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/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2023, IMT Atlantique. All rights reserved.
*
* Licensed under the BSD 4-clause license.
*
* See LICENSE file in the project root for full license information.
*/
package org.chocosolver.solver.propagation;
import org.chocosolver.solver.ICause;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.constraints.Constraint;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.exception.SolverException;
import org.chocosolver.solver.variables.Variable;
import org.chocosolver.solver.variables.events.IEventType;
import org.chocosolver.solver.variables.events.PropagatorEventType;
import org.chocosolver.util.objects.queues.CircularQueue;
import org.chocosolver.util.tools.ArrayUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Consumer;
/**
* This engine is priority-driven constraint-oriented seven queues engine.
*
On a call to {@code onVariableUpdate}, it stores the event generated and schedules the propagator in
* one of the 7 queues wrt to its priority for future revision.
*
*
*
* @author Charles Prud'homme
* @since 05/07/12
*/
public class PropagationEngine {
@SuppressWarnings("WeakerAccess")
public static boolean CHECK_SCOPE = false;
/**
* The model declaring this engine
*/
final Model model;
/**
* The array of propagators to execute
*/
final List> propagators;
/**
* To deal with propagators added dynamically
*/
private final DynPropagators dynPropagators;
/**
* The main structure of this engine: seven circular queues,
* each of them is dedicated to store propagator to execute wrt their priority.
*/
private final CircularQueue>[] pro_queue;
private final CircularQueue var_queue;
private final CircularQueue> awake_queue;
/**
* The last propagator executed
*/
protected Propagator lastProp;
/**
* One bit per queue: true if the queue is not empty.
*/
private int notEmpty;
/**
* PropagatorEventType's mask for delayed propagation
*/
private int delayedPropagationType;
/**
* Set to true once {@link #initialize()} has been called.
*/
private boolean init;
/**
* When set to '0b00', this works as a constraint-oriented propagation engine;
* when set to '0b01', this workds as an hybridization between variable and constraint oriented
* propagation engine.
* when set to '0b10', this workds as a variable- oriented propagation engine.
*/
private final byte hybrid;
/**
* For dynamyc addition, avoid creating a new lambda at each call
*/
@SuppressWarnings("Convert2Diamond")
private final Consumer> consumer = new Consumer>() {
@Override
public void accept(Propagator propagator) {
awake_queue.addLast(propagator);
}
};
/**
* A seven-queue propagation engine.
* Each of the seven queues deals with on priority.
* When a propagator needs to be executed, it is scheduled in the queue corresponding to its priority.
* The lowest priority queue is emptied before one element of the second lowest queue is popped, etc.
*
* @param model the declaring model
*/
public PropagationEngine(Model model) {
this.model = model;
int nbQueues = model.getSettings().getMaxPropagatorPriority() + 1;
//noinspection unchecked
this.pro_queue = new CircularQueue[nbQueues];
for (int i = 0; i < nbQueues; i++) {
pro_queue[i] = new CircularQueue<>(16);
}
this.var_queue = new CircularQueue<>(16);
this.awake_queue = new CircularQueue<>(16);
this.dynPropagators = new DynPropagators();
this.propagators = new ArrayList<>();
this.hybrid = model.getSettings().enableHybridizationOfPropagationEngine();
}
/**
* Build up internal structure, if not yet done, in order to allow propagation.
* If new constraints are added after having initializing the engine, dynamic addition is used.
* A call to clear erase the internal structure, and allow new initialisation.
*
* @throws SolverException if a constraint is declared more than once in this propagation engine
*/
public void initialize() throws SolverException {
if (!init) {
notEmpty = 0;
init = true;
Constraint[] constraints = model.getCstrs();
for (Constraint constraint : constraints) {
Propagator[] cprops = constraint.getPropagators();
Collections.addAll(propagators, cprops);
}
if (model.getSettings().sortPropagatorActivationWRTPriority()) {
propagators.sort(
(p1, p2) -> {
int p = p1.getPriority().getValue() - p2.getPriority().getValue();
if (p == 0) {
return p1.getNbVars() - p2.getNbVars();
} else {
return p;
}
});
}
for (int i = 0; i < propagators.size(); i++) {
Propagator propagator = propagators.get(i);
if (propagator.getPriority().getValue() >= pro_queue.length) {
throw new SolverException(
propagator+
"\nThis propagator declares a priority (" +
propagator.getPriority() + ") whose value (" + propagator.getPriority().getValue() +
") is greater than the maximum allowed priority (" +
model.getSettings().getMaxPropagatorPriority() +
").\n" +
"Either increase the maximum allowed priority (`Model model = new Model(Settings.init().setMaxPropagatorPriority(" +
(propagator.getPriority().getValue() + 1) +
"));`) " +
"or decrease the propagator priority.");
}
propagator.setPosition(i);
awake_queue.addLast(propagator);
}
}
}
/**
* Is the engine initialized?
* Important for dynamic addition of constraints
*
* @return true if the engine has been initialized
*/
public boolean isInitialized() {
return init;
}
/**
* Launch the proapagation, ie, active propagators if necessary, then reach a fix point
*
* @throws ContradictionException if a contradiction occurs
*/
public void propagate() throws ContradictionException {
activatePropagators();
do {
manageModifications();
for (int i = nextNotEmpty(); i > -1; i = nextNotEmpty()) {
assert !pro_queue[i].isEmpty() : "try to pop a propagator from an empty queue";
lastProp = pro_queue[i].pollFirst();
if (pro_queue[i].isEmpty()) {
notEmpty &= ~(1 << i);
}
// revision of the variable
lastProp.unschedule();
delayedPropagationType = 0;
propagateEvents();
if (hybrid < 0b01) {
manageModifications();
}
}
} while (!var_queue.isEmpty());
}
protected void propagateEvents() throws ContradictionException {
if (lastProp.reactToFineEvent()) {
lastProp.doFinePropagation();
// now we can check whether a delayed propagation has been scheduled
if (delayedPropagationType > 0) {
lastProp.propagate(delayedPropagationType);
}
} else if (lastProp.isActive()) { // need to be checked due to views
lastProp.propagate(PropagatorEventType.FULL_PROPAGATION.getMask());
}
}
/**
* Checks if some propagators were added or have to be propagated on backtrack
* @throws ContradictionException if a propagation fails
*/
private void activatePropagators() throws ContradictionException {
int cw = model.getEnvironment().getWorldIndex(); // get current index
dynPropagators.descending(cw, consumer);
while (!awake_queue.isEmpty()) {
execute(awake_queue.pollFirst());
}
}
/**
* Execute 'coarse' propagation on a newly added propagator
* or one that should be propagated on backtrack
*
* @param propagator a propagator to propagate
* @throws ContradictionException if propagation fails
*/
public void execute(Propagator propagator) throws ContradictionException {
if (propagator.isStateLess()) {
propagator.setActive();
}
if (propagator.isActive()) {
propagator.propagate(PropagatorEventType.FULL_PROPAGATION.getMask());
while (!var_queue.isEmpty()) {
var_queue.pollFirst().schedulePropagators(this);
}
}
}
private void manageModifications() {
if (!var_queue.isEmpty()) {
do {
var_queue.pollFirst().schedulePropagators(this);
} while (hybrid < 2 && !var_queue.isEmpty());
}
}
private int nextNotEmpty() {
if (notEmpty == 0) return -1;
return Integer.numberOfTrailingZeros(notEmpty);
}
/**
* Flush this, ie. remove every pending events
*/
public void flush() {
if (lastProp != null) {
lastProp.doFlush();
}
while (!var_queue.isEmpty()) {
var_queue.pollLast().clearEvents();
}
for (int i = nextNotEmpty(); i > -1; i = nextNotEmpty()) {
while (!pro_queue[i].isEmpty()) {
// revision of the variable
pro_queue[i].pollLast().doFlush();
}
notEmpty = notEmpty & ~(1 << i);
}
lastProp = null;
}
/**
* Take into account the modification of a variable
*
* @param variable modified variable
* @param type type of modification event
* @param cause origin of the modification
*/
public void onVariableUpdate(Variable variable, IEventType type, ICause cause) {
if (CHECK_SCOPE && Propagator.class.isAssignableFrom(cause.getClass())) {
// make sure the variable appears in prop scope
Propagator p = (Propagator) cause;
boolean found = false;
for (int i = 0; i < p.getNbVars() && !found; i++) {
found = (p.getVar(i) == variable);
}
assert found : variable + " not in scope of " + cause;
}
if (!variable.isScheduled()) {
var_queue.addLast(variable);
variable.schedule();
}
variable.storeEvents(type.getMask(), cause);
}
public void schedule(Propagator prop, int pindice, int mask) {
prop.doScheduleEvent(pindice, mask);
notEmpty |= (1 << prop.doSchedule(pro_queue));
}
/**
* Exeucte a delayed propagator
*
* @param propagator propagator to execute
* @param type type of event to execute
*/
public void delayedPropagation(Propagator propagator, PropagatorEventType type) {
assert propagator == lastProp;
assert delayedPropagationType == 0 || delayedPropagationType == type.getMask();
delayedPropagationType = type.getMask();
}
/**
* @return the propagator Event Type's mask for delayed propagation
*/
int getDelayedPropagation(){
return delayedPropagationType;
}
/**
* Action to do when a propagator is executed
*
* @param propagator propagator to execute
*/
public void onPropagatorExecution(Propagator propagator) {
desactivatePropagator(propagator);
}
/**
* Set the propagator as inactivated within the propagation engine
*
* @param propagator propagator to desactivate
*/
public void desactivatePropagator(Propagator propagator) {
if (propagator.reactToFineEvent()) {
propagator.doFlush();
}
}
/**
* Reset the propagation engine.
*/
public void reset() {
flush();
clear();
}
/**
* Clear internal structures
*/
public void clear() {
dynPropagators.clear();
awake_queue.clear();
propagators.clear();
notEmpty = 0;
init = false;
lastProp = null;
}
public void ignoreModifications() {
while (!var_queue.isEmpty()) {
var_queue.pollFirst().clearEvents();
}
}
/**
* Add a constraint to the propagation engine
*
* @param permanent does the constraint is permanently added
* @param ps propagators to add
* * @throws SolverException if a constraint is declared more than once in this propagation engine
*/
public void dynamicAddition(boolean permanent, Propagator... ps) throws SolverException {
int nbp = ps.length;
for (int i = 0; i < nbp; i++) {
if (permanent) {
ps[i].setPosition(propagators.size());
propagators.add(ps[i]);
dynPropagators.add(ps[i]);
}
}
}
/**
* Update the scope of variable of a propagator (addition or deletion are allowed -- p.vars are scanned)
*
* @param p a propagator
*/
public void updateInvolvedVariables(Propagator p) {
propagateOnBacktrack(p); // TODO: when p is not permanent AND a new var is added ... well, one looks for trouble!
}
/**
* Update the scope of variable of a propagator (addition or deletion are allowed -- p.vars are scanned)
*
* @param propagator a propagator
*/
public void propagateOnBacktrack(Propagator propagator) {
int idx = propagator.getPosition();
assert propagators.get(idx) == propagator : "Try to remove the wrong propagator";
shift(idx);
propagators.set(propagators.size() - 1, propagator);
propagator.setPosition(propagators.size() - 1);
dynPropagators.addOrUpdate(propagator);
}
/**
* Delete the list of propagators in input from the engine
*
* @param ps a list of propagators
*/
public void dynamicDeletion(Propagator... ps) {
for (Propagator toDelete : ps) {
if (lastProp == toDelete) {
lastProp = null;
}
if (toDelete.getPosition() > -1) {
dynPropagators.remove(toDelete);
remove(toDelete);
}
}
}
private void remove(Propagator propagator) {
int idx = propagator.getPosition();
if (idx > -1) {
assert propagators.get(idx) == propagator : "Try to remove the wrong propagator";
// todo: improve
shift(idx);
propagator.setPosition(-1);
propagators.remove(propagators.size() - 1);
}
}
private void shift(int from) {
for (int i = from; i < propagators.size() - 1; i++) {
propagators.set(i, propagators.get(i + 1));
propagators.get(i).setPosition(i);
}
}
private static class DynPropagators {
private Propagator[] elements;
private int[] keys;
private int size;
DynPropagators() {
elements = new Propagator[16];
keys = new int[16];
size = 0;
}
public void clear() {
size = 0;
}
public void add(Propagator e) {
ensureCapacity();
elements[size] = e;
keys[size++] = Integer.MAX_VALUE;
}
private void ensureCapacity() {
if (size >= elements.length - 1) {
int nsize = ArrayUtils.newBoundedSize(elements.length, 8);
elements = Arrays.copyOf(elements, nsize);
keys = Arrays.copyOf(keys, nsize);
}
}
void addOrUpdate(Propagator e) {
remove(e);
add(e);
}
public void remove(Propagator e) {
int p = indexOf(e);
if (p > -1) {
removeAt(p);
}
}
private void removeAt(int p) {
if (p < size - 1) {
System.arraycopy(elements, p + 1, elements, p, size - p);
System.arraycopy(keys, p + 1, keys, p, size - p);
}
elements[--size] = null;
keys[size] = 0;
}
private int indexOf(Propagator e) {
for (int i = 0; i < size; i++) {
if (e.equals(elements[i])) {
return i;
}
}
return -1;
}
void descending(int w, Consumer> cons) {
int i = size - 1;
while (i >= 0 && keys[i] >= w) {
cons.accept(elements[i]);
keys[i] = w;
i--;
}
}
}
}