67 lines
2.1 KiB
Rust
67 lines
2.1 KiB
Rust
//! Flyweight pattern implementation for messages to and from the media driver.
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use crate::concurrent::AtomicBuffer;
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use crate::util::{IndexT, Result};
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use std::marker::PhantomData;
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/// Flyweight holder object. Wrapper around an underlying `AtomicBuffer` and
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/// offset within that buffer that all future operations are relative to.
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pub struct Flyweight<A, S>
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where
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A: AtomicBuffer,
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{
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pub(in crate::command) buffer: A,
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base_offset: IndexT,
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_phantom: PhantomData<S>,
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}
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/// Marker struct.
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// We can't put this `new` method in the fully generic implementation because
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// Rust gets confused as to what type `S` should be.
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pub struct Unchecked;
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impl<A> Flyweight<A, Unchecked>
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where
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A: AtomicBuffer,
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{
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/// Create a new flyweight object. Performs a bounds check on initialization
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/// to ensure there is space available for `S`.
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#[allow(clippy::new_ret_no_self)]
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pub fn new<S>(buffer: A, offset: IndexT) -> Result<Flyweight<A, S>>
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where
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S: Sized,
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{
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buffer.overlay::<S>(offset)?;
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Ok(Flyweight {
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buffer,
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base_offset: offset,
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_phantom: PhantomData,
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})
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}
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}
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impl<A, S> Flyweight<A, S>
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where
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A: AtomicBuffer,
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S: Sized,
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{
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pub(crate) fn get_struct(&self) -> &S {
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// UNWRAP: Bounds check performed during initialization
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self.buffer.overlay::<S>(self.base_offset).unwrap()
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}
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pub(crate) fn get_struct_mut(&mut self) -> &mut S {
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// UNWRAP: Bounds check performed during initialization
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self.buffer.overlay_mut::<S>(self.base_offset).unwrap()
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}
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pub(crate) fn bytes_at(&self, offset: IndexT) -> &[u8] {
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let offset = (self.base_offset + offset) as usize;
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// FIXME: Unwrap is unjustified here.
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// C++ uses pointer arithmetic with no bounds checking, so I'm more comfortable
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// with the Rust version at least panicking. Is the idea that we're safe because
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// this is a crate-local (protected in C++) method?
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self.buffer.bounds_check(offset as IndexT, 0).unwrap();
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&self.buffer[offset..]
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}
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}
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