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seq.go
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seq.go
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// Copyright 2019 Zhenhua Yang. All rights reserved.
// Licensed under the MIT License that can be
// found in the LICENSE file in the root directory.
package executor
import (
"encoding/binary"
"github.com/dgraph-io/badger"
"log"
"sync"
)
const bandwidth = 128
type seq struct {
sync.Mutex
kv *badger.ManagedDB
key []byte
next uint64
leased uint64
}
var (
seqMap = make(map[string]*seq)
newSeqMutex sync.Mutex
)
func getSeq(key string) *seq {
newSeqMutex.Lock()
defer newSeqMutex.Unlock()
if s, ok := seqMap[key]; ok {
return s
} else {
s = &seq{
kv: GetDb().kv,
key: []byte(key),
next: 0,
leased: 0,
}
seqMap[key] = s
return s
}
}
func (s *seq) updateLease() error {
kvTxn := s.kv.NewTransactionAt(1, true)
defer kvTxn.Discard()
item, err := kvTxn.Get(s.key)
if err == badger.ErrKeyNotFound {
s.next = 0
} else if err != nil {
log.Printf("UpdateLease error: get: %v", err.Error())
return err
} else {
val, err := item.Value()
if err != nil {
log.Printf("UpdateLease error: value: %v", err.Error())
return err
}
s.next = binary.LittleEndian.Uint64(val)
}
lease := s.next + bandwidth
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], lease)
err = kvTxn.Set(s.key, buf[:])
if err != nil {
log.Printf("UpdateLease error: set: %v", err.Error())
return err
}
err = kvTxn.CommitAt(1, nil)
if err != nil {
log.Printf("UpdateLease error: commit: %v", err.Error())
return err
}
s.leased = lease
return nil
}
func (s *seq) getNext() (uint64, error) {
s.Lock()
defer s.Unlock()
if s.next >= s.leased {
if err := s.updateLease(); err != nil {
return 0, err
}
}
val := s.next
s.next++
return val, nil
}
func (s *seq) release() error {
s.Lock()
defer s.Unlock()
kvTxn := s.kv.NewTransactionAt(1, true)
defer kvTxn.Discard()
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], s.next)
err := kvTxn.Set(s.key, buf[:])
if err != nil {
return nil
}
err = kvTxn.CommitAt(1, nil)
if err != nil {
return err
}
s.leased = s.next
return nil
}