我如何同步该程序

Question

I'm trying to write a program that launches 1000 threads. Each Thread adds 1 to a variable sum that is initially 0. Doing this by passing sum by reference to each thread and I am told to do this using an Integer wrapper object to hold sum.

Code:

public class synchronizedsum {
    public static void main(String args[]){
        int sum=0;
        ExecutorService executor = Executors.newCachedThreadPool();
        for(int i=0;i<1000;i++){
            executor.execute(new Adder(sum));
        }
        executor.shutdown();
        while(!executor.isTerminated()){

        }
        System.out.println(sum);
}
private static class Adder implements Runnable{
    private int sum;
    Adder(int sum){
        this.sum = sum;
    }

    public synchronized void run(){
        sum+=1;
    }
}
}

I think I've got something wrong cause does not seem to be working.

EDIT: I keep getting output as 0 instead of 1000 that is the problem.

EDIT: I tried doing this seems to give me right output but not sure if it meets the condition of passing sum by reference to each Thread.

CODE:

public class synchronizedsum {

    private static Interger obj = new Interger();
    public static void main(String[] args) {

        ExecutorService executor = Executors.newCachedThreadPool();
        for(int i=0;i<1000;i++){
            executor.execute(new Add1());
        }
        executor.shutdown();
        while(!executor.isTerminated()){

        }
        System.out.println(obj.getSum());
    }
private static class Interger{
    private volatile int sum =0;
    private Lock lock = new ReentrantLock();
    public void add(int amount){
        lock.lock();
        try {
            sum+=amount;
            Thread.sleep(5);
        } catch (InterruptedException ex) {
            Logger.getLogger(Practice.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            lock.unlock();
        }
    }
    public int getSum(){
        return sum;
    }

}
public static class Add1 implements Runnable{

    public  void run(){
        obj.add(1);
    }
}
}

Answer 1

Will passing an AtomicInteger instead of an Integer help? You won't have to deal with synchronized methods as updating the value for AtomicInteger guarantees that for you.

Answer 2

Above code is needlessly complex. You can achieve it with a simple solution using AtomicInteger

Few suggestions:

1. Change newCachedThreadPool() to newFixedThreadPool(Runtime.getRuntime().availableProcessors());

2. Use incrementAndGet of AtomicInteger by removing Lock

You can refer to example code at this post and modify your code accordingly.

How can I access the property value of a running Thread