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package sequence
import (
"bytes"
"code.google.com/p/weed-fs/go/glog"
"code.google.com/p/weed-fs/go/metastore"
"encoding/gob"
"sync"
)
const (
FileIdSaveInterval = 10000
)
type Sequencer interface {
NextFileId(count int) (uint64, int)
}
type SequencerImpl struct {
fileFullPath string
volumeLock sync.Mutex
sequenceLock sync.Mutex
FileIdSequence uint64
fileIdCounter uint64
metaStore *metastore.MetaStore
}
func NewFileSequencer(filepath string) (m *SequencerImpl) {
m = &SequencerImpl{fileFullPath: filepath}
m.metaStore = &metastore.MetaStore{metastore.NewMetaStoreFileBacking()}
m.initilize()
return
}
func (m *SequencerImpl) initilize() {
if !m.metaStore.Has(m.fileFullPath) {
m.FileIdSequence = FileIdSaveInterval
glog.V(0).Infoln("Setting file id sequence", m.FileIdSequence)
} else {
var err error
if m.FileIdSequence, err = m.metaStore.GetUint64(m.fileFullPath); err != nil {
if data, err := m.metaStore.Get(m.fileFullPath); err == nil {
m.FileIdSequence = decode(data)
glog.V(0).Infoln("Decoding old version of FileIdSequence", m.FileIdSequence)
} else {
glog.V(0).Infof("No existing FileIdSequence: %s", err)
}
} else {
glog.V(0).Infoln("Loading file id sequence", m.FileIdSequence)
}
//in case the server stops between intervals
}
return
}
//count should be 1 or more
func (m *SequencerImpl) NextFileId(count int) (uint64, int) {
if count <= 0 {
return 0, 0
}
m.sequenceLock.Lock()
defer m.sequenceLock.Unlock()
if m.fileIdCounter < uint64(count) {
m.fileIdCounter = FileIdSaveInterval
m.FileIdSequence += FileIdSaveInterval
m.saveSequence()
}
m.fileIdCounter = m.fileIdCounter - uint64(count)
return m.FileIdSequence - m.fileIdCounter - uint64(count), count
}
func (m *SequencerImpl) saveSequence() {
glog.V(0).Infoln("Saving file id sequence", m.FileIdSequence, "to", m.fileFullPath)
if e := m.metaStore.SetUint64(m.fileFullPath, m.FileIdSequence); e != nil {
glog.Fatalf("Sequence id Save [ERROR] %s", e)
}
}
//decode are for backward compatible purpose
func decode(input string) uint64 {
var x uint64
b := bytes.NewReader([]byte(input))
decoder := gob.NewDecoder(b)
if e := decoder.Decode(&x); e == nil {
return x
}
return 0
}
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