Concurrency ExecutorService Counter from 1 to N

Question

Sup!

I am practicing & trying to cope with concurrency Now, I am attempting to count numbers from 1 to N (1000 in my example) using ExecutorService, but unluckily I am not able to receive the expectative result. Here I go:

class Exec {
AtomicInteger sum = new AtomicInteger(0);
public static void main(String[] args) {
    for (int i = 0; i < 30; i++) {
        Exec exec = new Exec();
        exec.run(exec);
    }
}

public void run(Exec exec) {
    ExecutorService executorService = Executors.newFixedThreadPool(5);
    IntStream.range(0, 1000).parallel().forEach(x -> executorService.submit(exec::synchCalc));

    executorService.shutdown();
    System.out.println(sum.get());
}
public synchronized void synchCalc() {
    sum.incrementAndGet();
} 
}

The output is:

I've tried several ways of solving my problem: volatile instead of AtomicInteger, synchronizing almost every method, but it doesn't make sense as well. The result is just the same - I never get all 1000 and I don't really realise why so.

I would appreciate any answer in due trouble. Thank you for any help!

Hi, have a look at the duplicates for instance https://stackoverflow.com/a/66830328/1366871 explains what is wrong with your code — dreamcrash, May 14 '21 at 20:32
You don't need the synchronized, you just need to wait before calling sum.get() — dreamcrash, May 14 '21 at 20:34

Concurrency ExecutorService Counter from 1 to N

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