.

wcfs/internal/zdata/δftail.go

@@ -96,7 +96,7 @@ type ΔFtail struct {
 // _ΔFileTail represents tail of revisional changes to one file.
 type _ΔFileTail struct {
 	root zodb.Oid      // .blktab as of @head
-	vδE  []_ΔFileEpoch // changes to ZBigFile object itself  ; nil if not yet rebuilt
+	vδE  []_ΔFileEpoch // epochs (changes to ZBigFile object itself)  ; nil if not yet rebuilt
 }
 
 // _ΔFileEpoch represent a change to ZBigFile object.
@@ -202,7 +202,8 @@ func (δFtail *ΔFtail) Track(file *ZBigFile, blk int64, path []btree.LONode, zb
 		δFtail.trackNew.Add(foid)
 	}
 	if δftail.root != roid {
-		panicf("zfile<%s> changed root from %s -> %s", foid, δftail.root, roid)
+		// .root can change during epochs, but in between them it must be stable
+		panicf("BUG: zfile<%s> root mutated from %s -> %s", foid, δftail.root, roid)
 	}
 
 
@@ -320,16 +321,9 @@ func (δftail *_ΔFileTail) rebuild1(foid zodb.Oid, δZtail *zodb.ΔTail, db *zo
 // It returns change in files space that corresponds to δZ.
 //
 // δZ should include all objects changed by ZODB transaction.
-//
-// XXX readd zhead?
-// // Zhead must be active connection at δFtail.Head() database state.
-// // Objects in Zhead must not be modified.
-// // During call to Update zhead must not be otherwise used - even for reading.
-//func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit, zhead *xzodb.ZConn) (_ ΔF, err error) {
 func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
 	defer xerr.Contextf(&err, "ΔFtail update %s -> %s", δFtail.Head(), δZ.Tid)
 
-	// XXX verify zhead.At() == δFtail.Head()
 	// XXX locking
 
 	// rebuild vδE for newly tracked files
@@ -361,7 +355,6 @@ func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
 		//fmt.Printf("zfile<%s> diff %s..%s   -> δ: %v\n", oid, headOld, δZ.Tid, δ)
 
 		if δ != nil {
-			// XXX rebuild first
 			δzfile[oid] = δ
 			δE := _ΔFileEpoch{
 				Rev:             δZ.Tid,