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// only used on Linux right now, so allow dead code elsewhere
#![cfg_attr(not(target_os = "linux"), allow(dead_code))]
use super::Mmap;
use alloc::vec;
use alloc::vec::Vec;
use core::cell::UnsafeCell;
/// A simple arena allocator for byte buffers.
pub struct Stash {
buffers: UnsafeCell<Vec<Vec<u8>>>,
mmap_aux: UnsafeCell<Option<Mmap>>,
}
impl Stash {
pub fn new() -> Stash {
Stash {
buffers: UnsafeCell::new(Vec::new()),
mmap_aux: UnsafeCell::new(None),
}
}
/// Allocates a buffer of the specified size and returns a mutable reference
/// to it.
pub fn allocate(&self, size: usize) -> &mut [u8] {
// SAFETY: this is the only function that ever constructs a mutable
// reference to `self.buffers`.
let buffers = unsafe { &mut *self.buffers.get() };
let i = buffers.len();
buffers.push(vec![0; size]);
// SAFETY: we never remove elements from `self.buffers`, so a reference
// to the data inside any buffer will live as long as `self` does.
&mut buffers[i]
}
/// Stores a `Mmap` for the lifetime of this `Stash`, returning a pointer
/// which is scoped to just this lifetime.
pub fn set_mmap_aux(&self, map: Mmap) -> &[u8] {
// SAFETY: this is the only location for a mutable pointer to
// `mmap_aux`, and this structure isn't threadsafe to shared across
// threads either. This also is careful to store at most one `mmap_aux`
// since overwriting a previous one would invalidate the previous
// pointer. Given that though we can safely return a pointer to our
// interior-owned contents.
unsafe {
let mmap_aux = &mut *self.mmap_aux.get();
assert!(mmap_aux.is_none());
*mmap_aux = Some(map);
mmap_aux.as_ref().unwrap()
}
}
}
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