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f4f958f99f
Background: DoubleBuffer is a handy buffer class in the kernel that allows you to keep writing to it from the "outside" while the "inside" reads from it. It's used for things like LocalSocket and TTY's. Internally, it has a read buffer and a write buffer, but the two will swap places when the read buffer is exhausted (by reading from it.) Before this patch, it was internally implemented as two Vector<u8> that we would swap between when the reader side had exhausted the data in the read buffer. Now instead we preallocate a large KBuffer (64KB*2) on DoubleBuffer construction and use that throughout its lifetime. This removes all the kmalloc heap traffic caused by DoubleBuffers :^)
65 lines
2.2 KiB
C++
65 lines
2.2 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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#pragma once
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#include <AK/Types.h>
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#include <Kernel/KBuffer.h>
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#include <Kernel/Lock.h>
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class DoubleBuffer {
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public:
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explicit DoubleBuffer(size_t capacity = 65536);
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ssize_t write(const u8*, ssize_t);
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ssize_t read(u8*, ssize_t);
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bool is_empty() const { return m_empty; }
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size_t space_for_writing() const { return m_space_for_writing; }
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private:
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void flip();
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void compute_lockfree_metadata();
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struct InnerBuffer {
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u8* data { nullptr };
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size_t size;
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};
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InnerBuffer* m_write_buffer { nullptr };
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InnerBuffer* m_read_buffer { nullptr };
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InnerBuffer m_buffer1;
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InnerBuffer m_buffer2;
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KBuffer m_storage;
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size_t m_capacity { 0 };
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size_t m_read_buffer_index { 0 };
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size_t m_space_for_writing { 0 };
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bool m_empty { true };
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mutable Lock m_lock { "DoubleBuffer" };
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};
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