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/*
* File: ParallelUtil.java
* Authors: Kevin R. Dixon
* Company: Sandia National Laboratories
* Project: Cognitive Foundry
*
* Copyright Oct 10, 2008, Sandia Corporation.
* Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
* license for use of this work by or on behalf of the U.S. Government.
* Export of this program may require a license from the United States
* Government. See CopyrightHistory.txt for complete details.
*
*/
package gov.sandia.cognition.algorithm;
import gov.sandia.cognition.util.DefaultNamedValue;
import gov.sandia.cognition.util.NamedValue;
import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Utility methods for creating parallel algorithms.
*
* @author Kevin R. Dixon
* @since 3.0
*/
public class ParallelUtil
extends Object
{
/**
* Indicates to the createThreadPool() method to estimate the "optimal"
* number of threads for the computer currently executing the codes.
*/
public static final int OPTIMAL_THREADS = -1;
/**
* Number of threads to use during a default call to createThreadPool()
*/
private static int DEFAULT_NUM_THREADS = OPTIMAL_THREADS;
/**
* Protected constructor since this is a utility class.
*/
protected ParallelUtil()
{
super();
}
/**
* Gets the current default number of threads to use when called using the
* default createThreadPool() method
* @return
* Number of threads to use during a default call to createThreadPool()
*/
public static int getDefaultNumThreads()
{
return DEFAULT_NUM_THREADS;
}
/**
* Sets the current default number of threads to use when calling the
* default createThreadPool() method
* @param defaultNumThreads
* Number of threads to use during a default call to createThreadPool()
*/
public static void setDefaultNumThreads(
final int defaultNumThreads)
{
DEFAULT_NUM_THREADS = defaultNumThreads;
}
/**
* Creates a thread pool with the "optimal" number of threads. The thread
* pool creates daemon threads, so if all the non-daemon threads are
* finished, then the application will not wait for the thread pool to be
* cleaned up.
*
* @return
* Thread pool with the "optimal" number of threads
*/
public static ThreadPoolExecutor createThreadPool()
{
return createThreadPool(getDefaultNumThreads());
}
/**
* Creates a thread pool with the given number of threads. The thread
* pool creates daemon threads, so if all the non-daemon threads are
* finished, then the application will not wait for the thread pool to be
* cleaned up.
*
* @param numRequestedThreads
* Number of threads to create, or OPTIMAL_THREADS an "optimal" number
* of threads for the current computer.
* @return
* Thread pool with the desired size that creates daemon threads.
*/
public static ThreadPoolExecutor createThreadPool(
int numRequestedThreads)
{
// Figure out how many cores or hyperthreads we have
int numProcessors = Runtime.getRuntime().availableProcessors();
int numThreads;
// If the user wants the "optimal" thread count, then let's roll
if (numRequestedThreads == OPTIMAL_THREADS)
{
// If we've got a two processors or less, then use all we got
if (numProcessors <= 2)
{
numThreads = numProcessors;
}
// If we've got more than 2 processors, then leave one thread for
// the GUI thread and the Operating System
else
{
numThreads = numProcessors - 1;
}
}
// If the user wants a specific number of treads, then let them
// eat cake!!
else
{
numThreads = numRequestedThreads;
}
// Make sure the user will get at least one thread
if (numThreads < 1)
{
numThreads = 1;
}
return (ThreadPoolExecutor) Executors.newFixedThreadPool(numThreads,
defaultDaemonThreadFactory());
}
/**
* Gets the number of threads in a ParallelAlgorithm by querying the
* thread pool
* @param algorithm
* ParallelAlgorithm to consider
* @return
* Number of threads used by the ParallelAlgorithm's thread pool
*/
public static int getNumThreads(
final ParallelAlgorithm algorithm)
{
return (algorithm == null) ? 0 : getNumThreads(algorithm.getThreadPool());
}
/**
* Gets the number of threads in a ThreadPoolExecutor
* @param threadPool
* ThreadPoolExecutor to consider
* @return
* Number of threads used by the thread pool
*/
public static int getNumThreads(
final ThreadPoolExecutor threadPool)
{
return (threadPool == null) ? 0 : threadPool.getMaximumPoolSize();
}
/**
* Executes the given Callable tasks in parallel using a default thread
* pool
* @param Type of results returned by the Callable tasks.
* @param tasks
* Callable tasks to be split across multiple cores
* @return
* Collection of results from the Callables
* @throws java.lang.InterruptedException
* If interrupted
* @throws java.util.concurrent.ExecutionException
* If the Callable task can't execute its method
*/
public static ArrayList executeInParallel(
final Collection> tasks)
throws InterruptedException, ExecutionException
{
return executeInParallel(tasks, ParallelUtil.createThreadPool());
}
/**
* Executes the given Callable tasks in parallel using a given thread
* pool
* @param Type of results returned by the Callable tasks.
* @param tasks
* Callable tasks to be split across multiple cores
* @param threadPool
* Thread pool to use for the parallelization
* @return
* Collection of results from the Callables
* @throws java.lang.InterruptedException
* If interrupted
* @throws java.util.concurrent.ExecutionException
* If the Callable task can't execute its method
*/
public static ArrayList executeInParallel(
Collection> tasks,
ThreadPoolExecutor threadPool)
throws InterruptedException, ExecutionException
{
Collection> futures = threadPool.invokeAll(tasks);
ArrayList results =
new ArrayList(futures.size());
for (Future future : futures)
{
results.add(future.get());
}
return results;
}
/**
* Executes the given Callable tasks in parallel using a given thread
* pool
* @param Type of results returned by the Callable tasks.
* @param tasks
* Callable tasks to be split across multiple cores
* @param algorithm
* Uses the embedded thread pool in the ParallelAlgorithm
* @return
* Collection of results from the Callables
* @throws java.lang.InterruptedException
* If interrupted
* @throws java.util.concurrent.ExecutionException
* If the Callable task can't execute its method
*/
public static ArrayList executeInParallel(
Collection> tasks,
ParallelAlgorithm algorithm )
throws InterruptedException, ExecutionException
{
return executeInParallel( tasks, algorithm.getThreadPool() );
}
/**
* Executes the given Callable tasks sequentially in series.
* @param Type of results returned by the Callable tasks.
* @param tasks
* Callable tasks to execute sequentially
* @return
* Results from the sequential execution
* @throws java.lang.Exception
* If one of the Callables can't execute its method.
*/
public static ArrayList executeInSequence(
Collection> tasks)
throws Exception
{
ArrayList results = new ArrayList(tasks.size());
for (Callable task : tasks)
{
results.add(task.call());
}
return results;
}
/**
* Compares the times needed by running the tasks sequentially versus
* parallel.
* @param Result types of the Callable tasks
* @param tasks
* Callable tasks to execute in parallel or sequentially
* @return
* Named value with the name being a report of the time taken for parallel
* execution, sequential execution, the parallel to sequential ratio, and
* the number of threads used in the parallel execution. The value
* is the parallel to sequential ratio. That is, 1.0 means it takes just
* as long to execute in parallel as sequentially. A value greater than
* 1.0 means it takes longer in parallel than sequentially. A value less
* than 1.0 means it takes longer sequentially than in parallel.
*/
public static NamedValue compareTimes(
Collection> tasks)
{
return compareTimes(tasks, createThreadPool());
}
/**
* Compares the times needed by running the tasks sequentially versus
* parallel.
* @param Result types of the Callable tasks
* @param tasks
* Callable tasks to execute in parallel or sequentially
* @param threadPool
* Thread pool to use for the parallelization
* @return
* Named value with the name being a report of the time taken for parallel
* execution, sequential execution, the parallel to sequential ratio, and
* the number of threads used in the parallel execution. The value
* is the parallel to sequential ratio. That is, 1.0 means it takes just
* as long to execute in parallel as sequentially. A value greater than
* 1.0 means it takes longer in parallel than sequentially. A value less
* than 1.0 means it takes longer sequentially than in parallel.
*/
public static NamedValue compareTimes(
Collection> tasks,
ThreadPoolExecutor threadPool)
{
try
{
// First, let's try things in series
long seriesStart = System.currentTimeMillis();
executeInSequence(tasks);
long seriesStop = System.currentTimeMillis();
long parallelStart = System.currentTimeMillis();
executeInParallel(tasks, threadPool);
long parallelStop = System.currentTimeMillis();
double seriesTime = (seriesStop - seriesStart) / 1000.0;
double parallelTime = (parallelStop - parallelStart) / 1000.0;
double parallelToSeriesRatio = parallelTime / seriesTime;
String name = "Series time = " + seriesTime + ", Parallel time = " +
parallelTime + ", Parallel/Series ratio = " +
parallelToSeriesRatio + " using " + ParallelUtil.getNumThreads(
threadPool) + " threads.";
return new DefaultNamedValue(name, parallelToSeriesRatio);
}
catch (Exception ex)
{
Logger.getLogger(ParallelUtil.class.getName()).log(Level.SEVERE,
null, ex);
}
return null;
}
/**
* Creates a version of the default thread factory from
* {@code Executors.defaultThreadFactory()} that creates daemon threads.
* Daemon threads mean that the application can exit even if the threads
* are still alive.
*
* @return
* A default thread factory that creates daemon threads.
*/
public static ThreadFactory defaultDaemonThreadFactory()
{
return new DaemonThreadFactory(Executors.defaultThreadFactory());
}
/**
* Implements a thread factory for daemon threads. It just uses another
* factory to actually create the threads and then calls
* {@code setDaemon(true)}.
*/
private static class DaemonThreadFactory
implements ThreadFactory
{
/** The base factory to actually create the threads with. */
protected ThreadFactory baseFactory;
/**
* Creates a new {@code DaemonThreadFactory}
*
* @param baseFactory
* The base factory to actually create threads with.
*/
public DaemonThreadFactory(
final ThreadFactory baseFactory)
{
super();
this.baseFactory = baseFactory;
}
public Thread newThread(
final Runnable r)
{
// Create the thread.
final Thread thread = this.baseFactory.newThread(r);
// Set the thread to be a daemon, if we need to.
if (!thread.isDaemon())
{
thread.setDaemon(true);
}
// Return the created thread.
return thread;
}
}
}