.

wcfs/wcfs.go

@@ -1243,6 +1243,22 @@ func (f *BigFile) readBlk(ctx context.Context, blk int64, dest []byte) (err erro
 
 	// noone was loading - we became responsible to load this block
 	blkdata, treepath, blkcov, zblk, blkrevMax, err := f.zfile.LoadBlk(ctx, blk)
+
+	// head/ - update δFtail + pin watchers
+	if f.head.rev == 0 && err == nil {
+		// update δFtail index
+		// see "3) for */head/data the following invariant is maintained..."
+		δFtail := f.head.bfdir.δFtail
+		δFtail.Track(f.zfile, blk, treepath, blkcov, zblk)
+
+		// we have the data - it can be used after watchers are updated
+		// XXX should we use ctx here? (see readPinWatchers comments)
+		err = f.readPinWatchers(ctx, blk, blkrevMax)
+		if err != nil {
+			blkdata = nil
+		}
+	}
+
 	loading.blkdata = blkdata
 	loading.err = err
 
@@ -1255,17 +1271,6 @@ func (f *BigFile) readBlk(ctx context.Context, blk int64, dest []byte) (err erro
 		return err
 	}
 
-	if f.head.rev == 0 {
-		// update δFtail index
-		// see "3) for */head/data the following invariant is maintained..."
-		δFtail := f.head.bfdir.δFtail
-		δFtail.Track(f.zfile, blk, treepath, blkcov, zblk)
-
-		// we have the data - it can be used after watchers are updated
-		// XXX should we use ctx here? (see readPinWatchers comments)
-		f.readPinWatchers(ctx, blk, blkrevMax)
-	}
-
 	// data can be used now
 	close(loading.ready)
 	copy(dest, blkdata) // TODO avoid copy
@@ -1483,7 +1488,9 @@ func (w *Watch) _pin(ctx context.Context, blk int64, rev zodb.Tid) (err error) {
 // XXX do we really need to use/propagate caller context here? ideally update
 // watchers should be synchronous, and in practice we just use 30s timeout.
 // Should a READ interrupt cause watch update failure? -> probably no
-func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, blkrevMax zodb.Tid) {
+func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, blkrevMax zodb.Tid) (err error) {
+	defer xerr.Context(&err, "pin watchers") // f.path and blk is already put into context by readBlk
+
 	// only head/ is being watched for
 	if f.head.rev != 0 {
 		panic("BUG: readPinWatchers: called for file under @revX/")
@@ -1526,7 +1533,7 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, blkrevMax zodb
 			var err error
 			blkrev, _, err = δFtail.BlkRevAt(ctx, f.zfile, blk, f.head.zconn.At())
 			if err != nil {
-				panic(err)	// XXX
+				return err
 			}
 			blkrevRough = false
 
@@ -1546,7 +1553,7 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, blkrevMax zodb
 		pinrev, _, err := δFtail.BlkRevAt(ctx, w.file.zfile, blk, w.at) // XXX move into go?
 		// XXX ^^^ w.file vs f ?
 		if err != nil {
-			panic(err)	// XXX
+			return err
 		}
 
 		//fmt.Printf("S: read #%d: watch @%s: pin -> @%s\n", blk, w.at, pinrev)
@@ -1558,10 +1565,7 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, blkrevMax zodb
 	}
 	f.watchMu.RUnlock()
 
-	err := wg.Wait()
-	if err != nil {
-		panic(err)	// XXX
-	}
+	return wg.Wait()
 }
 
 // setupWatch sets up or updates a Watch when client sends `watch <file> @<at>` request.