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// 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 Snapshot corresponds to a particular sequence number.
class Snapshot {
public:
SequenceNumber number_; // const after creation
private:
friend class SnapshotList;
// Snapshot is kept in a doubly-linked circular list
Snapshot* prev_;
Snapshot* next_;
SnapshotList* list_; // just for sanity checks
};
class SnapshotList {
public:
SnapshotList() {
list_.prev_ = &list_;
list_.next_ = &list_;
}
bool empty() const { return list_.next_ == &list_; }
Snapshot* oldest() const { assert(!empty()); return list_.next_; }
Snapshot* newest() const { assert(!empty()); return list_.prev_; }
const Snapshot* New(SequenceNumber seq) {
Snapshot* s = new Snapshot;
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 Snapshot* 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
Snapshot list_;
};
}
#endif // STORAGE_LEVELDB_DB_SNAPSHOT_H_
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