package com.bigdata.rdf.sail;
import java.util.NoSuchElementException;
import com.bigdata.bop.engine.IRunningQuery;
import cutthecrap.utils.striterators.ICloseableIterator;
/**
* Iteration construct wraps an {@link IRunningQuery} with logic to (a) verify
* that the {@link IRunningQuery} has not encountered an error; and (b) to
* cancel the {@link IRunningQuery} when the iterator draining the
* {@link IRunningQuery} is {@link #close() closed}.
*/
public class RunningQueryCloseableIterator<E>
implements ICloseableIterator<E> {
private final IRunningQuery runningQuery;
private final ICloseableIterator<E> src;
private boolean checkedFuture = false;
/**
* The next element is buffered so we can always return it if the
* {@link #runningQuery} was not aborted at the time that {@link #hasNext()}
* return <code>true</code>.
*/
private E current = null;
private volatile boolean open = true;
public RunningQueryCloseableIterator(final IRunningQuery runningQuery,
final ICloseableIterator<E> src) {
this.runningQuery = runningQuery;
this.src = src;
}
/**
* Test for abnormal completion of the {@link IRunningQuery}.
*/
private void checkFuture() {
// if (!checkedFuture && runningQuery.isDone()) {
try {
runningQuery.get();
} catch (InterruptedException e) {
/*
* Interrupted while waiting on the Future (should not happen
* since the Future is already done).
*/
throw new RuntimeException(e);
} catch (Throwable e) {
/*
* Exception thrown by the runningQuery.
*/
if (runningQuery.getCause() != null) {
// abnormal termination - wrap and rethrow.
throw new RuntimeException(e);
}
// otherwise this is normal termination.
}
checkedFuture = true;
// }
}
public void close() {
if (open) {
open = false;
runningQuery.cancel(true/* mayInterruptIfRunning */);
src.close();
checkFuture();
}
}
public boolean hasNext() {
if(open && _hasNext())
return true;
close();
return false;
}
private boolean _hasNext() {
if (current != null) {
// Already buffered.
return true;
}
if (!src.hasNext()) {
// Source is exhausted.
return false;
}
// buffer the next element.
current = src.next();
if (!checkedFuture && runningQuery.isDone()) {
checkFuture();
}
// the next element is now buffered.
return true;
}
public E next() {
if (!hasNext())
throw new NoSuchElementException();
final E tmp = current;
current = null;
return tmp;
}
/**
* Operation is not supported.
*/
public void remove() {
// Not supported since we are buffering ahead.
throw new UnsupportedOperationException();
}
}