| // 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() |
| } |
| } |
| } |