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kvstore.go
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kvstore.go
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// Copyright 2015 The etcd Authors
//
// 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 main
import (
"bytes"
"encoding/gob"
"encoding/json"
"log"
"sync"
"github.com/rfyiamcool/raft_kvs/consensus/snap"
)
// a key-value store backed by raft
type kvstore struct {
proposeC chan<- string // channel for proposing updates
commitC <-chan *string
errorC <-chan error
snapshotter *snap.Snapshotter
mu sync.RWMutex
kvStore map[string]string // current committed key-value pairs
}
type kv struct {
Key string
Val string
}
func newKVStore(snapshotter *snap.Snapshotter, proposeC chan<- string, commitC <-chan *string, errorC <-chan error) *kvstore {
var s = &kvstore{
proposeC: proposeC,
kvStore: make(map[string]string),
snapshotter: snapshotter,
commitC: commitC,
errorC: errorC,
}
return s
}
// start read commits from raft into kvStore map until error
func (s *kvstore) start() {
// replay log into key-value map
// s.readCommits(commitC, errorC)
go s.readCommits(s.commitC, s.errorC)
}
// Lookup 直接从map里获取数据
func (s *kvstore) Lookup(key string) (string, bool) {
s.mu.RLock()
defer s.mu.RUnlock()
v, ok := s.kvStore[key]
return v, ok
}
// Propose 把数据应用到
func (s *kvstore) Propose(k string, v string) error {
var buf bytes.Buffer
if err := gob.NewEncoder(&buf).Encode(kv{k, v}); err != nil {
return err
}
s.proposeC <- buf.String()
return nil
}
// readCommits 接收raft传递的log
func (s *kvstore) readCommits(commitC <-chan *string, errorC <-chan error) {
for data := range commitC {
if data == nil {
// done replaying log; new data incoming
// OR signaled to load snapshot
snapshot, err := s.snapshotter.Load()
if err == snap.ErrNoSnapshot {
// return
continue
}
if err != nil {
log.Panic(err)
}
log.Printf("loading snapshot at term %d and index %d", snapshot.Metadata.Term, snapshot.Metadata.Index)
if err := s.recoverFromSnapshot(snapshot.Data); err != nil {
log.Panic(err)
}
continue
}
var dataKv kv
dec := gob.NewDecoder(bytes.NewBufferString(*data))
if err := dec.Decode(&dataKv); err != nil {
log.Fatalf("raftexample: could not decode message (%v)", err)
}
s.mu.Lock()
s.kvStore[dataKv.Key] = dataKv.Val
s.mu.Unlock()
}
if err, ok := <-errorC; ok {
log.Fatal(err)
}
}
// getSnapshot 生成快照
func (s *kvstore) getSnapshot() ([]byte, error) {
s.mu.RLock()
defer s.mu.RUnlock()
return json.Marshal(s.kvStore)
}
// recoverFromSnapshot 恢复数据
func (s *kvstore) recoverFromSnapshot(snapshot []byte) error {
var store map[string]string
if err := json.Unmarshal(snapshot, &store); err != nil {
return err
}
s.mu.Lock()
defer s.mu.Unlock()
s.kvStore = store
return nil
}