    001package org.cpsolver.ifs.assignment.context;
    002
    003import org.cpsolver.ifs.assignment.Assignment;
    004import org.cpsolver.ifs.heuristics.NeighbourSelection;
    005import org.cpsolver.ifs.model.Value;
    006import org.cpsolver.ifs.model.Variable;
    007import org.cpsolver.ifs.solver.Solver;
    008
    009/**
    010 * A neighborhood selection with an assignment context. In order to be able to hold multiple assignments in memory
    011 * it is desired for all the assignment dependent data a selection may need (to keep its current state),
    012 * to store these data in a separate class (implementing the
    013 * {@link AssignmentContext} interface). This context is created by calling
    014 * {@link ConstraintWithContext#createAssignmentContext(Assignment)} and accessed by
    015 * {@link ConstraintWithContext#getContext(Assignment)}.
    016 *
    017 *
    018 * @see AssignmentContext
    019 *
    020 * @author  Tomáš Müller
    021 * @version IFS 1.3 (Iterative Forward Search)<br>
    022 *          Copyright (C) 2014 Tomáš Müller<br>
    023 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    024 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    025 * <br>
    026 *          This library is free software; you can redistribute it and/or modify
    027 *          it under the terms of the GNU Lesser General Public License as
    028 *          published by the Free Software Foundation; either version 3 of the
    029 *          License, or (at your option) any later version. <br>
    030 * <br>
    031 *          This library is distributed in the hope that it will be useful, but
    032 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    033 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    034 *          Lesser General Public License for more details. <br>
    035 * <br>
    036 *          You should have received a copy of the GNU Lesser General Public
    037 *          License along with this library; if not see <a href='http://www.gnu.org/licenses'>http://www.gnu.org/licenses</a>.
    038 * @param <V> Variable
    039 * @param <T> Value
    040 * @param <C> Assignment Context
    041 **/
    042public abstract class NeighbourSelectionWithContext<V extends Variable<V, T>, T extends Value<V, T>, C extends AssignmentContext> implements NeighbourSelection<V, T>, HasAssignmentContext<V, T, C>, CanHoldContext {
    043    private AssignmentContextReference<V, T, C> iContextReference = null;
    044    private AssignmentContext[] iContext = new AssignmentContext[CanHoldContext.sMaxSize];
    045    protected C iContextOverride = null;
    046
    047    @Override
    048    public void init(Solver<V, T> solver) {
    049        iContextReference = solver.currentSolution().getModel().createReference(this);
    050        if (isSingleContextSolver(solver))
    051            iContextOverride = createAssignmentContext(solver.currentSolution().getAssignment());
    052    }
    053
    054    /**
    055     * Returns true if there should be only one context for this neighbourhood selection.
    056     * @param solver current solver
    057     * @return {@link Solver#hasSingleSolution()}
    058     */
    059    protected boolean isSingleContextSolver(Solver<V, T> solver) {
    060        return solver.hasSingleSolution();
    061    }
    062
    063    /**
    064     * Returns an assignment context associated with this selection. If there is no
    065     * assignment context associated with this selection yet, one is created using the
    066     * {@link ConstraintWithContext#createAssignmentContext(Assignment)} method. From that time on,
    067     * this context is kept with the assignment.
    068     * @param assignment given assignment
    069     * @return assignment context associated with this selection and the given assignment
    070     */
    071    @Override
    072    public C getContext(Assignment<V, T> assignment) {
    073        if (iContextOverride != null)
    074            return iContextOverride;
    075        return AssignmentContextHelper.getContext(this, assignment);
    076    }
    077
    078    @Override
    079    public AssignmentContextReference<V, T, C> getAssignmentContextReference() { return iContextReference; }
    080
    081    @Override
    082    public void setAssignmentContextReference(AssignmentContextReference<V, T, C> reference) { iContextReference = reference; }
    083
    084    @Override
    085    public AssignmentContext[] getContext() { return iContext; }
    086
    087    /**
    088     * Has context override
    089     * @return true if all threads are using the same context
    090     */
    091    public boolean hasContextOverride() {
    092        return iContextOverride != null;
    093    }
    094}