XeOS/src/allocator/bump.rs

62 lines
1.7 KiB
Rust

use super::{align_up, Locked};
use alloc::alloc::{GlobalAlloc, Layout};
use core::ptr;
pub struct BumpAllocator {
heap_start: usize,
heap_end: usize,
next: usize,
allocations: usize,
}
impl BumpAllocator {
/// Creates a new empty bump allocator.
pub const fn new() -> Self {
BumpAllocator {
heap_start: 0,
heap_end: 0,
next: 0,
allocations: 0,
}
}
/// Initializes the bump allocator with the given heap bounds.
///
/// This method is unsafe because the caller must ensure that the given
/// memory range is unused. Also, this method must be called only once.
pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
self.heap_start = heap_start;
self.heap_end = heap_start + heap_size;
self.next = heap_start;
}
}
unsafe impl GlobalAlloc for Locked<BumpAllocator> {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
let mut bump = self.lock(); // get a mutable reference
let alloc_start = align_up(bump.next, layout.align());
let alloc_end = match alloc_start.checked_add(layout.size()) {
Some(end) => end,
None => return ptr::null_mut(),
};
if alloc_end > bump.heap_end {
ptr::null_mut() // out of memory
} else {
bump.next = alloc_end;
bump.allocations += 1;
alloc_start as *mut u8
}
}
unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
let mut bump = self.lock(); // get a mutable reference
bump.allocations -= 1;
if bump.allocations == 0 {
bump.next = bump.heap_start;
}
}
}