Data commit

Task/Dining-philosophers/Java/dining-philosophers.java

@@ -0,0 +1,113 @@
+package diningphilosophers;
+
+import java.util.ArrayList;
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
+enum PhilosopherState { Get, Eat, Pon }
+
+class Fork {
+    public static final int ON_TABLE = -1;
+    static int instances = 0;
+    public int id;
+    public AtomicInteger holder = new AtomicInteger(ON_TABLE);
+
+    Fork() { id = instances++; }
+}
+
+class Philosopher implements Runnable {
+    static final int maxWaitMs = 100;                          //  must be > 0
+    static AtomicInteger token = new AtomicInteger(0);
+    static int instances = 0;
+    static Random rand = new Random();
+    AtomicBoolean end = new AtomicBoolean(false);
+    int id;
+    PhilosopherState state = PhilosopherState.Get;
+    Fork left;
+    Fork right;
+    int timesEaten = 0;
+
+    Philosopher() {
+        id = instances++;
+        left = Main.forks.get(id);
+        right = Main.forks.get((id+1)%Main.philosopherCount);
+    }
+
+    void sleep() { try { Thread.sleep(rand.nextInt(maxWaitMs)); }
+        catch (InterruptedException ex) {} }
+
+    void waitForFork(Fork fork) {
+        do {
+            if (fork.holder.get() == Fork.ON_TABLE) {
+                fork.holder.set(id);                //  my id shows I hold it
+                return;
+            } else {                                //  someone still holds it
+                sleep();                            //  check again later
+            }
+        } while (true);
+    }
+
+    public void run() {
+        do {
+            if (state == PhilosopherState.Pon) {    //  all that pondering
+                state = PhilosopherState.Get;       //  made me hungry
+            } else { // ==PhilosopherState.Get
+                if (token.get() == id) {            //  my turn now
+                    waitForFork(left);
+                    waitForFork(right);             //  Ah needs me some foahks!
+                    token.set((id+2)% Main.philosopherCount);
+                    state = PhilosopherState.Eat;
+                    timesEaten++;
+                    sleep();                        //  eat for a while
+                    left.holder.set(Fork.ON_TABLE);
+                    right.holder.set(Fork.ON_TABLE);
+                    state = PhilosopherState.Pon;   //  ponder for a while
+                    sleep();
+                } else {                    //  token.get() != id, so not my turn
+                    sleep();
+                }
+            }
+        } while (!end.get());
+    }
+}
+
+public class Main {
+    static final int philosopherCount = 5; //  token +2 behavior good for odd #s
+    static final int runSeconds = 15;
+    static ArrayList<Fork> forks = new ArrayList<Fork>();
+    static ArrayList<Philosopher> philosophers = new ArrayList<Philosopher>();
+
+    public static void main(String[] args) {
+        for (int i = 0 ; i < philosopherCount ; i++) forks.add(new Fork());
+        for (int i = 0 ; i < philosopherCount ; i++)
+            philosophers.add(new Philosopher());
+        for (Philosopher p : philosophers) new Thread(p).start();
+        long endTime = System.currentTimeMillis() + (runSeconds * 1000);
+
+        do {                                                    //  print status
+            StringBuilder sb = new StringBuilder("|");
+
+            for (Philosopher p : philosophers) {
+                sb.append(p.state.toString());
+                sb.append("|");            //  This is a snapshot at a particular
+            }                              //  instant.  Plenty happens between.
+
+            sb.append("     |");
+
+            for (Fork f : forks) {
+                int holder = f.holder.get();
+                sb.append(holder==-1?"   ":String.format("P%02d",holder));
+                sb.append("|");
+            }
+
+            System.out.println(sb.toString());
+            try {Thread.sleep(1000);} catch (Exception ex) {}
+        } while (System.currentTimeMillis() < endTime);
+
+        for (Philosopher p : philosophers) p.end.set(true);
+        for (Philosopher p : philosophers)
+            System.out.printf("P%02d: ate %,d times, %,d/sec\n",
+                p.id, p.timesEaten, p.timesEaten/runSeconds);
+    }
+}