import java.util.ArrayList;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;

public class DeadlockMainV2 {

  private static class ConcurrentHashMapForJDK8<K, V> extends ConcurrentHashMap<K, V> {
    @Override
    public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
      V result;
      if (null == (result = get(key))) {
        result = super.computeIfAbsent(key, mappingFunction);
      }
      return result;
    }
  }

  static final int MAP_SIZE=20;
  static final int THREADS=20;
  static final ConcurrentHashMap<Integer,Integer> map = new ConcurrentHashMapForJDK8();
  static {
    for (int i = 0; i < MAP_SIZE; i++) map.put(i, i);
  }

  static class TestThread extends Thread {
    @Override
    public void run() {
      int i=0; int result =0;
      while(result<Integer.MAX_VALUE) {
        i = (i+1) % MAP_SIZE;
        result += map.computeIfAbsent(i, (key)->key+key);
      }
    }
  }

  public static void main(String[]v) throws InterruptedException {
    long startTime = System.currentTimeMillis();
    ArrayList<Thread> threads = new ArrayList<>();
    for (int i=0;i<THREADS;i++) {
      TestThread t = new TestThread();
      threads.add(t);
      t.start();
    }
    threads.get(0).join();
    long endTime = System.currentTimeMillis();
    System.out.println(String.format("Total cost: %d s", (endTime - startTime) / 1000));
  }
}