WangRunji
7 years ago
parent
7b57e64ff6
commit
316d32496c
@ -1,62 +0,0 @@
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use alloc::heap::{Alloc, AllocErr, Layout};
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use core::sync::atomic::{AtomicUsize, Ordering};
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/// A simple allocator that allocates memory linearly and ignores freed memory.
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#[derive(Debug)]
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pub struct BumpAllocator {
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heap_start: usize,
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heap_end: usize,
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next: AtomicUsize,
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}
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impl BumpAllocator {
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pub const fn new(heap_start: usize, heap_end: usize) -> Self {
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Self { heap_start, heap_end, next: AtomicUsize::new(heap_start) }
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}
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}
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unsafe impl<'a> Alloc for &'a BumpAllocator {
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unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
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loop {
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// load current state of the `next` field
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let current_next = self.next.load(Ordering::Relaxed);
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let alloc_start = align_up(current_next, layout.align());
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let alloc_end = alloc_start.saturating_add(layout.size());
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if alloc_end <= self.heap_end {
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// update the `next` pointer if it still has the value `current_next`
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let next_now = self.next.compare_and_swap(current_next, alloc_end,
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Ordering::Relaxed);
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if next_now == current_next {
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// next address was successfully updated, allocation succeeded
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return Ok(alloc_start as *mut u8);
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}
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} else {
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return Err(AllocErr::Exhausted{ request: layout })
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}
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}
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}
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unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
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// do nothing, leak memory
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}
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}
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/// Align downwards. Returns the greatest x with alignment `align`
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/// so that x <= addr. The alignment must be a power of 2.
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pub fn align_down(addr: usize, align: usize) -> usize {
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if align.is_power_of_two() {
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addr & !(align - 1)
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} else if align == 0 {
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addr
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} else {
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panic!("`align` must be a power of 2");
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}
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}
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/// Align upwards. Returns the smallest x with alignment `align`
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/// so that x >= addr. The alignment must be a power of 2.
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pub fn align_up(addr: usize, align: usize) -> usize {
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align_down(addr + align - 1, align)
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}
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