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Google HTTP Client Library for Java. Functionality that works on all supported Java platforms, including Java 5 (or higher) desktop (SE) and web (EE), Android, and Google App Engine.

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/*
 * 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.
   *
   * Example usage:
   *
   * 
   * long backOffMillis = backoff.nextBackOffMillis();
   * if (backOffMillis == Backoff.STOP) {
   * // do not retry operation
   * } else {
   * // sleep for backOffMillis milliseconds and retry operation
   * }
   * 
   */
  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;
        }
      };
}