Question

When the user launches my Android App, I fire up 2 threads to do some processing in the background. thread_1 does some calculations on the client, and thread_2 fetches some data from the server. That all works fine. None of the threads modify the UI. I have two follow up questions.

new Thread(new Runnable(){
    @Override
    public void run(){
        MyClass.someStaticVariable = doSomeCalculations();
    }
}).start();

1. What is the best practice to retrieve the data from the run() method of a thread? I currently have a static variable, and I assign the relavent calculated data/ fetched data to it. Or is it recommended to use the Handler class to get data out of threads? I imagined one only uses the handler if they wish to update the UI.

   while(true)
   {
       if (!thread1.isAlive() && !thread2.isAlive())  
       {
           startActivity(intent)
       }
   }
   

2. I need to wait until both threads are finished before I can pass the data from both threads via an Intent. How can I achieve that? I can do it using the code shown above, but that just seems wrong.

Answer 1

You could use a Future. It will block on get until the data is available: http://developer.android.com/reference/java/util/concurrent/Future.html

An alternative is to pass a CountDownLatch into the threads and call countDown() when exiting the run method: http://developer.android.com/reference/java/util/concurrent/CountDownLatch.html

final CountDownLatch latch = new CountDownLatch(2);
new Thread(new Runnable(){
  @Override
  public void run(){
    // Do something
    latch.countDown()
  }
}).start();
new Thread(new Runnable(){
  @Override
  public void run(){
    // Do something
    latch.countDown()
  }
}).start();

latch.await()
startActivity(intent)