/*******************************************************************************
* Copyright 2014 Analog Devices, Inc.
*
* 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.analog.lyric.collect;
import java.io.Serializable;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicStampedReference;
import net.jcip.annotations.Immutable;
import net.jcip.annotations.ThreadSafe;
/**
* Maintains a double value along with an integer "stamp" that can be updated atomically.
* <p>
* This is a slightly more efficient alternative to {@code AtomicStampedReference<Double>}
* and unlike that class is serializable.
*
* @see AtomicStampedReference
* @since 0.05
*/
@ThreadSafe
public class AtomicStampedDouble implements Serializable
{
/*-------
* State
*/
private static final long serialVersionUID = 1L;
@Immutable
protected static class Pair implements Serializable
{
private static final long serialVersionUID = 1L;
private final double _value;
private final int _stamp;
private Pair(double value, int stamp)
{
_value = value;
_stamp = stamp;
}
}
/**
* Holds the current value/stamp pair.
*/
protected final AtomicReference<Pair> _atomicRef;
/*--------------
* Construction
*/
/**
* Constructs with given value and stamp.
*/
public AtomicStampedDouble(double value, int stamp)
{
_atomicRef = new AtomicReference<Pair>(new Pair(value, stamp));
}
/**
* Constructs with given value and stamp set to zero.
*/
public AtomicStampedDouble(double value)
{
this(value, 0);
}
/**
* Constructs with value and stamp both set to zero.
*/
public AtomicStampedDouble()
{
this(0,0);
}
/**
* Copies value and stamp from another instance.
*/
public AtomicStampedDouble(AtomicStampedDouble that)
{
_atomicRef = new AtomicReference<Pair>(that._atomicRef.get());
}
/*---------
* Methods
*/
/**
* Attempts to change the stamp if value matches {@code expectedValue}.
*
* @return false if current value does not match {@code expectedValue} or if value
* or stamp is changed in another thread during this call.
* <p>
* @see #compareAndSet
*/
public final boolean attemptStamp(double expectedValue, int newStamp)
{
Pair pair = _atomicRef.get();
return Double.doubleToRawLongBits(expectedValue) == Double.doubleToRawLongBits(pair._value) &&
(newStamp == pair._stamp || _atomicRef.compareAndSet(pair, new Pair(expectedValue, newStamp)));
}
/**
* Attempts to change the value and stamp atomically if current values match old values.
*
* @return false if current value or stamp does not match expected values or if
* value or stamp is changed in another thread during this call.
* <p>
* @see #attemptStamp
* @see #setAndIncrementStamp(double)
*/
public final boolean compareAndSet(double expectedValue, double newValue, int expectedStamp, int newStamp)
{
Pair pair = _atomicRef.get();
return expectedStamp == pair._stamp &&
Double.doubleToRawLongBits(expectedValue) == Double.doubleToRawLongBits(pair._value) &&
((newValue == expectedValue && expectedStamp == newStamp) ||
_atomicRef.compareAndSet(pair, new Pair(newValue, newStamp)));
}
/**
* Gets the current value.
*/
public final double get()
{
return _atomicRef.get()._value;
}
/**
* Returns the current value and writes into {@code stampHolder} the current stamp value.
* @param stampHolder must have lenght of at least one.
*/
public final double get(int[] stampHolder)
{
Pair pair = _atomicRef.get();
stampHolder[0] = pair._stamp;
return pair._value;
}
/**
* Returns the current stamp value.
*/
public final int getStamp()
{
return _atomicRef.get()._stamp;
}
/**
* Atomically sets the value and its associated stamp.
*/
public final void set(double value, int stamp)
{
Pair pair = _atomicRef.get();
if (pair._value != value || pair._stamp != stamp)
{
_atomicRef.set(new Pair(value, stamp));
}
}
/**
* Sets the value and atomically increments the stamp if the value changed.
*
* @return false if the value was not set because it was set by another thread
*
* @see #compareAndSet
*/
public final boolean setAndIncrementStamp(double value)
{
Pair pair = _atomicRef.get();
if (Double.doubleToRawLongBits(value) != Double.doubleToRawLongBits(pair._value))
{
return _atomicRef.compareAndSet(pair, new Pair(value, pair._stamp + 1));
}
return true;
}
}