com.hazelcast.util.concurrent.BackoffIdleStrategy Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2016, Hazelcast, Inc. 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 com.hazelcast.util.concurrent;
import java.util.concurrent.locks.LockSupport;
import static com.hazelcast.util.Preconditions.checkNotNegative;
import static java.lang.Long.numberOfLeadingZeros;
import static java.lang.Math.min;
/**
* Idling strategy for threads when they have no work to do.
*
* Spin for maxSpins, then
* {@link Thread#yield()} for maxYields, then
* {@link LockSupport#parkNanos(long)} on an exponential backoff to maxParkPeriodNs
*/
public class BackoffIdleStrategy implements IdleStrategy {
private final long yieldThreshold;
private final long parkThreshold;
private final long minParkPeriodNs;
private final long maxParkPeriodNs;
private final int maxShift;
/**
* Create a set of state tracking idle behavior
*
* @param maxSpins to perform before moving to {@link Thread#yield()}
* @param maxYields to perform before moving to {@link LockSupport#parkNanos(long)}
* @param minParkPeriodNs to use when initiating parking
* @param maxParkPeriodNs to use when parking
*/
public BackoffIdleStrategy(long maxSpins, long maxYields, long minParkPeriodNs, long maxParkPeriodNs) {
checkNotNegative(maxSpins, "maxSpins must be positive or zero");
checkNotNegative(maxYields, "maxYields must be positive or zero");
checkNotNegative(minParkPeriodNs, "minParkPeriodNs must be positive or zero");
checkNotNegative(maxParkPeriodNs - minParkPeriodNs,
"maxParkPeriodNs must be greater than or equal to minParkPeriodNs");
this.yieldThreshold = maxSpins;
this.parkThreshold = maxSpins + maxYields;
this.minParkPeriodNs = minParkPeriodNs;
this.maxParkPeriodNs = maxParkPeriodNs;
this.maxShift = numberOfLeadingZeros(minParkPeriodNs) - numberOfLeadingZeros(maxParkPeriodNs);
}
/**
* {@inheritDoc}
*/
@Override public boolean idle(long n) {
if (n < yieldThreshold) {
return false;
}
if (n < parkThreshold) {
Thread.yield();
return false;
}
final long parkTime = parkTime(n);
LockSupport.parkNanos(parkTime);
return parkTime == maxParkPeriodNs;
}
long parkTime(long n) {
final long proposedShift = n - parkThreshold;
final long allowedShift = min(maxShift, proposedShift);
return proposedShift > maxShift ? maxParkPeriodNs
: proposedShift < maxShift ? minParkPeriodNs << allowedShift
: min(minParkPeriodNs << allowedShift, maxParkPeriodNs);
}
}