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. 4 5 #ifndef STORAGE_LEVELDB_DB_SNAPSHOT_H_ 6 #define STORAGE_LEVELDB_DB_SNAPSHOT_H_ 7 8 #include "leveldb/db.h" 9 10 namespace leveldb { 11 12 class SnapshotList; 13 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 { 17 public: 18 SequenceNumber number_; // const after creation 19 20 private: 21 friend class SnapshotList; 22 23 // SnapshotImpl is kept in a doubly-linked circular list 24 SnapshotImpl* prev_; 25 SnapshotImpl* next_; 26 27 SnapshotList* list_; // just for sanity checks 28 }; 29 30 class SnapshotList { 31 public: SnapshotList()32 SnapshotList() { 33 list_.prev_ = &list_; 34 list_.next_ = &list_; 35 } 36 empty()37 bool empty() const { return list_.next_ == &list_; } oldest()38 SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; } newest()39 SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; } 40 New(SequenceNumber seq)41 const SnapshotImpl* New(SequenceNumber seq) { 42 SnapshotImpl* s = new SnapshotImpl; 43 s->number_ = seq; 44 s->list_ = this; 45 s->next_ = &list_; 46 s->prev_ = list_.prev_; 47 s->prev_->next_ = s; 48 s->next_->prev_ = s; 49 return s; 50 } 51 Delete(const SnapshotImpl * s)52 void Delete(const SnapshotImpl* s) { 53 assert(s->list_ == this); 54 s->prev_->next_ = s->next_; 55 s->next_->prev_ = s->prev_; 56 delete s; 57 } 58 59 private: 60 // Dummy head of doubly-linked list of snapshots 61 SnapshotImpl list_; 62 }; 63 64 } // namespace leveldb 65 66 #endif // STORAGE_LEVELDB_DB_SNAPSHOT_H_ 67