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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.cassandra.utils;
import java.util.concurrent.TimeUnit;
import java.util.function.DoubleSupplier;
public interface Backoff
{
/**
* @return max attempts allowed, {@code == 0} implies no retries are allowed
*/
int maxAttempts();
long computeWaitTime(int retryCount);
TimeUnit unit();
enum None implements Backoff
{
INSTANCE;
@Override
public int maxAttempts()
{
return 0;
}
@Override
public long computeWaitTime(int retryCount)
{
throw new UnsupportedOperationException();
}
@Override
public TimeUnit unit()
{
throw new UnsupportedOperationException();
}
}
class ExponentialBackoff implements Backoff
{
private final int maxAttempts;
private final long baseSleepTimeMillis;
private final long maxSleepMillis;
private final DoubleSupplier randomSource;
public ExponentialBackoff(int maxAttempts, long baseSleepTimeMillis, long maxSleepMillis, DoubleSupplier randomSource)
{
this.maxAttempts = maxAttempts;
this.baseSleepTimeMillis = baseSleepTimeMillis;
this.maxSleepMillis = maxSleepMillis;
this.randomSource = randomSource;
}
@Override
public int maxAttempts()
{
return maxAttempts;
}
@Override
public long computeWaitTime(int retryCount)
{
long baseTimeMillis = baseSleepTimeMillis * (1L << retryCount);
// it's possible that this overflows, so fall back to max;
if (baseTimeMillis <= 0)
baseTimeMillis = maxSleepMillis;
// now make sure this is capped to target max
baseTimeMillis = Math.min(baseTimeMillis, maxSleepMillis);
return (long) (baseTimeMillis * (randomSource.getAsDouble() + 0.5));
}
@Override
public TimeUnit unit()
{
return TimeUnit.MILLISECONDS;
}
}
}