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package bbolt
import "sort"
// hashmapFreeCount returns count of free pages(hashmap version)
func (f *freelist) hashmapFreeCount() int {
// use the forwardMap to get the total count
count := 0
for _, size := range f.forwardMap {
count += int(size)
}
return count
}
// hashmapAllocate serves the same purpose as arrayAllocate, but use hashmap as backend
func (f *freelist) hashmapAllocate(txid txid, n int) pgid {
if n == 0 {
return 0
}
// if we have a exact size match just return short path
if bm, ok := f.freemaps[uint64(n)]; ok {
for pid := range bm {
// remove the span
f.delSpan(pid, uint64(n))
f.allocs[pid] = txid
for i := pgid(0); i < pgid(n); i++ {
delete(f.cache, pid+i)
}
return pid
}
}
// lookup the map to find larger span
for size, bm := range f.freemaps {
if size < uint64(n) {
continue
}
for pid := range bm {
// remove the initial
f.delSpan(pid, size)
f.allocs[pid] = txid
remain := size - uint64(n)
// add remain span
f.addSpan(pid+pgid(n), remain)
for i := pgid(0); i < pgid(n); i++ {
delete(f.cache, pid+i)
}
return pid
}
}
return 0
}
// hashmapReadIDs reads pgids as input an initial the freelist(hashmap version)
func (f *freelist) hashmapReadIDs(pgids []pgid) {
f.init(pgids)
// Rebuild the page cache.
f.reindex()
}
// hashmapGetFreePageIDs returns the sorted free page ids
func (f *freelist) hashmapGetFreePageIDs() []pgid {
count := f.free_count()
if count == 0 {
return nil
}
m := make([]pgid, 0, count)
for start, size := range f.forwardMap {
for i := 0; i < int(size); i++ {
m = append(m, start+pgid(i))
}
}
sort.Sort(pgids(m))
return m
}
// hashmapMergeSpans try to merge list of pages(represented by pgids) with existing spans
func (f *freelist) hashmapMergeSpans(ids pgids) {
for _, id := range ids {
// try to see if we can merge and update
f.mergeWithExistingSpan(id)
}
}
// mergeWithExistingSpan merges pid to the existing free spans, try to merge it backward and forward
func (f *freelist) mergeWithExistingSpan(pid pgid) {
prev := pid - 1
next := pid + 1
preSize, mergeWithPrev := f.backwardMap[prev]
nextSize, mergeWithNext := f.forwardMap[next]
newStart := pid
newSize := uint64(1)
if mergeWithPrev {
//merge with previous span
start := prev + 1 - pgid(preSize)
f.delSpan(start, preSize)
newStart -= pgid(preSize)
newSize += preSize
}
if mergeWithNext {
// merge with next span
f.delSpan(next, nextSize)
newSize += nextSize
}
f.addSpan(newStart, newSize)
}
func (f *freelist) addSpan(start pgid, size uint64) {
f.backwardMap[start-1+pgid(size)] = size
f.forwardMap[start] = size
if _, ok := f.freemaps[size]; !ok {
f.freemaps[size] = make(map[pgid]struct{})
}
f.freemaps[size][start] = struct{}{}
}
func (f *freelist) delSpan(start pgid, size uint64) {
delete(f.forwardMap, start)
delete(f.backwardMap, start+pgid(size-1))
delete(f.freemaps[size], start)
if len(f.freemaps[size]) == 0 {
delete(f.freemaps, size)
}
}
// initial from pgids using when use hashmap version
// pgids must be sorted
func (f *freelist) init(pgids []pgid) {
if len(pgids) == 0 {
return
}
size := uint64(1)
start := pgids[0]
if !sort.SliceIsSorted([]pgid(pgids), func(i, j int) bool { return pgids[i] < pgids[j] }) {
panic("pgids not sorted")
}
f.freemaps = make(map[uint64]pidSet)
f.forwardMap = make(map[pgid]uint64)
f.backwardMap = make(map[pgid]uint64)
for i := 1; i < len(pgids); i++ {
// continuous page
if pgids[i] == pgids[i-1]+1 {
size++
} else {
f.addSpan(start, size)
size = 1
start = pgids[i]
}
}
// init the tail
if size != 0 && start != 0 {
f.addSpan(start, size)
}
}
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