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