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#![cfg_attr(feature = "const_mut_refs", feature(const_mut_refs))]
#![cfg_attr(
feature = "alloc_ref",
feature(allocator_api, alloc_layout_extra, nonnull_slice_from_raw_parts)
)]
#![no_std]
#[cfg(test)]
#[macro_use]
extern crate std;
#[cfg(feature = "use_spin")]
extern crate spinning_top;
#[cfg(feature = "use_spin")]
use core::alloc::GlobalAlloc;
use core::alloc::Layout;
#[cfg(feature = "alloc_ref")]
use core::alloc::{AllocError, Allocator};
use core::convert::TryInto;
use core::mem::MaybeUninit;
#[cfg(feature = "use_spin")]
use core::ops::Deref;
use core::ptr::NonNull;
#[cfg(test)]
use hole::Hole;
use hole::HoleList;
#[cfg(feature = "use_spin")]
use spinning_top::Spinlock;
pub mod hole;
#[cfg(test)]
mod test;
/// A fixed size heap backed by a linked list of free memory blocks.
pub struct Heap {
bottom: *mut u8,
size: usize,
used: usize,
holes: HoleList,
}
unsafe impl Send for Heap {}
impl Heap {
/// Creates an empty heap. All allocate calls will return `None`.
#[cfg(not(feature = "const_mut_refs"))]
pub fn empty() -> Heap {
Heap {
bottom: core::ptr::null_mut(),
size: 0,
used: 0,
holes: HoleList::empty(),
}
}
#[cfg(feature = "const_mut_refs")]
pub const fn empty() -> Heap {
Heap {
bottom: core::ptr::null_mut(),
size: 0,
used: 0,
holes: HoleList::empty(),
}
}
/// Initializes an empty heap
///
/// # Safety
///
/// This function must be called at most once and must only be used on an
/// empty heap.
///
/// The bottom address must be valid and the memory in the
/// `[heap_bottom, heap_bottom + heap_size)` range must not be used for anything else.
/// This function is unsafe because it can cause undefined behavior if the given address
/// is invalid.
///
/// The provided memory range must be valid for the `'static` lifetime.
pub unsafe fn init(&mut self, heap_bottom: *mut u8, heap_size: usize) {
self.bottom = heap_bottom;
self.size = heap_size;
self.used = 0;
self.holes = HoleList::new(heap_bottom, heap_size);
}
/// Initialize an empty heap with provided memory.
///
/// The caller is responsible for procuring a region of raw memory that may be utilized by the
/// allocator. This might be done via any method such as (unsafely) taking a region from the
/// program's memory, from a mutable static, or by allocating and leaking such memory from
/// another allocator.
///
/// The latter method may be especially useful if the underlying allocator does not perform
/// deallocation (e.g. a simple bump allocator). Then the overlaid linked-list-allocator can
/// provide memory reclamation.
///
/// # Panics
///
/// This method panics if the heap is already initialized.
pub fn init_from_slice(&mut self, mem: &'static mut [MaybeUninit<u8>]) {
assert!(
self.bottom.is_null(),
"The heap has already been initialized."
);
let size = mem.len();
let address = mem.as_mut_ptr().cast();
// SAFETY: All initialization requires the bottom address to be valid, which implies it
// must not be 0. Initially the address is 0. The assertion above ensures that no
// initialization had been called before.
// The given address and size is valid according to the safety invariants of the mutable
// reference handed to us by the caller.
unsafe { self.init(address, size) }
}
/// Creates a new heap with the given `bottom` and `size`.
///
/// # Safety
///
/// The bottom address must be valid and the memory in the
/// `[heap_bottom, heap_bottom + heap_size)` range must not be used for anything else.
/// This function is unsafe because it can cause undefined behavior if the given address
/// is invalid.
///
/// The provided memory range must be valid for the `'static` lifetime.
pub unsafe fn new(heap_bottom: *mut u8, heap_size: usize) -> Heap {
if heap_size < HoleList::min_size() {
Self::empty()
} else {
Heap {
bottom: heap_bottom,
size: heap_size,
used: 0,
holes: HoleList::new(heap_bottom, heap_size),
}
}
}
/// Creates a new heap from a slice of raw memory.
///
/// This has the same effect as [`init_from_slice`] on an empty heap, but it is combined into a
/// single operation that can not panic.
pub fn from_slice(mem: &'static mut [MaybeUninit<u8>]) -> Heap {
let size = mem.len();
let address = mem.as_mut_ptr().cast();
// SAFETY: The given address and size is valid according to the safety invariants of the
// mutable reference handed to us by the caller.
unsafe { Self::new(address, size) }
}
/// Allocates a chunk of the given size with the given alignment. Returns a pointer to the
/// beginning of that chunk if it was successful. Else it returns `None`.
/// This function scans the list of free memory blocks and uses the first block that is big
/// enough. The runtime is in O(n) where n is the number of free blocks, but it should be
/// reasonably fast for small allocations.
//
// NOTE: We could probably replace this with an `Option` instead of a `Result` in a later
// release to remove this clippy warning
#[allow(clippy::result_unit_err)]
pub fn allocate_first_fit(&mut self, layout: Layout) -> Result<NonNull<u8>, ()> {
match self.holes.allocate_first_fit(layout) {
Ok((ptr, aligned_layout)) => {
self.used += aligned_layout.size();
Ok(ptr)
}
Err(err) => Err(err),
}
}
/// Frees the given allocation. `ptr` must be a pointer returned
/// by a call to the `allocate_first_fit` function with identical size and alignment.
///
/// This function walks the list of free memory blocks and inserts the freed block at the
/// correct place. If the freed block is adjacent to another free block, the blocks are merged
/// again. This operation is in `O(n)` since the list needs to be sorted by address.
///
/// # Safety
///
/// `ptr` must be a pointer returned by a call to the [`allocate_first_fit`] function with
/// identical layout. Undefined behavior may occur for invalid arguments.
pub unsafe fn deallocate(&mut self, ptr: NonNull<u8>, layout: Layout) {
self.used -= self.holes.deallocate(ptr, layout).size();
}
/// Returns the bottom address of the heap.
pub fn bottom(&self) -> *mut u8 {
self.bottom
}
/// Returns the size of the heap.
pub fn size(&self) -> usize {
self.size
}
/// Return the top address of the heap
pub fn top(&self) -> *mut u8 {
self.bottom.wrapping_add(self.size)
}
/// Returns the size of the used part of the heap
pub fn used(&self) -> usize {
self.used
}
/// Returns the size of the free part of the heap
pub fn free(&self) -> usize {
self.size - self.used
}
/// Extends the size of the heap by creating a new hole at the end
///
/// # Safety
///
/// The amount of data given in `by` MUST exist directly after the original
/// range of data provided when constructing the [Heap]. The additional data
/// must have the same lifetime of the original range of data.
pub unsafe fn extend(&mut self, by: usize) {
let top = self.top();
let layout = Layout::from_size_align(by, 1).unwrap();
self.holes
.deallocate(NonNull::new_unchecked(top as *mut u8), layout);
self.size += by;
}
}
#[cfg(all(feature = "alloc_ref", feature = "use_spin"))]
unsafe impl Allocator for LockedHeap {
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
if layout.size() == 0 {
return Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0));
}
match self.0.lock().allocate_first_fit(layout) {
Ok(ptr) => Ok(NonNull::slice_from_raw_parts(ptr, layout.size())),
Err(()) => Err(AllocError),
}
}
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
if layout.size() != 0 {
self.0.lock().deallocate(ptr, layout);
}
}
}
#[cfg(feature = "use_spin")]
pub struct LockedHeap(Spinlock<Heap>);
#[cfg(feature = "use_spin")]
impl LockedHeap {
/// Creates an empty heap. All allocate calls will return `None`.
#[cfg(feature = "use_spin_nightly")]
pub const fn empty() -> LockedHeap {
LockedHeap(Spinlock::new(Heap::empty()))
}
/// Creates an empty heap. All allocate calls will return `None`.
#[cfg(not(feature = "use_spin_nightly"))]
pub fn empty() -> LockedHeap {
LockedHeap(Spinlock::new(Heap::empty()))
}
/// Creates a new heap with the given `bottom` and `size`.
///
/// # Safety
///
/// The bottom address must be valid and the memory in the
/// `[heap_bottom, heap_bottom + heap_size)` range must not be used for anything else.
/// This function is unsafe because it can cause undefined behavior if the given address
/// is invalid.
///
/// The provided memory range must be valid for the `'static` lifetime.
pub unsafe fn new(heap_bottom: *mut u8, heap_size: usize) -> LockedHeap {
LockedHeap(Spinlock::new(Heap {
bottom: heap_bottom,
size: heap_size,
used: 0,
holes: HoleList::new(heap_bottom, heap_size),
}))
}
}
#[cfg(feature = "use_spin")]
impl Deref for LockedHeap {
type Target = Spinlock<Heap>;
fn deref(&self) -> &Spinlock<Heap> {
&self.0
}
}
#[cfg(feature = "use_spin")]
unsafe impl GlobalAlloc for LockedHeap {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
self.0
.lock()
.allocate_first_fit(layout)
.ok()
.map_or(core::ptr::null_mut(), |allocation| allocation.as_ptr())
}
unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
self.0
.lock()
.deallocate(NonNull::new_unchecked(ptr), layout)
}
}
/// Align downwards. Returns the greatest x with alignment `align`
/// so that x <= addr. The alignment must be a power of 2.
pub fn align_down_size(size: usize, align: usize) -> usize {
if align.is_power_of_two() {
size & !(align - 1)
} else if align == 0 {
size
} else {
panic!("`align` must be a power of 2");
}
}
pub fn align_up_size(size: usize, align: usize) -> usize {
align_down_size(size + align - 1, align)
}
/// Align upwards. Returns the smallest x with alignment `align`
/// so that x >= addr. The alignment must be a power of 2.
pub fn align_up(addr: *mut u8, align: usize) -> *mut u8 {
let offset = addr.align_offset(align);
addr.wrapping_offset(offset.try_into().unwrap())
}