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92 行
2.1 KiB
92 行
2.1 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_TABLE_ITERATOR_WRAPPER_H_
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#define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
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#include "leveldb/iterator.h"
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#include "leveldb/slice.h"
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namespace leveldb {
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// A internal wrapper class with an interface similar to Iterator that
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// caches the valid() and key() results for an underlying iterator.
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// This can help avoid virtual function calls and also gives better
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// cache locality.
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class IteratorWrapper {
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public:
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IteratorWrapper() : iter_(nullptr), valid_(false) {}
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explicit IteratorWrapper(Iterator* iter) : iter_(nullptr) { Set(iter); }
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~IteratorWrapper() { delete iter_; }
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Iterator* iter() const { return iter_; }
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// Takes ownership of "iter" and will delete it when destroyed, or
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// when Set() is invoked again.
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void Set(Iterator* iter) {
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delete iter_;
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iter_ = iter;
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if (iter_ == nullptr) {
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valid_ = false;
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} else {
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Update();
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}
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}
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// Iterator interface methods
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bool Valid() const { return valid_; }
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Slice key() const {
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assert(Valid());
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return key_;
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}
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Slice value() const {
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assert(Valid());
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return iter_->value();
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}
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// Methods below require iter() != nullptr
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Status status() const {
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assert(iter_);
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return iter_->status();
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}
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void Next() {
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assert(iter_);
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iter_->Next();
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Update();
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}
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void Prev() {
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assert(iter_);
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iter_->Prev();
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Update();
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}
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void Seek(const Slice& k) {
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assert(iter_);
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iter_->Seek(k);
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Update();
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}
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void SeekToFirst() {
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assert(iter_);
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iter_->SeekToFirst();
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Update();
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}
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void SeekToLast() {
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assert(iter_);
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iter_->SeekToLast();
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Update();
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}
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private:
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void Update() {
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valid_ = iter_->Valid();
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if (valid_) {
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key_ = iter_->key();
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}
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}
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Iterator* iter_;
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bool valid_;
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Slice key_;
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
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