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Java implementation of Raft Consensus, this module contains only the core algorithm, and does not have any dependency except Java SE 8, for interface implementations that required by this module, please checkout jraft-ext module

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/**
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  The ASF licenses 
 * this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.data.technology.jraft;

import java.util.concurrent.CompletableFuture;

public interface StateMachine {

	/**
	 * Starts the state machine, called by RaftConsensus, RaftConsensus will pass an instance of
	 * RaftMessageSender for the state machine to send logs to cluster, so that all state machines
	 * in the same cluster could be in synced
	 * @param raftMessageSender rpc message sender
	 */
	public void start(RaftMessageSender raftMessageSender);
	
    /**
     * Commit the log data at the {@code logIndex}
     * @param logIndex the log index in the logStore
     * @param data application data to commit
     */
    public void commit(long logIndex, byte[] data);

    /**
     * Rollback a preCommit item at index {@code logIndex}
     * @param logIndex log index to be rolled back
     * @param data application data to rollback
     */
    public void rollback(long logIndex, byte[] data);

    /**
     * PreCommit a log entry at log index {@code logIndex}
     * @param logIndex the log index to commit
     * @param data application data for pre-commit
     */
    public void preCommit(long logIndex, byte[] data);

    /**
     * Save data for the snapshot
     * @param snapshot the snapshot information
     * @param offset offset of the data in the whole snapshot
     * @param data part of snapshot data
     */
    public void saveSnapshotData(Snapshot snapshot, long offset, byte[] data);

    /**
     * Apply a snapshot to current state machine
     * @param snapshot the snapshot to be applied
     * @return true if successfully applied, otherwise false
     */
    public boolean applySnapshot(Snapshot snapshot);

    /**
     * Read snapshot data at the specified offset to buffer and return bytes read
     * @param snapshot the snapshot info
     * @param offset the offset of the snapshot data
     * @param buffer the buffer to be filled
     * @return bytes read
     */
    public int readSnapshotData(Snapshot snapshot, long offset, byte[] buffer);

    /**
     * Read the last snapshot information
     * @return last snapshot information in the state machine or null if none
     */
    public Snapshot getLastSnapshot();

    /**
     * Create a snapshot data based on the snapshot information asynchronously
     * set the future to true if snapshot is successfully created, otherwise, 
     * set it to false
     * @param snapshot the snapshot info
     * @return true if snapshot is created successfully, otherwise false
     */
    public CompletableFuture createSnapshot(Snapshot snapshot);
    
    /**
     * Save the state of state machine to ensure the state machine is in a good state, then exit the system
     * this MUST exits the system to protect the safety of the algorithm
     * @param code 0 indicates the system is gracefully shutdown, -1 indicates there are some errors which cannot be recovered
     */
    public void exit(int code);
}