rocksdb/db/managed_iterator.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#pragma once
#ifndef ROCKSDB_LITE
#include <mutex>
#include <queue>
#include <string>
#include <vector>
#include "db/column_family.h"
#include "rocksdb/db.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "util/arena.h"
namespace rocksdb {
class DBImpl;
struct SuperVersion;
class ColumnFamilyData;
/**
* ManagedIterator is a special type of iterator that supports freeing the
* underlying iterator and still being able to access the current key/value
* pair. This is done by copying the key/value pair so that clients can
* continue to access the data without getting a SIGSEGV.
* The underlying iterator can be freed manually through the call to
* ReleaseIter or automatically (as needed on space pressure or age.)
* The iterator is recreated using the saved original arguments.
*/
class ManagedIterator : public Iterator {
public:
ManagedIterator(DBImpl* db, const ReadOptions& read_options,
ColumnFamilyData* cfd);
virtual ~ManagedIterator();
virtual void SeekToLast() override;
virtual void Prev() override;
virtual bool Valid() const override;
void SeekToFirst() override;
virtual void Seek(const Slice& target) override;
virtual void SeekForPrev(const Slice& target) override;
virtual void Next() override;
virtual Slice key() const override;
virtual Slice value() const override;
virtual Status status() const override;
void ReleaseIter(bool only_old);
void SetDropOld(bool only_old) {
only_drop_old_ = read_options_.tailing || only_old;
}
private:
void RebuildIterator();
void UpdateCurrent();
void SeekInternal(const Slice& user_key, bool seek_to_first);
bool NeedToRebuild();
void Lock();
bool TryLock();
void UnLock();
DBImpl* const db_;
ReadOptions read_options_;
ColumnFamilyData* const cfd_;
ColumnFamilyHandleInternal cfh_;
uint64_t svnum_;
std::unique_ptr<Iterator> mutable_iter_;
// internal iterator status
Status status_;
bool valid_;
IterKey cached_key_;
IterKey cached_value_;
bool only_drop_old_ = true;
bool snapshot_created_;
bool release_supported_;
std::mutex in_use_; // is managed iterator in use
};
} // namespace rocksdb
#endif // !ROCKSDB_LITE