hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/StateMachineProcedure.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  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 org.apache.hadoop.hbase.procedure2;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;

import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
import org.apache.hadoop.hbase.protobuf.generated.ProcedureProtos.StateMachineProcedureData;

/**
 * Procedure described by a series of steps.
 *
 * The procedure implementor must have an enum of 'states', describing
 * the various step of the procedure.
 * Once the procedure is running, the procedure-framework will call executeFromState()
 * using the 'state' provided by the user. The first call to executeFromState()
 * will be performed with 'state = null'. The implementor can jump between
 * states using setNextState(MyStateEnum.ordinal()).
 * The rollback will call rollbackState() for each state that was executed, in reverse order.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public abstract class StateMachineProcedure<TEnvironment, TState>
    extends Procedure<TEnvironment> {
  private int stateCount = 0;
  private int[] states = null;

  protected enum Flow {
    HAS_MORE_STATE,
    NO_MORE_STATE,
  }

  /**
   * called to perform a single step of the specified 'state' of the procedure
   * @param state state to execute
   * @return Flow.NO_MORE_STATE if the procedure is completed,
   *         Flow.HAS_MORE_STATE if there is another step.
   */
  protected abstract Flow executeFromState(TEnvironment env, TState state)
    throws ProcedureYieldException;

  /**
   * called to perform the rollback of the specified state
   * @param state state to rollback
   * @throws IOException temporary failure, the rollback will retry later
   */
  protected abstract void rollbackState(TEnvironment env, TState state)
    throws IOException;

  /**
   * Convert an ordinal (or state id) to an Enum (or more descriptive) state object.
   * @param stateId the ordinal() of the state enum (or state id)
   * @return the state enum object
   */
  protected abstract TState getState(int stateId);

  /**
   * Convert the Enum (or more descriptive) state object to an ordinal (or state id).
   * @param state the state enum object
   * @return stateId the ordinal() of the state enum (or state id)
   */
  protected abstract int getStateId(TState state);

  /**
   * Return the initial state object that will be used for the first call to executeFromState().
   * @return the initial state enum object
   */
  protected abstract TState getInitialState();

  /**
   * Set the next state for the procedure.
   * @param state the state enum object
   */
  protected void setNextState(final TState state) {
    setNextState(getStateId(state));
  }

  @Override
  protected Procedure[] execute(final TEnvironment env)
      throws ProcedureYieldException {
    updateTimestamp();
    try {
      TState state = stateCount > 0 ? getState(states[stateCount-1]) : getInitialState();
      if (stateCount == 0) {
        setNextState(getStateId(state));
      }
      if (executeFromState(env, state) == Flow.NO_MORE_STATE) {
        // completed
        return null;
      }
      return (isWaiting() || isFailed()) ? null : new Procedure[] {this};
    } finally {
      updateTimestamp();
    }
  }

  @Override
  protected void rollback(final TEnvironment env) throws IOException {
    try {
      updateTimestamp();
      rollbackState(env, stateCount > 0 ? getState(states[stateCount-1]) : getInitialState());
      stateCount--;
    } finally {
      updateTimestamp();
    }
  }

  /**
   * Set the next state for the procedure.
   * @param stateId the ordinal() of the state enum (or state id)
   */
  private void setNextState(final int stateId) {
    if (states == null || states.length == stateCount) {
      int newCapacity = stateCount + 8;
      if (states != null) {
        states = Arrays.copyOf(states, newCapacity);
      } else {
        states = new int[newCapacity];
      }
    }
    states[stateCount++] = stateId;
  }

  @Override
  protected void serializeStateData(final OutputStream stream) throws IOException {
    StateMachineProcedureData.Builder data = StateMachineProcedureData.newBuilder();
    for (int i = 0; i < stateCount; ++i) {
      data.addState(states[i]);
    }
    data.build().writeDelimitedTo(stream);
  }

  @Override
  protected void deserializeStateData(final InputStream stream) throws IOException {
    StateMachineProcedureData data = StateMachineProcedureData.parseDelimitedFrom(stream);
    stateCount = data.getStateCount();
    if (stateCount > 0) {
      states = new int[stateCount];
      for (int i = 0; i < stateCount; ++i) {
        states[i] = data.getState(i);
      }
    } else {
      states = null;
    }
  }
}