11.10 Map

src/concurrency/HorseRace.java

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+package concurrency;//: concurrency/HorseRace.java
+// Using CyclicBarriers.
+import java.util.concurrent.*;
+import java.util.*;
+import static net.mindview.util.Print.*;
+
+class Horse implements Runnable {
+  private static int counter = 0;
+  private final int id = counter++;
+  private int strides = 0;
+  private static Random rand = new Random(47);
+  private static CyclicBarrier barrier;
+  public Horse(CyclicBarrier b) { barrier = b; }
+  public synchronized int getStrides() { return strides; }
+  public void run() {
+    try {
+      while(!Thread.interrupted()) {
+        synchronized(this) {
+          strides += rand.nextInt(3); // Produces 0, 1 or 2
+        }
+        barrier.await();
+      }
+    } catch(InterruptedException e) {
+      // A legitimate way to exit
+    } catch(BrokenBarrierException e) {
+      // This one we want to know about
+      throw new RuntimeException(e);
+    }
+  }
+  public String toString() { return "Horse " + id + " "; }
+  public String tracks() {
+    StringBuilder s = new StringBuilder();
+    for(int i = 0; i < getStrides(); i++) {
+        s.append("*");
+    }
+    s.append(id);
+    return s.toString();
+  }
+}
+
+public class HorseRace {
+  static final int FINISH_LINE = 75;
+  private List<Horse> horses = new ArrayList<Horse>();
+  private ExecutorService exec =
+    Executors.newCachedThreadPool();
+  private CyclicBarrier barrier;
+  public HorseRace(int nHorses, final int pause) {
+    barrier = new CyclicBarrier(nHorses, new Runnable() {
+      public void run() {
+        StringBuilder s = new StringBuilder();
+        for(int i = 0; i < FINISH_LINE; i++) {
+            s.append("="); // The fence on the racetrack
+        }
+        print(s);
+        for(Horse horse : horses) {
+            print(horse.tracks());
+        }
+        for(Horse horse : horses) {
+            if(horse.getStrides() >= FINISH_LINE) {
+              print(horse + "won!");
+              exec.shutdownNow();
+              return;
+            }
+        }
+        try {
+          TimeUnit.MILLISECONDS.sleep(pause);
+        } catch(InterruptedException e) {
+          print("barrier-action sleep interrupted");
+        }
+      }
+    });
+    for(int i = 0; i < nHorses; i++) {
+      Horse horse = new Horse(barrier);
+      horses.add(horse);
+      exec.execute(horse);
+    }
+  }
+  public static void main(String[] args) {
+    int nHorses = 7;
+    int pause = 200;
+    if(args.length > 0) { // Optional argument
+      int n = new Integer(args[0]);
+      nHorses = n > 0 ? n : nHorses;
+    }
+    if(args.length > 1) { // Optional argument
+      int p = new Integer(args[1]);
+      pause = p > -1 ? p : pause;
+    }
+    new HorseRace(nHorses, pause);
+  }
+} /* (Execute to see output) *///:~