fileutil: update watcher to use fsnotify and polling (#3663)

* fileutil: update watcher to use fsnotify and polling

* raise timeout

* maybe fix

internal/chanutil/batch.go

@@ -0,0 +1,76 @@
+package chanutil
+
+import "time"
+
+const (
+	defaultBatchMaxSize = 1024
+	defaultBatchMaxWait = time.Millisecond * 300
+)
+
+type batchConfig struct {
+	maxSize int
+	maxWait time.Duration
+}
+
+// A BatchOption customizes a batch operation.
+type BatchOption func(cfg *batchConfig)
+
+// WithBatchMaxSize sets the maximum batch size for a Batch operation.
+func WithBatchMaxSize(maxSize int) BatchOption {
+	return func(cfg *batchConfig) {
+		cfg.maxSize = maxSize
+	}
+}
+
+// WithBatchMaxWait sets the maximum wait duration for a Batch operation.
+func WithBatchMaxWait(maxWait time.Duration) BatchOption {
+	return func(cfg *batchConfig) {
+		cfg.maxWait = maxWait
+	}
+}
+
+// Batch returns a new channel that consumes all the items from `in` and batches them together.
+func Batch[T any](in <-chan T, options ...BatchOption) <-chan []T {
+	cfg := new(batchConfig)
+	WithBatchMaxSize(defaultBatchMaxSize)(cfg)
+	WithBatchMaxWait(defaultBatchMaxWait)(cfg)
+	for _, option := range options {
+		option(cfg)
+	}
+
+	out := make(chan []T)
+	go func() {
+		var buf []T
+		var timer <-chan time.Time
+		for {
+			if in == nil && timer == nil {
+				close(out)
+				return
+			}
+
+			select {
+			case item, ok := <-in:
+				if !ok {
+					in = nil
+					timer = time.After(0)
+					continue
+				}
+				buf = append(buf, item)
+				if timer == nil {
+					timer = time.After(cfg.maxWait)
+				}
+			case <-timer:
+				timer = nil
+				for len(buf) > 0 {
+					batch := buf
+					if len(batch) > cfg.maxSize {
+						batch = batch[:cfg.maxSize]
+					}
+					buf = buf[len(batch):]
+					out <- batch
+				}
+			}
+		}
+	}()
+	return out
+}