Merge pull request #58 from aristanetworks/upstream

Single shared Watcher used to avoid inotify limit

.travis.yml

@@ -11,4 +11,4 @@ go:
   - 1.4.2
 
 install:
-  - go get gopkg.in/fsnotify.v0
+  - go get gopkg.in/fsnotify.v1

tail.go

@@ -76,7 +76,6 @@ type Tail struct {
 
 	file   *os.File
 	reader *bufio.Reader
-	tracker *watch.InotifyTracker
 
 	watcher watch.FileWatcher
 	changes *watch.FileChanges
@@ -114,12 +113,7 @@ func TailFile(filename string, config Config) (*Tail, error) {
 	if t.Poll {
 		t.watcher = watch.NewPollingFileWatcher(filename)
 	} else {
-		t.tracker = watch.NewInotifyTracker()
-		w, err := t.tracker.NewWatcher()
-		if err != nil {
-			return nil, err
-		}
-		t.watcher = watch.NewInotifyFileWatcher(filename, w)
+		t.watcher = watch.NewInotifyFileWatcher(filename)
 	}
 
 	if t.MustExist {
@@ -308,11 +302,11 @@ func (tail *Tail) tailFileSync() {
 // reopened if ReOpen is true. Truncated files are always reopened.
 func (tail *Tail) waitForChanges() error {
 	if tail.changes == nil {
-		st, err := tail.file.Stat()
+		pos, err := tail.file.Seek(0, os.SEEK_CUR)
 		if err != nil {
 			return err
 		}
-		tail.changes = tail.watcher.ChangeEvents(&tail.Tomb, st)
+		tail.changes = tail.watcher.ChangeEvents(&tail.Tomb, pos)
 	}
 
 	select {
@@ -358,7 +352,7 @@ func (tail *Tail) openReader() {
 }
 
 func (tail *Tail) seekEnd() error {
-	return tail.seekTo(SeekInfo{Offset: 0, Whence: 2})
+	return tail.seekTo(SeekInfo{Offset: 0, Whence: os.SEEK_END})
 }
 
 func (tail *Tail) seekTo(pos SeekInfo) error {
@@ -402,7 +396,5 @@ func (tail *Tail) sendLine(line string) bool {
 // meant to be invoked from a process's exit handler. Linux kernel may not
 // automatically remove inotify watches after the process exits.
 func (tail *Tail) Cleanup() {
-	if tail.tracker != nil {
-		tail.tracker.CloseAll()
-	}
+	watch.Cleanup(tail.Filename)
 }

watch/inotify.go

@@ -8,7 +8,8 @@ import (
 	"path/filepath"
 
 	"github.com/hpcloud/tail/util"
-	"gopkg.in/fsnotify.v0"
+
+	"gopkg.in/fsnotify.v1"
 	"gopkg.in/tomb.v1"
 )
 
@@ -16,11 +17,10 @@ import (
 type InotifyFileWatcher struct {
 	Filename string
 	Size     int64
-	w        *fsnotify.Watcher
 }
 
-func NewInotifyFileWatcher(filename string, w *fsnotify.Watcher) *InotifyFileWatcher {
-	fw := &InotifyFileWatcher{filename, 0, w}
+func NewInotifyFileWatcher(filename string) *InotifyFileWatcher {
+	fw := &InotifyFileWatcher{filename, 0}
 	return fw
 }
 
@@ -28,11 +28,11 @@ func (fw *InotifyFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 	dirname := filepath.Dir(fw.Filename)
 
 	// Watch for new files to be created in the parent directory.
-	err := fw.w.WatchFlags(dirname, fsnotify.FSN_CREATE)
+	err := Watch(dirname)
 	if err != nil {
 		return err
 	}
-	defer fw.w.RemoveWatch(dirname)
+	defer RemoveWatch(dirname)
 
 	// Do a real check now as the file might have been created before
 	// calling `WatchFlags` above.
@@ -41,9 +41,11 @@ func (fw *InotifyFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 		return err
 	}
 
+	events := Events(fw.Filename)
+
 	for {
 		select {
-		case evt, ok := <-fw.w.Event:
+		case evt, ok := <-events:
 			if !ok {
 				return fmt.Errorf("inotify watcher has been closed")
 			} else if evt.Name == fw.Filename {
@@ -56,28 +58,30 @@ func (fw *InotifyFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 	panic("unreachable")
 }
 
-func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, fi os.FileInfo) *FileChanges {
+func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges {
 	changes := NewFileChanges()
 
-	err := fw.w.Watch(fw.Filename)
+	err := Watch(fw.Filename)
 	if err != nil {
-		util.Fatal("Error watching %v: %v", fw.Filename, err)
+		go changes.NotifyDeleted()
 	}
 
-	fw.Size = fi.Size()
+	fw.Size = pos
 
 	go func() {
-		defer fw.w.RemoveWatch(fw.Filename)
+		defer RemoveWatch(fw.Filename)
 		defer changes.Close()
 
+		events := Events(fw.Filename)
+
 		for {
 			prevSize := fw.Size
 
-			var evt *fsnotify.FileEvent
+			var evt fsnotify.Event
 			var ok bool
 
 			select {
-			case evt, ok = <-fw.w.Event:
+			case evt, ok = <-events:
 				if !ok {
 					return
 				}
@@ -86,14 +90,14 @@ func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, fi os.FileInfo) *FileCh
 			}
 
 			switch {
-			case evt.IsDelete():
+			case evt.Op&fsnotify.Remove == fsnotify.Remove:
 				fallthrough
 
-			case evt.IsRename():
+			case evt.Op&fsnotify.Rename == fsnotify.Rename:
 				changes.NotifyDeleted()
 				return
 
-			case evt.IsModify():
+			case evt.Op&fsnotify.Write == fsnotify.Write:
 				fi, err := os.Stat(fw.Filename)
 				if err != nil {
 					if os.IsNotExist(err) {

watch/inotify_tracker.go

@@ -3,49 +3,167 @@
 package watch
 
 import (
-	"gopkg.in/fsnotify.v0"
 	"log"
+	"os"
 	"sync"
+	"syscall"
+
+	"github.com/hpcloud/tail/util"
+
+	"gopkg.in/fsnotify.v1"
 )
 
 type InotifyTracker struct {
 	mux     sync.Mutex
-	watchers map[*fsnotify.Watcher]bool
+	watcher *fsnotify.Watcher
+	chans   map[string]chan fsnotify.Event
+	done    map[string]chan bool
+	watch   chan *watchInfo
+	remove  chan string
+	error   chan error
 }
 
-func NewInotifyTracker() *InotifyTracker {
-	t := new(InotifyTracker)
-	t.watchers = make(map[*fsnotify.Watcher]bool)
-	return t
+type watchInfo struct {
+	fname string
 }
 
-func (t *InotifyTracker) NewWatcher() (*fsnotify.Watcher, error) {
-	t.mux.Lock()
-	defer t.mux.Unlock()
-	w, err := fsnotify.NewWatcher()
-	if err == nil {
-		t.watchers[w] = true
+var (
+	// globally shared InotifyTracker; ensures only one fsnotify.Watcher is used
+	shared *InotifyTracker
+
+	// these are used to ensure the shared InotifyTracker is run exactly once
+	once  = sync.Once{}
+	goRun = func() {
+		shared = &InotifyTracker{
+			mux:    sync.Mutex{},
+			chans:  make(map[string]chan fsnotify.Event),
+			done:   make(map[string]chan bool),
+			watch:  make(chan *watchInfo),
+			remove: make(chan string),
+			error:  make(chan error),
 		}
-	return w, err
+		go shared.run()
 	}
 
-func (t *InotifyTracker) CloseWatcher(w *fsnotify.Watcher) (err error) {
-	t.mux.Lock()
-	defer t.mux.Unlock()
-	if _, ok := t.watchers[w]; ok {
-		err = w.Close()
-		delete(t.watchers, w)
+	logger = log.New(os.Stderr, "", log.LstdFlags)
+)
+
+// Watch signals the run goroutine to begin watching the input filename
+func Watch(fname string) error {
+	// start running the shared InotifyTracker if not already running
+	once.Do(goRun)
+
+	shared.watch <- &watchInfo{
+		fname: fname,
 	}
+	return <-shared.error
+}
+
+// RemoveWatch signals the run goroutine to remove the watch for the input filename
+func RemoveWatch(fname string) {
+	// start running the shared InotifyTracker if not already running
+	once.Do(goRun)
+
+	shared.mux.Lock()
+	done := shared.done[fname]
+	if done != nil {
+		delete(shared.done, fname)
+		close(done)
+	}
+	shared.mux.Unlock()
+
+	shared.remove <- fname
+}
+
+// Events returns a channel to which FileEvents corresponding to the input filename
+// will be sent. This channel will be closed when removeWatch is called on this
+// filename.
+func Events(fname string) chan fsnotify.Event {
+	shared.mux.Lock()
+	defer shared.mux.Unlock()
+
+	return shared.chans[fname]
+}
+
+// Cleanup removes the watch for the input filename if necessary.
+func Cleanup(fname string) {
+	RemoveWatch(fname)
+}
+
+// watchFlags calls fsnotify.WatchFlags for the input filename and flags, creating
+// a new Watcher if the previous Watcher was closed.
+func (shared *InotifyTracker) addWatch(fname string) error {
+	shared.mux.Lock()
+	defer shared.mux.Unlock()
+
+	if shared.chans[fname] == nil {
+		shared.chans[fname] = make(chan fsnotify.Event)
+		shared.done[fname] = make(chan bool)
+	}
+	return shared.watcher.Add(fname)
+}
+
+// removeWatch calls fsnotify.RemoveWatch for the input filename and closes the
+// corresponding events channel.
+func (shared *InotifyTracker) removeWatch(fname string) {
+	shared.mux.Lock()
+	defer shared.mux.Unlock()
+
+	if ch := shared.chans[fname]; ch != nil {
+		shared.watcher.Remove(fname)
+
+		delete(shared.chans, fname)
+		close(ch)
+	}
+}
+
+// sendEvent sends the input event to the appropriate Tail.
+func (shared *InotifyTracker) sendEvent(event fsnotify.Event) {
+	shared.mux.Lock()
+	ch := shared.chans[event.Name]
+	done := shared.done[event.Name]
+	shared.mux.Unlock()
+
+	if ch != nil && done != nil {
+		select {
+		case ch <- event:
+		case <-done:
+		}
+	}
+}
+
+// run starts the goroutine in which the shared struct reads events from its
+// Watcher's Event channel and sends the events to the appropriate Tail.
+func (shared *InotifyTracker) run() {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		util.Fatal("failed to create Watcher")
+	}
+	shared.watcher = watcher
+
+	for {
+		select {
+		case winfo := <-shared.watch:
+			shared.error <- shared.addWatch(winfo.fname)
+
+		case fname := <-shared.remove:
+			shared.removeWatch(fname)
+
+		case event, open := <-shared.watcher.Events:
+			if !open {
 				return
 			}
+			shared.sendEvent(event)
 
-func (t *InotifyTracker) CloseAll() {
-	t.mux.Lock()
-	defer t.mux.Unlock()
-	for w, _ := range t.watchers {
-		if err := w.Close(); err != nil {
-			log.Printf("Error closing watcher: %v", err)
-		}
-		delete(t.watchers, w)
+		case err, open := <-shared.watcher.Errors:
+			if !open {
+				return
+			} else if err != nil {
+				sysErr, ok := err.(*os.SyscallError)
+				if !ok || sysErr.Err != syscall.EINTR {
+					logger.Printf("Error in Watcher Error channel: %s", err)
+				}
+			}
+		}
 	}
 }

watch/polling.go

@@ -40,14 +40,19 @@ func (fw *PollingFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 	panic("unreachable")
 }
 
-func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, origFi os.FileInfo) *FileChanges {
+func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges {
 	changes := NewFileChanges()
 	var prevModTime time.Time
 
 	// XXX: use tomb.Tomb to cleanly manage these goroutines. replace
 	// the fatal (below) with tomb's Kill.
 
-	fw.Size = origFi.Size()
+	fw.Size = pos
+	origFi, err := os.Stat(fw.Filename)
+	if err != nil {
+		changes.NotifyDeleted()
+		return changes
+	}
 
 	go func() {
 		defer changes.Close()

watch/watch.go

@@ -2,10 +2,7 @@
 
 package watch
 
-import (
-	"gopkg.in/tomb.v1"
-	"os"
-)
+import "gopkg.in/tomb.v1"
 
 // FileWatcher monitors file-level events.
 type FileWatcher interface {
@@ -16,5 +13,7 @@ type FileWatcher interface {
 	// deletion, renames or truncations. Returned FileChanges group of
 	// channels will be closed, thus become unusable, after a deletion
 	// or truncation event.
-	ChangeEvents(*tomb.Tomb, os.FileInfo) *FileChanges
+	// In order to properly report truncations, ChangeEvents requires
+	// the caller to pass their current offset in the file.
+	ChangeEvents(*tomb.Tomb, int64) *FileChanges
 }