Start a thread once and only once

Question

I have one singleton object on which I would exactly one thread executing while the app is running.

So far I have created the thread in MainActiviy::onCreate

class MainActivity : AppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     thread{myobject.run()}
   }
}

But contrary to the documentation where the arrow leading to onCreate() is App process is killed , it looks like onCreate() is called every time the app is restarted regardless of if being killed or if its threads were still running.

object myobject{
   fun run(){
      while(true){
         do_stuff()
      }
   }
}

It is of course possible to acquire a lock to only start the thread once, but since there is a nice syntax in Kotlin for singleton objects, and this is a related (I assume very common) problem I came to believe there maybe could be a simple more elegant way for this.

Or is the preferred way to acquire a lock on the object?

Answer 1

You can achieve this by starting the thread in OnCreate of your Application class. Make a class extending the Application class and add this class in your manifest

MyApp.kt

class MyApp : Application() {

    override fun onCreate() {
        super.onCreate()
       thread{myobject.run()} //here
    }

}

AndroidManifest.xml

<application 
   android:name=".com.yourpakage.MyApp"
   android:label="@string/app_name" 
   ...>

Unlike the activity lifecycle Application's onCreate is called only once. So there will be only one thread throughout the life of your app.

Answer 2

You can use an IntentService and store the status on a SharedPreference . https://developer.android.com/training/run-background-service/create-service