Sequential composing AsyncTasks in Android with Kotlin

Issue

I'm pretty new to Kotlin and I want to compose AsyncTask executions similarly like I would do in Scala to make them run sequentialy(to avoid race condition):

def f(): Future[Unit]
def g(): Future[Unit]
f.map(_ -> g)

or

for {
  _ <- f
  _ <- g
} yield () 

To do this I would want to extend somehow my helper:

fun doAsync(handler: () -> Unit): AsyncTask<Void, Void, Unit> =
  object : AsyncTask<Void, Void, Unit>() {
    override fun doInBackground(vararg params: Void?) {
      try {
        handler()
      }
      catch (t: Throwable) { 
        Log.e("AsyncTask", "fail", t)
      }
    }
  }.execute()

I know there is something like onPostExecute but I don't know how to change my helper to use it.

Solution

Async tasks, after Honey Comb are run sequentially. Quoting from documentation

When first introduced, AsyncTasks were executed serially on a single background thread. Starting with Build.VERSION_CODES.DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with Build.VERSION_CODES.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.

And, async task is designed for small operations, if you have a long running one, better use other Api s.

Also, you can always specify an executor, by calling executeOnExecutor()

Answered By - Debanjan