android - Correct pattern to acquire a WakeLock in a BroadcastReceiver and release it in a Service

Question

Even after a lot of research I am still not completely sure if the way how I implement a WakeLock for a Service started by a BroadcastReceiver is correct - even though it seems to work fine. The broadcast receiver gets intents sent to it from an alarm, so to start with, from the API docs of AlarmManager:

If your alarm receiver called Context.startService(), it is possible that the phone will sleep before the requested service is launched. To prevent this, your BroadcastReceiver and Service will need to implement a separate wake lock policy to ensure that the phone continues running until the service becomes available.

So, in onReceive() I do:

    Intent serviceIntent = new Intent(context, SomeService.class);
    context.startService(serviceIntent);

    if(SomeService.wakeLock == null) {
        PowerManager powerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
        SomeService.wakeLock = powerManager.newWakeLock(
                PowerManager.PARTIAL_WAKE_LOCK, 
                SomeService.WAKE_LOCK_TAG);
    }
    if(! SomeService.wakeLock.isHeld()) {
        SomeService.wakeLock.acquire();
    }

and in the service I do:

    try {
        // Do some work
    } finally {
        if(wakeLock != null) {
            if(wakeLock.isHeld()) {
                wakeLock.release();
            }
            wakeLock = null;
        }
    }

The SomeService.wakeLockfield is package private, static and volatile.

What I am unsure about is the check using isHeld() - does it really tell me if a WakeLock is acquired or not, and do I need to do this check at all?

Answer 1

Manage you wakeLock inside a singleton (unique instance accessible through all your context and object)

Use a singleton instance of a custom class, then you may get wakelock object reference from call to call ,

here an singleton example

class MyData {
   private static MyData mMydata= null; // unique reference ( singleton objet container)

   private PowerManager.Wakelock myobject = null; // inside the unique object container we have the unique working object to be use  by the application
   // can't make instance from outside... we want to have single instance
   // we want that outside use method "getInstance" to be able to use the object
   private MyData() {
   }

   // retrieve and/or create new unique instance
   public static MyData getInstance() {
     if (mMydata ==  null) mMyData = new MyData();
     return   mMyData;
   }

   // Works with your memory stored object
   // get...
   public PowerManager.WakeLock getMyWakelock() {
   return myobject;
   }
   // set ...
   public void setMyWakeLock(PowerManager.WakeLock obj) {
    myobject = obj;
   }
}

in your application to handle your "wakelock" object your may access it like

// set a created wakelock
MyData.getInstance().setMyWakeLock(wl);
// get the saved wakelock object
PowerManager.WakeLock obj =  MyData.getInstance().getMyWakeLock();