//.........这里部分代码省略.........
				fileDeletions[file.Name] = file
				df, ok := p.model.CurrentFolderFile(p.folder, file.Name)
				// Local file can be already deleted, but with a lower version
				// number, hence the deletion coming in again as part of
				// WithNeed, furthermore, the file can simply be of the wrong
				// type if we haven't yet managed to pull it.
				if ok && !df.IsDeleted() && !df.IsSymlink() && !df.IsDirectory() {
					// Put files into buckets per first hash
					key := string(df.Blocks[0].Hash)
					buckets[key] = append(buckets[key], df)
				}
			}
		case file.IsDirectory() && !file.IsSymlink():
			// A new or changed directory
			if debug {
				l.Debugln("Creating directory", file.Name)
			}
			p.handleDir(file)
		default:
			// A new or changed file or symlink. This is the only case where we
			// do stuff concurrently in the background
			pullFileSize += file.Size()
			p.queue.Push(file.Name, file.Size(), file.Modified)
		}

		changed++
		return true
	})

	// Check if we are able to store all files on disk
	if pullFileSize > 0 {
		folder, ok := p.model.cfg.Folders()[p.folder]
		if ok {
			if free, err := osutil.DiskFreeBytes(folder.Path()); err == nil && free < pullFileSize {
				l.Infof("Puller (folder %q): insufficient disk space available to pull %d files (%.2fMB)", p.folder, changed, float64(pullFileSize)/1024/1024)
				return 0
			}
		}
	}

	// Reorder the file queue according to configuration

	switch p.order {
	case config.OrderRandom:
		p.queue.Shuffle()
	case config.OrderAlphabetic:
		// The queue is already in alphabetic order.
	case config.OrderSmallestFirst:
		p.queue.SortSmallestFirst()
	case config.OrderLargestFirst:
		p.queue.SortLargestFirst()
	case config.OrderOldestFirst:
		p.queue.SortOldestFirst()
	case config.OrderNewestFirst:
		p.queue.SortOldestFirst()
	}

	// Process the file queue

nextFile:
	for {
		fileName, ok := p.queue.Pop()
		if !ok {
			break
		}

//.........这里部分代码省略.........
				// sweep is complete. As we do retries, we'll queue the scan
				// for this file up to ten times, but the last nine of those
				// scans will be cheap...
				go f.scan.Scan([]string{file.Name})
				return
			}
		}
	}

	scanner.PopulateOffsets(file.Blocks)

	var blocks []protocol.BlockInfo
	var blocksSize int64
	var reused []int32

	// Check for an old temporary file which might have some blocks we could
	// reuse.
	tempBlocks, err := scanner.HashFile(tempName, protocol.BlockSize, nil)
	if err == nil {
		// Check for any reusable blocks in the temp file
		tempCopyBlocks, _ := scanner.BlockDiff(tempBlocks, file.Blocks)

		// block.String() returns a string unique to the block
		existingBlocks := make(map[string]struct{}, len(tempCopyBlocks))
		for _, block := range tempCopyBlocks {
			existingBlocks[block.String()] = struct{}{}
		}

		// Since the blocks are already there, we don't need to get them.
		for i, block := range file.Blocks {
			_, ok := existingBlocks[block.String()]
			if !ok {
				blocks = append(blocks, block)
				blocksSize += int64(block.Size)
			} else {
				reused = append(reused, int32(i))
			}
		}

		// The sharedpullerstate will know which flags to use when opening the
		// temp file depending if we are reusing any blocks or not.
		if len(reused) == 0 {
			// Otherwise, discard the file ourselves in order for the
			// sharedpuller not to panic when it fails to exclusively create a
			// file which already exists
			osutil.InWritableDir(os.Remove, tempName)
		}
	} else {
		// Copy the blocks, as we don't want to shuffle them on the FileInfo
		blocks = append(blocks, file.Blocks...)
		blocksSize = file.Size
	}

	if f.checkFreeSpace {
		if free, err := osutil.DiskFreeBytes(f.dir); err == nil && free < blocksSize {
			l.Warnf(`Folder "%s": insufficient disk space in %s for %s: have %.2f MiB, need %.2f MiB`, f.folderID, f.dir, file.Name, float64(free)/1024/1024, float64(blocksSize)/1024/1024)
			f.newError(file.Name, errors.New("insufficient space"))
			return
		}
	}

	// Shuffle the blocks
	for i := range blocks {
		j := rand.Intn(i + 1)
		blocks[i], blocks[j] = blocks[j], blocks[i]
	}

	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": f.folderID,
		"item":   file.Name,
		"type":   "file",
		"action": "update",
	})

	s := sharedPullerState{
		file:             file,
		folder:           f.folderID,
		tempName:         tempName,
		realName:         realName,
		copyTotal:        len(blocks),
		copyNeeded:       len(blocks),
		reused:           len(reused),
		updated:          time.Now(),
		available:        reused,
		availableUpdated: time.Now(),
		ignorePerms:      f.ignorePermissions(file),
		version:          curFile.Version,
		mut:              sync.NewRWMutex(),
		sparse:           f.allowSparse,
		created:          time.Now(),
	}

	l.Debugf("%v need file %s; copy %d, reused %v", f, file.Name, len(blocks), reused)

	cs := copyBlocksState{
		sharedPullerState: &s,
		blocks:            blocks,
	}
	copyChan <- cs
}

// handleFile queues the copies and pulls as necessary for a single new or
// changed file.
func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocksState, finisherChan chan<- *sharedPullerState) {
	curFile, ok := p.model.CurrentFolderFile(p.folder, file.Name)

	if ok && len(curFile.Blocks) == len(file.Blocks) && scanner.BlocksEqual(curFile.Blocks, file.Blocks) {
		// We are supposed to copy the entire file, and then fetch nothing. We
		// are only updating metadata, so we don't actually *need* to make the
		// copy.
		l.Debugln(p, "taking shortcut on", file.Name)

		events.Default.Log(events.ItemStarted, map[string]string{
			"folder": p.folder,
			"item":   file.Name,
			"type":   "file",
			"action": "metadata",
		})

		p.queue.Done(file.Name)

		var err error
		if file.IsSymlink() {
			err = p.shortcutSymlink(file)
		} else {
			err = p.shortcutFile(file)
		}

		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   file.Name,
			"error":  events.Error(err),
			"type":   "file",
			"action": "metadata",
		})

		if err != nil {
			l.Infoln("Puller: shortcut:", err)
			p.newError(file.Name, err)
		} else {
			p.dbUpdates <- dbUpdateJob{file, dbUpdateShortcutFile}
		}

		return
	}

	if free, err := osutil.DiskFreeBytes(p.dir); err == nil && free < file.Size() {
		l.Warnf(`Folder "%s": insufficient disk space in %s for %s: have %.2f MiB, need %.2f MiB`, p.folder, p.dir, file.Name, float64(free)/1024/1024, float64(file.Size())/1024/1024)
		p.newError(file.Name, errors.New("insufficient space"))
		return
	}

	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   file.Name,
		"type":   "file",
		"action": "update",
	})

	scanner.PopulateOffsets(file.Blocks)

	// Figure out the absolute filenames we need once and for all
	tempName := filepath.Join(p.dir, defTempNamer.TempName(file.Name))
	realName := filepath.Join(p.dir, file.Name)

	reused := 0
	var blocks []protocol.BlockInfo

	// Check for an old temporary file which might have some blocks we could
	// reuse.
	tempBlocks, err := scanner.HashFile(tempName, protocol.BlockSize, 0, nil)
	if err == nil {
		// Check for any reusable blocks in the temp file
		tempCopyBlocks, _ := scanner.BlockDiff(tempBlocks, file.Blocks)

		// block.String() returns a string unique to the block
		existingBlocks := make(map[string]struct{}, len(tempCopyBlocks))
		for _, block := range tempCopyBlocks {
			existingBlocks[block.String()] = struct{}{}
		}

		// Since the blocks are already there, we don't need to get them.
		for _, block := range file.Blocks {
			_, ok := existingBlocks[block.String()]
			if !ok {
				blocks = append(blocks, block)
			}
		}

		// The sharedpullerstate will know which flags to use when opening the
		// temp file depending if we are reusing any blocks or not.
		reused = len(file.Blocks) - len(blocks)
		if reused == 0 {
			// Otherwise, discard the file ourselves in order for the
			// sharedpuller not to panic when it fails to exclusively create a
			// file which already exists
			osutil.InWritableDir(osutil.Remove, tempName)
		}
	} else {
		blocks = file.Blocks
	}
//.........这里部分代码省略.........