Add ParallelCountBytes

Made it and CountBytes compute an MD5, so I could check that they match
(they do).

gcloud-java-examples/pom.xml

@@ -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

gcloud-java-examples/src/main/java/com/google/cloud/examples/nio/CountBytes.java

@@ -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;
 
 /**
@@ -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.");

gcloud-java-examples/src/main/java/com/google/cloud/examples/nio/ParallelCountBytes.java

@@ -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;
+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.
+ *
+ * <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;
+    public ByteBuffer buf;
+    public boolean full;
+    public Thread t;
+
+    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();
+          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);
+      int nBlocks = (int)Math.ceil( size / (double)bufSize);
+      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();
+      }
+
+      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();
+        }
+      }
+
+      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);
+    }
+  }
+}