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