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/*
 * Tencent is pleased to support the open source community by making Angel available.
 *
 * Copyright (C) 2017-2018 THL A29 Limited, a Tencent company. All rights reserved.
 *
 * Licensed 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
 *
 * https://opensource.org/licenses/Apache-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 com.tencent.angel.io.retry;


/**
 * 
 * Specifies a policy for retrying method failures. Implementations of this interface should be
 * immutable.
 * 
 */
public interface RetryPolicy {

  /**
   * Returned by {@link RetryPolicy#shouldRetry(Exception, int, int, boolean)}.
   */
  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
    }
  }

  /**
   * 
   * 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.
   * 
   *
   * @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 true 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 true if the method should be retried, false if the method
   * should not be retried but shouldn't fail with an exception (only for void methods)
   * @throws Exception The re-thrown exception e indicating that the method failed and
   *                   should not be retried further
   */
  public RetryAction shouldRetry(Exception e, int retries, int failovers,
    boolean isIdempotentOrAtMostOnce) throws Exception;
}