50 lines
1.7 KiB
Rust
50 lines
1.7 KiB
Rust
// only used on Linux right now, so allow dead code elsewhere
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#![cfg_attr(not(target_os = "linux"), allow(dead_code))]
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use super::Mmap;
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use alloc::vec;
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use alloc::vec::Vec;
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use core::cell::UnsafeCell;
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/// A simple arena allocator for byte buffers.
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pub struct Stash {
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buffers: UnsafeCell<Vec<Vec<u8>>>,
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mmaps: UnsafeCell<Vec<Mmap>>,
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}
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impl Stash {
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pub fn new() -> Stash {
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Stash {
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buffers: UnsafeCell::new(Vec::new()),
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mmaps: UnsafeCell::new(Vec::new()),
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}
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}
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/// Allocates a buffer of the specified size and returns a mutable reference
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/// to it.
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pub fn allocate(&self, size: usize) -> &mut [u8] {
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// SAFETY: this is the only function that ever constructs a mutable
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// reference to `self.buffers`.
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let buffers = unsafe { &mut *self.buffers.get() };
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let i = buffers.len();
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buffers.push(vec![0; size]);
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// SAFETY: we never remove elements from `self.buffers`, so a reference
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// to the data inside any buffer will live as long as `self` does.
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&mut buffers[i]
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}
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/// Stores a `Mmap` for the lifetime of this `Stash`, returning a pointer
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/// which is scoped to just this lifetime.
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pub fn cache_mmap(&self, map: Mmap) -> &[u8] {
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// SAFETY: this is the only location for a mutable pointer to
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// `mmaps`, and this structure isn't threadsafe to shared across
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// threads either. We also never remove elements from `self.mmaps`,
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// so a reference to the data inside the map will live as long as
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// `self` does.
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unsafe {
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let mmaps = &mut *self.mmaps.get();
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mmaps.push(map);
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mmaps.last().unwrap()
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}
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}
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}
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