Package com.cadiducho.telegrambotapi.handlers

Class ExponentialBackOff

  • public class ExponentialBackOff
extends Object
    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.

    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              maxElapsedTimeMillis

    Implementation is not thread-safe.

    Since:
    1.15
    Author:
    Ravi Mistry

    • Field Detail

      • DEFAULT_INITIAL_INTERVAL_MILLIS

        public static final int DEFAULT_INITIAL_INTERVAL_MILLIS
        The default initial interval value in milliseconds (0.5 seconds).
        See Also:
        Constant Field Values

      • DEFAULT_RANDOMIZATION_FACTOR

        public static final double DEFAULT_RANDOMIZATION_FACTOR
        The default randomization factor (0.5 which results in a random period ranging between 50% below and 50% above the retry interval).
        See Also:
        Constant Field Values

      • DEFAULT_MULTIPLIER

        public static final double DEFAULT_MULTIPLIER
        The default multiplier value (1.5 which is 50% increase per back off).
        See Also:
        Constant Field Values

      • DEFAULT_MAX_INTERVAL_MILLIS

        public static final int DEFAULT_MAX_INTERVAL_MILLIS
        The default maximum back off time in milliseconds (15 minutes).
        See Also:
        Constant Field Values

      • DEFAULT_MAX_ELAPSED_TIME_MILLIS

        public static final int DEFAULT_MAX_ELAPSED_TIME_MILLIS
        The default maximum elapsed time in milliseconds (60 minutes).
        See Also:
        Constant Field Values

    • Method Detail

      • reset

        public final void reset()
        Sets the interval back to the initial retry interval and restarts the timer.

      • nextBackOffMillis

        public long nextBackOffMillis()

        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.

        Returns:
        next back off millis

      • getInitialIntervalMillis

        public final int getInitialIntervalMillis()
        Returns the initial retry interval in milliseconds.
        Returns:
        the initial retry interval in milliseconds.

      • getRandomizationFactor

        public final double getRandomizationFactor()
        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.

        Returns:
        the randomization factor

      • getCurrentIntervalMillis

        public final int getCurrentIntervalMillis()
        Returns the current retry interval in milliseconds.
        Returns:
        the current retry interval in milliseconds.

      • getMultiplier

        public final double getMultiplier()
        Returns the value to multiply the current interval with for each retry attempt.
        Returns:
        the value to multiply the current interval

      • getMaxIntervalMillis

        public final int getMaxIntervalMillis()
        Returns the maximum value of the back off period in milliseconds. Once the current interval reaches this value it stops increasing.
        Returns:
        the maximum value of the back off period in milliseconds

      • getMaxElapsedTimeMillis

        public final int getMaxElapsedTimeMillis()
        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 this value. The elapsed time can be reset by calling reset().

        Returns:
        the maximum elapsed time in milliseconds

      • getElapsedTimeMillis

        public final long getElapsedTimeMillis()
        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 elapsed time in milliseconds