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/*
* Copyright (C) 2014-2021 Brian L. Browning
*
* This file is part of Beagle
*
* Beagle is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Beagle is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package blbutil;
import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.TimeUnit;
/**
* <p>Class {@code BlockLineReader} is a {@code blbutil.FileIt} that reads
* blocks of lines from a file. The order of lines in the source file is
* preserved by the returned string arrays. The {@code hasNext()} method
* always returns {@code true}. After the final block of lines is returned
* by the {@code next()} method, the {@code next()} method returns
* {@code BlockLineReader.SENTINAL} on all subsequent invocations.
* {@code BlockLineReader.SENTINAL} is guaranteed to be the only returned
* array that has length 0.
*
* <p>Instances of class {@code BlockLineReader} are thread-safe.</p>
*
* <p>Methods of this class will terminate the Java Virtual Machine with
* an error message if an I/O Exception is encountered.
* </p>
*
* @author Brian L. Browning {@code <browning@uw.edu>}
*/
public class BlockLineReader implements FileIt<String[]> {
/**
* The string array returned by {@code next()} after all blocks
* of lines have been read.
*/
public static String[] SENTINAL = new String[0];
private final FileIt<String> it;
private final LinkedBlockingDeque<String[]> q;
private final int blockSize;
private final ExecutorService fileReaderService;
private final CountDownLatch latch;
private volatile boolean shutDownNow;
/**
* Constructs and returns a new {@code BlockLineReader} for the specified
* data. The {@code close()} method of the returned object will invoke the
* {@code close()} method on the specified {@code FileIt<String>} iterator.
* The calling thread should not directly invoke any methods of the
* specified {@code FileIt<String>} after it is passed to the
* {@code BlockLineReader.create()} method.
* @param it a file iterator that returns the lines of text
* @param blockSize the maximum length a string array returned by
* {@code next()}
* @param nBlocks the maximum number of non-empty string arrays that will be
* buffered
* @return a {@code BlockLineReader} for the specified data.
* @throws IllegalArgumentException if {@code blockSize < 1 || nBlocks < 1}
* @throws NullPointerException if {@code it == null}
*/
public static BlockLineReader create(FileIt<String> it, int blockSize,
int nBlocks) {
BlockLineReader reader = new BlockLineReader(it, blockSize, nBlocks);
reader.startFileReadingThread();
return reader;
}
private BlockLineReader(FileIt<String> it, int blockSize, int nBlocks) {
if (blockSize<1) {
throw new IllegalArgumentException(String.valueOf(blockSize));
}
if (nBlocks<1) {
throw new IllegalArgumentException(String.valueOf(nBlocks));
}
this.it = it;
this.q = new LinkedBlockingDeque<>(nBlocks);
this.blockSize = blockSize;
this.fileReaderService = Executors.newSingleThreadExecutor();
this.latch = new CountDownLatch(1);
this.shutDownNow = false;
}
private void startFileReadingThread() {
fileReaderService.submit(() -> {
try {
List<String> buffer = new ArrayList<>(blockSize);
while (it.hasNext()) {
buffer.add(it.next());
if (buffer.size()==blockSize) {
flushBuffer(buffer);
if (shutDownNow) {
break;
}
}
}
if (buffer.size()>0) {
flushBuffer(buffer);
}
latch.countDown();
MultiThreadUtils.putInBlockingQ(q, SENTINAL);
}
catch (Throwable t) {
Utilities.exit(t);
}
});
}
/*
* Returns {@code false} if no more blocks of lines will be enqueued.
*/
private void flushBuffer(List<String> buffer) {
String[] sa = buffer.toArray(new String[0]);
buffer.clear();
boolean success = false;
while (success==false && shutDownNow==false) {
success = MultiThreadUtils.putInBlockingQ(q, sa, 100,
TimeUnit.MILLISECONDS);
}
}
@Override
public File file() {
return it.file();
}
@Override
public void close() {
shutDownNow = true;
MultiThreadUtils.await(latch);
it.close();
String[] tail = q.pollLast();
while (tail!=null && tail!=SENTINAL) {
tail = q.pollLast();
}
if (tail==SENTINAL) {
boolean success = q.offer(SENTINAL);
assert success;
}
MultiThreadUtils.shutdownExecService(fileReaderService);
}
/**
* Returns {@code true}. The {@code this.next()} method will return
* {@code BlockLineReader.SENTINAL} if the iterations has no
* more elements.
* @return {@code true}
*/
@Override
public boolean hasNext() {
return true;
}
/**
* Returns the next element in the iteration. Returns
* {@code BlockLineReader.SENTINAL} if the iterations has no
* more elements.
* @return the next element in the iteration
*/
@Override
public String[] next() {
assert hasNext();
String[] value = MultiThreadUtils.takeFromBlockingQ(q);
if (value==SENTINAL) {
boolean success = q.offer(SENTINAL);
assert success;
}
return value;
}
/**
* The {@code remove} method is not supported by this iterator.
* @throws UnsupportedOperationException if this method is invoked
*/
@Override
public void remove() {
throw new UnsupportedOperationException(this.getClass().toString());
}
}
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