Inside Bitcoin

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_TABLE_ITERATOR_WRAPPER_H_
6#define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
7
8#include "leveldb/iterator.h"
9#include "leveldb/slice.h"
10
11namespace leveldb {
12
13// A internal wrapper class with an interface similar to Iterator that
14// caches the valid() and key() results for an underlying iterator.
15// This can help avoid virtual function calls and also gives better
16// cache locality.
17class IteratorWrapper {
18 public:
19  IteratorWrapper() : iter_(nullptr), valid_(false) {}
20  explicit IteratorWrapper(Iterator* iter) : iter_(nullptr) { Set(iter); }
21  ~IteratorWrapper() { delete iter_; }
22  Iterator* iter() const { return iter_; }
23
24  // Takes ownership of "iter" and will delete it when destroyed, or
25  // when Set() is invoked again.
26  void Set(Iterator* iter) {
27    delete iter_;
28    iter_ = iter;
29    if (iter_ == nullptr) {
30      valid_ = false;
31    } else {
32      Update();
33    }
34  }
35
36  // Iterator interface methods
37  bool Valid() const { return valid_; }
38  Slice key() const {
39    assert(Valid());
40    return key_;
41  }
42  Slice value() const {
43    assert(Valid());
44    return iter_->value();
45  }
46  // Methods below require iter() != nullptr
47  Status status() const {
48    assert(iter_);
49    return iter_->status();
50  }
51  void Next() {
52    assert(iter_);
53    iter_->Next();
54    Update();
55  }
56  void Prev() {
57    assert(iter_);
58    iter_->Prev();
59    Update();
60  }
61  void Seek(const Slice& k) {
62    assert(iter_);
63    iter_->Seek(k);
64    Update();
65  }
66  void SeekToFirst() {
67    assert(iter_);
68    iter_->SeekToFirst();
69    Update();
70  }
71  void SeekToLast() {
72    assert(iter_);
73    iter_->SeekToLast();
74    Update();
75  }
76
77 private:
78  void Update() {
79    valid_ = iter_->Valid();
80    if (valid_) {
81      key_ = iter_->key();
82    }
83  }
84
85  Iterator* iter_;
86  bool valid_;
87  Slice key_;
88};
89
90}  // namespace leveldb
91
92#endif  // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
93