Perform a task 'n' times in parallel

Question

I am trying to figure out the easiest way to invoke a task 'x' times and all in parallel in java. The task has a string variable whose value should be unique for each invocation and it returns a string and int result.

I have been looking up resources in internet and now I am terribly confused.

Answer 1

In order to execute tasks in parallel, your first choice should be an ExecutorService. You get an instance of one like they say in the docs, that is

ExecutorService service = Executors.newFixedThreadPool(poolSize);

If your tasks must return a value, you should use the

Future<T> submit(Callable<T> task);

function. Make your tasks implement the Callable interface, returning the result you require. Submit your tasks to the service, then wait for the results through the Future objects. A rough sketch:

public class MyTask implements Callable<StringInt> {
    public MyTask(String inputParameter) { ... }
    public StringInt call() { ... }
}

...

List<Future<StringInt>> results = new ArrayList<Future<StringInt>>();
ExecutorService service = Executors.newFixedThreadPool(16);
for (String inputParameter : inputParameters) {
    // Create tasks and start parallel execution
    results.add(service.submit(new MyTask(inputParameter)));
}

for (Future<StringInt> result : results) {
    // Wait for tasks to end, and get result
    StringInt resultValue = result.get();
    ...
}