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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
package org.rocksdb;
import java.nio.ByteBuffer;
/**
* Defines the interface for an Iterator which provides
* access to data one entry at a time. Multiple implementations
* are provided by this library. In particular, iterators are provided
* to access the contents of a DB and Write Batch.
*
* Multiple threads can invoke const methods on an RocksIterator without
* external synchronization, but if any of the threads may call a
* non-const method, all threads accessing the same RocksIterator must use
* external synchronization.
*
* @see org.rocksdb.RocksObject
*/
public interface RocksIteratorInterface {
/**
* An iterator is either positioned at an entry, or
* not valid. This method returns true if the iterator is valid.
*
* @return true if iterator is valid.
*/
boolean isValid();
/**
* Position at the first entry in the source. The iterator is Valid()
* after this call if the source is not empty.
*/
void seekToFirst();
/**
* Position at the last entry in the source. The iterator is
* valid after this call if the source is not empty.
*/
void seekToLast();
/**
* Position at the first entry in the source whose key is at or
* past target.
*
* The iterator is valid after this call if the source contains
* a key that comes at or past target.
*
* @param target byte array describing a key or a
* key prefix to seek for.
*/
void seek(byte[] target);
/**
* Position at the first entry in the source whose key is that or
* before target.
*
* The iterator is valid after this call if the source contains
* a key that comes at or before target.
*
* @param target byte array describing a key or a
* key prefix to seek for.
*/
void seekForPrev(byte[] target);
/**
* Position at the first entry in the source whose key is that or
* past target.
*
* The iterator is valid after this call if the source contains
* a key that comes at or past target.
*
* @param target byte array describing a key or a
* key prefix to seek for. Supports direct buffer only.
*/
void seek(ByteBuffer target);
/**
* Position at the last key that is less than or equal to the target key.
*
* The iterator is valid after this call if the source contains
* a key that comes at or past target.
*
* @param target byte array describing a key or a
* key prefix to seek for. Supports direct buffer only.
*/
void seekForPrev(ByteBuffer target);
/**
* Moves to the next entry in the source. After this call, Valid() is
* true if the iterator was not positioned at the last entry in the source.
*
* REQUIRES: {@link #isValid()}
*/
void next();
/**
* Moves to the previous entry in the source. After this call, Valid() is
* true if the iterator was not positioned at the first entry in source.
*
* REQUIRES: {@link #isValid()}
*/
void prev();
/**
* If an error has occurred, return it. Else return an ok status.
* If non-blocking IO is requested and this operation cannot be
* satisfied without doing some IO, then this returns Status::Incomplete().
*
* @throws RocksDBException thrown if error happens in underlying
* native library.
*/
void status() throws RocksDBException;
/**
* If supported, the DB state that the iterator reads from is updated to
* the latest state. The iterator will be invalidated after the call.
* Regardless of whether the iterator was created/refreshed previously with
* or without a snapshot, the iterator will be reading the latest DB state
* after this call.
* Note that you will need to call a Seek*() function to get the iterator
* back into a valid state before calling a function that assumes the
* state is already valid, like Next().
*
* @throws RocksDBException thrown if the operation is not supported or an error happens in the
* underlying native library
*/
void refresh() throws RocksDBException;
/**
* Similar to {@link #refresh()} but the iterator will be reading the latest DB state under the
* given snapshot.
*/
void refresh(Snapshot snapshot) throws RocksDBException;
}