1#![allow(clippy::all)]
2// only used on Linux right now, so allow dead code elsewhere
3#![cfg_attr(not(target_os = "linux"), allow(dead_code))]
4
5use super::Mmap;
6use alloc::vec;
7use alloc::vec::Vec;
8use core::cell::UnsafeCell;
9
10/// A simple arena allocator for byte buffers.
11pub struct Stash {
12 buffers: UnsafeCell<Vec<Vec<u8>>>,
13 mmaps: UnsafeCell<Vec<Mmap>>,
14}
15
16impl Stash {
17 pub fn new() -> Stash {
18 Stash {
19 buffers: UnsafeCell::new(Vec::new()),
20 mmaps: UnsafeCell::new(Vec::new()),
21 }
22 }
23
24 /// Allocates a buffer of the specified size and returns a mutable reference
25 /// to it.
26 pub fn allocate(&self, size: usize) -> &mut [u8] {
27 // SAFETY: this is the only function that ever constructs a mutable
28 // reference to `self.buffers`.
29 let buffers = unsafe { &mut *self.buffers.get() };
30 let i = buffers.len();
31 buffers.push(vec![0; size]);
32 // SAFETY: we never remove elements from `self.buffers`, so a reference
33 // to the data inside any buffer will live as long as `self` does.
34 &mut buffers[i]
35 }
36
37 /// Stores a `Mmap` for the lifetime of this `Stash`, returning a pointer
38 /// which is scoped to just this lifetime.
39 pub fn cache_mmap(&self, map: Mmap) -> &[u8] {
40 // SAFETY: this is the only location for a mutable pointer to
41 // `mmaps`, and this structure isn't threadsafe to shared across
42 // threads either. We also never remove elements from `self.mmaps`,
43 // so a reference to the data inside the map will live as long as
44 // `self` does.
45 unsafe {
46 let mmaps = &mut *self.mmaps.get();
47 mmaps.push(map);
48 mmaps.last().unwrap()
49 }
50 }
51}
52