org.apache.sysml.runtime.controlprogram.parfor.LocalTaskQueue Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of systemml Show documentation
Show all versions of systemml Show documentation
Declarative Machine Learning
/*
* 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 org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* This class provides a way of dynamic task distribution to multiple workers
* in local multi-threaded environments. Its main purpose is inter-thread communication
* for achieving dynamic load balancing. A good load balance between parallel workers is crucial
* with regard to the overall speedup of parallelization (see Amdahl's law).
*
* From a technical perspective, a thread monitor concept is used for blocking of waiting writers
* and readers. Synchronized writes and reads ensure that each task is only read by exactly one
* reader. Furthermore, the queue is implemented as a simple FIFO.
*
*
*/
public class LocalTaskQueue
{
public static final int MAX_SIZE = 100000; //main memory constraint
public static final Object NO_MORE_TASKS = null; //object to signal NO_MORE_TASKS
private LinkedList _data = null;
private boolean _closedInput = false;
private static final Log LOG = LogFactory.getLog(LocalTaskQueue.class.getName());
public LocalTaskQueue()
{
_data = new LinkedList();
_closedInput = false;
}
/**
* Synchronized insert of a new task to the end of the FIFO queue.
*
* @param t
* @throws InterruptedException
*/
public synchronized void enqueueTask( T t )
throws InterruptedException
{
while( _data.size() + 1 > MAX_SIZE )
{
LOG.warn("MAX_SIZE of task queue reached.");
wait(); //max constraint reached, wait for read
}
_data.addLast( t );
notify(); //notify waiting readers
}
/**
* Synchronized read and delete from the top of the FIFO queue.
*
* @return
* @throws InterruptedException
*/
@SuppressWarnings("unchecked")
public synchronized T dequeueTask()
throws InterruptedException
{
while( _data.isEmpty() )
{
if( !_closedInput )
wait(); // wait for writers
else
return (T)NO_MORE_TASKS;
}
T t = _data.removeFirst();
notify(); // notify waiting writers
return t;
}
/**
* Synchronized (logical) insert of a NO_MORE_TASKS symbol at the end of the FIFO queue in order to
* mark that no more tasks will be inserted into the queue.
*/
public synchronized void closeInput()
{
_closedInput = true;
notifyAll(); //notify all waiting readers
}
/**
* Synchronized read of the current number of tasks in the queue.
*
* @return
* @throws InterruptedException
*/
public synchronized int size()
throws InterruptedException
{
return _data.size();
}
@Override
public synchronized String toString()
{
StringBuilder sb = new StringBuilder();
sb.append("TASK QUEUE (size=");
sb.append(_data.size());
sb.append(",close=");
sb.append(_closedInput);
sb.append(")\n");
int count = 1;
for( T t : _data )
{
sb.append(" TASK #");
sb.append(count);
sb.append(": ");
sb.append(t.toString());
sb.append("\n");
count++;
}
return sb.toString();
}
}