Class ExponentialBackOff (1.45.0)

Implementation of BackOff that increases the back off period for each retry attempt using a randomization function that grows exponentially.

#nextBackOffMillis() is calculated using the following formula:

randomized_interval = retry_interval * (random value in range [1 - randomization_factor, 1 + randomization_factor])

In other words #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.

Note: max_interval caps the retry_interval and not the randomized_interval.

If the time elapsed since an ExponentialBackOff instance is created goes past the max_elapsed_time then the method #nextBackOffMillis() starts returning BackOff#STOP. The elapsed time can be reset by calling #reset().

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:

 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              BackOff#STOP
 

Implementation is not thread-safe.

The default initial interval value in milliseconds (0.5 seconds).

The default maximum elapsed time in milliseconds (15 minutes).

The default maximum back off time in milliseconds (1 minute).

The default multiplier value (1.5 which is 50% increase per back off).

The default randomization factor (0.5 which results in a random period ranging between 50% below and 50% above the retry interval).

Creates an instance of ExponentialBackOffPolicy using default values.

To override the defaults use Builder.

• initialIntervalMillis defaults to #DEFAULT_INITIAL_INTERVAL_MILLIS
• randomizationFactor defaults to #DEFAULT_RANDOMIZATION_FACTOR
• multiplier defaults to #DEFAULT_MULTIPLIER
• maxIntervalMillis defaults to #DEFAULT_MAX_INTERVAL_MILLIS
• maxElapsedTimeMillis defaults in #DEFAULT_MAX_ELAPSED_TIME_MILLIS

Returns the current retry interval in milliseconds.

Returns the elapsed time in milliseconds since an ExponentialBackOff instance is created and is reset when #reset() is called.

The elapsed time is computed using System#nanoTime().

Returns the initial retry interval in milliseconds.

Returns the maximum elapsed time in milliseconds.

If the time elapsed since an ExponentialBackOff instance is created goes past the max_elapsed_time then the method #nextBackOffMillis() starts returning BackOff#STOP. The elapsed time can be reset by calling #reset().

Returns the maximum value of the back off period in milliseconds. Once the current interval reaches this value it stops increasing.

Returns the value to multiply the current interval with for each retry attempt.

Returns the randomization factor to use for creating a range around the retry interval.

A randomization factor of 0.5 results in a random period ranging between 50% below and 50% above the retry interval.

Gets the number of milliseconds to wait before retrying the operation or #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 }

This method calculates the next back off interval using the formula: randomized_interval = retry_interval +/- (randomization_factor * retry_interval)

Subclasses may override if a different algorithm is required.

Sets the interval back to the initial retry interval and restarts the timer.