.

wcfs/zδtail_i64.go

 // Code generated by gen-δtail I64 int64; DO NOT EDIT.
-// (from lab.nexedi.com/kirr/neo/go/zodb @ v1.9-2078-gae3c4829)
+// (from lab.nexedi.com/kirr/neo/go/zodb @ v1.9-2080-gd1f63f32)
 
 // Copyright (C) 2018-2019  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
@@ -24,18 +24,18 @@ package main
 
 import "lab.nexedi.com/kirr/neo/go/zodb"
 
+// XXX do we really need ΔTailI64 to be exported from zodb?
+// (other users are low level caches + maybe ZEO/NEO -> zplumbing? but then import cycle)
+
 import (
 	"fmt"
 )
 
-// XXX do we really need ΔTailI64 to be exported from zodb?
-// (other users are low level caches + maybe ZEO/NEO -> zplumbing? but then import cycle)
-
 // ΔTailI64 represents tail of revisional changes.
 //
 // It semantically consists of
 //
-//	[](rev↑, []id)
+//	[](rev↑, []id)				XXX + head?
 //
 // and index
 //
@@ -48,10 +48,10 @@ import (
 //
 // It provides operations to
 //
-//	- XXX Head
 //	- append information to the tail about next revision,
 //	- forget information in the tail past specified revision, and
 //	- query the tail about what is last revision that changed an id.
+//	- query the tail about what head/tail	XXX?
 //
 // ΔTailI64 is safe to access for multiple-readers / single writer.
 //
@@ -60,6 +60,7 @@ import (
 //	oid  - ZODB object identifier, when ΔTailI64 represents changes to ZODB objects,
 //	#blk - file block number, when ΔTailI64 represents changes to a file.
 type ΔTailI64 struct {
+	head  zodb.Tid
 	tailv []δRevEntryI64
 
 	lastRevOf map[int64]zodb.Tid // index for LastRevOf queries
@@ -78,9 +79,12 @@ func NewΔTailI64() *ΔTailI64 {
 	return &ΔTailI64{lastRevOf: make(map[int64]zodb.Tid)}
 }
 
-// XXX + .Head() -> max(rev)	XXX or 0 if len(tailv) == 0?
+// Head returns database state starting from which δtail has history coverage.	XXX
+//
+// For newly created ΔTailI64 Head returns 0.
+// Head is ↑, in particular it does not go back to 0 when δtail becomes empty.
 func (δtail *ΔTailI64) Head() zodb.Tid {
-	panic("TODO")
+	return δtail.head
 }
 
 // XXX add way to extend coverage without appending changed data? (i.e. if a
@@ -91,13 +95,11 @@ func (δtail *ΔTailI64) Head() zodb.Tid {
 // rev must be ↑.
 func (δtail *ΔTailI64) Append(rev zodb.Tid, changev []int64) {
 	// check rev↑
-	// XXX better also check even when δtail is ø (after forget)
-	if l := len(δtail.tailv); l > 0 {
-		if revPrev := δtail.tailv[l-1].rev; revPrev >= rev {
-			panic(fmt.Sprintf("δtail.Append: rev not ↑: %s -> %s", revPrev, rev))
-		}
+	if δtail.head >= rev {
+		panic(fmt.Sprintf("δtail.Append: rev not ↑: %s -> %s", δtail.head, rev))
 	}
 
+	δtail.head = rev
 	δtail.tailv = append(δtail.tailv, δRevEntryI64{rev, changev})
 	for _, id := range changev {
 		δtail.lastRevOf[id] = rev