bdda10a2f5
Change-Id: I2efa6f94f57e812c52371256a4e62d1d54ff5057 Reviewed-on: https://cl.tvl.fyi/c/depot/+/9925 Reviewed-by: flokli <flokli@flokli.de> Tested-by: BuildkiteCI
87 lines
2.9 KiB
Rust
87 lines
2.9 KiB
Rust
use magic_buffer::MagicBuffer;
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use std::cell::Cell;
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/// Buffer is a FIFO queue for bytes, built on a ring buffer.
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/// It always provides contiguous slices for both the readable and writable parts,
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/// using an underlying buffer that is "mirrored" in virtual memory.
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pub struct Buffer {
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buffer: MagicBuffer,
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/// first readable byte
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head: Cell<usize>,
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/// first writable byte
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tail: usize,
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}
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// SAFETY: MagicBuffer isn't bound to a thread, and neither are any of the other fields.
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// MagicBuffer ought to be Send+Sync itself, upstream PR at https://github.com/sklose/magic-buffer/pull/4
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unsafe impl Send for Buffer {}
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impl Buffer {
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/// Allocate a fresh buffer, with the specified capacity.
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/// The buffer can contain at most `capacity - 1` bytes.
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/// The capacity must be a power of two, and at least [Buffer::min_len].
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pub fn new(capacity: usize) -> Buffer {
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Buffer {
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// MagicBuffer::new verifies that `capacity` is a power of two,
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// and at least MagicBuffer::min_len().
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buffer: MagicBuffer::new(capacity).unwrap(),
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// `head == tail` means the buffer is empty.
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// In order to ensure that this remains unambiguous,
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// the buffer can only be filled with capacity-1 bytes.
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head: Cell::new(0),
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tail: 0,
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}
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}
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/// Returns the minimum buffer capacity.
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/// This depends on the operating system and architecture.
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pub fn min_capacity() -> usize {
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MagicBuffer::min_len()
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}
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/// Return the capacity of the buffer.
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/// This is equal to `self.data().len() + self.space().len() + 1`.
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pub fn capacity(&self) -> usize {
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self.buffer.len()
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}
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/// Return the valid, readable data in the buffer.
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pub fn data(&self) -> &[u8] {
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let len = self.buffer.len();
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let head = self.head.get();
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if head <= self.tail {
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&self.buffer[head..self.tail]
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} else {
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&self.buffer[head..self.tail + len]
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}
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}
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/// Mark `read_len` bytes of the readable data as consumed, freeing the space.
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pub fn consume(&self, read_len: usize) {
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debug_assert!(read_len <= self.data().len());
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let mut head = self.head.get();
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head += read_len;
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head &= self.buffer.len() - 1;
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self.head.set(head);
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}
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/// Return the empty, writable space in the buffer.
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pub fn space(&mut self) -> &mut [u8] {
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let len = self.buffer.len();
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let head = self.head.get();
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if head <= self.tail {
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&mut self.buffer[self.tail..head + len - 1]
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} else {
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&mut self.buffer[self.tail..head - 1]
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}
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}
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/// Mark `written_len` bytes of the writable space as valid, readable data.
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pub fn commit(&mut self, written_len: usize) {
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debug_assert!(written_len <= self.space().len());
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self.tail += written_len;
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self.tail &= self.buffer.len() - 1;
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}
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}
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