BackOff.java

/*
 * Copyright (c) 2011 Google Inc.
 *
 * 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
 *
 * 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 com.google.api.client.util;

import java.io.IOException;

/**
 * Back-off policy when retrying an operation.
 *
 * @since 1.15
 * @author Ravi Mistry
 */
public interface BackOff {

  /** Indicates that no more retries should be made for use in {@link #nextBackOffMillis()}. */
  static final long STOP = -1L;

  /** Reset to initial state. */
  void reset() throws IOException;

  /**
   * Gets the number of milliseconds to wait before retrying the operation or {@link #STOP} to
   * indicate that no retries should be made.
   *
   * <p>
   * Example usage:
   * </p>
   *
   * <pre>
   long backOffMillis = backoff.nextBackOffMillis();
   if (backOffMillis == Backoff.STOP) {
     // do not retry operation
   } else {
     // sleep for backOffMillis milliseconds and retry operation
   }
   * </pre>
   */
  long nextBackOffMillis() throws IOException;

  /**
   * Fixed back-off policy whose back-off time is always zero, meaning that the operation is retried
   * immediately without waiting.
   */
  BackOff ZERO_BACKOFF = new BackOff() {

    public void reset() throws IOException {
    }

    public long nextBackOffMillis() throws IOException {
      return 0;
    }
  };

  /**
   * Fixed back-off policy that always returns {@code #STOP} for {@link #nextBackOffMillis()},
   * meaning that the operation should not be retried.
   */
  BackOff STOP_BACKOFF = new BackOff() {

    public void reset() throws IOException {
    }

    public long nextBackOffMillis() throws IOException {
      return STOP;
    }
  };
}