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/*
* Copyright (c) OSGi Alliance (2015, 2016). All Rights Reserved.
*
* 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 org.osgi.util.pushstream;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.atomic.AtomicInteger;
/**
* {@link PushbackPolicyOption} provides a standard set of simple
* {@link PushbackPolicy} implementations.
*
* @see PushbackPolicy
*/
public enum PushbackPolicyOption {
/**
* Returns a fixed amount of back pressure, independent of how full the
* buffer is
*/
FIXED {
@Override
public <T, U extends BlockingQueue<PushEvent<? extends T>>> PushbackPolicy<T, U> getPolicy(long value) {
return q -> value;
}
},
/**
* Returns zero back pressure until the buffer is full, then it returns a
* fixed value
*/
ON_FULL_FIXED {
@Override
public <T, U extends BlockingQueue<PushEvent<? extends T>>> PushbackPolicy<T, U> getPolicy(long value) {
return q -> q.remainingCapacity() == 0 ? value : 0;
}
},
/**
* Returns zero back pressure until the buffer is full, then it returns an
* exponentially increasing amount, starting with the supplied value and
* doubling it each time. Once the buffer is no longer full the back
* pressure returns to zero.
*/
ON_FULL_EXPONENTIAL {
@Override
public <T, U extends BlockingQueue<PushEvent<? extends T>>> PushbackPolicy<T, U> getPolicy(long value) {
AtomicInteger backoffCount = new AtomicInteger(0);
return q -> {
if (q.remainingCapacity() == 0) {
return value << backoffCount.getAndIncrement();
}
backoffCount.set(0);
return 0;
};
}
},
/**
* Returns zero back pressure when the buffer is empty, then it returns a
* linearly increasing amount of back pressure based on how full the buffer
* is. The maximum value will be returned when the buffer is full.
*/
LINEAR {
@Override
public <T, U extends BlockingQueue<PushEvent<? extends T>>> PushbackPolicy<T, U> getPolicy(long value) {
return q -> {
long remainingCapacity = q.remainingCapacity();
long used = q.size();
return (value * used) / (used + remainingCapacity);
};
}
};
/**
* Create a {@link PushbackPolicy} instance configured with a base back
* pressure time in nanoseconds
*
* The actual backpressure returned will vary based on the selected
* implementation, the base value, and the state of the buffer.
*
* @param value
* @return A {@link PushbackPolicy} to use
*/
public abstract <T, U extends BlockingQueue<PushEvent<? extends T>>> PushbackPolicy<T, U> getPolicy(long value);
}
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