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/*
* Copyright 2022 Google LLC
*
* 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.google.android.libraries.mobiledatadownload.file.common.internal;
import static com.google.common.base.Preconditions.checkArgument;
import java.util.Iterator;
/**
* Provide an iterator for a infinite sequence of exponential backoffs. The sequence begins with the
* provided initial backoff and doubles up everytime a new backoff is acceessed, after the backoff
* reaches the upper bound, it always returns the upper bound backoff.
*/
public final class ExponentialBackoffIterator implements Iterator<Long> {
/**
* Create a new instance with positive integers. {@code upperBoundBackoff} should be no less than
* {@code initialBackoff}.
*/
public static ExponentialBackoffIterator create(long initialBackoff, long upperBoundBackoff) {
checkArgument(initialBackoff > 0);
checkArgument(upperBoundBackoff >= initialBackoff);
return new ExponentialBackoffIterator(initialBackoff, upperBoundBackoff);
}
private long nextBackoff;
private final long upperBoundBackoff;
private ExponentialBackoffIterator(long initialBackoff, long upperBoundBackoff) {
this.nextBackoff = initialBackoff;
this.upperBoundBackoff = upperBoundBackoff;
}
/**
* Returns if the iterator has the next delay. It always returns true because the sequence is
* infinite.
*/
@Override
public boolean hasNext() {
return true;
}
/** Returns the next delay. */
@Override
public Long next() {
long currentBackoff = nextBackoff;
if (nextBackoff >= upperBoundBackoff / 2) {
nextBackoff = upperBoundBackoff;
} else {
nextBackoff *= 2;
}
return currentBackoff;
}
}
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