.

wcfs/internal/xbtree/δbtail.go

@@ -672,13 +672,13 @@ func (δTtail *_ΔTtail) __rebuild(root zodb.Oid, δBtail *ΔBtail, releaseLock
 //
 // TODO optionally accept zconnOld/zconnNew from client
 func (δBtail *ΔBtail) Update(δZ *zodb.EventCommit) (_ ΔB, err error) {
+	headOld := δBtail.Head()
+	defer xerr.Contextf(&err, "ΔBtail.Update %s -> %s", headOld, δZ.Tid)
+
 	δBtail.mu.Lock()
 	defer δBtail.mu.Unlock()
 	// TODO verify that there is no in-progress readers/writers
 
-	headOld := δBtail.Head()
-	defer xerr.Contextf(&err, "ΔBtail.Update %s -> %s", headOld, δZ.Tid)
-
 	δB1, err := δBtail._Update1(δZ)
 
 	δB := ΔB{Rev: δZ.Tid, ByRoot: make(map[zodb.Oid]map[Key]ΔValue)}

wcfs/internal/zdata/δftail.go

@@ -316,6 +316,8 @@ func (δFtail *ΔFtail) rebuildAll() (err error) {
 //
 // it returns corresponding δftail for convenience. XXX
 // the only case when vδE actually needs to be rebuilt is when the file just started to be tracked.
+//
+// XXX naming -> vδEForFile ?
 func (δFtail *ΔFtail) rebuild1IfNeeded(foid zodb.Oid) (vδE []_ΔFileEpoch, headRoot zodb.Oid, err error) {
 	δFtail.mu.Lock() // TODO verify that there is no in-progress writers
 	defer δFtail.mu.Unlock()
@@ -359,12 +361,12 @@ func (δftail *_ΔFileTail) _rebuild1(foid zodb.Oid, δZtail *zodb.ΔTail, db *z
 //
 // δZ should include all objects changed by ZODB transaction.
 func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
-	defer xerr.Contextf(&err, "ΔFtail update %s -> %s", δFtail.Head(), δZ.Tid)
+	headOld := δFtail.Head()
+	defer xerr.Contextf(&err, "ΔFtail update %s -> %s", headOld, δZ.Tid)
 
-	// XXX locking
-	//δFtail.mu.Lock()
-	//defer δFtail.mu.Unlock()
-	//// TODO verify that there is no in-progress readers/writers
+	δFtail.mu.Lock()
+	defer δFtail.mu.Unlock()
+	// TODO verify that there is no in-progress readers/writers
 
 	// rebuild vδE for newly tracked files
 	err = δFtail.rebuildAll()
@@ -372,7 +374,6 @@ func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
 		return ΔF{}, err
 	}
 
-	headOld := δFtail.Head()
 	δB, err := δFtail.δBtail.Update(δZ)
 	if err != nil {
 		return ΔF{}, err