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