329 lines
12 KiB
Rust
329 lines
12 KiB
Rust
use std::{
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fmt::Debug,
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iter::Sum,
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ops::{Add, AddAssign, Range, Sub},
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};
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#[derive(Debug)]
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pub struct RangeAllocator<T> {
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/// The range this allocator covers.
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initial_range: Range<T>,
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/// A Vec of ranges in this heap which are unused.
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/// Must be ordered with ascending range start to permit short circuiting allocation.
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/// No two ranges in this vec may overlap.
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free_ranges: Vec<Range<T>>,
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}
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#[derive(Clone, Debug, PartialEq)]
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pub struct RangeAllocationError<T> {
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pub fragmented_free_length: T,
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}
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impl<T> RangeAllocator<T>
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where
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T: Clone + Copy + Add<Output = T> + AddAssign + Sub<Output = T> + Eq + PartialOrd + Debug,
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{
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pub fn new(range: Range<T>) -> Self {
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RangeAllocator {
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initial_range: range.clone(),
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free_ranges: vec![range],
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}
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}
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pub fn initial_range(&self) -> &Range<T> {
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&self.initial_range
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}
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pub fn grow_to(&mut self, new_end: T) {
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if let Some(last_range) = self.free_ranges.last_mut() {
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last_range.end = new_end;
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} else {
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self.free_ranges.push(self.initial_range.end..new_end);
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}
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self.initial_range.end = new_end;
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}
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pub fn allocate_range(&mut self, length: T) -> Result<Range<T>, RangeAllocationError<T>> {
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assert_ne!(length + length, length);
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let mut best_fit: Option<(usize, Range<T>)> = None;
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// This is actually correct. With the trait bound as it is, we have
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// no way to summon a value of 0 directly, so we make one by subtracting
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// something from itself. Once the trait bound can be changed, this can
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// be fixed.
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#[allow(clippy::eq_op)]
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let mut fragmented_free_length = length - length;
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for (index, range) in self.free_ranges.iter().cloned().enumerate() {
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let range_length = range.end - range.start;
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fragmented_free_length += range_length;
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if range_length < length {
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continue;
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} else if range_length == length {
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// Found a perfect fit, so stop looking.
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best_fit = Some((index, range));
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break;
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}
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best_fit = Some(match best_fit {
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Some((best_index, best_range)) => {
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// Find best fit for this allocation to reduce memory fragmentation.
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if range_length < best_range.end - best_range.start {
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(index, range)
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} else {
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(best_index, best_range.clone())
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}
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}
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None => (index, range),
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});
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}
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match best_fit {
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Some((index, range)) => {
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if range.end - range.start == length {
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self.free_ranges.remove(index);
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} else {
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self.free_ranges[index].start += length;
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}
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Ok(range.start..(range.start + length))
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}
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None => Err(RangeAllocationError {
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fragmented_free_length,
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}),
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}
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}
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pub fn free_range(&mut self, range: Range<T>) {
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assert!(self.initial_range.start <= range.start && range.end <= self.initial_range.end);
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assert!(range.start < range.end);
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// Get insertion position.
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let i = self
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.free_ranges
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.iter()
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.position(|r| r.start > range.start)
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.unwrap_or(self.free_ranges.len());
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// Try merging with neighboring ranges in the free list.
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// Before: |left|-(range)-|right|
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if i > 0 && range.start == self.free_ranges[i - 1].end {
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// Merge with |left|.
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self.free_ranges[i - 1].end =
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if i < self.free_ranges.len() && range.end == self.free_ranges[i].start {
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// Check for possible merge with |left| and |right|.
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let right = self.free_ranges.remove(i);
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right.end
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} else {
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range.end
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};
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return;
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} else if i < self.free_ranges.len() && range.end == self.free_ranges[i].start {
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// Merge with |right|.
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self.free_ranges[i].start = if i > 0 && range.start == self.free_ranges[i - 1].end {
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// Check for possible merge with |left| and |right|.
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let left = self.free_ranges.remove(i - 1);
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left.start
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} else {
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range.start
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};
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return;
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}
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// Debug checks
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assert!(
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(i == 0 || self.free_ranges[i - 1].end < range.start)
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&& (i >= self.free_ranges.len() || range.end < self.free_ranges[i].start)
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);
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self.free_ranges.insert(i, range);
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}
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/// Returns an iterator over allocated non-empty ranges
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pub fn allocated_ranges(&self) -> impl Iterator<Item = Range<T>> + '_ {
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let first = match self.free_ranges.first() {
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Some(Range { ref start, .. }) if *start > self.initial_range.start => {
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Some(self.initial_range.start..*start)
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}
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None => Some(self.initial_range.clone()),
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_ => None,
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};
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let last = match self.free_ranges.last() {
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Some(Range { end, .. }) if *end < self.initial_range.end => {
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Some(*end..self.initial_range.end)
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}
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_ => None,
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};
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let mid = self
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.free_ranges
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.iter()
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.zip(self.free_ranges.iter().skip(1))
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.map(|(ra, rb)| ra.end..rb.start);
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first.into_iter().chain(mid).chain(last)
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}
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pub fn reset(&mut self) {
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self.free_ranges.clear();
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self.free_ranges.push(self.initial_range.clone());
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}
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pub fn is_empty(&self) -> bool {
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self.free_ranges.len() == 1 && self.free_ranges[0] == self.initial_range
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}
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}
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impl<T: Copy + Sub<Output = T> + Sum> RangeAllocator<T> {
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pub fn total_available(&self) -> T {
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self.free_ranges
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.iter()
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.map(|range| range.end - range.start)
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.sum()
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_basic_allocation() {
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let mut alloc = RangeAllocator::new(0..10);
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// Test if an allocation works
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assert_eq!(alloc.allocate_range(4), Ok(0..4));
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assert!(alloc.allocated_ranges().eq(std::iter::once(0..4)));
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// Free the prior allocation
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alloc.free_range(0..4);
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// Make sure the free actually worked
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assert_eq!(alloc.free_ranges, vec![0..10]);
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assert!(alloc.allocated_ranges().eq(std::iter::empty()));
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}
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#[test]
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fn test_out_of_space() {
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let mut alloc = RangeAllocator::new(0..10);
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// Test if the allocator runs out of space correctly
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assert_eq!(alloc.allocate_range(10), Ok(0..10));
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assert!(alloc.allocated_ranges().eq(std::iter::once(0..10)));
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assert!(alloc.allocate_range(4).is_err());
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alloc.free_range(0..10);
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}
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#[test]
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fn test_grow() {
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let mut alloc = RangeAllocator::new(0..11);
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// Test if the allocator runs out of space correctly
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assert_eq!(alloc.allocate_range(10), Ok(0..10));
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assert!(alloc.allocated_ranges().eq(std::iter::once(0..10)));
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assert!(alloc.allocate_range(4).is_err());
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alloc.grow_to(20);
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assert_eq!(alloc.allocate_range(4), Ok(10..14));
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alloc.free_range(0..14);
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}
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#[test]
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fn test_dont_use_block_that_is_too_small() {
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let mut alloc = RangeAllocator::new(0..10);
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// Allocate three blocks then free the middle one and check for correct state
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assert_eq!(alloc.allocate_range(3), Ok(0..3));
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assert_eq!(alloc.allocate_range(3), Ok(3..6));
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assert_eq!(alloc.allocate_range(3), Ok(6..9));
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alloc.free_range(3..6);
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assert_eq!(alloc.free_ranges, vec![3..6, 9..10]);
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assert_eq!(
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alloc.allocated_ranges().collect::<Vec<Range<i32>>>(),
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vec![0..3, 6..9]
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);
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// Now request space that the middle block can fill, but the end one can't.
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assert_eq!(alloc.allocate_range(3), Ok(3..6));
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}
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#[test]
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fn test_free_blocks_in_middle() {
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let mut alloc = RangeAllocator::new(0..100);
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// Allocate many blocks then free every other block.
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assert_eq!(alloc.allocate_range(10), Ok(0..10));
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assert_eq!(alloc.allocate_range(10), Ok(10..20));
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assert_eq!(alloc.allocate_range(10), Ok(20..30));
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assert_eq!(alloc.allocate_range(10), Ok(30..40));
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assert_eq!(alloc.allocate_range(10), Ok(40..50));
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assert_eq!(alloc.allocate_range(10), Ok(50..60));
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assert_eq!(alloc.allocate_range(10), Ok(60..70));
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assert_eq!(alloc.allocate_range(10), Ok(70..80));
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assert_eq!(alloc.allocate_range(10), Ok(80..90));
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assert_eq!(alloc.allocate_range(10), Ok(90..100));
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assert_eq!(alloc.free_ranges, vec![]);
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assert!(alloc.allocated_ranges().eq(std::iter::once(0..100)));
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alloc.free_range(10..20);
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alloc.free_range(30..40);
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alloc.free_range(50..60);
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alloc.free_range(70..80);
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alloc.free_range(90..100);
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// Check that the right blocks were freed.
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assert_eq!(
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alloc.free_ranges,
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vec![10..20, 30..40, 50..60, 70..80, 90..100]
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);
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assert_eq!(
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alloc.allocated_ranges().collect::<Vec<Range<i32>>>(),
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vec![0..10, 20..30, 40..50, 60..70, 80..90]
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);
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// Fragment the memory on purpose a bit.
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assert_eq!(alloc.allocate_range(6), Ok(10..16));
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assert_eq!(alloc.allocate_range(6), Ok(30..36));
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assert_eq!(alloc.allocate_range(6), Ok(50..56));
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assert_eq!(alloc.allocate_range(6), Ok(70..76));
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assert_eq!(alloc.allocate_range(6), Ok(90..96));
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// Check for fragmentation.
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assert_eq!(
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alloc.free_ranges,
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vec![16..20, 36..40, 56..60, 76..80, 96..100]
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);
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assert_eq!(
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alloc.allocated_ranges().collect::<Vec<Range<i32>>>(),
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vec![0..16, 20..36, 40..56, 60..76, 80..96]
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);
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// Fill up the fragmentation
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assert_eq!(alloc.allocate_range(4), Ok(16..20));
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assert_eq!(alloc.allocate_range(4), Ok(36..40));
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assert_eq!(alloc.allocate_range(4), Ok(56..60));
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assert_eq!(alloc.allocate_range(4), Ok(76..80));
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assert_eq!(alloc.allocate_range(4), Ok(96..100));
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// Check that nothing is free.
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assert_eq!(alloc.free_ranges, vec![]);
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assert!(alloc.allocated_ranges().eq(std::iter::once(0..100)));
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}
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#[test]
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fn test_ignore_block_if_another_fits_better() {
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let mut alloc = RangeAllocator::new(0..10);
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// Allocate blocks such that the only free spaces available are 3..6 and 9..10
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// in order to prepare for the next test.
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assert_eq!(alloc.allocate_range(3), Ok(0..3));
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assert_eq!(alloc.allocate_range(3), Ok(3..6));
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assert_eq!(alloc.allocate_range(3), Ok(6..9));
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alloc.free_range(3..6);
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assert_eq!(alloc.free_ranges, vec![3..6, 9..10]);
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assert_eq!(
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alloc.allocated_ranges().collect::<Vec<Range<i32>>>(),
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vec![0..3, 6..9]
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);
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// Now request space that can be filled by 3..6 but should be filled by 9..10
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// because 9..10 is a perfect fit.
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assert_eq!(alloc.allocate_range(1), Ok(9..10));
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}
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#[test]
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fn test_merge_neighbors() {
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let mut alloc = RangeAllocator::new(0..9);
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assert_eq!(alloc.allocate_range(3), Ok(0..3));
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assert_eq!(alloc.allocate_range(3), Ok(3..6));
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assert_eq!(alloc.allocate_range(3), Ok(6..9));
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alloc.free_range(0..3);
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alloc.free_range(6..9);
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alloc.free_range(3..6);
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assert_eq!(alloc.free_ranges, vec![0..9]);
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assert!(alloc.allocated_ranges().eq(std::iter::empty()));
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}
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}
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