org.daisy.common.transform.Buffer Maven / Gradle / Ivy
package org.daisy.common.transform;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.function.Consumer;
import com.google.common.base.Optional;
import com.google.common.util.concurrent.SettableFuture;
import org.w3c.dom.Node;
/**
* Buffer to connect two XML transformer ports, one that pushes items and one that pulls items.
*
* The buffer is both a {@link XMLInputValue} and a {@link XMLOutputValue}. It is thread-safe in the
* sense that one thread can push and another thread can pull. The {@code hasNext} and {@code next}
* methods are blocking if a next item is not immediately available but the buffer is not closed
* yet.
*/
public class Buffer {
private XMLInputValue input = null;
private XMLOutputValue output = null;
private ItemBuffer nodeBuffer = null;
/**
* Should be called by the input if all items have been pushed.
*/
public void done() {
if (nodeBuffer == null)
nodeBuffer = new ItemBuffer<>();
nodeBuffer.done();
}
/**
* Can be called by the input if no more items can be pushed due to an error.
*/
public void error(TransformerException e) {
if (nodeBuffer == null)
nodeBuffer = new ItemBuffer<>();
nodeBuffer.error(e);
}
public XMLInputValue asInput() {
if (input == null) {
if (nodeBuffer == null)
nodeBuffer = new ItemBuffer<>();
input = new XMLInputValue(nodeBuffer);
}
return input;
}
public XMLOutputValue asOutput() {
if (output == null) {
if (nodeBuffer == null)
nodeBuffer = new ItemBuffer<>();
output = new XMLOutputValue(nodeBuffer);
}
return output;
}
protected static class ItemBuffer implements Iterator, Consumer {
private final Queue>> queue;
private SettableFuture> lastItem;
public ItemBuffer() {
queue = new ConcurrentLinkedQueue<>();
lastItem = SettableFuture.create();
queue.add(lastItem);
}
public void accept(I i) {
SettableFuture> nextItem = SettableFuture.create();
queue.add(nextItem);
lastItem.set(Optional.of(i));
lastItem = nextItem;
}
public void done() {
lastItem.set(Optional.absent());
}
/**
* Can be called by the input if no more items can be pushed due to an error.
*/
public void error(TransformerException e) {
lastItem.setException(e);
}
public boolean hasNext() throws TransformerException {
if (queue.isEmpty())
return false;
else
try {
return queue.peek().get().isPresent();
} catch (ExecutionException e) {
// if Buffer.setException() was previously called
try {
throw e.getCause();
} catch (TransformerException ee) {
throw ee;
} catch (Throwable ee) {
throw new RuntimeException(ee); // should not happen
}
} catch (InterruptedException e) {
// if "pulling" thread was interrupted during call
throw new RuntimeException(e);
}
}
public I next() throws TransformerException {
if (queue.isEmpty())
throw new NoSuchElementException();
else
try {
Optional next = queue.remove().get();
if (!next.isPresent())
throw new NoSuchElementException();
return next.get();
} catch (ExecutionException e) {
// if Buffer.setException() was previously called
try {
throw e.getCause();
} catch (TransformerException ee) {
throw ee;
} catch (Throwable ee) {
throw new RuntimeException(ee); // should not happen
}
} catch (InterruptedException e) {
// if "pulling" thread was interrupted during the call
throw new RuntimeException(e);
}
}
public void remove() {
throw new UnsupportedOperationException();
}
}
}