#![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 { /// The range this allocator covers. initial_range: Range, /// 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>, } #[derive(Clone, Debug, PartialEq)] pub struct RangeAllocationError { pub fragmented_free_length: T, } impl RangeAllocator where T: Clone + Copy + Add + AddAssign + Sub + Eq + PartialOrd + Debug, { pub fn new(range: Range) -> Self { RangeAllocator { initial_range: range.clone(), free_ranges: vec![range], } } pub fn initial_range(&self) -> &Range { &self.initial_range } pub fn allocate_range(&mut self, length: T) -> Result, RangeAllocationError> { assert_ne!(length + length, length); let mut best_fit: Option<(usize, Range)> = 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) { 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> { 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 + Sum> RangeAllocator { 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![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![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![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![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())); } }