Asynchronously write to walk output files (#118)

* Asynchronously write to walk output files

* Reduce number of goroutines to reduce memory usage (by ~3/4)

* Update linter version

.github/workflows/golangci-lint.yml

@@ -22,5 +22,5 @@ jobs:
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v3
         with:
-          version: v1.59.1
-          only-new-issues: true
+          version: v1.62.0
+          only-new-issues: true

walk/file.go

@@ -65,6 +65,45 @@ func (b *bufferedFile) Close() error {
 	return b.Closer.Close()
 }
 
+type asyncWriter struct {
+	mu     sync.Mutex
+	buffer [bufferSize]byte
+	len    int
+	err    error
+	io.WriteCloser
+}
+
+func (a *asyncWriter) Write(p []byte) (int, error) {
+	a.mu.Lock()
+
+	if a.err != nil {
+		defer a.mu.Unlock()
+
+		return 0, a.err
+	}
+
+	a.len = copy(a.buffer[:], p)
+
+	go func() {
+		defer a.mu.Unlock()
+
+		_, a.err = a.WriteCloser.Write(a.buffer[:a.len])
+	}()
+
+	return len(p), nil
+}
+
+func (a *asyncWriter) Close() error {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if a.err != nil {
+		return a.err
+	}
+
+	return a.WriteCloser.Close()
+}
+
 // Files represents a collection of output files that can be written to in a
 // round-robin.
 type Files struct {
@@ -101,8 +140,10 @@ func NewFiles(outDir string, n int) (*Files, error) {
 			return nil, err
 		}
 
-		files[i].Writer = bufio.NewWriterSize(file, bufferSize)
-		files[i].Closer = file
+		f := &asyncWriter{WriteCloser: file}
+
+		files[i].Writer = bufio.NewWriterSize(f, bufferSize)
+		files[i].Closer = f
 
 		outPaths[i] = path
 	}

walk/walk.go

@@ -274,12 +274,10 @@ func walkDirectory(ctx context.Context, dirent Dirent,
 	childControllers := make([]*flowController, len(children))
 
 	for n, child := range children {
-		childControllers[n] = newController()
-
 		if child.IsDir() {
+			childControllers[n] = newController()
+
 			go walkDirectory(ctx, child, childControllers[n], request, sendDirs)
-		} else {
-			go sendFileEntry(ctx, child, childControllers[n])
 		}
 	}
 
@@ -289,20 +287,17 @@ func walkDirectory(ctx context.Context, dirent Dirent,
 		sendEntry(ctx, dirent, control)
 	}
 
-	for _, childController := range childControllers {
-		childController.PassControl(control)
+	for n, childController := range childControllers {
+		if childController == nil {
+			sendEntry(ctx, children[n], control)
+		} else {
+			childController.PassControl(control)
+		}
 	}
 
 	flowControl.EndControl()
 }
 
-func sendFileEntry(ctx context.Context, dirent Dirent, flowControl *flowController) {
-	control := flowControl.GetControl()
-
-	sendEntry(ctx, dirent, control)
-	flowControl.EndControl()
-}
-
 func sendEntry(ctx context.Context, dirent Dirent, direntCh chan<- Dirent) {
 	select {
 	case <-ctx.Done():