ornamentalgarden.java

thinking in java 书中源码 第四版

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

class Count {
  private int count = 0;
  private Random rand = new Random(47);
  // Remove the synchronized keyword to see counting fail:
  public synchronized int increment() {
    int temp = count;
    if(rand.nextBoolean()) // Yield half the time
      Thread.yield();
    return (count = ++temp);
  }
  public synchronized int value() { return count; }
}

class Entrance implements Runnable {
  private static Count count = new Count();
  private static List<Entrance> entrances =
    new ArrayList<Entrance>();
  private int number = 0;
  // Doesn't need synchronization to read:
  private final int id;
  private static volatile boolean canceled = false;
  // Atomic operation on a volatile field:
  public static void cancel() { canceled = true; }
  public Entrance(int id) {
    this.id = id;
    // Keep this task in a list. Also prevents
    // garbage collection of dead tasks:
    entrances.add(this);
  }
  public void run() {
    while(!canceled) {
      synchronized(this) {
        ++number;
      }
      print(this + " Total: " + count.increment());
      try {
        TimeUnit.MILLISECONDS.sleep(100);
      } catch(InterruptedException e) {
        print("sleep interrupted");
      }
    }
    print("Stopping " + this);
  }
  public synchronized int getValue() { return number; }
  public String toString() {
    return "Entrance " + id + ": " + getValue();
  }
  public static int getTotalCount() {
    return count.value();
  }
  public static int sumEntrances() {
    int sum = 0;
    for(Entrance entrance : entrances)
      sum += entrance.getValue();
    return sum;
  }
}

public class OrnamentalGarden {
  public static void main(String[] args) throws Exception {
    ExecutorService exec = Executors.newCachedThreadPool();
    for(int i = 0; i < 5; i++)
      exec.execute(new Entrance(i));
    // Run for a while, then stop and collect the data:
    TimeUnit.SECONDS.sleep(3);
    Entrance.cancel();
    exec.shutdown();
    if(!exec.awaitTermination(250, TimeUnit.MILLISECONDS))
      print("Some tasks were not terminated!");
    print("Total: " + Entrance.getTotalCount());
    print("Sum of Entrances: " + Entrance.sumEntrances());
  }
} /* Output: (Sample)
Entrance 0: 1 Total: 1
Entrance 2: 1 Total: 3
Entrance 1: 1 Total: 2
Entrance 4: 1 Total: 5
Entrance 3: 1 Total: 4
Entrance 2: 2 Total: 6
Entrance 4: 2 Total: 7
Entrance 0: 2 Total: 8
...
Entrance 3: 29 Total: 143
Entrance 0: 29 Total: 144
Entrance 4: 29 Total: 145
Entrance 2: 30 Total: 147
Entrance 1: 30 Total: 146
Entrance 0: 30 Total: 149
Entrance 3: 30 Total: 148
Entrance 4: 30 Total: 150
Stopping Entrance 2: 30
Stopping Entrance 1: 30
Stopping Entrance 0: 30
Stopping Entrance 3: 30
Stopping Entrance 4: 30
Total: 150
Sum of Entrances: 150
*///:~