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https://github.com/RGBCube/serenity
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1cca5142af
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 PTY'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 :^)
59 lines
1.7 KiB
C++
59 lines
1.7 KiB
C++
#include <Kernel/DoubleBuffer.h>
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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))
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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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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 u8* data, ssize_t size)
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{
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if (!size)
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return 0;
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LOCKER(m_lock);
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ASSERT(size <= (ssize_t)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 += size;
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compute_lockfree_metadata();
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memcpy(write_ptr, data, size);
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return size;
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}
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ssize_t DoubleBuffer::read(u8* data, ssize_t size)
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{
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if (!size)
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return 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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ssize_t nread = min((ssize_t)m_read_buffer->size - (ssize_t)m_read_buffer_index, size);
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memcpy(data, m_read_buffer->data + m_read_buffer_index, nread);
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m_read_buffer_index += nread;
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compute_lockfree_metadata();
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return nread;
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}
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