Golang FileSystem.Remove方法代碼示例

func setCurrentFile(dirname string, fs db.FileSystem, fileNum uint64) error {
	newFilename := dbFilename(dirname, fileTypeCurrent, fileNum)
	oldFilename := fmt.Sprintf("%s.%06d.dbtmp", newFilename, fileNum)
	fs.Remove(oldFilename)
	f, err := fs.Create(oldFilename)
	if err != nil {
		return err
	}
	if _, err := fmt.Fprintf(f, "MANIFEST-%06d\n", fileNum); err != nil {
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	return fs.Rename(oldFilename, newFilename)
}

func (d *DB) writeLevel0Table(fs db.FileSystem, mem *memdb.MemDB) (meta fileMetadata, err error) {
	meta.fileNum = d.versions.nextFileNum()
	filename := dbFilename(d.dirname, fileTypeTable, meta.fileNum)
	// TODO: add meta.fileNum to a set of 'pending outputs' so that a
	// concurrent sweep of obsolete db files won't delete the fileNum file.
	// It is the caller's responsibility to remove that fileNum from the
	// set of pending outputs.

	var (
		file db.File
		tw   *table.Writer
		iter db.Iterator
	)
	defer func() {
		if iter != nil {
			err = firstError(err, iter.Close())
		}
		if tw != nil {
			err = firstError(err, tw.Close())
		}
		if file != nil {
			err = firstError(err, file.Close())
		}
		if err != nil {
			fs.Remove(filename)
			meta = fileMetadata{}
		}
	}()

	file, err = fs.Create(filename)
	if err != nil {
		return fileMetadata{}, err
	}
	tw = table.NewWriter(file, &db.Options{
		Comparer: d.icmp,
	})

	iter = mem.Find(nil, nil)
	iter.Next()
	meta.smallest = internalKey(iter.Key()).clone()
	for {
		meta.largest = iter.Key()
		if err1 := tw.Set(meta.largest, iter.Value(), nil); err1 != nil {
			return fileMetadata{}, err1
		}
		if !iter.Next() {
			break
		}
	}
	meta.largest = meta.largest.clone()

	if err1 := iter.Close(); err1 != nil {
		iter = nil
		return fileMetadata{}, err1
	}
	iter = nil

	if err1 := tw.Close(); err1 != nil {
		tw = nil
		return fileMetadata{}, err1
	}
	tw = nil

	// TODO: currently, closing a table.Writer closes its underlying file.
	// We have to re-open the file to Sync or Stat it, which seems stupid.
	file, err = fs.Open(filename)
	if err != nil {
		return fileMetadata{}, err
	}

	if err1 := file.Sync(); err1 != nil {
		return fileMetadata{}, err1
	}

	if stat, err1 := file.Stat(); err1 != nil {
		return fileMetadata{}, err1
	} else {
		size := stat.Size()
		if size < 0 {
			return fileMetadata{}, fmt.Errorf("leveldb: table file %q has negative size %d", filename, size)
		}
		meta.size = uint64(size)
	}

	// TODO: compaction stats.

	return meta, nil
}

// writeLevel0Table writes a memtable to a level-0 on-disk table.
//
// If no error is returned, it adds the file number of that on-disk table to
// d.pendingOutputs. It is the caller's responsibility to remove that fileNum
// from that set when it has been applied to d.versions.
//
// d.mu must be held when calling this, but the mutex may be dropped and
// re-acquired during the course of this method.
func (d *DB) writeLevel0Table(fs db.FileSystem, mem *memdb.MemDB) (meta fileMetadata, err error) {
	// meta用於記錄新創建的level0 db文件的元信息
	meta.fileNum = d.versions.nextFileNum()
	// filename：新db文件的文件名
	filename := dbFilename(d.dirname, fileTypeTable, meta.fileNum)

	d.pendingOutputs[meta.fileNum] = struct{}{}
	defer func(fileNum uint64) {
		// 如果異常退出(err不為nil)，則從d.pendingOutputs中刪除新db文件的記錄
		// 否則d.pendingOutputs是用來幹什麽的呢？
		if err != nil {
			delete(d.pendingOutputs, fileNum)
		}
	}(meta.fileNum)

	// Release the d.mu lock while doing I/O.
	// Note the unusual order: Unlock and then Lock.
	d.mu.Unlock()
	defer d.mu.Lock()

	var (
		file db.File
		tw   *table.Writer
		iter db.Iterator
	)
	defer func() {
		if iter != nil {
			err = firstError(err, iter.Close())
		}
		if tw != nil {
			err = firstError(err, tw.Close())
		}
		if file != nil {
			err = firstError(err, file.Close())
		}
		if err != nil {
			fs.Remove(filename)
			meta = fileMetadata{}
		}
	}()

	file, err = fs.Create(filename)
	if err != nil {
		return fileMetadata{}, err
	}

	// table為磁盤db文件封裝寫入方式
	tw = table.NewWriter(file, &db.Options{
		Comparer: d.icmp,
	})

	// Find返回一個迭代器，用於遍曆mem（這裏即是d.imm）中的數據
	// memtable是以skiplist來組織數據的，有序
	// 所以取到的第一個數據的key即為當前imm中最小的key
	iter = mem.Find(nil, nil)
	iter.Next()
	// meta.smallest記錄新db文件中最小的內部key，在寫入memtable時就已經將用戶key封裝成了內部key，那麽為什麽還要使用internalKey來做類型轉換？
	// 下麵的meta.largest就沒有進行類型轉換就調用clone()方法了。
	meta.smallest = internalKey(iter.Key()).clone()
	for {
		// 最後一次循環中的key即為最大的key，但為什麽不封裝成內部key呢？
		meta.largest = iter.Key()
		// 將key、value寫到新db文件中
		if err1 := tw.Set(meta.largest, iter.Value(), nil); err1 != nil {
			return fileMetadata{}, err1
		}
		// 如果imm中的數據已經遍曆完，全部存入新db文件，則break
		if !iter.Next() {
			break
		}
	}
	meta.largest = meta.largest.clone()

	if err1 := iter.Close(); err1 != nil {
		iter = nil
		return fileMetadata{}, err1
	}
	iter = nil

	if err1 := tw.Close(); err1 != nil {
		tw = nil
		return fileMetadata{}, err1
	}
	tw = nil

	// TODO: currently, closing a table.Writer closes its underlying file.
	// We have to re-open the file to Sync or Stat it, which seems stupid.
	file, err = fs.Open(filename)
	if err != nil {
		return fileMetadata{}, err
	}

//.........這裏部分代碼省略.........

// writeLevel0Table writes a memtable to a level-0 on-disk table.
//
// If no error is returned, it adds the file number of that on-disk table to
// d.pendingOutputs. It is the caller's responsibility to remove that fileNum
// from that set when it has been applied to d.versions.
//
// d.mu must be held when calling this, but the mutex may be dropped and
// re-acquired during the course of this method.
func (d *DB) writeLevel0Table(fs db.FileSystem, mem *memdb.MemDB) (meta fileMetadata, err error) {
	meta.fileNum = d.versions.nextFileNum()
	filename := dbFilename(d.dirname, fileTypeTable, meta.fileNum)
	d.pendingOutputs[meta.fileNum] = struct{}{}
	defer func(fileNum uint64) {
		if err != nil {
			delete(d.pendingOutputs, fileNum)
		}
	}(meta.fileNum)

	// Release the d.mu lock while doing I/O.
	// Note the unusual order: Unlock and then Lock.
	d.mu.Unlock()
	defer d.mu.Lock()

	var (
		file db.File
		tw   *table.Writer
		iter db.Iterator
	)
	defer func() {
		if iter != nil {
			err = firstError(err, iter.Close())
		}
		if tw != nil {
			err = firstError(err, tw.Close())
		}
		if file != nil {
			err = firstError(err, file.Close())
		}
		if err != nil {
			fs.Remove(filename)
			meta = fileMetadata{}
		}
	}()

	file, err = fs.Create(filename)
	if err != nil {
		return fileMetadata{}, err
	}
	tw = table.NewWriter(file, &db.Options{
		Comparer: d.icmp,
	})

	iter = mem.Find(nil, nil)
	iter.Next()
	meta.smallest = internalKey(iter.Key()).clone()
	for {
		meta.largest = iter.Key()
		if err1 := tw.Set(meta.largest, iter.Value(), nil); err1 != nil {
			return fileMetadata{}, err1
		}
		if !iter.Next() {
			break
		}
	}
	meta.largest = meta.largest.clone()

	if err1 := iter.Close(); err1 != nil {
		iter = nil
		return fileMetadata{}, err1
	}
	iter = nil

	if err1 := tw.Close(); err1 != nil {
		tw = nil
		return fileMetadata{}, err1
	}
	tw = nil

	// TODO: currently, closing a table.Writer closes its underlying file.
	// We have to re-open the file to Sync or Stat it, which seems stupid.
	file, err = fs.Open(filename)
	if err != nil {
		return fileMetadata{}, err
	}

	if err1 := file.Sync(); err1 != nil {
		return fileMetadata{}, err1
	}

	if stat, err1 := file.Stat(); err1 != nil {
		return fileMetadata{}, err1
	} else {
		size := stat.Size()
		if size < 0 {
			return fileMetadata{}, fmt.Errorf("leveldb: table file %q has negative size %d", filename, size)
		}
		meta.size = uint64(size)
	}

	// TODO: compaction stats.
//.........這裏部分代碼省略.........