.

wcfs/wcfs.go

@@ -1414,29 +1414,34 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, treepath []btr
 	blkrev := blkrevMax
 	blkrevRough := true
 
-	// XXX locking (f.watchTab)
-
 	wg, ctx := errgroup.WithContext(ctx)
-	for w := range f.watchTab {
+	for w := range f.watchTab {	// XXX locking (f.watchTab)
 		w := w
 
-		fmt.Printf("S: read -> pin watchers: w @%s\n", w.at)
+		// make sure w.at stays unchanged while we pin the block
+		w.atMu.RLock()
 
-		// XXX locking (w)
+		fmt.Printf("S: read -> pin watchers: w @%s\n", w.at)
 
 		// the block is already covered by @w.at database view
-		if blkrev <= w.at {	// XXX locking
+		if blkrev <= w.at {
+			w.atMu.RUnlock()
 			continue
 		}
 
 		// if blkrev is rough estimation and that upper bound is > w.at
 		// we have to recompute ~exact file[blk] revision @head.
 		if blkrevRough {
+			// unlock atMu while we are (re-)calculating blkrev
+			// we'll relock atMu again and recheck blkrev vs w.at after.
+			w.atMu.RUnlock()
+
 			blkrev, _ = f.LastBlkRev(ctx, blk, f.head.zconn.At())
 			blkrevRough = false
 
-			// XXX w.at could be only ↑ ? if not - locking is more complex
-			if blkrev <= w.at {	// XXX locking
+			w.atMu.RLock()
+			if blkrev <= w.at {
+				w.atMu.RUnlock()
 				continue
 			}
 		}
@@ -1447,10 +1452,11 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, treepath []btr
 		// and most of them would be on different w.at - cache of the file will
 		// be lost. Via pinning to particular block revision, we make sure the
 		// revision to pin is the same on all clients, and so file cache is shared.
-		pinrev, _ := w.file.LastBlkRev(ctx, blk, w.at)	// XXX locking (w), move into go?
+		pinrev, _ := w.file.LastBlkRev(ctx, blk, w.at)	// XXX move into go?
 
 		wg.Go(func() error {
 			// XXX close watcher on any error
+			defer w.atMu.RUnlock()
 			return w.pin(ctx, blk, pinrev)
 		})
 	}