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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/StringView.h>
#include <Kernel/InterruptDisabler.h>
#include <Kernel/Library/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;
}
ErrorOr<NonnullOwnPtr<DoubleBuffer>> DoubleBuffer::try_create(StringView name, size_t capacity)
{
auto storage = TRY(KBuffer::try_create_with_size(name, capacity * 2, Memory::Region::Access::ReadWrite));
return adopt_nonnull_own_or_enomem(new (nothrow) DoubleBuffer(capacity, move(storage)));
}
DoubleBuffer::DoubleBuffer(size_t capacity, NonnullOwnPtr<KBuffer> storage)
: m_write_buffer(&m_buffer1)
, m_read_buffer(&m_buffer2)
, m_storage(move(storage))
, 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()
{
VERIFY(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();
}
ErrorOr<size_t> DoubleBuffer::write(UserOrKernelBuffer const& data, size_t size)
{
if (!size)
return 0;
MutexLocker locker(m_lock);
size_t bytes_to_write = min(size, m_space_for_writing);
u8* write_ptr = m_write_buffer->data + m_write_buffer->size;
TRY(data.read(write_ptr, bytes_to_write));
m_write_buffer->size += bytes_to_write;
compute_lockfree_metadata();
if (m_unblock_callback && !m_empty)
m_unblock_callback();
return bytes_to_write;
}
ErrorOr<size_t> DoubleBuffer::read_impl(UserOrKernelBuffer& data, size_t size, MutexLocker&, bool advance_buffer_index)
{
if (size == 0)
return 0;
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;
size_t nread = min(m_read_buffer->size - m_read_buffer_index, size);
TRY(data.write(m_read_buffer->data + m_read_buffer_index, nread));
if (advance_buffer_index)
m_read_buffer_index += nread;
compute_lockfree_metadata();
if (m_unblock_callback && m_space_for_writing > 0)
m_unblock_callback();
return nread;
}
ErrorOr<size_t> DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
{
MutexLocker locker(m_lock);
return read_impl(data, size, locker, true);
}
ErrorOr<size_t> DoubleBuffer::peek(UserOrKernelBuffer& data, size_t size)
{
MutexLocker locker(m_lock);
return read_impl(data, size, locker, false);
}
}
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