Android AsyncTask异常和onPostExecute

Question

I have two AsyncTask classes. First:

private class NotationChanger extends AsyncTask <Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        synchronized(mutex) {
            try {
                this.infixToPostNotation();
            } catch(ParseErrorException e) {
                Log.i("Parse Error Exception", e.getMessage());
                changedNotationError = true;
            }
            finally {
                mutex.notify();                         //Calculator waits while notation is being changed
            }                                           //So we should wake it                      
        }
        return null;
    }


    @Override 
    protected void onPreExecute() {
        super.onPreExecute();
        changedNotation = false;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        changedNotation = true;
    } 

    ...
}

Second:

private class Calculator extends AsyncTask <Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... arg0) {
        synchronized(mutex) {
            while(!changedNotation) {
                try {
                    mutex.wait();
                }   catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

        Log.i("Calculation", "waked");

        if(!changedNotationError) {
            try {
                this.calculatePoints();
            } catch (CalculateException e) {
                Log.i("Calculate exception", e.getMessage());
            }
        }
        else {
            changedNotationError = false;
        }

        return null;
    }

    ...
}

As you can see when NotationChanger has done his work it wakes Calculator class. It works fine while there is no an exception. When I get a ParseErrorException in NotationChanger class method onPostExecute isn't called.

If I move

changedNotation = true; 

from onPostExecute function to finally block it works well every time. Does it mean that exception in doInBackground breaks calling of onPostExecute method or I don't understand anything?

Answer 1

If Calculator run first, and waiting in doInBackground(). I think that your NotationChanger can not enter doInBackground(). In my experience, all AsyncTask use only one thread to work.