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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.
#include "table/two_level_iterator.h"
#include "leveldb/table.h"
#include "table/block.h"
#include "table/format.h"
#include "table/iterator_wrapper.h"
namespace leveldb {
namespace {
typedef Iterator* (*BlockFunction)(void*, const ReadOptions&, const Slice&);
class TwoLevelIterator : public Iterator {
public:
TwoLevelIterator(Iterator* index_iter, BlockFunction block_function,
void* arg, const ReadOptions& options);
~TwoLevelIterator() override;
void Seek(const Slice& target) override;
void SeekToFirst() override;
void SeekToLast() override;
void Next() override;
void Prev() override;
bool Valid() const override { return data_iter_.Valid(); }
Slice key() const override {
assert(Valid());
return data_iter_.key();
}
Slice value() const override {
assert(Valid());
return data_iter_.value();
}
Status status() const override {
// It'd be nice if status() returned a const Status& instead of a Status
if (!index_iter_.status().ok()) {
return index_iter_.status();
} else if (data_iter_.iter() != nullptr && !data_iter_.status().ok()) {
return data_iter_.status();
} else {
return status_;
}
}
private:
void SaveError(const Status& s) {
if (status_.ok() && !s.ok()) status_ = s;
}
void SkipEmptyDataBlocksForward();
void SkipEmptyDataBlocksBackward();
void SetDataIterator(Iterator* data_iter);
void InitDataBlock();
BlockFunction block_function_;
void* arg_;
const ReadOptions options_;
Status status_;
IteratorWrapper index_iter_;
IteratorWrapper data_iter_; // May be nullptr
// If data_iter_ is non-null, then "data_block_handle_" holds the
// "index_value" passed to block_function_ to create the data_iter_.
std::string data_block_handle_;
};
TwoLevelIterator::TwoLevelIterator(Iterator* index_iter,
BlockFunction block_function, void* arg,
const ReadOptions& options)
: block_function_(block_function),
arg_(arg),
options_(options),
index_iter_(index_iter),
data_iter_(nullptr) {}
TwoLevelIterator::~TwoLevelIterator() = default;
void TwoLevelIterator::Seek(const Slice& target) {
index_iter_.Seek(target);
InitDataBlock();
if (data_iter_.iter() != nullptr) data_iter_.Seek(target);
SkipEmptyDataBlocksForward();
}
void TwoLevelIterator::SeekToFirst() {
index_iter_.SeekToFirst();
InitDataBlock();
if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
SkipEmptyDataBlocksForward();
}
void TwoLevelIterator::SeekToLast() {
index_iter_.SeekToLast();
InitDataBlock();
if (data_iter_.iter() != nullptr) data_iter_.SeekToLast();
SkipEmptyDataBlocksBackward();
}
void TwoLevelIterator::Next() {
assert(Valid());
data_iter_.Next();
SkipEmptyDataBlocksForward();
}
void TwoLevelIterator::Prev() {
assert(Valid());
data_iter_.Prev();
SkipEmptyDataBlocksBackward();
}
void TwoLevelIterator::SkipEmptyDataBlocksForward() {
while (data_iter_.iter() == nullptr || !data_iter_.Valid()) {
// Move to next block
if (!index_iter_.Valid()) {
SetDataIterator(nullptr);
return;
}
index_iter_.Next();
InitDataBlock();
if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
}
}
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();
}
}
void TwoLevelIterator::SetDataIterator(Iterator* data_iter) {
if (data_iter_.iter() != nullptr) SaveError(data_iter_.status());
data_iter_.Set(data_iter);
}
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);
}
}
}
} // namespace
Iterator* NewTwoLevelIterator(Iterator* index_iter,
BlockFunction block_function, void* arg,
const ReadOptions& options) {
return new TwoLevelIterator(index_iter, block_function, arg, options);
}
} // namespace leveldb
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