/**
* 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.hadoop.raid;
import java.io.OutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.util.Progressable;
import org.apache.hadoop.util.StringUtils;
/**
* Reads data from multiple input streams in parallel.
*/
public class ParallelStreamReader {
public static final Log LOG = LogFactory.getLog(ParallelStreamReader.class);
Progressable reporter;
InputStream[] streams;
ExecutorService readPool;
Semaphore slots;
int numThreads;
int bufSize;
long readTime = 0;
volatile boolean running = true;
public static class ReadResult {
public byte[][] readBufs;
public IOException[] ioExceptions;
ReadResult(int numStreams, int bufSize) {
this.readBufs = new byte[numStreams][];
for (int i = 0; i < readBufs.length; i++) {
this.readBufs[i] = new byte[bufSize];
}
this.ioExceptions = new IOException[readBufs.length];
}
void setException(int idx, Exception e) {
synchronized(ioExceptions) {
if (e == null) {
ioExceptions[idx] = null;
return;
}
if (e instanceof IOException) {
ioExceptions[idx] = (IOException) e;
} else {
ioExceptions[idx] = new IOException(e);
}
}
}
}
BlockingQueue<ReadResult> boundedBuffer;
Thread mainThread;
/**
* Reads data from multiple streams in parallel and puts the data in a queue.
* @param streams The input streams to read from.
* @param bufSize The amount of data to read from each stream in each go.
* @param numThreads Number of threads to use for parallelism.
* @param boundedBuffer The queue to place the results in.
*/
public ParallelStreamReader(
Progressable reporter,
InputStream[] streams,
int bufSize,
int numThreads,
int boundedBufferCapacity) {
this.reporter = reporter;
this.streams = new InputStream[streams.length];
for (int i = 0; i < streams.length; i++) {
this.streams[i] = streams[i];
streams[i] = null; // Take over ownership of streams.
}
this.bufSize = bufSize;
this.boundedBuffer =
new ArrayBlockingQueue<ReadResult>(boundedBufferCapacity);
if (numThreads > streams.length) {
this.numThreads = streams.length;
} else {
this.numThreads = numThreads;
}
this.slots = new Semaphore(this.numThreads);
this.readPool = Executors.newFixedThreadPool(this.numThreads);
this.mainThread = new MainThread();
}
public void start() {
this.mainThread.start();
}
public void shutdown() {
LOG.info("Shutting down parallel stream reader");
running = false;
try {
readPool.shutdownNow();
} catch (Exception e) {}
try {
mainThread.interrupt();
} catch (Exception e) {}
for (int i = 0; i < streams.length; i++) {
if (streams[i] != null) {
try {
streams[i].close();
streams[i] = null;
} catch (IOException e) {}
}
}
}
public ReadResult getReadResult() throws InterruptedException {
return boundedBuffer.take();
}
class MainThread extends Thread {
public void run() {
while (running) {
ReadResult readResult = new ReadResult(streams.length, bufSize);
try {
performReads(readResult);
// Enqueue to bounder buffer.
boundedBuffer.put(readResult);
} catch (InterruptedException e) {
running = false;
}
}
}
}
/**
* Performs a batch of reads from the given streams and waits
* for the reads to finish.
*/
private void performReads(ReadResult readResult) throws InterruptedException {
long start = System.currentTimeMillis();
for (int i = 0; i < streams.length; ) {
boolean acquired = slots.tryAcquire(1, 10, TimeUnit.SECONDS);
reporter.progress();
if (acquired) {
readPool.execute(new ReadOperation(readResult, i));
i++;
}
}
// All read operations have been submitted to the readPool.
// Now wait for the operations to finish and release the semaphore.
while (true) {
boolean acquired =
slots.tryAcquire(numThreads, 10, TimeUnit.SECONDS);
reporter.progress();
if (acquired) {
slots.release(numThreads);
break;
}
}
readTime += (System.currentTimeMillis() - start);
}
class ReadOperation implements Runnable {
ReadResult readResult;
int idx;
ReadOperation(ReadResult readResult, int idx) {
this.readResult = readResult;
this.idx = idx;
}
public void run() {
readResult.setException(idx, null);
try {
if (streams[idx] == null) {
// We encountered an error in this stream earlier, use zeros.
Arrays.fill(readResult.readBufs[idx], (byte) 0);
return;
}
boolean eofOK = true;
byte[] buffer = readResult.readBufs[idx];
RaidUtils.readTillEnd(streams[idx], buffer, eofOK);
} catch (Exception e) {
LOG.warn("Encountered exception in stream " + idx, e);
readResult.setException(idx, e);
try {
streams[idx].close();
} catch (IOException ioe) {}
streams[idx] = null;
} finally {
ParallelStreamReader.this.slots.release();
}
}
}
}