuffer::compute_lockfree_metadata()
{
InterruptDisabler disabler;
m_empty = m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size == 0;
m_space_for_writing = m_capacity - m_write_buffer->size;
}
DoubleBuffer::DoubleBuffer(size_t capacity)
: m_write_buffer(&m_buffer1)
, m_read_buffer(&m_buffer2)
, m_storage(KBuffer::create_with_size(capacity * 2, Region::Access::Read | Region::Access::Write, "DoubleBuffer"))
, m_capacity(capacity)
{
m_buffer1.data = m_storage.data();
m_buffer1.size = 0;
m_buffer2.data = m_storage.data() + capacity;
m_buffer2.size = 0;
m_space_for_writing = capacity;
}
void DoubleBuffer::flip()
{
ASSERT(m_read_buffer_index == m_read_buffer->size);
swap(m_read_buffer, m_write_buffer);
m_write_buffer->size = 0;
m_read_buffer_index = 0;
compute_lockfree_metadata();
}
ssize_t DoubleBuffer::write(const u8* data, ssize_t size)
{
if (!size)
return 0;
ASSERT(size > 0);
LOCKER(m_lock);
ssize_t bytes_to_write = min(static_cast<size_t>(size), m_space_for_writing);
u8* write_ptr = m_write_buffer->data + m_write_buffer->size;
m_write_buffer->size += bytes_to_write;
compute_lockfree_metadata();
memcpy(write_ptr, data, bytes_to_write);
return bytes_to_write;
}
ssize_t DoubleBuffer::read(u8* data, ssize_t size)
{
if (!size)
return 0;
ASSERT(size > 0);
LOCKER(m_lock);
if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0)
flip();
if (m_read_buffer_index >= m_read_buffer->size)
return 0;
ssize_t nread = min((ssize_t)m_read_buffer->size - (ssize_t)m_read_buffer_index, size);
memcpy(data, m_read_buffer->data + m_read_buffer_index, nread);
m_read_buffer_index += nread;
compute_lockfree_metadata();
return nread;
}
}
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