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Declarative Machine Learning
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.sysml.runtime.controlprogram.parfor;

import java.util.LinkedList;
import java.util.List;

import org.apache.sysml.runtime.DMLRuntimeException;
import org.apache.sysml.runtime.controlprogram.ParForProgramBlock;
import org.apache.sysml.runtime.controlprogram.parfor.Task.TaskType;
import org.apache.sysml.runtime.instructions.cp.IntObject;

/**
 * This factoring task partitioner virtually iterates over the given FOR loop (from, to, incr),
 * creates iterations and group them to tasks. Note that the task size is used here.
 * The tasks are created with decreasing size for good load balance of heterogeneous tasks.
 * 
 * 
 * See the original paper for details:
 * [Susan Flynn Hummel, Edith Schonberg, Lawrence E. Flynn: 
 * Factoring: a practical and robust method for scheduling parallel loops. 
 * SC 1991: 610-632]
 * 
 */
public class TaskPartitionerFactoring extends TaskPartitioner
{
	
	private int _numThreads = -1;
	
	public TaskPartitionerFactoring( long taskSize, int numThreads, String iterVarName, IntObject fromVal, IntObject toVal, IntObject incrVal ) 
	{
		super(taskSize, iterVarName, fromVal, toVal, incrVal);
		
		_numThreads = numThreads;
	}

	@Override
	public List createTasks() 
		throws DMLRuntimeException 
	{
		LinkedList tasks = new LinkedList();
		
		long lFrom  = _fromVal.getLongValue();
		long lTo    = _toVal.getLongValue();
		long lIncr  = _incrVal.getLongValue();
		
		int P = _numThreads;  // number of parallel workers
		long N = _numIter;     // total number of iterations
		long R = N;            // remaining number of iterations
		long K = -1;           // next _numThreads task sizes	
		TaskType type = null; // type of iterations: range tasks (similar to run-length encoding) make only sense if taskSize>3
		
		for( long i = lFrom; i<=lTo;  )
		{
			K = determineNextBatchSize(R, P);
			R -= (K * P);
			
			type = (ParForProgramBlock.USE_RANGE_TASKS_IF_USEFUL && K>3 ) ? 
					   TaskType.RANGE : TaskType.SET;
			
			//for each logical processor
			for( int j=0; j lTo ) //no more iterations
					break;
				
				//create new task and add to list of tasks
				Task lTask = new Task( type );
				tasks.addLast(lTask);
				
				// add iterations to task 
				if( type == TaskType.SET ) 
				{
					//value based tasks
					for( long k=0; k queue) 
		throws DMLRuntimeException 
	{		
		long numCreatedTasks = 0;
		
		long lFrom  = _fromVal.getLongValue();
		long lTo    = _toVal.getLongValue();
		long lIncr  = _incrVal.getLongValue();
		
		int P = _numThreads;     // number of parallel workers
		long N = _numIter;     // total number of iterations
		long R = N;               // remaining number of iterations
		long K = -1;              //next _numThreads task sizes	
	    TaskType type = null;    // type of iterations: range tasks (similar to run-length encoding) make only sense if taskSize>3
		
		try
		{
			for( long i = lFrom; i<=lTo;  )
			{
				K = determineNextBatchSize(R, P);
				R -= (K * P);
				
				type = (ParForProgramBlock.USE_RANGE_TASKS_IF_USEFUL && K>3 ) ? 
						   TaskType.RANGE : TaskType.SET;
				
				//for each logical processor
				for( int j=0; j lTo ) //no more iterations
						break;
					
					//create new task and add to list of tasks
					Task lTask = new Task( type );
					
					// add iterations to task 
					if( type == TaskType.SET ) 
					{
						//value based tasks
						for( long k=0; k