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Add ParallelCountBytes #983

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May 31, 2016
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4 changes: 4 additions & 0 deletions gcloud-java-examples/pom.xml
Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,10 @@
<mainClass>com.google.cloud.examples.nio.CountBytes</mainClass>
<name>CountBytes</name>
</program>
<program>
<mainClass>com.google.cloud.examples.nio.ParallelCountBytes</mainClass>
<name>ParallelCountBytes</name>
</program>
<program>
<mainClass>
com.google.cloud.examples.resourcemanager.ResourceManagerExample
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Original file line number Diff line number Diff line change
Expand Up @@ -18,13 +18,15 @@

import com.google.common.base.Stopwatch;

import javax.xml.bind.annotation.adapters.HexBinaryAdapter;
import java.io.IOException;
import java.net.URI;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.util.concurrent.TimeUnit;

/**
Expand Down Expand Up @@ -72,15 +74,19 @@ private static void countFile(String fname) {
SeekableByteChannel chan = Files.newByteChannel(path);
long total = 0;
int readCalls = 0;
MessageDigest md = MessageDigest.getInstance("MD5");
while (chan.read(buf) > 0) {
readCalls++;
md.update(buf.array(), 0, buf.position());
total += buf.position();
buf.flip();
}
readCalls++; // We must count the last call
long elapsed = sw.elapsed(TimeUnit.SECONDS);
System.out.println("Read all " + total + " bytes in " + elapsed + "s. " +
"(" + readCalls +" calls to chan.read)");
String hex = (new HexBinaryAdapter()).marshal(md.digest());
System.out.println("The MD5 is: 0x" + hex);
if (total != size) {
System.out.println("Wait, this doesn't match! We saw " + total + " bytes, " +
"yet the file size is listed at " + size + " bytes.");
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Original file line number Diff line number Diff line change
@@ -0,0 +1,174 @@
/*
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed 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 com.google.cloud.examples.nio;

import com.google.common.base.Stopwatch;

import javax.xml.bind.annotation.adapters.HexBinaryAdapter;

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import java.io.IOException;
import java.net.URI;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.util.concurrent.TimeUnit;

/**
* ParallelCountBytes will read through the whole file given as input.
*
* <p>This example shows how to go through all the contents of a file,
* in order, using multithreaded NIO reads.It also reports how long it took.

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*
* <p>See the README for compilation instructions. Run this code with
* {@code target/appassembler/bin/ParallelCountBytes <file>}
*/
public class ParallelCountBytes {

private class BufWithLock {
public Object lock;

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public ByteBuffer buf;

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public boolean full;
public Thread t;

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public BufWithLock(int size) {
this.buf = ByteBuffer.allocate(size);
this.lock = new Object();
}
}

/**
* See the class documentation.
*/
public static void main(String[] args) throws IOException {
new ParallelCountBytes().start(args);
}

public void start(String[] args) throws IOException {
if (args.length == 0 || args[0].equals("--help")) {
help();
return;
}
for (String a : args) {
countFile(a);
}
}

private void stridedRead(SeekableByteChannel chan, int blockSize, int firstBlock, int stride, BufWithLock output) {
try {
// stagger the threads a little bit.
Thread.sleep(250 * firstBlock);
long pos = firstBlock * blockSize;
synchronized(output.lock) {
while (true) {
if (pos > chan.size()) {
break;
}
chan.position(pos);
// read until buffer is full, or EOF
while (chan.read(output.buf) > 0) {};
output.full = true;
output.lock.notifyAll();

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if (output.buf.hasRemaining()) {
break;
}
// wait for main thread to process it
while (output.full) {
output.lock.wait();
}
output.buf.flip();
pos += stride * blockSize;
}
}
} catch (InterruptedException | IOException o) {
// this simple example doesn't handle errors, sorry.
}
}

/**
* Print the length of the indicated file.
*
* <p>This uses the normal Java NIO Api, so it can take advantage of any installed
* NIO Filesystem provider without any extra effort.
*/
private void countFile(String fname) throws IOException{
// large buffers pay off
final int bufSize = 50 * 1024 * 1024;
try {
Path path = Paths.get(new URI(fname));
long size = Files.size(path);
System.out.println(fname + ": " + size + " bytes.");
ByteBuffer buf = ByteBuffer.allocate(bufSize);

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int nBlocks = (int)Math.ceil( size / (double)bufSize);

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int nThreads = nBlocks;
if (nThreads > 4) nThreads = 4;
System.out.println("Reading the whole file using " + nThreads + " threads...");
Stopwatch sw = Stopwatch.createStarted();
final BufWithLock[] bufs = new BufWithLock[nThreads];
for (int i = 0; i < nThreads; i++) {
bufs[i] = new BufWithLock(bufSize);
final SeekableByteChannel chan = Files.newByteChannel(path);
final int finalNThreads = nThreads;
final int finalI = i;
bufs[i].t = new Thread(new Runnable() {
@Override
public void run() {
stridedRead(chan, bufSize, finalI, finalNThreads, bufs[finalI]);
}
});
bufs[i].t.start();

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}

long total = 0;
MessageDigest md = MessageDigest.getInstance("MD5");
for (int block = 0; block < nBlocks; block++) {
BufWithLock bwl = bufs[block % bufs.length];
synchronized (bwl.lock) {
while (!bwl.full) {
bwl.lock.wait();
}
md.update(bwl.buf.array(), 0, bwl.buf.position());
total += bwl.buf.position();
bwl.full = false;
bwl.lock.notifyAll();

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}
}

long elapsed = sw.elapsed(TimeUnit.SECONDS);
System.out.println("Read all " + total + " bytes in " + elapsed + "s. ");
String hex = (new HexBinaryAdapter()).marshal(md.digest());
System.out.println("The MD5 is: 0x" + hex);
if (total != size) {
System.out.println("Wait, this doesn't match! We saw " + total + " bytes, " +
"yet the file size is listed at " + size + " bytes.");
}
} catch (Exception ex) {
System.out.println(fname + ": " + ex.toString());
}
}

private static void help() {
String[] help =
{"The argument is a <path>",
"and we show the length of that file."
};
for (String s : help) {
System.out.println(s);
}
}
}