vfs: use call after functions in writeback to simplify code

This also fixes a bug in the uploader which didn't restart the timer
when the queue was empty.

vfs/vfscache/writeback.go

@@ -22,12 +22,13 @@ type putFn func(context.Context) error
 
 // writeBack keeps track of the items which need to be written back to the disk at some point
 type writeBack struct {
+	ctx     context.Context
 	mu      sync.Mutex
 	items   writeBackItems           // priority queue of *writeBackItem - writeBackItems are in here while awaiting transfer only
 	lookup  map[*Item]*writeBackItem // for getting a *writeBackItem from a *Item - writeBackItems are in here until cancelled
 	opt     *vfscommon.Options       // VFS options
 	timer   *time.Timer              // next scheduled time for the uploader
-	kick    chan struct{}            // send on this channel to wake up the uploader
+	expiry  time.Time                // time the next item exires or IsZero
 	uploads int                      // number of uploads in progress
 }
 
@@ -36,15 +37,12 @@ type writeBack struct {
 // cancel the context to stop the background goroutine
 func newWriteBack(ctx context.Context, opt *vfscommon.Options) *writeBack {
 	wb := &writeBack{
+		ctx:    ctx,
 		items:  writeBackItems{},
 		lookup: make(map[*Item]*writeBackItem),
 		opt:    opt,
-		timer:  time.NewTimer(time.Second),
-		kick:   make(chan struct{}, 1),
 	}
-	wb.timer.Stop()
 	heap.Init(&wb.items)
-	go wb.uploader(ctx)
 	return wb
 }
 
@@ -193,13 +191,31 @@ func (wb *writeBack) _peekItem() (wbItem *writeBackItem) {
 func (wb *writeBack) _resetTimer() {
 	wbItem := wb._peekItem()
 	if wbItem == nil {
+		if wb.expiry.IsZero() {
+			return
+		}
+		wb.expiry = time.Time{}
+		fs.Debugf(nil, "resetTimer STOP")
+		if wb.timer != nil {
 			wb.timer.Stop()
+			wb.timer = nil
+		}
 	} else {
+		if wb.expiry.Equal(wbItem.expiry) {
+			return
+		}
+		wb.expiry = wbItem.expiry
 		dt := time.Until(wbItem.expiry)
 		if dt < 0 {
 			dt = 0
 		}
-		wb.timer.Reset(dt)
+		fs.Debugf(nil, "resetTimer dt=%v", dt)
+		if wb.timer != nil {
+			wb.timer.Stop()
+		}
+		wb.timer = time.AfterFunc(dt, func() {
+			wb.processItems(wb.ctx)
+		})
 	}
 }
 
@@ -207,7 +223,7 @@ func (wb *writeBack) _resetTimer() {
 // is already there.
 //
 // if modified is false then it it doesn't a pending upload
-func (wb *writeBack) add(item *Item, name string, modified bool, putFn putFn) {
+func (wb *writeBack) add(item *Item, name string, modified bool, putFn putFn) *writeBackItem {
 	wb.mu.Lock()
 	defer wb.mu.Unlock()
 
@@ -224,6 +240,7 @@ func (wb *writeBack) add(item *Item, name string, modified bool, putFn putFn) {
 	}
 	wbItem.putFn = putFn
 	wb._resetTimer()
+	return wbItem
 }
 
 // Call when a file is removed. This cancels a writeback if there is
@@ -248,19 +265,6 @@ func (wb *writeBack) remove(item *Item) (found bool) {
 	return found
 }
 
-// kick the upload checker
-//
-// This should be called at the end of uploads just in case we had to
-// pause uploades because max items was exceeded
-//
-// call with the lock held
-func (wb *writeBack) _kickUploader() {
-	select {
-	case wb.kick <- struct{}{}:
-	default:
-	}
-}
-
 // upload the item - called as a goroutine
 //
 // uploading will have been incremented here already
@@ -276,7 +280,7 @@ func (wb *writeBack) upload(ctx context.Context, wbItem *writeBackItem) {
 
 	wbItem.cancel() // cancel context to release resources since store done
 
-	fs.Debugf(wbItem.name, "uploading = false %p item %p", wbItem, wbItem.item)
+	//fs.Debugf(wbItem.name, "uploading = false %p item %p", wbItem, wbItem.item)
 	wbItem.uploading = false
 	wb.uploads--
 
@@ -301,7 +305,7 @@ func (wb *writeBack) upload(ctx context.Context, wbItem *writeBackItem) {
 		// show that we are done with the item
 		wb._delItem(wbItem)
 	}
-	wb._kickUploader()
+	wb._resetTimer()
 	close(wbItem.done)
 }
 
@@ -348,7 +352,11 @@ func (wb *writeBack) processItems(ctx context.Context) {
 	wb.mu.Lock()
 	defer wb.mu.Unlock()
 
-	resetTimer := false
+	if wb.ctx.Err() != nil {
+		return
+	}
+
+	resetTimer := true
 	for wbItem := wb._peekItem(); wbItem != nil && time.Until(wbItem.expiry) <= 0; wbItem = wb._peekItem() {
 		// If reached transfer limit don't restart the timer
 		if wb.uploads >= fs.Config.Transfers {
@@ -356,10 +364,9 @@ func (wb *writeBack) processItems(ctx context.Context) {
 			resetTimer = false
 			break
 		}
-		resetTimer = true
 		// Pop the item, mark as uploading and start the uploader
 		wbItem = wb._popItem()
-		fs.Debugf(wbItem.name, "uploading = true %p item %p", wbItem, wbItem.item)
+		//fs.Debugf(wbItem.name, "uploading = true %p item %p", wbItem, wbItem.item)
 		wbItem.uploading = true
 		wb.uploads++
 		newCtx, cancel := context.WithCancel(ctx)
@@ -373,22 +380,6 @@ func (wb *writeBack) processItems(ctx context.Context) {
 	}
 }
 
-// Looks for items which need writing back and write them back until
-// the context is cancelled
-func (wb *writeBack) uploader(ctx context.Context) {
-	for {
-		select {
-		case <-ctx.Done():
-			wb.timer.Stop()
-			return
-		case <-wb.timer.C:
-			wb.processItems(ctx)
-		case <-wb.kick:
-			wb.processItems(ctx)
-		}
-	}
-}
-
 // return the number of uploads in progress
 func (wb *writeBack) getStats() (uploadsInProgress, uploadsQueued int) {
 	wb.mu.Lock()