leveldb源码分析之迭代器(七)—TwoLevelIterator
TwoLevelIterator是一个两级的迭代器，第一级为index_iter,第二级为data_iter。
重点函数如下:
1.获取状态
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virtual Status status() const { // It'd be nice if status() returned a const Status& instead of a Status //如果index_iter的状态不是OK，则返回index_iter的状态 if (!index_iter_.status().ok()) { return index_iter_.status(); //如果data_iter有效，且状态不是ok,则返回data_iter的状态 } else if (data_iter_.iter() != nullptr && !data_iter_.status().ok()) { return data_iter_.status(); } else { //返回迭代器的状态 return status_; } } |
2.迭代器的移动
先移动index_iter，后移动data_iter_
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void TwoLevelIterator::SeekToLast() { index_iter_.SeekToLast(); InitDataBlock(); if (data_iter_.iter() != nullptr) data_iter_.SeekToLast(); SkipEmptyDataBlocksBackward(); } |
3.与移动有关的两个函数
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void TwoLevelIterator::InitDataBlock() { if (!index_iter_.Valid()) { SetDataIterator(nullptr); } else { Slice handle = index_iter_.value(); if (data_iter_.iter() != nullptr && handle.compare(data_block_handle_) == 0) { // data_iter_ is already constructed with this iterator, so // no need to change anything } else { Iterator* iter = (*block_function_)(arg_, options_, handle); data_block_handle_.assign(handle.data(), handle.size()); SetDataIterator(iter); } } } |
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void TwoLevelIterator::SkipEmptyDataBlocksBackward() { while (data_iter_.iter() == nullptr || !data_iter_.Valid()) { // Move to next block if (!index_iter_.Valid()) { SetDataIterator(nullptr); return; } index_iter_.Prev(); InitDataBlock(); if (data_iter_.iter() != nullptr) data_iter_.SeekToLast(); } } |
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