| // Copyright (c) 2011 The LevelDB Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. See the AUTHORS file for names of contributors. |
| |
| #ifndef STORAGE_LEVELDB_DB_SNAPSHOT_H_ |
| #define STORAGE_LEVELDB_DB_SNAPSHOT_H_ |
| |
| #include "leveldb/db.h" |
| |
| namespace leveldb { |
| |
| class SnapshotList; |
| |
| // Snapshots are kept in a doubly-linked list in the DB. |
| // Each SnapshotImpl corresponds to a particular sequence number. |
| class SnapshotImpl : public Snapshot { |
| public: |
| SequenceNumber number_; // const after creation |
| |
| private: |
| friend class SnapshotList; |
| |
| // SnapshotImpl is kept in a doubly-linked circular list |
| SnapshotImpl* prev_; |
| SnapshotImpl* next_; |
| |
| SnapshotList* list_; // just for sanity checks |
| }; |
| |
| class SnapshotList { |
| public: |
| SnapshotList() { |
| list_.prev_ = &list_; |
| list_.next_ = &list_; |
| } |
| |
| bool empty() const { return list_.next_ == &list_; } |
| SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; } |
| SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; } |
| |
| const SnapshotImpl* New(SequenceNumber seq) { |
| SnapshotImpl* s = new SnapshotImpl; |
| s->number_ = seq; |
| s->list_ = this; |
| s->next_ = &list_; |
| s->prev_ = list_.prev_; |
| s->prev_->next_ = s; |
| s->next_->prev_ = s; |
| return s; |
| } |
| |
| void Delete(const SnapshotImpl* s) { |
| assert(s->list_ == this); |
| s->prev_->next_ = s->next_; |
| s->next_->prev_ = s->prev_; |
| delete s; |
| } |
| |
| private: |
| // Dummy head of doubly-linked list of snapshots |
| SnapshotImpl list_; |
| }; |
| |
| } // namespace leveldb |
| |
| #endif // STORAGE_LEVELDB_DB_SNAPSHOT_H_ |