Question

I am writing a multithreaded program in java. I have written something like this

exec.execute(p)  // where p is a runnable task working on an array
print array
exec.shutdown

The problem I am facing is that the array gets printed giving the correct output but then the rejected Execution Exception comes
I don’t understand why when the threads have processed and given the correct output why is the error coming…

Answer 1

I think you are shutting down your executor too early. This is an example how I think you should be working.

public class Main {
    public static void main(String[] args) throws Exception {

        // the array to modify
        final int[] array = new int[1000];

        // start the executor (that modifies the array)
        ExecutorService executor = Executors.newFixedThreadPool(10);

        for (int i = 0; i < 1000; i++) {
            final int c = i;
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    array[c] = c;
                }
            });
        }

        // wait for all tasks to quit
        executor.shutdown();
        while (!executor.awaitTermination(10, TimeUnit.SECONDS)); 

        // print the array
        System.out.println(Arrays.toString(array));
    }
}

Also note that working on the same array at the same time could cause inconsistency – you must be really sure that you are not doing work on the array that depends on the array.