.

wcfs/internal/zdata/δftail.go

@@ -325,7 +325,7 @@ func (δFtail *ΔFtail) rebuild1IfNeeded(foid zodb.Oid) (vδE []_ΔFileEpoch, he
 	// vδE needs to be built
 	job := δftail.rebuildJob
 
-	// rebuild is currently in-progress -> wait for corrsponding job to complete
+	// rebuild is currently in-progress -> wait for corresponding job to complete
 	if job != nil {
 		δFtail.mu.Unlock()
 		<-job.ready
@@ -362,7 +362,7 @@ func (δFtail *ΔFtail) rebuild1IfNeeded(foid zodb.Oid) (vδE []_ΔFileEpoch, he
 
 // _rebuildAll rebuilds vδE for all files from ftrackNew requests.
 //
-// must be calledwith δFtail.mu locked.
+// must be called with δFtail.mu locked.
 func (δFtail *ΔFtail) _rebuildAll() (err error) {
 	defer xerr.Contextf(&err, "ΔFtail rebuildAll")
 
@@ -619,7 +619,7 @@ func (δftail *_ΔFileTail) _forgetPast(revCut zodb.Tid) {
 // func (δFtail *ΔFtail) SliceByRev(lo, hi zodb.Tid) /*readonly*/ []ΔF
 
 // _ZinblkOverlay is used by SliceByFileRev.
-// It combiness read-only Zinblk base with read-write adjustment.
+// It combines read-only Zinblk base with read-write adjustment.
 // It provides the following operations:
 //
 //	- Get(zblk) -> {blk},
@@ -627,7 +627,7 @@ func (δftail *_ΔFileTail) _forgetPast(revCut zodb.Tid) {
 //	- DelBlk(zblk, blk)
 type _ZinblkOverlay struct {
 	Base map[zodb.Oid]setI64 // taken from _RootTrack.Zinblk or _ΔFileEpoch.oldZinblk
-	Adj  map[zodb.Oid]setI64 // adjustement over base; blk<0 reresents whitout
+	Adj  map[zodb.Oid]setI64 // adjustment over base; blk<0 represents whiteout
 }
 
 // SliceByFileRev returns history of file changes in (lo, hi] range.
@@ -724,10 +724,37 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 			// head
 			root = headRoot
 			head = δFtail.Head()
-			rt, ok := δFtail.byRoot[root]		// XXX locking
+
+			// take atomic Zinblk snapshot that covers vδZ
+			//
+			// - the reason we take snapshot is because simultaneous Track requests might
+			//   change Zinblk concurrently, and without snapshotting this might result
+			//   in changes to a block being not uniformly present in result (some
+			//   revision indicates change to that block, while another one - where the
+			//   block is too actually changed - does not indicate change to that block).
+			//
+			// - the reason we limit snapshot to vδZ is to reduce amount of under-lock
+			//   copying, because original Zinblk is potentially very large.
+			ZinblkSnap := map[zodb.Oid]setI64{}
+			δZAllOid := setOid{}
+			for _, δZ := range vδZ {
+				for _, oid := range δZ.Changev {
+					δZAllOid.Add(oid)
+				}
+			}
+			δFtail.mu.Lock()
+			rt, ok := δFtail.byRoot[root]
+			if ok {
+				for oid := range δZAllOid {
+					inblk, ok := rt.Zinblk[oid]
 					if ok {
-				Zinblk.Base = rt.Zinblk
+						ZinblkSnap[oid] = inblk.Clone()
+					}
 				}
+			}
+			δFtail.mu.Unlock()
+
+			Zinblk.Base = ZinblkSnap
 		} else {
 			δE := vδE[ie+1]
 			root = δE.oldRoot
@@ -1044,7 +1071,7 @@ func (δFtail *ΔFtail) _BlkRevAt(ctx context.Context, zfile *ZBigFile, blk int6
 }
 
 
-// ---- vδEBuild (rebuild core) ----
+// ---- vδEBuild (vδE rebuild core) ----
 
 // vδEBuild builds vδE for file from vδZ.
 func vδEBuild(foid zodb.Oid, δZtail *zodb.ΔTail, db *zodb.DB) (vδE []_ΔFileEpoch, err error) {