//******************************************************************************
//
// File: SharedObjectArray.java
// Package: edu.rit.pj.reduction
// Unit: Class edu.rit.pj.reduction.SharedObjectArray
//
// This Java source file is copyright (C) 2007 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************
package edu.rit.pj.reduction;
import java.util.concurrent.atomic.AtomicReferenceArray;
/**
* Class SharedObjectArray provides an array reduction variable with elements
* of an object type.
*
* Class SharedObjectArray is multiple thread safe. The methods use lock-free
* atomic compare-and-set.
*
* Note: Class SharedObjectArray is implemented using class
* java.util.concurrent.atomic.AtomicReferenceArray.
*
* @param Object data type.
*
* @author Alan Kaminsky
* @version 24-Aug-2007
*/
public class SharedObjectArray
{
// Hidden data members.
private AtomicReferenceArray myArray;
// Exported constructors.
/**
* Construct a new object array reduction variable with the given length.
* Each array element is initially null.
*
* @param len Length.
*
* @exception NegativeArraySizeException
* (unchecked exception) Thrown if len < 0.
*/
public SharedObjectArray
(int len)
{
myArray = new AtomicReferenceArray (len);
}
/**
* Construct a new object array reduction variable whose elements are copied
* from the given array.
*
* @param array Array to copy.
*
* @exception NullPointerException
* (unchecked exception) Thrown if array is null.
*/
public SharedObjectArray
(T[] array)
{
myArray = new AtomicReferenceArray (array);
}
// Exported operations.
/**
* Returns this array reduction variable's length.
*
* @return Length.
*/
public int length()
{
return myArray.length();
}
/**
* Returns this array reduction variable's current value at the given index.
*
* @param i Index.
*
* @return Current value.
*/
public T get
(int i)
{
return myArray.get (i);
}
/**
* Set this array reduction variable at the given index to the given value.
*
* @param i Index.
* @param value New value.
*/
public void set
(int i,
T value)
{
myArray.set (i, value);
}
/**
* Set this array reduction variable at the given index to the given value
* and return the previous value.
*
* @param i Index.
* @param value New value.
*
* @return Previous value.
*/
public T getAndSet
(int i,
T value)
{
return myArray.getAndSet (i, value);
}
/**
* Atomically set this array reduction variable at the given index to the
* given updated value if the current value equals the expected value.
*
* @param i Index.
* @param expect Expected value.
* @param update Updated value.
*
* @return True if the update happened, false otherwise.
*/
public boolean compareAndSet
(int i,
T expect,
T update)
{
return myArray.compareAndSet (i, expect, update);
}
/**
* Atomically set this array reduction variable at the given index to the
* given updated value if the current value equals the expected value. May
* fail spuriously.
*
* @param i Index.
* @param expect Expected value.
* @param update Updated value.
*
* @return True if the update happened, false otherwise.
*/
public boolean weakCompareAndSet
(int i,
T expect,
T update)
{
return myArray.weakCompareAndSet (i, expect, update);
}
/**
* Combine this array reduction variable at the given index with the given
* value using the given operation. (This array [i]) is set to
* (this array [i]) op (value), then (this array
* [i]) is returned.
*
* @param i Index.
* @param value Value.
* @param op Binary operation.
*
* @return (This array [i]) op (value).
*/
public T reduce
(int i,
T value,
ObjectOp op)
{
for (;;)
{
T oldvalue = myArray.get (i);
T newvalue = op.op (oldvalue, value);
if (myArray.compareAndSet (i, oldvalue, newvalue)) return newvalue;
}
}
/**
* Combine this array reduction variable with the given array using the
* given operation. For each index i from 0 to this array's
* length-1, (this array [i]) is set to (this array [i])
* op (src[i]).
*
* The reduce() method is multiple thread safe on a per-element
* basis. Each individual array element is updated atomically, but the
* array as a whole is not updated atomically.
*
* @param src Source array.
* @param op Binary operation.
*
* @exception NullPointerException
* (unchecked exception) Thrown if src is null. Thrown if
* op is null.
* @exception IndexOutOfBoundsException
* (unchecked exception) Thrown if any array index would be out of
* bounds.
*/
public void reduce
(T[] src,
ObjectOp op)
{
reduce (0, src, 0, myArray.length(), op);
}
/**
* Combine a portion of this array reduction variable with a portion of the
* given array using the given operation. For each index i from 0
* to len-1, (this array [dstoff+i]) is set to (this array
* [dstoff+i]) op (src[srcoff+i]).
*
* The reduce() method is multiple thread safe on a per-element
* basis. Each individual array element is updated atomically, but the
* array as a whole is not updated atomically.
*
* @param dstoff Index of first element to update in this array.
* @param src Source array.
* @param srcoff Index of first element to update from in the source
* array.
* @param len Number of array elements to update.
* @param op Binary operation.
*
* @exception NullPointerException
* (unchecked exception) Thrown if src is null. Thrown if
* op is null.
* @exception IndexOutOfBoundsException
* (unchecked exception) Thrown if len < 0. Thrown if any
* array index would be out of bounds.
*/
public void reduce
(int dstoff,
T[] src,
int srcoff,
int len,
ObjectOp op)
{
if
(len < 0 ||
dstoff < 0 || dstoff+len > myArray.length() ||
srcoff < 0 || srcoff+len > src.length)
{
throw new IndexOutOfBoundsException();
}
while (len > 0)
{
updateLoop: for (;;)
{
T oldvalue = myArray.get (dstoff);
T newvalue = op.op (oldvalue, src[srcoff]);
if (myArray.compareAndSet (dstoff, oldvalue, newvalue))
break updateLoop;
}
++ dstoff;
++ srcoff;
-- len;
}
}
/**
* Returns a string version of this array reduction variable.
*
* @return String version.
*/
public String toString()
{
return myArray.toString();
}
}
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