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/*******************************************************************************
* Copyright (c) 2010-2016, Andras Szabolcs Nagy, Zoltan Ujhelyi and Daniel Varro
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package org.eclipse.viatra.dse.api.strategy.impl;
import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.log4j.Logger;
import org.eclipse.viatra.dse.api.strategy.interfaces.IStrategy;
import org.eclipse.viatra.dse.base.GlobalContext;
import org.eclipse.viatra.dse.base.ThreadContext;
import org.eclipse.viatra.dse.objectives.Fitness;
import org.eclipse.viatra.dse.solutionstore.SolutionStore;
/**
* A breadth-first search algorithm implementation, that
* <ul>
* <li>can work with multiple threads,</li>
* <li>indeterministic,</li>
* <li>saves all states (trajectories) as solutions that fulfill all the hard objectives,</li>
* <li>can have a depth limit,</li>
* <li>will backtrack when a model satisfies the hard objectives (after saving it as a solution) and will not explore
* beyond that state.</li>
* </ul>
*
* @author Andras Szabolcs Nagy
*
*/
public class BreadthFirstStrategy implements IStrategy {
private static final class BfsSharedObject {
private final ConcurrentLinkedQueue<Object[]> trajectoryQueue1 = new ConcurrentLinkedQueue<>();
private final ConcurrentLinkedQueue<Object[]> trajectoryQueue2 = new ConcurrentLinkedQueue<>();
private final AtomicBoolean pushToQueue1 = new AtomicBoolean(false);
private final AtomicBoolean designSpaceTraversed = new AtomicBoolean(false);
public final CyclicBarrier barrier;
public BfsSharedObject(int numberOfThreads) {
barrier = new CyclicBarrier(numberOfThreads, () -> {
boolean oldValue = pushToQueue1.get();
pushToQueue1.set(!oldValue);
if (trajectoryQueue1.isEmpty() && trajectoryQueue2.isEmpty()) {
designSpaceTraversed.set(true);
}
});
}
public Object[] poll() {
if (pushToQueue1.get()) {
return trajectoryQueue2.poll();
} else {
return trajectoryQueue1.poll();
}
}
public void push(Object[] trajectory) {
if (pushToQueue1.get()) {
trajectoryQueue1.add(trajectory);
} else {
trajectoryQueue2.add(trajectory);
}
}
public boolean isDesignSpaceTraversed() {
return designSpaceTraversed.get();
}
}
private int maxDepth = 0;
private BfsSharedObject shared;
private boolean isInterrupted = false;
private ThreadContext context;
private Logger logger = Logger.getLogger(IStrategy.class);
private SolutionStore solutionStore;
private boolean isFirstThread = false;
/**
* Creates a new breadth-first search algorithm without depth limit.
*/
public BreadthFirstStrategy() {
this.maxDepth = Integer.MAX_VALUE;
}
/**
* Creates a new breadth-first search algorithm with depth limit.
*
* @param maxDepth
* A negative <code>maxDepth</code> means no depth limit, zero means the checking of the initial state.
*/
public BreadthFirstStrategy(int maxDepth) {
if (maxDepth < 0) {
this.maxDepth = Integer.MAX_VALUE;
} else {
this.maxDepth = maxDepth;
}
}
@Override
public void initStrategy(ThreadContext context) {
this.context = context;
this.solutionStore = context.getGlobalContext().getSolutionStore();
GlobalContext globalContext = context.getGlobalContext();
if (globalContext.getSharedObject() == null) {
isFirstThread = true;
shared = new BfsSharedObject(globalContext.getThreadPool().getMaximumPoolSize());
globalContext.setSharedObject(shared);
logger.info("Breadth-first exploration strategy is inited.");
} else {
shared = (BfsSharedObject) globalContext.getSharedObject();
}
}
@Override
public void explore() {
if (isFirstThread) {
boolean globalConstraintsAreSatisfied = context.checkGlobalConstraints();
if (!globalConstraintsAreSatisfied) {
logger.info("Global contraint is not satisifed in the first state. Terminate.");
return;
}
Fitness fitness = context.calculateFitness();
if (fitness.isSatisifiesHardObjectives()) {
context.newSolution();
logger.info("First state is a solution. Terminate.");
return;
}
Object[] currentTrajectory = context.getTrajectory().toArray(new Object[0]);
shared.push(currentTrajectory);
startThreads();
} else {
try {
shared.barrier.await();
} catch (InterruptedException | BrokenBarrierException e) {
}
}
mainLoop: while (!isInterrupted && !shared.isDesignSpaceTraversed()) {
Object[] next = shared.poll();
while (next == null) {
try {
logger.debug("Reached barrier.");
shared.barrier.await();
} catch (InterruptedException | BrokenBarrierException e1) {
}
if (isInterrupted || shared.isDesignSpaceTraversed()) {
break mainLoop;
}
next = shared.poll();
}
context.backtrackUntilRoot();
context.executeTrajectory(next);
Collection<Object> activationIds = context.getCurrentActivationIds();
int i = activationIds.size() - 1;
while (!isInterrupted && i >= 0) {
Iterator<Object> iterator = activationIds.iterator();
int index = i--;
while (iterator.hasNext() && index > 0) {
index--;
iterator.next();
}
Object activationIdToTry = iterator.next();
context.executeAcitvationId(activationIdToTry);
if (context.isCurrentStateAlreadyTraversed()) {
logger.info("The new state is already visited.");
} else if (!context.checkGlobalConstraints()) {
logger.debug("Global contraint is not satisifed.");
} else if (context.calculateFitness().isSatisifiesHardObjectives()) {
solutionStore.newSolution(context);
logger.debug("Found a solution.");
} else if (context.getDepth() >= maxDepth) {
logger.debug("Reached max depth.");
} else {
Object[] currentTrajectory = context.getTrajectory().toArray(new Object[0]);
shared.push(currentTrajectory);
}
context.backtrack();
}
}
}
private void startThreads() {
context.startAllThreads(() -> new BreadthFirstStrategy(maxDepth));
}
@Override
public void interruptStrategy() {
isInterrupted = true;
shared.barrier.reset();
}
}
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