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allocator.go
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allocator.go
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// Copyright 2017 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package kvenc
import (
"sync/atomic"
"github.com/pingcap/tidb/meta/autoid"
)
var _ autoid.Allocator = &Allocator{}
var (
step = int64(5000)
)
// NewAllocator creates an Allocator.
func NewAllocator() *Allocator {
return &Allocator{}
}
// Allocator is an id allocator, it is only used in lightning.
type Allocator struct {
base int64
}
// Alloc allocs a next autoID for table with tableID.
func (alloc *Allocator) Alloc(tableID int64) (int64, error) {
return atomic.AddInt64(&alloc.base, 1), nil
}
// Reset allow newBase smaller than alloc.base, and will set the alloc.base to newBase.
func (alloc *Allocator) Reset(newBase int64) {
atomic.StoreInt64(&alloc.base, newBase)
}
// Rebase not allow newBase smaller than alloc.base, and will skip the smaller newBase.
func (alloc *Allocator) Rebase(tableID, newBase int64, allocIDs bool) error {
// CAS
for {
oldBase := atomic.LoadInt64(&alloc.base)
if newBase <= oldBase {
break
}
if atomic.CompareAndSwapInt64(&alloc.base, oldBase, newBase) {
break
}
}
return nil
}
// Base returns the current base of Allocator.
func (alloc *Allocator) Base() int64 {
return atomic.LoadInt64(&alloc.base)
}
// End is only used for test.
func (alloc *Allocator) End() int64 {
return alloc.Base() + step
}
// NextGlobalAutoID returns the next global autoID.
func (alloc *Allocator) NextGlobalAutoID(tableID int64) (int64, error) {
return alloc.End() + 1, nil
}