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?

I think you should start your thread in onCreate() of Application so there will be only one thread throughout the life of your app — Sujan Poudel, Dec 13 '19 at 05:35
That is what I am doing but `onCreate()` is called when the user leaves and returns to the app so I get multiple threads — Simson, Dec 13 '19 at 05:37
You are doing this in onCreate of a activity I said do in onCreate of Application class https://stackoverflow.com/questions/18002227/why-extend-the-android-application-class — Sujan Poudel, Dec 13 '19 at 05:39
Like this: https://medium.com/@balakrishnanpt/android-application-class-a8a1d64c82d1 — Simson, Dec 13 '19 at 05:52
Whenever you have time, if you write this in an answer I will upvote and accept! — Simson, Dec 13 '19 at 05:57

score 3 · Accepted Answer · answered Dec 13 '19 at 06:06

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.

score 1 · Answer 2 · answered Dec 13 '19 at 05:37

1

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

answered Dec 13 '19 at 05:37

Christilyn Arjona

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So I should change myobject to a subclass of `IntentService` and start it from the manifest? – Simson Dec 13 '19 at 05:40
Refer to this for some examples https://www.zoftino.com/android-intentservice-example – Christilyn Arjona Dec 13 '19 at 05:46

Start a thread once and only once

2 Answers2