How to use synchronized the object in AsyncTask doInBackground()?

Question

I got the trouble with using synchronized the object in background thread. I've specified the problem in sample nutshell:

1. I write the simple class like that:

   public class UIThreadClass {
   
      MyObject object;
   
      UIThreadClass() {
         object = new MyObject();
   
         object.doActionOne();
         object.doActionTwo();
     }
   }
   

2. Now my task is improve the code by put two method to non-UI thread. I am using AsyncTask

   For doActionOne()

   private static class DoActionOneTask extends AsyncTask<Void, Void, Void> {
   
       private WeakReference<MyObject> wObject;
   
       DoActionOneTask(MyObject object) {
           wObject = new WeakReference<>(object);
       }
   
       @Override
       protected Void doInBackground(Void... voids) {
          if(wObject.get() != null) {
             MyObject myObject = wObject.get();
             myObject.doActionOne();
          }
   
          return null;
       }
   }
   

   For doActionTwo()

   private static class DoActionTwoTask extends AsyncTask<Void, Void, Void> {
   
       private WeakReference<MyObject> wObject;
   
       DoActionOneTask(MyObject object) {
           wObject = new WeakReference<>(object);
       }
   
       @Override
       protected Void doInBackground(Void... voids) {
          if(wObject.get() != null) {
             MyObject myObject = wObject.get();
             myObject.doActionTwo();
          }
   
          return null;
       }
   }
   

   Now call them in UI thread

   public class UIThreadClass {
   
      MyObject object;
   
      UIThreadClass() {
         object = new MyObject();
   
         new DoActionOneTask(object).execute();
         new DoActionTwoTask(object).execute();
     }
   }
   

The question is:

When using AsyncTask - how to synchronized the object to make sure that the doActionTwo() alway call after doActionOne() method ?.

I have tried using synchronized (myObject) {myObject.doActionOne();} in doInBackground() but the system is warning me that myObject just local variable and it is difficult to guarantee correctness.

Can anyone help me this situation ? Thanks a lot!

Answer 1

You don't need to do anything. They will execute serially as per the Android docs

Order of execution
When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution.

If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.