.

wcfs/internal/zdata/δftail.go

@@ -67,6 +67,7 @@ import (
 	"context"
 	"fmt"
 	"sort"
+	"sync"
 
 	"lab.nexedi.com/kirr/go123/xerr"
 	"lab.nexedi.com/kirr/neo/go/transaction"
@@ -137,7 +138,11 @@ type ΔFtail struct {
 	// ΔFtail merges ΔBtail with history of ZBlk
 	δBtail      *xbtree.ΔBtail
 
-	// XXX mu sync.Mutex  + comment
+	// mu protects ΔFtail data _and_ all _ΔFileTail data for all files.
+	//
+	// NOTE: even though this lock is global, since ... XXX
+	// working with retrieved vδE snapshot(?) does not need to hold the lock.
+	mu sync.Mutex
 
 	byFile      map[zodb.Oid]*_ΔFileTail // file -> vδf tail
 	filesByRoot map[zodb.Oid]setOid      // tree-root -> {} ZBigFile<oid>    as of @head
@@ -324,7 +329,7 @@ func (δFtail *ΔFtail) rebuild1IfNeeded(foid zodb.Oid) (vδE []_ΔFileEpoch, he
 		δBtail := δFtail.δBtail
 		err = δftail._rebuild1(foid, δBtail.ΔZtail(), δBtail.DB())
 	}
-	return δftail, err
+	return δftail.vδE, δftail.root, err
 }
 
 // _rebuild1 rebuilds vδE.
@@ -542,7 +547,7 @@ func (δFtail *ΔFtail) ForgetPast(revCut zodb.Tid) {
 	// TODO keep index which file changed epoch where (similarly to ΔBtail),
 	// and, instead of scanning all files, trim vδE only on files that is really necessary.
 	for _, δftail := range δFtail.byFile {
-		δftail.forgetPast(revCut)
+		δftail._forgetPast(revCut)
 	}
 }
 
@@ -844,13 +849,14 @@ func (δFtail *ΔFtail) _BlkRevAt(ctx context.Context, zfile *ZBigFile, blk int6
 
 	// XXX locking
 
-	δftail, err := δFtail.rebuild1IfNeeded(foid)
+//	δftail, err := δFtail.rebuild1IfNeeded(foid)
+	vδE, headRoot, err := δFtail.rebuild1IfNeeded(foid)
 	if err != nil {
 		return zodb.InvalidTid, false, err
 	}
 
 	// find epoch that covers at and associated blktab root/object
-	vδE := δftail.vδE
+//	vδE := δftail.vδE
 	//fmt.Printf("  vδE: %v\n", vδE)
 	l := len(vδE)
 	i := sort.Search(l, func(i int) bool {
@@ -862,7 +868,8 @@ func (δFtail *ΔFtail) _BlkRevAt(ctx context.Context, zfile *ZBigFile, blk int6
 	// root
 	var root zodb.Oid
 	if i == l {
-		root = δftail.root
+//		root = δftail.root
+		root = headRoot
 	} else {
 		root = vδE[i].oldRoot
 	}