115 lines
3.3 KiB
Go
115 lines
3.3 KiB
Go
// Copyright 2015 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package cindex
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import (
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"encoding/binary"
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"sync"
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"sync/atomic"
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"go.etcd.io/etcd/v3/mvcc/backend"
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)
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var (
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metaBucketName = []byte("meta")
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consistentIndexKeyName = []byte("consistent_index")
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)
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// ConsistentIndexer is an interface that wraps the Get/Set/Save method for consistentIndex.
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type ConsistentIndexer interface {
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// ConsistentIndex returns the consistent index of current executing entry.
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ConsistentIndex() uint64
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// SetConsistentIndex set the consistent index of current executing entry.
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SetConsistentIndex(v uint64)
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// UnsafeSave must be called holding the lock on the tx.
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// It saves consistentIndex to the underlying stable storage.
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UnsafeSave(tx backend.BatchTx)
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// SetBatchTx set the available backend.BatchTx for ConsistentIndexer.
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SetBatchTx(tx backend.BatchTx)
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}
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// consistentIndex implements the ConsistentIndexer interface.
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type consistentIndex struct {
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tx backend.BatchTx
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// consistentIndex represents the offset of an entry in a consistent replica log.
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// it caches the "consistent_index" key's value. Accessed
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// through atomics so must be 64-bit aligned.
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consistentIndex uint64
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// bytesBuf8 is a byte slice of length 8
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// to avoid a repetitive allocation in saveIndex.
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bytesBuf8 []byte
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mutex sync.Mutex
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}
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func NewConsistentIndex(tx backend.BatchTx) ConsistentIndexer {
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return &consistentIndex{tx: tx, bytesBuf8: make([]byte, 8)}
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}
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func (ci *consistentIndex) ConsistentIndex() uint64 {
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if index := atomic.LoadUint64(&ci.consistentIndex); index > 0 {
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return index
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}
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ci.mutex.Lock()
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defer ci.mutex.Unlock()
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ci.tx.Lock()
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defer ci.tx.Unlock()
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_, vs := ci.tx.UnsafeRange(metaBucketName, consistentIndexKeyName, nil, 0)
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if len(vs) == 0 {
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return 0
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}
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v := binary.BigEndian.Uint64(vs[0])
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atomic.StoreUint64(&ci.consistentIndex, v)
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return v
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}
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func (ci *consistentIndex) SetConsistentIndex(v uint64) {
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atomic.StoreUint64(&ci.consistentIndex, v)
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}
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func (ci *consistentIndex) UnsafeSave(tx backend.BatchTx) {
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bs := ci.bytesBuf8
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binary.BigEndian.PutUint64(bs, ci.consistentIndex)
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// put the index into the underlying backend
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// tx has been locked in TxnBegin, so there is no need to lock it again
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tx.UnsafePut(metaBucketName, consistentIndexKeyName, bs)
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}
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func (ci *consistentIndex) SetBatchTx(tx backend.BatchTx) {
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ci.mutex.Lock()
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defer ci.mutex.Unlock()
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ci.tx = tx
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}
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func NewFakeConsistentIndex(index uint64) ConsistentIndexer {
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return &fakeConsistentIndex{index: index}
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}
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type fakeConsistentIndex struct{ index uint64 }
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func (f *fakeConsistentIndex) ConsistentIndex() uint64 { return f.index }
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func (f *fakeConsistentIndex) SetConsistentIndex(index uint64) {
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atomic.StoreUint64(&f.index, index)
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}
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func (f *fakeConsistentIndex) UnsafeSave(tx backend.BatchTx) {}
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func (f *fakeConsistentIndex) SetBatchTx(tx backend.BatchTx) {}
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