.

go/neo/client/cache.go

@@ -50,6 +50,9 @@ type oidCacheEntry struct {
 	// cached revisions in ascending order
 	// [i].serial < [i].before <= [i+1].serial < [i+1].before
 	//
+	// XXX ^^^ .serial = 0 while loading is in progress
+	// XXX ^^^ .serial = 0 if err != nil
+	//
 	// XXX or?
 	// cached revisions in descending order
 	// .before > .serial >= next.before > next.serial ?
@@ -61,13 +64,6 @@ type revCacheEntry struct {
 	inLRU  listHead		// in Cache.lru
 	parent *oidCacheEntry	// oidCacheEntry holding us
 
-	//sync.Mutex	XXX not needed?
-
-	// oid revision
-	// 0 if don't know yet - loadBefore(.before) is in progress and actual
-	// serial not yet obtained from database.
-	serial    zodb.Tid
-
 	// we know that loadBefore(oid, .before) will give this .serial:oid.
 	//
 	// this is only what we currently know - not neccessarily covering
@@ -84,9 +80,10 @@ type revCacheEntry struct {
 	// case when loadBefore with tid > cache.before was called.
 	before zodb.Tid
 
-	// loading result: object data or error
-	data []byte
-	err  error
+	// loading result: object (data, serial) or error
+	data   []byte
+	serial zodb.Tid
+	err    error
 
 	ready chan struct{} // closed when loading finished
 }
@@ -231,18 +228,23 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 
 	// entry was not in cache - this goroutine becomes responsible for loading it
 	data, serial, err := c.stor.Load(xid)
-	// verify db gives serial < before
-	if serial >= rce.before {
-		// XXX err != nil - also check vvv?
-		// XXX loadSerial?
-		errDB(xid.Oid, "load(<%v) -> %v", rce.before, serial)
+
+	// normailize data/serial if it was error
+	if err != nil {
+		data = nil
+		serial = 0
 	}
 	rce.serial = serial
 	rce.data = data
 	rce.err = err
-	close(ready)
+	// verify db gives serial < before
+	if rce.serial >= rce.before {
+		// XXX loadSerial?
+		rce.errDB(xid.Oid, "load(<%v) -> %v", rce.before, serial)
+	}
 
-	δsize := len(data)
+	close(ready)
+	δsize := len(rce.data)
 
 	// merge rce with adjacent entries in parent
 	// ( e.g. loadBefore(3) and loadBefore(4) results in the same data loaded if
@@ -259,15 +261,15 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 	if i + 1 < len(oce.revv) {
 		rceNext := oce.revv[i+1]
 		if rceNext.loaded() && rceNext.serial < rce.before {	// XXX rceNext.serial=0 ?
+			// drop rce
+			oce.deli(i)
+			δsize -= len(rce.data)
+
 			// verify rce.serial == rceNext.serial
 			if rce.serial != rceNext.serial {
-				// XXX -> where to put? rce.err?
-				errDB(xid.Oid, "load(<%v) -> %v; load(<%v) -> %v", rce.before, rce.serial, rceNext.before, rceNext.serial)
+				rce.errDB(xid.Oid, "load(<%v) -> %v; load(<%v) -> %v", rce.before, rce.serial, rceNext.before, rceNext.serial)
 			}
 
-			// drop rce
-			oce.deli(i)
-			δsize -= len(rce.data)
 			rce = rceNext
 		}
 	}
@@ -276,10 +278,11 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 	if i > 0 {
 		rcePrev = oce.revv[i-1]
 		if rce.serial < rcePrev.before {
+			// XXX drop rcePrev here?
+
 			// verify rce.serial == rcePrev.serial (if that is ready)
 			if rcePrev.loaded() && rcePrev.serial != rce.serial {	// XXX rcePrev.serial=0 ?
-				// XXX -> where to put? rce.err?
-				errDB(xid.Oid, "load(<%v) -> %v; load(<%v) -> %v", rcePrev.before, rcePrev.serial, rce.before, rce.serial)
+				rce.errDB(xid.Oid, "load(<%v) -> %v; load(<%v) -> %v", rcePrev.before, rcePrev.serial, rce.before, rce.serial)
 			}
 
 			// drop rcePrev
@@ -345,3 +348,10 @@ func errDB(oid zodb.Oid, format string, argv ...interface{}) error {
 	// XXX -> separate type?
 	return fmt.Errorf("cache: database inconsistency: oid: %v: " + format, oid, ...argv)
 }
+
+// errDB marks rce with database inconsistency error
+func (rce *revCacheEntry) errDB(oid zodb.Oid, format string, argv ...interface{}) {
+	rce.err = errDB(oid, format, argv...)
+	rce.data = nil
+	rce.serial = 0
+}