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read_tx.go
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read_tx.go
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// Copyright 2017 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 backend
import (
"bytes"
"math"
"sync"
"github.com/boltdb/bolt"
)
// safeRangeBucket is a hack to avoid inadvertently reading duplicate keys;
// overwrites on a bucket should only fetch with limit=1, but safeRangeBucket
// is known to never overwrite any key so range is safe.
var safeRangeBucket = []byte("key")
type ReadTx interface {
Lock()
Unlock()
UnsafeRange(bucketName []byte, key, endKey []byte, limit int64) (keys [][]byte, vals [][]byte)
UnsafeForEach(bucketName []byte, visitor func(k, v []byte) error) error
}
type readTx struct {
// mu protects accesses to the txReadBuffer
mu sync.RWMutex
buf txReadBuffer
// txmu protects accesses to the Tx on Range requests
txmu sync.Mutex
tx *bolt.Tx
}
func (rt *readTx) Lock() { rt.mu.RLock() }
func (rt *readTx) Unlock() { rt.mu.RUnlock() }
func (rt *readTx) UnsafeRange(bucketName, key, endKey []byte, limit int64) ([][]byte, [][]byte) {
if endKey == nil {
// forbid duplicates for single keys
limit = 1
}
if limit <= 0 {
limit = math.MaxInt64
}
if limit > 1 && !bytes.Equal(bucketName, safeRangeBucket) {
panic("do not use unsafeRange on non-keys bucket")
}
keys, vals := rt.buf.Range(bucketName, key, endKey, limit)
if int64(len(keys)) == limit {
return keys, vals
}
rt.txmu.Lock()
// ignore error since bucket may have been created in this batch
k2, v2, _ := unsafeRange(rt.tx, bucketName, key, endKey, limit-int64(len(keys)))
rt.txmu.Unlock()
return append(k2, keys...), append(v2, vals...)
}
func (rt *readTx) UnsafeForEach(bucketName []byte, visitor func(k, v []byte) error) error {
dups := make(map[string]struct{})
f1 := func(k, v []byte) error {
dups[string(k)] = struct{}{}
return visitor(k, v)
}
f2 := func(k, v []byte) error {
if _, ok := dups[string(k)]; ok {
return nil
}
return visitor(k, v)
}
if err := rt.buf.ForEach(bucketName, f1); err != nil {
return err
}
rt.txmu.Lock()
err := unsafeForEach(rt.tx, bucketName, f2)
rt.txmu.Unlock()
return err
}