lib/db: Rework flush hooks (#6838)

lib/db/backend/leveldb_backend.go

@@ -59,7 +59,7 @@ func (b *leveldbBackend) newSnapshot() (leveldbSnapshot, error) {
 	}, nil
 }
 
-func (b *leveldbBackend) NewWriteTransaction() (WriteTransaction, error) {
+func (b *leveldbBackend) NewWriteTransaction(hooks ...CommitHook) (WriteTransaction, error) {
 	rel, err := newReleaser(b.closeWG)
 	if err != nil {
 		return nil, err
@@ -74,6 +74,7 @@ func (b *leveldbBackend) NewWriteTransaction() (WriteTransaction, error) {
 		ldb:             b.ldb,
 		batch:           new(leveldb.Batch),
 		rel:             rel,
+		commitHooks:     hooks,
 	}, nil
 }
 
@@ -142,9 +143,10 @@ func (l leveldbSnapshot) Release() {
 // an actual leveldb transaction)
 type leveldbTransaction struct {
 	leveldbSnapshot
-	ldb   *leveldb.DB
-	batch *leveldb.Batch
-	rel   *releaser
+	ldb         *leveldb.DB
+	batch       *leveldb.Batch
+	rel         *releaser
+	commitHooks []CommitHook
 }
 
 func (t *leveldbTransaction) Delete(key []byte) error {
@@ -157,8 +159,8 @@ func (t *leveldbTransaction) Put(key, val []byte) error {
 	return t.checkFlush(dbFlushBatchMax)
 }
 
-func (t *leveldbTransaction) Checkpoint(preFlush ...func() error) error {
-	return t.checkFlush(dbFlushBatchMin, preFlush...)
+func (t *leveldbTransaction) Checkpoint() error {
+	return t.checkFlush(dbFlushBatchMin)
 }
 
 func (t *leveldbTransaction) Commit() error {
@@ -174,19 +176,19 @@ func (t *leveldbTransaction) Release() {
 }
 
 // checkFlush flushes and resets the batch if its size exceeds the given size.
-func (t *leveldbTransaction) checkFlush(size int, preFlush ...func() error) error {
+func (t *leveldbTransaction) checkFlush(size int) error {
 	if len(t.batch.Dump()) < size {
 		return nil
 	}
-	for _, hook := range preFlush {
-		if err := hook(); err != nil {
-			return err
-		}
-	}
 	return t.flush()
 }
 
 func (t *leveldbTransaction) flush() error {
+	for _, hook := range t.commitHooks {
+		if err := hook(t); err != nil {
+			return err
+		}
+	}
 	if t.batch.Len() == 0 {
 		return nil
 	}