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SDK for Microsoft Azure Storage Clients
/**
* Copyright Microsoft Corporation
*
* 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.microsoft.azure.storage;
import java.net.HttpURLConnection;
import java.util.Random;
/**
* Represents a retry policy that performs a specified number of retries, using a randomized exponential backoff scheme
* to determine the interval between retries.
*
* This class extends the {@link com.microsoft.azure.storage.RetryPolicy} class and implements the
* {@link com.microsoft.azure.storage.RetryPolicyFactory} interface.
*/
public final class RetryExponentialRetry extends RetryPolicy implements RetryPolicyFactory {
/**
* Holds the random number generator used to calculate randomized backoff intervals.
*/
private final Random randRef = new Random();
/**
* Holds the actual maximum backoff interval to enforce.
*/
private int resolvedMaxBackoff = RetryPolicy.DEFAULT_MAX_BACKOFF;
/**
* Holds the actual minimum backoff interval to enforce.
*/
private int resolvedMinBackoff = RetryPolicy.DEFAULT_MIN_BACKOFF;
/**
* Creates an instance of the RetryExponentialRetry class.
*/
public RetryExponentialRetry() {
this(RetryPolicy.DEFAULT_CLIENT_BACKOFF, RetryPolicy.DEFAULT_CLIENT_RETRY_COUNT);
}
/**
* Creates an instance of the RetryExponentialRetry class using the specified delta backoff and maximum
* retry attempts.
*
* @param deltaBackoff
* The backoff interval, in milliseconds, between retries.
* @param maxAttempts
* The maximum number of retry attempts.
*/
public RetryExponentialRetry(final int deltaBackoff, final int maxAttempts) {
super(deltaBackoff, maxAttempts);
}
/**
* Creates an instance of the RetryExponentialRetry class using the specified minimum, maximum, and
* delta backoff amounts, and maximum number of retry attempts.
*
* @param minBackoff
* The minimum backoff interval, in milliseconds, between retries.
* @param deltaBackoff
* The backoff interval, in milliseconds, between retries.
* @param maxBackOff
* The maximum backoff interval, in milliseconds, between retries.
* @param maxAttempts
* The maximum retry attempts, in milliseconds, between retries.
*/
public RetryExponentialRetry(final int minBackoff, final int deltaBackoff, final int maxBackOff,
final int maxAttempts) {
super(deltaBackoff, maxAttempts);
this.resolvedMinBackoff = minBackoff;
this.resolvedMaxBackoff = maxBackOff;
}
/**
* Generates a new retry policy for the current request attempt.
*
* @param opContext
* An {@link OperationContext} object that represents the context for the current operation. This object
* is used to track requests to the storage service, and to provide additional runtime information about
* the operation.
*
* @return A {@link RetryPolicy} object that represents the retry policy for the current request attempt.
*/
@Override
public RetryPolicy createInstance(final OperationContext opContext) {
return new RetryExponentialRetry(this.resolvedMinBackoff, this.deltaBackoffIntervalInMs,
this.resolvedMaxBackoff, this.maximumAttempts);
}
/**
* Determines whether the operation should be retried and specifies the interval until the next retry.
*
* @param retryContext
* A {@link RetryContext} object that indicates the number of retries, last request's results, whether
* the next retry should happen in the primary or secondary location, and specifies the location mode.
* @param operationContext
* An {@link OperationContext} object for tracking the current operation.
* @return
* A {@link RetryInfo} object that indicates whether the next retry will happen in the primary or secondary
* location, and specifies the location mode. If null, the operation will not be retried.
*/
@Override
public RetryInfo evaluate(RetryContext retryContext, OperationContext operationContext) {
boolean secondaryNotFound = this.evaluateLastAttemptAndSecondaryNotFound(retryContext);
if (retryContext.getCurrentRetryCount() < this.maximumAttempts) {
// If this method is called after a successful response, it means
// we failed during the response body download. So, we should not
// check for success codes here.
int statusCode = retryContext.getLastRequestResult().getStatusCode();
if ((!secondaryNotFound && statusCode >= 300 && statusCode < 500 && statusCode != 408)
|| statusCode == HttpURLConnection.HTTP_NOT_IMPLEMENTED
|| statusCode == HttpURLConnection.HTTP_VERSION) {
return null;
}
// Calculate backoff Interval between 80% and 120% of the desired
// backoff, multiply by 2^n -1 for exponential
double incrementDelta = (Math.pow(2, retryContext.getCurrentRetryCount()) - 1);
final int boundedRandDelta = (int) (this.deltaBackoffIntervalInMs * 0.8)
+ this.randRef.nextInt((int) (this.deltaBackoffIntervalInMs * 1.2)
- (int) (this.deltaBackoffIntervalInMs * 0.8));
incrementDelta *= boundedRandDelta;
final long retryInterval = (int) Math.round(Math.min(this.resolvedMinBackoff + incrementDelta,
this.resolvedMaxBackoff));
return this.evaluateRetryInfo(retryContext, secondaryNotFound, retryInterval);
}
return null;
}
}