聊聊dapr的fswatcher

序

本文主要研究一下dapr的fswatcher

fswatcher

dapr/pkg/fswatcher/fswatcher.go

import (
	"context"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
	"github.com/pkg/errors"
)

func Watch(ctx context.Context, dir string, eventCh chan<- struct{}) error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return errors.Wrap(err, "failed to create watcher")
	}
	defer watcher.Close()

	if err := watcher.Add(dir); err != nil {
		return errors.Wrap(err, "watcher error")
	}

LOOP:
	for {
		select {
		// watch for events
		case event := <-watcher.Events:
			if event.Op == fsnotify.Create || event.Op == fsnotify.Write {
				if strings.Contains(event.Name, dir) {
					// give time for other updates to occur
					time.Sleep(time.Second * 1)
					eventCh <- struct{}{}
				}
			}
		case <-watcher.Errors:
			break LOOP
		case <-ctx.Done():
			break LOOP
		}
	}
	return nil
}

Watch方法使用fsnotify的watcher來監聽文件，之後通過for循環進行select，如果監聽到fsnotify.Create或者fsnotify.Write的時候判斷event.Name是否包含dir，如果包含則sleep一秒然後通知eventCh

Add

github.com/fsnotify/[email protected]/kqueue.go

// Add starts watching the named file or directory (non-recursively).
func (w *Watcher) Add(name string) error {
	w.mu.Lock()
	w.externalWatches[name] = true
	w.mu.Unlock()
	_, err := w.addWatch(name, noteAllEvents)
	return err
}

Add方法設置externalWatches[name]爲true，然後執行addWatch(name, noteAllEvents)

addWatch

github.com/fsnotify/[email protected]/kqueue.go

// addWatch adds name to the watched file set.
// The flags are interpreted as described in kevent(2).
// Returns the real path to the file which was added, if any, which may be different from the one passed in the case of symlinks.
func (w *Watcher) addWatch(name string, flags uint32) (string, error) {
	var isDir bool
	// Make ./name and name equivalent
	name = filepath.Clean(name)

	w.mu.Lock()
	if w.isClosed {
		w.mu.Unlock()
		return "", errors.New("kevent instance already closed")
	}
	watchfd, alreadyWatching := w.watches[name]
	// We already have a watch, but we can still override flags.
	if alreadyWatching {
		isDir = w.paths[watchfd].isDir
	}
	w.mu.Unlock()

	if !alreadyWatching {
		fi, err := os.Lstat(name)
		if err != nil {
			return "", err
		}

		// Don't watch sockets.
		if fi.Mode()&os.ModeSocket == os.ModeSocket {
			return "", nil
		}

		// Don't watch named pipes.
		if fi.Mode()&os.ModeNamedPipe == os.ModeNamedPipe {
			return "", nil
		}

		// Follow Symlinks
		// Unfortunately, Linux can add bogus symlinks to watch list without
		// issue, and Windows can't do symlinks period (AFAIK). To  maintain
		// consistency, we will act like everything is fine. There will simply
		// be no file events for broken symlinks.
		// Hence the returns of nil on errors.
		if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
			name, err = filepath.EvalSymlinks(name)
			if err != nil {
				return "", nil
			}

			w.mu.Lock()
			_, alreadyWatching = w.watches[name]
			w.mu.Unlock()

			if alreadyWatching {
				return name, nil
			}

			fi, err = os.Lstat(name)
			if err != nil {
				return "", nil
			}
		}

		watchfd, err = unix.Open(name, openMode, 0700)
		if watchfd == -1 {
			return "", err
		}

		isDir = fi.IsDir()
	}

	const registerAdd = unix.EV_ADD | unix.EV_CLEAR | unix.EV_ENABLE
	if err := register(w.kq, []int{watchfd}, registerAdd, flags); err != nil {
		unix.Close(watchfd)
		return "", err
	}

	if !alreadyWatching {
		w.mu.Lock()
		w.watches[name] = watchfd
		w.paths[watchfd] = pathInfo{name: name, isDir: isDir}
		w.mu.Unlock()
	}

	if isDir {
		// Watch the directory if it has not been watched before,
		// or if it was watched before, but perhaps only a NOTE_DELETE (watchDirectoryFiles)
		w.mu.Lock()

		watchDir := (flags&unix.NOTE_WRITE) == unix.NOTE_WRITE &&
			(!alreadyWatching || (w.dirFlags[name]&unix.NOTE_WRITE) != unix.NOTE_WRITE)
		// Store flags so this watch can be updated later
		w.dirFlags[name] = flags
		w.mu.Unlock()

		if watchDir {
			if err := w.watchDirectoryFiles(name); err != nil {
				return "", err
			}
		}
	}
	return name, nil
}

addWatch方法針對尚未watch的執行os.Lstat(name)及unix.Open(name, openMode, 0700)；之後註冊registerAdd；另外針對isDir的情況執行watchDirectoryFiles

watchDirectoryFiles

github.com/fsnotify/[email protected]/kqueue.go

// watchDirectoryFiles to mimic inotify when adding a watch on a directory
func (w *Watcher) watchDirectoryFiles(dirPath string) error {
	// Get all files
	files, err := ioutil.ReadDir(dirPath)
	if err != nil {
		return err
	}

	for _, fileInfo := range files {
		filePath := filepath.Join(dirPath, fileInfo.Name())
		filePath, err = w.internalWatch(filePath, fileInfo)
		if err != nil {
			return err
		}

		w.mu.Lock()
		w.fileExists[filePath] = true
		w.mu.Unlock()
	}

	return nil
}

watchDirectoryFiles遍歷files，挨個執行internalWatch

internalWatch

github.com/fsnotify/[email protected]/kqueue.go

func (w *Watcher) internalWatch(name string, fileInfo os.FileInfo) (string, error) {
	if fileInfo.IsDir() {
		// mimic Linux providing delete events for subdirectories
		// but preserve the flags used if currently watching subdirectory
		w.mu.Lock()
		flags := w.dirFlags[name]
		w.mu.Unlock()

		flags |= unix.NOTE_DELETE | unix.NOTE_RENAME
		return w.addWatch(name, flags)
	}

	// watch file to mimic Linux inotify
	return w.addWatch(name, noteAllEvents)
}

internalWatch針對dir設置的flag爲NOTE_DELETE、NOTE_RENAME

小結

dapr的fswatcher使用fsnotify的watcher來監聽文件，之後通過for循環進行select，如果監聽到fsnotify.Create或者fsnotify.Write的時候判斷event.Name是否包含dir，如果包含則sleep一秒然後通知eventCh。

doc

• dapr