diff options
Diffstat (limited to 'Kernel/Library/DoubleBuffer.cpp')
-rw-r--r-- | Kernel/Library/DoubleBuffer.cpp | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/Kernel/Library/DoubleBuffer.cpp b/Kernel/Library/DoubleBuffer.cpp new file mode 100644 index 0000000000..b0624acaff --- /dev/null +++ b/Kernel/Library/DoubleBuffer.cpp @@ -0,0 +1,93 @@ +/* + * 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); +} + +} |