fix data race

tail.go

@@ -10,6 +10,7 @@ import (
 	"log"
 	"os"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/hpcloud/tail/ratelimiter"
@@ -82,6 +83,8 @@ type Tail struct {
 	changes *watch.FileChanges
 
 	tomb.Tomb // provides: Done, Kill, Dying
+
+	lk sync.Mutex
 }
 
 var (
@@ -140,7 +143,9 @@ func (tail *Tail) Tell() (offset int64, err error) {
 	}
 	offset, err = tail.file.Seek(0, os.SEEK_CUR)
 	if err == nil {
+		tail.lk.Lock()
 		offset -= int64(tail.reader.Buffered())
+		tail.lk.Unlock()
 	}
 	return
 }
@@ -187,7 +192,9 @@ func (tail *Tail) reopen() error {
 }
 
 func (tail *Tail) readLine() (string, error) {
+	tail.lk.Lock()
 	line, err := tail.reader.ReadString('\n')
+	tail.lk.Unlock()
 	if err != nil {
 		// Note ReadString "returns the data read before the error" in
 		// case of an error, including EOF, so we return it as is. The
@@ -315,7 +322,10 @@ func (tail *Tail) waitForChanges() error {
 		if err != nil {
 			return err
 		}
-		tail.changes = tail.watcher.ChangeEvents(&tail.Tomb, pos)
+		tail.changes, err = tail.watcher.ChangeEvents(&tail.Tomb, pos)
+		if err != nil {
+			return err
+		}
 	}
 
 	select {

watch/inotify.go

@@ -55,14 +55,13 @@ func (fw *InotifyFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 	panic("unreachable")
 }
 
-func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges {
+func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {
-	changes := NewFileChanges()
-
 	err := Watch(fw.Filename)
 	if err != nil {
-		go changes.NotifyDeleted()
+		return nil, err
 	}
 
+	changes := NewFileChanges()
 	fw.Size = pos
 
 	go func() {
@@ -116,5 +115,5 @@ func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges
 		}
 	}()
 
-	return changes
+	return changes, nil
 }

watch/polling.go

@@ -3,11 +3,12 @@
 package watch
 
 import (
-	"github.com/hpcloud/tail/util"
-	"gopkg.in/tomb.v1"
 	"os"
 	"runtime"
 	"time"
+
+	"github.com/hpcloud/tail/util"
+	"gopkg.in/tomb.v1"
 )
 
 // PollingFileWatcher polls the file for changes.
@@ -40,7 +41,12 @@ func (fw *PollingFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 	panic("unreachable")
 }
 
-func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges {
+func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {
+	origFi, err := os.Stat(fw.Filename)
+	if err != nil {
+		return nil, err
+	}
+
 	changes := NewFileChanges()
 	var prevModTime time.Time
 
@@ -48,11 +54,6 @@ func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges
 	// the fatal (below) with tomb's Kill.
 
 	fw.Size = pos
-	origFi, err := os.Stat(fw.Filename)
-	if err != nil {
-		changes.NotifyDeleted()
-		return changes
-	}
 
 	go func() {
 		defer changes.Close()
@@ -110,7 +111,7 @@ func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) *FileChanges
 		}
 	}()
 
-	return changes
+	return changes, nil
 }
 
 func init() {

watch/watch.go

@@ -15,5 +15,5 @@ type FileWatcher interface {
 	// or truncation event.
 	// In order to properly report truncations, ChangeEvents requires
 	// the caller to pass their current offset in the file.
-	ChangeEvents(*tomb.Tomb, int64) *FileChanges
+	ChangeEvents(*tomb.Tomb, int64) (*FileChanges, error)
 }