concurrency chapter progress

concurrent/CompletablePizza.java

@@ -42,7 +42,6 @@ public class CompletablePizza {
   }
 }
 /* Output:
-/* Output:
 56
 Pizza 0: ROLLED
 Pizza 1: ROLLED

concurrent/DiningPhilosophers.java

@@ -2,63 +2,36 @@
 // (c)2016 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
-// Deadlock can be hidden in a program
-import java.util.stream.*;
+// Hidden deadlock
+import java.util.*;
 import java.util.concurrent.*;
 import static java.util.concurrent.TimeUnit.*;
 
 public class DiningPhilosophers {
-  static void stopAfter(int secs) {
+  private StickHolder[] sticks;
+  private Philosopher[] philosophers;
+  public DiningPhilosophers(int n) {
+    sticks = new StickHolder[n];
+    Arrays.setAll(sticks, i -> new StickHolder());
+    philosophers = new Philosopher[n];
+    Arrays.setAll(philosophers, i ->
+      new Philosopher(i,
+        sticks[i], sticks[(i + 1) % n]));    // [1]
+    // Fix by reversing stick order:
+    // philosophers[1] =                     // [2]
+    //   new Philosopher(0, sticks[0], sticks[1]);
+    Arrays.stream(philosophers)
+      .forEach(CompletableFuture::runAsync); // [3]
+  }
+  public static void main(String[] args) {
+    // Returns right away:
+    new DiningPhilosophers(5);               // [4]
+    // Keeps main() from exiting:
     ScheduledExecutorService sched =
       Executors.newScheduledThreadPool(1);
     sched.schedule( () -> {
-      System.out.println("Timeout");
-      Philosopher.running.set(false);
-      sched.shutdownNow();
-      System.exit(0);
-    }, secs, SECONDS);
-  }
-  public static void main(String[] args)
-  throws Exception {
-    stopAfter(3);
-    try {
-      IntStream.range(0, Philosopher.QUANTITY)
-        .mapToObj(Philosopher::new)
-        .map(CompletableFuture::runAsync)
-        .collect(Collectors.toList())
-        .forEach(CompletableFuture::join);
-    } catch(CompletionException ex) {
-      Philosopher.running.set(false);
-      System.out.println("Broken out of deadlock");
-      System.out.println("...");
-    }
-    Philosopher.trace.stream()
-      .skip(Philosopher.trace.size() - 20)
-      .forEach(System.out::println);
+      System.out.println("Shutdown");
+      sched.shutdown();
+    }, 3, SECONDS);
   }
 }
-/* Output:
-Broken out of deadlock
-...
-P2 grabbing right
-P1 grabbing left
-P3 eating
-P3 thinking
-P3 grabbing right
-P4 eating
-P2 grabbing left
-P4 thinking
-P0 eating
-P4 grabbing right
-P3 grabbing left
-P0 thinking
-P0 grabbing right
-P4 grabbing left
-P0 grabbing left
-P1 eating
-P2 eating
-P3 eating
-P0 eating
-P4 eating
-Timeout
-*/

concurrent/FrostedCake.java

@@ -3,7 +3,6 @@
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
 import java.util.concurrent.*;
-import java.util.function.*;
 import java.util.stream.*;
 import onjava.Nap;
 
@@ -20,6 +19,8 @@ public class FrostedCake {
   public FrostedCake(Baked baked, Frosting frosting) {
     new Nap(100);
   }
+  @Override
+  public String toString() { return "FrostedCake"; }
   public static void main(String[] args) {
     Baked.batch().forEach(baked -> baked
       .thenCombineAsync(Frosting.make(),

concurrent/ParallelPrime.java

@@ -7,7 +7,6 @@ import java.util.stream.*;
 import static java.util.stream.LongStream.*;
 import java.io.*;
 import java.nio.file.*;
-import java.nio.charset.*;
 import onjava.Timer;
 
 public class ParallelPrime {
@@ -32,6 +31,5 @@ public class ParallelPrime {
   }
 }
 /* Output:
-/* Output:
 616
 */

concurrent/Philosopher.java

@@ -2,58 +2,29 @@
 // (c)2016 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
-import java.util.*;
-import java.util.stream.*;
-import java.util.concurrent.*;
-import static java.util.concurrent.TimeUnit.*;
-import java.util.concurrent.atomic.*;
 
-class Philosopher implements Runnable {
-  static class Chopstick {}
-  public static final int QUANTITY = 5;
-  static Queue<String> trace =
-    new ConcurrentLinkedQueue<>();
-  static AtomicBoolean running =
-    new AtomicBoolean(true);
-  public static
-  List<BlockingQueue<Chopstick>> chopsticks =
-    IntStream.range(0, Philosopher.QUANTITY)
-      .mapToObj(i -> {
-        BlockingQueue<Chopstick> bd =
-          new ArrayBlockingQueue<>(1);
-        bd.add(new Chopstick());
-        return bd;
-      })
-      .collect(Collectors.toList());
-  private final int seatNumber;
-  private final int left, right;
-  public Philosopher(int seatNumber) {
-    this.seatNumber = left = seatNumber;
-    right = (seatNumber + 1) % QUANTITY;
-  }
-  @Override
-  public void run() {
-    try {
-      while(running.get()) {
-        trace.add(this + " thinking");
-        // Philosopher becomes hungry
-        trace.add(this + " grabbing right");
-        Chopstick rightStick =
-          chopsticks.get(right).poll(2, SECONDS);
-        trace.add(this + " grabbing left");
-        Chopstick leftStick =
-          chopsticks.get(left).poll(2, SECONDS);
-        trace.add(this + " eating");
-        // Finished, return chopsticks to table:
-        chopsticks.get(right).put(rightStick);
-        chopsticks.get(left).put(leftStick);
-      }
-    } catch(InterruptedException e) {
-      trace.add("exiting via interrupt");
-    }
+public class Philosopher implements Runnable {
+  private final int seat;
+  private final StickHolder left, right;
+  public Philosopher(int seat,
+    StickHolder left, StickHolder right) {
+    this.seat = seat;
+    this.left = left;
+    this.right = right;
   }
   @Override
   public String toString() {
-    return "P" + seatNumber;
+    return "P" + seat;
+  }
+  @Override
+  public void run() {
+    while(true) {
+      // System.out.println("Thinking");   // [1]
+      right.pickUp();
+      left.pickUp();
+      System.out.println(this + " eating");
+      right.putDown();
+      left.putDown();
+    }
   }
 }

concurrent/StickHolder.java

@@ -0,0 +1,27 @@
+// concurrent/StickHolder.java
+// (c)2016 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.concurrent.*;
+
+public class StickHolder {
+  private static class Chopstick {}
+  private Chopstick stick = new Chopstick();
+  private BlockingQueue<Chopstick> holder =
+    new ArrayBlockingQueue<>(1);
+  public StickHolder() { putDown(); }
+  public void pickUp() {
+    try {
+      holder.take(); // Blocks if unavailable
+    } catch(InterruptedException e) {
+      throw new RuntimeException(e);
+    }
+  }
+  public void putDown() {
+    try {
+      holder.put(stick);
+    } catch(InterruptedException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}