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package de.lmu.ifi.dbs.elki.parallel;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2014
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Core for parallel processing in ELKI, based on {@link ThreadPoolExecutor}.
*
* TODO: make configurable how many threads are used.
*
* @author Erich Schubert
*/
public class ParallelCore {
/**
* The number of CPUs to use.
*/
public static final int ALL_PROCESSORS = Runtime.getRuntime().availableProcessors();
/**
* Static core
*/
private static final ParallelCore STATIC = new ParallelCore(ALL_PROCESSORS);
/**
* Executor service.
*/
ThreadPoolExecutor executor;
/**
* Number of connected submitters.
*/
private AtomicInteger connected = new AtomicInteger(0);
/**
* Maximum number of processors to use.
*/
private int processors;
/**
* Constructor.
*/
protected ParallelCore(int processors) {
super();
this.processors = processors;
}
/**
* Get the static core object.
*
* @return Core
*/
public static ParallelCore getCore() {
return STATIC;
}
/**
* Get desired level of parallelism
*
* @return Number of threads to run in parallel
*/
public int getParallelism() {
return executor.getMaximumPoolSize();
}
/**
* Submit a task to the executor core.
*
* @param task Submitted task
*
* @return Future to observe completion
*/
public <T> Future<T> submit(Callable<T> task) {
return executor.submit(task);
}
/**
* Connect to the executor.
*/
public void connect() {
if(executor == null) {
synchronized(this) {
if(executor == null) {
executor = new ThreadPoolExecutor(0, processors, 10L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
executor.allowCoreThreadTimeOut(true);
}
}
}
int c = this.connected.incrementAndGet();
if(c == 1) {
executor.allowCoreThreadTimeOut(false);
executor.setCorePoolSize(executor.getMaximumPoolSize());
}
}
/**
* Disconnect to the executor.
*/
public void disconnect() {
int c = this.connected.decrementAndGet();
if(c == 0) {
synchronized(this) {
executor.allowCoreThreadTimeOut(true);
executor.setCorePoolSize(0);
}
}
}
}
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