.

wcfs/wcfs.go

@@ -509,7 +509,7 @@ type Head struct {
 	// XXX protected by ... zheadMu ?
 	wlinkTab map[*WatchLink]struct{}
 
-	// waiters for zconn.At to become ≥ their at.
+	// waiters for zhead.At to become ≥ their at.
 	hwaitMu sync.Mutex           // zheadMu.W  |  zheadMu.R + hwaitMu
 	hwait   map[hwaiter]struct{} // set{(at, ready)}
 }
@@ -560,7 +560,7 @@ type BigFile struct {
 	//
 	// Being a staging area for data to enter OS cache, loading has to be
 	// consulted/invalidated whenever wcfs logic needs to consult/invalidate OS cache.
-	loadMu  sync.Mutex	// XXX doc zheadMu.W  |  ...	?
+	loadMu  sync.Mutex              // zheadMu.W  |  zheadMu.R + loadMu
 	loading map[int64]*blkLoadState // #blk -> {... blkdata}
 
 	// watches attached to this file.
@@ -891,7 +891,7 @@ type hwaiter struct {
 
 // zheadWait waits till head.zconn.At becomes ≥ at.
 //
-// It returns error either if db is down or ctx is canceled.	XXX db -> wcfs?
+// It returns error either if wcfs is down or ctx is canceled.
 func (head *Head) zheadWait(ctx context.Context, at zodb.Tid) (err error) {
 	defer xerr.Contextf(&err, "wait zhead ≥ %s", at)
 
@@ -899,11 +899,13 @@ func (head *Head) zheadWait(ctx context.Context, at zodb.Tid) (err error) {
 		panic("must be called only for head/, not @revX/")
 	}
 
+	// XXX check wcfs.down
+
 	// check if zhead is already ≥ at
 	head.zheadMu.RLock()
 	if head.zconn.At() >= at {
 		head.zheadMu.RUnlock()
-		return
+		return nil
 	}
 
 	// no - we have to wait for it
@@ -1281,6 +1283,7 @@ retry:
 		break
 	}
 
+	// zheadMu rlocked.
 	// zwatcher is not currently trying to pause OS cache uploads.
 
 	// check if this block was already invalidated by zwatcher.