//: concurrency/FastSimulation.java
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.*;
import static net.mindview.util.Print.*;

public class FastSimulation {
  static final int N_ELEMENTS = 100000;
  static final int N_GENES = 30;
  static final int N_EVOLVERS = 50;
  static final AtomicInteger[][] GRID =
    new AtomicInteger[N_ELEMENTS][N_GENES];
  static Random rand = new Random(47);
  static class Evolver implements Runnable {
    public void run() {
      while(!Thread.interrupted()) {
        // Randomly select an element to work on:
        int element = rand.nextInt(N_ELEMENTS);
        for(int i = 0; i < N_GENES; i++) {
          int previous = element - 1;
          if(previous < 0) previous = N_ELEMENTS - 1;
          int next = element + 1;
          if(next >= N_ELEMENTS) next = 0;
          int oldvalue = GRID[element][i].get();
          // Perform some kind of modeling calculation:
          int newvalue = oldvalue +
            GRID[previous][i].get() + GRID[next][i].get();
          newvalue /= 3; // Average the three values
          if(!GRID[element][i]
            .compareAndSet(oldvalue, newvalue)) {
            // Policy here to deal with failure. Here, we
            // just report it and ignore it; our model
            // will eventually deal with it.
            print("Old value changed from " + oldvalue);
          }
        }
      }
    }
  }
  public static void main(String[] args) throws Exception {
    ExecutorService exec = Executors.newCachedThreadPool();
    for(int i = 0; i < N_ELEMENTS; i++)
      for(int j = 0; j < N_GENES; j++)
        GRID[i][j] = new AtomicInteger(rand.nextInt(1000));
    for(int i = 0; i < N_EVOLVERS; i++)
      exec.execute(new Evolver());
    TimeUnit.SECONDS.sleep(5);
    exec.shutdownNow();
  }
} /* (Execute to see output) *///:~