1
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2
// Use of this source code is governed by a BSD-style license that can be
3
// found in the LICENSE file. See the AUTHORS file for names of contributors.
5
#ifndef STORAGE_LEVELDB_DB_SNAPSHOT_H_
6
#define STORAGE_LEVELDB_DB_SNAPSHOT_H_
8
#include "leveldb/db.h"
14
// Snapshots are kept in a doubly-linked list in the DB.
15
// Each SnapshotImpl corresponds to a particular sequence number.
16
class SnapshotImpl : public Snapshot {
18
SequenceNumber number_; // const after creation
21
friend class SnapshotList;
23
// SnapshotImpl is kept in a doubly-linked circular list
27
SnapshotList* list_; // just for sanity checks
37
bool empty() const { return list_.next_ == &list_; }
38
SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; }
39
SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; }
41
const SnapshotImpl* New(SequenceNumber seq) {
42
SnapshotImpl* s = new SnapshotImpl;
46
s->prev_ = list_.prev_;
52
void Delete(const SnapshotImpl* s) {
53
assert(s->list_ == this);
54
s->prev_->next_ = s->next_;
55
s->next_->prev_ = s->prev_;
60
// Dummy head of doubly-linked list of snapshots
64
} // namespace leveldb
66
#endif // STORAGE_LEVELDB_DB_SNAPSHOT_H_