add other session providers (#5963)

vendor/github.com/lunny/nodb/multi.go

@@ -0,0 +1,73 @@
+package nodb
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrNestMulti = errors.New("nest multi not supported")
+	ErrMultiDone = errors.New("multi has been closed")
+)
+
+type Multi struct {
+	*DB
+}
+
+func (db *DB) IsInMulti() bool {
+	return db.status == DBInMulti
+}
+
+// begin a mutli to execute commands,
+// it will block any other write operations before you close the multi, unlike transaction, mutli can not rollback
+func (db *DB) Multi() (*Multi, error) {
+	if db.IsInMulti() {
+		return nil, ErrNestMulti
+	}
+
+	m := new(Multi)
+
+	m.DB = new(DB)
+	m.DB.status = DBInMulti
+
+	m.DB.l = db.l
+
+	m.l.wLock.Lock()
+
+	m.DB.sdb = db.sdb
+
+	m.DB.bucket = db.sdb
+
+	m.DB.index = db.index
+
+	m.DB.kvBatch = m.newBatch()
+	m.DB.listBatch = m.newBatch()
+	m.DB.hashBatch = m.newBatch()
+	m.DB.zsetBatch = m.newBatch()
+	m.DB.binBatch = m.newBatch()
+	m.DB.setBatch = m.newBatch()
+
+	return m, nil
+}
+
+func (m *Multi) newBatch() *batch {
+	return m.l.newBatch(m.bucket.NewWriteBatch(), &multiBatchLocker{}, nil)
+}
+
+func (m *Multi) Close() error {
+	if m.bucket == nil {
+		return ErrMultiDone
+	}
+	m.l.wLock.Unlock()
+	m.bucket = nil
+	return nil
+}
+
+func (m *Multi) Select(index int) error {
+	if index < 0 || index >= int(MaxDBNumber) {
+		return fmt.Errorf("invalid db index %d", index)
+	}
+
+	m.DB.index = uint8(index)
+	return nil
+}