frostfs-node/pkg/local_object_storage/pilorama/heap.go

package pilorama

import (
	"container/heap"
	"slices"
	"strings"
)

type heapInfo struct {
	id       MultiNode
	filename string
}

type filenameHeap []heapInfo

func (h filenameHeap) Len() int           { return len(h) }
func (h filenameHeap) Less(i, j int) bool { return h[i].filename < h[j].filename }
func (h filenameHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *filenameHeap) Push(x any) {
	*h = append(*h, x.(heapInfo))
}

func (h *filenameHeap) Pop() any {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

// fixedHeap maintains a fixed number of smallest elements started at some point.
type fixedHeap struct {
	start  *string
	sorted bool
	count  int
	h      *filenameHeap
}

func newHeap(start *string, count int) *fixedHeap {
	h := new(filenameHeap)
	heap.Init(h)

	return &fixedHeap{
		start: start,
		count: count,
		h:     h,
	}
}

const amortizationMultiplier = 5

func (h *fixedHeap) push(id MultiNode, filename string) bool {
	if h.start != nil && filename <= *h.start {
		return false
	}

	*h.h = append(*h.h, heapInfo{id: id, filename: filename})
	h.sorted = false

	if h.h.Len() > h.count*amortizationMultiplier {
		slices.SortFunc(*h.h, func(a, b heapInfo) int {
			return strings.Compare(a.filename, b.filename)
		})
		*h.h = (*h.h)[:h.count]
	}
	return true
}

func (h *fixedHeap) pop() (heapInfo, bool) {
	if !h.sorted {
		slices.SortFunc(*h.h, func(a, b heapInfo) int {
			return strings.Compare(a.filename, b.filename)
		})
		if len(*h.h) > h.count {
			*h.h = (*h.h)[:h.count]
		}
		h.sorted = true
	}
	if len(*h.h) != 0 {
		info := (*h.h)[0]
		*h.h = (*h.h)[1:]
		return info, true
	}
	return heapInfo{}, false
}