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Diffstat (limited to 'third_party/rust/range-alloc/src/lib.rs')
| -rw-r--r-- | third_party/rust/range-alloc/src/lib.rs | 309 |
1 files changed, 309 insertions, 0 deletions
diff --git a/third_party/rust/range-alloc/src/lib.rs b/third_party/rust/range-alloc/src/lib.rs new file mode 100644 index 0000000000..e3ef81e129 --- /dev/null +++ b/third_party/rust/range-alloc/src/lib.rs @@ -0,0 +1,309 @@ +#![warn( + trivial_casts, + trivial_numeric_casts, + unused_extern_crates, + unused_import_braces, + unused_qualifications +)] + +use std::{ + fmt::Debug, + iter::Sum, + ops::{Add, AddAssign, Range, Sub}, +}; + +#[derive(Debug)] +pub struct RangeAllocator<T> { + /// The range this allocator covers. + initial_range: Range<T>, + /// A Vec of ranges in this heap which are unused. + /// Must be ordered with ascending range start to permit short circuiting allocation. + /// No two ranges in this vec may overlap. + free_ranges: Vec<Range<T>>, +} + +#[derive(Clone, Debug, PartialEq)] +pub struct RangeAllocationError<T> { + pub fragmented_free_length: T, +} + +impl<T> RangeAllocator<T> +where + T: Clone + Copy + Add<Output = T> + AddAssign + Sub<Output = T> + Eq + PartialOrd + Debug, +{ + pub fn new(range: Range<T>) -> Self { + RangeAllocator { + initial_range: range.clone(), + free_ranges: vec![range], + } + } + + pub fn initial_range(&self) -> &Range<T> { + &self.initial_range + } + + pub fn allocate_range(&mut self, length: T) -> Result<Range<T>, RangeAllocationError<T>> { + assert_ne!(length + length, length); + let mut best_fit: Option<(usize, Range<T>)> = None; + let mut fragmented_free_length = length - length; + for (index, range) in self.free_ranges.iter().cloned().enumerate() { + let range_length = range.end - range.start; + fragmented_free_length += range_length; + if range_length < length { + continue; + } else if range_length == length { + // Found a perfect fit, so stop looking. + best_fit = Some((index, range)); + break; + } + best_fit = Some(match best_fit { + Some((best_index, best_range)) => { + // Find best fit for this allocation to reduce memory fragmentation. + if range_length < best_range.end - best_range.start { + (index, range) + } else { + (best_index, best_range.clone()) + } + } + None => (index, range), + }); + } + match best_fit { + Some((index, range)) => { + if range.end - range.start == length { + self.free_ranges.remove(index); + } else { + self.free_ranges[index].start += length; + } + Ok(range.start..(range.start + length)) + } + None => Err(RangeAllocationError { + fragmented_free_length, + }), + } + } + + pub fn free_range(&mut self, range: Range<T>) { + assert!(self.initial_range.start <= range.start && range.end <= self.initial_range.end); + assert!(range.start < range.end); + + // Get insertion position. + let i = self + .free_ranges + .iter() + .position(|r| r.start > range.start) + .unwrap_or(self.free_ranges.len()); + + // Try merging with neighboring ranges in the free list. + // Before: |left|-(range)-|right| + if i > 0 && range.start == self.free_ranges[i - 1].end { + // Merge with |left|. + self.free_ranges[i - 1].end = + if i < self.free_ranges.len() && range.end == self.free_ranges[i].start { + // Check for possible merge with |left| and |right|. + let right = self.free_ranges.remove(i); + right.end + } else { + range.end + }; + + return; + } else if i < self.free_ranges.len() && range.end == self.free_ranges[i].start { + // Merge with |right|. + self.free_ranges[i].start = if i > 0 && range.start == self.free_ranges[i - 1].end { + // Check for possible merge with |left| and |right|. + let left = self.free_ranges.remove(i - 1); + left.start + } else { + range.start + }; + + return; + } + + // Debug checks + assert!( + (i == 0 || self.free_ranges[i - 1].end < range.start) + && (i >= self.free_ranges.len() || range.end < self.free_ranges[i].start) + ); + + self.free_ranges.insert(i, range); + } + + /// Returns an iterator over allocated non-empty ranges + pub fn allocated_ranges<'a>(&'a self) -> impl 'a + Iterator<Item = Range<T>> { + let first = match self.free_ranges.first() { + Some(Range { ref start, .. }) if *start > self.initial_range.start => { + Some(self.initial_range.start..*start) + } + None => Some(self.initial_range.clone()), + _ => None, + }; + + let last = match self.free_ranges.last() { + Some(Range { end, .. }) if *end < self.initial_range.end => { + Some(*end..self.initial_range.end) + } + _ => None, + }; + + let mid = self + .free_ranges + .iter() + .zip(self.free_ranges.iter().skip(1)) + .map(|(ra, rb)| ra.end..rb.start); + + first.into_iter().chain(mid).chain(last) + } + + pub fn reset(&mut self) { + self.free_ranges.clear(); + self.free_ranges.push(self.initial_range.clone()); + } + + pub fn is_empty(&self) -> bool { + self.free_ranges.len() == 1 && self.free_ranges[0] == self.initial_range + } +} + +impl<T: Copy + Sub<Output = T> + Sum> RangeAllocator<T> { + pub fn total_available(&self) -> T { + self.free_ranges + .iter() + .map(|range| range.end - range.start) + .sum() + } +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn test_basic_allocation() { + let mut alloc = RangeAllocator::new(0..10); + // Test if an allocation works + assert_eq!(alloc.allocate_range(4), Ok(0..4)); + assert!(alloc.allocated_ranges().eq(std::iter::once(0..4))); + // Free the prior allocation + alloc.free_range(0..4); + // Make sure the free actually worked + assert_eq!(alloc.free_ranges, vec![0..10]); + assert!(alloc.allocated_ranges().eq(std::iter::empty())); + } + + #[test] + fn test_out_of_space() { + let mut alloc = RangeAllocator::new(0..10); + // Test if the allocator runs out of space correctly + assert_eq!(alloc.allocate_range(10), Ok(0..10)); + assert!(alloc.allocated_ranges().eq(std::iter::once(0..10))); + assert!(alloc.allocate_range(4).is_err()); + alloc.free_range(0..10); + } + + #[test] + fn test_dont_use_block_that_is_too_small() { + let mut alloc = RangeAllocator::new(0..10); + // Allocate three blocks then free the middle one and check for correct state + assert_eq!(alloc.allocate_range(3), Ok(0..3)); + assert_eq!(alloc.allocate_range(3), Ok(3..6)); + assert_eq!(alloc.allocate_range(3), Ok(6..9)); + alloc.free_range(3..6); + assert_eq!(alloc.free_ranges, vec![3..6, 9..10]); + assert_eq!( + alloc.allocated_ranges().collect::<Vec<Range<i32>>>(), + vec![0..3, 6..9] + ); + // Now request space that the middle block can fill, but the end one can't. + assert_eq!(alloc.allocate_range(3), Ok(3..6)); + } + + #[test] + fn test_free_blocks_in_middle() { + let mut alloc = RangeAllocator::new(0..100); + // Allocate many blocks then free every other block. + assert_eq!(alloc.allocate_range(10), Ok(0..10)); + assert_eq!(alloc.allocate_range(10), Ok(10..20)); + assert_eq!(alloc.allocate_range(10), Ok(20..30)); + assert_eq!(alloc.allocate_range(10), Ok(30..40)); + assert_eq!(alloc.allocate_range(10), Ok(40..50)); + assert_eq!(alloc.allocate_range(10), Ok(50..60)); + assert_eq!(alloc.allocate_range(10), Ok(60..70)); + assert_eq!(alloc.allocate_range(10), Ok(70..80)); + assert_eq!(alloc.allocate_range(10), Ok(80..90)); + assert_eq!(alloc.allocate_range(10), Ok(90..100)); + assert_eq!(alloc.free_ranges, vec![]); + assert!(alloc.allocated_ranges().eq(std::iter::once(0..100))); + alloc.free_range(10..20); + alloc.free_range(30..40); + alloc.free_range(50..60); + alloc.free_range(70..80); + alloc.free_range(90..100); + // Check that the right blocks were freed. + assert_eq!( + alloc.free_ranges, + vec![10..20, 30..40, 50..60, 70..80, 90..100] + ); + assert_eq!( + alloc.allocated_ranges().collect::<Vec<Range<i32>>>(), + vec![0..10, 20..30, 40..50, 60..70, 80..90] + ); + // Fragment the memory on purpose a bit. + assert_eq!(alloc.allocate_range(6), Ok(10..16)); + assert_eq!(alloc.allocate_range(6), Ok(30..36)); + assert_eq!(alloc.allocate_range(6), Ok(50..56)); + assert_eq!(alloc.allocate_range(6), Ok(70..76)); + assert_eq!(alloc.allocate_range(6), Ok(90..96)); + // Check for fragmentation. + assert_eq!( + alloc.free_ranges, + vec![16..20, 36..40, 56..60, 76..80, 96..100] + ); + assert_eq!( + alloc.allocated_ranges().collect::<Vec<Range<i32>>>(), + vec![0..16, 20..36, 40..56, 60..76, 80..96] + ); + // Fill up the fragmentation + assert_eq!(alloc.allocate_range(4), Ok(16..20)); + assert_eq!(alloc.allocate_range(4), Ok(36..40)); + assert_eq!(alloc.allocate_range(4), Ok(56..60)); + assert_eq!(alloc.allocate_range(4), Ok(76..80)); + assert_eq!(alloc.allocate_range(4), Ok(96..100)); + // Check that nothing is free. + assert_eq!(alloc.free_ranges, vec![]); + assert!(alloc.allocated_ranges().eq(std::iter::once(0..100))); + } + + #[test] + fn test_ignore_block_if_another_fits_better() { + let mut alloc = RangeAllocator::new(0..10); + // Allocate blocks such that the only free spaces available are 3..6 and 9..10 + // in order to prepare for the next test. + assert_eq!(alloc.allocate_range(3), Ok(0..3)); + assert_eq!(alloc.allocate_range(3), Ok(3..6)); + assert_eq!(alloc.allocate_range(3), Ok(6..9)); + alloc.free_range(3..6); + assert_eq!(alloc.free_ranges, vec![3..6, 9..10]); + assert_eq!( + alloc.allocated_ranges().collect::<Vec<Range<i32>>>(), + vec![0..3, 6..9] + ); + // Now request space that can be filled by 3..6 but should be filled by 9..10 + // because 9..10 is a perfect fit. + assert_eq!(alloc.allocate_range(1), Ok(9..10)); + } + + #[test] + fn test_merge_neighbors() { + let mut alloc = RangeAllocator::new(0..9); + assert_eq!(alloc.allocate_range(3), Ok(0..3)); + assert_eq!(alloc.allocate_range(3), Ok(3..6)); + assert_eq!(alloc.allocate_range(3), Ok(6..9)); + alloc.free_range(0..3); + alloc.free_range(6..9); + alloc.free_range(3..6); + assert_eq!(alloc.free_ranges, vec![0..9]); + assert!(alloc.allocated_ranges().eq(std::iter::empty())); + } +} |