/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.reasoner.rulesys.impl;
import java.util.*;
import org.apache.jena.graph.Triple ;
import org.apache.jena.reasoner.rulesys.BackwardRuleInfGraphI ;
import org.apache.jena.util.iterator.ClosableIterator ;
/**
* Wraps up the results an LP rule engine instance into a conventional
* iterator. Ensures that the engine is closed and detached from the
* inference graph if the iterator hits the end of the result set.
*/
public class LPTopGoalIterator implements ClosableIterator<Triple>, LPInterpreterContext {
/** The next result to be returned, or null if we have finished */
Triple lookAhead;
/** The parent backward chaining engine - nulled on close */
LPInterpreter interpreter;
/** The parent InfGraph -- retained on close to allow CME detection */
BackwardRuleInfGraphI infgraph;
/** The set of choice points that the top level interpter is waiting for */
protected Set<ConsumerChoicePointFrame> choicePoints = new HashSet<>();
/** The choice point most recently notified as ready to run. */
protected ConsumerChoicePointFrame nextToRun;
/** set to true if we should be able to usefully run */
protected boolean isReady = true;
/** set to true if at least one branch has block so an active readiness check is required */
protected boolean checkReadyNeeded = false;
/** True if the iteration has started */
boolean lookaheadValid = false;
/** Version stamp of the graph when we start */
protected int initialVersion;
/**
* Constructor. Wraps a top level goal state as an iterator
*/
public LPTopGoalIterator(LPInterpreter engine) {
this.interpreter = engine;
infgraph = engine.getEngine().getInfGraph();
initialVersion = infgraph.getVersion();
// engine.setState(this);
engine.setTopInterpreter(this);
}
/* A Note on lock ordering:
*
* Elsewhere code takes an LPBRuleEngine then an LPTopGoalIterator
* Ensure we do that lock order here as well as just synchronized
* on the method reverses the lock ordering, leading to deadlock.
*/
/**
* Find the next result in the goal state and put it in the
* lookahead buffer.
*/
private void moveForward() {
LPBRuleEngine lpEngine ;
synchronized(this)
{
checkClosed();
lpEngine = interpreter.getEngine();
}
synchronized (lpEngine) {
synchronized(this)
{
checkClosed();
lookaheadValid = true;
// TODO nasty dynamic typing here.
Object next = interpreter.next();
lookAhead = next instanceof Triple ? (Triple) next : null;
if (next == StateFlag.FAIL) {
if (choicePoints.isEmpty()) {
// Nothing left to try
close();
} else {
// Some options open, continue pumping
nextToRun = null;
lpEngine.pump(this);
if (nextToRun == null) {
// Reached final closure
close();
} else {
interpreter.setState(nextToRun);
moveForward();
}
}
}
}
}
}
/** Notify this context that a brach was suspended awaiting futher
* results from the given generator. */
@Override
public void notifyBlockedOn(ConsumerChoicePointFrame ccp) {
choicePoints.add(ccp);
checkReadyNeeded = true;
}
/**
* Notify this context that the given choice point has terminated
* and can be remove from the wait list.
*/
@Override
public void notifyFinished(ConsumerChoicePointFrame ccp) {
choicePoints.remove(ccp);
checkReadyNeeded = true;
}
/**
* Directly set that this generator is ready (because the generating
* for one of its generatingCPs has produced new results).
*/
@Override
public void setReady(ConsumerChoicePointFrame ccp) {
nextToRun = ccp;
isReady = true;
checkReadyNeeded = false;
}
/**
* Return true if the iterator is ready to be scheduled (i.e. it is not
* known to be complete and not known to be waiting for a dependent generator).
*/
@Override
public boolean isReady() {
if (checkReadyNeeded) {
isReady = false;
for ( ConsumerChoicePointFrame ccp : choicePoints )
{
if ( ccp.isReady() )
{
if ( nextToRun == null )
{
nextToRun = ccp;
}
isReady = true;
break;
}
}
checkReadyNeeded = false;
return isReady;
} else {
return isReady;
}
}
/**
* @see org.apache.jena.util.iterator.ClosableIterator#close()
*/
@Override
public void close() {
LPBRuleEngine lpEngine ;
synchronized(this)
{
if ( interpreter == null ) return ;
lpEngine = interpreter.getEngine();
}
synchronized (lpEngine) {
// Elsewhere code takes an LPBRuleEngine then an LPTopGoalIterator
// Ensure we do that lock order here as well as just synchronized
// on the method reverses the locks takne, leading to deadlock.
synchronized(this)
{
if (interpreter != null) {
// LogFactory.getLog( getClass() ).debug( "Entering close sync block on " + interpreter.getEngine() );
// Check for any dangling generators which are complete
interpreter.getEngine().checkForCompletions();
interpreter.close();
// Close this top goal
lookAhead = null;
//LogFactory.getLog( getClass() ).debug( "Nulling and closing LPTopGoalIterator " + interpreter );
interpreter.close();
// was TEMP experiment: interpreter.getEngine().detach(interpreter);
interpreter = null;
isReady = false;
checkReadyNeeded = false;
nextToRun = null;
// choicePoints = null; // disabled to prevent async close causing problems
//LogFactory.getLog( getClass() ).debug( "Leaving close sync block " );
}
}
}
}
/**
* @see java.util.Iterator#hasNext()
*/
@Override
public boolean hasNext() {
checkCME();
if (!lookaheadValid) moveForward();
return (lookAhead != null);
}
/**
* @see java.util.Iterator#next()
*/
@Override
public Triple next() {
checkCME();
if (!lookaheadValid) moveForward();
if (lookAhead == null) {
throw new NoSuchElementException("Overran end of LP result set");
}
Triple result = lookAhead;
lookaheadValid = false;
return result;
}
/**
* Check that the iterator has either cleanly closed or
* the version stamp is still valid
*/
private void checkCME() {
if (initialVersion != infgraph.getVersion()) {
throw new ConcurrentModificationException();
}
}
/**
* Check if the iterator has been closed and so we can't move forward safely
*/
private void checkClosed() {
if (interpreter == null || interpreter.getEngine() == null) {
throw new ConcurrentModificationException("Due to closed iterator");
}
}
/**
* @see java.util.Iterator#remove()
*/
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}