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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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