Question

I’m using using AsyncTask to download data over internet and I have a little problem. I need to be able to start one AsyncTask a few times, that’s why I’m creating a new instance everytime,but the thing that I notice is that it’s working without any problem the first three or four times,but after that my AsyncTask is stuck on onPreExecute() and doing nothing after that. Am I doing something wrong ? (Actually I am using two AsyncTasks one after another just for testing purposes). Here is the sample code which I’m using :

this is how I start the AsyncTasks :

    if (index == 1) {
        //Login - first way
        new FirstSync().execute(Synchronization.this);
    } else if (index == 2) {
        //SyncWithHash - second way
        SyncWithHash syncHash = new SyncWithHash();
        syncHash.execute(Synchronization.this);
    } else if (index == 3) {
        //Deactivate Collection - third way
        deactivateColl = new DeactivateCollection();
        deactivateColl.execute(Synchronization.this);
    }

I did try with three different ways to start the asyncTask,but no change. Here is my AsyncTask :

    // Sync With Hash
public class SyncWithHash extends AsyncTask <Context, Integer, Void> {
    @Override
    protected Void doInBackground(Context... arrContext) {
        try {

            String charset = "UTF-8";
            hash = getAuthHash();

            SharedPreferences lastUser = PreferenceManager.getDefaultSharedPreferences(Synchronization.this);
            int userId = lastUser.getInt("lastUser", 1);

            systemDbHelper = new SystemDatabaseHelper(Synchronization.this, null, 1);
            systemDbHelper.initialize(Synchronization.this);
            String sql = "SELECT dbTimestamp FROM users WHERE objectId=" + userId;
            Cursor cursor = systemDbHelper.executeSQLQuery(sql);
            if (cursor.getCount() < 0) {
                cursor.close();
            } else if (cursor.getCount() > 0) {
                cursor.moveToFirst();
                timeStamp = cursor.getString(cursor.getColumnIndex("dbTimestamp"));
                Log.d("", "timeStamp : " + timeStamp);
            }

                String query = String.format("debug_data=%s&"
                        + "client_auth_hash=%s&" + "timestamp=%s&"
                        + "client_api_ver=%s&"
                        + "set_locale=%s&" + "device_os_type=%s&"
                        + "device_sync_type=%s&"
                        + "device_identification_string=%s&"
                        + "device_identificator=%s&" + "device_resolution=%s",
                        URLEncoder.encode("1", charset),
                        URLEncoder.encode(hash, charset),
                        URLEncoder.encode(timeStamp, charset),
                        URLEncoder.encode(clientApiVersion, charset),
                        URLEncoder.encode(locale, charset),
                        URLEncoder.encode(version, charset),
                        URLEncoder.encode("14", charset),
                        URLEncoder.encode(version, charset),
                        URLEncoder.encode(deviceId, charset),
                        URLEncoder.encode(resolution, charset));

            SharedPreferences useSSLConnection = PreferenceManager
                    .getDefaultSharedPreferences(Synchronization.this);
            boolean useSSl = useSSLConnection.getBoolean("UseSSl", true);
            if (useSSl) {
                UseHttpsConnection(url, charset, query);
            } else {
                UseHttpConnection(url, charset, query);
            }
        } catch (Exception e2) {
            e2.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        //cancelDialog.setProgress(progress[0]);
    }
    @Override
    protected void onCancelled() {
        Log.d("","ON CANCELLED");
    } 
    @Override
    protected void onPreExecute() 
    {
        Log.d("","ON PRE EXECUTE");
       // myProgress = 0;
    }
    @Override
    protected void onPostExecute(Void v) {
        Log.d("","ON POST EXECUTE");
    }
  }

So any ideas why it’s happening and which is the best way to be able to use an AsyncTask a few times without any exceptions and bugs like the one that I get.

And another question : Is there anything in AsyncTask which can cause my connection to be Reset by peer , because I’m getting this error too (not every time).

Thanks a lot!

Answer 1

I think your doInBackground() is hanging. Make log statement when its entered and when its exited and check.

In the old days AsyncTask had a pool of threads, so if a doInBackground() hung, then it didnt affect the other AsyncTasks. That changed AFAIK with Android 2.2 or 2.3 to that a single thread took care of all AyncTasks, one at a time. Therefore, if your doInBackground() is hanging it might affect the next AsyncTasks being started and the will hang right after onPreExecute().

Edit: It was changed from a single thread, to multiple, and then back to a single thread:
http://developer.android.com/reference/android/os/AsyncTask.html#execute%28Params…%29 “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. After HONEYCOMB, it is planned to change this back to a single thread to avoid common application errors caused by parallel execution.”

If you really want an indefinite lot of stuff to ‘hang’ in parralel, then don’t use AsyncTask. Use good old threads, which, when they need to update the GUI, fire off a Runnable to be runned on the GUI thread:

Button knap1, knap2, knap3;
...

  Runnable r=new Runnable() {
    public void run() {
      // Do some stuff than hangs
      try { Thread.sleep(10000); } catch (InterruptedException ex) {}
      System.out.println("færdig!");

      // Update GUI thread
      Runnable r2=new Runnable() {
        public void run() {
          knap3.setText("færdig!");
        }
      };
      runOnUiThread(r2);
    }
  };
  new Thread(r).start();

(example from http://code.google.com/p/android-eksempler/source/browse/trunk/AndroidElementer/src/eks/asynkron/Asynkron1Thread.java?spec=svn109&r=109)