Implementing exponential backoff about google-api-php-client HOT 7 CLOSED

/**
 * Implementation of {@link BackOff} that increases the back off period for each retry attempt using
 * a randomization function that grows exponentially.
 *
 * <p>
 * {@link #nextBackOffMillis()} is calculated using the following formula:
 * </p>
 *
 * <pre>
   randomized_interval =
       retry_interval * (random value in range [1 - randomization_factor, 1 + randomization_factor])
 * </pre>
 *
 * <p>
 * In other words {@link #nextBackOffMillis()} will range between the randomization factor
 * percentage below and above the retry interval. For example, using 2 seconds as the base retry
 * interval and 0.5 as the randomization factor, the actual back off period used in the next retry
 * attempt will be between 1 and 3 seconds.
 * </p>
 *
 * <p>
 * <b>Note:</b> max_interval caps the retry_interval and not the randomized_interval.
 * </p>
 *
 * <p>
 * If the time elapsed since an {@link ExponentialBackOff} instance is created goes past the
 * max_elapsed_time then the method {@link #nextBackOffMillis()} starts returning
 * {@link BackOff#STOP}. The elapsed time can be reset by calling {@link #reset()}.
 * </p>
 *
 * <p>
 * Example: The default retry_interval is .5 seconds, default randomization_factor is 0.5, default
 * multiplier is 1.5 and the default max_interval is 1 minute. For 10 tries the sequence will be
 * (values in seconds) and assuming we go over the max_elapsed_time on the 10th try:
 * </p>
 *
 * <pre>
   request#     retry_interval     randomized_interval

   1             0.5                [0.25,   0.75]
   2             0.75               [0.375,  1.125]
   3             1.125              [0.562,  1.687]
   4             1.687              [0.8435, 2.53]
   5             2.53               [1.265,  3.795]
   6             3.795              [1.897,  5.692]
   7             5.692              [2.846,  8.538]
   8             8.538              [4.269, 12.807]
   9            12.807              [6.403, 19.210]
   10           19.210              {@link BackOffPolicy#STOP}
 * </pre>
 *
 * <p>
 * Implementation is not thread-safe.
 * </p>
 *
 * @since 1.15
 * @author Ravi Mistry
 */