tidb sequence_state 代码
文件路径：/sessionctx/variable/sequence_state.go
/ Copyright 2020 PingCAP, Inc.
/
/ Licensed under the Apache License, Version 2.0 (the "License");
/ you may not use this file except in compliance with the License.
/ You may obtain a copy of the License at
/
/ http://www.apache.org/licenses/LICENSE-2.0
/
/ Unless required by applicable law or agreed to in writing, software
/ distributed under the License is distributed on an "AS IS" BASIS,
/ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/ See the License for the specific language governing permissions and
/ limitations under the License.
package variable
import (
"sync"
)
/ SequenceState cache all sequence's latest value accessed by lastval() builtins. It's a session scoped
/ variable, and all public methods of SequenceState are currently-safe.
type SequenceState struct {
mu sync.Mutex
/ latestValueMap caches the last value obtained by nextval() for each sequence id.
latestValueMap map[int64]int64
}
/ NewSequenceState creates a SequenceState.
func NewSequenceState() *SequenceState {
return &SequenceState{mu: sync.Mutex{}, latestValueMap: make(map[int64]int64)}
}
/ UpdateState will update the last value of specified sequenceID in a session.
func (ss *SequenceState) UpdateState(sequenceID, value int64) {
ss.mu.Lock()
defer ss.mu.Unlock()
ss.latestValueMap[sequenceID] = value
}
/ GetLastValue will return last value of the specified sequenceID, bool(true) indicates
/ the sequenceID is not in the cache map and NULL will be returned.
func (ss *SequenceState) GetLastValue(sequenceID int64) (int64, bool, error) {
ss.mu.Lock()
defer ss.mu.Unlock()
if len(ss.latestValueMap) > 0 {
if last, ok := ss.latestValueMap[sequenceID]; ok {
return last, false, nil
}
}
return 0, true, nil
}
/ GetAllStates returns a copied latestValueMap.
func (ss *SequenceState) GetAllStates() map[int64]int64 {
ss.mu.Lock()
defer ss.mu.Unlock()
latestValueMap := make(map[int64]int64, len(ss.latestValueMap))
for seqID, latestValue := range ss.latestValueMap {
latestValueMap[seqID] = latestValue
}
return latestValueMap
}
/ SetAllStates sets latestValueMap as a whole.
func (ss *SequenceState) SetAllStates(latestValueMap map[int64]int64) {
ss.mu.Lock()
defer ss.mu.Unlock()
for seqID, latestValue := range latestValueMap {
ss.latestValueMap[seqID] = latestValue
}
}