.

wcfs/δbtail.go

@@ -217,10 +217,18 @@ type ΔTree struct {
 }
 
 
+// XXX is a set of PP(leafs) nodes	XXX -> PTreeSubSet ? TreePSubSet ?  TreePPSet ? PPSubSet ?
+//					XXX    PPNodeSet? TreePPSubSet ?
+//
+// where PP maps a leaf to {leaf, leaf.parent, leaf.parent.parent, ...} up to
+// top root node from where the leaf is reached.
+//
+// Every node in the set also has .parent pointer.
+//
 // XXX place
 type trackIndex map[zodb.Oid]*nodeTrack
 
-// XXX place
+// XXX place				XXX PTreeSubSetNode ?
 // nodeTrack represents tracking information about a node.
 type nodeTrack struct {
 	parent  zodb.Oid // parent node | InvalidOid for root
@@ -314,20 +322,37 @@ func (tidx trackIndex) verify() {
 	}
 }
 
-// Update tidx with trees subsets from tidx2.
-func (tidx trackIndex) Update(tidx2 trackIndex) {
-	//fmt.Printf("\n\nUpdate:\n")
-	//fmt.Printf("tidx:  %s\n", tidx)
-	//fmt.Printf("tidx2: %s\n", tidx2)
+// DifferenceInplace sets A = PP(A.leafs \ B.leafs)
+//
+// In other words it removes B nodes from A while still maintaining A as P-connected.
+func (A trackIndex) DifferenceInplace(B trackIndex) {
+	//fmt.Printf("\n\nDifferenceInplace:\n")
+	//fmt.Printf("A: %s\n", A)
+	//fmt.Printf("B: %s\n", B)
 
-	tidx.verify()
-	tidx2.verify()
+	A.verify()
+	B.verify()
+	defer A.verify()
+	panic("TODO")
+}
 
-	for oid, t2 := range tidx2 {
-		t, already := tidx[oid]
+// UnionInplace sets A = PP(A.leafs | B.leafs)
+//
+// In other words it adds B nodes to A.
+func (A trackIndex) UnionInplace(B trackIndex) {
+	//fmt.Printf("\n\nUnionInplace:\n")
+	//fmt.Printf("A: %s\n", A)
+	//fmt.Printf("B: %s\n", B)
+
+	A.verify()
+	B.verify()
+	defer A.verify()
+
+	for oid, t2 := range B {
+		t, already := A[oid]
 		if !already {
 			t = &nodeTrack{parent: t2.parent, nchild: t2.nchild}
-			tidx[oid] = t
+			A[oid] = t
 		} else {
 			if t2.parent != t.parent {
 				// XXX or verify this at Track time and require
@@ -343,12 +368,10 @@ func (tidx trackIndex) Update(tidx2 trackIndex) {
 			if t.parent != zodb.InvalidOid {
 				// this node is already present in both trees
 				// compensate for that in its parent (which must be present)
-				tidx[t.parent].nchild--
+				A[t.parent].nchild--
 			}
 		}
 	}
-
-	tidx.verify()
 }
 
 // ApplyΔ applies δ to trackIdx.	XXX
@@ -743,7 +766,7 @@ func (δBtail *ΔBtail) rebuild() (err error) {
 	//
 	// XXX -> teach diffT to return not only δtrack, but also δtrack*
 	// (conjugate) that would describe how track index changes if going A<-B ?
-	δBtail.trackIdx.Update(trackNew)
+	δBtail.trackIdx.UnionInplace(trackNew)
 
 	return nil
 }