Package edu.rit.pj.reduction

Class SharedObjectArray<T>

java.lang.Object

edu.rit.pj.reduction.SharedObjectArray<T>

Type Parameters:

T - Object data type.

public class SharedObjectArray<T>
extends Object

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.

Version:

24-Aug-2007

Author:

Alan Kaminsky

Constructor Summary

Constructors

Constructor	Description
SharedObjectArray(int len)	Construct a new object array reduction variable with the given length.
SharedObjectArray(T[] array)	Construct a new object array reduction variable whose elements are copied from the given array.

Method Summary

Modifier and Type	Method	Description
boolean	compareAndSet(int i, T expect, T update)	Atomically set this array reduction variable at the given index to the given updated value if the current value equals the expected value.
T	get(int i)	Returns this array reduction variable's current value at the given index.
T	getAndSet(int i, T value)	Set this array reduction variable at the given index to the given value and return the previous value.
int	length()	Returns this array reduction variable's length.
void	reduce(int dstoff, T[] src, int srcoff, int len, ObjectOp<T> op)	Combine a portion of this array reduction variable with a portion of the given array using the given operation.
T	reduce(int i, T value, ObjectOp<T> op)	Combine this array reduction variable at the given index with the given value using the given operation.
void	reduce(T[] src, ObjectOp<T> op)	Combine this array reduction variable with the given array using the given operation.
void	set(int i, T value)	Set this array reduction variable at the given index to the given value.
String	toString()	Returns a string version of this array reduction variable.
boolean	weakCompareAndSet(int i, T expect, T update)	Atomically set this array reduction variable at the given index to the given updated value if the current value equals the expected value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Details

SharedObjectArray

public SharedObjectArray(int len)

Construct a new object array reduction variable with the given length. Each array element is initially null.

Parameters:

len - Length.

Throws:

NegativeArraySizeException - (unchecked exception) Thrown if len < 0.

SharedObjectArray

public SharedObjectArray(T[] array)

Construct a new object array reduction variable whose elements are copied from the given array.

Parameters:

array - Array to copy.

Throws:

NullPointerException - (unchecked exception) Thrown if array is null.

Method Details

length

public int length()

Returns this array reduction variable's length.

Returns:

Length.

get

public T get(int i)

Returns this array reduction variable's current value at the given index.

Parameters:

i - Index.

Returns:

Current value.

set

public void set(int i,
 T value)

Set this array reduction variable at the given index to the given value.

Parameters:

i - Index.

value - New value.

getAndSet

public T getAndSet(int i,
 T value)

Set this array reduction variable at the given index to the given value and return the previous value.

Parameters:

i - Index.

value - New value.

Returns:

Previous value.

compareAndSet

public boolean compareAndSet(int i,
 T expect,
 T update)

Atomically set this array reduction variable at the given index to the given updated value if the current value equals the expected value.

Parameters:

i - Index.

expect - Expected value.

update - Updated value.

Returns:

True if the update happened, false otherwise.

weakCompareAndSet

public boolean weakCompareAndSet(int i,
 T expect,
 T 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.

Parameters:

i - Index.

expect - Expected value.

update - Updated value.

Returns:

True if the update happened, false otherwise.

reduce

public T reduce(int i,
 T value,
 ObjectOp<T> op)

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.

Parameters:

i - Index.

value - Value.

op - Binary operation.

Returns:

(This array [i]) op (value).

reduce

public void reduce(T[] src,
 ObjectOp<T> op)

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.

Parameters:

src - Source array.

op - Binary operation.

Throws:

NullPointerException - (unchecked exception) Thrown if src is null. Thrown if op is null.

IndexOutOfBoundsException - (unchecked exception) Thrown if any array index would be out of bounds.

reduce

public void reduce(int dstoff,
 T[] src,
 int srcoff,
 int len,
 ObjectOp<T> 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.

Parameters:

dstoff - Index of first element to update in this array.

src - Source array.

srcoff - Index of first element to update from in the source array.

len - Number of array elements to update.

op - Binary operation.

Throws:

NullPointerException - (unchecked exception) Thrown if src is null. Thrown if op is null.

IndexOutOfBoundsException - (unchecked exception) Thrown if len < 0. Thrown if any array index would be out of bounds.

toString

public String toString()

Returns a string version of this array reduction variable.

Overrides:

toString in class Object

Returns:

String version.