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backend.go
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backend.go
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// Copyright 2015 CoreOS, 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,
// 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 (
"fmt"
"hash/crc32"
"io"
"log"
"sync/atomic"
"time"
"github.com/coreos/etcd/Godeps/_workspace/src/github.com/boltdb/bolt"
)
type Backend interface {
BatchTx() BatchTx
Snapshot() Snapshot
Hash() (uint32, error)
// Size returns the current size of the backend.
Size() int64
ForceCommit()
Close() error
}
type Snapshot interface {
// Size gets the size of the snapshot.
Size() int64
// WriteTo writes the snapshot into the given writter.
WriteTo(w io.Writer) (n int64, err error)
// Close closes the snapshot.
Close() error
}
type backend struct {
db *bolt.DB
batchInterval time.Duration
batchLimit int
batchTx *batchTx
size int64
stopc chan struct{}
donec chan struct{}
}
func New(path string, d time.Duration, limit int) Backend {
return newBackend(path, d, limit)
}
func newBackend(path string, d time.Duration, limit int) *backend {
db, err := bolt.Open(path, 0600, nil)
if err != nil {
log.Panicf("backend: cannot open database at %s (%v)", path, err)
}
b := &backend{
db: db,
batchInterval: d,
batchLimit: limit,
stopc: make(chan struct{}),
donec: make(chan struct{}),
}
b.batchTx = newBatchTx(b)
go b.run()
return b
}
// BatchTx returns the current batch tx in coalescer. The tx can be used for read and
// write operations. The write result can be retrieved within the same tx immediately.
// The write result is isolated with other txs until the current one get committed.
func (b *backend) BatchTx() BatchTx {
return b.batchTx
}
// force commit the current batching tx.
func (b *backend) ForceCommit() {
b.batchTx.Commit()
}
func (b *backend) Snapshot() Snapshot {
tx, err := b.db.Begin(false)
if err != nil {
log.Fatalf("storage: cannot begin tx (%s)", err)
}
return &snapshot{tx}
}
func (b *backend) Hash() (uint32, error) {
h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
err := b.db.View(func(tx *bolt.Tx) error {
c := tx.Cursor()
for next, _ := c.First(); next != nil; next, _ = c.Next() {
b := tx.Bucket(next)
if b == nil {
return fmt.Errorf("cannot get hash of bucket %s", string(next))
}
h.Write(next)
b.ForEach(func(k, v []byte) error {
h.Write(k)
h.Write(v)
return nil
})
}
return nil
})
if err != nil {
return 0, err
}
return h.Sum32(), nil
}
func (b *backend) Size() int64 {
return atomic.LoadInt64(&b.size)
}
func (b *backend) run() {
defer close(b.donec)
for {
select {
case <-time.After(b.batchInterval):
case <-b.stopc:
b.batchTx.CommitAndStop()
return
}
b.batchTx.Commit()
}
}
func (b *backend) Close() error {
close(b.stopc)
<-b.donec
return b.db.Close()
}
type snapshot struct {
*bolt.Tx
}
func (s *snapshot) Close() error { return s.Tx.Rollback() }