What is the difference between Handler (MessageQueue) and AsyncTask (SERIAL_EXECUTOR), performance wise?

Question

There are a couple ways of getting data Asynchronously in your app. One is a Handler and another one is an AsyncTask. Now I've used both, and would like to know which one performs better/more efficiently at some tasks.

Thusfar, I've mostly used AsyncTasks in getting Webdata, and Handler's in getting data from Services to Activities.

I would like to know if there is an advantage to using Handler's for Webdata, or using AsyncTasks for refreshing UI from Services. What is the big difference?

Answer 1

Since AsyncTask uses a Handler, your comparison is... odd.

AsyncTask is great for transactional work: stuff that will take more than a few milliseconds and less than a few minutes. For that sort of work, if you have no need for your own thread management, AsyncTask is generally simpler to use.

If you have some particular characteristics that you need for your threading that AsyncTask will not readily handle, or if you need the thread for an indeterminate period of time (e.g., until the user presses a Stop button), use your own thread and something else to get work to the main application thread: a Handler, or post(), or runOnUiThread(). The "indeterminate period of time" recommendation assumes you are using one of the built-in thread pools -- I am never a fan of tying up a thread out of a thread pool that you didn't set up.

Answer 2

Looks like AsyncTask uses its own internal Handler. My testing is the "post" using a Handler is enqueued immediately. When used in onCreate this can be problematic as other actions must be enqueued after onCreate (haven't read through Android Activity etc source on this yet). So, trying to post to later load the layout did not work. Had to use an AsyncTask. Since AsyncTask has its own internal Handler; perhaps, then creating the task might occur in the queue directly after onCreate but the doInBackground and onPostExecute might occur later as they are later in a queue.

So, AsyncTask worked better for this UI need to load an overly large layout file later with setContentView - later meaning after the onCreate so a ProgressDialog could be shown. ProgressDialog doesn't show up until onCreate is done.

Also, see this article for how to choose when to use AsyncTask. Basically says when wanting to update UI. But actually you can do this with runOnUIThread so don't really need handler nor AsyncTask if you already know Java threading. runOnUIThread is like the invoke/invokeLater stuff in Swing.