Golang fileutil.NewLock函數代碼示例

// Create creates a WAL ready for appending records. The given metadata is
// recorded at the head of each WAL file, and can be retrieved with ReadAll.
func Create(dirpath string, metadata []byte) (*WAL, error) {
	if Exist(dirpath) {
		return nil, os.ErrExist
	}

	if err := os.MkdirAll(dirpath, privateDirMode); err != nil {
		return nil, err
	}

	p := path.Join(dirpath, walName(0, 0))
	f, err := os.OpenFile(p, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0600)
	if err != nil {
		return nil, err
	}
	l, err := fileutil.NewLock(f.Name())
	if err != nil {
		return nil, err
	}
	err = l.Lock()
	if err != nil {
		return nil, err
	}

	w := &WAL{
		dir:      dirpath,
		metadata: metadata,
		seq:      0,
		f:        f,
		encoder:  newEncoder(f, 0),
	}
	w.locks = append(w.locks, l)
	if err := w.saveCrc(0); err != nil {
		return nil, err
	}
	if err := w.encoder.encode(&walpb.Record{Type: metadataType, Data: metadata}); err != nil {
		return nil, err
	}
	if err = w.SaveSnapshot(walpb.Snapshot{}); err != nil {
		return nil, err
	}
	return w, nil
}

// Cut closes current file written and creates a new one ready to append.
func (w *WAL) Cut() error {
	// create a new wal file with name sequence + 1
	fpath := path.Join(w.dir, walName(w.seq+1, w.enti+1))
	f, err := os.OpenFile(fpath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	l, err := fileutil.NewLock(f.Name())
	if err != nil {
		return err
	}
	err = l.Lock()
	if err != nil {
		return err
	}
	w.locks = append(w.locks, l)
	if err = w.sync(); err != nil {
		return err
	}
	w.f.Close()

	// update writer and save the previous crc
	w.f = f
	w.seq++
	prevCrc := w.encoder.crc.Sum32()
	w.encoder = newEncoder(w.f, prevCrc)
	if err := w.saveCrc(prevCrc); err != nil {
		return err
	}
	if err := w.encoder.encode(&walpb.Record{Type: metadataType, Data: w.metadata}); err != nil {
		return err
	}
	if err := w.SaveState(&w.state); err != nil {
		return err
	}
	return w.sync()
}

// cut closes current file written and creates a new one ready to append.
// cut first creates a temp wal file and writes necessary headers into it.
// Then cut atomtically rename temp wal file to a wal file.
func (w *WAL) cut() error {
	// close old wal file
	if err := w.sync(); err != nil {
		return err
	}
	if err := w.f.Close(); err != nil {
		return err
	}

	fpath := path.Join(w.dir, walName(w.seq+1, w.enti+1))
	ftpath := fpath + ".tmp"

	// create a temp wal file with name sequence + 1, or tuncate the existing one
	ft, err := os.OpenFile(ftpath, os.O_WRONLY|os.O_APPEND|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return err
	}

	// update writer and save the previous crc
	w.f = ft
	prevCrc := w.encoder.crc.Sum32()
	w.encoder = newEncoder(w.f, prevCrc)
	if err := w.saveCrc(prevCrc); err != nil {
		return err
	}
	if err := w.encoder.encode(&walpb.Record{Type: metadataType, Data: w.metadata}); err != nil {
		return err
	}
	if err := w.saveState(&w.state); err != nil {
		return err
	}
	// close temp wal file
	if err := w.sync(); err != nil {
		return err
	}
	if err := w.f.Close(); err != nil {
		return err
	}

	// atomically move temp wal file to wal file
	if err := os.Rename(ftpath, fpath); err != nil {
		return err
	}

	// open the wal file and update writer again
	f, err := os.OpenFile(fpath, os.O_WRONLY|os.O_APPEND, 0600)
	if err != nil {
		return err
	}
	err = fileutil.Preallocate(f, segmentSizeBytes)
	if err != nil {
		plog.Errorf("failed to allocate space when creating new wal file (%v)", err)
		return err
	}

	w.f = f
	prevCrc = w.encoder.crc.Sum32()
	w.encoder = newEncoder(w.f, prevCrc)

	// lock the new wal file
	l, err := fileutil.NewLock(f.Name())
	if err != nil {
		return err
	}

	err = l.Lock()
	if err != nil {
		return err
	}
	w.locks = append(w.locks, l)

	// increase the wal seq
	w.seq++

	plog.Infof("segmented wal file %v is created", fpath)
	return nil
}

func openAtIndex(dirpath string, snap walpb.Snapshot, write bool) (*WAL, error) {
	names, err := fileutil.ReadDir(dirpath)
	if err != nil {
		return nil, err
	}
	names = checkWalNames(names)
	if len(names) == 0 {
		return nil, ErrFileNotFound
	}

	nameIndex, ok := searchIndex(names, snap.Index)
	if !ok || !isValidSeq(names[nameIndex:]) {
		return nil, ErrFileNotFound
	}

	// open the wal files for reading
	rcs := make([]io.ReadCloser, 0)
	ls := make([]fileutil.Lock, 0)
	for _, name := range names[nameIndex:] {
		f, err := os.Open(path.Join(dirpath, name))
		if err != nil {
			return nil, err
		}
		l, err := fileutil.NewLock(f.Name())
		if err != nil {
			return nil, err
		}
		err = l.TryLock()
		if err != nil {
			if write {
				return nil, err
			}
		}
		rcs = append(rcs, f)
		ls = append(ls, l)
	}
	rc := MultiReadCloser(rcs...)

	// create a WAL ready for reading
	w := &WAL{
		dir:     dirpath,
		start:   snap,
		decoder: newDecoder(rc),
		locks:   ls,
	}

	if write {
		// open the lastest wal file for appending
		seq, _, err := parseWalName(names[len(names)-1])
		if err != nil {
			rc.Close()
			return nil, err
		}
		last := path.Join(dirpath, names[len(names)-1])

		f, err := os.OpenFile(last, os.O_WRONLY|os.O_APPEND, 0)
		if err != nil {
			rc.Close()
			return nil, err
		}
		err = fileutil.Preallocate(f, segmentSizeBytes)
		if err != nil {
			rc.Close()
			plog.Errorf("failed to allocate space when creating new wal file (%v)", err)
			return nil, err
		}

		w.f = f
		w.seq = seq
	}

	return w, nil
}

func openAtIndex(dirpath string, index uint64, all bool) (*WAL, error) {
	names, err := fileutil.ReadDir(dirpath)
	if err != nil {
		return nil, err
	}
	names = checkWalNames(names)
	if len(names) == 0 {
		return nil, ErrFileNotFound
	}

	sort.Sort(sort.StringSlice(names))

	nameIndex, ok := searchIndex(names, index)
	if !ok || !isValidSeq(names[nameIndex:]) {
		return nil, ErrFileNotFound
	}

	// open the wal files for reading
	rcs := make([]io.ReadCloser, 0)
	ls := make([]fileutil.Lock, 0)
	for _, name := range names[nameIndex:] {
		f, err := os.Open(path.Join(dirpath, name))
		if err != nil {
			return nil, err
		}
		l, err := fileutil.NewLock(f.Name())
		if err != nil {
			return nil, err
		}
		err = l.TryLock()
		if err != nil {
			if all {
				return nil, err
			} else {
				log.Printf("wal: opened all the files until %s, since it is still in use by an etcd server", name)
				break
			}
		}
		rcs = append(rcs, f)
		ls = append(ls, l)
	}
	rc := MultiReadCloser(rcs...)

	// open the lastest wal file for appending
	seq, _, err := parseWalName(names[len(names)-1])
	if err != nil {
		rc.Close()
		return nil, err
	}
	last := path.Join(dirpath, names[len(names)-1])
	f, err := os.OpenFile(last, os.O_WRONLY|os.O_APPEND, 0)
	if err != nil {
		rc.Close()
		return nil, err
	}

	// create a WAL ready for reading
	w := &WAL{
		dir:     dirpath,
		ri:      index,
		decoder: newDecoder(rc),

		f:     f,
		seq:   seq,
		locks: ls,
	}
	return w, nil
}