edu.rit.pj.replica
Class ReplicatedByte

java.lang.Object
  extended by java.lang.Number
      extended by edu.rit.pj.replica.ReplicatedByte
All Implemented Interfaces:
Serializable

public class ReplicatedByte
extends Number

Class ReplicatedByte provides a replicated, shared reduction variable for a value of type byte.

A replicated, shared reduction variable is intended to be used in a cluster or hybrid parallel program for a data item shared among all the processes in the program and all the threads in each process. To use a replicated, shared reduction variable, do the following in each process of the parallel program:

  1. Construct an instance of class ReplicatedByte, specifying the reduction operator (class Op) to use when performing updates, and specifying the communicator (class Comm) and the message tag to use for sending updates among the processes. At this point a replica of the variable exists in each process.

  2. To read the variable, call the get() method. The current value of the local process's replicated variable is returned.

  3. To update the variable, call the reduce() method, specifying a new value. The reduce() method performs an atomic reduction (described below) on the local process's replicated variable with the new value. If the variable changed as a result of the reduction, the variable's (updated) value is flooded to all the processes in the communicator. Finally, the reduce() method returns the variable's value.

    Whenever one of the aforementioned flooded messages arrives, a separate thread performs an atomic reduction on the local process's variable with the received value.

    An atomic reduction consists of these steps, performed atomically: Call the reduction operator's op() method, passing in the current value of the local process's replicated variable and the new value (either the new value specified as an argument of reduce(), or the new value received in a flooded message). Then store the op() method's return value back into the local process's replicated variable.

Class ReplicatedByte does not itself guarantee consistency of the replicas' values. This is to avoid the message passing overhead of a distributed state update protocol. Instead, the parallel program must be written to operate correctly when the variable is updated as described above. Note that the value of a process's local replica can change asynchronously at any time, either because a thread in the current process updated the variable, or because a flooded message updated the variable.

Class ReplicatedByte is multiple thread safe. The methods use lock-free atomic compare-and-set.

Note: Class ReplicatedByte is implemented using class java.util.concurrent.atomic.AtomicInteger.

See Also:
Serialized Form

Constructor Summary
ReplicatedByte(ByteOp op)
          Construct a new replicated, shared byte reduction variable with the given reduction operator.
ReplicatedByte(ByteOp op, byte initialValue)
          Construct a new replicated, shared byte reduction variable with the given reduction operator and initial value.
ReplicatedByte(ByteOp op, byte initialValue, int tag)
          Construct a new replicated, shared byte reduction variable with the given reduction operator, initial value, and message tag.
ReplicatedByte(ByteOp op, byte initialValue, int tag, Comm comm)
          Construct a new replicated, shared byte reduction variable with the given reduction operator, initial value, message tag, and communicator.
 
Method Summary
 double doubleValue()
          Returns this reduction variable's current value converted to type double.
 float floatValue()
          Returns this reduction variable's current value converted to type float.
 byte get()
          Returns this replicated, shared reduction variable's current value.
 int intValue()
          Returns this reduction variable's current value converted to type int.
 long longValue()
          Returns this reduction variable's current value converted to type long.
 byte reduce(byte value)
          Update this replicated, shared reduction variable's current value.
 String toString()
          Returns a string version of this reduction variable.
 
Methods inherited from class java.lang.Number
byteValue, shortValue
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

ReplicatedByte

public ReplicatedByte(ByteOp op)
Construct a new replicated, shared byte reduction variable with the given reduction operator. The initial value is 0. A message tag of 0 is used. The world communicator is used.

Parameters:
op - Reduction operator.
Throws:
NullPointerException - (unchecked exception) Thrown if op is null.

ReplicatedByte

public ReplicatedByte(ByteOp op,
                      byte initialValue)
Construct a new replicated, shared byte reduction variable with the given reduction operator and initial value. A message tag of 0 is used. The world communicator is used.

Parameters:
op - Reduction operator.
initialValue - Initial value.
Throws:
NullPointerException - (unchecked exception) Thrown if op is null.

ReplicatedByte

public ReplicatedByte(ByteOp op,
                      byte initialValue,
                      int tag)
Construct a new replicated, shared byte reduction variable with the given reduction operator, initial value, and message tag. The world communicator is used.

Parameters:
op - Reduction operator.
initialValue - Initial value.
tag - Message tag.
Throws:
NullPointerException - (unchecked exception) Thrown if op is null. Thrown if comm is null.

ReplicatedByte

public ReplicatedByte(ByteOp op,
                      byte initialValue,
                      int tag,
                      Comm comm)
Construct a new replicated, shared byte reduction variable with the given reduction operator, initial value, message tag, and communicator.

Parameters:
op - Reduction operator.
initialValue - Initial value.
tag - Message tag.
comm - Communicator.
Throws:
NullPointerException - (unchecked exception) Thrown if op is null. Thrown if comm is null.
Method Detail

get

public byte get()
Returns this replicated, shared reduction variable's current value.

Returns:
Current value.

reduce

public byte reduce(byte value)
            throws IOException
Update this replicated, shared reduction variable's current value. This variable is combined with the given value using the reduction operation specified to the constructor (op). The result is stored back into this variable and is returned; the result may also be flooded to all processes in the communicator.

Parameters:
value - Value.
Returns:
(This variable) op (value).
Throws:
IOException - Thrown if an I/O error occurred.

toString

public String toString()
Returns a string version of this reduction variable.

Overrides:
toString in class Object
Returns:
String version.

intValue

public int intValue()
Returns this reduction variable's current value converted to type int.

Specified by:
intValue in class Number
Returns:
Current value.

longValue

public long longValue()
Returns this reduction variable's current value converted to type long.

Specified by:
longValue in class Number
Returns:
Current value.

floatValue

public float floatValue()
Returns this reduction variable's current value converted to type float.

Specified by:
floatValue in class Number
Returns:
Current value.

doubleValue

public double doubleValue()
Returns this reduction variable's current value converted to type double.

Specified by:
doubleValue in class Number
Returns:
Current value.


Copyright © 2005-2012 by Alan Kaminsky. All rights reserved. Send comments to ark­@­cs.rit.edu.