Class ExponentialBackOff
- java.lang.Object
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- com.google.api.client.util.ExponentialBackOff
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- All Implemented Interfaces:
BackOff
public class ExponentialBackOff extends Object implements BackOff
Implementation ofBackOff
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 methodnextBackOffMillis()
starts returningBackOff.STOP
. The elapsed time can be reset by callingreset()
.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.
- Since:
- 1.15
- Author:
- Ravi Mistry
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
ExponentialBackOff.Builder
Builder forExponentialBackOff
.
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Field Summary
Fields Modifier and Type Field Description static int
DEFAULT_INITIAL_INTERVAL_MILLIS
The default initial interval value in milliseconds (0.5 seconds).static int
DEFAULT_MAX_ELAPSED_TIME_MILLIS
The default maximum elapsed time in milliseconds (15 minutes).static int
DEFAULT_MAX_INTERVAL_MILLIS
The default maximum back off time in milliseconds (1 minute).static double
DEFAULT_MULTIPLIER
The default multiplier value (1.5 which is 50% increase per back off).static 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).-
Fields inherited from interface com.google.api.client.util.BackOff
STOP, STOP_BACKOFF, ZERO_BACKOFF
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Constructor Summary
Constructors Modifier Constructor Description ExponentialBackOff()
Creates an instance of ExponentialBackOffPolicy using default values.protected
ExponentialBackOff(ExponentialBackOff.Builder builder)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
getCurrentIntervalMillis()
Returns the current retry interval in milliseconds.long
getElapsedTimeMillis()
Returns the elapsed time in milliseconds since anExponentialBackOff
instance is created and is reset whenreset()
is called.int
getInitialIntervalMillis()
Returns the initial retry interval in milliseconds.int
getMaxElapsedTimeMillis()
Returns the maximum elapsed time in milliseconds.int
getMaxIntervalMillis()
Returns the maximum value of the back off period in milliseconds.double
getMultiplier()
Returns the value to multiply the current interval with for each retry attempt.double
getRandomizationFactor()
Returns the randomization factor to use for creating a range around the retry interval.long
nextBackOffMillis()
Gets the number of milliseconds to wait before retrying the operation orBackOff.STOP
to indicate that no retries should be made.void
reset()
Sets the interval back to the initial retry interval and restarts the timer.
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Field Detail
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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
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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
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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
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DEFAULT_MAX_INTERVAL_MILLIS
public static final int DEFAULT_MAX_INTERVAL_MILLIS
The default maximum back off time in milliseconds (1 minute).- See Also:
- Constant Field Values
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DEFAULT_MAX_ELAPSED_TIME_MILLIS
public static final int DEFAULT_MAX_ELAPSED_TIME_MILLIS
The default maximum elapsed time in milliseconds (15 minutes).- See Also:
- Constant Field Values
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Constructor Detail
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ExponentialBackOff
public ExponentialBackOff()
Creates an instance of ExponentialBackOffPolicy using default values.To override the defaults use
ExponentialBackOff.Builder
.initialIntervalMillis
defaults toDEFAULT_INITIAL_INTERVAL_MILLIS
randomizationFactor
defaults toDEFAULT_RANDOMIZATION_FACTOR
multiplier
defaults toDEFAULT_MULTIPLIER
maxIntervalMillis
defaults toDEFAULT_MAX_INTERVAL_MILLIS
maxElapsedTimeMillis
defaults inDEFAULT_MAX_ELAPSED_TIME_MILLIS
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ExponentialBackOff
protected ExponentialBackOff(ExponentialBackOff.Builder builder)
- Parameters:
builder
- builder
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Method Detail
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reset
public final void reset()
Sets the interval back to the initial retry interval and restarts the timer.
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nextBackOffMillis
public long nextBackOffMillis() throws IOException
Gets the number of milliseconds to wait before retrying the operation orBackOff.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.
- Specified by:
nextBackOffMillis
in interfaceBackOff
- Throws:
IOException
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getInitialIntervalMillis
public final int getInitialIntervalMillis()
Returns the initial retry interval in milliseconds.
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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.
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getCurrentIntervalMillis
public final int getCurrentIntervalMillis()
Returns the current retry interval in milliseconds.
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getMultiplier
public final double getMultiplier()
Returns the value to multiply the current interval with for each retry attempt.
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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.
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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 methodnextBackOffMillis()
starts returningBackOff.STOP
. The elapsed time can be reset by callingreset()
.
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getElapsedTimeMillis
public final long getElapsedTimeMillis()
Returns the elapsed time in milliseconds since anExponentialBackOff
instance is created and is reset whenreset()
is called.The elapsed time is computed using
System.nanoTime()
.
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