Service or Thread or AsyncTask

Question

Pardon my questions, as I'm still very new to programming so I don't fully understand the concepts of mainthreads, and async tasks, and services, and threads. I'm reading the documentation about Services for Android because I want to perform some tasks off the main thread. It says:

If you need to perform work outside your main thread, but only while the user is interacting with your application, then you should probably instead create a new thread and not a service.

1.Are they saying that a "thread" stops immediately after you leave the app (i.e: Home button)?

For example, if you want to play some music, but only while your activity is running, you might create a thread in onCreate(), start running it in onStart(), then stop it in onStop(). Also consider using AsyncTask or HandlerThread, instead of the traditional Thread class. See the Processes and Threading document for more information about threads.

2.If threads are baked into Java, why does android have AsyncTasks?

Remember that if you do use a service, it still runs in your application's main thread by default, so you should still create a new thread within the service if it performs intensive or blocking operations.

3.Does this basically mean, that almost every service is basically going to have a thread created inside it?

4.Would it be bad to start an AsyncTask inside of a service?

Answer 1

1.Are they saying that a "thread" stops immediately after you leave the app (i.e: Home button)?

A Thread should be destroyed when the Thread that started it is destroyed. So, if you start a Thread in an Activity then it should be destroyed when that Activity is destroyed or transferred to a Service. For instance, you can start music in a Thread and update the songs there but if you want it to keep playing when the Activity is destroyed then it should be moved to a Service

2.If threads are baked into Java, why does android have AsyncTasks?

An AsyncTask allows you to perform background work and easily update the UI before, during, and after the background work is done by utilizing any of its built-in methods except for doInBackground() because it is the only one that doesn't run on the UI Thread

3.Does this basically mean, that almost every service is basically going to have a thread created inside it?

Not necessarily but you could create a Thread inside of it

4.Would it be bad to start an AsyncTask inside of a service?

No. You could do this.

AsyncTask is a great way to do background work. Its methods make it very easy to update the UI. But you need to read through the documentation carefully (maybe even a few times) to make sure you completely understand how to use them. Also, remember that these are for short-lived operations so they can be good for downloading network data but shouldn't be used for things that last more than a few seconds (According to the docs)

Answer 2

1. A thread doesn't stop immediately when you leave the app. The suggestion to use a separate thread is only so you don't block your app's GUI.

2. AsyncTasks actually use a ThreadPool behind the scenes as creating a thread is an expensive process. If you have many short lived tasks, using AsyncTask is just a quick, easy, but efficient way to execute them without blocking your application's GUI.

3. Yes, essentially. A service is more heavy weight than a thread though. Using a service in place of a thread is not a good idea. Also services can actually be made to execute on a whole other process. Just FYI.

4. No. It would be a good idea, if you've many short lived tasks to execute.

If you are only trying to execute tasks off the main thread, you don't need a service. Just create another thread.

AsyncTask behind the scenes just submits your task to a thread pool for execution. If you have many short lived tasks, like parsing networking traffic, AsyncTask is great.

However, if you are handling a huge amount of requests, you might want more control over the thread pool executing your tasks.