com.scaleoutsoftware.soss.client.util

Class MergeTree<RESULT>

java.lang.Object

com.scaleoutsoftware.soss.client.util.MergeTree<RESULT>

Type Parameters:

RESULT - result type

public abstract class MergeTree<RESULT>
extends java.lang.Object

This is a base class which is used by its subclasses to create a pool of worker threads, each executing a task which produces a result object. The result objects are merged together. execute(ExecutorService) creates the thread pool, runs tasks, and returns the single merged result.

The sequence of merges is determined by the tree, where each node corresponds to the worker thread. The merges are thread safe, i.e., it is guaranteed that only one child node at a time is merging result to the parent node. Eventually, the final result is accumulated at the root node.

To define the worker behaviour, two methods have to be implemented: runTask() for the task, and doMerge(Object, Object) for merging two results together.

Optionally, getParentIndex(int) can be overridden to change the tree structure.

Constructor Summary

Constructors

Constructor and Description
MergeTree(int numberOfWorkers) Creates the merge tree with the given number of worker nodes.

Method Summary

Modifier and Type	Method and Description
abstract void	doMerge(RESULT to, RESULT from) Merge one result into another.
RESULT	execute(java.util.concurrent.ExecutorService service) Runs the workers, merges the results in the tree, and returns the final result.
protected int	getParentIndex(int childIndex) Returns the index of the parent node for the child node.
abstract RESULT	runTask() Run single task and get the result.

Methods inherited from class java.lang.Object

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

Constructor Detail

MergeTree

public MergeTree(int numberOfWorkers)

Creates the merge tree with the given number of worker nodes.

Parameters:

numberOfWorkers - number of workers

Method Detail

getParentIndex

protected int getParentIndex(int childIndex)

Returns the index of the parent node for the child node. This method can be overridden to change tree structure. The child index should be always greater than parent index. The root node has the index 0, which will not be submitted to that method.

Parameters:

childIndex - index of the child node

Returns:

index of the parent node

execute

public RESULT execute(java.util.concurrent.ExecutorService service)
               throws java.lang.InterruptedException,
                      java.util.concurrent.ExecutionException

Runs the workers, merges the results in the tree, and returns the final result.

Parameters:

service - the ExecutorService this merge tree will use.

Returns:

the merged result

Throws:

java.lang.InterruptedException - if worker was interrupted

java.util.concurrent.ExecutionException - if the exception occurred in one of the worker threads

runTask

public abstract RESULT runTask()
                        throws java.lang.Exception

Run single task and get the result.

Returns:

task result

Throws:

java.lang.Exception - if the exception occurred while running the task

doMerge

public abstract void doMerge(RESULT to,
                             RESULT from)
                      throws java.lang.Exception

Merge one result into another.

Parameters:

to - parent result to merge into

from - child result to be merged

Throws:

java.lang.Exception - if the exception occurred while merging results