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lru.go
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lru.go
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package cachingreader
import (
"bufio"
"io"
"os"
"path/filepath"
"syscall"
"time"
"github.com/Cloud-Foundations/Dominator/lib/format"
"github.com/Cloud-Foundations/Dominator/lib/fsutil"
"github.com/Cloud-Foundations/Dominator/lib/hash"
"github.com/Cloud-Foundations/Dominator/lib/objectcache"
)
const (
privateFilePerms = syscall.S_IRUSR | syscall.S_IWUSR
filePerms = privateFilePerms | syscall.S_IRGRP | syscall.S_IROTH
)
func (objSrv *ObjectServer) addToLruWithLock(object *objectType) {
if object.usageCount != 0 {
panic("object.usageCount != 0")
}
if objSrv.oldest == nil { // Empty list: initialise it.
objSrv.oldest = object
} else { // Update previous newest object.
if objSrv.newest == nil {
panic("LRU has oldest but not newest entry")
}
objSrv.newest.newer = object
}
object.older = objSrv.newest
objSrv.newest = object
objSrv.lruBytes += object.size
select {
case objSrv.lruUpdateNotifier <- struct{}{}:
default:
}
}
func (objSrv *ObjectServer) flusher(lruUpdateNotifier <-chan struct{}) {
flushTimer := time.NewTimer(time.Minute)
flushTimer.Stop()
for {
select {
case <-lruUpdateNotifier:
if !flushTimer.Stop() {
select {
case <-flushTimer.C:
default:
}
}
flushTimer.Reset(time.Minute)
case <-flushTimer.C:
objSrv.saveLru()
}
}
}
func (objSrv *ObjectServer) getObjectWithLock(hashVal hash.Hash) *objectType {
if object, ok := objSrv.objects[hashVal]; !ok {
return nil
} else {
if object.usageCount < 1 {
objSrv.removeFromLruWithLock(object)
}
object.usageCount++
return object
}
}
func (objSrv *ObjectServer) loadLru() error {
startTime := time.Now()
filename := filepath.Join(objSrv.baseDir, ".lru")
file, err := os.Open(filename)
if err != nil {
if os.IsNotExist(err) {
return nil
}
return err
}
defer file.Close()
reader := bufio.NewReader(file)
var hashVal hash.Hash
objSrv.lruBytes = 0
for { // First object is newest, last object is oldest.
if _, err := reader.Read((&hashVal)[:]); err != nil {
if err == io.EOF {
break
}
return err
}
if object, ok := objSrv.objects[hashVal]; ok {
objSrv.lruBytes += object.size
if objSrv.newest == nil { // Empty list: initialise it.
objSrv.newest = object
} else { // Make object the oldest.
object.newer = objSrv.oldest
objSrv.oldest.older = object
}
objSrv.oldest = object
}
}
objSrv.logger.Printf("Loaded LRU in %s\n",
format.Duration(time.Since(startTime)))
return nil
}
func (objSrv *ObjectServer) putObjectWithLock(object *objectType) {
if object.usageCount < 1 {
panic("object.usageCount == 0")
}
object.usageCount--
if object.usageCount == 0 {
objSrv.addToLruWithLock(object)
}
}
// Returns true if space is available.
func (objSrv *ObjectServer) releaseSpaceWithLock(size uint64) bool {
if objSrv.cachedBytes+objSrv.downloadingBytes+size <=
objSrv.maxCachedBytes {
return true
}
if objSrv.cachedBytes-objSrv.lruBytes+objSrv.downloadingBytes+size >
objSrv.maxCachedBytes {
return false // No amount of deleting unused objects will help.
}
for objSrv.oldest != nil {
filename := filepath.Join(objSrv.baseDir,
objectcache.HashToFilename(objSrv.oldest.hash))
if err := os.Remove(filename); err != nil {
objSrv.logger.Println(err)
return false
}
objSrv.removeFromLruWithLock(objSrv.oldest)
objSrv.cachedBytes -= objSrv.oldest.size
if objSrv.cachedBytes+objSrv.downloadingBytes+size <=
objSrv.maxCachedBytes {
return true
}
}
panic("not enough space despite freeing unused objects")
}
func (objSrv *ObjectServer) removeFromLruWithLock(object *objectType) {
if object.older == nil { // Object is the oldest.
objSrv.oldest = object.newer
if objSrv.oldest != nil {
objSrv.oldest.older = nil
}
} else {
object.older.newer = object.newer
}
if object.newer == nil { // Object is the newest.
objSrv.newest = object.older
if objSrv.newest != nil {
objSrv.newest.newer = nil
}
} else {
object.newer.older = object.older
}
object.newer = nil
object.older = nil
if objSrv.newest == nil && objSrv.oldest != nil {
panic("LRU has oldest but not newest entry")
}
if objSrv.oldest == nil && objSrv.newest != nil {
panic("LRU has newest but not oldest entry")
}
objSrv.lruBytes -= object.size
select {
case objSrv.lruUpdateNotifier <- struct{}{}:
default:
}
}
func (objSrv *ObjectServer) saveLru() {
objSrv.rwLock.RLock()
defer objSrv.rwLock.RUnlock()
filename := filepath.Join(objSrv.baseDir, ".lru")
writer, err := fsutil.CreateRenamingWriter(filename, filePerms)
if err != nil {
return
}
defer writer.Close()
w := bufio.NewWriter(writer)
defer w.Flush()
// Write newest first, oldest last.
for object := objSrv.newest; object != nil; object = object.older {
if _, err := w.Write(object.hash[:]); err != nil {
return
}
}
}