Close channels

Plus a little bit of cleanup.

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

@@ -19,6 +19,7 @@
 import com.google.common.base.Stopwatch;
 import com.google.common.io.BaseEncoding;
 
+import java.io.Closeable;
 import java.io.IOException;
 import java.net.URI;
 import java.nio.ByteBuffer;
@@ -49,8 +50,16 @@ public class ParallelCountBytes {
 
   /**
    * WorkUnit holds a buffer and the instructions for what to put in it.
+   *
+   * <p>Use it like this:
+   * <ol>
+   *   <li> call()
+   *   <li> the data is now in buf, you can access it directly
+   *   <li> if need more, call resetForIndex(...) and go back to the top.
+   *   <li> else, call close()
+   * </ol>
    */
-  private class WorkUnit implements Callable<WorkUnit> {
+  private static class WorkUnit implements Callable<WorkUnit>, Closeable {
     public final ByteBuffer buf;
     final SeekableByteChannel chan;
     final int blockSize;
@@ -70,7 +79,7 @@ public WorkUnit call() throws IOException {
         return this;
       }
       chan.position(pos);
-      // read until buffer is full, or EOF
+      // read until buffer it is full, or EOF
       while (chan.read(buf) > 0) {};
       return this;
     }
@@ -80,16 +89,16 @@ public WorkUnit resetForIndex(int blockIndex) {
       buf.flip();
       return this;
     }
+
+    public void close() throws IOException {
+      chan.close();
+    }
   }
 
   /**
    * See the class documentation.
    */
-  public static void main(String[] args) throws IOException {
-    new ParallelCountBytes().start(args);
-  }
-
-  public void start(String[] args) throws IOException {
+  public static void main(String[] args) throws Exception {
     if (args.length == 0 || args[0].equals("--help")) {
       help();
       return;
@@ -100,16 +109,15 @@ public void start(String[] args) throws IOException {
   }
 
   /**
-   * Print the length of the indicated file.
+   * Print the length and MD5 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{
+  private static void countFile(String fname) throws Exception {
     // large buffers pay off
     final int bufSize = 50 * 1024 * 1024;
     Queue<Future<WorkUnit>> work = new ArrayDeque<>();
-    try {
       Path path = Paths.get(new URI(fname));
       long size = Files.size(path);
       System.out.println(fname + ": " + size + " bytes.");
@@ -125,14 +133,15 @@ private void countFile(String fname) throws IOException{
       for (blockIndex = 0; blockIndex < nThreads; blockIndex++) {
         work.add(exec.submit(new WorkUnit(Files.newByteChannel(path), bufSize, blockIndex)));
       }
-      while (true) {
+      while (!work.isEmpty()) {
         WorkUnit full = work.remove().get();
         md.update(full.buf.array(), 0, full.buf.position());
         total += full.buf.position();
         if (full.buf.hasRemaining()) {
-          break;
+          full.close();
+        } else {
+          work.add(exec.submit(full.resetForIndex(blockIndex++)));
         }
-        work.add(exec.submit(full.resetForIndex(blockIndex++)));
       }
       exec.shutdown();
 
@@ -141,12 +150,9 @@ private void countFile(String fname) throws IOException{
       String hex = String.valueOf(BaseEncoding.base16().encode(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.");
+        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() {