Why AsyncTask are not prefered for Long Running Operations

Question

I have read the two reasons/issue mentioned on:
(Please read two reason on below link)
Android AsyncTask for Long Running Operations
1. "If you start an AsyncTask inside an Activity and you rotate the device, the Activity will be destroyed and a new instance will be created. But the AsyncTask will not die":
Lets suppose i have set the orientation of my activity to Portrait. Will this issue still be there?

2. Memory leak issue:
inner class will hold an invisible reference on its outer class instance : the Activity.
What if i am not using Inner AsyncTask instead created separate class. Also if i use weak reference.

Answer 1

The issues you mention arise only when life-cycle of AsyncTask is not handled properly, mainly from lack of understanding of how they work.

AsyncTask is a wrapper for running code on a separate thread. It is similar to plain Java's Runnable submitted to ExecutorService, with additional features of "pre" and "post" hooks to be run on main thread. So, its basically an enhanced version of Thread, Runnable and Handler setup.

By default AsycTask's share a single thread and hence not advised for long running tasks. Because when a single background thread is shared by many tasks, a long running task may block others. However, AsycTask can also run on a custom Executor, removing such restrictions of a shared worker thread.

All that means that AsyncTask's own design doesn't restrict its usage for long running tasks.

You can have a background Service run some continuous processing using AsyncTasks on a separate ThreadPoolExecutor.

You can have a Fragment load latest news using an AsyncTask and when Fragment's onDestroy() is called, you cancel the task, since its no longer meaningful.

Hence the answer to "how long and AsyncTask should run", entirely depends upon the usage context.

Answer 2

Additional problem of AsyncTask: losing your results.

Yes, you said:

Lets suppose i have set the orientation of my activity to Portrait. Will this issue still be there?

But, Activity could be recreated not only 'cause rotation. For example, if there is no enough resources in system, operation system can destroy your Activity.

So, for long running operations there is high risk that AsyncTask will have an invalid reference to its Activity in onPostExecute() after Activity recreation.

Another problem: parallelism.

new AsyncTask1().execute();
new AsyncTask2().execute();

Will these two tasks run at the same time or will AsyncTask2 start when AsyncTask1 is finished? Well... It depends on the API level.

And aboud API level...

Before API 1.6 (Donut): the tasks were executed serially. This means a task won't start before a previous task is finished.

API 1.6 to API 2.3 (Gingerbread): the Android developers team changed AsyncTasks to make possibility to start them in parallel on a separate worker thread.

API 3.0 (Honeycomb): the AsyncTasks where executed serially again. Of course the Android team provided the possibility to let them run parallel. This is done by the method executeOnExecutor(Executor). Check out the API documentation for more information on this.