Question

I am stuck with this following problem.
Say, I have a request which has 1000 items, and I would like to utilize Java Executor to resolve this.

Here is the main method

public static void main(String[] args) {

     //Assume that I have request object that contain arrayList of names
     //and VectorList is container for each request result

     ExecutorService threadExecutor = Executors.newFixedThreadPool(3);
     Vector<Result> vectorList = new Vector<Result();

     for (int i=0;i<request.size();i++) {
          threadExecutor.execute(new QueryTask(request.get(i).getNames, vectorList)
     }

      threadExecutor.shutdown();

      response.setResult(vectorList)

}

And here is the QueryTask class

public QueryTask() implements Runnable {

    private String names;
    private Vector<Result> vectorList;

    public QueryTask(String names, Vector<Result> vectorList) {
          this.names = names;
          this.vectorList = vectorList;
    }

    public void run() {
         // do something with names, for example, query database
         Result result = process names;

         //add result to vectorList
         vectorList.add(result);
    }


}

So, based on the example above, I want to make thread pool for each data I have in the request, run it simultaneously, and add result to VectorList.
And at the end of the process, I want to have all the result already in the Vector list.

I keep getting inconsistent result in the response.
For example, if I pass request with 10 names, I am getting back only 3 or 4, or sometimes nothing in the response.
I was expecting if I pass 10, then I will get 10 back.

Does anyone know whats causing the problem?

Any help will be appreciate it.

Thanks

Answer 1

The easy solution is to add a call to ExecutorService.awaitTermination()

public static void main(String[] args) {

     //Assume that I have request object that contain arrayList of names
     //and VectorList is container for each request result

     ExecutorService threadExecutor = Executors.newFixedThreadPool(3);
     Vector<Result> vectorList = new Vector<Result();

     for (int i=0;i<request.size();i++) {
          threadExecutor.execute(new QueryTask(request.get(i).getNames, vectorList)
     }

      threadExecutor.shutdown();
      threadExecutor.awaitTermination(aReallyLongTime,TimeUnit.SECONDS);

      response.setResult(vectorList)

}