Add polling as a fallback to native filesystem events in server watch

Fixes gohugoio#8720
Fixes gohugoio#6849
Fixes gohugoio#7930

commands/commands.go

@@ -204,6 +204,7 @@ type hugoBuilderCommon struct {
 	environment string
 
 	buildWatch bool
+	poll       bool
 
 	gc bool
 
@@ -291,6 +292,7 @@ func (cc *hugoBuilderCommon) handleFlags(cmd *cobra.Command) {
 	cmd.Flags().StringVarP(&cc.baseURL, "baseURL", "b", "", "hostname (and path) to the root, e.g. http://spf13.com/")
 	cmd.Flags().Bool("enableGitInfo", false, "add Git revision, date and author info to the pages")
 	cmd.Flags().BoolVar(&cc.gc, "gc", false, "enable to run some cleanup tasks (remove unused cache files) after the build")
+	cmd.Flags().BoolVar(&cc.poll, "poll", false, "use a poll based approach to watch for file system changes")
 
 	cmd.Flags().Bool("templateMetrics", false, "display metrics about template executions")
 	cmd.Flags().Bool("templateMetricsHints", false, "calculate some improvement hints when combined with --templateMetrics")

commands/hugo.go

@@ -523,7 +523,7 @@ func (c *commandeer) build() error {
 
 		c.logger.Printf("Watching for changes in %s%s{%s}\n", baseWatchDir, helpers.FilePathSeparator, rootWatchDirs)
 		c.logger.Println("Press Ctrl+C to stop")
-		watcher, err := c.newWatcher(watchDirs...)
+		watcher, err := c.newWatcher(c.h.poll, watchDirs...)
 		checkErr(c.Logger, err)
 		defer watcher.Close()
 
@@ -820,7 +820,7 @@ func (c *commandeer) fullRebuild(changeType string) {
 }
 
 // newWatcher creates a new watcher to watch filesystem events.
-func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
+func (c *commandeer) newWatcher(poll bool, dirList ...string) (*watcher.Batcher, error) {
 	if runtime.GOOS == "darwin" {
 		tweakLimit()
 	}
@@ -830,7 +830,7 @@ func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
 		return nil, err
 	}
 
-	watcher, err := watcher.New(1 * time.Second)
+	watcher, err := watcher.New(1*time.Second, poll)
 	if err != nil {
 		return nil, err
 	}
@@ -859,7 +859,7 @@ func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
 					// Need to reload browser to show the error
 					livereload.ForceRefresh()
 				}
-			case err := <-watcher.Errors:
+			case err := <-watcher.Errors():
 				if err != nil {
 					c.logger.Errorln("Error while watching:", err)
 				}

commands/server.go

@@ -262,7 +262,7 @@ func (sc *serverCmd) server(cmd *cobra.Command, args []string) error {
 		for _, group := range watchGroups {
 			jww.FEEDBACK.Printf("Watching for changes in %s\n", group)
 		}
-		watcher, err := c.newWatcher(watchDirs...)
+		watcher, err := c.newWatcher(sc.poll, watchDirs...)
 		if err != nil {
 			return err
 		}

watcher/batcher.go

@@ -17,23 +17,37 @@ import (
 	"time"
 
 	"github.com/fsnotify/fsnotify"
+	"github.com/gohugoio/hugo/watcher/filenotify"
 )
 
 // Batcher batches file watch events in a given interval.
 type Batcher struct {
-	*fsnotify.Watcher
+	filenotify.FileWatcher
 	interval time.Duration
 	done     chan struct{}
 
 	Events chan []fsnotify.Event // Events are returned on this channel
 }
 
 // New creates and starts a Batcher with the given time interval.
-func New(interval time.Duration) (*Batcher, error) {
-	watcher, err := fsnotify.NewWatcher()
+// It will fall back to a poll based watcher if native isn's supported.
+// To always use pollng, set poll to true.
+func New(interval time.Duration, poll bool) (*Batcher, error) {
+	var err error
+	var watcher filenotify.FileWatcher
+
+	if poll {
+		watcher = filenotify.NewPollingWatcher()
+	} else {
+		watcher, err = filenotify.New()
+	}
+
+	if err != nil {
+		return nil, err
+	}
 
 	batcher := &Batcher{}
-	batcher.Watcher = watcher
+	batcher.FileWatcher = watcher
 	batcher.interval = interval
 	batcher.done = make(chan struct{}, 1)
 	batcher.Events = make(chan []fsnotify.Event, 1)
@@ -42,7 +56,7 @@ func New(interval time.Duration) (*Batcher, error) {
 		go batcher.run()
 	}
 
-	return batcher, err
+	return batcher, nil
 }
 
 func (b *Batcher) run() {
@@ -51,7 +65,7 @@ func (b *Batcher) run() {
 OuterLoop:
 	for {
 		select {
-		case ev := <-b.Watcher.Events:
+		case ev := <-b.FileWatcher.Events():
 			evs = append(evs, ev)
 		case <-tick:
 			if len(evs) == 0 {
@@ -69,5 +83,5 @@ OuterLoop:
 // Close stops the watching of the files.
 func (b *Batcher) Close() {
 	b.done <- struct{}{}
-	b.Watcher.Close()
+	b.FileWatcher.Close()
 }

watcher/filenotify/filenotify.go

@@ -0,0 +1,43 @@
+// Package filenotify provides a mechanism for watching file(s) for changes.
+// Generally leans on fsnotify, but provides a poll-based notifier which fsnotify does not support.
+// These are wrapped up in a common interface so that either can be used interchangeably in your code.
+//
+// This package is adapted from https://github.com/moby/moby/tree/master/pkg/filenotify, Apache-2.0 License.
+// Hopefully this can be replaced with an external package sometime in the future, see https://github.com/fsnotify/fsnotify/issues/9
+package filenotify
+
+import "github.com/fsnotify/fsnotify"
+
+// FileWatcher is an interface for implementing file notification watchers
+type FileWatcher interface {
+	Events() <-chan fsnotify.Event
+	Errors() <-chan error
+	Add(name string) error
+	Remove(name string) error
+	Close() error
+}
+
+// New tries to use an fs-event watcher, and falls back to the poller if there is an error
+func New() (FileWatcher, error) {
+	if watcher, err := NewEventWatcher(); err == nil {
+		return watcher, nil
+	}
+	return NewPollingWatcher(), nil
+}
+
+// NewPollingWatcher returns a poll-based file watcher
+func NewPollingWatcher() FileWatcher {
+	return &filePoller{
+		events: make(chan fsnotify.Event),
+		errors: make(chan error),
+	}
+}
+
+// NewEventWatcher returns an fs-event based file watcher
+func NewEventWatcher() (FileWatcher, error) {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+	return &fsNotifyWatcher{watcher}, nil
+}

watcher/filenotify/fsnotify.go

@@ -0,0 +1,20 @@
+// This package is adapted from https://github.com/moby/moby/tree/master/pkg/filenotify, Apache-2.0 License.
+// Hopefully this can be replaced with an external package sometime in the future, see https://github.com/fsnotify/fsnotify/issues/9
+package filenotify
+
+import "github.com/fsnotify/fsnotify"
+
+// fsNotifyWatcher wraps the fsnotify package to satisfy the FileNotifier interface
+type fsNotifyWatcher struct {
+	*fsnotify.Watcher
+}
+
+// Events returns the fsnotify event channel receiver
+func (w *fsNotifyWatcher) Events() <-chan fsnotify.Event {
+	return w.Watcher.Events
+}
+
+// Errors returns the fsnotify error channel receiver
+func (w *fsNotifyWatcher) Errors() <-chan error {
+	return w.Watcher.Errors
+}