Add ScanNow()

Source: radovskyb#94

Author: dideler

watcher.go

@@ -22,6 +22,11 @@ var (
 	// from previously calling Start and not yet calling Close.
 	ErrWatcherRunning = errors.New("error: watcher is already running")
 
+	// ErrWatcherNotRunning occurs when trying to perform a ScanNow
+	// when the watcher is not running. It will also occur if Close is called
+	// whilst a ScanNow() is running / pending.
+	ErrWatcherNotRunning = errors.New("error: watcher is not running")
+
 	// ErrWatchedFileDeleted is an error that occurs when a file or folder that was
 	// being watched has been deleted.
 	ErrWatchedFileDeleted = errors.New("error: watched file or folder deleted")
@@ -129,6 +134,7 @@ type Watcher struct {
 	ops          map[Op]struct{}        // Op filtering.
 	ignoreHidden bool                   // ignore hidden files or not.
 	maxEvents    int                    // max sent events per cycle
+	scanNow      chan chan struct{}     // allows requests for immediate synchronous scans
 }
 
 // New creates a new Watcher.
@@ -147,6 +153,7 @@ func New() *Watcher {
 		files:   make(map[string]os.FileInfo),
 		ignored: make(map[string]struct{}),
 		names:   make(map[string]bool),
+		scanNow: make(chan chan struct{}),
 	}
 }
 
@@ -550,6 +557,8 @@ func (w *Watcher) Start(d time.Duration) error {
 	// Unblock w.Wait().
 	w.wg.Done()
 
+	var scanNowRequest chan struct{}
+
 	for {
 		// done lets the inner polling cycle loop know when the
 		// current cycle's method has finished executing.
@@ -589,7 +598,7 @@ func (w *Watcher) Start(d time.Duration) error {
 					}
 				}
 				numEvents++
-				if w.maxEvents > 0 && numEvents > w.maxEvents {
+				if scanNowRequest == nil && w.maxEvents > 0 && numEvents > w.maxEvents {
 					close(cancel)
 					break inner
 				}
@@ -604,8 +613,52 @@ func (w *Watcher) Start(d time.Duration) error {
 		w.files = fileList
 		w.mu.Unlock()
 
+		if scanNowRequest != nil {
+			close(scanNowRequest)
+			scanNowRequest = nil
+		}
+
 		// Sleep and then continue to the next loop iteration.
-		time.Sleep(d)
+		// If a request to do a full scan is received, handle it and then signal to the requester it is complete.
+		select {
+		case <-w.close: // break out of wait early if we get a Close
+		case scanNowRequest = <-w.scanNow: // sync scan request received
+		case <-time.After(d): // periodic re-roll time elapsed
+		}
+	}
+}
+
+// ScanNow can be called on a already running watcher to perform an immediate synchronous scan of all watched files
+// and generate the events for any changes. When ScanNow() returns to the caller, all events for any changed files
+// have been published. ScanNow() can be used when you know FS changes have occurred and you want to ensure all events
+// for the changes have been gathered before continuing, for example, to better process batched updates to groups of
+// files.
+// You can also specify a very long poll duration and then use ScanNow() to break from the poll wait and perform a scan
+// before going back to sleep.
+func (w *Watcher) ScanNow() error {
+	w.mu.Lock()
+	if !w.running {
+		w.mu.Unlock()
+		return ErrWatcherNotRunning
+	}
+	w.mu.Unlock()
+
+	scanComplete := make(chan struct{})
+	select {
+	case w.scanNow <- scanComplete:
+	case <-w.close:
+		// if the watcher is no longer running, or is closed whilst we're waiting for our scan to be accepted, return
+		// an error
+		return ErrWatcherNotRunning
+	}
+
+	select {
+	case <-w.close:
+		// if the watcher is closed whilst we're waiting for our scan to complete, return an error
+		return ErrWatcherNotRunning
+	case <-scanComplete:
+		// scan completed ok
+		return nil
 	}
 }
 
@@ -700,6 +753,7 @@ func (w *Watcher) Wait() {
 }
 
 // Close stops a Watcher and unlocks its mutex, then sends a close signal.
+// Note, it is not safe to Start() a Watcher again after closing it. You must create a new Watcher.
 func (w *Watcher) Close() {
 	w.mu.Lock()
 	if !w.running {
@@ -711,5 +765,6 @@ func (w *Watcher) Close() {
 	w.names = make(map[string]bool)
 	w.mu.Unlock()
 	// Send a close signal to the Start method.
-	w.close <- struct{}{}
+	// Use a channel close() rather than a channel write, so that ScanNow() can react to the closure also.
+	close(w.close)
 }

watcher_test.go

@@ -539,6 +539,90 @@ func TestTriggerEvent(t *testing.T) {
 	wg.Wait()
 }
 
+func TestScanNow(t *testing.T) {
+	testDir, teardown := setup(t)
+	defer teardown()
+
+	w := New()
+	w.FilterOps(Create)
+
+	// Add the testDir to the watchlist.
+	if err := w.AddRecursive(testDir); err != nil {
+		t.Fatal(err)
+	}
+
+	// should not be able to ScanNow() before the watcher is started
+	if err := w.ScanNow(); err != ErrWatcherNotRunning {
+		t.Fatal("expected an ErrWatcherNotRunning error, but didn't get one")
+	}
+
+	testFilePath := filepath.Join(testDir, "test_file1.txt")
+	done := make(chan struct{})
+	go func() {
+		evt := <-w.Event
+		if evt.Op == Create && evt.Path == testFilePath {
+			close(done)
+		} else {
+			t.Fatal("unexpected event")
+		}
+	}()
+
+	// Start scanning with a very long poll duration
+	go func() {
+		if err := w.Start(time.Hour); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	w.Wait()
+	defer w.Close()
+
+	// perform initial scan, which should yield no changes
+	// this ensures the initial scan has happened, and means the watcher is now waiting 1hr before scanning again
+	if err := w.ScanNow(); err != nil {
+		t.Error(err)
+	}
+
+	// wait for a short period just to ensure no unexpected events arrive
+	select {
+	case <-time.After(time.Millisecond * 100):
+	case <-done:
+		t.Fatal("should not have received an event as no changes have occurred since ScanNow() completed")
+	}
+
+	// create the test file, we will not receive events due to the 1hr poll duration
+	if err := ioutil.WriteFile(testFilePath, []byte{}, 0755); err != nil {
+		t.Error(err)
+	}
+
+	// wait for a short period just to ensure no unexpected events arrive now we've changed a file
+	select {
+	case <-time.After(time.Millisecond * 100):
+	case <-done:
+		t.Fatal("should not have received an event as a poll duration of 1 hour is used")
+	}
+
+	// issue a scan now, and we will receive the events while ScanNow() is running.
+	if err := w.ScanNow(); err != nil {
+		t.Error(err)
+	}
+
+	// all events should have been received *whilst* ScanNow() was running, so the done channel should already be
+	// closed
+	select {
+	case <-done:
+	default:
+		t.Fatal("events from ScanNow() should have been received before ScanNow() returned")
+	}
+
+	w.Close()
+
+	// issue a scan now after closing, should error
+	if err := w.ScanNow(); err != ErrWatcherNotRunning {
+		t.Fatal("expected an ErrWatcherNotRunning error, but didn't get one")
+	}
+}
+
 func TestEventAddFile(t *testing.T) {
 	testDir, teardown := setup(t)
 	defer teardown()