Executor Service and Main Thread not executing in parallel - multithreading

Question

I have a requirement that both Main thread and Executor service should execute in parallel. Main thread should not wait for all threads in executor service to finish. It should continue its execution while executor service is executing its threads.
Example Main Method
public static void main(String[] args) throws InterruptedException, ExecutionException {
String mess = "test completed";
//Start of ExecutorService - ThreadPool of size 500
ExecutorService executorService = Executors.newFixedThreadPool(500);
//Creating 500 tasks to execute
List<AsyncTask> callables = new ArrayList<>();
for(int i=1 ; i<= 500 ; i++){
callables.add(new AsyncTask(i));
}
//Submitting all 500 tasks to execute
List<Future<String>> futures = executorService.invokeAll(callables);
for(Future<String> future : futures){
System.out.println("future.get = " + future.get());
}
executorService.shutdown();
//End of Executor service
//Below code executes only when executor service is finished.
//I want below code to execute in parallel with executor service
//Means It should print this mess before executor service finishes
System.out.println(mess);
}
Callable Task
public class AsyncTask implements Callable<String>{
private int i;
public AsyncTask(int i) {
this.i = i;
}
#Override
public String call() throws Exception {
return "Task " +i;
}
}
OutPut :
future.get = Task 1
future.get = Task 2
future.get = Task 3
future.get = Task 4
.......continues till
future.get = Task 500
test completed
Expected output :
test completed message to be printed during some async tasks are finished or before start of async tasks
Sample output
future.get = Task 1
future.get = Task 2
test completed // Both Main method and Executor service is running in parallel
future.get = Task 3
...........
future.get = Task 500
I have not worked on Threads before, do i miss something ? whole idea of using executor service is to execute some tasks in parallel with main thread right ?
Please suggest me to fix this

Answer 1

ExecutorService.invokeAll will wait until all task was completed, so all code after it would not be executed until ExecutorService.invokeAll was returned. Put the service execution code to another thread will simply solve the problem.
class RunService extends Thread {
RunService () {
}
public void run() {
//Start of ExecutorService - ThreadPool of size 500
ExecutorService executorService = Executors.newFixedThreadPool(500);
//Creating 500 tasks to execute
List<AsyncTask> callables = new ArrayList<>();
for(int i=1 ; i<= 500 ; i++){
callables.add(new AsyncTask(i));
}
//Submitting all 500 tasks to execute
List<Future<String>> futures = executorService.invokeAll(callables);
for(Future<String> future : futures){
System.out.println("future.get = " + future.get());
}
executorService.shutdown();
//End of Executor service
}
}
public static void main(String[] args) throws InterruptedException, ExecutionException {
String mess = "test completed";
RunService rs = new RunService();
rs.Start();
//Below code executes only when executor service is finished.
//I want below code to execute in parallel with executor service
//Means It should print this mess before executor service finishes
System.out.println(mess);
}