Are Android's BroadcastReceivers started in a new thread?

Question

If I have an inner class that extends BroadcastReceiver within my Service class, should I care about synchronization, when the BroadcastReceiver class reads/writes to objects from the Service class? Or to put it in another way: Are BroadacstReceiver's onReceive() Methods started in an extra thread?

Answer 1

The onReceive() method is always called on the main thread (which is also referred to as "UI thread"), unless you requested it to be scheduled on a different thread using the registerReceiver() variant:

Context.registerReceiver(BroadcastReceiver receiver,                          IntentFilter filter,                          String broadcastPermission,                          Handler scheduler) 

Answer 2

Are Android's BroadcastReceivers started in a new thread?

Usually but not always, it all depends on how you register it.

If you register your BroadcastReceiver using:

registerReceiver(BroadcastReceiver receiver, IntentFilter filter) 

It will run in the main activity thread(aka UI thread).

If you register your BroadcastReceiver using a valid Handler running on a different thread:

registerReceiver (BroadcastReceiver receiver, IntentFilter filter, String broadcastPermission, Handler scheduler) 

It will run in the context of your Handler

For example:

HandlerThread handlerThread = new HandlerThread("ht"); handlerThread.start(); Looper looper = handlerThread.getLooper(); Handler handler = new Handler(looper); context.registerReceiver(receiver, filter, null, handler); // Will not run on main thread 

Details here & here.