hadoop-common-project/hadoop-common-client/src/main/java/org/apache/hadoop/io/retry/RetryPolicy.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.io.retry;

import org.apache.hadoop.classification.InterfaceStability;

/**
 * <p>
 * Specifies a policy for retrying method failures.
 * Implementations of this interface should be immutable.
 * </p>
 */
@InterfaceStability.Evolving
public interface RetryPolicy {
  
  /**
   * Returned by {@link RetryPolicy#shouldRetry(Exception, int, int, boolean)}.
   */
  @InterfaceStability.Evolving
  public static class RetryAction {
    
    // A few common retry policies, with no delays.
    public static final RetryAction FAIL =
        new RetryAction(RetryDecision.FAIL);
    public static final RetryAction RETRY =
        new RetryAction(RetryDecision.RETRY);
    public static final RetryAction FAILOVER_AND_RETRY =
        new RetryAction(RetryDecision.FAILOVER_AND_RETRY);
    
    public final RetryDecision action;
    public final long delayMillis;
    public final String reason;
    
    public RetryAction(RetryDecision action) {
      this(action, 0, null);
    }
    
    public RetryAction(RetryDecision action, long delayTime) {
      this(action, delayTime, null);
    }
    
    public RetryAction(RetryDecision action, long delayTime, String reason) {
      this.action = action;
      this.delayMillis = delayTime;
      this.reason = reason;
    }
    
    @Override
    public String toString() {
      return getClass().getSimpleName() + "(action=" + action
          + ", delayMillis=" + delayMillis + ", reason=" + reason + ")";
    }
    
    public enum RetryDecision {
      FAIL,
      RETRY,
      FAILOVER_AND_RETRY
    }
  }
  
  /**
   * <p>
   * Determines whether the framework should retry a method for the given
   * exception, and the number of retries that have been made for that operation
   * so far.
   * </p>
   * 
   * @param e The exception that caused the method to fail
   * @param retries The number of times the method has been retried
   * @param failovers The number of times the method has failed over to a
   *          different backend implementation
   * @param isIdempotentOrAtMostOnce <code>true</code> if the method is
   *          {@link Idempotent} or {@link AtMostOnce} and so can reasonably be
   *          retried on failover when we don't know if the previous attempt
   *          reached the server or not
   * @return <code>true</code> if the method should be retried,
   *         <code>false</code> if the method should not be retried but
   *         shouldn't fail with an exception (only for void methods)
   * @throws Exception The re-thrown exception <code>e</code> indicating that
   *           the method failed and should not be retried further
   */
  public RetryAction shouldRetry(Exception e, int retries, int failovers,
      boolean isIdempotentOrAtMostOnce) throws Exception;
}